











Transcriber's note:

   A few typographical errors have been corrected: they are listed
   at the end of the text. The Errata on page viii, which were in
   the original book, have been applied to this e-text.

   Page numbers within curly brackets (such as {iii} and {27}
   have been included so that the reader might use the index.





THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.

by

CHARLES DARWIN, M.A., F.R.S., &c.

IN TWO VOLUMES.--VOL. II.

With Illustrations.







LONDON:
John Murray, Albemarle Street.
1868.

The right of Translation is reserved.

London: Printed by William Clowes and Sons, Stamford Street, and Charing
Cross.




{iii}

CONTENTS OF VOLUME II.

CHAPTER XII.

INHERITANCE.

WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATED
ANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERS
INHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE INHERITED--DISEASES
IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL DEVIATIONS OF
STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER
AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED
PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS,
COLOUR OF FRUIT AND FLOWERS, COLOUR OF HORSES--NON-INHERITANCE IN CERTAIN
CASES--INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS
OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION
... Page 1

CHAPTER XIII.

INHERITANCE _continued_--REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS,
FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERAL
ANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSION
THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--IN
DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING A
DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHER
PROXIMATE CAUSES OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL
CHARACTERS--UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE
WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALL
ITS LATENT CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS
DUE IN SOME CASES TO REVERSION ... Page 28

CHAPTER XIV.

INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL
LIMITATION--CORRESPONDENCE OF AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF
INHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY,
IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER;
SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED
AND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIRED
CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE,
SOMETIMES LOST BY ONE SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OF
LIFE--THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS
EXHIBITED IN DOMESTICATED ANIMALS; AS EXHIBITED IN THE APPEARANCE AND
DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THE
CHILD THAN IN THE PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS ... Page
62

{iv}

CHAPTER XV.

ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN
THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE
OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY
THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS
OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS
INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLY
APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES, AND THE
FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE BRED TRUE FROM
THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT SPECIES IN RELATION TO
THE FORMATION OF DOMESTIC RACES ... Page 85

CHAPTER XVI.

CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OF
DOMESTICATION ON FERTILITY.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS
CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL
PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES
OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN
SOME DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TO
STERILITY NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OF
UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION ... Page
100

CHAPTER XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID
TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING, AND
ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED;
HALF-WILD CATTLE LONG KEPT IN THE SAME
PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS
ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS,
GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS,
FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZE
OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTS
WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE,
BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS
EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION ... Page 114

{v}

CHAPTER XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:
STERILITY FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF
LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE
COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF SECONDARY
SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OF
DOMESTICATED ANIMALS FROM CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OF
INDIVIDUAL ANIMALS--STERILITY OF PLANTS FROM CHANGED CONDITIONS OF
LIFE--CONTABESCENCE OF THE ANTHERS--MONSTROSITIES AS A CAUSE OF
STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE
DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY
BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS
FRUIT ... Page 145

CHAPTER XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON
FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED
CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE
DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS
WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE
PROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS--STERILITY OF CROSSED SPECIES
DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATED
THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY
STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY
BETWEEN CROSSED SPECIES AND CROSSED VARIETIES--CONCLUSION ... Page 173

CHAPTER XX.

SELECTION BY MAN.

SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL
SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN
SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS, AND
BY SEMI-CIVILISED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED
TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR
DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS
SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTS
AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THE
GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN ... Page 192

{vi}

CHAPTER XXI.

SELECTION--_continued._

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH
APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE
TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE
CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION
OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION
IS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO
DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO
AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO
CONVERGENCE--CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH
THEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF
INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT
TO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH
DOMESTIC RACES HAVE ORIGINATED--SUMMARY ... Page 224

CHAPTER XXII.

CAUSES OF VARIABILITY.

VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY
VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO
CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD,
EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE
VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO
CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
VARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW
CHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM
REVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER
DIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY
... Page 250

CHAPTER XXIII.

DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE
TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR
FOOD, ETC.--PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE
INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A
STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL
CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS OF
PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT
INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF
VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF
CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
UNNATURAL TREATMENT--SUMMARY ... Page 271

{vii}

CHAPTER XXIV.

LAWS OF VARIATION--USE AND DISUSE, ETC.

NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE
EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF
LIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH
THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS ... Page
293

CHAPTER XXV.

LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY.

EXPLANATION OF TERM--CORRELATION AS CONNECTED WITH
DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE
OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS
ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE HEAD AND THE
EXTREMITIES--BETWEEN THE SKIN AND DERMAL APPENDAGES--BETWEEN THE ORGANS OF
SIGHT AND HEARING--CORRELATED MODIFICATIONS IN THE ORGANS OF
PLANTS--CORRELATED MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND
EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTH
COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS
CORRELATED WITH CONSTITUTIONAL PECULIARITIES ... Page 319

CHAPTER XXVI.

LAWS OF VARIATION, _continued_--SUMMARY.

ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OF
MULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICAL
PRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THE
PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS OR
PARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS ... Page 339

CHAPTER XXVII.

PROVISIONAL HYPOTHESIS OF PANGENESIS.

PRELIMINARY REMARKS--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE
POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE DIRECT ACTION
OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE FUNCTIONAL INDEPENDENCE
OF THE ELEMENTS OR UNITS OF THE BODY--VARIABILITY--INHERITANCE--REVERSION.

SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY
ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE
SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION ... Page
357

{viii}

CHAPTER XXVIII.

CONCLUDING REMARKS.

DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND
DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO
SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH
PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED ... Page 405

INDEX ... Page 433

       *       *       *       *       *

ERRATA.

  Vol. II., pp. 18, 232, 258, for Cratægus oxycantha, read oxyacantha.
       ,,   p.  98, 8 lines from top, for Dianthus armoria read armeria.
       ,,   ,,  156, 15 lines from bottom, for Casuarinus read Casuarius.
       ,,   ,,   ,,  4 lines from bottom, for Grus cineria read cinerea.
       ,,   ,,  168, 11 lines from top, for Oesculus read Æsculus.
       ,,   ,,  300, 3 lines from top, for anastomising read anastomosing.
       ,,   ,,   ,,  foot-note, for Birckell read Brickell.

       *       *       *       *       *


{1} THE

VARIATION OF ANIMALS AND PLANTS

UNDER DOMESTICATION.

       *       *       *       *       *

CHAPTER XII.

INHERITANCE.

    WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATED
    ANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERS
    INHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE
    INHERITED--DISEASES IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL
    DEVIATIONS OF STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY
    DIGITS AFTER AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED
    FROM NON-AFFECTED PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING
    TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS, COLOUR OF
    HORSES--NON-INHERITANCE IN CERTAIN CASES--INHERITANCE OF STRUCTURE AND
    HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY
    RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION.

The subject of inheritance is an immense one, and has been treated by many
authors. One work alone, 'De l'Hérédité Naturelle,' by Dr. Prosper Lucas,
runs to the length of 1562 pages. We must confine ourselves to certain
points which have an important bearing on the general subject of variation,
both with domestic and natural productions. It is obvious that a variation
which is not inherited throws no light on the derivation of species, nor is
of any service to man, except in the case of perennial plants, which can be
propagated by buds.

If animals and plants had never been domesticated, and wild ones alone had
been observed, we should probably never have heard the saying, that "like
begets like." The proposition would have been as self-evident, as that all
the buds on the same tree are alike, though neither proposition is strictly
true. For, as has often been remarked, probably no two individuals are {2}
identically the same. All wild animals recognise each other, which shows
that there is some difference between them; and when the eye is well
practised, the shepherd knows each sheep, and man can distinguish a
fellow-man out of millions on millions of other men. Some authors have gone
so far as to maintain that the production of slight differences is as much
a necessary function of the powers of generation, as the production of
offspring like their parents. This view, as we shall see in a future
chapter, is not theoretically probable, though practically it holds good.
The saying that "like begets like" has in fact arisen from the perfect
confidence felt by breeders, that a superior or inferior animal will
generally reproduce its kind; but this very superiority or inferiority
shows that the individual in question has departed slightly from its type.

The whole subject of inheritance is wonderful. When a new character arises,
whatever its nature may be, it generally tends to be inherited, at least in
a temporary and sometimes in a most persistent manner. What can be more
wonderful than that some trifling peculiarity, not primordially attached to
the species, should be transmitted through the male or female sexual cells,
which are so minute as not to be visible to the naked eye, and afterwards
through the incessant changes of a long course of development, undergone
either in the womb or in the egg, and ultimately appear in the offspring
when mature, or even when quite old, as in the case of certain diseases? Or
again, what can be more wonderful than the well-ascertained fact that the
minute ovule of a good milking cow will produce a male, from whom a cell,
in union with an ovule, will produce a female, and she, when mature, will
have large mammary glands, yielding an abundant supply of milk, and even
milk of a particular quality? Nevertheless, the real subject of surprise
is, as Sir H. Holland has well remarked,[1] not that a character should be
inherited, but that any should ever fail to be inherited. In a future
chapter, devoted to an hypothesis which I have termed pangenesis, an
attempt will be made to show the means by which characters of all kinds are
transmitted from generation to generation.

{3}

Some writers,[2] who have not attended to natural history, have attempted
to show that the force of inheritance has been much exaggerated. The
breeders of animals would smile at such simplicity; and if they
condescended to make any answer, might ask what would be the chance of
winning a prize if two inferior animals were paired together? They might
ask whether the half-wild Arabs were led by theoretical notions to keep
pedigrees of their horses? Why have pedigrees been scrupulously kept and
published of the Shorthorn cattle, and more recently of the Hereford breed?
Is it an illusion that these recently improved animals safely transmit
their excellent qualities even when crossed with other breeds? have the
Shorthorns, without good reason, been purchased at immense prices and
exported to almost every quarter of the globe, a thousand guineas having
been given for a bull? With greyhounds pedigrees have likewise been kept,
and the names of such dogs, as Snowball, Major, &c., are as well known to
coursers as those of Eclipse and Herod on the turf. Even with the Gamecock
pedigrees of famous strains were formerly kept, and extended back for a
century. With pigs, the Yorkshire and Cumberland breeders "preserve and
print pedigrees;" and to show how such highly-bred animals are valued, I
may mention that Mr. Brown, who won all the first prizes for small breeds
at Birmingham in 1850, sold a young sow and boar of his breed to Lord Ducie
for 43 guineas; the sow alone was afterwards sold to the Rev. F. Thursby
for 65 guineas; who writes, "she paid me very well, having sold her produce
for 300_l_., and having now four breeding sows from her."[3] Hard cash paid
down, over and over again, is an excellent test of inherited superiority.
In fact, the whole art of breeding, from which such great results have been
attained during the present century, depends on the inheritance of each
small {4} detail of structure. But inheritance is not certain; for if it
were, the breeder's art[4] would be reduced to a certainty, and there would
be little scope left for all that skill and perseverance shown by the men
who have left an enduring monument of their success in the present state of
our domesticated animals.

It is hardly possible, within a moderate compass, to impress on the mind of
those who have not attended to the subject, the full conviction of the
force of inheritance which is slowly acquired by rearing animals, by
studying the many treatises which have been published on the various
domestic animals, and by conversing with breeders. I will select a few
facts of the kind, which, as far as I can judge, have most influenced my
own mind. With man and the domestic animals, certain peculiarities have
appeared in an individual, at rare intervals, or only once or twice in the
history of the world, but have reappeared in several of the children and
grandchildren. Thus Lambert, "the porcupine-man," whose skin was thickly
covered with warty projections, which were periodically moulted, had all
his six children and two grandsons similarly affected.[5] The face and body
being covered with long hair, accompanied by deficient teeth (to which I
shall hereafter refer), occurred in three successive generations in a
Siamese family; but this case is not unique, as a woman[6] with a
completely hairy face was exhibited in London in 1663, and another instance
has recently occurred. Colonel Hallam[7] has described a race of two-legged
pigs, "the hinder extremities being entirely wanting;" and this deficiency
was transmitted through three generations. In fact, all races presenting
any remarkable peculiarity, such as solid-hoofed swine, Mauchamp sheep,
niata cattle, &c., are instances of the long-continued inheritance of rare
deviations of structure.

When we reflect that certain extraordinary peculiarities have {5} thus
appeared in a single individual out of many millions, all exposed in the
same country to the same general conditions of life, and, again, that the
same extraordinary peculiarity has sometimes appeared in individuals living
under widely different conditions of life, we are driven to conclude that
such peculiarities are not directly due to the action of the surrounding
conditions, but to unknown laws acting on the organisation or constitution
of the individual;--that their production stands in hardly closer relation
to the conditions than does life itself. If this be so, and the occurrence
of the same unusual character in the child and parent cannot be attributed
to both having been exposed to the same unusual conditions, then the
following problem is worth consideration, as showing that the result cannot
be due, as some authors have supposed, to mere coincidence, but must be
consequent on the members of the same family inheriting something in common
in their constitution. Let it be assumed that, in a large population, a
particular affection occurs on an average in one out of a million, so that
the _à priori_ chance that an individual taken at random will be so
affected is only one in a million. Let the population consist of sixty
millions, composed, we will assume, of ten million families, each
containing six members. On these data, Professor Stokes has calculated for
me that the odds will be no less than 8333 millions to 1 that in the ten
million families there will not be even a single family in which one parent
and two children will be affected by the peculiarity in question. But
numerous cases could be given, in which several children have been affected
by the same rare peculiarity with one of their parents; and in this case,
more especially if the grandchildren be included in the calculation, the
odds against mere coincidence become something prodigious, almost beyond
enumeration.

In some respects the evidence of inheritance is more striking when we
consider the reappearance of trifling peculiarities. Dr. Hodgkin formerly
told me of an English family in which, for many generations, some members
had a single lock differently coloured from the rest of the hair. I knew an
Irish gentleman, who, on the right side of his head, had a small white lock
in the midst of his dark hair: he assured me that his grandmother had {6} a
similar lock on the same side, and his mother on the opposite side. But it
is superfluous to give instances; every shade of expression, which may
often be seen alike in parents and children, tells the same story. On what
a curious combination of corporeal structure, mental character, and
training, must handwriting depend! yet every one must have noted the
occasional close similarity of the handwriting in father and son, although
the father had not taught his son. A great collector of franks assured me
that in his collection there were several franks of father and son hardly
distinguishable except by their dates. Hofacker, in Germany, remarks on the
inheritance of handwriting; and it has even been asserted that English boys
when taught to write in France naturally cling to their English manner of
writing.[8] Gait, gestures, voice, and general bearing are all inherited,
as the illustrious Hunter and Sir A. Carlisle have insisted.[9] My father
communicated to me two or three striking instances, in one of which a man
died during the early infancy of his son, and my father, who did not see
this son until grown up and out of health, declared that it seemed to him
as if his old friend had risen from the grave, with all his highly peculiar
habits and manners. Peculiar manners pass into tricks, and several
instances could be given of their inheritance; as in the case, often
quoted, of the father who generally slept on his back, with his right leg
crossed over the left, and whose daughter, whilst an infant in the cradle,
followed exactly the same habit, though an attempt was made to cure
her.[10] I will give one instance which has fallen under my own
observation, and which is curious from being a trick associated with a
peculiar state of mind, namely, pleasurable emotion. A boy had the singular
habit, when pleased, of rapidly moving his fingers parallel to each other,
and, when much excited, of raising both hands, with the fingers still
moving, to the sides of his face on a level with the eyes; this boy, when
almost an old man, could still hardly resist this trick when much pleased,
but from its absurdity concealed it. He had eight children. Of these, a
girl, when {7} pleased, at the age of four and a half years, moved her
fingers in exactly the same way, and what is still odder, when much
excited, the raised both her hands, with her fingers still moving, to the
sides of her face, in exactly the same manner as her father had done, and
sometimes even still continued to do when alone. I never heard of any one
excepting this one man and his little daughter who had this strange habit;
and certainly imitation was in this instance out of the question.

Some writers have doubted whether those complex mental attributes, on which
genius and talent depend, are inherited, even when both parents are thus
endowed. But he who will read Mr. Galton's able paper[11] on hereditary
talent will have his doubts allayed.

Unfortunately it matters not, as far as inheritance is concerned, how
injurious a quality or structure may be if compatible with life. No one can
read the many treatises[12] on hereditary disease and doubt this. The
ancients were strongly of this opinion, or, as Ranchin expresses it, _Omnes
Græci, Arabes, et Latini in eo consentiunt_. A long catalogue could be
given of all sorts of inherited malformations and of predisposition to
various diseases. With gout, fifty per cent. of the cases observed in
hospital practice are, according to Dr. Garrod, inherited, and a greater
percentage in private practice. Every one knows how often insanity runs in
families, and some of the cases given by Mr. Sedgwick are awful,--as of a
surgeon, whose brother, father, and four paternal uncles were all insane,
the latter dying by suicide; of a Jew, whose father, mother, and six
brothers and sisters were all mad; and in some other cases several members
of the same family, during three or four successive generations, have
committed suicide. Striking instances {8} have been recorded of epilepsy,
consumption, asthma, stone in the bladder, cancer, profuse bleeding from
the slightest injuries, of the mother not giving milk, and of bad
parturition being inherited. In this latter respect I may mention an odd
case given by a good observer,[13] in which the fault lay in the offspring,
and not in the mother: in a part of Yorkshire the farmers continued to
select cattle with large hind-quarters, until they made a strain called
"Dutch-buttocked," and "the monstrous size of the buttocks of the calf was
frequently fatal to the cow, and numbers of cows were annually lost in
calving."

    Instead of giving numerous details on various inherited malformations
    and diseases, I will confine myself to one organ, that which is the
    most complex, delicate, and probably best-known in the human frame,
    namely, the eye, with its accessory parts. To begin with the latter: I
    have heard of a family in which parents and children were affected by
    drooping eyelids, in so peculiar a manner, that they could not see
    without throwing their heads backwards; and Sir A. Carlisle[14]
    specifies a pendulous fold to the eyelids as inherited. "In a family,"
    says Sir H. Holland,[15] "where the father had a singular elongation of
    the upper eyelid, seven or eight children were born with the same
    deformity; two or three other children having it not." Many persons, as
    I year from Mr. Paget, have two or three of the hairs in their eyebrows
    (apparently corresponding with the vibrissæ of the lower animals) much
    longer than the others; and even so trifling a peculiarity as this
    certainly runs in families.

    With respect to the eye itself, the highest authority in England, Mr.
    Bowman, has been so kind as to give me the following remarks on certain
    inherited imperfections. First, hypermetropia, or morbidly long sight:
    in this affection, the organ, instead of being spherical, is too flat
    from front to back, and is often altogether too small, so that the
    retina is brought too forward for the focus of the humours;
    consequently a convex glass is required for clear vision of near
    objects, and frequently even of distant ones. This state occurs
    congenitally, or at a very early age, often in several children of the
    same family, where one of the parents has presented it.[16] Secondly,
    myopia, or short-sight, in which the eye is egg-shaped, and too long
    from front to back; the retina in this case lies behind the focus, and
    is therefore fitted to see distinctly only very near objects. This
    condition is not commonly congenital, but comes on in youth, the
    liability to it being well known to be transmissible from parent to
    child. The change from the spherical to the ovoidal shape seems the
    immediate {9} consequence of something like inflammation of the coats,
    under which they yield, and there is ground for believing that it may
    often originate in causes acting directly on the individual affected,
    and may thenceforward become transmissible. When both parents are
    myopic Mr. Bowman has observed the hereditary tendency in this
    direction to be heightened, and some of the children to be myopic at an
    earlier age or in a higher degree than their parents. Thirdly,
    squinting is a familiar example of hereditary transmission: it is
    frequently a result of such optical defects as have been above
    mentioned; but the more primary and uncomplicated forms of it are also
    sometimes in a marked degree transmitted in a family. Fourthly,
    _Cataract_, or opacity of the crystalline lens, is commonly observed in
    persons whose parents have been similarly affected, and often at an
    earlier age in the children than in the parents. Occasionally more than
    one child in a family is thus afflicted, one of whose parents or other
    relation presents the senile form of the complaint. When cataract
    affects several members of a family in the same generation, it is often
    seen to commence at about the same age in each; _e.g._, in one family
    several infants or young persons may suffer from it; in another,
    several persons of middle age. Mr. Bowman also informs me that he has
    occasionally seen, in several members of the same family, various
    defects in either the right or left eye; and Mr. White Cooper has often
    seen peculiarities of vision confined to one eye reappearing in the
    same eye in the offspring.[17]

    The following cases are taken from an able paper by Mr. W. Sedgwick,
    and from Dr. Prosper Lucas.[18] Amaurosis, either congenital or coming
    on late in life, and causing total blindness, is often inherited; it
    has been observed in three successive generations. Congenital absence
    of the iris has likewise been transmitted for three generations, a
    cleft-iris for four generations, being limited in this latter case to
    the males of the family. Opacity of the cornea and congenital smallness
    of the eyes have been inherited. Portal records a curious case, in
    which a father and two sons were rendered blind, whenever the head was
    bent downwards, apparently owing to the crystalline lens, with its
    capsule, slipping through an unusually large pupil into the anterior
    chamber of the eye. Day-blindness, or imperfect vision under a bright
    light, is inherited, as is night-blindness, or an incapacity to see
    except under a strong light: a case has been recorded, by M. Cunier, of
    this latter defect having affected eighty-five members of the same
    family during six generations. The singular incapacity of
    distinguishing colours, which has been called _Daltonism_, is
    notoriously hereditary, and has been traced through five generations,
    in which it was confined to the female sex.

    With respect to the colour of the iris: deficiency of colouring matter
    is well known to be hereditary in albinoes. The iris of one eye being
    of a different colour from that of the other, and the iris being
    spotted, are cases which have been inherited. Mr. Sedgwick gives, in
    addition, on the {10} authority of Dr. Osborne,[19] the following
    curious instance of strong inheritance: a family of sixteen sons and
    five daughters all had eyes "resembling in miniature the markings on
    the back of a tortoiseshell cat." The mother of this large family had
    three sisters and a brother all similarly marked, and they derived this
    peculiarity from their mother, who belonged to a family notorious for
    transmitting it to their posterity.

    Finally, Dr. Lucas emphatically remarks that there is not one single
    faculty of the eye which is not subject to anomalies; and not one which
    is not subjected to the principle of inheritance. Mr. Bowman agrees
    with the general truth of this proposition; which of course does not
    imply that all malformations are necessarily inherited; this would not
    even follow if both parents were affected by an anomaly which in most
    cases was transmissible.

Even if no single fact had been known with respect to the inheritance of
disease and malformations by man, the evidence would have been ample in the
case of the horse. And this might have been expected, as horses breed much
quicker than man, are matched with care, and are highly valued. I have
consulted many works, and the unanimity of the belief by veterinaries of
all nations in the transmission of various morbid tendencies is surprising.
Authors, who have had wide experience, give in detail many singular cases,
and assert that contracted feet, with the numerous contingent evils, of
ring-bones, curbs, splints, spavin, founder and weakness of the front legs,
roaring or broken and thick wind, melanosis, specific ophthalmia, and
blindness (the great French veterinary Hazard going so far as to say that a
blind race could soon be formed), crib-biting, jibbing, and ill-temper, are
all plainly hereditary. Youatt sums up by saying "there is scarcely a
malady to which the horse is subject which is not hereditary;" and M.
Bernard adds that the doctrine "that there is scarcely a disease which does
not run in the stock, is gaining new advocates every day."[20] So it {11}
is in regard to cattle, with consumption, good and bad teeth, fine skin,
&c. &c. But enough, and more than enough, has been said on disease. Andrew
Knight, from his own experience, asserts that disease is hereditary with
plants; and this assertion is endorsed by Lindley.[21]

Seeing how hereditary evil qualities are, it is fortunate that good health,
vigour, and longevity are equally inherited. It was formerly a well-known
practice, when annuities were purchased to be received during the lifetime
of a nominee, to search out a person belonging to a family of which many
members had lived to extreme old age. As to the inheritance of vigour and
endurance, the English race-horse offers an excellent instance. Eclipse
begot 334, and King Herod 497 winners. A "cock-tail" is a horse not purely
bred, but with only one-eighth or one-sixteenth impure blood in his veins,
yet very few instances have ever occurred of such horses having won a great
race. They are sometimes as fleet for short distances as thoroughbreds, but
as Mr. Robson, the great trainer, asserts, they are deficient in wind, and
cannot keep up the pace. Mr. Lawrence also remarks, "perhaps no instance
has ever occurred of a three-part-bred horse saving his '_distance_' in
running two miles with thoroughbred racers." It has been stated by Cecil,
that when unknown horses, whose parents were not celebrated, have
unexpectedly won great races, as in the case of Priam, they can always be
proved to be descended on both sides, through many generations, from
first-rate ancestors. On the Continent, Baron Cameronn challenges, in a
German veterinary periodical, the opponents of the English race-horse, to
name one good horse on the Continent which has not some English race-blood
in his veins.[22]

With respect to the transmission of the many slight, but {12} infinitely
diversified characters, by which the domestic races of animals and plants
are distinguished, nothing need be said; for the very existence of
persistent races proclaims the power of inheritance.

A few special cases, however, deserve some consideration. It might have
been anticipated, that deviations from the law of symmetry would not have
been inherited. But Anderson[23] states that a rabbit produced in a litter
a young animal having only one ear; and from this animal a breed was formed
which steadily produced one-eared rabbits. He also mentions a bitch, with a
single leg deficient, and she produced several puppies with the same
deficiency. From Hofacker's account[24] it appears that a one-horned stag
was seen in 1781 in a forest in Germany, in 1788 two, and afterwards, from
year to year, many were observed with only one horn on the right side of
the head. A cow lost a horn by suppuration,[25] and she produced three
calves which had on the same side of the head, instead of a horn, a small
bony lump attached merely to the skin; but we here approach the doubtful
subject of inherited mutilations. A man who is left-handed, and a shell in
which the spire turns in the wrong direction, are departures from the
normal though a symmetrical condition, and they are well known to be
inherited.

    _Polydactylism._--Supernumerary fingers and toes are eminently liable,
    as various authors have insisted, to transmission, but they are noticed
    here chiefly on account of their occasional regrowth after amputation.
    Polydactylism graduates[26] by multifarious steps from a mere cutaneous
    appendage, not including any bone, to a double hand. But an additional
    digit, supported on a metacarpal bone, and furnished with all the
    proper muscles, nerves, and vessels, is sometimes so perfect, that it
    escapes detection, unless the fingers are actually counted.
    Occasionally there are several supernumerary digits; but usually only
    one, making the total number six. This one may represent either a thumb
    or finger, being attached to the inner or outer margin of the hand.
    Generally, through the law of correlation, both hands and feet are
    similarly affected. I have tabulated the cases recorded in various
    works or privately communicated {13} to me, of forty-six persons with
    extra digits on one or both hands and feet; if in each case all four
    extremities had been similarly affected, the table would have shown a
    total of ninety-two hands and ninety-two feet each with six digits. As
    it is, seventy-three hands and seventy-five feet were thus affected.
    This proves, in contradiction to the result arrived at by Dr.
    Struthers,[27] that the hands are not more frequently affected than the
    feet.

    The presence of more than five digits is a great anomaly, for this
    number is not normally exceeded by any mammal, bird, or existing
    reptile.[28] Nevertheless, supernumerary digits are strongly inherited;
    they have been transmitted through five generations; and in some cases,
    after disappearing for one, two, or even three generations, have
    reappeared through reversion. These facts are rendered, as Professor
    Huxley has observed, more remarkable from its being known in most cases
    that the affected person had not married one similarly affected. In
    such cases the child of the fifth generation would have only 1-32nd
    part of the blood of his first sedigitated ancestor. Other cases are
    rendered remarkable by the affection gathering force, as Dr. Struthers
    has shown, in each generation, though in each the affected person had
    married one not affected; moreover such additional digits are often
    amputated soon after birth, and can seldom have been strengthened by
    use. Dr. Struthers gives the following instance: in the first
    generation an additional digit appeared on one hand; in the second, on
    both hands; in the third, three brothers had both hands, and one of the
    brothers a foot affected; and in the fourth generation all four limbs
    were affected. Yet we must not over-estimate the force of inheritance.
    Dr. Struthers asserts that cases of non-inheritance and of the first
    appearance of additional digits in unaffected families are much more
    frequent than cases of inheritance. Many other deviations of structure,
    of a nature almost as anomalous as supernumerary digits, such as
    deficient phalanges, thickened joints, crooked fingers, &c., are in
    like manner strongly inherited, and are equally subject to intermission
    with reversion, though in such cases there is no reason to suppose that
    both parents had been similarly affected.[29]

    {14}

    Additional digits have been observed in negroes as well as in other
    races of man, and in several of the lower animals. Six toes have been
    described on the hind feet of the newt (_Salamandra cristata_), and, as
    it is said, of the frog. It deserves notice from what follows, that the
    six-toed newt, though adult, had preserved some of its larval
    characters; for part of the hyoidal apparatus, which is properly
    absorbed during the act of metamorphosis, was retained. In the dog, six
    toes on the hinder feet have been transmitted through three
    generations; and I have heard of a race of six-toed cats. In several
    breeds of the fowl the hinder toe is double, and is generally
    transmitted truly, as is well shown when Dorkings are crossed with
    common four-toed breeds.[30] With animals which have properly less than
    five digits, the number is sometimes increased to five, especially in
    the front legs, though rarely carried beyond that number; but this is
    due to the development of a digit already existing in a more or less
    rudimentary state. Thus the dog has properly four toes behind, but in
    the larger breeds a fifth toe is commonly, though not perfectly,
    developed. Horses, which properly have one toe alone fully developed
    with rudiments of the others, have been described with each foot
    bearing two or three small separate hoofs: analogous facts have been
    noticed with sheep, goats, and pigs.[31]

    The most interesting point with respect to supernumerary digits is
    their occasional regrowth after amputation. Mr. White[32] describes a
    child, three years old, with a thumb double from the first joint. He
    removed the lesser thumb, which was furnished with a nail; but to his
    astonishment it grew again, and reproduced a nail. The child was then
    taken to an eminent London surgeon, and the newly-grown thumb was
    wholly removed by its socket-joint, but again it grew and reproduced a
    nail. Dr. Struthers mentions a case of partial regrowth of an
    additional thumb, amputated when the child was three months old; and
    the late Dr. Falconer communicated to me an analogous case which had
    fallen under his own observation. A gentleman, who first called my
    attention to this subject, has given me the following facts which
    occurred in his own family. He himself, two brothers, and a sister were
    born with an extra digit to each extremity. His parents were not
    affected, and there was no tradition in the family, or in the village
    in which the family had long resided, of any member having been thus
    affected. Whilst a child, both additional toes, which were attached by
    bones, were rudely cut off; but the stump of one grew again, and a
    second operation was performed in his thirty-third year.

    {15}

    He has had fourteen children, of whom three have inherited additional
    digits; and one of them, when about six weeks old, was operated on by
    an eminent surgeon. The additional finger, which was attached by bone
    to the outer side of the hand, was removed at the joint; the wound
    healed, but immediately the digit began growing; and in about three
    months' time the stump was removed for the second time by the root. But
    it has since grown again, and is now fully a third of an inch in
    length, including a bone; so that it will for the third time have to be
    operated on.

    Now the normal digits in adult man and other mammals, in birds, and, as
    I believe, in true reptiles, have no power of regrowth. The nearest
    approach to this power is exhibited by the occasional reappearance in
    man of imperfect nails on the stumps of his fingers after
    amputation.[33] But man in his embryonic condition has a considerable
    power of reproduction, for Sir J. Simpson[34] has several times
    observed arms which had been cut off in the womb by bands of false
    membrane, and which had grown again to a certain extent. In one
    instance, the extremity was "divided into three minute nodules, on two
    of which small points of nails could be detected;" so that these
    nodules clearly represented fingers in process of regrowth. When,
    however, we descend to the lower vertebrate classes, which are
    generally looked at as representing the higher classes in their
    embryonic condition, we find ample powers of regrowth. Spallanzani[35]
    cut off the legs and tail of a salamander six times, and Bonnet eight
    times, successively, and they were reproduced. An additional digit
    beyond the proper number was occasionally formed after Bonnet had cut
    off or had divided longitudinally the hand or foot, and in one instance
    three additional digits were thus formed.[36] These latter cases appear
    at first sight quite distinct from the congenital production of
    additional digits in the higher animals; but theoretically, as we shall
    see in a future chapter, they probably present no real difference. The
    larvæ or tadpoles of the tailless Batrachians, but not the adults,[37]
    are capable of reproducing lost members.[38] Lastly, as I have been
    informed by Mr. J. J. Briggs and Mr. F. Buckland, when portions of the
    pectoral and tail fins of various {16} fresh-water fish are cut off,
    they are perfectly reproduced in about six weeks' time.

From these several facts we may infer that supernumerary digits in man
retain to a certain extent an embryonic condition, and that they resemble
in this respect the normal digits and limbs in the lower vertebrate
classes. They also resemble the digits of some of the lower animals in the
number exceeding five; for no mammal, bird, existing reptile, or amphibian
(unless the tubercle on the hind feet of the toad and other tailless
Batrachians be viewed as a digit) has more than five; whilst fishes
sometimes have in their pectoral fins as many as twenty metacarpal and
phalangeal bones, which, together with the bony filaments, apparently
represent our digits with their nails. So, again, in certain extinct
reptiles, namely, the Ichthyopterygia, "the digits may be seven, eight, or
nine in number, a significant mark," says Professor Owen, "of piscine
affinity."[39]

We encounter much difficulty in attempting to reduce these various facts to
any rule or law. The inconstant number of the additional digits--their
irregular attachment to either the inner or outer margin of the hand--the
gradation which can be traced from a mere loose rudiment of a single digit
to a completely double hand--the occasional appearance of additional digits
in the salamander after a limb has been amputated--these various facts
appear to indicate mere fluctuating monstrosity; and this perhaps is all
that can be safely said. Nevertheless, as supernumerary digits in the
higher animals, from their power of regrowth and from the number thus
acquired exceeding five, partake of the nature of the digits in the lower
vertebrate animals;--as they occur by no means rarely, and are transmitted
with remarkable strength, though perhaps not more strongly than some other
anomalies;--and as with animals which have fewer than five digits, when an
additional one appears it is generally due to the development of a visible
rudiment;--we are led in all cases to suspect, that, although no actual
rudiment can be detected, yet that a latent tendency to the formation of an
additional digit exists in all mammals, including man. On this view, as we
shall more plainly see in the {17} next chapter when discussing latent
tendencies, we should have to look at the whole case as one of reversion to
an enormously remote, lowly-organised, and multidigitate progenitor.

       *       *       *       *       *

I may here allude to a class of facts closely allied to, but somewhat
different from, ordinary cases of inheritance. Sir H. Holland[40] states
that brothers and sisters of the same family are frequently affected, often
at about the same age, by the same peculiar disease, not known to have
previously occurred in the family. He specifies the occurrence of diabetes
in three brothers under ten years old; he also remarks that children of the
same family often exhibit in common infantile diseases the same peculiar
symptoms. My father mentioned to me the case of four brothers who died
between the ages of sixty and seventy, in the same highly peculiar comatose
state. An instance has been already given of supernumerary digits appearing
in four children out of six in a previously unaffected family. Dr. Devay
states[41] that two brothers married two sisters, their first-cousins, none
of the four nor any relation being an albino; but the seven children
produced from this double marriage were all perfect albinoes. Some of these
cases, as Mr. Sedgwick[42] has shown, are probably the result of reversion
to a remote ancestor, of whom no record had been preserved; and all these
cases are so far directly connected with inheritance that no doubt the
children inherited a similar constitution from their parents, and, from
being exposed to nearly similar conditions of life, it is not surprising
that they should be affected in the same manner and at the same period of
life.

       *       *       *       *       *

Most of the facts hitherto given have served to illustrate the force of
inheritance, but we must now consider cases, grouped as well as the subject
allows into classes, showing how feeble, capricious, or deficient the power
of inheritance sometimes is. When a new peculiarity first appears, we can
never predict whether it will be inherited. If both parents from their
birth present {18} the same peculiarity, the probability is strong that it
will be transmitted to at least some of their offspring. We have seen that
variegation is transmitted much more feebly by seed from a branch which had
become variegated through bud-variation, than from plants which were
variegated as seedlings. With most plants the power of transmission
notoriously depends on some innate capacity in the individual: thus
Vilmorin[43] raised from a peculiarly coloured balsam some seedlings, which
all resembled their parent; but of these seedlings some failed to transmit
the new character, whilst others transmitted it to all their descendants
during several successive generations. So again with a variety of the rose,
two plants alone out of six were found by Vilmorin to be capable of
transmitting the desired character.

    The weeping or pendulous growth of trees is strongly inherited in some
    cases, and, without any assignable reason, feebly in other cases. I
    have selected this character as an instance of capricious inheritance,
    because it is certainly not proper to the parent-species, and because,
    both sexes being borne on the same tree, both tend to transmit the same
    character. Even supposing that there may have been in some instances
    crossing with adjoining trees of the same species, it is not probable
    that all the seedlings would have been thus affected. At Moccas Court
    there is a famous weeping oak; many of its branches "are 30 feet long,
    and no thicker in any part of this length than a common rope:" this
    tree transmits its weeping character, in a greater or less degree, to
    all its seedlings; some of the young oaks being so flexible that they
    have to be supported by props; others not showing the weeping tendency
    till about twenty years old.[44] Mr. Rivers fertilized, as he informs
    me, the flowers of a new Belgian weeping thorn (_Cratægus oxyacantha_)
    with pollen from a crimson not-weeping variety, and three young trees,
    "now six or seven years old, show a decided tendency to be pendulous,
    but as yet are not so much so as the mother-plant." According to Mr.
    MacNab,[45] seedlings from a magnificent weeping birch (_Betula alba_),
    in the Botanic Garden at Edinburgh, grew for the first ten or fifteen
    years upright, but then all became weepers like their parent. A peach
    with pendulous branches, like those of the weeping willow, has been
    found capable of propagation by seed.[46] Lastly, a weeping and almost
    prostrate yew (_Taxus baccata_) was found in a hedge in Shropshire; it
    was a male, but one branch bore female flowers, and produced berries;
    these, {19} being sown, produced seventeen trees, all of which had
    exactly the same peculiar habit with the parent-tree.[47]

    These facts, it might have been thought, would have been sufficient to
    render it probable that a pendulous habit would in all cases be
    strictly inherited. But let us look to the other side. Mr. MacNab[48]
    sowed seeds of the weeping beech (_Fagus sylvanica_), but succeeded in
    raising only common beeches. Mr. Rivers, at my request, raised a number
    of seedlings from three distinct varieties of weeping elm; and at least
    one of the parent-trees was so situated that it could not have been
    crossed by any other elm; but none of the young trees, now about a foot
    or two in height, show the least signs of weeping. Mr. Rivers formerly
    sowed above twenty thousand seeds of the weeping ash (_Fraxinus
    excelsior_), and not a single seedling was in the least degree
    pendulous: in Germany, M. Borchmeyer raised a thousand seedlings, with
    the same result. Nevertheless, Mr. Anderson, of the Chelsea Botanic
    Garden, by sowing seed from a weeping ash, which was found before the
    year 1780, in Cambridgeshire, raised several pendulous trees.[49]
    Professor Henslow also informs me that some seedlings from a female
    weeping ash in the Botanic Garden at Cambridge were at first a little
    pendulous, but afterwards became quite upright: it is probable that
    this latter tree, which transmits to a certain extent its pendulous
    habit, was derived by a bud from the same original Cambridgeshire
    stock; whilst other weeping ashes may have had a distinct origin. But
    the crowning case, communicated to me by Mr. Rivers, which shows how
    capricious is the inheritance of a pendulous habit, is that a variety
    of another species of ash (_F. lentiscifolia_) which was formerly
    pendulous, "now about twenty years old has long lost this habit, every
    shoot being remarkably erect; but seedlings formerly raised from it
    were perfectly prostrate, the stems not rising more than two inches
    above the ground." Thus the weeping variety of the common ash, which
    has been extensively propagated by buds during a long period, did not,
    with Mr. Rivers, transmit its character to one seedling out of above
    twenty thousand; whereas the weeping variety of a second species of
    ash, which could not, whilst grown in the same garden, retain its own
    weeping character, transmitted to its seedlings the pendulous habit in
    excess!

    Many analogous facts could be given, showing how apparently capricious
    is the principle of inheritance. All the seedlings from a variety of
    the Barberry (_B. vulgaris_) with red leaves inherited the same
    character; only about one-third of the seedlings of the copper Beech
    (_Fagus sylvatica_) had purple leaves. Not one out of a hundred
    seedlings of a variety of the _Cerasus padus_, with yellow fruit, bore
    yellow fruit: one-twelfth of the seedlings of the variety of _Cornus
    mascula_, with yellow fruit, came true:[50] and lastly, all the trees
    raised by my father from a yellow-berried holly (_Ilex aquifolium_),
    {20} found wild, produced yellow berries. Vilmorin[51] observed in a
    bed of _Saponaria calabrica_ an extremely dwarf variety, and raised
    from it a large number of seedlings; some of these partially resembled
    their parent, and he selected their seed; but the grandchildren were
    not in the least dwarfed: on the other hand, he observed a stunted and
    bushy variety of _Tagetes signata_ growing in the midst of the common
    varieties by which it was probably crossed; for most of the seedlings
    raised from this plant were intermediate in character, only two
    perfectly resembling their parent; but seed saved from these two plants
    reproduced the new variety so truly, that hardly any selection has
    since been necessary.

    Flowers transmit their colour truly, or most capriciously. Many annuals
    come true: thus I purchased German seeds of thirty-four named
    sub-varieties of one _race_ of ten-week stocks (_Matthiola annua_), and
    raised a hundred and forty plants, all of which, with the exception of
    a single plant, came true. In saying this, however, it must be
    understood that I could distinguish only twenty kinds out of the
    thirty-four named sub-varieties; nor did the colour of the flower
    always correspond with the name affixed to the packet; but I say that
    they came true, because in each of the thirty-six short rows every
    plant was absolutely alike, with the one single exception. Again, I
    procured packets of German seed of twenty-five named varieties of
    common and quilled asters, and raised a hundred and twenty-four plants;
    of these, all except ten were true in the above limited sense; and I
    considered even a wrong shade of colour as false.

    It is a singular circumstance that white varieties generally transmit
    their colour much more truly than any other variety. This fact probably
    stands in close relation with one observed by Verlot,[52] namely, that
    flowers which are normally white rarely vary into any other colour. I
    have found that the white varieties of _Delphinium consolida_ and of
    the Stock are the truest. It is, indeed, sufficient to look through a
    nurseryman's seed-list, to see the large number of white varieties
    which can be propagated by seed. The several coloured varieties of the
    sweet-pea (_Lathyrus odoratus_) are very true; but I hear from Mr.
    Masters, of Canterbury, who has particularly attended to this plant,
    that the white variety is the truest. The hyacinth, when propagated by
    seed, is extremely inconstant in colour, but "white hyacinths almost
    always give by seed white-flowered plants;"[53] and Mr. Masters informs
    me that the yellow varieties also reproduce their colour, but of
    different shades. On the other hand, pink and blue varieties, the
    latter being the natural colour, are not nearly so true: hence, as Mr.
    Masters has remarked to me, "we see that a garden variety may acquire a
    more permanent habit than a natural species;" but it should have been
    added, that this occurs under cultivation, and therefore under changed
    conditions.

    With many flowers, especially perennials, nothing can be more
    fluctuating than the colour of the seedlings, as is notoriously the
    case with verbenas, carnations, dahlias, cinerarias, and others.[54] I
    sowed seed of twelve {21} named varieties of Snapdragon (_Antirrhinum
    majus_), and utter confusion was the result. In most cases the
    extremely fluctuating colour of seedling plants is probably in chief
    part due to crosses between differently-coloured varieties during
    previous generations. It is almost certain that this is the case with
    the polyanthus and coloured primrose (_Primula veris_ and _vulgaris_),
    from their reciprocally dimorphic structure;[55] and these are plants
    which florists speak of as never come true by seed: but if care be
    taken to prevent crossing, neither species is by any means very
    inconstant in colour; thus I raised twenty-three plants from a purple
    primrose, fertilised by Mr. J. Scott with its own pollen, and eighteen
    came up purple of different shades, and only five reverted to the
    ordinary yellow colour: again, I raised twenty plants from a bright-red
    cowslip, similarly treated by Mr. Scott, and every one perfectly
    resembled its parent in colour, as likewise did, with the exception of
    a single plant, 73 grandchildren. Even with the most variable flowers,
    it is probable that each delicate shade of colour might be permanently
    fixed so as to be transmitted by seed, by cultivation in the same soil,
    by long-continued selection, and especially by the prevention of
    crosses. I infer this from certain annual larkspurs (_Delphinium
    consolida_ and _ajacis_), of which common seedlings present a greater
    diversity of colour than any other plant known to me; yet on procuring
    seed of five named German varieties of _D. consolida_, only nine plants
    out of ninety-four were false; and the seedlings of six varieties of
    _D. ajacis_ were true in the same manner and degree as with the stocks
    above described. A distinguished botanist maintains that the annual
    species of Delphinium are always self-fertilised; therefore I may
    mention that thirty-two flowers on a branch of _D. consolida_, enclosed
    in a net, yielded twenty-seven capsules, with an average of 17.2 seed
    in each; whilst five flowers, under the same net, which were
    artificially fertilised, in the same manner as must be effected by bees
    during their incessant visits, yielded five capsules with an average of
    35.2 fine seed; and this shows that the agency of insects is necessary
    for the full fertility of this plant. Analogous facts could be given
    with respect to the crossing of many other flowers, such as carnations,
    &c., of which the varieties fluctuate much in colour.

    As with flowers, so with our domesticated animals, no character is more
    variable than colour, and probably in no animal more so than with the
    horse. Yet with a little care in breeding, it appears that races of any
    colour might soon be formed. Hofacker gives the result of matching two
    hundred and sixteen mares of four different colours with like-coloured
    stallions, without regard to the colour of their ancestors; and of the
    two hundred and sixteen colts born, eleven alone failed to inherit the
    colour of their parents: Autenrieth and Ammon assert that, after two
    generations, colts of a uniform colour are produced with certainty.[56]

In a few rare cases peculiarities fail to be inherited, apparently from the
force of inheritance being too strong. I have been assured by breeders of
the canary-bird that to get a good {22} jonquil-coloured bird it does not
answer to pair two jonquils, as the colour then comes out too strong, or is
even brown. So again, if two crested canaries are paired, the young birds
rarely inherit this character:[57] for in crested birds a narrow space of
bare skin is left on the back of the head, where the feathers are up-turned
to form the crest, and, when both parents are thus characterised, the
bareness becomes excessive, and the crest itself fails to be developed. Mr.
Hewitt, speaking of Laced Sebright Bantams, says[58] that, "why this should
be so, I know not, but I am confident that those that are best laced
frequently produce offspring very far from perfect in their markings,
whilst those exhibited by myself, which have so often proved successful,
were bred from the union of heavily-laced birds with those that were
scarcely sufficiently laced."

It is a singular fact that, although several deaf-mutes often occur in the
same family, and though their cousins and other relations are often in the
same condition, yet their parents are very rarely deaf-mutes. To give a
single instance: not one scholar out of 148, who were at the same time in
the London Institution, was the child of parents similarly afflicted. So
again, when a male or a female deaf-mute marries a sound person, their
children are most rarely affected: in Ireland out of 203 children thus
produced one alone was mute. Even when both parents have been deaf-mutes,
as in the case of forty-one marriages in the United States and of six in
Ireland, only two deaf and dumb children were produced. Mr. Sedgwick,[59]
in commenting on this remarkable and fortunate failure in the power of
transmission in the direct line, remarks that it may possibly be owing to
"excess having reversed the action of some natural law in development." But
it is safer in the present state of our knowledge to look at the whole case
as simply unintelligible.

       *       *       *       *       *

With respect to the inheritance of structures mutilated by injuries or
altered by disease it is difficult to come to any {23} definite conclusion.
In some cases mutilations have been practised for a vast number of
generations without any inherited result. Godron has remarked[60] that
different races of man have from time immemorial knocked out their upper
incisors, cut off joints of their fingers, made holes of immense size
through the lobes of their ears or through their nostrils, made deep gashes
in various parts of their bodies, and there is no reason whatever to
suppose that these mutilations have ever been inherited. Adhesions due to
inflammation and pits from the small-pox (and formerly many consecutive
generations must have been thus pitted) are not inherited. With respect to
Jews, I have been assured by three medical men of the Jewish faith that
circumcision, which has been practised for so many ages, has produced no
inherited effect; Blumenbach, on the other hand, asserts[61] that in
Germany Jews are often born in a condition rendering circumcision
difficult, so that a name is here applied to them signifying "born
circumcised." The oak and other trees must have borne galls from primeval
times, yet they do not produce inherited excrescences; many other such
facts could be adduced.

On the other hand, various cases have been recorded of cats, dogs, and
horses, which have had their tails, legs, &c., amputated or injured,
producing offspring with the same parts ill-formed; but as it is not at all
rare for similar malformations to appear spontaneously, all such cases may
be due to mere coincidence. Nevertheless, Dr. Prosper Lucas has given, on
good authorities, such a long list of inherited injuries, that it is
difficult not to believe in them. Thus, a cow that had lost a horn from an
accident with consequent suppuration, produced three calves which were
hornless on the same side of the head. With the horse, there seems hardly a
doubt that bony exostoses on the legs, caused by too much travelling on
hard roads, are inherited. Blumenbach records the case of a man who had his
little finger on the right hand almost cut off, and which in consequence
grew crooked, and his sons had the same finger on the same hand similarly
crooked. A soldier, fifteen years before his marriage, lost his left eye
from purulent ophthalmia, and his {24} two sons were microphthalmic on the
same side.[62] In all such cases, if truthfully reported, in which the
parent has had an organ injured on one side, and more than one child has
been born with the same organ affected on the same side, the chances
against mere coincidence are enormous. But perhaps the most remarkable and
trustworthy fact is that given by Dr. Brown-Séquard,[63] namely, that many
young guinea-pigs inherited an epileptic tendency from parents which had
been subjected to a particular operation, inducing in the course of a few
weeks a convulsive disease like epilepsy: and it should be especially noted
that this eminent physiologist bred a large number of guinea-pigs from
animals which had not been operated on, and not one of these manifested the
epileptic tendency. On the whole, we can hardly avoid admitting, that
injuries and mutilations, especially when followed by disease, or perhaps
exclusively when thus followed, are occasionally inherited.

Although many congenital monstrosities are inherited, of which examples
have already been given, and to which may be added the lately recorded case
of the transmission during a century of hare-lip with a cleft-palate in the
writer's own family,[64] yet other malformations are rarely or never
inherited. Of these later cases, many are probably due to injuries in the
womb or egg, and would come under the head of non-inherited injuries or
mutilations. With plants, a long catalogue of inherited monstrosities of
the most serious and diversified nature could easily be given; and with
plants, there is no reason to suppose that monstrosities are caused by
direct injuries to the seed or embryo.

_Causes of Non-inheritance._

A large number of cases of non-inheritance are intelligible on the
principle, that a strong tendency to inheritance does exist, but {25} that
it is overborne by hostile or unfavourable conditions of life. No one would
expect that our improved pigs, if forced during several generations to
travel about and root in the ground for their own subsistence, would
transmit, as truly as they now do, their tendency to fatten, and their
short muzzles and legs. Dray-horses assuredly would not long transmit their
great size and massive limbs, if compelled to live on a cold, damp
mountainous region; we have indeed evidence of such deterioration in the
horses which have run wild on the Falkland Islands. European dogs in India
often fail to transmit their true character. Our sheep in tropical
countries lose their wool in a few generations. There seems also to be a
close relation between certain peculiar pastures and the inheritance of an
enlarged tail in fat-tailed sheep, which form one of the most ancient
breeds in the world. With plants, we have seen that the American varieties
of maize lose their proper character in the course of two or three
generations, when cultivated in Europe. Our cabbages, which here come so
true by seed, cannot form heads in hot countries. Under changed
circumstances, periodical habits of life soon fail to be transmitted, as
the period of maturity in summer and winter wheat, barley, and vetches. So
it is with animals; for instance, a person whose statement I can trust,
procured eggs of Aylesbury ducks from that town, where they are kept in
houses and are reared as early as possible for the London market; the ducks
bred from these eggs in a distant part of England, hatched their first
brood on January 24th, whilst common ducks, kept in the same yard and
treated in the same manner, did not hatch till the end of March; and this
shows that the period of hatching was inherited. But the grandchildren of
these Aylesbury ducks completely lost their early habit of incubation, and
hatched their eggs at the same time with the common ducks of the same
place.

Many cases of non-inheritance apparently result from the conditions of life
continually inducing fresh variability. We have seen that when the seeds of
pears, plums, apples, &c., are sown, the seedlings generally inherit some
degree of family likeness from the parent-variety. Mingled with these
seedlings, a few, and sometimes many, worthless, wild-looking plants
commonly appear; and their appearance may be attributed to the principle of
reversion. But scarcely a single seedling will be found {26} perfectly to
resemble the parent-form; and this, I believe, may be accounted for by
constantly recurring variability induced by the conditions of life. I
believe in this, because it has been observed that certain fruit-trees
truly propagate their kind whilst growing on their own roots, but when
grafted on other stocks, and by this process their natural state is
manifestly affected, they produce seedlings which vary greatly, departing
from the parental type in many characters.[65] Metzger, as stated in the
ninth chapter, found that certain kinds of wheat brought from Spain and
cultivated in Germany, failed during many years to reproduce themselves
truly; but that at last, when accustomed to their new conditions, they
ceased to be variable,--that is, they became amenable to the power of
inheritance. Nearly all the plants which cannot be propagated with any
approach to certainty by seed, are kinds which have long been propagated by
buds, cuttings, offsets, tubers, &c., and have in consequence been
frequently exposed during their individual lives to widely diversified
conditions of life. Plants thus propagated become so variable, that they
are subject, as we have seen in the last chapter, even to bud-variation.
Our domesticated animals, on the other hand, are not exposed during their
individual lives to such extremely diversified conditions, and are not
liable to such extreme variability; therefore they do not lose the power of
transmitting most of their characteristic features. In the foregoing
remarks on non-inheritance, crossed breeds are of course excluded, as their
diversity mainly depends on the unequal development of characters derived
from either parent, modified by the principles of reversion and prepotency.

_Conclusion._

It has, I think, been shown in the early part of this chapter how strongly
new characters of the most diversified nature, whether normal or abnormal,
injurious or beneficial, whether affecting organs of the highest or most
trifling importance, are inherited. Contrary to the common opinion, it is
often sufficient for the inheritance of some peculiar character, that one
parent alone should possess it, as in most cases in which the rarer {27}
anomalies have been transmitted. But the power of transmission is extremely
variable: in a number of individuals descended from the same parents, and
treated in the same manner, some display this power in a perfect manner,
and in some it is quite deficient; and for this difference no reason can be
assigned. In some cases the effects of injuries or mutilations apparently
are inherited; and we shall see in a future chapter that the effects of the
long-continued use and disuse of parts are certainly inherited. Even those
characters which are considered the most fluctuating, such as colour, are
with rare exceptions transmitted much more forcibly than is generally
supposed. The wonder, indeed, in all cases is not that any character should
be transmitted, but that the power of inheritance should ever fail. The
checks to inheritance, as far as we know them, are, firstly, circumstances
hostile to the particular character in question; secondly, conditions of
life incessantly inducing fresh variability; and lastly, the crossing of
distinct varieties during some previous generation, together with reversion
or atavism--that is, the tendency in the child to resemble its
grand-parents or more remote ancestors instead of its immediate parents.
This latter subject will be fully discussed in the following chapter.

       *       *       *       *       *


{28}

CHAPTER XIII.

INHERITANCE _continued_--REVERSION OR ATAVISM.

    DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN
    PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED
    PLANTS--REVERSION IN FERAL ANIMALS AND PLANTS--REVERSION IN CROSSED
    VARIETIES AND SPECIES--REVERSION THROUGH BUD-PROPAGATION, AND BY
    SEGMENTS IN THE SAME FLOWER OR FRUIT--IN DIFFERENT PARTS OF THE BODY IN
    THE SAME ANIMAL--THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION,
    VARIOUS CASES OF, WITH INSTINCTS--OTHER PROXIMATE CAUSES OF
    REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL CHARACTERS--UNEQUAL
    DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE WITH ADVANCING AGE
    OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALL ITS LATENT
    CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS DUE IN
    SOME CASES TO REVERSION.

The great principle of inheritance to be discussed in this chapter has been
recognised by agriculturists and authors of various nations, as shown by
the scientific term _Atavism_, derived from atavus, an ancestor; by the
English terms of _Reversion_, or _Throwing back_; by the French
_Pas-en-arrière_; and by the German _Rück-schlag_, or _Rück-schritt_. When
the child resembles either grandparent more closely than its immediate
parents, our attention is not much arrested, though in truth the fact is
highly remarkable; but when the child resembles some remote ancestor, or
some distant member in a collateral line,--and we must attribute the latter
case to the descent of all the members from a common progenitor,--we feel a
just degree of astonishment. When one parent alone displays some
newly-acquired and generally inheritable character, and the offspring do
not inherit it, the cause may lie in the other parent having the power of
prepotent transmission. But when both parents are similarly characterised,
and the child does not, whatever the cause may be, inherit the character in
question, but resembles its grandparents, we have one of the simplest cases
of reversion. We continually see another and even more simple case of
atavism, though not generally included under this head, namely, when {29}
the son more closely resembles his maternal than his paternal grandsire in
some male attribute, as in any peculiarity in the beard of man, the horns
of the bull, the hackles or comb of the cock, or, as in certain diseases
necessarily confined to the male sex; for the mother cannot possess or
exhibit such male attributes, yet the child has inherited them, through her
blood, from his maternal grandsire.

The cases of reversion may be divided into two main classes, which,
however, in some instances, blend into each other; namely, first, those
occurring in a variety or race which has not been crossed, but has lost by
variation some character that it formerly possessed, and which afterwards
reappears. The second class includes all cases in which a distinguishable
individual, sub-variety, race, or species, has at some former period been
crossed with a distinct form, and a character derived from this cross,
after having disappeared during one or several generations, suddenly
reappears. A third class, differing only in the manner of reproduction,
might be formed to include all cases of reversion effected by means of
buds, and therefore independent of true or seminal generation. Perhaps even
a fourth class might be instituted, to include reversions by segments in
the same individual flower or fruit, and in different parts of the body in
the same individual animal as it grows old. But the two first main classes
will be sufficient for our purpose.

       *       *       *       *       *

_Reversion to lost Characters by pure or uncrossed forms._--Striking
instances of this first class of cases were given in the sixth chapter,
namely, of the occasional reappearance, in variously-coloured pure breeds
of the pigeon, of blue birds with all the marks which characterise the wild
_Columba livia_. Similar cases were given in the case of the fowl. With the
common ass, as we now know that the legs of the wild progenitor are
striped, we may feel assured that the occasional appearance of such stripes
in the domestic animal is a case of simple reversion. But I shall be
compelled to refer again to these cases, and therefore will here pass them
over.

The aboriginal species from which our domesticated cattle and sheep are
descended, no doubt possessed horns; but several hornless breeds are now
well established. Yet in these--for instance, {30} in Southdown sheep--"it
is not unusual to find among the male lambs some with small horns." The
horns, which thus occasionally reappear in other polled breeds, either
"grow to the full size, or are curiously attached to the skin alone and
hang loosely down, or drop off."[66] The Galloways and Suffolk cattle have
been hornless for the last 100 or 150 years, but a horned calf, with the
horn often loosely attached, is occasionally born.[67]

There is reason to believe that sheep in their early domesticated condition
were "brown or dingy black;" but even in the time of David certain flocks
were spoken of as white as snow. During the classical period the sheep of
Spain are described by several ancient authors as being black, red, or
tawny.[68] At the present day, notwithstanding the great care which is
taken to prevent it, particoloured lambs and some entirely black are
occasionally dropped by our most highly improved and valued breeds, such as
the Southdowns. Since the time of the famous Bakewell, during the last
century, the Leicester sheep have been bred with the most scrupulous care;
yet occasionally grey-faced, or black-spotted, or wholly black lambs
appear.[69] This occurs still more frequently with the less improved
breeds, such as the Norfolks.[70] As bearing on this tendency in sheep to
revert to dark colours, I may state (though in doing so I trench on the
reversion of crossed breeds, and likewise on the subject of prepotency)
that the Rev. W. D. Fox was informed that seven white Southdown ewes were
put to a so-called Spanish ram, which had two small black spots on his
sides, and they produced thirteen lambs, all perfectly black. Mr. Fox
believes that this ram belonged to a breed which he has himself kept, and
which is always spotted with black and white; and he finds that Leicester
sheep crossed by rams of this breed always produce black lambs: he has gone
on recrossing these crossed sheep with pure white Leicesters during three
successive {31} generations, but always with the same result. Mr. Fox was
also told by the friend from whom the spotted breed was procured, that he
likewise had gone on for six or seven generations crossing with white
sheep, but still black lambs were invariably produced.

Similar facts could be given with respect to tailless breeds of various
animals. For instance, Mr. Hewitt[71] states that chickens bred from some
Rumpless fowls, which were reckoned so good that they won a prize at an
exhibition, "in a considerable number of instances were furnished with
fully developed tail-feathers." On inquiry, the original breeder of these
fowls stated that, from the time when he had first kept them, they had
often produced fowls furnished with tails; but that these latter would
again reproduce rumpless chickens.

Analogous cases of reversion occur in the vegetable kingdom; thus "from
seeds gathered from the finest cultivated varieties of Heartsease (_Viola
tricolor_), plants perfectly wild both in their foliage and their flowers
are frequently produced;"[72] but the reversion in this instance is not to
a very ancient period, for the best existing varieties of the heartsease
are of comparatively modern origin. With most of our cultivated vegetables
there is some tendency to reversion to what is known to be, or may be
presumed to be, their aboriginal state; and this would be more evident if
gardeners did not generally look over their beds of seedlings, and pull up
the false plants or "rogues" as they are called. It has already been
remarked, that some few seedling apples and pears generally resemble, but
apparently are not identical with, the wild trees from which they are
descended. In our turnip[73] and carrot-beds a few plants often
"break"--that is, flower too soon; and their roots are generally found to
be hard and stringy, as in the parent-species. By the aid of a little
selection, carried on during a few generations, most of our cultivated
plants could probably be brought back, without any great change in their
conditions of life, to a wild or nearly wild condition: Mr. Buckman has
effected this with the parsnip;[74] {32} and Mr. Hewett C. Watson, as he
informs me, selected, during three generations, "the most diverging plants
of Scotch kail, perhaps one of the least modified varieties of the cabbage;
and in the third generation some of the plants came very close to the forms
now established in England about old castle-walls, and called indigenous."

       *       *       *       *       *

_Reversion in Animals and Plants which have run wild._--In the cases
hitherto considered, the reverting animals and plants have not been exposed
to any great or abrupt change in their conditions of life which could have
induced this tendency; but it is very different with animals and plants
which have become feral or run wild. It has been repeatedly asserted in the
most positive manner by various authors, that feral animals and plants
invariably return to their primitive specific type. It is curious on what
little evidence this belief rests. Many of our domesticated animals could
not subsist in a wild state; thus, the more highly improved breeds of the
pigeon will not "field" or search for their own food. Sheep have never
become feral, and would be destroyed by almost every beast of prey. In
several cases we do not know the aboriginal parent-species, and cannot
possibly tell whether or not there has been any close degree of reversion.
It is not known in any instance what variety was first turned out; several
varieties have probably in some cases run wild, and their crossing alone
would tend to obliterate their proper character. Our domesticated animals
and plants, when they run wild, must always be exposed to new conditions of
life, for, as Mr. Wallace[75] has well remarked, they have to obtain their
own food, and are exposed to competition with the native productions. Under
these circumstances, if our domesticated animals did not undergo change of
some kind, the result would be quite opposed to the conclusions arrived at
in this work. Nevertheless, I do not doubt that the simple fact of animals
and plants becoming feral, does cause some tendency to reversion to the
primitive state; though this tendency has been much exaggerated by some
authors.

{33}

    I will briefly run through the recorded cases. With neither horses nor
    cattle is the primitive stock known; and it has been shown in former
    chapters that they have assumed different colours in different
    countries. Thus the horses which have run wild in South America are
    generally brownish-bay, and in the East dun-coloured; their heads have
    become larger and coarser, and this may be due to reversion. No careful
    description has been given of the feral goat. Dogs which have run wild
    in various countries have hardly anywhere assumed a uniform character;
    but they are probably descended from several domestic races, and
    aboriginally from several distinct species. Feral cats, both in Europe
    and La Plata, are regularly striped; in some cases they have grown to
    an unusually large size, but do not differ from the domestic animal in
    any other character. When variously-coloured tame rabbits are turned
    out in Europe, they generally reacquire the colouring of the wild
    animal; there can be no doubt that this does really occur, but we
    should remember that oddly-coloured and conspicuous animals would
    suffer much from beasts of prey and from being easily shot; this at
    least was the opinion of a gentleman who tried to stock his woods with
    a nearly white variety; and when thus destroyed, they would in truth be
    supplanted by, instead of being transformed into, the common rabbit. We
    have seen that the feral rabbits of Jamaica, and especially of Porto
    Santo, have assumed new colours and other new characters. The best
    known case of reversion, and that on which the widely-spread belief in
    its universality apparently rests, is that of pigs. These animals have
    run wild in the West Indies, South America, and the Falkland Islands,
    and have everywhere acquired the dark colour, the thick bristles, and
    great tusks of the wild boar; and the young have reacquired
    longitudinal stripes. But even in the case of the pig, Roulin describes
    the half-wild animals in different parts of South America as differing
    in several respects. In Louisiana the pig[76] has run wild, and is said
    to differ a little in form, and much in colour, from the domestic
    animal, yet does not closely resemble the wild boar of Europe. With
    pigeons and fowls,[77] it is not known what variety was first turned
    out, nor what character the feral birds have assumed. The guinea-fowl
    in the West Indies, when feral, seems to vary more than in the
    domesticated state.

    With respect to plants run wild, Dr. Hooker[78] has strongly insisted
    on what slight evidence the common belief in their power of reversion
    rests. Godron[79] describes wild turnips, carrots, and celery; but
    these plants in their cultivated state hardly differ from their wild
    prototypes, except in the {34} succulency and enlargement of certain
    parts,--characters which would be surely lost by plants growing in a
    poor soil and struggling with other plants. No cultivated plant has run
    wild on so enormous a scale as the cardoon (_Cynara cardunculus_) in La
    Plata. Every botanist who has seen it growing there, in vast beds, as
    high as a horse's back, has been struck with its peculiar appearance;
    but whether it differs in any important point from the cultivated
    Spanish form, which is said not to be prickly like its American
    descendant, or whether it differs from he wild Mediterranean species,
    which is said not to be social, I do not know.

       *       *       *       *       *

_Reversion to Characters derived from a Cross, in the case of
Sub-varieties, Races, and Species._--When an individual having some
recognizable peculiarity unites with another of the same sub-variety, not
having the peculiarity in question, it often reappears in the descendants
after an interval of several generations. Every one must have noticed, or
heard from old people of children closely resembling in appearance or
mental disposition, or in so small and complex a character as expression,
one of their grandparents, or some more distant collateral relation. Very
many anomalies of structure and diseases,[80] of which instances have been
given in the last chapter, have come into a family from one parent, and
have reappeared in the progeny after passing over two or three generations.
The following case has been communicated to me on good authority, and may,
I believe, be fully trusted: a pointer-bitch produced seven puppies; four
were marked with blue and white, which is so unusual a colour with pointers
that she was thought to have played false with one of the greyhounds, and
the whole litter was condemned; but the gamekeeper was permitted to save
one as a curiosity. Two years afterwards a friend of the owner saw the
young dog, and declared that he was the image of his old pointer-bitch
Sappho, the only blue and white pointer of pure descent which he had ever
seen. This led to close inquiry, and it was proved that he was the
great-great-grandson of Sappho; so that, according to the common
expression, he had only 1-16th of her blood in his veins. Here it can
hardly be doubted that a character derived from a cross with an individual
of the same variety reappeared after passing over three generations.

{35}

When two distinct races are crossed, it is notorious that the tendency in
the offspring to revert to one or both parent-forms is strong, and endures
for many generations. I have myself seen the clearest evidence of this in
crossed pigeons and with various plants. Mr. Sidney[81] states that, in a
litter of Essex pigs, two young ones appeared which were the image of the
Berkshire boar that had been used twenty-eight years before in giving size
and constitution to the breed. I observed in the farmyard at Betley Hall
some fowls showing a strong likeness to the Malay breed, and was told by
Mr. Tollet that he had forty years before crossed his birds with Malays;
and that, though he had at first attempted to get rid of this strain, he
had subsequently given up the attempt in despair, as the Malay character
would reappear.

This strong tendency in crossed breeds to revert has given rise to endless
discussions in how many generations after a single cross, either with a
distinct breed or merely with an inferior animal, the breed may be
considered as pure, and free from all danger of reversion. No one supposes
that less than three generations suffices, and most breeders think that
six, seven, or eight are necessary, and some go to still greater
lengths.[82] But neither in the case of a breed which has been contaminated
by a single cross, nor when, in the attempt to form an intermediate breed,
half-bred animals have been matched together during many generations, can
any rule be laid down how soon the tendency to reversion will be
obliterated. It depends on the difference in the strength or prepotency of
transmission in the two parent-forms, on their actual amount of difference,
and on the nature of the conditions of life to which the crossed offspring
are exposed. But we must be careful not to confound these cases of
reversion to characters gained from a cross, with those given under the
first class, in which characters originally common to _both_ parents, but
lost at some former period, reappear; for such characters may recur after
an almost indefinite number of generations.

{36}

The law of reversion is equally powerful with hybrids, when they are
sufficiently fertile to breed together, or when they are repeatedly crossed
with either pure parent-form, as with mongrels. It is not necessary to give
instances, for in the case of plants almost every one who has worked on
this subject from the time of Kölreuter to the present day has insisted on
this tendency. Gärtner has recorded some good instances; but no one has
given more striking cases than Naudin.[83] The tendency differs in degree
or strength in different groups, and partly depends, as we shall presently
see, on the fact of the parent-plants having been long cultivated. Although
the tendency to reversion is extremely general with nearly all mongrels and
hybrids, it cannot be considered as invariably characteristic of them;
there is, also, reason to believe that it may be mastered by long-continued
selection; but these subjects will more properly be discussed in a future
chapter on Crossing. From what we see of the power and scope of reversion,
both in pure races and when varieties or species are crossed, we may infer
that characters of almost every kind are capable of reappearance after
having been lost for a great length of time. But it does not follow from
this that in each particular case certain characters will reappear: for
instance, this will not occur when a race is crossed with another endowed
with prepotency of transmission. In some few cases the power of reversion
wholly fails, without our being able to assign any cause for the failure:
thus it has been stated that in a French family in which 85 out of above
600 members, during six generations, had been subject to night-blindness,
"there has not been a single example of this affection in the children of
parents who were themselves free from it."[84]

       *       *       *       *       *

_Reversion through Bud-propagation--Partial Reversion, by segments in the
same flower or fruit, or in different parts of the {37} body in the same
individual animal._--In the eleventh chapter, many cases of reversion by
buds, independently of seminal generation, were given--as when a leaf-bud
on a variegated, curled, or laciniated variety suddenly reassumes its
proper character; or as when a Provence-rose appears on a moss-rose, or a
peach on a nectarine-tree. In some of these cases only half the flower or
fruit, or a smaller segment, or mere stripes, reassumed their former
character; and here we have with buds reversion by segments. Vilmorin[85]
has also recorded several cases with plants derived from seed, of flowers
reverting by stripes or blotches to their primitive colours: he states that
in all such cases a white or pale-coloured variety must first be formed,
and, when this is propagated for a length of time by seed, striped
seedlings occasionally make their appearance; and these can afterwards by
care be multiplied by seed.

The stripes and segments just referred to are not due, as far as is known,
to reversion to characters derived from a cross, but to characters lost by
variation. These cases, however, as Naudin[86] insists in his discussion on
disjunction of character, are closely analogous with those given in the
eleventh chapter, in which crossed plants are known to have produced
half-and-half or striped flowers and fruit, or distinct kinds of flowers on
the same root resembling the two parent-forms. Many piebald animals
probably come under this same head. Such cases, as we shall see in the
chapter on Crossing, apparently result from certain characters not readily
blending together, and, as a consequence of this incapacity for fusion, the
offspring either perfectly resemble one of their two parents, or resemble
one parent in one part and the other parent in another part; or whilst
young are intermediate in character, but with advancing age revert wholly
or by segments to either parent-form, or to both. Thus young trees of the
_Cytisus adami_ are intermediate in foliage and flowers between the two
parent-forms; but when older the buds continually revert either partially
or wholly to both forms. The cases given in the eleventh chapter on the
changes which occurred during growth {38} in crossed plants of Tropæolum,
Cereus, Datura, and Lathyrus are all analogous. As however these plants are
hybrids of the first generation, and as their buds after a time come to
resemble their parents and not their grandparents, these cases do not at
first appear to come under the law of reversion in the ordinary sense of
the word; nevertheless, as the change is effected through a succession of
bud-generations on the same plant, they may be thus included.

Analogous facts have been observed in the animal kingdom, and are more
remarkable, as they occur strictly in the same individual, and not as with
plants through a succession of bud-generations. With animals the act of
reversion, if it can be so designated, does not pass over a true
generation, but merely over the early stages of growth in the same
individual. For instance, I crossed several white hens with a black cock,
and many of the chickens were during the first year perfectly white, but
acquired during the second year black feathers; on the other hand, some of
the chickens which were at first black became during the second year
piebald with white. A great breeder[87] says, that a Pencilled Brahma hen
which has any of the blood of the Light Brahma in her, will "occasionally
produce a pullet well pencilled during the first year, but she will most
likely moult brown on the shoulders and become quite unlike her original
colours in the second year." The same thing occurs with Light Brahmas if of
impure blood. I have observed exactly similar cases with the crossed
offspring from differently coloured pigeons. But here is a more remarkable
fact: I crossed a turbit, which has a frill formed by the feathers being
reversed on its breast, with a trumpeter; and one of the young pigeons thus
raised showed at first not a trace of the frill, but, after moulting
thrice, a small yet unmistakably distinct frill appeared on its breast.
According to Girou,[88] calves produced from a red cow by a black bull, or
from a black cow by a red bull, are not rarely born red, and subsequently
become black.

In the foregoing cases, the characters which appear with advancing age are
the result of a cross in the previous or some {39} former generation; but
in the following cases, the characters which thus reappear formerly
appertained to the species, and were lost at a more or less remote epoch.
Thus, according to Azara,[89] the calves of a hornless race of cattle which
originated in Corrientes, though at first quite hornless, as they become
adult sometimes acquire small, crooked, and loose horns; and these in
succeeding years occasionally become attached to the skull. White and black
bantams, both of which generally breed true, sometimes assume as they grow
old a saffron or red plumage. For instance, a first-rate black bantam has
been described, which during three seasons was perfectly black, but then
annually became more and more red; and it deserves notice that this
tendency to change, whenever it occurs in a bantam, "is almost certain to
prove hereditary."[90] The cuckoo or blue-mottled Dorking cock, when old,
is liable to acquire yellow or orange hackles in place of his proper
bluish-grey hackles.[91] Now, as _Gallus bankiva_ is coloured red and
orange, and as Dorking fowls and both kinds of bantams are descended from
this species, we can hardly doubt that the change which occasionally occurs
in the plumage of these birds as their age advances, results from a
tendency in the individual to revert to the primitive type.

       *       *       *       *       *

_Crossing as a direct cause of Reversion._--It has long been notorious that
hybrids and mongrels often revert to both or to one of their parent-forms,
after an interval of from two to seven or eight, or according to some
authorities even a greater number of generations. But that the act of
crossing in itself gives an impulse towards reversion, as shown by the
reappearance of long-lost characters, has never, I believe, been hitherto
proved. The proof lies in certain peculiarities, which do not characterise
the immediate parents, and therefore cannot have been derived from them,
frequently appearing in the offspring of two breeds when crossed, which
peculiarities never appear, or appear with extreme rarity, in these same
breeds, as long as they are {40} precluded from crossing. As this
conclusion seems to me highly curious and novel, I will give the evidence
in detail.

    My attention was first called to this subject, and I was led to make
    numerous experiments, by MM. Boitard and Corbié having stated that,
    when they crossed certain breeds, pigeons coloured like the wild _C.
    livia_, or the common dovecot, namely, slaty-blue, with double black
    wing-bars, sometimes chequered with black, white loins, the tail barred
    with black, with the outer feathers edged with white, were almost
    invariably produced. The breeds which I crossed, and the remarkable
    results attained, have been fully described in the sixth chapter. I
    selected pigeons, belonging to true and ancient breeds, which had not a
    trace of blue or any of the above specified marks; but when crossed,
    and their mongrels recrossed, young birds were continually produced,
    more or less plainly coloured slaty-blue, with some or all of the
    proper characteristic marks. I may recall to the reader's memory one
    case, namely, that of a pigeon, hardly distinguishable from the wild
    Shetland species, the grandchild of a red-spot, white fantail, and two
    black barbs, from any of which, when purely-bred, the production of a
    pigeon coloured like the wild _C. livia_ would have been almost a
    prodigy.

    I was thus led to make the experiments, recorded in the seventh
    chapter, on fowls. I selected long-established, pure breeds, in which
    there was not a trace of red, yet in several of the mongrels feathers
    of this colour appeared; and one magnificent bird, the offspring of a
    black Spanish cock and white Silk hen, was coloured almost exactly like
    the wild _Gallus bankiva_. All who know anything of the breeding of
    poultry will admit that tens of thousands of pure Spanish and of pure
    white Silk fowls might have been reared without the appearance of a red
    feather. The fact, given on the authority of Mr. Tegetmeier, of the
    frequent appearance, in mongrel fowls, of pencilled or
    transversely-barred feathers, like those common to many gallinaceous
    birds, is likewise apparently a case of reversion to a character
    formerly possessed by some ancient progenitor of the family. I owe to
    the kindness of this same excellent observer the inspection of some
    neck-hackles and tail-feathers from a hybrid between the common fowl
    and a very distinct species, the _Gallus varius_; and these feathers
    are transversely striped in a conspicuous manner with dark metallic
    blue and grey, a character which could not have been derived from
    either immediate parent.

    I have been informed by Mr. B. P. Brent, that he crossed a white
    Aylesbury drake and a black so-called Labrador duck, both of which are
    true breeds, and he obtained a young drake closely like the mallard
    (_A. boschas_). Of the musk-duck (_A. moschata_, Linn.) there are two
    sub-breeds, namely, white and slate-coloured; and these I am informed
    breed true, or nearly true. But the Rev. W. D. Fox tells me that, by
    putting a white drake to a slate-coloured duck, black birds, pied with
    white, like the wild musk-duck, were always produced.

    We have seen in the fourth chapter, that the so-called Himalayan
    rabbit, with its snow-white body, black ears, nose, tail, and feet,
    breeds {41} perfectly true. This race is known to have been formed by
    the union of two varieties of silver-grey rabbits. Now, when a
    Himalayan doe was crossed by a sandy-coloured buck, a silver-grey
    rabbit was produced; and this is evidently a case of reversion to one
    of the parent varieties. The young of the Himalayan rabbit are born
    snow-white, and the dark marks do not appear until some time
    subsequently; but occasionally young Himalayan rabbits are born of a
    light silver-grey, which colour soon disappears; so that here we have a
    trace of reversion, during an early period of life, to the
    parent-varieties, independently of any recent cross.

    In the third chapter is was shown that at an ancient period some breeds
    of cattle in the wilder parts of Britain were white with dark ears, and
    that the cattle now kept half wild in certain parks, and those which
    have run quite wild in two distant parts of the world, are likewise
    thus coloured. Now, an experienced breeder, Mr. J. Beasley, of
    Northamptonshire,[92] crossed some carefully selected West Highland
    cows with purely-bred shorthorn bulls. The bulls were red, red and
    white, or dark roan; and the Highland cows were all of a red colour,
    inclining to a light or yellow shade. But a considerable number of the
    offspring--and Mr. Beasley calls attention to this as a remarkable
    fact--were white, or white with red ears. Bearing in mind that none of
    the parents were white, and that they were purely-bred animals, it is
    highly probable that here the offspring reverted, in consequence of the
    cross, to the colour either of the aboriginal parent-species or of some
    ancient and half-wild parent-breed. The following case, perhaps, comes
    under the same head: cows in their natural state have their udders but
    little developed, and do not yield nearly so much milk as our
    domesticated animals. Now there is some reason to believe[93] that
    cross-bred animals between two kinds, both of which are good milkers,
    such as Alderneys and Shorthorns, often turn out worthless in this
    respect.

    In the chapter on the Horse reasons were assigned for believing that
    the primitive stock was striped and dun-coloured; and details were
    given, showing that in all parts of the world stripes of a dark colour
    frequently appear along the spine, across the legs, and on the
    shoulders, where they are occasionally double or treble, and even
    sometimes on the face and body of horses of all breeds and of all
    colours. But the stripes appear most frequently on the various kinds of
    duns. They may sometimes plainly be seen on foals, and subsequently
    disappear. The dun-colour and the stripes are strongly transmitted when
    a horse thus characterised is crossed with any other; but I was not
    able to prove that striped duns are generally produced from the
    crossing of two distinct breeds, neither of which are duns, though this
    does sometimes occur.

    The legs of the ass are often striped, and this may be considered as a
    reversion to the wild parent-form, the _Asinus tæniopus_ of
    Abyssinia,[94] which is thus striped. In the domestic animal the
    stripes on the shoulder are occasionally double, or forked at the
    extremity, as in certain zebrine {42} species. There is reason to
    believe that the foal is frequently more plainly striped on the legs
    than the adult animal. As with the horse, I have not acquired any
    distinct evidence that the crossing of differently-coloured varieties
    of the ass brings out the stripes.

    But now let us turn to the result of crossing the horse and ass.
    Although mules are not nearly so numerous in England as asses, I have
    seen a much greater number with striped legs, and with the stripes far
    more conspicuous than in either parent-form. Such mules are generally
    light-coloured, and might be called fallow-duns. The shoulder-stripe in
    one instance was deeply forked at the extremity, and in another
    instance was double, though united in the middle. Mr. Martin gives a
    figure of a Spanish mule with strong zebra-like marks on its legs,[95]
    and remarks, that mules are particularly liable to be thus striped on
    their legs. In South America, according to Roulin,[96] such stripes are
    more frequent and conspicuous in the mule than in the ass. In the
    United States, Mr. Gosse,[97] speaking of these animals, says, "that in
    a great number, perhaps in nine out of every ten, the legs are banded
    with transverse dark stripes."

    Many years ago I saw in the Zoological Gardens a curious triple hybrid,
    from a bay mare, by a hybrid from a male ass and female zebra. This
    animal when old had hardly any stripes; but I was assured by the
    superintendent, that when young it had shoulder-stripes, and faint
    stripes on its flanks and legs. I mention this case more especially as
    an instance of the stripes being much plainer during youth than in old
    age.

    As the zebra has such conspicuously striped legs, it might have been
    expected that the hybrids from this animal and the common ass would
    have had their legs in some degree striped; but it appears from the
    figures given in Dr. Gray's 'Knowsley Gleanings,' and still more
    plainly from that given by Geoffroy and F. Cuvier,[98] that the legs
    are much more conspicuously striped than the rest of the body; and this
    fact is intelligible only on the belief that the ass aids in giving,
    through the power of reversion, this character to its hybrid offspring.

    The quagga is banded over the whole front part of its body like a
    zebra, but has no stripes on its legs, or mere traces of them. But in
    the famous hybrid bred by Lord Morton,[99] from a chesnut, nearly
    purely-bred, Arabian mare, by a male quagga, the stripes were "more
    strongly defined and darker than those on the legs of the quagga." The
    mare was subsequently put to a black Arabian horse, and bore two colts,
    both of which, as formerly stated, were plainly striped on the legs,
    and one of them likewise had stripes on the neck and body.

    The _Asinus Indicus_[100] is characterised by a spinal stripe, without
    shoulder {43} or leg stripes; but traces of these latter stripes may
    occasionally be seen even in the adult;[101] and Colonel S. Poole, who
    has had ample opportunities for observation, informs me that in the
    foal, when first born, the head and legs are often striped, but the
    shoulder-stripe is not so distinct as in the domestic ass; all these
    stripes, excepting that along the spine, soon disappear. Now a hybrid,
    raised at Knowsley[102] from a female of this species by a male
    domestic ass, had all four legs transversely and conspicuously striped,
    had three short stripes on each shoulder, and had even some zebra-like
    stripes on its face! Dr. Gray informs me that he has seen a second
    hybrid of the same parentage similarly striped.

From these facts we see that the crossing of the several equine species
tends in a marked manner to cause stripes to appear on various parts of the
body, especially on the legs. As we do not know whether the primordial
parent of the genus was striped, the appearance of the stripes can only
hypothetically be attributed to reversion. But most persons, after
considering the many undoubted cases of variously coloured marks
reappearing by reversion in crossed pigeons, fowls, ducks, &c., will come
to the same conclusion with respect to the horse-genus; and in this case we
must admit that the progenitor of the group was striped on the legs,
shoulders, face, and probably over the whole body, like a zebra. If we
reject this view, the frequent and almost regular appearance of stripes in
the several foregoing hybrids is left without any explanation.

       *       *       *       *       *

It would appear that with crossed animals a similar tendency to the
recovery of lost characters holds good even with instincts. There are some
breeds of fowls which are called "everlasting layers," because they have
lost the instinct of incubation; and so rare is it for them to incubate
that I have seen notices published in works on poultry, when hens of such
breeds have taken to sit.[103] Yet the aboriginal species was of course a
good incubator; for with birds in a state of nature hardly any {44}
instinct is so strong as this. Now, so many cases have been recorded of the
crossed offspring from two races, neither of which are incubators, becoming
first-rate sitters, that the reappearance of this instinct must be
attributed to reversion from crossing. One author goes so far as to say,
"that a cross between two non-sitting varieties almost invariably produces
a mongrel that becomes broody, and sits with remarkable steadiness."[104]
Another author, after giving a striking example, remarks that the fact can
be explained only on the principle that "two negatives make a positive." It
cannot, however, be maintained that hens produced from a cross between two
non-sitting breeds invariably recover their lost instinct, any more than
that crossed fowls or pigeons invariably recover the red or blue plumage of
their prototypes. I raised several chickens from a Polish hen by a Spanish
cock,--breeds which do not incubate,--and none of the young hens at first
recovered their instinct, and this appeared to afford a well-marked
exception to the foregoing rule; but one of these hens, the only one which
was preserved, in the third year sat well on her eggs and reared a brood of
chickens. So that here we have the appearance with advancing age of a
primitive instinct, in the same manner as we have seen that the red plumage
of the _Gallus bankiva_ is sometimes reacquired by crossed and purely-bred
fowls of various kinds as they grow old.

The parents of all our domesticated animals were of course aboriginally
wild in disposition; and when a domesticated species is crossed with a
distinct species, whether this is a domesticated or only tamed animal, the
hybrids are often wild {45} to such a degree, that the fact is intelligible
only on the principle that the cross has caused a partial return to the
primitive disposition.

The Earl of Powis formerly imported some thoroughly domesticated humped
cattle from India, and crossed them with English breeds, which belong to a
distinct species; and his agent remarked to me, without any question having
been asked, how oddly wild the cross-bred animals were. The European wild
boar and the Chinese domesticated pig are almost certainly specifically
distinct: Sir F. Darwin crossed a sow of the latter breed with a wild
Alpine boar which had become extremely tame, but the young, though having
half-domesticated blood in their veins, were "extremely wild in
confinement, and would not eat swill like common English pigs." Mr. Hewitt,
who has had great experience in crossing tame cock-pheasants with fowls
belonging to five breeds, gives as the character of all "extraordinary
wildness;"[105] but I have myself seen one exception to this rule. Mr.
S. J. Salter,[106] who raised a large number of hybrids from a bantam-hen
by _Gallus Sonneratii_, states that "all were exceedingly wild." Mr.
Waterton[107] bred some wild ducks from eggs hatched under a common duck,
and the young were allowed to cross freely both amongst themselves and with
the tame ducks; they were "half wild and half tame; they came to the
windows to be fed, but still they had a wariness about them quite
remarkable."

On the other hand, mules from the horse and ass are certainly not in the
least wild, yet they are notorious for obstinacy and vice. Mr. Brent, who
has crossed canary-birds with many kinds of finches, has not observed, as
he informs me, that the hybrids were in any way remarkably wild. Hybrids
are often raised between the common and musk duck, and I have been assured
by three persons, who have kept these crossed birds, that they were not
wild; but Mr. Garnett[108] observed that his female hybrids exhibited
"migratory propensities," of which there is not a vestige in the common or
musk duck. No case is {46} known of this latter bird having escaped and
become wild in Europe or Asia, except, according to Pallas, on the Caspian
Sea; and the common domestic duck only occasionally becomes wild in
districts where large lakes and fens abound. Nevertheless, a large number
of cases have been recorded[109] of hybrids from these two ducks, although
so few are reared in comparison with purely-bred birds of either species,
having been shot in a completely wild state. It is improbable that any of
these hybrids could have acquired their wildness from the musk-duck having
paired with a truly wild duck; and this is known not to be the case in
North America; hence we must infer that they have reacquired, through
reversion, their wildness, as well as renewed powers of flight.

These latter facts remind us of the statements, so frequently made by
travellers in all parts of the world, on the degraded state and savage
disposition of crossed races of man. That many excellent and kind-hearted
mulattos have existed no one will dispute; and a more mild and gentle set
of men could hardly be found than the inhabitants of the island of Chiloe,
who consist of Indians commingled with Spaniards in various proportions. On
the other hand, many years ago, long before I had thought of the present
subject, I was struck with the fact that, in South America, men of
complicated descent between Negroes, Indians, and Spaniards, seldom had,
whatever the cause might be, a good expression.[110] Livingstone,--and a
more unimpeachable authority cannot be quoted,--after speaking of a
half-caste man on the Zambesi, described by the Portuguese as a rare
monster of inhumanity, remarks, "It is unaccountable why half-castes, such
as he, are so much more cruel than the Portuguese, but such is undoubtedly
the case." An inhabitant remarked to Livingstone, "God made white men, and
God made black men, but the Devil made half-castes."[111] When two races,
both {47} low in the scale, are crossed, the progeny seems to be eminently
bad. Thus the noble-hearted Humboldt, who felt none of that prejudice
against the inferior races now so current in England, speaks in strong
terms of the bad and savage disposition of Zambos, or half-castes between
Indians and Negroes; and this conclusion has been arrived at by various
observers.[112] From these facts we may perhaps infer that the degraded
state of so many half-castes is in part due to reversion to a primitive and
savage condition, induced by the act of crossing, as well as to the
unfavourable moral conditions under which they generally exist.

       *       *       *       *       *

_Summary on the proximate causes leading to Reversion._--When purely-bred
animals or plants reassume long-lost characters,--when the common ass, for
instance, is born with striped legs, when a pure race of black or white
pigeons throws a slaty-blue bird, or when a cultivated heartsease with
large and rounded flowers produces a seedling with small and elongated
flowers,--we are quite unable to assign any proximate cause. When animals
run wild, the tendency to reversion, which, though it has been greatly
exaggerated, no doubt exists, is sometimes to a certain extent
intelligible. Thus, with feral pigs, exposure to the weather will probably
favour the growth of the bristles, as is known to be the case with the hair
of other domesticated animals, and through correlation the tusks will tend
to be redeveloped. But the reappearance of coloured longitudinal stripes on
young feral pigs cannot be attributed to the direct action of external
conditions. In this case, and in many others, we can only say that changed
habits of life apparently have favoured a tendency, inherent or latent in
the species, to return to the primitive state.

It will be shown in a future chapter that the position of flowers on the
summit of the axis, and the position of seeds within the capsule, sometimes
determine a tendency towards reversion; and this apparently depends on the
amount of sap or nutriment which the flower-buds and seeds receive. The
position, also, of buds, either on branches or on roots, sometimes
determines, as was formerly shown, the transmission of the {48} proper
character of the variety, or its reversion to a former state.

We have seen in the last section that when two races or species are crossed
there is the strongest tendency to the reappearance in the offspring of
long-lost characters, possessed by neither parent nor immediate progenitor.
When two white, or red, or black pigeons, of well-established breeds, are
united, the offspring are almost sure to inherit the same colours; but when
differently-coloured birds are crossed, the opposed forces of inheritance
apparently counteract each other, and the tendency which is inherent in
both parents to produce slaty-blue offspring becomes predominant. So it is
in several other cases. But when, for instance, the ass is crossed with _A.
Indicus_ or with the horse,--animals which have not striped legs,--and the
hybrids have conspicuous stripes on their legs and even on their faces, all
that can be said is, that an inherent tendency to reversion is evolved
through some disturbance in the organisation caused by the act of crossing.

Another form of reversion is far commoner, indeed is almost universal with
the offspring from a cross, namely, to the characters proper to either pure
parent-form. As a general rule, crossed offspring in the first generation
are nearly intermediate between their parents, but the grandchildren and
succeeding generations continually revert, in a greater or lesser degree,
to one or both of their progenitors. Several authors have maintained that
hybrids and mongrels include all the characters of both parents, not fused
together, but merely mingled in different proportions in different parts of
the body; or, as Naudin[113] has expressed it, a hybrid is a living
mosaic-work, in which the eye cannot distinguish the discordant elements,
so completely are they intermingled. We can hardly doubt that, in a certain
sense, this is true, as when we behold in a hybrid the elements of both
species segregating themselves into segments in the same flower or fruit,
by a process of self-attraction or self-affinity; this segregation taking
place either by seminal or by bud-propagation. Naudin further believes that
the segregation of the two specific elements or essences is eminently
liable to occur in the male and female reproductive matter; and he thus
explains the almost {49} universal tendency to reversion in successive
hybrid generations. For this would be the natural result of the union of
pollen and ovules, in both of which the elements of the same species had
been segregated by self-affinity. If, on the other hand, pollen which
included the elements of one species happened to unite with ovules
including the elements of the other species, the intermediate or hybrid
state would still be retained, and there would be no reversion. But it
would, as I suspect, be more correct to say that the elements of both
parent-species exist in every hybrid in a double state, namely, blended
together and completely separate. How this is possible, and what the term
specific essence or element may be supposed to express, I shall attempt to
show in the hypothetical chapter on pangenesis.

But Naudin's view, as propounded by him, is not applicable to the
reappearance of characters lost long ago by variation; and it is hardly
applicable to races or species which, after having been crossed at some
former period with a distinct form, and having since lost all traces of the
cross, nevertheless occasionally yield an individual which reverts (as in
the case of the great-great-grandchild of the pointer Sappho) to the
crossing form. The most simple case of reversion, namely, of a hybrid or
mongrel to its grandparents, is connected by an almost perfect series with
the extreme case of a purely-bred race recovering characters which had been
lost during many ages; and we are thus led to infer that all the cases must
be related by some common bond.

Gärtner believed that only those hybrid plants which are highly sterile
exhibit any tendency to reversion to their parent-forms. It is rash to
doubt so good an observer, but this conclusion must I think be an error;
and it may perhaps be accounted for by the nature of the genera observed by
him, for he admits that the tendency differs in different genera. The
statement is also directly contradicted by Naudin's observations, and by
the notorious fact that perfectly fertile mongrels exhibit the tendency in
a high degree,--even in a higher degree, according to Gärtner himself, than
hybrids.[114]

Gärtner further states that reversions rarely occur with {50} hybrid plants
raised from species which have not been cultivated, whilst, with those
which have been long cultivated, they are of frequent occurrence. This
conclusion explains a curious discrepancy: Max Wichura,[115] who worked
exclusively on willows, which had not been subjected to culture, never saw
an instance of reversion; and he goes so far as to suspect that the careful
Gärtner had not sufficiently protected his hybrids from the pollen of the
parent-species: Naudin, on the other hand, who chiefly experimented on
cucurbitaceous and other cultivated plants, insists more strenuously than
any other author on the tendency to reversion in all hybrids. The
conclusion that the condition of the parent-species, as affected by
culture, is one of the proximate causes leading to reversion, agrees fairly
well with the converse case of domesticated animals and cultivated plants
being liable to reversion when they become feral; for in both cases the
organisation or constitution must be disturbed, though in a very different
way.

Finally, we have seen that characters often reappear in purely-bred races
without our being able to assign any proximate cause; but when they become
feral this is either indirectly or directly induced by the change in their
conditions of life. With crossed breeds, the act of crossing in itself
certainly leads to the recovery of long-lost characters, as well as of
those derived from either parent-form. Changed conditions, consequent on
cultivation, and the relative position of buds, flowers, and seeds on the
plant, all apparently aid in giving this same tendency. Reversion may occur
either through seminal or bud generation, generally at birth, but sometimes
only with an advance of age. Segments or portions of the individual may
alone be thus affected. That a being should be born resembling in certain
characters an ancestor removed by two or three, and in some cases by
hundreds or even thousands of generations, is assuredly a wonderful fact.
In these cases the child is commonly said to inherit such characters
directly from its grandparents or more remote ancestors. But this view is
hardly conceivable. If, however, we suppose that every character is derived
{51} exclusively from the father or mother, but that many characters lie
latent in both parents during a long succession of generations, the
foregoing facts are intelligible. In what manner characters may be
conceived to lie latent, will be considered in a future chapter to which I
have lately alluded.

       *       *       *       *       *

_Latent Characters._--But I must explain what is meant by characters lying
latent. The most obvious illustration is afforded by secondary sexual
characters. In every female all the secondary male characters, and in every
male all the secondary female characters, apparently exist in a latent
state, ready to be evolved under certain conditions. It is well known that
a large number of female birds, such as fowls, various pheasants,
partridges, peahens, ducks, &c., when old or diseased, or when operated on,
partly assume the secondary male characters of their species. In the case
of the hen-pheasant this has been observed to occur far more frequently
during certain seasons than during others.[116] A duck ten years old has
been known to assume both the perfect winter and summer plumage of the
drake.[117] Waterton[118] gives a curious case of a hen which had ceased
laying, and had assumed the plumage, voice, spurs, and warlike disposition
of the cock; when opposed to an enemy she would erect her hackles and show
fight. Thus every character, even to the instinct and manner of fighting,
must have lain dormant in this hen as long as her ovaria continued to act.
The females of two kinds of deer, when old, have been known to acquire
horns; and, as Hunter has remarked, we see something of an analogous nature
in the human species.

On the other hand, with male animals, it is notorious that the secondary
sexual characters are more or less completely lost when they are subjected
to castration. Thus, if the operation be performed on a young cock, he
never, as Yarrell states, crows {52} again; the comb, wattles, and spurs do
not grow to their full size, and the hackles assume an intermediate
appearance between true hackles and the feathers of the hen. Cases are
recorded of confinement alone causing analogous results. But characters
properly confined to the female are likewise acquired; the capon takes to
sitting on eggs, and will bring up chickens; and what is more curious, the
utterly sterile male hybrids from the pheasant and the fowl act in the same
manner, "their delight being to watch when the hens leave their nests, and
to take on themselves the office of a sitter."[119] That admirable observer
Réaumur[120] asserts that a cock, by being long confined in solitude and
darkness, can be taught to take charge of young chickens; he then utters a
peculiar cry, and retains during his whole life this newly acquired
maternal instinct. The many well-ascertained cases of various male mammals
giving milk, show that their rudimentary mammary glands retain this
capacity in a latent condition.

We thus see that in many, probably in all cases, the secondary characters
of each sex lie dormant or latent in the opposite sex, ready to be evolved
under peculiar circumstances. We can thus understand how, for instance, it
is possible for a good milking cow to transmit her good qualities through
her male offspring to future generations; for we may confidently believe
that these qualities are present, though latent, in the males of each
generation. So it is with the game-cock, who can transmit his superiority
in courage and vigour through his female to his male offspring; and with
man it is known [121] that diseases, such as hydrocele, necessarily
confined to the male sex, can be transmitted through the female to the
grandson. Such cases as these offer, as was remarked at the commencement of
this chapter, the simplest possible examples of reversion; and they are
intelligible on the belief that characters common to the grandparent and
grandchild of the same sex are present, though latent, in the intermediate
parent of the opposite sex.

The subject of latent characters is so important, as we shall see in a
future chapter, that I will give another illustration. {53} Many animals
have the right and left sides of their body unequally developed: this is
well known to be the case with flat-fish, in which the one side differs in
thickness and colour, and in the shape of the fins, from the other; and
during the growth of the young fish one eye actually travels, as shown by
Steenstrup, from the lower to the upper surface.[122] In most flat-fishes
the left is the blind side, but in some it is the right; though in both
cases "wrong fishes," which are developed in a reversed manner to what is
usual, occasionally occur, and in _Platessa flesus_ the right or left side
is indifferently developed, the one as often as the other. With gasteropods
or shell-fish, the right and left sides are extremely unequal; the far
greater number of species are dextral, with rare and occasional reversals
of development, and some few are normally sinistral; but certain species of
Bulimus, and, many Achatinellæ,[123] are as often sinistral as dextral. I
will give an analogous case in the great Articulate kingdom: the two sides
of Verruca[124] are so wonderfully unlike, that without careful dissection
it is extremely difficult to recognise the corresponding parts on the
opposite sides of the body; yet it is apparently a mere matter of chance
whether it be the right or the left side that undergoes so singular an
amount of change. One plant is known to me[125] in which the flower,
according as it stands on the one or other side of the spike, is unequally
developed. In all the foregoing cases the two sides of the animal are
perfectly symmetrical at an early period of growth. Now, whenever a species
is as liable to be unequally developed on the one as on the other side, we
may infer that the capacity for such development is present, though latent,
in the undeveloped side. And as a reversal of development occasionally
occurs in animals of many kinds, this latent capacity is probably very
common.

The best yet simplest instances of characters lying dormant are, perhaps,
those previously given, in which chickens and {54} young pigeons, raised
from a cross between differently coloured birds, are at first of one
colour, but in a year or two acquire feathers of the colour of the other
parent; for in this case the tendency to a change of plumage is clearly
latent in the young bird. So it is with hornless breeds of cattle, some of
which acquire, as they grow old, small horns. Purely bred black and white
bantams, and some other fowls, occasionally assume, with advancing years,
the red feathers of the parent-species. I will here add a somewhat
different case, as it connects in a striking manner latent characters of
two classes. Mr. Hewitt[126] possessed an excellent Sebright gold-laced hen
bantam, which, as she became old, grew diseased in her ovaria, and assumed
male characters. In this breed the males resemble the females in all
respects except in their combs, wattles, spurs, and instincts; hence it
might have been expected that the diseased hen would have assumed only
those masculine characters which are proper to the breed, but she acquired,
in addition, well-arched tail sickle-feathers quite a foot in length,
saddle-feathers on the loins, and hackles on the neck,--ornaments which, as
Mr. Hewitt remarks, "would be held as abominable in this breed." The
Sebright bantam is known[127] to have originated about the year 1800 from a
cross between a common bantam and a Polish fowl, recrossed by a hen-tailed
bantam, and carefully selected; hence there can hardly be a doubt that the
sickle-feathers and hackles which appeared in the old hen were derived from
the Polish fowl or common bantam; and we thus see that not only certain
masculine characters proper to the Sebright bantam, but other masculine
characters derived from the first progenitors of the breed, removed by a
period of above sixty years, were lying latent in this hen-bird, ready to
be evolved as soon as her ovaria became diseased.

From these several facts it must be admitted that certain characters,
capacities, and instincts may lie latent in an individual, and even in a
succession of individuals, without our being able to detect the least signs
of their presence. We have {55} already seen that the transmission of a
character from the grandparent to the grandchild, with its apparent
omission in the intermediate parent of the opposite sex, becomes simple on
this view. When fowls, pigeons, or cattle of different colours are crossed,
and their offspring change colour as they grow old, or when the crossed
turbit acquired the characteristic frill after its third moult, or when
purely-bred bantams partially assume the red plumage of their prototype, we
cannot doubt that these qualities were from the first present, though
latent, in the individual animal, like the characters of a moth in the
caterpillar. Now, if these animals had produced offspring before they had
acquired with advancing age their new characters, nothing is more probable
than that they would have transmitted them to some of their offspring,
which in this case would in appearance have received such characters from
their grandparents or more distant progenitors. We should then have had a
case of reversion, that is, of the reappearance in the child of an
ancestral character, actually present, though during youth completely
latent, in the parent; and this we may safely conclude is what occurs with
reversions of all kinds to progenitors however remote.

This view of the latency in each generation of all the characters which
appear through reversion, is also supported by their actual presence in
some cases during early youth alone, or by their more frequent appearance
and greater distinctness at this age than during maturity. We have seen
that this is often the case with the stripes on the legs and faces of the
several species of the horse-genus. The Himalayan rabbit, when crossed,
sometimes produces offspring which revert to the parent silver-grey breed,
and we have seen that in purely bred animals pale-grey fur occasionally
reappears during early youth. Black cats, we may feel assured, would
occasionally produce by reversion tabbies; and on young black kittens, with
a pedigree[128] known to have been long pure, faint traces of stripes may
almost always be seen which afterwards disappear. Hornless Suffolk cattle
occasionally produce by reversion horned animals; and Youatt[129] asserts
that even in hornless individuals {56} "the rudiment of a horn may be often
felt at an early age."

No doubt it appears at first sight in the highest degree improbable that in
every horse of every generation there should be a latent capacity and
tendency to produce stripes, though these may not appear once in a thousand
generations; that in every white, black, or other coloured pigeon, which
may have transmitted its proper colour during centuries, there should be a
latent capacity in the plumage to become blue and to be marked with certain
characteristic bars; that in every child in a six-fingered family there
should be the capacity for the production of an additional digit; and so in
other cases. Nevertheless there is no more inherent improbability in this
being the case than in a useless and rudimentary organ, or even in only a
tendency to the production of a rudimentary organ, being inherited during
millions of generations, as is well known to occur with a multitude of
organic beings. There is no more inherent improbability in each domestic
pig, during a thousand generations, retaining the capacity and tendency to
develop great tusks under fitting conditions, than in the young calf having
retained for an indefinite number of generations rudimentary incisor teeth,
which never protrude through the gums.

I shall give at the end of the next chapter a summary of the three
preceding chapters; but as isolated and striking cases of reversion have
here been chiefly insisted on, I wish to guard the reader against supposing
that reversion is due to some rare or accidental combination of
circumstances. When a character, lost during hundreds of generations,
suddenly reappears, no doubt some such combination must occur; but
reversions may be constantly observed, at least to the immediately
preceding generations, in the offspring of most unions. This has been
universally recognised in the case of hybrids and mongrels, but it has been
recognised simply from the difference between the united forms rendering
the resemblance of the offspring to their grandparents or more remote
progenitors of easy detection. Reversion is likewise almost invariably the
rule, as Mr. Sedgwick has shown, with certain diseases. Hence we must
conclude that a tendency to this peculiar form of transmission is an
integral part of the general law of inheritance. {57}

       *       *       *       *       *

_Monstrosities._--A large number of monstrous growths and of lesser
anomalies are admitted by every one to be due to an arrest of development,
that is to the persistence of an embryonic condition. If every horse or ass
had striped legs whilst young, the stripes which occasionally appear on
these animals when adult would have to be considered as due to the
anomalous retention of an early character, and not as due to reversion.
Now, the leg-stripes in the horse-genus, and some other characters in
analogous cases, are apt to occur during early youth and then to disappear;
thus the persistence of early characters and reversion are brought into
close connexion.

But many monstrosities can hardly be considered as the result of an arrest
of development; for parts of which no trace can be detected in the embryo,
but which occur in other members of the same class of animals or plants,
occasionally appear, and these may probably with truth be attributed to
reversion. For instance: supernumerary mammæ, capable of secreting milk,
are not extremely rare in women; and as many as five have been observed.
When four are developed, they are generally arranged symmetrically on each
side of the chest; and in one instance a woman (the daughter of another
with supernumerary mammæ) had one mamma, which yielded milk, developed in
the inguinal region. This latter case, when we remember the position of the
mammæ in some of the lower animals on both the chest and inguinal region,
is highly remarkable, and leads to the belief that in all cases the
additional mammæ in woman are due to reversion. The facts given in the last
chapter on the tendency in supernumerary digits to regrowth after
amputation, indicate their relation to the digits of the lower vertebrate
animals, and lead to the suspicion that their appearance may in some manner
be connected with reversion. But I shall have to recur, in the chapter on
pangenesis, to the abnormal multiplication of organs, and likewise to their
occasional transposition. The occasional development in man of the
coccygeal vertebræ into a short and free tail, though it thus becomes in
one sense more perfectly developed, may at the same time be considered as
an arrest of development, and as a case of reversion. The greater frequency
of a monstrous kind of proboscis in the pig than in any other mammal,
considering the position of the pig {58} in the mammalian series, has
likewise been attributed, perhaps truly, to reversion.[130]

    When flowers which are properly irregular in structure become regular
    or peloric, the change is generally looked at by botanists as a return
    to the primitive state. But Dr. Maxwell Masters,[131] who has ably
    discussed this subject, remarks that when, for instance, all the sepals
    of a Tropæolum become green and of the same shape, instead of being
    coloured with one alone prolonged into a spur, or when all the petals
    of a Linaria become simple and regular, such cases may be due merely to
    an arrest of development; for in these flowers all the organs during
    their earliest condition are symmetrical, and, if arrested at this
    stage of growth, they would not become irregular. If, moreover, the
    arrest were to take place at a still earlier period of development, the
    result would be a simple tuft of green leaves; and no one probably
    would call this a case of reversion. Dr. Masters designates the cases
    first alluded to as regular peloria; and others, in which all the
    corresponding parts assume a similar form of irregularity, as when all
    the petals in a Linaria become spurred, as irregular peloria. We have
    no right to attribute these latter cases to reversion, until it can be
    shown to be probable that the parent-form, for instance, of the genus
    Linaria had had all its petals spurred; for a change of this nature
    might result from the spreading of an anomalous structure, in
    accordance with the law, to be discussed in a future chapter, of
    homologous parts tending to vary in the same manner. But as both forms
    of peloria frequently occur on the same individual plant of the
    Linaria,[132] they probably stand in some close relation to each other.
    On the doctrine that peloria is simply the result of an arrest of
    development, it is difficult to understand how an organ arrested at a
    very early period of growth should acquire its full functional
    perfection;--how a petal, supposed to be thus arrested, should acquire
    its brilliant colours, and serve as an envelope to the flower, or a
    stamen produce efficient pollen; yet this occurs with many peloric
    flowers. That pelorism is not due to mere chance variability, but
    either to an arrest of development or to reversion, we may infer from
    an observation made by Ch. Morren,[133] namely, that families which
    have irregular flowers often "return by these monstrous growths to
    their regular form; whilst we never see a regular flower realise the
    structure of an irregular one."

    Some flowers have almost certainly become more or less completely
    peloric through reversion. _Corydalis tuberosa_ properly has one of its
    two nectaries colourless, destitute of nectar, only half the size of
    the other, and {59} therefore, to a certain extent, in a rudimentary
    state; the pistil is curved towards the perfect nectary, and the hood,
    formed of the inner petals, slips off the pistil and stamens in one
    direction alone, so that, when a bee sucks the perfect nectary, the
    stigma and stamens are exposed and rubbed against the insect's body. In
    several closely allied genera, as in Dielytra, &c., there are two
    perfect nectaries, the pistil is straight, and the hood slips off on
    either side, according as the bee sucks either nectary. Now, I have
    examined several flowers of _Corydalis tuberosa_, in which both
    nectaries were equally developed and contained nectar; in this we see
    only the redevelopment of a partially aborted organ; but with this
    redevelopment the pistil becomes straight, and the hood slips off in
    either direction; so that these flowers have acquired the perfect
    structure, so well adapted for insect agency, of Dielytra and its
    allies. We cannot attribute these coadapted modifications to chance, or
    to correlated variability; we must attribute them to reversion to a
    primordial condition of the species.

    The peloric flowers of Pelargonium have their five petals in all
    respects alike, and there is no nectary; so that they resemble the
    symmetrical flowers of the closely allied Geranium-genus; but the
    alternate stamens are also sometimes destitute of anthers, the
    shortened filaments being left as rudiments, and in this respect they
    resemble the symmetrical flowers of the closely allied genus, Erodium.
    Hence we are led to look at the peloric flowers of Pelargonium as
    having probably reverted to the state of some primordial form, the
    progenitor of the three closely related genera of Pelargonium,
    Geranium, and Erodium.

    In the peloric form of _Antirrhinum majus_, appropriately called the
    "_Wonder_," the tubular and elongated flowers differ wonderfully from
    those of the common snapdragon; the calyx and the mouth of the corolla
    consist of six equal lobes, and include six equal instead of four
    unequal stamens. One of the two additional stamens is manifestly formed
    by the development of a microscopically minute papilla, which may be
    found at the base of the upper lip of the flower in all common
    snapdragons, at least in nineteen plants examined by me. That this
    papilla is a rudiment of a stamen was well shown by its various degrees
    of development in crossed plants between the common and peloric
    Antirrhinum. Again, a peloric _Galeobdolon luteum_, growing in my
    garden, had five equal petals, all striped like the ordinary lower lip,
    and included five equal instead of four unequal stamens; but Mr. R.
    Keeley, who sent me this plant, informs me that the flowers vary
    greatly, having from four to six lobes to the corolla, and from three
    to six stamens.[134] Now, as the members of the two great families to
    which the Antirrhinum and Galeobdolon belong are properly pentamerous,
    with some of the parts confluent and others suppressed, we ought not to
    look at the sixth stamen and the sixth lobe to the corolla in either
    case as due to reversion, any more than the additional petals in double
    flowers in these same two families. But the case is different with the
    fifth stamen in the peloric Antirrhinum, which {60} is produced by the
    redevelopment of a rudiment always present, and which probably reveals
    to us the state of the flower, as far as the stamens are concerned, at
    some ancient epoch. It is also difficult to believe that the other four
    stamens and the petals, after an arrest of development at a very early
    embryonic age, would have come to full perfection in colour, structure,
    and function, unless these organs had at some former period normally
    passed through a similar course of growth. Hence it appears to me
    probable that the progenitor of the genus Antirrhinum must at some
    remote epoch have included five stamens and borne flowers in some
    degree resembling those now produced by the peloric form.

    Lastly, I may add that many instances have been recorded of flowers,
    not generally ranked as peloric, in which certain organs, normally few
    in number, have been abnormally augmented. As such an increase of parts
    cannot be looked at as an arrest of development, nor as due to the
    redevelopment of rudiments, for no rudiments are present, and as these
    additional parts bring the plant into closer relationship with its
    natural allies, they ought probably to be viewed as reversions to a
    primordial condition.

These several facts show us in an interesting manner how intimately certain
abnormal states are connected together; namely, arrests of development
causing parts to become rudimentary or to be wholly suppressed,--the
redevelopment of parts at present in a more or less rudimentary
condition,--the reappearance of organs of which not a vestige can now be
detected,--and to these may be added, in the case of animals, the presence
during youth, and subsequent disappearance, of certain characters which
occasionally are retained throughout life. Some naturalists look at all
such abnormal structures as a return to the ideal state of the group to
which the affected being belongs; but it is difficult to conceive what is
meant to be conveyed by this expression. Other naturalists maintain, with
greater probability and distinctness of view, that the common bond of
connection between the several foregoing cases is an actual, though
partial, return to the structure of the ancient progenitor of the group. If
this view be correct, we must believe that a vast number of characters,
capable of evolution, lie hidden in every organic being. But it would be a
mistake to suppose that the number is equally great in all beings. We know,
for instance, that plants of many orders occasionally become peloric; but
many more cases have been observed in the Labiatæ and Scrophulariaceæ than
in any other order; and in one genus of the Scrophulariaceæ, namely
Linaria, no less {61} than thirteen species have been described in a
peloric condition.[135] On this view of the nature of peloric flowers, and
bearing in mind what has been said with respect to certain monstrosities in
the animal kingdom, we must conclude that the progenitors of most plants
and animals, though widely different in structure, have left an impression
capable of redevelopment on the germs of their descendants.

The fertilised germ of one of the higher animals, subjected as it is to so
vast a series of changes from the germinal cell to old age,--incessantly
agitated by what Quatrefages well calls the _tourbillon vital_,--is perhaps
the most wonderful object in nature. It is probable that hardly a change of
any kind affects either parent, without some mark being left on the germ.
But on the doctrine of reversion, as given in this chapter, the germ
becomes a far more marvellous object, for, besides the visible changes to
which it is subjected, we must believe that it is crowded with invisible
characters, proper to both sexes, to both the right and left side of the
body, and to a long line of male and female ancestors separated by hundreds
or even thousands of generations from the present time; and these
characters, like those written on paper with invisible ink, all lie ready
to be evolved under certain known or unknown conditions.

       *       *       *       *       *


{62}

CHAPTER XIV.

INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL
LIMITATION--CORRESPONDENCE OF AGE.

    FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF
    INHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME
    FAMILY, IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN
    THE OTHER; SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND
    VISIBLE IN ONE BREED AND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY
    SEX--NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN
    TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX
    ALONE--INHERITANCE AT CORRESPONDING PERIODS OF LIFE--THE IMPORTANCE OF
    THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED
    ANIMALS; AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED
    DISEASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN THE
    PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS.

In the two last chapters the nature and force of Inheritance, the
circumstances which interfere with its power, and the tendency to
Reversion, with its many remarkable contingencies, were discussed. In the
present chapter some other related phenomena will be treated of, as fully
as my materials permit.

_Fixedness of Character._

It is a general belief amongst breeders that the longer any character has
been transmitted by a breed, the more firmly it will continue to be
transmitted. I do not wish to dispute the truth of the proposition, that
inheritance gains strength simply through long continuance, but I doubt
whether it can be proved. In one sense the proposition is little better
than a truism; if any character has remained constant during many
generations, it will obviously be little likely, the conditions of life
remaining the same, to vary during the next generation. So, again, in
improving a breed, if care be taken for a length of time to exclude all
inferior individuals, the breed will obviously tend to become truer, as it
will not have been crossed during many generations by an inferior animal.
We have previously seen, {63} but without being able to assign any cause,
that, when a new character appears, it is occasionally from the first well
fixed, or fluctuates much, or wholly fails to be transmitted. So it is with
the aggregate of slight differences which characterise a new variety, for
some propagate their kind from the first much truer than others. Even with
plants multiplied by bulbs, layers, &c., which may in one sense be said to
form parts of the same individual, it is well known that certain varieties
retain and transmit through successive bud-generations their newly-acquired
characters more truly than others. In none of these, nor in the following
cases, does there appear to be any relation between the force with which a
character is transmissible and the length of time during which it has
already been transmitted. Some varieties, such as white and yellow
hyacinths and white sweet-peas, transmit their colours more faithfully than
do the varieties which have retained their natural colour. In the Irish
family, mentioned in the twelfth chapter, the peculiar tortoiseshell-like
colouring of the eyes was transmitted far more faithfully than any ordinary
colour. Ancon and Mauchamp sheep and niata cattle, which are all
comparatively modern breeds, exhibit remarkably strong powers of
inheritance. Many similar cases could be adduced.

As all domesticated animals and cultivated plants have varied, and yet are
descended from aboriginally wild forms, which no doubt had retained the
same character from an immensely remote epoch, we see that scarcely any
degree of antiquity ensures a character being transmitted perfectly true.
In this case, however, it may be said that changed conditions of life
induce certain modifications, and not that the power of inheritance fails;
but in every case of failure, some cause, either internal or external, must
interfere. It will generally be found that the parts in our domesticated
productions which have varied, or which still continue to vary,--that is,
which fail to retain their primordial state,--are the same with the parts
which differ in the natural species of the same genus. As, on the theory of
descent with modification, the species of the same genus have been modified
since they branched off from a common progenitor, it follows that the
characters by which they differ from each other have varied whilst other
parts of the organisation have remained unchanged; and it might be argued
that {64} these same characters now vary under domestication, or fail to be
inherited, owing to their lesser antiquity. But we must believe structures,
which have already varied, would be more liable to go on varying, rather
than structures which during an immense lapse of time have remained
unaltered; and this variation is probably the result of certain relations
between the conditions of life and the organisation, quite independently of
the greater or less antiquity of each particular character.

Fixedness of character, or the strength of inheritance, has often been
judged of by the preponderance of certain characters in the crossed
offspring between distinct races; but prepotency of transmission here comes
into play, and this, as we shall immediately see, is a very different
consideration from the strength or weakness of inheritance. It has often
been observed[136] that breeds of animals inhabiting wild and mountainous
countries cannot be permanently modified by our improved breeds; and as
these latter are of modern origin, it has been thought that the greater
antiquity of the wilder breeds has been the cause of their resistance to
improvement by crossing; but it is more probably due to their structure and
constitution being better adapted to the surrounding conditions. When
plants are first subjected to culture, it has been found that, during
several generations, they transmit their characters truly, that is, do not
vary, and this has been attributed to ancient characters being strongly
inherited; but it may with equal or greater probability be consequent on
changed conditions of life requiring a long time for their accumulative
action. Notwithstanding these considerations, it would perhaps be rash to
deny that characters become more strongly fixed the longer they are
transmitted; but I believe that the proposition resolves itself into
this,--that all characters of all kinds, whether new or old, tend to be
inherited, and that those which have already withstood all counteracting
influences and been truly transmitted, will, as a general rule, continue to
withstand them, and consequently be faithfully inherited.

{65}

_Prepotency in the Transmission of Character._

When individuals distinct enough to be recognised, but of the same family,
or when two well-marked races, or two species, are crossed, the usual
result, as stated in the previous chapter, is, that the offspring in the
first generation are intermediate between their parents, or resemble one
parent in one part and the other parent in another part. But this is by no
means the invariable rule; for in many cases it is found that certain
individuals, races, and species are prepotent in transmitting their
likeness. This subject has been ably discussed by Prosper Lucas,[137] but
is rendered extremely complicated by the prepotency sometimes running
equally in both sexes, and sometimes more strongly in one sex than in the
other; it is likewise complicated by the presence of secondary sexual
characters, which render the comparison of mongrels with their
parent-breeds difficult.

It would appear that in certain families some one ancestor, and after him
others in the same family, must have had great power in transmitting their
likeness through the male line; for we cannot otherwise understand how the
same features should so often be transmitted after marriages with various
females, as has been the case with the Austrian Emperors, and as, according
to Niebuhr, formerly occurred in certain Roman families with their mental
qualities.[138] The famous bull Favourite is believed[139] to have had a
prepotent influence on the shorthorn race. It has also been observed[140]
with English race-horses that certain mares have generally transmitted
their own character, whilst other mares of equally pure blood have allowed
the character of the sire to prevail.

    The truth of the principle of prepotency comes out more clearly when
    certain races are crossed. The improved Shorthorns, notwithstanding
    that the breed is comparatively modern, are generally acknowledged to
    possess great power in impressing their likeness on all other breeds;
    and it is chiefly in consequence of this power that they are so highly
    valued {66} for exportation.[141] Godine has given a curious case of a
    ram of a goat-like breed of sheep from the Cape of Good Hope, which
    produced offspring hardly to be distinguished from himself, when
    crossed with ewes of twelve other breeds. But two of these half-bred
    ewes, when put to a merino ram, produced lambs closely resembling the
    merino breed. Girou de Buzareingues[142] found that of two races of
    French sheep the ewes of one, when crossed during successive
    generations with merino rams, yielded up their character far sooner
    than the ewes of the other race. Sturm and Girou have given analogous
    cases with other breeds of sheep and with cattle, the prepotency
    running in these cases through the male side; but I was assured on good
    authority in South America, that when niata cattle are crossed with
    common cattle, though the niata breed is prepotent whether males or
    females are used, yet that the prepotency is strongest through the
    female line. The Manx cat is tailless and has long hind legs; Dr.
    Wilson crossed a male Manx with common cats, and, out of twenty-three
    kittens, seventeen were destitute of tails; but when the female Manx
    was crossed by common male cats all the kittens had tails, though they
    were generally short and imperfect.[143]

    In making reciprocal crosses between pouter and fantail pigeons, the
    pouter-race seemed to be prepotent through both sexes over the fantail.
    But this is probably due to weak power in the fantail rather than to
    any unusually strong power in the pouter, for I have observed that
    barbs also preponderated over fantails. This weakness of transmission
    in the fantail, though the breed is an ancient one, is said[144] to be
    general; but I have observed one exception to the rule, namely, in a
    cross between a fantail and laugher. The most curious instance known to
    me of weak power in both sexes is in the trumpeter pigeon. This breed
    has been well known for at least 130 years: it breeds perfectly true,
    as I have been assured by those who have long kept many birds: it is
    characterised by a peculiar tuft of feathers over the beak, by a crest
    on the head, by a most peculiar coo quite unlike that of any other
    breed, and by much-feathered feet. I have crossed both sexes with
    turbits of two sub-breeds, with almond tumblers, spots, and runts, and
    reared many mongrels and recrossed them; and though the crest on the
    head and feathered feet were inherited (as is generally the case with
    most breeds), I have never seen a vestige of the tuft over the beak or
    heard the peculiar coo. Boitard and Corbié[145] assert that this is the
    invariable result of crossing trumpeters with any other breed:
    Neumeister,[146] however, states that in Germany mongrels have been
    obtained, though very rarely, which were furnished with the tuft and
    would trumpet: but a pair of these mongrels with a tuft, which I
    imported, never trumpeted. Mr. Brent states[147] that the crossed
    offspring of a trumpeter were crossed {67} with trumpeters for three
    generations, by which time the mongrels had 7-8ths of this blood in
    their veins, yet the tuft over the beak did not appear. At the fourth
    generation the tuft appeared, but the birds, though now having 15-16ths
    trumpeter's blood, still did not trumpet. This case well shows the wide
    difference between inheritance and prepotency; for here we have a
    well-established old race which transmits it characters faithfully, but
    which, when crossed with any other race, has the feeblest power of
    transmitting its two chief characteristic qualities.

    I will give one other instance with fowls and pigeons of weakness and
    strength in the transmission of the same character to their crossed
    offspring. The Silk-fowl breeds true, and there is reason to believe is
    a very ancient race; but when I reared a large number of mongrels from
    a Silk-hen by a Spanish cock, not one exhibited even a trace of the
    so-called silkiness. Mr. Hewitt also asserts that in no instance are
    the silky feathers transmitted by this breed when crossed with any
    other variety. But three birds out of many raised by Mr. Orton from a
    cross between a silk-cock and a bantam-hen, had silky feathers.[148] So
    that it is certain that this breed very seldom has the power of
    transmitting its peculiar plumage to its crossed progeny. On the other
    hand, there is a silk sub-variety of the fantail pigeon, which has its
    feathers in nearly the same state as in the Silk-fowl: now we have
    already seen that fantails, when crossed, possess singularly weak power
    in transmitting their general qualities; but the silk sub-variety when
    crossed with any other small-sized race invariably transmits its silky
    feathers![149]

    The law of prepotency comes into action when species are crossed, as
    with races and individuals. Gärtner has unequivocally shown[150] that
    this is the case with plants. To give one instance: when _Nicotiana
    paniculata_ and _vincæflora_ are crossed, the character of _N.
    paniculata_ is almost completely lost in the hybrid; but if _N.
    quadrivalvis_ be crossed with _N. vincæflora_, this later species,
    which was before so prepotent, now in its turn almost disappears under
    the power of _N. quadrivalvis_. It is remarkable that the prepotency of
    one species over another in transmission is quite independent, as shown
    by Gärtner, of the greater or less facility with which the one
    fertilises the other.

    With animals, the jackal is prepotent over the dog, as is stated by
    Flourens who made many crosses between these animals; and this was
    likewise the case with a hybrid which I once saw between a jackal and
    terrier. I cannot doubt, from the observations of Colin and others,
    that the ass is prepotent over the horse; the prepotency in this
    instance running more strongly through the male than through the female
    ass; so that the mule resembles the ass more closely than does the
    hinny.[151] The {68} male pheasant, judging from Mr. Hewitt's
    descriptions,[152] and from the hybrids which I have seen,
    preponderates over the domestic fowl; but the latter, as far as colour
    is concerned, has considerable power of transmission, for hybrids
    raised from five differently coloured hens differed greatly in plumage.
    I formerly examined some curious hybrids in the Zoological Gardens,
    between the Penguin variety of the common duck and the Egyptian goose
    (_Tadorna Ægyptiaca_); and although I will not assert that the
    domesticated variety preponderated over the natural species, yet it had
    strongly impressed its unnatural upright figure on these hybrids.

    I am aware that such cases as the foregoing have been ascribed by
    various authors, not to one species, race, or individual being
    prepotent over the other in impressing it character on its crossed
    offspring, but to such rules as that the father influences the external
    characters and the mother the internal or vital organs. But the great
    diversity of the rules given by various authors almost proves their
    falseness. Dr. Prosper Lucas has fully discussed this point, and has
    shown[153] that none of the rules (and I could add others to those
    quoted by him) apply to all animals. Similar rules have been enounced
    for plants, and have been proved by Gärtner[154] to be all erroneous.
    If we confine our view to the domesticated races of a single species,
    or perhaps even to the species of the same genus, some such rules may
    hold good; for instance, it seems that in reciprocally crossing various
    breeds of fowls the male generally gives colour;[155] but conspicuous
    exceptions have passed under my own eyes. In sheep it seems that the
    ram usually gives its peculiar horns and fleece to its crossed
    offspring, and the bull the presence or absence of horns.

    In the following chapter on Crossing I shall have occasion to show that
    certain characters are rarely or never blended by crossing, but are
    {69} transmitted in an unmodified state from either parent-form; I
    refer to this fact here because it is sometimes accompanied on the one
    side by prepotency, which thus acquires the false appearance of unusual
    strength. In the same chapter I shall show that the rate at which a
    species or breed absorbs and obliterates another by repeated crosses,
    depends in chief part on prepotency in transmission.

In conclusion, some of the cases above given,--for instance, that of the
trumpeter pigeon,--prove that there is a wide difference between mere
inheritance and prepotency. This latter power seems to us, in our
ignorance, to act in most cases quite capriciously. The very same
character, even though it be an abnormal or monstrous one, such as silky
feathers, may be transmitted by different species, when crossed, either
with prepotent force or singular feebleness. It is obvious, that a
purely-bred form of either sex, in all cases in which prepotency does not
run more strongly in one sex than the other, will transmit its character
with prepotent force over a mongrelized and already variable form.[156]
From several of the above-given cases we may conclude that mere antiquity
of character does not by any means necessarily make it prepotent. In some
cases prepotency apparently depends on the same character being present and
visible in one of the two breeds which are crossed, and latent or invisible
in the other breed; and in this case it is natural that the character which
is potentially present in both should be prepotent. Thus, we have reason to
believe that there is a latent tendency in all horses to be dun-coloured
and striped; and when a horse of this kind is crossed with one of any other
colour, it is said that the offspring are almost sure to be striped. Sheep
have a similar latent tendency to become dark-coloured, and we have seen
with what prepotent force a ram with a few black spots, when crossed with
sheep of various breeds, coloured its offspring. All pigeons have a latent
tendency to become slaty-blue, with certain characteristic marks, and it is
known that, when a bird thus coloured is crossed with one of any other
colour, it is most difficult afterwards to eradicate the blue tint. A
nearly parallel case is offered by those black bantams which, as they grow
{70} old, develop a latent tendency to acquire red feathers. But there are
exceptions to the rule: hornless breeds of cattle possess a latent capacity
to reproduce horns, yet when crossed with horned breeds they do not
invariably produce offspring bearing horns.

We meet with analogous cases with plants. Striped flowers, though they can
be propagated truly by seed, have a latent tendency to become uniformly
coloured, but when once crossed by a uniformly coloured variety, they ever
afterwards fail to produce striped seedlings.[157] Another case is in some
respects more curious: plants bearing peloric or regular flowers have so
strong a latent tendency to reproduce their normally irregular flowers,
that this often occurs by buds when a plant is transplanted into poorer or
richer soil.[158] Now I crossed the peloric snapdragon (_Antirrhinum
majus_), described in the last chapter, with pollen of the common form; and
the latter, reciprocally, with peloric pollen. I thus raised two great beds
of seedlings, and not one was peloric. Naudin[159] obtained the same result
from crossing a peloric Linaria with the common form. I carefully examined
the flowers of ninety plants of the crossed Antirrhinum in the two beds,
and their structure had not been in the least affected by the cross, except
that in a few instances the minute rudiment of the fifth stamen, which is
always present, was more fully or even completely developed. It must not be
supposed that this entire obliteration of the peloric structure in the
crossed plants can be accounted for by any incapacity of transmission; for
I raised a large bed of plants from the peloric Antirrhinum, artificially
fertilised by its own pollen, and sixteen plants, which alone survived the
winter, were all as perfectly peloric as the parent-plant. Here we have a
good instance of the wide difference between the inheritance of a character
and the power of transmitting it to crossed offspring. The crossed plants,
which perfectly resembled the common snapdragon, were allowed to sow
themselves, and, out of a hundred and twenty-seven seedlings, eighty-eight
proved to be common snapdragons, two were in an intermediate condition
between the peloric and normal state, {71} and thirty-seven were perfectly
peloric, having reverted to the structure of their one grandparent. This
case seems at first sight to offer an exception to the rule formerly given,
namely, that a character which is present in one form and latent in the
other is generally transmitted with prepotent force when the two forms are
crossed. For in all the Scrophulariaceæ, and especially in the genera
Antirrhinum and Linaria, there is, as was shown in the last chapter, a
strong latent tendency to become peloric; and there is also, as we have
just seen, a still stronger tendency in all peloric plants to reacquire
their normal irregular structure. So that we have two opposed latent
tendencies in the same plants. Now, with the crossed Antirrhinums the
tendency to produce normal or irregular flowers, like those of the common
Snapdragon, prevailed in the first generation; whilst the tendency to
pelorism, appearing to gain strength by the intermission of a generation,
prevailed to a large extent in the second set of seedlings. How it is
possible for a character to gain strength by the intermission of a
generation, will be considered in the chapter on pangenesis.

On the whole, the subject of prepotency is extremely intricate,--from its
varying so much in strength, even in regard to the same character, in
different animals,--from its running either equally in both sexes, or, as
frequently is the case with animals, but not with plants, much stronger in
the one sex than the other,--from the existence of secondary sexual
characters,--from the transmission of certain characters being limited, as
we shall immediately see, by sex,--from certain characters not blending
together,--and, perhaps, occasionally from the effects of a previous
fertilisation on the mother. It is therefore not surprising that every one
hitherto has been baffled in drawing up general rules on the subject of
prepotency.

_Inheritance as limited by Sex._

New characters often appear in one sex, and are afterwards transmitted to
the same sex, either exclusively or in a much greater degree than to the
other. This subject is important, because with animals of many kinds in a
state of nature, both high and low in the scale, secondary sexual
characters, not in {72} any way directly connected with the organs of
reproduction, are often conspicuously present. With our domesticated
animals, also, these same secondary characters are often found to differ
greatly from the state in which they exist in the parent-species. And the
principle of inheritance as limited by sex shows how such characters might
have been first acquired and subsequently modified.

    Dr. P. Lucas, who has collected many facts on this subject, shows[160]
    that when a peculiarity, in no manner connected with the reproductive
    organs, appears in either parent, it is often transmitted exclusively
    to the offspring of the same sex, or to a much greater number of them
    than of the opposite sex. Thus, in the family of Lambert, the horn-like
    projections on the skin were transmitted from the father to his sons
    and grandsons alone; so it has been with other cases of ichthyosis,
    with supernumerary digits, with a deficiency of digits and phalanges,
    and in a lesser degree with various diseases, especially with
    colour-blindness, and a hæmorrhagic diathesis, that is, an extreme
    liability to profuse and uncontrollable bleeding from trifling wounds.
    On the other hand, mothers have transmitted, during several
    generations, to their daughters alone, supernumerary and deficient
    digits, colour-blindness, and other peculiarities. So that we see that
    the very same peculiarity may become attached to either sex, and be
    long inherited by that sex alone; but the attachment in certain cases
    is much more frequent to one than the other sex. The same peculiarities
    also may be promiscuously transmitted to either sex. Dr. Lucas gives
    other cases, showing that the male occasionally transmits his
    peculiarities to his daughters alone, and the mother to her sons alone;
    but even in this case we see that inheritance is to a certain extent,
    though inversely, regulated by sex. Dr. Lucas, after weighing the whole
    evidence, comes to the conclusion that every peculiarity, according to
    the sex in which it first appears, tends to be transmitted in a greater
    or lesser degree to that sex.

    A few details from the many cases collected by Mr. Sedgwick,[161] may
    be here given. Colour-blindness, from some unknown cause, shows itself
    much oftener in males than in females; in upwards of two hundred cases
    collected by Mr. Sedgwick, nine-tenths related to men; but it is
    eminently liable to be transmitted through women. In the case given by
    Dr. Earle, members of eight related families were affected during five
    generations: these families consisted of sixty-one individuals, namely,
    of thirty-two males, of whom nine-sixteenths were incapable of
    distinguishing colour, and of twenty-nine females, of whom only
    one-fifteenth were thus affected. {73} Although colour-blindness thus
    generally clings to the male sex, nevertheless, in one instance in
    which it first appeared in a female, it was transmitted during five
    generations to thirteen individuals, all of whom were females. A
    hæmorrhagic diathesis, often accompanied by rheumatism, has been known
    to affect the males alone during five generations, being transmitted,
    however, through the females. It is said that deficient phalanges in
    the fingers have been inherited by the females alone during ten
    generations. In another case, a man thus deficient in both hands and
    feet, transmitted the peculiarity to his two sons and one daughter; but
    in the third generation, out of nineteen grandchildren, twelve sons had
    the family defect, whilst the seven daughters were free. In ordinary
    cases of sexual limitation, the sons or daughters inherit the
    peculiarity, whatever it may be, from their father or mother, and
    transmit it to their children of the same sex; but generally with the
    hæmorrhagic diathesis, and often with colour-blindness, and in some
    other cases, the sons never inherit the peculiarity directly from their
    fathers, but the daughters, and the daughters alone, transmit the
    latent tendency, so that the sons of the daughters alone exhibit it.
    Thus, the father, grandson, and great-great-grandson will exhibit a
    peculiarity,--the grandmother, daughter, and great-granddaughter having
    transmitted it in a latent state. Hence we have, as Mr. Sedgwick
    remarks, a double kind of atavism or reversion; each grandson
    apparently receiving and developing the peculiarity from his
    grandfather, and each daughter apparently receiving the latent tendency
    from her grandmother.

    From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick, and
    others, there can be no doubt that peculiarities first appearing in
    either sex, though not in any way necessarily or invariably connected
    with that sex, strongly tend to be inherited by the offspring of the
    same sex, but are often transmitted in a latent state through the
    opposite sex.

    Turning now to domesticated animals, we find that certain characters
    not proper to the parent-species are often confined to, and inherited
    by, one sex alone; but we do not know the history of the first
    appearance of such characters. In the chapter on Sheep, we have seen
    that the males of certain races differ greatly from the females in the
    shape of their horns, these being absent in the ewes of some breeds, in
    the development of fat in the tail in certain fat-tailed breeds, and in
    the outline of the forehead. These differences, judging from the
    character of the allied wild species, cannot be accounted for by
    supposing that they have been derived from distinct parent-forms. There
    is, also, a great difference between the horns of the two sexes in one
    Indian breed of goats. The bull zebu is said to have a larger hump than
    the cow. In the Scotch deer-hound the two sexes differ in size more
    than in any other variety of the dog,[162] and, judging from analogy,
    more than in the aboriginal parent-species. The peculiar colour called
    tortoise-shell is very rarely seen in a male cat; the males of this
    variety being of a rusty tint. A tendency to baldness in man before the
    advent of old age is certainly inherited; and in the European, or at
    least in the {74} Englishman, is an attribute of the male sex, and may
    almost be ranked as an incipient secondary sexual character.

    In various breeds of the fowl the males and females often differ
    greatly; and these differences are far from being the same with those
    which distinguish the two sexes in the parent-species, the _Gallus
    bankiva_; and consequently have originated under domestication. In
    certain sub-varieties of the Game race we have the unusual case of the
    hens differing from each other more than the cocks. In an Indian breed
    of a white colour stained with soot, the hens invariably have black
    skins, and their bones are covered by a black periosteum, whilst the
    cocks are never or most rarely thus characterised. Pigeons offer a more
    interesting case; for the two sexes rarely differ throughout the whole
    great family, and the males and females of the parent-form, the _C.
    livia_, are undistinguishable; yet we have seen that with Pouters the
    male has the characteristic quality of pouting more strongly developed
    than the female; and in certain sub-varieties[163] the males alone are
    spotted or striated with black. When male and female English
    carrier-pigeons are exhibited in separate pens, the difference in the
    development of the wattle over the beak and round the eyes is
    conspicuous. So that here we have instances of the appearance of
    secondary sexual characters in the domesticated races of a species in
    which such differences are naturally quite absent.

On the other hand, secondary sexual characters which properly belong to the
species are sometimes quite lost, or greatly diminished, under
domestication. We see this in the small size of the tusks in our improved
breeds of the pig, in comparison with those of the wild boar. There are
sub-breeds of fowls in which the males have lost the fine flowing
tail-feathers and hackles; and others in which there is no difference in
colour between the two sexes. In some cases the barred plumage, which in
gallinaceous birds is commonly the attribute of the hen, has been
transferred to the cock, as in the cuckoo sub-breeds. In other cases
masculine characters have been partly transferred to the female, as with
the splendid plumage of the golden-spangled Hamburgh hen, the enlarged comb
of the Spanish hen, the pugnacious disposition of the Game hen, and as in
the well-developed spurs which occasionally appear in the hens of various
breeds. In Polish fowls both sexes are ornamented with a topknot, that of
the male being formed of hackle-like feathers, and this is a new male
character in the genus Gallus. On the whole, as far as I can judge, new
characters are more apt {75} to appear in the males of our domesticated
animals than in the females, and afterwards to be either exclusively or
more strongly inherited by the males. Finally, in accordance with the
principle of inheritance as limited by sex, the appearance of secondary
sexual characters in natural species offers no especial difficulty, and
their subsequent increase and modification, if of any service to the
species, would follow through that form of selection which in my 'Origin of
Species' I have called sexual selection.

_Inheritance at corresponding periods of Life._

This is an important subject. Since the publication of my 'Origin of
Species,' I have seen no reason to doubt the truth of the explanation there
given of perhaps the most remarkable of all the facts in biology, namely,
the difference between the embryo and the adult animal. The explanation is,
that variations do not necessarily or generally occur at a very early
period of embryonic growth, and that such variations are inherited at a
corresponding age. As a consequence of this the embryo, even when the
parent-form undergoes a great amount of modification, is left only slightly
modified; and the embryos of widely-different animals which are descended
from a common progenitor remain in many important respects like each other
and their common progenitor. We can thus understand why embryology should
throw a flood of light on the natural system of classification, for this
ought to be as far as possible genealogical. When the embryo leads an
independent life, that is, becomes a larva, it has to be adapted to the
surrounding conditions in its structure and instincts, independently of
those of its parents; and the principle of inheritance at corresponding
periods of life renders this possible.

This principle is, indeed, in one way so obvious that it escapes attention.
We possess a number of races of animals and plants, which, when compared
with each other and with their parent-forms, present conspicuous
differences, both in the immature and mature states. Look at the seeds of
the several kinds of peas, beans, maize, which can be propagated truly, and
see how they differ in size, colour, and shape, whilst the {76} full-grown
plants differ but little. Cabbages on the other hand differ greatly in
foliage and manner of growth, but hardly at all in their seeds; and
generally it will be found that the differences between cultivated plants
at different periods of growth are not necessarily closely connected
together, for plants may differ much in their seeds and little when
full-grown, and conversely may yield seeds hardly distinguishable, yet
differ much when full-grown. In the several breeds of poultry, descended
from a single species, differences in the eggs and chickens, in the plumage
at the first and subsequent moults, in the comb and wattles during
maturity, are all inherited. With man peculiarities in the milk and second
teeth, of which I have received the details, are inheritable, and with man
longevity is often transmitted. So again with our improved breeds of cattle
and sheep, early maturity, including the early development of the teeth,
and with certain breeds of fowl the early appearance of secondary sexual
characters, all come under the same head of inheritance at corresponding
periods.

Numerous analogous facts could be given. The silk-moth, perhaps, offers the
best instance; for in the breeds which transmit their characters truly, the
eggs differ in size, colour, and shape;--the caterpillars differ, in
moulting three or four times, in colour, even in having a dark-coloured
mark like an eyebrow, and in the loss of certain instincts;--the cocoons
differ in size, shape, and in the colour and quality of the silk; these
several differences being followed by slight or barely distinguishable
differences in the mature moth.

But it may be said that, if in the above cases a new peculiarity is
inherited, it must be at the corresponding stage of development; for an egg
or seed can resemble only an egg or seed, and the horn in a full-grown ox
can resemble only a horn. The following cases show inheritance at
corresponding periods more plainly, because they refer to peculiarities
which might have supervened, as far as we can see, earlier or later in
life, yet are inherited at the same period at which they first appeared.

    In the Lambert family the porcupine-like excrescences appeared in the
    father and sons at the same age, namely, about nine weeks after {77}
    birth.[164] In the extraordinary hairy family described by Mr.
    Crawfurd,[165] children were produced during three generations with
    hairy ears; in the father the hair began to grow over his body at six
    years old; in his daughter somewhat earlier, namely, at one year; and
    in both generations the milk teeth appeared late in life, the permanent
    teeth being afterwards singularly deficient. Greyness of hair at an
    unusually early age has been transmitted in some families. These cases
    border on diseases inherited at corresponding periods of life, to which
    I shall immediately refer.

    It is a well-known peculiarity with almond-tumbler pigeons, that the
    full beauty and peculiar character of the plumage does not appear until
    the bird has moulted two or three times. Neumeister describes and
    figures a breed of pigeons in which the whole body is white except the
    breast, neck, and head; but before the first moult all the white
    feathers acquire coloured edges. Another breed is more remarkable: its
    first plumage is black, with rusty-red wing-bars and a crescent-shaped
    mark on the breast; these marks then became white, and remain so during
    three or four moults; but after this period the white spreads over the
    body, and the bird loses its beauty.[166] Prize canary-birds have their
    wings and tail black: "this colour, however, is only retained until the
    first moult, so that they must be exhibited ere the change takes place.
    Once moulted, the peculiarity has ceased. Of course all the birds
    emanating from this stock have black wings and tails the first
    year."[167] A curious and somewhat analogous account has been
    given[168] of a family of wild pied rooks which were first observed in
    1798, near Chalfont, and which every year from that date up to the
    period of the published notice, viz. 1837, "have several of their brood
    particoloured, black and white. This variegation of the plumage,
    however, disappears with the first moult; but among the next young
    families there are always a few pied ones." These changes of plumage,
    which appear and are inherited at various corresponding periods of life
    in the pigeon, canary-bird, and rook, are remarkable, because the
    parent-species undergo no such change.

    Inherited diseases afford evidence in some respects of less value than
    the foregoing cases, because diseases are not necessarily connected
    with any change in structure; but in other respects of more value,
    because the periods have been more carefully observed. Certain diseases
    are communicated to the child apparently by a process like inoculation,
    and the child is from the first affected; such cases may be here passed
    over. Large classes of diseases usually appear at certain ages, such as
    St. Vitus's dance in youth, consumption in early mid-life, gout later,
    and apoplexy still later; and these are naturally inherited at the same
    period. But even in diseases of this class, instances have been
    recorded, as with St. Vitus's {78} dance, showing that an unusually
    early or late tendency to the disease is inheritable.[169] In most
    cases the appearance of any inherited disease is largely determined by
    certain critical periods in each person's life, as well as by
    unfavourable conditions. There are many other diseases, which are not
    attached to any particular period, but which certainly tend to appear
    in the child at about the same age at which the parent was first
    attacked. An array of high authorities, ancient and modern, could be
    given in support of this proposition. The illustrious Hunter believed
    in it; and Piorry[170] cautions the physician to look closely to the
    child at the period when any grave inheritable disease attacked the
    parent. Dr. Prosper Lucas,[171] after collecting facts from every
    source, asserts that affections of all kinds, though not related to any
    particular period of life, tend to reappear in the offspring at
    whatever period of life they first appeared in the progenitor.

    As the subject is important, it may be well to give a few instances,
    simply as illustrations, not as proof; for proof, recourse must be had
    to the authorities above quoted. Some of the following cases have been
    selected for the sake of showing that, when a slight departure from the
    rule occurs, the child is affected somewhat earlier in life than the
    parent. In the family of Le Compte blindness was inherited during three
    generations, and no less than thirty-seven children and grandchildren
    were all affected at about the same age, namely seventeen or
    eighteen.[172] In another case a father and his four children all
    became blind at twenty-one years old; in another, a grandmother grew
    blind at thirty-five, her daughter at nineteen, and three grandchildren
    at the ages of thirteen and eleven.[173] So with deafness, two
    brothers, their father and paternal grandfather, all became deaf at the
    age of forty.[174]

    Esquirol gives several striking instances of insanity coming on at the
    same age, as that of a grandfather, father, and son, who all committed
    suicide near their fiftieth year. Many other cases could be given, as
    of a whole family who became insane at the age of forty.[175] Other
    cerebral affections sometimes follow the same rule,--for instance,
    epilepsy and apoplexy. A woman died of the latter disease when
    sixty-three years old; one of her daughters at forty-three, and the
    other at sixty-seven: the latter had twelve children, who all died from
    tubercular meningitis.[176] I mention this latter case because it
    illustrates a frequent occurrence, namely, a change in the precise
    nature of an inherited disease, though still affecting the same organ.

    {79}

    Asthma has attacked several members of the same family when forty years
    old, and other families during infancy. The most different diseases, as
    angina pectoris, stone in the bladder, and various affections of the
    skin, have appeared in successive generations at nearly the same age.
    The little finger of a man began from some unknown cause to grow
    inwards, and the same finger in his two sons began at the same age to
    bend inwards in a similar manner. Strange and inexplicable neuralgic
    affections have caused parents and children to suffer agonies at about
    the same period of life.[177]

    I will give only two other cases, which are interesting as illustrating
    the disappearance as well as the appearance of disease at the same age.
    Two brothers, their father, their paternal uncles, seven cousins, and
    their paternal grandfather, were all similarly affected by a
    skin-disease, called pityriasis versicolor; "the disease, strictly
    limited to the males of the family (though transmitted through the
    females), usually appeared at puberty, and disappeared at about the age
    of forty or forty-five years." The second case is that of four
    brothers, who when about twelve years old suffered almost every week
    from severe headaches, which were relieved only by a recumbent position
    in a dark room. Their father, paternal uncles, paternal grandfather,
    and paternal granduncles all suffered in the same way from headaches,
    which ceased at the age of fifty-four or fifty-five in all those who
    lived so long. None of the females of the family were affected.[178]

It is impossible to read the foregoing accounts, and the many others which
have been recorded, of diseases coming on during three or even more
generations, at the same age in several members of the same family,
especially in the case of rare affections in which the coincidence cannot
be attributed to chance, and doubt that there is a strong tendency to
inheritance in disease at corresponding periods of life. When the rule
fails, the disease is apt to come on earlier in the child than in the
parent; the exceptions in the other direction being vey much rarer. Dr.
Lucas[179] alludes to several cases of inherited diseases coming on at an
earlier period. I have already given one striking instance with blindness
during three generations; and Mr. Bowman remarks that this frequently
occurs with cataract. With cancer there seems to be a peculiar liability to
earlier inheritance: Mr. Paget, who has particularly {80} attended to this
subject, and tabulated a large number of cases, informs me that he believes
that in nine cases out of ten the later generation suffers from the disease
at an earlier period than the previous generation. He adds, "In the
instances in which the opposite relation holds, and the members of later
generations have cancer at a later age than their predecessors, I think it
will be found that the non-cancerous parents have lived to extreme old
ages." So that the longevity of a non-affected parent seems to have the
power of determining in the offspring the fatal period; and we thus
apparently get another element of complexity in inheritance.

The facts, showing that with certain diseases the period of inheritance
occasionally or even frequently advances, are important with respect to the
general descent-theory, for they render it in some degree probable that the
same thing would occur with ordinary modifications of structure. The final
result of a long series of such advances would be the gradual obliteration
of characters proper to the embryo and larva, which would thus come to
resemble more and more closely the mature parent-form. But any structure
which was of service to the embryo or larva would be preserved by the
destruction at this stage of growth of each individual which manifested any
tendency to lose at too early an age its own proper character.

Finally, from the numerous races of cultivated plants and domestic animals,
in which the seed or eggs, the young or old, differ from each other and
from their parent-species;--from the cases in which new characters have
appeared at a particular period, and afterwards have been inherited at the
same period;--and from what we know with respect to disease, we must
believe in the truth of the great principle of inheritance at corresponding
periods of life.

       *       *       *       *       *

_Summary of the three preceding Chapters._--Strong as is the force of
inheritance, it allows the incessant appearance of new characters. These,
whether beneficial or injurious, of the most trifling importance, such as a
shade of colour in a flower, a coloured lock of hair, or a mere gesture; or
of the highest importance, as when affecting the brain or an organ so
perfect {81} and complex as the eye; or of so grave a nature as to deserve
to be called a monstrosity, or so peculiar as not to occur normally in any
member of the same natural class, are all sometimes strongly inherited by
man, the lower animals, and plants. In numberless cases it suffices for the
inheritance of a peculiarity that one parent alone should be thus
characterised. Inequalities in the two sides of the body, though opposed to
the law of symmetry, may be transmitted. There is a considerable body of
evidence showing that even mutilations, and the effects of accidents,
especially or perhaps exclusively when followed by disease, are
occasionally inherited. There can be no doubt that the evil effects of
long-continued exposure in the parent to injurious conditions are sometimes
transmitted to the offspring. So it is, as we shall see in a future
chapter, with the effects of the use and disuse of parts, and of mental
habits. Periodical habits are likewise transmitted, but generally, as it
would appear, with little force.

Hence we are led to look at inheritance as the rule, and non-inheritance as
the anomaly. But this power often appears to us in our ignorance to act
capriciously, transmitting a character with inexplicable strength or
feebleness. The very same peculiarity, as the weeping habit of trees,
silky-feathers, &c., may be inherited either firmly or not at all by
different members of the same group, and even by different individuals of
the same species, though treated in the same manner. In this latter case we
see that the power of transmission is a quality which is merely individual
in its attachment. As with single characters, so it is with the several
concurrent slight differences which distinguish sub-varieties or races; for
of these, some can be propagated almost as truly as species, whilst others
cannot be relied on. The same rule holds good with plants, when propagated
by bulbs, offsets, &c., which in one sense still form parts of the same
individual, for some varieties retain or inherit through successive
bud-generations their character far more truly than others.

Some characters not proper to the parent-species have certainly been
inherited from an extremely remote epoch, and may therefore be considered
as firmly fixed. But it is doubtful whether length of inheritance in itself
gives fixedness of character; {82} though the chances are obviously in
favour of any character which has long been transmitted true or unaltered,
still being transmitted true as long as the conditions of life remain the
same. We know that many species, after having retained the same character
for countless ages, whilst living under their natural conditions, when
domesticated have varied in the most diversified manner, that is, have
failed to transmit their original form; so that no character appears to be
absolutely fixed. We can sometimes account for the failure of inheritance
by the conditions of life being opposed to the development of certain
characters; and still oftener, as with plants cultivated by grafts and
buds, by the conditions causing new and slight modifications incessantly to
appear. In this latter case it is not that inheritance wholly fails, but
that new characters are continually superadded. In some few cases, in which
both parents are similarly characterised, inheritance seems to gain so much
force by the combined action of the two parents, that it counteracts its
own power, and a new modification is the result.

In many cases the failure of the parents to transmit their likeness is due
to the breed having been at some former period crossed; and the child takes
after his grandparent or more remote ancestor of foreign blood. In other
cases, in which the breed has not been crossed, but some ancient character
has been lost through variation, it occasionally reappears through
reversion, so that the parents apparently fail to transmit their own
likeness. In all cases, however, we may safely conclude that the child
inherits all its characters from its parents, in whom certain characters
are latent, like the secondary sexual characters of one sex in the other.
When, after a long succession of bud-generations, a flower or fruit becomes
separated into distinct segments, having the colours or other attributes of
both parent-forms, we cannot doubt that these characters were latent in the
earlier buds, though they could not then be detected, or could be detected
only in an intimately commingled state. So it is with animals of crossed
parentage, which with advancing years occasionally exhibit characters
derived from one of their two parents, of which not a trace could at first
be perceived. Certain monstrosities, which resemble what naturalists call
the typical form of the group in question, {83} apparently come under the
same law of reversion. It is assuredly an astonishing fact that the male
and female sexual elements, that buds, and even full-grown animals, should
retain characters, during several generations in the case of crossed
breeds, and during thousands of generations in the case of pure breeds,
written as it were in invisible ink, yet ready at any time to be evolved
under the requisite conditions.

What these conditions are, we do not in many cases at all know. But the act
of crossing in itself, apparently from causing some disturbance in the
organisation, certainly gives a strong tendency to the reappearance of
long-lost characters, both corporeal and mental, independently of those
derived from the cross. A return of any species to its natural conditions
of life, as with feral animals and plants, favours reversion; though it is
certain that this tendency exists, we do not know how far it prevails, and
it has been much exaggerated. On the other hand, the crossed offspring of
plants which have had their organisation disturbed by cultivation, are more
liable to reversion than the crossed offspring of species which have always
lived under their natural conditions.

When distinguishable individuals of the same family, or races, or species
are crossed, we see that the one is often prepotent over the other in
transmitting its own character. A race may possess a strong power of
inheritance, and yet when crossed, as we have seen with trumpeter-pigeons,
yield to the prepotency of every other race. Prepotentcy of transmission
may be equal in the two sexes of the same species, but often runs more
strongly in one sex. It plays an important part in determining the rate at
which one race can be modified or wholly absorbed by repeated crosses with
another. We can seldom tell what makes one race or species prepotent over
another; but it sometimes depends on the same character being present and
visible in one parent, and latent or potentially present in the other.

Characters may first appear in either sex, but oftener in the male than in
the female, and afterwards be transmitted to the offspring of the same sex.
In this case we may feel confident that the peculiarity in question is
really present though latent in the opposite sex; hence the father may
transmit through his daughter any character to his grandson; and the mother
{84} conversely to her granddaughter. We thus learn, and the fact is an
important one, that transmission and development are distinct powers.
Occasionally these two powers seem to be antagonistic, or incapable of
combination in the same individual; for several cases have been recorded in
which the son has not directly inherited a character from his father, or
directly transmitted it to his son, but has received it by transmission
through his non-affected mother, and transmitted it through his
non-affected daughter. Owing to inheritance being limited by sex, we can
see how secondary sexual characters may first have arisen under nature;
their preservation and accumulation being dependent on their service to
either sex.

At whatever period of life a new character first appears, it generally
remains latent in the offspring until a corresponding age is attained, and
then it is developed. When this rule fails, the child generally exhibits
the character at an earlier period than the parent. On this principle of
inheritance at corresponding periods, we can understand how it is that most
animals display from the germ to maturity such a marvellous succession of
characters.

Finally, though much remains obscure with respect to Inheritance, we may
look at the following laws as fairly well established. Firstly, a tendency
in every character, new and old, to be transmitted by seminal and bud
generation, though often counteracted by various known and unknown causes.
Secondly, reversion or atavism, which depends on transmission and
development being distinct powers: it acts in various degrees and manners
through both seminal and bud generation. Thirdly, prepotency of
transmission, which may be confined to one sex, or be common to both sexes
of the prepotent form. Fourthly, transmission, limited by sex, generally to
the same sex in which the inherited character first appeared. Fifthly,
inheritance at corresponding periods of life, with some tendency to the
earlier development of the inherited character. In these laws of
Inheritance, as displayed under domestication, we see an ample provision
for the production, through variability and natural selection, of new
specific forms.

       *       *       *       *       *


{85}

CHAPTER XV.

ON CROSSING.

    FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED
    BREEDS--WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE
    ABSORBS THE OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF
    TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL
    ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN
    CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE
    SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES,
    AND THE FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE
    BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT
    SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.

In the two previous chapters, when discussing reversion and prepotency, I
was necessarily led to give many facts on crossing. In the present chapter
I shall consider the part which crossing plays in two opposed
directions,--firstly, in obliterating characters, and consequently in
preventing the formation of new races; and secondly, in the modification of
old races, or in the formation of new and intermediate races, by a
combination of characters. I shall also show that certain characters are
incapable of fusion.

The effects of free or uncontrolled breeding between the members of the
same variety or of closely allied varieties are important; but are so
obvious that they need not be discussed at much length. It is free
intercrossing which chiefly gives uniformity, both under nature and under
domestication, to the individuals of the same species or variety, when they
live mingled together and are not exposed to any cause inducing excessive
variability. The prevention of free crossing, and the intentional matching
of individual animals, are the corner-stones of the breeder's art. No man
in his senses would expect to improve or modify a breed in any particular
manner, or keep an old breed true and distinct, unless he separated his
animals. The killing of inferior animals in each generation comes to the
{86} same thing as their separation. In savage and semi-civilised
countries, where the inhabitants have not the means of separating their
animals, more than a single breed of the same species rarely or never
exists. In former times, even in a country so civilised as North America,
there were no distinct races of sheep, for all had been mingled
together.[180] The celebrated agriculturist Marshall[181] remarks that
"sheep that are kept within fences, as well as shepherded flocks in open
countries, have generally a similarity, if not a uniformity, of character
in the individuals of each flock;" for they breed freely together, and are
prevented from crossing with other kinds; whereas in the unenclosed parts
of England the unshepherded sheep, even of the same flock, are far from
true or uniform, owing to various breeds having mingled and crossed. We
have seen that the half-wild cattle in the several British parks are
uniform in character in each; but in the different parks, from not having
mingled and crossed during many generations, they differ in a slight
degree.

We cannot doubt that the extraordinary number of varieties and
sub-varieties of the pigeon, amounting to at least one hundred and fifty,
is partly due to their remaining, differently from other domesticated
birds, paired for life when once matched. On the other hand, breeds of cats
imported into this country soon disappear, for their nocturnal and rambling
habits render it hardly possible to prevent free crossing. Rengger[182]
gives an interesting case with respect to the cat in Paraguay: in all the
distant parts of the kingdom it has assumed, apparently from the effects of
the climate, a peculiar character, but near the capital this change has
been prevented, owing, as he asserts, to the native animal frequently
crossing with cats imported from Europe. In all cases like the foregoing,
the effects of an occasional cross will be augmented by the increased
vigour and fertility of the crossed offspring, of which fact evidence will
hereafter be given; for this will lead to the mongrels increasing more
rapidly than the pure parent-breeds.

{87}

When distinct breeds are allowed to cross freely, the result will be a
heterogenous body; for instance, the dogs in Paraguay are far from uniform,
and can no longer be affiliated to their parent-races.[183] The character
which a crossed body of animals will ultimately assume must depend on
several contingencies,--namely, on the relative numbers of the individuals
belonging to the two or more races which are allowed to mingle; on the
prepotency of one race over the other in the transmission of character; and
on the conditions of life to which they are exposed. When two commingled
breeds exist at first in nearly equal numbers, the whole will sooner or
later become intimately blended, but not so soon, both breeds being equally
favoured in all respects, as might have been expected. The following
calculation[184] shows that this is the case: if a colony with an equal
number of black and white men were founded, and we assume that they marry
indiscriminately, are equally prolific, and that one in thirty annually
dies and is born; then "in 65 years the number of blacks, whites, and
mulattoes would be equal. In 91 years the whites would be 1-10th, the
blacks 1-10th, and the mulattoes, or people of intermediate degrees of
colour, 8-10ths of the whole number. In three centuries not 1-100th part of
the whites would exist."

When one of two mingled races exceeds the other greatly in number, the
latter will soon be wholly, or almost wholly, absorbed and lost.[185] Thus
European pigs and dogs have been largely introduced into the islands of the
Pacific Ocean, and the native races have been absorbed and lost in the
course of about fifty or sixty years;[186] but the imported races no doubt
were favoured. Rats may be considered as semi-domesticated animals. Some
snake-rats (_Mus alexandrinus_) escaped in the Zoological Gardens of
London, "and for a long time afterwards the keepers frequently caught
cross-bred rats, at first half-breds, afterwards with less and less of the
character of the snake-rat, till at length all traces of it
disappeared."[187] On the other hand, {88} in some parts of London,
especially near the docks, where fresh rats are frequently imported, an
endless variety of intermediate forms may be found between the brown,
black, and snake rat, which are all three usually ranked as distinct
species.

How many generations are necessary for one species or race to absorb
another by repeated crosses has often been discussed;[188] and the
requisite number has probably been much exaggerated. Some writers have
maintained that a dozen, or score, or even more generations, are necessary;
but this in itself is improbable, for in the tenth generation there will be
only 1-1024th part of foreign blood in the offspring. Gärtner found,[189]
that with plants one species could be made to absorb another in from three
to five generations, and he believes that this could always be effected in
from six to seventh generations. In one instance, however, Kölreuter[190]
speaks of the offspring of _Mirabilis vulgaris_, crossed during eight
successive generations by _M. longiflora_, as resembling this latter
species so closely, that the most scrupulous observer could detect "vix
aliquam notabilem differentiam;"--he succeeded, as he says, "ad plenariam
fere transmutationem." But this expression shows that the act of absorption
was not even then absolutely complete, though these crossed plants
contained only the 1-256th part of _M. vulgaris_. The conclusions of such
accurate observers as Gärtner and Kölreuter are of far higher worth than
those made without scientific aim by breeders. The most remarkable
statement which I have met with of the persistent endurance of the effects
of a single cross is given by Fleischmann,[191] who, in reference to German
sheep, says "that the original coarse sheep have 5500 fibres of wool on a
square inch; grades of the third or fourth Merino cross produced about
8000, the twentieth cross 27,000, the perfect pure Merino blood 40,000 to
48,000." So that in this case common German sheep crossed twenty times
successively with Merinos have not by any means acquired wool as fine as
that of the pure breed. In all cases, the rate of absorption will {89}
depend largely on the conditions of life being favourable to any particular
character; and we may suspect that there would be under the climate of
Germany a constant tendency to degeneration in the wool of Merinos, unless
prevented by careful selection; and thus perhaps the foregoing remarkable
case may be explained. The rate of absorption must also depend on the
amount of distinguishable difference between the two forms which are
crossed, and especially, as Gärtner insists, on prepotency of transmission
in the one form over the other. We have seen in the last chapter that one
of two French breeds of sheep yielded up its character, when crossed with
Merinos, very much slower than the other; and the common German sheep
referred to by Fleischmann may present an analogous case. But in all cases
there will be during many subsequent generations more or less liability to
reversion, and it is this fact which has probably led authors to maintain
that a score or more of generations are requisite for one race to absorb
another. In considering the final result of the commingling of two or more
breeds, we must not forget that the act of crossing in itself tends to
bring back long-lost characters not proper to the immediate parent-forms.

With respect to the influence of the conditions of life on any two breeds
which are allowed to cross freely, unless both are indigenous and have long
been accustomed to the country where they live, they will, in all
probability, be unequally affected by the conditions, and this will modify
the result. Even with indigenous breeds, it will rarely or never occur that
both are equally well adapted to the surrounding circumstances; more
especially when permitted to roam freely, and not carefully tended, as will
generally be the case with breeds allowed to cross. As a consequence of
this, natural selection will to a certain extent come into action, and the
best fitted will survive, and this will aid in determining the ultimate
character of the commingled body.

How long a time it would require before such a crossed body of animals
would assume within a limited area a uniform character no one can say; that
they would ultimately become uniform from free intercrossing, and from the
survival of the fittest, we may feel assured; but the character thus
acquired would rarely or never, as we may infer from the several previous
{90} considerations, be exactly intermediate between that of the two
parent-breeds. With respect to the very slight differences by which the
individuals of the same sub-variety, or even of allied varieties, are
characterised, it is obvious that free crossing would soon obliterate such
small distinctions. The formation of new varieties, independently of
selection, would also thus be prevented; except when the same variation
continually recurred from the action of some strongly predisposing cause.
Hence we may conclude that free crossing has in all cases played an
important part in giving to all the members of the same domestic race, and
of the same natural species, uniformity of character, though largely
modified by natural selection and by the direct action of the surrounding
conditions.

_On the possibility of all organic beings occasionally intercrossing._--But
it may be asked, can free crossing occur with hermaphrodite animals and
plants? All the higher animals, and the few insects which have been
domesticated, have separated sexes, and must inevitably unite for each
birth. With respect to the crossing of hermaphrodites, the subject is too
large for the present volume, and will be more properly treated in a
succeeding work. In my 'Origin of Species,' however, I have given a short
abstract of the reasons which induce me to believe that all organic beings
occasionally cross, though perhaps in some cases only at long intervals of
time.[192] I will here just recall the fact that many plants, though
hermaphrodite in structure, are unisexual in function;--such as those
called by C. K. Sprengel _dichogamous_, in which the pollen and stigma of
the same flower are matured at different periods; or those called by me
_reciprocally dimorphic_, in which the flower's own pollen is not fitted to
fertilise its own stigma; or again, the many kinds in which curious
mechanical contrivances exist, effectually preventing self-fertilisation.
There are, however, many hermaphrodite plants which are not in any way
specially constructed to favour intercrossing, but which nevertheless
commingle almost as freely as animals with separated sexes. This is the
case with cabbages, radishes, and onions, as I know from {91} having
experimented on them: even the peasants of Liguria say that cabbages must
be prevented "from falling in love" with each other. In the orange tribe,
Gallesio[193] remarks that the amelioration of the various kinds is checked
by their continual and almost regular crossing. So it is with numerous
other plants.

Nevertheless some cultivated plants can be named which rarely intercross,
as the common pea, or which never intercross, as I have reason to believe
is the case with the sweet-pea (_Lathyrus odoratus_); yet the structure of
these flowers certainly favours an occasional cross. The varieties of the
tomato and aubergine (_Solanum_) and pimenta (_Pimenta vulgaris?_) are
said[194] never to cross, even when growing alongside each other. But it
should be observed that these are all exotic plants, and we do not know how
they would behave in their native country when visited by the proper
insects.

It must also be admitted that some few natural species appear under our
present state of knowledge to be perpetually self-fertilised, as in the
case of the Bee Ophrys (_O. apifera_), though adapted in its structure to
be occasionally crossed. The _Leersia oryzoides_ produces minute enclosed
flowers which cannot possibly be crossed, and these alone, to the exclusion
of the ordinary flowers, have as yet been known to yield seed.[195] A few
additional and analogous cases could be advanced. But these facts do not
make me doubt that it is a general law of nature that the individuals of
the same species occasionally intercross, and that some great advantage is
derived from this act. It is well known (and I shall hereafter have to give
instances) that some plants, both indigenous and naturalised, rarely or
never produce flowers; or, if they flower, never produce seeds. But no one
is thus led to doubt that it is a general law of nature that phanerogamic
plants should produce flowers, and that these flowers should produce seed.
When they fail, we believe that such plants would perform their proper
functions under different conditions, or that they formerly did so and will
do so again. On analogous grounds, I believe that the few flowers {92}
which do not now intercross, either would do so under different conditions,
or that they formerly fertilised each other at intervals--the means for
effecting this being generally still retained--and they will do so again at
some future period, unless indeed they become extinct. On this view alone,
many points in the structure and action of the reproductive organs in
hermaphrodite plants and animals are intelligible,--for instance, the male
and female organs never being so completely enclosed as to render access
from without impossible. Hence we may conclude that the most important of
all the means for giving uniformity to the individuals of the same species,
namely, the capacity of occasionally intercrossing, is present, or has been
formerly present, with all organic beings.

    _On certain Characters not blending._--When two breeds are crossed
    their characters usually become intimately fused together; but some
    characters refuse to blend, and are transmitted in an unmodified state
    either from both parents or from one. When grey and white mice are
    paired, the young are not piebald nor of an intermediate tint, but are
    pure white or of the ordinary grey colour: so it is when white and
    common collared turtle-doves are paired. In breeding Game fowls, a
    great authority, Mr. J. Douglas, remarks, "I may here state a strange
    fact: if you cross a black with a white game, you get birds of both
    breeds of the clearest colour." Sir R. Heron crossed during many years
    white, black, brown, and fawn-coloured Angora rabbits, and never once
    got these colours mingled in the same animal, but often all four
    colours in the same litter.[196] Additional cases could be given, but
    this form of inheritance is very far from universal even with respect
    to the most distinct colours. When turnspit dogs and ancon sheep, both
    of which have dwarfed limbs, are crossed with common breeds, the
    offspring are not intermediate in structure, but take after either
    parent. When tailless or hornless animals are crossed with perfect
    animals, it frequently, but by no means invariably, happens that the
    offspring are {93} either perfectly furnished with these organs or are
    quite destitute of them. According to Rengger, the hairless condition
    of the Paraguay dog is either perfectly or not at all transmitted to
    its mongrel offspring; but I have seen one partial exception in a dog
    of this parentage which had part of its skin hairy, and part naked; the
    parts being distinctly separated as in a piebald animal. When Dorking
    fowls with five toes are crossed with other breeds, the chickens often
    have five toes on one foot and four on the other. Some crossed pigs
    raised by Sir R. Heron between the solid-hoofed and common pig had not
    all four feet in an intermediate condition, but two feet were furnished
    with properly divided, and two with united hoofs.

    Analogous facts have been observed with plants: Major Trevor Clarke
    crossed the little, glabrous-leaved, annual stock (_Matthiola_), with
    pollen of a large, red-flowered, rough-leaved, biennial stock, called
    _cocardeau_ by the French, and the result was that half the seedlings
    had glabrous and the other half rough leaves, but none had leaves in an
    intermediate state. That the glabrous seedlings were the product of the
    rough-leaved variety, and not accidentally of the mother-plant's own
    pollen, was shown by their tall and strong habit of growth.[197] In the
    succeeding generations raised from the rough-leaved crossed seedlings,
    some glabrous plants appeared, showing that the glabrous character,
    though incapable of blending with and modifying the rough leaves, was
    all the time latent in this family of plants. The numerous plants
    formerly referred to, which I raised from reciprocal crosses between
    the peloric and common Antirrhinum, offer a nearly parallel case; for
    in the first generation all the plants resembled the common form, and
    in the next generation, out of one hundred and thirty-seven plants, two
    alone were in an intermediate condition, the others perfectly
    resembling either the peloric or common form. Major Trevor Clarke also
    fertilised the above-mentioned red-flowered stock with pollen from the
    purple Queen stock, and about half the seedlings scarcely differed in
    habit, and not at all in the red colour of the flower, from the
    mother-plant, the other half bearing blossoms of a rich purple, closely
    like those of the paternal plant. Gärtner crossed many white and
    yellow-flowered species and varieties of Verbascum; and these colours
    were never blended, but the offspring bore either pure white or pure
    yellow blossoms; the former in the larger proportion.[198] Dr. Herbert
    raised many seedlings, as he informed me, from Swedish turnips crossed
    by two other varieties, and these never produced flowers of an
    intermediate tint, but always like one of their parents. I fertilised
    the purple sweet-pea (_Lathyrus odoratus_), which has a dark
    reddish-purple standard-petal and violet-coloured wings and keel, with
    pollen of the painted-lady sweet-pea, which has a pale cherry-coloured
    standard, and almost white wings and keel; and from the same pod I
    twice raised plants perfectly resembling both sorts; the greater number
    resembling the father. So perfect was the resemblance, that I should
    have thought there had {94} been some mistake, if the plants which were
    at first identical with the paternal variety, namely, the painted-lady,
    had not later in the season produced, as mentioned in a former chapter,
    flowers blotched and streaked with dark purple. I raised grandchildren
    and great-grandchildren from these crossed plants, and they continued
    to resemble the painted-lady, but during the later generations became
    rather more blotched with purple, yet none reverted completely to the
    original mother-plant, the purple sweet-pea. The following case is
    slightly different, but still shows the same principle: Naudin[199]
    raised numerous hybrids between the yellow _Linaria vulgaris_ and the
    purple _L. purpurea_, and during three successive generations the
    colours kept distinct in different parts of the same flower.

    From such cases as the foregoing, in which the offspring of the first
    generation perfectly resemble either parent, we come by a small step to
    those cases in which differently coloured flowers borne on the same
    root resemble both parents, and by another step to those in which the
    same flower or fruit is striped or blotched with the two parental
    colours, or bears a single stripe of the colour or other characteristic
    quality of one of the parent-forms. With hybrids and mongrels it
    frequently or even generally happens that one part of the body
    resembles more or less closely one parent and another part the other
    parent; and here again some resistance to fusion, or, what comes to the
    same thing, some mutual affinity between the organic atoms of the same
    nature, apparently comes into play, for otherwise all parts of the body
    would be equally intermediate in character. So again, when the
    offspring of hybrids or mongrels, which are themselves nearly
    intermediate in character, revert either wholly or by segments to their
    ancestors, the principle of the affinity of similar, or the repulsion
    of dissimilar atoms, must come into action. To this principle, which
    seems to be extremely general, we shall recur in the chapter on
    pangenesis.

    It is remarkable, as has been strongly insisted upon by Isidore
    Geoffroy St. Hilaire in regard to animals, that the transmission of
    characters without fusion occurs most rarely when species are crossed;
    I know of one exception alone, namely, with the hybrids naturally
    produced between the common and hooded crow (_Corvus corone_ and
    _cornix_), which, however, are closely allied species, differing in
    nothing except colour. Nor have I met with any well-ascertained cases
    of transmission of this kind, even when one form is strongly prepotent
    over another, when two races are crossed which have been slowly formed
    by man's selection, and therefore resemble to a certain extent natural
    species. Such cases as puppies in the same litter closely resembling
    two distinct breeds, are probably due to super-foetation,--that is, to
    the influence of two fathers. All the characters above enumerated,
    which are transmitted in a perfect state to some of the offspring and
    not to others,--such as distinct colours, nakedness of skin, smoothness
    of leaves, absence of horns or tail, additional toes, pelorism, dwarfed
    structure, &c.,--have all been known to appear suddenly in individual
    animals and plants. From this fact, and from the several slight,
    aggregated differences which distinguish domestic races and species
    from {95} each other, not being liable to this peculiar form of
    transmission, we may conclude that it is in some way connected with the
    sudden appearance of the characters in question.

_On the Modification of old Races and the Formation of new Races by
Crossing._--We have hitherto chiefly considered the effects of crossing in
giving uniformity of character; we must now look to an opposite result.
There can be no doubt that crossing, with the aid of rigorous selection
during several generations, has been a potent means in modifying old races,
and in forming new ones. Lord Orford crossed his famous stud of greyhounds
once with the bulldog, which breed was chosen from being deficient in
scenting powers, and from having what was wanted, courage and perseverance.
In the course of six or seven generations all traces of the external form
of the bulldog were eliminated, but courage and perseverance remained.
Certain pointers have been crossed, as I hear from the Rev. W. D. Fox, with
the foxhound, to give them dash and speed. Certain strains of Dorking fowls
have had a slight infusion of Game blood; and I have known a great fancier
who on a single occasion crossed his turbit-pigeons with barbs, for the
sake of gaining greater breadth of beak.

In the foregoing cases breeds have been crossed once, for the sake of
modifying some particular character; but with most of the improved races of
the pig, which now breed true, there have been repeated crosses,--for
instance, the improved Essex owes its excellence to repeated crosses with
the Neapolitan, together probably with some infusion of Chinese blood.[200]
So with our British sheep: almost all the races, except the Southdown, have
been largely crossed; "this, in fact, has been the history of our principal
breeds."[201] To give an example, the "Oxfordshire Downs" now rank as an
established breed.[202] They were produced about the year 1830 by crossing
"Hampshire and in some instances Southdown ewes with Cotswold rams:" now
the Hampshire ram was itself produced by repeated crosses between the
native {96} Hampshire sheep and Southdowns; and the long-woolled Cotswold
were improved by crosses with the Leicester, which latter again is believed
to have been a cross between several long-woolled sheep. Mr. Spooner, after
considering the various cases which have been carefully recorded, concludes
"that from a judicious pairing of cross-bred animals it is practicable to
establish a new breed." On the Continent the history of several crossed
races of cattle and of other animals has been well ascertained. To give one
instance: the King of Wurtemberg, after twenty-five years' careful
breeding, that is after six or seven generations, made a new breed of
cattle from a cross between a Dutch and Swiss breed, combined with other
breeds.[203] The Sebright bantam, which breeds as true as any other kind of
fowl, was formed about sixty years ago by a complicated cross.[204] Dark
Brahmas, which are believed by some fanciers to constitute a distinct
species, were undoubtedly formed[205] in the United States, within a recent
period, by a cross between Chittagongs and Cochins. With plants I believe
there is little doubt that some kinds of turnips, now extensively
cultivated, are crossed races; and the history of a variety of wheat which
was raised from two very distinct varieties, and which after six years'
culture presented an even sample, has been recorded on good authority.[206]

Until quite lately, cautious and experienced breeders, though not averse to
a single infusion of foreign blood, were almost universally convinced that
the attempt to establish a new race, intermediate between two widely
distinct races, was hopeless: "they clung with superstitious tenacity to
the doctrine of purity of blood, believing it to be the ark in which alone
true safety could be found."[207] Nor was this conviction unreasonable:
when two distinct races are crossed, the offspring of the first generation
are generally nearly uniform in character; but even this sometimes fails to
be the case, especially with crossed dogs and fowls, the young of which
from the first are sometimes much {97} diversified. As cross-bred animals
are generally of large size and vigorous, they have been raised in great
numbers for immediate consumption. But for breeding they are found to be
utterly useless; for though they may be themselves uniform in character,
when paired together they yield during many generations offspring
astonishingly diversified. The breeder is driven to despair, and concludes
that he will never form an intermediate race. But from the cases already
given, and from others which have been recorded, it appears that patience
alone is necessary; as Mr. Spooner remarks, "nature opposes no barrier to
successful admixture; in the course of time, by the aid of selection and
careful weeding, it is practicable to establish a new breed." After six or
seven generations the hoped-for result will in most cases be obtained; but
even then an occasional reversion, or failure to keep true, may be
expected. The attempt, however, will assuredly fail if the conditions of
life be decidedly unfavourable to the characters of either
parent-breed.[208]

Although the grandchildren and succeeding generations of cross-bred animals
are generally variable in an extreme degree, some curious exceptions to the
rule have been observed, both with crossed races and species. Thus Boitard
and Corbié[209] assert that from a Pouter and a Runt "a Cavalier will
appear, which we have classed amongst pigeons of pure race, because it
transmits all its qualities to its posterity." The editor of the 'Poultry
Chronicle'[210] bred some bluish fowls from a black Spanish cock and a
Malay hen; and these remained true to colour "generation after generation."
The Himalayan breed of rabbits was certainly formed by crossing two
sub-varieties of the silver-grey rabbit; although it suddenly assumed its
present character, which differs much from that of either parent-breed, yet
it has ever since been easily and truly propagated. I crossed some Labrador
and Penguin ducks, and recrossed the mongrels with Penguins; afterwards,
most of the ducks reared during three generations were nearly uniform in
character, being brown with a white crescentic mark on the lower part of
the breast, {98} and with some white spots at the base of the beak; so that
by the aid of a little selection a new breed might easily have been formed.
In regard to crossed varieties of plants, Mr. Beaton remarks[211] that
"Melville's extraordinary cross between the Scotch kale and an early
cabbage is as true and genuine as any on record;" but in this case no doubt
selection was practised. Gärtner[212] has given five cases of hybrids, in
which the progeny kept constant; and hybrids between _Dianthus armeria_ and
_deltoides_ remained true and uniform to the tenth generation. Dr. Herbert
likewise showed me a hybrid from two species of Loasa which from its first
production had kept constant during several generations.

We have seen in the earlier chapters, that some of our domesticated
animals, such as dogs, cattle, pigs, &c., are almost certainly descended
from more than one species, or wild race, if any one prefers to apply this
latter term to forms which were enabled to keep distinct in a state of
nature. Hence the crossing of aboriginally distinct species probably came
into play at an early period in the formation of our present races. From
Rütimeyer's observations there can be little doubt that this occurred with
cattle; but in most cases some one of the forms which were allowed to cross
freely, will, it is probable, have absorbed and obliterated the others. For
it is not likely that semi-civilized men would have taken the necessary
pains to modify by selection their commingled, crossed, and fluctuating
stock. Nevertheless, those animals which were best adapted to their
conditions of life would have survived through natural selection; and by
this means crossing will often have indirectly aided in the formation of
primeval domesticated breeds.

Within recent times, as far as animals are concerned, the crossing of
distinct species has done little or nothing in the formation or
modification of our races. It is not yet known whether the species of
silk-moth which have been recently crossed in France will yield permanent
races. In the fourth chapter I alluded with some hesitation to the
statement that a new breed, between the hare and rabbit, called leporides,
had been formed in France, and was found capable of propagating {99}
itself; but it is now positively affirmed[213] that this is an error. With
plants which can be multiplied by buds and cuttings, hybridisation has done
wonders, as with many kinds of Roses, Rhododendrons, Pelargoniums,
Calceolarias, and Petunias. Nearly all these plants can be propagated by
seed; most of them freely; but extremely few or none come true by seed.

Some authors believe that crossing is the chief cause of variability,--that
is, of the appearance of absolutely new characters. Some have gone so far
as to look at it as the sole cause; but this conclusion is disproved by
some of the facts given in the chapter on Bud-variation. The belief that
characters not present in either parent or in their ancestors frequently
originate from crossing is doubtful; that they occasionally thus arise is
probable; but this subject will be more conveniently discussed in a future
chapter on the causes of Variability.

A condensed summary of this and of the three following chapters, together
with some remarks on Hybridism, will be given in the nineteenth chapter.

       *       *       *       *       *


{100}

CHAPTER XVI.

CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OF
DOMESTICATION ON FERTILITY.

    DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN
    CROSSED--VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF
    BREEDING AND SEXUAL PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE
    WHEN CROSSED--VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS,
    AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY STERILE--DOMESTICATION
    ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN
    CROSSED--ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS
    FROM DOMESTICATION AND CULTIVATION.

The domesticated races of both animals and plants, when crossed, are with
extremely few exceptions quite prolific,--in some cases even more so than
the purely bred parent-races. The offspring, also, raised from such crosses
are likewise, as we shall see in the following chapter, generally more
vigorous and fertile than their parents. On the other hand, species when
crossed, and their hybrid offspring, are almost invariability in some
degree sterile; and here there seems to exist a broad and insuperable
distinction between races and species. The importance of this subject as
bearing on the origin of species is obvious; and we shall hereafter recur
to it.

It is unfortunate how few precise observations have been made on the
fertility of mongrel animals and plants during several successive
generations. Dr. Broca[214] has remarked that no one has observed whether,
for instance, mongrel dogs, bred _inter se_, are indefinitely fertile; yet,
if a shade of infertility be detected by careful observation in the
offspring of natural forms when crossed, it is thought that their specific
distinction is proved. But so many breeds of sheep, cattle, pigs, dogs, and
poultry, have been crossed and recrossed in various ways, that any
sterility, if it had existed, would from being injurious {101} almost
certainly have been observed. In investigating the fertility of crossed
varieties many sources of doubt occur. Whenever the least trace of
sterility between two plants, however closely allied, was observed by
Kölreuter, and more especially by Gärtner, who counted the exact number of
seed in each capsule, the two forms were at once ranked as distinct
species; and if this rule be followed, assuredly it will never be proved
that varieties when crossed are in any degree sterile. We have formerly
seen that certain breeds of dogs do not readily pair together; but no
observations have been made whether, when paired, they produce the full
number of young, and whether the latter are perfectly fertile _inter se_;
but, supposing that some degree of sterility were found to exist,
naturalists would simply infer that these breeds were descended from
aboriginally distinct species; and it would be scarcely possible to
ascertain whether or not this explanation was the true one.

The Sebright Bantam is much less prolific than any other breed of fowls,
and is descended from a cross between two very distinct breeds, recrossed
by a third sub-variety. But it would be extremely rash to infer that the
loss of fertility was in any manner connected with its crossed origin, for
it may with more probability be attributed either to long-continued close
interbreeding, or to an innate tendency to sterility correlated with the
absence of hackles and sickle tail-feathers.

Before giving the few recorded cases of forms, which must be ranked as
varieties, being in some degree sterile when crossed, I may remark that
other causes sometimes interfere with varieties freely intercrossing. Thus
they may differ too greatly in size, as with some kinds of dogs and fowls:
for instance, the editor of the 'Journal of Horticulture, &c.,'[215] says
that he can keep Bantams with the larger breeds without much danger of
their crossing, but not with the smaller breeds, such as Games, Hamburgs,
&c. With plants a difference in the period of flowering serves to keep
varieties distinct, as with the various kinds of maize and wheat: thus
Colonel Le Couteur[216] remarks, "the Talavera wheat, from flowering much
earlier than any other kind, is sure to continue pure." In different parts
of {102} the Falkland Islands the cattle are breaking up into herds of
different colours; and those on the higher ground, which are generally
white, usually breed, as I am informed by Admiral Sulivan, three months
earlier than those on the lowlands; and this would manifestly tend to keep
the herds from blending.

Certain domestic races seem to prefer breeding with their own kind; and
this is a fact of some importance, for it is a step towards that
instinctive feeling which helps to keep closely allied species in a state
of nature distinct. We have now abundant evidence that, if it were not for
this feeling, many more hybrids would be naturally produced than is the
case. We have seen in the first chapter that the alco dog of Mexico
dislikes dogs of other breeds; and the hairless dog of Paraguay mixes less
readily with the European races, than the latter do with each other. In
Germany the female Spitz-dog is said to receive the fox more readily than
will other dogs; a female Australian Dingo in England attracted the wild
male foxes. But these differences in the sexual instinct and attractive
power of the various breeds may be wholly due to their descent from
distinct species. In Paraguay the horses have much freedom, and an
excellent observer[217] believes that the native horses of the same colour
and size prefer associating with each other, and that the horses which have
been imported from Entre Rios and Banda Oriental into Paraguay likewise
prefer associating together. In Circassia six sub-races of the horse are
known and have received distinct names; and a native proprietor of
rank[218] asserts that horses of three of these races, whilst living a free
life, almost always refuse to mingle and cross, and will even attack each
other.

It has been observed, in a district stocked with heavy Lincolnshire and
light Norfolk sheep, that both kinds, though bred together, when turned
out, "in a short time separate to a sheep;" the Lincolnshires drawing off
to the rich soil, and the Norfolks to their own dry light soil; and as long
as there is plenty of grass, "the two breeds keep themselves as distinct as
rooks and pigeons." In this case different habits of {103} life tend to
keep the races distinct. On one of the Faroe islands, not more than half a
mile in diameter, the half-wild native black sheep are said not to have
readily mixed with the imported white sheep. It is a more curious fact that
the semi-monstrous ancon sheep of modern origin "have been observed to keep
together, separating themselves from the rest of the flock, when put into
enclosures with other sheep."[219] With respect to fallow deer, which live
in a semi-domesticated condition, Mr. Bennett[220] states that the dark and
pale coloured herds, which have long been kept together in the Forest of
Dean, in High Meadow Woods, and in the New Forest, have never been known to
mingle: the dark-coloured deer, it may be added, are believed to have been
first brought by James I. from Norway, on account of their greater
hardiness. I imported from the island of Porto Santo two of the feral
rabbits, which differ, as described in the fourth chapter, from common
rabbits; both proved to be males, and, though they lived during some years
in the Zoological Gardens, the superintendent, Mr. Bartlett, in vain
endeavoured to make them breed with various tame kinds; but whether this
refusal to breed was due to any change in instinct, or simply to their
extreme wildness; or whether confinement had rendered them sterile, as
often occurs, cannot be told.

Whilst matching for the sake of experiment many of the most distinct breeds
of pigeons, it frequently appeared to me that the birds, though faithful to
their marriage vow, retained some desire after their own kind. Accordingly
I asked Mr. Wicking, who has kept a larger stock of various breeds together
than any man in England, whether he thought that they would prefer pairing
with their own kind, supposing that there were males and females enough of
each; and he without hesitation answered that he was convinced that this
was the case. It has often been noticed that the dovecot pigeon seems to
have an actual aversion towards the several fancy breeds;[221] yet all have
{104} certainly sprung from a common progenitor. The Rev. W. D. Fox informs
me that his flocks of white and common Chinese geese kept distinct.

These facts and statements, though some of them are incapable of proof,
resting only on the opinion of experienced observers, show that some
domestic races are led by different habits of life to keep to a certain
extent separate, and that others prefer coupling with their own kind, in
the same manner as species in a state of nature, though in a much less
degree.

    With respect to sterility from the crossing of domestic races, I know
    of no well-ascertained case with animals. This fact, seeing the great
    difference in structure between some breeds of pigeons, fowls, pigs,
    dogs, &c., is extraordinary, in contrast with the sterility of many
    closely allied natural species when crossed; but we shall hereafter
    attempt to show that it is not so extraordinary as it at first appears.
    And it may be well here to recall to mind that the amount of external
    difference between two species will not safely guide us in foretelling
    whether or not they will breed together,--some closely allied species
    when crossed being utterly sterile, and others which are extremely
    unlike being moderately fertile. I have said that no case of sterility
    in crossed races rests on satisfactory evidence; but here is one which
    at first seems trustworthy. Mr. Youatt,[222] and a better authority
    cannot be quoted, states, that formerly in Lancashire crosses were
    frequently made between longhorn and shorthorn cattle; the first cross
    was excellent, but the produce was uncertain; in the third or fourth
    generation the cows were bad milkers; "in addition to which, there was
    much uncertainty whether the cows would conceive; and full one-third of
    the cows among some of these half-breds failed to be in calf." This at
    first seems a good case; but Mr. Wilkinson states,[223] that a breed
    derived from this same cross was actually established in another part
    of England; and if it had failed in fertility, the fact would surely
    have been noticed. Moreover, supposing that Mr. Youatt had proved his
    case, it might be argued that the sterility was wholly due to the two
    parent-breeds being descended from primordially distinct species.

    I will give a case with plants, to show how difficult it is to get
    sufficient evidence. Mr. Sheriff, who has been so successful in the
    formation of new races of wheat, fertilised the Hopetoun with the
    Talavera; in the first and second generations the produce was
    intermediate in character, but in the fourth generation "it was found
    to consist of many varieties; nine-tenths of the florets proved barren,
    and many of the seeds seemed shrivelled abortions, void of vitality,
    and the whole race was evidently verging to extinction."[224] Now,
    considering how little these {105} varieties of wheat differ in any
    important character, it seems to me very improbable that the sterility
    resulted, as Mr. Sheriff thought, from the cross, but from some quite
    distinct cause. Until such experiments are many times repeated, it
    would be rash to trust them; but unfortunately they have been rarely
    tried even once with sufficient care.

    Gärtner has recorded a more remarkable and trustworthy case: he
    fertilised thirteen panicles (and subsequently nine others) on a dwarf
    maize bearing yellow seed[225] with pollen of a tall maize having red
    seed; and one head alone produced good seed, only five in number.
    Though these plants are monoecious, and therefore do not require
    castration, yet I should have suspected some accident in the
    manipulation had not Gärtner expressly stated that he had during many
    years grown these two varieties together, and they did not
    spontaneously cross; and this, considering that the plants are
    monoecious and abound with pollen, and are well known generally to
    cross freely, seems explicable only on the belief that these two
    varieties are in some degree mutually infertile. The hybrid plants
    raised from the above five seed were intermediate in structure,
    extremely variable, and perfectly fertile.[226] No one, I believe, has
    hitherto suspected that these varieties of maize are distinct species;
    but had the hybrids been in the least sterile, no doubt Gärtner would
    at once have so classed them. I may here remark, that with undoubted
    species there is not necessarily any close relation between the
    sterility of a first cross and that of the hybrid offspring. Some
    species can be crossed with facility, but produce utterly sterile
    hybrids; others can be crossed with extreme difficulty, but the hybrids
    when produced are moderately fertile. I am not aware, however, of any
    instance quite like this of the maize with natural species, namely, of
    a first cross made with difficulty, but yielding perfectly fertile
    hybrids.

    The following case is much more remarkable, and evidently perplexed
    Gärtner, whose strong wish it was to draw a broad line of distinction
    between species and varieties. In the genus Verbascum, he made, during
    eighteen years, a vast number of experiments, and crossed no less than
    1085 flowers and counted their seeds. Many of these experiments
    consisted in crossing white and yellow varieties of both _V. lychnitis_
    and _V. blattaria_ with nine other species and their hybrids. That the
    white and yellow flowered plants of these two species are really
    varieties, no one has doubted; and Gärtner actually raised in the case
    of both species one variety from the seed of the other. Now in two of
    his works[227] he distinctly asserts that crosses between
    similarly-coloured flowers yield more seed than between
    dissimilarly-coloured; so that the yellow-flowered variety of either
    species (and conversely with the white-flowered variety), when crossed
    with pollen of its own kind, yields more seed than when crossed with
    that of the white variety; and so it is when differently coloured
    species are crossed. The general results may be seen in the Table at
    the {106} end of his volume. In one instance he gives[228] the
    following details; but I must premise that Gärtner, to avoid
    exaggerating the degree of sterility in his crosses, always compares
    the _maximum_ number obtained from a cross with the _average_ number
    naturally given by the pure mother-plant. The white-variety of _V.
    lychnitis_, naturally fertilised by its own pollen, gave from an
    _average_ of twelve capsules ninety-six good seeds in each; whilst
    twenty flowers fertilised with pollen from the yellow variety of this
    same species, gave as the _maximum_ only eighty-nine good seed; so that
    we have the proportion of 1000 to 908, according to Gärtner's usual
    scale. I should have thought it possible that so small a difference in
    fertility might have been accounted for by the evil effects of the
    necessary castration; but Gärtner shows that the white variety of _V.
    lychnitis_, when fertilised first by the white variety of _V.
    blattaria_, and then by the yellow variety of this species, yielded
    seed in the proportion of 622 to 438; and in both these cases
    castration was performed. Now the sterility which results from the
    crossing of the differently coloured varieties of the same species, is
    fully as great as that which occurs in many cases when distinct species
    are crossed. Unfortunately Gärtner compared the results of the first
    unions alone, and not the sterility of the two sets of hybrids produced
    from the white variety of _V. lychnitis_ when fertilised by the white
    and yellow varieties of _V. blattaria_, for it is probable that they
    would have differed in this respect.

    Mr. J. Scott has given me the results of a series of experiments on
    Verbascum, made by him in the Botanic Gardens of Edinburgh. He repeated
    some of Gärtner's experiments on distinct species, but obtained only
    fluctuating results; some confirmatory, but the greater number
    contradictory; nevertheless these seem hardly sufficient to overthrow
    the conclusions arrived at by Gärtner from experiments tried on a much
    larger scale. In the second place Mr. Scott experimented on the
    relative fertility of unions between similarly and
    dissimilarly-coloured varieties of the same species. Thus he fertilised
    six flowers of the yellow variety of _V. lychnitis_ by its own pollen,
    and obtained six capsules, and calling, for the sake of having a
    standard of comparison, the average number of good seed in each one
    hundred, he found that this same yellow variety, when fertilised by the
    white variety, yielded from seven capsules an average of ninety-four
    seed. On the same principle, the white variety of _V. lychnitis_ by its
    own pollen (from six capsules), and by the pollen of the yellow variety
    (eight capsules), yielded seed in the proportion of 100 to 82. The
    yellow variety of _V. thapsus_ by its own pollen (eight capsules), and
    by that of the white variety (only two capsules), yielded seed in the
    proportion of 100 to 94. Lastly, the white variety of _V. blattaria_ by
    its own pollen (eight capsules), and by that of the yellow variety
    (five capsules), yielded seed in the proportion of 100 to 79. So that
    in every case the unions of dissimilarly-coloured varieties of the same
    species were less fertile than the unions of similarly-coloured
    varieties; when all the cases are grouped together, the difference of
    fertility is as 86 to 100. Some additional trials were made, and
    altogether thirty-six similarly-coloured unions yielded thirty-five
    good {107} capsules; whilst thirty-five dissimilarly-coloured unions
    yielded only twenty-six good capsules. Besides the foregoing
    experiments, the purple _V. phoeniceum_ was crossed by a rose-coloured
    and a white variety of the same species; these two varieties were also
    crossed together, and these several unions yielded less seed than _V.
    phoeniceum_ by its own pollen. Hence it follows from Mr. Scott's
    experiments, that in the genus Verbascum the similarly and
    dissimilarly-coloured varieties of the same species behave, when
    crossed, like closely allied but distinct species.[229]

    This remarkable fact of the sexual affinity of similarly-coloured
    varieties, as observed by Gärtner and Mr. Scott, may not be of very
    rare occurrence; for the subject has not been attended to by others.
    The following case is worth giving, partly to show how difficult it is
    to avoid error. Dr. Herbert[230] has remarked that variously-coloured
    double varieties of the hollyhock (_Althæa rosea_) may be raised with
    certainty by seed from plants growing close together. I have been
    informed that nurserymen who raise seed for sale do not separate their
    plants; accordingly I procured seed of eighteen named varieties; of
    these, eleven varieties produced sixty-two plants all perfectly true to
    their kind; and seven produced forty-nine plants, half of which were
    true and half false. Mr. Masters of Canterbury has given me a more
    striking case; he saved seed from a great bed of twenty-four named
    varieties planted in closely adjoining rows, and each variety
    reproduced itself truly with only sometimes a shade of difference in
    tint. Now in the hollyhock the pollen, which is abundant, is matured
    and nearly all shed before the stigma of the same flower is ready to
    receive it;[231] and as bees covered with pollen incessantly fly from
    plant to plant, it would appear that adjoining varieties could not
    escape being crossed. As, however, this does not occur, it appeared to
    me probable that the pollen {108} of each variety was prepotent on its
    own stigma over that of all other varieties. But Mr. C. Turner of
    Slough, well known for his success in the cultivation of this plant,
    informs me that it is the doubleness of the flowers which prevents the
    bees gaining access to the pollen and stigma; and he finds that it is
    difficult even to cross them artificially. Whether this explanation
    will fully account for varieties in close proximity propagating
    themselves so truly by seed, I do not know.

    The following cases are worth giving, as they relate to monoecious
    forms, which do not require, and consequently have not been injured by,
    castration. Girou de Buzareingues crossed what he designates three
    varieties of gourd,[232] and asserts that their mutual fertilisation is
    less easy in proportion to the difference which they present. I am
    aware how imperfectly the forms in this group were until recently
    known; but Sageret,[233] who ranked them according to their mutual
    fertility, considers the three forms above alluded to as varieties, as
    does a far higher authority, namely, M. Naudin.[234] Sageret[235] has
    observed that certain melons have a greater tendency, whatever the
    cause may be, to keep true than others; and M. Naudin, who has had such
    immense experience in this group, informs me that he believes that
    certain varieties intercross more readily than others of the same
    species; but he has not proved the truth of this conclusion; the
    frequent abortion of the pollen near Paris being one great difficulty.
    Nevertheless, he has grown close together, during seven years, certain
    forms of Citrullus, which, as they could be artificially crossed with
    perfect facility and produced fertile offspring, are ranked as
    varieties; but these forms when not artificially crossed kept true.
    Many other varieties, on the other hand, in the same group cross with
    such facility, as M. Naudin repeatedly insists, that without being
    grown far apart they cannot be kept in the least true.

    Another case, though somewhat different, may be here given, as it is
    highly remarkable, and is established on excellent evidence. Kölreuter
    minutely describes five varieties of the common tobacco,[236] which
    were reciprocally crossed, and the offspring were intermediate in
    character and as fertile as their parents: from this fact Kölreuter
    inferred that they are really varieties; and no one, as far as I can
    discover, seems to have doubted that such is the case. He also crossed
    reciprocally these five varieties with _N. glutinosa_, and they yielded
    very sterile hybrids; but those raised from the _var. perennis_,
    whether used as the father or mother plant, were not so sterile as the
    hybrids from the four other varieties.[237] So that the sexual {109}
    capacity of this one variety has certainly been in some degree
    modified, so as to approach in nature that of _N. glutinosa_.[238]

These facts with respect to plants show that in some few cases certain
varieties have had their sexual powers so far modified, that they cross
together less readily and yield less seed than other varieties of the same
species. We shall presently see that the sexual functions of most animals
and plants are eminently liable to be affected by the conditions of life to
which they are exposed; and hereafter we shall briefly discuss the conjoint
bearing of this and other facts on the difference in fertility between
crossed varieties and crossed species.

_Domestication eliminates the tendency to Sterility which is general with
Species when crossed._

This hypothesis was first propounded by Pallas,[239] and has been adopted
by several authors. I can find hardly any direct facts in its support; but
unfortunately no one has compared, in the case of either animals or plants,
the fertility of anciently domesticated varieties, when crossed with a
distinct species, with that of the wild parent-species when similarly
crossed. No one has compared, for instance, the fertility of _Gallus
bankiva_ and of the domesticated fowl, when crossed with a distinct species
of Gallus or Phasianus; and the {110} experiment would in all cases be
surrounded by many difficulties. Dureau de la Malle, who has so closely
studied classical literature, states[240] that in the time of the Romans
the common mule was produced with more difficulty than at the present day;
but whether this statement may be trusted I know not. A much more
important, though somewhat different, case is given by M. Groenland,[241]
namely, that plants, known from their intermediate character and sterility
to be hybrids between Ægilops and wheat, have perpetuated themselves under
culture since 1857, _with a rapid but varying increase of fertility in each
generation_. In the fourth generation the plants, still retaining their
intermediate character, had become as fertile as common cultivated wheat.

The indirect evidence in favour of the Pallasian doctrine appears to me to
be extremely strong. In the earlier chapters I have attempted to show that
our various breeds of dogs are descended from several wild species; and
this probably is the case with sheep. There can no longer be any doubt that
the Zebu or humped Indian ox belongs to a distinct species from European
cattle: the latter, moreover, are descended from two or three forms, which
may be called either species or wild races, but which co-existed in a state
of nature and kept distinct. We have good evidence that our domesticated
pigs belong to at least two specific types, _S. scrofa_ and _Indica_, which
probably lived together in a wild state in South-eastern Europe. Now, a
widely-extended analogy leads to the belief that if these several allied
species, in the wild state or when first reclaimed, had been crossed, they
would have exhibited, both in their first unions and in their hybrid
offspring, some degree of sterility. Nevertheless the several domesticated
races descended from them are now all, as far as can be ascertained,
perfectly fertile together. If this reasoning be trustworthy, and it is
apparently sound, we must admit the Pallasian doctrine that long-continued
domestication tends to eliminate that sterility which is natural to species
when crossed in their aboriginal state.

{111}

_On increased Fertility from Domestication and Cultivation._

Increased fertility from domestication, without any reference to crossing,
may be here briefly considered. This subject bears indirectly on two or
three points connected with the modification of organic beings. As Buffon
long ago remarked,[242] domestic animals breed oftener in the year and
produce more young at a birth than wild animals of the same species; they,
also, sometimes breed at an earlier age. The case would hardly have
deserved further notice, had not some authors lately attempted to show that
fertility increases and decreases in an inverse ratio with the amount of
food. This strange doctrine has apparently arisen from individual animals
when supplied with an inordinate quantity of food, and from plants of many
kinds when grown on excessively rich soil, as on a dunghill, becoming
sterile; but to this latter point I shall have occasion presently to
return. With hardly an exception, our domesticated animals, which have long
been habituated to a regular and copious supply of food, without the labour
of searching for it, are more fertile than the corresponding wild animals.
It is notorious how frequently cats and dogs breed, and how many young they
produce at a birth. The wild rabbit is said generally to breed four times
yearly, and to produce from four to eight young; the tame rabbit breeds six
or seven times yearly, and produces from four to eleven young. The ferret,
though generally so closely confined, is more prolific than its supposed
wild prototype. The wild sow is remarkably prolific, for she often breeds
twice in the year, and produces from four to eight and sometimes even
twelve young at a birth; but the domestic sow regularly breeds twice a
year, and would breed oftener if permitted; and a sow that produces less
than eight at a birth "is worth little, and the sooner she is fattened for
the butcher the better." The amount of food affects the fertility even of
the same individual: thus sheep, which on mountains never produce more than
one lamb at a birth, when brought {112} down to lowland pastures frequently
bear twins. This difference apparently is not due to the cold of the higher
land, for sheep and other domestic animals are said to be extremely
prolific in Lapland. Hard living, also, retards the period at which animals
conceive; for it has been found disadvantageous in the northern islands of
Scotland to allow cows to bear calves before they are four years old.[243]

    Birds offer still better evidence of increased fertility from
    domestication: the hen of the wild _Gallus bankiva_ lays from six to
    ten eggs, a number which would be thought nothing of with the domestic
    hen. The wild duck lays from five to ten eggs; the tame one in the
    course of the year from eighty to one hundred. The wild grey-lag goose
    lays from five to eight eggs; the tame from thirteen to eighteen, and
    she lays a second time; as Mr. Dixon has remarked, "high-feeding, care,
    and moderate warmth induce a habit of prolificacy which becomes in some
    measure hereditary." Whether the semi-domesticated dovecot pigeon is
    more fertile than the wild rock-pigeon _C. livia_, I know not; but the
    more thoroughly domesticated breeds are nearly twice as fertile as
    dovecots: the latter, however, when caged and highly fed, become
    equally fertile with house pigeons. The peahen alone of domesticated
    birds is rather more fertile, according to some accounts, when wild in
    its native Indian home, than when domesticated in Europe and exposed to
    our much colder climate.[244]

    With respect to plants, no one would expect wheat to tiller more, and
    each ear to produce more grain, in poor than in rich soil; or to get in
    poor soil a heavy crop of peas or beans. Seeds vary so much in number
    {113} that it is difficult to estimate them; but on comparing beds of
    carrots saved for seed in a nursery garden with wild plants, the former
    seemed to produce about twice as much seed. Cultivated cabbages yielded
    thrice as many pods by measure as wild cabbages from the rocks of South
    Wales. The excess of berries produced by the cultivated Asparagus in
    comparison with the wild plant is enormous. No doubt many highly
    cultivated plants, such as pears, pineapples, bananas, sugar-cane, &c.,
    are nearly or quite sterile; and I am inclined to attribute this
    sterility to excess of food and to other unnatural conditions; but to
    this subject I shall presently recur.

In some cases, as with the pig, rabbit, &c., and with those plants which
are valued for their seed, the direct selection of the more fertile
individuals has probably much increased their fertility; and in all cases
this may have occurred indirectly, from the better chance of the more
numerous offspring produced by the more fertile individuals having
survived. But with cats, ferrets, and dogs, and with plants like carrots,
cabbages, and asparagus, which are not valued for their prolificacy,
selection can have played only a subordinate part; and their increased
fertility must be attributed to the more favourable conditions of life
under which they have long existed.

       *       *       *       *       *


{114}

CHAPTER XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
INTERBREEDING.

    DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID
    TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING,
    AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY
    INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME
    PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS
    ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS,
    GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS,
    FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED
    SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON
    CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT,
    BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH
    DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION.

The gain in constitutional vigour, derived from an occasional cross between
individuals of the same variety, but belonging to distinct families, or
between distinct varieties, has not been so largely or so frequently
discussed, as have the evil effects of too close interbreeding. But the
former point is the more important of the two, inasmuch as the evidence is
more decisive. The evil results from close interbreeding are difficult to
detect, for they accumulate slowly, and differ much in degree with
different species; whilst the good effects which almost invariably follow a
cross are from the first manifest. It should, however, be clearly
understood that the advantage of close interbreeding, as far as the
retention of character is concerned, is indisputable, and often outweighs
the evil of a slight loss of constitutional vigour. In relation to the
subject of domestication, the whole question is of some importance, as too
close interbreeding interferes with the improvement of old races, and
especially with the formation of new ones. It is important as indirectly
bearing on Hybridism; and perhaps on the extinction of species, when any
form has become so rare that only a few individuals {115} remain within a
confined area. It bears in an important manner on the influence of free
intercrossing, in obliterating individual differences, and thus giving
uniformity of character to the individuals of the same race or species; for
if additional vigour and fertility be thus gained, the crossed offspring
will multiply and prevail, and the ultimate result will be far greater than
otherwise would have occurred. Lastly, the question is of high interest, as
bearing on mankind. Hence I shall discuss this subject at full length. As
the facts which prove the evil effects of close interbreeding are more
copious, though less decisive, than those on the good effects of crossing,
I shall, under each group of beings, begin with the former.

There is no difficulty in defining what is meant by a cross; but this is by
no means easy in regard to "breeding in and in" or "too close
interbreeding," because, as we shall see, different species of animals are
differently affected by the same degree of interbreeding. The pairing of a
father and daughter, or mother and son, or brothers and sisters, if carried
on during several generations, is the closest possible form of
interbreeding. But some good judges, for instance Sir J. Sebright, believe
that the pairing of a brother and sister is closer than that of parents and
children; for when the father is matched with his daughter he crosses, as
is said, with only half his own blood. The consequences of close
interbreeding carried on for too long a time, are, as is generally
believed, loss of size, constitutional vigour, and fertility, sometimes
accompanied by a tendency to malformation. Manifest evil does not usually
follow from pairing the nearest relations for two, three, or even four
generations; but several causes interfere with our detecting the evil--such
as the deterioration being very gradual, and the difficulty of
distinguishing between such direct evil and the inevitable augmentation of
any morbid tendencies which may be latent or apparent in the related
parents. On the other hand, the benefit from a cross, even when there has
not been any very close interbreeding, is almost invariably at once
conspicuous. There is reason to believe, and this was the opinion of that
most experienced observer Sir J. Sebright,[245] that the evil effects of
close interbreeding may be checked by the related individuals {116} being
separated during a few generations and exposed to different conditions of
life.

That evil directly follows from any degree of close interbreeding has been
denied by many persons; but rarely by any practical breeder; and never, as
far as I know, by one who has largely bred animals which propagate their
kind quickly. Many physiologists attribute the evil exclusively to the
combination and consequent increase of morbid tendencies common to both
parents: that this is an active source of mischief there can be no doubt.
It is unfortunately too notorious that men and various domestic animals
endowed with a wretched constitution, and with a strong hereditary
disposition to disease, if not actually ill, are fully capable of
procreating their kind. Close interbreeding, on the other hand, induces
sterility; and this indicates something quite distinct from the
augmentation of morbid tendencies common to both parents. The evidence
immediately to be given convinces me that it is a great law of nature, that
all organic beings profit from an occasional cross with individuals not
closely related to them in blood; and that, on the other hand,
long-continued close interbreeding is injurious.

Various general considerations have had much influence in leading me to
this conclusion; but the reader will probably rely more on special facts
and opinions. The authority of experienced observers, even when they do not
advance the grounds of their belief, is of some little value. Now almost
all men who have bred many kinds of animals and have written on the
subject, such as Sir J. Sebright, Andrew Knight, &c.,[246] have expressed
the strongest conviction on the impossibility of long-continued close
interbreeding. Those who have compiled works on agriculture, and have
associated much with breeders, such as the sagacious Youatt, Low, &c., have
strongly declared their opinion to the same effect. Prosper Lucas, trusting
largely to French authorities, has come to a similar conclusion. The
distinguished German agriculturist Hermann von Nathusius, who has written
the most able treatise on this subject which I have met with, concurs; and
as I shall have to quote from {117} this treatise, I may state that
Nathusius is not only intimately acquainted with works on agriculture in
all languages, and knows the pedigrees of our British breeds better than
most Englishmen, but has imported many of our improved animals, and is
himself an experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be
acquired in the case of animals, such as fowls, pigeons, &c., which
propagate quickly, and, from being kept in the same place, are exposed to
the same conditions. Now I have inquired of very many breeders of these
birds, and I have hitherto not met with a single man who was not thoroughly
convinced that an occasional cross with another strain of the same
sub-variety was absolutely necessary. Most breeders of highly-improved or
fancy birds value their own strain, and are most unwilling, at the risk, in
their opinion, of deterioration, to make a cross. The purchase of a
first-rate bird of another strain is expensive, and exchanges are
troublesome; yet all breeders, as far as I can hear, excepting those who
keep large stocks at different places for the sake of crossing, are driven
after a time to take this step.

Another general consideration which has had great influence on my mind is,
that with all hermaphrodite animals and plants, which it might have been
thought would have perpetually fertilised themselves, and thus have been
subjected for long ages to the closest interbreeding, there is no single
species, as far as I can discover, in which the structure ensures
self-fertilisation. On the contrary, there are in a multitude of cases, as
briefly stated in the fifteenth chapter, manifest adaptations which favour
or inevitably lead to an occasional cross between one hermaphrodite and
another of the same species; and these adaptive structures are utterly
purposeless, as far as we can see, for any other end.

    With _Cattle_ there can be no doubt that extremely close interbreeding
    may be long carried on, advantageously with respect to external
    characters and with no manifestly apparent evil as far as constitution
    is concerned. The same remark is applicable to sheep. Whether these
    animals have gradually been rendered less susceptible than others to
    this evil, in order to permit them to live in herds,--a habit which
    leads the old and vigorous males to expel all intruders, and in
    consequence often to pair with their own daughters, I will not pretend
    to decide. The case of Bakewell's Long-horns, which were closely
    interbred for a long period, has often been {118} quoted; yet Youatt
    says[247] the breed "had acquired a delicacy of constitution
    inconsistent with common management," and "the propagation of the
    species was not always certain." But the Shorthorns offer the most
    striking case of close interbreeding; for instance, the famous bull
    Favourite (who was himself the offspring of a half-brother and sister
    from Foljambe) was matched with his own daughter, granddaughter, and
    great-granddaughter; so that the produce of this last union, or the
    great-great-granddaughter, had 15-16ths, or 93.75 per cent. of the
    blood of Favourite in her veins. This cow was matched with the bull
    Wellington, having 62.5 per cent. of Favourite blood in his veins, and
    produced Clarissa; Clarissa was matched with the bull Lancaster, having
    68.75 of the same blood, and she yielded valuable offspring.[248]
    Nevertheless Collings, who reared these animals, and was a strong
    advocate for close breeding, once crossed his stock with a Galloway,
    and the cows from this cross realised the highest prices. Bates's herd
    was esteemed the most celebrated in the world. For thirteen years he
    bred most closely in and in; but during the next seventeen years,
    though he had the most exalted notion of the value of his own stock, he
    thrice infused fresh blood into his herd: it is said that he did this,
    not to improve the form of his animals, but on account of their
    lessened fertility. Mr. Bates's own view, as given by a celebrated
    breeder,[249] was, that "to breed in and in from a bad stock was ruin
    and devastation; yet that the practice may be safely followed within
    certain limits when the parents so related are descended from
    first-rate animals." We thus see that there has been extremely close
    interbreeding with Shorthorns; but Nathusius, after the most careful
    study of their pedigrees, says that he can find no instance of a
    breeder who has strictly followed this practice during his whole life.
    From this study and his own experience, he concludes that close
    interbreeding is necessary to ennoble the stock; but that in effecting
    this the greatest care is necessary, on account of the tendency to
    infertility and weakness. It may be added, that another high
    authority[250] asserts that many more calves are born cripples from
    Shorthorns than from other and less closely interbred races of cattle.

    Although by carefully selecting the best animals (as Nature effectually
    does by the law of battle) close interbreeding may be long carried on
    with cattle, yet the good effects of a cross between almost any two
    breeds is at once shown by the greater size and vigour of the
    offspring; as Mr. Spooner writes to me, "crossing distinct breeds
    certainly improves cattle for the butcher." Such crossed animals are of
    course of no value to the breeder; but they have been raised during
    many years in several {119} parts of England to be slaughtered;[251]
    and their merit is now so fully recognised, that at fat-cattle shows a
    separate class has been formed for their reception. The best fat ox at
    the great show at Islington in 1862 was a crossed animal.

    The half-wild cattle, which have been kept in British parks probably
    for 400 or 500 years, or even for a longer period, have been advanced
    by Culley and others as a case of long-continued interbreeding within
    the limits of the same herd without any consequent injury. With respect
    to the cattle at Chillingham, the late Lord Tankerville owned that they
    were bad breeders.[252] The agent, Mr. Hardy, estimates (in a letter to
    me, dated May, 1861) that in the herd of about fifty the average number
    annually slaughtered, killed by fighting, and dying, is about ten, or
    one in five. As the herd is kept up to nearly the same average number,
    the annual rate of increase must be likewise about one in five. The
    bulls, I may add, engage in furious battles, of which battles the
    present Lord Tankerville has given me a graphic description, so that
    there will always be rigorous selection of the most vigorous males. I
    procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton,
    the following account of the wild cattle kept in the Duke's park in
    Lanarkshire, which is about 200 acres in extent. The number of cattle
    varies from sixty-five to eighty; and the number annually killed (I
    presume by all causes) is from eight to ten; so that the annual rate of
    increase can hardly be more than one in six. Now in South America,
    where the herds are half-wild, and therefore offer a nearly fair
    standard of comparison, according to Azara the natural increase of the
    cattle on an estancia is from one-third to one-fourth of the total
    number, or one in between three and four; and this, no doubt, applies
    exclusively to adult animals fit for consumption. Hence the half-wild
    British cattle which have long interbred within the limits of the same
    herd are relatively far less fertile. Although in an unenclosed country
    like Paraguay there must be some crossing between the different herds,
    yet even there the inhabitants believe that the occasional introduction
    of animals from distant localities is necessary to prevent
    "degeneration in size and diminution of fertility."[253] The decrease
    in size from ancient times in the Chillingham and Hamilton cattle must
    have been prodigious, for Professor Rütimeyer has shown that they are
    almost certainly the descendants of the gigantic _Bos primigenius_. No
    doubt this decrease in size may be largely attributed to less
    favourable conditions of life; yet animals roaming over large parks,
    and fed during severe winters, can hardly be considered as placed under
    very unfavourable conditions.

    With _Sheep_ there has often been long-continued interbreeding within
    the limits of the same flock; but whether the nearest relations have
    been matched so frequently as in the case of Shorthorn cattle, I do not
    know. The Messrs. Brown during fifty years have never infused fresh
    blood into their excellent flock of Leicesters. Since 1810 Mr. Barford
    has acted on the same principle with the Foscote flock. He asserts that
    half a century {120} of experience has convinced him that when two
    nearly related animals are quite sound in constitution, in-and-in
    breeding does not induce degeneracy; but he adds that he "does not
    pride himself on breeding from the nearest affinities." In France the
    Naz flock has been bred for sixty years without the introduction of a
    single strange ram.[254] Nevertheless, most great breeders of sheep
    have protested against close interbreeding prolonged for too great a
    length of time.[255] The most celebrated of recent breeders, Jonas
    Webb, kept five separate families to work on, thus "retaining the
    requisite distance of relationship between the sexes."[256]

    Although by the aid of careful selection the near interbreeding of
    sheep may be long continued without any manifest evil, yet it has often
    been the practice with farmers to cross distinct breeds to obtain
    animals for the butcher, which plainly shows that good is derived from
    this practice. Mr. Spooner sums up his excellent Essay on Crossing by
    asserting that there is a direct pecuniary advantage in judicious
    cross-breeding, especially when the male is larger than the female. A
    former celebrated breeder, Lord Somerville, distinctly states that his
    half-breeds from Ryelands and Spanish sheep were larger animals than
    either the pure Ryelands or pure Spanish sheep.[257]

    As some of our British parks are ancient, it occurred to me that there
    must have been long-continued close interbreeding with the fallow deer
    (_Cervus dama_) kept in them; but on inquiry I find that it is a common
    practice to infuse new blood by procuring bucks from other parks. Mr.
    Shirley,[258] who has carefully studied the management of deer, admits
    that in some parks there has been no admixture of foreign blood from a
    time beyond the memory of man. But he concludes "that in the end the
    constant breeding in-and-in is sure to tell to the disadvantage of the
    whole herd, though it may take a very long time to prove it; moreover,
    when we find, as is very constantly the case, that the introduction of
    fresh blood has been of the very greatest use to deer, both by
    improving their size and appearance, and particularly by being of
    service in removing the taint of 'rickback,' if not of other diseases,
    to which deer are sometimes subject when the blood has not been
    changed, there can, I think, be no doubt but that a judicious cross
    with a good stock is of the greatest consequence, and is indeed
    essential, sooner or later, to the prosperity of every well-ordered
    park."

    Mr. Meynell's famous foxhounds have been adduced, as showing that no
    ill effects follow from close interbreeding; and Sir J. Sebright
    ascertained from him that he frequently bred from father and daughter,
    mother and {121} son, and sometimes even from brothers and sisters. Sir
    J. Sebright, however, declares,[259] that by breeding _in-and-in_, by
    which he means matching brothers and sisters, he has actually seen
    strong spaniels become weak and diminutive lapdogs. The Rev. W. D. Fox
    has communicated to me the case of a small lot of bloodhounds, long
    kept in the same family, which had become very bad breeders, and nearly
    all had a bony enlargement in the tail. A single cross with a distinct
    strain of bloodhounds restored their fertility, and drove away the
    tendency to malformation in the tail. I have heard the particulars of
    another case with bloodhounds, in which the female had to be held to
    the male. Considering how rapid is the natural increase of the dog, it
    is difficult to understand the high price of most highly improved
    breeds, which almost implies long-continued close interbreeding, except
    on the belief that this process lessens fertility and increases
    liability to distemper and other diseases. A high authority, Mr.
    Scrope, attributes the rarity and deterioration in size of the Scotch
    deerhound (the few individuals now existing throughout the country
    being all related) in large part to close interbreeding.

    With all highly-bred animals there is more or less difficulty in
    getting them to procreate quickly, and all suffer much from delicacy of
    constitution; but I do not pretend that these effects ought to be
    wholly attributed to close interbreeding. A great judge of rabbits[260]
    says, "the long-eared does are often too highly bred or forced in their
    youth to be of much value as breeders, often turning out barren or bad
    mothers." Again: "Very long-eared bucks will also sometimes prove
    barren." These highly-bred rabbits often desert their young, so that it
    is necessary to have nurse-rabbits.

    With _Pigs_ there is more unanimity amongst breeders on the evil
    effects of close interbreeding than, perhaps, with any other large
    animal. Mr. Druce, a great and successful breeder of the Improved
    Oxfordshires (a crossed race), writes, "without a change of boars of a
    different tribe, but of the same breed, constitution cannot be
    preserved." Mr. Fisher Hobbs, the raiser of the celebrated Improved
    Essex breed, divided his stock into three separate families, by which
    means he maintained the breed for more than twenty years, "by judicious
    selection from the _three distinct families_."[261] Lord Western was
    the first importer of a Neapolitan boar and sow. "From this pair he
    bred in-and-in, until the breed was in danger of becoming extinct, a
    sure result (as Mr. Sidney remarks) of in-and-in breeding." Lord
    Western then crossed his Neapolitan pigs with the old Essex, and made
    the first great step towards the Improved Essex breed. Here is a more
    interesting case. Mr. J. Wright, well known as a breeder, crossed[262]
    the same boar with the daughter, granddaughter, and
    great-granddaughter, and so on for seven generations. The result was,
    that in many instances the offspring failed to breed; in others they
    produced few that lived; and of the latter many were idiotic, without
    sense {122} even to suck, and when attempting to move could not walk
    straight. Now it deserves especial notice, that the two last sows
    produced by this long course of interbreeding were sent to other boars,
    and they bore several litters of healthy pigs. The best sow in external
    appearance produced during the whole seven generations was one in the
    last stage of descent; but the litter consisted of this one sow. She
    would not breed to her sire, yet bred at the first trial to a stranger
    in blood. So that, in Mr. Wright's case, long-continued and extremely
    close interbreeding did not affect the external form or merit of the
    young; but with many of them the general constitution and mental
    powers, and especially the reproductive functions, were seriously
    affected.

    Nathusius gives[263] an analogous and even more striking case: he
    imported from England a pregnant sow of the large Yorkshire breed, and
    bred the product closely in-and-in for three generations: the result
    was unfavourable, as the young were weak in constitution, with impaired
    fertility. One of the latest sows, which he esteemed a good animal,
    produced, when paired with her own uncle (who was known to be
    productive with sows of other breeds), a litter of six, and a second
    time a litter of only five weak young pigs. He then paired this sow
    with a boar of a small black breed, which he had likewise imported from
    England, and which boar, when matched with sows of his own breed,
    produced from seven to nine young: now, the sow of the large breed,
    which was so unproductive when paired with her own uncle, yielded to
    the small black boar, in the first litter twenty-one, and in the second
    litter eighteen young pigs; so that in one year she produced
    thirty-nine fine young animals!

    As in the case of several other animals already mentioned, even when no
    injury is perceptible from moderately close interbreeding, yet, to
    quote the words of Mr. Coate, a most successful breeder (who five times
    won the annual gold medal of the Smithfield Club Show for the best pen
    of pigs), "Crosses answer well for profit to the farmer, as you get
    more constitution and quicker growth; but for me, who sell a great
    number of pigs for breeding purposes, I find it will not do, as it
    requires many years to get anything like purity of blood again."[264]

Before passing on to Birds, I ought to refer to man, though I am unwilling
to enter on this subject, as it is surrounded by natural prejudices. It has
moreover been discussed by various authors under many points of view.[265]
Mr. Tylor[266] has shown {123} that with widely different races, in the
most distant quarters of the world, marriages between relations--even
between distant relations--have been strictly prohibited. A few exceptional
cases can be specified, especially with royal families; and these have been
enlarged on in a learned article[267] by Mr. W. Adam, and formerly in 1828
by Hofacker. Mr. Tylor is inclined to believe that the almost universal
prohibition of closely-related marriages has arisen from their evil effects
having been observed, and he ingeniously explains some apparent anomalies
in the prohibition not extending equally to the relations on both the male
and female side. He admits, however, that other causes, such as the
extension of friendly alliances, may have come into play. Mr. W. Adam, on
the other hand, concludes that related marriages are prohibited and viewed
with repugnance from the confusion which would thus arise in the descent of
property, and from other still more recondite reasons; but I cannot accept
this view, seeing that the savages of Australia and South America,[268] who
have no property to bequeath or fine moral feelings to confuse, hold the
crime of incest in abhorrence.

It would be interesting to know, if it could be ascertained, as throwing
light on this question with respect to man, what occurs with the higher
anthropomorphous apes--whether the young males and females soon wander away
from their parents, or whether the old males become jealous of their sons
and expel them, or whether any inherited instinctive feeling, from being
beneficial, has been generated, leading the young males and females of the
same family to prefer pairing with distinct families, and to dislike
pairing with each other. A considerable body of evidence has already been
advanced, showing that the offspring from parents which are not related are
more vigorous and fertile than those from parents which are closely
related; hence any slight feeling, arising from the sexual excitement of
novelty or other cause, which led to the former rather than to the latter
unions, would be augmented through natural selection, and thus might become
instinctive; for those individuals which had an innate preference of this
kind would increase in number. It seems more probable, that degraded
savages should {124} thus unconsciously have acquired their dislike and
even abhorrence of incestuous marriages, rather than that they should have
discovered by reasoning and observation the evil results. The abhorrence
occasionally failing is no valid argument against the feeling being
instinctive, for any instinct may occasionally fail or become vitiated, as
sometimes occurs with parental love and the social sympathies. In the case
of man, the question whether evil follows from close interbreeding will
probably never be answered by direct evidence, as he propagates his kind so
slowly and cannot be subjected to experiment; but the almost universal
practice of all races at all times of avoiding closely-related marriages is
an argument of considerable weight; and whatever conclusion we arrive at in
regard to the higher animals may be safely extended to man.

    Turning now to Birds: in the case of the _Fowl_ a whole array of
    authorities could be given against too close interbreeding. Sir J.
    Sebright positively asserts that he made many trials, and that his
    fowls, when thus treated, became long in the legs, small in the body,
    and bad breeders.[269] He produced the famous Sebright Bantams by
    complicated crosses, and by breeding in-and-in; and since his time
    there has been much close interbreeding with these Bantams; and they
    are now notoriously bad breeders. I have seen Silver Bantams, directly
    descended from his stock, which had become almost as barren as hybrids;
    for not a single chicken had been that year hatched from two full nests
    of eggs. Mr. Hewitt says that with these Bantams the sterility of the
    male stands, with rare exceptions, in the closest relation with their
    loss of certain secondary male characters: he adds, "I have noticed, as
    a general rule, that even the slightest deviation from feminine
    character in the tail of the male Sebright--say the elongation by only
    half an inch of the two principal tail-feathers--brings with it
    improved probability of increased fertility."[270]

    Mr. Wright states[271] that Mr. Clark, "whose fighting-cocks were so
    notorious, continued to breed from his own kind till they lost their
    disposition to fight, but stood to be cut up without making any
    resistance, and were so reduced in size as to be under those weights
    required for the best prizes; but on obtaining a cross from Mr.
    Leighton, they again resumed their former courage and weight." It
    should be borne in mind that game-cocks before they fought were always
    weighed, so that nothing was left to the imagination about any
    reduction or increase of {125} weight. Mr. Clark does not seem to have
    bred from brothers and sisters, which is the most injurious kind of
    union; and he found, after repeated trials, that there was a greater
    reduction in weight in the young from a father paired with his
    daughter, than from a mother with her son. I may add that Mr. Eyton, of
    Eyton, the well-known ornithologist, who is a large breeder of Grey
    Dorkings, informs me that they certainly diminish in size, and become
    less prolific, unless a cross with another strain is occasionally
    obtained. So it is with Malays, according to Mr. Hewitt, as far as size
    is concerned.[272]

    An experienced writer[273] remarks that the same amateur, as is well
    known, seldom long maintains the superiority of his birds; and this, he
    adds, undoubtedly is due to all his stock "being of the same blood;"
    hence it is indispensable that he should occasionally procure a bird of
    another strain. But this is not necessary with those who keep a stock
    of fowls at different stations. Thus, Mr. Ballance, who has bred Malays
    for thirty years, and has won more prizes with these birds than any
    other fancier in England, says that breeding in-and-in does not
    necessarily cause deterioration; "but all depends upon how this is
    managed." "My plan has been to keep about five or six distinct runs,
    and to rear about two hundred or three hundred chickens each year, and
    select the best birds from each run for crossing. I thus secure
    sufficient crossing to prevent deterioration."[274]

    We thus see that there is almost complete unanimity with
    poultry-breeders that, when fowls are kept at the same place, evil
    quickly follows from interbreeding carried on to an extent which would
    be disregarded in the case of most quadrupeds. On the other hand, it is
    a generally received opinion that cross-bred chickens are the hardiest
    and most easily reared.[275] Mr. Tegetmeier, who has carefully attended
    to poultry of all breeds, says[276] that Dorking hens, allowed to run
    with Houdan or Crevecoeur cocks, "produce in the early spring chickens
    that for size, hardihood, early maturity, and fitness for the market,
    surpass those of any pure breed that we have ever raised." Mr. Hewitt
    gives it as a general rule with fowls, that crossing the breed
    increases their size. He makes this remark after stating that hybrids
    from the pheasant and fowl are considerably larger than either
    progenitor: so again, hybrids from the male golden pheasant and hen
    common pheasant "are of far larger size than either parent-bird."[277]
    To this subject of the increased size of hybrids I shall presently
    return.

    With _Pigeons_, breeders are unanimous, as previously stated, that it
    is absolutely indispensable, notwithstanding the trouble and expense
    thus caused, occasionally to cross their much-prized birds with
    individuals of another strain, but belonging, of course, to the same
    variety. It deserves {126} notice that, when large size is one of the
    desired characters, as with pouters,[278] the evil effects of close
    interbreeding are much sooner perceived than when small birds, such as
    short-faced tumblers, are valued. The extreme delicacy of the high
    fancy breeds, such as these tumblers and improved English carriers, is
    remarkable; they are liable to many diseases, and often die in the egg
    or during the first moult; and their eggs have generally to be hatched
    under foster-mothers. Although these highly-prized birds have
    invariably been subjected to much close interbreeding, yet their
    extreme delicacy of constitution cannot perhaps be thus fully
    explained. Mr. Yarrell informed me that Sir J. Sebright continued
    closely interbreeding some owl-pigeons, until from their extreme
    sterility he as nearly as possible lost the whole family. Mr.
    Brent[279] tried to raise a breed of trumpeters, by crossing a common
    pigeon, and recrossing the daughter, granddaughter,
    great-granddaughter, and great-great-granddaughter, with the same male
    trumpeter, until he obtained a bird with 15/16ths of trumpeter's blood;
    but then the experiment failed, for "breeding so close stopped
    reproduction." The experienced Neumeister[280] also asserts that the
    offspring from dovecotes and various other breeds are "generally very
    fertile and hardy birds:" so again, MM. Boitard and Corbié,[281] after
    forty-five years' experience, recommend persons to cross their breeds
    for amusement; for, if they fail to make interesting birds, they will
    succeed under an economical point of view, "as it is found that
    mongrels are more fertile than pigeons of pure race."

    I will refer only to one other animal, namely, the Hive-bee, because a
    distinguished entomologist has advanced this as a case of inevitable
    close interbreeding. As the hive is tenanted by a single female, it
    might have been thought that her male and female offspring would always
    have bred together, more especially as bees of different hives are
    hostile to each other; a strange worker being almost always attacked
    when trying to enter another hive. But Mr. Tegetmeier has shown[282]
    that this instinct does not apply to drones, which are permitted to
    enter any hive; so that there is no _à priori_ improbability of a queen
    receiving a foreign drone. The fact of the union invariably and
    necessarily taking place on the wing, during the queen's nuptial
    flight, seems to be a special provision against continued
    interbreeding. However this may be, experience has shown, since the
    introduction of the yellow-banded Ligurian race into Germany and
    England, that bees freely cross: Mr. Woodbury, who introduced Ligurian
    bees into Devonshire, found during a single season that three stocks,
    at distances of from one to two miles from his hives, were crossed by
    his drones. In one case the Ligurian drones must have flown over the
    city of Exeter, and over several intermediate hives. On another
    occasion several common black queens were crossed by Ligurian drones at
    a distance of from one to three and a half miles.[283]

{127}

_Plants._

    When a single plant of a new species is introduced into any country, if
    propagated by seed, many individuals will soon be raised, so that if
    the proper insects be present there will be crossing. With
    newly-introduced trees or other plants not propagated by seed we are
    not here concerned. With old-established plants it is an almost
    universal practice occasionally to make exchanges of seed, by which
    means individuals which have been exposed to different conditions of
    life,--and this, as we have seen, diminishes the evil from close
    interbreeding,--will occasionally be introduced into each district.

    Experiments have not been tried on the effects of fertilising flowers
    with their own pollen during _several_ generations. But we shall
    presently see that certain plants, either normally or abnormally, are
    more or less sterile, even in the first generation, when fertilised by
    their own pollen. Although nothing is directly known on the evil
    effects of long-continued close interbreeding with plants, the converse
    proposition that great good is derived from crossing is well
    established.

    With respect to the crossing of individuals belonging to the same
    sub-variety, Gärtner, whose accuracy and experience exceeded that of
    all other hybridisers, states[284] that he has many times observed good
    effects from this step, especially with exotic genera, of which the
    fertility is somewhat impaired, such as Passiflora, Lobelia, and
    Fuchsia. Herbert also says,[285] "I am inclined to think that I have
    derived advantage from impregnating the flower from which I wished to
    obtain seed with pollen from another individual of the same variety, or
    at least from another flower, rather than with its own." Again,
    Professor Lecoq asserts that he has ascertained that crossed offspring
    are more vigorous and robust than their parents.[286]

    General statements of this kind, however, can seldom be fully trusted;
    consequently I have begun a series of experiments, which, if they
    continue to give the same results as hitherto, will for ever settle the
    question of the good effects of crossing two distinct plants of the
    same variety, and of the evil effects of self-fertilisation. A clear
    light will thus also be thrown on the fact that flowers are invariably
    constructed so as to permit, or favour, or necessitate the union of two
    individuals. We shall clearly understand why monoecious and
    dioecious,--why dimorphic and trimorphic plants exist, and many other
    such cases. The plan which I have followed in my experiments is to grow
    plants in the same pot, or in pots of the same size, or close together
    in the open ground; to carefully exclude insects; and then to fertilise
    some of the flowers with pollen from the same flower, and others on the
    same plant with pollen from a distinct but adjoining plant. In many,
    but not all, of these experiments, the crossed plants yielded much more
    seed than the self-fertilised plants; and I have never seen the {128}
    reversed case. The self-fertilised and crossed seeds thus obtained were
    allowed to germinate in the same glass vessel on damp sand; and as the
    seeds successively germinated, they were planted in pairs on opposite
    sides of the same pot, with a superficial partition between them, and
    were placed so as to be equally exposed to the light. In other cases
    the self-fertilised and crossed seeds were simply sown on opposite
    sides of the same small pot. I have, in short, followed different
    plans, but in every case have taken all the precautions which I could
    think of, so that the two lots should be equally favoured. Now, I have
    carefully observed the growth of plants raised from crossed and
    self-fertilised seed, from their germination to maturity, in species of
    the following genera, namely, Brassica, Lathyrus, Lupinus, Lobelia,
    Lactuca, Dianthus, Myosotis, Petunia, Linaria, Calceolaria, Mimulus,
    and Ipomoea, and the difference in their powers of growth, and of
    withstanding in certain cases unfavourable conditions, was most
    manifest and strongly marked. It is of importance that the two lots of
    seed should be sown or planted on opposite sides of the same pot, so
    that the seedlings may struggle against each other; for if sown
    separately in ample and good soil, there is often but little difference
    in their growth.

    I will briefly describe the two most striking cases as yet observed by
    me. Six crossed and six self-fertilised seeds of _Ipomoea purpurea_,
    from plants treated in the manner above described, were planted as soon
    as they had germinated, in pairs on opposite sides of two pots, and
    rods of equal thickness were given them to twine up. Five of the
    crossed plants grew from the first more quickly than the opposed
    self-fertilised plants; the sixth, however, was weakly and was for a
    time beaten, but at last its sounder constitution prevailed and it shot
    ahead of its antagonist. As soon as each crossed plant reached the top
    of its seven-foot rod its fellow was measured, and the result was that,
    when the crossed plants were seven feet high, the self-fertilised had
    attained the average height of only five feet four and a half inches.
    The crossed plants flowered a little before, and more profusely than
    the self-fertilised plants. On opposite sides of another _small_ pot a
    large number of crossed and self-fertilised seeds were sown, so that
    they had to struggle for bare existence; a single rod was given to each
    lot: here again the crossed plants showed from the first their
    advantage; they never quite reached the summit of the seven-foot rod,
    but relatively to the self-fertilised plants their average height was
    as seven feet to five feet two inches. The experiment was repeated in
    the two following generations with plants raised from the
    self-fertilised and crossed plants, treated in exactly the same manner,
    and with nearly the same result. In the second generation, the crossed
    plants, which were again crossed, produced 121 seed-capsules, whilst
    the self-fertilised plants, again self-fertilised, produced only 84
    capsules.

    Some flowers of the _Mimulus luteus_ were fertilised with their own
    pollen, and others were crossed with pollen from distinct plants
    growing in the same pot. The seeds after germinating were thickly
    planted on opposite sides of a pot. The seedlings were at first equal
    in height; but when the young crossed plants were exactly half an inch,
    the {129} self-fertilised plants were only a quarter of an inch high.
    But this inequality did not continue, for, when the crossed plants were
    four and a half inches high, the self-fertilised were three inches; and
    they retained the same relative difference till their growth was
    complete. The crossed plants looked far more vigorous than the
    uncrossed, and flowered before them; they produced also a far greater
    number of flowers, which yielded capsules (judging, however, from only
    a few) containing more seeds. As in the former case, the experiment was
    repeated in the same manner during the next two generations, and with
    exactly the same result. Had I not watched these plants of the Mimulus
    and Ipomoea during their whole growth, I could not have believed it
    possible, that a difference apparently so slight, as that of the pollen
    being taken from the same flower, and from a distinct plant growing in
    the same small pot, could have made so wonderful a difference in the
    growth and vigour of the plants thus produced. This, under a
    physiological point of view, is a most remarkable phenomenon.

       *       *       *       *       *

    With respect to the benefit derived from crossing distinct varieties,
    plenty of evidence has been published. Sageret[287] repeatedly speaks
    in strong terms of the vigour of melons raised by crossing different
    varieties, and adds that they are more easily fertilised than common
    melons, and produce numerous good seed. Here follows the evidence of an
    English gardener:[288] "I have this summer met with better success in
    my cultivation of melons, in an unprotected state, from the seeds of
    hybrids (_i.e._ mongrels) obtained by cross impregnation, than with old
    varieties. The offspring of three different hybridisations (one more
    especially, of which the parents were the two most dissimilar varieties
    I could select) each yielded more ample and finer produce than any one
    of between twenty and thirty established varieties."

    Andrew Knight[289] believed that his seedlings from crossed varieties
    of the apple exhibited increased vigour and luxuriance; and M.
    Chevreul[290] alludes to the extreme vigour of some of the crossed
    fruit-trees raised by Sageret.

    By crossing reciprocally the tallest and shortest peas, Knight[291]
    says, "I had in this experiment a striking instance of the stimulative
    effects of crossing the breeds; for the smallest variety, whose height
    rarely exceeded two feet, was increased to six feet; whilst the height
    of the large and luxuriant kind was very little diminished." Mr. Laxton
    gave me seed-peas produced from crosses between four distinct kinds;
    and the plants thus raised were extraordinarily vigorous, being in each
    case from one to two or three feet taller than the parent-forms growing
    close alongside them.

    {130}

    Wiegmann[292] made many crosses between several varieties of cabbage;
    and he speaks with astonishment of the vigour and height of the
    mongrels, which excited the amazement of all the gardeners who beheld
    them. Mr. Chaundy raised a great number of mongrels by planting
    together six distinct varieties of cabbage. These mongrels displayed an
    infinite diversity of character; "But the most remarkable circumstance
    was, that, while all the other cabbages and borecoles in the nursery
    were destroyed by a severe winter, these hybrids were little injured,
    and supplied the kitchen when there was no other cabbage to be had."

    Mr. Maund exhibited before the Royal Agricultural Society[293]
    specimens of crossed wheat, together with their parent varieties; and
    the editor states that they were intermediate in character, "united
    with that greater vigour of growth, which it appears, in the vegetable
    as in the animal world, is the result of a first cross." Knight also
    crossed several varieties of wheat,[294] and he says "that in the years
    1795 and 1796, when almost the whole crop of corn in the island was
    blighted, the varieties thus obtained, and these only, escaped in this
    neighbourhood, though sown in several different soils and situations."

    Here is a remarkable case: M. Clotzsch[295] crossed _Pinus sylvestris_
    and _nigricans_, _Quercus robur_ and _pedunculata, Alnus glutinosa_ and
    _incana_, _Ulmus campestris_ and _effusa_; and the cross-fertilised
    seeds, as well as seeds of the pure parent-trees, were all sown at the
    same time and in the same place. The result was, that after an interval
    of eight years, the hybrids were one-third taller than the pure trees!

       *       *       *       *       *

    The facts above given refer to undoubted varieties, excepting the trees
    crossed by Clotzsch, which are ranked by various botanists as
    strongly-marked races, sub-species, or species. That true hybrids
    raised from entirely distinct species, though they lose in fertility,
    often gain in size and constitutional vigour, is certain. It would be
    superfluous to quote any facts; for all experimenters, Kölreuter,
    Gärtner, Herbert, Sageret, Lecoq, and Naudin, have been struck with the
    wonderful vigour, height, size, tenacity of life, precocity, and
    hardiness of their hybrid productions. Gärtner[296] sums up his
    conviction on this head in the strongest terms. Kölreuter[297] gives
    numerous precise measurements of the weight and height of his hybrids
    in comparison with measurements of both parent-forms; and speaks with
    astonishment of their "_statura portentosa_," their "_ambitus
    vastissimus ac altitudo valde conspicua_." Some exceptions to the rule
    in the case of very sterile hybrids have, however, been noticed by
    Gärtner and {131} Herbert; but the most striking exceptions are given
    by Max Wichura,[298] who found that hybrid willows were generally
    tender in constitution, dwarf, and short-lived.

    Kölreuter explains the vast increase in the size of the roots, stems,
    &c., of his hybrids, as the result of a sort of compensation due to
    their sterility, in the same way as many emasculated animals are larger
    than the perfect males. This view seems at first sight extremely
    probable, and has been accepted by various authors;[299] but
    Gärtner[300] has well remarked that there is much difficulty in fully
    admitting it; for with many hybrids there is no parallelism between the
    degree of their sterility and their increased size and vigour. The most
    striking instances of luxuriant growth have been observed with hybrids
    which were not sterile in any extreme degree. In the genus Mirabilis,
    certain hybrids are unusually fertile, and their extraordinary
    luxuriance of growth, together with their enormous roots,[301] have
    been transmitted to their progeny. The increased size of the hybrids
    produced between the fowl and pheasant, and between the distinct
    species of pheasants, has been already noticed. The result in all cases
    is probably in part due to the saving of nutriment and vital force
    through the sexual organs not acting, or acting imperfectly, but more
    especially to the general law of good being derived from a cross. For
    it deserves especial attention that mongrel animals and plants, which
    are so far from being sterile that their fertility is often actually
    augmented, have, as previously shown, their size, hardiness, and
    constitutional vigour generally increased. It is not a little
    remarkable that an accession of vigour and size should thus arise under
    the opposite contingencies of increased and diminished fertility.

    It is a perfectly well ascertained fact[302] that hybrids will
    invariably breed more readily with either pure parent, and not rarely
    with a distinct species, than with each other. Herbert is inclined to
    explain even this fact by the advantage derived from a cross; but
    Gärtner more justly accounts for it by the pollen of the hybrid, and
    probably its ovules, being in some degree vitiated, whereas the pollen
    and ovules of both pure parents and of any third species are sound.
    Nevertheless there are some well-ascertained and remarkable facts,
    which, as we shall immediately see, show that the act of crossing in
    itself undoubtedly tends to increase or re-establish the fertility of
    hybrids.

_On certain Hermaphrodite Plants which, either normally or abnormally,
require to be fertilised by pollen from a distinct individual or species._

The facts now to be given differ from those hitherto detailed, as the
self-sterility does not here result from long-continued, {132} close
interbreeding. These facts are, however, connected with our present
subject, because a cross with a distinct individual is shown to be either
necessary or advantageous. Dimorphic and trimorphic plants, though they are
hermaphrodites, must be reciprocally crossed, one set of forms by the
other, in order to be fully fertile, and in some cases to be fertile in any
degree. But I should not have noticed these plants, had it not been for the
following cases given by Dr. Hildebrand:[303]--

    _Primula sinensis_ is a reciprocally dimorphic species: Dr. Hildebrand
    fertilised twenty-eight flowers of both forms, each by pollen of the
    other form, and obtained the full number of capsules containing on an
    average 42.7 seed per capsule; here we have complete and normal
    fertility. He then fertilised forty-two flowers of both forms with
    pollen of the same form, but taken from a distinct plant, and all
    produced capsules containing on an average only 19.6 seed. Lastly, and
    here we come to our more immediate point, he fertilised forty-eight
    flowers of both forms with pollen of the same form, taken from the same
    flower, and now he obtained only thirty-two capsules, and these
    contained on an average 18.6 seed, or one less per capsule than in the
    former case. So that, with these illegitimate unions, the act of
    impregnation is less assured, and the fertility slightly less, when the
    pollen and ovules belong to the same flower, than when belonging to two
    distinct individuals of the same form. Dr. Hildebrand has recently made
    analogous experiments on the long-styled form of _Oxalis rosea_, with
    the same result.[304]

It has recently been discovered that certain plants, whilst growing in
their native country under natural conditions, cannot be fertilised with
pollen from the same plant. They are sometimes so utterly self-impotent,
that, though they can readily be fertilised by the pollen of a distinct
species or even distinct genus, yet, wonderful as the fact is, they never
produce a single seed by their own pollen. In some cases, moreover, the
plant's own pollen and stigma mutually act on each other in a deleterious
manner. Most of the facts to be given relate to Orchids, but I will
commence with a plant belonging to a widely different family.

    Sixty-three flowers of _Corydalis cava_, borne on distinct plants, were
    fertilised by Dr. Hildebrand[305] with pollen from other plants of the
    same species; and fifty-eight capsules were obtained, including on an
    average {133} 4.5 seed in each. He then fertilised sixteen flowers
    produced by the same raceme, one with another, but obtained only three
    capsules, one of which alone contained any good seeds, namely, two in
    number. Lastly, he fertilised twenty-seven flowers, each with its own
    pollen; he left also fifty-seven flowers to be spontaneously
    fertilised, and this would certainly have ensued if it had been
    possible, for the anthers not only touch the stigma, but the
    pollen-tubes were seen by Dr. Hildebrand to penetrate it; nevertheless
    these eighty-four flowers did not produce a single seed-capsule! This
    whole case is highly instructive, as it shows how widely different the
    action of the same pollen is, according as it is placed on the stigma
    of the same flower, or on that of another flower on the same raceme, or
    on that of a distinct plant.

    With exotic Orchids several analogous cases have been observed, chiefly
    by Mr. John Scott.[306] _Oncidium sphacelatum_ has effective pollen,
    for with it Mr. Scott fertilised two distinct species; its ovules are
    likewise capable of impregnation, for they were readily fertilised by
    the pollen of _O. divaricatum_; nevertheless, between one and two
    hundred flowers fertilised by their own pollen did not produce a single
    capsule, though the stigmas were penetrated by the pollen-tubes. Mr.
    Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also informs
    me (1864) that a hundred and twenty flowers of this same species were
    fertilised by him with their own pollen, and did not produce a capsule,
    but eight flowers fertilised by the pollen of _O. divaricatum_ produced
    four fine capsules: again, between two and three hundred flowers of _O.
    divaricatum_, fertilised by their own pollen, did not set a capsule,
    but twelve flowers fertilised by _O. flexuosum_ produced eight fine
    capsules: so that here we have three utterly self-impotent species,
    with their male and female organs perfect, as shown by their mutual
    fertilisation. In these cases fertilisation was effected only by the
    aid of a distinct species. But, as we shall presently see, distinct
    plants, raised from seed, of _Oncidium flexuosum_, and probably of the
    other species, would have been perfectly capable of fertilising each
    other, for this is the natural process. Again, Mr. Scott found that the
    pollen of a plant of _O. microchilum_ was good, for with it he
    fertilised two distinct species; he found its ovules good, for they
    could be fertilised by the pollen of one of these species, and by the
    pollen of a distinct plant of _O. microchilum_; but they could not be
    fertilised by pollen of the same plant, though the pollen-tubes
    penetrated the stigma. An analogous case has been recorded by M.
    Rivière,[307] with two plants of _O. Cavendishianum_, which were both
    self-sterile, but reciprocally fertilised each other. All these cases
    refer to the genus Oncidium, but Mr. Scott found that _Maxillaria
    atro-rubens_ was "totally insusceptible of fertilisation with its own
    pollen," but fertilised, and was fertilised by, a widely distinct
    species, viz. _M. squalens_.

    As these orchids had grown under unnatural conditions, in {134}
    hot-houses, I concluded without hesitation that their self-sterility
    was due to this cause. But Fritz Müller informs me that at Desterro, in
    Brazil, he fertilised above one hundred flowers of the above-mentioned
    _Oncidium flexuosum_, which is there endemic, with its own pollen, and
    with that taken from distinct plants; all the former were sterile,
    whilst those fertilised by pollen from any _other plant_ of the same
    species were fertile. During the first three days there was no
    difference in the action of the two kinds of pollen: that placed on the
    stigma of the same plant separated in the usual manner into grains, and
    emitted tubes which penetrated the column, and the stigmatic chamber
    shut itself; but the flowers alone which had been fertilised by pollen
    taken from a distinct plant produced seed-capsules. On a subsequent
    occasion these experiments were repeated on a large scale with the same
    result. Fritz Müller found that four other endemic species of Oncidium
    were in like manner utterly sterile with their own pollen, but fertile
    with that from any other plant: some of them likewise produced
    seed-capsules when impregnated with pollen of widely distinct genera,
    such as Leptotes, Cyrtopodium, and Rodriguezia! _Oncidium crispum_,
    however, differs from the foregoing species in varying much in its
    self-sterility; some plants producing fine pods with their own pollen,
    others failing to do so; in two or three instances, Fritz Müller
    observed that the pods produced by pollen taken from a distinct flower
    on the same plant, were larger than those produced by the flower's own
    pollen. In _Epidendrum cinnabarinum_, an orchid belonging to another
    division of the family, fine pods were produced by the plant's own
    pollen, but they contained by weight only about half as much seed as
    the capsules which had been fertilized by pollen from a distinct plant,
    and in one instance from a distinct species; moreover, a very large
    proportion, and in some cases nearly all the seed produced by the
    plant's own pollen, was embryonless and worthless. Some self-fertilized
    capsules of a Maxillaria were in a similar state.

    Another observation made by Fritz Müller is highly remarkable, namely,
    that with various orchids the plant's own pollen not only fails to
    impregnate the flower, but acts on the stigma, and is acted on, in an
    injurious or poisonous manner. This is shown by the surface of the
    stigma in contact with the pollen, and by the pollen itself, becoming
    in from three to five days dark brown, and then decaying. The
    discolouration and decay are not caused by parasitic cryptogams, which
    were observed by Fritz Müller in only a single instance. These changes
    are well shown by placing on the same stigma, at the same time, the
    plant's own pollen and that from a distinct plant of the same species,
    or of another species, or even of another and widely remote genus.
    Thus, on the stigma of _Oncidium flexuosum_, the plant's own pollen and
    that from a distinct plant were placed side by side, and in five days'
    time the latter was perfectly fresh, whilst the plant's own pollen was
    brown. On the other hand, when the pollen of a distinct plant of the
    _Oncidium flexuosum_, and of the _Epidendrum zebra_ (_nov. spec.?_),
    were placed together on the same stigma, they behaved in exactly the
    same manner, the grains separating, emitting tubes, and penetrating the
    stigma, so that the two {135} pollen-masses, after an interval of
    eleven days, could not be distinguished except by the difference of
    their caudicles, which, of course, undergo no change. Fritz Müller has,
    moreover, made a large number of crosses between orchids belonging to
    distinct species and genera, and he finds that in all cases when the
    flowers are not fertilised their footstalks first begin to wither; and
    the withering slowly spreads upwards until the germens fall off, after
    an interval of one or two weeks, and in one instance of between six and
    seven weeks; but even in this latter case, and in most other cases, the
    pollen and stigma remained in appearance fresh. Occasionally, however,
    the pollen becomes brownish, generally on the external surface, and not
    in contact with the stigma, as is invariably the case when the plant's
    own pollen is applied.

    Fritz Müller observed the poisonous action of the plant's own pollen in
    the above-mentioned _Oncidium flexuosum_, _O. unicorne, pubes_ (_?_),
    and in two other unnamed species. Also in two species of Rodriguezia,
    in two of Notylia, in one of Burlingtonia, and of a fourth genus in the
    same group. In all these cases, except the last, it was proved that the
    flowers were, as might have been expected, fertile with pollen from a
    distinct plant of the same species. Numerous flowers of one species of
    Notylia were fertilized with pollen from the same raceme; in two days'
    time they all withered, the germens began to shrink, the pollen-masses
    became dark brown, and not one pollen-grain emitted a tube. So that in
    this orchid the injurious action of the plant's own pollen is more
    rapid than with _Oncidium flexuosum_. Eight other flowers on the same
    raceme were fertilized with pollen from a distinct plant of the same
    species: two of these were dissected, and their stigmas were found to
    be penetrated by numberless pollen-tubes; and the germens of the other
    six flowers became well developed. On a subsequent occasion many other
    flowers were fertilized with their own pollen, and all fell off dead in
    a few days; whilst some flowers on the same raceme which had been left
    simply unfertilised adhered and long remained fresh. We have seen that
    in cross-unions between extremely distinct orchids the pollen long
    remains undecayed; but Notylia behaved in this respect differently; for
    when its pollen was placed on the stigma of _Oncidium flexuosum_, both
    the stigma and pollen quickly became dark brown, in the same manner as
    if the plant's own pollen had been applied.

    Fritz Müller suggests that, as in all these cases the plant's own
    pollen is not only impotent (thus effectually preventing
    self-fertilization), but likewise prevents, as was ascertained in the
    case of the Notylia and _Oncidium flexuosum_, the action of
    subsequently applied pollen from a distinct individual, it would be an
    advantage to the plant to have its own pollen rendered more and more
    deleterious; for the germens would thus quickly be killed, and,
    dropping off, there would be no further waste in nourishing a part
    which ultimately could be of no avail. Fritz Müller's discovery that a
    plant's own pollen and stigma in some cases act on each other as if
    mutually poisonous, is certainly most remarkable.

We now come to cases closely analogous with those just {136} given, but
different, inasmuch as individual plants alone of the species are
self-impotent. This self-impotence does not depend on the pollen or ovules
being in a state unfit for fertilisation, for both have been found
effective in union with other plants of the same or of a distinct species.
The fact of these plants having spontaneously acquired so peculiar a
constitution, that they can be fertilised more readily by the pollen of a
distinct species than by their own, is remarkable. These abnormal cases, as
well as the foregoing normal cases, in which certain orchids, for instance,
can be much more easily fertilised by the pollen of a distinct species than
by their own, are exactly the reverse of what occurs with all ordinary
species. For in these latter the two sexual elements of the same individual
plant are capable of freely acting on each other; but are so constituted
that they are more or less impotent when brought into union with the sexual
elements of a distinct species, and produce more or less sterile hybrids.
It would appear that the pollen or ovules, or both, of the individual
plants which are in this abnormal state, have been affected in some strange
manner by the conditions to which they themselves or their parents have
been exposed; but whilst thus rendered self-sterile, they have retained the
capacity common to most species of partially fertilizing and being
partially fertilized by allied forms. However this may be, the subject, to
a certain extent, is related to our general conclusion that good is derived
from the act of crossing.

    Gärtner experimented on two plants of _Lobelia fulgens_, brought from
    separate places, and found[308] that their pollen was good, for he
    fertilised with it _L. cardinalis_ and _syphilitica_; their ovules were
    likewise good, for they were fertilised by the pollen of these same two
    species; but these two plants of _L. fulgens_ could not be fertilised
    by their own pollen, as can generally be effected with perfect ease
    with this species. Again, the pollen of a plant of _Verbascum nigrum_
    grown in a pot was found by Gärtner[309] capable of fertilising _V.
    lychnitis_ and _V. Austriacum_; the ovules could be fertilised by the
    pollen of _V. thapsus_; but the flowers could not be fertilised by
    their own pollen. Kölreuter, also,[310] gives the case of three {137}
    garden plants of _Verbascum phoeniceum_, which bore during two years
    many flowers; these he successfully fertilised by the pollen of no less
    than four distinct species, but they produced not a seed with their own
    apparently good pollen; subsequently these same plants, and others
    raised from seed, assumed a strangely fluctuating condition, being
    temporarily sterile on the male or female side, or on both sides, and
    sometimes fertile on both sides; but two of the plants were perfectly
    fertile throughout the summer.

    It appears[311] that certain flowers on certain plants of _Lilium
    candidum_ can be fertilised more easily by pollen from a distinct
    individual than by their own. So, again, with the varieties of the
    potato. Tinzmann,[312] who made many trials with this plant, says that
    pollen from another variety sometimes "exerts a powerful influence, and
    I have found sorts of potatoes which would not bear seed from
    impregnation with the pollen of their own flowers, would bear it when
    impregnated with other pollen." It does not, however, appear to have
    been proved that the pollen which failed to act on the flower's own
    stigma was in itself good.

    In the genus Passiflora it has long been known that several species do
    not produce fruit, unless fertilised by pollen taken from distinct
    species: thus, Mr. Mowbray[313] found that he could not get fruit from
    _P. alata_ and _racemosa_ except by reciprocally fertilising them with
    each other's pollen. Similar facts have been observed in Germany and
    France;[314] and I have received two authentic accounts of _P.
    quadrangularis_, which never produced fruit with its own pollen, but
    would do so freely when fertilised in one case with the pollen of _P.
    coerulea_, and in another case with that of _P. edulis_. So again, with
    respect to _P. laurifolia_, a cultivator of much experience has
    recently remarked[315] that the flowers "must be fertilised with the
    pollen of _P. coerulea_, or of some other common kind, as their own
    pollen will not fertilise them." But the fullest details on this
    subject have been given by Mr. Scott:[316] plants of _Passiflora
    racemosa_, _coerulea_, and _alata_ flowered profusely during many years
    in the Botanic Gardens of Edinburgh, and, though repeatedly fertilised
    by Mr. Scott and by others with their own pollen, never produced any
    seed; yet this occurred at once with all three species when they were
    crossed together in various ways. But in the case of _P. coerulea_,
    three plants, two of which grew in the Botanic Gardens, were all
    rendered fertile, merely by impregnating the one with pollen of the
    other. The same result was attained in the same manner with _P. alata_,
    but only with one plant out of three. As so many self-sterile species
    have been mentioned, it may be stated that in the case of _P.
    gracilis_, which is an annual, the flowers are nearly as fertile with
    their own pollen as with that from a distinct plant; thus sixteen
    flowers {138} spontaneously self-fertilised produced fruit, each
    containing on an average 21.3 seed, whilst fruit from fourteen crossed
    flowers contained 24.1 seed.

    Returning to _P. alata_, I have received (1866) some interesting
    details from Mr. Robinson Munro. Three plants, including one in
    England, have already been mentioned which were inveterately
    self-sterile, and Mr. Munro informs me of several others which, after
    repeated trials during many years, have been found in the same
    predicament. At some other places, however, this species fruits readily
    when fertilised with its own pollen. At Taymouth Castle there is a
    plant which was formerly grafted by Mr. Donaldson on a distinct
    species, name unknown, and ever since the operation it has produced
    fruit in abundance by its own pollen; so that this small and unnatural
    change in the state of this plant has restored its self-fertility! Some
    of the seedlings from the Taymouth Castle plant were found to be not
    only sterile with their own pollen, but with each other's pollen, and
    with the pollen of distinct species. Pollen from the Taymouth plant
    failed to fertilise certain plants of the same species, but was
    successful on one plant in the Edinburgh Botanic Gardens. Seedlings
    were raised from this latter union, and some of their flowers were
    fertilised by Mr. Munro with their own pollen; but they were found to
    be as self-impotent as the mother-plant had always proved, except when
    fertilised by the grafted Taymouth plant, and except, as we shall see,
    when fertilised by her own seedlings. For Mr. Munro fertilised eighteen
    flowers on the self-impotent mother-plant with pollen from these her
    own self-impotent seedlings, and obtained, remarkable as the fact is,
    eighteen fine capsules full of excellent seed! I have met with no case
    in regard to plants which shows so well as this of _P. alata_, on what
    small and mysterious causes complete fertility or complete sterility
    depends.

The facts hitherto given relate to the much-lessened or completely
destroyed fertility of pure species when impregnated with their own pollen,
in comparison with their fertility when impregnated by distinct individuals
or distinct species; but closely analogous facts have been observed with
hybrids.

    Herbert states[317] that having in flower at the same time nine hybrid
    Hippeastrums, of complicated origin, descended from several species, he
    found that "almost every flower touched with pollen from another cross
    produced seed abundantly, and those which were touched with their own
    pollen either failed entirely, or formed slowly a pod of inferior size,
    with fewer seeds." In the 'Horticultural Journal' he adds that, "the
    admission of the pollen of another cross-bred Hippeastrum (however
    complicated the cross) to any _one_ flower of the number, is almost
    sure to check the fructification of the others." In a letter written to
    me in 1839, Dr. Herbert says that he had already tried these
    experiments during five consecutive years, and he subsequently repeated
    them, with the same invariable result. {139} He was thus led to make an
    analogous trial on a pure species, namely, on the _Hippeastrum
    aulicum_, which he had lately imported from Brazil: this bulb produced
    four flowers, three of which were fertilised by their own pollen, and
    the fourth by the pollen of a triple cross between _H. bulbulosum_,
    _reginæ_, and _vittatum_; the result was, that "the ovaries of the
    three first flowers soon ceased to grow, and after a few days perished
    entirely: whereas the pod impregnated by the hybrid made vigorous and
    rapid progress to maturity, and bore good seed, which vegetated
    freely." This is, indeed, as Herbert remarks, "a strange truth," but
    not so strange as it then appeared.

    As a confirmation of these statements, I may add that Mr. M.
    Mayes,[318] after much experience in crossing the species of Amaryllis
    (Hippeastrum), says, "neither the species nor the hybrids will, we are
    well aware, produce seed so abundantly from their own pollen as from
    that of others." So, again, Mr. Bidwell, in New South Wales,[319]
    asserts that _Amaryllis belladonna_ bears many more seeds when
    fertilised by the pollen of _Brunswigia_ (_Amaryllis_ of some authors)
    _Josephinæ_ or of _B. multiflora_, than when fertilised by its own
    pollen. Mr. Beaton dusted four flowers of a Cyrtanthus with their own
    pollen, and four with the pollen of _Vallota_ (_Amaryllis_) _purpurea_;
    on the seventh day "those which received their own pollen slackened
    their growth, and ultimately perished; those which were crossed with
    the Vallota held on."[320] These latter cases, however, relate to
    uncrossed species, like those before given with respect to Passiflora,
    Orchids, &c., and are here referred to only because the plants belong
    to the same group of Amaryllidaceæ.

    In the experiments on the hybrid Hippeastrums, if Herbert had found
    that the pollen of two or three kinds alone had been more efficient on
    certain kinds than their own pollen, it might have been argued that
    these, from their mixed parentage, had a closer mutual affinity than
    the others; but this explanation is inadmissible, for the trials were
    made reciprocally backwards and forwards on nine different hybrids; and
    a cross, whichever way taken, always proved highly beneficial. I can
    add a striking and analogous case from experiments made by the Rev. A.
    Rawson, of Bromley Common, with some complex hybrids of Gladiolus. This
    skilful horticulturist possessed a number of French varieties,
    differing from each other only in the colour and size of the flowers,
    all descended from Gandavensis, a well-known old hybrid, said to be
    descended from _G. Natalensis_ by the pollen of _G.
    oppositiflorus_.[321] Mr. Rawson, after repeated trials, found that
    none of the varieties would set seed with their own pollen, although
    {140} taken from distinct plants of the same variety, which had, of
    course, been propagated by bulbs, but that they all seeded freely with
    pollen from any other variety. To give two examples: Ophir did not
    produce a capsule with its own pollen, but when fertilised with that of
    Janire, Brenchleyensis, Vulcain, and Linné, it produced ten fine
    capsules; but the pollen of Ophir was good, for when Linné was
    fertilised by it seven capsules were produced. This later variety, on
    the other hand, was utterly barren with its own pollen, which we have
    seen was perfectly efficient on Ophir. Altogether, Mr. Rawson, in the
    year 1861, fertilised twenty-six flowers borne by four varieties with
    pollen taken from other varieties, and every single flower produced a
    fine seed-capsule; whereas fifty-two flowers on the same plants,
    fertilised at the same time with their own pollen, did not yield a
    single seed-capsule. Mr. Rawson fertilised, in some cases, the
    alternate flowers, and in other cases all those down one side of the
    spike, with pollen of other varieties, and the remaining flowers with
    their own pollen; I saw these plants when the capsules were nearly
    mature, and their curious arrangement at once brought full conviction
    to the mind that an immense advantage had been derived from crossing
    these hybrids.

    Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made
    numerous experiments in crossing the species of Cistus, but as not yet
    published the results, that, when any of these hybrids are fertile,
    they may be said to be, in regard to function, dioecious; "for the
    flowers are always sterile when the pistil is fertilised by pollen
    taken from the same flower or from flowers on the same plant. But they
    are often fertile if pollen be employed from a distinct individual of
    the same hybrid nature, or from a hybrid made by a reciprocal cross."

_Conclusion._--The facts just given, which show that certain plants are
self-sterile, although both sexual elements are in a fit state for
reproduction when united with distinct individuals of the same or other
species, appear at first sight opposed to all analogy. The sexual elements
of the same flower have become, as already remarked, differentiated in
relation to each other, almost like those of two distinct species.

With respect to the species which, whilst living under their natural
conditions, have their reproductive organs in this peculiar state, we may
conclude that it has been naturally acquired for the sake of effectually
preventing self-fertilisation. The case is closely analous with dimorphic
and trimorphic plants, which can be fully fertilised only by plants belong
to the opposite form, and not, as in the foregoing cases, in differently by
any other plant. Some of these dimorphic plants are completely sterile with
pollen taken from the same plant or from the same {141} form. It is
interesting to observe the graduated series from plants which, when
fertilised by their own pollen, yield the full number of seed, but with the
seedlings a little dwarfed in stature--to plants which when self-fertilised
yield few seeds--to those with yield none--and, lastly, to those in which
the plant's own pollen and stigma act on each other like poison. This
peculiar state of the reproductive organs, when occurring in certain
individuals alone, is evidently abnormal; and as it chiefly affects exotic
plants, or indigenous plants cultivated in pots, we may attribute it to
some change in the conditions of life, acting on the plants themselves or
on their parents. The self-impotent _Passiflora alata_, which recovered its
self-fertility after having been grafted on a distinct stock, shows how
small a change is sufficient to act powerfully on the reproductive system.
The possibility of a plant becoming under culture self-impotent is
interesting as throwing light on the occurrence of this same condition in
natural species. A cultivated plant in this state generally remains so
during its whole life; and from this fact we may infer that the state is
probably congenital.

Kölreuter, however, has described some plants of Verbascum which varied in
this respect even during the same season. As in all the normal cases, and
in many, probably in most, of the abnormal cases, any two self-impotent
plants can reciprocally fertilize each other, we may infer that a very
slight difference in the nature of their sexual elements suffices to give
fertility; but in other instances, as with some Passifloras and the hybrid
Gladioli, a greater degree of differentiation appears to be necessary, for
with these plants fertility is gained only by the union of distinct
species, or of hybrids of distinct parentage. These facts all point to the
same general conclusion, namely, that good is derived from a cross between
individuals, which either innately, or from exposure to dissimilar
conditions, have come to differ in sexual constitution.

Exotic animals confined in menageries are sometimes in nearly the same
state as the above-described self-impotent plants; for, as we shall see in
the following chapter, certain monkeys, the larger carnivora, several
finches, geese, and pheasants, cross together, quite as freely as, or even
more freely than, the individuals of the same species breed together. Cases
will, {142} also, be given of sexual incompatibility between certain male
and female domesticated animals, which, nevertheless, are fertile when
matched with any other individual of the same kind.

In the early part of this chapter it was shown that the crossing of
distinct forms, whether closely or distantly allied, gives increased size
and constitutional vigour, and, except in the case of crossed species,
increased fertility, to the offspring. The evidence rests on the universal
testimony of breeders (for it should be observed that I am not here
speaking of the evil results of close interbreeding), and is practically
exemplified in the higher value of cross-bred animals for immediate
consumption. The good results of crossing have also been demonstrated, in
the case of some animals and of numerous plants, by actual weight and
measurement. Although animals of pure blood will obviously be deteriorated
by crossing, as far as their characteristic qualities are concerned, there
seems to be no exception to the rule that advantages of the kind just
mentioned are thus gained, even when there has not been any previous close
interbreeding. The rule applies to all animals, even to cattle and sheep,
which can long resist breeding in-and-in between the nearest
blood-relations. It applies to individuals of the same sub-variety but of
distinct families, to varieties or races, to sub-species, as well as to
quite distinct species.

In this latter case, however, whilst size, vigour, precocity, and hardiness
are, with rare exceptions, gained, fertility, in a greater or less degree,
is lost; but the gain cannot be exclusively attributed to the principle of
compensation; for there is no close parallelism between the increased size
and vigour of the offspring and their sterility. Moreover it has been
clearly proved that mongrels which are perfectly fertile gain these same
advantages as well as sterile hybrids.

The evil consequences of long-continued close interbreeding are not so
easily recognised as the good effects from crossing, for the deterioration
is gradual. Nevertheless it is the general opinion of those who have had
most experience, especially with animals which propagate quickly, that evil
does inevitably follow sooner or later, but at different rates with
different animals. No doubt a false belief may widely prevail like a
superstition; yet it is difficult to suppose that so many acute and
original {143} observers have all been deceived at the expense of much cost
and trouble. A male animal may sometimes be paired with his daughter,
granddaughter, and so on, even for seven generations, without any manifest
bad result; but the experiment has never been tried of matching brothers
and sisters, which is considered the closest form of interbreeding, for an
equal number of generations. There is good reason to believe that by
keeping the members of the same family in distinct bodies, especially if
exposed to somewhat different conditions of life, and by occasionally
crossing these families, the evil results may be much diminished, or quite
eliminated. These results are loss of constitutional vigour, size, and
fertility; but there is no necessary deterioration in the general form of
the body, or in other good qualities. We have seen that with pigs
first-rate animals have been produced after long-continued close
interbreeding, though they had become extremely infertile when paired with
their near relations. The loss of fertility, when it occurs, seems never to
be absolute, but only relative to animals of the same blood; so that this
sterility is to a certain extent analogous with that of self-impotent
plants which cannot be fertilised by their own pollen, but are perfectly
fertile with pollen of any other plant of the same species. The fact of
infertility of this peculiar nature being one of the results of
long-continued interbreeding, shows that interbreeding does not act merely
by combining and augmenting various morbid tendencies common to both
parents; for animals with such tendencies, if not at the time actually ill,
can generally propagate their kind. Although offspring descended from the
nearest blood-relations are not necessarily deteriorated in structure, yet
some authors[322] believe that they are eminently liable to malformations;
and this is not improbable, as everything which lessens the vital powers
acts in this manner. Instances of this kind have been recorded in the case
of pigs, bloodhounds, and some other animals.

Finally, when we consider the various facts now given which plainly show
that good follows from crossing, and less plainly {144} that evil follows
from close interbreeding, and when we bear in mind that throughout the
whole organic world elaborate provision has been made for the occasional
union of distinct individuals, the existence of a great law of nature is,
if not proved, at least rendered in the highest degree probable; namely,
that the crossing of animals and plants which are not closely related to
beach other is highly beneficial or even necessary, and that interbreeding
prolonged during many generations is highly injurious.

       *       *       *       *       *


{145}

CHAPTER XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:
STERILITY FROM VARIOUS CAUSES.

    ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF
    LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE
    COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF
    SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF
    STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM CHANGED
    CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF
    PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE
    ANTHERS--MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE
    FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE DEVELOPMENT OF
    THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY
    BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND
    SEEDLESS FRUIT.

_On the Good derived from slight Changes in the Conditions of Life._--In
considering whether any facts were known which might throw light on the
conclusion arrived at in the last chapter, namely, that benefits ensue from
crossing, and that it is a law of nature that all organic beings should
occasionally cross, it appeared to me probable that the good derived from
slight changes in the conditions of life, from being an analogous
phenomenon, might serve this purpose. No two individuals, and still less no
two varieties, are absolutely alike in constitution and structure; and when
the germ of one is fertilised by the male element of another, we may
believe that it is acted on in a somewhat similar manner as an individual
when exposed to slightly changed conditions. Now, every one must have
observed the remarkable influence on convalescents of a change of
residence, and no medical man doubts the truth of this fact. Small farmers
who hold but little land are convinced that their cattle derive great
benefit from a change of pasture. In the case of plants, the evidence is
strong that a great advantage is derived from exchanging seeds, tubers,
bulbs, and cuttings from one soil or place to another as different as
possible. {146}

    The belief that plants are thus benefited, whether or not well founded,
    has been firmly maintained from the time of Columella, who wrote
    shortly after the Christian era, to the present day; and it now
    prevails in England, France, and Germany.[323] A sagacious observer,
    Bradley, writing in 1724,[324] says, "When we once become Masters of a
    good Sort of Seed, we should at least put it into Two or Three Hands,
    where the Soils and Situations are as different as possible; and every
    Year the Parties should change with one another; by which Means, I find
    the Goodness of the Seed will be maintained for several Years. For Want
    of this Use many Farmers have failed in their Crops and been great
    Losers." He then gives his own practical experience on this head. A
    modern writer[325] asserts, "Nothing can be more clearly established in
    agriculture than that the continual growth of any one variety in the
    same district makes it liable to deterioration either in quality or
    quantity." Another writer states that he sowed close together in the
    same field two lots of wheat-seed, the product of the same original
    stock, one of which had been grown on the same land, and the other at a
    distance, and the difference in favour of the crop from the latter seed
    was remarkable. A gentleman in Surrey who has long made it his business
    to raise wheat to sell for seed, and who has constantly realised in the
    market higher prices than others, assures me that he finds it
    indispensable continually to change his seed; and that for this purpose
    he keeps two farms differing much in soil and elevation.

    With respect to the tubers of the potato, I find that at the present
    day the practice of exchanging sets is almost everywhere followed. The
    great growers of potatoes in Lancashire formerly used to get tubers
    from Scotland, but they found that "a change from the moss-lands, and
    _vice versâ_, was generally sufficient." In former times in France the
    crop of potatoes in the Vosges had become reduced in the course of
    fifty or sixty years in the proportion from 120-150 to 30-40 bushels;
    and the famous Oberlin attributed the surprising good which he effected
    in large part to changing the sets.[326]

    A well-known practical gardener, Mr. Robson[327] positively states that
    he has himself witnessed decided advantage from obtaining bulbs of the
    onion, tubers of the potato, and various seeds, all of the same kind,
    from different soils and distant parts of England. He further states
    that with {147} plants propagated by cuttings, as with the Pelargonium,
    and especially the Dahlia, manifest advantage is derived from getting
    plans of the same variety, which have been cultivated in another place;
    or, "where the extent of the place allows, to take cuttings from one
    description of soil to plant on another, so as to afford the change
    that seems so necessary to the well-being of the plants." He maintains
    that after a time an exchange of this nature is "forced on the grower,
    whether he be prepared for it or not." Similar remarks have been made
    by another excellent gardener, Mr. Fish, namely, that cuttings of the
    same variety of Calceolaria, which he obtained from a neighbour,
    "showed much greater vigour than some of his own that were treated in
    exactly the same manner," and he attributed this solely to his own
    plants having become "to a certain extent worn out or tired of their
    quarters." Something of this kind apparently occurs in grafting and
    budding fruit-trees; for, according to Mr. Abbey, grafts or buds
    generally take on a distinct variety or even species, or on a stock
    previously grafted, with greater facility than on stocks raised from
    seeds of the variety which is to be grafted; and he believes this
    cannot be altogether explained by the stocks in question being better
    adapted to the soil and climate of the place. It should, however, be
    added, that varieties grafted or budded on very distinct kinds, though
    they may take more readily and grow at first more vigorously than when
    grafted on closely allied stocks, afterwards often become unhealthy.

    I have studied M. Tessier's careful and elaborate experiments,[328]
    made to disprove the common belief that good is derived from a change
    of seed; and he certainly shows that the same seed may with care be
    cultivated on the same farm (it is not stated whether on exactly the
    same soil) for ten consecutive years without loss. Another excellent
    observer, Colonel Le Couteur,[329] has come to the same conclusion; but
    then he expressly adds, if the same seed be used, "that which is grown
    on land manured from the mixen one year becomes seed for land prepared
    with lime, and that again becomes seed for land dressed with ashes,
    then for land dressed with mixed manure, and so on." But this in effect
    is a systematic exchange of seed, within the limits of the same farm.

On the whole the belief, which has long been held by many skilful
cultivators, that good follows from exchanging seed, tubers, &c., seems to
be fairly well founded. Considering the small size of most seeds, it seems
hardly credible that the advantage thus derived can be due to the seeds
obtaining in one soil some chemical element deficient in the other soil. As
plants after once germinating naturally become fixed to the same spot, it
might have been anticipated that they would show the good effects of a
change more plainly than animals, which continually wander about; and this
apparently is the {148} case. Life depending on, or consisting in, an
incessant play of the most complex forces, it would appear that their
action is in some way stimulated by slight changes in the circumstances to
which each organism is exposed. All forces throughout nature, as Mr.
Herbert Spencer[330] remarks, tend towards an equilibrium, and for the life
of each being it is necessary that this tendency should be checked. If
these views and the foregoing facts can be trusted, they probably throw
light, on the one hand, on the good effects of crossing the breed, for the
germ will be thus slightly modified or acted on by new forces; and on the
other hand, on the evil effects of close interbreeding prolonged during
many generations, during which the germ will be acted on by a male having
almost identically the same constitution.

_Sterility from changed Conditions of Life._

I will now attempt to show that animals and plants, when removed from their
natural conditions, are often rendered in some degree infertile or
completely barren; and this occurs even when the conditions have not been
greatly changed. This conclusion is not necessarily opposed to that at
which we have just arrived, namely, that lesser changes of other kinds are
advantageous to organic beings. Our present subject is of some importance,
from having an intimate connexion with the causes of variability.
Indirectly it perhaps bears on the sterility of species when crossed: for
as, on the one hand, slight changes in the conditions of life are
favourable to plants and animals, and the crossing of varieties adds to the
size, vigour, and fertility of their offspring; so, on the other hand,
certain other changes in the conditions of life cause sterility; and as
this likewise ensues from crossing much-modified forms or species, we have
a parallel and double series of facts, which apparently stand in close
relation to each other.

It is notorious that many animals, though perfectly tamed, {149} refuse to
breed in captivity. Isidore Geoffroy St. Hilaire[331] consequently has
drawn a broad distinction between tamed animals which will not breed under
captivity, and truly domesticated animals which breed freely--generally
more freely, as shown in the sixteenth chapter, than in a state of nature.
It is possible and generally easy to tame most animals; but experience has
shown that it is difficult to get them to breed regularly, or even at all.
I shall discuss this subject in detail; but will give only those cases
which seem most illustrative. My materials are derived from notices
scattered through various works, and especially from a Report, drawn up for
me by the kindness of the officers of the Zoological Society of London,
which has especial value, as it records all the cases, during nine years
from 1838-46, in which the animals were seen to couple but produced no
offspring, as well as the cases in which they never, as far as known,
coupled. This MS. Report I have corrected by the annual Reports
subsequently published. Many facts are given on the breeding of the animals
in that magnificent work, 'Gleanings from the Menageries of Knowsley Hall,'
by Dr. Gray. I made, also, particular inquiries from the experienced keeper
of the birds in the old Surrey Zoological Gardens. I should premise that a
slight change in the treatment of animals sometimes makes a great
difference in their fertility; and it is probable that the results observed
in different menageries would differ. Indeed some animals in our Zoological
Gardens have become more productive since the year 1846. It is, also,
manifest from F. Cuvier's account of the Jardin des Plantes,[332] that the
animals formerly bred much less freely there than with us; for instance, in
the Duck tribe, which is highly prolific, only one species had at that
period produced young.

    The most remarkable cases, however, are afforded by animals kept in
    their native country, which, though perfectly tamed, quite healthy, and
    allowed some freedom, are absolutely incapable of breeding.
    Rengger,[333] who in Paraguay particularly attended to this subject,
    specifies six quadrupeds in this condition; and he mentions two or
    three others which most rarely {150} breed. Mr. Bates, in his admirable
    work on the Amazons, strongly insists on similar cases;[334] and he
    remarks, that the fact of thoroughly tamed native mammals and birds not
    breeding when kept by the Indians, cannot be wholly accounted for by
    their negligence or indifference, for the turkey is valued by them, and
    the fowl has been adopted by the remotest tribes. In almost every part
    of the world--for instance, in the interior of Africa, and in several
    of the Polynesian islands--the natives are extremely fond of taming the
    indigenous quadrupeds and birds; but they rarely or never succeed in
    getting them to breed.

    The most notorious case of an animal not breeding in captivity is that
    of the elephant. Elephants are kept in large numbers in their native
    Indian home, live to old age, and are vigorous enough for the severest
    labour; yet, with one or two exceptions, they have never been known
    even to couple, though both males and females have their proper
    periodical seasons. If, however, we proceed a little eastward to Ava,
    we hear from Mr. Crawfurd[335] that their "breeding in the domestic
    state, or at least in the half-domestic state in which the female
    elephants are generally kept, is of every-day occurrence;" and Mr.
    Crawfurd informs me that he believes that the difference must be
    attributed solely to the females being allowed to roam the forests with
    some degree of freedom. The captive rhinoceros, on the other hand,
    seems from Bishop Heber's account[336] to breed in India far more
    readily than the elephant. Four wild species of the horse genus have
    bred in Europe, though here exposed to a great change in their natural
    habits of life; but the species have generally been crossed one with
    another. Most of the members of the pig family breed readily in our
    menageries: even the Red River hog (_Potamochoerus penicillatus_), from
    the sweltering plains of West Africa, has bred twice in the Zoological
    Gardens. Here also the Peccary (_Dicotyles torquatus_) has bred several
    times; but another species, the _D. labiatus_, though rendered so tame
    as to be half-domesticated, breeds so rarely in its native country of
    Paraguay, that according to Rengger[337] the fact requires
    confirmation. Mr. Bates remarks that the tapir, though often kept tame
    in Amazonia by the Indians, never breeds.

    Ruminants generally breed quite freely in England, though brought from
    widely different climates, as may be seen in the Annual Reports of the
    Zoological Gardens, and in the Gleanings from Lord Derby's menagerie.

    The Carnivora, with the exception of the Plantigrade division,
    generally breed (though with capricious exceptions) almost as freely as
    ruminants. Many species of Felidæ have bred in various menageries,
    although imported from various climates and closely confined. Mr.
    Bartlett, the present superintendent of the Zoological Gardens,[338]
    remarks that the lion appears to breed more frequently and to bring
    forth more young at a birth than any other species of the family. He
    adds that the tiger has rarely bred; {151} "but there are several
    well-authenticated instances of the female tiger breeding with the
    lion." Strange as the fact may appear, many animals under confinement
    unite with distinct species and produce hybrids quite as freely as, or
    even more freely than, with their own species. On inquiring from Dr.
    Falconer and others, it appears that the tiger when confined in India
    does not breed, though it has been known to couple. The cheetah (_Felis
    jubata_) has never been known by Mr. Bartlett to breed in England, but
    it has bred at Frankfort; nor does it breed in India, where it is kept
    in large numbers for hunting; but no pains would be taken to make them
    breed, as only those animals which have hunted for themselves in a
    state of nature are serviceable and worth training.[339] According to
    Rengger, two species of wild cats in Paraguay, though thoroughly tamed,
    have never bred. Although so many of the Felidæ breed readily in the
    Zoological Gardens, yet conception by no means always follows union: in
    the nine-year Report, various species are specified which were observed
    to couple seventy-three times, and no doubt this must have passed many
    times unnoticed; yet from the seventy-three unions only fifteen births
    ensued. The Carnivora in the Zoological Gardens were formerly less
    freely exposed to the air and cold than at present, and this change of
    treatment, as I was assured by the former superintendent, Mr. Miller,
    greatly increased their fertility. Mr. Bartlett, and there cannot be a
    more capable judge, says, "it is remarkable that lions breed more
    freely in travelling collections than in the Zoological Gardens;
    probably the constant excitement and irritation produced by moving from
    place to place, or change of air, may have considerable influence in
    the matter."

    Many members of the Dog family breed readily when confined. The Dhole
    is one of the most untameable animals in India, yet a pair kept there
    by Dr. Falconer produced young. Foxes, on the other hand, rarely breed,
    and I have never heard of such an occurrence with the European fox: the
    silver fox of North America (_Canis argentatus_), however, has bred
    several times in the Zoological Gardens. Even the otter has bred there.
    Every one knows how readily the semi-domesticated ferret breeds, though
    shut up in miserably small cages; but other species of Viverra and
    Paradoxurus absolutely refuse to breed in the Zoological Gardens. The
    Genetta has bred both here and in the Jardin des Plantes, and produced
    hybrids. The _Herpestes fasciatus_ has likewise bred; but I was
    formerly assured that the _H. griseus_, though many were kept in the
    Gardens, never bred.

    The Plantigrade Carnivora breed under confinement much less freely,
    without our being able to assign any reason, than other members of the
    group. In the nine-year Report it is stated that the bears had been
    seen in the Zoological Gardens to couple freely, but previously to 1848
    had most rarely conceived. In the Reports published since this date
    three species have produced young (hybrids in one case), and, wonderful
    to relate, the white Polar bear has produced young. The badger (_Meles
    taxus_) has bred several times in the Gardens; but I have not heard of
    this {152} occurring elsewhere in England, and the event must be very
    rare, for an instance in Germany has been thought worth recording.[340]
    In Paraguay the native Nasua, though kept in pairs during many years
    and perfectly tamed, has never been known, according to Rengger, to
    breed or show any sexual passion; nor, as I hear from Mr. Bates, does
    this animal, or the Cercoleptes, breed in the region of the Amazons.
    Two other plantigrade genera, Procyon and Gulo, though often kept tame
    in Paraguay, never breed there. In the Zoological Gardens species of
    Nasua and Procyon have been seen to couple; but they did not produce
    young.

    As domesticated rabbits, guinea-pigs, and white mice breed so
    abundantly when closely confined under various climates, it might have
    been thought that most other members of the Rodent order would have
    bred in captivity, but this is not the case. It deserves notice, as
    showing how the capacity to breed sometimes goes by affinity, that the
    one native rodent of Paraguay, which there breeds _freely_ and has
    yielded successive generations, is the _Cavia aperea_; and this animal
    is so closely allied to the guinea-pig, that it has been erroneously
    thought to be the parent-form.[341] In the Zoological Gardens, some
    rodents have coupled, but have never produced young; some have neither
    coupled nor bred; but a few have bred, as the porcupine more than once,
    the Barbary mouse, lemming, chinchilla, and the agouti (_Dasyprocta
    aguti_), several times. This latter animal has also produced young in
    Paraguay, though they were born dead and ill-formed; but in Amazonia,
    according to Mr. Bates, it never breeds, though often kept tame about
    the houses. Nor does the paca (_Coelogenys paca_) breed there. The
    common hare when confined has, I believe, never bred in Europe;[342]
    though, according to a recent statement, it has crossed with the
    rabbit. I have never heard of the dormouse breeding in confinement. But
    squirrels offer a more curious case: with one exception, no species has
    ever bred in the Zoological Gardens, yet as many as fourteen
    individuals of _S. palmarum_ were kept together during several years.
    The _S. cinerea_ has been seen to couple, but it did not produce young;
    nor has this species, when rendered extremely tame in its native
    country, North America, been ever known to breed.[343] At Lord Derby's
    menagerie squirrels of many kinds were kept in numbers, but Mr.
    Thompson, the superintendent, told me that none had ever bred there, or
    elsewhere as far as he knew. I have never heard of the English squirrel
    breeding in confinement. But the species which has bred more than once
    in the Zoological Gardens is the one which perhaps might have been
    least expected, namely, the flying squirrel (_Sciuropterus volucella_):
    it has, also, bred several times {153} near Birmingham; but the female
    never produced more than two young at a birth, whereas in its native
    American home she bears from three to six young.[344]

    Monkeys, in the nine-year Report from the Zoological Gardens, are
    stated to unite most freely, but during this period, though many
    individuals were kept, there were only seven births. I have heard of
    one American monkey alone, the Ouistiti, breeding in Europe.[345] A
    Macacus, according to Flourens, bred in Paris; and more than one
    species of this genus has produced young in London, especially the
    _Macacus rhesus_, which everywhere shows a special capacity to breed
    under confinement. Hybrids have been produced both in Paris and London
    from this same genus. The Arabian baboon, or _Cynocephalus
    hamadryas_,[346] and a Cercopithecus have bred in the Zoological
    Gardens, and the latter species at the Duke of Northumberland's.
    Several members of the family of Lemurs have produced hybrids in the
    Zoological Gardens. It is much more remarkable that monkeys very rarely
    breed when confined in their native country; thus the Cay (_Cebus
    azaræ_) is frequently and completely tamed in Paraguay, but
    Rengger[347] says that it breeds so rarely, that he never saw more than
    two females which had produced young. A similar observation has been
    made with respect to the monkeys which are frequently tamed by the
    aborigines in Brazil.[348] In the region of the Amazons, these animals
    are so often kept in a tame state, that Mr. Bates in walking through
    the streets of Parà counted thirteen species; but, as he asserts, they
    have never been known to breed in captivity.[349]

_Birds._

    Birds offer in some respects better evidence than quadrupeds, from
    their breeding more rapidly and being kept in greater numbers. We have
    seen that carnivorous animals are more fertile under confinement than
    most other mammals. The reverse holds good with carnivorous birds. It
    is said[350] that as many as eighteen species have been used in Europe
    for hawking, and several others in Persia and India;[351] they have
    been kept in their native country in the finest condition, and have
    been flown during six, eight, or nine years;[352] yet there is no
    record of their having ever produced young. As these birds were
    formerly caught whilst young, at great expense, being imported from
    Iceland, Norway, and Sweden, there can {154} be little doubt that, if
    possible, they would have been propagated. In the Jardin des Plantes,
    no bird of prey has been known to couple.[353] No hawk, vulture, or owl
    has ever produced fertile eggs in the Zoological Gardens, or in the old
    Surrey Gardens, with the exception, in the former place on one
    occasion, of a condor and a kite (_Milvus niger_). Yet several species,
    namely, the _Aquila fusca_, _Haliætus leucocephalus_, _Falco
    tinnunculus_, _F. subbuteo_, and _Buteo vulgaris_, have been seen to
    couple in the Zoological Gardens. Mr. Morris[354] mentions as a unique
    fact that a kestrel (_Falco tinnunculus_) bred in an aviary. The one
    kind of owl which has been known to couple in the Zoological Gardens
    was the Eagle Owl (_Bubo maximus_); and this species shows a special
    inclination to breed in captivity; for a pair at Arundel Castle, kept
    more nearly in a state of nature "than ever fell to the lot of an
    animal deprived of its liberty,"[355] actually reared their young. Mr.
    Gurney has given another instance of this same owl breeding in
    confinement; and he records the case of a second species of owl, the
    _Strix passerina_, breeding in captivity.[356]

    Of the smaller graminivorous birds, many kinds have been kept tame in
    their native countries, and have lived long; yet, as the highest
    authority on cage-birds[357] remarks, their propagation is "uncommonly
    difficult." The canary-bird shows that there is no inherent difficulty
    in these birds breeding freely in confinement; and Audubon says[358]
    that the _Fringilla_ (_Spiza_) _ciris_ of North America breeds as
    perfectly as the canary. The difficulty with the many finches which
    have been kept in confinement is all the more remarkable as more than a
    dozen species could be named which have yielded hybrids with the
    canary; but hardly any of these, with the exception of the siskin
    (_Fringilla spinus_), have reproduced their own kind. Even the
    bullfinch (_Loxia pyrrhula_) has bred as frequently with the canary,
    though belonging to a distinct genus, as with its own species.[359]
    With respect to the skylark (_Alauda arvensis_), I have heard of birds
    living for seven years in an aviary, which never produced young; and a
    great London bird-fancier assured me that he had never known an
    instance of their breeding; nevertheless one case has been
    recorded.[360] In the nine-year Report from the Zoological Society,
    twenty-four incessorial species are enumerated which had not bred, and
    of these only four were known to have coupled.

    Parrots are singularly long-lived birds; and Humboldt mentions the
    curious fact of a parrot in South America, which spoke the language of
    {155} an extinct Indian tribe, so that this bird preserved the sole
    relic of a lost language. Even in this country there is reason to
    believe[361] that parrots have lived to the age of nearly one hundred
    years; yet, though many have been kept in Europe, they breed so rarely
    that the event has been thought worth recording in the gravest
    publications.[362] According to Bechstein[363] the African _Psittacus
    erithacus_ breeds oftener than any other species: the _P. macoa_
    occasionally lays fertile eggs, but rarely succeeds in hatching them;
    this bird, however, has the instinct of incubation sometimes so
    strongly developed, that it will hatch the eggs of fowls or pigeons. In
    the Zoological Gardens and in the old Surrey Gardens some few species
    have coupled, but, with the exception of three species of parrakeets,
    none have bred. It is a much more remarkable fact that in Guiana
    parrots of two kinds, as I am informed by Sir E. Schomburgk, are often
    taken from the nests by the Indians and reared in large numbers; they
    are so tame that they fly freely about the houses, and come when called
    to be fed, like pigeons; yet he has never heard of a single instance of
    their breeding.[364] In Jamaica, a resident naturalist, Mr. R.
    Hill,[365] says, "no birds more readily submit to human dependence than
    the parrot-tribe, but no instance of a parrot breeding in this tame
    life has been known yet." Mr. Hill specifies a number of other native
    birds kept tame in the West Indies, which never breed in this state.

    The great pigeon family offers a striking contrast with parrots: in the
    nine-year Report thirteen species are recorded as having bred, and,
    what is more noticeable, only two were seen to couple without any
    result. Since the above date every annual Report gives many cases of
    various pigeons breeding. The two magnificent crowned pigeons (_Goura
    coronata_ and _Victoriæ_) produced hybrids; nevertheless, of the former
    species more than a dozen birds were kept, as I am informed by Mr.
    Crawfurd, in a park at Penang, under a perfectly well-adapted climate,
    but never once bred. The _Columba migratoria_ in its native country,
    North America, invariably lays two eggs, but in Lord Derby's menagerie
    never more than one. The same fact has been observed with the _C.
    leucocephala_.[366]

    Gallinaceous birds of many genera likewise show an eminent capacity for
    breeding under captivity. This is particularly the case with pheasants;
    yet our English species seldom lays more than ten eggs in confinement;
    whilst from eighteen to twenty is the usual number in the wild
    state.[367] With the Gallinaceæ, as with all other orders, there are
    marked and {156} inexplicable exceptions in regard to the fertility of
    certain species and genera under confinement. Although many trials have
    been made with the common partridge, it has rarely bred, even when
    reared in large aviaries; and the hen will never hatch her own
    eggs.[368] The American tribe of Guans or Cracidæ are tamed with
    remarkable ease, but are very shy breeders in this country;[369] but
    with care various species were formerly made to breed rather freely in
    Holland.[370] Birds of this tribe are often kept in a perfectly tamed
    condition in their native country by the Indians, but they never
    breed.[371] It might have been expected that grouse from their habits
    of life would not have bred in captivity, more especially as they are
    said soon to languish and die.[372] But many cases are recorded of
    their breeding: the capercailzie (_Tetrao urogallus_) has bred in the
    Zoological Gardens; it breeds without much difficulty when confined in
    Norway, and in Russia five successive generations have been reared:
    _Tetrao tetrix_ has likewise bred in Norway; _T. Scoticus_ in Ireland;
    _T. umbellus_ at Lord Derby's; and _T. cupido_ in North America.

    It is scarcely possible to imagine a greater change in habits than that
    which the members of the ostrich family must suffer, when cooped up in
    small enclosures under a temperate climate, after freely roaming over
    desert and tropical plains or entangled forests. Yet almost all the
    kinds, even the mooruk (_Casuarius  Bennettii_) from New Ireland, has
    frequently produced young in the various European menageries. The
    African ostrich, though perfectly healthy and living long in the South
    of France, never lays more than from twelve to fifteen eggs, though in
    its native country it lays from twenty-five to thirty.[373] Here we
    have another instance of fertility impaired, but not lost, under
    confinement, as with the flying squirrel, the hen-pheasant, and two
    species of American pigeons.

    Most Waders can be tamed, as the Rev. E. S. Dixon informs me, with
    remarkable facility; but several of them are short-lived under
    confinement, so that their sterility in this state is not surprising.
    The cranes breed more readily than other genera: _Grus montigresia_ has
    bred several times in Paris and in the Zoological Gardens, as has _G.
    cinerea_ at the latter place, and _G. antigone_ at Calcutta. Of other
    members of this great order, _Tetrapteryx paradisea_ has bred at
    Knowsley, a Porphyrio in Sicily, and the _Gallinula chloropus_ in the
    Zoological Gardens. On the other hand, several {157} birds belonging to
    this order will not breed in their native country, Jamaica; and the
    Psophia, though often kept by the Indians of Guiana about their houses,
    "is seldom or never known to breed."[374]

    No birds breed with such complete facility under confinement as the
    members of the great Duck family; yet, considering their aquatic and
    wandering habits, and the nature of their food, this could not have
    been anticipated. Even some time ago above two dozen species had bred
    in the Zoological Gardens; and M. Selys-Longchamps has recorded the
    production of hybrids from forty-four different members of the family;
    and to these Professor Newton has added a few more cases.[375] "There
    is not," says Mr. Dixon,[376] "in the wide world, a goose which is not
    in the strict sense of the word domesticable;" that is, capable of
    breeding under confinement; but this statement is probably too bold.
    The capacity to breed sometimes varies in individuals of the same
    species; thus Audubon[377] kept for more than eight years some wild
    geese (_Anser Canadensis_), but they would not mate; whilst other
    individuals of the same species produced young during the second year.
    I know of but one instance in the whole family of a species which
    absolutely refuses to breed in captivity, namely, the _Dendrocygna
    viduata_, although, according to Sir R. Schomburgk,[378] it is easily
    tamed, and is frequently kept by the Indians of Guiana. Lastly, with
    respect to Gulls, though many have been kept in the Zoological Gardens
    and in the old Surrey Gardens, no instance was known before the year
    1848 of their coupling or breeding; but since that period the herring
    gull (_Larus argentatus_) has bred many times in the Zoological Gardens
    and at Knowsley.

    There is reason to believe that insects are affected by confinement
    like the higher animals. It is well known that the Sphingidæ rarely
    breed when thus treated. An entomologist[379] in Paris kept twenty-five
    specimens of _Saturnia pyri_, but did not succeed in getting a single
    fertile egg. A number of females of _Orthosia munda_ and of _Mamestra
    suasa_ reared in confinement were unattractive to the males.[380] Mr.
    Newport kept nearly a hundred individuals of two species of Vanessa,
    but not one paired; this, however, might have been due to their habit
    of coupling on the wing.[381] Mr. Atkinson could never succeed in India
    in making the Tarroo silk-moth breed in confinement.[382] It appears
    that a number of moths, especially the Sphingidæ, when hatched in the
    autumn out of their proper season, {158} are completely barren; but
    this latter case is still involved in some obscurity.[383]

Independently of the fact of many animals under confinement not coupling,
or, if they couple, not producing young, there is evidence of another kind,
that their sexual functions are thus disturbed. For many cases have been
recorded of the loss by male birds when confined of their characteristic
plumage. Thus the common linnet (_Linota cannabina_) when caged does not
acquire the fine crimson colour on its breast, and one of the buntings
(_Emberiza passerina_) loses the black on its head. A Pyrrhula and an
Oriolus have been observed to assume the quiet plumage of the hen-bird; and
the _Falco albidus_ returned to the dress of an earlier age.[384] Mr.
Thomson, the superintendent of the Knowsley menagerie, informed me that he
had often observed analogous facts. The horns of a male deer (_Cervus
Canadensis_) during the voyage from America were badly developed; but
subsequently in Paris perfect horns were produced.

When conception takes place under confinement, the young are often born
dead, or die soon, or are ill-formed. This frequently occurs in the
Zoological Gardens, and, according to Rengger, with native animals confined
in Paraguay. The mother's milk often fails. We may also attribute to the
disturbance of the sexual functions the frequent occurrence of that
monstrous instinct which leads the mother to devour her own offspring,--a
mysterious case of perversion, as it at first appears.

Sufficient evidence has now been advanced to prove that animals when first
confined are eminently liable to suffer in their reproductive systems. We
feel at first naturally inclined to attribute the result to loss of health,
or at least to loss of vigour; but this view can hardly be admitted when we
reflect how healthy, long-lived, and vigorous many animals are under {159}
captivity, such as parrots, and hawks when used for hawking, chetahs when
used for hunting, and elephants. The reproductive organs themselves are not
diseased; and the diseases, from which animals in menageries usually
perish, are not those which in any way affect their fertility. No domestic
animal is more subject too disease than the sheep, yet it is remarkably
prolific. The failure of animals to breed under confinement has been
sometimes attributed exclusively to a failure in their sexual instincts:
this may occasionally come into play, but there is no obvious reason why
this instinct should be especially liable to be affected with perfectly
tamed animals, except indeed indirectly through the reproductive system
itself being disturbed. Moreover, numerous cases have been given of various
animals which couple freely under confinement, but never conceive; or, if
they conceive and produce young, these are fewer in number than is natural
to the species. In the vegetable kingdom instinct of course can play no
part; and we shall presently see that plants when removed from their
natural conditions are affected in nearly the same manner as animals.
Change of climate cannot be the cause of the loss of fertility, for, whilst
many animals imported into Europe from extremely different climates breed
freely, many others when confined in their native land are completely
sterile. Change of food cannot be the chief cause; for ostriches, ducks,
and many other animals, which must have undergone a great change in this
respect, breed freely. Carnivorous birds when confined are extremely
sterile; whilst most carnivorous mammals, except plantigrades, are
moderately fertile. Nor can the amount of food be the cause; for a
sufficient supply will certainly be given to valuable animals; and there is
no reason to suppose that much more food would be given to them, than to
our choice domestic productions which retain their full fertility. Lastly,
we may infer from the case of the elephant, chetah, various hawks, and of
many animals which are allowed to lead an almost free life in their native
land, that want of exercise is not the sole cause.

It would appear that any change in the habits of life, whatever these
habits may be, if great enough, tends to affect in an inexplicable manner
the powers of reproduction. The result {160} depends more on the
constitution of the species than on the nature of the change; for certain
whole groups are affected more than others; but exceptions always occur,
for some species in the most fertile groups refuse to breed, and some in
the most sterile groups breed freely. Those animals which usually breed
freely under confinement, rarely breed, as I was assured, in the Zoological
Gardens, within a year or two after their first importation. When an animal
which is generally sterile under confinement happens to breed, the young
apparently do not inherit this power; for had this been the case, various
quadrupeds and birds, which are valuable for exhibition, would have become
common. Dr. Broca even affirms[385] that many animals in the Jardin des
Plantes, after having produced young for three or four successive
generations, become sterile; but this may be the result of too close
interbreeding. It is a remarkable circumstance that many mammals and birds
have produced hybrids under confinement quite as readily as, or even more
readily than, they have procreated their own kind. Of this fact many
instances have been given;[386] and we are thus reminded of those plants
which when cultivated refuse to be fertilised by their own pollen, but can
easily be fertilised by that of a distinct species. Finally, we must
conclude, limited as the conclusion is, that changed conditions of life
have an especial power of acting injuriously on the reproductive system.
The whole case is quite peculiar, for these organs, though not diseased,
are thus rendered incapable of performing their proper functions, or
perform them imperfectly.

    _Sterility of Domesticated Animals from changed conditions._--With
    respect to domesticated animals, as their domestication mainly depends
    on the accident of their breeding freely under captivity, we ought not
    to expect that their reproductive system would be affected by any
    moderate degree of change. Those orders of quadrupeds and birds, of
    which the wild species breed most readily in our menageries, have
    afforded us the greatest number of domesticated productions. Savages in
    most parts of the world are fond of taming animals;[387] and if any of
    these regularly produced {161} young, and were at the same time useful,
    they would be at once domesticated. If, when their masters migrated
    into other countries, they were in addition found capable of
    withstanding various climates, they would be still more valuable; and
    it appears that the animals which breed readily in captivity can
    generally withstand different climates. Some few domesticated animals,
    such as the reindeer and camel, offer an exception to this rule. Many
    of our domesticated animals can bear with undiminished fertility the
    most unnatural conditions; for instance, rabbits, guinea-pigs, and
    ferrets breed in miserably confined hutches. Few European dogs of any
    kind withstand without degeneration the climate of India; but as long
    as they survive, they retain, as I hear from Mr. Falconer, their
    fertility; so it is, according to Dr. Daniell, with English dogs taken
    to Sierra Leone. The fowl, a native of the hot jungles of India,
    becomes more fertile than its parent-stock in every quarter of the
    world, until we advance as far north as Greenland and Northern Siberia,
    where this bird will not breed. Both fowls and pigeons, which I
    received during the autumn direct from Sierra Leone, were at once ready
    to couple.[388] I have, also, seen pigeons breeding as freely as the
    common kinds within a year after their importation from the Upper Nile.
    The guinea-fowl, an aboriginal of the hot and dry deserts of Africa,
    whilst living under our damp and cool climate, produces a large supply
    of eggs.

    Nevertheless, our domesticated animals under new conditions
    occasionally show signs of lessened fertility. Roulin asserts that in
    the hot valleys of the equatorial Cordillera sheep are not fully
    fecund;[389] and according to Lord Somerville,[390] the merino-sheep
    which he imported from Spain were not at first perfectly fertile. It is
    said[391] that mares brought up on dry food in the stable, and turned
    out to grass, do not at first breed. The peahen, as we have seen, is
    said not to lay so many eggs in England as in India. It was long before
    the canary-bird was fully fertile, and even now first-rate breeding
    birds are not common.[392] In the hot and dry province of Delhi, the
    eggs of the turkey, as I hear from Dr. Falconer, though placed under a
    hen, are extremely liable to fail. According to Roulin, geese taken
    within a recent period to the lofty plateau of Bogota, at first laid
    seldom, and then only a few eggs; of these scarcely a fourth were
    hatched, and half the young birds died: in the second generation they
    were more fertile; and when Roulin wrote they were becoming as {162}
    fertile as our geese in Europe. In the Philippine Archipelago the
    goose, it is asserted, will not breed or even lay eggs.[393] A more
    curious case is that of the fowl, which, according to Roulin, when
    first introduced would not breed at Cusco in Bolivia, but subsequently
    became quite fertile; and the English Game fowl, lately introduced, had
    not as yet arrived a its full fertility, for to raise two or three
    chickens from a nest of eggs was thought fortunate. In Europe close
    confinement has a marked effect on the fertility of the fowl: it has
    been found in France that with fowls allowed considerable freedom only
    twenty per cent. of the eggs failed; when allowed less freedom forty
    per cent. failed; and in close confinement sixty out of the hundred
    were not hatched.[394] So we see that unnatural and changed conditions
    of life produce some effect on the fertility of our most thoroughly
    domesticated animals, in the same manner, though in a far less degree,
    as with captive wild animals.

    It is by no means rare to find certain males and females which will not
    breed together, though both are known to be perfectly fertile with
    other males and females. We have no reason to suppose that this is
    caused by these animals having been subjected to any change in their
    habits of life; therefore such cases are hardly related to our present
    subject. The cause apparently lies in an innate sexual incompatibility
    of the pair which are matched. Several instances have been communicated
    to me by Mr. W. C. Spooner (well known for his essay on
    Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and othe
    breeders, and especially by Mr. Waring of Chelsfield, in relation to
    horses, cattle, pigs, foxhounds, other dogs, and pigeons.[395] In these
    cases, females, which either previously or subsequently were proved to
    be fertile, failed to breed with certain males, with whom it was
    particularly desired to match them. A change in the constitution of the
    female may sometimes have occurred before she was put to the second
    male; but in other cases this explanation is hardly tenable, for a
    female, known not to be barren, has been unsuccessfully paired seven or
    eight times with the same male likewise known to be perfectly fertile.
    With cart-mares, which sometimes will not breed with stallions of pure
    blood, but subsequently have bred with cart-stallions, Mr. Spooner is
    inclined to attribute the failure to the lesser sexual power of the
    race-horse. But I have heard from the greatest breeder of race-horses
    at the present day, through Mr. Waring, that "it frequently occurs with
    a mare to be put several times during one or two seasons to a
    particular stallion of acknowledged power, and yet prove barren; the
    mare afterwards breeding at once with some other horse." These facts
    are worth recording, as they show, like so many previous facts, on what
    slight constitutional differences the fertility of an animal often
    depends.

{163}

_Sterility of Plants from changed Conditions of Life, and from other
causes._

In the vegetable kingdom cases of sterility frequently occur, analogous
with those previously given in the animal kingdom. But the subject is
obscured by several circumstances, presently to be discussed, namely, the
contabescence of the anthers, as Gärtner has named a certain
affection--monstrosities--doubleness of the flower--much-enlarged
fruit--and long-continued or excessive propagation by buds.

    It is notorious that many plants in our gardens and hot-houses, though
    preserved in the most perfect health, rarely or never produce seed. I
    do not allude to plants which run to leaves, from being kept too damp,
    or too warm, or too much manured; for these do not produce the
    reproductive individual or flower, and the case may be wholly
    different. Nor do I allude to fruit not ripening from want of heat, or
    rotting from too much moisture. But many exotic plants, with their
    ovules and pollen appearing perfectly sound, will not set any seed. The
    sterility in many cases, as I know from my own observation, is simply
    due to the absence of the proper insects for carrying the pollen to the
    stigma. But after excluding the several cases just specified, there are
    many plants in which the reproductive system has been seriously
    affected by the altered conditions of life to which they have been
    subjected.

    It would be tedious to enter on many details. Linnæus long ago
    observed[396] that Alpine plants, although naturally laded with seed,
    produce either few or none when cultivated in gardens. But exceptions
    often occur: the _Draba sylvestris_, one of our most thoroughly Alpine
    plants, multiplies itself by seed in Mr. H. C. Watson's garden, near
    London; and Kerner, who has particularly attended to the cultivation of
    Alpine plants, found that various kinds, when cultivated, spontaneously
    sowed themselves.[397] Many plants which naturally grow in peat-earth
    are entirely sterile in our gardens. I have noticed the same fact with
    several liliaceous plants, which nevertheless grew vigorously.

    Too much manure renders some kinds utterly sterile, as I have myself
    observed. The tendency to sterility from this cause runs in families;
    thus, according to Gärtner,[398] it is hardly possible to give too much
    manure to most Gramineæ, Cruciferæ, and Leguminosæ, whilst succulent
    and bulbous-rooted plants are easily affected. Extreme poverty of soil
    is less {164} apt to induce sterility; but dwarfed plants of _Trifolium
    minus_ and _repens_, growing on a lawn often mown and never manured,
    did not produce any seed. The temperature of the soil, and the season
    at which plants are watered, often have a marked effect on their
    fertility, as was observed by Kölreuter in the case of Mirabilis.[399]
    Mr. Scott in the Botanic Gardens of Edinburgh observed that _Oncidium
    divaricatum_ would not set seed when grown in a basket in which it
    throve, but was capable of fertilisation in a pot where it was a little
    damper. _Pelargonium fulgidum_, for many years after its introduction,
    seeded freely; it then became sterile; now it is fertile[400] if kept
    in a dry stove during the winter. Other varieties of pelargonium are
    sterile and others fertile without our being able to assign any cause.
    Very slight changes in the position of a plant, whether planted on a
    bank or at its base, sometimes make all the difference in its producing
    seed. Temperature apparently has a much more powerful influence on the
    fertility of plants than on that of animals. Nevertheless it is
    wonderful what changes some few plants will withstand with undiminished
    fertility: thus the _Zephyranthes candida_, a native of the moderately
    warm banks of the Plata, sows itself in the hot dry country near Lima,
    and in Yorkshire resists the severest frosts, and I have seen seeds
    gathered from pods which had been covered with snow during three
    weeks.[401] _Berberis Wallichii_, from the hot Khasia range in India,
    is uninjured by our sharpest frosts, and ripens its fruit under our
    cool summers. Nevertheless I presume we must attribute to change of
    climate the sterility of many foreign plants; thus the Persian and
    Chinese lilacs (_Syringa Persica_ and _Chinensis_), though perfectly
    hardly, never here produce a seed; the common lilac (_S. vulgaris_)
    seeds with us moderately well, but in parts of Germany the capsules
    never contain seed.[402]

    Some of the cases, given in the last chapter, of self-impotent plants,
    which are fertile both on the male and female side when united with
    distinct individuals or species, might have been here introduced; for
    as this peculiar form of sterility generally occurs with exotic plants
    or with endemic plants cultivated in pots, and as it disappeared in the
    _Passiflora alata_ when grafted, we may conclude that in these cases it
    is the result of the treatment to which the plants or their parents
    have been exposed.

    The liability of plants to be affected in their fertility by slightly
    changed conditions is the more remarkable, as the pollen when once in
    process of formation is not easily injured; a plant may be
    transplanted, or a branch with flower-buds be cut off and placed in
    water, and the pollen will be matured. Pollen, also, when once mature,
    may be kept for weeks or even months.[403] The female organs are more
    sensitive, for Gärtner[404] found that dicotyledonous plants, when
    carefully removed so that they did not in the least flag, could seldom
    be fertilised; this occurred even with potted {165} plants if the roots
    had grown out of the hole at the bottom. In some few cases, however, as
    with Digitalis, transplantation did not prevent fertilisation; and
    according to the testimony of Mawz, _Brassica rapa_, when pulled up by
    its roots and placed in water, ripened its seed. Flower-stems of
    several monocotyledonous plants when cut off and placed in water
    likewise produce seed. But in these cases I presume that the flowers
    had been already fertilised, for Herbert[405] found with the Crocus
    that the plants might be removed or mutilated after the act of
    fertilisation, and would still perfect their seeds; but that, if
    transplanted before being fertilised, the application of pollen was
    powerless.

    Plants which have been long cultivated can generally endure with
    undiminished fertility various and great changes; but not in most cases
    so great a change of climate as domesticated animals. It is remarkable
    that many plants under these circumstances are so much affected that
    the proportions and the nature of their chemical ingredients are
    modified, yet their fertility is unimpaired. Thus, as Dr. Falconer
    informs me, there is a great difference in the character of the fibre
    in hemp, in the quantity of oil in the seed of the Linum, in the
    proportion of narcotin to morphine in the poppy, in gluten to starch in
    wheat, when these plants are cultivated on the plains and on the
    mountains of India; nevertheless, they all remain fully fertile.

    _Contabescence._--Gärtner has designated by this term a peculiar
    condition of the anthers in certain plants, in which they are
    shrivelled, or become brown and tough, and contain no good pollen. When
    in this state they exactly resemble the anthers of the most sterile
    hybrids. Gärtner,[406] in his discussion on this subject, has shown
    that plants of many orders are occasionally thus affected; but the
    Caryophyllaceæ and Liliaceæ suffer most, and to these orders, I think,
    the Ericaceæ may be added. Contabescence varies in degree, but on the
    same plant all the flowers are generally affected to nearly the same
    extent. The anthers are affected at a very early period in the
    flower-bud, and remain in the same state (with one recorded exception)
    during the life of the plant. The affection cannot be cured by any
    change of treatment, and is propagated by layers, cuttings, &c., and
    perhaps even by seed. In contabescent plants the female organs are
    seldom affected, or merely become precocious in their development. The
    cause of this affection is doubtful, and is different in different
    cases. Until I read Gärtner's discussion I attributed it, as apparently
    did Herbert, to the unnatural treatment of the plants; but its
    permanence under changed conditions, and the female organs not being
    affected, seem incompatible with this view. The fact of several endemic
    plants becoming contabescent in our gardens seems, at first sight,
    equally incompatible with this view; but Kölreuter believes that this
    is the result of their transplantation. The contabescent plants of
    Dianthus and Verbascum, found wild by Wiegmann, grew on a dry and
    sterile bank. The fact that exotic {166} plants are eminently liable to
    this affection also seems to show that it is in some manner caused by
    their unnatural treatment. In some instances, as with Silene, Gärtner's
    view seems the most probable, namely, that it is caused by an inherent
    tendency in the species to become dioecious. I can add another cause,
    namely, the illegitimate unions of reciprocally dimorphic or trimorphic
    plants, for I have observed seedlings of three species of Primula and
    of _Lythrum salicaria_, which had been raised from plants
    illegitimately fertilised by their own-form pollen, with some or all
    their anthers in a contabescent state. There is perhaps an additional
    cause, namely, self-fertilisation; for many plants of Dianthus and
    Lobelia, which had been raised from self-fertilised seeds, had their
    anthers in this state; but these instances are not conclusive, as both
    genera are liable from other causes to this affection.

    Cases of an opposite nature likewise occur, namely, plants with the
    female organs struck with sterility, whilst the male organs remain
    perfect. _Dianthus Japonicus_, a Passiflora, and Nicotiana, have been
    described by Gärtner[407] as being in this unusual condition.

    _Monstrosities as a cause of Sterility._--Great deviations of
    structure, even when the reproductive organs themselves are not
    seriously affected, sometimes cause plants to become sterile. But in
    other cases plants may become monstrous to an extreme degree and yet
    retain their full fertility. Gallesio, who certainly had great
    experience,[408] often attributes sterility to this cause; but it may
    be suspected that in some of his cases sterility was the cause, and not
    the result, of the monstrous growths. The curious St. Valery apple,
    although it bears fruit, rarely produces seed. The wonderfully
    anomalous flowers of _Begonia frigida_, formerly described, though they
    appear fit for fructification, are sterile.[409] Species of Primulæ, in
    which the calyx is brightly coloured, are said[410] to be often
    sterile, though I have known them to be fertile. On the other hand,
    Verlot gives several cases of proliferous flowers which can be
    propagated by seed. This was the case with a poppy, which had become
    monopetalous by the union of its petals.[411] Another extraordinary
    poppy, with the stamens replaced by numerous small supplementary
    capsules, likewise reproduces itself by seed. This has also occurred
    with a plant of _Saxifraga geum_, in which a series of adventitious
    carpels, bearing ovules on their margins, had been developed between
    the stamens and the normal carpels.[412] Lastly, with respect to
    peloric flowers, which depart wonderfully from the natural
    structure,--those of _Linaria vulgaris_ seem generally to be more or
    less sterile, whilst those before described of _Antirrhinum majus_,
    when artificially fertilised with their own pollen, are perfectly {167}
    fertile, though sterile when left to themselves, for bees are unable to
    crawl into the narrow tubular flower. The peloric flowers of _Corydalis
    solida_, according to Godron,[413] are barren; whilst those of Gloxinia
    are well known to yield plenty of seed. In our greenhouse Pelargoniums,
    the central flower of the truss is often peloric, and Mr. Masters
    informs me that he tried in vain during several years to get seed from
    these flowers. I likewise made many vain attempts, but sometimes
    succeeded in fertilising them with pollen from a normal flower of
    another variety; and conversely I several times fertilised ordinary
    flowers with peloric pollen. Only once I succeeded in raising a plant
    from a peloric flower fertilised by pollen from a peloric flower borne
    by another variety; but the plant, it may be added, presented nothing
    particular in its structure. Hence we may conclude that no general rule
    can be laid down; but any great deviation from the normal structure,
    even when the reproductive organs themselves are not seriously
    affected, certainly often leads to sexual impotence.

    _Double Flowers._--When the stamens are converted into petals, the
    plant becomes on the male side sterile; when both stamens and pistils
    are thus changed, the plant becomes completely barren. Symmetrical
    flowers having numerous stamens and petals are the most liable to
    become double, as perhaps follows from all multiple organs being the
    most subject to variability. But flowers furnished with only a few
    stamens, and others which are asymmetrical in structure, sometimes
    become double, as we see with the double gorse or Ulex, Petunia, and
    Antirrhinum. The Compositæ bear what are called double flowers by the
    abnormal development of the corolla of their central florets.
    Doubleness is sometimes connected with prolification,[414] or the
    continued growth of the axis of the flower. Doubleness is strongly
    inherited. No one has produced, as Lindley remarks,[415] double flowers
    by promoting the perfect health of the plant. On the contrary,
    unnatural conditions of life favour their production. There is some
    reason to believe that seeds kept during many years, and seeds believed
    to be imperfectly fertilised, yield double flowers more freely than
    fresh and perfectly fertilised seed.[416] Long-continued cultivation in
    rich soil seems to be the commonest exciting cause. A double narcissus
    and a double _Anthemis nobilis_, transplanted into very poor soil, have
    been observed to become single;[417] and I have seen a completely
    double white primrose rendered permanently single by being divided and
    transplanted whilst in full flower. It has been observed by Professor
    Morren that doubleness of the flowers and variegation of the leaves are
    antagonistic states; but so many exceptions to the rule have lately
    been recorded,[418] that, though general, it cannot be looked at as
    invariable. {168} Variegation seems generally to result from a feeble
    or atrophied condition of the plant, and a large proportion of the
    seedlings raised from parents both of which are variegated usually
    perish at an early age; hence we may perhaps infer that doubleness,
    which is the antagonistic state, commonly arises from a plethoric
    condition. On the other hand, extremely poor soil sometimes, though
    rarely, appears to cause doubleness: I formerly described[419] some
    completely double, bud-like, flowers produced in large numbers by
    stunted wild plants of _Gentiana amarella_ growing on a poor chalky
    bank. I have also noticed a distinct tendency to doubleness in the
    flowers of a Ranunculus, Horse-chesnut, and Bladder-nut (_Ranunculus
    repens_, _Æsculus pavia_, and _Staphylea_), growing under very
    unfavourable conditions. Professor Lehman[420] found several wild
    plants growing near a hot spring with double flowers. With respect to
    the cause of doubleness, which arises, as we see, under widely
    different circumstances, I shall presently attempt to show that the
    most probable view is that unnatural conditions first give a tendency
    to sterility, and that then, on the principle of compensation, as the
    reproductive organs do not perform their proper functions, they either
    become developed into petals, or additional petals are formed. This
    view has lately been supported by Mr. Laxton,[421] who advances the
    case of some common peas, which, after long-continued heavy rain,
    flowered a second time, and produced double flowers.

    _Seedless Fruit._--Many of our most valuable fruits, although
    consisting in a homological sense of widely different organs, are
    either quite sterile, or produce extremely few seeds. This is
    notoriously the case with our best pears, grapes, and figs, with the
    pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms, and
    some members of the orange-tribe. Poorer varieties of these same fruits
    either habitually or occasionally yield seed.[422] Most horticulturists
    look at the great size and anomalous development of the fruit as the
    cause, and sterility as the result; but the opposite view, as we shall
    presently see, is more probable.

    _Sterility from the excessive development of the Organs of Growth or
    Vegetation._--Plants which from any cause grow too luxuriantly, and
    produce leaves, stems, runners, suckers, tubers, bulbs, &c., in excess,
    sometimes do not flower, or if they flower do not yield seed. To make
    European vegetables under the hot climate of India yield seed, it is
    necessary to check their growth; and, when one-third grown, they are
    taken up, and their stems and {169} tap-roots are cut or
    mutilated.[423] So it is with hybrids; for instance, Prof. Lecoq[424]
    had three plants of Mirabilis, which, though they grew luxuriantly and
    flowered, were quite sterile; but after beating one with a stick until
    a few branches alone were left, these at once yielded good seed. The
    sugar-cane, which grows vigorously and produces a large supply of
    succulent stems, never, according to various observers, bears seed in
    the West Indies, Malaga, India, Cochin China, or the Malay
    Archipelago.[425] Plants which produce a large number of tubers are apt
    to be sterile, as occurs, to a certain extent, with the common potato;
    and Mr. Fortune informs me that the sweet potato (_Convolvulus
    batatas_) in China never, as far as he has seen, yields seed. Dr. Royle
    remarks[426] that in India the _Agave vivipara_, when grown in rich
    soil, invariably produces bulbs, but no seeds; whilst a poor soil and
    dry climate leads to an opposite result. In China, according to Mr.
    Fortune, an extraordinary number of little bulbs are developed in the
    axils of the leaves of the yam, and this plant does not bear seed.
    Whether in these cases, as in those of double flowers and seedless
    fruit, sexual sterility from changed conditions of life is the primary
    cause which leads to the excessive development of the organs of
    vegetation, is doubtful; though some evidence might be advanced in
    favour of this view. It is perhaps a more probable view that plants
    which propagate themselves largely by one method, namely by buds, have
    not sufficient vital power or organised matter for the other method of
    sexual generation.

    Several distinguished botanists and good practical judges believe that
    long-continued propagation by cuttings, runners, tubers, bulbs, &c.,
    independently of any excessive development of these parts, is the cause
    of many plants failing to produce flowers and of others failing to
    produce fertile flowers,--it is as if they had lost the habit of sexual
    generation.[427] That many plants when thus propagated are sterile
    there can be no doubt, but whether the long continuance of this form of
    propagation is the actual cause of their sterility, I will not venture,
    from the want of sufficient evidence, to express an opinion.

    That plants may be propagated for long periods by buds, without the aid
    of sexual generation, we may safely infer from this being the case with
    many plants which must have long survived in a state of nature. As I
    have had occasion before to allude to this subject, I will here give
    such cases as I have collected. Many alpine plants ascend mountains
    beyond the height at which they can produce seed.[428] Certain species
    of {170} Poa and Festuca, when growing on mountain-pastures, propagate
    themselves, as I hear from Mr. Bentham, almost exclusively by bulblets.
    Kalm gives a more curious instance[429] of several American trees,
    which grow so plentifully in marshes or in thick woods, that they are
    certainly well adapted for these stations, yet scarcely ever produce
    seeds; but when accidentally growing on the outside of the marsh or
    wood, are loaded with seed. The common ivy is found in Northern Sweden
    and Russia, but flowers and fruits only in the southern provinces. The
    _Acorus calamus_ extends over a large portion of the globe, but so
    rarely perfects its fruit that this has been seen but by few
    botanists.[430] The _Hypericum calycinum_, which propagates itself so
    freely in our shrubberies by rhizomas and is naturalised in Ireland,
    blossoms profusely, but sets no seed; nor did it set any when
    fertilised in my garden by pollen from plants growing at a distance.
    The _Lysimachia nummularia_, which is furnished with long runners, so
    seldom produces seed-capsules, that Prof. Decaisne,[431] who has
    especially attended to this plant, has never seen it in fruit. The
    _Carex rigida_ often fails to perfect its seed in Scotland, Lapland,
    Greenland, Germany, and New Hampshire in the United States.[432] The
    periwinkle (_Vinca minor_), which spreads largely by runners, is said
    scarcely ever to produce fruit in England;[433] but this plant requires
    insect-aid for its fertilisation, and the proper insects may be absent
    or rare. The _Jussiæa grandiflora_ has become naturalised in Southern
    France, and has spread by its rhizomas so extensively as to impede the
    navigation of the waters, but never produces fertile seed.[434] The
    horse-radish (_Cochlearia armoracia_) spreads pertinaciously and is
    naturalised in various parts of Europe; though it bears flowers, these
    rarely produce capsules: Professor Caspary also informs me that he has
    watched this plant since 1851, but has never seen its fruit; nor is
    this surprising, as he finds scarcely a grain of good pollen. The
    common little _Ranunculus ficaria_ rarely, and some say never, bears
    seed in England, France, or Switzerland; but in 1863 I observed seeds
    on several plants growing near my house. According to M. Chatin, there
    are two forms of this Ranunculus; and it is the bulbiferous form which
    does not yield seed from producing no pollen.[435] Other cases {171}
    analogous with the foregoing could be given; for instance, some kinds
    of mosses and lichens have never been seen to fructify in France.

    Some of these endemic and naturalised plants are probably rendered
    sterile from excessive multiplication by buds, and their consequent
    incapacity to produce and nourish seed. But the sterility of others
    more probably depends on the peculiar conditions under which they live,
    as in the case of the ivy in the northern parts of Europe, and of the
    trees in the swamps of the United States; yet these plants must be in
    some respects eminently well adapted for the stations which they
    occupy, for they hold their places against a host of competitors.

Finally, when we reflect on the sterility which accompanies the doubling of
flowers,--the excessive development of fruit,--and a great increase in the
organs of vegetation, we must bear in mind that the whole effect has seldom
been caused at once. An incipient tendency is observed, and continued
selection completes the work, as is known to be the case with our double
flowers and best fruits. The view which seems the most probable, and which
connects together all the foregoing facts and brings them within our
present subject, is, that changed and unnatural conditions of life first
give a tendency to sterility; and in consequence of this, the organs of
reproduction being no longer able fully to perform their proper functions,
a supply of organised matter, not required for the development of the seed,
flows either into these same organs and renders them foliaceous, or into
the fruit, stems, tubers, &c., increasing their size and succulency. But I
am far from wishing to deny that there exists, independently of any
incipient sterility, an antagonism between the two forms of reproduction,
namely, by seed and by buds, when either is carried to an extreme degree.
That incipient sterility plays an important part in the doubling of
flowers, and in the other cases just specified, I infer chiefly from the
following facts. When fertility is lost from a wholly different cause,
namely, from hybridism, there is a strong tendency, as Gärtner[436]
affirms, for flowers to become double, and this tendency is inherited.
Moreover it is notorious that with hybrids the male organs become sterile
before the female organs, and with double flowers the stamens first become
{172} foliaceous. This latter fact is well shown by the male flowers of
dioecious plants, which, according to Gallesio,[437] first become double.
Again, Gärtner[438] often insists that the flowers of even utterly sterile
hybrids, which do not produce any seed, generally yield perfect capsules or
fruit,--a fact which has likewise been repeatedly observed by Naudin with
the Cucurbitaceæ; so that the production of fruit by plants rendered
sterile through any other and distinct cause is intelligible. Kölreuter has
also expressed his unbounded astonishment at the size and development of
the tubers in certain hybrids; and all experimentalists[439] have remarked
on the strong tendency in hybrids to increase by roots, runners, and
suckers. Seeing that hybrid plants, which from their nature are more or
less sterile, thus tend to produce double flowers; that they have the parts
including the seed, that is the fruit, perfectly developed, even when
containing no seed; that they sometimes yield gigantic roots; that they
almost invariably tend to increase largely by suckers and other such
means;--seeing this, and knowing, from the many facts given in the earlier
parts of this chapter, that almost all organic beings when exposed to
unnatural conditions tend to become more or less sterile, it seems much the
most probable view that with cultivated plants sterility is the exciting
cause, and double flowers, rich seedless fruit, and in some cases
largely-developed organs of vegetation, &c., are the indirect
results--these results having been in most cases largely increased through
continued selection by man.

       *       *       *       *       *


{173}

CHAPTER XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

    ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON
    FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED
    CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON
    THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND
    VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON
    HYBRIDISM BY THE ILLEGITIMATE PROGENY OF DIMORPHIC AND TRIMORPHIC
    PLANTS--STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE
    REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS
    WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS
    BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND
    CROSSED VARIETIES--CONCLUSION.

It was shown in the fifteenth chapter that when individuals of the same
variety, or even of a distinct variety, are allowed freely to intercross,
uniformity of character is ultimately acquired. Some few characters,
however, are incapable of fusion, but these are unimportant, as they are
almost always of a semi-monstrous nature, and have suddenly appeared.
Hence, to preserve our domesticated breeds true, or to improve them by
methodical selection, it is obviously necessary that they should be kept
separate. Nevertheless, through unconscious selection, a whole body of
individuals may be slowly modified, as we shall see in a future chapter,
without separating them into distinct lots. Domestic races have often been
intentionally modified by one or two crosses, made with some allied race,
and occasionally even by repeated crosses with very distinct races; but in
almost all such cases, long-continued and careful selection has been
absolutely necessary, owing to the excessive variability of the crossed
offspring, due to the principle of reversion. In a few instances, however,
mongrels have retained a uniform character from their first production.

When two varieties are allowed to cross freely, and one is {174} much more
numerous than the other, the former will ultimately absorb the latter.
Should both varieties exist in nearly equal numbers, it is probable that a
considerable period would elapse before the acquirement of a uniform
character; and the character ultimately acquired would largely depend on
prepotency of transmission, and on the conditions of life; for the nature
of these conditions would generally favour one variety more than another,
so that a kind of natural selection would come into play. Unless the
crossed offspring were slaughtered by man without the least discrimination,
some degree of unmethodical selection would likewise come into action. From
these several considerations we may infer, that when two or more closely
allied species first came into the possession of the same tribe, their
crossing will not have influenced, in so great a degree as has often been
supposed, the character of the offspring in future times; although in some
cases it probably has had a considerable effect.

Domestication, as a general rule, increases the prolificness of animals and
plants. It eliminates the tendency to sterility which is common to species
when first taken from a state of nature and crossed. On this latter head we
have no direct evidence; but as our races of dogs, cattle, pigs, &c., are
almost certainly descended from aboriginally distinct stocks, and as these
races are now fully fertile together, or at least incomparably more fertile
than most species when crossed, we may with much confidence accept this
conclusion.

Abundant evidence has been given that crossing adds to the size, vigour,
and fertility of the offspring. This holds good when there has been no
previous close interbreeding. It applies to the individuals of the same
variety but belonging to different families, to distinct varieties,
sub-species, and partially even to species. In the latter case, though size
is often gained, fertility is lost; but the increased size, vigour, and
hardiness of many hybrids cannot be accounted for solely on the principle
of compensation from the inaction of the reproductive system. Certain
plants, both of pure and hybrid origin, though perfectly healthy, have
become self-impotent, apparently from the unnatural conditions to which
they have been exposed; and such plants, as well as others in their normal
state, can be stimulated to {175} fertility only by crossing them with
other individuals of the same species or even of a distinct species.

On the other hand, long-continued close interbreeding between the nearest
relations diminishes the constitutional vigour, size, and fertility of the
offspring; and occasionally leads to malformations, but not necessarily to
general deterioration of form or structure. This failure of fertility shows
that the evil results of interbreeding are independent of the augmentation
of morbid tendencies common to both parents, though this augmentation no
doubt is often highly injurious. Our belief that evil follows from close
interbreeding rests to a large extent on the experience of practical
breeders, especially of those who have reared many animals of the kinds
which can be propagated quickly; but it likewise rests on several carefully
recorded experiments. With some animals close interbreeding may be carried
on for a long period with impunity by the selection of the most vigorous
and healthy individuals; but sooner or later evil follows. The evil,
however, comes on so slowly and gradually that it easily escapes
observation, but can be recognised by the almost instantaneous manner in
which size, constitutional vigour, and fertility are regained when animals
that have long been interbred are crossed with a distinct family.

These two great classes of facts, namely, the good derived from crossing,
and the evil from close interbreeding, with the consideration of the
innumerable adaptations throughout nature for compelling, or favouring, or
at least permitting, the occasional union of distinct individuals, taken
together, lead to the conclusion that it is a law of nature that organic
beings shall not fertilise themselves for perpetuity. This law was first
plainly hinted at in 1799, with respect to plants, by Andrew Knight,[440]
and, not long afterwards, that sagacious observer Kölreuter, after showing
how well the Malvaceæ are adapted for {176} crossing, asks, "an id aliquid
in recessu habeat, quod hujuscemodi flores nunquam proprio suo pulvere, sed
semper eo aliarum suæ speciei impregnentur, merito quæritur? Certe natura
nil facit frustra." Although we may demur to Kölreuter's saying that nature
does nothing in vain, seeing how many organic beings retain rudimentary and
useless organs, yet undoubtedly the argument from the innumerable
contrivances, which favour the crossing of distinct individuals of the same
species, is of the greatest weight. The most important result of this law
is that it leads to uniformity of character in the individuals of the same
species. In the case of certain hermaphrodites, which probably intercross
only at long intervals of time, and with unisexual animals inhabiting
somewhat separated localities, which can only occasionally come into
contact and pair, the greater vigour and fertility of the crossed offspring
will ultimately prevail in giving uniformity of character to the
individuals of the same species. But when we go beyond the limits of the
same species, free intercrossing is barred by the law of sterility.

In searching for facts which might throw light on the cause of the good
effects from crossing, and of the evil effects from close interbreeding, we
have seen that, on the one hand, it is a widely prevalent and ancient
belief that animals and plants profit from slight changes in their
condition of life; and it would appear that the germ, in a somewhat
analogous manner, is more effectually stimulated by the male element, when
taken from a distinct individual, and therefore slightly modified in
nature, than when taken from a male having the same identical constitution.
On the other hand, numerous facts have been given, showing that when
animals are first subjected to captivity, even in their native land, and
although allowed much liberty, their reproductive functions are often
greatly impaired or quite annulled. Some groups of animals are more
affected than others, but with apparently capricious exceptions in every
group. Some animals never or rarely couple: some couple freely, but never
or rarely conceive. The secondary male characters, the maternal functions
and instincts, are occasionally affected. With plants, when first subjected
to cultivation, analogous facts have been observed. We probably owe our
double flowers, rich seedless {177} fruits, and in some cases greatly
developed tubers, &c., to incipient sterility of the above nature combined
with a copious supply of nutriment. Animals which have long been
domesticated, and plants which have long been cultivated, can generally
withstand with unimpaired fertility great changes in their conditions of
life; though both are sometimes slightly affected. With animals the
somewhat rare capacity of breeding freely under confinement has mainly
determined, together with their utility, the kinds which have been
domesticated.

We can in no case precisely say what is the cause of the diminished
fertility of an animal when first captured, or of a plant when first
cultivated; we can only infer that it is caused by a change of some kind in
the natural conditions of life. The remarkable susceptibility of the
reproductive system to such changes,--a susceptibility not common to any
other organ,--apparently has an important bearing on Variability, as we
shall see in a future chapter.

It is impossible not to be struck with the double parallelism between the
two classes of facts just alluded to. On the one hand, slight changes in
the conditions of life, and crosses between slightly modified forms or
varieties, are beneficial as far as prolificness and constitutional vigour
are concerned. On the other hand, changes in the conditions greater in
degree, or of a different nature, and crosses between forms which have been
slowly and greatly modified by natural means,--in other words, between
species,--are highly injurious, as far as the reproductive system is
concerned, and in some few instances as far as constitutional vigour is
concerned. Can this parallelism be accidental? Does it not rather indicate
some real bond of connection? As a fire goes out unless it be stirred up,
so the vital forces are always tending, according to Mr. Herbert Spencer,
to a state of equilibrium, unless disturbed and renovated through the
action of other forces.

In some few cases varieties tend to keep distinct, by breeding at different
periods, by great differences in size, or by sexual preference,--in this
latter respect more especially resembling species in a state of nature. But
the actual crossing of varieties, far from diminishing, generally adds to
the fertility of both the first union and the mongrel offspring. Whether
all {178} the most widely distinct domestic varieties are invariably quite
fertile when crossed, we do not positively know; much time and trouble
would be requisite for the necessary experiments, and many difficulties
occur, such as the descent of the various races from aboriginally distinct
species, and the doubts whether certain forms ought to be ranked as species
or varieties. Nevertheless, the wide experience of practical breeders
proves that the great majority of varieties, even if some should hereafter
prove not to be indefinitely fertile _inter se_, are far more fertile when
crossed, than the vast majority of closely allied natural species. A few
remarkable cases have, however, been given on the authority of excellent
observers, showing that with plants certain forms, which undoubtedly must
be ranked as varieties, yield fewer seeds when crossed than is natural to
the parent-species. Other varieties have had their reproductive powers so
far modified that they are either more or less fertile than are their
parents, when crossed with a distinct species.

Nevertheless, the fact remains indisputable that domesticated varieties of
animals and of plants, which differ greatly from each other in structure,
but which are certainly descended from the same aboriginal species, such as
the races of the fowl, pigeon, many vegetables, and a host of other
productions, are extremely fertile when crossed; and this seems to make a
broad and impassable barrier between domestic varieties and natural
species. But, as I will now attempt to show, the distinction is not so
great and overwhelmingly important as it at first appears.

_On the Difference in Fertility between Varieties and Species when
crossed._

This work is not the proper place for fully treating the subject of
hybridism, and I have already given in my 'Origin of Species' a moderately
full abstract. I will here merely enumerate the general conclusions which
may be relied on, and which bear on our present point.

_Firstly_, the laws governing the production of hybrids are identical, or
nearly identical, in the animal and vegetable kingdoms.

_Secondly_, the sterility of distinct species when first united, {179} and
that of their hybrid offspring, graduates, by an almost infinite number of
steps, from zero, when the ovule is never impregnated and a seed-capsule is
never formed, up to complete fertility. We can only escape the conclusion
that some species are fully fertile when crossed, by determining to
designate as varieties all the forms which are quite fertile. This high
degree of fertility is, however, rare. Nevertheless plants, which have been
exposed to unnatural conditions, sometimes become modified in so peculiar a
manner, that they are much more fertile when crossed by a distinct species
than when fertilised by their own pollen. Success in effecting a first
union between two species, and the fertility of their hybrids, depends in
an eminent degree on the conditions of life being favourable. The innate
sterility of hybrids of the same parentage and raised from the same
seed-capsule often differs much in degree.

_Thirdly_, the degree of sterility of a first cross between two species
does not always run strictly parallel with that of their hybrid offspring.
Many cases are known of species which can be crossed with ease, but yield
hybrids excessively sterile; and conversely some which can be crossed with
great difficulty, but produce fairly fertile hybrids. This is an
inexplicable fact, on the view that species have been specially endowed
with mutual sterility in order to keep them distinct.

_Fourthly_, the degree of sterility often differs greatly in two species
when reciprocally crossed; for the first will readily fertilise the second;
but the latter is incapable, after hundreds of trials, of fertilising the
former. Hybrids produced from reciprocal crosses between the same two
species, likewise sometimes differ in their degree of sterility. These
cases also are utterly inexplicable on the view of sterility being a
special endowment.

_Fifthly_, the degree of sterility of first crosses and of hybrids runs, to
a certain extent, parallel with the general or systematic affinity of the
forms which are united. For species belonging to distinct genera can
rarely, and those belonging to distinct families can never, be crossed. The
parallelism, however, is far from complete; for a multitude of closely
allied species will not unite, or unite with extreme difficulty, whilst
other species, widely different from each other, can be crossed with
perfect facility. Nor does the difficulty depend on ordinary {180}
constitutional differences, for annual and perennial plants, deciduous and
evergreen trees, plants flowering at different seasons, inhabiting
different stations, and naturally living under the most opposite climates,
can often be crossed with ease. The difficulty or facility apparently
depends exclusively on the sexual constitution of the species which are
crossed; or on their sexual elective affinity, _i. e._ _Wahlverwandtschaft_
of Gärtner. As species rarely or never become modified in one character,
without being at the same time modified in many, and as systematic affinity
includes all visible resemblances and dissimilarities, any difference in
sexual constitution between two species would naturally stand in more or
less close relation with their systematic position.

_Sixthly_, the sterility of species when first crossed, and that of
hybrids, may possibly depend to a certain extent on distinct causes. With
pure species the reproductive organs are in a perfect condition, whilst
with hybrids they are often plainly deteriorated. A hybrid embryo which
partakes of the constitution of its father and mother is exposed to
unnatural conditions, as long as it is nourished within the womb, or egg,
or seed of the mother-form; and as we know that unnatural conditions often
induce sterility, the reproductive organs of the hybrid might at this early
age be permanently affected. But this cause has no bearing on the
infertility of first unions. The diminished number of the offspring from
first unions may often result, as is certainly sometimes the case, from the
premature death of most of the hybrid embryos. But we shall immediately see
that a law of an unknown nature apparently exists, which causes the
offspring from unions, which are infertile, to be themselves more or less
infertile; and this at present is all that can be said.

_Seventhly_, hybrids and mongrels present, with the one great exception of
fertility, the most striking accordance in all other respects; namely, in
the laws of their resemblance to their two parents, in their tendency to
reversion, in their variability, and in being absorbed through repeated
crosses by either parent-form.

Since arriving at the foregoing conclusions, condensed from my former work,
I have been led to investigate a subject which throws considerable light on
hybridism, namely, the fertility of {181} reciprocally dimorphic and
trimorphic plants, when illegitimately united. I have had occasion several
times to allude to these plants, and I may here give a brief abstract[441]
of my observations. Several plants belonging to distinct orders present two
forms, which exist in about equal numbers, and which differ in no respect
except in their reproductive organs; one form having a long pistil with
short stamens, the other a short pistil with long stamens; both with
differently sized pollen-grains. With trimorphic plants there are three
forms likewise differing in the lengths of their pistils and stamens, in
the size and colour of the pollen-grains, and in some other respects; and
as in each of the three forms there are two sets of stamens, there are
altogether six sets of stamens and three kinds of pistils. These organs are
so proportioned in length to each other that, in any two of the forms, half
the stamens in each stand on a level with the stigma of the third form. Now
I have shown, and the result has been confirmed by other observers, that,
in order to obtain full fertility with these plants, it is necessary that
the stigma of the one form should be fertilised by pollen taken from the
stamens of corresponding height in the other form. So that with dimorphic
species two unions, which may be called legitimate, are fully fertile, and
two, which may be called illegitimate, are more or less infertile. With
trimorphic species six unions are legitimate or fully fertile, and twelve
are illegitimate or more or less infertile.

The infertility which may be observed in various dimorphic and trimorphic
plants, when they are illegitimately fertilised, that is, by pollen taken
from stamens not corresponding in height with the pistil, differs much in
degree, up to absolute and utter sterility; just in the same manner as
occurs in crossing distinct species. As the degree of sterility in the
latter case depends in an eminent degree on the conditions of life being
more or less favourable, so I have found it with illegitimate unions. It is
well known that if pollen of a distinct species be placed on the stigma of
a flower, and its own pollen be afterwards, even {182} after a considerable
interval of time, placed on the same stigma, its action is so strongly
prepotent that it generally annihilates the effect of the foreign pollen;
so it is with the pollen of the several forms of the same species, for
legitimate pollen is strongly prepotent over illegitimate pollen, when both
are placed on the same stigma. I ascertained this by fertilising several
flowers, first illegitimately, and twenty-four hours afterwards
legitimately, with pollen taken from a peculiarly coloured variety, and all
the seedlings were similarly coloured; this shows that the legitimate
pollen, though applied twenty-four hours subsequently, had wholly destroyed
or prevented the action of the previously applied illegitimate pollen.
Again, as, in making reciprocal crosses between the same two species, there
is occasionally a great difference in the result, so something analogous
occurs with dimorphic plants; for a short-styled cowslip (_P. veris_)
yields more seed when fertilised by the long-styled form, and less seed
when fertilised by its own form, compared with a long-styled cowslip when
fertilised in the two corresponding methods.

In all these respects the forms of the same undoubted species, when
illegitimately united, behave in exactly the same manner as do two distinct
species when crossed. This led me carefully to observe during four years
many seedlings, raised from several illegitimate unions. The chief result
is that these illegitimate plants, as they may be called, are not fully
fertile. It is possible to raise from dimorphic species, both long-styled
and short-styled illegitimate plants, and from trimorphic plants all three
illegitimate forms. These can then be properly united in a legitimate
manner. When this is done, there is no apparent reason why they should not
yield as many seeds as did their parents when legitimately fertilised. But
such is not the case; they are all infertile, but in various degrees; some
being so utterly and incurably sterile that they did not yield during four
seasons a single seed or even seed-capsule. These illegitimate plants,
which are so sterile, although united with each other in a legitimate
manner, may be strictly compared with hybrids when crossed _inter se_, and
it is well known how sterile these latter generally are. When, on the other
hand, a hybrid is crossed with either pure parent-species, the sterility is
usually much lessened: and so it is when an illegitimate plant is
fertilised by {183} a legitimate plant. In the same manner as the sterility
of hybrids does not always run parallel with the difficulty of making the
first cross between the two parent species, so the sterility of certain
illegitimate plants was unusually great, whilst the sterility of the union
from which they were derived was by no means great. With hybrids raised
from the same seed-capsule the degree of sterility is innately variable, so
it is in a marked manner with illegitimate plants. Lastly, many hybrids are
profuse and persistent flowerers, whilst other and more sterile hybrids
produce few flowers, and are weak, miserable dwarfs; exactly similar cases
occur with the illegitimate offspring of various dimorphic and trimorphic
plants.

Altogether there is the closest identity in character and behaviour between
illegitimate plants and hybrids. It is hardly an exaggeration to maintain
that the former are hybrids, but produced within the limits of the same
species by the improper union of certain forms, whilst ordinary hybrids are
produced from an improper union between so-called distinct species. We have
already seen that there is the closest similarity in all respects between
first illegitimate unions, and first crosses between distinct species. This
will perhaps be made more fully apparent by an illustration: we may suppose
that a botanist found two well-marked varieties (and such occur) of the
long-styled form of the trimorphic _Lythrum salicaria_, and that he
determined to try by crossing whether they were specifically distinct. He
would find that they yielded only about one-fifth of the proper number of
seed, and that they behaved in all the other above-specified respects as if
they had been two distinct species. But to make the case sure, he would
raise plants from his supposed hybridised seed, and he would find that the
seedlings were miserably dwarfed and utterly sterile, and that they behaved
in all other respects like ordinary hybrids. He might then maintain that he
had actually proved, in accordance with the common view, that his two
varieties were as good and as distinct species as any in the world; but he
would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are important,
because they show us, firstly, that the physiological {184} test of
lessened fertility, both in first crosses and in hybrids, is no safe
criterion of specific distinction; secondly, because we may conclude that
there must be some unknown law or bond connecting the infertility of
illegitimate unions with that of their illegitimate offspring, and we are
thus led to extend this view to first crosses and hybrids; thirdly, because
we find, and this seems to me of especial importance, that with trimorphic
plants three forms of the same species exist, which when crossed in a
particular manner are infertile, and yet these forms differ in no respect
from each other, except in their reproductive organs,--as in the relative
length of the stamens and pistils, in the size, form, and colour of the
pollen-grains, in the structure of the stigma, and in, the number and size
of the seeds. With these differences and no others, either in organisation
or constitution, we find that the illegitimate unions and the illegitimate
progeny of these three forms are more or less sterile, and closely resemble
in a whole series of relations the first unions and hybrid offspring of
distinct species. From this we may infer that the sterility of species when
crossed and of their hybrid progeny is likewise in all probability
exclusively due to differences confined to the reproductive system. We have
indeed been brought to a similar conclusion by observing that the sterility
of crossed species does not strictly coincide with their systematic
affinity, that is, with the sum of their external resemblances; nor does it
coincide with their similarity in general constitution. But we are more
especially led to this same conclusion by considering reciprocal crosses,
in which the male of one species cannot be united, or can be united with
extreme difficulty, with the female of a second species, whilst the
converse cross can be effected with perfect facility; for this difference
in the facility of making reciprocal crosses, and in the fertility of their
offspring, must be attributed either to the male or female element in the
first species having been differentiated with reference to the sexual
element of the second species in a higher degree than in the converse case.
In so complex a subject as Hybridism it is of considerable importance thus
to arrive at a definitive conclusion, namely, that the sterility which
almost invariably follows the union of distinct {185} species depends
exclusively on differences in their sexual constitution.

       *       *       *       *       *

On the principle which makes it necessary for man, whilst he is selecting
and improving his domestic varieties, to keep them separate, it would
clearly be advantageous to varieties in a state of nature, that is to
incipient species, if they could be kept from blending, either through
sexual aversion, or by becoming mutually sterile. Hence it at one time
appeared to me probable, as it has to others, that this sterility might
have been acquired through natural selection. On this view we must suppose
that a shade of lessened fertility first spontaneously appeared, like any
other modification, in certain individuals of a species when crossed with
other individuals of the same species; and that successive slight degrees
of infertility, from being advantageous, were slowly accumulated. This
appears all the more probable, if we admit that the structural differences
between the forms of dimorphic and trimorphic plants, as the length and
curvature of the pistil, &c., have been co-adapted through natural
selection; for if this be admitted, we can hardly avoid extending the same
conclusion to their mutual infertility. Sterility moreover has been
acquired through natural selection for other and widely different purposes,
as with neuter insects in reference to their social economy. In the case of
plants, the flowers on the circumference of the truss in the guelder-rose
(_Viburnum opulus_) and those on the summit of the spike in the
feather-hyacinth (_Muscari comosum_) have been rendered conspicuous, and
apparently in consequence sterile, in order that insects might easily
discover and visit the other flowers. But when we endeavour to apply the
principle of natural selection to the acquirement by distinct species of
mutual sterility, we meet with great difficulties. In the first place, it
may be remarked that separate regions are often inhabited by groups of
species or by single species, which when brought together and crossed are
found to be more or less sterile; now it could clearly have been of no
advantage to such separated species to have been rendered mutually sterile,
and consequently this could not have been effected through natural
selection; but it may perhaps be argued, that, if a species were rendered
sterile with {186} some one compatriot, sterility with other species would
follow as a necessary consequence. In the second place, it is as much
opposed to the theory of natural selection, as to the theory of special
creation, that in reciprocal crosses the male element of one form should
have been rendered utterly impotent on a second form, whilst at the same
time the male element of this second form is enabled freely to fertilise
the first form; for this peculiar state of the reproductive system could
not possibly be advantageous to either species.

In considering the probability of natural selection having come into action
in rendering species mutually sterile, one great difficulty will be found
to lie in the existence of many graduated steps from slightly lessened
fertility to absolute sterility. It may be admitted, on the principle above
explained, that it would profit an incipient species if it were rendered in
some slight degree sterile when crossed with its parent-form or with some
other variety; for thus fewer bastardised and deteriorated offspring would
be produced to commingle their blood with the new species in process of
formation. But he who will take the trouble to reflect on the steps by
which this first degree of sterility could be increased through natural
selection to that higher degree which is common to so many species, and
which is universal with species which have been differentiated to a generic
or family rank, will find the subject extraordinarily complex. After mature
reflection it seems to me that this could not have been effected through
natural selection; for it could have been of no direct advantage to an
individual animal to breed badly with another individual of a different
variety, and thus leave few offspring; consequently such individuals could
not have been preserved or selected. Or take the case of two species which
in their present state, when crossed, produce few and sterile offspring;
now, what is there which could favour the survival of those individuals
which happened to be endowed in a slightly higher degree with mutual
infertility and which thus approached by one small step towards absolute
sterility? yet an advance of this kind, if the theory of natural selection
be brought to bear, must have incessantly occurred with many species, for a
multitude are mutually quite barren. With sterile neuter insects we have
reason to {187} believe that modifications in their structure have been
slowly accumulated by natural selection, from an advantage having been thus
indirectly given to the community to which they belonged over other
communities of the same species; but an individual animal, if rendered
slightly sterile when crossed with some other variety, would not thus in
itself gain any advantage, or indirectly give any advantage to its nearest
relatives or to other individuals of the same variety, leading to their
preservation. I infer from these considerations that, as far as animals are
concerned, the various degrees of lessened fertility which occur with
species when crossed cannot have been slowly accumulated by means of
natural selection.

With plants, it is possible that the case may be somewhat different. With
many kinds, insects constantly carry pollen from neighbouring plants to the
stigmas of each flower; and with some species this is effected by the wind.
Now, if the pollen of a variety, when deposited on the stigma of the same
variety, should become by spontaneous variation in ever so slight a degree
prepotent over the pollen of other varieties, this would certainly be an
advantage to the variety; for its own pollen would thus obliterate the
effects of the pollen of other varieties, and prevent deterioration of
character. And the more prepotent the variety's own pollen could be
rendered through natural selection, the greater the advantage would be. We
know from the researches of Gärtner that, with species which are mutually
sterile, the pollen of each is always prepotent on its own stigma over that
of the other species; but we do not know whether this prepotency is a
consequence of the mutual sterility, or the sterility a consequence of the
prepotency. If the latter view be correct, as the prepotency became
stronger through natural selection, from being advantageous to a species in
process of formation, so the sterility consequent on prepotency would at
the same time be augmented; and the final result would be various degrees
of sterility, such as occurs with existing species. This view might be
extended to animals, if the female before each birth received several
males, so that the sexual element of the prepotent male of her own variety
obliterated the effects of the access of previous males belonging to other
varieties; but we have no reason to believe, at least {188} with
terrestrial animals, that this is the ease; as most males and females pair
for each birth, and some few for life.

On the whole we may conclude that with animals the sterility of crossed
species has not been slowly augmented through natural selection; and as
this sterility follows the same general laws in the vegetable as in the
animal kingdom, it is improbable, though apparently possible, that with
plants crossed species should have been rendered sterile by a different
process. From this consideration, and remembering that species which have
never co-existed in the same country, and which therefore could not have
received any advantage from having been rendered mutually infertile, yet
are generally sterile when crossed; and bearing in mind that in reciprocal
crosses between the same two species there is sometimes the widest
difference in their sterility, we must give up the belief that natural
selection has come into play.

As species have not been rendered mutually infertile through the
accumulative action of natural selection, and as we may safely conclude,
from the previous as well as from other and more general considerations,
that they have not been endowed through an act of creation with this
quality, we must infer that it has arisen incidentally during their slow
formation in connection with other and unknown changes in their
organisation. By a quality arising incidentally, I refer to such cases as
different species of animals and plants being differently affected by
poisons to which they are not naturally exposed; and this difference in
susceptibility is clearly incidental on other and unknown differences in
their organisation. So again the capacity in different kinds of trees to be
grafted on each other, or on a third species, differs much, and is of no
advantage to these trees, but is incidental on structural or functional
differences in their woody tissues. We need not feel surprise at sterility
incidentally resulting from crosses between distinct species,--the modified
descendants of a common progenitor,--when we bear in mind how easily the
reproductive system is affected by various causes--often by extremely
slight changes in the conditions of life, by too close interbreeding, and
by other agencies. It is well to bear in mind such cases, as that of the
_Passiflora alata_, which recovered its self-fertility from {189} being
grafted on a distinct species--the cases of plants which normally or
abnormally are self-impotent, but can readily be fertilised by the pollen
of a distinct species--and lastly the cases of individual domesticated
animals which evince towards each other sexual incompatibility.

       *       *       *       *       *

We now at last come to the immediate point under discussion: how is it
that, with some few exceptions in the case of plants, domesticated
varieties, such as those of the dog, fowl, pigeon, several fruit-trees, and
culinary vegetables, which differ from each other in external characters
more than many species, are perfectly fertile when crossed, or even fertile
in excess, whilst closely allied species are almost invariably in some
degree sterile? We can, to a certain extent, give a satisfactory answer to
this question. Passing over the fact that the amount of external difference
between two species is no sure guide to their degree of mutual sterility,
so that similar differences in the case of varieties would be no sure
guide, we know that with species the cause lies exclusively in differences
in their sexual constitution. Now the conditions to which domesticated
animals and cultivated plants have been subjected, have had so little
tendency towards modifying the reproductive system in a manner leading to
mutual sterility, that we have good grounds for admitting the directly
opposite doctrine of Pallas, namely, that such conditions generally
eliminate this tendency; so that the domesticated descendants of species,
which in their natural state would have been in some degree sterile when
crossed, become perfectly fertile together. With plants, so far is
cultivation from giving a tendency towards mutual sterility, that in
several well-authenticated cases, already often alluded to, certain species
have been affected in a very different manner, for they have become
self-impotent, whilst still retaining the capacity of fertilising, and
being fertilised by, distinct species. If the Pallasian doctrine of the
elimination of sterility through long-continued domestication be admitted,
and it can hardly be rejected, it becomes in the highest degree improbable
that similar circumstances should commonly both induce and eliminate the
same tendency; though in certain cases, with species having a peculiar
constitution, sterility might occasionally be thus {190} induced. Thus, as
I believe, we can understand why with domesticated animals varieties have
not been produced which are mutually sterile; and why with plants only a
few such cases have been observed, namely, by Gärtner, with certain
varieties of maize and verbascum, by other experimentalists with varieties
of the gourd and melon, and by Kölreuter with one kind of tobacco.

With respect to varieties which have originated in a state of nature, it is
almost hopeless to expect to prove by direct evidence that they have been
rendered mutually sterile; for if even a trace of sterility could be
detected, such varieties would at once be raised by almost every naturalist
to the rank of distinct species. If, for instance, Gärtner's statement were
fully confirmed, that the blue and red-flowered forms of the pimpernel
(_Anagallis arvensis_) are sterile when crossed, I presume that all the
botanists who now maintain on various grounds that these two forms are
merely fleeting varieties, would at once admit that they were specifically
distinct.

The real difficulty in our present subject is not, as it appears to me, why
domestic varieties have not become mutually infertile when crossed, but why
this has so generally occurred with natural varieties as soon as they have
been modified in a sufficient and permanent degree to take rank as species.
We are far from precisely knowing the cause; nor is this surprising, seeing
how profoundly ignorant we are in regard to the normal and abnormal action
of the reproductive system. But we can see that species, owing to their
struggle for life with numerous competitors, must have been exposed to more
uniform conditions during long periods of time, than have been domestic
varieties; and this may well make a wide difference in the result. For we
know how commonly wild animals and plants, when taken from their natural
conditions and subjected to captivity, are rendered sterile; and the
reproductive functions of organic beings which have always lived and been
slowly modified under natural conditions would probably in like manner be
eminently sensitive to the influence of an unnatural cross. Domesticated
productions, on the other hand, which, as shown by the mere fact of their
domestication, were not originally highly sensitive to changes in their
conditions of life, and which can now generally resist {191} with
undiminished fertility repeated changes of conditions, might be expected to
produce varieties, which would be little liable to have their reproductive
powers injuriously affected by the act of crossing with other varieties
which had originated in a like manner.

Certain naturalists have recently laid too great stress, as it appears to
me, on the difference in fertility between varieties and species when
crossed. Some allied species of trees cannot be grafted on each other,--all
varieties can be so grafted. Some allied animals are affected in a very
different manner by the same poison, but with varieties no such case until
recently was known, but now it has been proved that immunity from certain
poisons stands in some cases in correlation with the colour of the hair.
The period of gestation generally differs much with distinct species, but
with varieties until lately no such difference had been observed. The time
required for the germination of seeds differs in an analogous manner, and I
am not aware that any difference in this respect has as yet been detected
with varieties. Here we have various physiological differences, and no
doubt others could be added, between one species and another of the same
genus, which do not occur, or occur with extreme rarity, in the case of
varieties; and these differences are apparently wholly or in chief part
incidental on other constitutional differences, just in the same manner as
the sterility of crossed species is incidental on differences confined to
the sexual system. Why, then, should these latter differences, however
serviceable they may indirectly be in keeping the inhabitants of the same
country distinct, be thought of such paramount importance, in comparison
with other incidental and functional differences? No sufficient answer to
this question can be given. Hence the fact that the most distinct domestic
varieties are, with rare exceptions, perfectly fertile when crossed, and
produce fertile offspring, whilst closely allied species are, with rare
exceptions, more or less sterile, is not nearly so formidable an objection
as it appears at first to the theory of the common descent of allied
species.

       *       *       *       *       *


{192}

CHAPTER XX.

SELECTION BY MAN.

    SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL
    SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN
    SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS,
    AND BY SEMI-CIVILIZED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED
    TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR
    DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS
    SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME
    SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF
    SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST
    VALUED BY MAN.

The power of Selection, whether exercised by man, or brought into play
under nature through the struggle for existence and the consequent survival
of the fittest, absolutely depends on the variability of organic beings.
Without variability nothing can be effected; slight individual differences,
however, suffice for the work, and are probably the sole differences which
are effective in the production of new species. Hence our discussion on the
causes and laws of variability ought in strict order to have preceded our
present subject, as well as the previous subjects of inheritance, crossing,
&c.; but practically the present arrangement has been found the most
convenient. Man does not attempt to cause variability; though he
unintentionally effects this by exposing organisms to new conditions of
life, and by crossing breeds already formed. But variability being granted,
he works wonders. Unless some degree of selection be exercised, the free
commingling of the individuals of the same variety soon obliterates, as we
have previously seen, the slight differences which may arise, and gives to
the whole body of individuals uniformity of character. In separated
districts, long-continued exposure to different conditions of life may
perhaps produce new races without the aid of selection; but to this
difficult subject {193} of the direct action of the conditions of life we
shall in a future chapter recur.

When animals or plants are born with some conspicuous and firmly inherited
new character, selection is reduced to the preservation of such
individuals, and to the subsequent prevention of crosses; so that nothing
more need be said on the subject. But in the great majority of cases a new
character, or some superiority in an old character, is at first faintly
pronounced, and is not strongly inherited; and then the full difficulty of
selection is experienced. Indomitable patience, the finest powers of
discrimination, and sound judgment must be exercised during many years. A
clearly predetermined object must be kept steadily in view. Few men are
endowed with all these qualities, especially with that of discriminating
very slight differences; judgment can be acquired only by long experience;
but if any of these qualities be wanting, the labour of a life may be
thrown away. I have been astonished when celebrated breeders, whose skill
and judgment have been proved by their success at exhibitions, have shown
me their animals, which appeared all alike, and have assigned their reasons
for matching this and that individual. The importance of the great
principle of Selection mainly lies in this power of selecting scarcely
appreciable differences, which nevertheless are found to be transmissible,
and which can be accumulated until the result is made manifest to the eyes
of every beholder.

The principle of selection may be conveniently divided into three kinds.
_Methodical selection_ is that which guides a man who systematically
endeavours to modify a breed according to some predetermined standard.
_Unconscious selection_ is that which follows from men naturally preserving
the most valued and destroying the less valued individuals, without any
thought of altering the breed; and undoubtedly this process slowly works
great changes. Unconscious selection graduates into methodical, and only
extreme cases can be distinctly separated; for he who preserves a useful or
perfect animal will generally breed from it with the hope of getting
offspring of the same character; but as long as he has not a predetermined
purpose to improve the breed, he may be said to be selecting {194}
unconsciously.[442] Lastly, we have _Natural selection_, which implies that
the individuals which are best fitted for the complex, and in the course of
ages changing conditions to which they are exposed, generally survive and
procreate their kind. With domestic productions, with which alone we are
here strictly concerned, natural selection comes to a certain extent into
action, independently of, and even in opposition to, the will of man.

       *       *       *       *       *

_Methodical Selection._--What man has effected within recent times in
England by methodical selection is clearly shown by our exhibitions of
improved quadrupeds and fancy birds. With respect to cattle, sheep, and
pigs, we owe their great improvement to a long series of well-known
names--Bakewell, Colling, Ellman, Bates, Jonas Webb, Lords Leicester and
Western, Fisher Hobbs, and others. Agricultural writers are unanimous on
the power of selection: any number of statements to this effect could be
quoted; a few will suffice. Youatt, a sagacious and experienced observer,
writes,[443] the principle of selection is "that which enables the
agriculturist, not only to modify the character of his flock, but to change
it altogether." A great breeder of shorthorns[444] says, "In the anatomy of
the shoulder modern breeders have made great improvements on the Ketton
shorthorns by correcting the defect in the knuckle or shoulder-joint, and
by laying the top of the shoulder more snugly into the crop, and thereby
filling up the hollow behind it.... The eye has its fashion at different
periods: at one time the eye high and outstanding from the head, and at
another time the sleepy eye sunk into the head; but these extremes have
merged into the medium of a full, clear, and prominent eye with a placid
look."

Again, hear what an excellent judge of pigs[445] says: "The legs {195}
should be no longer than just to prevent the animal's belly from trailing
on the ground. The leg is the least profitable portion of the hog, and we
therefore require no more of it than is absolutely necessary for the
support of the rest." Let any one compare the wild-boar with any improved
breed, and he will see how effectually the legs have been shortened.

Few persons, except breeders, are aware of the systematic care taken in
selecting animals, and of the necessity of having a clear and almost
prophetic vision into futurity. Lord Spencer's skill and judgment were well
known; and he writes,[446] "It is therefore very desirable, before any man
commences to breed either cattle or sheep, that he should make up his mind
to the shape and qualities he wishes to obtain, and steadily pursue this
object." Lord Somerville, in speaking of the marvellous improvement of the
New Leicester sheep, effected by Bakewell and his successors, says, "It
would seem as if they had first drawn a perfect form, and then given it
life." Youatt[447] urges the necessity of annually drafting each flock, as
many animals will certainly degenerate "from the standard of excellence,
which the breeder has established in his own mind." Even with a bird of
such little importance as the canary, long ago (1780-1790) rules were
established, and a standard of perfection was fixed, according to which the
London fanciers tried to breed the several sub-varieties.[448] A great
winner of prizes at the Pigeon-shows,[449] in describing the Short-faced
Almond Tumbler, says, "There are many first-rate fanciers who are
particularly partial to what is called the goldfinch-beak, which is very
beautiful; others say, take a full-size round cherry, then take a
barley-corn, and judiciously placing and thrusting it into the cherry, form
as it were your beak; and that is not all, for it will form a good head and
beak, provided, as I said before, it is judiciously done; others take an
oat; but as I think the goldfinch-beak the handsomest, I would advise the
inexperienced fancier to get the head of a goldfinch, and keep it by him
for his observation." Wonderfully different as is the beak of the
rock-pigeon and goldfinch, undoubtedly, as far as {196} external shape and
proportions are concerned, the end has been nearly gained.

Not only should our animals be examined with the greatest care whilst
alive, but, as Anderson remarks,[450] their carcases should be scrutinised,
"so as to breed from the descendants of such only as, in the language of
the butcher, cut up well." The "grain of the meat" in cattle, and its being
well marbled with fat,[451] and the greater or less accumulation of fat in
the abdomen of our sheep, have been attended to with success. So with
poultry, a writer,[452] speaking of Cochin-China fowls, which are said to
differ much in the quality of their flesh, says, "the best mode is to
purchase two young brother-cocks, kill, dress, and serve up one; if he be
indifferent, similarly dispose of the other, and try again; if, however, he
be fine and well-flavoured, his brother will not be amiss for breeding
purposes for the table."

The great principle of the division of labour has been brought to bear on
selection. In certain districts[453] "the breeding of bulls is confined to
a very limited number of persons, who by devoting their whole attention to
this department, are able from year to year to furnish a class of bulls
which are steadily improving the general breed of the district." The
rearing and letting of choice rams has long been, as is well known, a chief
source of profit to several eminent breeders. In parts of Germany this
principle is carried with merino sheep to an extreme point.[454] "So
important is the proper selection of breeding animals considered, that the
best flock-masters do not trust to their own judgment, or to that of their
shepherds, but employ persons called 'sheep-classifiers,' who make it their
special business to attend to this part of the management of several
flocks, and thus to preserve, or if possible to improve, the best qualities
of both parents in the lambs." In Saxony, "when the lambs are weaned, each
in his turn is placed upon a table that his wool and form may be minutely
observed. {197} The finest are selected for breeding and receive a first
mark. When they are one year old, and prior to shearing them, another close
examination of those previously marked takes place: those in which no
defect can be found receive a second mark, and the rest are condemned. A
few months afterwards a third and last scrutiny is made; the prime rams and
ewes receive a third and final mark, but the slightest blemish is
sufficient to cause the rejection of the animal." These sheep are bred and
valued almost exclusively for the fineness of their wool; and the result
corresponds with the labour bestowed on their selection. Instruments have
been invented to measure accurately the thickness of the fibres; and "an
Austrian fleece has been produced of which twelve hairs equalled in
thickness one from a Leicester sheep."

Throughout the world, wherever silk is produced, the greatest care is
bestowed on selecting the cocoons from which the moths for breeding are to
be reared. A careful cultivator[455] likewise examines the moths
themselves, and destroys those that are not perfect. But what more
immediately concerns us is that certain families in France devote
themselves to raising eggs for sale.[456] In China, near Shanghai, the
inhabitants of two small districts have the privilege of raising eggs for
the whole surrounding country, and that they may give up their whole time
to this business, they are interdicted by law from producing silk.[457]

The care which successful breeders take in matching their birds is
surprising. Sir John Sebright, whose fame is perpetuated by the "Sebright
Bantam," used to spend "two and three days in examining, consulting, and
disputing with a friend which were the best of five or six birds."[458] Mr.
Bult, whose pouter-pigeons won so many prizes and were exported to North
America under the charge of a man sent on purpose, told me that he always
deliberated for several days before he matched each pair. Hence we can
understand the advice of an eminent fancier, who writes,[459] "I would here
particularly guard {198} you against having too great a variety of pigeons,
otherwise you will know a little of all, but nothing about one as it ought
to be known." Apparently it transcends the power of the human intellect to
breed all kinds: "it is possible that there may be a few fanciers that have
a good general knowledge of fancy pigeons; but there are many more who
labour under the delusion of supposing they know what they do not." The
excellence of one sub-variety, the Almond Tumbler, lies in the plumage,
carriage, head, beak, and eye; but it is too presumptuous in the beginner
to try for all these points. The great judge above quoted says, "there are
some young fanciers who are over-covetous, who go for all the above five
properties at once; they have their reward by getting nothing." We thus see
that breeding even fancy pigeons is no simple art: we may smile at the
solemnity of these precepts, but he who laughs will win no prizes.

What methodical selection has effected for our animals is sufficiently
proved, as already remarked, by our Exhibitions. So greatly were the sheep
belonging to some of the earlier breeders, such as Bakewell and Lord
Western, changed, that many persons could not be persuaded that they had
not been crossed. Our pigs, as Mr. Corringham remarks,[460] during the last
twenty years have undergone, through rigorous selection together with
crossing, a complete metamorphosis. The first exhibition for poultry was
held in the Zoological Gardens in 1845; and the improvement effected since
that time has been great. As Mr. Baily, the great judge, remarked to me, it
was formerly ordered that the comb of the Spanish cock should be upright,
and in four or five years all good birds had upright combs; it was ordered
that the Polish cock should have no comb or wattles, and now a bird thus
furnished would be at once disqualified; beards were ordered, and out of
fifty-seven pens lately (1860) exhibited at the Crystal Palace, all had
beards. So it has been in many other cases. But in all cases the judges
order only what is occasionally produced and what can be improved and
rendered constant by selection. The steady increase of weight during the
last few years in our {199} fowls, turkeys, ducks, and geese is notorious;
"six-pound ducks are now common, whereas four pounds was formerly the
average." As the actual time required to make a change has not often been
recorded, it may be worth mentioning that it took Mr. Wicking thirteen
years to put a clean white head on an almond tumbler's body, "a triumph,"
says another fancier, "of which he may be justly proud."[461]

Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descended
from good milkers, for the sole purpose of improving his cattle for the
production of cheese; he steadily tested the milk with the lactometer, and
in eight years he increased, as I was informed by him, the product in the
proportion of four to three. Here is a curious case[462] of steady but slow
progress, with the end not as yet fully attained: in 1784 a race of
silkworms was introduced into France, in which one hundred out of the
thousand failed to produce white cocoons; but now, after careful selection
during sixty-five generations, the proportion of yellow cocoons has been
reduced to thirty-five in the thousand.

With plants selection has been followed with the same good results as with
animals. But the process is simpler, for plants in the great majority of
cases bear both sexes. Nevertheless, with most kinds it is necessary to
take as much care to prevent crosses as with animals or unisexual plants;
but with some plants, such as peas, this care does not seem to be
necessary. With all improved plants, excepting of course those which are
propagated by buds, cuttings, &c., it is almost indispensable to examine
the seedlings and destroy those which depart from the proper type. This is
called "roguing," and is, in fact, a form of selection, like the rejection
of inferior animals. Experienced horticulturists and agriculturists
incessantly urge every one to preserve the finest plants for the production
of seed.

Although plants often present much more conspicuous variations than
animals, yet the closest attention is generally requisite to detect each
slight and favourable change. Mr. Masters relates[463] how "many a patient
hour was devoted," whilst he was {200} young, to the detection of
differences in peas intended for seed. Mr. Barnet[464] remarks that the old
scarlet American strawberry was cultivated for more than a century without
producing a single variety; and another writer observes how singular it was
that when gardeners first began to attend to this fruit it began to vary;
the truth no doubt being that it had always varied, but that, until slight
varieties were selected and propagated by seed, no conspicuous result was
obtained. The finest shades of difference in wheat have been discriminated
and selected with almost as much care, as we see in Colonel Le Couteur's
works, as in the case of the higher animals; but with our cereals the
process of selection has seldom or never been long continued.

It may be worth while to give a few examples of methodical selection with
plants; but in fact the great improvement of all our anciently cultivated
plants may be attributed to selection long carried on, in part
methodically, and in part unconsciously. I have shown in a former chapter
how the weight of the gooseberry has been increased by systematic selection
and culture. The flowers of the Heartsease have been similarly increased in
size and regularity of outline. With the Cineraria, Mr. Glenny[465] "was
bold enough, when the flowers were ragged and starry and ill defined in
colour, to fix a standard which was then considered outrageously high and
impossible, and which, even if reached, it was said, we should be no
gainers by, as it would spoil the beauty of the flowers. He maintained that
he was right; and the event has proved it to be so." The doubling of
flowers has several times been effected by careful selection: the Rev. W.
Williamson,[466] after sowing during several years seed of _Anemone
coronaria_, found a plant with one additional petal; he sowed the seed of
this, and by perseverance in the same course obtained several varieties
with six or seven rows of petals. The single Scotch rose was doubled, and
yielded eight good varieties in nine or ten years.[467] The Canterbury bell
(_Campanula medium_) was doubled by careful selection in four
generations.[468] In four years Mr. Buckman,[469] by culture and {201}
careful selection, converted parsnips, raised from wild seed, into a new
and good variety. By selection during a long course of years, the early
maturity of peas has been hastened from ten to twenty-one days.[470] A more
curious case is offered by the beet-plant, which, since its cultivation in
France, has almost exactly doubled its yield of sugar. This has been
effected by the most careful selection; the specific gravity of the roots
being regularly tested, and the best roots saved for the production of
seed.[471]

_Selection by Ancient and Semi-civilised People._

In attributing so much importance to the selection of animals and plants,
it may be objected that methodical selection would not have been carried on
during ancient times. A distinguished naturalist considers it as absurd to
suppose that semi-civilised people should have practised selection of any
kind. Undoubtedly the principle has been systematically acknowledged and
followed to a far greater extent within the last hundred years than at any
former period, and a corresponding result has been gained; but it would be
a great error to suppose, as we shall immediately see, that its importance
was not recognised and acted on during the most ancient times, and by
semi-civilised people. I should premise that many facts now to be given
only show that care was taken in breeding; but when this is the case,
selection is almost sure to be practised to a certain extent. We shall
hereafter be enabled better to judge how far selection, when only
occasionally carried on, by a few of the inhabitants of a country, will
slowly produce a great effect.

In a well-known passage in the thirtieth chapter of Genesis, rules are
given for influencing, as was then thought possible, the colour of sheep;
and speckled and dark breeds are spoken of as being kept separate. By the
time of David the fleece was likened to snow. Youatt,[472] who has
discussed all the passages in relation to breeding in the Old Testament,
concludes that {202} at this early period "some of the best principles of
breeding must have been steadily and long pursued." It was ordered,
according to Moses, that "Thou shalt not let thy cattle gender with a
diverse kind;" but mules were purchased,[473] so that at this early period
other nations must have crossed the horse and ass. It is said[474] that
Erichthonius, some generations before the Trojan war, had many brood-mares,
"which by his care and judgment in the choice of stallions produced a breed
of horses superior to any in the surrounding countries." Homer (Book v.)
speaks of Æneas's horses as bred from mares which were put to the steeds of
Laomedon. Plato, in his 'Republic,' says to Glaucus, "I see that you raise
at your house a great many dogs for the chase. Do you take care about
breeding and pairing them? Among animals of good blood, are there not
always some which are superior to the rest?" To which Glaucus answers in
the affirmative.[475] Alexander the Great selected the finest Indian cattle
to send to Macedonia to improve the breed.[476] According to Pliny,[477]
King Pyrrhus had an especially valuable breed of oxen; and he did not
suffer the bulls and cows to come together till four years old, that the
breed might not degenerate. Virgil, in his Georgics (lib. iii.), gives as
strong advice as any modern agriculturist could do, carefully to select the
breeding stock; "to note the tribe, the lineage, and the sire; whom to
reserve for husband of the herd;"--to brand the progeny;--to select sheep
of the purest white, and to examine if their tongues are swarthy. We have
seen that the Romans kept pedigrees of their pigeons, and this would have
been a senseless proceeding had not great care been taken in breeding them.
Columella gives detailed instructions about breeding fowls: "Let the
breeding hens therefore be of a choice colour, a robust body, square-built,
full-breasted, with large heads, with upright and bright-red combs. Those
are believed to be the best bred which have five toes."[478] According to
Tacitus, the Celts attended to the races of their domestic animals; {203}
and Cæsar states that they paid high prices to merchants for fine imported
horses.[479] In regard to plants, Virgil speaks of yearly culling the
largest seeds; and Celsus says, "where the corn and crop is but small, we
must pick out the best ears of corn, and of them lay up our seed separately
by itself."[480]

Coming down the stream of time, we may be brief. At about the beginning of
the ninth century Charlemagne expressly ordered his officers to take great
care of his stallions; and if any proved bad or old, to forewarn him in
good time before they were put to the mares.[481] Even in a country so
little civilised as Ireland during the ninth century, it would appear from
some ancient verses,[482] describing a ransom demanded by Cormac, that
animals from particular places, or having a particular character, were
valued. Thus it is said,--

  Two pigs of the pigs of Mac Lir,
  A ram and ewe both round and red,
  I brought with me from Aengus.
  I brought with me a stallion and a mare
  From the beautiful stud of Manannan,
  A bull and a white cow from Druim Cain.

Athelstan, in 930, received as a present from Germany, running-horses; and
he prohibited the exportation of English horses. King John imported "one
hundred chosen stallions from Flanders."[483] On June 16th, 1305, the
Prince of Wales wrote to the Archbishop of Canterbury, begging for the loan
of any choice stallion, and promising its return at the end of the
season.[484] There are numerous records at ancient periods in English
history of the importation of choice animals of various kinds, and of
foolish laws against their exportation. In the reigns of Henry VII. and
VIII. it was ordered that the magistrates, at Michaelmas, should scour the
heaths and commons, and destroy all mares beneath a certain size.[485] Some
of our earlier kings passed laws against the slaughtering rams of any good
breed before they were seven years old, so that they {204} might have time
to breed. In Spain Cardinal Ximenes issued, in 1509, regulations on the
_selection_ of good rams for breeding.[486]

The Emperor Akbar Khan before the year 1600 is said to have "wonderfully
improved" his pigeons by crossing the breeds; and this necessarily implies
careful selection. About the same period the Dutch attended with the
greatest care to the breeding of these birds. Belon in 1555 says that good
managers in France examined the colour of their goslings in order to get
geese of a white colour and better kinds. Markham in 1631 tells the breeder
"to elect the largest and goodliest conies," and enters into minute
details. Even with respect to seeds of plants for the flower-garden, Sir J.
Hanmer writing about the year 1660[487] says, in "choosing seed, the best
seed is the most weighty, and is had from the lustiest and most vigorous
stems;" and he then gives rules about leaving only a few flowers on plants
for seed; so that even such details were attended to in our flower-gardens
two hundred years ago. In order to show that selection has been silently
carried on in places where it would not have been expected, I may add that
in the middle of the last century, in a remote part of North America, Mr.
Cooper improved by careful selection all his vegetables, "so that they were
greatly superior to those of any other person. When his radishes, for
instance, are fit for use, he takes ten or twelve that he most approves,
and plants them at least 100 yards from others that blossom at the same
time. In the same manner he treats all his other plants, varying the
circumstances according to their nature."[488]

In the great work on China published in the last century by the Jesuits,
and which is chiefly compiled from ancient Chinese encyclopædias, it is
said that with sheep "improving the breed consists in choosing with
particular care the lambs which are destined for propagation, in nourishing
them well, and in keeping the flocks separate." The same principles were
applied by the Chinese to various plants and fruit-trees.[489] An {205}
imperial edict recommends the choice of seed of remarkable size; and
selection was practised even by imperial hands, for it is said that the
Ya-mi, or imperial rice, was noticed at an ancient period in a field by the
Emperor Khang-hi, was saved and cultivated in his garden, and has since
become valuable from being the only kind which will grow north of the Great
Wall.[490] Even with flowers, the tree pæony (_P. moutan_) has been
cultivated, according to Chinese traditions, for 1400 years; between 200
and 300 varieties have been raised, which are cherished like tulips
formerly were by the Dutch.[491]

Turning now to semi-civilised people and to savages: it occurred to me,
from what I had seen of several parts of South America, where fences do not
exist, and where the animals are of little value, that there would be
absolutely no care in breeding or selecting them; and this to a large
extent is true. Roulin,[492] however, describes in Colombia a naked race of
cattle, which are not allowed to increase, on account of their delicate
constitution. According to Azara[493] horses are often born in Paraguay
with curly hair; but, as the natives do not like them, they are destroyed.
On the other hand, Azara states that a hornless bull, born in 1770, was
preserved and propagated its race. I was informed of the existence in Banda
Oriental of a breed with reversed hair; and the extraordinary niata cattle
first appeared and have since been kept distinct in La Plata. Hence certain
conspicuous variations have been preserved, and others have been habitually
destroyed, in these countries, which are so little favourable for careful
selection. We have also seen that the inhabitants sometimes introduce
cattle on their estates to prevent the evil effects of close interbreeding.
On the other hand, I have heard on reliable authority that the Gauchos of
the Pampas never take any pains in selecting the best bulls or stallions
for breeding; and this probably accounts for the cattle and horses being
remarkably uniform in character throughout the immense range of the
Argentine republic.

Looking to the Old World, in the Sahara Desert "The Touareg is as careful
in the selection of his breeding Mahari {206} (a fine race of the
dromedary) as the Arab is in that of his horse. The pedigrees are handed
down, and many a dromedary can boast a genealogy far longer than the
descendants of the Darley Arabian."[494] According to Pallas the Mongolians
endeavour to breed the Yaks or horse-tailed buffaloes with white tails, for
these are sold to the Chinese mandarins as fly-flappers; and Moorcroft,
about seventy years after Pallas, found that white-tailed animals were
still selected for breeding.[495]

We have seen in the chapter on the Dog that savages in different parts of
North America and in Guiana cross their dogs with wild Canidæ, as did the
ancient Gauls, according to Pliny. This was done to give their dogs
strength and vigour, in the same way as the keepers in large warrens now
sometimes cross their ferrets (as I have been informed by Mr. Yarrell) with
the wild polecat, "to give them more devil." According to Varro, the wild
ass was formerly caught and crossed with the tame animal to improve the
breed, in the same manner as at the present day the natives of Java
sometimes drive their cattle into the forests to cross with the wild
Banteng (_Bos sondaicus_).[496] In Northern Siberia, among the Ostyaks the
dogs vary in markings in different districts, but in each place they are
spotted black and white in a remarkably uniform manner;[497] and from this
fact alone we may infer careful breeding, more especially as the dogs of
one locality are famed throughout the country for their superiority. I have
heard of certain tribes of Esquimaux who take pride in their teams of dogs
being uniformly coloured. In Guiana, as Sir R. Schomburgk informs me,[498]
the dogs of the Turuma Indians are highly valued and extensively bartered:
the price of a good one is the same as that given for a wife: they are kept
in a sort of cage, and the Indians "take great care when the female is in
season to prevent her uniting with a dog of an inferior description." The
Indians told Sir Robert that, if a dog proved bad or useless, {207} he was
not killed, but was left to die from sheer neglect. Hardly any nation is
more barbarous than the Fuegians, but I hear from Mr. Bridges, the
Catechist to the Mission, that, "when these savages have a large, strong,
and active bitch, they take care to put her to a fine dog, and even take
care to feed her well, that her young may be strong and well favoured."

In the interior of Africa, negroes, who have not associated with white men,
show great anxiety to improve their animals: they "always choose the larger
and stronger males for stock:" the Malakolo were much pleased at
Livingstone's promise to send them a bull, and some Bakalolo carried a live
cock all the way from Loanda into the interior.[499] Further south on the
same continent, Andersson states that he has known a Damara give two fine
oxen for a dog which struck his fancy. The Damaras take great delight in
having whole droves of cattle of the same colour, and they prize their oxen
in proportion to the size of their horns. "The Namaquas have a perfect
mania for a uniform team; and almost all the people of Southern Africa
value their cattle next to their women, and take a pride in possessing
animals that look high-bred." "They rarely or never make use of a handsome
animal as a beast of burden."[500] The power of discrimination which these
savages possess is wonderful, and they can recognise to which tribe any
cattle belong. Mr. Andersson further informs me that the natives frequently
match a particular bull with a particular cow.

The most curious case of selection by semi-civilised people, or indeed by
any people, which I have found recorded, is that given by Garcilazo de la
Vega, a descendant of the Incas, as having been practised in Peru before
the country was subjugated by the Spaniards.[501] The Incas annually held
great hunts, when all the wild animals were driven from an immense circuit
to a central point. The beasts of prey were first destroyed as injurious.
The wild Guanacos and Vicunas were sheared; the old males and females
killed, and the others set at liberty. The various kinds of deer were
examined; the old males and females {208} were likewise killed; "but the
young females, with a certain number of males, selected from the most
beautiful and strong," were given their freedom. Here, then, we have
selection by man aiding natural selection. So that the Incas followed
exactly the reverse system of that which our Scottish sportsmen are accused
of following, namely, of steadily killing the finest stags, thus causing
the whole race to degenerate.[502] In regard to the domesticated llamas and
alpacas, they were separated in the time of the Incas according to colour;
and if by chance one in a flock was born of the wrong colour, it was
eventually put into another flock.

In the genus Auchenia there are four forms,--the Guanaco and Vicuna, found
wild and undoubtedly distinct species; the Llama and Alpaca, known only in
a domesticated condition. These four animals appear so different, that most
professed naturalists, especially those who have studied these animals in
their native country, maintain that they are specifically distinct,
notwithstanding that no one pretends to have seen a wild llama or alpaca.
Mr. Ledger, however, who has closely studied these animals both in Peru and
during their exportation to Australia, and who has made many experiments on
their propagation, adduces arguments[503] which seem to me conclusive, that
the llama is the domesticated descendant of the guanaco, and the alpaca of
the vicuna. And now that we know that these animals many centuries ago were
systematically bred and selected, there is nothing surprising in the great
amount of change which they have undergone.

It appeared to me at one time probable that, though ancient and
semi-civilised people might have attended to the improvement of their more
useful animals in essential points, yet that they would have disregarded
unimportant characters. But human nature is the same throughout the world:
fashion everywhere reigns supreme, and man is apt to value whatever he may
chance to possess. We have seen that in South America the niata cattle,
which certainly are not made useful by their shortened faces and upturned
nostrils, have been preserved. The Damaras of South Africa value their
cattle for uniformity {209} of colour and enormously long horns. The
Mongolians value their yaks for their white tails. And I shall now show
that there is hardly any peculiarity in our most useful animals which, from
fashion, superstition, or some other motive, has not been valued, and
consequently preserved. With respect to cattle, "an early record,"
according to Youatt,[504] "speaks of a hundred white cows with red ears
being demanded as a compensation by the princes of North and South Wales.
If the cattle were of a dark or black colour, 150 were to be presented." So
that colour was attended to in Wales before its subjugation by England. In
Central Africa, an ox that beats the ground with its tail is killed; and in
South Africa some of the Damaras will not eat the flesh of a spotted ox.
The Kaffirs value an animal with a musical voice; and "at a sale in British
Kaffraria the low of a heifer excited so much admiration that a sharp
competition sprung up for her possession, and she realised a considerable
price."[505] With respect to sheep, the Chinese prefer rams without horns;
the Tartars prefer them with spirally wound horns, because the hornless are
thought to lose courage.[506] Some of the Damaras will not eat the flesh of
hornless sheep. In regard to horses, at the end of the fifteenth century
animals of the colour described as _liart pommé_ were most valued in
France. The Arabs have a proverb, "Never buy a horse with four white feet,
for he carries his shroud with him;"[507] the Arabs also, as we have seen,
despise dun-coloured horses. So with dogs, Xenophon and others at an
ancient period were prejudiced in favour of certain colours; and "white or
slate-coloured hunting dogs were not esteemed."[508]

Turning to poultry, the old Roman gourmands thought that the liver of a
white goose was the most savoury. In Paraguay black-skinned fowls are kept
because they are thought to be more productive, and their flesh the most
proper for invalids.[509] In Guiana, as I am informed by Sir R. Schomburgk,
the aborigines will not eat the flesh or eggs of the fowl, but two {210}
races are kept distinct merely for ornament. In the Philippines, no less
than nine sub-varieties of the game cock are kept and named, so that they
must be separately bred.

At the present time in Europe, the smallest peculiarities are carefully
attended to in our most useful animals, either from fashion, or as a mark
of purity of blood. Many examples could be given, two will suffice. "In the
Western counties of England the prejudice against a white pig is nearly as
strong as against a black one in Yorkshire." In one of the Berkshire
sub-breeds, it is said, "the white should be confined to four white feet, a
white spot between the eyes, and a few white hairs behind each shoulder."
Mr. Saddler possessed "three hundred pigs, every one of which was marked in
this manner."[510] Marshall, towards the close of the last century, in
speaking of a change in one of the Yorkshire breeds of cattle, says the
horns have been considerably modified, as "a clean, small, sharp horn has
been _fashionable_ for the last twenty years."[511] In a part of Germany
the cattle of the Race de Gfoehl are valued for many good qualities, but
they must have horns of a particular curvature and tint, so much so that
mechanical means are applied if they take a wrong direction; but the
inhabitants "consider it of the highest importance that the nostrils of the
bull should be flesh-coloured, and the eyelashes light; this is an
indispensable condition. A calf with blue nostrils would not be purchased,
or purchased at a very low price."[512] Therefore let no man say that any
point or character is too trifling to be methodically attended to and
selected by breeders.

       *       *       *       *       *

_Unconscious Selection._--By this term I mean, as already more than once
explained, the preservation by man of the most valued, and the destruction
of the least valued individuals, without any conscious intention on his
part of altering the breed. It is difficult to offer direct proofs of the
results which follow from this kind of selection; but the indirect evidence
is abundant. In fact, except that in the one case man acts intentionally,
and in the other unintentionally, there is little difference between {211}
methodical and unconscious selection. In both cases man preserves the
animals which are most useful or pleasing to him, and destroys or neglects
the others. But no doubt a far more rapid result follows from methodical
than from unconscious selection. The "roguing" of plants by gardeners, and
the destruction by law in Henry VIII.'s reign of all under-sized mares, are
instances of a process the reverse of selection in the ordinary sense of
the word, but leading to the same general result. The influence of the
destruction of individuals having a particular character is well shown by
the necessity of killing every lamb with a trace of black about it, in
order to keep the flock white; or again, by the effects on the average
height of the men of France of the destructive wars of Napoleon, by which
many tall men were killed, the short ones being left to be the fathers of
families. This at least is the conclusion of those who have closely studied
the subject of the conscription; and it is certain that since Napoleon's
time the standard for the army has been lowered two or three times.

Unconscious selection so blends into methodical that it is scarcely
possible to separate them. When a fancier long ago first happened to notice
a pigeon with an unusually short beak, or one with the tail-feathers
unusually developed, although he bred from these birds with the distinct
intention of propagating the variety, yet he could not have intended to
make a short-faced tumbler or a fantail, and was far from knowing that he
had made the first step towards this end. If he could have seen the final
result, he would have been struck with astonishment, but, from what we know
of the habits of fanciers, probably not with admiration. Our English
carriers, barbs, and short-faced tumblers have been greatly modified in the
same manner, as we may infer both from the historical evidence given in the
chapters on the Pigeon, and from the comparison of birds brought from
distant countries.

So it has been with dogs; our present fox-hounds differ from the old
English hound; our greyhounds have become lighter; the wolf-dog, which
belonged to the greyhound class, has become extinct; the Scotch deer-hound
has been modified, and is now rare. Our bulldogs differ from those which
were formerly used for baiting bulls. Our pointers and Newfoundlands do not
{212} closely resemble any native dog now found in the countries whence
they were brought, These changes have been effected partly by crosses; but
in every case the result has been governed by the strictest selection.
Nevertheless there is no reason to suppose that man intentionally and
methodically made the breeds exactly what they now are. As our horses
became fleeter, and the country more cultivated and smoother, fleeter
fox-hounds were desired and produced, but probably without any one
distinctly foreseeing what they would become. Our pointers and setters, the
latter almost certainly descended from large spaniels, have been greatly
modified in accordance with fashion and the desire for increased speed.
Wolves have become extinct, deer have become rarer, bulls are no longer
baited, and the corresponding breeds of the dog have answered to the
change. But we may feel almost sure that when, for instance, bulls were no
longer baited, no man said to himself, I will now breed my dogs of smaller
size, and thus create the present race. As circumstances changed, men
unconsciously and slowly modified their course of selection.

With race-horses selection for swiftness has been followed methodically,
and our horses can now easily beat their progenitors. The increased size
and different appearance of the English race-horse led a good observer in
India to ask, "Could any one in this year of 1856, looking at our
race-horses, conceive that they were the result of the union of the Arab
horse and the African mare?"[513] This change has, it is probable, been
largely effected through unconscious selection, that is, by the general
wish to breed as fine horses as possible in each generation, combined with
training and high feeding, but without any intention to give to them their
present appearance. According to Youatt,[514] the introduction in Oliver
Cromwell's time of three celebrated Eastern stallions speedily affected the
English breed; "so that Lord Harleigh, one of the old school, complained
that the great horse was fast disappearing." This is an excellent proof how
carefully selection must have been attended to; for without such care, all
traces of so small an infusion of Eastern blood would soon have been
absorbed and {213} lost. Notwithstanding that the climate of England has
never been esteemed particularly favourable to the horse, yet
long-continued selection, both methodical and unconscious, together with
that practised by the Arabs during a still longer and earlier period, has
ended in giving us the best breed of horses in the world. Macaulay[515]
remarks, "Two men whose authority on such subjects was held in great
esteem, the Duke of Newcastle and Sir John Fenwick, pronounced that the
meanest hack ever imported from Tangier would produce a finer progeny than
could be expected from the best sire of our native breed. They would not
readily have believed that a time would come when the princes and nobles of
neighbouring lands would be as eager to obtain horses from England as ever
the English had been to obtain horses from Barbary."

The London dray-horse, which differs so much in appearance from any natural
species, and which from its size has so astonished many Eastern princes,
was probably formed by the heaviest and most powerful animals having been
selected during many generations in Flanders and England, but without the
least intention or expectation of creating a horse such as we now see. If
we go back to an early period of history, we behold in the antique Greek
statues, as Schaaffhausen has remarked,[516] a horse equally unlike a race
or dray horse, and differing from any existing breed.

The results of unconscious selection, in an early stage, are well shown in
the difference between the flocks descended from the same stock, but
separately reared by careful breeders. Youatt gives an excellent instance
of this fact in the sheep belonging to Messrs. Buckley and Burgess, which
"have been purely bred from the original stock of Mr. Bakewell for upwards
of fifty years. There is not a suspicion existing in the mind of any one at
all acquainted with the subject that the owner of either flock has deviated
in any one instance from the pure blood of Mr. Bakewell's flock; yet the
difference between the sheep possessed by these two gentlemen is so great,
that they have the appearance of being quite different varieties."[517] I
have seen several analogous and {214} well-marked cases with pigeons: for
instance, I had a family of barbs, descended from those long bred by Sir J.
Sebright, and another family long bred by another fancier, and the two
families plainly differed from each other. Nathusius--and a more competent
witness could not be cited--observes that, though the Shorthorns are
remarkably uniform inn appearance (except in colouring), yet that the
individual character and wishes of each breeder become impressed on his
cattle, so that different herds differ slightly from each other.[518] The
Hereford cattle assumed their present well-marked character soon after the
year 1769, through careful selection by Mr. Tomkins,[519] and the breed has
lately split into two strains--one strain having a white face, and
differing slightly, it is said,[520] in some other points; but there is no
reason to believe that this split, the origin of which is unknown, was
intentionally made; it may with much more probability be attributed to
different breeders having attended to different points. So again, the
Berkshire breed of swine in the year 1810 had greatly changed from what it
had been in 1780; and since 1810 at least two distinct sub-breeds have
borne this same name.[521] When we bear in mind how rapidly all animals
increase, and that some must be annually slaughtered and some saved for
breeding, then, if the same breeder during a long course of years
deliberately settles which shall be saved and which shall be killed, it is
almost inevitable that his individual frame of mind will influence the
character of his stock, without his having had any intention to modify the
breed or form a new strain.

Unconscious selection in the strictest sense of the word, that is, the
saving of the more useful animals and the neglect or slaughter of the less
useful, without any thought of the future, must have gone on occasionally
from the remotest period and amongst the most barbarous nations. Savages
often suffer from famines, and are sometimes expelled by war from their own
homes. In such cases it can hardly be doubted that they would save their
most useful animals. When the Fuegians {215} are hard pressed by want, they
kill their old women for food rather than their dogs; for, as we were
assured, "old women no use--dogs catch otters." The same sound sense would
surely lead them to preserve their more useful dogs when still harder
pressed by famine. Mr. Oldfield, who has seen so much of the aborigines of
Australia, informs me that "they are all very glad to get a European
kangaroo dog, and several instances have been known of the father killing
his own infant that the mother might suckle the much-prized puppy."
Different kinds of dogs would be useful to the Australian for hunting
opossums and kangaroos, and to the Fuegian for catching fish and otters;
and the occasional preservation in the two countries of the most useful
animals would ultimately lead to the formation of two widely distinct
breeds.

       *       *       *       *       *

With plants, from the earliest dawn of civilisation, the best variety which
at each period was known would generally have been cultivated and its seeds
occasionally sown; so that there will have been some selection from an
extremely remote period, but without any prefixed standard of excellence or
thought of the future. We at the present day profit by a course of
selection occasionally and unconsciously carried on during thousands of
years. This is proved in an interesting manner by Oswald Heer's researches
on the lake-inhabitants of Switzerland, as given in a former chapter; for
he shows that the grain and seed of our present varieties of wheat, barley,
oats, peas, beans, lentils, and poppy, exceed in size those which were
cultivated in Switzerland during the Neolithic and Bronze periods. These
ancient people, during the Neolithic period, possessed also a crab
considerably larger than that now growing wild on the Jura.[522] The pears
described by Pliny were evidently extremely inferior in quality to our
present pears. We can realise the effects of long-continued selection and
cultivation in another way, for would any one in his senses expect to raise
a first-rate apple from the seed of a truly wild crab, or a luscious
melting pear from the wild pear? Alphonse De Candolle informs me that he
has lately seen on an ancient mosaic at Rome a representation of {216} the
melon; and as the Romans, who were such gourmands, are silent on this
fruit, he infers that the melon has been greatly ameliorated since the
classical period.

Coming to later times, Buffon,[523] on comparing the flowers, fruit, and
vegetables which were then cultivated, with some excellent drawings made a
hundred and fifty years previously, was struck with surprise at the great
improvement which had been effected; and remarks that these ancient flowers
and vegetables would now be rejected, not only by a florist but by a
village gardener. Since the time of Buffon the work of improvement has
steadily and rapidly gone on. Every florist who compares our present
flowers with those figured in books published not long since, is astonished
at the change. A well-known amateur,[524] in speaking of the varieties of
Pelargonium raised by Mr. Garth only twenty-two years before, remarks,
"what a rage they excited: surely we had attained perfection, it was said;
and now not one of the flowers of those days will be looked at. But none
the less is the debt of gratitude which we owe to those who saw what was to
be done, and did it." Mr. Paul, the well-known horticulturist, in writing
of the same flower,[525] says he remembers when young being delighted with
the portraits in Sweet's work; "but what are they in point of beauty
compared with the Pelargoniums of this day? Here again nature did not
advance by leaps; the improvement was gradual, and, if we had neglected
those very gradual advances, we must have foregone the present grand
results." How well this practical horticulturist appreciates and
illustrates the gradual and accumulative force of selection! The Dahlia has
advanced in beauty in a like manner; the line of improvement being guided
by fashion, and by the successive modifications which the flower slowly
underwent.[526] A steady and gradual change has been noticed in many other
flowers: thus an old florist,[527] after describing the leading varieties
of the Pink which were grown in 1813, adds, "the pinks of those days would
now be scarcely grown as border-flowers." The improvement of {217} so many
flowers and the number of the varieties which have been raised is all the
more striking when we hear that the earliest known flower-garden in Europe,
namely at Padua, dates only from the year 1545.[528]

       *       *       *       *       *

_Effects of Selection, as shown by the parts most valued by man presenting
the greatest amount of Difference._--The power of long-continued selection,
whether methodical or unconscious, or both combined, is well shown in a
general way, namely, by the comparison of the differences between the
varieties of distinct species, which are valued for different parts, such
as for the leaves, or stems, or tubers, the seed, or fruit, or flowers.
Whatever part man values most, that part will be found to present the
greatest amount of difference. With trees cultivated for their fruit,
Sageret remarks that the fruit is larger than in the parent-species, whilst
with those cultivated for the seed, as with nuts, walnuts, almonds,
chesnuts, &c., it is the seed itself which is larger; and he accounts for
this fact by the fruit in the one case, and by the seed in the other,
having been carefully attended to and selected during many ages. Gallesio
has made the same observation. Godron insists on the diversity of the tuber
in the potato, of the bulb in the onion, and of the fruit in the melon; and
on the close similarity in these same plants of the other parts.[529]

In order to judge how far my own impression on this subject was correct, I
cultivated numerous varieties of the same species close to each other. The
comparison of the amount of difference between widely different organs is
necessarily vague; I will therefore give the results in only a few cases.
We have previously seen in the ninth chapter how greatly the varieties of
the cabbage differ in their foliage and stems, which are the selected
parts, and how closely they resembled each other in their flowers,
capsules, and seeds. In seven varieties of the radish, the roots differed
greatly in colour and shape, but no difference {218} whatever could be
detected in their foliage, flowers, or seeds. Now what a contrast is
presented, if we compare the flowers of the varieties of these two plants
with those of any species cultivated in our flower-gardens for ornament; or
if we compare their seeds with those of the varieties of maize, peas,
beans, &c., which are valued and cultivated for their seeds. In the ninth
chapter it was shown that the varieties of the pea differ but little except
in the tallness of the plant, moderately in the shape of the pod, and
greatly in the pea itself, and these are all selected points. The
varieties, however, of the _Pois sans parchemin_ differ much more in their
pods, and these are eaten and valued. I cultivated twelve varieties of the
common bean; one alone, the Dwarf Fan, differed considerably in general
appearance; two differed in the colour of their flowers, one being an
albino, and the other being wholly instead of partially purple; several
differed considerably in the shape and size of the pod, but far more in the
bean itself, and this is the valued and selected part. Toker's bean, for
instance, is twice-and-a-half as long and broad as the horse-bean, and is
much thinner and of a different shape.

The varieties of the gooseberry, as formerly described, differ much in
their fruit, but hardly perceptibly in their flowers or organs of
vegetation. With the plum, the differences likewise appear to be greater in
the fruit than in the flowers or leaves. On the other hand, the seed of the
strawberry, which corresponds with the fruit of the plum, differs hardly at
all; whilst every one knows how greatly the fruit--that is, the enlarged
receptacle--differs in the several varieties. In apples, pears, and peaches
the flowers and leaves differ considerably, but not, as far as I can judge,
in proportion with the fruit. The Chinese double-flowering peaches, on the
other hand, show that varieties of this tree have been formed, which differ
more in the flower than in fruit. If, as is highly probable, the peach is
the modified descendant of the almond, a surprising amount of change has
been effected in the same species, in the fleshy covering of the former and
in the kernels of the latter.

When parts stand in such close relation to each other as the fleshy
covering of the fruit (whatever its homological nature may be) and the
seed, when one part is modified, so generally is the other, but by no means
necessarily in the same degree. With {219} the plum-tree, for instance,
some varieties produce plums which are nearly alike, but include stones
extremely dissimilar in shape; whilst conversely other varieties produce
dissimilar fruit with barely distinguishable stones; and generally the
stones, though they have never been subjected to selection, differ greatly
in the several varieties of the plum. In other cases organs which are not
manifestly related, through some unknown bond vary together, and are
consequently liable, without any intention on man's part, to be
simultaneously acted on by selection. Thus the varieties of the stock
(Matthiola) have been selected solely for the beauty of their flowers, but
the seeds differ greatly in colour and somewhat in size. Varieties of the
lettuce have been selected solely on account of their leaves, yet produce
seeds which likewise differ in colour. Generally, through the law of
correlation, when a variety differs greatly from its fellow-varieties in
any one character, it differs to a certain extent in several other
characters. I observed this fact when I cultivated together many varieties
of the same species, for I used first to make a list of the varieties which
differed most from each other in their foliage and manner of growth,
afterwards of those that differed most in their flowers, then in their
seed-capsules, and lastly in their mature seed; and I found that the same
names generally occurred in two, three, or four of the successive lists.
Nevertheless the greatest amount of difference between the varieties was
always exhibited, as far as I could judge, by that part or organ for which
the plant was cultivated.

When we bear in mind that each plant was at first cultivated because useful
to man, and that its variation was a subsequent, often a long subsequent,
event, we cannot explain the greater amount of diversity in the valuable
parts by supposing that species endowed with an especial tendency to vary
in any particular manner, were originally chosen. We must attribute the
result to the variations in these parts having been successively preserved,
and thus continually augmented; whilst other variations, excepting such as
inevitably appeared through correlation, were neglected and lost. Hence we
may infer that most plants might be made, through long-continued selection,
to yield races as different from each other in any character {220} as they
now are in those parts for which they are valued and cultivated.

With animals we see something of the same kind; but they have not been
domesticated in sufficient number or yielded sufficient varieties for a
fair comparison. Sheep are valued for their wool, and the wool differs much
more in the several races than the hair in cattle. Neither sheep, goats,
European cattle, nor pigs are valued for their fleetness or strength; and
we do not possess breeds differing in these respects like the race-horse
and dray-horse. But fleetness and strength are valued in camels and dogs;
and we have with the former the swift dromedary and heavy camel; with the
latter the greyhound and mastiff. But dogs are valued even in a higher
degree for their mental qualities and senses; and every one knows how
greatly the races differ in these respects. On the other hand, where the
dog is valued solely to serve for food, as in the Polynesian islands and
China, it is described as an extremely stupid animal.[530] Blumenbach
remarks that "many dogs, such as the badger-dog, have a build so marked and
so appropriate for particular purposes, that I should find it very
difficult to persuade myself that this astonishing figure was an accidental
consequence of degeneration."[531] But had Blumenbach reflected on the
great principle of selection, he would not have used the term degeneration,
and he would not have been astonished that dogs and other animals should
become excellently adapted for the service of man.

On the whole we may conclude that whatever part or character is most
valued--whether the leaves, stems, tubers, bulbs, flowers, fruit, or seed
of plants, or the size, strength, fleetness, hairy covering, or intellect
of animals--that character will almost invariably be found to present the
greatest amount of difference both in kind and degree. And this result may
be safely attributed to man having preserved during a long course of
generations the variations which were useful to him, and neglected the
others.

I will conclude this chapter by some remarks on an important subject. With
animals such as the giraffe, of which {221} the whole structure is
admirably co-ordinated for certain purposes, it has been supposed that all
the parts must have been simultaneously modified; and it has been argued
that, on the principle of natural selection, this is scarcely possible. But
in thus arguing, it has been tacitly assumed that the variations must have
been abrupt and great. No doubt, if the neck of a ruminant were suddenly to
become greatly elongated, the fore limbs and back would have to be
simultaneously strengthened and modified; but it cannot be denied that an
animal might have its neck, or head, or tongue, or fore-limbs elongated a
very little without any corresponding modification in other parts of the
body; and animals thus slightly modified would, during a dearth, have a
slight advantage, and be enabled to browse on higher twigs, and thus
survive. A few mouthfuls more or less every day would make all the
difference between life and death. By the repetition of the same process,
and by the occasional intercrossing of the survivors, there would be some
progress, slow and fluctuating though it would be, towards the admirably
co-ordinated structure of the giraffe. If the short-faced tumbler-pigeon,
with its small conical beak, globular head, rounded body, short wings, and
small feet--characters which appear all in harmony--had been a natural
species, its whole structure would have been viewed as well fitted for its
life; but in this case we know that inexperienced breeders are urged to
attend to point after point, and not to attempt improving the whole
structure at the same time. Look at the greyhound, that perfect image of
grace, symmetry, and vigour; no natural species can boast of a more
admirably co-ordinated structure, with its tapering head, slim body, deep
chest, tucked-up abdomen, rat-like tail, and long muscular limbs, all
adapted for extreme fleetness, and for running down weak prey. Now, from
what we see of the variability of animals, and from what we know of the
method which different men follow in improving their stock--some chiefly
attending to one point, others to another point, others again correcting
defects by crosses, and so forth--we may feel assured that if we could see
the long line of ancestors of a first-rate greyhound, up to its wild
wolf-like progenitor, we should behold an infinite number of the finest
gradations, sometimes in one character and sometimes in another, but all
leading towards our {222} present perfect type. By small and doubtful steps
such as these, nature, as we may confidently believe, has progressed on her
grand march of improvement and development.

A similar line of reasoning is as applicable to separate organs as to the
whole organisation. A writer[532] has recently maintained that "it is
probably no exaggeration to suppose that, in order to improve such an organ
as the eye at all, it must be improved in ten different ways at once. And
the improbability of any complex organ being produced and brought to
perfection in any such way is an improbability of the same kind and degree
as that of producing a poem or a mathematical demonstration by throwing
letters at random on a table." If the eye were abruptly and greatly
modified, no doubt many parts would have to be simultaneously altered, in
order that the organ should remain serviceable.

But is this the case with smaller changes? There are persons who can see
distinctly only in a dull light, and this condition depends, I believe, on
the abnormal sensitiveness of the retina, and is known to be inherited.
Now, if a bird, for instance, received some great advantage from seeing
well in the twilight, all the individuals with the most sensitive retina
would succeed best and be the most likely to survive; and why should not
all those which happened to have the eye itself a little larger, or the
pupil capable of greater dilatation, be likewise preserved, whether or not
these modifications were strictly simultaneous? These individuals would
subsequently intercross and blend their respective advantages. By such
slight successive changes, the eye of a diurnal bird would be brought into
the condition of that of an owl, which has often been advanced as an
excellent instance of adaptation. Short-sight, which is often inherited,
permits a person to see distinctly a minute object at so near a distance
that it would be indistinct to ordinary eyes; and here we have a capacity
which might be serviceable under certain conditions, abruptly gained. The
Fuegians on board the {223} Beagle could certainly see distant objects more
distinctly than our sailors with all their long practice; I do not know
whether this depends on nervous sensitiveness or on the power of adjustment
in the focus; but this capacity for distant vision might, it is probable,
be slightly augmented by successive modifications of either kind.
Amphibious animals, which are enabled to see both in the water and in the
air, require and possess, as M. Plateau has shown,[533] eyes constructed on
the following plan: "the cornea is always flat, or at least much flattened
in front of the crystalline and over a space equal to the diameter of that
lens, whilst the lateral portions may be much curved." The crystalline is
very nearly a sphere, and the humours have nearly the same density as
water. Now, as a terrestrial animal slowly became more and more aquatic in
its habits, very slight changes, first in the curvature of the cornea or
crystalline, and then in the density of the humours, or conversely, might
successively occur, and would be advantageous to the animal whilst under
water, without serious detriment to its power of vision in the air. It is
of course impossible to conjecture by what steps the fundamental structure
of the eye in the Vertebrata was originally acquired, for we know
absolutely nothing about this organ in the first progenitors of the class.
With respect to the lowest animals in the scale, the transitional states
through which the eye at first probably passed, can by the aid of analogy
be indicated, as I have attempted to show in my 'Origin of Species.'[534]

       *       *       *       *       *


{224}

CHAPTER XXI.

SELECTION, _continued_.

    NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH
    APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES
    FAVOURABLE TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE
    NATURE OF THE CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE
    INDISPENSABLE--THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS
    ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE
    NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION--TENDENCY IN MAN
    TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING
    TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE--CHARACTERS
    CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY
    VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE
    VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE
    POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC
    RACES HAVE ORIGINATED--SUMMARY.

_Natural Selection, or the Survival of the Fittest, as affecting domestic
productions._--We know little on this head. But as animals kept by savages
have to provide their own food, either entirely or to a large extent,
throughout the year, it can hardly be doubted that, in different countries,
varieties differing in constitution and in various characters would succeed
best, and so be naturally selected. Hence perhaps it is that the few
domesticated animals kept by savages partake, as has been remarked by more
than one writer, of the wild appearance of their masters, and likewise
resemble natural species. Even in long-civilised countries, at least in the
wilder parts, natural selection must act on our domestic races. It is
obvious that varieties, having very different habits, constitution, and
structure, would succeed best on mountains and on rich lowland pastures.
For example, the improved Leicester sheep were formerly taken to the
Lammermuir Hills; but an intelligent sheep-master reported that "our coarse
lean pastures were unequal to the task of supporting such heavy-bodied
sheep; and they gradually dwindled away into less and less bulk: {225} each
generation was inferior to the preceding one; and when the spring was
severe, seldom more than two-thirds of the lambs survived the ravages of
the storms."[535] So with the mountain cattle of North Wales and the
Hebrides, it has been found that they could not withstand being crossed
with the larger and more delicate lowland breeds. Two French naturalists,
in describing the horses of Circassia, remark that, subjected as they are
to extreme vicissitudes of climate, having to search for scanty pasture,
and exposed to constant danger from wolves, the strongest and most vigorous
alone survive.[536]

Every one must have been struck with the surpassing grace, strength, and
vigour of the Game-cock, with its bold and confident air, its long, yet
firm neck, compact body, powerful and closely pressed wings, muscular
thighs, strong beak massive at the base, dense and sharp spurs set low on
the legs for delivering the fatal blow, and its compact, glossy, and
mail-like plumage serving as a defence. Now the English game-cock has not
only been improved during many years by man's careful selection, but in
addition, as Mr. Tegetmeier has remarked,[537] by a kind of natural
selection, for the strongest, most active and courageous birds have
stricken down their antagonists in the cockpit, generation after
generation, and have subsequently served as the progenitors of their kind.

In Great Britain, in former times, almost every district had its own breed
of cattle and sheep; "they were indigenous to the soil, climate, and
pasturage of the locality on which they grazed: they seemed to have been
formed for it and by it."[538] But in this case we are quite unable to
disentangle the effects of the direct action of the conditions of life,--of
use or habit--of natural selection--and of that kind of selection which we
have seen is occasionally and unconsciously followed by man even during the
rudest periods of history.

Let us now look to the action of natural selection on special characters.
Although nature is difficult to resist, yet man often strives against her
power, and sometimes, as we shall see, with {226} success. From the facts
to be given, it will also be seen that natural selection would powerfully
affect many of our domestic productions if left unprotected. This is a
point of much interest, for we thus learn that differences apparently of
very slight importance would certainly determine the survival of a form
when forced to struggle for its own existence. It may have occurred to some
naturalists, as it formerly did to me, that, though selection acting under
natural conditions would determine the structure of all important organs,
yet that it could not affect characters which are esteemed by us of little
importance; but this is an error to which we are eminently liable, from our
ignorance of what characters are of real value to each living creature.

When man attempts to breed an animal with some serious defect in structure,
or in the mutual relation of parts, he will either partially or completely
fail, or encounter much difficulty; and this is in fact a form of natural
selection. We have seen that the attempt was once made in Yorkshire to
breed cattle with enormous buttocks, but the cows perished so often in
bringing forth their calves, that the attempt had to be given up. In
rearing short-faced tumblers, Mr. Eaton says,[539] "I am convinced that
better head and beak birds have perished in the shell than ever were
hatched; the reason being that the amazingly short-faced bird cannot reach
and break the shell with its beak, and so perishes." Here is a more curious
case, in which natural selection comes into play only at long intervals of
time: during ordinary seasons the Niata cattle can graze as well as others,
but occasionally, as from 1827 to 1830, the plains of La Plata suffer from
long-continued droughts and the pasture is burnt up; at such times common
cattle and horses perish by the thousand, but many survive by browsing on
twigs, reeds, &c.; this the Niata cattle cannot so well effect from their
upturned jaws and the shape of their lips; consequently, if not attended
to, they perish before the other cattle. In Colombia, according to Roulin,
there is a breed of nearly hairless cattle, called Pelones; these succeed
in their native hot district, but are found too tender for the Cordillera;
in this case, natural selection {227} determines only the range of the
variety. It is obvious that a host of artificial races could never survive
in a state of nature;--such as Italian greyhounds,--hairless and almost
toothless Turkish dogs,--fantail pigeons, which cannot fly well against a
strong wind,--barbs with their vision impeded by their eye-wattle,--Polish
fowls with their vision impeded by their great topknots,--hornless bulls
and rams which consequently cannot cope with other males, and thus have a
poor chance of leaving offspring,--seedless plants, and many other such
cases.

Colour is generally esteemed by the systematic naturalist as unimportant:
let us, therefore, see how far it indirectly affects our domestic
productions, and how far it would affect them if they were left exposed to
the full force of natural selection. In a future chapter I shall have to
show that constitutional peculiarities of the strangest kind, entailing
liability to the action of certain poisons, are correlated with the colour
of the skin. I will here give a single case, on the high authority of
Professor Wyman; he informs me that, being surprised at all the pigs in a
part of Virginia being black, he made inquiries, and ascertained that these
animals feed on the roots of the _Lachnanthes tinctoria_, which colours
their bones pink, and, excepting in the case of the black varieties, causes
the hoofs to drop off. Hence, as one of the squatters remarked, "we select
the black members of the litter for raising, as they alone have a good
chance of living." So that here we have artificial and natural selection
working hand in hand. I may add that in the Tarentino the inhabitants keep
black sheep alone, because the _Hypericum crispum_ abounds there; and this
plant does not injure black sheep, but kills the white ones in about a
fortnight's time.[540]

Complexion, and liability to certain diseases, are believed to run together
in man and the lower animals. Thus white terriers suffer more than terriers
of any other colour from the fatal Distemper.[541] In North America
plum-trees are liable to a disease which Downing[542] believes is not
caused by insects; the kinds bearing purple fruit are most affected, "and
we have never known the green or yellow fruited varieties infected {228}
until the other sorts had first become filled with the knots." On the other
hand, peaches in North America suffer much from a disease called the
_yellows_, which seems to be peculiar to that continent, and "more than
nine-tenths of the victims, when the disease first appeared, were the
yellow-fleshed peaches. The white-fleshed kinds are much more rarely
attacked; in some parts of the country never." In Mauritius, the white
sugar-canes have of late years been so severely attacked by a disease, that
many planters have been compelled to give up growing this variety (although
fresh plants were imported from China for trial), and cultivate only red
canes.[543] Now, if these plants had been forced to struggle with other
competing plants and enemies, there cannot be a doubt that the colour of
the flesh or skin of the fruit, unimportant as these characters are
considered, would have rigorously determined their existence.

Liability to the attacks of parasites is also connected with colour. It
appears that white chickens are certainly more subject than dark-coloured
chickens to the _gapes_, which is caused by a parasitic worm in the
trachea.[544] On the other hand, experience has shown that in France the
caterpillars which produce white cocoons resist the deadly fungus better
than those producing yellow cocoons.[545] Analogous facts have been
observed with plants: a new and beautiful white onion, imported from
France, though planted close to other kinds, was alone attacked by a
parasitic fungus.[546] White verbenas are especially liable to mildew.[547]
Near Malaga, during an early period of the vine-disease, the green sorts
suffered most; "and red and black grapes, even when interwoven with the
sick plants, suffered not at all." In France whole groups of varieties were
comparatively free, and others, such as the Chasselas, did not afford a
single fortunate exception; but I do not know whether any correlation
between colour and liability to disease was here observed.[548] In a former
chapter it was shown how curiously liable one variety of the strawberry is
to mildew.

{229}

It is certain that insects regulate in many cases the range and even the
existence of the higher animals, whilst living under their natural
conditions. Under domestication light-coloured animals suffer most: in
Thuringia[549] the inhabitants do not like grey, white, or pale cattle,
because they are much more troubled by various kinds of flies than the
brown, red, or black cattle. An Albino negro, it has been remarked,[550]
was peculiarly sensitive to the bites of insects. In the West Indies[551]
it is said that "the only horned cattle fit for work are those which have a
good deal of black in them. The white are terribly tormented by the
insects; and they are weak and sluggish in proportion to the white."

In Devonshire there is a prejudice against white pigs, because it is
believed that the sun blisters them when turned out;[552] and I knew a man
who would not keep white pigs in Kent, for the same reason. The scorching
of flowers by the sun seems likewise to depend much on colour; thus, dark
pelargoniums suffer most; and from various accounts it is clear that the
cloth-of-gold variety will not withstand a degree of exposure to sunshine
which other varieties enjoy. Another amateur asserts that not only all
dark-coloured verbenas, but likewise scarlets, suffer from the sun; "the
paler kinds stand better, and pale blue is perhaps the best of all." So
again with the heartsease (_Viola tricolor_); hot weather suits the
blotched sorts, whilst it destroys the beautiful markings of some other
kinds.[553] During one extremely cold season in Holland all red-flowered
hyacinths were observed to be very inferior in quality. It is believed by
many agriculturists that red wheat is hardier in northern climates than
white wheat.[554]

With animals, white varieties from being conspicuous are the most liable to
be attacked by beasts and birds of prey. In parts of France and Germany
where hawks abound, persons are advised not to keep white pigeons; for, as
Parmentier says, "it {230} is certain that in a flock the white always
first fall victims to the kite." In Belgium, where so many societies have
been established for the flight of carrier-pigeons, white is the one colour
which for the same reason is disliked.[555] On the other hand, it is said
that the sea-eagle (_Falco ossifragus_, Linn.) on the west coast of Ireland
picks out the black fowls, so that "the villagers avoid as much as possible
rearing birds of that colour." M. Daudin,[556] speaking of white rabbits
kept in warrens in Russia, remarks that their colour is a great
disadvantage, as they are thus more exposed to attack, and can be seen
during bright nights from a distance. A gentleman in Kent, who failed to
stock his woods with a nearly white and hardy kind of rabbit, accounted in
the same manner for their early disappearance. Any one who will watch a
white cat prowling after her prey will soon perceive under what a
disadvantage she lies.

The white Tartarian cherry, "owing either to its colour being so much like
that of the leaves, or to the fruit always appearing from a distance
unripe," is not so readily attacked by birds as other sorts. The
yellow-fruited raspberry, which generally comes nearly true by seed, "is
very little molested by birds, who evidently are not fond of it; so that
nets may be dispensed with in places where nothing else will protect the
red fruit."[557] This immunity, though a benefit to the gardener, would be
a disadvantage in a state of nature both to the cherry and raspberry, as
their dissemination depends on birds. I noticed during several winters that
some trees of the yellow-berried holly, which were raised from seed from a
wild tree found by my father, remained covered with fruit, whilst not a
scarlet berry could be seen on the adjoining trees of the common kind. A
friend informs me that a mountain-ash (_Pyrus aucuparia_) growing in his
garden bears berries which, though not differently coloured, are always
devoured by birds before those on the other trees. This variety of the
mountain-ash would thus be more freely disseminated, and the yellow-berried
variety of the holly less freely, than the common varieties of these two
trees.

{231}

Independently of colour, other trifling differences are sometimes found to
be of importance to plants under cultivation, and would be of paramount
importance if they had to fight their own battle and to struggle with many
competitors. The thin-shelled peas, called _pois sans parchemin_, are
attacked by birds[558] much more than common peas. On the other hand, the
purple-podded pea, which has a hard shell, escaped the attacks of tomtits
(_Parus major_) in my garden far better than any other kind. The
thin-shelled walnut likewise suffers greatly from the tomtit.[559] These
same birds have been observed to pass over and thus favour the filbert,
destroying only the other kinds of nuts which grew in the same
orchard.[560]

Certain varieties of the pear have soft bark, and these suffer severely
from boring wood-beetles; whilst other varieties are known to resist their
attacks much better.[561] In North America the smoothness, or absence of
down on the fruit, makes a great difference in the attacks of the weevil,
"which is the uncompromising foe of all smooth stone-fruits;" and the
cultivator "has the frequent mortification of seeing nearly all, or indeed
often the whole crop, fall from the trees when half or two-thirds grown."
Hence the nectarine suffers more than the peach. A particular variety of
the Morello cherry, raised in North America, is without any assignable
cause more liable to be injured by this same insect than other
cherry-trees.[562] From some unknown cause, the Winter Majetin apple enjoys
the great advantage of not being infested by the coccus. On the other hand,
a particular case has been recorded in which aphides confined themselves to
the Winter Nelis pear, and touched no other kind in an extensive
orchard.[563] The existence of minute glands on the leaves of peaches,
nectarines, and apricots, would not be esteemed by botanists as a character
of the least importance, for they are present or absent in closely related
sub-varieties, descended from the same parent-tree; yet there is good
evidence[564] that the {232} absence of glands leads to mildew, which is
highly injurious to these trees.

A difference either in flavour or in the amount of nutriment in certain
varieties causes them to be more eagerly attacked by various enemies than
other varieties of the same species. Bullfinches (_Pyrrhula vulgaris_)
injure our fruit-trees by devouring the flower-buds, and a pair of these
birds have been seen "to denude a large plum-tree in a couple of days of
almost every bud;" but certain varieties[565] of the apple and thorn
(_Cratægus oxyacantha_) are more especially liable to be attacked. A
striking instance of this was observed in Mr. Rivers's garden, in which two
rows of a particular variety of plum[566] had to be carefully protected, as
they were usually stripped of all their buds during the winter, whilst
other sorts growing near them escaped. The root (or enlarged stem) of
Laing's Swedish turnip is preferred by hares, and therefore suffers more
than other varieties. Hares and rabbits eat down common rye before St.
John's-day-rye, when both grow together.[567] In the South of France, when
an orchard of almond-trees is formed, the nuts of the bitter variety are
sown, "in order that they may not be devoured by field-mice;"[568] so we
see the use of the bitter principle in almonds.

Other slight differences, which would be thought quite unimportant, are no
doubt sometimes of great service both to plants and animals. The
Whitesmith's gooseberry, as formerly stated, produces its leaves later than
other varieties, and, as the flowers are thus left unprotected, the fruit
often fails. In one variety of the cherry, according to Mr. Rivers,[569]
the petals are much curled backwards, and in consequence of this the
stigmas were observed to be killed by a severe frost; whilst at the same
time, in another variety with incurved petals, the stigmas were not in the
least injured. The straw of the Fenton wheat is remarkably unequal in
height; and a competent observer believes that this variety is highly
productive, partly because the ears, from being distributed at various
heights above the ground, {233} are less crowded together. The same
observer maintains that in the upright varieties the divergent awns are
serviceable by breaking the shocks when the ears are dashed together by the
wind.[570] If several varieties of a plant are grown together, and the seed
is indiscriminately harvested, it is clear that the hardier and more
productive kinds will, by a sort of natural selection, gradually prevail
over the others; this takes place, as Colonel Le Couteur believes,[571] in
our wheat-fields, for, as formerly shown, no variety is quite uniform in
character. The same thing, as I am assured by nurserymen, would take place
in our flower-gardens, if the seed of the different varieties were not
separately saved. When the eggs of the wild and tame duck are hatched
together, the young wild ducks almost invariably perish, from being of
smaller size and not getting their fair share of food.[572]

Facts in sufficient number have now been given showing that natural
selection often checks, but occasionally favours, man's power of selection.
These facts teach us, in addition, a valuable lesson, namely, that we ought
to be extremely cautious in judging what characters are of importance in a
state of nature to animals and plants, which have to struggle from the hour
of their birth to that of their death for existence,--their existence
depending on conditions, about which we are profoundly ignorant.

_Circumstances favourable to Selection by Man._

The possibility of selection rests on variability, and this, as we shall
see in the following chapters, mainly depends on changed conditions of
life, but is governed by infinitely complex, and, to a great extent,
unknown laws. Domestication, even when long continued, occasionally causes
but a small amount of variability, as in the case of the goose and turkey.
The slight differences, however, which characterise each individual animal
and plant would in most, probably in all cases, suffice for the production
of distinct races through careful and prolonged selection. We see what
selection, though acting on mere individual differences, can effect when
families of cattle, sheep, {234} pigeons, &c., of the same race, have been
separately bred during a number of years by different men without any wish
on their part to modify the breed. We see the same fact in the difference
between hounds bred for hunting in different districts,[573] and in many
other such cases.

In order that selection should produce any result, it is manifest that the
crossing of distinct races must be prevented; hence facility in pairing, as
with the pigeon, is highly favourable for the work; and difficulty in
pairing, as with cats, prevents the formation of distinct breeds. On nearly
the same principle the cattle of the small island of Jersey have been
improved in their milking qualities "with a rapidity that could not have
been obtained in a widely extended country like France."[574] Although free
crossing is a danger on the one side which every one can see, too close
interbreeding is a hidden danger on the other side. Unfavourable conditions
of life overrule the power of selection. Our improved heavy breeds of
cattle and sheep could not have been formed on mountainous pastures; nor
could dray-horses have been raised on a barren and inhospitable land, such
as the Falkland islands, where even the light horses of La Plata rapidly
decrease in size. Nor could the wool of sheep have been much increased in
length within the Tropics; yet selection has kept Merino sheep nearly true
under diversified and unfavourable conditions of life. The power of
selection is so great, that breeds of the dog, sheep, and poultry, of the
largest and least size, long and short beaked pigeons, and other breeds
with opposite characters, have had their characteristic qualities
augmented, though treated in every way alike, being exposed to the same
climate and fed on the same food. Selection, however, is either checked or
favoured by the effects of use or habit. Our wonderfully-improved pigs
could never have been formed if they had been forced to search for their
own food; the English racehorse and greyhound could not have been improved
up to their present high standard of excellence without constant training.

As conspicuous deviations of structure occur rarely, the improvement of
each breed is generally the result, as already {235} remarked, of the
selection of slight individual differences. Hence the closest attention,
the sharpest powers of observation, and indomitable perseverance, are
indispensable. It is, also, highly important that many individuals of the
breed which is to be improved should be raised; for thus there will be a
better chance of the appearance of variations in the right direction, and
individuals varying in an unfavourable manner may be freely rejected or
destroyed. But that a large number of individuals should be raised, it is
necessary that the conditions of life should favour the propagation of the
species. Had the peacock been bred as easily as the fowl, we should
probably ere this have had many distinct races. We see the importance of a
large number of plants, from the fact of nursery gardeners almost always
beating amateurs in the exhibition of new varieties. In 1845 it was
estimated[575] that between 4000 and 5000 pelargoniums were annually raised
from seed in England, yet a decidedly improved variety is rarely obtained.
At Messrs. Carter's grounds, in Essex, where such flowers as the Lobelia,
Nemophila, Mignonette, &c., are grown by the acre for seed, "scarcely a
season passes without some new kinds being raised, or some improvement
affected on old kinds."[576] At Kew, as Mr. Beaton remarks, where many
seedlings of common plants are raised, "you see new forms of Laburnums,
Spiræas, and other shrubs."[577] So with animals: Marshall,[578] in
speaking of the sheep in one part of Yorkshire, remarks, "as they belong to
poor people, and are mostly in small lots, they never can be improved."
Lord Rivers, when asked how he succeeded in always having first-rate
greyhounds, answered, "I breed many, and hang many." This, as another man
remarks, "was the secret of his success; and the same will be found in
exhibiting fowls,--successful competitors breed largely, and keep the
best."[579]

It follows from this that the capacity of breeding at an early age and at
short successive intervals, as with pigeons, rabbits, &c., facilitates
selection; for the result is thus soon made visible, and perseverance in
the work is encouraged. It can hardly be {236} accidental that the great
majority of the culinary and agricultural plants which have yielded
numerous races are annuals or biennials, which therefore are capable of
rapid propagation and thus of improvement. Sea-kale, asparagus, common and
Jerusalem artichokes, potatoes, and onions, alone are perennials. Onions
are propagated like annuals, and of the other plants just specified, none,
with the exception of the potato, have yielded more than one or two
varieties. No doubt fruit-trees, which cannot be propagated quickly by
seed, have yielded a host of varieties, though not permanent races; but
these, judging from pre-historic remains, were produced at a later and more
civilised epoch than the races of culinary and agricultural plants.

A species may be highly variable, but distinct races will not be formed, if
from any cause selection be not applied. The carp is highly variable, but
it would be extremely difficult to select slight variations in fishes
whilst living in their natural state, and distinct races have not been
formed;[580] on the other hand, a closely allied species, the gold-fish,
from being reared in glass or open vessels, and from having been carefully
attended to by the Chinese, has yielded many races. Neither the bee, which
has been semi-domesticated from an extremely remote period, nor the
cochineal insect, which was cultivated by the aboriginal Mexicans, has
yielded races; and it would be impossible to match the queen-bee with any
particular drone, and most difficult to match cochineal insects.
Silk-moths, on the other hand, have been subjected to rigorous selection,
and have produced a host of races. Cats, which from their nocturnal habits
cannot be selected for breeding, do not, as formerly remarked, yield
distinct races in the same country. The ass in England varies much in
colour and size; but it is an animal of little value, bred by poor people;
consequently there has been no selection, and distinct races have not been
formed. We must not attribute the inferiority of our asses to climate, for
in India they are of even smaller size than in Europe. But when selection
is brought to bear on the ass, all is changed. Near Cordova, as I am
informed (Feb. 1860) by Mr. W. E. Webb, C.E., they are carefully bred, as
much as 200l. having been paid for a stallion ass, {237} and they have been
immensely improved. In Kentucky, asses have been imported (for breeding
mules) from Spain, Malta, and France; these "seldom averaged more than
fourteen hands high; but the Kentuckians, by great care, have raised them
up to fifteen hands, and sometimes even to sixteen. The prices paid for
these splendid animals, for such they really are, will prove how much they
are in request. One male, of great celebrity, was sold for upwards of one
thousand pounds sterling." These choice asses are sent to cattle-shows, one
day being given to their exhibition.[581]

Analogous facts have been observed with plants: the nutmeg-tree in the
Malay archipelago is highly variable, but there has been no selection, and
there are no distinct races.[582] The common mignonette (_Reseda odorata_),
from bearing inconspicuous flowers, valued solely for their fragrance,
"remains in the same unimproved condition as when first introduced."[583]
Our common forest-trees are very variable, as may be seen in every
extensive nursery-ground; but as they are not valued like fruit-trees, and
as they seed late in life, no selection has been applied to them;
consequently, as Mr. Patrick Matthews remarks,[584] they have not yielded
distinct races, leafing at different periods, growing to different sizes,
and producing timber fit for different purposes. We have gained only some
fanciful and semi-monstrous varieties, which no doubt appeared suddenly as
we now see them.

Some botanists have argued that plants cannot have so strong a tendency to
vary as is generally supposed, because many species long grown in botanic
gardens, or unintentionally cultivated year after year mingled with our
corn crops, have not produced distinct races; but this is accounted for by
slight variations not having been selected and propagated. Let a plant
which is now grown in a botanic garden, or any common weed, be cultivated
on a large scale, and let a sharp-sighted gardener look out for each slight
variety and sow the seed, and then, if distinct races are not produced, the
argument will be valid.

{238}

The importance of selection is likewise shown by considering special
characters. For instance, with most breeds of fowls the form of the comb
and the colour of the plumage have been attended to, and are eminently
characteristic of each race; but in Dorkings, fashion has never demanded
uniformity of comb or colour; and the utmost diversity in these respects
prevails. Rose-combs, double-combs, cup-combs, &c., and colours of all
kinds, may be seen in purely-bred and closely related Dorking fowls, whilst
other points, such as the general form of body, and the presence of an
additional toe, have been attended to, and are invariably present. It has
also been ascertained that colour can be fixed in this breed, as well as in
any other.[585]

       *       *       *       *       *

During the formation or improvement of a breed, its members will always be
found to vary much in those characters to which especial attention is
directed, and of which each slight improvement is eagerly sought and
selected. Thus with short-faced tumbler-pigeons, the shortness of the beak,
shape of head and plumage,--with carriers, the length of the beak and
wattle,--with fantails, the tail and carriage,--with Spanish fowls, the
white face and comb,--with long-eared rabbits, the length of ear, are all
points which are eminently variable. So it is in every case, and the large
price paid for first-rate animals proves the difficulty of breeding them up
to the highest standard of excellence. This subject has been discussed by
fanciers,[586] and the greater prizes given for highly improved breeds, in
comparison with those given for old breeds which are not now undergoing
rapid improvement, has been fully justified. Nathusius makes[587] a similar
remark when discussing the less uniform character of improved Shorthorn
cattle and of the English horse, in comparison, for example, with the
unennobled cattle of Hungary, or with the horses of the Asiatic steppes.
This want of uniformity in the parts which at the time are undergoing
selection, chiefly depends on the strength of the principle of reversion
but it likewise depends to a certain extent on the continued {239}
variability of the parts which have recently varied. That the same parts do
continue varying in the same manner we must admit, for, if it were not so,
there could be no improvement beyond an early standard of excellence, and
we know that such improvement is not only possible, but is of general
occurrence.

As a consequence of continued variability, and more especially of
reversion, all highly improved races, if neglected or not subjected to
incessant selection, soon degenerate. Youatt gives a curious instance of
this in some cattle formerly kept in Glamorganshire; but in this case the
cattle were not fed with sufficient care. Mr. Baker, in his memoir on the
Horse, sums up: "It must have been observed in the preceding pages that,
whenever there has been neglect, the breed has proportionally
deteriorated."[588] If a considerable number of improved cattle, sheep, or
other animals of the same race, were allowed to breed freely together, with
no selection, but with no change in their condition of life, there can be
no doubt that after a score or hundred generations they would be very far
from excellent of their kind; but, from what we see of the many common
races of dogs, cattle, fowls, pigeons, &c., which without any particular
care have long retained nearly the same character, we have no grounds for
believing that they would altogether depart from their type.

It is a general belief amongst breeders that characters of all kinds become
fixed by long-continued inheritance. But I have attempted to show in the
fourteenth chapter that this belief apparently resolves itself into the
following proposition, namely, that all characters whatever, whether
recently acquired or ancient, tend to be transmitted, but that those which
have already long withstood all counteracting influences, will, as a
general rule, continue to withstand them, and consequently be faithfully
transmitted.

_Tendency in Man to carry the practice of Selection to an extreme point._

It is an important principle that in the process of selection man almost
invariably wishes to go to an extreme point. Thus, in useful qualities,
there is no limit to his desire to breed certain {240} horses and dogs as
fleet as possible, and others as strong as possible; certain kinds of sheep
for extreme fineness, and others for extreme length of wool; and he wishes
to produce fruit, grain, tubers, and other useful parts of plants, as large
and excellent as possible. With animals bred for amusement, the same
principle is even more powerful; for fashion, as we see even in our dress,
always runs to extremes. This view has been expressly admitted by fanciers.
Instances were given in the chapters on the pigeon, but here is another:
Mr. Eaton, after describing a comparatively new variety, namely, the
Archangel, remarks, "What fanciers intend doing with this bird I am at a
loss to know, whether they intend to breed it down to the tumbler's head
and beak, or carry it out to the carrier's head and beak; leaving it as
they found it, is not progressing." Ferguson, speaking of fowls, says,
"their peculiarities, whatever they may be, must necessarily be fully
developed: a little peculiarity forms nought but ugliness, seeing it
violates the existing laws of symmetry." So Mr. Brent, in discussing the
merits of the sub-varieties of the Belgian canary-bird, remarks, "Fanciers
always go to extremes; they do not admire indefinite properties."[589]

This principle, which necessarily leads to divergence of character,
explains the present state of various domestic races. We can thus see how
it is that race-horses and dray-horses, greyhounds and mastiffs, which are
opposed to each other in every character,--how varieties so distinct as
Cochin-China fowls and bantams, or carrier-pigeons with very long beaks,
and tumblers with excessively short beaks, have been derived from the same
stock. As each breed is slowly improved, the inferior varieties are first
neglected and finally lost. In a few cases, by the aid of old records, or
from intermediate varieties still existing in countries where other
fashions have prevailed, we are enabled partially to trace the graduated
changes through which certain breeds have passed. Selection, whether
methodical or unconscious, always tending towards an extreme point,
together with the neglect and slow extinction of the intermediate and
less-valued forms, is the key which unlocks the mystery how man has
produced such wonderful results.

{241}

In a few instances selection, guided by utility for a single purpose, has
led to convergence of character. All the improved and different races of
the pig, as Nathusius has well shown,[590] closely approach each other in
character, in their shortened legs and muzzles, their almost hairless,
large, rounded bodies, and small tusks. We see some degree of convergence
in the similar outline of the body in well-bred cattle belonging to
distinct races.[591] I know of no other such cases.

Continued divergence of character depends on, and is indeed a clear proof,
as previously remarked, of the same parts continuing to vary in the same
direction. The tendency to mere general variability or plasticity of
organisation can certainly be inherited, even from one parent, as has been
shown by Gärtner and Kölreuter, in the production of varying hybrids from
two species, of which one alone was variable. It is in itself probable
that, when an organ has varied in any manner, it will again vary in the
same manner, if the conditions which first caused the being to vary remain,
as far as can be judged, the same. This is either tacitly or expressly
admitted by all horticulturists: if a gardener observes one or two
additional petals in a flower, he feels confident that in a few generations
he will be able to raise a double flower, crowded with petals. Some of the
seedlings from the weeping Moccas oak were so prostrate that they only
crawled along the ground. A seedling from the fastigate or upright Irish
yew is described as differing greatly from the parent-form "by the
exaggeration of the fastigate habit of its branches."[592] Mr. Sheriff, who
has been more successful than any other man in raising new kinds of wheat,
remarks, "A good variety may safely be regarded as the forerunner of a
better one."[593] A great rose-grower, Mr. Rivers, has made the same remark
with respect to roses. Sageret,[594] who had large experience, in speaking
of the future progress of fruit-trees, observes that the most important
principle is "that the more plants have departed from their original type,
the more they tend to depart from it." There is apparently much truth in
this {242} remark; for we can in no other way understand the surprising
amount of difference between varieties in the parts or qualities which are
valued, whilst other parts retain nearly their original character.

The foregoing discussion naturally leads to the question, what is the limit
to the possible amount of variation in any part or quality, and,
consequently, is there any limit to what selection can effect? Will a
race-horse ever be reared fleeter than Eclipse? Can our prize-cattle and
sheep be still further improved? Will a gooseberry ever weigh more than
that produced by "London" in 1852? Will the beet-root in France yield a
greater percentage of sugar? Will future varieties of wheat and other grain
produce heavier crops than our present varieties? These questions cannot be
positively answered; but it is certain that we ought to be cautious in
answering by a negative. In some lines of variation the limit has probably
been reached. Youatt believes that the reduction of bone in some of our
sheep has already been carried so far that it entails great delicacy of
constitution.[595] But seeing the great improvement within recent times in
our cattle and sheep, and especially in our pigs; seeing the wonderful
increase in weight in our poultry of all kinds during the last few years;
he would be a bold man who would assert that perfection has been reached.
Eclipse perhaps may never be beaten until all our race-horses have been
rendered swifter, through the selection of the best horses during many
generations; and then the old Eclipse may possibly be eclipsed; but, as Mr.
Wallace has remarked, there must be an ultimate limit to the fleetness of
every animal, whether under nature or domestication; and with the horse
this limit has perhaps been reached. Until our fields are better manured,
it may be impossible for a new variety of wheat to yield a heavier crop.
But in many cases those who are best qualified to judge do not believe that
the extreme point has as yet been reached even with respect to characters
which have already been carried to a high standard of perfection. For
instance, the short-faced tumbler-pigeon has been greatly modified;
nevertheless, according to Mr. Eaton,[596] "the field is still as open for
fresh competitors as it was one hundred years ago." Over and over again it
has been said that {243} perfection had been attained with our flowers, but
a higher standard has soon been reached. Hardly any fruit has been more
improved than the strawberry, yet a great authority remarks,[597] "it must
not be concealed that we are far from the extreme limits at which we may
arrive."

Time is an important element in the formation of our domestic races, as it
permits innumerable individuals to be born, and these when exposed to
diversified conditions are rendered variable. Methodical selection has been
occasionally practised from an ancient period to the present day, even by
semi-civilised people, and during former times will have produced some
effect. Unconscious selection will have been still more effective; for
during a lengthened period the more valuable individual animals will
occasionally have been saved, and the less valuable neglected. In the
course, also, of time, different varieties, especially in the less
civilised countries, will have been more or less modified through natural
selection. It is generally believed, though on this head we have little or
no evidence, that new characters in time become fixed; and after having
long remained fixed it seems possible that under new conditions they might
again be rendered variable.

How great the lapse of time has been since man first domesticated animals
and cultivated plants, we begin dimly to see. When the lake-buildings of
Switzerland were inhabited during the Neolithic period, several animals
were already domesticated and various plants cultivated. If we may judge
from what we now see of the habits of savages, it is probable that the men
of the earlier Stone period--when many great quadrupeds were living which
are now extinct, and when the face of the country was widely different from
what it now is--possessed at least some few domesticated animals, although
their remains have not as yet been discovered. If the science of language
can be trusted, the art of ploughing and sowing the land was followed, and
the chief animals had been already domesticated, at an epoch so immensely
remote, that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavonic
languages had not as yet diverged from their common parent-tongue.[598]

{244}

It is scarcely possible to overrate the effects of selection occasionally
carried on in various ways and places during thousands of generations. All
that we know, and, in a still stronger degree, all that we do not
know,[599] of the history of the great majority of our breeds, even of our
more modern breeds, agrees with the view that their production, through the
action of unconscious and methodical selection, has been almost insensibly
slow. When a man attends rather more closely than is usual to the breeding
of his animals, he is almost sure to improve them to a slight extent. They
are in consequence valued in his immediate neighbourhood, and are bred by
others; and their characteristic features, whatever these may be, will then
slowly but steadily be increased, sometimes by methodical and almost always
by unconscious selection. At last a strain, deserving to be called a
sub-variety, becomes a little more widely known, receives a local name, and
spreads. The spreading will have been extremely slow during ancient and
less civilised times, but now is rapid. By the time that the new breed had
assumed a somewhat distinct character, its history, hardly noticed at the
time, will have been completely forgotten; for, as Low remarks,[600] "we
know how quickly the memory of such events is effaced."

As soon as a new breed is thus formed, it is liable through the same
process to break up into new strains and sub-varieties. For different
varieties are suited for, and are valued under, different circumstances.
Fashion changes, but, should a fashion last for even a moderate length of
time, so strong is the principle of inheritance, that some effect will
probably be impressed on the breed. Thus varieties go on increasing in
number, and history shows us how wonderfully they have increased since the
earliest records.[601] As each new variety is produced, the earlier,
intermediate, and less valuable forms will be neglected, and perish. When a
breed, from not being valued, is kept in small numbers, its extinction
almost inevitably follows sooner or later, either from accidental causes of
destruction or from close interbreeding; and this is an event which, in the
case of well-marked breeds, excites attention. The birth or production of a
new domestic race is so slow a process that it {245} escapes notice; its
death or destruction is comparatively sudden, is often recorded, and when
too late sometimes regretted.

Several authors have drawn a wide distinction between artificial and
natural races. The latter are more uniform in character, possessing in a
high degree the character of natural species, and are of ancient origin.
They are generally found in less civilised countries, and have probably
been largely modified by natural selection, and only to a small extent by
man's unconscious and methodical selection. They have, also, during a long
period, been directly acted on by the physical conditions of the countries
which they inhabit. The so-called artificial races, on the other hand, are
not so uniform in character; some have a semi-monstrous character, such as
"the wry-legged terriers so useful in rabbit-shooting,"[602] turnspit dogs,
ancon sheep, niata oxen, Polish fowls, fantail-pigeons, &c.; their
characteristic features have generally been acquired suddenly, though
subsequently increased in many cases by careful selection. Other races,
which certainly must be called artificial, for they have been largely
modified by methodical selection and by crossing, as the English
race-horse, terrier-dogs, the English game-cock, Antwerp carrier-pigeons,
&c., nevertheless cannot be said to have an unnatural appearance; and no
distinct line, as it seems to me, can be drawn between natural and
artificial races.

It is not surprising that domestic races should generally present a
different aspect from natural species. Man selects and propagates
modifications solely for his own use or fancy, and not for the creature's
own good. His attention is struck by strongly marked modifications, which
have appeared suddenly, due to some great disturbing cause in the
organisation. He attends almost exclusively to external characters; and
when he succeeds in modifying internal organs,--when for instance he
reduces the bones and offal, or loads the viscera with fat, or gives early
maturity, &c.,--the chances are strong that he will at the same time weaken
the constitution. On the other hand, when an animal has to struggle
throughout its life with many competitors and enemies, under circumstances
inconceivably complex and liable to change, modifications of the most
varied nature--in the internal organs as well as in external characters, in
the {246} functions and mutual relations of parts--will be rigorously
tested, preserved, or rejected. Natural selection often checks man's
comparatively feeble and capricious attempts at improvement; and if this
were not so, the result of his work, and of nature's work, would be even
still more different. Nevertheless, we must not overrate the amount of
difference between natural species and domestic races; the most experienced
naturalists have often disputed whether the latter are descended from one
or from several aboriginal stocks, and this clearly shows that there is no
palpable difference between species and races.

Domestic races propagate their kind far more truly, and endure for much
longer periods, than most naturalists are willing to admit. Breeders feel
no doubt on this head; ask a man who has long reared Shorthorn or Hereford
cattle, Leicester or Southdown sheep, Spanish or Game poultry, tumbler or
carrier-pigeons, whether these races may not have been derived from common
progenitors, and he will probably laugh you to scorn. The breeder admits
that he may hope to produce sheep with finer or longer wool and with better
carcases, or handsomer fowls, or carrier-pigeons with beaks just
perceptibly longer to the practised eye, and thus be successful at an
exhibition. Thus far he will go, but no farther. He does not reflect on
what follows from adding up during a long course of time many, slight,
successive modifications; nor does he reflect on the former existence of
numerous varieties, connecting the links in each divergent line of descent.
He concludes, as was shown in the earlier chapters, that all the chief
breeds to which he has long attended are aboriginal productions. The
systematic naturalist, on the other hand, who generally knows nothing of
the art of breeding, who does not pretend to know how and when the several
domestic races were formed, who cannot have seen the intermediate
gradations, for they do not now exist, nevertheless feels no doubt that
these races are sprung from a single source. But ask him whether the
closely allied natural species which he has studied may not have descended
from a common progenitor, and he in his turn will perhaps reject the notion
with scorn. Thus the naturalist and breeder may mutually learn a useful
lesson from each other.

       *       *       *       *       *

_Summary on Selection by Man._--There can be no doubt that {247} methodical
selection has effected and will effect wonderful results. It was
occasionally practised in ancient times, and is still practised by
semi-civilised people. Characters of the highest importance, and others of
trifling value, have been attended to, and modified. I need not here repeat
what has been so often said on the part which unconscious selection has
played: we see its power in the difference between flocks which have been
separately bred, and in the slow changes, as circumstances have slowly
changed, which many animals have undergone in the same country, or when
transported into a foreign land. We see the combined effects of methodical
and unconscious selection in the great amount of difference between
varieties in those parts or qualities which are valued by man, in
comparison with those which are not valued, and consequently have not been
attended to. Natural selection often determines man's power of selection.
We sometimes err in imagining that characters, which are considered as
unimportant by the systematic naturalist, could not be affected by the
struggle for existence, and therefore be acted on by natural selection; but
striking cases have been given, showing how great an error this is.

The possibility of selection coming into action rests on variability; and
this is mainly caused, as we shall hereafter see, by changes in the
conditions of life. Selection is sometimes rendered difficult, or even
impossible, by the conditions being opposed to the desired character or
quality. It is sometimes checked by the lessened fertility and weakened
constitution which follow from long-continued close interbreeding. That
methodical selection may be successful, the closest attention and
discernment, combined with unwearied patience, are absolutely necessary;
and these same qualities, though not indispensable, are highly serviceable
in the case of unconscious selection. It is almost necessary that a large
number of individuals should be reared; for thus there will be a fair
chance of variations of the desired nature arising, and every individual
with the slightest blemish or in any degree inferior may be freely
rejected. Hence length of time is an important element of success. Thus,
also, propagation at an early age and at short intervals favours the work.
Facility in pairing animals, or their inhabiting a confined area, is
advantageous as a check to free crossing. Whenever and {248} wherever
selection is not practised, distinct races are not formed. When any one
part of the body or quality is not attended to, it remains either unchanged
or varies in a fluctuating manner, whilst at the same time other parts and
other qualities may become permanently and greatly modified. But from the
tendency to reversion and to continued variability, those parts or organs
which are now undergoing rapid improvement through selection, are likewise
found to vary much. Consequently highly-bred animals, when neglected, soon
degenerate; but we have no reason to believe that the effects of
long-continued selection would, if the conditions of life remained the
same, be soon and completely lost.

Man always tends to go to an extreme point in the selection, whether
methodical or unconscious, of all useful and pleasing qualities. This is an
important principle, as it leads to continued divergence, and in some rare
cases to convergence of character. The possibility of continued divergence
rests on the tendency in each part or organ to go on varying in the same
manner in which it has already varied; and that this occurs, is proved by
the steady and gradual improvement of many animals and plants during
lengthened periods. The principle of divergence of character, combined with
the neglect and final extinction of all previous, less-valued, and
intermediate varieties, explains the amount of difference and the
distinctness of our several races. Although we may have reached the utmost
limit to which certain characters can be modified, yet we are far from
having reached, as we have good reason to believe, the limit in the
majority of cases. Finally, from the difference between selection as
carried on by man and by nature, we can understand how it is that domestic
races often, though by no means always, differ in general aspect from
closely allied natural species.

Throughout this chapter and elsewhere I have spoken of selection as the
paramount power, yet its action absolutely depends on what we in our
ignorance call spontaneous or accidental variability. Let an architect be
compelled to build an edifice with uncut stones, fallen from a precipice.
The shape of each fragment may be called accidental; yet the shape of each
has been determined by the force of gravity, the nature {249} of the rock,
and the slope of the precipice,--events and circumstances, all of which
depend on natural laws; but there is no relation between these laws and the
purpose for which each fragment is used by the builder. In the same manner
the variations of each creature are determined by fixed and immutable laws;
but these bear no relation to the living structure which is slowly built up
through the power of selection, whether this be natural or artificial
selection.

If our architect succeeded in rearing a noble edifice, using the rough
wedge-shaped fragments for the arches, the longer stones for the lintels,
and so forth, we should admire his skill even in a higher degree than if he
had used stones shaped for the purpose. So it is with selection, whether
applied by man or by nature; for though variability is indispensably
necessary, yet, when we look at some highly complex and excellently adapted
organism, variability sinks to a quite subordinate position in importance
in comparison with selection, in the same manner as the shape of each
fragment used by our supposed architect is unimportant in comparison with
his skill.

       *       *       *       *       *


{250}

CHAPTER XXII.

CAUSES OF VARIABILITY.

    VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES
    ASSIGNED BY VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF
    EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH
    CHANGES--CLIMATE, FOOD, EXCESS OF NUTRIMENT--SLIGHT CHANGES
    SUFFICIENT--EFFECTS OF GRAFTING ON THE VARIABILITY OF
    SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO CHANGED
    CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
    INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
    VARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW
    CHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM
    REVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH
    EITHER DIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE
    VARIABILITY.

We will now consider, as far as we can, the causes of the almost universal
variability of our domesticated productions. The subject is an obscure one;
but it may be useful to probe our ignorance. Some authors, for instance Dr.
Prosper Lucas, look at variability as a necessary contingent on
reproduction, and as much an aboriginal law, as growth or inheritance.
Others have of late encouraged, perhaps unintentionally, this view by
speaking of inheritance and variability as equal and antagonistic
principles. Pallas maintained, and he has had some followers, that
variability depends exclusively on the crossing of primordially distinct
forms. Other authors attribute the tendency to variability to an excess of
food, and with animals to an excess relatively to the amount of exercise
taken, or again to the effects of a more genial climate. That these causes
are all effective is highly probable. But we must, I think, take a broader
view, and conclude that organic beings, when subjected during several
generations to any change whatever in their conditions, tend to vary; the
kind of variation which ensues depending in a far higher degree on the
nature or constitution of the being, than on the nature of the changed
conditions. {251}

Those authors who believe that it is a law of nature that each individual
should differ in some slight degree from every other, may maintain,
apparently with truth, that this is the fact, not only with all
domesticated animals and cultivated plants, but likewise with all organic
beings in a state of nature. The Laplander by long practice knows and gives
a name to each reindeer, though, as Linnæus remarks, "to distinguish one
from another among such multitudes was beyond my comprehension, for they
were like ants on an ant-hill." In Germany shepherds have won wagers by
recognising each sheep in a flock of a hundred, which they had never seen
until the previous fortnight. This power of discrimination, however, is as
nothing compared to that which some florists have acquired. Verlot mentions
a gardener who could distinguish 150 kinds of camellia, when not in flower;
and it has been positively asserted that the famous old Dutch florist
Voorhelm, who kept above 1200 varieties of the hyacinth, was hardly ever
deceived in knowing each variety by the bulb alone. Hence we must conclude
that the bulbs of the hyacinth and the branches and leaves of the camellia,
though appearing to an unpractised eye absolutely undistinguishable, yet
really differ.[603]

As Linnæus has compared the reindeer in number to ants, I may add that each
ant knows its fellow of the same community. Several times I carried ants of
the same species (_Formica rufa_) from one ant-hill to another, inhabited
apparently by tens of thousands of ants; but the strangers were instantly
detected and killed. I then put some ants taken from a very large nest into
a bottle strongly perfumed with assafoetida, and after an interval of
twenty-four hours returned them to their home; they were at first
threatened by their fellows, but were soon recognised and allowed to pass.
Hence each ant certainly recognises, independently of odour, its fellow;
and if all the ants of the same community have not some countersign or
watchword, they must present to each other's senses some distinguishable
character.

{252}

The dissimilarity of brothers or sisters of the same family, and of
seedlings from the same capsule, may be in part accounted for by the
unequal blending of the characters of the two parents, and by the more or
less complete recovery through reversion of ancestral characters on either
side; but we thus only push the difficulty further back in time, for what
made the parents or their progenitors different? Hence the belief[604] that
an innate tendency to vary exists, independently of external conditions,
seems at first sight probable. But even the seeds nurtured in the same
capsule are not subjected to absolutely uniform conditions, as they draw
their nourishment from different points; and we shall see in a future
chapter that this difference sometimes suffices greatly to affect the
character of the future plant. The less close similarity of the successive
children of the same family in comparison with human twins, which often
resemble each other in external appearance, mental disposition, and
constitution, in so extraordinary a manner, apparently proves that the
state of the parents at the exact period of conception, or the nature of
the subsequent embryonic development, has a direct and powerful influence
on the character of the offspring. Nevertheless, when we reflect on the
{253} individual differences between organic beings in a state of nature,
as shown by every wild animal knowing its mate; and when we reflect on the
infinite diversity of the many varieties of our domesticated productions,
we may well be inclined to exclaim, though falsely as I believe, that
Variability must be looked at as an ultimate fact, necessarily contingent
on reproduction.

Those authors who adopt this latter view would probably deny that each
separate variation has its own proper exciting cause. Although we can
seldom trace the precise relation between cause and effect, yet the
considerations presently to be given lead to the conclusion that each
modification must have its own distinct cause. When we hear of an infant
born, for instance, with a crooked finger, a misplaced tooth, or other
slight deviation of structure, it is difficult to bring the conviction home
to the mind that such abnormal cases are the result of fixed laws, and not
of what we blindly call accident. Under this point of view the following
case, which has been carefully examined and communicated to me by Dr.
William Ogle, is highly instructive. Two girls, born as twins, and in all
respects extremely alike, had their little fingers on both hands crooked;
and in both children the second bicuspid tooth in the upper jaw, of the
second dentition, was misplaced; for these teeth, instead of standing in a
line with the others, grew from the roof of the mouth behind the first
bicuspids. Neither the parents nor any other member of the family had
exhibited any similar peculiarity. Now, as both these children were
affected in exactly the same manner by both deviations of structure, the
idea of accident is at once excluded; and we are compelled to admit that
there must have existed some precise and sufficient cause which, if it had
occurred a hundred times, would have affected a hundred children.

We will now consider the general arguments, which appear to me to have
great weight, in favour of the view that variations of all kinds and
degrees are directly or indirectly caused by the conditions of life to
which each being, and more especially its ancestors, have been exposed.

No one doubts that domesticated productions are more variable than organic
beings which have never been removed from their {254} natural conditions.
Monstrosities graduate so insensibly into mere variations that it is
impossible to separate them; and all those who have studied monstrosities
believe that they are far commoner with domesticated than with wild animals
and plants;[605] and in the case of plants, monstrosities would be equally
noticeable in the natural as in the cultivated state. Under nature, the
individuals of the same species are exposed to nearly uniform conditions,
for they are rigorously kept to their proper places by a host of competing
animals and plants; they have, also, long been habituated to their
conditions of life; but it cannot be said that they are subject to quite
uniform conditions, and they are liable to a certain amount of variation.
The circumstances under which our domestic productions are reared are
widely different: they are protected from competition; they have not only
been removed from their natural conditions and often from their native
land, but they are frequently carried from district to district, where they
are treated differently, so that they never remain during a considerable
length of time exposed to closely similar conditions. In conformity with
this, all our domesticated productions, with the rarest exceptions, vary
far more than natural species. The hive-bee, which feeds itself and follows
in most respects its natural habits of life, is the least variable of all
domesticated animals, and probably the goose is the next least variable;
but even the goose varies more than almost any wild bird, so that it cannot
be affiliated with perfect certainty to any natural species. Hardly a
single plant can be named, which has long been cultivated and propagated by
seed, that is not highly variable; common rye (_Secale cereale_) has
afforded fewer and less marked varieties than almost any other cultivated
plant;[606] but it may be doubted whether the variations of this, the least
valuable of all our cereals, have been closely observed.

Bud-variation, which was fully discussed in a former chapter, shows us that
variability may be quite independent of seminal reproduction, and likewise
of reversion to long-lost ancestral characters. No one will maintain that
the sudden appearance {255} of a moss-rose on a Provence-rose is a return
to a former state, for mossiness of the calyx has been observed in no
natural species; the same argument is applicable to variegated and
laciniated leaves; nor can the appearance of nectarines on peach-trees be
accounted for with any probability on the principle of reversion. But
bud-variations more immediately concern us, as they occur far more
frequently on plants which have been highly cultivated during a length of
time, than on other and less highly cultivated plants; and very few
well-marked instances have been observed with plants growing under strictly
natural conditions. I have given one instance of an ash-tree growing in a
gentleman's pleasure-grounds; and occasionally there may be seen, on beech
and other trees, twigs leafing at a different period from the other
branches. But our forest trees in England can hardly be considered as
living under strictly natural conditions; the seedlings are raised and
protected in nursery-grounds, and must often be transplanted into places
where wild trees of the kind would not naturally grow. It would be esteemed
a prodigy if a dog-rose growing in a hedge produced by bud-variation a
moss-rose, or a wild bullace or wild cherry-tree yielded a branch bearing
fruit of a different shape and colour from the ordinary fruit. The prodigy
would be enhanced if these varying branches were found capable of
propagation, not only by grafts, but sometimes by seed; yet analogous cases
have occurred with many of our highly cultivated trees and herbs.

These several considerations alone render it probable that variability of
every kind is directly or indirectly caused by changed conditions of life.
Or, to put the case under another point of view, if it were possible to
expose all the individuals of a species during many generations to
absolutely uniform conditions of life, there would be no variability.

_On the Nature of the Changes in the Conditions of Life which induce
Variability._

From a remote period to the present day, under climates and circumstances
as different as it is possible to conceive, organic beings of all kinds,
when domesticated or cultivated, have {256} varied. We see this with the
many domestic races of quadrupeds and birds belonging to different orders,
with gold-fish and silkworms, with plants of many kinds, raised in various
quarters of the world. In the deserts of northern Africa the date-palm has
yielded thirty-eight varieties; in the fertile plains of India it is
notorious how many varieties of rice and of a host of other plants exist;
in a single Polynesian island, twenty-four varieties of the bread-fruit,
the same number of the banana, and twenty-two varieties of the arum, are
cultivated by the natives; the mulberry-tree in India and Europe has
yielded many varieties serving as food for the silkworm; and in China
sixty-three varieties of the bamboo are used for various domestic
purposes.[607] These facts alone, and innumerable others could be added,
indicate that a change of almost any kind in the conditions of life
suffices to cause variability--different changes acting on different
organisms.

Andrew Knight[608] attributed the variation of both animals and plants to a
more abundant supply of nourishment, or to a more favourable climate, than
that natural to the species. A more genial climate, however, is far from
necessary; the kidney-bean, which is often injured by our spring frosts,
and peaches, which require the protection of a wall, have varied much in
England, as has the orange-tree in northern Italy, where it is barely able
to exist.[609] Nor can we overlook the fact, though not immediately
connected with our present subject, that the plants and shells of the
arctic regions are eminently variable.[610] Moreover, it does not appear
that a change of climate, whether more or less genial, is one of the most
potent causes of variability; for in regard to plants Alph. De Candolle, in
his 'Géographie {257} Botanique,' repeatedly shows that the native country
of a plant, where in most cases it has been longest cultivated, is that
where it has yielded the greatest number of varieties.

It is doubtful whether a change in the nature of the food is a potent cause
of variability. Scarcely any domesticated animal has varied more than the
pigeon or the fowl, but their food, especially that of highly-bred pigeons,
is generally the same. Nor can our cattle and sheep have been subjected to
any great change in this respect. But in all these cases the food probably
is much less varied in kind than that which was consumed by the species in
its natural state.[611]

Of all the causes which induce variability, excess of food, whether or not
changed in nature, is probably the most powerful. This view was held with
regard to plants by Andrew Knight, and is now held by Schleiden, more
especially in reference to the inorganic elements of the food.[612] In
order to give a plant more food it suffices in most cases to grow it
separately, and thus prevent other plants robbing its roots. It is
surprising, as I have often seen, how vigorously our common wild plants
flourish when planted by themselves, though not in highly manured land.
Growing plants separately is, in fact, the first step in cultivation. We
see the converse of the belief that excess of food induces variability in
the following statement by a great raiser of seeds of all kinds.[613] "It
is a rule invariably with us, when we desire to keep a true stock of any
one kind of seed, to grow it on poor land without dung; but when we grow
for quantity, we act contrary, and sometimes have dearly to repent of it."

In the case of animals the want of a proper amount of exercise, as
Bechstein has remarked, has perhaps played, independently of the direct
effects of the disuse of any particular organ, an important part in causing
variability. We can see in a vague manner that, when the organised and
nutrient fluids of the body are not used during growth, or by the wear and
tear of the tissues, {258} they will be in excess; and as growth,
nutrition, and reproduction are intimately allied processes, this
superfluity might disturb the due and proper action of the reproductive
organs, and consequently affect the character of the future offspring. But
it may be argued that neither an excess of food nor a superfluity in the
organised fluids of the body necessarily induces variability. The goose and
the turkey have been well fed for many generations, yet have varied very
little. Our fruit-trees and culinary plants, which are so variable, have
been cultivated from an ancient period, and, though they probably still
receive more nutriment than in their natural state, yet they must have
received during many generations nearly the same amount; and it might be
thought that they would have become habituated to the excess. Nevertheless,
on the whole, Knight's view, that excess of food is one of the most potent
causes of variability, appears, as far as I can judge, probable.

Whether or not our various cultivated plants have received nutriment in
excess, all have been exposed to changes of various kinds. Fruit-trees are
grafted on different stocks, and grown in various soils. The seeds of
culinary and agricultural plants are carried from place to place; and
during the last century the rotation of our crops and the manures used have
been greatly changed.

Slight changes of treatment often suffice to induce variability. The simple
fact of almost all our cultivated plants and domesticated animals having
varied in all places and at all times, leads to this conclusion. Seeds
taken from common English forest-trees, grown under their native climate,
not highly manured or otherwise artificially treated, yield seedlings which
vary much, as may be seen in every extensive seed-bed. I have shown in a
former chapter what a number of well marked and singular varieties the
thorn (_Cratægus oxyacantha_) has produced; yet this tree has been
subjected to hardly any cultivation. In Staffordshire I carefully examined
a large number of two British plants, namely, _Geranium phæum_ and
_Pyrenaicum_, which have never been highly cultivated. These plants had
spread spontaneously by seed from a common garden into an open plantation;
and the seedlings varied in almost every single character, both in their
flowers and foliage, to a degree which {259} I have never seen exceeded;
yet they could not have been exposed to any great change in their
conditions.

With respect to animals, Azara has remarked with much surprise,[614] that,
whilst the feral horses on the Pampas are always of one of three colours,
and the cattle always of a uniform colour, yet these animals, when bred on
the unenclosed estancias, though kept in a state which can hardly be called
domesticated, and apparently exposed to almost identically the same
conditions as when they are feral, nevertheless display a great diversity
of colour. So again in India several species of fresh-water fish are only
so far treated artificially, that they are reared in great tanks; but this
small change is sufficient to induce much variability.[615]

Some facts on the effects of grafting, in regard to the variability of
trees, deserve attention. Cabanis asserts that when certain pears are
grafted on the quince, their seeds yield more varieties than do the seeds
of the same variety of pear when grafted on the wild pear.[616] But as the
pear and quince are distinct species, though so closely related that the
one can be readily grafted and succeeds admirably on the other, the fact of
variability being thus caused is not surprising; we are, however, here
enabled to see the cause, namely, the different nature of the stock with
its roots and the rest of the tree. Several North American varieties of the
plum and peach are well known to reproduce themselves truly by seed; but
Downing asserts,[617] "that when a graft is taken from one of these trees
and placed upon another stock, this grafted tree is found to lose its
singular property of producing the same variety by seed, and becomes like
all other worked trees;"--that is, its seedlings become highly variable.
Another case is worth giving: the Lalande variety of the walnut-tree leafs
between April 20th and May 15th, and its seedlings invariably inherit the
same habit; whilst several other varieties of the walnut leaf in June. Now,
if seedlings are raised from the May-leafing Lalande variety, grafted on
another May-leafing variety, though both stock and graft have the same
early habit of leafing, yet the seedlings leaf at various times, {260} even
as late as the 5th of June.[618] Such facts as these are well fitted to
show, on what obscure and slight causes variability rests.

    I may here just allude to the appearance of new and valuable varieties
    of fruit-trees and of wheat in woods and waste places, which at first
    sight seems a most anomalous circumstance. In France a considerable
    number of the best pears have been discovered in woods; and this has
    occurred so frequently, that Poiteau asserts that "improved varieties
    of our cultivated fruits rarely originate with nurserymen."[619] In
    England, on the other hand, no instance of a good pear having been
    found wild has been recorded; and Mr. Rivers informs me that he knows
    of only one instance with apples, namely, the Bess Poole, which was
    discovered in a wood in Nottinghamshire. This difference between the
    two countries may be in part accounted for by the more favourable
    climate of France, but chiefly from the great number of seedlings which
    spring up there in the woods. I infer that this is the case from a
    remark made by a French gardener,[620] who regards it as a national
    calamity that such a number of pear-trees are periodically cut down for
    firewood, before they have borne fruit. The new varieties which thus
    spring up in the woods, though they cannot have received any excess of
    nutriment, will have been exposed to abruptly changed conditions, but
    whether this is the cause of their production is very doubtful. These
    varieties, however, are probably all descended[621] from old cultivated
    kinds growing in adjoining orchards,--a circumstance which will account
    for their variability; and out of a vast number of varying trees there
    will always be a good chance of the appearance of a valuable kind. In
    North America, where fruit-trees frequently spring up in waste places,
    the Washington pear was found in a hedge, and the Emperor peach in a
    wood.[622]

    With respect to wheat, some writers have spoken[623] as if it were an
    ordinary event for new varieties to be found in waste places; the
    Fenton wheat was certainly discovered growing on a pile of basaltic
    detritus in a quarry, but in such a situation the plant would probably
    receive a sufficient amount {261} of nutriment. The Chidham wheat was
    raised from an ear found _on_ a hedge; and Hunter's wheat was
    discovered _by_ the roadside in Scotland, but it is not said that this
    latter variety grew where it was found.[624]

Whether our domestic productions would ever become so completely habituated
to the conditions under which they now live, as to cease varying, we have
no sufficient means for judging. But, in fact, our domestic productions are
never exposed for a great length of time to uniform conditions, and it is
certain that our most anciently cultivated plants, as well as animals,
still go on varying, for all have recently undergone marked improvement. In
some few cases, however, plants have become habituated to new conditions.
Thus Metzger, who cultivated in Germany during many years numerous
varieties of wheat, brought from different countries,[625] states that some
kinds were at first extremely variable, but gradually, in one instance
after an interval of twenty-five years, became constant; and it does not
appear that this resulted from the selection of the more constant forms.

       *       *       *       *       *

_On the Accumulative Action of changed Conditions of Life._--We have good
grounds for believing that the influence of changed conditions accumulates,
so that no effect is produced on a species until it has been exposed during
several generations to continued cultivation or domestication. Universal
experience shows us that when new flowers are first introduced into our
gardens they do not vary; but ultimately all, with the rarest exceptions,
vary to a greater or less extent. In a few cases the requisite number of
generations, as well as the successive steps in the progress of variation,
have been recorded, as in the often-quoted instance of the Dahlia.[626]
After several years' culture the Zinnia has only lately (1860) begun to
vary in any great degree. "In the first seven or eight years of high
cultivation the Swan River daisy (_Brachycome iberidifolia_) kept to its
original colour; it then varied into lilac and purple and other minor
shades."[627] Analogous facts have been recorded with the Scotch rose. In
discussing the variability of plants several experienced horticulturists
have spoken to the {262} same general effect. Mr. Salter[628] remarks,
"Every one knows that the chief difficulty is in breaking through the
original form and colour of the species, and every one will be on the
look-out for any natural sport, either from seed or branch; that being once
obtained, however trifling the change may be, the result depends upon
himself." M. de Jonghe, who has had so much success in raising new
varieties of pears and strawberries,[629] remarks with respect to the
former, "There is another principle, namely, that the more a type has
entered into a state of variation, the greater is its tendency to continue
doing so; and the more it has varied from the original type, the more it is
disposed to vary still farther." We have, indeed, already discussed this
latter point when treating of the power which man possesses, through
selection, of continually augmenting in the same direction each
modification; for this power depends on continued variability of the same
general kind. The most celebrated horticulturist in France, namely,
Vilmorin,[630] even maintains that, when any particular variation is
desired, the first step is to get the plant to vary in any manner whatever,
and to go on selecting the most variable individuals, even though they vary
in the wrong direction; for the fixed character of the species being once
broken, the desired variation will sooner or later appear.

As nearly all our animals were domesticated at an extremely remote epoch,
we cannot, of course, say whether they varied quickly or slowly when first
subjected to new conditions. But Dr. Bachman[631] states that he has seen
turkeys raised from the eggs of the wild species lose their metallic tints
and become spotted with white in the third generation. Mr. Yarrell many
years ago informed me that the wild ducks bred on the ponds in St. James's
Park, which had never been crossed, as it is believed, with domestic ducks,
lost their true plumage after a few generations. An excellent
observer,[632] who has often reared birds from the eggs of the wild duck,
and who took precautions {263} that there should be no crossing with
domestic breeds, has given, as previously stated, full details on the
changes which they gradually undergo. He found that he could not breed
these wild ducks true for more than five or six generations, "as they then
proved so much less beautiful. The white collar round the neck of the
mallard became much broader and more irregular, and white feathers appeared
in the ducklings' wings." They increased also in size of body; their legs
became less fine, and they lost their elegant carriage. Fresh eggs were
then procured from wild birds; but again the same result followed. In these
cases of the duck and turkey we see that animals, like plants, do not
depart from their primitive type until they have been subjected during
several generations to domestication. On the other hand, Mr. Yarrell
informed me that the Australian dingos, bred in the Zoological Gardens,
almost invariably produced in the first generation puppies marked with
white and other colours; but these introduced dingos had probably been
procured from the natives, who keep them in a semi-domesticated state. It
is certainly a remarkable fact that changed conditions should at first
produce, as far as we can see, absolutely no effect; but that they should
subsequently cause the character of the species to change. In the chapter
on pangenesis I shall attempt to throw a little light on this fact.

       *       *       *       *       *

Returning now to the causes which are supposed to induce variability. Some
authors[633] believe that close interbreeding gives this tendency, and
leads to the production of monstrosities. In the seventeenth chapter some
few facts were advanced, showing that monstrosities are, as it appears,
occasionally thus caused; and there can be no doubt that close
interbreeding induces lessened fertility and a weakened constitution; hence
it may lead to variability: but I have not sufficient evidence on this
head. On the other hand, close interbreeding, if not carried to an
injurious extreme, far from causing variability, tends to fix the character
of each breed.

It was formerly a common belief, still held by some persons, that the
imagination of the mother affects the child in {264} the womb.[634] This
view is evidently not applicable to the lower animals, which lay
unimpregnated eggs, or to plants. Dr. William Hunter, in the last century,
told my father that during many years every woman in a large London
Lying-in Hospital was asked before her confinement whether anything had
specially affected her mind, and the answer was written down; and it so
happened that in no one instance could a coincidence be detected between
the woman's answer and any abnormal structure; but when she knew the nature
of the structure, she frequently suggested some fresh cause. The belief in
the power of the mother's imagination may perhaps have arisen from the
children of a second marriage resembling the previous father, as certainly
sometimes occurs, in accordance with the facts given in the eleventh
chapter.

       *       *       *       *       *

_Crossing as a Cause of Variability._--In an early part of this chapter it
was stated that Pallas[635] and a few other naturalists maintain that
variability is wholly due to crossing. If this means that new characters
never spontaneously appear in our domestic races, but that they are all
directly derived from certain aboriginal species, the doctrine is little
less than absurd; for it implies that animals like Italian greyhounds,
pug-dogs, bull-dogs, pouter and fantail pigeons, &c., were able to exist in
a state of nature. But the doctrine may mean something widely different,
namely, that the crossing of distinct species is the sole cause of the
first appearance of new characters, and that without this aid man could not
have formed his various breeds. As, however, new characters have appeared
in certain cases by bud-variation, we may conclude with certainty that
crossing is not necessary for variability. It is, moreover, almost certain
that the breeds of various animals, such as of the rabbit, pigeon, duck,
&c., and the varieties of several plants, are the modified descendants of a
single wild species. Nevertheless, it is probable that the crossing of two
forms, when one or both have long been domesticated or cultivated, adds to
the variability of the offspring, independently of the commingling of the
characters derived from the two parent-forms; and this implies {265} that
new characters actually arise. But we must not forget the facts advanced in
the thirteenth chapter, which clearly prove that the act of crossing often
leads to the reappearance or reversion of long-lost characters; and in most
cases it would be impossible to distinguish between the reappearance of
ancient characters and the first appearance of new characters. Practically,
whether new or old, they would be new to the breed in which they
reappeared.

    Gärtner declares,[636] and his experience is of the highest value on
    such a point, that, when he crossed native plants which had not been
    cultivated, he never once saw in the offspring any new character; but
    that from the odd manner in which the characters derived from the
    parents were combined, they sometimes appeared as if new. When, on the
    other hand, he crossed cultivated plants, he admits that new characters
    occasionally appeared, but he is strongly inclined to attribute their
    appearance to ordinary variability, not in any way to the cross. An
    opposite conclusion, however, appears to me the more probable.
    According to Kölreuter, hybrids in the genus Mirabilis vary almost
    infinitely, and he describes new and singular characters in the form of
    the seeds, in the colour of the anthers, in the cotyledons being of
    immense size, in new and highly peculiar odours, in the flowers
    expanding early in the season, and in their closing at night. With
    respect to one lot of these hybrids, he remarks that they presented
    characters exactly the reverse of what might have been expected from
    their parentage.[637]

    Prof. Lecoq[638] speaks strongly to the same effect in regard to this
    same genus, and asserts that many of the hybrids from _Mirabilis
    jalapa_ and _multiflora_ might easily be mistaken for distinct species,
    and adds that they differed in a greater degree, than the other species
    of the genus, from _M. jalapa_. Herbert, also, has described[639] the
    offspring from a hybrid Rhododendron as being "as _unlike all others_
    in foliage, as if they had been a separate species." The common
    experience of floriculturists proves that the crossing and recrossing
    of distinct but allied plants, such as the species of Petunia,
    Calceolaria, Fuchsia, Verbena, &c., induces excessive variability;
    hence the appearance of quite new characters is probable. M.
    Carrière[640] has lately discussed this subject: he states that
    _Erythrina cristagalli_ had been multiplied by seed for many years, but
    had not yielded any varieties: it was then crossed with the allied _E.
    herbacea_, and "the resistance was now overcome, and varieties were
    produced with flowers of extremely different size, form, and colour."

    From the general and apparently well-founded belief that the crossing
    {266} of distinct species, besides commingling their characters, adds
    greatly to their variability, it has probably arisen that some
    botanists have gone so far as to maintain[641] that, when a genus
    includes only a single species, this when cultivated never varies. The
    proposition made so broadly cannot be admitted; but it is probably true
    that the variability of cultivated monotypic genera is much less than
    that of genera including numerous species, and this quite independently
    of the effects of crossing. I have stated in my 'Origin of Species,'
    and in a future work shall more fully show, that the species belonging
    to small genera generally yield a less number of varieties in a state
    of nature than those belonging to large genera. Hence the species of
    small genera would, it is probable, produce fewer varieties under
    cultivation than the already variable species of larger genera.

    Although we have not at present sufficient evidence that the crossing
    of species, which have never been cultivated, leads to the appearance
    of new characters, this apparently does occur with species which have
    been already rendered in some degree variable through cultivation.
    Hence crossing, like any other change in the conditions of life, seems
    to be an element, probably a potent one, in causing variability. But we
    seldom have the means of distinguishing, as previously remarked,
    between the appearance of really new characters and the reappearance of
    long-lost characters, evoked through the act of crossing. I will give
    an instance of the difficulty in distinguishing such cases. The species
    of Datura may be divided into two sections, those having white flowers
    with green stems, and those having purple flowers with brown stems: now
    Naudin[642] crossed _Datura lævis_ and _ferox_, both of which belong to
    the white section, and raised from them 205 hybrids. Of these hybrids,
    every one had brown stems and bore purple flowers; so that they
    resembled the species of the other section of the genus, and not their
    own two parents. Naudin was so much astonished at this fact, that he
    was led carefully to observe both parent-species, and he discovered
    that the pure seedlings of _D. ferox_, immediately after germination,
    had dark purple stems, extending from the young roots up to the
    cotyledons, and that this tint remained ever afterwards as a ring round
    the base of the stem of the plant when old. Now I have shown in the
    thirteenth chapter that the retention or exaggeration of an early
    character is so intimately related to reversion, that it evidently
    comes under the same principle. Hence probably we ought to look at the
    purple flowers and brown stems of these hybrids, not as new characters
    due to variability, but as a return to the former state of some ancient
    progenitor.

    Independently of the appearance of new characters from crossing, a few
    words may be added to what has been said in former chapters on the
    unequal combination and transmission of the characters proper to the
    two parent-forms. When two species or races are crossed, the offspring
    of {267} the first generation are generally uniform, but subsequently
    they display an almost infinite diversity of character. He who wishes,
    says Kölreuter,[643] to obtain an endless number of varieties from
    hybrids should cross and recross them. There is also much variability
    when hybrids or mongrels are reduced or absorbed by repeated crosses
    with either pure parent-form; and a still higher degree of variability
    when three distinct species, and most of all when four species, are
    blended together by successive crosses. Beyond this point Gärtner,[644]
    on whose authority the foregoing statements are made, never succeeded
    in effecting a union; but Max Wichura[645] united six distinct species
    of willows into a single hybrid. The sex of the parent-species affects
    in an inexplicable manner the degree of variability of hybrids; for
    Gärtner[646] repeatedly found that when a hybrid was used as the
    father, and either one of the pure parent-species, or a third species,
    was used as the mother, the offspring were more variable than when the
    same hybrid was used as the mother, and either pure parent or the same
    third species as the father: thus seedlings from _Dianthus barbatus_
    crossed by the hybrid _D. chinensi-barbatus_ were more variable than
    those raised from this latter hybrid fertilised by the pure _D.
    barbatus_. Max Wichura[647] insists strongly on an analogous result
    with his hybrid willows. Again Gärtner[648] asserts that the degree of
    variability sometimes differs in hybrids raised from reciprocal crosses
    between the same two species; and here the sole difference is, that the
    one species is first used as the father and then as the mother. On the
    whole we see that, independently of the appearance of new characters,
    the variability of successive crossed generations is extremely complex,
    partly from the offspring partaking unequally of the characters of the
    two parent-forms, and more especially from their unequal tendency to
    revert to these same characters or to those of more ancient
    progenitors.

       *       *       *       *       *

_On the Manner and on the Period of Action of the Causes which induce
Variability._--This is an extremely obscure subject, and we need here only
briefly consider, firstly, whether inherited variations are caused by the
organisation being directly acted on, or indirectly through the
reproductive system; and secondly, at what period of life or growth they
are primarily caused. We shall see in the two following chapters that
various agencies, such as an abundant supply of food, exposure to a
different climate, increased use or disuse of parts, &c., prolonged during
several generations, certainly modify either the whole organisation or
certain organs. This direct action of changed conditions perhaps comes into
play much more frequently than can be proved, and it is at least clear that
in all cases of {268} bud-variation the action cannot have been through the
reproductive system.

    With respect to the part which the reproductive system takes in causing
    variability, we have seen in the eighteenth chapter that even slight
    changes in the conditions of life have a remarkable power in causing a
    greater or less degree of sterility. Hence it seems not improbable that
    being generated though a system so easily affected should themselves be
    affected, or should fail to inherit, or inherit in excess, characters
    proper to their parents. We know that certain groups of organic beings,
    but with exceptions in each group, have their reproductive systems much
    more easily affected by changed conditions than other groups; for
    instance, carnivorous birds more readily than carnivorous mammals, and
    parrots more readily than pigeons; and this fact harmonizes with the
    apparently capricious manner and degree in which various groups of
    animals and plants vary under domestication.

    Kölreuter[649] was struck with the parallelism between the excessive
    variability of hybrids when crossed and recrossed in various
    ways,--these hybrids having their reproductive powers more or less
    affected,--and the variability of anciently cultivated plants. Max
    Wichura[650] has gone one step farther, and shows that with many of our
    highly cultivated plants, such as the hyacinth, tulip, auricula,
    snapdragon, potato, cabbage, &c., which there is no reason to believe
    have been hybridized, the anthers contain many irregular pollen-grains,
    in the same state as in hybrids. He finds also in certain wild forms,
    the same coincidence between the state of the pollen and a high degree
    of variability, as in many species of Rubus; but in _R. cæsius_ and
    _idæus_, which are not highly variable species, the pollen is sound. It
    is also notorious that many cultivated plants, such as the banana,
    pine-apple, breadfruit, and others previously mentioned, have their
    reproductive organs so seriously affected as to be generally quite
    sterile; and when they do yield seed, the seedlings, judging from the
    large number of cultivated races which exist, must be variable in an
    extreme degree. These facts indicate that there is some relation
    between the state of the reproductive organs and a tendency to
    variability; but we must not conclude that the relation is strict.
    Although many of our highly cultivated plants may have their pollen in
    a deteriorated condition, yet, as we have previously seen, they yield
    more seed, and our anciently domesticated animals are more prolific,
    than the corresponding species in a state of nature. The peacock is
    almost the only bird which is believed to be less fertile under
    domestication than in its native state, and it has varied in a
    remarkably small degree. From these considerations it would seem that
    changes in the conditions of life lead either to sterility or to
    variability, or to both; and not that sterility induces variability. On
    the whole it is probable that any cause affecting the organs of
    reproduction would likewise affect their product,--that is, the
    offspring thus generated.

    {269}

    The period of life at which the causes that induce variability act, is
    another obscure subject, which has been discussed by various
    authors.[651] In some of the cases, to be given in the following
    chapter, of modifications from the direct action of changed conditions,
    which are inherited, there can be no doubt that the causes have acted
    on the mature or nearly mature animal. On the other hand,
    monstrosities, which cannot be distinctly separated from lesser
    variations, are often caused by the embryo being injured whilst in the
    mother's womb or in the egg. Thus I. Geoffroy St. Hilaire[652] asserts
    that poor women who work hard during their pregnancy, and the mothers
    of illegitimate children troubled in their minds and forced to conceal
    their state, are far more liable to give birth to monsters than women
    in easy circumstances. The eggs of the fowl when placed upright or
    otherwise treated unnaturally frequently produce monstrous chickens. It
    would, however, appear that complex monstrosities are induced more
    frequently during a rather late than during a very early period of
    embryonic life; but this may partly result from some one part, which
    has been injured during an early period, affecting by its abnormal
    growth other parts subsequently developed; and this would be less
    likely to occur with parts injured at a later period.[653] When any
    part or organ becomes monstrous through abortion, a rudiment is
    generally left, and this likewise indicates that its development had
    already commenced.

    Insects sometimes have their antennæ or legs in a monstrous condition,
    and yet the larvæ from which they are metamorphosed do not possess
    either antennæ or legs; and in those cases, as Quatrefages[654]
    believes, we are enabled to see the precise period at which the normal
    progress of development has been troubled. But the nature of the food
    given to a caterpillar sometimes affects the colours of the moth,
    without the caterpillar itself being affected; therefore it seems
    possible that other characters in the mature insect might be indirectly
    modified through the larvæ. There is no reason to suppose that organs
    which have been rendered monstrous have always been acted on during
    their development; the cause may have acted on the organisation at a
    much earlier stage. It is even probable that either the male or female
    sexual elements, or both, before their union, may be affected in such a
    manner as to lead to modifications in organs developed at a late period
    of life; in nearly the same manner as a child may inherit from his
    father a disease which does not appear until old age.

    In accordance with the facts above given, which prove that in many
    cases a close relation exists between variability and the sterility
    following from changed conditions, we may conclude that the exciting
    cause often acts at the earliest possible period, namely, on the sexual
    elements, before impregnation has taken place. That an affection of the
    female sexual element may induce variability we may likewise infer as
    probable from the occurrence of bud-variations; for a bud seems to be
    the analogue of an ovule. But the male element is apparently much
    oftener affected by changed {270} conditions, at least in a visible
    manner, than the female element or ovule; and we know from Gärtner's
    and Wichura's statements that a hybrid used as the father and crossed
    with a pure species gives a greater degree of variability to the
    offspring, than does the same hybrid when used as the mother. Lastly,
    it is certain that variability may be transmitted through either sexual
    element, whether or not originally excited in them, for Kölreuter and
    Gärtner[655] found that when two species were crossed, if either one
    was variable, the offspring were rendered variable.

       *       *       *       *       *

_Summary._--From the facts given in this chapter, we may conclude that the
variability of organic beings under domestication, although so general, is
not an inevitable contingent on growth and reproduction, but results from
the conditions to which the parents have been exposed. Changes of any kind
in the conditions of life, even extremely slight changes, often suffice to
cause variability. Excess of nutriment is perhaps the most efficient single
exciting cause. Animals and plants continue to be variable for an immense
period after their first domestication; but the conditions to which they
are exposed never long remain quite constant. In the course of time they
can be habituated to certain changes, so as to become less variable; and it
is possible that when first domesticated they may have been even more
variable than at present. There is good evidence that the power of changed
conditions accumulates; so that two, three, or more generations must be
exposed to new conditions before any effect is visible. The crossing of
distinct forms, which have already become variable, increases in the
offspring the tendency to further variability, by the unequal commingling
of the characters of the two parents, by the reappearance of long-lost
characters, and by the appearance of absolutely new characters. Some
variations are induced by the direct action of the surrounding conditions
on the whole organisation, or on certain parts alone, and other variations
are induced indirectly through the reproductive system being affected in
the same manner as is so common with organic beings when removed from their
natural conditions. The causes which induce variability act on the mature
organism, on the embryo, and, as we have good reason to believe, on both
sexual elements before impregnation has been effected.

       *       *       *       *       *


{271}

CHAPTER XXIII.

DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.

    SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
    CONDITIONS IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF
    THE TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED
    CLIMATE OR FOOD, ETC.--PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT,
    AND BY THE INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC
    BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL
    CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS
    OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT
    INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF
    VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF
    CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
    UNNATURAL TREATMENT--SUMMARY.

If we ask ourselves why this or that character has been modified under
domestication, we are, in most cases lost in utter darkness. Many
naturalists, especially of the French school, attribute every modification
to the "monde ambiant," that is, to changed climate, with all its
diversities of heat and cold, dampness and dryness, light and electricity,
to the nature of the soil, and to varied kinds and amount of food. By the
term definite action, as used in this chapter, I mean an action of such a
nature that, when many individuals of the same variety are exposed during
several generations to any change in their physical conditions of life,
all, or nearly all the individuals, are modified in the same manner. A new
sub-variety would thus be produced without the aid of selection.

I do not include under the term of definite action the effects of habit or
of the increased use and disuse of various organs. Modifications of this
nature, no doubt, are definitely caused by the conditions to which the
beings are subjected; but they depend much less on the nature of the
conditions than on the laws of growth; hence they are included under a
distinct head in the {272} following chapter. We know, however, far too
little of the causes and laws of variation to make a sound classification.
The direct action of the conditions of life, whether leading to definite or
indefinite results, is a totally distinct consideration from the effects of
natural selection; for natural selection depends on the survival under
various and complex circumstances of the best-fitted individuals, but has
no relation whatever to the primary cause of any modification of structure.

I will first give in detail all the facts which I have been able to
collect, rendering it probable that climate, food, &c., have acted so
definitely and powerfully on the organisation of our domesticated
productions, that they have sufficed to form new sub-varieties or races,
without the aid of selection by man or of natural selection. I will then
give the facts and considerations opposed to this conclusion, and finally
we will weigh, as fairly as we can, the evidence on both sides.

When we reflect that distinct races of almost all our domesticated animals
exist in each kingdom of Europe, and formerly even in each district of
England, we are at first strongly inclined to attribute their origin to the
definite action of the physical conditions of each country; and this has
been the conclusion of many authors. But we should bear in mind that man
annually has to choose which animals shall be preserved for breeding, and
which shall be slaughtered. We have also seen that both methodical and
unconscious selection were formerly practised, and are now occasionally
practised by the most barbarous races, to a much greater extent than might
have been anticipated. Hence it is very difficult to judge how far the
difference in conditions between, for instance, the several districts in
England, could have sufficed without the aid of selection to modify the
breeds which have been reared in each. It may be argued that, as numerous
wild animals and plants have ranged during many ages throughout Great
Britain, and still retain the same character, the difference in conditions
between the several districts could not have modified in so marked a manner
the various native races of cattle, sheep, pigs, and horses. The same
difficulty of distinguishing between selection and the definite effects of
the conditions of life, is encountered in a still higher degree when we
compare closely allied natural {273} forms, inhabiting two countries, such
as North America and Europe, which do not differ greatly in climate, nature
of soil, &c., for in this case natural selection will inevitably and
rigorously have acted during a long succession of ages.

    From the importance of the difficulty just alluded to, it will be
    advisable to give as large a body of facts as possible, showing that
    extremely slight differences in treatment, either in different parts of
    the same country, or during different seasons, certainly cause an
    appreciable effect, at least on varieties which are already in an
    unstable condition. Ornamental flowers are good for this purpose, as
    they are highly variable, and are carefully observed. All
    floriculturists are unanimous that certain varieties are affected by
    very slight differences in the nature of the artificial compost in
    which they are grown, and by the natural soil of the district, and by
    the season. Thus, a skilful judge, in writing on Carnations and
    Picotees,[656] asks "where can Admiral Curzon be seen possessing the
    colour, size, and strength which it has in Derbyshire? Where can
    Flora's Garland be found equal to those at Slough? Where do
    high-coloured flowers revel better than at Woolwich and Birmingham? Yet
    in no two of these districts do the same varieties attain an equal
    degree of excellence, although each may be receiving the attention of
    the most skilful cultivators." The same writer then recommends every
    cultivator to keep five different kinds of soil and manure, "and to
    endeavour to suit the respective appetites of the plants you are
    dealing with, for without such attention all hope of general success
    will be vain." So it is with the Dahlia:[657] the Lady Cooper rarely
    succeeds near London, but does admirably in other districts; the
    reverse holds good with other varieties; and again, there are others
    which succeed equally well in various situations. A skilful
    gardener[658] states that he procured cuttings of an old and well-known
    variety (pulchella) of Verbena, which from having been propagated in a
    different situation presented a slightly different shade of colour; the
    two varieties were afterwards multiplied by cuttings, being carefully
    kept distinct; but in the second year they could hardly be
    distinguished, and in the third year no one could distinguish them.

    The nature of the season has an especial influence on certain varieties
    of the Dahlia: in 1841 two varieties were pre-eminently good, and the
    next year these same two were pre-eminently bad. A famous amateur[659]
    asserts that in 1861 many varieties of the Rose came so untrue in
    character, "that it was hardly possible to recognise them, and the
    thought was not seldom entertained that the grower had lost his tally."
    The same amateur[660] states that in 1862 two-thirds of his Auriculas
    produced central trusses of flowers, and these are remarkable from not
    keeping true; {274} and he adds that in some seasons certain varieties
    of this plant all prove good, and the next season all prove bad; whilst
    exactly the reverse happens with other varieties. In 1845 the editor of
    the 'Gardener's Chronicle'[661] remarked how singular it was that this
    year many Calceolarias tended to assume a tubular form. With
    Heartsease[662] the blotched sorts do not acquire their proper
    character until hot weather sets in; whilst other varieties lose their
    beautiful marks as soon as this occurs.

    Analogous facts have been observed with leaves: Mr. Beaton asserts[663]
    that he raised at Shrubland, during six years, twenty thousand
    seedlings from the Punch Pelargonium, and not one had variegated
    leaves; but at Surbiton, in Surrey, one-third, or even a greater
    proportion, of the seedlings from this same variety were more or less
    variegated. The soil of another district in Surrey has a strong
    tendency to cause variegation, as appears from information given me by
    Sir F. Pollock. Verlot[664] states that the variegated strawberry
    retains its character as long as grown in a dryish soil, but soon loses
    it when planted in fresh and humid soil. Mr. Salter, who is well known
    for his success in cultivating variegated plants, informs me that rows
    of strawberries were planted in his garden in 1859, in the usual way;
    and at various distances in one row, several plants simultaneously
    became variegated, and what made the case more extraordinary, all were
    variegated in precisely the same manner. These plants were removed, but
    during the three succeeding years other plants in the same row became
    variegated, and in no instance were the plants in any adjoining row
    affected.

    The chemical qualities, odours, and tissues of plants are often
    modified by a change which seems to us slight. The Hemlock is said not
    to yield conicine in Scotland. The root of the _Aconitum napellus_
    becomes innocuous in frigid climates. The medicinal properties of the
    Digitalis are easily affected by culture. The Rhubarb flourishes in
    England, but does not produce the medicinal substance which makes the
    plant so valuable in Chinese Tartary. As the _Pistacia lentiscus_ grows
    abundantly in the South of France, the climate must suit it, but it
    yields no mastic. The _Laurus sassafras_ in Europe loses the odour
    proper to it in North America.[665] Many similar facts could be given,
    and they are remarkable because it might have been thought that
    definite chemical compounds would have been little liable to change
    either in quality or quantity.

    The wood of the American Locust-tree (_Robinia_) when grown in England
    is nearly worthless, as is that of the Oak-tree when grown at the Cape
    of Good Hope.[666] Hemp and flax, as I hear from Dr. Falconer, flourish
    and yield plenty of seed on the plains of India, but their fibres are
    brittle {275} and useless. Hemp, on the other hand, fails to produce in
    England that resinous matter which is so largely used in India as an
    intoxicating drug.

    The fruit of the Melon is greatly influenced by slight differences in
    culture and climate. Hence it is generally a better plan, according to
    Naudin, to improve an old kind than to introduce a new one into any
    locality. The seed of the Persian Melon produces near Paris fruit
    inferior to the poorest market kinds, but at Bordeaux yields delicious
    fruit.[667] Seed is annually brought from Thibet to Kashmir,[668] and
    produces fruit weighing from four to ten pounds, but plants raised from
    seed saved in Kashmir next year give fruit weighing only from two to
    three pounds. It is well known that American varieties of the Apple
    produce in their native land magnificent and brightly-coloured fruit,
    but in England of poor quality and a dull colour. In Hungary there are
    many varieties of the Kidney-bean, remarkable for the beauty of their
    seeds, but the Rev. M. J. Berkeley[669] found that their beauty could
    hardly ever be preserved in England, and in some cases the colour was
    greatly changed. We have seen in the ninth chapter, with respect to
    wheat, what a remarkable effect transportal from the North to the South
    of France, and reversely, produced on the weight of the grain.

When man can perceive no change in plants or animals which have been
exposed to a new climate or to different treatment, insects can sometimes
perceive a marked change. The same species of cactus has been carried to
India from Canton, Manilla, Mauritius, and from the hot-houses of Kew, and
there is likewise a so-called native kind, formerly introduced from South
America; all these plants are alike in appearance, but the cochineal insect
flourishes only on the native kind, on which it thrives prodigiously.[670]
Humboldt remarks[671] that white men "born in the torrid zone walk barefoot
with impunity in the same apartment where a European, recently landed, is
exposed to the attacks of the _Pulex penetrans_." This insect, the too
well-known chigoe, must therefore be able to distinguish what the most
delicate chemical analysis fails to distinguish, namely, a difference
between the blood or tissues of a European and those of a white man born in
the country. But the discernment of the chigoe is not so surprising as it
at first appears; for {276} according to Liebig[672] the blood of men with
different complexions, though inhabiting the same country, emits a
different odour.

    Diseases peculiar to certain localities, heights, or climates, may be
    here briefly noticed, as showing the influence of external
    circumstances on the human body. Diseases confined to certain races of
    man do not concern us, for the constitution of the race may play the
    more important part, and this may have been determined by unknown
    causes. The Plica Polonica stands, in this respect, in a nearly
    intermediate position; for it rarely affects Germans, who inhabit the
    neighbourhood of the Vistula, where so many Poles are grievously
    affected; and on the other hand, it does not affect Russians, who are
    said to belong to the same original stock with the Poles.[673] The
    elevation of a district often governs the appearance of diseases; in
    Mexico the yellow fever does not extend above 924 mètres; and in Peru,
    people are affected with the _verugas_ only between 600 and 1600 mètres
    above the sea; many other such cases could be given. A peculiar
    cutaneous complaint, called the _Bouton d'Alep_, affects in Aleppo and
    some neighbouring districts almost every native infant, and some few
    strangers; and it seems fairly well established that this singular
    complaint depends on drinking certain waters. In the healthy little
    island of St. Helena the scarlet-fever is dreaded like the Plague;
    analogous facts have been observed in Chili and Mexico.[674] Even in
    the different departments of France it is found that the various
    infirmities which render the conscript unfit for serving in the army,
    prevail with remarkable inequality, revealing, as Boudin observes, that
    many of them are endemic, which otherwise would never have been
    suspected.[675] Any one who will study the distribution of disease will
    be struck with surprise at what slight differences in the surrounding
    circumstances govern the nature and severity of the complaints by which
    man is at least temporarily affected.

The modifications as yet referred to have been extremely slight, and in
most cases have been caused, as far as we can judge, by equally slight
changes in the conditions. But can it be safely maintained that such
changed conditions, if acting during a long series of generations, would
not produce a marked effect? It is commonly believed that the people of the
United States differ in appearance from the parent Anglo-Saxon race; and
selection cannot have come into action within so short a period. A good
observer[676] states that a general absence of fat, {277} a thin and
elongated neck, stiff and lank hair, are the chief characteristics. The
change in the nature of the hair is supposed to be caused by the dryness of
the atmosphere. If immigration into the United States were now stopped, who
can say that the character of the whole people would not be greatly
modified in the course of two or three thousand years?

    The direct and definite action of changed conditions, in
    contradistinction to the accumulation of indefinite variations, seems
    to me so important that I will give a large additional body of
    miscellaneous facts. With plants, a considerable change of climate
    sometimes produces a conspicuous result. I have given in detail in the
    ninth chapter the most remarkable case known to me, namely, that in
    Germany several varieties of maize brought from the hotter parts of
    America were transformed in the course of only two or three
    generations. Dr. Falconer informs me that he has seen the English
    Ribston-pippin apple, a Himalayan oak, Prunus and Pyrus, all assume in
    the hotter parts of India a fastigate or pyramidal habit; and this fact
    is the more interesting, as a Chinese tropical species of Pyrus
    naturally has this habit of growth. Although in these cases the changed
    manner of growth seems to have been directly caused by the great heat,
    we know that many fastigate trees have originated in their temperate
    homes. In the Botanic Gardens of Ceylon the apple-tree[677] "sends out
    numerous runners under ground, which continually rise into small stems,
    and form a growth around the parent-tree." The varieties of the cabbage
    which produce heads in Europe fail to do so in certain tropical
    countries.[678] The _Rhododendron ciliatum_ produced at Kew flowers so
    much larger and paler-coloured than those which it bears on its native
    Himalayan mountain, that Dr. Hooker[679] would hardly have recognised
    the species by the flowers alone. Many similar facts with respect to
    the colour and size of flowers could be given.

    The experiments of Vilmorin and Buckman on carrots and parsnips prove
    that abundant nutriment produces a definite and inheritable effect on
    the so-called roots, with scarcely any change in other parts of the
    plant. Alum directly influences the colour of the flowers of the
    Hydrangea.[680] Dryness seems generally to favour the hairyness or
    villosity of plants. Gärtner found that hybrid Verbascums became
    extremely woolly when grown in pots. Mr. Masters, on the other hand,
    states that the _Opuntia leucotricha_ "is well clothed with beautiful
    white hairs when grown in a damp heat; but in a dry heat exhibits none
    of this peculiarity."[681] Slight variations of many kinds, not worth
    specifying in detail, are retained only as {278} long as plants are
    grown in certain soils, of which Sageret[682] gives from his own
    experience some instances. Odart, who insists strongly on the
    permanence of the varieties of the grape, admits[683] that some
    varieties, when grown under a different climate or treated differently,
    vary in an extremely slight degree, as in the tint of the fruit and in
    the period of ripening. Some authors have denied that grafting causes
    even the slightest difference in the scion; but there is sufficient
    evidence that the fruit is sometimes slightly affected in size and
    flavour, the leaves in duration, and the flowers in appearance.[684]

    With animals there can be no doubt, from the facts given in the first
    chapter, that European dogs deteriorate in India, not only in their
    instincts but in structure; but the changes which they undergo are of
    such a nature, that they may be partly due to reversion to a primitive
    form, as in the case of feral animals. In parts of India the turkey
    becomes reduced in size, "with the pendulous appendage over the beak
    enormously developed."[685] We have seen how soon the wild duck, when
    domesticated, loses its true character, from the effects of abundant or
    changed food, or from taking little exercise. From the direct action of
    a humid climate and poor pasture the horse rapidly decreases in size in
    the Falkland Islands. From information which I have received, this
    seems likewise to be the case to a certain extent with sheep in
    Australia.

    Climate definitely influences the hairy covering of animals; in the
    West Indies a great change is produced in the fleece of sheep, in about
    three generations. Dr. Falconer states[686] that the Thibet mastiff and
    goat, when brought down from the Himalaya to Kashmir, lose their fine
    wool. At Angora not only goats, but shepherd-dogs and cats, have fine
    fleecy hair, and Mr. Ainsworth[687] attributes the thickness of the
    fleece to the severe winters, and its silky lustre to the hot summers.
    Burnes states positively[688] that the Karakool sheep lose their
    peculiar black curled fleeces when removed into any other country. Even
    within the limits of England, I have been assured that with two breeds
    of sheep the wool was slightly changed by the flocks being pastured in
    different localities.[689] It has been asserted on good authority[690]
    that horses kept during several years in the deep coal-mines of Belgium
    become covered with velvety hair, almost like that on the mole. These
    cases probably stand in close relation to the natural change of coat in
    winter and summer. Naked varieties of several domestic animals have
    occasionally appeared; but there is no reason to {279} believe that
    this is in any way related to the nature of the climate to which they
    have been exposed.[691]

    It appears at first sight probable that the increased size, the
    tendency to fatten, the early maturity and altered forms of our
    improved cattle, sheep, and pigs, have directly resulted from their
    abundant supply of food. This is the opinion of many competent judges,
    and probably is to a great extent true. But as far as form is
    concerned, we must not overlook the equal or more potent influence of
    lessened use on the limbs and lungs. We see, moreover, as far as size
    is concerned, that selection is apparently a more powerful agent than a
    large supply of food, for we can thus only account for the existence,
    as remarked to me by Mr. Blyth, of the largest and smallest breeds of
    sheep in the same country, of Cochin-China fowls and Bantams, of small
    Tumbler and large Runt pigeons, all kept together and supplied with
    abundant nourishment. Nevertheless there can be little doubt that our
    domesticated animals have been modified, independently of the increased
    or lessened use of parts, by the conditions to which they have been
    subjected, without the aid of selection. For instance, Prof.
    Rütimeyer[692] shows that the bones of all domesticated quadrupeds can
    be distinguished from those of wild animals by the state of their
    surface and general appearance. It is scarcely possible to read
    Nathusius's excellent 'Vorstudien,'[693] and doubt that, with the
    highly improved races of the pig, abundant food has produced a
    conspicuous effect on the general form of the body, on the breadth of
    the head and face, and even on the teeth. Nathusius rests much on the
    case of a purely bred Berkshire pig, which when two months old became
    diseased in its digestive organs, and was preserved for observation
    until nineteen months old; at this age it had lost several
    characteristic features of the breed, and had acquired a long, narrow
    head, of large size relatively to its small body, and elongated legs.
    But in this case and in some others we ought not to assume that,
    because certain characters are lost, perhaps through reversion, under
    one course of treatment, therefore that they had been at first directly
    produced by an opposite course.

    In the case of the rabbit, which has become feral on the island of
    Porto Santo, we are at first strongly tempted to attribute the whole
    change--the greatly reduced size, the altered tints of the fur, and the
    loss of certain characteristic marks--to the definite action of the new
    conditions to which it has been exposed. But in all such cases we have
    to consider in addition the tendency to reversion to progenitors more
    or less remote, and the natural selection of the finest shades of
    difference.

    The nature of the food sometimes either definitely induces certain
    peculiarities, or stands in some close relation with them. Pallas long
    ago asserted that the fat-tailed sheep of Siberia degenerated and lost
    their enormous tails when removed from certain saline pastures; and
    recently {280} Erman[694] states that this occurs with the Kirgisian
    sheep when brought to Orenburgh.

    It is well known that hemp-seed causes bullfinches and certain other
    birds to become black. Mr. Wallace has communicated to me some much
    more remarkable facts of the same nature. The natives of the Amazonian
    region feed the common green parrot (_Chrysotis festiva_, Linn.) with
    the fat of large Siluroid fishes, and the birds thus treated become
    beautifully variegated with red and yellow feathers. In the Malayan
    archipelago, the natives of Gilolo alter in an analogous manner the
    colours of another parrot, namely, the _Lorius garrulus_, Linn., and
    thus produce the _Lori rajah_ or King-Lory. These parrots in the Malay
    Islands and South America, when fed by the natives on natural vegetable
    food, such as rice and plantains, retain their proper colours. Mr.
    Wallace has, also, recorded[695] a still more singular fact. "The
    Indians (of S. America) have a curious art by which they change the
    colours of the feathers of many birds. They pluck out those from the
    part they wish to paint, and inoculate the fresh wound with the milky
    secretion from the skin of a small toad. The feathers grow of a
    brilliant yellow colour, and on being plucked out, it is said, grow
    again of the same colour without any fresh operation."

    Bechstein[696] does not entertain any doubt that seclusion from light
    affects, at least temporarily, the colours of cage-birds.

    It is well known that the shells of land-mollusca are affected by the
    abundance of lime in different districts. Isidore Geoffroy St.
    Hilaire[697] gives the case of _Helix lactea_, which has recently been
    carried from Spain to the South of France and to the Rio Plata, and in
    both these countries now presents a distinct appearance, but whether
    this has resulted from food or climate is not known. With respect to
    the common oyster, Mr. F. Buckland informs me that he can generally
    distinguish the shells from different districts; young oysters brought
    from Wales and laid down in beds where "_natives_" are indigenous, in
    the short space of two months begin to assume the "native" character.
    M. Costa[698] has recorded a much more remarkable case of the same
    nature, namely, that young shells taken from the shores of England and
    placed in the Mediterranean, at once altered their manner of growth and
    formed prominent diverging rays, like those on the shells of the proper
    Mediterranean oyster. The same individual shell, showing both forms of
    growth, was exhibited before a society in Paris. Lastly, it is well
    known that caterpillars fed on different food sometimes either
    themselves acquire a different colour or produce moths different in
    colour.[699]

    {281}

    It would be travelling beyond my proper limits here to discuss how far
    organic beings in a state of nature are definitely modified by changed
    conditions. In my 'Origin of Species' I have given a brief abstract of
    the facts bearing on this point, and have shown the influence of light
    on the colours of birds, and of residence near the sea on the lurid
    tints of insects, and on the succulency of plants. Mr. Herbert
    Spencer[700] has recently discussed with much ability this whole
    subject on broad and general grounds. He argues, for instance, that
    with all animals the external and internal tissues are differently
    acted on by the surrounding conditions, and they invariably differ in
    intimate structure. So again the upper and lower surfaces of true
    leaves, as well as of stems and petioles, when these assume the
    function and occupy the position of leaves, are differently
    circumstanced with respect to light, &c., and apparently in consequence
    differ in structure. But, as Mr. Herbert Spencer admits, it is most
    difficult in all such cases to distinguish between the effects of the
    definite action of physical conditions and the accumulation through
    natural selection of inherited variations which are serviceable to the
    organism, and which have arisen independently of the definite action of
    these conditions.

Although we are not here concerned with organic beings in a state of
nature, yet I may call attention to one case. Mr. Meehan,[701] in a
remarkable paper, compares twenty-nine kinds of American trees, belonging
to various orders, with their nearest European allies, all grown in close
proximity in the same garden and under as nearly as possible the same
conditions. In the American species Mr. Meehan finds, with the rarest
exceptions, that the leaves fall earlier in the season, and assume before
falling a brighter tint; that they are less deeply toothed or serrated;
that the buds are smaller; that the trees are more diffuse in growth and
have fewer branchlets; and, lastly, that the seeds are smaller--all in
comparison with the corresponding European species. Now, considering that
these trees belong to distinct orders, it is out of the question that the
peculiarities just specified should have been inherited in the one
continent from one progenitor, and in the other from another progenitor;
and considering that the trees inhabit widely different stations, these
peculiarities can hardly be supposed to be of any special {282} service to
the two series in the Old and New Worlds; therefore these peculiarities
cannot have been naturally selected. Hence we are led to infer that they
have been definitely caused by the long-continued action of the different
climate of the two continents on the trees.

_Galls._--Another class of facts, not relating to cultivated plants,
deserves attention. I allude to the production of galls. Every one knows
the curious, bright-red, hairy productions on the wild rose-tree, and the
various different galls produced by the oak. Some of the latter resemble
fruit, with one face as rosy as the rosiest apple. These bright colours can
be of no service either to the gall-forming insect or to the tree, and
probably are the direct result of the action of the light, in the same
manner as the apples of Nova Scotia or Canada are brighter coloured than
English apples. The strongest upholder of the doctrine that organic beings
are created beautiful to please mankind would not, I presume, extend this
view to galls. According to Osten Sacken's latest revision, no less than
fifty-eight kinds of galls are produced on the several species of oak, by
Cynips with its sub-genera; and Mr. B. D. Walsh[702] states that he can add
many others to the list. One American species of willow, the _Salix
humilis_, bears ten distinct kinds of galls. The leaves which spring from
the galls of various English willows differ completely in shape from the
natural leaves. The young shoots of junipers and firs, when punctured by
certain insects, yield monstrous growths like flowers and cones; and the
flowers of some plants become from the same cause wholly changed in
appearance. Galls are produced in every quarter of the world; of several
sent to me by Mr. Thwaites from Ceylon, some were as symmetrical as a
composite flower when in bud, others smooth and spherical like a berry;
some protected by long spines, others clothed with yellow wool formed of
long cellular hairs, others with regularly tufted hairs. In some galls the
internal structure is simple, but in others it is highly complex; thus M.
Lucaze-Duthiers[703] has figured in the common ink-gall no less than seven
concentric layers, composed of distinct tissue, {283} namely, the
epidermic, sub-epidermic, spongy, intermediate, and the hard protective
layer formed of curiously thickened woody cells, and, lastly, the central
mass abounding with starch-granules on which the larvæ feed.

Galls are produced by insects of various orders, but the greater number by
species of Cynips. It is impossible to read M. Lucaze-Duthier's discussion
and doubt that the poisonous secretion of the insect causes the growth of
the gall, and every one knows how virulent is the poison secreted by wasps
and bees, which belong to the same order with Cynips. Galls grow with
extraordinary rapidity, and it is said that they attain their full size in
a few days;[704] it is certain that they are almost completely developed
before the larvæ are hatched. Considering that many gall-insects are
extremely small, the drop of secreted poison must be excessively minute; it
probably acts on one or two cells alone, which, being abnormally
stimulated, rapidly increase by a process of self-division. Galls, as Mr.
Walsh[705] remarks, afford good, constant, and definite characters, each
kind keeping as true to form as does any independent organic being. This
fact becomes still more remarkable when we hear that, for instance, seven
out of the ten different kinds of galls produced on _Salix humilis_ are
formed by gall-gnats (_Cecidomyidæ_) which, "though essentially distinct
species, yet resemble one another so closely that in almost all cases it is
difficult, and in some cases impossible, to distinguish the full-grown
insects one from the other."[706] For in accordance with a wide-spread
analogy we may safely infer that the poison secreted by insects so closely
allied would not differ much in nature; yet this slight difference is
sufficient to induce widely different results. In some few cases the same
species of gall-gnat produces on distinct species of willows galls which
cannot be distinguished; the _Cynips fecundatrix_, also, has been known to
produce on the Turkish oak, to which it is not properly attached, exactly
the same kind of gall as on the European oak.[707] These latter facts
apparently prove that the nature of the poison is a much more powerful
{284} agent in determining the form of the gall than the specific character
of the tree which is acted on.

As the poisonous secretion of insects belonging to various orders has the
special power of affecting the growth of various plants;--as a slight
difference in the nature of the poison suffices to produce widely different
results;--and lastly, as we know that the chemical compounds secreted by
plants are eminently liable to be modified by changed conditions of life,
we may believe it possible that various parts of a plant might be modified
through the agency of its own altered secretions. Compare, for instance,
the mossy and viscid calyx of a moss-rose, which suddenly appears through
bud-variation on a Provence-rose, with the gall of red moss growing from
the inoculated leaf of a wild rose, with each filament symmetrically
branched like a microscopical spruce-fir, bearing a glandular tip and
secreting odoriferous gummy matter.[708] Or compare, on the one hand, the
fruit of the peach, with its hairy skin, fleshy covering, hard shell and
kernel, and on the other hand one of the more complex galls with its
epidermic, spongy, and woody layers, surrounding tissue loaded with starch
granules. These normal and abnormal structures manifestly present a certain
degree of resemblance. Or, again, reflect on the cases above given of
parrots which have had their plumage brightly decorated through some change
in their blood, caused by having been fed on certain fishes, or locally
inoculated with the poison of a toad. I am far from wishing to maintain
that the moss-rose or the hard shell of the peach-stone or the bright
colours of birds are actually due to any chemical change in the sap or
blood; but these cases of galls and of parrots are excellently adapted to
show us how powerfully and singularly external agencies may affect
structure. With such facts before us, we need feel no surprise at the
appearance of any modification in any organic being.

    I may, also, here allude to the remarkable effects which parasitic
    fungi sometimes produce on plants. Reissek[709] has described a
    Thesium, affected by an Oecidium, which was greatly modified, and
    assumed some of the {285} characteristic features of certain allied
    species, or even genera. Suppose, says Reissek, "the condition
    originally caused by the fungus to become constant in the course of
    time, the plant would, if found growing wild, be considered as a
    distinct species or even as belonging to a new genus." I quote this
    remark to show how profoundly, yet in how natural a manner, this plant
    must have been modified by the parasitic fungus.

_Facts and Considerations opposed to the belief that the Conditions of Life
act in a potent manner in causing definite Modifications of Structure._

I have alluded to the slight differences in species when naturally living
in distinct countries under different conditions; and such differences we
feel at first inclined, probably to a limited extent with justice, to
attribute to the definite action of the surrounding conditions. But it must
be borne in mind that there are a far greater number of animals and plants
which range widely and have been exposed to great diversities of
conditions, yet remain nearly uniform in character. Some authors, as
previously remarked, account for the varieties of our culinary and
agricultural plants by the definite action of the conditions to which they
have been exposed in the different parts of Great Britain; but there are
about 200 plants[710] which are found in every single English county; these
plants must have been exposed for an immense period to considerable
differences of climate and soil, yet do not differ. So, again, some birds,
insects, other animals, and plants range over large portions of the world,
yet retain the same character.

    Notwithstanding the facts previously given on the occurrence of highly
    peculiar local diseases and on the strange modifications of structure
    in plants caused by the inoculated poison of insects, and other
    analogous cases; still there are a multitude of variations--such as the
    modified skull of the niata ox and bulldog, the long horns of Caffre
    cattle, the conjoined toes of the solid-hoofed swine, the immense crest
    and protuberant skull of Polish fowls, the crop of the pouter-pigeon,
    and a host of other such cases--which we can hardly attribute to the
    definite action, in the sense before specified, of the external
    conditions of life. No doubt in every case there must have been some
    exciting cause; but as we see innumerable individuals exposed to nearly
    the same conditions, and one alone is affected, we may conclude that
    the constitution of the individual is of far higher {286} importance
    than the conditions to which it has been exposed. It seems, indeed, to
    be a general rule that conspicuous variations occur rarely, and in one
    individual alone out of many thousands, though all may have been
    exposed, as far as we can judge, to nearly the same conditions. As the
    most strongly marked variations graduate insensibly into the most
    trifling, we are led by the same train of thought to attribute each
    slight variation much more to innate differences of constitution,
    however caused, than to the definite action of the surrounding
    conditions.

    We are led to the same conclusion by considering the cases, formerly
    alluded to, of fowls and pigeons, which have varied and will no doubt
    go on varying in directly opposite ways, though kept during many
    generations under nearly the same conditions. Some, for instance, are
    born with their beaks, wings, tails, legs, &c., a little longer, and
    others with these same parts a little shorter. By the long-continued
    selection of such slight individual differences, which occur in birds
    kept in the same aviary, widely different races could certainly be
    formed; and long-continued selection, important as is the result, does
    nothing but preserve the variations which appear to us to arise
    spontaneously.

    In these cases we see that domesticated animals vary in an indefinite
    number of particulars, though treated as uniformly as is possible. On
    the other hand, there are instances of animals and plants, which,
    though exposed to very different conditions, both under nature and
    domestication, have varied in nearly the same manner. Mr. Layard
    informs me that he has observed amongst the Caffres of South Africa a
    dog singularly like an arctic Esquimaux dog. Pigeons in India present
    nearly the same wide diversities of colour as in Europe; and I have
    seen chequered and simply barred pigeons, and pigeons with blue and
    white loins, from Sierra Leone, Madeira, England, and India. New
    varieties of flowers are continually raised in different parts of Great
    Britain, but many of these are found by the judges at our exhibitions
    to be almost identical with old varieties. A vast number of new
    fruit-trees and culinary vegetables have been produced in North
    America: these differ from European varieties in the same general
    manner as the several varieties raised in Europe differ from each
    other; and no one has ever pretended that the climate of America has
    given to the many American varieties any general character by which
    they can be recognised. Nevertheless, from the facts previously
    advanced on the authority of Mr. Meehan with respect to American and
    European forest-trees, it would be rash to affirm that varieties raised
    in the two countries would not in the course of ages assume a
    distinctive character. Mr. Masters has recorded a striking fact[711]
    bearing on this subject: he raised numerous plants of _Hybiscus
    Syriacus_ from seed collected in South Carolina and the Holy Land,
    where the parent-plants must have been exposed to considerably
    different conditions; yet the seedlings from both localities broke into
    two similar strains, one with obtuse leaves and purple or crimson
    flowers, and the other with elongated leaves and more or less pink
    flowers.

    {287}

    We may, also, infer the prepotent influence of the constitution of the
    organism over the definite action of the conditions of life, from the
    several cases given in the earlier chapters of parallel series of
    varieties,--an important subject, hereafter to be more fully discussed.
    Sub-varieties of the several kinds of wheat, gourds, peaches, and other
    plants, and to a certain limited extent sub-varieties of the fowl,
    pigeon, and dog, have been shown either to resemble or to differ from
    each other in a closely corresponding and parallel manner. In other
    cases, a variety of one species resembles a distinct species; or the
    varieties of two distinct species resemble each other. Although these
    parallel resemblances no doubt often result from reversion to the
    former characters of a common progenitor; yet in other cases, when new
    characters first appear, the resemblance must be attributed to the
    inheritance of a similar constitution, and consequently to a tendency
    to vary in the same manner. We see something of a similar kind in the
    same monstrosity appearing and reappearing many times in the same
    animal, and, as Dr. Maxwell Masters has remarked to me, in the same
    plant.

We may at least conclude thus far, that the amount of modification which
animals and plants have undergone under domestication, does not correspond
with the degree to which they have been subjected to changed circumstances.
As we know the parentage of domesticated birds far better than of most
quadrupeds, we will glance through the list. The pigeon has varied in
Europe more than almost any other bird; yet it is a native species, and has
not been exposed to any extraordinary change of conditions. The fowl has
varied equally, or almost equally, with the pigeon, and is a native of the
hot jungles of India. Neither the peacock, a native of the same country,
nor the guinea-fowl, an inhabitant of the dry deserts of Africa, has varied
at all, or only in colour. The turkey, from Mexico, has varied but little.
The duck, on the other hand, a native of Europe, has yielded some
well-marked races; and as this is an aquatic bird, it must have been
subjected to a far more serious change in its habits than the pigeon or
even the fowl, which nevertheless have varied in a much higher degree. The
goose, a native of Europe and aquatic like the duck, has varied less than
any other domesticated bird, except the peacock.

Bud-variation is, also, important under our present point of view. In some
few cases, as when all the eyes or buds on the same tuber of the potato, or
all the fruit on the same plum-tree, or all the flowers on the same plant,
have suddenly varied in the same manner, it might be argued that the {288}
variation had been definitely caused by some change in the conditions to
which the plants had been exposed; yet, in other cases, such an admission
is extremely difficult. As new characters sometimes appear by
bud-variation, which do not occur in the parent-species or in any allied
species, we may reject, at least in these cases, the idea that they are due
to reversion. Now it is well worth while to reflect maturely on some
striking case of bud-variation, for instance that of the peach. This tree
has been cultivated by the million in various parts of the world, has been
treated differently, grown on its own roots and grafted on various stocks,
planted as a standard, against a wall, and under glass; yet each bud of
each sub-variety keeps true to its kind. But occasionally, at long
intervals of time, a tree in England, or under the widely-different climate
of Virginia, produces a single bud, and this yields a branch which ever
afterwards bears nectarines. Nectarines differ, as every one knows, from
peaches in their smoothness, size, and flavour; and the difference is so
great, that some botanists have maintained that they are specifically
distinct. So permanent are the characters thus suddenly acquired, that a
nectarine produced by bud-variation has propagated itself by seed. To guard
against the supposition that there is some fundamental distinction between
bud and seminal variation, it is well to bear in mind that nectarines have
likewise been produced from the stone of the peach; and, reversely, peaches
from the stone of the nectarine. Now is it possible to conceive external
conditions more closely alike than those to which the buds on the same tree
are exposed? Yet one bud alone, out of the many thousands borne by the same
tree, has suddenly without any apparent cause produced a nectarine. But the
case is even stronger than this, for the same flower-bud has yielded a
fruit, one-half or one-quarter a nectarine, and the other half or
three-quarters a peach. Again, seven or eight varieties of the peach have
yielded by bud-variation nectarines: the nectarines thus produced, no
doubt, differ a little from each other; but still they are nectarines. Of
course there must be some cause, internal or external, to excite the
peach-bud to change its nature; but I cannot imagine a class of facts
better adapted to force on our minds the conviction that what we call the
external conditions of life are quite insignificant in {289} relation to
any particular variation, in comparison with the organisation or
constitution of the being which varies.

It is known from the labours of Geoffroy St. Hilaire, and recently from
those of Dareste and others, that eggs of the fowl, if shaken, placed
upright, perforated, covered in part with varnish, &c., produce monstrous
chickens. Now these monstrosities may be said to be directly caused by such
unnatural conditions, but the modifications thus induced are not of a
definite nature. An excellent observer, M. Camille Dareste,[712] remarks
"that the various species of monstrosities are not determined by specific
causes; the external agencies which modify the development of the embryo
act solely in causing a perturbation--a perversion in the normal course of
development." He compares the result to what we see in illness: a sudden
chill, for instance, affects one individual alone out of many, causing
either a cold, or sore-throat, rheumatism, or inflammation of the lungs or
pleura. Contagious matter acts in an analogous manner.[713] We may take a
still more specific instance: seven pigeons were struck by
rattle-snakes;[714] some suffered from convulsions; some had their blood
coagulated, in others it was perfectly fluid; some showed ecchymosed spots
on the heart, others on the intestines, &c.; others again showed no visible
lesion in any organ. It is well known that excess in drinking causes
different diseases in different men; but men living under a cold and
tropical climate are differently affected:[715] and in this case we see the
definite influence of opposite conditions. The foregoing facts apparently
give us as good an idea as we are likely for a long time to obtain, how in
many cases external conditions act directly, though not definitely, in
causing modifications of structure.

       *       *       *       *       *

_Summary._--There can be no doubt, from the facts given in the early part
of this chapter, that extremely slight changes in {290} the conditions of
life sometimes act in a definite manner on our already variable
domesticated productions; and, as the action of changed conditions in
causing general or indefinite variability is accumulative, so it may be
with their definite action. Hence it is possible that great and definite
modifications of structure may result from altered conditions acting during
a long series of generations. In some few instances a marked effect has
been produced quickly on all, or nearly all, the individuals which have
been exposed to some considerable change of climate, food, or other
circumstance. This has occurred, and is now occurring, with European men in
the United States, with European dogs in India, with horses in the Falkland
Islands, apparently with various animals at Angora, with foreign oysters in
the Mediterranean, and with maize grown in Europe from tropical seed. We
have seen that the chemical compounds secreted by plants and the state of
their tissues are readily affected by changed conditions. In some cases a
relation apparently exists between certain characters and certain
conditions, so that if the latter be changed the character is lost--as with
cultivated flowers, with some few culinary plants, with the fruit of the
melon, with fat-tailed sheep, and other sheep having peculiar fleeces.

The production of galls, and the change of plumage in parrots when fed on
peculiar food or when inoculated by the poison of a toad, prove to us what
great and mysterious changes in structure and colour may be the definite
result of chemical changes in the nutrient fluids or tissues.

We have also reason to believe that organic beings in a state of nature may
be modified in various definite ways by the conditions to which they have
been long exposed, as in the case of American trees in comparison with
their representatives in Europe. But in all such cases it is most difficult
to distinguish between the definite results of changed conditions, and the
accumulation through natural selection of serviceable variations which have
arisen independently of the nature of the conditions. If, for instance, a
plant had to be modified so as to become fitted to inhabit a humid instead
of an arid station, we have no reason to believe that variations of the
right kind would occur more frequently if the parent-plant inhabited a
station a little more {291} humid than usual. Whether the station was
unusually dry or humid, variations adapting the plant in a slight degree
for directly opposite habits of life would occasionally arise, as we have
reason to believe from what we know in other cases.

In most, perhaps in all cases, the organisation or constitution of the
being which is acted on, is a much more important element than the nature
of the changed conditions, in determining the nature of the variation. We
have evidence of this in the appearance of nearly similar modifications
under different conditions, and of different modifications under apparently
nearly the same conditions. We have still better evidence of this in
closely parallel varieties being frequently produced from distinct races,
or even distinct species, and in the frequent recurrence of the same
monstrosity in the same species. We have also seen that the degree to which
domesticated birds have varied, does not stand in any close relation with
the amount of change to which they have been subjected.

To recur once again to bud-variations. When we reflect on the millions of
buds which many trees have produced, before some one bud has varied, we are
lost in wonder what the precise cause of each variation can be. Let us
recall the case given by Andrew Knight of the forty-year-old tree of the
yellow magnum bonum plum, an old variety which has been propagated by
grafts on various stocks for a very long period throughout Europe and North
America, and on which a single bud suddenly produced the red magnum bonum.
We should also bear in mind that distinct varieties, and even distinct
species,--as in the case of peaches, nectarines, and apricots,--of certain
roses and camellias,--although separated by a vast number of generations
from any progenitor in common, and although cultivated under diversified
conditions, have yielded by bud-variation closely analogous varieties. When
we reflect on these facts we become deeply impressed with the conviction
that in such cases the nature of the variation depends but little on the
conditions to which the plant has been exposed, and not in any especial
manner on its individual character, but much more on the general nature or
constitution, inherited from some remote progenitor, of the whole group of
allied beings to which the plant belongs. We are thus driven to conclude
that in most {292} cases the conditions of life play a subordinate part in
causing any particular modification; like that which a spark plays, when a
mass of combustibles bursts into flame--the nature of the flame depending
on the combustible matter, and not on the spark.

No doubt each slight variation must have its efficient cause; but it is as
hopeless an attempt to discover the cause of each as to say why a chill or
a poison affects one man differently from another. Even with modifications
resulting from the definite action of the conditions of life, when all or
nearly all the individuals, which have been similarly exposed, are
similarly affected, we can rarely see the precise relation between cause
and effect. In the next chapter it will be shown that the increased use or
disuse of various organs, produces an inherited effect. It will further be
seen that certain variations are bound together by correlation and other
laws. Beyond this we cannot at present explain either the causes or manner
of action of Variation.

Finally, as indefinite and almost illimitable variability is the usual
result of domestication and cultivation, with the same part or organ
varying in different individuals in different or even in directly opposite
ways; and as the same variation, if strongly pronounced, usually recurs
only after long intervals of time, any particular variation would generally
be lost by crossing, reversion, and the accidental destruction of the
varying individuals, unless carefully preserved by man. Hence, although it
must be admitted that new conditions of life do sometimes definitely affect
organic beings, it may be doubted whether well-marked races have often been
produced by the direct action of changed conditions without the aid of
selection either by man or nature.

       *       *       *       *       *


{293}

CHAPTER XXIV.

LAWS OF VARIATION--USE AND DISUSE, ETC.

    NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON
    THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS
    OF LIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY
    WHICH THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS.

In this and the two following chapters I shall discuss, as well as the
difficulty of the subject permits, the several laws which govern
Variability. These may be grouped under the effects of use and disuse,
including changed habits and acclimatisation--arrests of
development--correlated variation--the cohesion of homologous parts--the
variability of multiple parts--compensation of growth--the position of buds
with respect to the axis of the plant--and lastly, analogous variation.
These several subjects so graduate into each other that their distinction
is often arbitrary.

It may be convenient first briefly to discuss that co-ordinating and
reparative power which is common, in a higher or lower degree, to all
organic beings, and which was formerly designated by physiologists as the
_nisus formativus_.

    Blumenbach and others[716] have insisted that the principle which
    permits a Hydra, when cut into fragments, to develop itself into two or
    more perfect animals, is the same with that which causes a wound in the
    higher animals to heal by a cicatrice. Such cases as that of the Hydra
    are evidently analogous with the spontaneous division or fissiparous
    generation of the lowest animals, and likewise with the budding of
    plants. Between these extreme cases and that of a mere cicatrice we
    have every gradation. Spallanzani,[717] by cutting off the legs and
    tail of a Salamander, got in the course of three months six crops of
    these members; so that 687 perfect bones were reproduced by one animal
    during one season. At whatever {294} point the limb was cut off, the
    deficient part, and no more, was exactly reproduced. Even with man, as
    we have seen in the twelfth chapter, when treating of polydactylism,
    the entire limb whilst in an embryonic state, and supernumerary digits,
    are occasionally, though imperfectly, reproduced after amputation. When
    a diseased bone has been removed, a new one sometimes "gradually
    assumes the regular form, and all the attachments of muscles,
    ligaments, &c., become as complete as before."[718]

    This power of regrowth does not, however, always act perfectly: the
    reproduced tail of a lizard differs in the forms of the scales from the
    normal tail: with certain Orthopterous insects the large hind legs are
    reproduced of smaller size:[719] the white cicatrice which in the
    higher animals unites the edges of a deep wound is not formed of
    perfect skin, for elastic tissue is not produced till long
    afterwards.[720] "The activity of the _nisus formativus_," says
    Blumenbach, "is in an inverse ratio to the age of the organised body."
    To this may be added that its power is greater in animals the lower
    they are in the scale of organisation; and animals low in the scale
    correspond with the embryos of higher animals belonging to the same
    class. Newport's observations[721] afford a good illustration of this
    fact, for he found that "myriapods, whose highest development scarcely
    carries them beyond the larvæ of perfect insects, can regenerate limbs
    and antennæ up to the time of their last moult;" and so can the larvæ
    of true insects, but not the mature insect. Salamanders correspond in
    development with the tadpoles or larvæ of the tailless Batrachians, and
    both possess to a large extent the power of regrowth; but not so the
    mature tailless Batrachians.

    Absorption often plays an important part in the repairs of injuries.
    When a bone is broken, and does not unite, the ends are absorbed and
    rounded, so that a false joint is formed; or if the ends unite, but
    overlap, the projecting parts are removed.[722] But absorption comes
    into action, as Virchow remarks, during the normal growth of bones;
    parts which are solid during youth become hollowed out for the
    medullary tissue as the bone increases in size. In trying to understand
    the many well-adapted cases of regrowth when aided by absorption, we
    should remember that most parts of the organisation, even whilst
    retaining the same form, undergo constant renewal; so that a part which
    was not renewed would naturally be liable to complete absorption.

    Some cases, usually classed under the so-called _nisus formativus_, at
    first appear to come under a distinct head; for not only are old
    structures reproduced, but structures which appear new are formed.
    Thus, after inflammation "false membranes," furnished with
    blood-vessels, lymphatics, and nerves, are developed; or a foetus
    escapes from the Fallopian tubes, and falls into the abdomen, "nature
    pours out a quantity of plastic lymph, which forms itself into
    organised membrane, richly supplied with blood-vessels," and the foetus
    is nourished for a time. In certain cases of {295} hydrocephalus the
    open and dangerous spaces in the skull are filled up with new bones,
    which interlock by perfect serrated sutures.[723] But most
    physiologists, especially on the Continent, have now given up the
    belief in plastic lymph or blastema, and Virchow[724] maintains that
    every structure, new or old, is formed by the proliferation of
    pre-existing cells. On this view false membranes, like cancerous or
    other tumours, are merely abnormal developments of normal growths; and
    we can thus understand how it is that they resemble adjoining
    structures; for instance, that "false membrane in the serous cavities
    acquires a covering of epithelium exactly like that which covers the
    original serous membrane; adhesions of the iris may become black
    apparently from the production of pigment-cells like those of the
    uvea."[725]

    No doubt the power of reparation, though not always quite perfect, is
    an admirable provision, ready for various emergencies, even for those
    which occur only at long intervals of time.[726] Yet this power is not
    more wonderful than the growth and development of every single
    creature, more especially of those which are propagated by fissiparous
    generation. This subject has been here noticed, because we may infer
    that, when any part or organ is either greatly increased in size or
    wholly suppressed through variation and continued selection, the
    co-ordinating power of the organisation will continually tend to bring
    all the parts again into harmony with each other.

_On the Effects of the Increased Use and Disuse of Organs._

It is notorious, and we shall immediately adduce proofs, that increased use
or action strengthens muscles, glands, sense-organs, &c.; and that disuse,
on the other hand, weakens them. I have not met with any clear explanation
of this fact in works on Physiology. Mr. Herbert Spencer[727] maintains
that when muscles are much used, or when intermittent pressure is applied
to the epidermis, an excess of nutritive matter exudes from the vessels,
and that this gives additional development to the adjoining parts. That an
increased flow of blood towards an organ leads to its greater development
is probable, if not certain. Mr. Paget[728] thus accounts for the long,
thick, and dark-coloured hair which occasionally grows, even in young
children, near old-standing inflamed surfaces or fractured bones. When
Hunter {296} inserted the spur of a cock into the comb, which is well
supplied with blood-vessels, it grew in one case in a spiral direction to a
length of six inches, and in another case forward, like a horn, so that the
bird could not touch the ground with its beak. But whether Mr. Herbert
Spencer's view of the exudation of nutritive matter due to increased
movement and pressure, will fully account for the augmented size of bones,
ligaments, and especially of internal glands and nerves, seems doubtful.
According to the interesting observations of M. Sedillot,[729] when a
portion of one bone of the leg or fore-arm of an animal is removed and is
not replaced by growth, the associated bone enlarges till it attains a bulk
equal to that of the two bones, of which it has to perform the functions.
This is best exhibited in dogs in which the tibia has been removed; the
companion bone, which is naturally almost filiform and not one-fifth the
size of the other, soon acquires a size equal to or greater than the tibia.
Now, it is at first difficult to believe that increased weight acting on a
straight bone could, by alternately increased and diminished pressure,
cause nutritive matter to exude from the vessels which permeate the
periosteum. Nevertheless, the observations adduced by Mr. Spencer,[730] on
the strengthening of the bowed bones of rickety children, along their
concave sides, leads to the belief that this is possible.

Mr. H. Spencer has also shown that the ascent of the sap in trees is aided
by the rocking movement caused by the wind; and the sap strengthens the
trunk "in proportion to the stress to be borne; since the more severe and
the more repeated the strains, the greater must be the exudation from the
vessels into the surrounding tissue, and the greater the thickening of this
tissue by secondary deposits."[731] But woody trunks may be formed of hard
tissue without their having been subjected to any movement, as we see with
ivy closely attached to old walls. In all these cases, it is very difficult
to disentangle the effects of long-continued selection from those
consequent on the increased action or movement of the part. Mr. H.
Spencer[732] acknowledges this difficulty, and gives as an instance the
spines {297} or thorns of trees, and the shells of nuts. Here we have
extremely hard woody tissue without the possibility of any movement to
cause exudation, and without, as far as we can see, any other directly
exciting cause; and as the hardness of these parts is of manifest service
to the plant, we may look at the result as probably due to the selection of
so-called spontaneous variations. Every one knows that hard work thickens
the epidermis on the hands; and when we hear that with infants long before
their birth the epidermis is thicker on the palms and soles of the feet
than on any other part of the body, as was observed with admiration by
Albinus,[733] we are naturally inclined to attribute this to the inherited
effects of long-continued use or pressure. We are tempted to extend the
same view even to the hoofs of quadrupeds; but who will pretend to
determine how far natural selection may have aided in the formation of
structures of such obvious importance to the animal?

    That use strengthens the muscles may be seen in the limbs of artisans
    who follow different trades; and when a muscle is strengthened, the
    tendons, and the crests of bone to which they are attached, become
    enlarged; and this must likewise be the case with the blood-vessels and
    nerves. On the other hand, when a limb is not used, as by Eastern
    fanatics, or when the nerve supplying it with nervous power is
    effectually destroyed, the muscles wither. So again, when the eye is
    destroyed the optic nerve becomes atrophied, sometimes even in the
    course of a few months.[734] The Proteus is furnished with branchiæ as
    well as with lungs: and Schreibers[735] found that when the animal was
    compelled to live in deep water the branchiæ were developed to thrice
    their ordinary size, and the lungs were partially atrophied. When, on
    the other hand, the animal was compelled to live in shallow water, the
    lungs became larger and more vascular, whilst the branchiæ disappeared
    in a more or less complete degree. Such modifications as these are,
    however, of comparatively little value for us, as we do not actually
    know that they tend to be inherited.

    In many cases there is reason to believe that the lessened use of
    various organs has affected the corresponding parts in the offspring.
    But there is no good evidence that this ever follows in the course of a
    single generation. It appears, as in the case of general or indefinite
    variability, that several generations must be subjected to changed
    habits for any appreciable result. Our domestic fowls, ducks, and geese
    have almost lost, not {298} only in the individual but in the race,
    their power of flight; for we do not see a chicken, when frightened,
    take flight like a young pheasant. Hence I was led carefully to compare
    the limb-bones of fowls, ducks, pigeons, and rabbits, with the same
    bones in the wild parent-species. As the measurements and weights were
    fully given in the earlier chapters, I need here only recapitulate the
    results. With domestic pigeons, the length of the sternum, the
    prominence of its crest, the length of the scapulæ and furcula, the
    length of the wings as measured from tip to tip of the radius, are all
    reduced relatively to the same parts in the wild pigeon. The wing and
    tail feathers, however, are increased in length, but this may have as
    little connection with the use of the wings or tail, as the lengthened
    hair on a dog with the amount of exercise which the breed has
    habitually taken. The feet of pigeons, except in the long-beaked races,
    are reduced in size. With fowls the crest of the sternum is less
    prominent, and is often distorted or monstrous; the wing-bones have
    become lighter relatively to the leg-bones, and are apparently a little
    shorter in comparison with those of the parent-form, the _Gallus
    bankiva_. With ducks, the crest of the sternum is affected in the same
    manner as in the foregoing cases: the furcula, coracoids, and scapulæ
    are all reduced in weight relatively to the whole skeleton: the bones
    of the wings are shorter and lighter, and the bones of the legs longer
    and heavier, relatively to each other, and relatively to the whole
    skeleton, in comparison with the same bones in the wild-duck. The
    decreased weight and size of the bones, in the foregoing cases, is
    probably the indirect result of the reaction of the weakened muscles on
    the bones. I failed to compare the feathers of the wings of the tame
    and wild duck; but Gloger[736] asserts that in the wild duck the tips
    of the wing-feathers reach almost to the end of the tail, whilst in the
    domestic duck they often hardly reach to its base. He remarks, also, on
    the greater thickness of the legs, and says that the swimming membrane
    between the toes is reduced; but I was not able to detect this latter
    difference.

    With the domesticated rabbit the body, together with the whole
    skeleton, is generally larger and heavier than in the wild animal, and
    the leg-bones are heavier in due proportion; but whatever standard of
    comparison be taken, neither the leg-bones nor the scapulæ have
    increased in length proportionally with the increased dimensions of the
    rest of the skeleton. The skull has become in a marked manner narrower,
    and, from the measurements of its capacity formerly given, we may
    conclude, that this narrowness results from the decreased size of the
    brain, consequent on the mentally inactive life led by these
    closely-confined animals.

    We have seen in the eighth chapter that silk-moths, which have been
    kept during many centuries closely confined, emerge from their cocoons
    with their wings distorted, incapable of flight, often greatly reduced
    in size, or even, according to Quatrefages, quite rudimentary. This
    condition of the wings may be largely owing to the same kind of
    monstrosity which often affects wild Lepidoptera when artificially
    reared from the cocoon; or it may {299} be in part due to an inherent
    tendency, which is common to the females of many Bombycidæ, to have
    their wings in a more or less rudimentary state; but part of the effect
    may probably be attributed to long-continued disuse.

From the foregoing facts there can be no doubt that certain parts of the
skeleton in our anciently domesticated animals, have been modified in
length and weight by the effects of decreased or increased use; but they
have not been modified, as shown in the earlier chapters, in shape or
structure. We must, however, be cautious in extending this latter
conclusion to animals living a free life; for these will occasionally be
exposed during successive generations to the severest competition. With
wild animals it would be an advantage in the struggle for life that every
superfluous and useless detail of structure should be removed or absorbed;
and thus the reduced bones might ultimately become changed in structure.
With highly-fed domesticated animals, on the other hand, there is no
economy of growth; nor any tendency to the elimination of trifling and
superfluous details of structure.

Turning now to more general observations, Nathusius has shown that, with
the improved races of the pig, the shortened legs and snout, the form of
the articular condyles of the occiput, and the position of the jaws with
the upper canine teeth projecting in a most anomalous manner in front of
the lower canines, may be attributed to these parts not having been fully
exercised. For the highly-cultivated races do not travel in search of food,
nor root up the ground with their ringed muzzles. These modifications of
structure, which are all strictly inherited, characterise several improved
breeds, so that they cannot have been derived from any single domestic or
wild stock.[737] With respect to cattle, Professor Tanner has remarked that
the lungs and liver in the improved breeds "are found to be considerably
reduced in size when compared with those possessed by animals having
perfect liberty;"[738] and the reduction of these organs affects the
general shape of the body. The cause of the reduced lungs in highly-bred
animals which take little exercise is {300} obvious; and perhaps the liver
may be affected by the nutritious and artificial food on which they largely
subsist.

    It is well known that, when an artery is tied, the anastomosing
    branches, from being forced to transmit more blood, increase in
    diameter; and this increase cannot be accounted for by mere extension,
    as their coats gain in strength. Mr. Herbert Spencer[739] has argued
    that with plants the flow of sap from the point of supply to the
    growing part first elongates the cells in this line; and that the cells
    then become confluent, thus forming the ducts; so that, on this view,
    the vessels in plants are formed by the mutual reaction of the flowing
    sap and cellular tissue. Dr. W. Turner has remarked,[740] with respect
    to the branches of arteries, and likewise to a certain extent with
    nerves, that the great principle of compensation frequently comes into
    play; for "when two nerves pass to adjacent cutaneous areas, an inverse
    relation as regards size may subsist between them; a deficiency in one
    may be supplied by an increase in the other, and thus the area of the
    former may be trespassed on by the latter nerve." But how far in these
    cases the difference in size in the nerves and arteries is due to
    original variation, and how far to increased use or action, is not
    clear.

    In reference to glands, Mr. Paget observes that "when one kidney is
    destroyed the other often becomes much larger, and does double
    work."[741] If we compare the size of the udders and their power of
    secretion in cows which have been long domesticated, and in certain
    goats in which the udders nearly touch the ground, with the size and
    power of secretion of these organs in wild or half-domesticated
    animals, the difference is great. A good cow with us daily yields more
    than five gallons, or forty pints of milk, whilst a first-rate animal,
    kept, for instance, by the Damaras of South Africa,[742] "rarely gives
    more than two or three pints of milk daily, and, should her calf be
    taken from her, she absolutely refuses to give any." We may attribute
    the excellence of our cows, and of certain goats, partly to the
    continued selection of the best milking animals, and partly to the
    inherited effects of the increased action, through man's art, of the
    secreting glands.

    It is notorious, as was remarked in the twelfth chapter, that
    short-sight is inherited; and if we compare watchmakers or engravers
    with, for instance, sailors, we can hardly doubt that vision
    continually directed towards a near object permanently affects the
    structure of the eye.

    Veterinarians are unanimous that horses become affected with spavins,
    splints, ringbones, &c., from being shod, and from travelling on hard
    roads, and they are almost equally unanimous that these injuries are
    transmitted. Formerly horses were not shod in North Carolina, and it
    has been asserted that they did not then suffer from these diseases of
    the legs and feet.[743]

{301}

Our domesticated quadrupeds are all descended, as far as is known, from
species having erect ears; yet few kinds can be named, of which at least
one race has not drooping ears. Cats in China, horses in parts of Russia,
sheep in Italy and elsewhere, the guinea-pig in Germany, goats and cattle
in India, rabbits, pigs, and dogs in all long-civilised countries, have
dependent ears. With wild animals, which constantly use their ears like
funnels to catch every passing sound, and especially to ascertain the
direction whence it comes, there is not, as Mr. Blyth has remarked, any
species with drooping ears except the elephant. Hence the incapacity to
erect the ears is certainly in some manner the result of domestication; and
this incapacity has been attributed by various authors[744] to disuse, for
animals protected by man are not compelled habitually to use their ears.
Col. Hamilton Smith[745] states that in ancient effigies of the dog, "with
the exception of one Egyptian instance, no sculpture of the earlier Grecian
era produces representations of hounds with completely drooping ears; those
with them half pendulous are missing in the most ancient; and this
character increases, by degrees, in the works of the Roman period." Godron
also has remarked that "the pigs of the ancient Egyptians had not their
ears enlarged and pendent."[746] But it is remarkable that the drooping of
the ears, though probably the effect of disuse, is not accompanied by any
decrease in size; on the contrary, when we remember that animals so
different as fancy rabbits, certain Indian breeds of the goat, our petted
spaniels, bloodhounds, and other dogs, have enormously elongated ears, it
would appear as if disuse actually caused an increase in length. With
rabbits, the drooping of the much elongated ears has affected even the
structure of the skull.

The tail of no wild animal, as remarked to me by Mr. Blyth, is curled;
whereas pigs and some races of dogs have their tails much curled. This
deformity, therefore, appears to be the result of domestication, but
whether in any way connected with the lessened use of the tail is doubtful.

{302}

The epidermis on our hands is easily thickened, as every one knows, by hard
work. In a district of Ceylon the sheep have "horny callosities that defend
their knees, and which arise from their habit of kneeling down to crop the
short herbage, and this distinguishes the Jaffna flocks from those of other
portions of the island;" but it is not stated whether this peculiarity is
inherited.[747]

The mucous membrane which lines the stomach is continuous with the external
skin of the body; therefore it is not surprising that its texture should be
affected by the nature of the food consumed, but other and more interesting
changes likewise follow. Hunter long ago observed that the muscular coat of
the stomach of a gull (_Larus tridactylus_) which had been fed for a year
chiefly on grain was thickened; and, according to Dr. Edmondston, a similar
change periodically occurs in the Shetland Islands in the stomach of the
_Larus argentatus_, which in the spring frequents the corn-fields and feeds
on the seed. The same careful observer has noticed a great change in the
stomach of a raven which had been long fed on vegetable food. In the case
of an owl (_Strix grallaria_) similarly treated, Menetries states that the
form of the stomach was changed, the inner coat became leathery, and the
liver increased in size. Whether these modifications in the digestive
organs would in the course of generations become inherited is not
known.[748]

The increased or diminished length of the intestines, which apparently
results from changed diet, is a more remarkable case, because it is
characteristic of certain animals in their domesticated condition, and
therefore must be inherited. The complex absorbent system, the
blood-vessels, nerves, and muscles, are necessarily all modified together
with the intestines. According to Daubenton, the intestines of the domestic
cat are one-third longer than those of the wild cat of Europe; and although
this species is not the parent-stock of the domestic animal, yet, as
Isidore Geoffroy has remarked, the several species {303} of cats are so
closely allied that the comparison is probably a fair one. The increased
length appears to be due to the domestic cat being less strictly
carnivorous in its diet than any wild feline species; I have seen a French
kitten eating vegetables as readily as meat. According to Cuvier, the
intestines of the domesticated pig exceed greatly in proportionate length
those of the wild boar. In the tame and wild rabbit the change is of an
opposite nature, and probably results from the nutritious food given to the
tame rabbit.[749]

       *       *       *       *       *

_Changed Habits of Life, independently of the Use or Disuse of particular
Organs._--This subject, as far as the mental powers of animals are
concerned, so blends into instinct, on which I shall treat in a future
work, that I will here only remind the reader of the many cases which occur
under domestication, and which are familiar to every one--for instance the
tameness of our animals--the pointing or retrieving of dogs--their not
attacking the smaller animals kept by man--and so forth. How much of these
changes ought to be attributed to inherited habit, and how much to the
selection of individuals which have varied in the desired manner,
irrespectively of the special circumstances under which they have been
kept, can seldom be told. We have already seen that animals may be
habituated to a changed diet; but a few additional instances may here be
given.

In the Polynesian Islands and in China the dog is fed exclusively on
vegetable matter, and the taste for this kind of food is to a certain
extent inherited.[750] Our sporting dogs will not touch the bones of game
birds, whilst other dogs devour them with greediness. In some parts of the
world sheep have been largely fed on fish. The domestic hog is fond of
barley, the wild boar is said to disdain it; and the disdain is partially
inherited, for some young wild pigs bred in captivity showed an aversion
for this grain, whilst others of the same brood relished it.[751] One of my
relations bred some young pigs from {304} a Chinese sow by a wild Alpine
boar; they lived free in the park, and were so tame that they came to the
house to be fed; but they would not touch swill, which was devoured by the
other pigs. An animal when once accustomed to an unnatural diet, which can
generally be effected only during youth, dislikes its proper food, as
Spallanzani found to be the case with a pigeon which had been long fed on
meat. Individuals of the same species take to new food with different
degrees of readiness; one horse, it is stated, soon learned to eat meat,
whilst another would have perished from hunger rather than have partaken of
it.[752]

The caterpillars of the _Bombyx hesperus_ feed in a state of nature on the
leaves of the _Café diable_, but, after having been reared on the
Ailanthus, they would not touch the _Café diable_, and actually died of
hunger.[753]

It has been found possible to accustom marine fish to live in fresh water;
but as such changes in fish, and other marine animals, have been chiefly
observed in a state of nature, they do not properly belong to our present
subject. The period of gestation and of maturity, as shown in the earlier
chapters,--the season and the frequency of the act of breeding,--have all
been greatly modified under domestication. With the Egyptian goose the rate
of change in the season has been recorded.[754] The wild drake pairs with
one female, the domestic drake is polygamous. Certain breeds of fowls have
lost the habit of incubation. The paces of the horse, and the manner of
flight in certain breeds of the pigeon, have been modified, and are
inherited. The voice differs much in certain fowls and pigeons. Some breeds
are clamorous and others silent, as in the Call and common duck, or in the
Spitz and pointer dog. Every one knows how dogs differ from each other in
their manner of hunting, and in their ardour after different kinds of game
or vermin.

With plants the period of vegetation is easily changed and is inherited, as
in the case of summer and winter wheat, barley, {305} and vetches; but to
this subject we shall immediately return under acclimatisation. Annual
plants sometimes become perennial under a new climate, as I hear from Dr.
Hooker is the case with the stock and mignonette in Tasmania. On the other
hand, perennials sometimes become annuals, as with the Ricinus in England,
and as, according to Captain Mangles, with many varieties of the
heartsease. Von Berg[755] raised from seed of _Verbascum phoenicium_, which
is usually a biennial, both annual and perennial varieties. Some deciduous
bushes become evergreen in hot countries.[756] Rice requires much water,
but there is one variety in India which can be grown without
irrigation.[757] Certain varieties of the oat and of our other cereals are
best fitted for certain soils.[758] Endless similar facts could be given in
the animal and vegetable kingdoms. They are noticed here because they
illustrate analogous differences in closely allied natural species, and
because such changed habits of life, whether due to use and disuse, or to
the direct action of external conditions, or to so-called spontaneous
variation, would be apt to lead to modifications of structure.

       *       *       *       *       *

_Acclimatisation._--From the previous remarks we are naturally led to the
much disputed subject of acclimatisation. There are two distinct questions:
Do varieties descended from the same species differ in their power of
living under different climates? And secondly, if they so differ, how have
they become thus adapted? We have seen that European dogs do not succeed
well in India, and it is asserted,[759] that no one has succeeded in there
keeping the Newfoundland long alive; but then it may be argued, probably
with truth, that these northern breeds are specifically distinct from the
native dogs which flourish in India. The same remark may be made with
respect to different breeds of sheep, of which, according to Youatt,[760]
not one brought "from a torrid climate lasts out the second year," in the
Zoological Gardens. But sheep are capable of some degree of
acclimatisation, for Merino sheep bred at the Cape of Good Hope have been
found {306} far better adapted for India than those imported from
England.[761] It is almost certain that the breeds of the fowl are
descended from the same species; but the Spanish breed, which there is good
reason to believe originated near the Mediterranean,[762] though so fine
and vigorous in England, suffers more from frost than any other breed. The
Arrindy silk-moth introduced from Bengal, and the Ailanthus moth from the
temperate province of Shan Tung, in China, belong to the same species, as
we may infer from their identity in the caterpillar, cocoon, and mature
states;[763] yet they differ much in constitution: the Indian form "will
flourish only in warm latitudes," the other is quite hardy and withstands
cold and rain.

    Plants are more strictly adapted to climate than are animals. The
    latter when domesticated withstand such great diversities of climate,
    that we find nearly the same species in tropical and temperate
    countries; whilst the cultivated plants are widely dissimilar. Hence a
    larger field is open for inquiry in regard to the acclimatisation of
    plants than of animals. It is no exaggeration to say that with almost
    every plant which has long been cultivated varieties exist, which are
    endowed with constitutions fitted for very different climates; I will
    select only a few of the more striking cases, as it would be tedious to
    give all. In North America numerous fruit-trees have been raised, and
    in horticultural publications,--for instance, in Downing,--lists are
    given of the varieties which are best able to withstand the severe
    climate of the northern States and Canada. Many American varieties of
    the pear, plum, and peach are excellent in their own country, but until
    recently hardly one was known that succeeded in England; and with
    apples,[764] not one succeeds. Though the American varieties can
    withstand a severer winter than ours, the summer here is not hot
    enough. Fruit-trees have originated in Europe as in America with
    different constitutions, but they are not here much noticed, as the
    same nurserymen do not supply a wide area. The Forelle pear flowers
    early, and when the flowers have just set, and this is the critical
    period, they have been observed, both in France and England, to
    withstand with complete impunity a frost of 18° and even 14° Fahr.,
    which killed the flowers, whether fully expanded or in bud, of all
    other kinds of pears.[765] This power in the flower of resisting cold
    and afterwards producing fruit does not invariably depend, as we know
    on good authority,[766] on general constitutional vigour.

    {307}

    In proceeding northward, the number of varieties which are enabled to
    resist the climate rapidly decreases, as may be seen in the list of the
    varieties of the cherry, apple, and pear, which can be cultivated in
    the neighbourhood of Stockholm.[767] Near Moscow, Prince Troubetzkoy
    planted for experiment in the open ground several varieties of the
    pear, but one alone, the _Poire sans Pepins_, withstood the cold of
    winter.[768] We thus see that our fruit-trees, like distinct species of
    the same genus, certainly differ from each other in their
    constitutional adaptation to different climates.

    With the varieties of many plants, the adaptation to climate is often
    very close. Thus it has been proved by repeated trials "that few if any
    of the English varieties of wheat are adapted for cultivation in
    Scotland;"[769] but the failure in this case is at first only in the
    quantity, though ultimately in the quality, of the grain produced. The
    Rev. J. M. Berkeley sowed wheat-seed from India, and got "the most
    meagre ears," on land which would certainly have yielded a good crop
    from English wheat.[770] In these cases varieties have been carried
    from a warmer to a cooler climate; in the reverse case, as "when wheat
    was imported directly from France into the West Indian Islands, it
    produced either wholly barren spikes or furnished with only two or
    three miserable seeds, while West Indian seed by its side yielded an
    enormous harvest."[771] Here is another case of close adaptation to a
    slightly cooler climate; a kind of wheat which in England may be used
    indifferently either as a winter or summer variety, when sown under the
    warmer climate of Grignan, in France, behaved exactly as if it had been
    a true winter wheat.[772]

    Botanists believe that all the varieties of maize belong to the same
    species; and we have seen that in North America, in proceeding
    northward, the varieties cultivated in each zone produce their flowers
    and ripen their seed within shorter and shorter periods. So that the
    tall, slowly maturing southern varieties do not succeed in New England,
    and the New English varieties do not succeed in Canada. I have not met
    with any statement that the southern varieties are actually injured or
    killed by a degree of cold which the northern varieties withstand with
    impunity, though this is probable; but the production of early
    flowering and early seeding varieties deserves to be considered as one
    form of acclimatisation. Hence it has been found possible, according to
    Kalm, to cultivate maize further and further northwards in America. In
    Europe, also, as we learn from the evidence given by Alph. De Candolle,
    the culture of maize has extended since the end of the last century
    thirty leagues north of its former boundary.[773] On the authority of
    the great Linnæus,[774] I may quote an {308} analogous case, namely,
    that in Sweden tobacco raised from home-grown seed ripens its seed a
    month sooner and is less liable to miscarry than plants raised from
    foreign seed.

    With the Vine, differently from the maize, the line of practical
    culture has retreated a little southward since the middle ages;[775]
    but this seems due to commerce, including that of wine, being now freer
    or more easy. Nevertheless the fact of the vine not having spread
    northward shows that acclimatisation has made no progress during
    several centuries. There is, however, a marked difference in the
    constitution of the several varieties,--some being hardy, whilst
    others, like the muscat of Alexandria, require a very high temperature
    to come to perfection. According to Labat,[776] vines taken from France
    to the West Indies succeed with extreme difficulty, whilst those
    imported from Madeira, or the Canary Islands, thrive admirably.

    Gallesio gives a curious account of the naturalisation of the Orange in
    Italy. Daring many centuries the sweet orange was propagated
    exclusively by grafts, and so often suffered from frosts that it
    required protection. After the severe frost of 1709, and more
    especially after that of 1763, so many trees were destroyed that
    seedlings from the sweet orange were raised, and, to the surprise of
    the inhabitants, their fruit was found to be sweet. The trees thus
    raised were larger, more productive, and hardier than the former kinds;
    and seedlings are now continually raised. Hence Gallesio concludes that
    much more was effected for the naturalisation of the orange in Italy by
    the accidental production of new kinds during a period of about sixty
    years, than had been effected by grafting old varieties during many
    ages.[777] I may add that Risso[778] describes some Portuguese
    varieties of the orange as extremely sensitive to cold, and as much
    tenderer than certain other varieties.

    The peach was known to Theophrastus, 322 B.C.[779] According to the
    authorities quoted by Dr. F. Rolle,[780] it was tender when first
    introduced into Greece, and even in the island of Rhodes only
    occasionally bore fruit. If this be correct, the peach, in spreading
    during the last two thousand years over the middle parts of Europe,
    must have become much hardier. At the present day different varieties
    differ much in hardiness: some French varieties will not succeed in
    England; and near Paris, the _Pavie de Bonneuil_ does not ripen its
    fruit till very late, even when grown on a wall; "it is, therefore,
    only fit for a very hot southern climate."[781]

    I will briefly give a few other cases. A variety of _Magnolia
    grandiflora_, raised by M. Roy, withstands cold several degrees lower
    than that which any other variety can resist. With camellias there is
    much difference in hardiness. One particular variety of Noisette rose
    withstood the severe frost of 1860 "untouched and hale amidst a
    universal destruction of other {309} Noisettes." In New York the "Irish
    yew is quite hardy, but the common yew is liable to be cut down." I may
    add that there are varieties of the sweet potato (_Convolvulus
    batatas_) which are suited for warmer, as well as for colder,
    climates.[782]

The plants as yet mentioned have been found capable of resisting an unusual
degree of cold or heat, when fully grown. The following cases refer to
plants whilst young. In a large bed of young Araucarias of the same age,
growing close together and equally exposed, it was observed,[783] after the
unusually severe winter of 1860-61, that, "in the midst of the dying,
numerous individuals remained on which the frost had absolutely made no
kind of impression." Dr. Lindley, after alluding to this and other similar
cases, remarks, "Among the lessons which the late formidable winter has
taught us, is that, even in their power of resisting cold, individuals of
the same species of plants are remarkably different." Near Salisbury, there
was a sharp frost on the night of May 24th, 1836, and all the French beans
(_Phaseolus vulgaris_) in a bed were killed except about one in thirty,
which completely escaped.[784] On the same day of the month, but in the
year 1864, there was a severe frost in Kent, and two rows of
scarlet-runners (_P. multiflorus_) in my garden, containing 390 plants of
the same age and equally exposed, were all blackened and killed except
about a dozen plants. In an adjoining row of "Fulmer's dwarf bean" (_P.
vulgaris_), one single plant escaped. A still more severe frost occurred
four days afterwards, and of the dozen plants which had previously escaped
only three survived; these were not taller or more vigorous than the other
young plants, but they escaped completely, with not even the tips of their
leaves browned. It was impossible to behold these three plants, with their
blackened, withered, and dead brethren all round them, and not see at a
glance that they differed widely in constitutional power of resisting
frost.

This work is not the proper place to show that wild plants {310} of the
same species, naturally growing at different altitudes or under different
latitudes, become to a certain extent acclimatised, as is proved by the
different behaviour of their seedlings when raised in England. In my
'Origin of Species' I have alluded to some cases, and I could add others.
One instance must suffice: Mr. Grigor, of Forres,[785] states that
seedlings of the Scotch fir (_Pinus sylvestris_), raised from seed from the
Continent and from the forests of Scotland, differ much. "The difference is
perceptible in one-year-old, and more so in two-year-old seedlings; but the
effects of the winter on the second year's growth almost uniformly makes
those from the Continent quite brown, and so damaged, that by the month of
March they are quite unsaleable, while the plants from the native Scotch
pine, under the same treatment, and standing alongside, although
considerably shorter, are rather stouter and quite green, so that the beds
of the one can be known from the other when seen from the distance of a
mile." Closely similar facts have been observed with seedling larches.

    Hardy varieties would alone be valued or noticed in Europe; whilst
    tender varieties, requiring more warmth, would generally be neglected;
    but such occasionally arise. Thus Loudon[786] describes a Cornish
    variety of the elm which is almost an evergreen, and of which the
    shoots are often killed by the autumnal frosts, so that its timber is
    of little value. Horticulturists know that some varieties are much more
    tender than others: thus all the varieties of the broccoli are more
    tender than cabbages; but there is much difference in this respect in
    the sub-varieties of the broccoli; the pink and purple kinds are a
    little hardier than the white Cape broccoli, "but they are not to be
    depended on after the thermometer falls below 24° Fahr.:" the Walcheren
    broccoli is less tender than the Cape, and there are several varieties
    which will stand much severer cold than the Walcheren.[787]
    Cauliflowers seed more freely in India than cabbages.[788] To give one
    instance with flowers: eleven plants raised from a hollyhock, called
    the _Queen of the Whites_,[789] were found to be much more tender than
    various other seedlings. It may be presumed that all tender varieties
    would succeed better under a climate warmer than ours. With
    fruit-trees, it is well known that certain varieties, for instance of
    the peach, stand forcing in a hot-house better than others; and this
    shows {311} either pliability of organisation or some constitutional
    difference. The same individual cherry-tree, when forced, has been
    observed during successive years gradually to change its period of
    vegetation.[790] Few pelargoniums can resist the heat of a stove, but
    _Alba multiflora_ will, as a most skilful gardener asserts, "stand
    pine-apple top and bottom heat the whole winter, without looking any
    more drawn than if it had stood in a common greenhouse; and _Blanche
    Fleur_ seems as if it had been made on purpose for growing in winter,
    like many bulbs, and to rest all summer."[791] There can hardly be a
    doubt that the _Alba multiflora_ pelargonium must have a widely
    different constitution from that of most other varieties of this plant;
    it would probably withstand even an equatorial climate.

    We have seen that according to Labat the vine and wheat require
    acclimatisation in order to succeed in the West Indies. Similar facts
    have been observed at Madras: "two parcels of mignonette-seed, one
    direct from Europe, the other saved at Bangalore (of which the mean
    temperature is much below that of Madras) were sown at the same time:
    they both vegetated equally favourably, but the former all died off a
    few days after they appeared above ground; the latter still survive,
    and are vigorous healthy plants." So again, "turnip and carrot seed
    saved at Hyderabad are found to answer better at Madras than seed from
    Europe or from the Cape of Good Hope."[792] Mr. J. Scott, of the
    Calcutta Botanic Gardens, informs me that seeds of the sweet-pea
    (_Lathyrus odoratus_) imported from England produce plants, with thick,
    rigid stems and small leaves, which rarely blossom and never yield
    seed; plants raised from French seed blossom sparingly, but all the
    flowers are sterile; on the other hand, plants raised from sweet-peas
    grown near Darjeeling in Upper India, but originally derived from
    England, can be successfully cultivated on the plains of India; for
    they flower and seed profusely, and their stems are lax and scandent.
    In some of the foregoing cases, as Dr. Hooker has remarked to me, the
    greater success may perhaps be attributed to the seeds having been more
    fully ripened under a more favourable climate; but this view can hardly
    be extended to so many cases, including plants, which, from being
    cultivated under a climate hotter than their native one, become fitted
    for a still hotter climate. We may therefore safely conclude that
    plants can to a certain extent become accustomed to a climate either
    hotter or colder than their own; although these latter cases have been
    more frequently observed.

We will now consider the means by which acclimatisation may be effected,
namely, through the spontaneous appearance of varieties having a different
constitution, and through the effects of use or habit. In regard to the
first process, there is no evidence that a change in the constitution of
the {312} offspring necessarily stands in any direct relation with the
nature of the climate inhabited by the parents. On the contrary, it is
certain that hardy and tender varieties of the same species appear in the
same country. New varieties thus spontaneously arising become fitted to
slightly different climates in two different ways; firstly, they may have
the power, either as seedlings or when full-grown, of resisting intense
cold, as with the Moscow pear, or of resisting intense heat, as with some
kinds of Pelargonium, or the flowers may withstand severe frost, as with
the Forelle pear. Secondly, plants may become adapted to climates widely
different from their own, from flowering and fruiting either earlier or
later in the season. In both these cases the power of acclimatisation by
man consists simply in the selection and preservation of new varieties. But
without any direct intention on his part of securing a hardier variety,
acclimatisation may be unconsciously effected by merely raising tender
plants from seed, and by occasionally attempting their cultivation further
and further northwards, as in the case of maize, the orange, and the peach.

How much influence ought to be attributed to inherited habit or custom in
the acclimatisation of animals and plants is a much more difficult
question. In many cases natural selection can hardly have failed to have
come into play and complicated the result. It is notorious that mountain
sheep resist severe weather and storms of snow which would destroy lowland
breeds; but then mountain sheep have been thus exposed from time
immemorial, and all delicate individuals will have been destroyed, and the
hardiest preserved. So with the Arrindy silk-moths of China and India; who
can tell how far natural selection may have taken a share in the formation
of the two races, which are now fitted for such widely different climates?
It seems at first probable that the many fruit-trees, which are so well
fitted for the hot summers and cold winters of North America, in contrast
with their poor success under our climate, have become adapted through
habit; but when we reflect on the multitude of seedlings annually raised in
that country, and that none would succeed unless born with a fitting
constitution, it is possible that mere habit may have done nothing towards
their acclimatisation. On the other hand, when we {313} hear that Merino
sheep, bred during no great number of generations at the Cape of Good
Hope--that some European plants raised during only a few generations in the
cooler parts of India, withstand the hotter parts of that country much
better than the sheep or seeds imported directly from England, we must
attribute some influence to habit. We are led to the same conclusion when
we hear from Naudin[793] that the races of melons, squashes, and gourds,
which have long been cultivated in Northern Europe, are comparatively more
precocious, and need much less heat for maturing their fruit, than the
varieties of the same species recently brought from tropical regions. In
the reciprocal conversion of summer and winter wheat, barley, and vetches
into each other, habit produces a marked effect in the course of a very few
generations. The same thing apparently occurs with the varieties of maize,
which, when carried from the Southern to the Northern States of America, or
into Germany, soon become accustomed to their new homes. With vine-plants
taken to the West Indies from Madeira, which are said to succeed better
than plants brought directly from France, we have some degree of
acclimatisation in the individual, independently of the production of new
varieties by seed.

The common experience of agriculturists is of some value, and they often
advise persons to be cautious in trying in one country the productions of
another. The ancient agricultural writers of China recommend the
preservation and cultivation of the varieties peculiar to each country.
During the classical period, Columella wrote, "Vernaculum pecus peregrino
longe præstantius est."[794]

I am aware that the attempt to acclimatise either animals or plants has
been called a vain chimæra. No doubt the attempt in most cases deserves to
be thus called, if made independently of the production of new varieties
endowed with a different constitution. Habit, however much prolonged,
rarely produces any effect on a plant propagated by buds; it apparently
acts only through successive seminal generations. {314} The laurel, bay,
laurestinus, &c., and the Jerusalem artichoke, which are propagated by
cuttings or tubers, are probably now as tender in England as when first
introduced; and this appears to be the case with the potato, which until
recently was seldom multiplied by seed. With plants propagated by seed, and
with animals, there will be little or no acclimatisation unless the hardier
individuals are either intentionally or unconsciously preserved. The
kidney-bean has often been advanced as an instance of a plant which has not
become hardier since its first introduction into Britain. We hear, however,
on excellent authority,[795] that some very fine seed, imported from
abroad, produced plants "which blossomed most profusely, but were nearly
all but abortive, whilst plants grown alongside from English seed podded
abundantly;" and this apparently shows some degree of acclimatisation in
our English plants. We have also seen that seedlings of the kidney-bean
occasionally appear with a marked power of resisting frost; but no one, as
far as I can hear, has ever separated such hardy seedlings, so as to
prevent accidental crossing, and then gathered their seed, and repeated the
process year after year. It may, however, be objected with truth that
natural selection ought to have had a decided effect on the hardiness of
our kidney-beans; for the tenderest individuals must have been killed
during every severe spring, and the hardier preserved. But it should be
borne in mind that the result of increased hardiness would simply be that
gardeners, who are always anxious for as early a crop as possible, would
sow their seed a few days earlier than formerly. Now, as the period of
sowing depends much on the soil and elevation of each district, and varies
with the season; and as new varieties have often been imported from abroad,
can we feel sure that our kidney-beans are not somewhat hardier? I have not
been able, by searching old horticultural works, to answer this question
satisfactorily.

On the whole the facts now given show that, though habit does something
towards acclimatisation, yet that the spontaneous appearance of
constitutionally different individuals is a far more effective agent. As no
single instance has been recorded, either with animals or plants, of
hardier individuals {315} having been long and steadily selected, though
such selection is admitted to be indispensable for the improvement of any
other character, it is not surprising that man has done little in the
acclimatisation of domesticated animals and cultivated plants. We need not,
however, doubt that under nature new races and new species would become
adapted to widely different climates, by spontaneous variation, aided by
habit, and regulated by natural selection.

_Arrests of Development: Rudimentary and Aborted Organs._

    These subjects are here introduced because there is reason to believe
    that rudimentary organs are in many cases the result of disuse.
    Modifications of structure from arrested development, so great or so
    serious as to deserve to be called monstrosities, are of common
    occurrence, but, as they differ much from any normal structure, they
    require here only a passing notice. When a part or organ is arrested
    during its embryonic growth, a rudiment is generally left. Thus the
    whole head may be represented by a soft nipple-like projection, and the
    limbs by mere papillæ. These rudiments of limbs are sometimes
    inherited, as has been observed in a dog.[796]

    Many lesser anomalies in our domesticated animals appear to be due to
    arrested development. What the cause of the arrest may be, we seldom
    know, except in the case of direct injury to the embryo within the egg
    or womb. That the cause does not generally act at a very early
    embryonic period we may infer from the affected organ seldom being
    wholly aborted,--a rudiment being generally preserved. The external
    ears are represented by mere vestiges in a Chinese breed of sheep; and
    in another breed, the tail is reduced "to a little button, suffocated,
    in a manner, by fat."[797] In tailless dogs and cats a stump is left;
    but I do not know whether it includes at an early embryonic age
    rudiments of all the caudal vertebræ. In certain breeds of fowls the
    comb and wattles are reduced to rudiments; in the Cochin-China breed
    scarcely more than rudiments of spurs exist. With polled Suffolk
    cattle, "rudiments of horns can often be felt at an early age;"[798]
    and with species in a state of nature, the relatively greater
    development of rudimentary organs at an early period of life is highly
    characteristic of such organs. With hornless breeds of cattle and
    sheep; another and singular kind of rudiment has been observed, namely,
    minute dangling horns attached to the skin alone, and which are often
    shed and grow again. With hornless goats, according to Desmarest,[799]
    {316} the bony protuberances which properly support the horns exist as
    mere rudiments.

    With cultivated plants it is far from rare to find the petals, stamens,
    and pistils represented by rudiments, like those observed in natural
    species. So it is with the whole seed in many fruits; thus near
    Astrakhan there is a grape with mere traces of seeds, "so small and
    lying so near the stalk that they are not perceived in eating the
    grape."[800] In certain varieties of the gourd, the tendrils, according
    to Naudin, are represented by rudiments or by various monstrous
    growths. In the broccoli and cauliflower the greater number of the
    flowers are incapable of expansion, and include rudimentary organs. In
    the Feather hyacinth (_Muscari comosum_) the upper and central flowers
    are brightly coloured but rudimentary; under cultivation the tendency
    to abortion travels downwards and outwards, and all the flowers become
    rudimentary; but the abortive stamens and pistils are not so small in
    the lower as in the upper flowers. In the _Viburnum opulus_, on the
    other hand, the outer flowers naturally have their organs of
    fructification in a rudimentary state, and the corolla is of large
    size; under cultivation, the change spreads to the centre, and all the
    flowers become affected; thus the well-known Snow-ball bush is
    produced. In the Compositæ, the so-called doubling of the flowers
    consists in the greater development of the corolla of the central
    florets, generally accompanied with some degree of sterility; and it
    has been observed[801] that the progressive doubling invariably spreads
    from the circumference to the centre,--that is, from the ray florets,
    which so often include rudimentary organs, to those of the disc. I may
    add, as bearing on this subject, that, with Asters, seeds taken from
    the florets of the circumference have been found to yield the greatest
    number of double flowers.[802] In these several cases we have a natural
    tendency in certain parts to become rudimentary, and this under culture
    spreads either to, or from, the axis of the plant. It deserves notice,
    as showing how the same laws govern the changes which natural species
    and artificial varieties undergo, that in a series of species in the
    genus Carthamus, one of the Compositæ, a tendency in the seeds to the
    abortion of the pappus may be traced extending from the circumference
    to the centre of the disc: thus, according to A. de Jussieu,[803] the
    abortion is only partial in _Carthamus creticus_, but more extended in
    _C. lanatus_; for in this species two or three alone of the central
    seeds are furnished with a pappus, the surrounding seeds being either
    quite naked or furnished with a few hairs; and lastly, in _C.
    tinctorius_, even the central seeds are destitute of pappus, and the
    abortion is complete.

    With animals and plants under domestication, when an organ disappears,
    leaving only a rudiment, the loss has generally been sudden, as with
    hornless and tailless breeds; and such cases may be ranked as inherited
    monstrosities. But in some few cases the loss has been gradual, and
    {317} has been partly effected by selection, as with the rudimentary
    combs and wattles of certain fowls. We have also seen that the wings of
    some domesticated birds have been slightly reduced by disuse, and the
    great reduction of the wings in certain silk-moths, with mere rudiments
    left, has probably been aided by disuse.

    With species in a state of nature, rudimentary organs are so extremely
    common that scarcely one can be named which is wholly free from a
    blemish of this nature. Such organs are generally variable, as several
    naturalists have observed; for, being useless, they are not regulated
    by natural selection, and they are more or less liable to reversion.
    The same rule certainly holds good with parts which have become
    rudimentary under domestication. We do not know through what steps
    under nature rudimentary organs have passed in being reduced to their
    present condition; but we so incessantly see in species of the same
    group the finest gradations between an organ in a rudimentary and
    perfect state, that we are led to believe that the passage must have
    been extremely gradual. It may be doubted whether a change of structure
    so abrupt as the sudden loss of an organ would ever be of service to a
    species in a state of nature; for the conditions to which all organisms
    are closely adapted usually change very slowly. Even if an organ did
    suddenly disappear in some one individual by an arrest of development,
    intercrossing with the other individuals of the same species would
    cause it to reappear in a more or less perfect manner, so that its
    final reduction could only be effected by the slow process of continued
    disuse or natural selection. It is much more probable that, from
    changed habits of life, organs first become of less and less use, and
    ultimately superfluous; or their place may be supplied by some other
    organ; and then disuse, acting on the offspring through inheritance at
    corresponding periods of life, would go on reducing the organ; but as
    most organs could be of no use at an early embryonic period, they would
    not be affected by disuse; consequently they would be preserved at this
    stage of growth, and would remain as rudiments. In addition to the
    effects of disuse, the principle of economy of growth, already alluded
    to in this chapter, would lead to the still further reduction of all
    superfluous parts. With respect to the final and total suppression or
    abortion of any organ, another and distinct principle, which will be
    discussed in the chapter on pangenesis, probably takes a share in the
    work.

    With animals and plants reared by man there is no severe or recurrent
    struggle for existence, and the principle of economy will not come into
    action. So far, indeed, is this from being the case, that in some
    instances organs, which are naturally rudimentary in the
    parent-species, become partially redeveloped in the domesticated
    descendants. Thus cows, like most other ruminants, properly have four
    active and two rudimentary mammæ; but in our domesticated animals, the
    latter occasionally become considerably developed and yield milk. The
    atrophied mammæ, which, in male domesticated animals, including man,
    have in some rare cases grown to full size and secreted milk, perhaps
    offer an analogous case. The hind feet of dogs include rudiments of a
    fifth toe, and in certain large breeds these toes, though still
    rudimentary, become considerably developed {318} and are furnished with
    claws. In the common Hen, the spurs and comb are rudimentary, but in
    certain breeds these become, independently of age or disease of the
    ovaria, well developed. The stallion has canine teeth, but the mare has
    only traces of the alveoli, which, as I am informed by the eminent
    veterinary Mr. G. T. Brown, frequently contain minute irregular nodules
    of bone. These nodules, however, sometimes become developed into
    imperfect teeth, protruding through the gums and coated with enamel;
    and occasionally they grow to a third or even a fourth of the length of
    the canines in the stallion. With plants I do not know whether the
    redevelopment of rudimentary organs occurs more frequently under
    culture than under nature. Perhaps the pear-tree may be a case in
    point, for when wild it bears thorns, which though useful as a
    protection are formed of branches in a rudimentary condition, but, when
    the tree is cultivated, the thorns are reconverted into branches.

Finally, though organs which must be classed as rudimentary frequently
occur in our domesticated animals and cultivated plants, these have
generally been formed suddenly, through an arrest of development. They
usually differ in appearance from the rudiments which so frequently
characterise natural species. In the latter, rudimentary organs have been
slowly formed through continued disuse, acting by inheritance at a
corresponding age, aided by the principle of the economy of growth, all
under the control of natural selection. With domesticated animals, on the
other hand, the principle of economy is far from coming into action, and
their organs, although often slightly reduced by disuse, are not thus
almost obliterated with mere rudiments left.

       *       *       *       *       *


{319}

CHAPTER XXV.

LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY.

    EXPLANATION OF TERM--CORRELATION AS CONNECTED WITH
    DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED
    SIZE OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET
    IN BIRDS ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE
    HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND DERMAL
    APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED
    MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED
    MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND EARS--SKULL AND CREST
    OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTH COMPLICATED BY THE
    ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS CORRELATED WITH
    CONSTITUTIONAL PECULIARITIES.

All the parts of the organisation are to a certain extent connected or
correlated together; but the connexion may be so slight that it hardly
exists, as with compound animals or the buds on the same tree. Even in the
higher animals various parts are not at all closely related; for one part
may be wholly suppressed or rendered monstrous without any other part of
the body being affected. But in some cases, when one part varies, certain
other parts always, or nearly always, simultaneously vary; they are then
subject to the law of correlated variation. Formerly I used the somewhat
vague expression of correlation of growth, which may be applied to many
large classes of facts. Thus, all the parts of the body are admirably
coordinated for the peculiar habits of life of each organic being, and they
may be said, as the Duke of Argyll insists in his 'Reign of Law,' to be
correlated for this purpose. Again, in large groups of animals certain
structures always co-exist; for instance, a peculiar form of stomach with
teeth of peculiar form, and such structures may in one sense be said to be
correlated. But these cases have no necessary connexion with the law to be
discussed in the present chapter; for we do not know that {320} the initial
or primary variations of the several parts were in any way related; slight
modifications or individual differences may have been preserved, first in
one and then in another part, until the final and perfectly co-adapted
structure was acquired; but to this subject I shall presently recur. Again,
in many groups of animals the males alone are furnished with weapons, or
are ornamented with gay colours; and these characters manifestly stand in
some sort of correlation with the male reproductive organs, for when the
latter are destroyed these characters disappear. But it was shown in the
twelfth chapter that the very same peculiarity may become attached at any
age to either sex, and afterwards be exclusively transmitted by the same
sex at a corresponding age. In these cases we have inheritance limited by,
or correlated with, both sex and age; but we have no reason for supposing
that the original cause of the variation was necessarily connected with the
reproductive organs, or with the age of the affected being.

In cases of true correlated variation, we are sometimes able to see the
nature of the connexion; but in most cases the bond is hidden from us, and
certainly differs in different cases. We can seldom say which of two
correlated parts first varies, and induces a change in the other; or
whether the two are simultaneously produced by some distinct cause.
Correlated variation is an important subject for us; for when one part is
modified through continued selection, either by man or under nature, other
parts of the organisation will be unavoidably modified. From this
correlation it apparently follows that, with our domesticated animals and
plants, varieties rarely or never differ from each other by some single
character alone.

One of the simplest cases of correlation is that a modification which
arises during an early stage of growth tends to influence the subsequent
development of the same part, as well as of other and intimately connected
parts. Isidore Geoffroy St. Hilaire states[804] that this may constantly be
observed with monstrosities {321} in the animal kingdom; and
Moquin-Tandon[805] remarks, that, as with plants the axis cannot become
monstrous without in some way affecting the organs subsequently produced
from it, so axial anomalies are almost always accompanied by deviations of
structure in the appended parts. We shall presently see that with
short-muzzled races of the dog certain histological changes in the basal
elements of the bones arrest their development and shorten them, and this
affects the position of the subsequently developed molar teeth. It is
probable that certain modifications in the larvæ of insects would affect
the structure of the mature insects. But we must be very careful not to
extend this view too far, for, during the normal course of development,
certain members in the same group of animals are known to pass through an
extraordinary course of change, whilst other and closely allied members
arrive at maturity with little change of structure.

Another simple case of correlation is that with the increased or decreased
dimensions of the whole body, or of any particular part, certain organs are
increased or diminished in number, or are otherwise modified. Thus
pigeon-fanciers have gone on selecting pouters for length of body, and we
have seen that their vertebræ are generally increased in number, and their
ribs in breadth. Tumblers have been selected for their small bodies, and
their ribs and primary wing-feathers are generally lessened in number.
Fantails have been selected for their large, widely-expanded tails, with
numerous tail-feathers, and the caudal vertebræ are increased in size and
number. Carriers have been selected for length of beak, and their tongues
have become longer, but not in strict accordance with the length of beak.
In this latter breed and in others having large feet, the number of the
scutellæ on the toes is greater than in the breeds with small feet. Many
similar cases could be given. In Germany it has been observed that the
period of gestation is longer in large-sized than in small-sized breeds of
cattle. With our highly-improved animals of all kinds the period of
maturity has advanced, both with respect to the full growth of the body and
the period of reproduction; and, in correspondence with this, the teeth are
now developed earlier than formerly, so that, {322} to the surprise of
agriculturists, the ancient rules for judging the age of an animal by the
state of its teeth are no longer trustworthy.[806]

_Correlated Variation of Homologous Parts._--Parts which are homologous
tend to vary in the same manner; and this is what might have been expected,
for such parts are identical in form and structure during an early period
of embryonic development, and are exposed in the egg or womb to similar
conditions. The symmetry, in most kinds of animals, of the corresponding or
homologous organs on the right and left sides of the body, is the simplest
case in point; but this symmetry sometimes fails, as with rabbits having
only one ear, or stags with one horn, or with many-horned sheep which
sometimes carry an additional horn on one side of their heads. With flowers
which have regular corollas, the petals generally vary in the same manner,
as we see in the same complicated and elegant pattern, on the flowers of
the Chinese pink; but with irregular flowers, though the petals are of
course homologous, this symmetry often fails, as with the varieties of the
_Antirrhinum_ or snapdragon, or that variety of the kidney-bean (_Phaseolus
multiflorus_) which has a white standard-petal.

In the vertebrata the front and hind limbs are homologous, and they tend to
vary in the same manner, as we see in long and short-legged, or in thick
and thin-legged races of the horse and dog. Isidore Geoffroy[807] has
remarked on the tendency of supernumerary digits in man to appear, not only
on the right and left sides, but on the upper and lower extremities. Meckel
has insisted[808] that, when the muscles of the arm depart in number or
arrangement from their proper type, they almost always imitate those of the
leg; and so conversely the varying muscles of the leg imitate the normal
muscles of the arm.

In several distinct breeds of the pigeon and fowl, the legs and the two
outer toes are heavily feathered, so that in the trumpeter pigeon they
appear like little wings. In the feather-legged bantam the "boots" or
feathers, which grow from the outside of the leg and generally from the two
outer toes, have, {323} according to the excellent authority of Mr.
Hewitt,[809] been seen to exceed the wing-feathers in length, and in one
case were actually nine and a half inches in length! As Mr. Blyth has
remarked to me, these leg-feathers resemble the primary wing-feathers, and
are totally unlike the fine down which naturally grows on the legs of some
birds, such as grouse and owls. Hence it may be suspected that excess of
food has first given redundancy to the plumage, and then that the law of
homologous variation has led to the development of feathers on the legs, in
a position corresponding with those on the wing, namely, on the outside of
the tarsi and toes. I am strengthened in this belief by the following
curious case of correlation, which for a long time seemed to me utterly
inexplicable, namely, that in pigeons of any breed, if the legs are
feathered, the two outer toes are partially connected by skin. These two
outer toes correspond with our third and fourth toes. Now, in the wing of
the pigeon or any other bird, the first and fifth digits are wholly
aborted; the second is rudimentary and carries the so-called
"bastard-wing;" whilst the third and fourth digits are completely united
and enclosed by skin, together forming the extremity of the wing. So that
in feather-footed pigeons, not only does the exterior surface support a row
of long feathers, like wing-feathers, but the very same digits which in the
wing are completely united by skin become partially united by skin in the
feet; and thus by the law of the correlated variation of homologous parts
we can understand the curious connection of feathered legs and membrane
between the two outer toes.

Andrew Knight[810] has remarked that the face or head and the limbs vary
together in general proportions. Compare, for instance, the head and limbs
of a dray and race-horse, or of a greyhound and mastiff. What a monster a
greyhound would appear with the head of a mastiff! The _modern_ bulldog,
however, has fine limbs, but this is a recently-selected character. From
the measurements given in the sixth chapter, we clearly see that in all the
breeds of the pigeon the length of the beak and the size of the feet are
correlated. The view which, as before explained, seems the most probable
is, that disuse in all cases tends {324} to diminish the feet, the beak
becoming at the same time through correlation shorter; but that in those
few breeds in which length of beak has been a selected point, the feet,
notwithstanding disuse, have through correlation increased in size.

With the increased length of the beak in pigeons, not only the tongue
increases in length, but likewise the orifice of the nostrils. But the
increased length of the orifice of the nostrils perhaps stands in closer
correlation with the development of the corrugated skin or wattle at the
base of the beak; for when there is much wattle round the eyes, the eyelids
are greatly increased or even doubled in length.

There is apparently some correlation even in colour between the head and
the extremities. Thus with horses a large white star or blaze on the
forehead is generally accompanied by white feet.[811] With white rabbits
and cattle, dark marks often co-exist on the tips of the ears and on the
feet. In black and tan dogs of different breeds, tan-coloured spots over
the eyes and tan-coloured feet almost invariably go together. These latter
cases of connected colouring may be due either to reversion or to analogous
variation,--subjects to which we shall hereafter return,--but this does not
necessarily determine the question of their original correlation. If those
naturalists are correct who maintain that the jaw-bones are homologous with
the limb-bones, then we can understand why the head and limbs tend to vary
together in shape and even in colour; but several highly competent judges
dispute the correctness of this view.

The lopping forwards and downwards of the immense ears of fancy rabbits is
in part due to the disuse of the muscles, and in part to the weight and
length of the ears, which have been increased by selection during many
generations. Now, with the increased size and changed direction of the
ears, not only has the bony auditory meatus become changed in outline,
direction, and greatly in size, but the whole skull has been slightly
modified. This could be clearly seen in "half-lops"--that is, in rabbits
with one ear alone lopping forward--for the opposite sides of their skulls
were not strictly symmetrical. This seems to me a curious instance of
correlation, between hard {325} bones and organs so soft and flexible, as
well as so unimportant under a physiological point of view, as the external
ears. The result no doubt is largely due to mere mechanical action, that
is, to the weight of the ears, on the same principle that the skull of a
human infant is easily modified by pressure.

The skin and the appendages of hair, feathers, hoofs, horns, and teeth, are
homologous over the whole body. Every one knows that the colour of the skin
and that of the hair usually vary together; so that Virgil advises the
shepherd to look whether the mouth and tongue of the ram are black, lest
the lambs should not be purely white. With poultry and certain ducks we
have seen that the colour of the plumage stands in some connexion with the
colour of the shell of the egg,--that is, with the mucous membrane which
secretes the shell. The colour of the skin and hair, and the odour emitted
by the glands of the skin, are said[812] to be connected, even in the same
race of men. Generally the hair varies in the same way all over the body in
length, fineness, and curliness. The same rule holds good with feathers, as
we see with the laced and frizzled breeds both of fowls and pigeons. In the
common cock the feathers on the neck and loins are always of a particular
shape, called hackles: now in the Polish breed, both sexes are
characterised by a tuft of feathers on the head; but through correlation
these feathers in the male always assume the form of hackles. The wing and
tail-feathers, though arising from parts not homologous, vary in length
together; so that long or short winged pigeons generally have long or short
tails. The case of the Jacobin-pigeon is more curious, for the wing and
tail feathers are remarkably long; and this apparently has arisen in
correlation with the elongated and reversed feathers on the back of the
neck, which form the hood.

The hoofs and hair are homologous appendages; and a careful observer,
namely Azara,[813] states that in Paraguay horses of various colours are
often born with their hair curled and twisted like that on the head of a
negro. This peculiarity is strongly inherited. But what is remarkable is
that the hoofs of these horses "are absolutely like those of a mule." The
hair also of the mane and tail is invariably much shorter than usual, being
only from four {326} to twelve inches in length; so that curliness and
shortness of the hair are here, as with the negro, apparently correlated.

With respect to the horns of sheep, Youatt[814] remarks that "multiplicity
of horns is not found in any breed of much value: it is generally
accompanied by great length and coarseness of the fleece." Several tropical
breeds of sheep, which are clothed with hair instead of wool, have horns
almost like those of a goat. Sturm[815] expressly declares that in
different races the more the wool is curled the more the horns are spirally
twisted. We have seen in the third chapter, where other analogous facts
have been given, that the parent of the Mauchamp breed, so famous for its
fleece, had peculiarly shaped horns. The inhabitants of Angora assert[816]
that "only the white goats which have horns wear the fleece in the long
curly locks that are so much admired; those which are not horned having a
comparatively close coat." From these cases we may conclude that the hair
or wool and the horns vary in a correlated manner. Those who have tried
hydropathy are aware that the frequent application of cold water stimulates
the skin; and whatever stimulates the skin tends to increase the growth of
the hair, as is well shown in the abnormal growth of hair near old inflamed
surfaces. Now, Professor Low[817] is convinced that with the different
races of British cattle thick skin and long hair depend on the humidity of
the climate which they inhabit. We can thus see how a humid climate might
act on the horns--in the first place directly on the skin and hair, and
secondly by correlation on the horns. The presence or absence of horns,
moreover, both in the case of sheep and cattle, acts, as will presently be
shown, by some sort of correlation on the skull.

With respect to hair and teeth, Mr. Yarrell[818] found many of the teeth
deficient in three hairless "_Ægyptian_" dogs, and in a hairless terrier.
The incisors, canines, and premolars suffered most, but in one case all the
teeth, except the large tubercular molar on each side, were deficient. With
man several striking cases have been recorded[819] of inherited baldness
with {327} inherited deficiency, either complete or partial, of the teeth.
We see the same connexion in those rare cases in which the hair has been
renewed in old age, for this has "usually been accompanied by a renewal of
the teeth." I have remarked in a former part of this volume that the great
reduction in the size of the tusks in domestic boars probably stands in
close relation with their diminished bristles, due to a certain amount of
protection; and that the reappearance of the tusks in boars, which have
become feral and are fully exposed to the weather, probably depends on the
reappearance of the bristles. I may add, though not strictly connected with
our present point, that an agriculturist[820] asserts that "pigs with
little hair on their bodies are most liable to lose their tails, showing a
weakness of the tegumental structure. It may be prevented by crossing with
a more hairy breed."

In the previous cases deficient hair, and teeth deficient in number or
size, are apparently connected. In the following cases abnormally redundant
hair, and teeth either deficient or redundant, are likewise connected. Mr.
Crawfurd[821] saw at the Burmese Court a man, thirty years old, with his
whole body, except the hands and feet, covered with straight silky hair,
which on the shoulders and spine was five inches in length. At birth the
ears alone were covered. He did not arrive at puberty, or shed his milk
teeth, until twenty years old; and at this period he acquired five teeth in
the upper jaw, namely four incisors and one canine, and four incisor teeth
in the lower jaw; all the teeth were small. This man had a daughter, who
was born with hair within her ears; and the hair soon extended over her
body. When Captain Yule[822] visited the Court, he found this girl grown
up; and she presented a strange appearance with even her nose densely
covered with soft hair. Like her father, she was furnished with incisor
teeth alone. The King had with difficulty bribed a man to marry her, and of
her two children, one, a boy fourteen months old, had hair growing out of
his ears, with a beard and moustache. This strange peculiarity had,
therefore, been inherited for three generations, with the molar teeth
deficient in the grandfather and mother; whether {328} these teeth would
likewise fail in the infant could not be told. Here is another case
communicated to me by Mr. Wallace on the authority of Dr. Purland, a
dentist: Julia Pastrana, a Spanish dancer, was a remarkably fine woman, but
she had a thick masculine beard and a hairy forehead; she was photographed,
and her stuffed skin was exhibited as a show; but what concerns us is, that
she had in both the upper and lower jaw an irregular double set of teeth,
one row being placed within the other, of which Dr. Purland took a cast.
From the redundancy of the teeth her mouth projected, and her face had a
gorilla-like appearance. These cases and those of the hairless dogs
forcibly call to mind the fact, that the two orders of mammals--namely, the
Edentata and Cetacea--which are the most abnormal in their dermal covering,
are likewise the most abnormal either by deficiency or redundancy of teeth.

The organs of sight and hearing are generally admitted to be homologous,
both with each other and with the various dermal appendages; hence these
parts are liable to be abnormally affected in conjunction. Mr. White Cowper
says "that in all cases of double microphthalmia brought under his notice
he has at the same time met with defective development of the dental
system." Certain forms of blindness seem to be associated with the colour
of the hair; a man with black hair and a woman with light-coloured hair,
both of sound constitution, married and had nine children, all of whom were
born blind; of these children, five "with dark hair and brown iris were
afflicted with amaurosis; the four others, with light-coloured hair and
blue iris, had amaurosis and cataract conjoined." Several cases could be
given, showing that some relation exists between various affections of the
eyes and ears; thus Liebreich states that out of 241 deaf-mutes in Berlin,
no less than fourteen suffered from the rare disease called pigmentary
retinitis. Mr. White Cowper and Dr. Earle have remarked that inability to
distinguish different colours, or colour-blindness, "is often associated
with a corresponding inability to distinguish musical sounds."[823]

{329}

Here is a more curious case: white cats, if they have blue eyes, are almost
always deaf. I formerly thought that the rule was invariable, but I have
heard of a few authentic exceptions. The first two notices were published
in 1829, and relate to English and Persian cats: of the latter, the Rev.
W. T. Bree possessed a female, and he states "that of the offspring
produced at one and the same birth, such as, like the mother, were entirely
white (with blue eyes) were, like her, invariably deaf; while those that
had the least speck of colour on their fur, as invariably possessed the
usual faculty of hearing."[824] The Rev. W. Darwin Fox informs me that he
has seen more than a dozen instances of this correlation in English,
Persian, and Danish cats; but he adds "that, if one eye, as I have several
times observed, be not blue, the cat hears. On the other hand, I have never
seen a white cat with eyes of the common colour that was deaf." In France
Dr. Sichel[825] has observed during twenty years similar facts; he adds the
remarkable case of the iris beginning, at the end of four months, to grow
dark-coloured, and then the cat first began to hear.

This case of correlation in cats has struck many persons as marvellous.
There is nothing unusual in the relation between blue eyes and white fur;
and we have already seen that the organs of sight and hearing are often
simultaneously affected. In the present instance the cause probably lies in
a slight arrest of development in the nervous system in connection with the
sense-organs. Kittens during the first nine days, whilst their eyes are
closed, appear to be completely deaf; I have made a great clanging noise
with a poker and shovel close to their heads, both when they were asleep
and awake, without producing any effect. The trial must not be made by
shouting close to their ears, for they are, even when asleep, extremely
sensitive to a breath of air. Now, as long as the eyes continue closed, the
iris is no doubt blue, for in all the kittens which I have seen this colour
remains for some time after the eyelids open. Hence, if we suppose the
development of the organs of sight and hearing to be arrested at the stage
of the closed eyelids, the eyes would {330} remain permanently blue and the
ears would be incapable of perceiving sound; and we should thus understand
this curious case. As, however, the colour of the fur is determined long
before birth, and as the blueness of the eyes and the whiteness of the fur
are obviously connected, we must believe that some primary cause acts at an
early period.

The instances of correlated variability hitherto given have been chiefly
drawn from the animal kingdom, and we will now turn to plants. Leaves,
sepals, petals, stamens, and pistils are all homologous. In double flowers
we see that the stamens and pistils vary in the same manner, and assume the
form and colour of the petals. In the double columbine (_Aquilegia
vulgaris_), the successive whorls of stamens are converted into
cornucopias, which are enclosed within each other and resemble the petals.
In hose-and-hose flowers the sepals mock the petals. In some cases the
flowers and leaves vary together in tint: in all the varieties of the
common pea, which have purple flowers, a purple mark may be seen on the
stipules. In other cases the leaves and fruit and seeds vary together in
colour, as in a curious pale-leaved variety of the sycamore, which has
recently been described in France,[826] and as in the purple-leaved hazel,
in which the leaves, the husk of the nut, and the pellicle round the kernel
are all coloured purple.[827] Pomologists can predict to a certain extent,
from the size and appearance of the leaves of their seedlings, the probable
nature of the fruit; for, as Van Mons remarks,[828] variations in the
leaves are generally accompanied by some modification in the flower, and
consequently in the fruit. In the Serpent melon, which has a narrow
tortuous fruit above a yard in length, the stem of the plant, the peduncle
of the female flower, and the middle lobe of the leaf, are all elongated in
a remarkable manner. On the other hand, several varieties of Cucurbita,
which have dwarfed stems, all produce, as Naudin remarks with surprise,
leaves of the same peculiar shape. Mr. G. Maw informs me that all the
varieties of the scarlet Pelargoniums which have contracted or imperfect
leaves have contracted flowers: the difference between {331} "Brilliant"
and its parent "Tom Thumb" is a good instance of this. It may be suspected
that the curious case described by Risso,[829] of a variety of the Orange
which produces on the young shoots rounded leaves with winged petioles, and
afterwards elongated leaves on long but wingless petioles, is connected
with the remarkable change in form and nature which the fruit undergoes
during its development.

In the following instance we have the colour and form of the petals
apparently correlated, and both dependent on the nature of the season. An
observer, skilled in the subject, writes,[830] "I noticed, during the year
1842, that every Dahlia, of which the colour had any tendency to scarlet,
was deeply notched--indeed to so great an extent as to give the petals the
appearance of a saw; the indentures were, in some instances, more than a
quarter of an inch deep." Again, Dahlias which have their petals tipped
with a different colour from the rest are very inconstant, and during
certain years some, or even all the flowers, become uniformly coloured; and
it has been observed with several varieties,[831] that when this happens
the petals grow much elongated and lose their proper shape. This, however,
may be due to reversion, both in colour and form, to the aboriginal
species.

       *       *       *       *       *

In this discussion on correlation, we have hitherto treated of cases in
which we can partly understand the bond of connexion; but I will now give
cases in which we cannot even conjecture, or can only very obscurely see,
what is the nature of the bond. Isidore Geoffroy St. Hilaire, in his work
on Monstrosities, insists,[832] "que certaines anomalies coexistent
rarement entr'elles, d'autres fréquemment, d'autres enfin presque
constamment, malgré la différence très-grande de leur nature, et
quoiqu'elles puissent paraître _complètement indépendantes_ les unes des
autres." We see something analogous in certain diseases: thus I hear from
Mr. Paget that in a rare affection of the {332} renal capsules (of which
the functions are unknown), the skin becomes bronzed; and in hereditary
syphilis, both the milk and the second teeth assume a peculiar and
characteristic form. Professor Rolleston, also, informs me that the incisor
teeth are sometimes furnished with a vascular rim in correlation with
intra-pulmonary deposition of tubercles. In other cases of phthisis and of
cyanosis the nails and finger-ends become clubbed like acorns. I believe
that no explanation has been offered of these and of many other cases of
correlated disease.

What can be more curious and less intelligible than the fact previously
given, on the authority of Mr. Tegetmeier, that young pigeons of all
breeds, which when mature have white, yellow, silver-blue, or dun-coloured
plumage, come out of the egg almost naked; whereas pigeons of other colours
when first born are clothed with plenty of down? White Pea-fowls, as has
been observed both in England and France,[833] and as I have myself seen,
are inferior in size to the common coloured kind; and this cannot be
accounted for by the belief that albinism is always accompanied by
constitutional weakness; for white or albino moles are generally larger
than the common kind.

To turn to more important characters: the niata cattle of the Pampas are
remarkable from their short foreheads, upturned muzzles, and curved lower
jaws. In the skull the nasal and premaxillary bones are much shortened, the
maxillaries are excluded from any junction with the nasals, and all the
bones are slightly modified, even to the plane of the occiput. From the
analogical case of the dog, hereafter to be given, it is probable that the
shortening of the nasal and adjoining bones is the proximate cause of the
other modifications in the skull, including the upward curvature of the
lower jaw, though we cannot follow out the steps by which these changes
have been effected.

Polish fowls have a large tuft of feathers on their heads; and their skulls
are perforated by numerous holes, so that a pin can be driven into the
brain without touching any bone. That this deficiency of bone is in some
way connected with the tuft of feathers is clear from tufted ducks and
geese likewise having {333} perforated skulls. The case would probably be
considered by some authors as one of balancement or compensation. In the
chapter on Fowls, I have shown that with Polish fowls the tuft of feathers
was probably at first small; by continued selection it became larger, and
then rested on a fleshy or fibrous mass; and finally, as it became still
larger, the skull itself became more and more protuberant until it acquired
its present extraordinary structure. Through correlation with the
protuberance of the skull, the shape and even the relative connexion of the
premaxillary and nasal bones, the shape of the orifice of the nostrils, the
breadth of the frontal bone, the shape of the post-lateral processes of the
frontal and squamosal bones, and the direction of the bony cavity of the
ear, have all been modified. The internal configuration of the skull and
the whole shape of the brain have likewise been altered in a truly
marvellous manner.

After this case of the Polish fowl it would be superfluous to do more than
refer to the details previously given on the manner in which the changed
form of the comb, in various breeds of the fowl, has affected the skull,
causing by correlation crests, protuberances, and depressions on its
surface.

With our cattle and sheep the horns stand in close connexion with the size
of the skull, and with the shape of the frontal bones; thus Cline[834]
found that the skull of a horned ram weighed five times as much as that of
a hornless ram of the same age. When cattle become hornless, the frontal
bones are "materially diminished in breadth towards the poll;" and the
cavities between the bony plates "are not so deep, nor do they extend
beyond the frontals."[835]

       *       *       *       *       *

It may be well here to pause and observe how the effects of correlated
variability, of the increased use of parts, and of the accumulation through
natural selection of so-called spontaneous variations, are in many cases
inextricably commingled. We may borrow an illustration from Mr. Herbert
Spencer, who remarks that, when the Irish elk acquired its gigantic horns,
weighing above one hundred pounds, numerous co-ordinated {334} changes of
structure would have been indispensable,--namely, a thickened skull to
carry the horns; strengthened cervical vertebræ, with strengthened
ligaments; enlarged dorsal vertebræ to support the neck, with powerful
fore-legs and feet; all these parts being supplied with proper muscles,
blood-vessels, and nerves. How then could these admirably co-ordinated
modifications of structure have been acquired? According to the doctrine
which I maintain, the horns of the male elk were slowly gained through
sexual selection,--that is, by the best-armed males conquering the
worse-armed, and leaving a greater number of descendants. But it is not at
all necessary that the several parts of the body should have simultaneously
varied. Each stag presents individual differences, and in the same district
those which had slightly heavier horns, or stronger necks, or stronger
bodies, or were the most courageous, would secure the greater number of
does, and consequently leave a greater number of offspring. The offspring
would inherit, in a greater or less degree, these same qualities, would
occasionally intercross with each other, or with other individuals varying
in some favourable manner; and of their offspring, those which were the
best endowed in any respect would continue multiplying; and so onwards,
always progressing, sometimes in one direction, and sometimes in another,
towards the present excellently co-ordinated structure of the male elk. To
make this clear, let us reflect on the probable steps, as shown in the
twentieth chapter, by which our race and dray-horses have arrived at their
present state of excellence; if we could view the whole series of
intermediate forms between one of these animals and an early unimproved
progenitor, we should behold a vast number of animals, not equally improved
in each generation throughout their entire structure, but sometimes a
little more in one point, and sometimes in another, yet on the whole
gradually approaching in character to our present race or dray-horses,
which are so admirably fitted in the one case for fleetness and in the
other for draught.

Although natural selection would thus[836] tend to give to the {335} male
elk its present structure, yet it is probable that the inherited influence
of use has played an equal or more important part. As the horns gradually
increased in weight, the muscles of the neck, with the bones to which they
are attached, would increase in size and strength; and these parts would
react on the body and legs. Nor must we overlook the fact that certain
parts of the skull and the extremities would, judging by analogy, tend from
the first to vary in a correlated manner. The increased weight of the horns
would also act directly on the skull, in the same manner as, when one bone
is removed in the leg of a dog, the other bone, which has to carry the
whole weight of the body, increases in thickness. But from the facts given
with respect to horned and hornless cattle, it is probable that the horns
and skull would immediately act on each other through the principle of
correlation. Lastly, the growth and subsequent wear and tear of the
augmented muscles and bones would require an increased supply of blood, and
consequently an increased supply of food; and this again would require
increased powers of mastication, digestion, respiration, and excretion.

_Colour as Correlated with Constitutional Peculiarities._

It is an old belief that with man there is a connexion between complexion
and constitution; and I find that some of the best authorities believe in
this to the present day.[837] Thus Dr. Beddoe by his tables shows[838] that
a relation exists between liability to consumption and the colour of the
hair, eyes, and skin. It has been affirmed[839] that, in the French army
which invaded Russia, soldiers having a dark complexion, from the {336}
southern parts of Europe, withstood the intense cold better than those with
lighter complexions from the north; but no doubt such statements are liable
to error.

In the second chapter on Selection I have given several cases proving that
with animals and plants differences in colour are correlated with
constitutional differences, as shown by greater or less immunity from
certain diseases, from the attacks of parasitic plants and animals, from
burning by the sun, and from the action of certain poisons. When all the
individuals of any one variety possess an immunity of this nature, we
cannot feel sure that it stands in any sort of correlation with their
colour; but when several varieties of the same species, which are similarly
coloured, are thus characterised, whilst other coloured varieties are not
thus favoured, we must believe in the existence of a correlation of this
kind. Thus in the United States purple-fruited plums of many kinds are far
more affected by a certain disease than green or yellow-fruited varieties.
On the other hand, yellow-fleshed peaches of various kinds suffer from
another disease much more than the white-fleshed varieties. In the
Mauritius red sugar-canes are much less affected by a particular disease
than the white canes. White onions and verbenas are the most liable to
mildew; and in Spain the green-fruited grapes suffered from the
vine-disease more than other coloured varieties. Dark-coloured pelargoniums
and verbenas are more scorched by the sun than varieties of other colours.
Red wheats are believed to be hardier than white; whilst red-flowered
hyacinths were more injured during one particular winter in Holland than
other coloured varieties. With animals, white terriers suffer most from the
distemper, white chickens from a parasitic worm in their tracheæ, white
pigs from scorching by the sun, and white cattle from flies; but the
caterpillars of the silk-moth which yield white cocoons suffered in France
less from the deadly parasitic fungus than those producing yellow silk.

The cases of immunity from the action of certain vegetable poisons, in
connexion with colour, are more interesting, and are at present wholly
inexplicable. I have already given a remarkable instance, on the authority
of Professor Wyman, of all the hogs, excepting those of a black colour,
suffering severely in Virginia from eating the root of the _Lachnanthes
tinctoria_. {337} According to Spinola and others,[840] buckwheat
(_Polygonum fagopyrum_), when in flower, is highly injurious to white or
white-spotted pigs, if they are exposed to the heat of the sun, but is
quite innocuous to black pigs. By two accounts, the _Hypericum crispum_ in
Sicily is poisonous to white sheep alone; their heads swell, their wool
falls off, and they often die; but this plant, according to Lecce, is
poisonous only when it grows in swamps; nor is this improbable, as we know
how readily the poisonous principle in plants is influenced by the
conditions under which they grow.

Three accounts have been published in Eastern Prussia, of white and
white-spotted horses being greatly injured by eating mildewed and
honeydewed vetches; every spot of skin bearing white hairs becoming
inflamed and gangrenous. The Rev. J. Rodwell informs me that his father
turned out about fifteen cart-horses into a field of tares which in parts
swarmed with black aphides, and which no doubt were honeydewed, and
probably mildewed; the horses, with two exceptions, were chesnuts and bays
with white marks on their faces and pasterns, and the white parts alone
swelled and became angry scabs. The two bay horses with no white marks
entirely escaped all injury. In Guernsey, when horses eat fools' parsley
(_Æthusa cynapium_) they are sometimes violently purged; and this plant
"has a peculiar effect on the nose and lips, causing deep cracks and
ulcers, particularly on horses with white muzzles."[841] With cattle,
independently of the action of any poison, cases have been published by
Youatt and Erdt of cutaneous diseases with much constitutional disturbance
(in one instance after exposure to a hot sun) affecting every single point
which bore a white hair, but completely passing over other parts of the
body. Similar cases have been observed with horses.[842]

We thus see that not only do those parts of the skin which bear white hair
differ in a remarkable manner from those bearing {338} hair of any other
colour, but that in addition some great, constitutional difference must
stand in correlation with the colour of the hair; for in the
above-mentioned cases, vegetable poisons caused fever, swelling of the
head, as well as other symptoms, and even death, to all the white or
white-spotted animals.

       *       *       *       *       *


{339}

CHAPTER XXVI.

LAWS OF VARIATION, _continued_--SUMMARY.

    ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OF
    MULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICAL
    PRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THE
    PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS OR
    PARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS.

_On the Affinity of Homologous Parts._--This law was first generalised by
Geoffroy Saint Hilaire, under the expression of _La loi de l'affinité de
soi pour soi_. It has been fully discussed and illustrated by his son,
Isidore Geoffroy, with respect to monsters in the animal kingdom,[843] and
by Moquin-Tandon, with respect to monstrous plants. When similar or
homologous parts, whether belonging to the same embryo or to two distinct
embryos, are brought during an early stage of development into contact,
they often blend into a single part or organ; and this complete fusion
indicates some mutual affinity between the parts, otherwise they would
simply cohere. Whether any power exists which tends to bring homologous
parts into contact seems more doubtful. The tendency to complete fusion is
not a rare or exceptional fact. It is exhibited in the most striking manner
by double monsters. Nothing can be more extraordinary than the manner, as
shown in various published plates, in which the corresponding parts of two
embryos become intimately fused together. This is perhaps best seen in
monsters with two heads, which are united, summit to summit, or face to
face, or, Janus-like, back to back, or obliquely side to side. In one
instance of two heads united almost face to face, but a little obliquely,
four ears were developed, and on one side a perfect face, which was
manifestly formed by the union of two {340} half-faces. Whenever two bodies
or two heads are united, each bone, muscle, vessel, and nerve on the line
of junction seems to seek out its fellow, and becomes completely fused with
it. Lereboullet,[844] who carefully studied the development of double
monsters in fishes, observed in fifteen instances the steps by which two
heads gradually became fused into one. In this and other such cases, no
one, I presume, supposes that the two already formed heads actually blend
together, but that the corresponding parts of each head grow into one
during the further progress of development, accompanied as it always is
with incessant absorption and renovation. Double monsters were formerly
thought to be formed by the union of two originally distinct embryos
developed upon distinct vitelli; but now it is admitted that "their
production is due to the spontaneous divarication of the embryonic mass
into two halves;"[845] this, however, is effected by different methods. But
the belief that double monsters originate from the division of one germ,
does not necessarily affect the question of subsequent fusion, or render
less true the law of the affinity of homologous parts.

The cautious and sagacious J. Müller,[846] when speaking of Janus-like
monsters, says, that "without the supposition that some kind of affinity or
attraction is exerted between corresponding parts, unions of this kind are
inexplicable." On the other hand, Vrolik, and he is followed by others,
disputes this conclusion, and argues from the existence of a whole series
of monstrosities, graduating from a perfectly double monster to a mere
rudiment of an additional digit, that "an excess of formative power" is the
cause and origin of every monstrous duplicity. That there are two distinct
classes of cases, and that parts may be doubled independently of the
existence of two embryos, is certain; for a single embryo, or even a single
adult animal, may produce doubled organs. Thus Valentin, as quoted by
Vrolik, injured the caudal extremity of an embryo, and three days
afterwards it produced rudiments of a double pelvis and of double hind
limbs. {341} Hunter and others have observed lizards with their tails
reproduced and doubled. When Bonnet divided longitudinally the foot of the
salamander, several additional digits were occasionally formed. But neither
these cases, nor the perfect series from a double monster to an additional
digit, seem to me opposed to the belief that corresponding parts have a
mutual affinity, and consequently tend to fuse together. A part may be
doubled and remain in this state, or the two parts thus formed may
afterwards through the law of affinity become blended; or two homologous
parts in two separate embryos may, through the same principle, unite and
form a single part.

The law of the affinity and fusion of similar parts applies to the
homologous organs of the same individual animal, as well as to double
monsters. Isidore Geoffroy gives a number of instances of two or more
digits, of two whole legs, of two kidneys, and of several teeth becoming
symmetrically fused together in a more or less perfect manner. Even the two
eyes have been known to unite into a single eye, forming a cyclopean
monster, as have the two ears, though naturally standing so far apart. As
Geoffroy remarks, these facts illustrate in an admirable manner the normal
fusion of various organs which during an early embryonic period are double,
but which afterwards always unite into a single median organ. Organs of
this nature are generally found in a permanently double condition in other
members of the same class. These cases of normal fusion appear to me to
afford the strongest support in favour of the present law. Adjoining parts
which are not homologous sometimes cohere; but this cohesion appears to
result from mere juxtaposition, and not from mutual affinity.

In the vegetable kingdom Moquin-Tandon[847] gives a long list of cases,
showing how frequently homologous parts, such as leaves, petals, stamens,
and pistils, as well as aggregates of homologous parts, such as buds,
flowers, and fruit, become blended into each other with perfect symmetry.
It is interesting to examine a compound flower of this nature, formed of
exactly double the proper number of sepals, petals, stamens, and pistils,
with each whorl of organs circular, and with no trace left of the {342}
process of fusion. The tendency in homologous parts to unite during their
early development, Moquin-Tandon considers as one of the most striking laws
governing the production of monsters. It apparently explains a multitude of
cases, both in the animal and vegetable kingdoms; it throws a clear light
on many normal structures which have evidently been formed by the union of
originally distinct parts, and it possesses, as we shall see in a future
chapter, much theoretical interest.

       *       *       *       *       *

_On the Variability of Multiple and Homologous Parts._--Isidore
Geoffroy[848] insists that, when any part or organ is repeated many times
in the same animal, it is particularly liable to vary both in number and
structure. With respect to number, the proposition may, I think, be
considered as fully established; but the evidence is chiefly derived from
organic beings living under their natural conditions, with which we are not
here concerned. When the vertebræ, or teeth, or rays in the fins of fishes,
or feathers in the tails of birds, or petals, stamens, pistils, and seeds
in plants, are very numerous, the number is generally variable. The
explanation of this simple fact is by no means obvious. With respect to the
variability in structure of multiple parts, the evidence is not so
decisive; but the fact, as far as it may be trusted, probably depends on
multiple parts being of less physiological importance than single parts;
consequently their perfect standard of structure has been less rigorously
enforced by natural selection.

       *       *       *       *       *

_Compensation of Growth, or Balancement._--This law, as applied to natural
species, was propounded by Goethe and Geoffroy St. Hilaire at nearly the
same time. It implies that, when much organised matter is used in building
up some one part, other parts are starved and become reduced. Several
authors, especially botanists, believe in this law; others reject it. As
far as I can judge, it occasionally holds good; but its importance has
probably been exaggerated. It is scarcely possible to distinguish between
the supposed effects of such compensation of growth, and the effects of
long-continued selection, which {343} may at the same time lead to the
augmentation of one part and the diminution of another. There can be no
doubt that an organ may be greatly increased without any corresponding
diminution in the adjoining parts. To recur to our former illustration of
the Irish elk, it may be asked what part has suffered in consequence of the
immense development of the horns?

It has already been observed that the struggle for existence does not bear
hard on our domesticated productions; consequently the principle of economy
of growth will seldom affect them, and we ought not to expect to find
frequent evidence of compensation. We have, however, some such cases.
Moquin-Tandon describes a monstrous bean,[849] in which the stipules were
enormously developed, and the leaflets apparently in consequence completely
aborted; this case is interesting, as it represents the natural condition
of _Lathyrus aphaca_, with its stipules of great size, and its leaves
reduced to mere threads, which act as tendrils. De Candolle[850] has
remarked that the varieties of _Raphanus sativus_ which have small roots
yield numerous seed, valuable from containing oil, whilst those with large
roots are not productive in this latter respect; and so it is with
_Brassica asperifolia_. The varieties of the potato which produce tubers
very early in the season rarely bear flowers; but Andrew Knight,[851] by
checking the growth of the tubers, forced the plants to flower. The
varieties of _Cucurbita pepo_ which produce large fruit yield, according to
Naudin, few in number; whilst those producing small fruit yield a vast
number. Lastly, I have endeavoured to show in the eighteenth chapter that
with many cultivated plants unnatural treatment checks the full and proper
action of the reproductive organs, and they are thus rendered more or less
sterile; consequently, in the way of compensation, the fruit becomes
greatly enlarged, and, in double flowers, the petals are greatly increased
in number.

With animals, it has been found difficult to produce cows which should
first yield much milk, and afterwards be capable of {344} fattening well.
With fowls which have large topknots and beards the comb and wattles are
generally much reduced in size. Perhaps the entire absence of the oil-gland
in fantail pigeons may be connected with the great development of their
tails.

       *       *       *       *       *

_Mechanical Pressure as a Cause of Modifications._--In some few cases there
is reason to believe that mere mechanical pressure has affected certain
structures. Every one knows that savages alter the shape of their infants'
skulls by pressure at an early age; but there is no reason to believe that
the result is ever inherited. Nevertheless Vrolik and Weber[852] maintain
that the shape of the human head is influenced by the shape of the mother's
pelvis. The kidneys in different birds differ much in form, and St.
Ange[853] believes that this is determined by the form of the pelvis, which
again, no doubt, stands in close relation with their various habits of
locomotion. In snakes, the viscera are curiously displaced, in comparison
with their position in other vertebrates; and this has been attributed by
some authors to the elongation of their bodies; but here, as in so many
previous cases, it is impossible to disentangle any direct result of this
kind from that consequent on natural selection. Godron has argued[854] that
the normal abortion of the spur on the inner side of the flower in
Corydalis, is caused by the buds being closely pressed at a very early
period of growth, whilst under ground, against each other and against the
stem. Some botanists believe that the singular difference in the shape both
of the seed and corolla, in the interior and exterior florets in certain
compositous and umbelliferous plants, is due to the pressure to which the
inner florets are subjected; but this conclusion is doubtful.

The facts just given do not relate to domesticated productions, and
therefore do not strictly concern us. But here is a more appropriate case:
H. Müller[855] has shown that in {345} short-faced races of the dog some of
the molar teeth are placed in a slightly different position from that which
they occupy in other dogs, especially in those having elongated muzzles;
and as he remarks, any inherited change in the arrangement of the teeth
deserves notice, considering their classificatory importance. This
difference in position is due to the shortening of certain facial bones,
and the consequent want of space; and the shortening results from a
peculiar and abnormal state of the basal cartilages of the bones.

_Relative Position of Flowers with respect to the Axis, and of Seeds in the
Capsule, as inducing Variation._

    In the thirteenth chapter various peloric flowers were described, and
    their production was shown to be due either to arrested development, or
    to reversion to a primordial condition. Moquin-Tandon has remarked that
    the flowers which stand on the summit of the main stem or of a lateral
    branch are more liable to become peloric than those on the sides;[856]
    and he adduces, amongst other instances, that of _Teucrium
    campanulatum_. In another Labiate plant grown by me, viz. the
    _Galeobdolon luteum_, the peloric flowers were always produced on the
    summit of the stem, where flowers are not usually borne. In
    Pelargonium, a _single_ flower in the truss is frequently peloric, and
    when this occurs I have during several years invariably observed it to
    be the central flower. This is of such frequent occurrence that one
    observer[857] gives the names of ten varieties flowering at the same
    time, in every one of which the central flower was peloric.
    Occasionally more than one flower in the truss is peloric, and then of
    course the additional ones must be lateral. These flowers are
    interesting as showing how the whole structure is correlated. In the
    common Pelargonium the upper sepal is produced into a nectary which
    coheres with the flower-peduncle; the two upper petals differ a little
    in shape from the three lower ones, and are marked with dark shades of
    colour; the stamens are graduated in length and upturned. In the
    peloric flowers, the nectary aborts; all the petals become alike both
    in shape and colour; the stamens are generally reduced in number and
    become straight, so that the whole flower resembles that of the allied
    genus Erodium. The correlation between these changes is well shown when
    one of the two upper petals alone loses its dark mark, for in this case
    the nectary does not entirely abort, but is usually much reduced in
    length.[858]

    {346}

    Morren has described[859] a marvellous flask-shaped flower of the
    Calceolaria, nearly four inches in length, which was almost completely
    peloric; it grew on the summit of the plant, with a normal flower on
    each side; Prof. Westwood also has described[860] three similar peloric
    flowers, which all occupied a central position on the flower-branches.
    In the Orchideous genus, Phalænopsis, the terminal flower has been seen
    to become peloric.

    In a Laburnum-tree I observed that about a fourth part of the racemes
    produced terminal flowers which had lost their papilionaceous
    structure. These were produced after almost all the other flowers on
    the same racemes had withered. The most perfectly pelorised examples
    had six petals, each marked with black striæ like those on the
    standard-petal. The keel seemed to resist the change more than the
    other petals. Dutrochet has described[861] an exactly similar case in
    France, and I believe these are the only two instances of pelorism in
    the laburnum which have been recorded. Dutrochet remarks that the
    racemes on this tree do not properly produce a terminal flower, so
    that, as in the case of the Galeobdolon, their position as well as
    their structure are both anomalies, which no doubt are in some manner
    related. Dr. Masters has briefly described another leguminous
    plant,[862] namely, a species of clover, in which the uppermost and
    central flowers were regular or had lost their papilionaceous
    structure. In some of these plants the flower-heads were also
    proliferous.

    Lastly, Linaria produces two kinds of peloric flowers, one having
    simple petals, and the other having them all spurred. The two forms, as
    Naudin remarks,[863] not rarely occur on the same plant, but in this
    case the spurred form almost invariably stands on the summit of the
    spike.

    The tendency in the terminal or central flower to become peloric more
    frequently than other flowers, probably results from "the bud which
    stands on the end of a shoot receiving the most sap; it grows out into
    a stronger shoot than those situated lower down."[864] I have discussed
    the connection between pelorism and a central position, partly because
    some few plants are known normally to produce a terminal flower
    different in structure from the lateral ones; but chiefly on account of
    the following case, in which we see a tendency to variability or to
    reversion connected with the same position. A great judge of
    Auriculas[865] states that when an Auricula throws up a side bloom it
    is pretty sure to keep its character; but that if it grows from the
    centre or heart of the plant, whatever the colour of the edging ought
    to be, "it is just as likely to come in any other class as in the one
    to which it properly belongs." This is so notorious a {347} fact, that
    some florists regularly pinch off the central trusses of flowers.
    Whether in the highly improved varieties the departure of the central
    trusses from their proper type is due to reversion, I do not know. Mr.
    Dombrain insists that, whatever may be the commonest kind of
    imperfection in each variety, this is generally exaggerated in the
    central truss. Thus one variety "sometimes has the fault of producing a
    little green floret in the centre of the flower," and in central blooms
    these become excessive in size. In some central blooms, sent to me by
    Mr. Dombrain, all the organs of the flower were rudimentary in
    structure, of minute size, and of a green colour, so that by a little
    further change all would have been converted into small leaves. In this
    case we clearly see a tendency to prolification--a term which, I may
    explain to those who have never attended to botany, means the
    production of a branch or flower, or head of flowers, out of another
    flower. Now Dr. Masters[866] states that the central or uppermost
    flower on a plant is generally the most liable to prolification. Thus,
    in the varieties of the Auricula, the loss of their proper character
    and a tendency to prolification, and in other plants a tendency to
    prolification and pelorism, are all connected together, and are due
    either to arrested development, or to reversion to a former condition.

    The following is a more interesting case; Metzger[867] cultivated in
    Germany several kinds of maize brought from the hotter parts of
    America, and he found, as has been previously described, that in two or
    three generations the grains became greatly changed in form, size, and
    colour; and with respect to two races he expressly states that in the
    first generation, whilst the lower grains on each head retained their
    proper character, the uppermost grains already began to assume that
    character which in the third generation all the grains acquired. As we
    do not know the aboriginal parent of the maize, we cannot tell whether
    these changes are in any way connected with reversion.

    In the two following cases, reversion, as influenced by the position of
    the seed in the capsule, evidently acts. The Blue Imperial pea is the
    offspring of the Blue Prussian, and has larger seed and broader pods
    than its parent. Now Mr. Masters, of Canterbury, a careful observer and
    a raiser of new varieties of the pea, states[868] that the Blue
    Imperial always has a strong tendency to revert to its parent-stock,
    and the reversion "occurs in this manner: the last (or uppermost) pea
    in the pod is frequently much smaller than the rest; and if these small
    peas are carefully collected and sown separately, very many more, in
    proportion, will revert to their origin, than those taken from the
    other parts of the pod." Again M. Chaté[869] says that in raising
    seedling stocks he succeeds in getting eighty per cent. to bear double
    flowers, by leaving only a few of the secondary branches to seed; but
    in addition to this, "at the time of extracting the seeds, the upper
    portion of the pod is separated and {348} placed aside, because it has
    been ascertained that the plants coming from the seeds situated in this
    portion of the pod, give eighty per cent. of single flowers." Now the
    production of single-flowering plants from the seed of double-flowering
    plants is clearly a case of reversion. These latter facts, as well as
    the connection between a central position and pelorism and
    prolification, show in an interesting manner how small a
    difference--namely a little greater freedom in the flow of sap towards
    one part of the same plant--determines important changes of structure.

       *       *       *       *       *

_Analogous or Parallel Variation._--By this term I wish to express that
similar characters occasionally make their appearance in the several
varieties or races descended from the same species, and more rarely in the
offspring of widely distinct species. We are here concerned, not as
hitherto with the causes of variation, but with the results; but this
discussion could not have been more conveniently introduced elsewhere. The
cases of analogous variation, as far as their origin is concerned, may be
grouped, disregarding minor subdivisions, under two main heads; firstly,
those due to unknown causes having acted on organic beings with nearly the
same constitution, and which consequently vary in an analogous manner; and
secondly, those due to the reappearance of characters which were possessed
by a more or less remote progenitor. But these two main divisions can often
be only conjecturally separated, and graduate, as we shall presently see,
into each other.

    Under the first head of analogous variations, not due to reversion, we
    have the many cases of trees belonging to quite different orders which
    have produced pendulous and fastigate varieties. The beech, hazel, and
    barberry have given rise to purple-leaved varieties; and as Bernhardi
    has remarked,[870] a multitude of plants, as distinct as possible, have
    yielded varieties with deeply-cut or laciniated leaves. Varieties
    descended from three distinct species of Brassica have their stems, or
    so-called roots, enlarged into globular masses. The nectarine is the
    offspring of the peach; and the varieties of both these trees offer a
    remarkable parallelism in the fruit being white, red, or yellow
    fleshed--in being clingstones or freestones--in the flowers being large
    or small--in the leaves being serrated or crenated, furnished with
    globose or reniform glands, or quite destitute of glands. It should be
    remarked that each variety of the nectarine has not derived its
    character from a corresponding variety of the peach. The several
    varieties also of a closely allied genus, namely the apricot, differ
    from each other in nearly the same parallel manner. There is no reason
    {349} to believe that in any of these cases long-lost characters have
    reappeared, and in most of them this certainly has not occurred.

    Three species of Cucurbita have yielded a multitude of races, which
    correspond so closely in character that, as Naudin insists, they may be
    arranged in an almost strictly parallel series. Several varieties of
    the melon are interesting from resembling in important characters other
    species, either of the same genus or of allied genera; thus, one
    variety has fruit so like, both externally and internally, the fruit of
    a perfectly distinct species, namely, the cucumber, as hardly to be
    distinguished from it; another has long cylindrical fruit twisting
    about like a serpent; in another the seeds adhere to portions of the
    pulp; in another the fruit, when ripe, suddenly cracks and falls into
    pieces; and all these highly remarkable peculiarities are
    characteristic of species belonging to allied genera. We can hardly
    account for the appearance of so many unusual characters by reversion
    to a single ancient form; but we must believe that all the members of
    the family have inherited a nearly similar constitution from an early
    progenitor. Our cereal and many other plants offer similar cases.

    With animals we have fewer cases of analogous variation, independently
    of direct reversion. We see something of the kind in the resemblance
    between the short-muzzled races of the dog, such as the pug and
    bulldog; in feather-footed races of the fowl, pigeon, and canary-bird;
    in horses of the most different races presenting the same range of
    colour; in all black-and-tan dogs having tan-coloured eye-spots and
    feet, but in this latter case reversion may possibly have played a
    part. Low has remarked[871] that several breeds of cattle are
    "sheeted,"--that is, have a broad band of white passing round their
    bodies like a sheet; this character is strongly inherited and sometimes
    originates from a cross; it may be the first step in reversion to an
    original or early type, for, as was shown in the third chapter, white
    cattle with dark ears, feet, and tip of tail formerly existed, and now
    exist in a feral or semi-feral condition in several quarters of the
    world.

    Under our second main division, namely, of analogous variations due to
    reversion, the best cases are afforded by animals, and by none better
    than by pigeons. In all the most distinct breeds sub-varieties
    occasionally appear coloured exactly like the parent rock-pigeon, with
    black wing-bars, white loins, banded tail, &c.; and no one can doubt
    that these characters are simply due to reversion. So with minor
    details; turbits properly have white tails, but occasionally a bird is
    born with a dark-coloured and banded tail; pouters properly have white
    primary wing-feathers, but not rarely a "sword-flighted" bird, that is,
    one with the few first primaries dark-coloured, appears; and in these
    cases we have characters proper to the rock-pigeon, but new to the
    breed, evidently appearing from reversion. In some domestic varieties
    the wing-bars, instead of being simply black, as in the rock-pigeon,
    are beautifully edged with different zones of colour, and they then
    present a striking analogy with the wing-bars in certain natural
    species of the same family, such as _Phaps chalcoptera_; and this may
    probably be accounted for by {350} all the forms descended from the
    same remote progenitor having a tendency to vary in the same manner.
    Thus also we can perhaps understand the fact of some Laugher-pigeons
    cooing almost like turtle-doves, and of several races having
    peculiarities in their flight, for certain natural species (viz. _C.
    torquatrix_ and _palumbus_) display singular vagaries in this respect.
    In other cases a race, instead of imitating in character a distinct
    species, resembles some other race; thus certain runts tremble and
    slightly elevate their tails, like fantails; and turbits inflate the
    upper part of their oesophagus, like pouter-pigeons.

    It is a common circumstance to find certain coloured marks persistently
    characterising all the species of a genus, but differing much in tint;
    and the same thing occurs with the varieties of the pigeon: thus,
    instead of the general plumage being blue with the wing-bars black,
    there are snow-white varieties with red bars, and black varieties with
    white bars; in other varieties the wing-bars, as we have seen, are
    elegantly zoned with different tints. The Spot pigeon is characterised
    by the whole plumage being white, excepting the tail and a spot on the
    forehead; but these parts may be red, yellow, or black. In the
    rock-pigeon and in many varieties the tail is blue, with the outer
    edges of the outer feathers white; but in one sub-variety of the
    monk-pigeon we have a reversed variation, for the tail is white, except
    the outer edges of the outer feathers, which are black.[872]

    With some species of birds, for instance with gulls, certain coloured
    parts appear as if almost washed out, and I have observed exactly the
    same appearance in the terminal dark tail-bar in certain pigeons, and
    in the whole plumage of certain varieties of the duck. Analogous facts
    in the vegetable kingdom could be given.

    Many sub-varieties of the pigeon have reversed and somewhat lengthened
    feathers on the back part of their heads, and this is certainly not due
    to reversion to the parent-species, which shows no trace of such
    structure; but when we remember that sub-varieties of the fowl, turkey,
    canary-bird, duck, and goose, all have topknots or reversed feathers on
    their heads; and when we remember that scarcely a single large natural
    group of birds can be named, in which some members have not a tuft of
    feathers on their heads, we may suspect that reversion to some
    extremely remote form has come into action.

    Several breeds of the fowl have either spangled or pencilled feathers;
    and these cannot be derived from the parent-species, the _Gallus
    bankiva_; though of course it is possible that an early progenitor of
    this species may have been spangled, and a still earlier or a later
    progenitor may have been pencilled. But as many gallinaceous birds are
    spangled or pencilled, it is a more probable view that the several
    domestic breeds of the fowl have acquired this kind of plumage from all
    the members of the family inheriting a tendency to vary in a like
    manner. The same principle may account for the ewes in certain breeds
    of sheep being hornless, like the females of some other hollow-horned
    ruminants; it may account for certain domestic cats having
    slightly-tufted ears, like those of the lynx; and for the skulls of
    domestic rabbits often differing from each {351} other in the same
    characters by which the skulls of the various species of the genus
    Lepus differ.

    I will only allude to one other case, already discussed. Now that we
    know that the wild parent of the ass has striped legs, we may feel
    confident that the occasional appearance of stripes on the legs of the
    domestic ass is due to direct reversion; but this will not account for
    the lower end of the shoulder-stripe being sometimes angularly bent or
    slightly forked. So, again, when we see dun and other coloured horses
    with stripes on the spine, shoulders, and legs, we are led, from
    reasons formerly given, to believe that they reappear from direct
    reversion to the wild parent-horse. But when horses have two or three
    shoulder-stripes with one of them occasionally forked at the lower end,
    or when they have stripes on their faces, or as foals are faintly
    striped over nearly their whole bodies, with the stripes angularly bent
    one under the other on the forehead, or irregularly branched in other
    parts, it would be rash to attribute such diversified characters to the
    reappearance of those proper to the aboriginal wild horse. As three
    African species of the genus are much striped, and as we have seen that
    the crossing of the unstriped species often leads to the hybrid
    offspring being conspicuously striped--bearing also in mind that the
    act of crossing certainly causes the reappearance of long-lost
    characters--it is a more probable view that the above-specified stripes
    are due to reversion, not to the immediate wild parent-horse, but to
    the striped progenitor of the whole genus.

I have discussed this subject of analogous variation at considerable
length, because, in a future work on natural species, it will be shown that
the varieties of one species frequently mock distinct species--a fact in
perfect harmony with the foregoing cases, and explicable only on the theory
of descent. Secondly, because these facts are important from showing, as
remarked in a former chapter, that each trifling variation is governed by
law, and is determined in a much higher degree by the nature of the
organisation, than by the nature of the conditions to which the varying
being has been exposed. Thirdly, because these facts are to a certain
extent related to a more general law, namely, that which Mr. B. D.
Walsh[873] has called the "Law of _Equable Variability_," or, as he
explains it, "if any given character is very variable in one species of a
group, it will tend to be variable in allied species; and if any given
character is perfectly constant in one species of a group, it will tend to
be constant in allied species."

This leads me to recall a discussion in the chapter on Selection, in which
it was shown that with domestic races, which are {352} now undergoing rapid
improvement, those parts or characters which are the most valued vary the
most. This naturally follows from recently selected characters continually
tending to revert to their former less improved standard, and from their
being still acted on by the same agencies, whatever these may be, which
first caused the characters in question to vary. The same principle is
applicable to natural species, for, as stated in my 'Origin of Species,'
generic characters are less variable than specific characters; and the
latter are those which have been modified by variation and natural
selection, since the period when all the species belonging to the same
genus branched off from a common progenitor, whilst generic characters are
those which have remained unaltered from a much more remote epoch, and
accordingly are now less variable. This statement makes a near approach to
Mr. Walsh's law of Equable Variability. Secondary sexual characters, it may
be added, rarely serve to characterise distinct genera, for they usually
differ much in the species of the same genus, and are highly variable in
the individuals of the same species; we have also seen in the earlier
chapters of this work how variable secondary sexual characters become under
domestication.

_Summary of the three previous Chapters, on the Laws of Variation._

In the twenty-third chapter we have seen that changed conditions
occasionally act in a definite manner on the organisation, so that all, or
nearly all, the individuals thus exposed become modified in the same
manner. But a far more frequent result of changed conditions, whether
acting directly on the organisation or indirectly through the reproductive
system being affected is indefinite and fluctuating variability. In the
three latter chapters we have endeavoured to trace some of the laws by
which such variability is regulated.

Increased use adds the size of a muscle, together with the blood-vessels,
nerves, ligaments, the crests of bone to which these are attached, the
whole bone and other connected bones. So it is with various glands.
Increased functional activity strengthens the sense-organs. Increased and
intermittent pressure thickens the epidermis; and a change in the nature of
the food sometimes modifies the coats of the stomach, and increases or
{353} decreases the length of the intestines. Continued disuse, on the
other hand, weakens and diminishes all parts of the organisation. Animals
which during many generations have taken but little exercise, have their
lungs reduced in size, and as a consequence the bony fabric of the chest,
and the whole form of the body, become modified. With our anciently
domesticated birds, the wings have been little used, and they are slightly
reduced; with their decrease, the crest of the sternum, the scapulæ,
coracoids, and furcula, have all been reduced.

With domesticated animals, the reduction of a part from disuse is never
carried so far that a mere rudiment is left, but we have good reason to
believe that this has often occurred under nature. The cause of this
difference probably is that with domestic animals not only sufficient time
has not been granted for so profound a change, but that, from not being
exposed to a severe struggle for life, the principle of the economy of
organisation does not come into action. On the contrary, we sometimes see
that structures which are rudimentary in the parent-species become
partially redeveloped in their domesticated progeny. When rudiments are
formed or left under domestication, they are the result of a sudden arrest
of development, and not of long-continued disuse with the absorption of all
superfluous parts; nevertheless they are of interest, as showing that
rudiments are the relics of organs once perfectly developed.

Corporeal, periodical, and mental habits, though the latter have been
almost passed over in this work, become changed under domestication, and
the changes are often inherited. Such changed habits in any organic being,
especially when living a free life, would often lead to the augmented or
diminished use of various organs, and consequently to their modification.
From long-continued habit, and more especially from the occasional birth of
individuals with a slightly different constitution, domestic animals and
cultivated plants become to a certain extent acclimatised, or adapted to a
climate different from that proper to the parent-species.

Through the principle of correlated variability, when one part varies other
parts vary,--either simultaneously, or one after the other. Thus an organ
modified during an early embryonic period affects other parts subsequently
developed. When an {354} organ, such as the beak, increases or decreases in
length, adjoining or correlated parts, as the tongue and the orifice of the
nostrils, tend to vary in the same manner. When the whole body increases or
decreases in size, various parts become modified; thus with pigeons the
ribs increase or decrease in number and breadth. Homologous parts, which
are identical during their early development and are exposed to similar
conditions, tend to vary in the same or in some connected manner,--as in
the case of the right and left sides of the body, of the front and hind
limbs, and even of the head and limbs. So it is with the organs of sight
and hearing; for instance, white cats with blue eyes are almost always
deaf. There is a manifest relation throughout the body between the skin and
its various appendages of hair, feathers, hoofs, horns, and teeth. In
Paraguay, horses with curly hair have hoofs like those of a mule; the wool
and the horns of sheep vary together; hairless dogs are deficient in their
teeth; men with redundant hair have abnormal teeth, either deficient or in
excess. Birds with long wing-feathers usually have long tail-feathers. When
long feathers grow from the outside of the legs and toes of pigeons, the
two outer toes are connected by membrane; for the whole leg tends to assume
the structure of the wing. There is a manifest relation between a crest of
feathers on the head and a marvellous amount of change in the skull of
various fowls; and in a lesser degree, between the greatly elongated,
lopping ears of rabbits and the structure of their skulls. With plants, the
leaves, various parts of the flower, and the fruit, often vary together in
a correlated manner.

In some cases we find correlation without being able even to conjecture
what is the nature of the connexion, as with various correlated
monstrosities and diseases. This is likewise the case with the colour of
the adult pigeon, in connexion with the presence of down on the young bird.
Numerous curious instances have been given of peculiarities of
constitution, in correlation with colour, as shown by the immunity of
individuals of some one colour from certain diseases, from the attacks of
parasites, and from the action of certain vegetable poisons.

Correlation is an important subject; for with species, and in a lesser
degree with domestic races, we continually find that {355} certain parts
have been greatly modified to serve some useful purpose; but we almost
invariably find that other parts have likewise been more or less modified,
without our being able to discover any advantage in the change. No doubt
great caution is necessary in coming to this conclusion, for it is
difficult to overrate our ignorance on the use of various parts of the
organisation; but from what we have now seen, we may believe that many
modifications are of no direct service, having arisen in correlation with
other and useful changes.

Homologous parts during their early development evince an affinity for each
other,--that is, they tend to cohere and fuse together much more readily
than other parts. This tendency to fusion explains a multitude of normal
structures. Multiple and homologous organs are especially liable to vary in
number and probably in form. As the supply of organised matter is not
unlimited, the principle of compensation sometimes comes into action; so
that, when one part is greatly developed, adjoining parts or functions are
apt to be reduced; but this principle is probably of much less importance
than the more general one of the economy of growth. Through mere mechanical
pressure hard parts occasionally affect soft adjoining parts. With plants
the position of the flowers on the axis, and of the seeds in the capsule,
sometimes leads, through a freer flow of sap, to changes of structure; but
these changes are often due to reversion. Modifications, in whatever manner
caused, will be to a certain extent regulated by that co-ordinating power
or _nisus formativus_, which is in fact a remnant of one of the forms of
reproduction, displayed by many lowly organised beings in their power of
fissiparous generation and budding. Finally, the effects of the laws, which
directly or indirectly govern variability, may be largely influenced by
man's selection, and will so far be determined by natural selection that
changes advantageous to any race will be favoured and disadvantageous
changes checked.

Domestic races descended from the same species, or from two or more allied
species, are liable to revert to characters derived from their common
progenitor, and, as they have much in common in their constitutions, they
are also liable under changed conditions to vary in the same manner; from
these {356} two causes analogous varieties often arise. When we reflect on
the several foregoing laws, imperfectly as we understand them, and when we
bear in mind how much remains to be discovered, we need not be surprised at
the extremely intricate manner in which our domestic productions have
varied, and still go on varying.

       *       *       *       *       *


{357}

CHAPTER XXVII.

PROVISIONAL HYPOTHESIS OF PANGENESIS.

    PRELIMINARY REMARKS.--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A
    SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE
    DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE
    FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE
    BODY--VARIABILITY--INHERITANCE--REVERSION.

    SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY
    ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE
    SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.

In the previous chapters large classes of facts, such as those bearing on
bud-variation, the various forms of inheritance, the causes and laws of
variation, have been discussed; and it is obvious that these subjects, as
well as the several modes of reproduction, stand in some sort of relation
to each other. I have been led, or rather forced, to form a view which to a
certain extent connects these facts by a tangible method. Every one would
wish to explain to himself, even in an imperfect manner, how it is possible
for a character possessed by some remote ancestor suddenly to reappear in
the offspring; how the effects of increased or decreased use of a limb can
be transmitted to the child; how the male sexual element can act not solely
on the ovule, but occasionally on the mother-form; how a limb can be
reproduced on the exact line of amputation, with neither too much nor too
little added; how the various modes of reproduction are connected, and so
forth. I am aware that my view is merely a provisional hypothesis or
speculation; but until a better one be advanced, it may be serviceable by
bringing together a multitude of facts which are at present left
disconnected by any efficient cause. As Whewell, the historian of the
inductive sciences, remarks:--"Hypotheses may often be of service to
science, when they involve a certain portion of incompleteness, and even of
error." Under this point of view I venture to advance the hypothesis of
Pangenesis, which {358} implies that the whole organisation, in the sense
of every separate atom or unit, reproduces itself. Hence ovules and
pollen-grains,--the fertilised seed or egg, as well as buds,--include and
consist of a multitude of germs thrown off from each separate atom of the
organism.

In the First Part I will enumerate as briefly as I can the groups of facts
which seem to demand connection; but certain subjects, not hitherto
discussed, must be treated at disproportionate length. In the Second Part
the hypothesis will be given; and we shall see, after considering how far
the necessary assumptions are in themselves improbable, whether it serves
to bring under a single point of view the various facts.

PART I.

Reproduction may be divided into two main classes, namely, sexual and
asexual. The latter is effected in many ways--by gemmation, that is by the
formation of buds of various kinds, and by fissiparous generation, that is
by spontaneous or artificial division. It is notorious that some of the
lower animals, when cut into many pieces, reproduce so many perfect
individuals: Lyonnet cut a Nais or freshwater worm into nearly forty
pieces, and these all reproduced perfect animals.[874] It is probable that
segmentation could be carried much further in some of the protozoa, and
with some of the lowest plants each cell will reproduce the parent-form.
Johannes Müller thought that there was an important distinction between
gemmation and fission; for in the latter case the divided portion, however
small, is more perfectly organised; but most physiologists are now
convinced that the two processes are essentially alike.[875] Prof. Huxley
remarks, "fission is little more than a peculiar {359} mode of budding,"
and Prof. H. J. Clark, who has especially attended to this subject, shows
in detail that there is sometimes "a compromise between self-division and
budding." When a limb is amputated, or when the whole body is bisected, the
cut extremities are said to bud forth; and as the papilla, which is first
formed, consists of undeveloped cellular tissue like that forming an
ordinary bud, the expression is apparently correct. We see the connection
of the two processes in another way; for Trembley observed that with the
hydra the reproduction of the head after amputation was checked as soon as
the animal began to bud.[876]

Between the production, by fissiparous generation, of two or more complete
individuals, and the repair of even a very slight injury, we have, as
remarked in a former chapter, so perfect and insensible a gradation, that
it is impossible to doubt that they are connected processes. Between the
power which repairs a trifling injury in any part, and the power which
previously "was occupied in its maintenance by the continued mutation of
its particles," there cannot be any great difference; and we may follow Mr.
Paget in believing them to be the selfsame power. As at each stage of
growth an amputated part is replaced by one in the same state of
development, we must likewise follow Mr. Paget in admitting "that the
powers of development from the embryo are identical with those exercised
for the restoration from injuries: in other words, that the powers are the
same by which perfection is first achieved, and by which, when lost, it is
recovered."[877] Finally, we may conclude that the several forms of
gemmation, and of fissiparous generation, the repair of injuries, the
maintenance of each part in its proper state, and the growth or progressive
development of the whole structure of the embryo, are all essentially the
results of one and the same great power.

_Sexual Generation._--The union of the two sexual elements seems to make a
broad distinction between sexual and asexual reproduction. But the
well-ascertained cases of Parthenogenesis prove that the distinction is not
really so great as it at first appears; for ovules occasionally, and even
in some cases {360} frequently, become developed into perfect beings,
without the concourse of the male element. J. Müller and others admit that
ovules and buds have the same essential nature. Certain bodies, which
during their early development cannot be distinguished by any external
character from true ovules, nevertheless must be classed as buds, for
though formed within the ovarium they are incapable of fertilisation. This
is the case with the germ-balls of the Cecidomyide larvæ, as described by
Leuckart.[878] Ovules and the male element, before they become united,
have, like buds, an independent existence.[879] Both have the power of
transmitting every single character possessed by the parent-form. We see
this clearly when hybrids are paired _inter se_, for the characters of
either grandparent often reappear, either perfectly or by segments, in the
progeny. It is an error to suppose that the male transmits certain
characters and the female other characters; though no doubt, from unknown
causes, one sex sometimes has a stronger power of transmission than the
other.

It has been maintained by some authors that a bud differs essentially from
a fertilised germ, by always reproducing the perfect character of the
parent-stock; whilst fertilised germs become developed into beings which
differ, in a greater or less degree, from each other and from their
parents. But there is no such broad distinction as this. In the eleventh
chapter, numerous cases were given showing that buds occasionally grow into
plants having new and strongly marked characters; and varieties thus
produced can be propagated for a length of time by buds, and occasionally
by seed. Nevertheless, it must be admitted that beings produced sexually
are much more liable to vary than those produced asexually; and of this
fact a partial explanation will hereafter be attempted. The variability in
both cases is determined by the same general causes, and is governed by the
same laws. Hence new varieties arising from buds cannot be distinguished
from those arising from seed. Although bud-varieties usually retain their
character during {361} successive bud-generations, yet they occasionally
revert, even after a long series of bud-generations, to their former
character. This tendency to reversion in buds is one of the most remarkable
of the several points of agreement between the offspring from bud and
seminal reproduction.

There is, however, one difference between beings produced sexually and
asexually, which is very general. The former usually pass in the course of
their development from a lower to a higher grade, as we see in the
metamorphoses of insects and in the concealed metamorphoses of the
vertebrata; but this passage from a lower to a higher grade cannot be
considered as a necessary accompaniment of sexual reproduction, for hardly
anything of the kind occurs in the development of Aphis amongst insects, or
with certain crustaceans, cephalopods, or with any of the higher vascular
plants. Animals propagated asexually by buds or fission are on the other
hand never known to undergo a retrogressive metamorphosis; that is, they do
not first sink to a lower, before passing on to their higher and final
stage of development. But during the act of asexual production or
subsequently to it, they often advance in organisation, as we see in the
many cases of "alternate generation." In thus speaking of alternate
generation, I follow those naturalists who look at the process as
essentially one of internal budding or of fissiparous generation. Some of
the lower plants, however, such as mosses and certain algæ, according to
Dr. L. Radlkofer,[880] when propagated asexually, do undergo a
retrogressive metamorphosis. We can to a certain extent understand, as far
as the final cause is concerned, why beings propagated by buds should so
rarely retrogress during development; for with each organism the structure
acquired at each stage of development must be adapted to its peculiar
habits. Now, with beings produced by gemmation,--and this, differently from
sexual reproduction, may occur at any period of growth,--if there were
places for the support of many individuals at some one stage of
development, the simplest plan would be that they should be multiplied by
gemmation at that stage, and not that they should first retrograde in their
development to an earlier or simpler structure, which might not be fitted
for the surrounding conditions.

{362}

From the several foregoing considerations we may conclude that the
difference between sexual and asexual generation is not nearly so great as
it at first appears; and we have already seen that there is the closest
agreement between gemmation, fissiparous generation, the repair of
injuries, and ordinary growth or development. The capacity of fertilisation
by the male element seems to be the chief distinction between an ovule and
a bud; and this capacity is not invariably brought into action, as in the
cases of parthenogenetic reproduction. We are here naturally led to inquire
what the final cause can be of the necessity in ordinary generation for the
concourse of the two sexual elements.

Seeds and ova are often highly serviceable as the means of disseminating
plants and animals, and of preserving them during one or more seasons in a
dormant state; but unimpregnated seeds or ova, and detached buds, would be
equally serviceable for both purposes. We can, however, indicate two
important advantages gained by the concourse of the two sexes, or rather of
two individuals belonging to opposite sexes; for, as I have shown in a
former chapter, the structure of every organism appears to be especially
adapted for the concurrence, at least occasionally, of two individuals. In
nearly the same manner as it is admitted by naturalists that hybridism,
from inducing sterility, is of service in keeping the forms of life
distinct and fitted for their proper places; so, when species are rendered
highly variable by changed conditions of life, the free intercrossing of
the varying individuals will tend to keep each form fitted for its proper
place in nature; and crossing can be effected only by sexual generation,
but whether the end thus gained is of sufficient importance to account for
the first origin of sexual intercourse is very doubtful. Secondly, I have
shown, from the consideration of a large body of facts, that, as a slight
change in the conditions of life is beneficial to each creature, so, in an
analogous manner, is the change effected in the germ by sexual union with a
distinct individual; and I have been led, from observing the many
widely-extended provisions throughout nature for this purpose, and from the
greater vigour of crossed organisms of all kinds, as proved by direct
experiments, as well as from the evil effects of close interbreeding when
long {363} continued, to believe that the advantage thus gained is very
great. Besides these two important ends, there may, of course, be others,
as yet unknown to us, gained by the concourse of the two sexes.

Why the germ, which before impregnation undergoes a certain amount of
development, ceases to progress and perishes, unless it be acted on by the
male element; and why conversely the male element, which is enabled to keep
alive for even four or five years within the spermatheca of a female
insect, likewise perishes, unless it acts on or unites with the germ, are
questions which cannot be answered with any certainty. It is, however,
possible that both sexual elements perish, unless brought into union,
simply from including too little formative matter for independent existence
and development; for certainly they do not in ordinary cases differ in
their power of giving character to the embryo. This view of the importance
of the quantity of formative matter seems probable from the following
considerations. There is no reason to suspect that the spermatozoa or
pollen-grains of the same individual animal or plant differ from each
other; yet Quatrefages has shown in the case of the Teredo,[881] as did
formerly Prevost and Dumas with other animals, that more than one
spermatozoon is requisite to fertilise an ovule. This has likewise been
clearly proved by Newport,[882] who adds the important fact, established by
numerous experiments, that, when a very small number of spermatozoa are
applied to the ova of Batrachians, they are only partially impregnated and
the embryo is never fully developed: the first step, however, towards
development, namely, the partial segmentation of the yelk, does occur to a
greater or less extent, but is never completed up to granulation. The rate
of the segmentation is likewise determined by the number of the
spermatozoa. With respect to plants, nearly the same results were obtained
by Kölreuter and Gärtner. This last careful observer found,[883] after
making successive trials on a Malva with more and more pollen-grains, that
even thirty grains did not fertilise a single seed; but when forty grains
were applied to the {364} stigma, a few seeds of small size were formed.
The pollen-grains of Mirabilis are extraordinarily large, and the ovarium
contains only a single ovule; and these circumstances led Naudin[884] to
make the following interesting experiments: a flower was fertilised by
three grains and succeeded perfectly; twelve flowers were fertilised by two
grains, and seventeen flowers by a single grain, and of these one flower
alone in each lot perfected its seed; and it deserves especial notice that
the plants produced by these two seeds never attained their proper
dimensions, and bore flowers of remarkably small size. From these facts we
clearly see that the quantity of the peculiar formative matter which is
contained within the spermatozoa and pollen-grains is an all-important
element in the act of fertilisation, not only in the full development of
the seed, but in the vigour of the plant produced from such seed. We see
something of the same kind in certain cases of parthenogenesis, that is,
when the male element is wholly excluded; for M. Jourdan[885] found that,
out of about 58,000 eggs laid by unimpregnated silk-moths, many passed
through their early embryonic stages, showing that they were capable of
self-development, but only twenty-nine out of the whole number produced
caterpillars. Therefore it is not an improbable view that deficient bulk or
quantity in the formative matter, contained within the sexual elements, is
the main cause of their not having the capacity of prolonged separate
existence and development. The belief that it is the function of the
spermatozoa to communicate life to the ovule seems a strange one, seeing
that the unimpregnated ovule is already alive and continues for a
considerable time alive. We shall hereafter see that it is probable that
the sexual elements, or possibly only the female element, include certain
primordial cells, that is, such as have undergone no differentiation, and
which are not present in an active state in buds.

_Graft-hybrids._--When discussing in the eleventh chapter the curious case
of the _Cytisus adami_, facts were given which render it to a certain
degree probable, in accordance with the belief of some distinguished
botanists, that, when the tissues of two plants {365} belonging to distinct
species or varieties are intimately united, buds are afterwards
occasionally produced which, like hybrids, combine the characters of the
two united forms. It is certain that when trees with variegated leaves are
grafted or budded on a common stock, the latter sometimes produces buds
bearing variegated leaves; but this may perhaps be looked at as a case of
inoculated disease. Should it ever be proved that hybridised buds can be
formed by the union of two distinct vegetative tissues, the essential
identity of sexual and asexual reproduction would be shown in the most
interesting manner; for the power of combining in the offspring the
characters of both parents, is the most striking of all the functions of
sexual generation.

_Direct Action of the Male Element on the Female._--In the chapter just
referred to, I have given abundant proofs that foreign pollen occasionally
affects the mother-plant in a direct manner. Thus, when Gallesio fertilised
an orange-flower with pollen from the lemon, the fruit bore stripes of
perfectly characterised lemon-peel: with peas, several observers have seen
the colour of the seed-coats and even of the pod directly affected by the
pollen of a distinct variety; so it has been with the fruit of the apple,
which consists of the modified calyx and upper part of the flower-stalk.
These parts in ordinary cases are wholly formed by the mother-plant. We
here see the male element affecting and hybridising not that part which it
is properly adapted to affect, namely the ovule, but the partially
developed tissues of a distinct individual. We are thus brought half-way
towards a graft-hybrid, in which the cellular tissue of one form, instead
of its pollen, is believed to hybridise the tissues of a distinct form. I
formerly assigned reasons for rejecting the belief that the mother-plant is
affected through the intervention of the hybridised embryo; but even if
this view were admitted, the case would become one of graft-hybridism, for
the fertilised embryo and the mother-plant must be looked at as distinct
individuals.

With animals which do not breed until nearly mature, and of which all the
parts are then fully developed, it is hardly possible that the male element
should directly affect the female. But we have the analogous and perfectly
well-ascertained case of the male element of a distinct form, as with the
{366} quagga and Lord Morton's mare, affecting the ovarium of the female,
so that the ovules and offspring subsequently produced by her when
impregnated by other males are plainly affected and hybridised by the first
male.

_Development._--The fertilised germ reaches maturity by a vast number of
changes: these are either slight and slowly effected, as when the child
grows into the man, or are great and sudden, as with the metamorphoses of
most insects. Between these extremes we have, even within the same class,
every gradation: thus, as Sir J. Lubbock has shown,[886] there is an
Ephemerous insect which moults above twenty times, undergoing each time a
slight but decided change of structure; and these changes, as he further
remarks, probably reveal to us the normal stages of development which are
concealed and hurried through, or suppressed, in most other insects. In
ordinary metamorphoses, the parts and organs appear to become changed into
the corresponding parts in the next stage of development; but there is
another form of development, which has been called by Professor Owen
metagenesis. In this case "the new parts are not moulded upon the inner
surface of the old ones. The plastic force has changed its course of
operation. The outer case, and all that gave form and character to the
precedent individual, perish and are cast off; they are not changed into
the corresponding parts of the new individual. These are due to a new and
distinct developmental process," &c.[887] Metamorphosis, however, graduates
so insensibly into metagenesis, that the two processes cannot be distinctly
separated. For instance, in the last change which Cirripedes undergo, the
alimentary canal and some other organs are moulded on pre-existing parts;
but the eyes of the old and the young animal are developed in entirely
different parts of the body; the tips of the mature limbs are formed within
the larval limbs, and may be said to be metamorphosed from them; but their
basal portions and the whole thorax are developed in a plane actually at
right angles to the limbs and thorax of the larva; and this {367} may be
called metagenesis. The metagenetic process is carried to an extreme degree
in the development of some Echinoderms, for the animal in the second stage
of development is formed almost like a bud within the animal of the first
stage, the latter being then cast off like an old vestment, yet sometimes
still maintaining for a short period an independent vitality.[888]

If, instead of a single individual, several were to be thus developed
metagenetically within a pre-existing form, the process would be called one
of alternate generation. The young thus developed may either closely
resemble the encasing parent-form, as with the larvæ of Cecidomyia, or may
differ to an astonishing degree, as with many parasitic worms and with
jelly-fishes; but this does not make any essential difference in the
process, any more than the greatness or abruptness of the change in the
metamorphoses of insects.

The whole question of development is of great importance for our present
subject. When an organ, the eye for instance, is metagenetically formed in
a part of the body where during the previous stage of development no eye
existed, we must look at it as a new and independent growth. The absolute
independence of new and old structures, which correspond in structure and
function, is still more obvious when several individuals are formed within
a previous encasing form, as in the cases of alternate generation. The same
important principle probably comes largely into play even in the case of
continuous growth, as we shall see when we consider the inheritance of
modifications at corresponding ages.

We are led to the same conclusion, namely, the independence of parts
successively developed, by another and quite distinct group of facts. It is
well known that many animals belonging to the same class, and therefore not
differing widely from each other, pass through an extremely different
course of development. Thus certain beetles, not in any way remarkably
different from others of the same order, undergo what has been called a
hyper-metamorphosis--that is, they pass through an early stage wholly
different from the ordinary grub-like larva. In the same sub-order of
crabs, namely, the Macroura, as Fritz {368} Müller remarks, the river
cray-fish is hatched under the same form which it ever afterwards retains;
the young lobster has divided legs, like a Mysis; the Palæmon appears under
the form of a Zoea, and Peneus under the Nauplius-form; and how wonderfully
these larval forms differ from each other, is known to every
naturalist.[889] Some other crustaceans, as the same author observes, start
from the same point and arrive at nearly the same end, but in the middle of
their development are widely different from each other. Still more striking
cases could be given with respect to the Echinodermata. With the Medusæ or
jelly-fishes Professor Allman observes, "the classification of the Hydroida
would be a comparatively simple task if, as has been erroneously asserted,
generically-identical medusoids always arose from generically-identical
polypoids; and on the other hand, that generically-identical polypoids
always gave origin to generically-identical medusoids." So, again, Dr.
Strethill Wright remarks, "in the life-history of the Hydroidæ any phase,
planuloid, polypoid, or medusoid, may be absent."[890]

According to the belief now generally accepted by our best naturalists, all
the members of the same order or class, the Macrourous crustaceans for
instance, are descended from a common progenitor. During their descent they
have diverged much in structure, but have retained much in common; and this
divergence and retention of character has been effected, though they have
passed and still pass through marvellously different metamorphoses. This
fact well illustrates how independent each structure must be from that
which precedes and follows it in the course of development.

_The Functional Independence of the Elements or Units of the
Body._--Physiologists agree that the whole organism consists of a multitude
of elemental parts, which are to a great extent independent of each other.
Each organ, says Claude Bernard,[891] {369} has its proper life, its
autonomy; it can develop and reproduce itself independently of the
adjoining tissues. The great German authority, Virchow,[892] asserts still
more emphatically that each system, as the nervous or osseous system, or
the blood, consists of an "enormous mass of minute centres of action....
Every element has its own special action, and even though it derive its
stimulus to activity from other parts, yet alone effects the actual
performance of its duties.... Every single epithelial and muscular
fibre-cell leads a sort of parasitical existence in relation to the rest of
the body.... Every single bone-corpuscle really possesses conditions of
nutrition peculiar to itself." Each element, as Mr. Paget remarks, lives
its appointed time, and then dies, and, after being cast off or absorbed,
is replaced.[893] I presume that no physiologist doubts that, for instance,
each bone-corpuscle of the finger differs from the corresponding corpuscle
in the corresponding joint of the toe; and there can hardly be a doubt that
even those on the corresponding sides of the body differ, though almost
identical in nature. This near approach to identity is curiously shown in
many diseases in which the same exact points on the right and left sides of
the body are similarly affected; thus Mr. Paget[894] gives a drawing of a
diseased pelvis, in which the bone has grown into a most complicated
pattern, but "there is not one spot or line on one side which is not
represented, as exactly as it would be in a mirror, on the other."

Many facts support this view of the independent life of each minute element
of the body. Virchow insists that a single bone-corpuscle or a single cell
in the skin may become diseased. The spur of a cock, after being inserted
into the eye of an ox, lived for eight years, and acquired a weight of 306
grammes, or nearly fourteen ounces.[895] The tail of a pig has been grafted
into the middle of its back, and reacquired sensibility. Dr. Ollier[896]
inserted a piece of periosteum from the bone of a young dog under the skin
of a rabbit, and true bone was developed. A multitude of similar facts
could be given. The {370} frequent presence of hairs and of perfectly
developed teeth, even teeth of the second dentition, in ovarian
tumours,[897] are facts leading to the same conclusion.

Whether each of the innumerable autonomous elements of the body is a cell
or the modified product of a cell, is a more doubtful question, even if so
wide a definition be given to the term, as to include cell-like bodies
without walls and without nuclei.[898] Professor Lionel Beale uses the term
"germinal matter" for the contents of cells, taken in this wide
acceptation, and he draws a broad distinction between germinal matter and
"formed material" or the various products of cells.[899] But the doctrine
of _omnis cellula e cellulâ_ is admitted for plants, and is a widely
prevalent belief with respect to animals.[900] Thus Virchow, the great
supporter of the cellular theory, whilst allowing that difficulties exist,
maintains that every atom of tissue is derived from cells, and these from
pre-existing cells, and these primarily from the egg, which he regards as a
great cell. That cells, still retaining the same nature, increase by
self-division or proliferation, is admitted by almost every one. But when
an organism undergoes a great change of structure during development, the
cells, which at each stage are supposed to be directly derived from
previously-existing cells, must likewise be greatly changed in nature; this
change is apparently attributed by the supporters of the cellular doctrine
to some inherent power which the cells possess, and not to any external
agency.

Another school maintains that cells and tissues of all kinds may be formed,
independently of pre-existing cells, from plastic lymph or blastema; and
this it is thought is well exhibited in the repair of wounds. As I have not
especially attended to histology, it would be presumptuous in me to express
an opinion on the two opposed doctrines. But every one appears to admit
that the body consists of a multitude of "organic units,"[901] {371} each
of which possesses its own proper attributes, and is to a certain extent
independent of all others. Hence it will be convenient to use indifferently
the terms cells or organic units or simply units.

_Variability and Inheritance._--We have seen in the twenty-second chapter
that variability is not a principle co-ordinate with life or reproduction,
but results from special causes, generally from changed conditions acting
during successive generations. Part of the fluctuating variability thus
induced is apparently due to the sexual system being easily affected by
changed conditions, so that it is often rendered impotent; and when not so
seriously affected, it often fails in its proper function of transmitting
truly the characters of the parents to the offspring. But variability is
not necessarily connected with the sexual system, as we see from the cases
of bud-variation; and although we may not be able to trace the nature of
the connexion, it is probable that many deviations of structure which
appear in sexual offspring result from changed conditions acting directly
on the organisation, independently of the reproductive organs. In some
instances we may feel sure of this, when all, or nearly all the individuals
which have been similarly exposed are similarly and definitely affected--as
in the dwarfed and otherwise changed maize brought from hot countries when
cultivated in Germany; in the change of the fleece in sheep within the
tropics; to a certain extent in the increased size and early maturity of
our highly-improved domesticated animals; in inherited gout from
intemperance; and in many other such cases. Now, as such changed conditions
do not especially affect the reproductive organs, it seems mysterious on
any ordinary view why their product, the new organic being, should be
similarly affected.

How, again, can we explain to ourselves the inherited effects of the use or
disuse of particular organs? The domesticated duck flies less and walks
more than the wild duck, and its limb-bones have become in a corresponding
manner diminished and increased in comparison with those of the wild duck.
A horse is trained to certain paces, and the colt inherits similar
consensual movements. The domesticated rabbit becomes tame from close
confinement; the dog intelligent from associating with man; the retriever
is taught to fetch and carry: and these {372} mental endowments and bodily
powers are all inherited. Nothing in the whole circuit of physiology is
more wonderful. How can the use or disuse of a particular limb or of the
brain affect a small aggregate of reproductive cells, seated in a distant
part of the body, in such a manner that the being developed from these
cells inherits the characters of either one or both parents? Even an
imperfect answer to this question would be satisfactory.

Sexual reproduction does not essentially differ, as we have seen, from
budding or self-division, and these processes graduate through the repair
of injuries into ordinary development and growth; it might therefore be
expected that every character would be as regularly transmitted by all the
methods of reproduction as by continued growth. In the chapters devoted to
inheritance it was shown that a multitude of newly-acquired characters,
whether injurious or beneficial, whether of the lowest or highest vital
importance, are often faithfully transmitted--frequently even when one
parent alone possesses some new peculiarity. It deserves especial attention
that characters appearing at any age tend to reappear at a corresponding
age. We may on the whole conclude that in all cases inheritance is the
rule, and non-inheritance the anomaly. In some instances a character is not
inherited, from the conditions of life being directly opposed to its
development; in many instances, from the conditions incessantly inducing
fresh variability, as with grafted fruit-trees and highly cultivated
flowers. In the remaining cases the failure may be attributed to reversion,
by which the child resembles its grandparents or more remote progenitors,
instead of its parents.

This principle of Reversion is the most wonderful of all the attributes of
Inheritance. It proves to us that the transmission of a character and its
development, which ordinarily go together and thus escape discrimination,
are distinct powers; and these powers in some cases are even antagonistic,
for each acts alternately in successive generations. Reversion is not a
rare event, depending on some unusual or favourable combination of
circumstances, but occurs so regularly with crossed animals and plants, and
so frequently with uncrossed breeds, that it is evidently an essential part
of the principle of inheritance. We know that {373} changed conditions have
the power of evoking long-lost characters, as in the case of some feral
animals. The act of crossing in itself possesses this power in a high
degree. What can be more wonderful than that characters, which have
disappeared during scores, or hundreds, or even thousands of generations,
should suddenly reappear perfectly developed, as in the case of pigeons and
fowls when purely bred, and especially when crossed; or as with the zebrine
stripes on dun-coloured horses, and other such cases? Many monstrosities
come under this same head, as when rudimentary organs are redeveloped, or
when an organ which we must believe was possessed by an early progenitor,
but of which not even a rudiment is left, suddenly reappears, as with the
fifth stamen in some Scrophulariaceæ. We have already seen that reversion
acts in bud-reproduction; and we know that it occasionally acts during the
growth of the same individual animal, especially, but not exclusively, when
of crossed parentage,--as in the rare cases described of individual fowls,
pigeons, cattle, and rabbits, which have reverted as they advanced in years
to the colours of one of their parents or ancestors.

We are led to believe, as formerly explained, that every character which
occasionally reappears is present in a latent form in each generation, in
nearly the same manner as in male and female animals secondary characters
of the opposite sex lie latent, ready to be evolved when the reproductive
organs are injured. This comparison of the secondary sexual characters
which are latent in both sexes, with other latent characters, is the more
appropriate from the case recorded of the Hen, which assumed some of the
masculine characters, not of her own race, but of an early progenitor; she
thus exhibited at the same time the redevelopment of latent characters of
both kinds and connected both classes. In every living creature we may feel
assured that a host of lost characters lie ready to be evolved under proper
conditions. How can we make intelligible, and connect with other facts,
this wonderful and common capacity of reversion,--this power of calling
back to life long-lost characters? {374}

PART II.

I have now enumerated the chief facts which every one would desire to
connect by some intelligible bond. This can be done, as it seems to me, if
we make the following assumptions; if the first and chief one be not
rejected, the others, from being supported by various physiological
considerations, will not appear very improbable. It is almost universally
admitted that cells, or the units of the body, propagate themselves by
self-division or proliferation, retaining the same nature, and ultimately
becoming converted into the various tissues and substances of the body. But
besides this means of increase I assume that cells, before their conversion
into completely passive or "formed material," throw off minute granules or
atoms, which circulate freely throughout the system, and when supplied with
proper nutriment multiply by self-division, subsequently becoming developed
into cells like those from which they were derived. These granules for the
sake of distinctness may be called cell-gemmules, or, as the cellular
theory is not fully established, simply gemmules. They are supposed to be
transmitted from the parents to the offspring, and are generally developed
in the generation which immediately succeeds, but are often transmitted in
a dormant state during many generations and are then developed. Their
development is supposed to depend on their union with other partially
developed cells or gemmules which precede them in the regular course of
growth. Why I use the term union, will be seen when we discuss the direct
action of pollen on the tissues of the mother-plant. Gemmules are supposed
to be thrown off by every cell or unit, not only during the adult state,
but during all the stages of development. Lastly, I assume that the
gemmules in their dormant state have a mutual affinity for each other,
leading to their aggregation either into buds or into the sexual elements.
Hence, speaking strictly, it is not the reproductive elements, nor the
buds, which generate new organisms, but the cells themselves throughout the
body. These assumptions constitute the provisional hypothesis which I have
called Pangenesis. Nearly {375} similar views have been propounded, as I
find, by other authors, more especially by Mr. Herbert Spencer;[902] but
they are here modified and amplified.

{376}

Before proceeding to show, firstly, how far these assumptions are in
themselves probable, and secondly, how far they connect and explain the
various groups of facts with which we are concerned, it may be useful to
give an illustration of the hypothesis. If one of the simplest Protozoa be
formed, as appears under the microscope, of a small mass of homogeneous
gelatinous matter, a minute atom thrown off from any part and nourished
under favourable circumstances would naturally reproduce the whole; but if
the upper and lower surfaces were to differ in texture from the central
portion, then all three parts would have to throw off atoms or gemmules,
which when aggregated by mutual affinity would form either buds or the
sexual elements. Precisely the same view may be extended to one of the
higher animals; although in this case many thousand gemmules must be thrown
off from the various parts of the body. Now, when the leg, for instance, of
a salamander is cut off, a slight crust forms over the wound, and beneath
this crust the uninjured cells or units of bone, muscle, nerves, &c., are
supposed to unite with the diffused gemmules of those cells which in the
perfect leg come next in order; and these as they become slightly developed
unite with others, and so on until a papilla of soft cellular tissue, the
"budding leg," is formed, and in time a perfect leg.[903] Thus, that
portion of the leg which had {377} been cut off, neither more nor less,
would be reproduced. If the tail or leg of a young animal had been cut off,
a young tail or leg would have been reproduced, as actually occurs with the
amputated tail of the tadpole; for gemmules of all the units which compose
the tail are diffused throughout the body at all ages. But during the adult
state the gemmules of the larval tail would remain dormant, for they would
not meet with pre-existing cells in a proper state of development with
which to unite. If from changed conditions or any other cause any part of
the body should become permanently modified, the gemmules, which are merely
minute portions of the contents of the cells forming the part, would
naturally reproduce the same modification. But gemmules previously derived
from the same part before it had undergone any change, would still be
diffused throughout the organisation, and would be transmitted from
generation to generation, so that under favourable circumstances they might
be redeveloped, and then the new modification would be for a time or for
ever lost. The aggregation of gemmules derived from every part of the body,
through their mutual affinity, would form buds, and their aggregation in
some special manner, apparently in small quantity, together probably with
the presence of gemmules of certain primordial cells, would constitute the
sexual elements. By means of these illustrations the hypothesis of
pangenesis has, I hope, been rendered intelligible.

       *       *       *       *       *

Physiologists maintain, as we have seen, that each cell, though to a large
extent dependent on others, is likewise, to a certain extent, independent
or autonomous. I go one small step further, and assume that each cell casts
off a free gemmule, which is capable of reproducing a similar cell. There
is some analogy between this view and what we see in compound animals and
in the flower-buds on the same tree; for these are distinct individuals
capable of true or seminal reproduction, yet have parts in common and are
dependent on each other; thus {378} the tree has its bark and trunk, and
certain corals, as the Virgularia, have not only parts, but movements in
common.

The existence of free gemmules is a gratuitous assumption, yet can hardly
be considered as very improbable, seeing that cells have the power of
multiplication through the self-division of their contents. Gemmules differ
from true ovules or buds inasmuch as they are supposed to be capable of
multiplication in their undeveloped state. No one probably will object to
this capacity as improbable. The blastema within the egg has been known to
divide and give birth to two embryos; and Thuret[904] has seen the zoospore
of an alga divide itself, and both halves germinate. An atom of small-pox
matter, so minute as to be borne by the wind, must multiply itself many
thousand-fold in a person thus inoculated.[905] It has recently been
ascertained[906] that a minute portion of the mucous discharge from an
animal affected with rinderpest, if placed in the blood of a healthy ox,
increases so fast that in a short space of time "the whole mass of blood,
weighing many pounds, is infected, and every small particle of that blood
contains enough poison to give, within less than forty-eight hours, the
disease to another animal."

The retention of free and undeveloped gemmules in the same body from early
youth to old age may appear improbable, but we should remember how long
seeds lie dormant in the earth and buds in the bark of a tree. Their
transmission from generation to generation may appear still more
improbable; but here again we should remember that many rudimentary and
useless organs are transmitted and have been transmitted during an
indefinite number of generations. We shall presently see how well the
long-continued transmission of undeveloped gemmules explains many facts.

As each unit, or group of similar units throughout the body, casts off its
gemmules, and as all are contained within the smallest egg or seed, and
within each spermatozoon or pollen-grain, their number and minuteness must
be something {379} inconceivable. I shall hereafter recur to this
objection, which at first appears so formidable; but it may here be
remarked that a cod-fish has been found to produce 4,872,000 eggs, a single
Ascaris about 64,000,000 eggs, and a single Orchidaceous plant probably as
many million seeds.[907] In these several cases, the spermatozoa and
pollen-grains must exist in considerably larger numbers. Now, when we have
to deal with numbers such as these, which the human intellect cannot grasp,
there is no good reason for rejecting our present hypothesis on account of
the assumed existence of cell-gemmules a few thousand times more numerous.

The gemmules in each organism must be thoroughly diffused; nor does this
seem improbable considering their minuteness, and the steady circulation of
fluids throughout the body. So it must be with the gemmules of plants, for
with certain kinds even a minute fragment of a leaf will reproduce the
whole. But a difficulty here occurs; it would appear that with plants, and
probably with compound animals, such as corals, the gemmules do not spread
from bud to bud, but only through the tissues developed from each separate
bud. We are led to this conclusion from the stock being rarely affected by
the insertion of a bud or graft from a distinct variety. This non-diffusion
of the gemmules is still more plainly shown in the case of ferns; for Mr.
Bridgman[908] has proved that, when spores (which it should be remembered
are of the nature of buds) are taken from a monstrous part of a frond, and
others from an ordinary part, {380} each reproduces the form of the part
whence derived. But this non-diffusion of the gemmules from bud to bud may
be only apparent, depending, as we shall hereafter see, on the nature of
the first-formed cells in the buds.

The assumed elective affinity of each gemmule for that particular cell
which precedes it in the order of development is supported by many
analogies. In all ordinary cases of sexual reproduction the male and female
elements have a mutual affinity for each other: thus, it is believed that
about ten thousand species of Compositæ exist, and there can be no doubt
that if the pollen of all these species could be, simultaneously or
successively, placed on the stigma of any one species, this one would elect
with unerring certainty its own pollen. This elective capacity is all the
more wonderful, as it must have been acquired since the many species of
this great group of plants branched off from a common progenitor. On any
view of the nature of sexual reproduction, the protoplasm contained within
the ovules and within the sperm-cells (or the "spermatic force" of the
latter, if so vague a term be preferred) must act on each other by some law
of special affinity, either during or subsequently to impregnation, so that
corresponding parts alone affect each other; thus, a calf produced from a
short-horned cow by a long-horned bull has its horns and not its horny
hoofs affected by the union of the two forms, and the offspring from two
birds with differently coloured tails have their tails and not their whole
plumage affected.

The various tissues of the body plainly show, as many physiologists have
insisted,[909] an affinity for special organic substances, whether natural
or foreign to the body. We see this in the cells of the kidneys attracting
urea from the blood; in the worrara poison affecting the nerves; upas and
digitalis the muscles; the Lytta vesicatoria the kidneys; and in the
poisonous matter of many diseases, as small-pox, scarlet-fever,
hooping-cough, glanders, cancer, and hydrophobia, affecting certain
definite parts of the body or certain tissues or glands.

The affinity of various parts of the body for each other during {381} their
early development was shown in the last chapter, when discussing the
tendency to fusion in homologous parts. This affinity displays itself in
the normal fusion of organs which are separate at an early embryonic age,
and still more plainly in those marvellous cases of double monsters in
which each bone, muscle, vessel, and nerve in the one embryo, blends with
the corresponding part in the other. The affinity between homologous organs
may come into action with single parts, or with the entire individual, as
in the case of flowers or fruits which are symmetrically blended together
with all their parts doubled, but without any other trace of fusion.

It has also been assumed that the development of each gemmule depends on
its union with another cell or unit which has just commenced its
development, and which, from preceding it in order of growth, is of a
somewhat different nature. Nor is it a very improbable assumption that the
development of a gemmule is determined by its union with a cell slightly
different in nature, for abundant evidence was given in the seventeenth
chapter, showing that a slight degree of differentiation in the male and
female sexual elements favours in a marked manner their union and
subsequent development. But what determines the development of the gemmules
of the first-formed or primordial cell in the unimpregnated ovule, is
beyond conjecture.

It must also be admitted that analogy fails to guide us towards any
determination on several other points: for instance, whether cells, derived
from the same parent-cell, may, in the regular course of growth, become
developed into different structures, from absorbing peculiar kinds of
nutriment, independently of their union with distinct gemmules. We shall
appreciate this difficulty if we call to mind, what complex yet symmetrical
growths the cells of plants yield when they are inoculated by the poison of
a gall-insect. With animals various polypoid excrescences and tumours are
now generally admitted[910] to be the direct product, through
proliferation, of normal cells which have become abnormal. In the regular
growth and repair of bones, the tissues undergo, as Virchow remarks,[911] a
whole series of permutations and substitutions. "The cartilage-cells may be
{382} converted by a direct transformation into marrow-cells, and continue
as such; or they may first be converted into osseous and then into
medullary tissue; or lastly, they may first be converted into marrow and
then into bone. So variable are the permutations of these tissues, in
themselves so nearly allied, and yet in their external appearance so
completely distinct." But as these tissues thus change their nature at any
age, without any obvious change in their nutrition, we must suppose in
accordance with our hypothesis that gemmules derived from one kind of
tissue combine with the cells of another kind, and cause the successive
modifications.

It is useless to speculate at what period of development each organic unit
casts off its gemmules; for the whole subject of the development of the
various elemental tissues is as yet involved in much doubt. Some
physiologists, for instance, maintain that muscle or nerve-fibres are
developed from cells, which are afterwards nourished by their own proper
powers of absorption; whilst other physiologists deny their cellular
origin; and Beale maintains that such fibres are renovated exclusively by
the conversion of fresh germinal matter (that is the so-called nuclei) into
"formed material." However this may be, it appears probable that all
external agencies, such as changed nutrition, increased use or disuse, &c.,
which induced any permanent modification in a structure, would at the same
time or previously act on the cells, nuclei, germinal or formative matter,
from which the structures in question were developed, and consequently
would act on the gemmules or cast-off atoms.

There is another point on which it is useless to speculate, namely, whether
all gemmules are free and separate, or whether some are from the first
united into small aggregates. A feather, for instance, is a complex
structure, and, as each separate part is liable to inherited variations, I
conclude that each feather certainly generates a large number of gemmules;
but it is possible that these may be aggregated into a compound gemmule.
The same remark applies to the petals of a flower, which in some cases are
highly complex, with each ridge and hollow contrived for special purposes,
so that each part must have been separately modified, and the modifications
transmitted; consequently, separate gemmules, according to our hypothesis,
{383} must have been thrown off from each cell or part. But, as we
sometimes see half an anther or a small portion of a filament becoming
petaliform, or parts or mere stripes of the calyx assuming the colour and
texture of the corolla, it is probable that with petals the gemmules of
each cell are not aggregated together into a compound gemmule, but are
freely and separately diffused.

       *       *       *       *       *

Having now endeavoured to show that the several foregoing assumptions are
to a certain extent supported by analogous facts, and having discussed some
of the most doubtful points, we will consider how far the hypothesis brings
under a single point of view the various cases enumerated in the First
Part. All the forms of reproduction graduate into each other and agree in
their product; for it is impossible to distinguish between organisms
produced from buds, from self-division, or from fertilised germs; such
organisms are liable to variations of the same nature and to reversion of
character; and as we now see that all the forms of reproduction depend on
the aggregation of gemmules derived from the whole body, we can understand
this general agreement. It is satisfactory to find that sexual and asexual
generation, by both of which widely different processes the same living
creature is habitually produced, are fundamentally the same.
Parthenogenesis is no longer wonderful; in fact, the wonder is that it
should not oftener occur. We see that the reproductive organs do not
actually create the sexual elements; they merely determine or permit the
aggregation of the gemmules in a special manner. These organs, together
with their accessory parts, have, however, high functions to perform; they
give to both elements a special affinity for each other, independently of
the contents of the male and female cells, as is shown in the case of
plants by the mutual reaction of the stigma and pollen-grains; they adapt
one or both elements for independent temporary existence, and for mutual
union. The contrivances for these purposes are sometimes wonderfully
complex, as with the spermatophores of the Cephalopoda. The male element
sometimes possesses attributes which, if observed in an independent animal,
would be put down to instinct guided by sense-organs, as when the {384}
spermatozoon of an insect finds its way into the minute micropyle of the
egg, or as when the antherozoids of certain algæ swim by the aid of their
ciliæ to the female plant, and force themselves into a minute orifice. In
these latter cases, however, we must believe that the male element has
acquired its powers, on the same principle with the larvæ of animals,
namely by successive modifications developed at corresponding periods of
life: we can hardly avoid in these cases looking at the male element as a
sort of premature larva, which unites, or, like one of the lower algæ,
conjugates, with the female element. What determines the aggregation of the
gemmules within the sexual organs we do not in the least know; nor do we
know why buds are formed in certain definite places, leading to the
symmetrical growth of trees and corals, nor why adventitious buds may be
formed almost anywhere, even on a petal, and frequently upon healed
wounds.[912] As soon as the gemmules have aggregated themselves,
development apparently commences, but in the case of buds is often
afterwards suspended, and in the case of the sexual elements soon ceases,
unless the elements of the opposite sexes combine; even after this has
occurred, the fertilised germ, as with seeds buried in the ground, may
remain during a lengthened period in a dormant state.

The antagonism which has long been observed,[913] though exceptions
occur,[914] between active growth and the power of sexual
reproduction--between the repair of injuries and gemmation--and with
plants, between rapid increase by buds, rhizomes, &c., and the production
of seed, is partly explained by the gemmules not existing in sufficient
numbers for both processes. {385} But this explanation hardly applies to
those plants which naturally produce a multitude of seeds, but which,
through a comparatively small increase in the number of the buds on their
rhizomes or offsets, yield few or no seed. As, however, we shall presently
see that buds probably include tissue which has already been to a certain
extent developed or differentiated, some additional organised matter will
thus have been expended.

From one of the forms of Reproduction, namely, spontaneous self-division,
we are led by insensible steps to the repair of the slightest injury; and
the existence of gemmules, derived from every cell or unit throughout the
body and everywhere diffused, explains all such cases,--even the wonderful
fact that, when the limbs of the salamander were cut off many times
successively by Spallanzani and Bonnet, they were exactly and completely
reproduced. I have heard this process compared with the recrystallisation
which occurs when the angles of a broken crystal are repaired; and the two
processes have this much in common, that in the one case the polarity of
the molecules is the efficient cause, and in the other the affinity of the
gemmules for particular nascent cells.

Pangenesis does not throw much light on Hybridism, but agrees well with
most of the ascertained facts. We may conclude from the fact of a single
spermatozoon or pollen-grain being insufficient for impregnation, that a
certain number of gemmules derived from each cell or unit are required for
the development of each part. From the occurrence of parthenogenesis, more
especially in the case of the silk-moth, in which the embryo is often
partially formed, we may also infer that the female element includes nearly
sufficient gemmules of all kinds for independent development, so that when
united with the male element the gemmules must be superabundant. Now, as a
general rule, when two species or races are crossed reciprocally, the
offspring do not differ, and this shows that both sexual elements agree in
power, in accordance with the view that they include the same gemmules.
Hybrids and mongrels are generally intermediate in character between the
two parent-forms, yet occasionally they closely resemble one parent in one
part and the other parent in another part, or even in their whole
structure: nor is this difficult to understand on {386} the admission that
the gemmules in the fertilised germ are superabundant in number, and that
those derived from one parent have some advantage in number, affinity, or
vigour over those derived from the other parent. Crossed forms sometimes
exhibit the colour or other characters of either parent in stripes or
blotches; and this may occur in the first generation, or through reversion
in succeeding bud and seminal generations, as in the several instances
given in the eleventh chapter. In these cases we must follow Naudin,[915]
and admit that the "essence" or "element" of the two species, which terms I
should translate into the gemmules, have an affinity for their own kind,
and thus separate themselves into distinct stripes or blotches; and reasons
were given, when discussing in the fifteenth chapter the incompatibility of
certain characters to unite, for believing in such mutual affinity. When
two forms are crossed, one is not rarely found to be prepotent in the
transmission of character over the other; and this we can explain only by
again assuming that the one form has some advantage in the number, vigour,
or affinity of its gemmules, except in those cases, where certain
characters are present in the one form and latent in the other. For
instance, there is a latent tendency in all pigeons to become blue, and,
when a blue pigeon is crossed with one of any other colour, the blue tint
is generally prepotent. When we consider latent characters, the explanation
of this form of prepotency will be obvious.

When one species is crossed with another it is notorious that they do not
yield the full or proper number of offspring; and we can only say on this
head that, as the development of each organism depends on such
nicely-balanced affinities between a host of gemmules and developing cells
or units, we need not feel at all surprised that the commixture of gemmules
derived from two distinct species should lead to a partial or complete
failure of development. With respect to the sterility of hybrids produced
from the union of two distinct species, it was shown in the nineteenth
chapter that this depends exclusively on the reproductive organs being
specially affected; but why these organs should be thus affected we do not
know, any more than {387} why unnatural conditions of life, though
compatible with health, should cause sterility; or why continued close
interbreeding, or the illegitimate unions of dimorphic and trimorphic
plants, induce the same result. The conclusion that the reproductive organs
alone are affected, and not the whole organisation, agrees perfectly with
the unimpaired or even increased capacity in hybrid plants for propagation
by buds; for this implies, according to our hypothesis, that the cells of
the hybrids throw off hybridised cell-gemmules, which become aggregated
into buds, but fail to become aggregated within the reproductive organs, so
as to form the sexual elements. In a similar manner many plants, when
placed under unnatural conditions, fail to produce seed, but can readily be
propagated by buds. We shall presently see that pangenesis agrees well with
the strong tendency to reversion exhibited by all crossed animals and
plants.

It was shown in the discussion on graft-hybrids that there is some reason
to believe that portions of cellular tissue taken from distinct plants
become so intimately united, as afterwards occasionally to produce crossed
or hybridised buds. If this fact were fully established, it would, by the
aid of our hypothesis, connect gemmation and sexual reproduction in the
closest manner.

Abundant evidence has been advanced proving that pollen taken from one
species or variety and applied to the stigma of another sometimes directly
affects the tissues of the mother-plant. It is probable that this occurs
with many plants during fertilisation, but can only be detected when
distinct forms are crossed. On any ordinary theory of reproduction this is
a most anomalous circumstance, for the pollen-grains are manifestly adapted
to act on the ovule, but in these cases they act on the colour, texture,
and form of the coats of the seeds, on the ovarium itself, which is a
modified leaf, and even on the calyx and upper part of the flower-peduncle.
In accordance with the hypothesis of pangenesis pollen includes gemmules,
derived from every part of the organisation, which diffuse themselves and
multiply by self-division; hence it is not surprising that gemmules within
the pollen, which are derived from the parts near the reproductive organs,
should sometimes be able to affect the same parts, whilst still undergoing
development, in the mother-plant. {388}

As, during all the stages of development, the tissues of plants consist of
cells, and as new cells are not known to be formed between, or
independently of, pre-existing cells, we must conclude that the gemmules
derived from the foreign pollen do not become developed merely in contact
with pre-existing cells, but actually penetrate the nascent cells of the
mother-plant. This process may be compared with the ordinary act of
fertilisation, during which the contents of the pollen-tubes penetrate the
closed embryonic sack within the ovule, and determine the development of
the embryo. According to this view, the cells of the mother-plant may
almost literally be said to be fertilised by the gemmules derived from the
foreign pollen. With all organisms, as we shall presently see, the cells or
organic units of the embryo during the successive stages of development may
in like manner be said to be fertilised by the gemmules of the cells, which
come next in the order of formation.

Animals, when capable of sexual reproduction, are fully developed, and it
is scarcely possible that the male element should affect the tissues of the
mother in the same direct manner as with plants; nevertheless it is certain
that her ovaria are sometimes affected by a previous impregnation, so that
the ovules subsequently fertilised by a distinct male are plainly
influenced in character; and this, as in the case of foreign pollen, is
intelligible through the diffusion, retention, and action of the gemmules
included within the spermatozoa of the previous male.

Each organism reaches maturity through a longer or shorter course of
development. The changes may be small and insensibly slow, as when a child
grows into a man, or many, abrupt, and slight, as in the metamorphoses of
certain ephemerous insects, or again few and strongly marked, as with most
other insects. Each part may be moulded within a previously existing and
corresponding part, and in this case it will appear, falsely as I believe,
to be formed from the old part; or it may be developed within a wholly
distinct part of the body, as in the extreme cases of metagenesis. An eye,
for instance, may be developed at a spot where no eye previously existed.
We have also seen that allied organic beings in the course of their
metamorphoses sometimes attain nearly the same structure after passing
{389} through widely different forms; or conversely, after passing through
nearly the same early forms, arrive at a widely different termination. In
these cases it is very difficult to believe that the early cells or units
possess the inherent power, independently of any external agent, of
producing new structures wholly different in form, position, and function.
But these cases become plain on the hypothesis of pangenesis. The organic
units, during each stage of development, throw off gemmules, which,
multiplying, are transmitted to the offspring. In the offspring, as soon as
any particular cell or unit in the proper order of development becomes
partially developed, it unites with (or to speak metaphorically is
fertilised by) the gemmule of the next succeeding cell, and so onwards.
Now, supposing that at any stage of development, certain cells or
aggregates of cells had been slightly modified by the action of some
disturbing cause, the cast-off gemmules or atoms of the cell-contents could
hardly fail to be similarly affected, and consequently would reproduce the
same modification. This process might be repeated until the structure of
the part at this particular stage of development became greatly changed,
but this would not necessarily affect other parts whether previously or
subsequently developed. In this manner we can understand the remarkable
independence of structure in the successive metamorphoses, and especially
in the successive metageneses of many animals.

The term growth ought strictly to be confined to mere increase of size, and
development to change of structure.[916] Now, a child is said to grow into
a man, and a foal into a horse, but, as in these cases there is much change
of structure, the process properly belongs to the order of development. We
have indirect evidence of this in many variations and diseases supervening
during so-called growth at a particular period, and being inherited at a
corresponding period. In the case, however, of diseases which supervene
during old age, subsequently to the ordinary period of procreation, and
which nevertheless are sometimes inherited, as occurs with brain and heart
complaints, we {390} must suppose that the organs were in fact affected at
an earlier age and threw off at this period affected gemmules; but that the
affection became visible or injurious only after the prolonged growth of
the part in the strict sense of the word. In all the changes of structure
which regularly supervene during old age, we see the effects of
deteriorated growth, and not of true development.

In the so-called process of _alternate generation_ many individuals are
generated asexually during very early or later stages of development. These
individuals may closely resemble the preceding larval form, but generally
are wonderfully dissimilar. To understand this process we must suppose that
at a certain stage of development the gemmules are multiplied at an unusual
rate, and become aggregated by mutual affinity at many centres of
attraction, or buds. These buds, it may be remarked, must include gemmules
not only of all the succeeding but likewise of all the preceding stages of
development; for when mature they have the power of transmitting by sexual
generation gemmules of all the stages, however numerous these may be. It
was shown in the First Part, at least in regard to animals, that the new
beings which are thus at any period asexually generated do not retrograde
in development--that is, they do not pass through those earlier stages,
through which the fertilised germ of the same animal has to pass; and an
explanation of this fact was attempted as far as the final or teleological
cause is concerned. We can likewise understand the proximate cause, if we
assume, and the assumption is far from improbable, that buds, like
chopped-up fragments of a hydra, are formed of tissue which has already
passed through several of the earlier stages of development; for in this
case their component cells or units would not unite with the gemmules
derived from the earlier-formed cells, but only with those which came next
in the order of development. On the other hand, we must believe that, in
the sexual elements, or probably in the female alone, gemmules of certain
primordial cells are present; and these, as soon as their development
commences, unite in due succession with the gemmules of every part of the
body, from the first to the last period of life.

The principle of the independent formation of each part, in {391} so far as
its development depends on the union of the proper gemmules with certain
nascent cells, together with the superabundance of the gemmules derived
from both parents and self-multiplied, throws light on a widely different
group of facts, which on any ordinary view of development appears very
strange. I allude to organs which are abnormally multiplied or transposed.
Thus gold-fish often have supernumerary fins placed on various parts of
their bodies. We have seen that, when the tail of a lizard is broken off, a
double tail is sometimes reproduced, and when the foot of the salamander is
divided longitudinally, additional digits are occasionally formed. When
frogs, toads, &c., are born with their limbs doubled, as sometimes occurs,
the doubling, as Gervais remarks,[917] cannot be due to the complete fusion
of two embryos, with the exception of the limbs, for the larvæ are
limbless. The same argument is applicable[918] to certain insects produced
with multiple legs or antennæ, for these are metamorphosed from apodal or
antennæless larvæ. Alphonse Milne-Edwards[919] has described the curious
case of a crustacean in which one eye-peduncle supported, instead of a
complete eye, only an imperfect cornea, out of the centre of which a
portion of an antenna was developed. A case has been recorded[920] of a man
who had during both dentitions a double tooth in place of the left second
incisor, and he inherited this peculiarity from his paternal grandfather.
Several cases are known[921] of additional teeth having been developed in
the palate, more especially with horses, and in the orbit of the eye.
Certain breeds of sheep bear a whole crowd of horns on their foreheads.
Hairs occasionally appear in strange situations, as within the ears of the
Siamese hairy family; and hairs "quite natural in structure" have been
observed "within the substance of the brain."[922] As many as five spurs
have been seen on both legs in certain Game-fowls. In the Polish fowl the
male is ornamented with a topknot of hackles {392} like those on his neck,
whilst the female has one of common feathers. In feather-footed pigeons and
fowls, feathers like those on the wing arise from the outer side of the
legs and toes. Even the elemental parts of the same feather may be
transposed; for in the Sebastopol goose, barbules are developed on the
divided filaments of the shaft.

Analogous cases are of such frequent occurrence with plants that they do
not strike us with sufficient surprise. Supernumerary petals, stamens, and
pistils, are often produced. I have seen a leaflet low down in the compound
leaf of _Vicia sativa_ converted into a tendril, and a tendril possesses
many peculiar properties, such as spontaneous movement and irritability.
The calyx sometimes assumes, either wholly or by stripes, the colour and
texture of the corolla. Stamens are so frequently converted, more or less
completely, into petals, that such cases are passed over as not deserving
notice; but as petals have special functions to perform, namely, to protect
the included organs, to attract insects, and in not a few cases to guide
their entrance by well-adapted contrivances, we can hardly account for the
conversion of stamens into petals merely by unnatural or superfluous
nourishment. Again, the edge of a petal may occasionally be found including
one of the highest products of the plant, namely the pollen; for instance,
I have seen in an Ophrys a pollen-mass with its curious structure of little
packets, united together and to the caudicle by elastic threads, formed
between the edges of an upper petal. The segments of the calyx of the
common pea have been observed partially converted into carpels, including
ovules, and with their tips converted into stigmas. Numerous analogous
facts could be given.[923]

I do not know how physiologists look at such facts as the foregoing.
According to the doctrine of pangenesis, the free and superabundant
gemmules of the transposed organs are developed in the wrong place, from
uniting with wrong cells or aggregates of cells during their nascent state;
and this would follow from a slight modification in the elective affinity
of such cells, or possibly of certain gemmules. Nor ought we to feel much
surprise at the affinities of cells and gemmules varying {393} under
domestication, when we remember the many curious cases given, in the
seventeenth chapter, of cultivated plants which absolutely refuse to be
fertilised by their own pollen or by that of the same species, but are
abundantly fertile with pollen of a distinct species; for this implies that
their sexual elective affinities--and this is the term used by
Gärtner--have been modified. As the cells of adjoining or homologous parts
will have nearly the same nature, they will be liable to acquire by
variation each other's elective affinities; and we can thus to a certain
extent understand such cases as a crowd of horns on the heads in certain
sheep, of several spurs on the leg, and of hackles on the head of the fowl,
and with the pigeon the occurrence of wing-feathers on their legs and of
membrane between their toes; for the leg is the homologue of the wing. As
all the organs of plants are homologous and spring from a common axis, it
is natural that they should be eminently liable to transposition. It ought
to be observed that when any compound part, such as an additional limb or
an antenna, springs from a false position, it is only necessary that the
few first gemmules should be wrongly attached; for these whilst developing
would attract others in due succession, as in the regrowth of an amputated
limb. When parts which are homologous and similar in structure, as the
vertebræ in snakes or the stamens in polyandrous flowers, &c., are repeated
many times in the same organism, closely allied gemmules must be extremely
numerous, as well as the points to which they ought to become united; and,
in accordance with the foregoing views, we can to a certain extent
understand Isid. Geoffroy St. Hilaire's law, namely, that parts, which are
already multiple, are extremely liable to vary in number.

The same general principles apply to the fusion of homologous parts; and
with respect to mere cohesion there is probably always some degree of
fusion, at least near the surface. When two embryos during their early
development come into close contact, as both include corresponding
gemmules, which must be in all respects almost identical in nature, it is
not surprising that some derived from one embryo and some from the other
should unite at the point of contact with a single nascent cell or
aggregate of cells, and thus give rise to a single part or organ. For
instance, two embryos might thus come to have on their {394} adjoining
sides a single symmetrical arm, which in one sense will have been formed by
the fusion of the bones, muscles, &c., belonging to the arms of both
embryos. In the case of the fish described by Lereboullet, in which a
double head was seen gradually to fuse into a single one, the same process
must have taken place, together with the absorption of all the parts which
had been already formed. These cases are exactly the reverse of those in
which a part is doubled either spontaneously or after an injury; for in the
case of doubling, the superabundant gemmules of the same part are
separately developed in union with adjoining points; whilst in the case of
fusion the gemmules derived from two homologous parts become mingled and
form a single part; or it may be that the gemmules from one of two
adjoining embryos alone become developed.

       *       *       *       *       *

Variability often depends, as I have attempted to show, on the reproductive
organs being injuriously affected by changed conditions; and in this case
the gemmules derived from the various parts of the body are probably
aggregated in an irregular manner, some superfluous and others deficient.
Whether a superabundance of gemmules, together with fusion during
development, would lead to the increased size of any part cannot be told;
but we can see that their partial deficiency, without necessarily leading
to the entire abortion of the part, might cause considerable modifications;
for in the same manner as a plant, if its own pollen be excluded, is easily
hybridised, so, in the case of a cell, if the properly succeeding gemmules
were absent, it would probably combine easily with other and allied
gemmules. We see this in the case of imperfect nails growing on the stumps
of amputated fingers,[924] for the gemmules of the nails have manifestly
been developed at the nearest point.

In variations caused by the direct action of changed conditions, whether of
a definite or indefinite nature, as with the fleeces of sheep in hot
countries, with maize grown in cold countries, with inherited gout, &c.,
the tissues of the body, according to the doctrine of pangenesis, are
directly affected by the new conditions, and consequently throw off
modified gemmules, which are transmitted with their newly acquired
peculiarities to the offspring. On any ordinary view it is unintelligible
how changed {395} conditions, whether acting on the embryo, the young or
adult animal, can cause inherited modifications. It is equally or even more
unintelligible on any ordinary view, how the effects of the long-continued
use or disuse of any part, or of changed habits of body or mind, can be
inherited. A more perplexing problem can hardly be proposed; but on our
view we have only to suppose that certain cells become at last not only
functionally but structurally modified; and that these throw off similarly
modified gemmules. This may occur at any period of development, and the
modification will be inherited at a corresponding period; for the modified
gemmules will unite in all ordinary cases with the proper preceding cells,
and they will consequently be developed at the same period at which the
modification first arose. With respect to mental habits or instincts, we
are so profoundly ignorant on the relation between the brain and the power
of thought that we do not know whether an inveterate habit or trick induces
any change in the nervous system; but when any habit or other mental
attribute, or insanity, is inherited, we must believe that some actual
modification is transmitted;[925] and this implies, according to our
hypothesis, that gemmules derived from modified nerve-cells are transmitted
to the offspring.

It is generally, perhaps always, necessary that an organism should be
exposed during several generations to changed conditions or habits, in
order that any modification in the structure of the offspring should ensue.
This may be partly due to the changes not being at first marked enough to
catch the attention, but this explanation is insufficient; and I can
account for the fact, only by the assumption, which we shall see under the
head of reversion is strongly supported, that gemmules derived from each
cell before it had undergone the least modification are transmitted in
large numbers to successive generations, but that the gemmules derived from
the same cells after modification, naturally go on increasing under the
same favouring conditions, until at last they become sufficiently numerous
to overpower and supplant the old gemmules.

Another difficulty may be here noticed; we have seen that {396} there is an
important difference in the frequency, though not in the nature, of the
variations in plants propagated by sexual and asexual generation. As far as
variability depends on the imperfect action of the reproductive organs
under changed conditions, we can at once see why seedlings should be far
more variable than plants propagated by buds. We know that extremely slight
causes,--for instance, whether a tree has been grafted or grows on its own
stock, the position of the seeds within the capsule, and of the flowers on
the spike,--sometimes suffice to determine the variation of a plant, when
raised from seed. Now, it is probable, as explained when discussing
alternate generation, that a bud is formed of a portion of already
differentiated tissue; consequently an organism thus formed does not pass
through the earlier phases of development, and cannot be so freely exposed,
at the age when its structure would be most readily modified, to the
various causes inducing variability; but it is very doubtful whether this
is a sufficient explanation of the difficulty.

With respect to the tendency to reversion, there is a similar difference
between plants propagated from buds and seed. Many varieties, whether
originally produced from seed or buds, can be securely propagated by buds,
but generally or invariably revert by seed. So, also, hybridised plants can
be multiplied to any extent by buds, but are continually liable to
reversion by seed,--that is, to the loss of their hybrid or intermediate
character. I can offer no satisfactory explanation of this fact. Here is a
still more perplexing case: certain plants with variegated leaves, phloxes
with striped flowers, barberries with seedless fruit, can all be securely
propagated by the buds on cuttings; but the buds developed from the roots
of these cuttings almost invariably lose their character and revert to
their former condition.

Finally, we can see on the hypothesis of pangenesis that variability
depends on at least two distinct groups of causes. Firstly, on the
deficiency, superabundance, fusion, and transposition of gemmules, and on
the redevelopment of those which have long been dormant. In these cases the
gemmules themselves have undergone no modification; but the mutations in
the above respects will amply account for much fluctuating {397}
variability. Secondly, in the cases in which the organisation has been
modified by changed conditions, the increased use or disuse of parts, or
any other cause, the gemmules cast off from the modified units of the body
will be themselves modified, and, when sufficiently multiplied, will be
developed into new and changed structures.

       *       *       *       *       *

Turning now to Inheritance: if we suppose a homogeneous gelatinous
protozoon to vary and assume a reddish colour, a minute separated atom we
aid naturally, as it grew to full size, retain the same colour; and we
should have the simplest form of inheritance.[926] Precisely the same view
may be extended to the infinitely numerous and diversified units of which
the whole body in one of the higher animals is composed; and the separated
atoms are our gemmules. We have already sufficiently discussed the
inheritance of the direct effects of changed conditions, and of increased
use or disuse of parts, and, by implication, the important principle of
inheritance at corresponding ages. These groups of facts are to a large
extent intelligible on the hypothesis of pangenesis, and on no other
hypothesis as yet advanced.

A few words must be added on the complete abortion or suppression of
organs. When a part becomes diminished by disuse prolonged during many
generations, the principle of economy of growth, as previously explained,
will tend to reduce it still further; but this will not account for the
complete or almost complete obliteration of, for instance, a minute papilla
of cellular tissue representing a pistil, or of a microscopically minute
nodule of bone representing a tooth. In certain cases of suppression not
yet completed, in which a rudiment occasionally reappears through
reversion, diffused gemmules derived from this part must, according to our
view, still exist; hence we must suppose that the cells, in union with
which the rudiment was formerly developed, in these cases fail in their
affinity for such gemmules. But in the cases of complete and final abortion
the gemmules themselves no doubt have perished; nor is this {398} in any
way improbable, for, though a vast number of active and long-dormant
gemmules are diffused and nourished in each living creature, yet there must
be some limit to their number; and it appears natural that gemmules derived
from an enfeebled and useless rudiment would be more liable to perish than
those derived from other parts which are still in full functional activity.

With respect to mutilations, it is certain that a part may be removed or
injured during many generations, and no inherited result follow; and this
is an apparent objection to the hypothesis which will occur to every one.
But, in the first place, a being can hardly be intentionally mutilated
during its early stages of growth whilst in the womb or egg; and such
mutilations, when naturally caused, would appear like congenital
deficiencies, which are occasionally inherited. In the second place,
according to our hypothesis, gemmules multiply by self-division and are
transmitted from generation to generation; so that during a long period
they would be present and ready to reproduce a part which was repeatedly
amputated. Nevertheless it appears, from the facts given in the twelfth
chapter, that in some rare cases mutilations have been inherited, but in
most of these the mutilated surface became diseased. In this case it may be
conjectured that the gemmules of the lost part were gradually all attracted
by the partially diseased surface, and thus perished. Although this would
occur in the injured individual alone, and therefore in only one parent,
yet this might suffice for the inheritance of a mutilation, on the same
principle that a hornless animal of either sex, when crossed with a perfect
animal of the opposite sex, often transmits its deficiency.

The last subject that need here be discussed, namely Reversion, rests on
the principle that transmission and development, though generally acting in
conjunction, are distinct powers; and the transmission of gemmules and
their subsequent development show us how the existence of these two
distinct powers is possible. We plainly see this distinction in the many
cases in which a grandfather transmits to his grandson, through his
daughter, characters which she does not, or cannot, possess. Why the
development of certain characters, not necessarily in any way connected
with the reproductive organs, should be confined to one sex alone--that is,
why certain cells in one sex {399} should unite with and cause the
development of certain gemmules--we do not in the least know; but it is the
common attribute of most organic beings in which the sexes are separate.

The distinction between transmission and development is likewise seen in
all ordinary cases of Reversion; but before discussing this subject it may
be advisable to say a few words on those characters which I have called
latent, and which would not be classed under Reversion in its usual sense.
Most, or perhaps all, the secondary characters, which appertain to one sex,
lie dormant in the other sex; that is, gemmules capable of development into
the secondary male sexual characters are included within the female; and
conversely female characters in the male. Why in the female, when her
ovaria become diseased or fail to act, certain masculine gemmules become
developed, we do not clearly know, any more than why when a young bull is
castrated his horns continue growing until they almost resemble those of a
cow; or why, when a stag is castrated, the gemmules derived from the
antlers of his progenitors quite fail to be developed. But in many cases,
with variable organic beings, the mutual affinities of the cells and
gemmules become modified, so that parts are transposed or multiplied; and
it would appear that a slight change in the constitution of an animal, in
connection with the state of the reproductive organs, leads to changed
affinities in the tissues of various parts of the body. Thus, when male
animals first arrive at puberty, and subsequently during each recurrent
season, certain cells or parts acquire an affinity for certain gemmules,
which become developed into the secondary masculine characters; but if the
reproductive organs be destroyed, or even temporarily disturbed by changed
conditions, these affinities are not excited. Nevertheless, the male,
before he arrives at puberty, and during the season when the species does
not breed, must include the proper gemmules in a latent state. The curious
case formerly given of a Hen which assumed the masculine characters, not of
her own breed but of a remote progenitor, illustrates the connexion between
latent sexual characters and ordinary reversion. With those animals and
plants which habitually produce several forms, as with certain butterflies
described by Mr. Wallace, in which three female forms and {400} the male
exist, or as with the trimorphic species of Lythrum and Oxalis, gemmules
capable of reproducing several widely-different forms must be latent in
each individual.

The same principle of the latency of certain characters, combined with the
transposition of organs, may be applied to those singular cases of
butterflies and other insects, in which exactly one half or one quarter of
the body resembles the male, and the other half or three quarters the
female; and when this occurs the opposite sides of the body, separated from
each other by a distinct line, sometimes differ in the most conspicuous
manner. Again, these same principles apply to the cases given in the
thirteenth chapter, in which the right and left sides of the body differ to
an extraordinary degree, as in the spiral winding of certain shells, and as
in the genus Verruca among cirripedes; for in these cases it is known that
either side indifferently may undergo the same remarkable change of
development.

Reversion, in the ordinary sense of the word, comes into action so
incessantly, that it evidently forms an essential part of the general law
of inheritance. It occurs with beings, however propagated, whether by buds
or seminal generation, and sometimes may even be observed in the same
individual as it advances in age. The tendency to reversion is often
induced by a change of conditions, and in the plainest manner by the act of
crossing. Crossed forms are generally at first nearly intermediate in
character between their two parents; but in the next generation the
offspring generally revert to one or both of their grandparents, and
occasionally to more remote ancestors. How can we account for these facts?
Each organic unit in a hybrid must throw off, according to the doctrine of
pangenesis, an abundance of hybridised gemmules, for crossed plants can be
readily and largely propagated by buds; but by the same hypothesis there
will likewise be present dormant gemmules derived from both pure
parent-forms; and as these latter retain their normal condition, they
would, it is probable, be enabled to multiply largely during the lifetime
of each hybrid. Consequently the sexual elements of a hybrid will include
both pure and hybridised gemmules; and when two hybrids pair, the
combination of pure gemmules derived from the one hybrid with the pure
gemmules of the same parts derived from the other would {401} necessarily
lead to complete reversion of character; and it is, perhaps, not too bold a
supposition that unmodified and undeteriorated gemmules of the same nature
would be especially apt to combine. Pure gemmules in combination with
hybridised gemmules would lead to partial reversion. And lastly, hybridised
gemmules derived from both parent-hybrids would simply reproduce the
original hybrid form.[927] All these cases and degrees of reversion
incessantly occur.

It was shown in the fifteenth chapter that certain characters are
antagonistic to each other or do not readily blend together; hence, when
two animals with antagonistic characters are crossed, it might well happen
that a sufficiency of gemmules in the male alone for the reproduction of
his peculiar characters, and in the female alone for the reproduction of
her peculiar characters, would not be present; and in this case dormant
gemmules derived from some remote progenitor might easily gain the
ascendency, and cause the reappearance of long-lost characters. For
instance, when black and white pigeons, or black and white fowls, are
crossed,--colours which do not readily blend,--blue plumage in the one
case, evidently derived from the rock-pigeon, and red plumage in the other
case, derived from the wild jungle-cock, occasionally reappear. With
uncrossed breeds the same result would follow, under conditions which
favoured the multiplication and development of certain dormant gemmules, as
when animals become feral and revert to their pristine character. A certain
number of gemmules being requisite for the development of each character,
as is known to be the case from several spermatozoa or pollen-grains being
necessary for fertilisation, and time favouring their multiplication, will
together account for the curious cases, insisted on by Mr. Sedgwick, of
certain diseases regularly appearing in alternate generations. This
likewise holds good, more or less strictly, with other weakly inherited
modifications. Hence, as I have heard it remarked, certain diseases appear
actually to gain strength by the intermission of a generation. The
transmission of dormant gemmules during many successive generations is
hardly in itself more improbable, as {402} previously remarked, than the
retention during many ages of rudimentary organs, or even only of a
tendency to the production of a rudiment; but there is no reason to suppose
that all dormant gemmules would be transmitted and propagated for ever.
Excessively minute and numerous as they are believed to be, an infinite
number derived, during a long course of modification and descent, from each
cell of each progenitor, could not be supported or nourished by the
organism. On the other hand, it does not seem improbable that certain
gemmules, under favourable conditions, should be retained and go on
multiplying for a longer period than others. Finally, on the views here
given, we certainly gain some clear insight into the wonderful fact that
the child may depart from the type of both its parents, and resemble its
grandparents, or ancestors removed by many generations.

_Conclusion._

The hypothesis of Pangenesis, as applied to the several great classes of
facts just discussed, no doubt is extremely complex; but so assuredly are
the facts. The assumptions, however, on which the hypothesis rests cannot
be considered as complex in any extreme degree--namely, that all organic
units, besides having the power, as is generally admitted, of growing by
self-division, throw off free and minute atoms of their contents, that is
gemmules. These multiply and aggregate themselves into buds and the sexual
elements; their development depends on their union with other nascent cells
or units; and they are capable of transmission in a dormant state to
successive generations.

In a highly organised and complex animal, the gemmules thrown off from each
different cell or unit throughout the body must be inconceivably numerous
and minute. Each unit of each part, as it changes during development, and
we know that some insects undergo at least twenty metamorphoses, must throw
off its gemmules. All organic beings, moreover, include many dormant
gemmules derived from their grandparents and more remote progenitors, but
not from all their progenitors. These almost infinitely numerous and minute
gemmules must be included in each bud, ovule, spermatozoon, and
pollen-grain. Such an admission will be declared impossible; but, as
previously {403} remarked, number and size are only relative difficulties,
and the eggs or seeds produced by certain animals or plants are so numerous
that they cannot be grasped by the intellect.

The organic particles with which the wind is tainted over miles of space by
certain offensive animals must be infinitely minute and numerous; yet they
strongly affect the olfactory nerves. An analogy more appropriate is
afforded by the contagious particles of certain diseases, which are so
minute that they float in the atmosphere and adhere to smooth paper; yet we
know how largely they increase within the human body, and how powerfully
they act. Independent organisms exist which are barely visible under the
highest powers of our recently-improved microscopes, and which probably are
fully as large as the cells or units in one of the higher animals; yet
these organisms no doubt reproduce themselves by germs of extreme
minuteness, relatively to their own minute size. Hence the difficulty,
which at first appears insurmountable, of believing in the existence of
gemmules so numerous and so small as they must be according to our
hypothesis, has really little weight.

The cells or units of the body are generally admitted by physiologists to
be autonomous, like the buds on a tree, but in a less degree. I go one step
further and assume that they throw off reproductive gemmules. Thus an
animal does not, as a whole, generate its kind through the sole agency of
the reproductive system, but each separate cell generates its kind. It has
often been said by naturalists that each cell of a plant has the actual or
potential capacity of reproducing the whole plant; but it has this power
only in virtue of containing gemmules derived from every part. If our
hypothesis be provisionally accepted, we must look at all the forms of
asexual reproduction, whether occurring at maturity or as in the case of
alternate generation during youth, as fundamentally the same, and dependent
on the mutual aggregation and multiplication of the gemmules. The regrowth
of an amputated limb or the healing of a wound is the same process
partially carried out. Sexual generation differs in some important
respects, chiefly, as it would appear, in an insufficient number of
gemmules being aggregated within the separate sexual elements, and probably
in the presence of certain primordial cells. The development of each being,
including all the {404} forms of metamorphosis and metagenesis, as well as
the so-called growth of the higher animals, in which structure changes
though not in a striking manner, depends on the presence of gemmules thrown
off at each period of life, and on their development, at a corresponding
period, in union with preceding cells. Such cells may be said to be
fertilised by the gemmules which come next in the order of development.
Thus the ordinary act of impregnation and the development of each being are
closely analogous processes. The child, strictly speaking, does not grow
into the man, but includes germs which slowly and successively become
developed and form the man. In the child, as well as in the adult, each
part generates the same part for the next generation. Inheritance must be
looked at as merely a form of growth, like the self-division of a
lowly-organised unicellular plant. Reversion depends on the transmission
from the forefather to his descendants of dormant gemmules, which
occasionally become developed under certain known or unknown conditions.
Each animal and plant may be compared to a bed of mould full of seeds, most
of which soon germinate, some lie for a period dormant, whilst others
perish. When we hear it said that a man carries in his constitution the
seeds of an inherited disease, there is much literal truth in the
expression. Finally, the power of propagation possessed by each separate
cell, using the term in its largest sense, determines the reproduction, the
variability, the development and renovation of each living organism. No
other attempt, as far as I am aware, has been made, imperfect as this
confessedly is, to connect under one point of view these several grand
classes of facts. We cannot fathom the marvellous complexity of an organic
being; but on the hypothesis here advanced this complexity is much
increased. Each living creature must be looked at as a microcosm--a little
universe, formed of a host of self-propagating organisms, inconceivably
minute and as numerous as the stars in heaven.

       *       *       *       *       *


{405}

CHAPTER XXVIII.

CONCLUDING REMARKS.

    DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE
    AND DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES
    FAVOURABLE TO SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE
    QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY
    PREORDAINED.

As summaries have been added to nearly all the chapters, and as, in the
chapter on pangenesis, various subjects, such as the forms of reproduction,
inheritance, reversion, the causes and laws of variability, &c., have been
recently discussed, I will here only make a few general remarks on the more
important conclusions which may be deduced from the multifarious details
given throughout this work.

Savages in all parts of the world easily succeed in taming wild animals;
and those inhabiting any country or island, when first invaded by man,
would probably have been still more easily tamed. Complete subjugation
generally depends on an animal being social in its habits, and on receiving
man as the chief of the herd or family. Domestication implies almost
complete fertility under new and changed conditions of life, and this is
far from being invariably the case. An animal would not have been worth the
labour of domestication, at least during early times, unless of service to
man. From these circumstances the number of domesticated animals has never
been large. With respect to plants, I have shown in the ninth chapter how
their varied uses were probably first discovered, and the early steps in
their cultivation. Man could not have known, when he first domesticated an
animal or plant, whether it would flourish and multiply when transported to
other countries, therefore he could not have been thus influenced in his
choice. We see that the close adaptation of the reindeer and camel to
extremely cold and hot countries has not prevented their domestication.
Still less {406} could man have foreseen whether his animals and plants
would vary in succeeding generations and thus give birth to new races; and
the small capacity of variability in the goose and ass has not prevented
their domestication from the remotest epoch.

With extremely few exceptions, all animals and plants which have been long
domesticated, have varied greatly. It matters not under what climate, or
for what purpose, they are kept, whether as food for man or beast, for
draught or hunting, for clothing or mere pleasure,--under all these
circumstances domesticated animals and plants have varied to a much greater
extent than the forms which in a state of nature are ranked as one species.
Why certain animals and plants have varied more under domestication than
others we do not know, any more than why some are rendered more sterile
than others under changed conditions of life. But we frequently judge of
the amount of variation by the production of numerous and diversified
races, and we can clearly see why in many cases this has not occurred,
namely, because slight successive variations have not been steadily
accumulated; and such variations will never be accumulated when an animal
or plant is not closely observed, or much valued, or kept in large numbers.

The fluctuating, and, as far as we can judge, never-ending variability of
our domesticated productions,--the plasticity of their whole
organisation,--is one of the most important facts which we learn from the
numerous details given in the earlier chapters of this work. Yet
domesticated animals and plants can hardly have been exposed to greater
changes in their conditions than have many natural species during the
incessant geological, geographical, and climatal changes of the whole
world. The former will, however, commonly have been exposed to more sudden
changes and to less continuously uniform conditions. As man has
domesticated so many animals and plants belonging to widely different
classes, and as he certainly did not with prophetic instinct choose those
species which would vary most, we may infer that all natural species, if
subjected to analogous conditions, would, on an average, vary to the same
degree. Few men at the present day will maintain that animals and plants
were created with a tendency to vary, which long remained dormant, in order
that fanciers in after ages might {407} rear, for instance, curious breeds
of the fowl, pigeon, or canary-bird.

From several causes it is difficult to judge of the amount of modification
which our domestic productions have undergone. In some cases the primitive
parent-stock has become extinct, or cannot be recognised with certainty
owing to its supposed descendants having been so much modified. In other
cases two or more closely allied forms, after being domesticated, have
crossed; and then it is difficult to estimate how much of the change ought
to be attributed to variation. But the degree to which our domestic breeds
have been modified by the crossing of distinct natural forms has probably
been exaggerated by some authors. A few individuals of one form would
seldom permanently affect another form existing in much greater numbers;
for, without careful selection, the stain of the foreign blood would soon
be obliterated, and during early and barbarous times, when our animals were
first domesticated, such care would seldom have been taken.

There is good reason to believe that several of the breeds of the dog, ox,
pig, and of some other animals, are respectively descended from distinct
wild prototypes; nevertheless the belief in the multiple origin of our
domesticated animals has been extended by some few naturalists and by many
breeders to an unauthorised extent. Breeders refuse to look at the whole
subject under a single point of view; I have heard one, who maintained that
our fowls were the descendants of at least half-a-dozen aboriginal species,
protest that he was in no way concerned with the origin of pigeons, ducks,
rabbits, horses, or any other animal. They overlook the improbability of
many species having been domesticated at an early and barbarous period.
They do not consider the improbability of species having existed in a state
of nature which, if like our present domestic breeds, would have been
highly abnormal in comparison with all their congeners. They maintain that
certain species, which formerly existed, have become extinct or unknown,
although the world is now so much better known. The assumption of so much
recent extinction is no difficulty in their eyes; for they do not judge of
its probability by the facility or difficulty of the extinction of other
closely allied wild forms. Lastly, {408} they often ignore the whole
subject of geographical distribution as completely as if its laws were the
result of chance.

Although from the reasons just assigned it is often difficult to judge
accurately of the amount of change which our domesticated productions have
undergone, yet this can be ascertained in the cases in which we know that
all the breeds are descended from a single species, as with the pigeon,
duck, rabbit, and almost certainly with the fowl; and by the aid of analogy
this is to a certain extent possible in the case of animals descended from
several wild stocks. It is impossible to read the details given in the
earlier chapters, and in many published works, or to visit our various
exhibitions, without being deeply impressed with the extreme variability of
our domesticated animals and cultivated plants. I have in many instances
purposely given details on new and strange peculiarities which have arisen.
No part of the organisation escapes the tendency to vary. The variations
generally affect parts of small vital or physiological importance, but so
it is with the differences which exist between closely allied species. In
these unimportant characters there is often a greater difference between
the breeds of the same species than between the natural species of the same
genus, as Isidore Geoffroy has shown to be the case with size, and as is
often the case with the colour, texture, form, &c., of the hair, feathers,
horns, and other dermal appendages.

It has often been asserted that important parts never vary under
domestication, but this is a complete error. Look at the skull of the pig
in any one of the highly improved breeds, with the occipital condyles and
other parts greatly modified; or look at that of the niata ox. Or again, in
the several breeds of the rabbit, observe the elongated skull, with the
differently shaped occipital foramen, atlas, and other cervical vertebræ.
The whole shape of the brain, together with the skull, has been modified in
Polish fowls; in other breeds of the fowl the number of the vertebræ and
the forms of the cervical vertebræ have been changed. In certain pigeons
the shape of the lower jaw, the relative length of the tongue, the size of
the nostrils and eyelids, the number and shape of the ribs, the form and
size of the oesophagus, have all varied. In certain quadrupeds the length
of the intestines has been much increased or {409} diminished. With plants
we see wonderful differences in the stones of various fruits. In the
Cucurbitaceæ several highly important characters have varied, such as the
sessile position of the stigmas on the ovarium, the position of the carpels
within the ovarium, and its projection out of the receptacle. But it would
be useless to run through the many facts given in the earlier chapters.

It is notorious how greatly the mental disposition, tastes, habits,
consensual movements, loquacity or silence, and the tone of voice have
varied and been inherited with our domesticated animals. The dog offers the
most striking instance of changed mental attributes, and these differences
cannot be accounted for by descent from distinct wild types. New mental
characters have certainly often been acquired, and natural ones lost, under
domestication.

New characters may appear and disappear at any stage of growth, and be
inherited at a corresponding period. We see this in the difference between
the eggs of various breeds of the fowl, and in the down on chickens; and
still more plainly in the differences between the caterpillars and cocoons
of various breeds of the silk-moth. These facts, simple as they appear,
throw light on the characters which distinguish the larval and adult states
of natural species, and on the whole great subject of embryology. New
characters are liable to become attached exclusively to that sex in which
they first appeared, or they may be developed in a much higher degree in
the one than the other sex; or again, after having become attached to one
sex, they may be partially transferred to the opposite sex. These facts,
and more especially the circumstance that new characters seem to be
particularly liable, from some unknown cause, to become attached to the
male sex, have an important bearing on the acquirement by animals in a
state of nature of secondary sexual characters.

It has sometimes been said that our domestic productions do not differ in
constitutional peculiarities, but this cannot be maintained. In our
improved cattle, pigs, &c., the period of maturity, including that of the
second dentition, has been much hastened. The period of gestation varies
much, but has been modified in a fixed manner in only one or two cases. In
{410} our poultry and pigeons the acquirement of down and of the first
plumage by the young, and of the secondary sexual characters by the males,
differ. The number of moults through which the larvæ of silk-moths pass,
varies. The tendency to fatten, to yield much milk, to produce many young
or eggs at a birth or during life, differs in different breeds. We find
different degrees of adaptation to climate, and different tendencies to
certain diseases, to the attacks of parasites, and to the action of certain
vegetable poisons. With plants, adaptation to certain soils, as with some
kinds of plums, the power of resisting frost, the period of flowering and
fruiting, the duration of life, the period of shedding the leaves and of
retaining them throughout the winter, the proportion and nature of certain
chemical compounds in the tissues or seeds, all vary.

There is, however, one important constitutional difference between domestic
races and species; I refer to the sterility which almost invariably
follows, in a greater or less degree, when species are crossed, and to the
perfect fertility of the most distinct domestic races, with the exception
of a very few plants, when similarly crossed. It certainly appears a
remarkable fact that many closely allied species which in appearance differ
extremely little should yield when united only a few, more or less sterile
offspring, or none at all; whilst domestic races which differ conspicuously
from each other, are when united remarkably fertile, and yield perfectly
fertile offspring. But this fact is not in reality so inexplicable as it at
first appears. In the first place, it was clearly shown in the nineteenth
chapter that the sterility of crossed species does not closely depend on
differences in their external structure or general constitution, but
results exclusively from differences in the reproductive system, analogous
with those which cause the lessened fertility of the illegitimate unions
and illegitimate offspring of dimorphic and trimorphic plants. In the
second place, the Pallasian doctrine, that species after having been long
domesticated lose their natural tendency to sterility when crossed, has
been shown to be highly probable; we can scarcely avoid this conclusion
when we reflect on the parentage and present fertility of the several
breeds of the dog, of Indian and European cattle, sheep, and pigs. Hence it
would be unreasonable to expect that races formed under domestication {411}
should acquire sterility when crossed, whilst at the same time we admit
that domestication eliminates the normal sterility of crossed species. Why
with closely allied species their reproductive systems should almost
invariably have been modified in so peculiar a manner as to be mutually
incapable of acting on each other--though in unequal degrees in the two
sexes, as shown by the difference in fertility between reciprocal crosses
in the same species--we do not know, but may with much probability infer
the cause to be as follows. Most natural species have been habituated to
nearly uniform conditions of life for an incomparably longer period of time
than have domestic races; and we positively know that changed conditions
exert an especial and powerful influence on the reproductive system. Hence
this difference in habituation may well account for the different action of
the reproductive organs when domestic races and when species are crossed.
It is a nearly analogous fact, that most domestic races may be suddenly
transported from one climate to another, or be placed under widely
different conditions, and yet retain their fertility unimpaired; whilst a
multitude of species subjected to lesser changes are rendered incapable of
breeding.

With the exception of fertility, domestic varieties resemble species when
crossed in transmitting their characters in the same unequal manner to
their offspring, in being subject to the prepotency of one form over the
other, and in their liability to reversion. By repeated crosses a variety
or a species may be made completely to absorb another. Varieties, as we
shall see when we treat of their antiquity, sometimes inherit their new
characters almost, or even quite, as firmly as species. With both, the
conditions leading to variability and the laws governing its nature appear
to be the same. Domestic varieties can be classed in groups under groups,
like species under genera, and these under families and orders; and the
classification may be either artificial,--that is, founded on any arbitrary
character,--or natural. With varieties a natural classification is
certainly founded, and with species is apparently founded, on community of
descent, together with the amount of modification which the forms have
undergone. The characters by which domestic varieties differ from each
other are more {412} variable than those distinguishing species, though
hardly more so than with certain protean species; but this greater degree
of variability is not surprising, as varieties have generally been exposed
within recent times to fluctuating conditions of life, are much more liable
to have been crossed, and are still in many cases undergoing, or have
recently undergone, modification by man's methodical or unconscious
selection.

Domestic varieties as a general rule certainly differ from each other in
less important parts of their organisation than do species; and when
important differences occur, they are seldom firmly fixed; but this fact is
intelligible if we consider man's method of selection. In the living animal
or plant he cannot observe internal modifications in the more important
organs; nor does he regard them as long as they are compatible with health
and life. What does the breeder care about any slight change in the molar
teeth of his pigs, or for an additional molar tooth in the dog; or for any
change in the intestinal canal or other internal organ? The breeder cares
for the flesh of his cattle being well marbled with fat, and for an
accumulation of fat within the abdomen of his sheep, and this he has
effected. What would the floriculturist care for any change in the
structure of the ovarium or of the ovules? As important internal organs are
certainly liable to numerous slight variations, and as these would probably
be inherited, for many strange monstrosities are transmitted, man could
undoubtedly effect a certain amount of change in these organs. When he has
produced any modification in an important part, it has generally been
unintentionally in correlation with some other conspicuous part, as when he
has given ridges and protuberances to the skulls of fowls, by attending to
the form of the comb, and in the case of the Polish fowl to the plume of
feathers on the head. By attending to the external form of the
pouter-pigeon, he has enormously increased the size of the oesophagus, and
has added to the number of the ribs, and given them greater breadth. With
the carrier-pigeon, by increasing, through steady selection, the wattles on
the upper mandible, he has greatly modified the form of the lower mandible;
and so in many other cases. Natural species, on the other hand, have been
modified exclusively for their own good, to fit them for infinitely {413}
diversified conditions of life, to avoid enemies of all kinds, and to
struggle against a host of competitors. Hence, under such complex
conditions, it would often happen that modifications of the most varied
kinds, in important as well as in unimportant parts, would be advantageous
or even necessary; and they would slowly but surely be acquired through the
survival of the fittest. Various indirect modifications would likewise
arise through the law of correlated variation.

Domestic breeds often have an abnormal or semi-monstrous character, as the
Italian greyhound, bulldog, Blenheim spaniel, and bloodhound amongst
dogs,--some breeds of cattle and pigs, several breeds of the fowl, and the
chief breeds of the pigeon. The differences between such abnormal breeds
occur in parts which in closely-allied natural species differ but slightly
or not at all. This may be accounted for by man's often selecting,
especially at first, conspicuous and semi-monstrous deviations of
structure. We should, however, be cautious in deciding what deviations
ought to be called monstrous: there can hardly be a doubt that, if the
brush of horse-like hair on the breast of the turkey-cock had first
appeared on the domesticated bird, it would have been considered a
monstrosity; the great plume of feathers on the head of the Polish cock has
been thus designated, though plumes are common with many kinds of birds; we
might call the wattle or corrugated skin round the base of the beak of the
English carrier-pigeon a monstrosity, but we do not thus speak of the
globular fleshy excrescence at the base of the beak of the male _Carpophaga
oceanica_.

Some authors have drawn a wide distinction between artificial and natural
breeds; although in extreme cases the distinction is plain, in many other
cases an arbitrary line has to be drawn. The difference depends chiefly on
the kind of selection which has been applied. Artificial breeds are those
which have been intentionally improved by man; they frequently have an
unnatural appearance, and are especially liable to loss of excellence
through reversion and continued variability. The so-called natural breeds,
on the other hand, are those which are now found in semi-civilised
countries, and which formerly inhabited separate districts in nearly all
the European kingdoms. They have been rarely acted on by man's {414}
intentional selection; more frequently, it is probable, by unconscious
selection, and partly by natural selection, for animals kept in
semi-civilised countries have to provide largely for their own wants. Such
natural breeds will also, it may be presumed, have been directly acted on
to some extent by the differences, though slight, in the surrounding
physical conditions.

It is a much more important distinction that some breeds have been from
their first origin modified in so slow and insensible a manner, that if we
could see their early progenitors we should hardly be able to say when or
how the breed first arose; whilst other breeds have originated from a
strongly-marked or semi-monstrous deviation of structure, which, however,
may subsequently have been augmented by selection. From what we know of the
history of the racehorse, greyhound, gamecock, &c., and from their general
appearance, we may feel nearly confident that they were formed by a slow
process of improvement: and with the carrier-pigeon, as well as with some
other pigeons, we know that this has been the case. On the other hand, it
is certain that the ancon and mauchamp breeds of sheep, and almost certain
that the niata cattle, turnspit and pug-dogs, jumper and frizzled fowls,
short-faced tumbler pigeons, hook-billed ducks, &c., and with plants a
multitude of varieties, suddenly appeared in nearly the same state as we
now see them. The frequency of these cases is likely to lead to the false
belief that natural species have often originated in the same abrupt
manner. But we have no evidence of the appearance, or at least of the
continued procreation, under nature, of abrupt modifications of structure;
and various general reasons could be assigned against such a belief: for
instance, without separation a single monstrous variation would almost
certainly be soon obliterated by crossing.

On the other hand, we have abundant evidence of the constant occurrence
under nature of slight individual differences of the most diversified
kinds; and thus we are led to conclude that species have generally
originated by the natural selection, not of abrupt modifications, but of
extremely slight differences. This process may be strictly compared with
the slow and gradual improvement of the racehorse, greyhound, and gamecock.
As every detail of structure in each species is closely adapted to its
general {415} habits of life, it will rarely happen that one part alone
will be modified; but the co-adapted modifications, as formerly shown, need
not be absolutely simultaneous. Many variations, however, are from the
first connected by the law of correlation. Hence it follows that even
closely-allied species rarely or never differ from each other by some one
character alone; and this same remark applies to a certain extent to
domestic races; for these, if they differ much, generally differ in many
respects.

Some naturalists boldly insist[928] that species are absolutely distinct
productions, never passing by intermediate links into each other; whilst
they maintain that domestic varieties can always be connected either with
each other or with their parent-forms. But if we could always find the
links between the several breeds of the dog, horse, cattle, sheep, pigs,
&c., the incessant doubts whether they are descended from one or several
species would not have arisen. The greyhound genus, if such a term may be
used, cannot be closely connected with any other breed, unless, perhaps, we
go back to the ancient Egyptian monuments. Our English bulldog also forms a
very distinct breed. In all these cases crossed breeds must of course be
excluded, for the most distinct natural species can thus be connected. By
what links can the Cochin fowl be closely united with others? By searching
for breeds still preserved in distant lands, and by going back to
historical records, tumbler-pigeons, carriers, and barbs can be closely
connected with the parent rock-pigeon; but we cannot thus connect the
turbit or the pouter. The degree of distinctness between the various
domestic breeds depends on the amount of modification which they have
undergone, and especially on the neglect and final extinction of the
linking, intermediate, and less valued forms.

It has often been argued that no light is thrown, from the admitted changes
of domestic races, on the changes which natural species are believed to
undergo, as the former are said to be mere temporary productions, always
reverting, as soon as they become feral, to their pristine form. This
argument has been well combated by Mr. Wallace;[929] and full details were
given in the thirteenth chapter, showing that the tendency to reversion in
feral {416} animals and plants has been greatly exaggerated, though no
doubt to a certain extent it exists. It would be opposed to all the
principles inculcated in this work, if domestic animals, when exposed to
new conditions and compelled to struggle for their own wants against a host
of foreign competitors, were not in the course of time in some manner
modified. It should also be remembered that many characters lie latent in
all organic beings ready to be evolved under fitting conditions; and in
breeds modified within recent times the tendency to reversion is
particularly strong. But the antiquity of various breeds clearly proves
that they remain nearly constant as long as their conditions of life remain
the same.

It has been boldly maintained by some authors that the amount of variation
to which our domestic productions are liable is strictly limited; but this
is an assertion resting on little evidence. Whether or not the amount in
any particular direction is fixed, the tendency to general variability
seems unlimited. Cattle, sheep, and pigs have been domesticated and have
varied from the remotest period, as shown by the researches of Rütimeyer
and others, yet these animals have, within quite recent times, been
improved in an unparalleled degree; and this implies continued variability
of structure. Wheat, as we know from the remains found in the Swiss
lake-habitations, is one of the most anciently cultivated plants, yet at
the present day new and better varieties occasionally arise. It may be that
an ox will never be produced of larger size or finer proportions than our
present animals, or a race-horse fleeter than Eclipse, or a gooseberry
larger than the London variety; but he would be a bold man who would assert
that the extreme limit in these respects has been finally attained. With
flowers and fruit it has repeatedly been asserted that perfection has been
reached, but the standard has soon been excelled. A breed of pigeons may
never be produced with a beak shorter than that of the present short-faced
tumbler, or with one longer than that of the English carrier, for these
birds have weak constitutions and are bad breeders; but the shortness and
length of the beak are the points which have been steadily improved during
at least the last 150 years; and some of the best judges deny that the goal
has yet been reached. We may, also, reasonably suspect, from what {417} we
see in natural species of the variability of extremely modified parts, that
any structure, after remaining constant during a long series of
generations, would, under new and changed conditions of life, recommence
its course of variability, and might again be acted on by selection.
Nevertheless, as Mr. Wallace[930] has recently remarked with much force and
truth, there must be both with natural and domestic productions a limit to
change in certain directions; for instance, there must be a limit to the
fleetness of any terrestrial animal, as this will be determined by the
friction to be overcome, the weight to be carried, and the power of
contraction in the muscular fibres. The English racehorse may have reached
this limit; but it already surpasses in fleetness its own wild progenitor,
and all other equine species.

It is not surprising, seeing the great difference between many domestic
breeds, that some few naturalists have concluded that all are descended
from distinct aboriginal stocks, more especially as the principle of
selection has been ignored, and the high antiquity of man, as a breeder of
animals, has only recently become known. Most naturalists, however, freely
admit that various extremely dissimilar breeds are descended from a single
stock, although they do not know much about the art of breeding, cannot
show the connecting links, nor say where and when the breeds arose. Yet
these same naturalists will declare, with an air of philosophical caution,
that they can never admit that one natural species has given birth to
another until they behold all the transitional steps. But fanciers have
used exactly the same language with respect to domestic breeds; thus an
author of an excellent treatise says he will never allow that carrier and
fantail pigeons are the descendants of the wild rock-pigeon, until the
transitions have "actually been observed, and can be repeated whenever man
chooses to set about the task." No doubt it is difficult to realise that
slight changes added up during long centuries can produce such results; but
he who wishes to understand the origin of domestic breeds or natural
species must overcome this difficulty.

The causes inducing and the laws governing variability have been so lately
discussed, that I need here only enumerate the leading points. As
domesticated organisms are much more {418} liable to slight deviations of
structure and to monstrosities, than species living under their natural
conditions, and as widely-ranging species vary more than those which
inhabit restricted areas, we may infer that variability mainly depends on
changed conditions of life. We must not overlook the effects of the unequal
combination of the characters derived from both parents, nor reversion to
former progenitors. Changed conditions have an especial tendency to render
the reproductive organs more or less impotent, as shown in the chapter
devoted to this subject; and these organs consequently often fail to
transmit faithfully the parental characters. Changed conditions also act
directly and definitely on the organisation, so that all or nearly all the
individuals of the same species thus exposed become modified in the same
manner; but why this or that part is especially affected we can seldom or
never say. In most cases, however, of the direct action of changed
conditions, independently of the indirect variability caused by the
reproductive organs being affected, indefinite modifications are the
result; in nearly the same manner as exposure to cold or the absorption of
the same poison affects different individuals in various ways. We have
reason to suspect that an habitual excess of highly nutritious food, or an
excess relatively to the wear and tear of the organisation from exercise,
is a powerful exciting cause of variability. When we see the symmetrical
and complex outgrowths, caused by a minute atom of the poison of a
gall-insect, we may believe that slight changes in the chemical nature of
the sap or blood would lead to extraordinary modifications of structure.

The increased use of a muscle with its various attached parts, and the
increased activity of a gland or other organ, lead to their increased
development. Disuse has a contrary effect. With domesticated productions
organs sometimes become rudimentary through abortion; but we have no reason
to suppose that this has ever followed from mere disuse. With natural
species, on the contrary, many organs appear to have been rendered
rudimentary through disuse, aided by the principle of the economy of
growth, and by the hypothetical principle discussed in the last chapter,
namely, the final destruction of the germs or gemmules of such useless
parts. This difference may be partly {419} accounted for by disuse having
acted on domestic forms for an insufficient length of time, and partly from
their exemption from any severe struggle for existence, entailing rigid
economy in the development of each part, to which all species under nature
are subjected. Nevertheless the law of compensation or balancement
apparently affects, to a certain extent, our domesticated productions.

We must not exaggerate the importance of the definite action of changed
conditions in modifying all the individuals of the same species in the same
manner, or of use and disuse. As every part of the organisation is highly
variable, and as variations are so easily selected, both consciously and
unconsciously, it is very difficult to distinguish between the effects of
the selection of indefinite variations, and the direct action of the
conditions of life. For instance, it is possible that the feet of our
water-dogs, and of the American dogs which have to travel much over the
snow, may have become partially webbed from the stimulus of widely
extending their toes; but it is far more probable that the webbing, like
the membrane between the toes of certain pigeons, spontaneously appeared
and was afterwards increased by the best swimmers and the best
snow-travellers being preserved during many generations. A fancier who
wished to decrease the size of his bantams or tumbler-pigeons would never
think of starving them, but would select the smallest individuals which
spontaneously appeared. Quadrupeds are sometimes born destitute of hair,
and hairless breeds have been formed, but there is no reason to believe
that this is caused by a hot climate. Within the tropics heat often causes
sheep to lose their fleeces, and on the other hand wet and cold act as a
direct stimulus to the growth of hair; it is, however, possible that these
changes may merely be an exaggeration of the regular yearly change of coat;
and who will pretend to decide how far this yearly change, or the thick fur
of arctic animals, or as I may add their white colour, is due to the direct
action of a severe climate, and how far to the preservation of the best
protected individuals during a long succession of generations?

Of all the laws governing variability, that of correlation is the most
important. In many cases of slight deviations of structure as well as of
grave monstrosities, we cannot even {420} conjecture what is the nature of
the bond of connexion. But between homologous parts--between the fore and
hind limbs--between the hair, hoofs, horns, and teeth--we can see that
parts which are closely similar during their early development, and which
are exposed to similar conditions, would be liable to be modified in the
same manner. Homologous parts, from having the same nature, are apt to
blend together and, when many exist, to vary in number.

Although every variation is either directly or indirectly caused by some
change in the surrounding conditions, we must never forget that the nature
of the organisation which is acted on essentially governs the result.
Distinct organisms, when placed under similar conditions, vary in different
manners, whilst closely-allied organisms under dissimilar conditions often
vary in nearly the same manner. We see this in the same modification
frequently reappearing at long intervals of time in the same variety, and
likewise in the several striking cases given of analogous or parallel
varieties. Although some of these latter cases are simply due to reversion,
others cannot thus be accounted for.

From the indirect action of changed conditions on the organisation, through
the impaired state of the reproductive organs--from the direct action of
such conditions (and this will cause the individuals of the same species
either to vary in the same manner, or differently in accordance with slight
differences in their constitution)--from the effects of the increased or
decreased use of parts,--and from correlation,--the variability of our
domesticated productions is complicated in an extreme degree. The whole
organisation becomes slightly plastic. Although each modification must have
its proper exciting cause, and though each is subjected to law, yet we can
so rarely trace the precise relation between cause and effect, that we are
tempted to speak of variations as if they spontaneously arose. We may even
call them accidental, but this must be only in the sense in which we say
that a fragment of rock dropped from a height owes its shape to accident.

       *       *       *       *       *

It may be worth while briefly to consider the results of the exposure to
unnatural conditions of a large number of animals of the same species,
allowed to cross freely, with no selection of any {421} kind; and
afterwards to consider the results when selection is brought into play. Let
us suppose that 500 wild rock-pigeons were confined in their native land in
an aviary, and fed in the same manner as pigeons usually are; and that they
were not allowed to increase in number. As pigeons propagate so rapidly, I
suppose that a thousand or fifteen hundred birds would have to be annually
killed by mere chance. After several generations had been thus reared, we
may feel sure that some of the young birds would vary, and the variations
would tend to be inherited; for at the present day slight deviations of
structure often occur, but, as most breeds are already well established,
these modifications are rejected as blemishes. It would be tedious even to
enumerate the multitude of points which still go on varying or have
recently varied. Many variations would occur in correlation, as the length
of the wing and tail feathers--the number of the primary wing-feathers, as
well as the number and breadth of the ribs, in correlation with the size
and form of the body--the number of the scutellæ, with the size of the
feet--the length of the tongue, with the length of the beak--the size of
the nostrils and eyelids and the form of lower jaw in correlation with the
development of wattle--the nakedness of the young with the future colour of
the plumage--the size of the feet and beak, and other such points. Lastly,
as our birds are supposed to be confined in an aviary, they would use their
wings and legs but little, and certain parts of the skeleton, such as the
sternum and scapulæ and the feet, would in consequence become slightly
reduced in size.

As in our assumed case many birds have to be indiscriminately killed every
year, the chances are against any new variety surviving long enough to
breed. And as the variations which arise are of an extremely diversified
nature, the chances are very great against two birds pairing which have
varied in the same manner; nevertheless, a varying bird even when not thus
paired would occasionally transmit its character to its young; and these
would not only be exposed to the same conditions which first caused the
variation in question to appear, but would in addition inherit from their
one modified parent a tendency again to vary in the same manner. So that,
if the conditions decidedly tended to induce some particular variation, all
the birds might {422} in the course of time become similarly modified. But
a far commoner result would be, that one bird would vary in one way and
another bird in another way; one would be born with a little longer beak,
and another with a shorter beak; one would gain some black feathers,
another some white or red feathers. And as these birds would be continually
intercrossing, the final result would be a body of individuals differing
from each other slightly in many ways, yet far more than did the original
rock-pigeons. But there would not be the least tendency to the formation of
distinct breeds.

If two separate lots of pigeons were to be treated in the manner just
described, one in England and the other in a tropical country, the two lots
being supplied with different food, would they, after many generations had
passed, differ? When we reflect on the cases given in the twenty-third
chapter, and on such facts as the difference in former times between the
breeds of cattle, sheep, &c., in almost every district of Europe, we are
strongly inclined to admit that the two lots would be differently modified
through the influence of climate and food. But the evidence on the definite
action of changed conditions is in most cases insufficient; and, with
respect to pigeons, I have had the opportunity of examining a large
collection of domesticated birds, sent to me by Sir W. Elliot from India,
and they varied in a remarkably similar manner with our European birds.

If two distinct breeds were to be confined together in equal numbers, there
is reason to suspect that they would to a certain extent prefer pairing
with their own kind; but they would likewise intercross. From the greater
vigour and fertility of the crossed offspring, the whole body would by this
means become interblended sooner than would otherwise have occurred. From
certain breeds being prepotent over others, it does not follow that the
interblended progeny would be strictly intermediate in character. I have,
also, proved that the act of crossing in itself gives a strong tendency to
reversion, so that the crossed offspring would tend to revert to the state
of the aboriginal rock-pigeon. In the course of time they would probably be
not much more heterogeneous in character than in our first case, when birds
of the same breed were confined together. {423}

I have just said that the crossed offspring would gain in vigour and
fertility. From the facts given in the seventeenth chapter there can be no
doubt of this; and there can be little doubt, though the evidence on this
head is not so easily acquired, that long-continued close interbreeding
leads to evil results. With hermaphrodites of all kinds, if the sexual
elements of the same individual habitually acted on each other, the closest
possible interbreeding would be perpetual. Therefore we should bear in mind
that with all hermaphrodite animals, as far as I can learn, their structure
permits and frequently necessitates a cross with a distinct individual.
With hermaphrodite plants we incessantly meet with elaborate and perfect
contrivances for this same end. It is no exaggeration to assert that, if
the use of the talons and tusks of a carnivorous animal, or the use of the
viscid threads of a spider's web, or of the plumes and hooks on a seed may
be safely inferred from their structure, we may with equal safety infer
that many flowers are constructed for the express purpose of ensuring a
cross with a distinct plant. From these various considerations, the
conclusion arrived at in the chapter just referred to--namely, that great
good of some kind is derived from the sexual concourse of distinct
individuals--must be admitted.

To return to our illustration: we have hitherto assumed that the birds were
kept down to the same number by indiscriminate slaughter; but if the least
choice be permitted in their preservation and slaughter, the whole result
will be changed. Should the owner observe any slight variation in one of
his birds, and wish to obtain a breed thus characterised, he would succeed
in a surprisingly short time by carefully selecting and pairing the young.
As any part which has once varied generally goes on varying in the same
direction, it is easy, by continually preserving the most strongly marked
individuals, to increase the amount of difference up to a high,
predetermined standard of excellence. This is methodical selection.

If the owner of the aviary, without any thought of making a new breed,
simply admired, for instance, short-beaked more than long-beaked birds, he
would, when he had to reduce the number, generally kill the latter; and
there can be no doubt that he would thus in the course of time sensibly
modify his {424} stock. It is improbable, if two men were to keep pigeons
and act in this manner, that they would prefer exactly the same characters;
they would, as we know, often prefer directly opposite characters, and the
two lots would ultimately come to differ. This has actually occurred with
strains or families of cattle, sheep, and pigeons, which have been long
kept and carefully attended to by different breeders without any wish on
their part to form new and distinct sub-breeds. This unconscious kind of
selection will more especially come into action with animals which are
highly serviceable to man; for every one tries to get the best dog, horse,
cow, or sheep, and these animals will transmit more or less surely their
good qualities to their offspring. Hardly any one is so careless as to
breed from his worst animals. Even savages, when compelled from extreme
want to kill some of their animals, would destroy the worst and preserve
the best. With animals kept for use and not for mere amusement, different
fashions prevail in different districts, leading to the preservation, and
consequently to the transmission, of all sorts of trifling peculiarities of
character. The same process will have been pursued with our fruit-trees and
vegetables, for the best will always have been the most largely cultivated,
and will occasionally have yielded seedlings better than their parents.

The different strains, just alluded to, which have been raised by different
breeders without any wish for such a result, and the unintentional
modification of foreign breeds in their new homes, both afford excellent
evidence of the power of unconscious selection. This form of selection has
probably led to far more important results than methodical selection, and
is likewise more important under a theoretical point of view from closely
resembling natural selection. For during this process the best or most
valued individuals are not separated and prevented crossing with others of
the same breed, but are simply preferred and preserved; but this inevitably
leads during a long succession of generations to their increase in number
and to their gradual improvement; so that finally they prevail to the
exclusion of the old parent-form.

With our domesticated animals natural selection checks the production of
races with any injurious deviation of {425} structure. In the case of
animals kept by savages and semi-civilised people, which have to provide
largely for their own wants under different circumstances, natural
selection will probably play a more important part. Hence such animals
often closely resemble natural species.

As there is no limit to man's desire to possess animals and plants more and
more useful in any respect, and as the fancier always wishes, from fashion
running into extremes, to produce each character more and more strongly
pronounced, there is a constant tendency in every breed, through the
prolonged action of methodical and unconscious selection, to become more
and more different from its parent-stock; and when several breeds have been
produced and are valued for different qualities, to differ more and more
from each other. This leads to Divergence of Character. As improved
sub-varieties and races are slowly formed, the older and less improved
breeds are neglected and decrease in number. When few individuals of any
breed exist within the same locality, close interbreeding, by lessening
their vigour and fertility, aids in their final extinction. Thus the
intermediate links are lost, and breeds which have already diverged gain
Distinctness of Character.

In the chapters on the Pigeon, it was proved by historical details and by
the existence of connecting sub-varieties in distant lands that several
breeds have steadily diverged in character, and that many old and
intermediate sub-breeds have become extinct. Other cases could be adduced
of the extinction of domestic breeds, as of the Irish wolf-dog, the old
English hound, and of two breeds in France, one of which was formerly
highly valued.[931] Mr. Pickering remarks[932] that "the sheep figured on
the most ancient Egyptian monuments is unknown at the present day; and at
least one variety of the bullock, formerly known in Egypt, has in like
manner become extinct." So it has been with some animals, and with several
plants cultivated by the ancient inhabitants of Europe during the neolithic
period. In Peru, Von Tschudi[933] found in certain tombs, apparently prior
to the dynasty of the Incas, two kinds of maize not now known in the
country. With our flowers and culinary vegetables, {426} the production of
new varieties and their extinction has incessantly recurred. At the present
time improved breeds sometimes displace at an extraordinarily rapid rate
older breeds; as has recently occurred throughout England with pigs. The
Long-horn cattle in their native home were "suddenly swept away as if by
some murderous pestilence," by the introduction of Short-horns.[934]

What grand results have followed from the long-continued action of
methodical and unconscious selection, checked and regulated to a certain
extent by natural selection, is seen on every side of us. Compare the many
animals and plants which are displayed at our exhibitions with their
parent-forms when these are known, or consult old historical records with
respect to their former state. Almost all our domesticated animals have
given rise to numerous and distinct races, excepting those which cannot be
easily subjected to selection--such as cats, the cochineal insect, and the
hive-bee,--and excepting those animals which are not much valued. In
accordance with what we know of the process of selection, the formation of
our many races has been slow and gradual. The man who first observed and
preserved a pigeon with its oesophagus a little enlarged, its beak a little
longer, or its tail a little more expanded than usual, never dreamed that
he had made the first step in the creation of the pouter, carrier, and
fantail-pigeon. Man can create not only anomalous breeds, but others with
their whole structure admirably co-ordinated for certain purposes, such as
the race-horse and dray-horse, or the greyhound. It is by no means
necessary that each small change of structure throughout the body, leading
towards excellence, should simultaneously arise and be selected. Although
man seldom attends to differences in organs which are important under a
physiological point of view, yet he has so profoundly modified some breeds,
that assuredly, if found wild, they would be ranked under distinct genera.

The best proof of what selection has effected is perhaps afforded by the
fact that whatever part or quality in any animal, and more especially in
any plant, is most valued by man, that part or quality differs most in the
several races. This result is well seen by comparing the amount of
difference {427} between the fruits produced by the varieties of the same
fruit-tree, between the flowers of the varieties in our flower-garden,
between the seeds, roots, or leaves of our culinary and agricultural
plants, in comparison with the other and not valued parts of the same
plants. Striking evidence of a different kind is afforded by the fact
ascertained by Oswald Heer,[935] namely, that the seeds of a large number
of plants,--wheat, barley, oats, peas, beans, lentils, poppies,--cultivated
for their seed by the ancient Lake-inhabitants of Switzerland, were all
smaller than the seeds of our existing varieties. Rütimeyer has shown that
the sheep and cattle which were kept by the earlier Lake-inhabitants were
likewise smaller than our present breeds. In the middens of Denmark, the
earliest dog of which the remains have been found was the weakest; this was
succeeded during the Bronze age by a stronger kind, and this again during
the Iron age by one still stronger. The sheep of Denmark during the Bronze
period had extraordinarily slender limbs, and the horse was smaller than
our present animal.[936] No doubt in these cases the new and larger breeds
were generally introduced from foreign lands by the immigration of new
hordes of men. But it is not probable that each larger breed, which in the
course of time supplanted a previous and smaller breed, was the descendant
of a distinct and larger species; it is far more probable that the domestic
races of our various animals were gradually improved in different parts of
the great Europæo-Asiatic continent, and thence spread to other countries.
This fact of the gradual increase in size of our domestic animals is all
the more striking as certain wild or half-wild animals, such as red-deer,
aurochs, park-cattle, and boars,[937] have within nearly the same period
decreased in size.

The conditions favourable to selection by man are,--the closest attention
being paid to every character,--long-continued perseverance,--facility in
matching or separating animals,--and especially a large number being kept,
so that the inferior individuals may be freely rejected or destroyed, and
the better ones preserved. When many are kept there will also be a {428}
greater chance of the occurrence of well-marked deviations of structure.
Length of time is all-important; for as each character, in order to become
strongly pronounced, has to be augmented by the selection of successive
variations of the same nature, this can only be effected during a long
series of generations. Length of time will, also, allow any new feature to
become fixed by the continued rejection of those individuals which revert
or vary, and the preservation of those which inherit the new character.
Hence, although some few animals have varied rapidly in certain respects
under new conditions of life, as dogs in India and sheep in the West
Indies, yet all the animals and plants which have produced strongly marked
races were domesticated at an extremely remote epoch, often before the dawn
of history. As a consequence of this, no record has been preserved of the
origin of our chief domestic breeds. Even at the present day new strains or
sub-breeds are formed so slowly that their first appearance passes
unnoticed. A man attends to some particular character, or merely matches
his animals with unusual care, and after a time a slight difference is
perceived by his neighbours;--the difference goes on being augmented by
unconscious and methodical selection, until at last a new sub-breed is
formed, receives a local name, and spreads; but, by this time, its history
is almost forgotten. When the new breed has spread widely, it gives rise to
new strains and sub-breeds, and the best of these succeed and spread,
supplanting other and older breeds; and so always onwards in the march of
improvement.

When a well-marked breed has once been established, if not supplanted by
still improving sub-breeds, and if not exposed to greatly changed
conditions of life, inducing further variability or reversion to long-lost
characters, it may apparently last for an enormous period. We may infer
that this is the case from the high antiquity of certain races; but some
caution is necessary on this head, for the same variation may appear
independently after long intervals of time, or in distant places. We may
safely assume that this has occurred with the turnspit-dog which is figured
on the ancient Egyptian monuments, with the solid-hoofed swine[938]
mentioned by Aristotle, with five-toed fowls {429} described by Columella,
and certainly with the nectarine. The dogs represented on the Egyptian
monuments, about 2000 B.C., show us that some of the chief breeds then
existed, but it is extremely doubtful whether any are identically the same
with our present breeds. A great mastiff sculptured on an Assyrian tomb,
640 B.C., is said to be the same with the dog still imported into the same
region from Thibet. The true greyhound existed during the Roman classical
period. Coming down to a later period, we have seen that, though most of
the chief breeds of the pigeon existed between two and three centuries ago,
they have not all retained to the present day exactly the same character;
but this has occurred in certain cases in which improvement was not
desired, for instance in the case of the Spot or the Indian ground-tumbler.

De Candolle[939] has fully discussed the antiquity of various races of
plants; he states that the black-seeded poppy was known in the time of
Homer, the white-seeded sesamum by the ancient Egyptians, and almonds with
sweet and bitter kernels by the Hebrews; but it does not seem improbable
that some of these varieties may have been lost and reappeared. One variety
of barley and apparently one of wheat, both of which were cultivated at an
immensely remote period by the Lake-inhabitants of Switzerland, still
exist. It is said[940] that "specimens of a small variety of gourd which is
still common in the market of Lima were exhumed from an ancient cemetery in
Peru." De Candolle remarks that, in the books and drawings of the sixteenth
century, the principal races of the cabbage, turnip, and gourd can be
recognised; this might have been expected at so late a period, but whether
any of these plants are absolutely identical with our present sub-varieties
is not certain. It is, however, said that the Brussels sprout, a variety
which in some places is liable to degeneration, has remained genuine for
more than four centuries in the district where it is believed to have
originated.[941]

       *       *       *       *       *

In accordance with the views maintained by me in this work and elsewhere,
not only the various domestic races, but the {430} most distinct genera and
orders within the same great class,--for instance, whales, mice, birds, and
fishes--are all the descendants of one common progenitor, and we must admit
that the whole vast amount of difference between these forms of life has
primarily arisen from simple variability. To consider the subject under
this point of view is enough to strike one dumb with amazement. But our
amazement ought to be lessened when we reflect that beings, almost infinite
in number, during an almost infinite lapse of time, have often had their
whole organisation rendered in some degree plastic, and that each slight
modification of structure which was in any way beneficial under excessively
complex conditions of life, will have been preserved, whilst each which was
in any way injurious will have been rigorously destroyed. And the
long-continued accumulation of beneficial variations will infallibly lead
to structures as diversified, as beautifully adapted for various purposes,
and as excellently co-ordinated, as we see in the animals and plants all
around us. Hence I have spoken of selection as the paramount power, whether
applied by man to the formation of domestic breeds, or by nature to the
production of species. I may recur to the metaphor given in a former
chapter: if an architect were to rear a noble and commodious edifice,
without the use of cut stone, by selecting from the fragments at the base
of a precipice wedge-formed stones for his arches, elongated stones for his
lintels, and flat stones for his roof, we should admire his skill and
regard him as the paramount power. Now, the fragments of stone, though
indispensable to the architect, bear to the edifice built by him the same
relation which the fluctuating variations of each organic being bear to the
varied and admirable structures ultimately acquired by its modified
descendants.

Some authors have declared that natural selection explains nothing, unless
the precise cause of each slight individual difference be made clear. Now,
if it were explained to a savage utterly ignorant of the art of building,
how the edifice had been raised stone upon stone, and why wedge-formed
fragments were used for the arches, flat stones for the roof, &c.; and if
the use of each part and of the whole building were pointed out, it would
be unreasonable if he declared that nothing had been {431} made clear to
him, because the precise cause of the shape of each fragment could not be
given. But this is a nearly parallel case with the objection that selection
explains nothing, because we know not the cause of each individual
difference in the structure of each being.

The shape of the fragments of stone at the base of our precipice may be
called accidental, but this is not strictly correct; for the shape of each
depends on a long sequence of events, all obeying natural laws; on the
nature of the rock, on the lines of deposition or cleavage, on the form of
the mountain which depends on its upheaval and subsequent denudation, and
lastly on the storm or earthquake which threw down the fragments. But in
regard to the use to which the fragments may be put, their shape may be
strictly said to be accidental. And here we are led to face a great
difficulty, in alluding to which I am aware that I am travelling beyond my
proper province. An omniscient Creator must have foreseen every consequence
which results from the laws imposed by Him. But can it be reasonably
maintained that the Creator intentionally ordered, if we use the words in
any ordinary sense, that certain fragments of rock should assume certain
shapes so that the builder might erect his edifice? If the various laws
which have determined the shape of each fragment were not predetermined for
the builder's sake, can it with any greater probability be maintained that
He specially ordained for the sake of the breeder each of the innumerable
variations in our domestic animals and plants;--many of these variations
being of no service to man, and not beneficial, far more often injurious,
to the creatures themselves? Did He ordain that the crop and tail-feathers
of the pigeon should vary in order that the fancier might make his
grotesque pouter and fantail breeds? Did He cause the frame and mental
qualities of the dog to vary in order that a breed might be formed of
indomitable ferocity, with jaws fitted to pin down the bull for man's
brutal sport? But if we give up the principle in one case,--if we do not
admit that the variations of the primeval dog were intentionally guided in
order that the greyhound, for instance, that perfect image of symmetry and
vigour, might be formed,--no shadow of reason can be assigned for the
belief that variations, alike in nature and the result {432} of the same
general laws, which have been the groundwork through natural selection of
the formation of the most perfectly adapted animals in the world, man
included, were intentionally and specially guided. However much we may wish
it, we can hardly follow Professor Asa Gray in his belief "that variation
has been led along certain beneficial lines," like a stream "along definite
and useful lines of irrigation." If we assume that each particular
variation was from the beginning of all time preordained, the plasticity of
organisation, which leads to many injurious deviations of structure, as
well as that redundant power of reproduction which inevitably leads to a
struggle for existence, and, as a consequence, to the natural selection or
survival of the fittest, must appear to us superfluous laws of nature. On
the other hand, an omnipotent and omniscient Creator ordains everything and
foresees everything. Thus we are brought face to face with a difficulty as
insoluble as is that of free will and predestination.

       *       *       *       *       *


{433}

                  INDEX.

  ABBAS Pacha, a fancier of fantailed pigeons, i. 206.
  ABBEY, Mr., on grafting, ii. 147;
    on mignonette, ii. 237.
  ABBOTT, Mr. Keith, on the Persian tumbler pigeon, i. 150.
  ABBREVIATION of the facial bones, i. 73.
  ABORTION of organs, ii. 315-318, 397.
  ABSORPTION of minority in crossed races, ii. 87-89, 174.
  ACCLIMATISATION, ii. 305-315;
    of maize, i. 322.
  ACERBI, on the fertility of domestic animals in Lapland, ii. 112.
  _Achatinella_, ii. 53.
  _Achillea millefolium_, bud variation in, i. 408.
  _Aconitum napellus_, roots of, innocuous in cold climates, ii. 274.
  _Acorus calamus_, sterility of, ii. 170.
  ACOSTA, on fowls in South America at its discovery, i. 237.
  _Acropera_, number of seeds in, ii. 379.
  ADAM, Mr., origin of _Cytisus Adami_, i. 390.
  ADAM, W., on consanguineous marriages, ii. 123.
  ADAMS, Mr., on hereditary diseases, ii. 7.
  ADVANCEMENT in scale of organisation, i. 8.
  _Ægilops triticoides_, observations of Fabre and Godron on, i. 313;
    increasing fertility of hybrids of, with wheat, ii. 110.
  _Æsculus flava_ and _rubicunda_, i. 392.
  _Æsculus pavia_, tendency of, to become double, ii. 168.
  _Æthusa cynapium_, ii. 337.
  AFFINITY, sexual elective, ii. 180.
  AFRICA, white bull from, i. 91;
    feral cattle in, i. 85;
    food-plants of savages of, i. 307-309;
    South, diversity of breeds of cattle in, i. 80;
    West, change in fleece of sheep in, i. 98.
  _Agave vivipara_, seeding of, in poor soil, ii. 169.
  AGE, changes in trees, dependent on, i. 387.
  AGOUTI, fertility of, in captivity, ii. 152.
  AGRICULTURE, antiquity of, ii. 243.
  _Agrostis_, seeds of, used as food, i. 309.
  AGUARA, i. 26.
  AINSWORTH, Mr., on the change in the hair of animals at Angora, ii. 278.
  AKBAR Khan, his fondness for pigeons, i. 205; ii. 204.
  _Alauda arvensis_, ii. 154.
  ALBIN, on "Golden Hamburgh" fowls, i. 247;
    figure of the hook-billed duck, i. 277.
  ALBINISM, i. 111, ii. 17.
  ALBINO, negro, attacked by insects, ii. 229.
  ALBINOES, heredity of, ii. 9.
  ALBINUS, thickness of the epidermis on the palms of the hands in man, ii.
      297.
  ALCO, i. 31, ii. 102.
  ALDROVANDI, on rabbits, i. 104;
    description of the nun pigeon, i. 156;
    on the fondness of the Dutch for pigeons in the seventeenth century, i.
        205;
    notice of several varieties of pigeons, i. 207-210;
    on the breeds of fowls, i. 247;
    on the origin of the domestic duck, i. 278.
  ALEFIELD, Dr., on the varieties of peas and their specific unity, i. 326;
    on the varieties of beans, i. 330.
  ALEXANDER the Great, his selection of Indian cattle, ii. 202.
  ALGÆ, retrogressive metamorphosis in, ii. 361;
    division of zoospores of, ii. 378.
  ALLEN, W., on feral fowls, i. 237; ii. 33.
  ALLMAN, Professor, on a monstrous _Saxifraga geum_, ii. 166;
    on the development of the Hydroida, ii. 368.
  ALMOND, i. 337;
    antiquity of, ii. 429;
    bitter, not eaten by mice, ii. 232.
  _Alnus glutinosa_ and _incana_, hybrids of, ii. 130.
  ALPACA, selection of, ii. 208.
  _Althæa rosea_, i. 378, ii. 107.
  _Amaryllis_, ii. 139.
  _Amaryllis vittata_, effect of foreign pollen on, i. 400.
  AMAUROSIS, hereditary, ii. 9.
  AMERICA, limits within which no useful plants have been furnished by, i.
      310;
    colours of feral horses in, i. 60-61;
    North, native cultivated plants of, i. 312;
    skin of feral pig from, i. 77;
    South, variations in cattle of, i. 88, 92.
  _Amygdalus persica_, i. 336-344, 374.
  {434}
  AMMON, on the persistency of colour in horses, ii. 21.
  _Anagallis arvensis_, ii. 190.
  ANALOGOUS variation, i. 409, ii. 348-352;
    in horses, i. 55;
    in the horse and ass, i. 64;
    in fowls, i. 243-246.
  _Anas boschas_, i. 277, ii. 40;
    skull of, figured, i. 282.
  _Anas moschata_, ii. 40.
  "ANCON" sheep of Massachusetts, i. 100, ii. 103.
  ANDALUSIAN fowls, i. 227.
  ANDALUSIAN rabbits, i. 105.
  ANDERSON, J., on the origin of British sheep, i. 94;
    on the selection of qualities in cattle, ii. 196;
    on a one-eared breed of rabbits, i. 108;
    on the inheritance of characters from a one-eared rabbit and
        three-legged bitch, ii. 12;
    on the persistency of varieties of peas, i. 329;
    on the production of early peas by selection, ii. 201;
    on the varieties of the potato, i. 330-331;
    on crossing varieties of the melon, i. 399;
    on reversion in the barberry, i. 384.
  ANDERSON, Mr., on the reproduction of the weeping ash by seed, ii. 19;
    on the cultivation of the tree pæony in China, ii. 205.
  ANDERSSON, Mr., on the Damara, Bechuana, and Namaqua cattle, i. 88;
    on the cows of the Damaras, ii. 300;
    selection practised by the Damaras and Namaquas, ii. 207;
    on the use of grass-seeds and the roots of reeds as food in South
        Africa, i. 309.
  _Anemone coronaria_, doubled by selection, ii. 200.
  ANGINA pectoris, hereditary, occurring at a certain age, ii. 79.
  ANGLESEA, cattle of, i. 80.
  ANGOLA sheep, i. 95.
  ANGORA, change in hair of animals at, ii. 278;
    cats of, i. 45, 47;
    rabbits of, i. 106, 120.
  ANIMALS, domestication of, facilitated by fearlessness of man, i. 20;
    refusal of wild, to breed in captivity, ii. 149;
    compound, individual peculiarities of, reproduced by budding, i. 374;
    variation by selection in useful qualities of, ii. 220.
  ANNUAL plants, rarity of bud-variation in, i. 408.
  ANOMALIES in the osteology of the horse, i. 50.
  ANOMALOUS breeds of pigs, i. 75;
    of cattle, i. 89.
  _Anser albifrons_, characters of, reproduced in domestic geese, i. 288.
  _Anser ægyptiacus_, i. 282; ii. 68.
  _Anser canadensis_, ii. 157.
  _Anser cygnoides_, i. 237.
  _Anser ferus_, the original of the domestic goose, i. 287;
    fertility of cross of, with domestic goose, i. 288.
  ANSON, on feral fowls in the Ladrones, i. 238.
  ANTAGONISM between growth and reproduction, ii. 384.
  _Anthemis nobilis_, bud-variation in flowers of, i. 379;
    becomes single in poor soil, ii. 167.
  ANTHEROZOIDS, apparent independence of, in algæ, ii. 384.
  ANTHERS, contabescence of, ii. 165-166.
  ANTIGUA, cats of, i. 46;
    changed fleece of sheep in, i. 98.
  _Antirrhinum majus_, peloric, i. 365; ii. 59, 70, 166;
    double-flowered, ii. 167;
    bud-variation in, i. 381.
  ANTS, individual recognition of, ii. 251.
  APES, anthropomorphous, ii. 123.
  APHIDES, attacking pear-trees, ii. 231;
    development of, ii. 361-362.
  APOPLEXY, hereditary, occurring at a certain age, ii. 78.
  APPLE, i. 348-350;
    fruit of, in Swiss lake-dwellings, i. 317;
    rendered fastigate by heat in India, i. 361;
    bud-variation in the, i. 376;
    with dimidiate fruit, i. 392-393;
    with two kinds of fruit on the same branch, i. 392;
    artificial fecundation of, i. 401;
    St. Valéry, i. 401; ii. 166;
    reversion in seedlings of, ii. 31;
    crossing of varieties of, ii. 129;
    growth of the, in Ceylon, ii. 277;
    Winter Majetin, not attacked by _coccus_, ii. 231;
    flower-buds of, attacked by bullfinches, ii. 232;
    American, change of when grown in England, ii. 275.
  APRICOT, i. 344-345;
    glands on the leaves of, ii. 231;
    analogous variation in the, ii. 348.
  _Aquila fusca_, copulating in captivity, ii. 154.
  _Aquilegia vulgaris_, i. 365; ii. 330.
  ARAB boarhound, described by Harcourt, i. 17.
  _Arabis blepharophylla_ and _A. Soyeri,_ effects of crossing, i. 400.
  _Aralia trifoliata_, bud-variation in leaves of, i. 382.
  ARAUCARIAS, young, variable resistance of, to frost, ii. 309.
  ARCHANGEL pigeon, ii. 240.
  ARCTIC regions, variability of plants and shells of, ii. 256.
  _Aria vestita_, grafted on thorns, i. 387.
  ARISTOPHANES, fowls mentioned by, i. 246.
  ARISTOTLE, on solid-hoofed pigs, i. 75;
    domestic duck unknown to, i. 277;
    on the assumption of male characters by old hens, ii. 51.
  {435}
  ARNI, domestication of the, i. 82.
  ARREST of development, ii. 315-318.
  ARTERIES, increase of anastomosing branches of, when tied, ii. 230.
  ARU islands, wild pig of, i. 67.
  ARUM, Polynesian varieties of, ii. 256.
  _Ascaris_, number of eggs of, ii. 379.
  ASH, varieties of the, i. 360;
    weeping, i. 361;
    simple-leaved, i. 362;
    bud-variation in, i. 382;
    effects of graft upon the stock in the, i. 394;
    production of the blotched Breadalbane, _ibid._;
    weeping, capricious reproduction of, by seed, ii. 19.
  _Asinus Burchellii_, i. 64.
  _Asinus hemionus_, ii. 43.
  _Asinus indicus_, ii. 42-43, 48.
  _Asinus quagga_, i. 64.
  _Asinus tæniopus_, ii. 41;
    the original of the domestic ass, i. 62.
  ASPARAGUS, increased fertility of cultivated, ii. 113.
  ASS, early domestication of the, i. 62;
    breeds of, _ibid._;
    small size of, in India, _ibid._;
    stripes of, i. 62-63; ii. 351;
    dislike of to cross water, i. 181;
    reversion in, ii. 41-43, 47;
    hybrid of the, with mare and zebra, ii. 42;
    prepotency of the, over the horse, ii. 67-68;
    crossed with wild ass, ii. 206;
    variation and selection of the, ii. 236.
  ASSYRIAN sculpture of a mastiff, i. 17.
  ASTERS, ii. 20, 316.
  ASTHMA, hereditary, ii. 8, 79.
  ATAVISM. _See_ Reversion.
  ATHELSTAN, his care of horses, ii. 203.
  ATKINSON, Mr., on the sterility of the Tarroo silk-moth in confinement,
      ii. 157.
  AUBERGINE, ii. 91.
  AUDUBON, on feral hybrid ducks, i. 190; ii. 46;
    on the domestication of wild ducks on the Mississippi, i. 278;
    on the wild cock turkey visiting domestic hens, i. 292;
    fertility of _Fringilla ciris_ in captivity, ii. 154;
    fertility of _Columba migratoria_ and _leucocephala_ in captivity, ii.
        155;
    breeding of _Anser canadensis_ in captivity, ii. 157.
  AUDUBON and Bachman, on the change of coat in _Ovis montana_, i. 99;
    sterility of _Sciurus cinerea_ in confinement, ii. 152.
  AURICULA, effect of seasonal conditions on the, ii. 273;
    blooming of, ii. 346.
  AUSTRALIA, no generally useful plants derived from, i. 310;
    useful plants of, enumerated by Hooker, i. 311.
  AUSTRIA, heredity of character in emperors of, ii. 65.
  AUTENRIETH, on persistency of colour in horses, ii. 21.
  AVA, horses of, i. 53.
  _Avena fatua_, cultivability of, i. 313.
  AYEEN Akbery, pigeons mentioned in the, i. 150, 155, 185, 205, 207, 208.
  AYRES, W. P., on bud-variation in pelargoniums, i. 378.
  _Azalea indica_, bud-variation in, i. 377.
  AZARA, on the feral dogs of La Plata, i. 27;
    on the crossing of domestic with wild cats in Paraguay, i. 45;
    on hornlike processes in horses, i. 50;
    on curled hair in horses, i. 54; ii. 205, 325;
    on the colours of feral horses, i. 60, 61; ii. 259;
    on the cattle of Paraguay and La Plata, i. 82, 86, 89; ii. 250;
    on a hornless bull, ii. 205;
    on the increase of cattle in South America, ii. 119;
    on the growth of horns in the hornless cattle of Corrientes, ii. 39;
    on the "Niata" cattle, i. 90;
    on naked quadrupeds, ii. 279;
    on a race of black-skinned fowls in South America, i. 258; ii. 209;
    on a variety of maize, i. 321.

  BABINGTON, C. C., on the origin of the plum, i. 345;
    British species of the genus _Rosa_, i. 366;
    distinctness of _Viola lutea_ and _tricolor_, i. 368.
  BACHMANN, Mr., on the turkey, ii. 262.
    _See also_ Audubon.
  BADGER, breeding in confinement, ii. 151.
  "BAGADOTTEN-TAUBE," i. 141.
  BAILY, Mr., on the effect of selection on fowls, ii. 198;
    on Dorking fowls, ii. 238.
  BAIRD, S., on the origin of the turkey, i. 292.
  BAKER, Mr., on heredity in the horse, ii. 11;
    on the degeneration of the horse by neglect, ii. 239;
    orders of Henrys VII. and VIII. for the destruction of undersized
        mares, ii. 203.
  BAKEWELL, change in the sheep effected by, ii. 198.
  BALANCEMENT, ii. 342-344;
    of growth, law of, i. 274.
  BALDHEAD, pigeon, i. 151.
  BALDNESS, in man, inherited, ii. 73-74;
    with deficiency in teeth, ii. 326-327.
  BALLANCE, Mr., on the effects of interbreeding on fowls, ii. 125;
    on variation in the eggs of fowls, i. 248.
  _Ballota nigra_, transmission of variegated leaves in, i. 383.
  BAMBOO, varieties of the, ii. 256.
  BANANA, variation of the, i. 372; ii. 256, 258;
    bud-variation in the, i. 377;
    sterility of the, ii. 268.
  BANTAM fowls, i. 230;
    Sebright, origin of, ii. 96;
    sterility of, ii. 101.
  BARB (Pigeon), i. 144-146, 210; ii. 227;
  {436}
    figure of, i. 145;
    figure of lower jaw of, i. 164.
  BARBS, of wheat, i. 314.
  BARBERRY, dark or red-leaved variety, i. 362; ii. 19;
    reversion in suckers of seedless variety, i. 384.
  BARBUT, J., on the dogs of Guinea, i. 25;
    on the domestic pigeons in Guinea, i. 186;
    fowls not native in Guinea, i. 237.
  BARKING, acquisition of the habit of, by various dogs, i. 27.
  BARLEY, wild, i. 313;
    of the lake-dwellings, i. 317-318;
    ancient variety of, ii. 429.
  BARNES, Mr., production of early peas by selection, ii. 201.
  BARNET, Mr., on the intercrossing of strawberries, i. 351;
    dioeciousness of the Hautbois strawberry, i. 353;
    on the scarlet American strawberry, ii. 200.
  BARTH, Dr., use of grass-seeds as food in Central Africa, i. 308.
  BARTLETT, A. D., on the origin of "Himalayan" rabbits by intercrossing,
      i. 109;
    on the feral rabbits of Porto Santo, i. 114;
    on geese with reversed feathers on the head and neck, i. 288;
    on the young of the black-shouldered peacock, i. 290;
    on the breeding of the Felidæ in captivity, ii. 150.
  BARTRAM, on the black wolf-dog of Florida, i. 22.
  BATES, H. W., refusal of wild animals to breed in captivity, ii. 150,
      152;
    sterility of American monkeys in captivity, ii. 153;
    sterility of tamed guans, ii. 156.
  BATRACHIA, regeneration of lost parts in, ii. 15.
  BEACH, raised, in Peru, containing heads of maize, i. 320.
  BEAK, variability of, in fowls, i. 258;
    individual differences of, in pigeons, i. 160;
    correlation of, with the feet in pigeons, i. 171-174.
  BEALE, Lionel, on the contents of cells, ii. 370;
    on the multiplication of infectious atoms, ii. 378;
    on the origin of fibres, ii. 382.
  BEANS, i. 330;
    of Swiss lake-dwellings, i. 319;
    varieties of, produced by selection, ii. 218;
    French and scarlet, variable resistance of to frost, ii. 309, 314;
    superiority of native seed of, ii. 314;
    a symmetrical variation of scarlet, ii. 322;
    experiments on kidney, i. 330;
    with monstrous stipules and abortive leaflets, ii. 343.
  BEARD, pigeon, i. 151.
  BEARS, breeding in captivity, ii. 151.
  BEASLEY, J., reversion in crossed cattle, ii. 41.
  BEATON, D., effect of soil upon strawberries, i. 353;
    on varieties of pelargonium, i. 364, ii. 274, 311;
    bud-variation in _Gladiolus colvillii_, i. 382;
    cross between Scotch kail and cabbage, ii. 98;
    hybrid gladiolus, ii. 139;
    constant occurrence of new forms among seedlings, ii. 235;
    on the doubling of the compositæ, ii. 316.
  BECHUANA cattle, i. 88.
  BECK, Mr., constitutional differences in pelargoniums, i. 364.
  BECKMANN, on changes in the odours of plants, ii. 274.
  BECKSTEIN, on the burrowing of wolves, i. 27;
    "Spitz" dog, i. 31;
    origin of the Newfoundland dog, i. 42;
    crossing of domestic and wild swine, i. 66;
    on the Jacobin pigeon, i. 154, 209;
    notice of swallow-pigeons, i. 156;
    on a fork-tailed pigeon, i. 157;
    variations in the colour of the croup in pigeons, i. 184;
    on the German dove-cot pigeon, i. 185;
    fertility of mongrel pigeons, i. 192;
    on hybrid turtle-doves, i. 193;
    on crossing the pigeon with _Columba oenas_, _C. palumbus_, _Turtur
        risoria_, and _T. vulgaris_, i. 193;
    development of spurs in the silk-hen, i. 256;
    on Polish fowls, i. 257, 264;
    on crested birds, i. 257;
    on the Canary-bird, i. 295, ii. 22, 161;
    German superstition about the turkey, i. 293;
    occurrence of horns in hornless breeds of sheep, ii. 30;
    hybrids of the horse and ass, ii. 68;
    crosses of tailless fowls, ii. 92;
    difficulty of pairing dove-cot and fancy pigeons, ii. 103;
    fertility of tame ferrets and rabbits, ii. 112;
    fertility of wild sow, _ibid._;
    difficulty of breeding caged birds, ii. 154;
    comparative fertility of _Psittacus erithacus_ in captivity, ii. 155;
    on changes of plumage in captivity, ii. 158;
    liability of light-coloured cattle to the attacks of flies, ii. 229;
    want of exercise a cause of variability, ii. 257;
    effect of privation of light upon the plumage of birds, ii. 280;
    on a sub-variety of the monk-pigeon, ii. 350.
  BEDDOE, Dr., correlation of complexion with consumption, ii. 335.
  BEDEGUAR gall, ii. 284.
  BEE, persistency of character of, ii. 236, 254;
    intercrossing, ii. 126;
    conveyance, of pollen of peas by, i. 329.
  BEE-OPHRYS, self-fertilisation of, ii. 91.
  BEECH, dark-leaved, i. 362, ii. 19;
    fern-leaved, reversion of, i. 382;
    weeping, non-production of by seed, ii. 19.
  BEECHEY, horses of Loochoo Islands, i. 53.
  BEET, i. 326;
    increase of sugar in, by selection, ii. 201.
  {437}
  _Begonia frigida_, singular variety of, i. 365;
    sterility of, ii. 166.
  BELGIAN rabbit, i. 106.
  BELL, T., statement that white cattle have coloured ears, i. 85.
  BELL, W., bud-variation in _Cistus tricuspis_, i. 377.
  BELLINGERI, observations on gestation in the dog, i. 30;
    on the fertility of dogs and cats, ii. 112.
  BELON, on high-flying pigeons in Paphlagonia, i. 209;
    varieties of the goose, i. 289.
  BENGUELA, cattle of, i. 88.
  BENNETT, Dr. G., pigs of the Pacific islands, i. 70, 87;
    dogs of the Pacific islands, i. 87;
    varieties of cultivated plants in Tahiti, ii. 256.
  BENNETT, Mr., on the fallow deer, ii. 103.
  BENTHAM, G., number and origin of cultivated plants, i. 306;
    cereals all cultivated varieties, i. 312;
    species of the orange group, i. 334-335;
    distinctions of almond and peach, i. 338;
    British species of _Rosa_, i. 366;
    identity of _Viola lutea_ and _tricolor_, i. 368.
  _Berberis vulgaris_, i. 384, ii. 19.
  _Berberis Wallichii_, indifference of, to climate, ii. 164.
  BERJEAN, on the history of the dog, i. 16, 18.
  BERKELEY, G. F., production of hen-cocks in a strain of game-fowls, i.
      253.
  BERKELEY, M. J., crossing of varieties of the pea, i. 397;
    effect of foreign pollen on grapes, i. 400;
    on hybrid plants, ii. 131;
    analogy between pollen of highly-cultivated plants and hybrids, ii.
        268;
    on Hungarian kidney-beans, ii. 275;
    failure of Indian wheat in England, ii. 307;
    bud developed on the petal of a _Clarkia_, ii. 384.
  BERNARD, inheritance of disease in the horse, ii. 10.
  BERNARD, C., independence of the organs of the body, ii. 368-369;
    special affinities of the tissues, ii. 380.
  BERNHARDI, varieties of plants with laciniated leaves, ii. 348.
  _Bernicla antarctica_, i. 288.
  BERTERO, on feral pigeons in Juan Fernandez, i. 190.
  _Betula alba_, ii. 18.
  BEWICK, on the British wild cattle, i. 84.
  BIBLE, reference to breeding studs of horses in, i. 54;
    references to domestic pigeons in the, i. 205;
    indications of selection of sheep in the, ii. 201;
    notice of mules in the, ii. 202.
  BIDWELL, Mr., on self-impotence in _Amaryllis_, ii. 139.
  BIRCH, weeping, i. 387, ii. 18.
  BIRCH, Dr. S., on the ancient domestication of the pigeon in Egypt, i.
      205;
    notice of bantam fowls in a Japanese encyclopædia, i. 230, 247.
  BIRCH, Wyrley, on silver-grey rabbits, i. 109-110.
  BIRDS, sterility caused in, by change of conditions, ii. 153-157.
  BLADDER-NUT, tendency of the, to become double, ii. 168.
  BLAINE, Mr., on wry-legged terriers, ii. 245.
  BLAINVILLE, origin and history of the dog, i. 15-16;
    variations in the number of teeth in dogs, i. 34;
    variations in the number of toes in dogs, i. 35;
    on mummies of cats, i. 43;
    on the osteology of solid-hoofed pigs, i. 75;
    on feral Patagonian and N. American pigs, i. 77.
  "BLASS-TAUBE," i. 156.
  BLEEDING, hereditary, ii. 7, 8;
    sexual limitation of excessive, ii. 73.
  BLENDING of crossed races, time occupied by the, ii. 87.
  BLINDNESS, hereditary, ii. 9;
    at a certain age, ii. 78;
    associated with colour of hair, ii. 328.
  BLOODHOUNDS, degeneration of, caused by interbreeding, ii. 121.
  BLUMENBACH, on the protuberance of the skull in Polish fowls, i. 257;
    on the effect of circumcision, ii. 23;
    inheritance of a crooked finger, ii. 23;
    on badger-dogs and other varieties of the dog, ii. 220;
    on _Hydra_, ii. 293;
    on the "nisus formativus," ii. 294.
  BLYTH, E., on the Pariah dog, i. 24;
    hybrids of dog and jackal, i. 32;
    early domestication of cats in India, i. 43;
    origin of domestic cat, _ib._;
    crossing of domestic and wild cats, i. 44;
    on Indian cats resembling _Felis chaus_, i. 45;
    on striped Burmese ponies, i. 58;
    on the stripes of the ass, i. 63;
    on Indian wild pigs, i. 66;
    on humped cattle, i. 79, 80;
    occurrence of _Bos frontosus_ in Irish crannoges, i. 81;
    fertile crossing of zebus and common cattle, i. 83;
    on the species of sheep, i. 94;
    on the fat-tailed Indian sheep, i. 96;
    origin of the goat, i. 101;
    on rabbits breeding in India, i. 112;
    number of tail-feathers in fantails, i. 146;
    Lotan tumbler pigeons, i. 150;
    number of tail-feathers in _Ectopistes_, i. 159;
    on _Columba affinis_, i. 183;
    pigeons roosting in trees, i. 181;
    on _Columba leuconota_, i. 182;
    on _Columba intermedia_ of Strickland, i. 184;
    variation in colour of croup in pigeons, i. 184-185, 197;
    voluntary domestication of rock-pigeons in India, i. 185;
    feral pigeons on the Hudson, i. 190;
  {438}
    occurrence of sub-species of pigeons, i. 204;
    notice of pigeon-fanciers in Delhi, &c., i. 206;
    hybrids of _Gallus Sonneratii_ and the domestic hen, i. 234;
    supposed hybridity of _Gallus Temminckii_, i. 235;
    variations and domestication of _Gallus bankiva_, i. 235-236, 237;
    crossing of wild and tame fowls in Burmah, i. 236;
    restricted range of the larger gallinaceous birds, i. 237;
    feral fowls in the Nicobar islands, i. 238;
    black-skinned fowls occurring near Calcutta, i. 256;
    weight of _Gallus bankiva_, i. 272;
    degeneration of the turkey in India, i. 294, ii. 278;
    on the colour of gold-fish, i. 296;
    on the Ghor-Khur (_Asinus indicus_), ii. 42;
    on _Asinus hemionus_, ii. 43;
    number of eggs of _Gallus bankiva_, ii. 112;
    on the breeding of birds in captivity, ii. 157;
    co-existence of large and small breeds in the same country, ii. 279;
    on the drooping ears of the elephant, ii. 301;
    homology of leg and wing feathers, ii. 323.
  BOETHIUS on Scotch wild cattle, i. 85.
  BOITARD and Corbié, on the breeds of pigeons, i. 132;
    Lille pouter pigeon, i. 138;
    notice of a gliding pigeon, i. 156;
    variety of the pouter pigeon, i. 162;
    dove-cot pigeon, i. 185;
    crossing pigeons, i. 192-193, ii. 97, 126;
    sterility of hybrids of turtle-doves, i. 193;
    reversion of crossed pigeons, i. 197, ii. 40;
    on the fantail, i. 208, ii. 66;
    on the trumpeter, ii. 66;
    prepotency of transmission in silky fantail, ii. 67, 69;
    secondary sexual characters in pigeons, ii. 74;
    crossing of white and coloured turtle-doves, ii. 92;
    fertility of pigeons, ii. 112.
  BOMBYCIDÆ, wingless females of, ii. 299.
  _Bombyx hesperus_, ii. 304.
  _Bombyx Huttoni_, i. 302.
  _Bombyx mori_, i. 300-304.
  BONAFOUS, on maize, i. 320, 321.
  BONAPARTE, number of species of Columbidæ, i. 133;
    number of tail-feathers in pigeons, i. 158;
    size of the feet in Columbidæ, i. 174;
    on _Columba guinea_, i. 182;
    _Columba turricola_, _rupestris_, and _Schimperi_, i. 184.
  _Bonatea speciosa_, development of ovary of, i. 403.
  BONAVIA, Dr., growth of cauliflowers in India, ii. 310.
  BONES, removal of portions of, ii. 296;
    regeneration of, ii. 294;
    growth and repair of, ii. 381-382.
  BONNET, on the salamander, ii. 15, 341, 358, 385;
    theory of reproduction, ii. 385.
  BORCHMEYER, experiments with the seeds of the weeping ash, ii. 19.
  BORECOLE, i. 323.
  BORELLI, on Polish fowls, i. 247.
  BORNEO, fowls of, with tail-bands, i. 235.
  BORNET, E., condition of the ovary in hybrid _Cisti_, i. 389;
    self-impotence of hybrid _Cisti_, ii. 140.
  BORROW, G., on pointers, i. 42.
  BORY de Saint-Vincent, on gold-fish, i. 297.
  _Bos_, probable origin of European domestic cattle from three species of,
      i. 83.
  _Bos frontosus_, i. 79, 81-82.
  _Bos indicus_, i. 79.
  _Bos longifrons_, i. 79, 81.
  _Bos primigenius_, i. 79-81, 119.
  _Bos sondaicus_, ii. 206.
  _Bos taurus_, i. 79.
  _Bos trochoceros_, i. 81.
  BOSC, heredity in foliage-varieties of the elm, i. 362.
  BOSSE, production of double flowers from old seed, ii. 167.
  BOSSI, on breeding dark-coloured silkworms, i. 302.
  BOUCHARDAT, on the vine disease, i. 334.
  BOUDIN, on local diseases, ii. 276;
    resistance to cold of dark-complexioned men, ii. 335.
  "BOULANS," i. 137.
  "BOUTON d'Alep," ii. 276.
  BOWEN, Prof., doubts as to the importance of inheritance, ii. 3.
  BOWMAN, Mr., hereditary peculiarities in the human eye, ii. 8-10;
    hereditary cataract, ii. 79.
  BRACE, Mr., on Hungarian cattle, i. 80.
  _Brachycome iberidifolia_, ii. 261.
  BRACTS, unusual development of, in gooseberries, i. 355.
  BRADLEY, Mr., effect of grafts upon the stock in the ash, i. 394;
    effect of foreign pollen upon apples, i. 401;
    on change of soil, ii. 146.
  "BRAHMA Pootras," a new breed of fowls, i. 245.
  BRAIN, proportion of, in hares and rabbits, i. 126-129.
  BRANDT, origin of the goat, i. 101.
  _Brassica_, varieties of, with enlarged stems, ii. 348.
  _Brassica asperifolia_, ii. 343.
  _Brassica napus_, i. 325.
  _Brassica oleracea_, i. 323.
  _Brassica rapa_, i. 325, ii. 165.
  BRAUN, A., bud-variation in the vine, i. 375;
    in the currant, i. 376;
    in _Mirabilis jalapa_, i. 382;
    in _Cytisus adami_, i. 388;
    on reversion in the foliage of trees, i. 382;
    spontaneous production of _Cytisus purpureo-elongatus_, i. 390;
    reversion of flowers by stripes and blotches, ii. 37;
    excess of nourishment a source of variability, ii. 257.
  {439}
  BRAZIL, cattle of, i. 88.
  BREAD-FRUIT, varieties of, ii. 256;
    sterility and variability of, ii. 262.
  BREE, W. T., bud-variation in _Geranium pratense_ and _Centaurea cyanus_,
      i. 379;
    by tubers in the dahlia, i. 385;
    on the deafness of white cats with blue eyes, ii. 329.
  BREEDING, high, dependent on inheritance, ii. 3-4.
  BREEDS, domestic, persistency of, ii. 246, 428-429;
    artificial and natural, ii. 413-414;
    extinction of, ii. 425;
    of domestic cats, i. 45-47;
    of pigs produced by crossing, i. 78;
    of cattle, i. 86-87, 91-93;
    of goats, i. 101.
  BREHM, on _Columba amaliæ_, i. 183.
  BRENT, B. P., number of mammæ in rabbits, i. 106;
    habits of the tumbler pigeon, i. 151;
    Laugher pigeon, i. 155;
    colouring of the kite tumbler, i. 160;
    crossing of the pigeon with _Columba oenas_, i. 193;
    mongrels of the trumpeter pigeon, ii. 66;
    close interbreeding of pigeons, ii. 126;
    opinion on Aldrovandi's fowls, i. 247;
    on stripes in chickens, i. 249-250;
    on the combs of fowls, i. 253;
    double-spurred Dorking fowls, i. 255;
    effect of crossing on colour of plumage in fowls, i. 258;
    incubatory instinct of mongrels between non-sitting varieties of fowls,
        ii. 44;
    origin of the domestic duck, i. 277;
    fertility of the hook-billed duck, _ibid._;
    occurrence of the plumage of the wild duck in domestic breeds, i. 280;
    voice of ducks, i. 281;
    occurrence of a short upper mandible in crosses of hook-billed and
        common ducks, i. 281;
    reversion in ducks produced by crossing, ii. 40;
    variation of the canary-bird, i. 295;
    fashion in the canary, ii. 240;
    hybrids of canary and finches, ii. 45.
  BRICKELL, on raising nectarines from seed, i. 340;
    on the horses of North Carolina, ii. 300.
  BRIDGES, Mr., on the dogs of Tierra del Fuego, i. 39;
    on the selection of dogs by the Fuegians, ii. 207.
  BRIDGMAN, W. K., reproduction of abnormal ferns, i. 383, ii. 379.
  BRIGGS, J. J., regeneration of portions of the fins of fishes, ii. 15.
  BROCA, P., on the intercrossing of dogs, i. 31-32;
    on hybrids of hare and rabbit, i. 105;
    on the rumpless fowl, i. 259;
    on the character of half-castes, ii. 47;
    degree of fertility of mongrels, ii. 100;
    sterility of descendants of wild animals bred in captivity, ii. 160.
  BROCCOLI, i. 323;
    rudimentary flowers in, ii. 316;
    tenderness of, ii. 310.
  BROMEHEAD, W., doubling of the Canterbury bell by selection, ii. 200.
  BROMFIELD, Dr., sterility of the ivy and _Acorus calamus_, ii. 170.
  _Bromus secalinus_, i. 314.
  BRONN, H. G., bud-variation in _Anthemis_, i. 379;
    effects of cross-breeding on the female, i. 404;
    on heredity in a one-horned cow, ii. 12, 13;
    propagation of a pendulous peach by seed, ii. 18;
    absorption of the minority in crossed races, ii. 88;
    on the crossing of horses, ii. 92;
    fertility of tame rabbits and sheep, ii. 112;
    changes of plumage in captivity, ii. 158;
    on the dahlia, ii. 261.
  BRONZE period, dog of, i. 18.
  BROWN, G., variations in the dentition of the horse, i. 50.
  BROWN-SÉQUARD, Dr., inheritance of artificially-produced epilepsy in the
      guinea-pig, ii. 24.
  _Brunswigia_, ii. 139.
  BRUSSELS Sprouts, i. 323, ii. 429.
  _Bubo maximus_, ii. 154.
  BUCKLAND, F., on oysters, ii. 280;
    number of eggs in a codfish, ii. 379.
  BUCKLE, Mr., doubts as to the importance of inheritance, ii. 3.
  BUCKLEY, Miss, carrier-pigeons roosting in trees, i. 181.
  BUCKMAN, Prof., cultivation of _Avena fatua_, i. 313;
    cultivation of the wild parsnip, i. 326, ii. 201, 277;
    reversion in the parsnip, ii. 31.
  BUCKWHEAT, injurious to white pigs, when in flower, ii. 337.
  BUD and seed, close analogy of, i. 411.
  BUD-REVERSION, ii. 37.
  BUDS, adventitious, ii. 384.
  BUD-VARIATION, i. 373-411, ii. 254, 287-288, 291;
    contrasted with seminal reproduction, i. 373;
    peculiar to plants, i. 374;
    in the peach, i. 340, 374;
    in plums, i. 375;
    in the cherry, _ibid._;
    in grapes, _ibid._;
    in the gooseberry, currant, pear, and apple, i. 376;
    in the banana, camellia, hawthorn, _Azalea indica_, and _Cistus
        tricuspis_, i. 377;
    in the hollyhock and pelargonium, i. 378;
    in _Geranium pratense_ and the chrysanthemum, i. 379;
    in roses, i. 367, 379-381;
    in sweet williams, carnations, pinks, stocks, and snapdragons, i. 381;
    in wall-flowers, cyclamen, _Oenothera biennis_, _Gladiolus colvillii_,
        fuchsias, and _Mirabilis jalapa_, i. 382;
    in foliage of various trees, i. 382-384;
    in cryptogamic plants, i. 383;
    by suckers in _Phlox_ and barberry, i. 384;
    by tubers in the potato, _ibid._;
    in the dahlia, i. 385;
    by bulbs in hyacinths, _Imatophyllum miniatum_, and tulips, i. 385;
    in _Tigridia conchiflora_, i. 386;
  {440}
    in _Hemerocallis_, _ibid._;
    doubtful cases, i. 386-387;
    in _Cytisus Adami_, i. 387-394;
    probable in _Æsculus rubicunda_, i. 392;
    summary of observations on, 406.
  BUFFON, on crossing the wolf and dog, i. 32;
    increase of fertility by domestication, ii. 111;
    improvement of plants by unconscious selection, ii. 216;
    theory of reproduction, ii. 375.
  _Bulimus_, ii. 53.
  BULL, apparent influence of, on offspring, ii. 68.
  BULLACE, i. 345.
  BULLDOG, recent modifications of, i. 42.
  BULLFINCH, breeding in captivity, ii. 154;
    attacking flower-buds, ii. 232.
  BULT, Mr., selection of pouter pigeons, ii. 197.
  "BÜNDTNERSCHWEIN," i. 67.
  BUNTING, reed, in captivity, ii. 158.
  BURDACH, crossing of domestic and wild animals, i. 66;
    aversion of the wild boar to barley, ii. 303.
  BURKE, Mr., inheritance in the horse, ii. 10.
  _Burlingtonia_, ii. 135.
  BURMAH, cats of, i. 47.
  BURMESE ponies, striped, i. 58, 59.
  BURNES, Sir A., on the Karakool sheep, i. 98, ii. 278;
    varieties of the vine in Cabool, i. 333;
    hawks, trained in Scinde, ii. 153;
    pomegranates producing seed, ii. 168.
  BURTON Constable, wild cattle at, i. 84.
  "BURZEL-TAUBEN," i. 150.
  BUSSORAH carrier, i. 141.
  _Buteo vulgaris_, copulation of, in captivity, ii. 154.
  BUTTERFLIES, polymorphic, ii. 399-400.
  BUZAREINGUES, Girou de, inheritance of tricks, ii. 6.

  CABANIS, pears grafted on the quince, ii. 239.
  CABBAGE, i. 323-326;
    varieties of, i. 323;
    unity of character in flowers and seeds of, i. 323-324;
    cultivated by ancient Celts, i. 324;
    classification of varieties of, _ibid._;
    ready crossing of, _ibid._, ii. 90, 91, 98, 130;
    origin of, i. 325;
    increased fertility of, when cultivated, ii. 113;
    growth of, in tropical countries, ii. 277.
  CABOOL, vines of, i. 333.
  CABRAL, on early cultivation in Brazil, i. 311.
  CACTUS, growth of cochineal on, in India, ii. 275.
  CÆSAR, _Bos primigenius_ wild in Europe in the time of, i. 81;
    notice of fowls in Britain, i. 246;
    notice of the importation of horses by the Celts, ii. 203.
  CAFFRE fowls, i. 230.
  CAFFRES, different kinds of cattle possessed by the, i. 88.
  "CÁGIAS," a breed of sheep, i. 95.
  CALCEOLARIAS, i. 364; ii. 147;
    effects of seasonal conditions on, ii. 274;
    peloric flowers in, ii. 346.
  "CALONGOS," a Columbian breed of cattle, i. 88.
  CALVER, Mr., on a seedling peach producing both peaches and nectarines,
      i. 341.
  CALYX, segments of the, converted into carpels, ii. 392.
  CAMEL, its dislike to crossing water, i. 181.
  _Camellia_, bud-variations in, i. 377;
    recognition of varieties of, ii. 251;
    variety in, hardiness of, ii. 308.
  CAMERON, D., on the cultivation of Alpine plants, ii. 163.
  CAMERONN, Baron, value of English blood in race-horses, ii. 11.
  _Campanula medium_, ii. 200.
  CANARY-BIRD, i. 295;
    conditions of inheritance in, ii. 22;
    hybrids of, ii. 45;
    period of perfect plumage in, ii. 77;
    diminished fertility of, ii. 161;
    standard of perfection in, ii. 195;
    analogous variation in, ii. 349.
  CANCER, heredity of, ii. 7, 8, 79.
  CANINE teeth, development of the, in mares, ii. 318.
  _Canis alopex_, i. 29.
  _Canis antarcticus_, i. 20.
  _Canis argentatus_, ii. 151.
  _Canis aureus_, i. 29.
  _Canis cancrivorus_, domesticated and crossed in Guiana, i. 23.
  _Canis cinereo-variegatus_, i. 29.
  _Canis fulvus_, i. 29.
  _Canis Ingæ_, the naked Peruvian dog, i. 23.
  _Canis latrans_, resemblance of, to the Hare Indian dog, i. 22;
    one of the original stocks, i. 26.
  _Canis lupaster_, i. 25.
  _Canis lupus_, var. _occidentalis_, resemblance of, to North American
      dogs, i. 21;
    crossed with dogs, i. 22;
    one of the original stocks, i. 26.
  _Canis mesomelas_, i. 25, 29.
  _Canis primævus_, tamed by Mr. Hodgson, i. 26.
  _Canis sabbar_, i. 25.
  _Canis simensis_, possible original of greyhounds, i. 33.
  _Canis thaleb_, i. 29.
  _Canis variegatus_, i. 29.
  CANTERBURY Bell, doubled by selection, ii. 200.
  CAPE of Good Hope, different kinds of cattle at the, i. 88;
  {441}
    no useful plants derived from the, i. 310.
  CAPERCAILZIE, breeding in captivity, ii. 156.
  _Capra ægagrus_ and _C. Falconeri_, probable parents of domestic goat, i.
      101.
  CAPSICUM, i. 371.
  CARDAN, on a variety of the walnut, i. 356;
    on grafted walnuts, ii. 259-260.
  CARDOON, ii. 34.
  _Carex rigida_, local sterility of the, ii. 170.
  CARLIER, early selection of sheep, ii. 204.
  CARLISLE, Sir A., inheritance of peculiarities, ii. 6, 8;
    of polydactylism, ii. 13.
  "CARME" pigeon, i. 156.
  CARNATION, bud-variation in, i. 381;
    variability of, i. 370;
    striped, produced by crossing red and white, i. 393;
    effect of conditions of life on the, ii. 273.
  CARNIVORA, general fertility of, in captivity, ii. 150.
  CAROLINE Archipelago, cats of, i. 47.
  CARP, ii. 236.
  CARPELS, variation of, in cultivated cucurbitaceæ, i. 359.
  CARPENTER, W. B., regeneration of bone, ii. 294;
    production of double monsters, ii. 340;
    number of eggs in an _Ascaris_, ii. 379.
  _Carpinus betulus_, i. 362.
  _Carpophaga littoralis_ and _luctuosa_, i. 182.
  CARRIER pigeon, i. 139-142;
    English, i. 139-141;
    figured, i. 140;
    skull figured, i. 163;
    history of the, i. 211;
    Persian, i. 141;
    Bussorah, _ibid._;
    Bagadotten, skull figured, i. 163;
    lower jaw figured, i. 165.
  CARRIÈRE, cultivation of the wild carrot, i. 326;
    intermediate form between the almond and the peach, i. 338;
    glands of peach-leaves, i. 343;
    bud-variation in the vine, i. 375;
    grafts of _Aria vestita_ upon thorns, i. 387;
    variability of hybrids of _Erythrina_, ii. 265.
  CARROT, wild, effects of cultivation on the, i. 326;
    reversion in the, ii. 31;
    run wild, ii. 33;
    increased fertility of cultivated, ii. 113;
    experiments on the, ii. 277;
    acclimatisation of the, in India, ii. 311.
  _Carthamus_, abortion of the pappus in, ii. 316.
  CARTIER, cultivation of native plants in Canada, i. 312.
  CARYOPHYLLACEÆ, frequency of contabescence in the, ii. 165.
  CASPARY, bud-variation in the moss-rose, i. 380;
    on the ovules and pollen of _Cytisus_, i. 388-389;
    crossing of _Cytisus purpureus_ and _C. laburnum_, i. 389;
    trifacial orange, i. 391;
    differently-coloured flowers in the wild _Viola lutea,_ i. 408;
    sterility of the horse-radish, ii. 170.
  CASTELNAU, on Brazilian cattle, i. 88.
  CASTRATION, assumption of female characters caused by, ii. 51-52.
  _Casuarius bennettii_, ii. 156.
  CAT, domestic, i. 43-48;
    early domestication and probable origin of the, i. 43-44;
    intercrossing of with wild species, i. 44-45;
    variations of, i. 45-48;
    feral, i. 47, ii. 33;
    anomalous, i. 48;
    polydactylism in, ii. 14;
    black, indications of stripes in young, ii. 55;
    tortoiseshell, ii. 73;
    effects of crossing in, ii. 86;
    fertility of, ii. 111;
    difficulty of selection in, ii. 234, 236;
    length of intestines in, ii. 302;
    white with blue eyes, deafness of, ii. 329;
    with tufted ears, ii. 350.
  CATARACT, hereditary, ii. 9, 79.
  CATERPILLARS, effect of changed food on, ii. 280.
  CATLIN, G., colour of feral horses in North America, i. 61.
  CATTLE, European, their probable origin from three original species, i.
      79-82;
    humped, or Zebus, i. 79-80;
    intercrossing of, i. 83, 91-93;
    wild, of Chillingham, Hamilton, Chartley, Burton Constable, and
        Gisburne, i. 84, ii. 119;
    colour of feral, i. 84-85, ii. 102;
    British breeds of, i. 86-87;
    South African breeds of, i. 88;
    South American breeds of, i. 89, ii. 205;
    Niata, i. 89-91, ii. 205, 208, 332;
    effects of food and climate on, i. 91-92;
    effects of selection on, i. 92-93;
    Dutch-buttocked, ii. 8;
    hornless, production of horns in, ii. 29-30, 39;
    reversion in, when crossed, ii. 41;
    wildness of hybrid, ii. 45;
    short-horned, prepotency of, ii. 65;
    wild, influence of crossing and segregation on, ii. 86;
    crosses of, ii. 96, 104, 118;
    of Falkland islands, ii. 102;
    mutual fertility of all varieties of, ii. 110;
    effects of interbreeding on, ii. 117-119;
    effects of careful selection on, ii. 194, 199;
    naked, of Columbia, ii. 205;
    crossed with wild banteng in Java, ii. 206;
    with reversed hair in Banda Oriental, ii. 205;
    selection of trifling characters in, ii. 209;
    fashion in, ii. 210;
    similarity of best races of, ii. 241;
    unconscious selection in, ii. 214;
    effects of natural selection on anomalous breeds of, ii. 226-227;
    light-coloured, attacked by flies, ii. 229, 336;
    Jersey, rapid improvement of, ii. 234;
    effects of disuse of parts in, ii. 299;
    rudimentary horns in, ii. 315;
    supposed influence of humidity on the hair of, ii. 326;
  {442}
    white spots of, liable to disease, ii. 337;
    supposed analogous variation in, ii. 349;
    displacement of long-horned by short-horned, ii. 426.
  CAULIFLOWER, i. 323;
    free-seeding of, in India, ii. 310;
    rudimentary flowers in, ii. 316.
  CAVALIER pigeon, ii. 97.
  _Cavia aperea_, ii. 152.
  CAY (_Cebus azaræ_), sterility of, in confinement, ii. 153.
  _Cebus azaræ_, ii. 153.
  _Cecidomyia_, larval development of, ii. 283, 360, 367;
    and _Misocampus_, i. 5.
  CEDARS of Lebanon and Atlas, i. 364.
  CELERY, turnip-rooted, i. 336;
    run wild, ii. 33.
  CELL-THEORY, ii. 370.
  _Celosia cristata_, i. 365.
  CELSUS, on the selection of seed-corn, i. 318, ii. 203.
  CELTS, early cultivation of the cabbage by the, i. 324;
    selection of cattle and horses by the, ii. 202-203.
  _Cenchrus_, seeds of a, used as food, i. 309.
  _Centaurea cyanus_, bud-variation in, i. 379.
  CEPHALOPODA, spermatophores of, ii. 383.
  _Cerasus padus_, yellow-fruited, ii. 19.
  _Cercoleptes_, sterility of, in captivity, ii. 152.
  _Cercopithecus_, breeding of a species of, in captivity, ii. 153.
  CEREALS, i. 312-313;
    of the Neolithic period in Switzerland, i. 317;
    adaptation of, to soils, ii. 305.
  _Cereus_, ii. 38.
  _Cereus speciosissimus_ and _phyllanthus_, reversion in hybrids of, i.
      392.
  _Cervus canadensis_, ii. 158.
  _Cervus dama_, ii. 120.
  CETACEA, correlation of dermal system and teeth in the, ii. 328.
  CEYLON, cats of, i. 46;
    pigeon-fancying in, i. 206.
  _Chamærops humilis_, crossed with date palm, i. 399.
  CHAMISSO, on seeding bread-fruit, ii. 168.
  CHANNEL islands, breeds of cattle in, i. 80.
  CHAPMAN, Professor, peach-trees producing nectarines, i. 341.
  CHAPUIS, F., sexual peculiarities in pigeons, i. 162, ii. 74;
    effect produced by first male upon the subsequent progeny of the
        female, i. 405;
    sterility of the union of some pigeons, ii. 162.
  CHARACTERS, fixity of, ii. 239;
    latent, ii. 51-56, 399-400;
    continued divergence of, ii. 241;
    antagonistic, ii. 401.
  CHARDIN, abundance of pigeons in Persia, i. 205.
  CHARLEMAGNE, orders as to the selection of stallions, ii. 203.
  CHARTLEY, wild cattle of, i. 84.
  CHATÉ, reversion of the upper seeds in the pods of stocks, ii. 347-348.
  CHATIN, on _Ranunculus ficaria_, ii. 170.
  CHAUNDY, Mr., crossed varieties of cabbage, ii. 130.
  CHEETAH, general sterility of, in captivity, ii. 151.
  _Cheiranthus cheiri_, i. 382.
  CHERRIES, i. 347-348;
    bud-variation in, i. 375;
    white Tartarian, ii. 230;
    variety of, with curled petals, ii. 232;
    period of vegetation of, changed by forcing, ii. 311.
  CHEVREUL, on crossing fruit-trees, ii. 129.
  CHICKENS, differences in characters of, i. 249-250;
    white, liable to gapes, ii. 228, 336.
  CHIGOE, ii. 275.
  CHILE, sheep of, i. 95.
  CHILLINGHAM cattle, identical with _Bos primigenius_, i. 81;
    characters of, i. 83-84.
  CHILOE, half-castes of, ii. 46.
  CHINA, cats of, with drooping ears, i. 47;
    horses of, i. 53;
    striped ponies of, i. 59;
    asses of, i. 62;
    notice of rabbits in, by Confucius, i. 103;
    breeds of pigeons reared in, i. 206;
    breeds of fowls of, in fifteenth century, i. 232, 247;
    goose of, i. 237.
  CHINCHILLA, fertility of, in captivity, ii. 152.
  CHINESE, selection practised by the, ii. 204-205;
    preference of the, for hornless rams, ii. 209;
    recognition of the value of native breeds by the, ii. 313.
  CHINESE, or Himalayan rabbit, i. 108.
  "CHIVOS," a breed of cattle in Paraguay, i. 89.
  CHOUX-RAVES, i. 323.
  CHRIST, H., on the plants of the Swiss Lake-dwellings, i. 309, 318;
    intermediate forms between _Pinus sylvestris_ and _montana_, i. 363.
  CHRYSANTHEMUM, i. 379.
  _Chrysotis festiva_, ii. 280.
  CINERARIA, effects of selection on the, ii. 200.
  CIRCASSIA, horses of, ii. 102.
  CIRCUMCISION, ii. 23.
  CIRRIPEDES, metagenesis in, ii. 366.
  _Cistus_, intercrossing and hybrids of, i. 336, 389, ii. 140.
  _Cistus tricuspis_, bud-variation in, i. 377.
  CITRONS, i. 334-335.
  "_Citrus aurantium fructu variabili_," i. 336.
  _Citrus decumana_, i. 335.
  _Citrus lemonum_, i. 336.
  {443}
  _Citrus medica_, i. 335-336.
  CLEFT palate, inheritance of, ii. 24.
  CLEMENTE, on wild vines in Spain, i. 332.
  CLERMONT-TONNERRE, on the St. Valery apple, i. 401.
  CLAPHAM, A., bud-variation in the hawthorn, i. 377.
  "CLAQUANT," i. 138.
  "CLAQUERS" (pigeons), i. 156.
  CLARK, G., on the wild dogs of Juan de Nova, i. 27;
    on striped Burmese and Javanese ponies, i. 59;
    breeds of goats imported into the Mauritius, i. 101;
    variations in the mammæ of goats, i. 102;
    bilobed scrotum of Muscat goat, _ibid._
  CLARK, H. J., on fission and gemmation, ii. 359.
  CLARKE, R. T., intercrossing of strawberries, i. 352.
  CLARKE, T., hybridisation of stocks, i. 399, ii. 93.
  CLARKSON, Mr., prize-cultivation of the gooseberry, i. 355.
  CLASSIFICATION, explained by the theory of natural selection, i. 11.
  CLIMATE, effect of, upon breeds of dogs, i. 37;
    on horses, i. 52, 53;
    on cattle, i. 91, 92;
    on the fleece of sheep, i. 98, 99;
    on seeds of wheat, i. 316;
    on cultivated cabbages, i. 325;
    adaptation of maize to, i. 322.
  CLIMATE and pasture, adaptation of breeds of sheep to, i. 96-97.
  CLIMATE and soil, effects of, upon strawberries, i. 353.
  CLINE, Mr., on the skull in horned and hornless rams, ii. 333.
  CLOS, on sterility in _Ranunculus ficaria_, ii. 170.
  CLOTZSCH, hybrids of various trees, ii. 130.
  CLOVER, pelorism in, ii. 340.
  COATE, Mr., on interbreeding pigs, ii. 122.
  COCCUS of apple trees, ii. 231.
  COCHIN fowls, i. 227, 250, 252, 260-261;
    occipital foramen of, figured, i. 261;
    section of skull of, figured, i. 263;
    cervical vertebra of, figured, i. 267.
  COCHINEAL, persistence of, ii. 236;
    preference of, for a particular cactus, ii. 275.
  _Cochlearia armoracia_, ii. 170.
  COCK, game, natural selection in, ii. 225;
    spur of, grafted on the comb, ii. 296;
    spur of, inserted into the eye of an ox, ii. 369;
    effect of castration upon the, ii. 51-52.
  COCK'S-COMB, varieties of the, i. 365.
  COCOONS, of silkworms, variations in, i. 302-303.
  CODFISH, bulldog, i. 89;
    number of eggs in the, ii. 379.
  _Coelogenys paca_, ii. 152.
  COLIN, prepotency of the ass over the horse, ii. 67-68;
    on cross-breeding, ii. 97;
    on change of diet, ii. 304.
  COLLINSON, Peter, peach-tree producing a nectarine, i. 340.
  COLORATION, in pigeons, an evidence of unity of descent, i. 195-197.
  COLOUR, correlation of, in dogs, i. 28-29;
    persistence of, in horses, i. 50;
    inheritance and diversity of, in horses, i. 55;
    variations of, in the ass, i. 62-63;
    of wild or feral cattle, i. 85;
    transmission of, in rabbits, i. 107;
    peculiarities of, in Himalayan rabbits, i. 111;
    influence of, ii. 227-230;
    correlation of, in head and limbs, ii. 324;
    correlated with constitutional peculiarities, ii. 335-338.
  COLOUR and odour, correlation of, ii. 325.
  COLOUR-BLINDNESS, hereditary, ii. 9;
    more common in men than in women, ii. 72-73;
    associated with inability to distinguish musical sounds, ii. 328.
  COLOURS, sometimes not blended by crossing, ii. 92.
  _Columba affinis_, Blyth, a variety of _C. livia_, i. 183.
  _Columba amaliæ_, Brehm, a variety of _C. livia_, i. 183.
  _Columba guinea_, i. 182.
  _Columba gymnocyclus_, Gray, a form of _C. livia_, i. 184.
  _Columba gymnophthalmos_, hybrids of, with _C. oenas_, i. 193;
    with _C. maculosa_, i. 194.
  _Columba intermedia_, Strickland, a variety of _C. livia_, i. 184.
  _Columba leucocephala_, ii. 155.
  _Columba leuconota_, i. 182, 195.
  _Columba littoralis_, i. 182.
  _Columba livia_, ii. 29, 40;
    the parent of domestic breeds of pigeons, i. 183;
    measurements of, i. 134;
    figured, i. 135;
    skull figured, i. 163;
    lower jaw figured, i. 164, 168;
    scapula figured, i. 167.
  _Columba luctuosa_, i. 182.
  _Columba migratoria_ and _leucocephala_, diminished fertility of, in
      captivity, ii. 155.
  _Columba oenas_, i. 183;
    crossed with common pigeon and _C. gymnophthalmos_, i. 193.
  _Columba palumbus_, i. 193, ii. 350.
  _Columba rupestris_, i. 182, 184, 195.
  _Columba Schimperi_, i. 184.
  _Columba torquatrix_, ii. 350.
  _Columba turricola_, i. 184.
  COLUMBIA, cattle of, i. 88.
  COLUMBINE, double, i. 365, ii. 330.
  {444}
  COLUMBUS, on West Indian dogs, i. 23.
  COLUMELLA, on Italian shepherd's dogs, i. 23;
    on domestic fowls, i. 231,  247, ii. 202, 429;
    on the keeping of ducks, i. 277;
    on the selection of seed-corn, i. 318;
    on the benefits of change of soil to plants, ii. 146;
    on the value of native breeds, ii. 313.
  COLZA, i. 325.
  COMB, in fowls, variations of, i. 253-254;
    sometimes rudimentary, ii. 315.
  COMPENSATION, law of, i. 274.
  COMPENSATION of growth, ii. 342-344.
  COMPLEXION, connexion of, with constitution, ii. 335.
  COMPOSITÆ, double flowers of, i. 365, ii. 167, 316.
  CONCEPTION, earlier in Alderney and Zetland cows than in other breeds, i.
      87.
  CONDITIONS of life, changed, effect of, ii. 418-419;
    on horses, i. 52;
    upon variation in pigeons, i. 212-213;
    upon wheat, i. 315-316;
    upon trees, i. 361;
    in producing bud-variation, i. 408;
    advantages of, ii. 145-148, 176-177;
    sterility caused by, ii. 148-165;
    conducive to variability, ii. 255-261, 394;
    accumulative action of, ii. 261-263;
    direct action of, ii. 271-292.
  CONDOR, breeding in captivity, ii. 154.
  CONFINEMENT, effect of, upon the cock, ii. 52.
  CONFUCIUS, on the breeding of rabbits in China, i. 103.
  CONOLLY, Mr., on Angora goats, ii. 326.
  CONSTITUTIONAL differences in sheep, i. 96-97;
    in varieties of apples, i. 349-350;
    in pelargoniums, i. 364;
    in dahlias, i. 370.
  CONSTITUTIONAL peculiarities in strawberries, i. 353;
    in roses, i. 367.
  CONSUMPTION, hereditary, ii. 8;
    period of appearance of, ii. 77;
    correlated with complexion, ii. 335.
  CONTABESCENCE, ii. 165-166.
  _Convolvulus batatas_, ii. 169, 309.
  _Convolvulus tricolor_, bud-variation in, i. 408.
  COOPER, Mr., improvement of vegetables by selection, ii. 204.
  COOPER, White, hereditary peculiarities of vision, ii. 9;
    association of affections of the eyes with those of other systems, ii.
        328.
  CORALS, bud-variation in, i. 374;
    non-diffusion of cell-gemmules in, ii. 379.
  CORBIÉ. _See_ Boitard.
  CORNEA, opacity of, inherited, ii. 9.
  _Cornus mascula_, yellow-fruited, ii. 19.
  CORRELATION, ii. 319;
    of neighbouring parts, ii. 320;
    of change in the whole body and in some of its parts, ii. 321;
    of homologous parts, ii. 322-331;
    inexplicable, ii. 331-333;
    commingling of, with the effects of other agencies, ii. 333-335.
  CORRELATION of skull and limbs in swine, i. 73;
    of tusks and bristles in swine, i. 76;
    of multiplicity of horns and coarseness of wool in sheep, i. 95;
    of beak and feet in pigeons, i. 172-173;
    between nestling down and colour of plumage in pigeons, i. 194;
    of changes in silkworms, i. 304;
    in plants, ii. 219;
    in maize, i. 323;
    in pigeons, i. 167-171, 218;
    in fowls, i. 274-275.
  CORRESPONDING periods, inheritance at, ii. 75-80.
  CORRIENTES, dwarf cattle of, i. 89.
  CORRINGHAM, Mr., influence of selection on pigs, ii. 198.
  CORSICA, ponies of, i. 52.
  "CORTBECK" (pigeon) of Aldrovandi, i. 209.
  _Corvus corone_ and _C. cornix_, hybrids of, ii. 94.
  _Corydalis_, flower of, ii. 304.
  _Corydalis cava_, ii. 132-133.
  _Corydalis solida_, sterile when peloric, ii. 167.
  _Corydalis tuberosa_, peloric by reversion, ii. 58-59.
  _Corylus avellana_, i. 357.
  COSTA, A., on shells transferred from England to the Mediterranean, ii.
      280.
  "COUVE TRONCHUDA," i. 323.
  COW, inheritance of loss of one horn in the, ii. 12, 23;
    amount of milk furnished by the, ii. 300;
    development of six mammæ in, ii. 317.
  COWSLIP, ii. 21, 182.
  CRACIDÆ, sterility of the, in captivity, ii. 156.
  CRANES, fertility of, in captivity, ii. 156.
  _Cratægus oxyacantha_, i. 363, ii. 18, 232, 258, 377.
  _Cratægus monogyna_, i. 364.
  _Cratægus sibirica_, i. 364.
  CRAWFURD, J., Malasian cats, i. 47;
    horses of the Malay Archipelago, i. 49;
    horses of Japan, i. 53;
    occurrence of stripes in young wild pigs of Malacca, i. 76;
    on a Burmese hairy family with deficient teeth, ii. 77, 327;
    Japanese origin of the bantam, i. 230;
    game fowls of the Philippine islands, i. 232;
    hybrids of _Gallus varius_ and domestic fowl, i. 234;
    domestication of _Gallus bankiva_, i. 236;
    feral fowls in the Pellew islands, i. 238;
    history of the fowl, i. 246;
    history of the domestic duck, i. 277;
    domestication of the goose, i. 287;
    cultivated plants of New Zealand, i. 312;
  {445}
    breeding of tame elephants in Ava, ii. 150;
    sterility of _Goura coronata_ in confinement, ii. 155;
    geese of the Philippine islands, ii. 162.
  CREEPERS, a breed of fowls, i. 230.
  CRESTED fowl, i. 227;
    figured, i. 229.
  "CRÈVE-COEUR," a French sub-breed of fowls, i. 229.
  CRISP, Dr., on the brains of the hare and rabbit, i. 126.
  CROCKER, C. W., singular form of _Begonia frigida_, i. 365-366, ii. 166;
    sterility in _Ranunculus ficaria_, ii. 170.
  CROCUS, ii. 165.
  CROSS-BREEDING, permanent effect of, on the female, i. 404.
  CROSSING, ii. 85-144, 173-192;
    a cause of uniformity, ii. 85-90, 173;
    occurs in all organised beings, ii. 90-92;
    some characters not blended by, ii. 92-95, 173;
    modifications and new races produced by, ii. 95-99;
    causes which check, ii. 100-109;
    domestication and cultivation favourable to, ii. 109-113, 189;
    beneficial effects of, ii. 114-131, 174-176;
    necessary in some plants, ii. 131-140, 175-176, 423;
    summary of subject of, ii. 140-144;
    of dogs with wolves in North America, i. 21-22;
    with _Canis cancrivorus_ in Guiana, i. 23;
    of dog with wolf, described by Pliny and others, i. 24;
    characters furnished by, brought out by reversion in the progeny, ii.
        34-36;
    a direct cause of reversion, ii. 39-47, 48;
    a cause of variability, ii. 264-267.
  CRUSTACEA, macrourous, differences in the development of the, ii. 368.
  CRUSTACEAN with an antenna-like development of the eye-peduncle, ii. 391.
  CRYPTOGAMIC plants, bud-variation in, i. 383.
  CUBA, wild dogs of, i. 27.
  "CUCKOO," sub-breeds of fowls, i. 244.
  CUCUMBER, variation in number of carpels of, i. 359;
    supposed crossing of varieties of the, i. 400.
  _Cucumis momordica_, i. 360.
  _Cucumis sativa_, i. 359.
  _Cucurbita_, dwarf, correlation of leaves in, ii. 330.
  _Cucurbita maxima_, i. 357, 359.
  _Cucurbita moschata_, i. 357, 359.
  _Cucurbita pepo_, i. 357, ii. 108;
    varieties of, i. 358;
    relation in size and number of fruit of, ii. 343.
  CUCURBITACEÆ, i. 357-360;
    supposed crossing of, i. 399;
    Naudin's observations on hybrids of, ii. 172;
    acclimatisation of, ii. 313.
  "CULBUTANTS" (pigeons), i. 150.
  CULTIVATION of plants, origin of, among savages, i. 309-310;
    fertility increased by, ii. 111-113.
  CUNIER, on hereditary night-blindness, ii. 9.
  CURRANTS, of Tierra del Fuego, i. 309;
    bud-variation in, i. 376.
  CURTIS, Mr., bud-variation in the rose, i. 381.
  CUVIER, on the gestation of the wolf, i. 29;
    the odour of the jackal, an obstacle to domestication, i. 30;
    differences of the skull in dogs, i. 34;
    external characters of dogs, i. 35;
    elongation of the intestines in domestic pigs, i. 73, ii. 303;
    fertility of the hook-billed duck, i. 277;
    number of digits, ii. 13;
    hybrid of ass and zebra, ii. 42;
    breeding of animals in the Jardin des Plantes, ii. 149;
    sterility of predaceous birds in captivity, ii. 154;
    facility of hybridisation in confinement, ii. 160.
  CYANOSIS, affection of fingers in, ii. 332.
  CYCLAMEN, bud-variation in, i. 382.
  _Cynara cardunculus_, ii. 34.
  _Cynips fecundatrix_, ii. 283.
  _Cynocephalus hamadryas_, ii. 153.
  _Cyprinus auratus_, i. 296-297.
  _Cyrtanthus_, ii. 139.
  _Cyrtopodium_, ii. 134.
  _Cytisus Adami_, ii. 364;
    its bud-variation, i. 387-389, 406, ii. 37;
    seedlings from, i. 388;
    different views of its origin, i. 389-390;
    experiments in crossing _C. purpureus_ and _laburnum_ to produce, i.
        389;
    its production by M. Adam, i. 390;
    discussion of origin of, i. 396.
  _Cytisus alpino-laburnum_, ovules and pollen of, i. 389;
    origin of, i. 390.
  _Cytisus alpinus_, i. 388.
  _Cytisus laburnum_, i. 387, 389, 390, 396.
  _Cytisus purpureo-elongatus_, ovules and pollen of, i. 389;
    production of, i. 390.
  _Cytisus purpureus_, i. 387, 388, 389, 390, 396.

  DAHLBOM, effects of food on hymenoptera, ii. 281.
  DAHLIA, i. 369-370, ii. 147;
    bud-variation by tubers in the, i. 385;
    improvement of, by selection, ii. 216;
    steps in cultivation of, ii. 261;
    effect of conditions of life on, ii. 273;
    correlation of form and colour in, ii. 331.
  DAISY, hen and chicken, i. 365;
    Swan River, ii. 261.
  DALBRET, varieties of wheat, i. 314.
  DALIBERT, changes in the odours of plants, ii. 274.
  DALLY, Dr., on consanguineous marriages, ii. 122.
  DALTONISM, hereditary, ii. 9.
  DAMARAS, cattle of, i. 88, ii. 207-208.
  {446}
  DAMSON, i. 347.
  DANDOLO, Count, on silkworms, i. 301.
  DANIELL, fertility of English dogs in Sierra Leone, ii. 161.
  DANISH Middens, remains of dogs in, i. 18.
  DAPPLING in horses, asses, and hybrids, i. 55.
  DARESTE. C., on the skull of the Polish fowl, i. 262;
    on the production of monstrous chickens, ii. 289;
    co-existence of anomalies, ii. 331;
    production of double monsters, ii. 340.
  DARVILL, Mr., heredity of good qualities in horses, ii. 11.
  DARWIN, C., on _Lepus magellanicus_, i. 112;
    on the wild potato, i. 330;
    dimorphism in the polyanthus and primrose, ii. 21.
  DARWIN, Dr., improvement of vegetables by selection, ii. 204.
  DARWIN, Sir F., wildness of crossed pigs, ii. 45.
  D'ASSO, monogynous condition of the hawthorn in Spain, i. 364.
  _Dasyprocta aguti_, ii. 152.
  Date-palm, varieties of the, ii. 256;
    effect of pollen of, upon the fruit of _Chamærops_, i. 299.
  _Datura_, ii. 38;
    variability in, ii. 266.
  _Datura lævis_ and _stramonium_, reversion in hybrids of, i. 392.
  _Datura stramonium_, ii. 67.
  DAUBENTON, variations in the number of mammæ in dogs, i. 35;
    proportions of intestines in wild and domestic cats, i. 48, ii. 302.
  DAUDIN, on white rabbits, ii. 230.
  DAVY, Dr., on sheep in the West Indies, i. 98.
  DAWKINS and Sandford, early domestication of _Bos longifrons_ in Britain,
      i. 81.
  DEAF-MUTES, non-heredity of, ii. 22.
  DEAFNESS, inheritance of, ii. 78.
  DEBY, wild hybrids of common and musk ducks, ii. 46.
  DE CANDOLLE, Alph., number and origin of cultivated plants, i. 306-307,
      371;
    regions which have furnished no useful plants, i. 310;
    wild wheat, i. 312-313;
    wild rye and oats, i. 313;
    antiquity of varieties of wheat, i. 316;
    apparent inefficacy of selection in wheat, i. 318;
    origin and cultivation of maize, i. 320, ii. 307;
    colours of seeds of maize, i. 321;
    varieties and origin of the cabbage, i. 324-325;
    origin of the garden-pea, i. 326;
    on the vine, i. 332, ii. 308;
    cultivated species of the orange group, i. 335;
    probable Chinese origin of the peach, i. 337;
    on the peach and nectarine, i. 340, 342;
    varieties of the peach, i. 342;
    origin of the apricot, i. 344;
    origin and varieties of the plum, i. 345;
    origin of the cherry, i. 347;
    varieties of the gooseberry, i. 354;
    selection practised with forest-trees, i. 361;
    wild fastigate oak, i. 361;
    dark-leaved varieties of trees, i. 362;
    conversion of stamens into pistils in the poppy, i. 365;
    variegated foliage, i. 366;
    heredity of white hyacinths, i. 371, ii. 20;
    changes in oaks dependent on age, i. 387;
    inheritance of anomalous characters, ii. 19;
    variation of plants in their native countries, ii. 256;
    deciduous bushes becoming evergreen in hot climates, ii. 305;
    antiquity of races of plants, ii. 429.
  DE CANDOLLE, P., non-variability of monotypic genera, ii. 266;
    relative development of root and seed in _Raphanus sativus_, ii. 343.
  DECAISNE, on the cultivation of the wild carrot, i. 326;
    varieties of the pear, i. 350;
    inter-crossing of strawberries, i. 351;
    fruit of the apple, i. 401;
    sterility of _Lysimachia nummularia_, ii. 170;
    tender variety of the peach, ii. 308.
  DEER, assumption of horns by female, ii. 51;
    imperfect development of horns in a, on a voyage, ii. 158.
  DEER, fallow, ii. 103.
  DEERHOUND. Scotch, difference in size of the sexes of, ii. 73;
    deterioration of, ii. 121.
  DEGENERATION of high-bred races, under neglect, ii. 239.
  DE JONGHE, J., on strawberries, i. 352, ii. 243;
    soft-barked pears, ii. 231;
    on accumulative variation, ii. 262;
    resistance of blossoms to frost, ii. 306.
  DELAMER, E. S., on rabbits, i. 107, 112.
  _Delphinium ajacis_, ii. 21.
  _Delphinium consolida_, ii. 20-21.
  _Dendrocygna viduata_, i. 182, ii. 157.
  DENTITION, variations of, in the horse, i. 50.
  DEODAR, i. 364.
  DESMAREST, distribution of white on dogs, i. 29;
    cat from the Cape of Good Hope, i. 47;
    cats of Madagascar, i. 47;
    occurrence of striped young in Turkish pigs, i. 76;
    French breeds of cattle, i. 80;
    horns of goats, i. 102;
    on hornless goats, ii. 315.
  DESOR, E., on the Anglo-Saxon race in America, ii. 276.
  DESPORTES, number of varieties of roses, i. 367.
  DEVAY, Dr., singular case of albinism, ii. 17;
    on the marriage of cousins, ii. 122;
    on the effects of close interbreeding, ii. 143, 263.
  DEVELOPMENT and metamorphosis, ii. 388-389.
  DEVELOPMENT, arrests of, ii. 315-318.
  DEVELOPMENT, embryonic, ii. 366-368.
  {447}
  D'HERVEY-Saint-Denys, L., on the ya-mi, or imperial rice of the Chinese,
      ii. 205.
  DHOLE, fertility of the, in captivity, ii. 151.
  DIABETES, occurrence of, in three brothers, ii. 17.
  _Dianthus_, contabescent plants of, ii. 165-166;
    hybrid varieties of, ii. 267.
  _Dianthus armeria_ and _deltoides_, hybrids of, ii. 98.
  _Dianthus barbatus_, i. 381.
  _Dianthus caryophyllus_, i. 381.
  _Dianthus japonicus_, contabescence of female organs in, ii. 166.
  DICHOGAMOUS plants, ii. 90.
  DICKSON, Mr., on "running" in carnations, i. 381;
    on the colours of tulips, i. 386.
  _Dicotyles torquatus_ and _labiatus_, ii. 150.
  DIEFFENBACH, dog of New Zealand, i. 26;
    feral cats in New Zealand, i. 47;
    polydactylism in Polynesia, ii. 14.
  _Dielytra_, ii. 59.
  DIET, change of, ii. 303-304.
  _Digitalis_, properties of, affected by culture, ii. 274;
    poison of, ii. 380.
  DIGITS, supernumerary, ii. 57;
    analogy of, with embryonic conditions, ii. 16;
    fusion of, ii. 341.
  DIMORPHIC plants, ii. 166;
    conditions of reproduction in, ii. 181-184.
  DIMORPHISM, reciprocal, ii. 90.
  DINGO, i. 25;
    variation of, in colour, i. 28;
    half-bred, attempting to burrow, i. 28;
    attraction of foxes by a female, i. 31;
    variations of, in confinement, ii. 263.
  DIOECIOUSNESS of strawberries, i. 353.
  DISEASES, inheritance of, ii. 7-8;
    family uniformity of, ii. 57;
    inherited at corresponding periods of life, ii. 77-80;
    peculiar to localities and climates, ii. 276;
    obscure correlations in, ii. 331-332;
    affecting certain parts of the body, ii. 380;
    occurring in alternate generations, ii. 401.
  DISTEMPER, fatal to white terriers, ii. 227.
  DISUSE and use of parts, effects of, ii. 295-303, 352-353, 418-419;
    in the skeleton of rabbits, i. 124-128;
    in pigeons, i. 171-177;
    in fowls, i. 270-274;
    in ducks, i. 284-286;
    in the silk-moth, i. 300-304.
  DIVERGENCE, influence of, in producing breeds of pigeons, i. 220.
  DIXON, E. S., on the musk duck, i. 182;
    on feral ducks, i. 190;
    on feral pigeons in Norfolk Island, i. 190;
    crossing of pigeons, i. 192;
    origin of domestic fowls, i. 230;
    crossing of _Gallus Sonneratii_ and common fowl, i. 234;
    occurrence of white in the young chicks of black fowls, i. 244;
    Paduan fowl of Aldrovandi, i. 247;
    peculiarities of the eggs of fowls, i. 248;
    chickens, i. 249-250;
    late development of the tail in Cochin cocks, i. 250;
    comb of lark-crested fowls, i. 256;
    development of webs in Polish fowls, i. 259;
    on the voice of fowls, i. 259;
    origin of the duck, i. 277;
    ducks kept by the Romans, i. 278;
    domestication of the goose, i. 287;
    gander frequently white, i. 288;
    breeds of turkeys, i. 293;
    incubatory instinct of mongrels of non-sitting races of fowls, ii. 44;
    aversion of the dove-cot pigeon to pair with fancy birds, ii. 103;
    fertility of the goose, ii. 112;
    general sterility of the guans in captivity, ii. 156;
    fertility of geese in captivity, ii. 157;
    white peafowl, ii. 332.
  DOBELL, H., inheritance of anomalies of the extremities, ii. 14;
    non-reversion to a malformation, ii. 36.
  DOBRIZHOFFER, abhorrence of incest by the Abipones, ii. 123.
  DOGS, origin of, i. 15;
    ancient breeds of, i. 17, ii. 429;
    of neolithic, bronze and iron periods in Europe, i. 18-19, ii. 427;
    resemblance of to various species of canidæ, i. 21;
    of North America compared with wolves, i. 21-22;
    of the West Indies, South America, and Mexico, i. 23, 31;
    of Guiana, i. 23;
    naked dogs of Paraguay and Peru, _ibid._ and 31;
    dumb, on Juan Fernandez, i. 27;
    of Juan de Nova, i. 27;
    of La Plata, i. 27;
    of Cuba, i. 27;
    of St. Domingo, i. 28;
    correlation of colour in, i. 28-29;
    gestation of, i. 29-30;
    hairless Turkish, i. 30, ii. 227;
    inter-crossing of different breeds of, i. 31;
    characters of different breeds of, discussed, i. 34-37;
    degeneration of European, in warm climates, i. 36, 38; ii. 278, 305;
    liability to certain diseases in different breeds of, i. 36 and _note_;
    causes of differences of breeds discussed, i. 37-43;
    catching fish and crabs in New Guinea and Tierra del Fuego, i. 39;
    webbing of the feet in, i. 39;
    influence of selection in producing different breeds of, i. 39, 43;
    retention of original habits by, i. 182;
    inheritance of polydactylism in, ii. 14;
    feral, ii. 33;
    reversion in fourth generation of, ii. 34;
    of the Pacific Islands, ii. 87, 220, 303;
    mongrel, ii. 92-93;
    comparative facility of crossing different breeds of, ii. 102;
    fertility of, ii. 111, 151;
    inter-breeding of, ii. 120-121;
    selection of, among the Greeks, ii. 202, 209;
    among savages, ii. 206-207;
    unconscious selection of, ii. 211-212;
    valued by the Fuegians, ii. 215;
    climatal changes in hair of, ii. 278;
    production of drooping ears in, ii. 301;
  {448}
    rejection of bones of game by, ii. 303;
    inheritance of rudiments of limbs in, ii. 315;
    development of fifth toe in, ii. 317;
    hairless, deficiency of teeth in, ii. 326;
    short-faced, teeth of, ii. 345;
    probable analogous variation in, ii. 349;
    extinction of breeds of, ii. 425.
  DOMBRAIN, H. H., on the auricula, ii. 346-347.
  DOMESTICATION, essential points in, ii. 405-406;
    favourable to crossing, ii. 109-110;
    fertility increased by, ii. 111-113, 174.
  DOMESTICATED animals, origin of, ii. 160-161;
    occasional sterility of, under changed conditions, ii. 161-162.
  DONDERS, Dr., hereditary hypermetropia, ii. 8.
  DORKING fowl, i. 227, 261;
    furcula of, figured, i. 268.
  DORMOUSE, ii. 152.
  DOUBLE FLOWERS, ii. 167-168, 171-172;
    produced by selection, ii. 200.
  DOUBLEDAY, H., cultivation of the filbert pine strawberry, i. 354.
  DOUGLAS, J., crossing of white and black game-fowls, ii. 92.
  DOWNING, Mr., wild varieties of the hickory, i. 310;
    peaches and nectarines from seed, i. 339-340;
    origin of the Boston nectarine, i. 340;
    American varieties of the peach, i. 343;
    North American apricot, i. 344;
    varieties of the plum, i. 346;
    origin and varieties of the cherry, i. 347-348;
    "twin cluster pippins," i. 349;
    varieties of the apple, i. 350;
    on strawberries, i. 351, 353;
    fruit of the wild gooseberry, i. 355;
    effects of grafting upon the seed, ii. 26;
    diseases of plum and peach trees, ii. 227-228;
    injury done to stone fruit in America by the "weevil," ii. 231;
    grafts of the plum and peach, ii. 259;
    wild varieties of pears, ii. 260;
    varieties of fruit-trees suitable to different climates, ii. 306.
  _Draba sylvestris_, ii. 163.
  DRAGON, pigeon, i. 139, 141.
  "DRAIJER" (pigeon), i. 156.
  DRINKING, effects of, in different climates, ii. 289.
  DROMEDARY, selection of, ii. 205-206.
  DRUCE, Mr., inter-breeding of pigs, ii. 121.
  DU CHAILLU, fruit-trees in West Africa, i. 309.
  DUCHESNE on _Fragaria vesca_, i. 351, 352, 353.
  DUFOUR, Léon, on _Cecidomyia_ and _Misocampus_, i. 5.
  DUCK, musk, retention of perching habit by the, i. 182;
    feral hybrid of, i. 190.
  DUCK, penguin, hybrid of, with Egyptian goose, ii. 68.
  DUCK, wild, difficulty of rearing, ii. 233;
    effects of domestication on, ii. 278.
  DUCKS, breeds of, i. 276-277;
    origin of, i. 277;
    history of, _ibid._;
    wild, easily tamed, i. 278-279;
    fertility of breeds of, when crossed, i. 279;
    with the plumage of _Anas boschas_, i. 280;
    Malayan penguin, identical in plumage with English, i. 280;
    characters of the breeds of, i. 281-284;
    eggs of, i. 281;
    effects of use and disuse in, i. 284-286, ii. 298;
    feral, in Norfolk, i. 190;
    Aylesbury, inheritance of early hatching by, ii. 25;
    reversion in, produced by crossing, ii. 40;
    wildness of half-bred wild, ii. 45;
    hybrids of, with the musk duck, ii. 45-46;
    assumption of male plumage by, ii. 51;
    crossing of Labrador and penguin, ii. 97;
    increased fertility of, by domestication, ii. 112;
    general fertility of, in confinement, ii. 157;
    increase of size of, by care in breeding, ii. 199;
    change produced by domestication in, ii. 262.
  DUMÉRIL, Aug., breeding of _Siredon_ in the branchiferous stage, ii. 384.
  DUN-coloured horses, origin of, i. 59.
  DUREAU de la Malle, feral pigs in Louisiana, ii. 33;
    feral fowls in Africa, _ibid._;
    bud-variation in the pear, i. 376;
    production of mules among the Romans, ii. 110.
  _Dusicyon sylvestris_, i. 23.
  DUTCH rabbit, i. 107.
  DUTCH roller pigeon, i. 151.
  DUTROCHET, pelorism in the laburnum, ii. 346.
  DUVAL, growth of pears in woods in France, ii. 260.
  DUVAL-Jouve, on _Leersia oryzoides_, ii. 91.
  DUVERNOY, self-impotence in _Lilium candidum_, ii. 137.
  DZIERZON, variability in the characters and habits of bees, i. 298.

  EARLE, Dr., on colour-blindness, ii. 72, 328.
  EARS, of fancy rabbits, i. 106;
    deficiency of, in breeds of rabbits, i. 108;
    rudimentary, in Chinese sheep, ii. 315;
    drooping, ii. 301;
    fusion of, ii. 341.
  EATON, J. M., on fancy pigeons, i. 148, 153;
    variability of characters in breeds of pigeons, i. 161;
    reversion of crossed pigeons to coloration of _Columba livia_, i. 198;
    on pigeon-fancying, i. 206, 215-216;
    on tumbler-pigeons, i. 209, ii. 242;
    carrier-pigeon, i. 211;
    effects of interbreeding on pigeons, ii. 126;
    properties of pigeons, ii. 197-198;
    death of short-faced tumblers in the egg, ii. 226;
  {449}
    Archangel pigeon, ii. 240.
  ECHINODERMATA, metagenesis in, ii. 367.
  _Ectopistes_, specific difference in number of tail-feathers in, i. 159.
  _Ectopistes migratorius_, sterile hybrids of, with _Turtur vulgaris_, i.
      193.
  EDENTATA, correlation of dermal system and teeth in the, ii. 328.
  EDGEWORTH, Mr., use of grass-seeds as food in the Punjab, i. 309.
  EDMONSTON, Dr., on the stomach in _Larus argentatus_ and the raven, ii.
      302.
  EDWARDS and COLIN, on English wheat in France, ii. 307.
  EDWARDS, W. F., absorption of the minority in crossed races, ii. 87.
  EDWARDS, W. W., occurrence of stripes in a nearly thoroughbred horse, i.
      57;
    in foals of racehorses, i. 59.
  EGGS, of fowls, characters of, i. 248;
    variations of, in ducks, i. 281;
    of the silkmoth, i. 301.
  EGYPT, ancient dogs of, i. 17-18;
    ancient domestication of the pigeon in, i. 204;
    absence of the fowl in ancient, i. 246.
  EGYPTIAN goose, hybrids of, with penguin duck, i. 282.
  EHRENBERG, Prof., multiple origin of the dog, i. 16;
    dogs of Lower Egypt, i. 25;
    mummies of _Felis maniculata_, i. 43.
  ELEMENT, male, compared to a premature larva, ii. 384.
  ELEMENTS of the body, functional independence of the, ii. 368-371.
  ELEPHANT, its sterility in captivity, ii. 150.
  ELK, Irish, correlations in the, ii. 333-334.
  ELLIOT, Sir Walter, on striped horses, i. 58;
    Indian domestic and wild swine, i. 66;
    pigeons from Cairo and Constantinople, i. 132;
    fantail pigeons, i. 146;
    Lotan tumbler pigeons, i. 150;
    a pigeon uttering the sound _Yahu_, i. 155;
    _Gallus bankiva_ in Pegu, i. 236.
  ELLIS, Mr., varieties of cultivated plants in Tahiti, ii. 256.
  ELM, nearly evergreen Cornish variety of the, i. 363, ii. 310;
    foliage-varieties of the, i. 362.
  ELM, weeping, i. 361;
    not reproduced by seed, ii. 19.
  _Emberiza passerina_, ii. 158.
  EMBRYOS, similarity of, i. 12;
    fusion of, ii. 339.
  ENGEL, on _Laurus sassafras_, ii. 274.
  ENGLAND, domestication of _Bos longifrons_ in, i. 81;
    selection of horses in, in mediæval times, ii. 203;
    laws against the early slaughter of rams in, ii. 203.
  EPHEMERIDÆ, development of the, ii. 366.
  _Epidendrum cinnabarinum_ and _E. zebra_, ii. 134.
  EPILEPSY, hereditary, ii. 8, 78.
  ERDT, disease of the white parts of cattle, ii. 337.
  ERICACEÆ, frequency of contabescence in the, ii. 165.
  ERICHTHONIUS, an improver of horses by selection, ii. 202.
  ERMAN, on the fat-tailed Kirghisian sheep, i. 98, ii. 280;
    on the dogs of the Ostyaks, ii. 206.
  _Erodium_, ii. 59.
  _Erythrina Crista-galli_ and _E. herbacea_, hybrids of, ii. 265.
  ESQUILANT, Mr., on the naked young of dun-coloured pigeons, i. 170.
  ESQUIMAUX dogs, their resemblance to wolves, i. 21;
    selection of, ii. 206.
  EUDES-DESLONGCHAMPS, on appendages under the jaw of pigs, i. 75-76.
  _Euonymus Japonicus_, i. 383.
  EUROPEAN cultivated plants, still wild in Europe, i. 307.
  EVANS, Mr., on the Lotan tumbler pigeon, i. 150.
  EVELYN, pansies grown in his garden, i. 368.
  EVEREST, R., on the Newfoundland dog in India, i. 36, ii. 305;
    degeneration of setters in India, i. 38;
    Indian wild boars, i. 66.
  EWES, hornless, ii. 350.
  EXTINCTION of domestic races, i. 221.
  EYES, hereditary peculiarities of the, ii. 8-10;
    loss of, causing microphthalmia in children, ii. 24;
    modification of the structure of, by natural selection, ii. 222-223;
    fusion of, ii. 341.
  EYEBROWS, hereditary elongation of hairs in, ii. 8.
  EYELIDS, inherited peculiarities of the, ii. 8.
  EYTON, Mr., on gestation in the dog, i. 30;
    variability in number of vertebræ in the pig, i. 74;
    individual sterility, ii. 162.

  _Faba vulgaris_, i. 330.
  FABRE, observations on _Ægilops triticoides,_ i. 313.
  _Fagus sylvatica_, ii. 19.
  FAIRWEATHER, Mr., production of double flowers from old seed, ii. 167.
  _Falco albidus_, resumption of young plumage by, in captivity, ii. 158.
  _Falco ossifragus_, ii. 230.
  _Falco subbuteo_, copulating in captivity, ii. 154.
  _Falco tinnunculus_, breeding in captivity, ii. 154.
  {450}
  FALCONER, Dr., sterility of English bulldogs in India, i, 38;
    resemblance between _Sivatherium_ and Niata cattle, i. 89;
    selection of the silkworm in India, i. 301;
    fastigate apple-trees in Calcutta, i. 361;
    reproduction of a supernumerary thumb after amputation, ii. 14;
    fertility of the dhole in captivity, ii. 151;
    fertility of English dogs in India, ii. 161;
    sterility of the tiger in captivity, ii. 151;
    turkeys at Delhi, ii. 161;
    on Indian cultivated plants, ii. 165;
    Thibet mastiff and goat, ii. 278.
  FALCONS, sterility of, in captivity, ii. 153.
  FALKLAND Islands, horses of the, i. 52-53, 61;
    feral pigs of the, i. 77;
    feral cattle of the, i. 82, 86;
    feral rabbits of the, i. 112.
  FALLOW deer, ii. 103, 120.
  FANTAIL pigeons, i. 146-148, ii. 227;
    figured, i. 147;
    furcula of, figured, i. 167;
    history of, i. 208;
    absence of oil-gland in, ii. 344.
  FAROE Islands, pigeons of the, i. 183.
  FASHION, influence of, in breeding, ii. 240.
  FASTIGATE trees, ii. 277, 348.
  FAUNAS, geographical differences, of, i. 10.
  "FAVOURITE" bull, ii. 65, 118.
  FEATHERS, homologous variation in, ii. 325.
  FEET, of pigeons, individual differences of, i. 160;
    correlations of external characters in, i. 170-171.
  FEET and beak, correlation of, in pigeons, i. 171-174.
  FELIDÆ, fertility of, in captivity, ii. 150.
  _Felis bubastes_, i. 43.
  _Felis caffra_, i. 44.
  _Felis caligulata_, i. 43.
  _Felis chaus_, i. 43-44.
  _Felis jubata_, ii. 151.
  _Felis lybica_, i. 44.
  _Felis maniculata_, i. 43.
  _Felis manul_, i. 45.
  _Felis ornata_, i. 45.
  _Felis sylvestris_, i. 44.
  _Felis torquata_, i. 45.
  FEMALE, affected by male element, ii. 365, 387-388.
  FEMALE flowers, in male panicle of maize, i. 321.
  FENNEL, Italian variety of, i. 326.
  FERAL cats, i. 47;
    cattle, i. 86;
    rabbits, i. 111-115;
    Guinea fowl, i. 294;
    animals and plants, reversion in, ii. 32-34, 47.
  FERGUSON, Mr., supposed plurality of origin of domestic fowls, i. 231;
    chickens of black game-fowls, i. 244;
    relative size of eggs of fowls, i. 248;
    yolk of eggs of game-fowls, i. 249;
    early pugnacity of game-cocks, i. 250;
    voice of the Malay fowl, i. 259;
    effects of interbreeding on fowls, ii. 124;
    selection in Cochin China fowls, ii. 196;
    on fashion in poultry, ii. 240.
  FERNANDEZ, on Mexican dogs, i. 23.
  FERNS, reproduction of abnormal forms of, by spores, i. 383;
    non-diffusion of cell-gemmules in, ii. 379.
  FERRETS, ii. 111, 151, 206.
  FERTILISATION, artificial, of the St. Valery apple, i. 350.
  FERTILITY, various degrees of, in sheep, i. 97;
    unlimited mutual, of breeds of pigeons, i. 192-194;
    comparative of mongrels and hybrids, ii. 100-101, 178-180;
    influence of nourishment on, ii. 111;
    diminished by close interbreeding, ii. 118, 175;
    reduced, of Chillingham wild cattle, ii. 119;
    of domesticated varieties when crossed, ii. 189.
  _Festuca_, species of, propagated by bulblets, ii. 170.
  FILBERTS, spared by tomtits, ii. 231.
  FILIPPI, on the breeding of branchiferous tritons, ii. 384.
  FINCHES, general sterility of, in captivity, ii. 154.
  FINNIKIN (pigeon), i. 156.
  FINNOCHIO, i. 326.
  FIR, Scotch, acclimatisation of, ii. 310.
  FISH, Mr., advantage of change of soil to plants, ii. 147.
  FISHES, regeneration of portions of fins of, ii. 15;
    variability of, when kept in tanks, ii. 259;
    marine, living in fresh water, ii. 304;
    double monsters of, ii. 340.
  FISSION and gemmation, ii. 358.
  FITCH, Mr., persistency of a variety of the pea, i. 329.
  FITTEST, survival of the, i. 6.
  FITZINGER, origin of sheep, i. 94;
    African maned sheep, i. 96.
  FIXEDNESS of character, conditions of, discussed, ii. 62-64.
  FLAX, found in the Swiss lake-dwellings, i. 317;
    climatal difference in products of, ii. 274.
  FLEECE, fineness of, in Austrian merinos, ii. 197.
  FLEISCHMANN, on German sheep crossed with merinos, ii. 88-89.
  "FLORENTINER-TAUBE," i. 142-143.
  FLOUNDER, ii. 53.
  FLOURENS, crossing of wolf and dog, i. 32;
    prepotency of the jackal over the dog, ii. 67;
    hybrids of the horse and ass, ii. 68;
    breeding of monkeys in Europe, ii. 153.
  {451}
  FLOWER-GARDEN, earliest known, in Europe, ii. 217.
  FLOWERS, capricious transmission of colour-varieties in, ii. 20-21;
    tendency to uniformity in striped, ii. 70;
    scorching of, dependent on colour, ii. 229;
    change in, caused by conditions of life, ii. 273;
    rudimentary, ii. 316;
    relative position of, to the axis, ii. 345.
  FOETATION, abdominal, ii. 294.
  FOLEY, Mr., wild varieties of pears, ii. 260.
  FOLIAGE, inherited peculiarities of, i. 362;
    variegation, of, i. 366;
    bud-variation in, i. 382-384.
  FOOD, influence of, on the pig, i. 72;
    on cattle, i. 91;
    excess of, a cause of variability, ii. 257.
  FORBES, D., on Chilian sheep, i. 95;
    on the horses of Spain, Chili, and the Pampas, i. 52.
  _Formica rufa_, ii. 251.
  FORTUNE, R., sterility of the sweet potato in China, ii. 169;
    development of axillary bulbs in the yam, _ibid._
  FOWL, common, breeds of, i. 225-230;
    supposed plurality of origin, i. 230;
    early history of, i. 231-233;
    causes of production of breeds of, i. 233;
    origin of from _Gallus bankiva_, i. 236-239, 245;
    feral, notices of, i. 237-238;
    reversion and analogous variation in, i. 239-246, ii. 35, 38, 39, 40,
        349, 350;
    "cuckoo" sub-breeds of, i. 244;
    history of, i. 246-247;
    structural characters of, i. 247-250;
    sexual peculiarities of, i. 251-257, ii. 74;
    external differences of, i. 257-260;
    differences of breeds of, from _G. bankiva_, i. 260;
    osteological characters of, i. 260-270;
    effects of disuse of parts in, i. 270-274, ii. 298;
    feral, i. 190, ii. 33;
    polydactylism in, ii. 14;
    fertility of, increased by domestication, ii. 112, 167;
    sterility of, under certain conditions, ii. 162;
    influence of selection on, ii. 196, 198, 209, 210;
    evils of close interbreeding of, ii. 124-125;
    crossing of, ii. 95, 96, 97;
    prepotency of transmission in, ii. 67;
    rudimentary organs in, ii. 315;
    crossing of non-sitting varieties of, ii. 43-44;
    homology of wing and leg feathers in, ii. 323;
    hybrids of, with pheasants and _Gallus Sonneratii_, ii. 45;
    black-skinned, ii. 209-210;
    black, preyed upon by the osprey in Iceland, ii. 230;
    five-toed, mentioned by Columella, ii. 429;
    rumpless, tailed chickens produced by, ii. 31;
    Dorking, crosses of, ii. 93;
    form of comb and colour of plumage in, ii. 238;
    game, crossing of white and black, ii. 92;
    five-spurred, ii. 391;
    Spanish, liable to suffer from frost, ii. 306;
    Polish, peculiarities of skull of, ii. 332-333.
  FOX, sterility of, in captivity, ii. 151.
  FOX, S. Bevan, races of bees, i. 298.
  FOX, W. Darwin, gestation of the dog, i. 30;
    "Negro" cat, i. 46;
    reversion of sheep in colour, ii. 30;
    period of gestation in the pig, i. 74;
    young of the Himalayan rabbit, i. 109;
    crossing of wild and domestic turkeys, i. 292;
    reversion in crossed musk ducks, ii. 40;
    spontaneous segregation of varieties of geese, ii. 104;
    effects of close interbreeding  upon bloodhounds, ii. 121;
    deafness of white cats with blue eyes, ii. 329.
  FOXHOUNDS, i. 40, ii. 120.
  _Fragaria chiloensis_, i. 351.
  _Fragaria collina_, i. 351.
  _Fragaria dioica_ of Duchesne, i. 353.
  _Fragaria elatior_, i. 351.
  _Fragaria grandiflora_, i. 351.
  _Fragaria vesca_, i. 351.
  _Fragaria virginiana_, i. 351.
  _Fraxinus excelsior_, i. 360, 362, ii. 19.
  _Fraxinus lentiscifolia_, ii. 19.
  FRIESLAND cattle, probably descended from _Bos primigenius_, i. 81.
  FRILLBACK (pigeon), i. 155;
    Indian, i. 153.
  _Fringilla ciris_, ii. 154.
  _Fringilla spinus_, ii. 154.
  FRIZZLED fowls, i. 230;
    horses, i. 54.
  FROG, polydactylism in the, ii. 14.
  FRUIT, seedless, ii. 168.
  FRUIT-TREES, varieties of, occurring wild, i. 310.
  FRY, Mr., on fertile hybrid cats, i. 44;
    on feral fowls in Ascension, i. 238.
  FUCHSIAS, origin of, i. 364;
    bud-variation in, i. 382.
  _Fuchsia coccinea_ and _fulgens_, twin seed produced by crossing, i. 391.
  FUEGIANS, their superstition about killing young water-fowl, i. 310;
    selection of dogs by the, ii. 207;
    their comparative estimation of dogs and old women, ii. 215;
    their power of distant vision, ii. 223.
  FUNGI, parasitic, ii. 284-285.
  FURCULA, characters and variations of the, in pigeons, i. 167;
    alteration of, by disuse, in pigeons, i. 175;
    characters of, in fowls, i. 268.
  FUSION of homologous parts, ii. 393.

  GAIT, inheritance of peculiarities of, ii. 6.
  GALAPAGOS Archipelago, its peculiar fauna and flora, i. 9.
  _Galeobdolon luteum_, pelorism in, ii. 59, 345.
  {452}
  GALLS, ii. 282-284.
  GALL-GNATS, ii. 283.
  GALL-LIKE excrescences not inherited, ii. 23.
  GALLINACEOUS birds, restricted range of large, i. 237;
    general fertility of in captivity, ii. 155.
  _Gallinula chloropus_, ii. 156.
  _Gallinula nesiotis_, i. 287.
  GALTON, Mr., fondness of savages for taming animals, i. 20, ii. 160;
    cattle of Benguela, i. 88;
    on hereditary talent, ii. 7.
  GALLESIO, species of oranges, i. 334, 335, 336;
    hybridisation of oranges, i. 336;
    persistency of races in the peach, i. 339;
    supposed specific distinctions of peach and nectarine, i. 340;
    Bizzaria orange, i. 391;
    crossing of red and white carnations, i. 393;
    crossing of the orange and lemon, i. 399, ii. 365;
    effect of foreign pollen on maize, i. 400;
    spontaneous crossing of oranges, ii. 91;
    monstrosities a cause of sterility in plants, ii. 166;
    seeding of ordinarily seedless fruits, ii. 168;
    sterility of the sugar cane, ii. 169;
    tendency of male flowers to become double, ii. 171;
    effects of selection in enlarging fruit, &c., ii. 217;
    variation of the orange tree in North Italy, ii. 256;
    naturalisation of the orange in Italy, ii. 309.
  _Gallus æneus_, a hybrid of _G. varius_ and the domestic fowl, i. 235.
  _Gallus bankiva_, probable original of domestic fowls, i. 233, 236-239,
      245;
    game-fowl, nearest to, i. 226;
    crossed with _G. Sonneratii_, i. 234;
    its character and habits, i. 235-236, ii. 109;
    differences of various breeds of fowls from, i. 260;
    occipital foramen of, figured, i. 261;
    skull of, figured, i. 262;
    cervical vertebra of, figured, i. 267;
    furcula of, figured, i. 268;
    reversion to, in crossed fowls, ii. 39-40;
    hybrid of, with _G. varius_, i. 235, ii. 40;
    number of eggs of, ii. 112.
  _Gallus ferrugineus_, i. 226.
  _Gallus furcatus_, i. 234.
  _Gallus giganteus_, i. 235.
  _Gallus Sonneratii_, characters and habits of, i. 233;
    hybrids of, i. 234, ii. 45.
  _Gallus Stanleyi_, hybrids of, i. 234.
  _Gallus Temminckii_, probably a hybrid, i. 235.
  _Gallus varius_, character and habits of, i. 234;
    hybrids and probable hybrids of, i. 234-235.
  GAMBIER, Lord, his early cultivation of the pansy, i. 368.
  GAME-FOWL, i. 226, 250, 251, 252.
  GAPES, ii. 228.
  GARCILAZO de la Vega, annual hunts of the Peruvian Incas, ii. 207.
  GARNETT, Mr., migratory propensities of hybrid ducks, ii. 45.
  GARROD, Dr., on hereditary gout, ii. 7.
  GASPARINI, a genus of pumpkins, founded on stigmatic characters, i. 359.
  GAUDICHAUD, bud-variation in the pear, i. 376;
    apple tree with two kinds of fruit on branch, i. 392.
  GAUDRY, anomalous structure in the feet of horses, i. 50.
  GAY, on _Fragaria grandiflora_, i. 351;
    on _Viola lutea_ and _tricolor_, i. 368;
    on the nectary of _Viola grandiflora_, i. 369.
  GAYAL, domestication of the, i. 82.
  GAYOT, _see_ Moll.
  GÄRTNER, on the sterility of hybrids, i. 192, ii. 101;
    acquired sterility of varieties of plants when crossed, i. 358;
    sterility in transplanted plants, and in the lilac in Germany, ii. 164;
    mutual sterility of blue and red flowers of the pimpernel, ii. 190;
    supposed rules of transmission in crossing plants, ii. 68;
    on crossing plants, ii. 98, 127, 130, 131;
    on repeated crossing, ii. 267;
    absorption of one species by another, when crossed, ii. 88;
    crossing of varieties of the pea, i. 397;
    crossing maize, ii. 105;
    crossing of species of _Verbascum_, ii. 93, 105;
    reversion in hybrids, ii. 36, 49, 50;
    of _Cereus_, i. 392;
    of _Tropæolum majus_ and _minus_, i. 392;
    variability of hybrids, ii. 265;
    variable hybrids from one variable parent, ii. 270;
    graft hybrid produced by inosculation in the vine, i. 395;
    effect produced by grafts on the stock, i. 394, ii. 278;
    tendency of hybrid plants to produce double flowers, ii. 171;
    production of perfect fruit by sterile hybrids, ii. 172;
    sexual elective affinity, ii. 180;
    self-impotence in _Lobelia_, _Verbascum_, _Lilium_, and _Passiflora_,
        ii. 136-137;
    on the action of pollen, ii. 108;
    fertilisation of _Malva_, i. 402-403, ii. 363;
    prepotency of pollen, ii. 187;
    prepotency of transmission in species of _Nicotiana_, ii. 67;
    bud-variation in _Pelargonium zonale_, i. 375;
    in _Oenothera biennis_, i. 382;
    in _Achillæa millefolium_, i. 408;
    effect of manure on the fertility of plants, ii. 163;
    on contabescence, ii. 165-166;
    inheritance of plasticity, ii. 241;
    villosity of plants, ii. 277.
  GEESE (_anseres_) general fertility of, in captivity, ii. 157.
  GEGENBAUR, on the number of digits, ii. 13.
  GEMMATION and fission, ii. 358.
  {453}
  GEMMULES, or cell-gemmules, ii. 374, 378-381, 384.
  GENET, fertility of the, in captivity, ii. 151.
  GENERATION, alternate, ii. 361, 367, 390.
  GENERATION, sexual, ii. 359-364.
  GENIUS, inheritance of, ii. 7.
  _Gentiana amarella_, ii. 168.
  GEOFFROY Saint-Hilaire, production of monstrous chickens, ii. 289;
    "_Loi de l'affinité de soi pour soi_," ii. 339;
    compensation of growth, ii. 342.
  GEOFFROY Saint-Hilaire, Isid., origin of the dog, i. 66;
    barking of a jackal, i. 27;
    period of gestation and odour of the jackal, i. 30;
    anomalies in the teeth of dogs, i. 34;
    variations in the proportions of dogs, i. 35;
    webbed feet of Newfoundland dogs, i. 39;
    crossing of domestic and wild cats, i. 44;
    domestication of the arni, i. 82;
    supposed introduction of cattle into Europe from the East, _ibid._;
    absence of interdigital pits in sheep, i. 95;
    origin of the goat, i. 101;
    feral geese, i. 190;
    ancient history of the fowl, i. 246;
    skull of the Polish fowl, i. 262;
    preference of the Romans for the liver of white geese, i. 289;
    polydactylism, ii. 12;
    assumption of male characters by female birds, ii. 51;
    supernumerary mammæ in women, ii. 58;
    development of a proboscis in the pig, _ibid._;
    transmission and blending of characters in hybrids, ii. 94;
    refusal of animals to breed in captivity, ii. 149;
    on the Guinea pig, ii. 152;
    silkworms producing white cocoons, ii. 199;
    on the carp, ii. 236;
    on _Helix lactea_, ii. 280;
    on monstrosities, ii. 254;
    injury to the embryo a cause of monstrosity, ii. 269;
    alteration in the coat of horses in coal mines, ii. 278;
    length of the intestines in wild and tame animals, ii. 302-303;
    inheritance of rudimentary limbs in the dog, ii. 315;
    correlation in monstrosities, ii. 320;
    supernumerary digits in man, ii. 322;
    co-existence of anomalies, ii. 331;
    fusion of homologous parts, ii. 341-342;
    presence of hairs and teeth in ovarian tumours, ii. 370;
    development of teeth on the palate in the horse, ii. 391.
  GEOGRAPHICAL differences of faunas, i. 10.
  GEOLOGICAL succession of organisms, i. 11.
  _Geranium_, ii. 59.
  _Geranium phæum_ and _pyrenaicum_, ii. 258.
  _Geranium pratense_, i. 379.
  GERARD, asserted climatal change in Burgundian bees, i. 297.
  GERARDE, on varieties of the hyacinth, i. 370.
  GERSTÄCKER, on hive-bees, i. 299.
  GERVAIS, Prof., origin of the dog, i. 16;
    resemblance of dogs and jackals, i. 24;
    taming of the jackal, i. 26;
    number of teeth in dogs, i. 34;
    breeds of dogs, i. 36;
    on tertiary horses, i. 51;
    biblical notices of horses, i. 55;
    species of _Ovis_, i. 94;
    wild and domestic rabbits, i. 103;
    rabbits from Mount Sinai and Algeria, i. 105;
    earless rabbits, i. 108;
    batrachia with doubled limbs, ii. 391.
  GESTATION, period of, in the dog, wolf, &c, i. 29-30;
    in the pig, i. 74;
    in cattle, i. 87, ii. 321;
    in sheep, i. 97.
  GESTURES, inheritance of peculiarities in, ii. 6.
  "GHOONDOOKS" a sub-breed of fowls, i. 229.
  GHOR-KHUR, ii. 42.
  GILES, Mr., effect of cross-breeding in the pig, i. 404.
  GIRAFFE, co-ordination of structure of, ii. 221.
  GIRARD, period of appearance of permanent teeth in dogs, i. 35.
  GIROU de Buzareingues, inheritance in the horse, ii. 10;
    reversion by age in cattle, ii. 38;
    prepotency of transmission of character in sheep and cattle, ii. 66;
    on crossing gourds, ii. 108.
  GISBURNE, wild cattle at, i. 84.
  _Gladiolus_, i. 364;
    self-impotence of hybrids of, ii. 139.
  _Gladiolus colvillii_, bud-variation in, i. 382.
  GLANDS, compensatory development of, ii. 300.
  GLASTONBURY thorn, i. 364.
  GLENNY, Mr., on the _Cineraria_, ii. 200.
  GLOEDE, F., on strawberries, i. 353.
  GLOGER, on the wings of ducks, ii. 298.
  "GLOUGLOU" (pigeon), i. 154.
  _Gloxiniæ_, peloric, i. 365, ii. 167.
  GMELIN, on red cats, at Tobolsk, i. 47.
  GOAT, i. 101-102, ii. 33;
    polydactylism in the, ii. 14;
    sexual differences in horns of, ii. 73;
    valued by South Africans, ii. 207;
    Thibet, ii. 278;
    amount of milk and development of udders in the, ii. 300;
    hornless, rudimentary bony cores in, ii. 316;
    Angora, ii. 326.
  GODRON, odour of the hairless Turkish dog, i. 30;
    differences in the skull of dogs, i. 34;
    increase of breeds of horses, i. 51;
    crossing of domestic and wild swine, i. 66;
    on goats, i. 101-102;
    colour of the skin in fowls, i. 258;
    bees of north and south of France, i. 297;
    introduction of the silkworm into Europe, i. 300;
    variability in the silkworm, i. 304;
    supposed species of wheat, i. 312-314;
    on _Ægilops triticoides_, i. 313;
    variable presence of barbs in grasses, i. 314;
  {454}
    colours of the seeds of maize, i. 321;
    unity of character in cabbages, i. 323;
    correlation of colour and odour, i. 325;
    effect of heat and moisture on the cabbage, i. 325;
    on the cultivated species of _Brassica_, i. 325;
    on the Rouncival and sugar peas, i. 327;
    variation in the numbers of peas in the same pod, i. 328;
    wild vines in Spain, i. 332;
    on raising peaches from seed, i. 339;
    supposed specific distinctness of peach and nectarine, i. 340;
    nectarine producing peaches, i. 341;
    on the flower of _Corydalis_, i. 344;
    origin and variations of the plum, i. 345;
    origin of the cherry, i. 347;
    reversion of single-leaved strawberries, i. 353;
    five-leaved variety of _Fragaria collina_, i. 353;
    supposed immutability of specific characters, i. 358-359;
    varieties of _Robinia_, i. 361;
    permanency of the simple-leaved ash, i. 362;
    non-inheritance of certain mutilations, ii. 23;
    wild turnips, carrots, and celery, ii. 33;
    pre-potency of a goat-like ram, ii. 66;
    benefit of change of soil to plants, ii. 146;
    fertility of peloric flowers of _Corydalis solida_, ii. 167;
    seeding of ordinarily seedless fruit, ii. 168;
    sexual sterility of plants propagated by buds, &c., ii. 169;
    increase of sugar in beet-root, ii. 201;
    effects of selection in enlarging particular parts of plants, ii. 217;
    growth of the cabbage in the tropics, ii. 277;
    rejection of bitter almonds by mice, ii. 232;
    influence of marshy pasture on the fleece of sheep, ii. 278;
    on the ears of ancient Egyptian pigs, ii. 301;
    primitive distinctness of species, ii. 415;
    solid hoofed swine, ii. 429.
  GOETHE, on compensation of growth, ii. 342.
  GOLDFISH, i. 296-297, ii. 236.
  GOMARA, on South American cats, i. 46.
  GONGORA, number of seeds in the, ii. 379.
  GOOSE, ancient domestication of, i. 287;
    sacred to Juno in Rome, _ibid._;
    inflexibility of organisation of, i. 288;
    skull perforated in tufted, i. 288;
    characters of breeds and sub-breeds of, i. 288-289;
    variety of, from Sebastopol, i. 289, ii. 392;
    feral in La Plata, i. 190;
    Egyptian, hybrid of, with penguin duck, ii. 68;
    spontaneous segregation of varieties of, ii. 104;
    fertility of, increased by domestication, ii. 112;
    decreased fertility of, in Bogota, ii. 161;
    sterility of, in the Philippine Islands, ii. 162;
    selection of, ii. 204;
    white, preference of the Romans for the liver of, ii. 209;
    persistency of character in, ii. 254;
    Egyptian, change in breeding season of, ii. 304.
  GOOSEBERRY, i. 354-356;
    bud-variation in the, i. 376;
    Whitesmith's, ii. 232.
  GÖPPERT, on monstrous poppies, ii. 166.
  GOSSE, P. H., feral dogs in Jamaica, i. 28;
    feral pigs of Jamaica, i. 77-78;
    feral rabbits of Jamaica, i. 112;
    on _Columba leucocephala_, i. 183;
    feral Guinea fowl in Jamaica, i. 190;
    reproduction of individual peculiarities by gemmation in a coral, i.
        374;
    frequency of striped legs in mules, ii. 42.
  GOULD, Dr., on hereditary hæmorrhage, ii. 7.
  GOULD, John, origin of the turkey, i. 292.
  _Goura coronata_ and _Victoriæ_, hybrids of, i. 194, ii. 155.
  GOURDS, i. 357;
    crossing of varieties of, ii. 108;
    ancient Peruvian variety of, ii. 429.
  GOUT, inheritance of, ii. 7;
    period of appearance of, ii. 77.
  GRABA, on the pigeon of the Faroe islands, i. 183.
  GRAFTING, ii. 147;
    effects of, ii. 259, 278;
    upon the stock, i. 394-395;
    upon the variability of trees, ii. 259;
    changes analogous to bud-variation produced by, i. 387, 389.
  GRAFT-HYBRIDS, i. 390-391, 394-397, ii. 364-365.
  GRAPES, bud-variation in, i. 375;
    cross of white and purple, i. 393;
    green, liable to disease, ii. 336;
    effect of foreign pollen on, i. 400.
  GRASSES, seeds of, used as food by savages, i. 307-309.
  GRAY, Asa, superior wild varieties of fruit-trees, i. 310;
    cultivated native plants of North America, i. 312, 357;
    non-variation of weeds, i. 317;
    supposed spontaneous crossing of pumpkins, i. 399;
    pre-ordination of variation, ii. 432;
    progeny of husked form of maize, i. 320;
    wild intermediate forms of strawberries, i. 352.
  GRAY, G. R., on _Columba gymnocyclus_, i. 184.
  GRAY, J. E., on _Sus pliciceps_, i. 70;
    on a variety of the gold-fish, i. 297;
    hybrids of the ass and zebra, ii. 42-43;
    on the breeding of animals at Knowsley, ii. 149;
    on the breeding of birds in captivity, ii. 157.
  GREENE, J. Reay, on the development of the echinodermata, ii. 367.
  GREENHOW, Mr., on a Canadian web-footed dog, i. 39.
  GREENING, Mr., experiments on _Abraxas grossulariata_, ii. 280.
  GREGSON, Mr., experiments on _Abraxas grossulariata_, ii. 280.
  GREY, Sir George, preservation of seed-bearing plants by the Australian
      savages, i. 310;
  {455}
    detestation of incest by Australian savages, ii. 123.
  GREYHOUNDS, sculptured on Egyptian monuments, and in the Villa of
      Antoninus, i. 17;
    modern breed of, i. 41;
    crossed with the bulldog, by Lord Orford, ii. 95;
    co-ordination of structure of, due to selection, ii. 221-222;
    Italian, ii. 227.
  GREYNESS, inherited at corresponding periods of life, ii. 77.
  GRIEVE, Mr., on early-flowering dahlias, i. 370.
  GRIGOR, Mr., acclimatisation of the Scotch fir, ii. 310.
  GROOM-NAPIER, C. O., on the webbed feet of the otter-hound, i. 40.
  "GROSSES-GORGES" (pigeons), i. 137.
  GROUND-TUMBLER, Indian, i. 150.
  GROUSE, fertility of, in captivity, ii. 156.
  GRÖNLAND, hybrids of _Ægilops_ and wheat, ii. 110.
  _Grus montigresia_, _cinerea_, and _Antigone_, ii. 156.
  GUANACOS, selection of, ii. 207.
  GUANS, general fertility of, in captivity, ii. 156.
  GUELDER-ROSE, ii. 185.
  GUELDERLAND fowls, i. 230.
  GUIANA, selection of dogs by the Indians of, ii. 206.
  GUINEA FOWL, i. 294;
    feral in Ascension, and Jamaica, i. 190, ii. 33;
    indifference of to change of climate, ii. 161.
  GUINEA pig, ii. 24, 152.
  GÜLDENSTADT, on the jackal, i. 25.
  GULL, herring, breeding in confinement, ii. 157.
  GULLS, general sterility of, in captivity, ii. 157.
  _Gulo_, sterility of, in captivity, ii. 152.
  GÜNTHER, A., on tufted ducks and geese, i. 274;
    on the regeneration of lost parts in batrachia, ii. 15.
  GURNEY, Mr., owls breeding in captivity, ii. 154;
    appearance of "black-shouldered" among ordinary peacocks, i. 291.

  HABIT, influence of, in acclimatisation, ii. 312-315.
  HABITS, inheritance of, ii. 395.
  HÄCKEL, on cells, ii. 370;
    on the double reproduction of medusæ, ii. 384;
    on inheritance, ii. 397.
  HACKLES, peculiarities of, in fowls, i. 254.
  HAIR, on the face, inheritance of, in man, ii. 4;
    peculiar lock of, inherited, ii. 5;
    growth of, under stimulation of skin, ii. 326;
    homologous variation of, ii. 325;
    development of, within the ears and in the brain, ii. 391.
  HAIR and teeth, correlation of, ii. 326-328.
  HAIRY family, corresponding period of inheritance in, ii. 77.
  HALF-CASTES, character of, ii. 46.
  HALF-LOP rabbits, figured and described, i. 107-108;
    skull of, i. 119.
  _Haliætus leucocephalus_, copulating in captivity, ii. 154.
  HALLAM, Col., on a two-legged race of pigs, ii. 4.
  HAMBURGH fowl, i. 227, 261;
    figured, i. 228.
  HAMILTON, wild cattle of, i. 84.
  HAMILTON, Dr., on the assumption of male plumage by the hen pheasant, ii.
      51.
  HAMILTON, F. Buchanan, on the shaddock, i. 335;
    varieties of Indian cultivated plants, ii. 256.
  HANCOCK, Mr., sterility of tamed birds, ii. 155-157.
  HANDWRITING, inheritance of peculiarities in, ii. 6.
  HANMER, Sir J., on selection of flower seeds, ii. 204.
  HANSELL, Mr., inheritance of dark yolks in duck's eggs, i. 281.
  HARCOURT, E. V., on the Arab boar-hound, i. 17;
    aversion of the Arabs to dun-coloured horses, i. 55.
  HARDY, Mr., effect of excess of nourishment on plants, ii. 257.
  HARE, hybrids of, with rabbit, i. 105;
    sterility of the, in confinement, ii. 152;
    preference of, for particular plants, ii. 232.
  HARE-LIP, inheritance of, ii. 24.
  HARLAN, Dr., on hereditary diseases, ii. 7.
  HARMER, Mr., on the number of eggs in a codfish, ii. 379.
  HARVEY, Mr., monstrous red and white African bull, i. 91.
  HARVEY, Prof., singular form of _Begonia frigida_, i. 365-366;
    effects of cross-breeding on the female, i. 404;
    monstrous saxifrage, ii. 166.
  HASORA wheat, i. 313.
  HAUTBOIS strawberry, i. 353.
  HAWKER, Col., on call or decoy ducks, i. 281.
  HAWTHORN, varieties of, i. 360-364;
    pyramidal, i. 361;
    pendulous hybridised, ii. 18;
    changes of, by age, i. 364, 387;
    bud-variation in the, i. 377;
    flower buds of, attacked by bullfinches, ii. 232.
  HAYES, Dr., character of Esquimaux dogs, i. 21-22.
  HAYWOOD, W., on the feral rabbits of Porto Santo, i. 114.
  HAZEL, purple-leaved, i. 362, 395, ii. 330.
  HEAD of wild boar and Yorkshire pig, figured, i. 72.
  {456}
  HEAD and limbs, correlated variability of, ii. 323.
  HEADACHE, inheritance of, ii. 79.
  HEARTSEASE, i. 368-369;
    change produced in the, by transplantation, i. 386;
    reversion in, ii. 31, 47;
    effects of selection on, ii. 200;
    scorching of, ii. 229;
    effects of seasonal conditions on the, ii. 274;
    annual varieties of the, ii. 305.
  HEAT, effect of, upon the fleece of sheep, i. 98.
  HEBER, Bishop, on the breeding of the rhinoceros in captivity, ii. 150.
  HEBRIDES, cattle of the, i. 80;
    pigeons of the, i. 183.
  HEER, O., on the plants of the Swiss lake-dwellings, i. 309, ii. 215,
      427;
    on the cereals, i. 317-319;
    on the peas, i. 326;
    on the vine growing in Italy in the bronze age, i. 332.
  _Helix lactea_, ii. 280.
  _Hemerocallis fulva_ and _flava_, interchanging by bud-variation, i. 386.
  HEMLOCK yields no conicine in Scotland, ii. 274.
  HEMP, differences of, in various parts of India, ii. 165;
    climatal difference in products of, ii. 274.
  HEMPSEED, effect of, upon the colour of birds, ii. 280.
  HERMAPHRODITE flowers, occurrence of, in Maize, i. 321.
  HEN, assumption of male characters by the, ii. 51, 54;
    development of spurs in the, ii. 318.
  "HENNIES," or hen-like male fowls, i. 252.
  HENRY, T. A., a variety of the ash produced by grafting, i. 394;
    crossing of species of _Rhododendron_ and _Arabis_, i. 400.
  HENSLOW, Prof., individual variation in wheat, i. 314;
    bud-variation in the Austrian bramble rose, i. 381;
    partial reproduction of the weeping ash by seed, ii. 19.
  HEPATICA, changed by transplantation, i. 386.
  HERBERT, Dr., variations of _Viola grandiflora_, i. 368;
    bud-variation in camellias, i. 377;
    seedlings from reverted _Cytisus Adami_, i. 388;
    crosses of Swedish and other turnips, ii. 93;
    on hollyhocks, ii. 107;
    breeding of hybrids, ii. 131;
    self-impotence in hybrid hippeastrums, ii. 138-139;
    hybrid _Gladiolus_, ii. 139;
    on _Zephyranthes candida_, ii. 164;
    fertility of the crocus, ii. 165;
    on contabescence, ii. 165;
    hybrid _Rhododendron_, ii. 265.
  HERCULANEUM, figure of a pig found in, i. 67.
  HERON, Sir R., appearance of "black-shouldered" among ordinary peacocks,
      i. 290-291;
    non-inheritance of monstrous characters by goldfish, i. 296;
    crossing of white and coloured Angora rabbits, ii. 92;
    crosses of solid-hoofed pigs, ii. 93.
  _Herpestes fasciatus_ and _griseus_, ii. 151.
  HEUSINGER, on the sheep of the Tarentino, ii. 227;
    on correlated constitutional peculiarities, ii. 337.
  HEWITT, Mr., reversion in bantam cocks, i. 240;
    degeneration of silk fowls, i. 243;
    partial sterility of hen-like male fowls, i. 252;
    production of tailed chickens by rumpless fowls, i. 259;
    on taming and rearing wild ducks, i. 278-279, ii. 233, 262-263;
    conditions of inheritance in laced Sebright bantams, ii. 22;
    reversion in rumpless fowls, ii. 31;
    reversion in fowls by age, ii. 39;
    hybrids of pheasant and fowl, ii. 45, 68;
    assumption of male characters by female pheasants, ii. 51;
    development of latent characters in a barren bantam hen, ii. 54;
    mongrels from the silk-fowl, ii. 67;
    effects of close interbreeding on fowls, ii. 124-125;
    on feathered-legged bantams, ii. 323.
  HIBBERT, Mr., on the pigs of the Shetland Islands, i. 70.
  HIGHLAND cattle, descended from _Bos longifrons_, i. 81.
  HILDEBRAND, Dr., on the fertilisation of _Orchideæ_, i. 402-403;
    occasional necessary crossing of plants, ii. 90;
    on _Primula sinensis_ and _Oxalis rosea_, ii. 132;
    on _Corydalis cava_, ii. 132-133.
  HILL, R., on the Alco, i. 31;
    feral rabbits in Jamaica, i. 112;
    feral peacocks in Jamaica, i. 190;
    variation of the Guinea fowl in Jamaica, i. 294;
    sterility of tamed birds in Jamaica, ii. 155, 157.
  HIMALAYA, range of gallinaceous birds in the, i. 237.
  HIMALAYAN rabbit, i. 107, 108-111;
    skull of, i. 120.
  HIMALAYAN sheep, i. 95.
  HINDMARSH, Mr., on Chillingham cattle, i. 84.
  "HINKEL-TAUBE," i. 142-143.
  HINNY and mule, difference of, ii. 67-68.
  _Hipparion_, anomalous resemblance to in horses, i. 50.
  _Hippeastrum_, hybrids of, ii. 138-139.
  HIVE-BEES, ancient domestication of, i. 297;
    breeds of, i. 298;
    smaller when produced in old combs, i. 297;
    variability in, i. 298;
    crossing of Ligurian and common, i. 299.
  "HOCKER-TAUBE," i. 141.
  HOBBS, Fisher, on interbreeding pigs, ii. 121.
  HODGKIN, Dr., on the attraction of foxes by a female Dingo, i. 31;
  {457}
    origin of the Newfoundland dog, i. 42;
    transmission of a peculiar lock of hair, ii. 5.
  HODGSON, Mr., domestication of _Canis primævus_, i. 26;
    development of a fifth digit in Thibet mastiffs, i. 35;
    number of ribs in humped cattle, i. 79;
    on the sheep of the Himalaya, i. 95;
    presence of four mammæ in sheep, _ibid._;
    arched nose in sheep, i. 96;
    measurements of the intestines of goats, i. 102;
    presence of interdigital pits in goats, _ibid._;
    disuse a cause of drooping ears, ii. 301.
  HOFACKER, persistency of colour in horses, i. 51, ii. 21;
    production of dun horses from parents of different colours, i. 59;
    inheritance of peculiarities in handwriting, ii. 6;
    heredity in a one-horned stag, ii. 12;
    on consanguineous marriages, ii. 123.
  HOG, Red River, ii. 150.
  HOGG, Mr., retardation of breeding in cows by hard living, ii. 112.
  HOLLAND, Sir H., necessity of inheritance, ii. 2;
    on hereditary diseases, ii. 7;
    hereditary peculiarity in the eyelid, ii. 8;
    morbid uniformity in the same family, ii. 17;
    transmission of hydrocele through the female, ii. 52;
    inheritance of habits and tricks, ii. 395.
  HOLLY, varieties of the, i. 360, 362;
    bud-reversion in, i. 384;
    yellow-berried, ii. 19, 230.
  HOLLYHOCK, bud-variation in, i. 378;
    non-crossing of double varieties of, ii. 107;
    tender variety of the, ii. 310.
  HOMER, notice of Geese, i. 287;
    breeding of the horses of Æneas, ii. 202.
  HOMOLOGOUS parts, correlated variability of, ii. 322-331, 354-355;
    fusion of, ii. 393;
    affinity of, ii. 339-342.
  HOOFS, correlated with hair in variation, ii. 325.
  HOOK-BILLED DUCK, skull figured, i. 282.
  HOOKER, Dr. J. D., forked shoulder-stripe in Syrian asses, i. 63;
    voice of the cock in Sikkim, i. 259;
    use of Arum-roots as food, i. 307;
    native useful plants of  Australia, i. 311;
    wild walnut of the Himalayas, i. 356;
    variety of the plane tree, i. 362;
    production of _Thuja orientalis_ from seeds of _T. pendula_, i. 362;
    singular form of _Begonia frigida_, i. 365;
    reversion in plants run wild, ii. 33;
    on the sugar-cane, ii. 169;
    on Arctic plants, ii. 256;
    on the oak grown at the Cape of Good Hope, ii. 274;
    on _Rhododendron ciliatum_, ii. 277;
    stock and mignonette, perennial in Tasmania, ii. 305.
  HOPKIRK, Mr., bud-variation in the rose, i. 381;
    in _Mirabilis jalapa_, i. 382;
    in _Convolvulus tricolor_, i. 408.
  HORNBEAM, heterophyllous, i. 362.
  HORNED fowl, i. 229;
    skull figured, i. 265.
  HORNLESS cattle in Paraguay, i. 89.
  HORNS of sheep, i. 95;
    correlation of, with fleece in sheep, ii. 326;
    correlation of, with the skull, ii. 333;
    rudimentary in young polled cattle, ii. 315;
    of goats, i. 102.
  HORSES, in Swiss lake-dwellings, i. 49;
    different breeds of, in Malay Archipelago, i. 49;
    anomalies in osteology and dentition of, i. 50;
    mutual fertility of different breeds, i. 51;
    feral, i. 51;
    habit of scraping away snow, i. 53;
    mode of production of breeds of, i. 54;
    inheritance and diversity of colour in, i. 55;
    dark stripes in, i. 56-61, ii. 351;
    dun-coloured, origin of, i. 59;
    colours of feral, i. 60-61;
    effect of fecundation by a Quagga on the subsequent progeny of, i.
        403-404;
    inheritance of peculiarities in, ii. 10-11;
    polydactylism in, ii. 14;
    inheritance of colour in, ii. 21;
    inheritance of exostoses in legs of, ii. 23;
    reversion in, ii. 33, 41;
    hybrids of, with ass and zebra, ii. 42;
    prepotency of transmission in the sexes of, ii. 65;
    segregation of, in Paraguay, ii. 102;
    wild species of, breeding in captivity, ii. 150;
    curly, in Paraguay, ii. 205, 325;
    selection of, for trifling characters, ii. 209;
    unconscious selection of, ii. 212-213;
    natural selection in Circassia, ii. 225;
    alteration of coat of, in coal-mines, ii. 278;
    degeneration of, in the Falkland Islands, ii. 278;
    diseases of, caused by shoeing, ii. 300;
    feeding on meat, ii. 305;
    white and white-spotted, poisoned by mildewed vetches, ii. 337;
    analogous variations in the colour of, ii. 349;
    teeth developed on palate of, ii. 391;
    of bronze period in Denmark, ii. 427.
  HORSE-CHESNUT, early, at the Tuileries, i. 362;
    tendency to doubleness in, ii. 168.
  HORSE-RADISH, general sterility of the, ii. 170.
  "HOUDAN," a French sub-breed of fowls, i. 229.
  HOWARD, C., on an Egyptian monument, i. 17;
    on crossing sheep, ii. 95, 120.
  HUC, on the Emperor Khang-hi, ii. 205;
    Chinese varieties of the bamboo, ii. 256.
  HUMBOLDT, A., character of the Zambos, ii. 47;
    parrot speaking the language of an extinct tribe, ii. 154;
    on _Pulex penetrans_, ii. 275.
  HUMIDITY, injurious effect of, upon horses, i. 53.
  HUMPHREYS, Col., on Ancon sheep, i. 100.
  HUNGARIAN cattle, i. 80.
  {458}
  HUNTER, John, period of gestation in the dog, i. 29;
    on secondary sexual characters, i. 179;
    fertile crossing of _Anser ferus_ and the domestic goose, i. 288;
    inheritance of peculiarities in gestures, voice, &c., ii. 6;
    assumption of male characters by the human female, ii. 51;
    period of appearance of hereditary diseases, ii. 78;
    graft of the spur of a cock upon its comb, ii. 296;
    on the stomach of _Larus tridentatus_, ii. 302;
    double-tailed lizards, ii. 341.
  HUNTER, W., evidence against the influence of imagination upon the
      offspring, ii. 264.
  HUTTON, Capt., on the variability of the silk moth, i. 303;
    on the number of species of silkworms, i. 300;
    markings of silkworms, i. 302;
    domestication of the rock-pigeon in India, i. 185;
    domestication and crossing of _Gallus bankiva_, i. 236.
  HUTCHINSON, Col., liability of dogs to distemper, i. 35.
  HUXLEY, Prof., on the transmission of polydactylism, ii. 13;
    on unconscious selection, ii. 194;
    on correlation in the mollusca, ii. 320;
    on gemmation and fission, ii. 359;
    development of star-fishes, ii. 366.
  HYACINTHS, i. 370-371;
    bud-variation in, i. 385;
    graft-hybrid by union of half bulbs of, i. 395;
    white, reproduced by seed, ii. 20;
    red, ii. 229, 336;
    varieties of, recognisable by the bulb, ii. 251.
  HYACINTH, feather, ii. 185, 316.
  _Hyacinthus orientalis_, i. 370.
  _Hybiscus syriacus_, ii. 286.
  HYBRIDS, of hare and rabbit, i. 105;
    of various species of _Gallus_, i. 234-236;
    of almond, peach, and nectarine, i. 339;
    naturally produced, of species of _Cytisus_, i. 390;
    from twin-seed of _Fuchsia coccinea_ and _fulgens_, i. 391;
    reversion of, i. 392-394, ii. 36, 48-50;
    from mare, ass, and zebra, ii. 42;
    of tame animals, wildness of, ii. 44-46;
    female instincts of sterile male, ii. 52;
    transmission and blending of characters in, ii. 92-95;
    breed better with parent species than with each other, ii. 131;
    self-impotence in, ii. 138-140;
    readily produced in captivity, ii. 151.
  HYBRIDISATION, singular effects of, in oranges, i. 336;
    of cherries, i. 347;
    difficulty of, in _Cucurbitæ_, i. 358;
    of roses, i. 366.
  HYBRIDISM, ii. 178-191;
    the cause of a tendency to double flowers, ii. 171;
    in relation to pangenesis, ii. 385.
  HYBRIDITY in cats, i. 44-45;
    supposed of peach and nectarine, i. 342.
  _Hydra_, i. 374, ii. 293, 359.
  HYDRANGEA, colour of flowers of, influenced by alum, ii. 277.
  HYDROCELE, ii. 52.
  HYDROCEPHALUS, ii. 295.
  _Hypericum calycinum_, ii. 170.
  _Hypericum crispum_, ii. 227, 337.
  HYPERMETAMORPHOSIS, ii. 367.
  HYPERMETROPIA, hereditary, ii. 8.

  ICHTHYOPTERYGIA, number of digits in the, ii. 16.
  _Ilex aquifolium_, ii. 19.
  IMAGINATION, supposed effect of, on offspring, ii. 263.
  _Imatophyllum miniatum_, bud-variation in, i. 385.
  INCEST, abhorred by savages, ii. 123-124.
  INCUBATION, by crossed fowls of non-sitting varieties, ii. 43-44.
  INDIA, striped horses of, i. 58;
    pigs of, i. 66, 67, 76;
    breeding of rabbits in, i. 112;
    cultivation of pigeons in, i. 205-206.
  INDIVIDUAL variability in pigeons, i. 158-160.
  INGLEDEW, Mr., cultivation of European vegetables in India, ii. 169.
  "INDISCHE Taube," ii. 144.
  INHERITANCE, ii. 1-84, 371-373, 395, 397-402;
    doubts entertained of by some writers, ii. 3;
    importance of to breeders, 3-4;
    evidence of, derived from statistics of chances, 5;
    of peculiarities in man, 5-7, 12-16;
    of disease, 7-8, 17;
    of peculiarities in the eye, 8-10;
    of deviations from symmetry, 12;
    of polydactylism, 12-16;
    capriciousness of, 17-22, 27;
    of mutilations, 22-24;
    of congenital monstrosities, 24;
    causes of absence of, 24-26;
    by reversion or atavism, 28-61;
    its connexion with fixedness of character, 62-64;
    affected by prepotency of transmission of character, 65-71;
    limited by sex, 71-75;
    at corresponding periods of life, 75-80;
    summary of the subject of, 80-84;
    laws of, the same in seminal and bud varieties, i. 409;
    of characters in the horse, i. 10-11;
    in cattle, i. 87;
    in rabbits, i. 107;
    in the peach, i. 339;
    in the nectarine, i. 340;
    in plums, i. 347;
    in apples, i. 350;
    in pears, i. 351;
    in the pansy, i. 369;
    of primary characters of _Columba livia_ in crossed pigeons, i. 201;
    of peculiarities of plumage in pigeons, i. 160-161;
    of peculiarities of foliage in trees, i. 362;
    effects of, in varieties of the cabbage, i. 325.
  INSANITY, inheritance of, ii. 7, 78.
  INSECTS, regeneration of lost parts in, ii. 15, 294;
    agency of, in fecundation of larkspurs, ii. 21;
    effect of changed conditions upon, ii. 157;
    sterile neuter, ii. 186-187;
  {459}
    monstrosities in, ii. 269, 391.
  INSTINCTS, defective, of silkworms, i. 304.
  INTERBREEDING, close, ill effects of, ii. 114-131, 175.
  INTERCROSSING, of species, as a cause of variation, i. 188;
    natural, of plants, i. 336;
    of species of Canidæ and breeds of dogs, i. 31-33;
    of domestic and wild cats, i. 44-45;
    of breeds of pigs, i. 71, 78;
    of cattle, i. 83;
    of varieties of cabbage, i. 324;
    of peas, i. 326, 329-330;
    of varieties of orange, i. 336;
    of species of strawberries, i. 351-352;
    of _Cucurbitæ_, i. 357-358;
    of flowering plants, i. 364;
    of pansies, i. 368.
  INTERDIGITAL pits, in goats, i. 102.
  INTERMARRIAGES, close, ii. 122-123.
  INTESTINES, elongation of, in pigs, i. 73;
    relative measurements of parts of, in goats, i. 102;
    effects of changed diet on, ii. 302.
  _Ipomoea purpurea_, ii. 128.
  IRELAND, remains of _Bos frontosus_ and _longifrons_ found in, i. 81.
  IRIS, hereditary absence of the, ii. 9;
    hereditary peculiarities of colour of the, ii. 9-10.
  IRISH, ancient, selection practised by the, ii. 203.
  IRON period, in Europe, dog of, i. 18.
  ISLANDS, oceanic, scarcity of useful plants on, i. 311.
  ISLAY, pigeons of, i. 183.
  ISOLATION, effect of, in favour of selection, ii. 233-234.
  ITALY, vine growing in, during the bronze period, i. 332.
  IVY, sterility of, in the north of Europe, ii. 170.

  JACK, Mr., effect of foreign pollen on grapes, i. 400.
  JACKAL, i. 24, 27, 30;
    hybrids of, with the dog, i. 32;
    prepotency of, over the dog, ii. 67.
  JACOBIN pigeon, i. 154, 208.
  JACQUEMET-BONNEFORT, on the mulberry, i. 334.
  JAGUAR, with crooked legs, i. 17.
  JAMAICA, feral dogs of, i. 28;
    feral pigs of, i. 77;
    feral rabbits of, i. 112.
  JAPAN, horses of, i. 53.
  JAPANESE pig (figured), i. 69.
  JARDINE, Sir W., crossing of domestic and wild cats, i. 44.
  JARVES, J., silkworm in the Sandwich islands, i. 301.
  JAVA, Fantail pigeon in, i. 148.
  JAVANESE ponies, i. 53, 59.
  JEMMY BUTTON, i. 309.
  JENYNS, L., whiteness of ganders, i. 288;
    sunfish-like variety of the goldfish, i. 297.
  JERDON, J. C., number of eggs laid by the pea-hen, ii. 112;
    origin of domestic fowl, i. 237.
  JERSEY, arborescent cabbages of, i. 323.
  JESSAMINE, i. 394.
  JEITTELES, Hungarian sheep-dogs, i. 24;
    crossing of domestic and wild cats, i. 44.
  JOHN, King, importation of stallions from Flanders by, ii. 203.
  JOHNSON, D., occurrence of stripes on young wild pigs in India, i. 76.
  JORDAN, A., on Vibert's experiments on the vine, i. 332;
    origin of varieties of the apple, i. 350;
    varieties of pears found wild in woods, ii. 260.
  JOURDAN, parthenogenesis in the silk moth, ii. 364.
  JUAN DE NOVA, wild dogs on, i. 27.
  JUAN FERNANDEZ, dumb dogs on, i. 27.
  _Juglans regia_, i. 356-357.
  JUKES, Prof., origin of the Newfoundland dog, i. 42.
  JULIEN, Stanislas, early domestication of pigs in China, i. 68;
    antiquity of the domestication of the silk-worm in China, i. 300.
  JUMPERS, a breed of fowls, i. 230.
  JUNIPER, variations of the, i. 361, 364.
  _Juniperus suecica_, i. 361.
  _Jussiæa grandiflora_, ii. 170.
  JUSSIEU, A. de, structure of the pappus in _Carthamus_, ii. 316.

  KAIL, Scotch, reversion in, ii. 32.
  "KALA-PAR" pigeon, i. 142.
  KALES, i. 323.
  KALM, P., on maize, i. 322, ii. 307;
    introduction of wheat into Canada, i. 315;
    sterility of trees growing in marshes and dense woods, ii. 170.
  "KALMI Lotan," tumbler pigeon, i. 151.
  KANE, Dr., on Esquimaux dogs, i. 21.
  KARAKOOL sheep, i. 98.
  KARKEEK, on inheritance in the horse, ii. 10.
  "KARMELITEN Taube," i. 156.
  KARSTEN on _Pulex penetrans_, ii. 275.
  KATTYWAR horses, i. 58.
  KEELEY, R., pelorism in _Galeobdolon luteum_, ii. 59.
  KERNER on the culture of Alpine plants, ii. 163.
  KESTREL, breeding in captivity, ii. 154.
  "KHANDÉSI," i. 141.
  KHANG-HI, selection of a variety of rice by, ii. 205.
  KIANG, ii. 43.
  KIDD, on the canary bird, i. 77, ii. 275.
  KIDNEY Bean, i. 371;
    varieties of, ii. 256, 275.
  {460}
  KIDNEYS, compensatory development of the, ii. 300;
    fusion of the, ii. 341;
    shape of, in birds, influenced by the form of the pelvis, ii. 344.
  KING, Col., domestication of rock doves from the Orkneys, i. 184, 185.
  KING, P. S., on the Dingo, i. 21, 28.
  KIRBY and Spence, on the growth of galls, ii. 283.
  KIRGHISIAN sheep, i. 98.
  KITE, breeding in captivity, ii. 154.
  KLEINE, variability of bees, i. 298.
  KNIGHT, Andrew, on crossing horses of different breeds, i. 51;
    crossing varieties of peas, i. 326, ii. 129;
    persistency of varieties of peas, i. 329;
    origin of the peach, i. 338;
    hybridisation of the morello by the Elton cherry, i. 347;
    on seedling cherries, _ibid._;
    variety of the apple not attacked by coccus, i. 349;
    intercrossing of strawberries, i, 351, 352;
    broad variety of the cock's comb, i. 365;
    bud variation in the cherry and plum, i. 375;
    crossing of white and purple grapes, i. 393;
    experiments in crossing apples, i. 402, ii. 129;
    hereditary disease in plants, ii. 11;
    on interbreeding, ii. 116;
    crossed varieties of wheat, ii. 130;
    necessity of intercrossing in plants, ii. 175;
    on variation, ii. 256, 257;
    effects of grafting, i. 387, ii. 278;
    bud-variation in a plum, ii. 289;
    compulsory flowering of early potatoes, ii. 343;
    correlated variation of head and limbs, ii. 323.
  KNOX, Mr., breeding of the eagle owl in captivity, ii. 154.
  KOCH, degeneracy in the turnip, i. 325.
  KOHLRABI, i. 323.
  KÖLREUTER, reversion in hybrids, i. 392, ii. 36;
    acquired sterility of crossed varieties of plants, i. 358, ii. 101;
    absorption of _Mirabilis vulgaris_ by _M. longiflora_, ii. 88;
    crosses of species of _Verbascum_, ii. 93, 107;
    on the hollyhock, ii. 107;
    crossing varieties of tobacco, ii. 108;
    benefits of crossing plants, ii. 130, 131, 175-176;
    self-impotence in _Verbascum_, ii. 136, 141;
    effects of conditions of growth upon fertility in _Mirabilis_, ii. 164;
    great development of tubers in hybrid plants, ii. 172;
    inheritance of plasticity, ii. 241;
    variability of hybrids of _Mirabilis_, ii. 265;
    repeated crossing a cause of variation, ii. 267-268;
    number of pollen-grains necessary for fertilization, ii. 363.
  "KRAUSESCHWEIN," i. 67.
  KROHN, on the double reproduction of Medusæ, ii. 384.
  "KROPF-TAUBEN," i. 137.

  LABAT, on the tusks of feral bears in the West Indies, i. 77;
    on French wheat grown in the West Indies, ii. 307;
    on the culture of the vine in the West Indies, ii. 308.
  LABURNUM, Adam's, see _Cytisus Adami_;
    oak-leaved, reversion of, i. 382;
    pelorism in the, ii. 346;
    Waterer's, i. 390.
  LACHMANN, on gemmation and fission, ii. 358.
  _Lachnanthes tinctoria_, ii. 227, 336.
  LACTATION, imperfect, hereditary, ii. 8;
    deficient, of wild animals in captivity, ii. 158.
  LADRONE islands, cattle of, i. 86.
  LAING, Mr., resemblance of Norwegian and Devonshire cattle, i. 82.
  LAKE-DWELLINGS, sheep of, i. 94, ii. 427;
    cattle of, ii. 427;
    absence of the fowl in, i. 246;
    cultivated plants of, i. 309, ii. 427, 429;
    cereals of, i. 317-319;
    peas found in, i. 326;
    beans found in, i. 330.
  LAMARE-PIQUOT, observations on half-bred North American wolves, i. 22.
  LAMBERT, A. B., on _Thuja pendula_ or _filiformis_, i. 362.
  LAMBERT family, ii. 4, 76.
  LAMBERTYE on strawberries, i. 351, 352;
    five-leaved variety of _Fragaria collina_, i. 353.
  LANDT, L., on sheep in the Faroe islands, ii. 103.
  LA PLATA, wild dogs of, i. 27;
    feral cat from, i. 47.
  LARCH, ii. 310.
  LARKSPURS, insect agency necessary for the full fecundation of, ii. 21.
  _Larus argentatus_, ii. 157.
  _Larus tridactylus_, ii. 302.
  LASTERYE, merino sheep in different countries, i. 99.
  LATENT characters, ii. 51-56.
  LATHAM, on the fowl not breeding in the extreme north, ii. 161.
  _Lathyrus_, ii. 38.
  _Lathyrus aphaca_, ii. 343.
  _Lathyrus odoratus_, ii. 20, 91, 93, 311, 393.
  LA TOUCHE, J. D., on a Canadian apple with dimidiate fruit, i. 392-393.
  "LATZ-TAUBE," i. 154.
  LAUGHER pigeon, i. 155, 207.
  _Laurus sassafras_, ii. 274.
  LAWRENCE, J., production of a new breed of fox-hounds, i. 40;
    occurrence of canines in mares, i. 50;
    on three-parts-bred horses, i. 54;
    on inheritance in the horse, ii. 10-11.
  LAWSON, Mr., varieties of the potato, i. 330.
  LAXTON, Mr., bud-variation in the gooseberry, i. 376;
    crossing of varieties of the pea, i. 397-398;
  {461}
    double-flowered peas, ii. 168.
  LAYARD, E. L., resemblance of a Caffre dog to the Esquimaux breed, i. 25,
      ii. 286;
    crossing of the domestic cat with _Felis Caffra_, i. 44;
    feral pigeons in Ascension, i. 190;
    domestic pigeons of Ceylon, i. 206;
    on _Gallus Stanleyi_, i. 234;
    on black-skinned Ceylonese fowls, i. 256.
  LE COMPTE family, blindness inherited in, ii. 78.
  LECOQ, bud-variation in _Mirabilis jalapa_, i. 382;
    hybrids of _Mirabilis_, i. 393, ii. 169, 265;
    crossing in plants, ii. 127;
    fecundation of _Passiflora_, ii. 137;
    hybrid _Gladiolus_, ii. 139;
    sterility of _Ranunculus ficaria_, ii. 170;
    villosity in plants, ii. 277;
    double asters, ii. 316.
  LE COUTEUR, J., varieties of wheat, i. 313-315;
    acclimatisation of exotic wheat in Europe, i. 315;
    adaptation of wheat to soil and climate, i. 316;
    selection of seed-corn, i. 318;
    on change of soil, ii. 147;
    selection of wheat, ii. 200;
    natural selection in wheat, ii. 233;
    cattle of Jersey, ii. 234.
  LEDGER, Mr., on the Llama and Alpaca, ii. 208.
  LEE, Mr., his early culture of the pansy, i. 368.
  _Leersia oryzoides_, ii. 91.
  LEFOUR, period of gestation in cattle, i. 87.
  LEGS, of fowls, effects of disuse on, i. 270-272;
    characters and variations of, in ducks, i. 284-288;
    fusion of, ii. 341.
  LEGUAT, cattle of the Cape of Good Hope, i. 88.
  LEHMANN, occurrence of wild double-flowered plants near a hot spring, ii.
      168.
  LEIGHTON, W. A., propagation of a weeping yew by seed, ii. 19.
  LEITNER, effects of the removal of anthers, ii. 167.
  LEMMING, ii. 152.
  LEMOINE, variegated _Symphytum_ and _Phlox_, i. 384.
  LEMON, i. 334, 335;
    orange fecundated by pollen of the, i. 399.
  LEMURS, hybrid, ii. 153.
  LEPORIDES, ii. 98-99, 152.
  LEPSIUS, figures of ancient Egyptian dogs, i. 17;
    domestication of pigeons in ancient Egypt, i. 204.
  _Leptotes_, ii. 134.
  _Lepus glacialis_, i. 111.
  _Lepus magellanicus_, i. 112.
  _Lepus nigripes_, i. 108.
  _Lepus tibetanus_, i. 111.
  _Lepus variabilis_, i. 111.
  LEREBOULLET, double monsters of fishes, ii. 340.
  LESLIE, on Scotch wild cattle, i. 85.
  LESSON, on _Lepus magellanicus_, i. 112.
  LEUCKART on the larva of Cecidomyidæ, ii. 360.
  LEWIS, G., cattle of the West Indies, ii. 229.
  LHERBETTE and Quatrefages, on the horses of Circassia, ii. 102, 225.
  LIEBIG, differences in human blood, according to complexion, ii. 276.
  LIEBREICH, occurrence of pigmentary retinitis in deaf-mutes, ii. 328.
  LICHENS, sterility in, ii. 171.
  LICHTENSTEIN, resemblance of Bosjesman's dogs to _Canis mesomelas_, i.
      25;
    Newfoundland dog at the Cape of Good Hope, i. 36.
  LILACS, ii. 164.
  LILIACEÆ, contabescence in, ii. 165.
  _Lilium candidum_, ii. 137.
  LIMBS, regeneration of, ii. 376-377.
  LIMBS and head, correlated variation of, ii. 323.
  LIME, effect of, upon shells of the mollusca, ii. 280.
  LIME tree, changes of by age, i. 364, 387.
  LIMITATION, sexual, ii. 71-75.
  LIMITATION, supposed, of variation, ii. 416.
  _Linaria_, pelorism in, ii. 58, 61, 346;
    peloric, crossed with the normal form, ii. 70;
    sterility of, ii. 166.
  _Linaria vulgaris_ and _purpurea_, hybrids of, ii. 94.
  LINDLEY, John, classification of varieties of cabbages, i. 324;
    origin of the peach, i. 338;
    influence of soil on peaches and nectarines, i. 340;
    varieties of the peach and nectarine, i. 343;
    on the New Town pippin, i. 349;
    freedom of the Winter Majetin apple from coccus, i. 349;
    production of monoecious Hautbois strawberries by bud-selection, i.
        353;
    origin of the large tawny nectarine, i. 375;
    bud-variation in the gooseberry, i. 376;
    hereditary disease in plants, ii. 11;
    on double flowers, ii. 167;
    seeding of ordinarily seedless fruits, ii. 168;
    sterility of _Acorus calamus_, ii. 170;
    resistance of individual plants to cold, ii. 309.
  LINNÆUS, summer and winter wheat regarded as distinct species by, i. 315;
    on the single-leaved strawberry, i. 353;
    sterility of Alpine plants in gardens, ii. 163;
    recognition of individual reindeer by the Laplanders, ii. 251;
    growth of tobacco in Sweden, ii. 307.
  LINNET, ii. 158.
  _Linota cannabina_, ii. 158.
  {462}
  LINUM, ii. 165.
  LION, fertility of, in captivity, ii. 150, 151.
  LIPARI, feral rabbits of, i. 113.
  LIVINGSTONE, Dr., striped young pigs on the Zambesi, i. 77;
    domestic rabbits at Loanda, i. 112;
    use of grass-seeds as food in Africa, i. 308;
    planting of fruit-trees by the Batokas, i. 309;
    character of half-castes, ii. 46;
    taming of animals among the Barotse, ii. 160;
    selection practised in South Africa, ii. 207, 209.
  LIVINGSTONE, Mr., disuse a cause of drooping ears, ii. 301.
  LIZARDS, reproduction of tail in, ii. 294;
    with a double tail, ii. 341.
  LLAMA, selection of, ii. 208.
  LLOYD, Mr., taming of the wolf, i. 26;
    English dogs in northern Europe, i. 36;
    fertility of the goose increased by domestication, i. 288;
    number of eggs laid by the wild goose, ii. 112;
    breeding of the capercailzie in captivity, ii. 156.
  LOANDA, domestic rabbits at, i. 112.
  _Loasa_, hybrid of two species of, ii. 98.
  _Lobelia_, reversion in hybrids of, ii. 392;
    contabescence in, ii. 166.
  _Lobelia fulgens_, _cardinalis_, and _syphilitica_, ii. 136.
  LOCKHART, Dr., on Chinese pigeons, i. 206.
  LOCUST-TREE, ii. 274.
  LOISELEUR-DESLONGCHAMPS, originals of cultivated plants, i. 307;
    Mongolian varieties of wheat, i. 313;
    characters of the ear in wheat, i. 314;
    acclimatisation of exotic wheat in Europe, i. 315;
    effect of change of climate on wheat, i. 316;
    on the supposed necessity of the coincident variation of weeds and
        cultivated plants, i. 317;
    advantage of change of soil to plants, ii. 146.
  _Lolium temulentum_, variable presence of barbs in, i. 314.
  LONG-TAILED sheep, i. 94, 95.
  LOOCHOO islands, horses of, i. 53.
  LORD, J. K., on Canis latrans, i. 22.
  "LORI RAJAH," how produced, ii. 280.
  _Lorius garrulus_, ii. 280.
  "LOTAN," tumbler pigeon, i. 150.
  LOUDON, J. W., varieties of the carrot, i. 326;
    short duration of varieties of peas, i. 329;
    on the glands of peach-leaves, i. 343;
    presence of bloom on Russian apples, i. 349;
    origin of varieties of the apple, i. 350;
    varieties of the gooseberry, i. 354;
    on the nut tree, i. 357;
    varieties of the ash, i. 360;
    fastigate juniper (_J. suecica_), i. 361;
    on _Ilex aquifolium ferox_, i. 362;
    varieties of the Scotch fir, i. 363;
    varieties of the hawthorn, _ibid._;
    variation in the persistency of leaves on the elm and Turkish oak, i.
        363;
    importance of cultivated varieties, _ibid._;
    varieties of _Rosa spinosissima_, i. 367;
    variation of dahlias from the same seed, i. 370;
    production of Provence roses from seeds of the moss rose, i. 380;
    effect of grafting the purple-leaved upon the common hazel, i. 395;
    nearly evergreen Cornish variety of the elm, ii. 310.
  LOW, G., on the pigs of the Orkney islands, i. 70.
  LOW, Prof., pedigrees of greyhounds, ii. 3;
    origin of the dog, i. 10;
    burrowing instinct of a half-bred Dingo, i. 28;
    inheritance of qualities in horses, i. 51;
    comparative powers of English race-horses, Arabs, &c., i. 54;
    British breeds of cattle, i. 80;
    wild cattle of Chartley, i. 84;
    effect of abundance of food on the size of cattle, i. 91;
    effects of climate on the skin of cattle, i. 92, ii. 326;
    on interbreeding, ii. 116;
    selection in Hereford cattle, ii. 214;
    formation of new breeds, ii. 244;
    on "sheeted" cattle, ii. 349.
  LOWE, Mr., on hive bees, i. 299.
  LOWE, REV. Mr., on the range of _Pyrus malus_ and _P. acerba_, i. 348.
  "LOWTAN" tumbler pigeon, i. 150.
  _Loxia pyrrhula_, ii. 154.
  LUBBOCK, Sir J., developments of the Ephemeridæ, ii. 366.
  LUCAS, P., effects of cross-breeding on the female, i. 404;
    hereditary diseases, ii. 7, 78-79;
    hereditary affections of the eye, ii. 9-10;
    inheritance of anomalies in the human eye and in that of the horse, ii.
        10, 11;
    inheritance of polydactylism, ii. 13;
    morbid uniformity in the same family, ii. 17;
    inheritance of mutilations, ii. 23;
    persistency of cross-reversion, ii. 35;
    persistency of character in breeds of animals in wild countries, ii.
        64;
    prepotency of transmission, ii. 65, 68;
    supposed rules of transmission in crossing animals, ii. 68;
    sexual limitations of transmission of peculiarities, ii. 72-73;
    absorption of the minority in crossed races, ii. 88;
    crosses without blending of certain characters, ii. 92;
    on interbreeding, ii. 116;
    variability dependent on reproduction, ii. 250;
    period of action of variability, ii. 260;
    inheritance of deafness in cats, ii. 329;
    complexion and constitution, ii. 335.
  LUCAZE-DUTHIERS, structure and growth of galls, ii. 282-284.
  LUIZET, grafting of a peach-almond on a peach, i. 338.
  {463}
  LÜTKE, cats of the Caroline Archipelago, i. 47.
  LUXURIANCE, of vegetative organs, a cause of sterility in plants, ii.
      168-171.
  LYONNET, on the scission of _Nais_, ii. 358.
  _Lysimachia nummularia_, sterility of, ii. 170.
  _Lythrum_, trimorphic species of, ii. 400.
  _Lythrum salicaria_, ii. 183;
    contabescence in, ii. 166.
  _Lytta vesicatoria_, affecting the kidneys, ii. 380.

  _Macacus_, species of, bred in captivity, ii. 153.
  MACAULAY, Lord, improvement of the English horse, ii. 213.
  MCCLELLAND, Dr., variability of fresh-water fishes in India, ii. 259.
  MCCOY, Prof., on the dingo, i. 26.
  MACFAYDEN, influence of soil in producing sweet or bitter oranges from
      the same seed, i. 335.
  MACGILLIVRAY, domestication of the rock-dove, i. 185;
    feral pigeons in Scotland, i. 190;
    number of vertebræ in birds, i. 266;
    on wild geese, i. 287;
    number of eggs of wild and tame ducks, ii. 112.
  MACKENZIE, Sir G., peculiar variety of the potato, i. 330.
  MACKENZIE, P., bud-variation in the currant, i. 376.
  MACKINNON, Mr., horses of the Falkland islands, i. 52;
    feral cattle of the Falkland islands, i. 86.
  MACKNIGHT, C., on interbreeding cattle, ii. 118.
  MACNAB, Mr., on seedling weeping birches, ii. 18;
    non-production of the weeping beech by seed, ii. 19.
  MADAGASCAR, cats of, i. 47.
  MADDEN, H., on interbreeding cattle, ii. 118.
  MADEIRA, rock pigeon of, i. 184.
  _Magnolia grandiflora_, ii. 308.
  MAIZE, its unity of origin, i. 320;
    antiquity of, _ibid._;
    with husked grains said to grow wild, _ibid._;
    variation of, i. 321;
    irregularities in the flowers of, i. 321;
    persistence of varieties, _ibid._;
    adaptation of to climate, i. 322, ii. 307;
    acclimatisation of, ii. 313, 347;
    crossing of, i. 400, ii. 104-105;
    extinct Peruvian varieties of, ii. 425.
  MALAY fowl, i. 227.
  MALAY Archipelago, horses of, i. 53;
    short-tailed cats of, i. 47;
    striped young wild pigs of, i. 76;
    ducks of, i. 280.
  MALE, influence of, on the fecundated female, i. 397-406;
    supposed influence of, on offspring, ii. 68.
  MALE flowers, appearance of, among female flowers in maize, i. 321.
  MALFORMATIONS, hereditary, ii. 79.
  _Malva_, fertilisation of, i. 402, ii. 363.
  _Mamestra suasa_, ii. 157.
  MAMMÆ, variable in number in the pig, i. 74;
    rudimentary, occasional full development of, in cows, i. 87, ii. 317;
    four present in some sheep, i. 95;
    variable in number in rabbits, i. 106;
    latent functions of, in male animals, ii. 52, 317;
    supernumerary and inguinal, in women, ii. 57.
  MANGLES, Mr., annual varieties of the heartsease, ii. 305.
  MANTELL, Mr., taming of birds by the New Zealanders, ii. 161.
  MANU, domestic fowl noticed in the Institutes of, i. 246.
  MANURE, effect of, on the fertility of plants, ii. 163.
  MANX cats, i. 46, ii. 66.
  MARCEL de Serres, fertility of the ostrich, ii. 156.
  MARIANNE islands, varieties of _Pandanus_ in, ii. 256.
  MARKHAM, Gervase, on rabbits, i. 104, ii. 204.
  MARKHOR, probably one of the parents of the goat, i. 101.
  MARQUAND, cattle of the channel islands, i. 80.
  MARRIMPOEY, inheritance in the horse, ii. 10.
  MARROW, vegetable, i. 357.
  MARRYATT, Capt., breeding of asses in Kentucky, ii. 237.
  MARSDEN, notice of _Gallus giganteus_, i. 235.
  MARSHALL, Mr., voluntary selection of pasture by sheep, i. 96;
    adaptation of wheats to soil and climate, i. 316;
    "Dutch-buttocked" cattle, ii. 8;
    segregation of herds of sheep, ii. 103;
    advantage of change of soil to wheat and potatoes, ii. 146;
    fashionable change in the horns of cattle, ii. 210;
    sheep in Yorkshire, ii. 235.
  MARSHALL, Prof., growth of the brain in microcephalous idiots, ii. 389.
  MARTENS, E. Von, on _Achatinella_, ii. 53.
  MARTIN, W. C. L., origin of the dog, i. 16;
    Egyptian dogs, i. 18;
    barking of a Mackenzie River dog, i. 27;
    African hounds in the Tower menagerie, i. 32;
    on dun horses and dappled asses, i. 55;
    breeds of the horse, i. 49;
    wild horses, i. 51;
    Syrian breeds of asses, i. 62;
    asses without stripes, i. 63;
    effects of cross-breeding on the female in dogs, i. 404;
    striped legs of mules, ii. 42.
  MARTINS, defective instincts of silkworms, i. 304.
  MARTINS, C., fruit trees of Stockholm, ii. 307.
  {464}
  MASON, W., bud-variation in the ash, i. 382.
  MASTERS, Dr., reversion in the spiral-leaved weeping willow, i. 383;
    on peloric flowers, ii. 58;
    pelorism in a clover, ii. 346;
    position as a cause of pelorism, ii. 345, 347.
  MASTERS, Mr., persistence of varieties of peas, i. 329;
    reproduction of colour in hyacinths, ii. 20;
    on hollyhocks, ii. 107;
    selection of peas for seed, ii. 199-200;
    on _Opuntia leucotricha_, ii. 286;
    reversion by the terminal pea in the pod, ii. 347.
  MASTIFF, sculptured on an Assyrian monument, i. 17, ii. 429;
    Tibetan, i. 35-36, ii. 278.
  MATTHEWS, Patrick, on forest trees, ii. 237.
  _Matthiola annua_, i. 399, ii. 20.
  _Matthiola incana_, i. 381, 399.
  MAUCHAMP, merino sheep, i. 100.
  MAUDUYT, crossing of wolves and dogs in the Pyrenees, i. 24.
  MAUND, Mr. crossed varieties of wheat, ii. 130.
  MAUPERTUIS, axiom of "least action," i. 12.
  MAURITIUS, importation of goats into, i. 101.
  MAW, G., correlation of contracted leaves and flowers in pelargoniums,
      ii. 330, 331.
  MAWZ, fertility of _Brassica rapa_, ii. 165.
  _Maxillaria_, self-fertilised capsules of, ii. 134;
    number of seeds in, ii. 379.
  _Maxillaria atro-rubens_, fertilisation of, by _M. squalens_, ii. 133.
  MAYES, M., self-impotence in _Amaryllis_, ii. 139.
  MECKEL, on the number of digits, ii. 13;
    correlation of abnormal muscles in the leg and arm, ii. 322.
  MEDUSÆ, development of, ii. 368, 384.
  MEEHAN, Mr., comparison of European and American trees, ii. 281.
  _Meleagris mexicana_, i. 292.
  _Meles taxus_, ii. 151.
  MELONS, i. 359-360;
    mongrel, supposed to be produced from a twin-seed, i. 391;
    crossing of varieties of, i. 399, ii. 108, 129;
    inferiority of, in Roman times, ii. 216;
    changes in, by culture and climate, ii. 275;
    serpent, correlation of variations in, ii. 330;
    analogous variations in, ii. 349.
  MEMBRANES, false, ii. 294-295.
  MÉNÉTRIES, on the stomach of _Strix grallaria_, ii. 302.
  MENINGITIS, tubercular, inherited, ii. 78.
  METAGENESIS, ii. 366.
  METAMORPHOSIS, ii. 366.
  METAMORPHOSIS and development, ii. 388, 389.
  METZGER, on the supposed species of wheat, i. 312-313;
    tendency of wheat to vary, i. 315;
    variation of maize, i. 321-322;
    cultivation of American maize in Europe, i. 322, ii. 347;
    on cabbages, i. 323-325;
    acclimatisation of Spanish wheat in Germany, ii. 26;
    advantage of change of soil to plants, ii. 146;
    on rye, ii. 254;
    cultivation of different kinds of wheat, ii. 261.
  MEXICO, dog from, with tan spots on the eyes, i. 29;
    colours of feral horses in, i. 61.
  MEYEN, on sending of bananas, ii. 168.
  MICE, grey and white, colours of, not blended by crossing, ii. 92;
    rejection of bitter almonds by, ii. 232;
    naked, ii. 279.
  MICHAUX, F., roan-coloured feral horses of Mexico, i. 61;
    origin of domestic turkey, i. 292;
    on raising peaches from seed, i. 339.
  MICHEL, F., selection of horses in mediæval times, ii. 203;
    horses preferred on account of slight characters, ii. 209.
  MICHELY, effects of food on caterpillars, ii. 280;
    on _Bombyx hesperus_, ii. 304.
  MICROPHTHALMIA, associated with defective teeth, ii. 328.
  MIDDENS, Danish, remains of dogs in, i. 18, ii. 427.
  MIGNONETTE, ii. 237, 311.
  MILLET, i. 371.
  MILLS, J., diminished fertility of mares when first turned out to grass,
      ii. 161.
  MILNE-EDWARDS, on the development of the crustacea, ii. 368.
  MILNE-EDWARDS, A., on a crustacean with a monstrous eye-peduncle, ii.
      391.
  _Milvus niger_, ii. 154.
  _Mimulus luteus_, ii. 128.
  MINOR, W. C., gemmation and fission in the Annelida, ii. 358.
  _Mirabilis_, fertilisation of, ii. 363;
    hybrids of, ii. 131, 169, 265.
  _Mirabilis jalapa_, i. 382, 393.
  _Mirabilis longiflora_, ii. 88.
  _Mirabilis vulgaris_, ii. 88.
  _Misocampus_ and _Cecidomyia_, i. 5.
  MITCHELL, Dr., effects of the poison of the rattlesnake, ii. 289.
  MITFORD, Mr., notice of the breeding of horses by Erichthonius, ii. 202.
  MOCCAS Court, weeping oak at, ii. 18.
  MOGFORD, horses poisoned by fool's parsley, ii. 337.
  MÖLLER, L., effects of food on insects, ii. 281.
  MOQUIN-TANDON, original form of maize, i. 320;
    variety of the double columbine, i. 365;
  {465}
    peloric flowers, ii. 58-59, 61;
    position as a cause of pelorism in flowers, ii. 345;
    tendency of peloric flowers to become irregular, ii. 70;
    on monstrosities, ii. 254;
    correlation in the axis and appendages of plants, ii. 321;
    fusion of homologous parts in plants, ii. 339, 341-342;
    on a bean with monstrous stipules and abortive leaflets, ii. 343;
    conversion of parts of flowers, ii. 392.
  MOLE, white, ii. 332.
  MOLL and Gayot, on cattle, i. 80, ii. 96, 210.
  MOLLUSCA, change in shells of, ii. 280.
  MONKE, Lady, culture of the pansy by, i. 368.
  MONKEYS, rarely fertile in captivity, ii. 153.
  MONNIER, identity of summer and winter wheat, i. 315.
  MONSTER, cyclopean, ii. 341.
  MONSTERS, double, ii. 339-340.
  MONSTROSITIES, occurrence of, in domesticated animals and cultivated
      plants, i. 366, ii. 254;
    due to persistence of embryonic conditions, ii. 57;
    occurring by reversion, ii. 57-60;
    a cause of sterility, ii. 166-167;
    caused by injury to the embryo, ii. 269.
  MONTEGAZZA, growth of a cock's-spur inserted into the eye of an ox, ii.
      369.
  MONTGOMERY, E., formation of cells, ii. 370.
  MOOR, J. H., deterioration of the horse in Malasia, i. 53.
  MOORCROFT, Mr., on Hasora wheat, i. 313;
    selection of white-tailed yaks, ii. 206;
    melon of Kaschmir, ii. 275;
    varieties of the apricot cultivated in Ladakh, i. 345;
    varieties of the walnut cultivated in Kaschmir, i. 356.
  MOORE, Mr., on breeds of pigeons, i. 148, 156, 208, 209, 211.
  MOORUK, fertility of, in captivity, ii. 156.
  MORLOT, dogs of the Danish Middens, i. 18;
    sheep and horse of the bronze period, ii. 427.
  _Mormodes ignea_, ii. 53.
  MOROCCO, estimation of pigeons in, i. 205.
  MORREN, C., on pelorism, ii. 58;
    in _Calceolaria_, ii. 346;
    non-coincidence of double flowers and variegated leaves, ii. 167.
  MORRIS, Mr., breeding of the Kestrel in captivity, ii. 154.
  MORTON, Lord, effect of fecundation by a quagga on an Arab mare, i.
      403-404.
  MORTON, Dr., origin of the dog, i. 16;
    hybrid of zebra and mare, ii. 42.
  _Morus alba_, i. 334.
  MOSCOW, rabbits of, i. 106, 120;
    effects of cold on pear-trees at, ii. 307.
  MOSSES, sterility in, ii. 171;
    retrogressive metamorphosis in, ii. 361.
  MOSS-ROSE, probable origin of, from _Rosa centifolia_, i. 379;
    Provence roses produced from seeds of, i. 380.
  MOSTO, Cada, on the introduction of rabbits into Porto Santo, i. 113.
  MOTTLING of fruits and flowers, i. 400.
  MOUFFLON, i. 94.
  MOUNTAIN-ASH, ii. 230.
  MOUSE, Barbary, ii. 152.
  "MÖVEN-TAUBE," i. 148.
  MOWBRAY, Mr., on the eggs of game fowls, i. 248;
    early pugnacity of game cocks, i. 251;
    diminished fecundity of the pheasant in captivity, ii. 155.
  MOWBRAY, Mr., reciprocal fecundation of _Passiflora alata_ and
      _racemosa_, ii. 137.
  MULATTOS, character of, ii. 46.
  MULBERRY, i. 334, ii. 256.
  MULE and hinny, differences in the, ii. 67-68.
  MULES, striped colouring of, ii. 42;
    obstinacy of, ii. 45;
    production of, among the Romans, ii. 110;
    noticed in the Bible, ii. 202.
  MÜLLER, Fritz, reproduction of orchids, ii. 134-135;
    development of crustacea, ii. 368;
    number of seeds in a _maxillaria_, ii. 379.
  MÜLLER, H., on the face and teeth in dogs, i. 34, 73, ii. 345.
  MÜLLER, J., production of imperfect nails after partial amputation of the
      fingers, ii. 15;
    tendency to variation, ii. 252;
    atrophy of the optic nerve consequent on destruction of the eye, ii.
        297;
    on Janus-like monsters, ii. 340;
    on gemmation and fission, ii. 358;
    identity of ovules and buds, ii. 360;
    special affinities of the tissues, ii. 380.
  MÜLLER, Max, antiquity of agriculture, ii. 243.
  MULTIPLICITY of origin of pigeons, hypotheses of, discussed, i. 188-194.
  MUNIZ, F., on Niata cattle, i. 90.
  MUNRO, R., on the fertilisation of orchids, ii. 133;
    reproduction of _Passiflora alata_, ii. 138.
  "MURASSA" pigeon, i. 144.
  MURPHY, J. J., the structure of the eye not producible by selection, ii.
      222.
  _Mus alexandrinus_, ii. 87-88.
  _Musa sapientum_, _Chinensis_ and _Cavendishii_, i. 377.
  _Muscari comosum_, ii. 185, 316.
  MUSCLES, effects of use on, ii. 297.
  MUSK duck, feral hybrid of, with the common duck, i. 190.
  {466}
  MUSMON, female, sometimes hornless, i. 95.
  MUTILATIONS, inheritance or non-inheritance of, ii. 22-24, 397.
  MYATT, on a five-leaved variety of the strawberry, i. 353.
  MYOPIA, hereditary, ii. 8.
  MYRIAPODA, regeneration of lost parts in, ii. 15, 294.

  NAILS, growing on stumps of fingers, ii. 394.
  NAIS, scission of, ii. 358.
  NAMAQUAS, cattle of the, i. 88, ii. 207.
  NARCISSUS, double, becoming single in poor soil, ii. 167.
  NARVAEZ, on the cultivation of native plants in Florida, i. 312.
  _Nasua_, sterility of, in captivity, ii. 152.
  "NATAS," or Niatas, a South American breed of cattle, i. 89-91.
  NATHUSIUS, H. von, on the pigs of the Swiss lake-dwellings, i. 68;
    on the races of pigs, i. 65-68;
    convergence of character in highly-bred pigs, i. 73, ii. 241;
    causes of changes in the form of the pig's skull, i. 72-73;
    changes in breeds of pigs by crossing, i. 78;
    change of form in the pig, ii. 279;
    effects of disuse of parts in the pig, ii. 299;
    period of gestation in the pig, i. 74;
    appendages to the jaw in pigs, i. 76;
    on _Sus pliciceps_, i. 70;
    period of gestation in sheep, i. 97;
    on Niata cattle, i. 89;
    on short-horn cattle, ii. 118;
    on interbreeding, ii. 116;
    in the sheep, ii. 120;
    in pigs, ii. 122;
    unconscious selection in cattle and pigs, ii. 214;
    variability of highly selected races, ii. 238.
  NATO, P., on the Bizzaria orange, i. 391.
  NATURAL selection, its general principles, i. 2-14.
  NATURE, sense in which the term is employed, i. 6.
  NAUDIN, supposed rules of transmission in crossing plants, ii. 68;
    on the nature of hybrids, ii. 48-49;
    essences of the species in hybrids, ii. 386, 401;
    reversion of hybrids, ii. 36, 49-50;
    reversion in flowers by stripes and blotches, ii. 37;
    hybrids of _Linaria vulgaris_ and _purpurea_, ii. 94;
    pelorism in _Linaria_, ii. 58, 346;
    crossing of peloric _Linaria_ with the normal form, ii. 70;
    variability in _Datura_, ii. 266;
    hybrids of _Datura lævis_ and _stramonium_, i. 392;
    prepotency of transmission of _Datura stramonium_ when crossed, ii. 67;
    on the pollen of _Mirabilis_ and of hybrids, i. 389;
    fertilisation of _Mirabilis_, ii. 363;
    crossing of _Chamærops humilis_ and the date palm, i. 399;
    cultivated Cucurbitaceæ, i. 357-360, ii. 108;
    rudimentary tendrils in gourds, ii. 316;
    dwarf _Cucurbitæ_, ii. 330;
    relation between the size and number of the fruit in _Cucurbita pepo_,
        ii. 343;
    analogous variation in _Cucurbitæ_, ii. 349;
    acclimatisation of Cucurbitaceæ, ii. 313;
    production of fruit by sterile hybrid Cucurbitaceæ, ii. 172;
    on the melon, i. 360, ii. 108, 275;
    incapacity of the cucumber to cross with other species, i. 359.
  NECTARINE, i. 336-344;
    derived from the peach, i. 337, 339-342;
    hybrids of, i. 339;
    persistency of characters in seedling, i. 340;
    origin of, _ibid._;
    produced on peach trees, i. 340-341;
    producing peaches, i. 341;
    variation in, i. 342-343;
    bud-variation in, i. 374;
    glands in the leaves of the, ii. 231;
    analogous variation in, ii. 348.
  NECTARY, variations of, in pansies, i. 369.
  NEES, on changes in the odour of plants, ii. 274.
  "NEGRO" cat, i. 46.
  NEGROES, polydactylism in, ii. 14;
    selection of cattle practised by, ii. 207.
  NEOLITHIC period, domestication of _Bos longifrons_ and _primigenius_ in
      the, i. 81;
    cattle of the, distinct from the original species, i. 87;
    domestic goat in the, i. 101;
    cereals of the, i. 317.
  NERVE, optic, atrophy of the, ii. 297.
  NEUMEISTER, on the Dutch and German pouter pigeons, i. 138;
    on the Jacobin pigeon, i. 154;
    duplication of the middle flight feather in pigeons, i. 159;
    on a peculiarly coloured breed of pigeons, "Staarhalsige Taube," i.
        161;
    fertility of hybrid pigeons, i. 192;
    mongrels of the trumpeter pigeon, ii. 66;
    period of perfect plumage in pigeons, ii. 77;
    advantage of crossing pigeons, ii. 126.
  NEURALGIA, hereditary, ii. 79.
  NEW ZEALAND, feral cats of, i. 47;
    cultivated plants of, i. 311.
  NEWFOUNDLAND dog, modification of, in England, i. 42.
  NEWMAN, E., sterility of Sphingidæ under certain conditions, ii. 158.
  NEWPORT, G., non-copulation of _Vanessæ_ in confinement, ii. 157;
    regeneration of limbs in myriapoda, ii. 294;
    fertilisation of the ovule in batrachia, ii. 363.
  NEWT, polydactylism in the, ii. 14.
  NEWTON, A., absence of sexual distinctions in the Columbidæ, i. 162;
    production of a "black-shouldered" pea-hen among the ordinary kind, i.
        291;
    on hybrid ducks, ii. 157.
  NGAMI, Lake, cattle of, i. 88.
  "NIATA" cattle, i. 89-91;
    resemblance of to _Sivatherium_, i. 89;
  {467}
    prepotency of transmission of character by, ii. 66.
  "NICARD" rabbit, i. 107.
  NICHOLSON, Dr., on the cats of Antigua, i. 46;
    on the sheep of Antigua, i. 98.
  _Nicotiana_, crossing of varieties and species of, ii. 108;
    prepotency of transmission of characters in species of, ii. 67;
    contabescence of female organs in, ii. 166.
  _Nicotiana glutinosa_, ii. 108.
  NIEBUHR, on the heredity of mental characteristics in some Roman
      families, ii. 65.
  NIGHT-BLINDNESS, non-reversion to, ii. 36.
  NILSSON, Prof., on the barking of a young wolf, i. 27;
    parentage of European breeds of cattle, i. 80, 81;
    on _Bos frontosus_ in Scania, i. 81.
  NIND, Mr., on the dingo, i. 39.
  "NISUS formativus," i. 293, 294, 355.
  NITZSCH, on the absence of the oil-gland in certain Columbæ, i. 147.
  NON-INHERITANCE, causes of, ii. 24-26.
  "NONNAIN" pigeon, i. 154.
  NORDMANN, dogs of Awhasie, i. 25.
  NORMANDY, pigs of, with appendages under the jaw, i. 75.
  NORWAY, striped ponies of, i. 58.
  NOTT and Gliddon, on the origin of the dog, i. 16;
    mastiff represented on an Assyrian tomb, i. 17;
    on Egyptian dogs, i. 18;
    on the Hare-Indian dog, i. 22.
  _Notylia_, ii. 135.
  NOURISHMENT, excess of, a cause of variability, ii. 257.
  NUMBER, importance of, in selection, ii. 235.
  _Numida ptilorhyncha_, the original of the Guinea-fowl, i. 294.
  NUN pigeon, i. 155;
    known to Aldrovandi, i. 207.
  NUTMEG tree, ii. 237.

  OAK, weeping, i. 361, ii. 18, 241;
    pyramidal, i. 361;
    Hessian, i. 361;
    late-leaved, i. 363;
    variation in persistency of leaves of, i. 363;
    valueless as timber at the Cape of Good Hope, ii. 274;
    changes in, dependent on age, i. 387;
    galls of the, ii. 282.
  OATS, wild, i. 313;
    in the Swiss lake-dwellings, i. 319.
  OBERLIN, change of soil beneficial to the potato, ii. 146.
  ODART, Count, varieties of the vine, i. 333, ii. 278;
    bud-variation in the vine, i. 375.
  ODOUR and colour, correlation of, ii. 325.
  _Oecidium_, ii. 284.
  _Oenothera biennis_, bud-variation in, i. 382.
  OGLE, W., resemblance of twins, ii. 252.
  OIL-GLAND, absence of, in fantail pigeons, i. 147, 160.
  OLDFIELD, Mr., estimation of European dogs among the natives of
      Australia, ii. 215.
  OLEANDER, stock affected by grafting in the, i. 394.
  OLLIER, Dr., insertion of the periosteum of a dog beneath the skin of a
      rabbit, ii. 369.
  _Oncidium_, reproduction of, ii. 133-135, 164.
  ONIONS, crossing of, ii. 90;
    white, liable to the attacks of fungi and disease, ii. 228, 336.
  _Ophrys apifera_, self-fertilisation of, ii. 91;
    formation of pollen by a petal in, ii. 392.
  _Opuntia leucotricha_, ii. 277.
  ORANGE, i. 334-336;
    crossing of, ii. 91;
    with the lemon, i. 399, ii. 365;
    naturalisation of, in Italy, ii. 308;
    variation of, in North Italy, ii. 256;
    peculiar variety of, ii. 331;
    Bizzaria, i. 391;
    trifacial, _ibid._
  ORCHIDS, reproduction of, i. 402, 403; ii. 133-135.
  ORFORD, Lord, crossing greyhounds with the bulldog, i. 41.
  ORGANISMS, origin of, i. 13.
  ORGANISATION, advancement in, i. 8.
  ORGANS, rudimentary and aborted, ii. 315-318;
    multiplication of abnormal, ii. 391.
  ORIOLE, assumption of hen-plumage by a male in confinement, ii. 158.
  ORKNEY islands, pigs of, i. 70;
    pigeons of, i. 184.
  ORTHOPTERA, regeneration of hind legs in the, ii. 294.
  _Orthosia munda_, ii. 157.
  ORTON, R., on the effects of cross-breeding on the female, i. 404;
    on the Manx cat, ii. 66;
    on mongrels from the silk-fowl, ii. 67.
  OSBORNE, Dr., inherited mottling of the iris, ii. 10.
  OSPREY, preying on Black-fowls, ii. 230.
  OSTEN-SACKEN, Baron, on American oak galls, ii. 282.
  OSTEOLOGICAL characters of pigs, i. 66, 67, 71-74;
    of rabbits, i. 115-130;
    of pigeons, i. 162-167;
    of ducks, i. 282-284.
  OSTRICH, diminished fertility of the, in captivity, ii. 156.
  OSTYAKS, selection of dogs by the, ii. 206.
  OTTER, ii. 151.
  "OTTER" sheep of Massachusetts, i. 100.
  OUDE, feral humped cattle in, i. 79.
  OUISTITI, breed in Europe, ii. 153.
  {468}
  OVARY, variation of, in _Cucurbita moschata_, i. 359;
    development of, independently of pollen, i. 403.
  _Ovis montana_, i. 99.
  OVULES and buds, identity of nature of, ii. 360.
  OWEN, Capt., on stiff-haired cats at Mombas, i. 46.
  OWEN, Prof. R., palæontological evidence as to the origin of dogs, i. 15;
    on _Bos longifrons_, i. 81;
    on the skull of the "Niata" cattle, i. 89, 90;
    on fossil remains of rabbits, i. 104;
    on the significance of the brain, i. 124;
    on the number of digits in the Ichthyopterygia, ii. 16;
    on metagenesis, ii. 366;
    theory of reproduction and parthenogenesis, ii. 375.
  OWL, eagle, breeding in captivity, ii. 154.
  OWL pigeon, i. 148;
    African, figured, i. 149;
    known in 1735, i. 209.
  _Oxalis_, trimorphic species of, ii. 400.
  _Oxalis rosea_, ii. 132.
  OXLEY, Mr., on the nutmeg tree, ii. 237.
  OYSTERS, differences in the shells of, ii. 280.

  PACA, sterility of the, in confinement, ii. 152.
  PACIFIC islands, pigs of the, i. 70.
  PADUA, earliest known flower garden at, ii. 217.
  PADUAN fowl of Aldrovandi, i. 247.
  _Pæonia moutan_, ii. 205.
  PÆONY, tree, ancient cultivation of, in China, ii. 205.
  PAMPAS, feral cattle on the, i. 85.
  _Pandanus_, ii. 256.
  PANGENESIS, hypothesis of, ii. 357-404.
  _Panicum_, seeds of, used as food, i. 309;
    found in the Swiss lake-dwellings, i. 317.
  PANSY, i. 368-370.
  PAPPUS, abortion of the, in _Carthamus_, ii. 316.
  PAGET, on the Hungarian sheep dog, i. 24.
  PAGET, inheritance of cancer, ii. 7;
    hereditary elongation of hairs in the eyebrow, ii. 8;
    period of inheritance of cancer, ii. 79-80;
    on _Hydra_, ii. 293;
    on the healing of wounds, ii. 294;
    on the reparation of bones, _ibid._;
    growth of hair near inflamed surfaces or fractures, ii. 295;
    on false membranes, _ibid._;
    compensatory development of the kidney, ii. 300;
    bronzed skin in disease of supra-renal capsules, ii. 331;
    unity of growth and gemmation, ii. 359;
    independence of the elements of the body, ii. 369;
    affinity of the tissues for special organic substances, ii. 380.
  PALLAS, on the influence of domestication upon the sterility of
      intercrossed species, i. 31, 83, 193, ii. 109;
    hypothesis that variability is wholly due to crossing, i. 188, 374, ii.
        250, 264;
    on the origin of the dog, i. 16;
    variation in dogs, i. 33;
    crossing of dog and jackal, i. 25;
    origin of domestic cats, i. 43;
    origin of Angora cat, i. 45;
    on wild horses, i. 52, 60;
    on Persian sheep, i. 94;
    on Siberian fat-tailed sheep, ii. 279;
    on Chinese sheep, ii. 315;
    on Crimean varieties of the vine, i. 333;
    on a grape with rudimentary seeds, ii. 316;
    on feral musk-ducks, ii. 46;
    sterility of Alpine plants in gardens, ii. 163;
    selection of white-tailed yaks, ii. 206.
  _Paradoxurus_, sterility of species of, in captivity, ii. 151.
  PARAGUAY, cats of, i. 46;
    cattle of, i. 89;
    horses of, ii. 102;
    dogs of, ii. 102;
    black-skinned domestic fowl of, i. 232.
  PARALLEL variation, ii. 348-352.
  PARAMOS, woolly pigs of, i. 78.
  PARASITES, liability to attacks of, dependent on colour, ii. 228.
  PARIAH dog, with crooked legs, i. 17;
    resembling the Indian wolf, i. 24.
  PARISET, inheritance of handwriting, ii. 6.
  PARKER, W. K., number of vertebræ in fowls, i. 266.
  PARKINSON, Mr., varieties of the hyacinth, i. 370.
  PARKYNS, Mansfield, on _Columba guinea_, i. 183.
  PARMENTIER, differences in the nidification of pigeons, i. 178;
    on white pigeons, ii. 230.
  PARROTS, general sterility of, in confinement, ii. 155;
    alteration of plumage of, ii. 280.
  PARSNIP, reversion in, ii. 31;
    influence of selection on, ii. 201;
    experiments on, ii. 277;
    wild, enlargement of roots of, by cultivation, i. 326.
  PARTHENOGENESIS, ii. 359, 364.
  PARTRIDGE, sterility of, in captivity, ii. 156.
  PARTURITION, difficult, hereditary, ii. 8.
  _Parus major_, ii. 231.
  _Passiflora_, self-impotence in species of, ii. 137-138;
    contabescence of female organs in, ii. 166.
  _Passiflora alata_, fertility of, when grafted, ii. 188.
  PASTURE and climate, adaptation of breeds of sheep to, i. 96, 97.
  PASTRANA, Julia, peculiarities in the hair and teeth of, ii. 328.
  PATAGONIA, crania of pigs from, i. 77.
  PATAGONIAN rabbit, i. 105.
  {469}
  PATERSON, R., on the Arrindy silk moth, ii. 306.
  PAUL, W., on the hyacinth, i. 370;
    varieties of pelargoniums, i. 378;
    improvement of pelargoniums, ii. 216.
  _Pavo cristatus_ and _muticus_, hybrids of, i. 290.
  _Pavo nigripennis_, i. 290-291.
  "PAVODOTTEN-TAUBE," i. 141.
  PEACH, i. 336-344;
    derived from the almond, i. 337;
    stones of, figured, _ibid._;
    contrasted with almonds, i. 338;
    double-flowering, i. 338-339, 343;
    hybrids of, i. 339;
    persistency of races of, _ibid._;
    trees producing nectarines, i. 340-341;
    variation in, i. 342-343, ii. 256;
    bud-variation in, i. 374;
    pendulous, ii. 18;
    variation by selection in, ii. 218;
    peculiar disease of the, ii. 228;
    glands on the leaves of the, ii. 231;
    antiquity of the, ii. 308;
    increased hardiness of the, _ibid._;
    varieties of, adapted for forcing, ii. 310;
    yellow-fleshed, liable to certain diseases, ii. 336.
  PEACH-ALMOND, i. 338.
  PEAFOWL, origin of, i. 290;
    japanned or black-shouldered, i. 290-291;
    feral, in Jamaica, i. 190;
    comparative fertility of, in wild and tame states, ii. 112, 268;
    white, ii. 332.
  PEARS, i. 350;
    bud-variation in, i. 376;
    reversion in seedling, ii. 31;
    inferiority of, in Pliny's time, ii. 215;
    winter nelis, attacked by aphides, ii. 231;
    soft-barked varieties of, attacked by wood-boring beetles, ii. 231;
    origination of good varieties of, in woods, ii. 260;
    Forelle, resistance of, to frost, ii. 306.
  PEAS, i. 326-330;
    origin of, 326;
    varieties of, 326-329;
    found in Swiss lake-dwellings, i. 317, 319, 326-329;
    fruit and seeds figured, i. 328;
    persistency of varieties, i. 329;
    intercrossing of varieties, i. 330, 397, ii. 129;
    effect of crossing on the female organs in, i. 398;
    double-flowered, ii. 168;
    maturity of, accelerated by selection, ii. 201;
    varieties of, produced by selection, ii. 218;
    thin-shelled, liable to the attacks of birds, ii. 231;
    reversion of, by the terminal seed in the pod, ii. 347.
  PECCARY, breeding of the, in captivity, ii. 150.
  PEDIGREES of horses, cattle, greyhounds, game-cocks, and pigs, ii. 3.
  PEGU, cats of, i. 47;
    horses of, i. 53.
  PELARGONIUMS, multiple origin of, i. 364;
    zones of, i. 366;
    bud-variation in, i. 378;
    variegation in, accompanied by dwarfing, i. 384;
    pelorism in, ii. 167, 345;
    by reversion, ii. 59;
    advantage of change of soil to, ii. 147;
    improvement of, by selection, ii. 216;
    scorching of, ii. 229;
    numbers of, raised from seed, ii. 235;
    effects of conditions of life on, ii. 274;
    stove-variety of, ii. 311;
    correlation of contracted leaves and flowers in, ii. 330-331.
  _Pelargonium fulgidum_, conditions of fertility in, ii. 164.
  "PELONES," a Columbian breed of cattle, i. 88.
  PELORIC flowers, tendency of, to acquire the normal form, ii. 70;
    fertility or sterility of, ii. 166-167.
  PELORIC races of _Gloxinia speciosa_ and _Antirrhinum majus_, i. 365.
  PELORISM, ii. 58-60, 345-346.
  PELVIS, characters of, in rabbits, i. 122-123;
    in pigeons, i. 166;
    in fowls, i. 268;
    in ducks, i. 284.
  PEMBROKE cattle, i. 81.
  PENDULOUS trees, i. 361, ii. 348;
    uncertainty of transmission of, ii. 18-19.
  PENGUIN ducks, i. 280, 282;
    hybrid of the, with the Egyptian goose, i. 282.
  PENNANT, production of wolf-like curs at Fochabers, i. 37;
    on the Duke of Queensberry's wild cattle, i. 84.
  _Pennisetum_, seeds of, used as food in the Punjab, i. 309.
  _Pennisetum distichum_, seeds of, used as food in Central Africa, i. 308.
  PERCIVAL, Mr., on inheritance in horses, ii. 10;
    on horn-like processes in horses, i. 50.
  _Perdix rubra_, occasional fertility of, in captivity, ii. 156.
  PERIOD of action of causes of variability, ii. 269.
  PERIOSTEUM of a dog, producing bone in a rabbit, ii. 369.
  PERIWINKLE, sterility of, in England, ii. 170.
  PERSIA, estimation of pigeons in, i. 205;
    carrier pigeon of, i. 141;
    tumbler pigeon of, i. 150;
    cats of, i. 45-47;
    sheep of, i. 94.
  _Persica intermedia_, i. 338.
  PERSISTENCE of colour in horses, i. 50;
    of generic peculiarities, i. 111.
  PERU, antiquity of maize in, i. 320;
    peculiar potato from, i. 331;
    selection of wild animals practised by the Incas of, ii. 207-208.
  "PERÜCKEN-TAUBE," i. 154.
  PETALS, rudimentary, in cultivated plants, ii. 316;
    producing pollen, ii. 392.
  PETUNIAS, multiple origin of, i. 364;
    double-flowered, ii. 167.
  "PFAUEN-TAUBE," i. 146.
  _Phacochoerus Africanus_, i. 76.
  _Phalænopsis_, pelorism in, ii. 346.
  PHALANGES, deficiency of, ii. 73.
  {470}
  _Phaps chalcoptera_, ii. 349.
  _Phaseolus multiflorus_, ii. 309, 322.
  _Phaseolus vulgaris_, ii. 309.
  _Phasianus pictus_, i. 275.
  _Phasianus Amherstiæ_, i. 275.
  PHEASANT, assumption of male plumage by the hen, ii. 51;
    wildness of hybrids of, with the common fowl, ii. 45;
    prepotency of the, over the fowl, ii. 68;
    diminished fecundity of the, in captivity, ii. 155.
  PHEASANTS, golden and Lady Amherst's, i. 275.
  PHEASANT-FOWLS, i. 244.
  PHILIPEAUX, regeneration of limbs in the salamander, ii. 376.
  PHILIPPAR, on the varieties of wheat, i. 314.
  PHILIPPINE Islands, named breeds of game fowl in the, i. 232.
  PHILLIPS, Mr., on bud-variation in the potato, i. 385.
  _Phlox_, bud-variation by suckers in, i. 384.
  PHTHISIS, affection of the fingers in, ii. 332.
  PICKERING, Mr., on the grunting voice of humped cattle, i. 79;
    occurrence of the head of a fowl in an ancient Egyptian procession, i.
        246;
    seeding of ordinarily seedless fruits, ii. 168;
    extinction of ancient Egyptian breeds of sheep and oxen, ii. 425;
    on an ancient Peruvian gourd, ii. 429.
  PICOTEES, effect of conditions of life on, ii. 273.
  PICTET, A., oriental names of the pigeon, i. 205.
  PICTET, Prof., origin of the dog, i. 15;
    on fossil oxen, i. 81.
  PIEBALDS, probably due to reversion, ii. 37.
  PIGEAUX, hybrids of the hare and rabbit, ii. 99, 152.
  PIGEON à cravate, i. 148.
  PIGEON Bagadais, i. 142, 143.
  PIGEON coquille, i. 155.
  PIGEON cygne, i. 143.
  PIGEON heurté, i. 156.
  PIGEON Patu plongeur, i. 156.
  PIGEON Polonais, i. 144.
  PIGEON Romain, i. 142, 144.
  PIGEON tambour, i. 154.
  PIGEON Turc, i. 139.
  PIGEONS, origin of, i. 131-134, 180-204;
    classified table of breeds of, i. 136;
    pouter, i. 137-139;
    carrier, i. 139-142;
    runt, i. 142-144;
    barbs, i. 144-146;
    fantail, i. 146-148;
    turbit and owl, i. 148-149;
    tumbler, i. 150-153;
    Indian frill-back, i. 153;
    Jacobin, i. 154;
    trumpeter, i. 154;
    other breeds of, i. 155-157;
    differences of, equal to generic, i. 157-158;
    individual variations of, i. 158-160;
    variability of peculiarities characteristic of breeds in, i. 161;
    sexual variability in, i. 161-162;
    osteology of, i. 162-167;
    correlation of growth in, i. 167-171, ii. 321;
    young of some varieties naked when hatched, i. 170, ii. 332;
    effects of disuse in, i. 172-177;
    settling and roosting in trees, i. 181;
    floating in the Nile to drink, i. 181;
    Dovecot, i. 185-186;
    arguments for unity of origin of, i. 188-204;
    feral in various places, i. 190, ii. 33;
    unity of coloration in, i. 195-197;
    reversion of mongrel, to coloration of, _C. livia_, i. 197-202;
    history of the cultivation of, i. 205-207;
    history of the principal races of, i. 207-212;
    mode of production of races of, i. 212-224;
    reversion in, ii. 29, 47;
    by age, ii. 38;
    produced by crossing in, ii. 40, 48;
    prepotency of transmission of character in breeds of, ii. 66-67;
    sexual differences in some varieties of, ii. 74;
    period of perfect plumage in, ii. 77;
    effect of segregation on, ii. 86;
    preferent pairing of, within the same breed, ii. 103;
    fertility of, increased by domestication, ii. 112, 155;
    effects of interbreeding and necessity of crossing, ii. 125-126;
    indifference of, to change of climate, ii. 161;
    selection of, ii. 195, 199, 204;
    among the Romans, ii. 202;
    unconscious selection of, ii. 211, 214;
    facility of selection of, ii. 234;
    white, liable to the attacks of hawks, ii. 230;
    effects of disuse of parts in, ii. 298;
    fed upon meat, ii. 304;
    effect of first male upon the subsequent progeny of the female, i. 405;
    homology of the leg and wing feathers in, ii. 323;
    union of two outer toes in feather-legged, _ibid._;
    correlation of beak, limbs, tongue, and nostrils in, ii. 324;
    analogous variation in, ii. 349-350;
    permanence of breeds of, ii. 429.
  PIGS, of Swiss lake-dwellings, i. 67-68;
    types of, derived from _Sus scrofa_ and _Sus indica_, i. 66-67;
    Japanese (_Sus pliciceps_, Gray), figured, i. 69;
    of Pacific islands, i. 70, ii. 87;
    modifications, of skull in, i. 71-73;
    length of intestines in, i. 73, ii. 303;
    period of gestation of, i. 74;
    number of vertebræ and ribs in, i. 74;
    anomalous forms, i. 75-76;
    development of tusks and bristles in, i. 76;
    striped young of, i. 76-77;
    reversion of feral, to wild type, i. 77-78, ii. 33, 47;
    production and changes of breeds of, by intercrossing, i. 78;
    effects produced by the first male upon the subsequent progeny of the
        female, i. 404;
    two-legged race of, ii. 4;
  {471}
    polydactylism in, ii. 14;
    cross-reversion in, ii. 35;
    hybrid, wildness of, ii. 45;
    monstrous development of a proboscis in, ii. 57;
    disappearance of tusks in male under domestication, ii, 74;
    solid hoofed, ii. 429;
    crosses of, ii. 93, 95;
    mutual fertility of all varieties of, ii. 110;
    increased fertility by domestication, ii. 111;
    ill effects of close interbreeding in, ii. 121-122;
    influence of selection on, ii. 198;
    prejudice against certain colours in, ii. 210, 229, 336;
    unconscious selection of, ii. 214;
    black Virginian, ii. 227, 336;
    similarity of the best breeds of, ii. 241;
    change of form in, ii. 279;
    effects of disuse of parts in, ii. 299;
    ears of, ii. 301;
    correlations in, ii. 327;
    white, buck-wheat injurious to, ii. 337;
    tail of, grafted upon the back, ii. 369;
    extinction of the older races of, ii. 426.
  PIMENTA, ii. 91.
  PIMPERNEL, ii. 190.
  PINE-APPLE, sterility and variability of the, ii. 262.
  PINK, Chinese. 322.
  PINKS, bud-variation in, i. 381;
    improvement of, ii. 216.
  _Pinus pumilio_, _Mughus_, and _nana_, varieties of _P. sylvestris_, i.
      363.
  _Pinus sylvestris_, i. 363, ii. 310;
    hybrids of, with _P. nigricans_, ii. 130.
  PIORRY, on hereditary disease, ii. 7, 78.
  _Pistacia lentiscus_, ii. 274.
  PISTILS, rudimentary, in cultivated plants, ii. 316.
  PISTOR, sterility of some mongrel pigeons, i. 192;
    fertility of pigeons, ii. 112.
  _Pisum arvense_ and _sativum_, i. 326.
  PITYRIASIS versicolor, inheritance of, ii. 79.
  PLANCHON, G., on a fossil vine, i. 332;
    sterility of _Jussiæa grandifiora_ in France, ii. 170.
  PLANE tree, variety of the, i. 362.
  PLANTIGRADE carnivora, general sterility of the, in captivity, ii. 151.
  PLANTS, progress of cultivation of, i. 305-312;
    cultivated, their geographical derivation, i. 311;
    crossing of, ii. 98, 99, 127;
    comparative fertility of wild and cultivated, ii. 112-113;
    self-impotent, ii. 131-140;
    dimorphic and trimorphic, ii. 132, 140;
    sterility of, from changed conditions, ii. 163-165;
    from contabescence of anthers, ii. 165-166;
    from monstrosities, ii. 166-167;
    from doubling of the flowers, ii. 167-168;
    from seedless fruit, ii. 168;
    from excessive development of vegetative organs, ii. 168-171;
    influence of selection on, ii. 199-201;
    variation by selection, in useful parts of, ii. 217-219;
    variability of, ii. 237;
    variability of, induced by crossing, ii. 265;
    direct action of change of climate on, ii. 277;
    change of period of vegetation in, ii. 304-305;
    varieties of, suitable to different climates, ii. 306;
    correlated variability of, ii. 330-331;
    antiquity of races of, ii. 429.
  PLASTICITY, inheritance of, ii. 241.
  PLATEAU, F., on the vision of amphibious animals, ii. 223.
  _Platessa flesus_, ii. 53.
  PLATO, notice of selection in breeding dogs by, ii. 212.
  PLICA polonica, ii. 276.
  PLINY, on the crossing of shepherd's dogs with the wolf, i. 24;
    on Pyrrhus' breed of cattle, ii. 202;
    on the estimation of pigeons among the Romans, i. 205;
    pears described by, ii. 215.
  PLUM, i. 345-347;
    stones figured, i. 345;
    varieties of the, i. 345-346, ii. 219;
    bud-variation in the, i. 375;
    peculiar disease of the, ii. 227;
    flower-buds of, destroyed by bullfinches, ii. 232;
    purple-fruited, liable to certain diseases, ii. 336.
  PLUMAGE, inherited peculiarities of, in pigeons, i. 160-161;
    sexual peculiarities of, in fowls, i. 251-255.
  PLURALITY of races, Pouchet's views on, i. 2.
  _Poa_, seeds of, used as food, i. 308;
    species of, propagated by bulblets, ii. 170.
  PODOLIAN cattle, i. 80.
  POINTERS, modification of, i. 42;
    crossed with the foxhound, ii. 95.
  POIS sans parchemin, ii. 231.
  POITEAU, origin of _Cytisus Adami_, i. 390;
    origin of cultivated varieties of fruit-trees, ii. 260.
  POLISH fowl, i. 227, 250, 254, 256-257, 262;
    skull figured, i. 262;
    section of skull figured, i. 263;
    development of protuberance of skull, i. 250;
    furcula figured, i. 268.
  POLISH, or Himalayan rabbit, i. 108.
  POLLEN, ii. 363-364;
    action of, ii. 108;
    injurious action of, in some orchids, ii. 134-135;
    resistance of, to injurious treatment, ii. 164;
    prepotency of, ii. 187.
  POLLOCK, Sir F., transmission of variegated leaves in _Ballota nigra_, i.
      383;
    on local tendency to variegation, ii. 274.
  POLYANTHUS, ii. 21.
  POLYDACTYLISM, inheritance of, ii. 12-16;
    significance of, ii. 16-17.
  _Polyplectron_, i. 255.
  PONIES, most frequent on islands and mountains, i. 52;
    Javanese, i. 53.
  POOLE, Col., on striped Indian horses, i. 58, 59;
  {472}
    on the young of _Asinus indicus_, ii. 43.
  POPLAR, Lombardy, i. 361.
  PÖPPIG, on Cuban wild dogs, i. 27.
  POPPY, found in the Swiss lake-dwellings, i. 317, 319;
    with the stamens converted into pistils, i. 365;
    differences of the, in different parts of India, ii. 165;
    monstrous, fertility of, ii. 166;
    black-seeded, antiquity of, ii. 429.
  PORCUPINE, breeding of, in captivity, ii. 152.
  PORCUPINE family, ii. 4, 76.
  _Porphyrio_, breeding of a species of, in captivity, ii. 156.
  PORTAL, on a peculiar hereditary affection of the eye, ii. 9.
  PORTO Santo, feral rabbits of, i. 112.
  _Potamochoerus penicillatus_, ii. 150.
  POTATO, i. 330-331;
    bud-variation by tubers in the, i. 384-385;
    graft-hybrid of, by union of half-tubers, i. 395;
    individual self-impotence in the, ii. 137;
    sterility of, ii. 169;
    advantage of change of soil to the, ii. 146;
    relation of tubers and flowers in the, ii. 343.
  POTATO, sweet, sterility of the, in China, ii. 169;
    varieties of the, suited to different climates, ii. 309.
  POUCHET, M., his views on plurality of races, i. 2.
  POUTER pigeons, i. 137-139;
    furcula figured, i. 167;
    history of, i. 207.
  POWIS, Lord, experiments in crossing humped and English cattle, i. 83,
      ii. 45.
  POYNTER, Mr., on a graft-hybrid rose, i. 396.
  PRAIRIE wolf, i. 22.
  PRECOCITY of highly-improved breeds, ii. 321.
  PREPOTENCY of pollen, ii. 187.
  PREPOTENCY of transmission of character, ii. 65, 174;
    in the Austrian emperors and some Roman families, ii. 65;
    in cattle, ii. 65-66;
    in sheep, ii. 66;
    in cats, _ibid._;
    in pigeons, ii. 66-67;
    in fowls, ii. 67;
    in plants, _ibid._;
    in a variety of the pumpkin, i. 358;
    in the jackal over the dog, ii. 67;
    in the ass over the horse, _ibid._;
    in the pheasant over the fowl, ii. 68;
    in the penguin duck over the Egyptian goose, _ibid._;
    discussion of the phenomena of, ii. 69-71.
  PRESCOTT, Mr., on the earliest known European flower-garden, ii. 217.
  PRESSURE, mechanical, a cause of modification, ii. 344-345.
  PREVOST and Dumas, on the employment of several spermatozoids to
      fertilise one ovule, ii. 363.
  PRICE, Mr., variations in the structure of the feet in horses, i. 50.
  PRICHARD, Dr., on polydactylism in the negro, ii. 14;
    on the Lambert family, ii. 77;
    on an albino negro, ii. 229;
    on Plica polonica, ii. 276.
  PRIMROSE, ii. 21;
    double, rendered single by transplantation, ii. 167.
  _Primula_, intercrossing of species of, i. 336;
    contabescence in, ii. 166;
    hose and hose, i. 365;
    with coloured calyces, sterility of, ii. 166.
  _Primula sinensis_, reciprocally dimorphic, ii. 132.
  _Primula veris_, ii. 21, 109, 182.
  _Primula vulgaris_, ii. 21, 109.
  PRINCE, Mr., on the intercrossing of strawberries, i. 352.
  _Procyon_, sterility of, in captivity, ii. 152.
  PROLIFICACY, increased by domestication, ii. 174.
  PROPAGATION, rapidity of, favourable to selection, ii. 297.
  PROTOZOA, reproduction of the, ii. 376.
  _Prunus armeniaca_, i. 344-345.
  _Prunus avium_, i. 347.
  _Prunus cerasus_, i. 347, 375.
  _Prunus domestica_, i. 345.
  _Prunus insititia_, i. 345-347.
  _Prunus spinosa_, i. 345.
  PRUSSIA, wild horses in, i. 60.
  _Psittacus erithacus_, ii. 155.
  _Psittacus macoa_, ii. 155.
  _Psophia_, general sterility of, in captivity, ii. 157.
  PTARMIGAN fowls, i. 228.
  _Pulex penetrans_, ii. 275.
  PUMPKINS, i. 357.
  PUNO ponies of the Cordillera, i. 52.
  PURSER, Mr. on _Cytisus Adami_, i. 389.
  PUSEY, Mr., preference of hares and rabbits for common rye, ii. 232.
  PUTSCHE and Vertuch, varieties of the potato, i. 330.
  PUVIS, effects of foreign pollen on apples, i. 401;
    supposed non-variability of monotypic genera, ii. 266.
  _Pyrrhula vulgaris_, ii. 232;
    assumption of the hen-plumage by the male, in confinement, ii. 158.
  PYRRHUS, his breed of cattle, ii. 202.
  _Pyrus_, fastigate Chinese species of, ii. 277.
  _Pyrus acerba_, i. 348.
  _Pyrus aucuparia_, ii. 230.
  _Pyrus communis_, i. 350, 376.
  _Pyrus malus_, i. 348, 376.
  _Pyrus paradisiaca_, i. 348.
  _Pyrus præcox_, i. 348.

  QUAGGA, effect of fecundation by, on the subsequent progeny of a mare, i.
      403-404.
  QUATREFAGES, A. de, on the burrowing of a bitch to litter, i. 77;
  {473}
    selection in the silkworm, i. 301;
    development of the wings in the silkmoth, i. 303, ii. 298;
    on varieties of the mulberry, i. 334;
    special raising of eggs of the silkmoth, ii. 197;
    on disease of the silkworm, ii. 228;
    on monstrosities in insects, ii. 269, 391;
    on the Anglo-Saxon race in America, ii. 276;
    on a change in the breeding season of the Egyptian goose, ii. 304;
    fertilisation of the _Teredo_, ii. 363;
    tendency to similarity in the best races, ii. 241;
    on his "_tourbillon vital_," ii. 61;
    on the independent existence of the sexual elements, ii. 360.
  _Quercus cerris_, i. 363.
  _Quercus robur_ and _pedunculata_, hybrids of, ii. 130.
  QUINCE, pears grafted on the, ii. 259.

  RABBITS, domestic, their origin, i. 103-105;
    of Mount Sinai and Algeria, i. 105;
    breeds of, i. 105-111;
    Himalayan, Chinese, Polish, or Russian, i. 108-111, ii. 97;
    feral, i. 111-115;
    of Jamaica, i. 112;
    of the Falkland islands, i. 112;
    of Porto Santo, i. 112-115, ii. 103, 279;
    osteological characters of, i. 115-129;
    discussion of modifications in, i. 129-130;
    one-eared, transmission of peculiarity of, ii. 12;
    reversion in feral, ii. 33;
    in the Himalayan, ii. 41;
    crossing of white and coloured Angora, ii. 92;
    comparative fertility of wild and tame, ii. 111;
    high-bred, often bad breeders, ii. 121;
    selection of, ii. 204;
    white, liable to destruction, ii. 230;
    effects of disuse of parts in, ii. 298;
    skull of, affected by drooping ears, ii. 301;
    length of intestines in, ii. 303;
    correlation of ears and skull in, ii. 324-325;
    variations in skull of, ii. 350;
    periosteum of a dog producing bone in, ii. 369.
  RACE-HORSE, origin of, i. 54.
  RACES, modification and formation of, by crossing, ii. 95-99;
    natural and artificial, ii. 245;
    Pouchet's views on plurality of, i. 2;
    of pigeons, i. 207-212.
  RADISHES, i. 326; crossing of, ii. 90;
    varieties of, ii. 217-218.
  RADCLYFFE, W. F., effect of climate and soil on strawberries, i. 354;
    constitutional differences in roses, i. 367.
  RADLKOFER, retrogressive metamorphosis in mosses and algæ, ii. 361.
  RAFFLES, Sir Stamford, on the crossing of Javanese cattle with _Bos
      sondaicus_, ii. 206.
  RAM, goat-like, from the Cape of Good Hope, ii. 66.
  RANCHIN, heredity of diseases, ii. 7.
  RANGE of gallinaceous birds on the Himalaya, i. 237.
  _Ranunculus ficaria_, ii. 170.
  _Ranunculus repens_, ii. 168.
  RAPE, i. 325.
  _Raphanus sativus_, ii. 343.
  RASPBERRY, yellow-fruited, ii. 230.
  RATTLESNAKE, experiments with poison of the, ii. 289.
  RAVEN, stomach of, affected by vegetable diet, ii. 302.
  RAWSON, A., self-impotence in hybrids of _Gladiolus_, ii. 139-140.
  RÉ, Le Compte, on the assumption of a yellow colour by all varieties of
      maize, i. 321.
  RÉAUMUR, effect of confinement upon the cock, ii. 52;
    fertility of fowls in most climates, ii. 161.
  REED, Mr., atrophy of the limbs of rabbits, consequent on the destruction
      of their nerves, ii. 297.
  REGENERATION of amputated parts in man, ii. 14;
    in the human embryo, ii. 15;
    in the lower vertebrata, insects, and myriapoda, _ibid._
  REINDEER, individuals recognised by the Laplanders, ii. 251.
  REGNIER, early cultivation of the cabbage by the Celts, i. 324.
  REISSEK, experiments in crossing _Cytisus purpureus_ and _laburnum_, i.
      389;
    modification of a _Thesium_ by _Oecidium_, ii. 284.
  RELATIONS, characters of, reproduced in children, ii. 34.
  RENGGER, occurrence of jaguars with crooked legs in Paraguay, i. 17;
    naked dogs of Paraguay, i. 23, 31, ii. 93, 102;
    feral dogs of La Plata, i. 27;
    on the aguara, i. 26;
    cats of Paraguay, i. 46, ii. 86, 151;
    dogs of Paraguay, ii. 87;
    feral pigs of Buenos Ayres, i. 77;
    on the refusal of wild animals to breed in captivity, ii. 149;
    on _Dicotyles labiatus_, ii. 150;
    sterility of plantigrade carnivora in captivity, ii. 152;
    on _Cavia aperea_, ii. 152;
    sterility of _Cebus azaræ_ in captivity, ii. 153;
    abortions produced by wild animals in captivity, ii. 158.
  REPRODUCTION, sexual and asexual, contrasted, ii. 361;
    unity of forms of, ii. 383;
    antagonism of, to growth, ii. 384.
  _Reseda odorata_, ii. 237.
  RETINITIS, pigmentary, in deaf-mutes, ii. 328.
  REVERSION, ii. 28-29, 372-373, 396, 398-402;
    in pigeons, ii. 29;
    in cattle, ii. 29-30;
    in sheep, ii. 30;
    in fowls, ii. 31;
    in the heartsease, _ibid._;
    in vegetables, _ibid._;
    in feral animals and plants, ii. 32-34;
    to characters derived from a previous cross in man, dogs, pigeons,
        pigs, and fowls, ii. 34-35;
  {474}
    in hybrids, ii. 36;
    by bud-propagation in plants, ii. 36-38;
    by age in fowls, cattle, &c., ii. 38-39;
    caused by crossing, ii. 39-51;
    explained by latent characters, ii. 51-56;
    producing monstrosities, ii. 57;
    producing peloric flowers, ii. 58-60;
    of feral pigs to the wild type, i. 77-78;
    of supposed feral rabbits to the wild type, i. 104, 111, 115;
    of pigeons, in coloration, when crossed, i. 197-202;
    in fowls, i. 239-246;
    in the silkworm, i. 302;
    in the pansy, i. 369;
    in a pelargonium, i. 378;
    in Chrysanthemums, i. 379;
    of varieties of the China rose in St. Domingo, i. 380;
    by buds in pinks and carnations, i. 381;
    of laciniated varieties of trees to the normal form, i. 382;
    in variegated leaves of plants, i. 383-384;
    in tulips, i. 386;
    of suckers of the seedless barberry to the common form, i. 384;
    by buds in hybrids of _Tropæolum_, i. 392;
    in plants, i. 409;
    of crossed peloric snapdragons, ii. 71;
    analogous variations due to, ii. 349-351.
  REYNIER, selection practised by the Celts, ii. 202-203.
  RHINOCEROS, breeding in captivity in India, ii. 150.
  _Rhododendron_, hybrid, ii. 265.
  _Rhododendron ciliatum_, ii. 277.
  _Rhododendron Dalhousiæ_, effect of pollen of _R. Nuttallii_ upon, i.
      400.
  RHUBARB, not medicinal when grown in England, ii. 274.
  _Ribes grossularia_, i. 354-356, 376.
  _Ribes rubrum_, i. 376.
  RIBS, number and characters of, in fowls, i. 267;
    characters of, in ducks, i. 283-284.
  RICE, Imperial, of China, ii. 205;
    Indian varieties of, ii. 256;
    variety of, not requiring water, ii. 305.
  RICHARDSON, H. D., on jaw-appendages in Irish pigs, i. 76;
    management of pigs in China, i. 68;
    occurrence of striped young in Westphalian pigs, i. 76;
    on crossing pigs, ii. 95;
    on interbreeding pigs, ii. 122;
    on selection in pigs, ii. 194.
  RICHARDSON, Sir John, observations on the resemblance between North
      American dogs and wolves, i. 21-22;
    on the burrowing of wolves, i. 27;
    on the broad feet of dogs, wolves, and foxes in North America, i. 40;
    on North American horses scraping away the snow, i. 53.
  _Ricinus_, annual in England, ii. 305.
  RIEDEL, on the "Bagadotte" pigeon, i. 141;
    on the Jacobin pigeon, i. 154;
    fertility of hybrid pigeons, i. 192.
  RINDERPEST, ii. 378.
  RISSO, on varieties of the orange, i. 336, ii. 308, 331.
  RIVERS, Lord, on the selection of greyhounds, ii. 235.
  RIVERS, Mr., persistency of characters in seedling potatoes, i. 331;
    on the peach, i. 338, 339;
    persistency of races in the peach and nectarine, i. 339, 340;
    connexion between the peach and the nectarine, i. 340;
    persistency of character in seedling apricots, i. 344;
    origin of the plum, i. 345;
    seedling varieties of the plum, i. 346;
    persistency of character in seedling plums, i. 347;
    bud-variation in the plum, i. 375;
    plum, attacked by bullfinches, ii. 232;
    seedling apples with surface-roots, i. 349;
    variety of the apple found in a wood, ii. 260;
    on roses, i. 366-367;
    bud-variation in roses, i. 379-381;
    production of Provence roses from seeds of the moss-rose, i. 380;
    effect produced by grafting on the stock in jessamine, i. 394;
    in the ash, i. 394;
    on grafted hazels, i. 395;
    hybridisation of a weeping thorn, ii. 18;
    experiments with the seed of the weeping elm and ash, ii. 19;
    variety of the cherry with curled petals, ii. 232.
  RIVIÈRE, reproduction of _Oncidium Cavendishianum_, ii. 133.
  ROBERTS, Mr., on inheritance in the horse, ii. 10.
  ROBERTSON, Mr., on glandular-leaved peaches, i. 343.
  ROBINET, on the silkworm, i. 301-304, ii. 197.
  _Robinia_, ii. 274.
  ROBSON, Mr., deficiencies of half-bred horses, ii. 11.
  ROBSON, Mr., on the advantage of change of soil to plants, ii. 146-147;
    on the growth of the verbena, ii. 273;
    on broccoli, ii. 310.
  ROCK pigeon, measurements of the, i. 134;
    figured, i. 135.
  RODENTS, sterility of, in captivity, ii. 152.
  _Rodriguezia_, ii. 134, 135.
  RODWELL, J., poisoning of horses by mildewed tares, ii. 337.
  ROHILCUND, feral humped cattle in, i. 79.
  ROLLE, F., on the history of the peach, ii. 308.
  ROLLER-PIGEONS, Dutch, i. 151.
  ROLLESTON, Prof., incisor teeth affected in form in cases of pulmonary
      tubercle, ii. 332.
  ROMANS, estimation of pigeons by, i. 205;
    breeds of fowls possessed by, i. 231, 247.
  {475}
  ROOKS, pied, ii. 77.
  _Rosa_, cultivated species of, i. 366.
  _Rosa devoniensis_, graft-hybrid produced by, on the white Banksian rose,
      i. 396.
  _Rosa indica_ and _centifolia_, fertile hybrids of, i. 366.
  _Rosa spinosissima_, history of the culture of, i. 367.
  ROSELLINI, on Egyptian dogs, i. 17.
  ROSES, i. 366-367;
    origin of, i. 364;
    bud-variation in, i. 379-381;
    Scotch, doubled by selection, ii. 200;
    continuous variation of, ii. 241;
    effect of seasonal conditions on, ii. 273;
    noisette, ii. 308;
    galls of, ii. 284.
  ROUENNAIS rabbit, i. 105.
  ROULIN, on the dogs of Juan Fernandez, i. 27;
    on South American cats, i. 46;
    striped young pigs, i. 77;
    feral pigs in South America, i. 78, ii. 33;
    on Columbian cattle, i. 88, ii. 205, 226;
    effects of heat on the hides of cattle in South America, i. 92;
    fleece of sheep in the hot valleys of the Cordilleras, i. 98;
    diminished fertility of these sheep, ii. 161;
    on black-boned South American fowls, i. 258;
    variation of the guinea-fowl in tropical America, i. 294;
    frequency of striped legs in mules, ii. 42;
    geese in Bogota, ii. 161;
    sterility of fowls introduced into Bolivia, ii. 162.
  ROY, M., on a variety of _Magnolia grandiflora_, ii. 308.
  ROYLE, Dr., Indian varieties of the mulberry, i. 334;
    on _Agave vivipara_, ii. 169;
    variety of rice not requiring irrigation, ii. 305;
    sheep from the Cape in India, ii. 306.
  _Rubus_, pollen of, ii. 268.
  RUDIMENTARY organs, i. 12, ii. 315-318.
  RUFZ de Lavison, extinction of breeds of dogs in France, ii. 425.
  RUMINANTS, general fertility of, in captivity, ii. 150.
  RUMPLESS fowls, i. 230.
  RUNTS, i. 142-144;
    history of, i. 210;
    lower jaws and skull figured, i. 164-165.
  RUSSIAN or Himalayan rabbit, i. 108.
  RÜTIMEYER, Prof., dogs of the Neolithic period, i. 19;
    horses of Swiss lake-dwellings, i. 49;
    diversity of early domesticated horses i. 51;
    pigs of the Swiss lake-dwellings, i. 65, 67-68;
    on humped cattle, i. 80;
    parentage of European breeds of cattle, i. 80, 81, ii. 427;
    on "Niata" cattle, i. 89;
    sheep of the Swiss lake-dwellings, i. 94, ii. 427;
    goats of the Swiss lake-dwellings, i. 101;
    absence of fowls in the Swiss lake-dwellings, i. 246;
    on crossing cattle, ii. 98;
    differences in the bones of wild and domesticated animals, ii. 279;
    decrease in size of wild European animals, ii. 427.
  RYE, wild, De Candolle's observations on, i. 313;
    found in the Swiss lake-dwellings, i. 319;
    common, preferred by hares and rabbits, ii. 232;
    less variable than other cultivated plants, ii. 254.

  SABINE, Mr., on the cultivation of _Rosa spinosissima_, i. 367;
    on the cultivation of the dahlia, i. 369-370, ii. 261;
    effect of foreign pollen on the seed-vessel in _Amaryllis vittata_, i.
        400.
  ST. ANGE, influence of the pelvis on the shape of the kidneys in birds,
      ii. 344.
  ST. DOMINGO, wild dogs of, i. 28;
    bud-variation of dahlias in, i. 385.
  ST. HILAIRE, Aug., milk furnished by cows in South America, ii. 300;
    husked form of maize, i. 320.
  ST. JOHN, C., feral cats in Scotland, i. 47;
    taming of wild ducks, i. 278.
  ST. VALERY apple, singular structure of the, i. 350;
    artificial fecundation of the, i. 401.
  ST. VITUS' Dance, period of appearance of, ii. 77.
  SAGERET, origin and varieties of the cherry, i. 347-348;
    origin of varieties of the apple, i. 350;
    incapacity of the cucumber for crossing with other species, i. 359;
    varieties of the melon, i. 360;
    supposed twin-mongrel melon, i. 391;
    crossing melons, ii. 108, 129;
    on gourds, ii. 108;
    effects of selection in enlarging fruit, ii. 217;
    on the tendency to depart from type, ii. 241;
    variation of plants in particular soils, ii. 278.
  SALAMANDER, experiments on the, ii. 293, 341;
    regeneration of lost parts in the, ii. 15, 376, 385.
  _Salamandra cristata_, polydactylism in, ii. 14.
  SALISBURY, Mr., on the production of nectarines by peach-trees, i. 341;
    on the dahlia, i. 369-370.
  _Salix_, intercrossing of species of, i. 336.
  _Salix humilis_, galls of, ii. 282, 283.
  SALLÉ, feral guinea-fowl in St. Domingo, i. 294.
  SALMON, early breeding of male, ii. 384.
  SALTER, Mr., on bud-variation in pelargoniums, i. 378;
    in the Chrysanthemum, i. 379;
    transmission of variegated leaves by seed, i. 383;
    bud-variation by suckers in _Phlox_, i. 384;
    application of selection to bud-varieties of plants, i. 411;
    accumulative effect of changed conditions of life, ii. 262;
    on the variegation of strawberry leaves, ii. 274.
  SALTER, S. J., hybrids of _Gallus Sonneratii_ and the common fowl, i.
      234, ii. 45;
  {476}
    crossing of races or species of rats, ii. 87-88.
  SAMESREUTHER, on inheritance in cattle, ii. 10.
  SANDFORD. _See_ DAWKINS.
  SAP, ascent of the, ii. 296.
  _Saponaria calabrica_, ii. 20.
  SARDINIA, ponies of, i. 52.
  SARS, on the development of the hydroida, ii. 368.
  SATIATION of the stigma, i. 402-403.
  _Saturnia pyri_, sterility of, in confinement, ii. 157.
  SAUL, on the management of prize gooseberries, i. 356.
  SAUVIGNY, varieties of the goldfish, i. 296.
  SAVAGES, their indiscriminate use of plants as food, i. 307-310;
    fondness of, for taming animals, ii. 160.
  SAVI, effect of foreign pollen on maize, i. 400.
  _Saxifraga geum_, ii. 166.
  SAYZID MOHAMMED MUSARI, on carrier-pigeons, i. 141;
    on a pigeon which utters the sound "Yahu," i. 155.
  SCANDEROONS (pigeons), i. 142, 143.
  SCANIA, remains of _Bos frontosus_ found in, i. 81.
  SCAPULA, characters of, in rabbits, i. 123;
    in fowls, i. 268;
    in pigeons, i. 167;
    alteration of, by disuse, in pigeons, i. 175.
  SCARLET fever, ii. 276.
  SCHAAFFHAUSEN, on the horses represented in Greek statues, ii. 213.
  SCHACHT, H., on adventitious buds, ii. 384.
  SCHLEIDEN, excess of nourishment a cause of variability, ii. 257.
  SCHOMBURGK, Sir R., on the dogs of the Indians of Guiana, i. 19, 23, ii.
      206;
    on the musk duck, i. 182;
    bud-variation in the Banana, i. 377;
    reversion of varieties of the China rose in St. Domingo, i. 380;
    sterility of tame parrots in Guiana, ii. 155;
    on _Dendrocygna viduata_, ii. 157;
    selection of fowls in Guiana, ii. 209.
  SCHREIBERS, on _Proteus_, ii. 297.
  _Sciuropterus volucella_, ii. 152.
  _Sciurus palmarum_ and _cinerea_, ii. 152.
  SCLATER, P. L., on _Asinus tæniopus_, i. 62, ii. 41;
    on _Asinus indicus_, ii. 42;
    striped character of young wild pigs, i. 70;
    osteology of _Gallinula nesiotis_, i. 287;
    on the black-shouldered peacock, i. 290;
    on the breeding of birds in captivity, ii. 157.
  SCHMERLING, Dr., varieties of the dog, found in a cave, i. 19.
  SCOTCH fir, local variation of, i. 363.
  SCOTCH kail and cabbage, cross between, ii. 98.
  SCOTT, John, irregularities in the sex of the flowers of Maize, i. 321;
    bud-variation in _Imatophyllum miniatum_, i. 385;
    crossing of species of _Verbascum_, ii. 106-107;
    experiments on crossing _Primulæ_, ii. 109;
    reproduction of orchids, ii. 133;
    fertility of _Oncidium divaricatum_, ii. 164;
    acclimatisation of the sweet pea in India, ii. 311;
    number of seeds in _Acropera_ and _Gongora_, ii. 379.
  SCOTT, Sir W., former range of wild cattle in Britain, i. 85.
  SCROPE, on the Scotch deerhound, ii. 73, 121.
  SEBRIGHT, Sir John, effects of close interbreeding in dogs, ii. 121;
    care taken by, in selection of fowls, ii. 197.
  _Secale cereale_, ii. 254.
  SEDGWICK, W., effects of crossing on the female, i. 404;
    on the "Porcupine-man," ii. 4;
    on hereditary diseases, ii. 7;
    hereditary affections of the eye, ii. 9, 78-79;
    inheritance of polydactylism and anomalies of the extremities, ii.
        13-14;
    morbid uniformity in the same family, ii. 17;
    on deaf-mutes, ii. 22;
    inheritance of injury to the eye, ii. 24;
    atavism in diseases and anomalies of structure, ii. 34;
    non-reversion to night-blindness, ii. 36;
    sexual limitation of the transmission of peculiarities in man, ii.
        72-73;
    on the effects of hard-drinking, ii. 289;
    inherited baldness with deficiency of teeth, ii. 326-327;
    occurrence of a molar tooth in place of an incisor, ii. 391;
    diseases occurring in alternate generations, ii. 401.
  SEDILLOT, on the removal of portions of bone, ii. 296.
  SEEDS, early selection of, ii. 204;
    rudimentary, in grapes, ii. 316;
    relative position of, in the capsule, ii. 345.
  SEEDS and buds, close analogies of, i. 411.
  SEEMANN, B., crossing of the wolf and Esquimaux dog, i. 22.
  SELBY, P. J., on the bud-destroying habits of the bullfinch, ii. 232.
  SELECTION, ii. 192-249;
    methodical, i. 214, ii. 194-210;
    by the ancients and semi-civilised people, ii. 201-210;
    of trifling characters, ii. 208-210;
    unconscious, i. 214, 217, ii. 174, 210-217;
    effects of, shown by differences in most valued parts, ii. 217-220;
    produced by accumulation of variability, ii. 220-223;
    natural, as affecting domestic productions, ii. 185-189, 224-233;
    as the origin of species, genera and other groups, ii. 429-432;
    circumstances favourable to, ii. 233-239;
    tendency of towards extremes, ii. 239-242;
  {477}
    possible limit of, ii. 242;
    influence of time on, ii. 243-244;
    summary of subject, ii. 246-249;
    effects of, in modifying breeds of cattle, i. 92, 93;
    in preserving the purity of breeds of sheep, i. 99-100;
    in producing varieties of pigeons, i. 213-218;
    in breeding fowls, i. 232-233;
    in the goose, i. 289;
    in the canary, i. 295;
    in the goldfish, i. 296;
    in the silkworm, i. 300-301;
    contrasted in cabbages and cereals, i. 323;
    in the white mulberry, i. 334;
    on gooseberries, i. 356;
    applied to wheat, i. 317-318;
    exemplified in carrots, &c., i. 326;
    in the potato, i. 331;
    in the melon, i. 360;
    in flowering plants, i. 365;
    in the hyacinth, i. 371;
    applied to bud-varieties of plants, i. 411;
    illustrations of, ii. 421-428.
  SELECTION, sexual, ii. 75.
  SELF-IMPOTENCE in plants, ii. 131-140;
    in individual plants, ii. 136-138;
    of hybrids, ii. 174.
  SELWYN, Mr., on the Dingo, i. 26.
  SELYS-LONGCHAMPS, on hybrid ducks, i. 190, ii. 46, 157;
    hybrid of the hook-billed duck and Egyptian goose, i. 282.
  SERINGE, on the St. Valery apple, i. 350.
  SERPENT Melon, i. 360.
  SERRES, Olivier de, wild poultry in Guiana, i. 237.
  SESAMUM, white-seeded, antiquity of the, ii. 429.
  _Setaria_, found in the Swiss lake-dwellings, i. 317.
  SETTERS, degeneration of, in India, i. 38;
    Youatt's remarks on, i. 41.
  SEX, secondary characters of, latent, ii. 51-52;
    of parents, influence of, on hybrids, ii. 267.
  SEXUAL characters, sometimes lost in domestication, ii. 74.
  SEXUAL limitation of characters, ii. 71-75.
  SEXUAL peculiarities, induced by domestication in sheep, i. 95;
    in fowls, i. 251-257;
    transfer of, i. 255-257.
  SEXUAL variability in pigeons, i. 161-162.
  SEXUAL selection, ii. 75.
  SHADDOCK, i. 335.
  SHAILER, Mr., on the moss-rose, i. 379-380.
  SHANGHAI fowls, i. 227.
  SHANGHAI sheep, their fecundity, i. 97.
  SHAN ponies, striped, i. 58.
  SHEEP, disputed origin of, i. 94;
    early domestication of, i. 94;
    large-tailed, i. 94, 95, 98, ii. 279;
    variations in horns, mammæ and other characters of, i. 95;
    sexual characters of, induced by domestication, i. 95, 96;
    adaptation of, to climate and pasture, i. 96, 97;
    periods of gestation of, i. 97;
    effect of heat on the fleece of, i. 98-99, ii. 278;
    effect of selection on, i. 99-101;
    "ancon" or "otter" breeds of, i. 17, 92, 100;
    "Mauchamp-merino," i. 100-101;
    cross of German and merino, ii. 85-89;
    black, of the Tarentino, ii. 227;
    Karakool, ii. 278;
    Jaffna, with callosities on the knees, ii. 302;
    Chinese, ii. 315;
    Danish, of the bronze period, ii. 427;
    polydactylism in, ii. 14;
    occasional production of horns in hornless breeds of, ii. 30;
    reversion of colour in, ii. 30;
    influence of male, on offspring, ii. 68;
    sexual differences in, ii. 73;
    influence of crossing or segregation on, ii. 86, 95-96, 102-103;
    interbreeding of, ii. 119-120;
    effect of nourishment on the fertility of, ii. 111-112;
    diminished fertility of, under certain conditions, ii. 161;
    unconscious selection of, ii. 213;
    natural selection in breeds of, ii. 224, 225, 227;
    reduction of bones in, ii. 242;
    individual differences of, ii. 251;
    local changes in the fleece of, in England, ii. 278;
    partial degeneration of, in Australia, ii. 278;
    with numerous horns, ii. 291;
    correlation of horns and fleece in, ii. 326;
    feeding on flesh, ii. 303;
    acclimatisation of, ii. 305-306;
    mountain, resistance of, to severe weather, ii. 312;
    white, poisoned by _Hypericum crispum_, ii. 337.
  SHEEP dogs resembling wolves, i. 24.
  SHELLS, sinistral and dextral, ii. 53.
  SHERIFF, Mr. new varieties of wheat, i. 315, 317;
    on crossing wheat, ii. 104-105;
    continuous variation of wheat, ii. 241.
  SIAM, cats of, i. 47; horses of, i. 53.
  SHIRLEY, E. P., on the fallow-deer, ii. 103, 120.
  SHORT, D., hybrids of the domestic cat and _Felis ornata_, i, 45.
  SIBERIA, northern range of wild horses in, i. 52.
  SICHEL, J., on the deafness of white cats with blue eyes, ii. 329.
  SIDNEY, S., on the pedigrees of pigs, ii. 3;
    on cross-reversion in pigs, ii. 35;
    period of gestation in the pig, i. 74;
    production of breeds of pigs by intercrossing, i. 78, 95;
    fertility of the pig, ii. 112;
    effects of interbreeding on pigs, ii. 121-122;
    on the colours of pigs, ii. 210, 229.
  SIEBOLD, on the sweet potato, ii. 309.
  SIEBOLD, von Carl, on parthenogenesis, ii. 364.
  _Silene_, contabescence in, ii. 166.
  SILK-FOWLS, i. 230, ii. 67, 69.
  {478}
  SILK-MOTH, Arrindy, ii. 306, 312;
    Tarroo, ii. 157.
  SILK-MOTHS, i. 300-304;
    domesticated species of, i. 300;
    history of, _ibid._;
    causes of modification in, i. 300-301;
    differences presented by, i. 301-304;
    crossing of, ii. 98;
    disease in, ii. 228;
    effects of disuse of parts in, ii. 298;
    selection practised with, ii. 197, 199;
    variation of, ii. 236;
    parthenogenesis in, ii. 364.
  SILKWORMS, variations of, i. 301-302;
    yielding white cocoons, less liable to disease, ii. 336.
  SILVER-GREY rabbit, i. 108, 111, 120.
  SIMONDS, J. B., period of maturity in various breeds of cattle, i. 87;
    differences in the periods of dentition in sheep, i. 96;
    on the teeth in cattle, sheep, &c., ii. 322;
    on the breeding of superior rams, ii. 196.
  SIMON, on the raising of eggs of the silk-moth in China, ii. 197.
  SIMPSON, Sir J., regenerative power of the human embryo, ii. 15.
  _Siredon_, breeding in the branchiferous stage, ii. 384.
  SISKIN, breeding in captivity, ii. 154.
  _Sivatherium_, resemblance of the, to Niata cattle, i. 89.
  SIZE, difference of, an obstacle to crossing, ii. 101.
  SKIN, and its appendages, homologous, ii. 325;
    hereditary affections of the, ii. 79.
  SKIRVING, R. S., on pigeons settling on trees in Egypt, i. 181.
  SKULL, characters of the, in breeds of dogs, i. 34;
    in breeds of pigs, i. 71;
    in rabbits, i. 116-120, 127;
    in breeds of pigeons, i. 163-165;
    in breeds of fowls, i. 260-266;
    in ducks, i. 282-283.
  SKULL and horns, correlation of the, ii. 333.
  SKYLARK, ii. 154.
  SLEEMAN, on the Cheetah, ii. 151.
  SLOE, i. 345.
  SMALL-POX, ii. 378.
  SMITER (pigeon), i. 156.
  SMITH, Sir A., on Caffrarian cattle, i. 88;
    on the use of numerous plants as food in South Africa, i. 307.
  SMITH, Colonel Hamilton, on the odour of the jackal, i. 30;
    on the origin of the dog, i. 16;
    wild dogs in St. Domingo, i. 28;
    on the Thibet mastiff and the alco, i. 28-29;
    development of the fifth toe in the hind feet of mastiffs, i. 35;
    differences in the skull of dogs, i. 34;
    history of the pointer, i. 42;
    on the ears of the dog, ii. 301;
    on the breeds of horses, i. 49;
    origin of the horse, i. 51;
    dappling of horses, i. 55;
    striped horses in Spain, i. 58;
    original colour of the horse, i. 60;
    on horses scraping away snow, i. 52;
    on _Asinus hemionus_, ii. 43;
    feral pigs of Jamaica, i. 77-78.
  SMITH, Sir J. E., production of nectarines and peaches by the same tree,
      i. 340;
    on _Viola amoena_, i. 368;
    sterility of _Vinca minor_ in England, ii. 170.
  SMITH, J., development of the ovary in _Bonatea speciosa_, by irritation
      of the stigma, i. 403.
  SMITH, N. H., influence of the bull "Favourite" on the breed of
      Short-horn cattle, ii. 65.
  SMITH, W., on the inter-crossing of strawberries, i. 352.
  SNAKE-RAT, ii. 87, 88.
  SNAKES, form of the viscera in, ii. 344.
  SNAPDRAGON, bud-variation in, i. 381;
    non-inheritance of colour in, ii. 21;
    peloric, crossed with the normal form, ii. 70, 93;
    asymmetrical variation of the, ii. 322.
  SOIL, adaptation of plums to, i. 346;
    influence of, on the zones of pelargoniums, i. 366;
    on roses, i. 367;
    on the variegation of leaves, i. 383;
    advantages of change of, ii. 146-148.
  SOIL and climate, effects of, on strawberries, i. 353.
  _Solanum_, non-intercrossing of species of, ii. 91.
  _Solanum tuberosum_, i. 330-331.
  SOLID-HOOFED pigs, i. 75.
  SOLOMON, his stud of horses, i. 55.
  SOMERVILLE, Lord, on the fleece of Merino sheep, i. 99;
    on crossing sheep, ii. 120;
    on selection of sheep, ii. 195;
    diminished fertility of Merino sheep brought from Spain, ii. 161.
  SOOTY fowls, i. 230, 256.
  SOTO, Ferdinand de, on the cultivation of native plants in Florida, i.
      312.
  _Sorghum_, i. 371.
  SPAIN, hawthorn monogynous in, i. 364.
  SPALLANZANI, on feral rabbits in Lipari, i. 113;
    experiments on salamanders, ii. 15, 293, 385;
    experiments in feeding a pigeon with meat, ii. 304.
  SPANIELS, in India, i. 38;
    King Charles's, i. 41;
    degeneration of, caused by interbreeding, ii. 121.
  SPANISH fowls, i. 227, 250, 253;
    figured, i. 226;
    early development of sexual characters in, i. 250, 251;
    furcula of, figured, i. 268.
  SPECIES, difficulty of distinguishing from varieties, i. 4;
    conversion of varieties into, i. 5;
    origin of, by natural selection, ii. 414-415;
    by mutual sterility of varieties, ii. 185-189.
  {479}
  SPENCER, Lord, on selection in breeding, ii. 195.
  SPENCER, Herbert, on the "survival of the fittest," i. 6;
    increase of fertility by domestication, ii. 111;
    on life, ii. 148, 177;
    changes produced by external conditions, ii. 281;
    effects of use on organs, ii. 295, 296;
    ascent of the sap in trees, ii. 296;
    correlation exemplified in the Irish elk, ii. 333-334;
    on "physiological units," ii. 375;
    antagonism of growth and reproduction, ii. 384;
    formation of ducts in plants, ii. 300.
  SPERMATOPHORES of the cephalopoda, ii. 383.
  SPERMATOZOIDS, ii. 363-364;
    apparent independence of, in insects, ii. 384.
  SPHINGIDÆ, sterility of, in captivity, ii. 157.
  SPINOLA, on the injurious effect produced by flowering buckwheat on white
      pigs, ii. 337.
  SPITZ dog, i. 31.
  SPOONER, W. C., cross-breeding of sheep, i. 100, ii. 95-96, 120;
    on the effects of crossing, ii. 96-97;
    on crossing cattle, ii. 118;
    individual sterility, ii. 162.
  SPORES, reproduction of abnormal forms by, i. 383.
  SPORTS, i. 373; in pigeons, i. 213.
  SPOT pigeon, i. 156, 207.
  SPRENGEL, C. K., on dichogamous plants, ii. 90;
    on the hollyhock, ii. 107;
    on the functions of flowers, ii. 175.
  SPROULE, Mr., inheritance of cleft-palate and hare-lip, ii. 24.
  SPURS, of fowls, i. 255;
    development of, in hens, ii. 318.
  SQUASHES, i. 357.
  SQUINTING, hereditary, ii. 9.
  SQUIRRELS, generally sterile in captivity, ii. 152.
  SQUIRRELS, flying, breeding in confinement, ii. 152.
  "STAARHALSIGE Taube," i. 161.
  STAG, one-horned, supposed heredity of character in, ii. 12;
    degeneracy of, in the Highlands, ii. 208.
  STAMENS, occurrence of rudimentary, ii. 316;
    conversion of, into pistils, i. 365;
    into petals, ii. 392.
  _Staphylea_, ii. 168.
  STEENSTRUP, Prof., on the dog of the Danish Middens, i. 18;
    on the obliquity of flounders, ii. 53.
  STEINAN, J., on hereditary diseases, ii. 7, 79.
  STERILITY, in dogs, consequent on close confinement, i. 32;
    comparative, of crosses, ii. 103, 104;
    from changed conditions of life, ii. 148-165;
    occurring in the descendants of wild animals bred in captivity, ii.
        160;
    individual, ii. 162;
    resulting from propagation by buds, cuttings, bulbs, &c., ii. 169;
    in hybrids, ii. 178-180, 386, 410-411;
    in specific hybrids of pigeons, i. 193;
    as connected with natural selection, ii. 185-189.
  STERNUM, characters of the, in rabbits, i. 123;
    in pigeons, i. 167, 174-175;
    in fowls, i. 268, 273;
    effects of disuse on the, i. 174-175, 273.
  STEPHENS, J. F., on the habits of the Bombycidæ, i. 303.
  STEWART, H., on hereditary disease, ii. 79.
  STIGMA, variation of the, in cultivated Cucurbitaceæ, i. 359;
    satiation of the, i. 402-403.
  STOCKS, bud-variation in, i. 381;
    effect of crossing upon the colour of the seed of, i. 398-399;
    true by seed, ii. 20;
    crosses of, ii. 93;
    varieties of, produced by selection, ii. 219;
    reversion by the upper seeds in the pods of, ii. 347-348.
  STOCKHOLM, fruit-trees of, ii. 307.
  STOKES, Prof., calculation of the chance of transmission of abnormal
      peculiarities in man, ii. 5.
  STOLONS, variations in the production of, by strawberries, i. 353.
  STOMACH, structure of the, affected by food, ii. 302.
  STONE in the bladder, hereditary, ii. 8, 79.
  STRAWBERRIES, i. 351-354;
    remarkable varieties of, i. 352-353;
    hautbois, dioecious, i. 353;
    selection in, ii. 200;
    mildew of, ii. 228;
    probable further modification of, ii. 243;
    variegated, effects of soil on, ii. 274.
  STRICKLAND, A., on the domestication of _Anser ferus_, i. 287;
    on the colour of the bill and legs in geese, i. 288.
  _Strictoenas_, i. 183.
  STRIPES on young of wild swine, i. 76;
    of domestic pigs of Turkey, Westphalia, and the Zambesi, i. 76-77;
    of feral swine of Jamaica and New Granada, i. 77;
    of fruit and flowers, i. 400, ii. 37;
    in horses, i. 56-60;
    in the ass, i. 62-63;
    production of, by crossing species of Equidæ, ii. 42-43.
  _Strix grallaria_, ii. 302.
  _Strix passerina_, ii. 154.
  "STRUPP-TAUBE," i. 155.
  STRUTHERS, Mr., osteology of the feet in solid-hoofed pigs, i. 75;
    on polydactylism, ii. 13-14.
  STURM, prepotency of transmission of characters in sheep and cattle, ii.
      66;
    absorption of the minority in crossed races, ii. 88;
    correlation of twisted horns and curled wool in sheep, ii. 326.
  {480}
  SUB-SPECIES, wild, of _Columba livia_ and other pigeons, i. 204.
  SUCCESSION, geological, of organisms, i. 11.
  SUCKERS, bud-variation by, i. 384.
  SUGAR cane, sterility of, in various countries, ii. 169;
    white, liability of, to disease, ii. 228, 336.
  SUICIDE, hereditary tendency to, ii. 7, 78.
  SULIVAN, Admiral, on the horses of the Falkland Islands, i. 53;
    wild pigs of the Falkland Islands, i. 77;
    feral cattle of the Falkland Islands, i. 86, 102;
    feral rabbits of the Falkland Islands, i. 112.
  SULTAN fowl, i. 228, 255.
  _Sus indica_, i. 65, 67-70, ii. 110.
  _Sus pliciceps_, i. 69 (figured).
  _Sus scrofa_, i. 65, 66, ii. 110.
  _Sus scrofa palustris_, i. 68.
  _Sus vittatus_, i. 67.
  SWALLOWS, a breed of pigeons, i. 156.
  SWAYNE, Mr., on artificial crossing of varieties of the pea, i. 397.
  SWEET Peas, ii. 91;
    crosses of, ii. 93, 94;
    varieties of, coming true by seed, ii. 20;
    acclimatisation of, in India, ii. 311.
  SWEET William, bud-variation in, i. 381.
  SWINHOE, R., on Chinese pigeons, i. 28, 206;
    on striped Chinese horses, i. 59.
  SWITZERLAND, ancient dogs of, i. 19;
    pigs of, in the Neolithic period, i. 67-68;
    goats of, i. 101.
  SYCAMORE, pale-leaved variety of the, ii. 330.
  SYKES, Colonel, on a Pariah dog with crooked legs, i. 17;
    on small Indian asses, i. 62;
    on _Gallus Sonneratii_, i. 233;
    on the voice of the Indian Kulm cock, i. 259;
    fertility of the fowl in most climates, ii. 161.
  SYMMETRY, hereditary departures from, ii. 12.
  _Symphytum_, variegated, i. 384.
  SYPHILIS, hereditary, ii. 332.
  SYRIA, asses of, i. 62.
  _Syringa persica_, _chinensis_, and _vulgaris_, ii. 164.

  TACITUS, on the care taken by the Celts in breeding animals, ii. 202.
  _Tagetes signata_, dwarf variety of, ii. 20.
  TAHITI, varieties of cultivated plants in, ii. 256.
  TAIL, occasional development of, in man, ii. 57;
    never curled in wild animals, ii. 301;
    rudimentary in Chinese sheep, ii. 315.
  TAIL-FEATHERS, numbers of, in breeds of pigeons, i. 158-159;
    peculiarities of, in cocks, i. 254-255;
    variability of, in fowls, i. 258;
    curled, in _Anas boschas_, and tame drakes, i. 280.
  TALENT, hereditary, ii. 7.
  TANKERVILLE, Earl of, on Chillingham cattle, i. 84, ii. 119.
  TANNER, Prof., effects of disuse of parts in cattle, ii. 299.
  TAPIR, sterility of the, in captivity, ii. 150.
  TARGIONI-TOZZETTI, on cultivated plants, i. 306;
    on the vine, i. 332;
    varieties of the peach, i. 342;
    origin and varieties of the plum, i. 345;
    origin of the cherry, i. 347;
    origin of roses, i. 366.
  TARSUS, variability of the, in fowls, i. 259;
    reproduction of the, in a thrush, ii. 15.
  TARTARS, their preference for spiral-horned sheep, ii. 209.
  TAVERNIER, abundance of pigeons in Persia, i. 205.
  _Taxus baccata_, ii. 18.
  TEEBAY, Mr., reversion in fowls, ii. 38.
  TEETH, number and position of, in dogs, i. 34;
    deficiency of, in naked Turkish dogs, i. 35;
    period of appearance of, in breeds of dogs, i. 35;
    precocity of, in highly bred animals, ii. 322;
    correlation of, with hair, ii. 326;
    double row of, with redundant hair, in Julia Pastrana, ii. 328;
    affected in form by hereditary syphilis and by pulmonary tubercle, ii.
        332;
    fusion of, ii. 341;
    developed on the palate, ii. 391.
  TEGETMEIER, Mr., on a cat with monstrous teeth, i. 48;
    on a swift-like pigeon, i. 157;
    naked young of some pigeons, i. 170;
    fertility of hybrid pigeons, i. 192;
    on white pigeons, ii. 230;
    reversion in crossed breeds of fowls, i. 239-244;
    chicks of the white silk-fowl, i. 249;
    development of the cranial protuberance in Polish fowls, i. 250;
    on the skull in the Polish fowl, i. 257, 262;
    on the intelligence of Polish fowls, i. 264;
    correlation of the cranial protuberance and crest in Polish fowls, i.
        274;
    development of the web in the feet of Polish fowls, i. 259;
    early development of several peculiarities in Spanish cocks, i. 250;
    on the comb in Spanish fowls, i. 253;
    on the Spanish fowl, ii. 306;
    varieties of game-fowls, i. 252;
    pedigrees of game-fowls, ii. 3;
    assumption of female plumage by a game cock, i. 253;
    natural selection in the game cock, ii. 225;
    pugnacity of game hens, i. 256;
    length of the middle toe in Cochin fowls, i. 259;
    origin of the Sebright bantam, ii. 54;
    differences in the size of fowls, i. 257;
    effect of crossing in fowls, i. 258, ii. 96;
    effects of interbreeding in fowls, ii. 124-125;
    incubation by mongrels of non-sitting races of fowls, ii. 44;
    inverse correlation of crest and comb in fowls, i. 274;
  {481}
    occurrence of pencilled feathers in fowls, ii. 40;
    on a variety of the goose from Sebastopol, i. 289;
    on the fertility of the peahen, ii. 112;
    on the intercrossing of bees, ii. 126.
  TEMMINCK, origin of domestic cats, i. 43;
    origin of domestic pigeons, i. 180;
    on _Columba guinea_, i. 182;
    on _Columba leucocephala_, i. 183;
    asserted reluctance of some breeds of pigeons to cross, i. 192;
    sterility of hybrid turtle-doves, i. 193;
    variations of _Gallus bankiva_, i. 235;
    on a buff-coloured breed of Turkeys, i. 293;
    number of eggs laid by the peahen, ii. 112;
    breeding of Guans in captivity, ii. 156;
    behaviour of grouse in captivity, _ibid._;
    sterility of the partridge in captivity, _ibid._
  TENDRILS in Cucurbitaceæ, i. 358, ii. 316.
  TENNENT, Sir J. E., on the goose, i. 287;
    on the growth of the apple in Ceylon, ii. 277;
    on the Jaffna sheep, ii. 302.
  _Teredo_, fertilisation in, ii. 363.
  TERRIERS, wry-legged, ii. 245;
    white, subject to distemper, ii. 336.
  TESCHEMACHER, on a husked form of maize, i. 320.
  TESSIER, on the period of gestation of the dog, i. 29;
    of the pig, i. 74;
    in cattle, i. 87;
    experiments on change of soil, ii. 147.
  _Tetrao_, breeding of species of, in captivity, ii. 156.
  _Tetrapteryx paradisea_, ii. 156.
  _Teucrium campanulatum_, pelorism in, ii. 345.
  TEXAS, feral cattle in, i. 85.
  THEOGNIS, his notice of the domestic fowl, i. 246.
  THEOPHRASTUS, his notice of the peach, ii. 308.
  _Thesium_, ii. 284.
  THOMPSON, Mr., on the peach and nectarine, i. 342;
    on the varieties of the apricot, i. 344;
    classification of varieties of cherries, i. 347-348;
    on the "Sister ribston-pippin," i. 350;
    on the varieties of the gooseberry, i. 354, 355.
  THOMPSON, William, on the pigeons of Islay, i. 184;
    feral pigeons in Scotland, i. 190;
    colour of the bill and legs in geese, i. 288;
    breeding of _Tetrao scotius_ in captivity, ii. 156;
    destruction of black-fowls by the osprey, ii. 230.
  THOMPSON, Prof. W., on the obliquity of the flounder, ii. 53.
  THORNS, reconversion of, into branches, in pear trees, ii. 318.
  THORN, grafting of early and late, i. 363;
    Glastonbury, i. 364.
  THRUSH, asserted reproduction of the tarsus in a, ii. 15.
  _Thuja pendula_ or _filiformis_, a variety of _T. orientalis_, i. 362.
  THURET, on the division of the zoospores of an alga, ii. 378.
  THWAITES, G. H., on the cats of Ceylon, i. 46;
    on a twin seed of _Fuchsia coccinea_ and _fulgens_, i. 391.
  TIBURTIUS, experiments in rearing wild ducks, i. 278.
  TIGER, rarely fertile in captivity, ii. 150, 151.
  _Tigridia conchiflora_, bud-variation in, i. 386.
  TIME, importance of, in the production of races, ii. 243.
  TINZMANN, self-impotence in the potato, ii. 137.
  TISSUES, affinity of, for special organic substances, ii. 380.
  TITMICE, destructive to thin-shelled walnuts, i. 356;
    attacking nuts, i. 357;
    attacking peas, ii. 231.
  TOBACCO, crossing of varieties of, ii. 108;
    cultivation of in Sweden, ii. 307.
  TOBOLSK, red-coloured cats of, i. 47.
  TOES, relative length of, in fowls, i. 259;
    development of fifth in dogs, ii. 317.
  TOLLET, Mr., his selection of cattle, ii. 199.
  TOMATO, ii. 91.
  TOMTITS. See _Titmice_.
  TONGUE, relation of, to the beak in pigeons, i. 168.
  TOOTH, occurrence of a molar, in place of an incisor, ii. 391.
  "TORFSCHWEIN,"  i. 68.
  TRAIL, R., on the union of half-tubers of different kinds of potatoes, i.
      395.
  TREES, varieties of, suddenly produced, i. 361;
    weeping or pendulous, i. 361;
    fastigate or pyramidal, i. 361;
    with variegated or changed foliage, i. 362;
    early or late in leaf, i. 362-363;
    forest, non-application of selection to, ii. 237.
  "TREMBLEUR" (pigeons), i. 146.
  TREMBLEY, on reproduction in Hydra, ii. 359.
  "TREVOLTINI" silkworms, i. 301-302.
  _Trichosanthes anguina_, i. 360.
  TRICKS, inheritance of, ii. 6-7, 395.
  _Trifolium minus_ and _repens_, ii. 164.
  TRIMORPHIC plants, conditions of reproduction in, ii. 181-184.
  TRISTRAM, H. B., selection of the dromedary, ii. 205-206.
  _Triticum dicoccum_, i. 319.
  _Triticum monococcum_, i. 319.
  _Triticum spelta_, i. 319.
  _Triticum turgidum_, i. 319.
  _Triticum vulgare_, wild in Asia, i. 312.
  {482}
  TRITON, breeding in the branchiferous stage, ii. 384.
  "TROMMEL-TAUBE," i. 154.
  "TRONFO" pigeon, i. 144.
  _Tropæolum_, ii. 38.
  _Tropæolum minus_ and _majus_, reversion in hybrids of, i. 392.
  TROUBETZKOY, Prince, experiments with pear-trees at Moscow, ii. 307.
  TROUSSEAU, Prof., pathological resemblance of twins, ii. 252.
  TRUMPETER pigeon, i. 154;
    known in 1735, i. 207.
  TSCHARNER, H. A. de, graft-hybrid produced by inosculation in the vine,
      i. 395.
  TSCHUDI, on the naked Peruvian dog, i. 23;
    extinct varieties of maize from Peruvian tombs, i. 320, ii. 425.
  TUBERS, bud-variation by, i. 384-385.
  TUCKERMAN, Mr., sterility of _Carex rigida_, ii. 170.
  TUFTED ducks, i. 281.
  TULIPS, variability of, i. 370;
    bud-variation in, i. 385-386;
    influence of soil in "breaking," i. 385.
  TUMBLER pigeon, i. 150-153;
    short-faced, figured, i. 152;
    skull figured, i. 163;
    lower jaw figured, i. 165;
    scapula and furcula figured, i. 167;
    early known in India, i. 207;
    history of, i. 209;
    sub-breeds of, i. 220;
    young unable to break the egg-shell, ii. 226;
    probable further modification of, ii. 242.
  "TÜMMLER" (pigeons), i. 150.
  TUMOURS, ovarian, occurrence of hairs and teeth in, ii. 370;
    polypoid, origin of, ii. 381.
  "TÜRKISCHE TAUBE," i. 139.
  TURBIT (pigeon), i. 148.
  TURKEY, domestic, origin of, i. 292-293;
    crossing of with North American wild Turkey, i. 292-293;
    breeds of, i. 293;
    crested white cock, i. 293;
    wild, characters of, i. 293-294;
    degeneration of, in India, i. 294, ii. 278;
    failure of eggs of, in Delhi, ii. 161;
    feral on the Parana, i. 190;
    change produced in by domestication, ii. 262.
  TURKEY, striped young pigs in, i. 76.
  TURNER (pigeon), i. 156.
  TURNER, W., on compensation in arteries and veins, ii. 300;
    on cells, ii. 370.
  TURNIPS, origin of, i. 325;
    reversion in, ii. 31;
    run wild, ii. 33;
    crosses of, ii. 93, 96;
    Swedish, preferred by hares, ii. 232;
    acclimatisation of, in India, ii. 311.
  TURNSPIT, on an Egyptian monument, i. 17;
    crosses of the, ii. 92.
  TURTLE-DOVE, white and coloured, crossing of, ii. 92.
  _Turtur auritus_, hybrids of, with _T. cambayensis_ and _T. suratensis_,
      i. 194.
  _Turtur risorius_, crossing of, with the common pigeon, i. 193;
    hybrid of, with _T. vulgaris_, _ibid._
  _Turtur suratensis_, sterile hybrids of, with _T. vulgaris_, i. 193;
    hybrids of, with _T. auritus_, i. 194.
  _Turtur vulgaris_, crossing of, with the common pigeon, i. 193;
    hybrid of, with _T. risorius_, _ibid._;
    sterile hybrids of, with _T. suratensis_ and _Ectopistes migratorius_,
        _ibid._
  TUSKS of wild and domesticated pigs, i. 76, 77.
  _Tussilago farfara_, variegated, i. 384.
  TWIN-SEED _Fuchsia coccinea_ and _fulgens_, i. 391.
  TYERMAN, B., on the pigs of the Pacific islands, i. 70, ii. 87;
    on the dogs of the Pacific islands, ii. 87.
  TYLOR, Mr., on the prohibition of consanguineous marriages, ii. 122-123.

  UDDERS, development of the, ii. 300.
  _Ulex_, double-flowered, ii. 167.
  _Ulmus campestris_ and _effusa_, hybrids of, ii. 130.
  UNIFORMITY of character, maintained by crossing, ii. 85-90.
  UNITS of the body, functional independence of the, ii. 368-371.
  UNITY or plurality of origin of organisms, i. 13.
  UPAS poison, ii. 380.
  UREA, secretion of, ii. 380.
  USE and disuse of parts, effects of, ii. 295-303, 352-353, 418-419;
    in rabbits, i. 124-128;
    in ducks, i. 284-286.
  UTILITY, considerations of, leading to uniformity, ii. 241.

  VALENTIN, experimental production of double monsters by, ii. 340.
  _Vallota_, ii. 139.
  VAN BECK, Barbara, a hairy-faced woman, ii. 4.
  VAN MONS on wild fruit-trees, i. 312, ii. 260;
    production of varieties of the vine, i. 333;
    correlated variability in fruit-trees, ii. 330;
    production of almond-like fruit by peach-seedlings, i. 339.
  _Vanessa_, species of, not copulating in captivity, ii. 157.
  VARIABILITY, i. 4, ii. 371-373, 394-397, 406-420;
    causes of, ii. 250-270;
    correlated, ii. 319-338, 353-355, 419-420;
    law of equable, ii. 351-352;
    necessity of, for selection, ii. 192;
    of selected characters, ii. 238-239;
    of multiple homologous parts, ii. 342.
  {483}
  VARIATION, laws of, ii. 293-356;
    continuity of, ii. 241;
    possible limitation of, ii. 242, 416-417;
    in domestic cats, i. 45-48;
    origin of breeds of cattle by, i. 88;
    in osteological characters of rabbits, i. 115-130;
    of important organs, i. 359;
    analogous or parallel, i. 348-352;
    in horses, i. 55;
    in the horse and ass, i. 64;
    in fowls, i. 243-246;
    in geese, i. 288;
    exemplified in the production of fleshy stems in cabbages, &c., i. 326;
    in the peach, nectarine, and apricot, i. 342, 344;
    individual, in wheat, i. 314.
  VARIEGATION of foliage, i. 383, ii. 167-168.
  VARIETIES and species, resemblance of, i. 4, ii. 411-413;
    conversion of, into species, i. 5;
    abnormal, ii. 413;
    domestic, gradually produced, ii. 414.
  VARRO, on domestic ducks, i. 277;
    on feral fowls, ii. 33;
    crossing of the wild and domestic ass, ii. 206.
  VASEY, Mr., on the number of sacral vertebræ in ordinary and humped
      cattle, i. 79;
    on Hungarian cattle, i. 80.
  VAUCHER, sterility of _Ranunculus ficaria_ and _Acorus calamus_, ii. 170.
  VEGETABLES, cultivated, reversion in, ii. 31-32;
    European, culture of, in India, ii. 168-169.
  VEITH, Mr., on breeds of horses, i. 49.
  _Verbascum_, intercrossing of species of, i. 336, ii. 93, 105-107;
    reversion in hybrids of, i. 392;
    contabescent, wild plants of, ii. 165;
    villosity in, ii. 277.
  _Verbascum austriacum_, ii. 136.
  _Verbascum blattaria_, ii. 105-106.
  _Verbascum lychnitis_, ii. 105-106, 136.
  _Verbascum nigrum_, ii. 136.
  _Verbascum phoeniceum_, ii. 107, 137;
    variable duration of, ii. 305.
  _Verbascum thapsus_, ii. 106.
  VERBENAS, origin of, i. 364;
    white, liability of, to mildew, ii. 228, 336;
    scorching of dark, ii. 229, 336;
    effect of changed conditions of life on, ii. 273.
  VERLOT, on the darkleaved Barberry, i. 362;
    inheritance of peculiarities of foliage in trees, i. 362;
    production of _Rosa cannabifolia_ by bud-variation from _R. alba_, i.
        381;
    bud-variation in _Aralia trifoliata_, i. 382;
    variegation of leaves, i. 383;
    colours of tulips, i. 386;
    uncertainty of inheritance, ii. 18;
    persistency of white flowers, ii. 20;
    peloric flowers of _Linaria_, ii. 58;
    tendency of striped flowers to uniformity of colour, ii. 70;
    non-intercrossing of certain allied plants, ii. 91;
    sterility of _Primulæ_ with coloured calyces, ii. 166;
    on fertile proliferous flowers, _ibid._;
    on the Irish yew, ii. 241;
    differences in the _Camellia_, ii. 251;
    effect of soil on the variegated strawberry, ii. 274;
    correlated variability in plants, ii. 330.
  _Verruca_, ii. 53, 400.
  VERTEBRÆ, characters of, in rabbits, i. 120-122;
    in ducks, i. 283-284;
    number and variations of, in pigeons, i. 165-166;
    number and characters of, in fowls, i. 266-268;
    variability of number of, in the pig, i. 74.
  VERTUCH, see Putsche.
  "VERUGAS," ii. 276.
  VESPUCIUS, early cultivation in Brazil, i. 311.
  VIBERT'S experiments on the cultivation of the vine from seed, i. 332.
  _Viburnum opulus_, ii. 185, 316.
  _Vicia sativa_, leaflet converted into a tendril in, ii. 392.
  VICUNAS, selection of, ii. 207.
  VILLOSITY of plants, influenced by dryness, ii. 277.
  VILMORIN, cultivation of the wild carrot, i. 326, ii. 217;
    colours of tulips, i. 386;
    uncertainty of inheritance in balsams and roses, ii. 18;
    experiments with dwarf varieties of _Saponaria calabrica_ and _Tagetes
        signata_, ii. 20;
    reversion of flowers by stripes and blotches, ii. 37;
    on variability, ii. 262.
  _Vinca minor_, sterility in, ii. 170.
  VINE, i. 332-334;
    parsley-leaved, reversion of, i. 382;
    graft-hybrid produced by inosculation in the, i. 395;
    disease of, influenced by colour of grapes, ii. 228;
    influence of climate, &c., on varieties of the, ii. 278;
    diminished extent of cultivation of the, ii. 308;
    acclimatisation of the, in the West Indies, ii. 313.
  _Viola_, species of, i. 368.
  _Viola lutea_, different coloured flowers in, i. 408.
  _Viola tricolor_, reversion in, ii. 31, 47.
  VIRCHOW, Prof., blindness occurring in the offspring of consanguineous
      marriages, ii. 143;
    on the growth of bones, ii. 294, 381;
    on cellular prolification, ii. 295;
    independence of the elements of the body, ii. 369;
    on the cell-theory, ii. 370;
    presence of hairs and teeth in ovarian tumours, ii. 370;
    of hairs in the brain, ii. 391;
    special affinities of the tissues, ii. 380;
    origin of polypoid excrescences and tumours, ii. 381.
  VIRGIL on the selection of seed-corn, i. 318, ii. 203;
    of cattle and sheep, ii. 202.
  VIRGINIAN islands, ponies of, i. 52.
  _Virgularia_, ii. 378.
  VISION, hereditary peculiarities of, ii. 8-9;
  {484}
    in amphibious animals, ii. 223;
    varieties of, ii. 300;
    affections of organs of, correlated with other peculiarities, ii. 328.
  _Vitis vinifera_, i. 332-334, 375.
  _Viverra_, sterility of species of, in captivity, ii. 151.
  VOGEL, varieties of the date palm, ii. 256.
  VOGT, on the indications of stripes on black kittens, ii. 55.
  VOICE, differences of, in fowls, i. 259;
    peculiarities of, in ducks, i. 281;
    inheritance of peculiarities of, ii. 6.
  VOLZ, on the history of the dog, i. 16;
    ancient history of the fowl, i. 246;
    domestic ducks unknown to Aristotle, i. 277;
    Indian cattle sent to Macedonia by Alexander, ii. 202;
    mention of mules in the Bible, ii. 202;
    history of the increase of breeds, ii. 244.
  VON BERG on _Verbascum phoeniceum_, ii. 305.
  VOORHELM, G., his knowledge of hyacinths, i. 371, ii. 251.
  VROLIK, Prof., on polydactylism, ii. 12;
    on double monsters, ii. 340;
    influence of the shape of the mother's pelvis on her child's head, ii.
        344.

  WADERS, behaviour of, in confinement, ii. 156.
  WAHLENBERG, on the propagation of Alpine plants by buds, runners, bulbs,
      &c., ii. 169.
  "WAHLVERWANDTSCHAFT" of Gärtner, ii. 180.
  WALES, white cattle of, in the 10th century, i. 85.
  WALKER, A., on intermarriage, i. 404;
    on the inheritance of polydactylism, ii. 13.
  WALKER, D., advantage of change of soil to wheat, ii. 146.
  WALLACE, A. R., on a striped Javanese horse, i. 59;
    on the conditions of life of feral animals, ii. 32;
    artificial alteration of the plumage of birds, ii. 280;
    on polymorphic butterflies, ii. 399-400;
    on reversion, ii. 415;
    on the limit of change, ii. 417.
  WALLACE, Dr., on the sterility of Sphingidæ hatched in autumn, ii. 158.
  WALLACHIAN sheep, sexual peculiarities in the horns of, i. 96.
  WALLFLOWER, bud-variation in, i. 382.
  WALLICH, Dr., on _Thuja pendula_ or _filiformis_, i. 362.
  WALNUTS, i. 356-357;
    thin-shelled, attacked by tomtits, ii. 231;
    grafting of, ii. 259.
  WALSH, B. D., on galls, ii. 282, 283;
    his "Law of equable variability," ii. 351-352.
  WALTHER, F. L., on the history of the dog, i. 16;
    on the intercrossing of the zebu and ordinary cattle, i. 83.
  WARING, Mr., on individual sterility, ii. 162.
  WART hog, i. 76.
  WATERER, Mr., spontaneous production of _Cytisus alpino-laburnum_, i.
      390.
  WATER melon, i. 357.
  WATERHOUSE, G. R., on the winter-colouring of _Lepus variabilis_, i. 111.
  WATERTON, C., production of tailless foals, i. 53;
    on taming wild ducks, i. 278;
    on the wildness of half-bred wild ducks, ii. 45;
    assumption of male characters by a hen, ii. 51.
  WATSON, H. C., on British wild fruit-trees, i. 312;
    on the non-variation of weeds, i. 317;
    origin of the plum, i. 345;
    variation in _Pyrus malus_, i. 348;
    on _Viola amoena_ and _tricolor_, i. 368;
    on reversion in Scotch kail, ii. 32;
    fertility of _Draba sylvestris_ when cultivated, ii. 163;
    on generally distributed British plants, ii. 285.
  WATTLES, rudimentary, in some fowls, ii. 315.
  WATTS, Miss, on Sultan fowls, i. 228.
  WEBB, James, interbreeding of sheep, ii. 120.
  WEBER, effect of the shape of the mother's pelvis on her child's head,
      ii. 344.
  WEEDS, supposed necessity for their modification, coincidently with
      cultivated plants, i. 317.
  WEEPING varieties of trees, i. 361.
  WEEPING habit of trees, capricious inheritance of, ii. 18-19.
  WEEVIL, injury done to stone-fruit by, in North America, ii. 231.
  WELSH cattle, descended from _Bos longifrons_, i. 81.
  WEST Indies, feral pigs of, i. 77;
    effect of climate of, upon sheep, i. 98.
  WESTERN, Lord, change effected by, in the sheep, ii. 198.
  WESTPHALIA, striped young pigs in, i. 76.
  WESTWOOD, J. O., on peloric flowers of _Calceolaria_, ii. 346.
  WHATELY, Archbishop, on grafting early and late thorns, i. 363.
  WHEAT, specific unity or diversity of, i. 312-313, 316-317;
    Hasora, i. 313;
    presence or absence of barbs in, i. 314;
    Godron on variations in, _ibid._;
    varieties of, i. 314-315;
    effects of soil and climate on, i. 316;
    deterioration of, _ibid._;
    crossing of varieties of, _ibid._, ii. 96, 104-105, 130;
    in the Swiss lake-dwellings, i. 317-319;
    selection applied to, i. 318, ii. 200;
    increased fertility of hybrids of, with _Ægilops_, ii. 110;
    advantage of change of soil to, ii. 146;
  {485}
    differences of, in various parts of India, ii. 165;
    continuous variation in, ii. 200;
    red, hardiness of, ii. 229, 336;
    Fenton, ii. 232;
    natural selection in, ii. 233;
    varieties of, found wild, ii. 260;
    effects of change of climate on, ii. 307;
    ancient variety of, ii. 429.
  WHITBY, Mrs., on the markings of silkworms, i. 302;
    on the silkmoth, i. 303.
  WHITE, Mr., reproduction of supernumerary digits after amputation, ii.
      14;
    time occupied in the blending of crossed races, ii. 87.
  WHITE, Gilbert, vegetable diet of dogs, ii. 303.
  WHITE and white-spotted animals, liability of, to disease, ii. 336-337.
  WHITE flowers, most truly reproduced by seed, ii. 20.
  WICHURA, Max, on hybrid willows, ii. 50, 131, 267;
    analogy between the pollen of old-cultivated plants, and of hybrids,
        ii. 268.
  WICKING, Mr., inheritance of the primary characters of _Columba livia_ in
      cross-bred pigeons, i. 201;
    production of a white head in almond tumblers, ii. 199.
  WICKSTED, Mr., on cases of individual sterility, ii. 162.
  WIEGMANN, spontaneous crossing of blue and white peas, i. 397;
    crossing of varieties of cabbage, ii. 130;
    on contabescence, ii. 165.
  WIGHT, Dr., sexual sterility of plants propagated by buds, &c., ii. 169.
  WILDE, Sir W. R., occurrence of _Bos frontosus_ and _longifrons_ in Irish
      crannoges, i. 81;
    attention paid to breeds of animals by the ancient Irish, ii. 203.
  WILDMAN, on the dahlia, ii. 216, 273.
  WILDNESS of the progeny of crossed tame animals, ii. 44-46.
  WILKES, Capt., on the taming of pigeons among the Polynesians, ii. 161.
  WILKINSON, J., on crossed cattle, ii. 104.
  WILLIAMS, Mr., change of plumage in a Hamburgh hen, i. 258.
  WILLIAMS, Mr., intercrossing of strawberries, i. 352.
  WILLIAMSON, Capt., degeneration of dogs in India, i. 37;
    on small Indian asses, i. 62.
  WILLIAMSON, Rev. W., doubling of _Anemone coronaria_ by selection, ii.
      200.
  WILLOWS, weeping, i. 361;
    reversion of spiral-leaved weeping, i. 383;
    hybrids of, ii. 267;
    galls of, ii. 282-283.
  WILLOUGHBY, F., notice of spot pigeons, i. 156;
    on a fantail pigeon, i. 208;
    on tumbler pigeons, i. 209;
    on the turbit, i. 209;
    on the barb and carrier pigeons, i. 211;
    on the hook-billed duck, i. 277.
  WILMOT, Mr., on a crested white Turkey cock, i. 293;
    reversion of sheep in colour, ii. 30.
  WILSON, B. O., fertility of hybrids of humped and ordinary cattle in
      Tasmania, i. 83.
  WILSON, Dr., prepotency of the Manx over the common cat, ii. 66.
  WILSON, James, origin of dogs, i. 16.
  WILSON, Mr., on prepotency of transmission in sheep, ii. 69;
    on the breeding of bulls, ii. 196.
  WINGS, proportionate length of, in different breeds of pigeons, i.
      175-176;
    of fowls, effects of disuse on, i. 270-272;
    characters and variations of, in ducks, i. 284-286;
    diminution of, in birds of small islands, i. 286-287.
  WING-FEATHERS, number of, in pigeons, i. 159;
    variability of, in fowls, i. 258.
  WOLF, recent existence of, in Ireland, i. 16;
    barking of young, i. 27;
    hybrids of, with the dog, i. 32.
  WOLF-DOG, black, of Florida, i. 22.
  WOLVES, North American, their resemblance to dogs of the same region, i.
      21-22;
    burrowing of, i. 27.
  WOODBURY, Mr., crossing of the Ligurian and common hive bees, i. 299, ii.
      126;
    variability of bees, i. 298.
  WOODWARD, S. P., on Arctic Mollusca, ii. 256.
  WOOD, Willoughby, on Mr. Bates' cattle, ii. 118.
  WOOLER, W. A., on the young of the Himalayan rabbit, i. 109;
    persistency of the coloured calyx in a crossed Polyanthus, i. 365.
  WORRARA poison, ii. 380.
  WOUNDS, healing of, ii. 294.
  WRIGHT, J., production of crippled calves by shorthorned cattle, ii. 118;
    on selection in cattle, ii. 194;
    effect of close interbreeding on pigs, ii. 121-122;
    deterioration of game cocks by close interbreeding, ii. 124.
  WRIGHT, Strethill, on the development of the hydroida, ii. 368.
  WYMAN, Dr., on Niata cattle, and on a similar malformation in the
      codfish, i. 89;
    on Virginian pigs, ii. 227.

  XENOPHON, on the colours of hunting dogs, ii. 209.
  XIMENES, Cardinal, regulations for the selection of rams, ii. 204.

  "YAHOO," the name of the pigeon in Persia, i. 155.
  YAKS, domestication of, i. 82;
    selection of white-tailed, ii. 206, 209.
  {486}
  YAM, development of axillary bulbs in the, ii. 169.
  YARRELL, Mr., deficiency of teeth in hairless dogs, i. 34, ii. 326;
    on ducks, i. 279, ii. 262;
    characters of domestic goose, resembling those of _Anser albifrons_, i.
        288;
    whiteness of ganders, i. 288;
    variations in goldfish, i. 296-297;
    assumption of male plumage by the hen-pheasant, ii. 51;
    effect of castration upon the cock, ii. 51-52;
    breeding of the skylark in captivity, ii. 154;
    plumage of the male linnet in confinement, ii. 158;
    on the dingo, ii. 263.
  YELLOW fever, in Mexico, ii. 276.
  YEW, fastigate, ii. 241.
  YEW, Irish, hardy in New York, ii. 309.
  YEW, weeping, i. 361;
    propagation of, by seed, ii. 18-19.
  YOLK, variations of, in the eggs of ducks, i. 281.
  YOUATT, Mr., history of the dog, i. 16-17;
    variations of the pulse in breeds of dogs, i. 35;
    liability to disease in dogs, i. 35, ii. 227;
    inheritance of goître in dogs, ii. 10;
    on the greyhound, i. 34, 41;
    on King Charles' spaniels, i. 41;
    on the setter, i. 41;
    on breeds of horses, i. 49;
    variation in the number of ribs in the horse, i. 50;
    inheritance of diseases in the horse, ii. 10, 11;
    introduction of Eastern blood into English horses, ii. 212-213;
    on white Welsh cattle, i. 85, ii. 209;
    improvement of British breeds of cattle, i. 93;
    rudiments of horns in young hornless cattle, ii. 55, 315;
    on crossed cattle, ii. 104, 119;
    on Bakewell's long-horned cattle, ii. 118;
    selection of qualities in cattle, ii. 196;
    degeneration of cattle by neglect, ii. 239;
    on the skull in hornless cattle, ii. 333;
    disease of white parts of cattle, ii. 337;
    displacement of long-horned by short-horned cattle, ii. 426;
    on Angola sheep, i. 95;
    on the fleece of sheep, i. 99;
    correlation of horns and fleece in sheep, i. 95;
    adaptation of breeds of sheep to climate and pasture, i. 96;
    horns of Wallachian sheep, i. 96;
    exotic sheep in the Zoological Gardens, i. 96-97, ii. 305;
    occurrence of horns in hornless breeds of sheep, ii. 30;
    on the colour of sheep, ii. 30;
    on interbreeding sheep, ii. 120;
    on Merino rams in Germany, ii. 196;
    effect of unconscious selection on sheep, ii. 213;
    reversion of Leicester sheep on the Lammermuir Hills, ii. 224;
    on many-horned sheep, ii. 326;
    reduction of bone in sheep, ii. 242;
    persistency of character in breeds of animals in mountainous countries,
        ii. 64;
    on interbreeding, ii. 116;
    on the power of selection, ii. 194-195;
    slowness of production of breeds, ii. 244;
    passages in the Bible relating to the breeding of animals, ii. 201-202.
  YOUNG, J., on the Belgian rabbit, i. 106.
  YULE, Capt., on a Burmese hairy family, ii. 77, 327.

  ZAMBESI, striped young pigs on the, i. 77.
  ZAMBOS, character of the, ii. 47.
  ZANO, J. G., introduction of rabbits into Porto Santo by, i. 112.
  _Zea Mays_, i. 320.
  ZEBU, i. 79;
    domestication of the, i. 82;
    fertile crossing of, with European cattle, i. 83, ii. 110.
  ZEBRA, hybrids of, with the ass and mare, ii. 42.
  _Zephyranthes candida_, ii. 164.
  _Zinnia_, cultivation of, ii. 261.
  ZOLLINGER on Malayan penguin ducks, i. 280.
  ZOOSPORE, division of, in Algæ, ii. 378.
  "ZOPF-TAUBE," i. 154.

THE END.

LONDON: PRINTED BY W. CLOWES AND SONS, DUKE STREET, STAMFORD STREET, AND
CHARING CROSS.

       *       *       *       *       *


NOTES

[1] 'Medical Notes and Reflections,' 3rd edit., 1855, p. 267.

[2] Mr. Buckle, in his grand work on 'Civilisation,' expresses doubts on
the subject owing to the want of statistics. _See_ also Mr. Bowen,
Professor of Moral Philosophy, in 'Proc. American Acad. of Sciences,' vol.
v. p. 102

[3] For greyhounds, _see_ Low's 'Domest. Animals of the British Islands,'
1845, p. 721. For game-fowls, _see_ 'The Poultry Book,' by Mr. Tegetmeier,
1866, p. 123. For pigs, _see_ Mr. Sidney's edit. of 'Youatt on the Pig,'
1860, pp. 11, 22.

[4] 'The Stud Farm,' by Cecil, p. 39.

[5] 'Philosophical Transactions,' 1755, p. 23. I have seen only second-hand
accounts of the two grandsons. Mr. Sedgwick, in a paper to which I shall
hereafter often refer, states that _four_ generations were affected, and in
each the males alone.

[6] Barbara Van Beck, figured, as I am informed by the Rev. W. D. Fox, in
Woodburn's 'Gallery of Rare Portraits,' 1816, vol. ii.

[7] 'Proc. Zoolog. Soc.,' 1833, p. 16

[8] Hofacker, 'Ueber die Eigenschaften,' &c., 1828, s. 34. Report by
Pariset in 'Comptes Rendus,' 1847, p. 592.

[9] Hunter, as quoted in Harlan's 'Med. Researches,' p. 530. Sir A.
Carlisle, 'Phil. Transact.,' 1814, p. 94.

[10] Girou de Buzareignues, 'De la Génération,' p. 282.

[11] 'Macmillan's Magazine,' July and August, 1865.

[12] The works which I have read and found most useful are Dr. Prosper
Lucas's great work, 'Traité de l'Hérédité Naturelle,' 1847. Mr. W.
Sedgwick, in 'British and Foreign Medico-Chirurg. Review,' April and July,
1861, and April and July, 1863: Dr. Garrod on Gout is quoted in these
articles. Sir Henry Holland, 'Medical Notes and Reflections,' 3rd edit.,
1855. Piorry, 'De l'Hérédité dans les Maladies,' 1840. Adams, 'A
Philosophical Treatise on Hereditary Peculiarities,' 2nd edit., 1815. Essay
on 'Hereditary Diseases,' by Dr. J. Steinan, 1843. _See_ Paget, in 'Medical
Times,' 1857, p. 192, on the Inheritance of Cancer; Dr. Gould, in 'Proc. of
American Acad. of Sciences,' Nov. 8, 1853, gives a curious case of
hereditary bleeding in four generations. Harlan, 'Medical Researches,' p.
593.

[13] Marshall, quoted by Youatt in his work on Cattle, p. 284.

[14] 'Philosoph. Transact.,' 1814, p. 94.

[15] 'Medical Notes and Reflections,' 3rd edit., p. 33.

[16] This affection, as I hear from Mr. Bowman, has been ably described and
spoken of as hereditary by Dr. Dondera, of Utrecht, whose work was
published in English by the Sydenham Society in 1864.

[17] Quoted by Mr. Herbert Spencer, 'Principles of Biology,' vol. i. p.
244.

[18] 'British and Foreign Medico-Chirurg. Review, 'April, 1861, p. 482-6;
'l'Héréd. Nat.,' tom. i. pp. 391-408.

[19] Dr. Osborne, Pres. of Royal College of Phys. in Ireland, published
this case in the 'Dublin Medical Journal' for 1835.

[20] These various statements are taken from the following works and
papers:--Youatt on 'The Horse,' pp. 35, 220. Lawrence, 'The Horse,' p. 30.
Karkeek, in an excellent paper in 'Gard. Chronicle,' 1853, p. 92. Mr.
Burke, in 'Journal of R. Agricul. Soc. of England,' vol. v. p. 511.
'Encyclop. of Rural Sports,' p. 279. Girou de Buzareignues, 'Philosoph.
Phys.,' p. 215. _See_ following papers in 'The Veterinary:' Roberts, in
vol. ii. p. 144; M. Marrimpoey, vol. ii. p. 387; Mr. Karkeek, vol. iv. p.
5; Youatt on Goître in Dogs, vol. v. p. 483; Youatt, in vol. vi. pp. 66,
348, 412; M. Bernard, vol. xi. p. 539; Dr. Samesreuther, on Cattle, in vol.
xii. p. 181; Percivall, in vol. xiii. p. 47. With respect to blindness in
horses, _see_ also a whole row of authorities in Dr. P. Lucas's great work,
tom. i. p. 399. Mr. Baker, in 'The Veterinary,' vol. xiii. p. 721, gives a
strong case of hereditary imperfect vision and of jibbing.

[21] Knight on 'The Culture of the Apple and Pear,' p. 31. Lindley's
'Horticulture,' p. 180.

[22] These statements are taken from the following works in order:--Youatt
on 'The Horse,' p. 48; Mr. Darvill, in 'The Veterinary,' vol. viii. p. 50.
With respect to Robson, _see_ 'The Veterinary,' vol. iii. p. 580; Mr.
Lawrence on 'The Horse,' 1829, p. 9; 'The Stud Farm,' by Cecil, 1851; Baron
Cameronn, quoted in 'The Veterinary,' vol x. p. 500.

[23] 'Recreations in Agriculture and Nat. Hist.,' vol. i. p. 68.

[24] 'Ueber die Eigenschaften,' &c., 1828, s. 107.

[25] Bronn's 'Geschichte der Natur,' band ii. s. 132.

[26] Vrolik has discussed this point at full length in a work published in
Dutch, from which Mr. Paget has kindly translated for me passages. _See_,
also, Isidore Geoffroy St. Hilaire's 'Hist. des Anomalies,' 1832, tom. i.
p. 684.

[27] 'Edinburgh New Phil. Journal,' July, 1863.

[28] Some great anatomists, as Cuvier and Meckel, believe that the tubercle
one side of the hinder foot of the tailless Batrachians represents a sixth
digit. Certainly, when the hinder foot of a toad, as soon as it first
sprouts from the tadpole, is dissected, the partially ossified cartilage of
this tubercle resembles under the microscope, in a remarkable manner, a
digit. But the highest authority on such subjects, Gegenbaur (Untersuchung.
zur vergleich. anat. der Wirbelthiere: Carpus et Tarsus, 1864, s. 63),
concludes that this resemblance is not real, only superficial.

[29] For these several statements, _see_ Dr. Struthers, in work cited,
especially on intermissions in the line of descent. Prof. Huxley, 'Lectures
on our Knowledge of Organic Nature,' 1863, p. 97. With respect to
inheritance, _see_ Dr. Prosper Lucas, 'L'Hérédité Nat.,' tom. i. p. 325.
Isid. Geoffroy, 'Anom.,' tom. i. p. 701. Sir A. Carlisle, in 'Phil.
Transact.,' 1814, p. 94. A. Walker, on 'Intermarriage,' 1838, p. 140, gives
a case of five generations; as does Mr. Sedgwick, in 'Brit. and Foreign
Medico-Chirurg. Review,' April, 1863, p. 462. On the inheritance of other
anomalies in the extremities, _see_ Dr. H. Dobell, in vol. xlvi. of
'Medico-Chirurg. Transactions,' 1863; also Mr. Sedgwick, in op. cit.,
April, 1863, p. 460. With respect to additional digits in the negro, _see_
Prichard, 'Physical History of Mankind.' Dr. Dieffenbach ('Journ. Royal
Geograph. Soc.,' 1841, p. 208) says this anomaly is not uncommon with the
Polynesians of the Chatham Islands.

[30] 'The Poultry Chronicle,' 1854, p. 559.

[31] The statements in this paragraph are taken from Isidore Geoffroy St.
Hilaire, 'Hist. des Anomalies,' tom. i. pp. 688-693.

[32] As quoted by Carpenter, 'Princ. of Comp. Physiology,' 1854, p. 480.

[33] Müller's 'Phys.,' Eng. translat., vol. i. 1838, p. 407. A thrush,
however, was exhibited before the British Association at Hull, in 1853,
which had lost its tarsus, and this member, it was asserted, had been
thrice reproduced: I presume it was lost each time by disease.

[34] 'Monthly Journal of Medical Science,' Edinburgh, 1848, new series,
vol. ii. p. 890.

[35] 'An Essay on Animal Reproduction,' trans. by Dr. Maty, 1769, p. 79.

[36] Bonnet, 'Oeuvres d'Hist. Nat.,' tom. v., part i., 4to. edit., 1781,
pp. 343, 350, 353.

[37] So with insects, the larvæ reproduce lost limbs, but, except in one
order, the mature insect has no such power. But the Myriapoda, which
apparently represent the larvæ of true insects, have, as Newport has shown,
this power until their last moult. _See_ an excellent discussion on this
whole subject by Dr. Carpenter in his 'Princ. Comp. Phys.,' 1854, p. 479.

[38] Dr. Günther, in Owen's 'Anatomy of Vertebrates,' vol. i., 1866, p.
567. Spallanzani has made similar observations.

[39] 'On the Anatomy of Vertebrates,' 1866, p. 170: with respect to the
pectoral fins of fishes, pp. 166-168.

[40] 'Medical Notes and Reflections,' 1839, pp. 24, 34. _See_, also, Dr. P.
Lucas, 'l'Héréd. Nat.,' tom. ii. p. 33.

[41] 'Du Danger des Mariages Consanguins,' 2nd edit., 1862, p. 103.

[42] 'British and Foreign Medico-Chirurg. Review,' July, 1863, pp. 183,
189.

[43] Verlot, 'La Production des Variétés,' 1865, p. 32.

[44] Loudon's 'Gard. Mag.,' vol. xii., 1836, p. 368.

[45] Verlot, 'La Product. des Variétés,' 1865, p. 94.

[46] Bronn's 'Geschichte der Natur,' b. ii. s. 121.

[47] Rev. W. A. Leighton, 'Flora of Shropshire,' p. 497; and Charlesworth's
'Mag. of Nat. Hist.,' vol. i, 1837, p. 30.

[48] Verlot, op. cit., p. 93.

[49] For these several statements, _see_ Loudon's 'Gard. Magazine,' vol.
x., 1834, pp. 408, 180; and vol. ix., 1833, p. 597.

[50] These statements are taken from Alph. De Candolle, 'Bot. Géograph.,'
p. 1083.

[51] Verlot, op. cit., p. 38.

[52] Op. cit., p. 59.

[53] Alph. De Candolle, 'Géograph. Bot.,' p. 1082.

[54] _See_ 'Cottage Gardener,' April 10, 1860, p. 18, and Sept. 10, 1861,
p. 456; 'Gard. Chron.,' 1845, p. 102.

[55] Darwin, in 'Journal of Proc. Linn. Soc. Bot.,' 1862, p. 94.

[56] Hofacker, 'Ueber die Eigenschaften,' &c., s. 10.

[57] Bechstein, 'Naturgesch. Deutschlands,' b. iv. s. 462. Mr. Brent, a
great breeder of canaries, informs me that he believes that these
statements are correct.

[58] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 245.

[59] 'British and Foreign Med.-Chirurg. Review,' July, 1861, pp. 200-204.
Mr. Sedgwick has given such full details on this subject, with ample
references, that I need refer to no other authorities.

[60] 'De l'Espèce,' tom. ii., 1859, p. 299.

[61] 'Philosoph. Magazine,' vol. iv., 1799, p. 5.

[62] This last case is quoted by Mr. Sedgwick in 'British and Foreign
Medico-Chirurg. Review,' April, 1861, p. 484. For Blumenbach, _see_
above-cited paper. _See_, also, Dr. P. Lucas, 'Traité de l'Héréd. Nat.,'
tom. ii. p. 492. Also 'Transact. Lin. Soc.,' vol. ix. p. 323. Some curious
cases are given by Mr. Baker in 'The Veterinary,' vol. xiii. p. 723.
Another curious case is given in the 'Annales des Scienc. Nat.,' 1st
series, tom. xi. p. 324.

[63] 'Proc. Royal Soc.,' vol. x. p. 297.

[64] Mr. Sproule, in 'British Medical Journal,' April 18, 1863.

[65] Downing, 'Fruits of America,' p. 5; Sageret, 'Pom. Phys.,' pp. 43, 72.

[66] Youatt on Sheep, pp. 20, 234. The same fact of loose horns
occasionally appearing in hornless breeds has been observed in Germany:
Bechstein, 'Naturgesch. Deutschlands,' b. i. s. 362.

[67] Youatt on Cattle, pp. 155, 174.

[68] Youatt on Sheep, 1838, pp. 17, 145.

[69] I have been informed of this fact through the Rev. W. D. Fox, on the
excellent authority of Mr. Wilmot: _see_, also, remarks on this subject in
an original article in the 'Quarterly Review,' 1849, p. 395.

[70] Youatt, pp. 19, 234.

[71] 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 231.

[72] Loudon's 'Gard. Mag.,' vol. x., 1834, p. 396: a nurseryman, with much
experience on this subject, has likewise assured me that this sometimes
occurs.

[73] 'Gardener's Chron.,' 1855, p. 777.

[74] Ibid., 1862, p. 721.

[75] _See_ some excellent remarks on this subject by Mr. Wallace, 'Journal
Proc. Linn. Soc.,' 1858, vol. iii. p. 60.

[76] Dureau de la Malle, in 'Comptes Rendus,' tom. xli., 1855, p. 807. From
the statements above given, the author concludes that the wild pigs of
Louisiana are not descended from the European _Sus scrofa_.

[77] Capt. W. Allen, in his 'Expedition to the Niger,' states that fowls
have run wild on the island of Annobon, and have become modified in form
and voice. The account is so meagre and vague that it did not appear to me
worth copying; but I now find that Dureau de la Malle ('Comptes Rendus,'
tom. xli., 1855, p. 690) advances this as a good instance of reversion to
the primitive stock, and as confirmatory of a still more vague statement in
classical times by Varro.

[78] 'Flora of Australia,' 1859, Introduct., p. ix.

[79] 'De l'Espèce,' tom. ii. pp. 54, 58, 60.

[80] Mr. Sedgwick gives many instances in the 'British and Foreign
Med.-Chirurg. Review,' April and July, 1863, pp. 448, 188.

[81] In his edit. of 'Youatt on the Pig,' 1860, p. 27.

[82] Dr. P. Lucas, 'Héréd. Nat.,' tom. ii. pp. 314, 892: _see_ a good
practical article on this subject in 'Gard. Chronicle,' 1856, p. 620. I
could add a vast number of references, but they would be superfluous.

[83] Kölreuter gives cases in his 'Dritte Fortsetzung,' 1766, s. 53, 59;
and in his well-known 'Memoirs on Lavatera and Jalapa.' Gärtner,
'Bastarderzeugung,' s. 437, 441, &c. Naudin, in his 'Recherches sur
l'Hybridité, Nouvelles Archives du Muséum,' tom. i. p. 25.

[84] Quoted by Mr. Sedgwick in 'Med.-Chirurg. Review,' April, 1861, p. 485.
Dr. H. Dobell, in 'Med.-Chirurg. Transactions,' vol. xlvi., gives an
analogous case, in which, in a large family, fingers with thickened joints
were transmitted to several members during five generations; but when the
blemish once disappeared it never reappeared.

[85] Verlot, 'Des Variétés,' 1865, p. 63.

[86] 'Nouvelles Archives du Muséum,' tom. i. p. 25. Alex. Braun (in his
'Rejuvenescence,' Ray Soc., 1853, p. 315) apparently holds a similar
opinion.

[87] Mr. Teebay, in 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 72.

[88] Quoted by Hofacker, 'Ueber die Eigenschaften,' &c., s. 98.

[89] 'Essais Hist. Nat. du Paraguay,' tom. ii. 1801, p. 372.

[90] These facts are given on the high authority of Mr. Hewitt, in 'The
Poultry Book,' by Mr. Tegetmeier, 1866, p. 248.

[91] 'The Poultry Book,' by Tegetmeier, 1866, p. 97.

[92] 'Gardener's Chron. and Agricultural Gazette,' 1866, p. 528.

[93] Ibid., 1860, p. 343.

[94] Sclater, in 'Proc. Zoolog. Soc.,' 1862, p. 163.

[95] 'History of the Horse,' p. 212.

[96] 'Mém. présentés par divers Savans à l'Acad. Royale,' tom. vi. 1835, p.
338.

[97] 'Letters from Alabama,' 1859, p. 280.

[98] 'Hist. Nat. des Mammifères,' 1820, tom. i.

[99] 'Philosoph. Transact.,' 1821, p. 20.

[100] Sclater, in 'Proc. Zoolog. Soc.,' 1862, p. 163: this species is the
Ghor-Khur of N.W. India, and has often been called the Hemionus of Pallas.
_See_, also, Mr. Blyth's excellent paper in 'Journ. of Asiatic Soc. of
Bengal,' vol. xxviii., 1860, p. 229.

[101] Another species of wild ass, the true _A. hemionus_ or _Kiang_, which
ordinarily has no shoulder-stripes, is said occasionally to have them; and
these, as with the horse and ass, are sometimes double: _see_ Mr. Blyth, in
the paper just quoted, and in 'Indian Sporting Review,' 1856, p. 320; and
Col. Hamilton Smith, in 'Nat. Library, Horses,' p. 318; and 'Dict. Class.
d'Hist. Nat.,' tom. iii. p. 563.

[102] Figured in the 'Gleanings from the Knowsley Menageries,' by Dr. J. E.
Gray.

[103] Cases of both Spanish and Polish hens sitting are given in the
'Poultry Chronicle,' 1855, vol. iii. p. 477.

[104] 'The Poultry Book,' by Mr. Tegetmeier, 1866, pp. 119, 163. The
author, who remarks on the two negatives ('Journ. of Hort.,' 1862, p. 325),
states that two broods were raised from a Spanish cock and Silver-pencilled
Hamburgh hen, neither of which are incubators, and no less than seven out
of eight hens in these two broods "showed a perfect obstinacy in sitting."
The Rev. E. S. Dixon ('Ornamental Poultry,' 1848, p. 200) says that
chickens reared from a cross between Golden and Black Polish fowls, are
"good and steady birds to sit." Mr. B. P. Brent informs me that he raised
some good sitting hens by crossing Pencilled Hamburgh and Polish breeds. A
cross-bred bird from a Spanish non-incubating cock and Cochin incubating
hen is mentioned in the 'Poultry Chronicle,' vol. iii. p. 13, as an
"exemplary mother." On the other hand, an exceptional case is given in the
'Cottage Gardener,' 1860, p. 388, of a hen raised from a Spanish cock and
black Polish hen which did not incubate.

[105] 'The Poultry Book,' by Tegetmeier, 1866, pp. 165, 167.

[106] 'Natural History Review,' 1863, April, p. 277.

[107] 'Essays on Natural History,' p. 197.

[108] As stated by Mr. Orton, in his 'Physiology of Breeding,' p. 12.

[109] M. E. de Selys-Longchamps refers ('Bulletin Acad. Roy. de Bruxelles,'
tom. xii. No. 10) to more than seven of these hybrids shot in Switzerland
and France. M. Deby asserts ('Zoologist,' vol. v., 1845-46, p. 1254) that
several have been shot in various parts of Belgium and Northern France.
Audubon ('Ornitholog. Biography,' vol. iii. p. 168), speaking of these
hybrids, says that, in North America, they "now and then wander off and
become quite wild."

[110] 'Journal of Researches,' 1845, p. 71.

[111] 'Expedition to the Zambesi,' 1865, pp. 25, 150.

[112] Dr. P. Broca, on 'Hybridity in the Genus Homo,' Eng. translat., 1864,
p. 39.

[113] 'Nouvelles Archives du Muséum,' tom. i. p. 151.

[114] 'Bastarderzeugung,' s. 582, 438, &c.

[115] 'Die Bastardbefruchtung ... der Weiden,' 1865, s. 23. For Gärtner's
remarks on this head, _see_ 'Bastarderzeugung,' s. 474, 582.

[116] Yarrell, 'Phil. Transact.,' 1827, p. 268; Dr. Hamilton, in 'Proc.
Zoolog. Soc.,' 1862, p. 23.

[117] 'Archiv. Skand. Beiträge zur Naturgesch.,' viii. s. 397-413.

[118] In his 'Essays on Nat. Hist.,' 1838. Mr. Hewitt gives analogous cases
with hen-pheasants in 'Journal of Horticulture,' July 12, 1864, p. 37.
Isidore Geoffroy Saint Hilaire, in his 'Essais de Zoolog. Gén.' (suites à
Buffon, 1842, pp. 496-513), has collected such cases in ten different kinds
of birds. It appears that Aristotle was well aware of the change in mental
disposition in old hens. The case of the female deer acquiring horns is
given at p. 513.

[119] 'Cottage Gardener,' 1860, p. 379.

[120] 'Art de faire Eclorre,' &c., 1749, tom. ii. p. 8.

[121] Sir H. Holland, 'Medical Notes and Reflections,' 3rd edit., 1855, p.
31.

[122] Prof. Thomson on Steenstrup's Views on the Obliquity of Flounders:
'Annals and Mag. of Nat. Hist.,' May, 1865, p. 361.

[123] Dr. E. von Martens, in 'Annals and Mag. of Nat. Hist.,' March, 1866,
p. 209.

[124] Darwin, 'Balanidæ,' Ray Soc., 1854, p. 499: _see_ also the appended
remarks on the apparently capricious development of the thoracic limbs on
the right and left sides in the higher crustaceans.

[125] Mormodes ignea: Darwin, 'Fertilization of Orchids,' 1862, p. 251.

[126] 'Journal of Horticulture,' July, 1864, p. 38. I have had the
opportunity of examining these remarkable feathers through the kindness of
Mr. Tegetmeier.

[127] 'The Poultry Book,' by Mr. Tegetmeier, 1866, p. 241.

[128] Carl Vogt, 'Lectures on Man,' Eng. translat., 1864, p. 411.

[129] On Cattle, p. 174.

[130] Isid. Geoffroy St. Hilaire, 'Des Anomalies,' tom. iii. p. 353. With
respect to the mammæ in women, _see_ tom. i. p. 710.

[131] 'Natural Hist. Review,' April, 1863, p. 258. _See_ also his Lecture,
Royal Institution, March 16, 1860. On same subject, _see_ Moquin-Tandon,
'Eléments de Tératologie,' 1841, pp. 184, 352.

[132] Verlot, 'Des Variétés,' 1865, p. 89; Naudin, 'Nouvelles Archives du
Muséum,' tom. i. p. 137.

[133] In his discussion on some curious peloric calceolarias, quoted in
'Journal of Horticulture,' Feb. 24, 1863, p. 152.

[134] For other cases of six divisions in peloric flowers of the Labiatæ
and Scrophulariaceæ, _see_ Moquin-Tandon, 'Tératologie,' p. 192.

[135] Moquin-Tandon, 'Tératologie,' p. 186.

[136] _See_ Youatt on Cattle, pp. 92, 69, 78, 88, 163: also Youatt on
Sheep, p. 325. Also Dr. Lucas, 'L'Héréd. Nat.,' tom. ii. p. 310.

[137] 'Héréd. Nat.,' tom. ii. pp. 112-120.

[138] Sir H. Holland, 'Chapters on Mental Physiology,' 1852, p. 234.

[139] 'Gardener's Chronicle,' 1860, p. 270.

[140] Mr. N. H. Smith, Observations on Breeding, quoted in 'Encyclop. of
Rural Sports,' p. 278.

[141] Quoted by Bronn, 'Geschichte der Natur,' b. ii. s. 170. _See_ Sturm,
'Ueber Racen,' 1825, s. 104-107. For the niata cattle, _see_ my 'Journal of
Researches,' 1845, p. 146.

[142] Lucas, 'l'Hérédité Nat.,' tom. ii. p. 112.

[143] Mr. Orton, 'Physiology of Breeding,' 1855, p. 9.

[144] Boitard and Corbié, 'Les Pigeons,' 1824, p. 224.

[145] 'Les Pigeons, pp. 168, 198.

[146] 'Das Ganze,' &c., 1837, s. 39.

[147] 'The Pigeon Book,' p. 46.

[148] 'Physiology of Breeding,' p.22; Mr. Hewitt, in 'The Poultry Book,' by
Tegetmeier, 1866, p. 224.

[149] Boitard and Corbié, 'Les Pigeons,' 1824, p. 226.

[150] 'Bastarderzeugung,' s. 256, 290, &c. Naudin ('Nouvelles Archives du
Muséum,' tom. i. p. 149) gives a striking instance of prepotency in _Datura
stramonium_ when crossed with two other species.

[151] Flourens, 'Longévité Humaine,' p. 144, on crossed jackals. With
respect to the difference between the mule and the hinny, I am aware that
this has generally been attributed to the sire and dam transmitting their
characters differently; but Colin, who has given in his 'Traité Phys.
Comp.,' tom. ii. pp. 537-539, the fullest description which I have met with
of these reciprocal hybrids, is strongly of opinion that the ass
preponderates in both crosses, but in an unequal degree. This is likewise
the conclusion of Flourens, and of Bechstein in his 'Naturgeschichte
Deutschlands,' b. i. s. 294. The tail of the hinny is much more like that
of the horse than is the tail of the mule, and this is generally accounted
for by the males of both species transmitting with greater power this part
of their structure; but a compound hybrid which I saw in the Zoological
Gardens, from a mare by a hybrid ass-zebra, closely resembled its mother in
its tail.

[152] Mr. Hewitt, who has had such great experience in raising these
hybrids, says ('Poultry Book,' by Mr. Tegetmeier, 1866, pp. 165-167) that
in all, the head was destitute of wattles, comb, and ear-lappets; and all
closely resembled the pheasant in the shape of the tail and general contour
of the body. These hybrids were raised from hens of several breeds by a
cock-pheasant; but another hybrid, described by Mr. Hewitt, was raised from
a hen-pheasant by a silver-laced Bantam cock, and this possessed a
rudimental comb and wattles.

[153] 'L'Héréd. Nat.,' tom. ii. book ii. ch. i.

[154] 'Bastarderzeugung,' s. 264-266. Naudin ('Nouvelles Archives du
Muséum,' tom. i. p. 148) has arrived at a similar conclusion.

[155] 'Cottage Gardener,' 1856, pp. 101, 137.

[156] _See_ some remarks on this head with respect to sheep by Mr. Wilson,
in 'Gardener's Chronicle,' 1863, p. 15.

[157] Verlot, 'Des Variétés,' 1865, p. 66.

[158] Moquin-Tandon, 'Tératologie,' p. 191.

[159] 'Nouvelles Archives du Muséum,' tom. i. p. 137.

[160] 'L'Héréd. Nat.,' tom. ii. pp. 137-165. _See_, also, Mr. Sedgwick's
four memoirs, immediately to be referred to.

[161] On Sexual Limitation in Hereditary Diseases, 'Brit. and For.
Med.-Chirurg. Review,' April, 1861, p. 477; July, p. 198; April, 1863, p.
44; and July, p. 159.

[162] W. Scrope, 'Art of Deer Stalking,' p. 354.

[163] Boitard and Corbié, 'Les Pigeons,' p. 173; Dr. F. Chapuis, 'Le Pigeon
Voyageur Belge,' 1865, p. 87.

[164] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 349.

[165] 'Embassy to the Court of Ava,' vol. i. p. 320. The third generation
is described by Capt. Yule in his 'Narrative of the Mission to the Court of
Ava,' 1855, p. 94.

[166] 'Das Ganze der Taubenzucht,' 1837, s. 21, tab. i., fig. 4; s. 24,
tab. iv., fig. 2.

[167] Kidd's 'Treatise on the Canary,' p. 18.

[168] Charlesworth, 'Mag. of Nat. Hist.,' vol. i., 1837, p. 167.

[169] Dr. Prosper Lucas, 'Héréd. Nat.,' tom. ii. p. 713.

[170] 'L'Héréd. dans les Maladies,' 1840, p. 135. For Hunter, _see_
Harlan's 'Med. Researches,' p. 530.

[171] 'L'Héréd. Nat.,' tom. ii. p. 850.

[172] Sedgwick, 'Brit. and For. Med.-Chirurg. Review,' April 1861, p. 485.
I have seen three accounts, all taken from the same original authority
(which I have not been able to consult), and all differ in the details! but
as they agree in the main facts, I have ventured to quote this case.

[173] Prosper Lucas, 'Héréd. Nat.,' tom. i. p. 400.

[174] Sedgwick, idem, July, 1861, p. 202.

[175] Piorry, p. 109; Prosper Lucas, tom. ii. p. 759.

[176] Prosper Lucas, tom. ii. p. 748.

[177] Prosper Lucas, tom. ii. pp. 678, 700, 702; Sedgwick, idem, April,
1863, p. 449, and July, 1863, p. 162; Dr. J. Steinan, 'Essay on Hereditary
Disease,' 1843, pp. 27, 34.

[178] These cases are given by Mr. Sedgwick, on the authority of Dr. H.
Stewart, in 'Med.-Chirurg. Review,' April, 1863, pp. 449, 477.

[179] 'Héréd. Nat.,' tom. ii. p. 852.

[180] Communications to the Board of Agriculture, vol. i. p. 367.

[181] 'Review of Reports, North of England,' 1808, p. 200.

[182] 'Säugethiere von Paraguay,' 1830, s. 212.

[183] Rengger, 'Säugethiere,' &c., s. 154.

[184] White, 'Regular Gradation in Man,' p. 146.

[185] Dr. W. F. Edwards, in his 'Charactères Physiolog. des Races
Humaines,' p. 23, first called attention to this subject, and ably
discussed it.

[186] Rev. D. Tyerman, and Bennett, 'Journal of Voyages,' 1821-1829, vol.
i. p. 300.

[187] Mr. S. J. Salter, 'Journal Linn. Soc.,' vol. vi., 1862, p. 71.

[188] Sturm, 'Ueber Racen, &c.,' 1825, s. 107. Bronn, 'Geschichte der
Natur.,' b. ii. s. 170, gives a table of the proportions of blood after
successive crosses. Dr. P. Lucas, 'l'Hérédité Nat.,' tom. ii. p. 308.

[189] 'Bastarderzeugung,' s. 463, 470.

[190] 'Nova Acta Petrop.,' 1794, p. 393: _see_ also previous volume.

[191] As quoted in the 'True Principles of Breeding,' by C. H. Macknight
and Dr. H. Madden, 1865, p. 11.

[192] With respect to plants, an admirable essay on this subject (Die
Geschlechter-Vertheilung bei den Pflanzen: 1867) has lately been published
by Dr. Hildebrand, who arrives at the same general conclusions as I have
done.

[193] 'Teoria della Riproduzione Vegetal,' 1816, p. 12.

[194] Verlot, 'Des Variétés,' 1865, p. 72.

[195] Duval-Jouve, 'Bull. Soc. Bot. de France,' tom. x., 1863, p. 194.

[196] Extract of a letter from Sir R. Heron, 1838, given me by Mr. Yarrell.
With respect to mice, _see_ 'Annal. des Sc. Nat.,' tom. i. p. 180; and I
have heard of other similar cases. For turtle-doves, Boitard and Corbié,
'Les Pigeons,' &c., p. 238. For the Game fowl, 'The Poultry Book,' 1866, p.
128. For crosses of tailless fowls, _see_ Bechstein, 'Naturges. Deutsch.'
b. iii. s. 403. Bronn, 'Geschichte der Natur,' b. ii. s. 170, gives
analogous facts with horses. On the hairless condition of crossed South
American dogs, _see_ Rengger, 'Säugethiere von Paraguay,' s. 152: but I saw
in the Zoological Gardens mongrels, from a similar cross, which were
hairless, quite hairy, or hairy in patches, that is, piebald with hair. For
crosses of Dorking and other fowls, _see_ 'Poultry Chronicle,' vol. ii. p.
355. About the crossed pigs, extract of letter from Sir R. Heron to Mr.
Yarrell. For other cases, _see_ P. Lucas, 'Héréd. Nat.,' tom. i. p. 212.

[197] 'Internat. Hort. and Bot. Congress of London,' 1866.

[198] 'Bastarderzeugung,' s. 307. Kölreuter ('Dritte Fortsetszung,' s. 34,
39), however, obtained intermediate tints from similar crosses in the genus
Verbascum. With respect to the turnips, _see_ Herbert's 'Amaryllidaceæ,'
1837, p. 370.

[199] 'Nouvelles Archives du Muséum,' tom. i. p. 100.

[200] Richardson, 'Pigs,' 1847, pp. 37, 42; S. Sidney's edition of 'Youatt
on the Pig,' 1860, p. 3.

[201] _See_ Mr. W. C. Spooner's excellent paper on Cross-Breeding, 'Journal
Royal Agricult. Soc.,' vol. xx., part ii.: _see_ also an equally good
article by Mr. Ch. Howard, in 'Gardener's Chronicle,' 1860, p. 320.

[202] 'Gardener's Chronicle,' 1857, pp. 649, 652.

[203] 'Bulletin de la Soc. d'Acclimat.,' 1862, tom. ix. p. 463. _See_ also,
for other cases, MM. Moll and Gayot, 'Du Boeuf,' 1860, p. xxxii.

[204] 'Poultry Chronicle,' vol. ii., 1854, p. 36.

[205] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 58.

[206] 'Gardener's Chronicle,' 1852, p. 765.

[207] Spooner, in 'Journal Royal Agricult. Soc.,' vol. xx., part ii.

[208] _See_ Colin's 'Traité de Phys. Comp. des Animaux Domestiques,' tom.
ii. p. 536, where this subject is well treated.

[209] 'Les Pigeons,' p. 37.

[210] Vol. i., 1854, p. 101.

[211] 'Cottage Gardener,' 1856, p. 110.

[212] 'Bastarderzeugung,' s. 553.

[213] Dr. Pigeaux, in 'Bull. Soc. d'Acclimat.,' tom. iii., July 1866, as
quoted in 'Annals and Mag. of Nat. Hist.,' 1867, vol. xx. p. 75.

[214] 'Journal de Physiolog.,' tom. ii., 1859, p. 385.

[215] Dec. 1863, p. 484.

[216] On the Varieties of Wheat, p. 66.

[217] Rengger, 'Säugethiere von Paraguay,' s. 336.

[218] _See_ a memoir by MM. Lherbette and De Quatrefages, in 'Bull. Soc.
d'Acclimat.,' tom. viii., July, 1861, p. 312.

[219] For the Norfolk sheep, _see_ Marshall's 'Rural Economy of Norfolk,'
vol. ii. p. 133. _See_ Rev. L. Landt's 'Description of Faroe,' p. 66. For
the ancon sheep, _see_ 'Phil. Transact.,' 1813, p. 90.

[220] White's 'Nat. Hist. of Selbourne,' edited by Bennett, p. 39. With
respect to the origin of the dark-coloured deer, _see_ 'Some Account of
English Deer Parks,' by E. P. Shirley, Esq.

[221] 'The Dovecote,' by the Rev. E. S. Dixon, p. 155; Bechstein,
'Naturgesch. Deutschlands,' Band iv., 1795, s. 17.

[222] 'Cattle,' p. 202.

[223] Mr. J. Wilkinson, in 'Remarks addressed to Sir J. Sebright,' 1820, p.
38.

[224] 'Gardener's Chronicle,' 1858, p. 771.

[225] 'Bastarderzeugung,' s. 87, 169. _See_ also the Table at the end of
volume.

[226] 'Bastarderzeugung,' s. 87, 577.

[227] 'Kenntniss der Befruchtung,' s. 137; 'Bastarderzeugung,' s. 92, 181.
On raising the two varieties from seed _see_ s. 307.

[228] 'Bastarderzeugung,' s. 216.

[229] The following facts, given by Kölreuter in his 'Dritte Fortsetzung,'
s. 34, 39, appear at first sight strongly to confirm Mr. Scott's and
Gärtner's statements; and to a certain limited extent they do so. Kölreuter
asserts, from innumerable observations, that insects incessantly carry
pollen from one species and variety of Verbascum to another; and I can
confirm this assertion; yet he found that the white and yellow varieties of
_Verbascum lychnitis_ often grew wild mingled together: moreover, he
cultivated these two varieties in considerable numbers during four years in
his garden, and they kept true by seed; but when he crossed them, they
produced flowers of an intermediate tint. Hence it might have thought that
both varieties must have a stronger elective affinity for the pollen of
their own variety than for that of the other; this elective affinity, I may
add, of each species for its own pollen (Kölreuter, 'Dritte Forts.,' s. 39,
and Gärtner, 'Bastarderz.,' _passim_) being a perfectly well-ascertained
power. But the force of the foregoing facts is much lessened by Gärtner's
numerous experiments, for, differently from Kölreuter, he never once got
('Bastarderz.,' s. 307) an intermediate tint when he crossed the yellow and
white flowered varieties of Verbascum. So that the fact of the white and
yellow varieties keeping true to their colour by seed does not prove that
they were not mutually fertilised by the pollen carried by insects from one
to the other.

[230] 'Amaryllidaceæ,' 1837, p. 366. Gärtner has made a similar
observation.

[231] Kölreuter first observed this fact. 'Mém. de l'Acad. St. Petersburg,'
vol. iii. p. 197. _See_ also C. K. Sprengel, 'Das Entdeckte Geheimniss,' s.
345.

[232] Namely, Barbarines, Pastissons, Giraumous: 'Annal. des Sc. Nat.,'
tom. xxx., 1833, pp. 398 and 405.

[233] 'Mémoire sur les Cucurbitaceæ,' 1826, pp. 46, 55.

[234] 'Annales des Se. Nat.,' 4th series, tom. vi. M. Naudin considers
these forms as undoubtedly varieties of _Cucurbita pepo_.

[235] 'Mém. Cucurb.,' p. 8.

[236] 'Zweite Forts.,' s. 53, namely, Nicotiana major vulgaris; (2)
perennis; (3) Transylvanica; (4) a sub-var. of the last; (5) major latifol.
fl. alb.

[237] Kölreuter was so much struck with this fact that he suspected that a
little pollen of _N. glutinosa_ in one of his experiments might have
accidentally got mingled with that of _var. perennis_, and thus aided its
fertilising power. But we now know conclusively from Gärtner
('Bastarderz.,' s. 34, 431) that two kinds of pollen never act _conjointly_
on a third species; still less will the pollen of a distinct species,
mingled with a plant's own pollen, if the latter be present in sufficient
quantity, have any effect. The sole effect of mingling two kinds of pollen
is to produce in the same capsule seeds which yield plants, some taking
after the one and some after the other parent.

[238] Mr. Scott has made some observations on the absolute sterility of a
purple and white primrose (_Primula vulgaris_) when fertilised by pollen
from the primrose ('Journal of Proc. of Linn. Soc.,' vol. viii., 1864, p.
98); but these observations require confirmation. I raised a number of
purple-flowered long-styled seedlings from seed kindly sent me by Mr.
Scott, and, though they were all some degree sterile, they were much more
fertile with pollen taken from the common primrose than with their own
pollen. Mr. Scott has likewise described a red equal-styled cowslip (_P.
veris_, idem, p. 106), which was found by him to be highly sterile when
crossed with the common cowslip; but this was not the case with several
equal-styled red seedlings raised by me from his plant. This variety of the
cowslip presents the remarkable peculiarity of combining male organs in
every respect like those of the short-styled form, with female organs
resembling in function and partly in structure those of the long-styled
form; so that we have the singular anomaly of the two forms combined in the
same flower. Hence it is not surprising that these flowers should be
spontaneously self-infertile in a high degree.

[239] 'Act. Acad. St. Petersburg,' 1780, part ii., pp. 84, 100.

[240] 'Annales des Sc. Nat.,' tom. xxi. (1st series), p. 61.

[241] 'Bull. Bot. Soc. de France,' Dec. 27th, 1861, tom. viii. p. 612.

[242] Quoted by Isid. Geoffroy St. Hilaire, 'Hist. Naturelle Générale,'
tom. iii. p. 476. Since this MS. has been sent to press a full discussion
on the present subject has appeared in Mr. Herbert Spencer's 'Principles of
Biology,' vol. ii. 1867, p. 457 _et seq._

[243] For cats and dogs, &c., _see_ Bellingeri, in 'Annal. des Sc. Nat.,'
2nd series, Zoolog., tom. xii. p. 155. For ferrets, Bechstein,
'Naturgeschichte Deutschlands,' Band i., 1801, s. 786, 795. For rabbits,
ditto, s. 1123, 1131; and Bronn's 'Geschichte der Natur,' B. ii. s. 99. For
mountain sheep, ditto, s. 102. For the fertility of the wild sow, _see_
Bechstein's 'Naturgesch. Deutschlands,' B. i., 1801, s. 534; for the
domestic pig, Sidney's edit. of Youatt on the Pig, 1860, p. 62. With
respect to Lapland, _see_ Acerbi's 'Travels to the North Cape,' Eng.
translat., vol. ii. p. 222. About the Highland cows, _see_ Hogg on Sheep,
p. 263.

[244] For the eggs of _Gallus bankiva_, _see_ Blyth, in 'Annals and Mag. of
Nat. Hist., 2nd series, vol. i., 1848, p. 456. For wild and tame ducks,
Macgillivray, 'British Birds,' vol. v. p. 37; and 'Die Enten,' s. 87. For
wild geese, L. Lloyd, 'Scandinavian Adventures,' vol. ii. 1854, p. 413; and
for tame geese, 'Ornamental Poultry,' by Rev. E. S. Dixon, p. 139. On the
breeding of pigeons, Pistor, 'Das Ganze der Taubenzucht,' 1831, s. 46; and
Boitard and Corbié, 'Les Pigeons,' p. 158. With respect to peacocks,
according to Temminck ('Hist. Nat. Gén. des Pigeons,' &c., 1813, tom. ii.
p. 41), the hen lays in India even as many as twenty eggs; but according to
Jerdon and another writer (quoted in Tegetmeier's 'Poultry Book,' 1866, pp.
280, 282), she there lays only from four to nine or ten eggs: in England
she is said, in the 'Poultry Book,' to lay five or six, but another writer
says from eight to twelve eggs.

[245] 'The Art of Improving the Breed, &c.,' 1809, p. 16.

[246] For Andrew Knight, _see_ A. Walker, on 'Intermarriage,' 1838, p. 227.
Sir J. Sebright's Treatise has just been quoted.

[247] 'Cattle,' p. 199.

[248] Nathusius, 'Ueber Shorthorn Rindvieh,' 1857, s. 71: _see_ also
'Gardener's Chronicle,' 1860, p. 270. Many analogous cases are given in a
pamphlet recently published by Mr. C. Macknight and Dr. H. Madden, 'On the
True Principles of Breeding;' Melbourne, Australia, 1865.

[249] Mr. Willoughby Wood, in 'Gardener's Chronicle,' 1855, p. 411; and
1860, p. 270. _See_ the very clear tables and pedigrees given in Nathusius'
'Rindvieh,' s. 72-77.

[250] Mr. Wright, 'Journal of Royal Agricult. Soc.,' vol. vii., 1846, p.
204.

[251] Youatt on Cattle, p. 202.

[252] Report British Assoc., Zoolog. Sect., 1838.

[253] Azara, 'Quadrupèdes du Paraguay,' tom. ii. pp. 354, 368.

[254] For the case of the Messrs. Brown, _see_ 'Gard. Chronicle,' 1855, p.
26. For the Foscote flock, 'Gard. Chron.,' 1860, p. 416. For the Naz flock,
'Bull. de la Soc. d'Acclimat.,' 1860, p. 477.

[255] Nathusius, 'Rindvieh,' s. 65; Youatt on Sheep, p. 495.

[256] 'Gard. Chronicle,' 1861, p. 631.

[257] Lord Somerville, 'Facts on Sheep and Husbandry,' p. 6. Mr. Spooner,
in 'Journal of Royal Agricult. Soc. of England,' vol. xx., part ii. _See_
also an excellent paper on the same subject in 'Gard. Chronicle,' 1860, p.
321, by Mr. Charles Howard.

[258] 'Some Account of English Deer Parks,' by Evelyn P. Shirley, 1867.

[259] 'The Art of Improving the Breed,' &c., p. 13. With respect to Scotch
deer-hounds, _see_ Scrope's 'Art of Deer Stalking,' pp. 350-353.

[260] 'Cottage Gardener,' 1861, p. 327.

[261] Sidney's edit. of Youatt on the Pig, 1860, p. 30; p. 33, quotation
from Mr. Druce; p. 29, on Lord Western's case.

[262] 'Journal, Royal Agricult. Soc. of England,' 1846, vol. vii. p. 205.

[263] 'Ueber Rindvieh,' &c., s. 78.

[264] Sidney on the Pig, p. 36. _See_ also note, p. 34. Also Richardson on
the Pig, 1847, p. 26.

[265] Dr. Dally has published an excellent article (translated in the
'Anthropolog. Review,' May, 1864, p. 65), criticising all writers who have
maintained that evil follows from consanguineous marriages. No doubt on
this side of the question many advocates have injured their cause by
inaccuracies: thus it has been stated (Devay, 'Du Danger des Mariages,'
&c., 1862, p. 141) that the marriages of cousins have been prohibited by
the legislature of Ohio; but I have been assured, in answer to inquiries
made in the United States, that this statement is a mere fable.

[266] _See_ his most interesting work on the 'Early History of Man,' 1865,
chap. x.

[267] On Consanguinity in Marriage, in the 'Fortnightly Review,' 1865, p.
710; Hofacker, 'Ueber die Eigenschaften,' &c.

[268] Sir G. Grey's 'Journal of Expeditions into Australia,' vol. ii. p.
243; and Dobrizhoffer, 'On the Abipones of South America.'

[269] 'The Art of Improving the Breed,' p. 13.

[270] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 245.

[271] 'Journal Royal Agricult. Soc.' 1846, vol. vii. p. 205; _see_ also
Ferguson on the Fowl, pp. 83, 317; _see_ also 'The Poultry Book,' by
Tegetmeier, 1866, p. 135, with respect to the extent to which cock-fighters
found that they could venture to breed in-and-in, viz., occasionally a hen
with her own son; "but they were cautious not to repeat the in-and-in
breeding."

[272] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 79.

[273] 'The Poultry Chronicle,' 1854, vol. i. p. 43.

[274] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 79.

[275] 'The Poultry Chronicle,' vol. i. p. 89.

[276] 'The Poultry Book,' 1866, p. 210.

[277] Ibid, 1866, p. 167; and 'Poultry Chronicle,' vol. iii., 1855, p. 15.

[278] 'A Treatise on Fancy Pigeons,' by J. M. Eaton, p. 56.

[279] 'The Pigeon Book,' p. 46.

[280] 'Das Ganze der Taubenzucht,' 1837, s. 18.

[281] 'Les Pigeons,' 1824, p. 35.

[282] 'Proc. Entomolog. Soc.,' Aug. 6th, 1860, p. 126.

[283] 'Journal of Horticulture,' 1861, pp. 39, 77, 158; and 1864, p. 206.

[284] 'Beiträge zur Kenntniss der Befruchtung,' 1844, s. 366.

[285] 'Amaryllidaceæ,' p. 371.

[286] 'De la Fécondation,' 2nd edit., 1862, p. 79.

[287] 'Mémoire sur les Cucurbitacées,' pp. 36, 28, 30.

[288] Loudon's 'Gard. Mag.,' vol. viii., 1832, p. 52.

[289] 'Transact. Hort. Soc.,' vol. i. p. 25.

[290] 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. vi. p. 189.

[291] 'Philosophical Transactions,' 1799, p. 200.

[292] 'Ueber die Bastarderzeugung,' 1828, s. 32, 33. For Mr. Chaundy's
case, _see_ Loudon's 'Gard. Mag.,' vol. vii., 1831, p. 696.

[293] 'Gardener's Chron.,' 1846, p. 601.

[294] 'Philosoph. Transact.,' 1799, p. 201.

[295] Quoted in 'Bull. Bot. Soc. France,' vol. ii., 1855, p. 327.

[296] Gärtner, 'Bastarderzeugung,' s. 259, 518, 526 _et seq._

[297] 'Fortsetzung,' 1763, s. 29; 'Dritte Fortsetzung,' s. 44, 96; 'Act.
Acad. St. Petersburg,' 1782, part ii., p. 251; 'Nova Acta,' 1793, pp. 391,
394; 'Nova Acta,' 1795, pp. 316, 323.

[298] 'Die Bastardbefruchtung,' &c., 1865, s. 31, 41, 42.

[299] Max Wichura fully accepts this view ('Bastardbefruchtung,' s. 43), as
does the Rev. M. J. Berkeley, in 'Journal of Hort. Soc.,' Jan. 1866, p. 70.

[300] 'Bastarderzeugung,' s. 394, 526, 528.

[301] Kölreuter,' Nova Acta,' 1795, p. 316.

[302] Gärtner, 'Bastarderzeugung,' s. 430.

[303] 'Botanische Zeitung,' Jan. 1864, s. 3.

[304] 'Monatsbericht Akad. Wissen,' Berlin, 1866, s. 372.

[305] International Hort. Congress, London, 1866.

[306] 'Proc. Bot. Soc. of Edinburgh,' May, 1863: these observations are
given in abstract, and others are added, in the 'Journal of Proc. of Linn.
Soc.,' vol. viii. Bot., 1864, p. 162.

[307] Prof. Lecoq, 'De la Fécondation,' 2nd edit., 1862, p. 76.

[308] 'Bastarderzeugung,' s. 64, 357.

[309] Idem, s. 357.

[310] 'Zweite Fortsetzung,' s. 10; 'Dritte Fort.,' s. 40.

[311] Duvernoy, quoted by Gärtner, 'Bastarderzeugung,' s. 334.

[312] 'Gardner's Chronicle,' 1846, p. 183.

[313] 'Transact. Hort. Soc.,' vol. vii., 1830, p. 95.

[314] Prof. Lecoq, 'De la Fécondation,' 1845, p. 70; Gärtner,
'Bastarderzeugung,' s. 64.

[315] 'Gardener's Chron.' 1866, p. 1068.

[316] 'Journal of Proc. of Linn. Soc.,' vol. viii., 1864, p. 168.

[317] 'Amaryllidaceæ,' 1837, p. 371; 'Journal of Hort. Soc.,' vol. ii.,
1847, p. 19.

[318] Loudon's 'Gardener's Magazine,' vol. xi., 1835, p. 260.

[319] 'Gardener's Chronicle,' 1850, p. 470.

[320] 'Journal Hort. Soc., vol. v. p. 135. The seedlings thus raised were
given to the Hort. Soc.; but I find, on inquiry, that they unfortunately
died the following winter.

[321] Mr. D. Beaton, in 'Journal of Hort.,' 1861, p. 453. Lecoq, however
('De la Fécond.,' 1862, p. 369), states that this hybrid is descended from
_G. psittacinus_ and _cardinalis_; but this is opposed to Herbert's
experience, who found that the former species could not be crossed.

[322] This is the conclusion of Prof. Devay, 'Du Danger des Mariages
Consang.,' 1862, p. 97. Virchow quotes, in the 'Deutsche Jahrbücher,' 1863,
s. 354, some curious evidence on half the cases of a peculiar form of
blindness occurring in the offspring from near relations.

[323] For England, _see_ below. For Germany, _see_ Metzger,
'Getreidearten,' 1841, s. 63. For France, Loiseleur-Deslongchamps ('Consid.
sur les Céreales,' 1843, p. 200) gives numerous references on this subject.
For Southern France, _see_ Godron, 'Florula Juvenalis,' 1854, p. 28.

[324] 'A general Treatise of Husbandry,' vol. iii. p. 58.

[325] 'Gardener's Chronicle and Agricult. Gazette,' 1858, p. 247; and for
the second statement, idem, 1850, p. 702. On this same subject, _see_ also
Rev. D. Walker's 'Prize Essay of Highland Agricult. Soc.,' vol. ii. p. 200.
Also Marshall's 'Minutes of Agriculture,' November, 1775.

[326] Oberlin's 'Memoirs,' Eng. translat., p. 73. For Lancashire, _see_
Marshall's 'Review of Reports,' 1808, p. 295.

[327] 'Cottage Gardener,' 1856, p. 186. For Mr. Robson's subsequent
statements, _see_ 'Journal of Horticulture,' Feb. 18, 1866, p. 121. For Mr.
Abbey's remarks on grafting, &c., idem, July 18, 1865, p. 44.

[328] 'Mém. de l'Acad. des Sciences,' 1790, p. 209.

[329] 'On the Varieties of Wheat,' p. 52.

[330] Mr. Spencer has fully and ably discussed this whole subject in his
'Principles of Biology,' 1864, vol. ii. ch. x. In the first edition of my
'Origin of Species,' 1859, p. 267, I spoke of the good effects from slight
changes in the conditions of life and from cross-breeding, and of the evil
effects from great changes in the conditions and from crossing widely
distinct forms, as a series of facts "connected together by some common but
unknown bond, which is essentially related to the principle of life."

[331] 'Essais de Zoologie Générale,' 1841, p. 256.

[332] Du Rut, 'Annales du Muséum,' 1807, tom. ix. p. 120.

[333] 'Säugethiere von Paraguay,' 1830, s. 49, 106, 118, 124, 201, 208,
249, 265, 327.

[334] 'The Naturalist on the Amazons,' 1863, vol. i. pp. 99, 193; vol. ii.
p. 113.

[335] 'Embassy to the Court of Ava,' vol. i. p. 534.

[336] 'Journal,' vol. i. p. 213.

[337] 'Säugethiere,' s. 327.

[338] On the Breeding of the larger Felidæ, 'Proc. Zoolog. Soc.,' 1861, p.
140.

[339] Sleeman's 'Rambles in India,' vol. ii. p. 10.

[340] Wiegmann's 'Archif für Naturgesch.,' 1837, s. 162.

[341] Rengger, 'Säugethiere,' &c., s. 276. On the parentage of the
guinea-pig, _see_ also Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gén.'

[342] Although the existence of the _Leporides_, as described by Dr. Broca
('Journal de Phys.,' tom. ii. p. 370), is now positively denied, yet Dr.
Pigeaux ('Annals and Mag. of Nat. Hist.,' vol. xx., 1867, p. 75) affirms
that the hare and rabbit have produced hybrids.

[343] 'Quadrupeds of North America,' by Audubon and Bachman, 1846, p. 268.

[344] Loudon's 'Mag. of Nat. Hist.,' vol. ix., 1836, p. 571; Audubon and
Bachman's 'Quadrupeds of North America,' p. 221.

[345] Flourens, 'De l'Instinct,' &c., 1845, p. 88.

[346] _See_ 'Annual Reports Zoolog. Soc.,' 1855, 1858, 1863, 1864; 'Times'
newspaper, Aug. 10th, 1847; Flourens, 'De l'Instinct,' p. 85.

[347] 'Säugethiere,' &c., s. 34, 49.

[348] Art. Brazil, 'Penny Cyclop.,' p. 363.

[349] 'The Naturalist on the River Amazon,' vol. i. p. 99.

[350] 'Encyclop. of Rural Sports,' p. 691.

[351] According to Sir A. Burnes ('Cabool,' &c., p. 51), eight species are
used for hawking in Scinde.

[352] Loudon's 'Mag. of Nat. Hist.,' vol. vi., 1833, p. 110.

[353] F. Cuvier, 'Annal. du Muséum,' tom. ix. p. 128.

[354] 'The Zoologist,' vol. vii.-viii., 1849-50, p. 2648.

[355] Knox, 'Ornithological Rambles in Sussex,' p. 91.

[356] 'The Zoologist,' vol. vii.-viii., 1849-50, p. 2566; vol. ix.-x.,
1851-2, p. 3207.

[357] Bechstein, 'Naturgesch. der Stubenvögel,' 1840, s. 20.

[358] 'Ornithological Biography,' vol. v. p. 517.

[359] A case is recorded in 'The Zoologist,' vol. i.-ii., 1843-45, p. 453.
For the siskin breeding, vol. iii.-iv., 1845-46, p. 1075. Bechstein,
'Stubenvögel,' s. 139, speaks of bullfinches making nests, but rarely
producing young.

[360] Yarrell's 'Hist. British Birds,' 1839, vol. i. p. 412.

[361] Loudon's 'Mag. of Nat. History,' vol. ix., 1836, p. 347.

[362] 'Mémoires du Muséum d'Hist. Nat.,' tom. x. p. 314: five cases of
parrots breeding in France are here recorded. _See_, also, 'Report Brit.
Assoc. Zoolog.,' 1843.

[363] 'Stubenvögel,' s. 105, 83.

[364] Dr. Hancock remarks ('Charlesworth's Mag. of Nat. Hist.,' vol. ii.,
1838, p. 492), "it is singular that, amongst the numerous useful birds that
are indigenous to Guiana, none are found to propagate among the Indians;
yet the common fowl is reared in abundance throughout the country."

[365] 'A Week at Port Royal,' 1855, p. 7.

[366] Audubon, 'American Ornithology,' vol. v. pp. 552, 557.

[367] Moubray on Poultry, 7th edit., p. 133.

[368] Temminck, 'Hist. Nat. Gén. des Pigeons,' &c., 1813, tom. iii. pp.
288, 382; 'Annals and Mag. of Nat. Hist.,' vol. xii., 1843, p. 453. Other
species of partridge have occasionally bred; as the red-legged (_P.
rubra_), when kept in a large court in France (_see_ 'Journal de Physique,'
tom. xxv. p. 294), and in the Zoological Gardens in 1856.

[369] Rev. E. S. Dixon, 'The Dovecote,' 1851, pp. 243-252.

[370] Temminck, 'Hist. Nat. Gén. des Pigeons,' &c., tom. ii. pp. 456, 458;
tom. iii. pp. 2, 13, 47.

[371] Bates, 'The Naturalist on the Amazons,' vol. i. p. 193; vol. ii. p.
112.

[372] Temminck, 'Hist. Nat. Gén.,' &c., tom. iii. p. 125. For _Tetrao
urogallus_, _see_ L. Lloyd, 'Field Sports of North of Europe,' vol. i. pp.
287, 314; and 'Bull. de la Soc. d'Acclimat.,' tom. vii., 1860, p. 600. For
_T. Scoticus_, Thompson, 'Nat. Hist. of Ireland,' vol. ii., 1850, p. 49.
For _T. cupido_, 'Boston Journal of Nat. Hist.,' vol. iii. p. 199.

[373] Marcel de Serres, 'Annales des Sci. Nat.,' 2nd series, Zoolog., tom.
xiii. p. 175.

[374] Dr. Hancock, in 'Charlesworth's Mag. of Nat. Hist.' vol. ii., 1838,
p. 491; R. Hill, 'A Week at Port Royal,' p. 8; 'Guide to the Zoological
Gardens,' by P. L. Sclater, 1859, pp. 11, 12; 'The Knowsley Menagerie,' by
Dr. Gray, 1846, pl. xiv.; E. Blyth, 'Report Asiatic Soc. of Bengal,' May,
1855.

[375] Prof. Newton, in 'Proc. Zoolog. Soc.,' 1860, p. 336.

[376] 'The Dovecote and Aviary,' p. 428.

[377] 'Ornithological Biography,' vol. iii. p. 9.

[378] 'Geograph. Journal,' vol. xiii., 1844, p. 32.

[379] Loudon's 'Mag. of Nat. Hist.,' vol. v., 1832, p. 153.

[380] 'Zoologist,' vols. v.-vi., 1847-48, p. 1660.

[381] 'Transact. Entomolog. Soc.,' vol.  iv., 1845, p. 60.

[382] 'Transact. Linn. Soc.,' vol. vii. p. 40.

[383] _See_ an interesting paper by Mr. Newman, in the 'Zoologist,' 1857,
p. 5764; and Dr. Wallace, in 'Proc. Entomolog. Soc.,' June 4th, 1860, p.
119.

[384] Yarrell's 'British Birds,' vol. i. p. 506; Bechstein, 'Stubenvögel,'
s. 185; 'Philosoph. Transact.,' 1772, p. 271. Bronn ('Geschichte der
Natur,' Band ii. s. 96) has collected a number of cases. For the case of
the deer, _see_ 'Penny Cyclop.,' vol. viii. p. 350.

[385] 'Journal de Physiologie,' tom. ii. p. 347.

[386] For additional evidence on this subject, _see_ F. Cuvier, in 'Annales
du Muséum,' tom. xii. p. 119.

[387] Numerous instances could be given. Thus Livingstone ('Travels,' p.
217) states that the King of the Barotse, an inland tribe which never had
any communication with white men, was extremely fond of taming animals, and
every young antelope was brought to him. Mr. Galton informs me that the
Damaras are likewise fond of keeping pets. The Indians of South America
follow the same habit. Capt. Wilkes states that the Polynesians of the
Samoan Islands tamed pigeons; and the New Zealanders, as Mr. Mantell
informs me, kept various kinds of birds.

[388] For analogous cases with the fowl, _see_ Réaumur, 'Art de faire
Eclorre,' &c., 1749, p. 243; and Col. Sykes, in 'Proc. Zoolog. Soc.,' 1832,
&c. With respect to the fowl not breeding in northern regions, _see_
Latham's 'Hist. of Birds,' vol. viii., 1823, p. 169.

[389] 'Mém. par divers Savans, Acad. des Sciences,' tom. vi., 1835, p. 347.

[390] Youatt on Sheep, p. 181.

[391] J. Mills, 'Treatise on Cattle,' 1776, p. 72.

[392] Bechstein, 'Stubenvögel,' s. 242.

[393] Crawfurd's 'Descriptive Dict. of the Indian Islands,' 1856, p. 145.

[394] 'Bull. de la Soc. Acclimat., tom. ix., 1862, pp. 380, 384.

[395] For pigeons, _see_ Dr. Chapuis, 'Le Pigeon Voyageur Belge,' 1865, p.
66.

[396] 'Swedish Acts,' vol. i., 1739, p. 3. Pallas makes the same remark in
his Travels (Eng. translat.), vol. i. p. 292.

[397] A. Kerner, 'Die Cultur der Alpenflanzen,' 1864, s. 139; Watson's
'Cybele Britannica,' vol. i. p. 131; Mr. D. Cameron, also, has written on
the culture of Alpine plants in 'Gard. Chronicle,' 1848, pp. 253, 268, and
mentions a few which seed.

[398] 'Beiträge zur Kenntniss der Befruchtung,' 1844, s. 333.

[399] 'Nova Acta Petrop.,' 1793, p. 391.

[400] 'Cottage Gardener,' 1856, pp. 44, 109.

[401] Dr. Herbert, 'Amaryllidaceæ,' p. 176.

[402] Gärtner, 'Beiträge zur Kenntniss,' &c., s. 560, 564.

[403] 'Gardener's Chronicle,' 1844, p. 215; 1850, p. 470.

[404] 'Beiträge zur Kenntniss,' &c., s. 252, 333.

[405] 'Journal of Hort. Soc.,' vol. ii. 1847, p. 83.

[406] 'Beiträge zur Kenntniss,' &c., s. 117 _et seq._; Kölreuter, 'Zweite
Fortsetzung,' s. 10, 121; 'Dritte Fortsetzung,' s. 57. Herbert,
'Amaryllidaceæ,' p. 355. Wiegmann, 'Ueber die Bastarderzeugung,' s. 27.

[407] 'Bastarderzeugung,' s. 356.

[408] 'Teoria della Riproduzione,' 1816, p. 84; 'Traité du Citrus,' 1811,
p. 67.

[409] Mr. C. W. Crocker, in 'Gard. Chronicle,' 1861, p. 1092.

[410] Verlot, 'Des Variétés,' 1865, p. 80.

[411] Verlot, idem, p. 88.

[412] Prof. Allman, Brit. Assoc., quoted in the 'Phytologist,' vol. ii. p.
483. Prof. Harvey, on the authority of Mr. Andrews, who discovered the
plant, informed me that this monstrosity could be propagated by seed. With
respect to the poppy, _see_ Prof. Goeppert, as quoted in 'Journal of
Horticulture,' July 1st, 1863, p. 171.

[413] 'Comptes Rendus,' Dec. 19th, 1864, p. 1039.

[414] 'Gardener's Chronicle,' 1866, p. 681.

[415] 'Theory of Horticulture,' p. 333.

[416] Mr. Fairweather, in 'Transact. Hort. Soc.,' vol. iii. p. 406; Bosse,
quoted by Bronn, 'Geschichte der Natur,' B. ii. s. 77. On the effects of
the removal of the anthers, _see_ Mr. Leitner, in Silliman's 'North
American Journ. of Science,' vol. xxiii. p. 47; and Verlot, 'Des Variétés,'
1865, p. 84.

[417] Lindley's 'Theory of Horticulture,' p. 333.

[418] 'Gardener's Chronicle,' 1865, p. 626; 1866, pp. 290, 730; and Verlot,
'Des Variétés,' p. 75.

[419] 'Gardener's Chronicle,' 1843, p. 628. In this article I suggested the
following theory on the doubleness of flowers.

[420] Quoted by Gärtner, 'Bastarderzeugung,' s. 567.

[421] 'Gardener's Chronicle,' 1866, p. 901.

[422] Lindley, 'Theory of Horticulture,' p. 175-179; Godron, 'De l'Espèce,'
tom. i. p. 106: Pickering, 'Races of Man;' Gallesio, 'Teoria della
Riproduzione,' 1816, p. 101-110. Meyen ('Reise um Erde,' Th. ii. s. 214)
states that at Manilla one variety of the banana is full of seeds; and
Chamisso (Hooker's 'Bot. Misc.,' vol. i. p. 310) describes a variety of the
bread-fruit in the Mariana Islands with small fruit, containing seeds which
are frequently perfect. Burnes, in his 'Travels in Bokhara,' remarks on the
pomegranate seeding in Mazenderan, as a remarkable peculiarity.

[423] Ingledew, in 'Transact. of Agricult. and Hort. Soc. of India,' vol.
ii.

[424] 'De la Fécondation,' 1862, p. 308.

[425] Hooker's 'Bot. Misc.,' vol. i. p. 99; Gallesio, 'Teoria della
Riproduzione,' p. 110.

[426] 'Transact. Linn. Soc.,' vol. xvii. p. 563.

[427] Godron, 'De l'Espèce,' tom. ii. p. 106; Herbert on Crocus, in
'Journal of Hort. Soc.,' vol. i., 1846, p. 254.--Dr. Wight, from what he
has seen in India, believes in this view; 'Madras Journal of Lit. and
Science,' vol. iv., 1836, p. 61.

[428] Wahlenberg specifies eight species in this state on the Lapland Alps:
_see_ Appendix to Linnæus' 'Tour in Lapland,' translated by Sir J. E.
Smith, vol. ii. pp. 274-280.

[429] 'Travels in North America,' Eng. translat., vol. iii. p. 175.

[430] With respect to the ivy and Acorus, _see_ Dr. Bromfield in the
'Phytologist,' vol. iii. p. 376. _See_ also Lindley and Vaucher on the
Acorus.

[431] 'Annal. des Sc. Nat.,' 3rd series, Zool., tom. iv. p. 280. Prof.
Decaisne refers also to analogous cases with mosses and lichens near Paris.

[432] Mr. Tuckerman, in Silliman's 'American Journal of Science,' vol. xlv.
p. 41.

[433] Sir J. E. Smith, 'English Flora,' vol. i. p. 339.

[434] G. Planchon, 'Flora de Montpellier,' 1864, p. 20.

[435] On the non-production of seeds in England _see_ Mr. Crocker, in
'Gardener's Weekly Magazine,' 1852, p. 70; Vaucher, 'Hist. Phys. Plantes
d'Europe,' tom. i. p. 33; Lecoq, 'Géograph. Bot. de l'Europe,' tom. iv. p.
466; Dr. D. Clos, in 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. xvii.,
1852, p. 129: this latter author refers to other analogous cases. On the
non-production of pollen by this Ranunculus _see_ Chatin, in 'Comptes
Rendus,' June 11th, 1866.

[436] 'Bastarderzeugung,' s. 565. Kölreuter ('Dritte Fortsetzung,' s. 73,
87, 119) also shows that when two species, one single and the other double,
are crossed, the hybrids are apt to be extremely double.

[437] 'Teoria della Riproduzione Veg.,' 1816, p. 73.

[438] 'Bastarderzeugung,' s. 573.

[439] Ibid., s. 527.

[440] 'Transactions Phil. Soc.,' 1799, p. 202. For Kölreuter, _see_ 'Mém.
de l'Acad. de St. Pétersbourg,' tom. iii., 1809 (published 1811), p. 197.
In reading C. K. Sprengel's remarkable work, 'Das entdeckte Geheimniss,'
&c., 1793, it is curious to observe how often this wonderfully acute
observer failed to understand the full meaning of the structure of the
flowers which he has so well described, from not always having before his
mind the key to the problem, namely, the good derived from the crossing of
distinct individual plants.

[441] This abstract was published in the fourth edition (1866) of my
'Origin of Species;' but as this edition will be in the hands of but few
persons, and as my original observations on this point have not as yet been
published in detail, I have ventured here to reprint the abstract.

[442] The term _unconscious selection_ has been objected to as a
contradiction: but _see_ some excellent observations on this head by Prof.
Huxley ('Nat. Hist. Review,' Oct. 1864, p. 578), who remarks that when the
wind heaps up sand-dunes it sifts and _unconsciously selects_ from the
gravel on the beach grains of sand of equal size.

[443] Sheep, 1838, p. 60.

[444] Mr. J. Wright on Shorthorn Cattle, in 'Journal of Royal Agricult.
Soc.,' vol. vii. pp. 208, 209.

[445] H. D. Richardson on Pigs, 1817, p. 44.

[446] 'Journal of R. Agricult. Soc.,' vol. i. p. 24.

[447] Sheep, pp. 520, 319.

[448] Loudon's 'Mag. of Nat. Hist.,' vol. viii., 1835, p. 618.

[449] 'A Treatise on the Art of Breeding the Almond Tumbler,' 1851, p. 9.

[450] 'Recreations in Agriculture,' vol. ii. p. 409.

[451] Youatt on Cattle, pp. 191, 227.

[452] Ferguson, 'Prize Poultry,' 1854, p. 208.

[453] Wilson, in 'Transact. Highland Agricult. Soc.,' quoted in 'Gard.
Chronicle,' 1844, p. 29.

[454] Simmonds, quoted in 'Gard. Chronicle,' 1855, p. 637. And for the
second quotation, _see_ Youatt on Sheep, p. 171.

[455] Robinet, 'Vers à Soie,' 1848, p. 271.

[456] Quatrefages, 'Les Maladies du Ver à Soie,' 1859, p. 101.

[457] M. Simon, in 'Bull. de la Soc. d'Acclimat.,' tom. ix., 1862, p. 221.

[458] 'The Poultry Chronicle,' vol. i., 1854, p. 607.

[459] J. M. Eaton, 'A Treatise on Fancy Pigeons,' 1852, p. xiv., and 'A
Treatise on the Almond Tumbler,' 1851, p. 11.

[460] 'Journal Royal Agricultural Soc.,' vol. vi. p. 22.

[461] 'Poultry Chronicle,' vol. ii., 1855, p. 596.

[462] Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gén.,' tom. iii. p. 254.

[463] 'Gardener's Chronicle,' 1850, p. 198.

[464] 'Transact. Hort. Soc.,' vol. vi. p. 152.

[465] 'Journal of Horticulture,' 1862, p. 369.

[466] 'Transact. Hort. Soc.,' vol. iv. p. 381.

[467] 'Transact. Hort. Soc.,' vol. iv. p. 285.

[468] Rev. W. Bromehead, in 'Gard. Chronicle,' 1857, p. 550.

[469] 'Gard. Chronicle,' 1862, p. 721.

[470] Dr. Anderson, in 'The Bee,' vol. vi. p. 96; Mr. Barnes, in 'Gard.
Chronicle,' 1844, p. 476.

[471] Godron, 'De l'Espèce,' 1859, tom. ii. p. 69; 'Gard. Chronicle,' 1854,
p. 258.

[472] On Sheep, p. 18.

[473] Volz, 'Beiträge zur Kulturgeschichte,' 1852, s. 47.

[474] Mitford's 'History of Greece,' vol. i. p. 73.

[475] Dr. Dally, translated in 'Anthropological Review,' May 1864, p. 101.

[476] Volz, 'Beiträge,' &c., 1852, s. 80.

[477] 'History of the World,' ch. 45.

[478] 'Gardener's Chronicle,' 1848, p. 323.

[479] Reynier, 'De l'Economie des Celtes,' 1818, pp. 487, 503.

[480] Le Couteur on Wheat, p. 15.

[481] Michel, 'Des Haras,' 1861, p. 84.

[482] Sir W. Wilde, an 'Essay on Unmanufactured Animal Remains,' &c., 1860,
p. 11.

[483] Col. Hamilton Smith, 'Nat. Library,' vol. xii., Horses, pp. 135, 140.

[484] Michel, 'Des Haras,' p. 90.

[485] Mr. Baker, 'History of the Horse,' Veterinary, vol. xiii. p. 423.

[486] M. l'Abbé Carlier, in 'Journal de Physique,' vol. xxiv., 1784, p.
181: this memoir contains much information on the ancient selection of
sheep; and is my authority for rams not being killed young in England.

[487] 'Gardener's Chronicle,' 1843, p. 389.

[488] Communications to Board of Agriculture, quoted in Dr. Darwin's
'Phytologia,' 1800, p. 451.

[489] 'Mémoire sur les Chinois,' 1786, tom. xi. p. 55; tom. v. p. 507.

[490] 'Recherches sur l'Agriculture des Chinois,' par L.
D'Hervey-Saint-Denys, 1850, p. 229. With respect to Khang-hi, _see_ Huc's
'Chinese Empire,' p. 311.

[491] Anderson, in 'Linn. Transact.,' vol. xii. p. 253.

[492] 'Mém. de l'Acad.' (divers savans), tom. vi., 1835, p. 333.

[493] 'Des Quadrupèdes du Paraguay,' 1801, tom. ii. p. 333, 371.

[494] 'The Great Sahara,' by the Rev. H. B. Tristram, 1860, p. 238.

[495] Pallas, 'Act. Acad. St. Petersburg,' 1777, p. 249; Moorcroft and
Trebeck, 'Travels in the Himalayan Provinces,' 1841.

[496] Quoted from Raffles, in the 'Indian Field,' 1859, p. 196; for Varro,
_see_ Pallas, _ut supra_.

[497] Erman's 'Travels in Siberia,' Eng. translat., vol. i. p. 453.

[498] _See_ also 'Journal of R. Geograph. Soc.,' vol. xiii. part i. p. 65.

[499] Livingstone's 'First Travels,' pp. 191, 439, 565; _see_ also
'Expedition to the Zambesi,' 1865, p. 465, for an analogous case respecting
a good breed of goats.

[500] Andersson's 'Travels in South Africa,' pp. 232, 318, 319.

[501] Dr. Vavasseur, in 'Bull. de la Soc. d'Acclimat.,' tom. viii., 1861,
p. 136.

[502] 'The Natural History of Dee Side,' 1855, p. 476.

[503] 'Bull. de la Soc. d'Acclimat.,' tom. vii., 1860, p. 457.

[504] 'Cattle,' p. 48.

[505] Livingstone's Travels, p. 576; Andersson, 'Lake Ngami,' 1856, p. 222.
With respect to the sale in Kaffraria, _see_ 'Quarterly Review,' 1860, p.
139.

[506] 'Mémoire sur les Chinois' (by the Jesuits), 1786, tom. xi. p. 57.

[507] F. Michel, 'Des Haras,' pp. 47, 50.

[508] Col. Hamilton Smith, Dogs, in 'Nat. Lib.,' vol. x. p. 103.

[509] Azara, 'Quadrupèdes du Paraguay,' tom. ii. p. 324.

[510] Sidney's edit. of Youatt, 1860, pp. 24, 25.

[511] 'Rural Economy of Yorkshire,' vol. ii. p. 182.

[512] Moll et Gayot, 'Du Boeuf,' 1860, p. 547.

[513] 'The India Sporting Review,' vol. ii. p. 181; 'The Stud Farm,' by
Cecil, p. 58.

[514] 'The Horse,' p. 22.

[515] 'History of England,' vol. i. p. 316.

[516] 'Uber Beständigkeit der Arten.'

[517] Youatt on Sheep, p. 315.

[518] 'Ueber Shorthorn Rindvieh,' 1857, s. 51.

[519] Low, 'Domesticated Animals,' 1845, p. 363.

[520] 'Quarterly Review,' 1849, p. 392.

[521] H. von Nathusius, 'Vorstudien ... Schweineschædel,' 1864, s. 140.

[522] _See_ also Dr. Christ, in 'Rütimeyer's Pfahlbauten,' 1861, s. 226.

[523] The passage is given 'Bull. Soc. d'Acclimat.,' 1858, p. 11.

[524] 'Journal of Horticulture,' 1862, p. 394.

[525] 'Gardener's Chronicle,' 1857, p. 85.

[526] _See_ Mr. Wildman's address to the Floricult. Soc., in 'Gardener's
Chronicle,' 1843, p. 86.

[527] 'Journal of Horticulture,' Oct. 24th, 1865, p. 239.

[528] Prescott's 'Hist. of Mexico,' vol. ii. p. 61.

[529] Sageret, 'Pomologie Physiologique,' 1830, p. 47; Gallesio, 'Teoria
della Riproduzione,' 1816, p. 88; Godron, 'De l'Espèce,' 1859, tom. ii. pp.
63, 67, 70. In my tenth and eleventh chapters I have given details on the
potato; and I can confirm similar remarks with respect to the onion. I have
also shown how far Naudin concurs in regard to the varieties of the melon.

[530] Godron, 'De l'Espèce,' tom. ii. p. 27.

[531] 'The Anthropological Treatises of Blumenbach,' 1865, p. 292.

[532] Mr. J. J. Murphy in his opening address to the Belfast Nat. Hist.
Soc., as given in the Belfast Northern Whig, Nov. 19, 1866. Mr. Murphy here
follows the line of argument against my views previously and more
cautiously given by the Rev. C. Pritchard, Pres. Royal Astronomical Soc.,
in his sermon (Appendix, p. 33) preached before the British Association at
Nottingham, 1866.

[533] On the Vision of Fishes and Amphibia, translated in 'Annals and Mag.
of Nat. Hist.,' vol. xviii., 1866, p. 469.

[534] Fourth edition, 1866, p. 215.

[535] Quoted by Youatt on Sheep, p. 325. _See_ also Youatt on Cattle, pp.
62, 69.

[536] MM. Lherbette and De Quatrefages, in 'Bull. Soc. Acclimat.,' tom.
viii., 1861, p. 311.

[537] 'The Poultry Book,' 1866, p. 123.

[538] Youatt on Sheep, p. 312.

[539] 'Treatise on the Almond Tumbler,' 1851, p. 33.

[540] Dr. Heusinger, 'Wochenschrift für die Heilkunde,' Berlin, 1846, s.
279.

[541] Youatt on the Dog, p. 232.

[542] 'The Fruit-trees of America,' 1845, p. 270: for peaches, p. 466.

[543] 'Proc. Royal Soc. of Arts and Sciences of Mauritius,' 1852, p. cxxxv.

[544] 'Gardener's Chronicle,' 1856, p. 379.

[545] Quatrefages, 'Maladies Actuelles du Ver à Soie,' 1859, pp. 12, 214.

[546] 'Gardener's Chronicle,' 1851, p. 595.

[547] 'Journal of Horticulture,' 1862, p. 476.

[548] 'Gardener's Chronicle,' 1852, pp. 435, 691.

[549] Bechstein, 'Naturgesch. Deutschlands,' 1801, B. i. s. 310.

[550] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 224.

[551] G. Lewis's 'Journal of Residence in West Indies,' 'Home and Col.
Library,' p. 100.

[552] Sidney's edit. of Youatt on the Pig, p.24.

[553] 'Journal of Horticulture,' 1862, pp. 476, 498; 1865, p. 460. With
respect to the heartsease, 'Gardener's Chronicle,' 1863, p. 628.

[554] 'Des Jacinthes, de leur Culture,' 1768, p. 53: on wheat, 'Gardener's
Chronicle,' 1846, p. 653.

[555] W. B. Tegetmeier, 'The Field,' Feb. 25, 1865. With respect to black
fowls, _see_ a quotation in Thompson's 'Nat. Hist. of Ireland,' 1849, vol.
i. p. 22.

[556] 'Bull. de la Soc. d'Acclimat.,' tom. vii. 1860, p. 359.

[557] 'Transact. Hort. Soc.,' vol. i. 2nd series, 1835, p. 275. For
raspberries, _see_ 'Gard. Chronicle,' 1855, p. 154, and 1863, p. 245.

[558] 'Gardener's Chronicle,' 1843, p. 806.

[559] Ibid., 1850, p. 732.

[560] Ibid., 1860, p. 956.

[561] J. De Jonghe, in 'Gard. Chronicle,' 1860, p. 120.

[562] Downing, 'Fruit-trees of North America,' pp. 266, 501: in regard to
the cherry, p. 198.

[563] 'Gardener's Chronicle,' 1849, p. 755.

[564] 'Journal of Horticulture,' Sept. 26th, 1865, p. 254; _see_ other
references given in chap. x.

[565] Mr. Selby, in 'Mag. of Zoology and Botany,' Edinburgh, vol. ii.,
1838, p. 393.

[566] The Reine Claude de Bavay, 'Journal of Horticulture,' Dec. 27, 1864,
p. 511.

[567] Mr. Pusey, in 'Journal of R. Agricult. Soc., vol. vi. p. 179. For
Swedish turnips, _see_ 'Gard. Chron.,' 1847, p. 91.

[568] Godron, 'De l'Espèce,' tom. ii. p. 98.

[569] 'Gardener's Chron.,' 1866, p. 732.

[570] 'Gardener's Chronicle,' 1862, pp. 820, 821.

[571] 'On the Varieties of Wheat,' p. 59.

[572] Mr. Hewitt and others, in 'Journal of Hort.,' 1862, p. 773.

[573] 'Encyclop. of Rural Sports,' p. 405.

[574] Col. Le Couteur, 'Journal Roy. Agricult. Soc.,' vol. iv. p. 43.

[575] 'Gardener's Chronicle,' 1845, p. 273.

[576] 'Journal of Horticulture,' 1862, p. 157.

[577] 'Cottage Gardener,' 1860, p. 368.

[578] 'A Review of Reports,' 1808, p. 406.

[579] 'Gardener's Chronicle,' 1853, p. 45.

[580] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gén.,' tom. iii. p. 49. On
the Cochineal Insect, p. 46.

[581] Capt. Marryat, quoted by Blyth in 'Journ. Asiatic Soc. of Bengal,'
vol. xxviii. p. 229.

[582] Mr. Oxley, 'Journal of the Indian Archipelago,' vol. ii., 1848, p.
645.

[583] Mr. Abbey, in 'Journal of Horticulture,' Dec. 1, 1863, p. 430.

[584] 'On Naval Timber,' 1831, p. 107.

[585] Mr. Baily, in 'The Poultry Chronicle,' vol. ii., 1854, p. 150. Also
vol. i. p. 342; vol. iii. p. 245.

[586] 'Cottage Gardener,' 1855, December, p. 171; 1856, January, pp. 248,
323.

[587] 'Ueber Shorthorn Rindvieh,' 1857, s. 51.

[588] 'The Veterinary,' vol. xiii. p. 720. For the Glamorganshire cattle,
_see_ Youatt on Cattle, p. 51.

[589] J. M. Eaton, 'A Treatise on Fancy Pigeons,' p. 82; Ferguson, on 'Rare
and Prize Poultry,' p. 162; Mr. Brent, in 'Cottage Gardener,' Oct. 1860. p.
13.

[590] 'Die Racen des Schweines,' 1860, s. 48.

[591] _See_ some good remarks on this head by M. de Quatrefages, 'Unité de
l'Espèce Humaine,' 1861, p. 119.

[592] Verlot, 'Des Variétés,' 1865, p. 94.

[593] Mr. Patrick Sheriff, in 'Gard. Chronicle,' 1858, p. 771.

[594] 'Pomologie Physiolog.,' 1830, p. 106.

[595] Youatt on Sheep, p. 521.

[596] 'A Treatise on the Almond Tumbler,' p. i.

[597] M. J. de Jonghe, in 'Gard. Chron.,' 1858, p. 173.

[598] Max. Müller, 'Science of Language,' 1861, p. 223.

[599] Youatt on Cattle, pp. 116, 128.

[600] 'Domesticated Animals,' p. 188.

[601] Volz, 'Beiträge zur Kulturgeschichte,' 1852, s. 99 _et passim_.

[602] Blaine, 'Encyclop. of Rural Sports,' p. 213.

[603] 'Des Jacinthes,' &c., Amsterdam, 1768, p. 43; Verlot, 'Des Variétés,'
&c., p. 86. On the reindeer, _see_ Linnæus, 'Tour in Lapland,' translated
by Sir J. E. Smith, vol. i. p. 314. The statement in regard to German
shepherds is given on the authority of Dr. Weinland.

[604] Müller's 'Physiology,' Eng. translation, vol. ii. p. 1662. With
respect to the similarity of twins in constitution, Dr. William Ogle has
given me the following extract from Professor Trousseau's Lectures
('Clinique Médicale,' tom. i. p. 523), in which a curious case is
recorded:--"J'ai donné mes soins à deux frères jumeaux, tous deux si
extraordinairement ressemblants qu'il m'était impossible de les
reconnaître, à moins de les voir l'un à côté de l'autre. Cette ressemblance
physique s'étendait plus loin: ils avaient, permettez-moi l'expression, une
similitude pathologique plus remarquable encore. Ainsi l'un d'eux que je
voyais aux néothermes à Paris malade d'une ophthalmie rhumatismale me
disait, 'En ce moment mon frère doit avoir une ophthalmie comme la mienne;'
et comme je m'étais récrié, il me montrait quelques jours après une lettre
qu'il venait de recevoir de ce frère alors à Vienne, et qui lui écrivait en
effet--'J'ai mon ophthalmie, tu dois avoir la tienne.' Quelque singulier
que ceci puisse paraître, le fait non est pas moins exact: on ne me l'a pas
raconté, je l'ai vu, et j'en ai vu d'autres analogues dans ma pratique. Ces
deux jumeaux étaient aussi tous deux asthmatiques, et asthmatiques à un
effroyable degré. Originaires de Marseille, ils n'ont jamais pu demeurer
dans cette ville, où leurs intérêts les appelaient souvent, sans être pris
de leurs accès; jamais ils n'en éprouvaient à Paris. Bien mieux, il leur
suffisait de gagner Toulon pour être guéris de leurs attaques de
Marseilles. Voyageant sans cesse et dans tous pays pour leurs affaires, ils
avaient remarqué que certaines localités leur étaient funestes, que dans
d'autres ils étaient exempts de tout phénomène d'oppression."

[605] Isid. Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. iii. p. 352;
Moquin Tandon, 'Tératologie Végétale,' 1841, p. 115.

[606] Metzger, 'Die Getreidearten,' 1841, s. 39.

[607] On the date-palm, _see_ Vogel, 'Annals and Mag. of Nat. Hist.,' 1854,
p. 460. On Indian varieties, Dr. F. Hamilton, 'Transact. Linn. Soc.,' vol.
xiv. p. 296. On the varieties cultivated in Tahiti, _see_ Dr. Bennett, in
Loudon's 'Mag. of N. Hist.,' vol. v., 1832, p. 484. Also Ellis, 'Polynesian
Researches,' vol. i. pp. 375, 370. On twenty varieties of the Pandanus and
other trees in the Marianne Island, _see_ 'Hooker's Miscellany,' vol. i. p.
308. On the bamboo in China, _see_ Huc's 'Chinese Empire,' vol. ii. p. 307.

[608] 'Treatise on the Culture of the Apple,' &c., p. 3.

[609] Gallesio, 'Teoria della Riproduzione Veg.,' p. 125.

[610] _See_ Dr. Hooker's Memoir on Arctic Plants in 'Linn. Transact.,' vol.
xxiii, part ii. Mr. Woodward, and a higher authority cannot be quoted,
speaks of the Arctic mollusca (in his 'Rudimentary Treatise,' 1856, p. 355)
as remarkably subject to variation.

[611] Bechstein, in his 'Naturgeschichte der Stubenvögel,' 1840, s. 238,
has some good remarks on this subject. He states that his canary-birds
varied in colour, though kept on uniform food.

[612] 'The Plant,' by Schleiden, translated by Henfrey, 1848, p. 169. _See_
also Alex. Braun, in 'Bot. Memoirs,' Ray. Soc., 1853, p. 313.

[613] Messrs. Hardy and Son, of Maldon, in 'Gard. Chronicle,' 1856, p. 458.

[614] 'Quadrupèdes du Paraguay,' 1801, tom. ii. p. 319.

[615] McClelland on Indian Cyprinidæ, 'Asiatic Researches,' vol. xix. part
ii., 1839, pp. 266, 268, 313.

[616] Quoted by Sageret, 'Pom. Phys.,' 1830, p. 43.

[617] 'The Fruits of America,' 1845, p. 5.

[618] M. Cardan, in 'Comptes Rendus,' Dec. 1848, quoted in 'Gard.
Chronicle,' 1849, p. 101.

[619] M. Alexis Jordan mentions four excellent pears found in woods in
France, and alludes to others ('Mém. Acad. de Lyon,' tom. ii. 1852, p.
159). Poiteau's remark is quoted in 'Gardener's Mag.,' vol. iv., 1828, p.
385. _See_ 'Gard. Chronicle,' 1862, p. 335, for another case of a new
variety of the pear found in a hedge in France. Also for another case,
_see_ Loudon's 'Encyclop. of Gardening,' p. 901. Mr. Rivers has given me
similar information.

[620] Duval, 'Hist. du Poirier,' 1849, p. 2.

[621] I infer that this is the fact from Van Mons' statement ('Arbres
Fruitiers,' 1835, tom. i. p. 446) that he finds in the woods seedlings
resembling all the chief cultivated races of both the pear and apple. Van
Mons, however, looked at these wild varieties as aboriginal species.

[622] Downing, 'Fruit-trees of North America,' p. 422; Foley, in 'Transact.
Hort. Soc.,' vol. vi. p. 412.

[623] 'Gard. Chronicle,' 1847, p. 244.

[624] 'Gardener's Chronicle,' 1841, p. 383; 1850, p. 700; 1854, p. 650.

[625] 'Die Getreidearten,' 1843, s. 66, 116, 117.

[626] Sabine, in 'Hort. Transact.,' vol. iii. p. 225; Bronn, 'Geschichte
der Natur,' b. ii. s. 119.

[627] 'Journal of Horticulture,' 1861, p. 112; on Zinnia, 'Gardener's
Chronicle,' 1860, p. 852.

[628] 'The Chrysanthemum, its History, &c.,' 1865, p. 3.

[629] 'Gardener's Chron.,' 1855, p. 54; 'Journal of Horticulture,' May 9,
1865, p. 363.

[630] Quoted by Verlot, 'Des Variétés,' &c., 1865, p. 28.

[631] 'Examination of the Characteristics of Genera and Species:'
Charleston, 1855, p. 14.

[632] Mr Hewitt, 'Journal of Hort.,' 1863, p. 39.

[633] Devay, 'Mariages Consanguins,' pp. 97, 125. In conversation I have
found two or three naturalists of the same opinion.

[634] Müller has conclusively argued against this belief, 'Elements of
Phys.,' Eng. translat., vol. ii., 1842, p. 1405.

[635] 'Act. Acad. St. Petersburg,' 1780, part ii. p. 84, &c.

[636] 'Bastarderzeugung,' s. 249, 255, 295.

[637] 'Nova Acta, St. Petersburg,' 1794, p. 378; 1795, pp. 307, 313, 316;
1787, p. 407.

[638] 'De la Fécondation,' 1862, p. 311.

[639] 'Amaryllidaceæ,' 1837, p. 362.

[640] Abstracted in 'Gard. Chronicle,' 1860, p. 1081.

[641] This was the opinion of the elder De Candolle, as quoted in 'Dic.
Class. d'Hist. Nat.,' tom. viii. p. 405. Puvis, in his work, 'De la
Dégénération,' 1837, p. 37, has discussed this same point.

[642] 'Comptes Rendus,' Novembre 21, 1864, p. 838.

[643] 'Nova Acta, St. Petersburg,' 1794, p. 391.

[644] 'Bastarderzeugung,' s. 507, 516, 572.

[645] 'Die Bastardbefruchtung,' &c., 1865, s. 24.

[646] 'Bastarderzeugung,' s. 452, 507.

[647] 'Die Bastardbefruchtung,' s. 56.

[648] 'Bastarderzeugung,' s. 423.

[649] 'Dritte Fortsetzung,' &c., 1766, s. 85.

[650] 'Die Bastardbefruchtung,' &c., 1865, s. 92; _see_ also the Rev. M. J.
Berkeley on the same subject, in 'Journal of Royal Hort. Soc.,' 1866, p.
80.

[651] Dr. P. Lucas has given a history of opinion on this subject: 'Héréd.
Nat.,' 1847, tom. i. p. 175.

[652] 'Hist. des Anomalies,' tom. iii. p. 499.

[653] Idem., tom. iii. pp. 392, 502.

[654] _See_ his interesting work, 'Métamorphoses de l'Homme,' &c., 1862, p.
129.

[655] 'Dritte Fortsetzung,' &c., s. 123; 'Bastarderzeugung,' s. 249.

[656] 'Gardener's Chronicle,' 1853, p. 183.

[657] Mr. Wildman, 'Floricultural Soc.,' Feb. 7, 1843, reported in 'Gard.
Chron.,' 1843, p. 86.

[658] Mr. Robson, in 'Journal of Horticulture,' Feb. 13th, 1866, p. 122.

[659] 'Journal of Horticulture,' 1861, p. 24.

[660] Ibid., 1862, p. 83.

[661] 'Gard. Chron.,' 1845, p. 660.

[662] Ibid., 1863, p. 628.

[663] 'Journal of Hort.,' 1861, pp. 64, 309.

[664] 'Des Variétés,' &c., p. 76.

[665] Engel, 'Sur les Prop. Médicales des Plantes,' 1860, pp. 10, 25. On
changes in the odours of plants, _see_ Dalibert's Experiments, quoted by
Beckman, 'Inventions,' vol. ii. p. 344; and Nees, in Ferussac, 'Bull. des
Sc. Nat.,' 1824, tom. i. p. 60. With respect to the rhubarb, &c., _see_
also 'Gardener's Chronicle,' 1849, p. 355; 1862, p. 1123.

[666] Hooker, 'Flora Indica,' p. 32.

[667] Naudin, 'Annales des Sc. Nat.,' 4th series, Bot., tom. xi., 1859, p.
81. 'Gardener's Chronicle,' 1859, p. 464.

[668] Moorcroft's 'Travels,' &c., vol. ii. p. 143.

[669] 'Gardener's Chronicle,' 1861, p. 1113.

[670] Royle, 'Productive Resources of India,' p. 59.

[671] 'Personal Narrative,' Eng. translat., vol. v. p. 101. This statement
has been confirmed by Karsten ('Beitrag zur Kenntniss der Rhynchoprion:'
Moscow, 1864. s. 39), and by others.

[672] 'Organic Chemistry,' Eng. translat., 1st edit., p. 369.

[673] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 155.

[674] Darwin, 'Journal of Researches,' 1845, p. 434.

[675] These statements on disease are taken from Dr. Boudin's 'Géographie
et de Statistique Médicales,' 1857, tom. i. p. xliv. and lii.; tom. ii. p.
315.

[676] E. Desor, quoted in the 'Anthrop. Rev.,' 1863, p. 180. For much
confirmatory evidence, _see_ Quatrefages, 'Unité de l'Espèce Humaine,'
1861, p. 131.

[677] 'Ceylon,' by Sir J. E. Tennent, vol. i., 1859, p. 89.

[678] Godron, 'De l'Espèce,' tom. ii. p. 52.

[679] 'Journal of Horticultural Soc.,' vol. vii., 1852, p. 117.

[680] 'Journal of Hort. Soc.,' vol. i. p. 160.

[681] _See_ Lecoq on the Villosity of Plants, 'Geograph. Bot.,' tom. iii.
pp. 287, 291; Gärtner, 'Bastarderz.,' s. 261; Mr. Musters, on the Opuntia,
in 'Gard. Chronicle,' 1846, p. 444.

[682] 'Pom. Phys.,' p. 136.

[683] 'Ampelographie,' 1849, p. 19.

[684] Gärtner, 'Bastarderz.,' s. 606, has collected nearly all recorded
facts. Andrew Knight (in 'Transact. Hort. Soc.,' vol. ii. p. 160) goes so
far as to maintain that few varieties are absolutely permanent in character
when propagated by buds or grafts.

[685] Mr. Blyth, in 'Annals and Mag. of Nat. Hist.,' vol. xx., 1847, p.
391.

[686] 'Natural History Review,' 1862, p. 113.

[687] 'Journal of Roy. Geographical Soc.,' vol. ix., 1839, p. 275.

[688] 'Travels in Bokhara,' vol. iii. p. 151.

[689] _See_ also, on the influence of marshy pastures on the wool, Godron,
'L'Espèce,' tom. ii. p. 22.

[690] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gén.,' tom. iii. p. 438.

[691] Azara has made some good remarks on this subject, 'Quadrupèdes du
Paraguay,' tom. ii. p. 337. _See_ an account of a family of naked mice
produced in England, 'Proc. Zoolog.  Soc.,' 1856, p. 38.

[692] 'Die Fauna der Pfahlbauten,' 1861, s. 15.

[693] 'Schweinschædel,' 1864, s. 99.

[694] 'Travels in Siberia,' Eng. translat., vol. i. p. 228.

[695] A. R. Wallace, 'Travels on the Amazon and Rio Negro,' p. 294.

[696] 'Naturgeschichte der Stubenvögel,' 1840, s. 262, 308.

[697] 'Hist. Nat. Gén.,' tom. iii. p. 402.

[698] 'Bull. de la Soc. Imp. d'Acclimat.,' tom. viii. p. 351.

[699] _See_ an account of Mr. Gregson's experiments on the _Abraxus
grossulariata_, 'Proc. Entomolog. Soc.,' Jan. 6th, 1862: these experiments
have been confirmed by Mr. Greening, in 'Proc. of the Northern Entomolog.
Soc.,' July 28th, 1862. For the effects of food on caterpillars, see a
curious account by M. Michely, in 'Bull. de la Soc. Imp. d'Acclimat.,' tom.
viii. p. 563. For analogous facts from Dahlbom on Hymenoptera, _see_
Westwood's 'Modern Class. of Insects,' vol. ii. p. 98. _See_ also Dr. L.
Möller, 'Die Abhängigkeit der Insecten,' 1867, s. 70.

[700] 'The Principles of Biology,' vol. ii. 1866. The present chapters were
written before I had read Mr. Herbert Spencer's work, so that I have not
been able to make so much use of it as I should otherwise probably have
done.

[701] 'Proc. Acad. Nat. Soc. of Philadelphia,' Jan. 28th, 1862.

[702] _See_ Mr. B. D. Walsh's excellent papers in 'Proc. Entomolog. Soc.
Philadelphia,' Dec. 1866, p. 284. With respect to the willow, _see_ idem,
1864, p. 546.

[703] _See_ his admirable Histoire des Galles, in 'Annal. des Sc. Nat.
Bot.,' 3rd series, tom. xix., 1853, p. 273.

[704] Kirby and Spence's 'Entomology,' 1818, vol. i. p. 450;
Lucaze-Duthiers, idem, p. 284.

[705] 'Proc. Entomolog. Soc. Philadelphia,' 1864, p. 558.

[706] Mr. B. D. Walsh, idem, p. 633; and Dec. 1866, p. 275.

[707] Mr. B. D. Walsh, idem, 1864, p. 545, 411, 495; and Dec. 1866, p. 278.
_See_ also Lucaze-Duthiers.

[708] Lucaze-Duthiers, idem, pp. 325, 328.

[709] 'Linnæa,' vol. xvii., 1843; quoted by Dr. M. T. Masters, Royal
Institution, March 16th, 1860.

[710] Hewett C. Watson, 'Cybele Britannica,' vol. i., 1847, p. 11.

[711] 'Gardener's Chronicle,' 1857, p. 629.

[712] 'Mémoire sur la Production Artificielle des Monstrosités,' 1862, pp.
8-12; 'Recherches sur les Conditions, &c., chez les Monstres,' 1863, p. 6.
An abstract is given of Geoffroy's Experiments by his son, in his 'Vie,
Travaux, &c.,' 1847, p. 290.

[713] Paget, 'Lectures on Surgical Pathology,' 1853, vol. i. p. 483.

[714] 'Researches upon the Venom of the Rattle-snake,' Jan. 1861, by Dr.
Mitchell, p. 67.

[715] Mr. Sedgwick, in 'British and Foreign Medico-Chirurg. Review,' July
1863, p. 175.

[716] 'An Essay on Generation,' Eng. translat., p. 18; Paget, 'Lectures on
Surgical Pathology,' 1853, vol. i. p. 209.

[717] 'An Essay on Animal Reproduction,' Eng. translat., 1769, p. 79.

[718] Carpenter's 'Principles of Comp. Physiology,' 1854, p. 479.

[719] Charlesworth's 'Mag. of Nat. Hist.,' vol. i., 1837, p. 145.

[720] Paget, 'Lectures on Surgical Pathology,' vol. i. p. 239.

[721] Quoted by Carpenter, 'Comp. Phys.,' p. 479.

[722] Paget, 'Lectures,' &c., p. 257.

[723] These cases are given by Blumenbach in his 'Essay on Generation,' pp.
52, 54.

[724] 'Cellular Pathology,' trans. by Dr. Chance, 1860, pp. 27, 441.

[725] Paget, 'Lectures on Pathology,' vol. i., 1853, p. 357.

[726] Paget, idem, p. 150.

[727] 'The Principles of Biology,' vol. ii., 1866, chap. 3-5.

[728] 'Lectures on Pathology,' 1853, vol. i. p. 71.

[729] 'Comptes Rendus,' Sept. 26th, 1864, p. 539.

[730] 'The Principles of Biology,' vol. ii. p. 243.

[731] Idem, vol. ii. p. 269.

[732] Idem, vol. ii. p. 273.

[733] Paget, 'Lectures on Pathology,' vol. ii. p. 209.

[734] Müller's 'Phys.,' Eng. translat., pp. 54, 791. Prof. Reed has given
('Physiological and Anat. Researches,' p. 10) a curious account of the
atrophy of the limbs of rabbits after the destruction of the nerve.

[735] Quoted by Lecoq, in 'Geograph. Bot.,' tom. i., 1854, p. 182.

[736] 'Das Abändern der Vögel,' 1833, s. 74.

[737] Nathusius, 'Die Racen des Schweines,' 1860, s. 53, 57; 'Vorstudien
... Schweineschædel,' 1864, s. 103, 130, 133.

[738] 'Journal of Agriculture of Highland Soc.,' July, 1860, p. 321.

[739] 'Principles of Biology,' vol. ii. p. 263.

[740] 'Natural History Review,' vol. iv., Oct. 1864, p. 617.

[741] 'Lectures on Surgical Pathology,' 1853, vol. i. p. 27.

[742] Andersson, 'Travels in South Africa,' p. 318. For analogous cases in
South America, _see_ Aug. St. Hilaire, 'Voyage dans le Province de Goyaz,'
tom. i. p. 71.

[743] Brickell's 'Nat. Hist. of North Carolina,' 1739, p. 53.

[744] Livingstone, quoted by Youatt on Sheep, p. 142. Hodgson, in 'Journal
of Asiatic Soc. of Bengal,' vol. xvi., 1847, p. 1006, &c. &c.

[745] 'Naturalist Library,' Dogs, vol. ii. 1840, p. 104.

[746] 'De l'Espèce,' tom. i., 1859, p. 367.

[747] 'Ceylon,' by Sir J. E. Tennent, 1859, vol. ii. p. 531.

[748] For the foregoing statements, _see_ Hunter's 'Essays and
Observations,' 1861, vol. ii. p. 329; Dr. Edmondston, as quoted in
Macgillivray's 'British Birds,' vol. v. p. 550; Menetries, as quoted in
Bronn's 'Geschichte der Natur,' B. ii. s. 110.

[749] These statements on the intestines are taken from Isidore Geoffroy
St. Hilaire, 'Hist. Nat. Gén.,' tom. iii. pp. 427, 441.

[750] Gilbert White, 'Nat. Hist. Selbourne,' 1825, vol. ii. p. 121.

[751] Burdach, 'Traité de Phys.,' tom. ii. p. 267, as quoted by Dr. P.
Lucas, 'L'Héréd. Nat.,' tom. i. p. 388.

[752] This and several other cases are given by Colin, 'Physiologie Comp.
des Animaux Dom.,' 1854, tom. i. p. 426.

[753] M. Michely de Cayenne, in 'Bull. Soc. d'Acclimat.,' tom. viii., 1861,
p. 563.

[754] Quatrefages, 'Unité de l'Espèce Humaine,' 1861, p. 79.

[755] 'Flora,' 1835, B. ii. p. 504.

[756] Alph. De Candolle, 'Géograph. Bot.,' tom. ii. p. 1078.

[757] Royle, 'Illustrations of the Botany of the Himalaya,' p. 19.

[758] 'Gardener's Chronicle,' 1850, pp. 204, 219.

[759] Rev. R. Everest, 'Journal As. Soc. of Bengal,' vol. iii. p. 19.

[760] Youatt on Sheep, 1838, p. 491.

[761] Royle, 'Prod. Resources of India,' p. 153.

[762] Tegetmeier, 'Poultry Book,' 1866, p. 102.

[763] Dr. R. Paterson, in a paper communicated to Bot. Soc. of Canada,
quoted in the 'Reader,' 1863. Nov. 13th.

[764] _See_ remarks by Editor in 'Gard. Chronicle,' 1848, p. 5.

[765] 'Gard. Chronicle,' 1860, p. 938. Remarks by Editor and quotation from
Decaisne.

[766] J. de Jonghe, of Brussels, in 'Gard. Chronicle,' 1857, p. 612.

[767] Ch. Martius, 'Voyage Bot. Côtes Sept. de la Norvège,' p. 26.

[768] 'Journal de l'Acad. Hort. de Gand,' quoted in 'Gard. Chron.,' 1859,
p. 7.

[769] 'Gard. Chronicle,' 1851, p. 396.

[770] Idem., 1862, p. 235.

[771] On the authority of Labat, quoted in 'Gard. Chron.,' 1862, p. 235.

[772] MM. Edwards and Colin, 'Annal. des Sc. Nat.,' 2nd series, Bot., tom.
v. p. 22.

[773] 'Géograph. Bot.,' p. 337.

[774] 'Swedish Acts,' Eng. translat., 1739-40, vol. i. Kalm, in his
'Travels,' vol. ii. p. 166, gives an analogous case with cotton-plants
raised in New Jersey from Carolina seed.

[775] De Candolle, 'Géograph. Bot.,' p. 339.

[776] 'Gard. Chronicle,' 1862, p. 235.

[777] Gallesio, 'Teoria della Riproduzione Veg.,' 1816, p. 125; and 'Traité
du Citrus,' 1811, p. 359.

[778] 'Essai sur l'Hist. des Orangers,' 1813, p. 20, &c.

[779] Alph. De Candolle, 'Géograph. Bot.,' p. 882.

[780] 'Ch. Darwin's Lehre von der Entstehung,' &c., 1862, s. 87.

[781] Decaisne, quoted in 'Gard. Chronicle,' 1865, p. 271.

[782] For the magnolia, _see_ Loudon's 'Gard. Mag.,' vol. xiii., 1837, p.
21. For camellias and roses, _see_ 'Gard. Chron.,' 1860, p. 384. For the
yew, 'Journal of Hort.,' March 3rd, 1863, p. 174. For sweet potatoes, _see_
Col. von Siebold, in 'Gard. Chron.,' 1855, p. 822.

[783] The Editor, 'Gard. Chron.,' 1861, p. 239.

[784] Loudon's 'Gard. Mag.,' vol. xii., 1836, p. 378.

[785] 'Gardeners Chron.,' 1865, p. 699.

[786] 'Arboretum et Fruticetum,' vol. iii. p. 1376.

[787] Mr. Robson, in 'Journal of Horticulture,' 1861, p. 23.

[788] Dr. Bonavia, 'Report of the Agri.-Hort. Soc. of Oudh,' 1866.

[789] 'Cottage Gardener,' 1860, April, 24th, p. 57.

[790] 'Gardener's Chronicle,' 1841, p. 291.

[791] Mr. Beaton, in 'Cottage Gardener,' March 20th, 1860, p. 377. Queen
Mab will also stand stove heat, _see_ 'Gard. Chronicle,' 1845, p. 226.

[792] 'Gardener's Chronicle,' 1841, p. 439.

[793] Quoted by Asa Gray, in 'Am. Journ. of Sci.,' 2nd series, Jan. 1865,
p. 106.

[794] For China, _see_ 'Mémoire sur les Chinois,' tom, xi., 1786, p. 60.
Columella is quoted by Carlier, in 'Journal de Physique,' tom. xxiv. 1784.

[795] Messrs. Hardy and Son, in 'Gard. Chronicle,' 1856, p. 589.

[796] Isid. Geoffroy St. Hilaire, 'Hist. Nat. des Anomalies,' 1836, tom.
ii. pp. 210, 223, 224, 395; 'Philosoph. Transact.,' 1775, p. 313.

[797] Pallas, quoted by Youatt on Sheep, p. 25.

[798] Youatt on Cattle, 1834, p. 174.

[799] 'Encyclop. Méthod.,' 1820, p. 483: _see_ p. 500, on the Indian zebu
casting its horns. Similar cases in European cattle were given in the third
chapter.

[800] Pallas, 'Travels,' Eng. translat., vol. i. p. 243.

[801] Mr. Beaton, in 'Journal of Horticulture,' May 21, 1861, p. 133.

[802] Lecoq, 'De la Fécondation,' 1862, p. 233.

[803] 'Annales du Muséum,' tom. vi. p. 319.

[804] 'Hist. des Anomalies,' tom. iii. p. 392. Prof. Huxley applies the
same principle in accounting for the remarkable, though normal, differences
in the arrangement of the nervous system in the Mollusca, in his great
paper on the Morphology of the Cephalous Mollusca, in 'Phil. Transact.,'
1853, p. 56.

[805] 'Eléments de Tératologie Veg.,' 1841, p. 113.

[806] Prof. J. B. Simonds, on the Age of the Ox, Sheep, &c., quoted in
'Gard. Chronicle,' 1854, p. 588.

[807] 'Hist. des Anomalies,' tom. i. p. 674.

[808] Quoted by Isid. Geoffroy, idem, tom. i. p. 635.

[809] 'The Poultry Book,' by W. B. Tegetmeier, 1866, p. 250.

[810] A. Walker on Intermarriage, 1838, p. 160.

[811] 'The Farrier and Naturalist,' vol. i., 1828, p. 456.

[812] Godron, 'Sur l'Espèce,' tom. ii. p. 217.

[813] 'Quadrupèdes du Paraguay,' tom. ii. p. 333.

[814] On Sheep, p. 142.

[815] 'Ueber Racen, Kreuzungen, &c.,' 1825, s. 24.

[816] Quoted from Conolly, in 'The Indian Field,' Feb. 1859, vol. ii. p.
266.

[817] 'Domesticated Animals of the British Islands,' pp. 307, 368.

[818] 'Proceedings Zoolog. Soc.,' 1833, p. 113.

[819] Sedgwick, 'Brit. and Foreign Medico-Chirurg. Review,' April 1863, p.
453.

[820] 'Gard. Chronicle,' 1849, p. 205.

[821] 'Embassy to the Court of Ava,' vol. i. p. 320.

[822] 'Narrative of a Mission to the Court of Ava in 1855,' p. 94.

[823] Those statements are taken from Mr. Sedgwick, in the 'Medico-Chirurg.
Review,' July 1861, p. 198; April 1863, pp. 455 and 458. Liebreich is
quoted by Professor Devay, in his 'Mariages Consanguins,' 1862, p. 116.

[824] Loudon's 'Mag. of Nat. Hist.,' vol. i., 1829, pp. 66, 178. _See_ also
Dr. P. Lucas, 'L'Héréd. Nat.,' tom. i. p. 428, on the inheritance of
deafness in cats.

[825] 'Annales des Sc. Nat.' Zoolog., 3rd series, 1847, tom. viii. p. 239.

[826] 'Gardener's Chron.,' 1864, p. 1202.

[827] Verlot gives several other instances, 'Des Variétés,' 1865, p. 72.

[828] 'Arbres Fruitiers,' 1836, tom. ii. pp. 204, 226.

[829] 'Annales du Muséum,' tom. xx. p. 188.

[830] 'Gardener's Chron.,' 1843, p. 877.

[831] Ibid., 1845, p. 102.

[832] 'Hist. des Anomalies,' tom. iii. p. 402. _See_ also M. Camille
Dareste, 'Recherches sur les Conditions,' &c., 1863, pp. 16, 48.

[833] Rev. E. S. Dixon, 'Ornamental Poultry,' 1848, p. 111; Isidore
Geoffroy, 'Hist. Anomalies,' tom. i. p. 211.

[834] 'On the Breeding of Domestic Animals,' 1829, p. 6.

[835] Youatt on Cattle, 1834, p. 283.

[836] Mr. Herbert Spencer ('Principles of Biology,' 1864, vol. i. pp. 452,
468) takes a different view; and in one place remarks: "We have seen reason
to think that, as fast as essential faculties multiply, and as fast as the
number of organs that co-operate in any given function increases, indirect
equilibration through natural selection becomes less and less capable of
producing specific adaptations; and remains fully capable only of
maintaining the general fitness of constitution to conditions." This view
that natural selection can do little in modifying the higher animals
surprises me, seeing that man's selection has undoubtedly effected much
with our domesticated quadrupeds and birds.

[837] Dr. Prosper Lucas apparently disbelieves in any such connexion,
'L'Héréd. Nat.,' tom. ii. pp. 88-94.

[838] 'British Medical Journal,' 1862, p. 433.

[839] Boudin, 'Geograph. Médicale,' tom. i. p. 406.

[840] This fact and the following cases, when not stated to the contrary,
are taken from a very curious paper by Prof. Heusinger, in 'Wochenschrift
für Heilkunde,' May 1846, s. 277.

[841] Mr. Mogford, in the 'Veterinarian,' quoted in 'The Field,' Jan. 22,
1861, p. 545.

[842] 'Edinburgh Veterinary Journal,' Oct. 1860, p. 347.

[843] 'Hist. des Anomalies,' 1832, tom. i. pp. 22, 537-556; tom. iii. p.
462.

[844] 'Comptes Rendus,' 1855, pp. 855, 1029.

[845] Carpenter's 'Comp. Phys.,' 1854, p. 480; _see_ also Camille Dareste,
'Comptes Rendus,' March 20th, 1865, p. 562.

[846] 'Elements of Physiology,' Eng. translat, vol. i., 1838, p. 412. With
respect to Vrolik, _see_ Todd's 'Cyclop. of Anat. and Phys.,' vol. iv.,
1849-52, p. 973.

[847] 'Tératologie Vég.,' 1841, livre iii.

[848] 'Hist. des Anomalies,' tom. iii. pp. 4, 5, 6.

[849] 'Tératologie Vég.,' p. 156. _See_ also my paper on climbing plants in
'Journal of Linn. Soc. Bot.,' vol. ix., 1865, p. 114.

[850] 'Mémoires du Muséum,' &c., tom. viii. p. 178.

[851] Loudon's 'Encyclop. of Gardening,' p. 829.

[852] Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 324.

[853] 'Annales des Sc. Nat.,' 1st series, tom. xix. p. 327.

[854] 'Comptes Rendus,' Dec. 1864, p. 1039.

[855] Ueber Fötale Rachites, 'Würzburger Medicin. Zeitschrift,' 1860, B. i.
s. 265.

[856] 'Tératologie Vég.,' p. 192. Dr. M. Masters informs me that he doubts
the truth of this conclusion; but the facts to be given seem to be
sufficient to establish it.

[857] 'Journal of Horticulture,' July 2nd, 1861, p. 253.

[858] It would be worth trial to fertilise with the same pollen the central
and lateral flowers of the pelargonium, and of some other highly cultivated
plants, protecting them of course from insects: then to sow the seed
separately, and observe whether the one or the other lot of seedlings
varied the most.

[859] Quoted in 'Journal of Horticulture,' Feb. 24, 1863, p. 152.

[860] 'Gardener's Chronicle,' 1866, p. 612. For the Phalænopsis, _see_
idem, 1867, p. 211.

[861] Mémoires ... des Végétaux,' 1837, tom. ii. p. 170.

[862] 'Journal of Horticulture,' July 23, 1861, p. 311.

[863] 'Nouvelles Archives du Muséum,' tom. i. p. 137.

[864] Hugo von Mohl, 'The Vegetable Cell,' Eng. tr., 1852, p. 76.

[865] The Rev. H. H. Dombrain, in 'Journal of Horticulture,' 1861, June
4th, p. 174; and June 25th, p. 234; 1862, April 29th, p. 83.

[866] 'Transact. Linn. Soc.,' vol. xxiii., 1861, p. 360.

[867] 'Die Getreidearten,' 1843, s. 208, 209.

[868] 'Gardener's Chronicle,' 1850, p. 198.

[869] Quoted in 'Gardener's Chron.,' 1866, p. 74.

[870] 'Ueber den Begriff der Pflanzenart,' 1834, s. 14.

[871] 'Domesticated Animals,' 1845, p. 351.

[872] Bechstein, 'Naturgeschichte Deutschlands,' Band iv., 1795, s. 31.

[873] 'Proc. Entomolog. Soc. of Philadelphia,' Oct. 1863, p. 213.

[874] Quoted by Paget, 'Lectures on Pathology,' 1853, p. 159.

[875] Dr. Lachmann, also, observes ('Annals and Mag. of Nat. History,' 2nd
series, vol. xix., 1857, p. 231) with respect to infusoria, that "fissation
and gemmation pass into each other almost imperceptibly." Again, Mr. W. C.
Minor ('Annals and Mag. of Nat. Hist.,' 3rd series, vol. xi. p. 328) shows
that with Annelids the distinction that has been made between fission and
budding is not a fundamental one. _See_ Bonnet, 'Oeuvres d'Hist. Nat.,'
tom. v., 1781, p. 339, for remarks on the budding-out of the amputated
limbs of Salamanders. _See_, also, Professor Clark's work 'Mind in Nature,'
New York, 1865, pp. 62, 94.

[876] Paget, 'Lectures on Pathology,' 1853, p. 158.

[877] Idem, pp. 152, 164.

[878] On the Asexual Reproduction of Cecydomyide Larvæ, translated in
'Annals and Mag. of Nat. Hist.,' March 1866, pp. 167, 171.

[879] _See_ some excellent remarks on this head by Quatrefages, in 'Annales
des Sc. Nat.,' Zoolog., 3rd series, 1850, p. 138.

[880] 'Annals and Mag. of Nat. Hist.,' 2nd series, vol. xx., 1857, pp.
153-455.

[881] 'Annales des Sc. Nat.,' 3rd series, 1850, tom. xiii.

[882] 'Transact. Phil. Soc.,' 1851, pp. 196, 208, 210; 1853, p. 245, 247.

[883] 'Beitrage zur Kenntniss,' &c., 1844, s. 345.

[884] 'Nouvelles Archives du Muséum,' tom. i. p. 27.

[885] As quoted by Sir J. Lubbock in 'Nat. Hist. Review,' 1862, p. 345.

[886] 'Transact. Linn. Soc.,' vol. xxiv., 1863, p. 62.

[887] 'Parthenogenesis,' 1849, pp. 25-26. Prof. Huxley has some excellent
remarks ('Medical Times,' 1856, p. 637) on this subject, in reference to
the development of star-fishes, and shows how curiously metamorphosis
graduates into gemmation or zoid-formation, which is in fact the same as
metagenesis.

[888] Prof. J. Reay Greene, in Günther's 'Record of Zoolog. Lit.,' 1865, p.
625.

[889] Fritz Müller's 'Für Darwin,' 1864, s. 65, 71. The highest authority
on crustaceans, Prof. Milne Edwards, insists ('Annal. des Sci. Nat.,' 2nd
series, Zoolog., tom. iii. p. 322) on their metamorphoses differing even in
closely allied genera.

[890] Prof. Allman, in 'Annals and Mag. of Nat. Hist.,' 3rd series, vol.
xiii., 1864, p. 348; Dr. S. Wright, idem, vol. viii., 1861, p. 127. _See_
also p. 358 for analogous statements by Sars.

[891] 'Tissus Vivants,' 1866, p. 22.

[892] 'Cellular Pathology,' translat. by Dr. Chance, 1860, pp. 14, 18, 83,
460.

[893] Paget, 'Surgical Pathology,' vol. i., 1853, pp. 12-14.

[894] Idem, p. 19.

[895] Mantegazza, quoted in 'Popular Science Review,' July 1865, p. 522.

[896] 'De la Production Artificielle des Os,' p. 8.

[897] Isidore Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. ii. pp.
549, 560, 562; Virchow, idem, p. 484.

[898] For the most recent classification of cells, _see_ Ernst Häckel's
'Generelle Morpholog.,' Band ii., 1866, s. 275.

[899] 'The Structure and Growth of Tissues,' 1865, p. 21, &c.

[900] Dr. W. Turner, 'The present Aspect of Cellular Pathology,' 'Edinburgh
Medical Journal,' April, 1863.

[901] This term is used by Dr. E. Montgomery ('On the Formation of
so-called Cells in Animal Bodies,' 1867, p. 42), who denies that cells are
derived from other cells by a process of growth, but believes that they
originate through certain chemical changes.

[902] Prof. Huxley has called my attention to the views of Buffon and
Bonnet. The former ('Hist. Nat. Gén.,' edit. of 1749, tom. ii. pp. 54, 62,
329, 333, 420, 425) supposes that organic molecules exist in the food
consumed by every living creature; and that these molecules are analogous
in nature with the various organs by which they are absorbed. When the
organs thus become fully developed, the molecules being no longer required
collect and form buds or the sexual elements. If Buffon had assumed that
his organic molecules had been formed by each separate unit throughout the
body, his view and mine would have been closely similar.

Bonnet ('Oeuvres d'Hist. Nat.,' tom. v., part i., 1781, 4to edit., p. 334)
speaks of the limbs having germs adapted for the reparation of all possible
losses; but whether these germs are supposed to be the same with those
within the buds and sexual organs is not clear. His famous but now exploded
theory of _emboîtement_ implies that perfect germs are included within
germs in endless succession, pre-formed and ready for all succeeding
generations. According to my view, the germs or gemmules of each separate
part were not originally pre-formed, but are continually produced at all
ages during each generation, with some handed down from preceding
generations.

Prof. Owen remarks ('Parthenogenesis,' 1849, pp. 5-8), "Not all the progeny
of the primary impregnated germ-cell are required for the formation of the
body in all animals: certain of the derivative germ-cells may remain
unchanged and become included in that body which has been composed of their
metamorphosed and diversely combined or confluent brethren: so included,
any derivative germ-cell, or the nucleus of such, may commence and repeat
the same processes of growth by imbibition, and of propagation by
spontaneous fission, as those to which itself owed its origin;" &c. By the
agency of these germ-cells Prof. Owen accounts for parthenogenesis, for
propagation by self-division during successive generations, and for the
repairs of injuries. His view agrees with mine in the assumed transmission
and multiplication of his germ-cells, but differs fundamentally from mine
in the belief that the primary germ-cell was formed within the ovarium of
the female and was fertilised by the male. My gemmules are supposed to be
formed, quite independently of sexual concourse, by each separate cell or
unit throughout the body, and to be merely aggregated within the
reproductive organs.

Lastly, Mr. Herbert Spencer ('Principles of Biology,' vol. i., 1863-4,
chaps. iv. and viii.) has discussed at considerable length what he
designates as physiological units. These agree with my gemmules in being
supposed to multiply and to be transmitted from parent to child; the sexual
elements are supposed to serve merely as their vehicles; they are the
efficient agents in all the forms of reproduction and in the repairs of
injuries; they account for inheritance, but they are not brought to bear on
reversion or atavism, and this is unintelligible to me; they are supposed
to possess polarity, or, as I call it, affinity; and apparently they are
believed to be derived from each separate part of the whole body. But
gemmules differ from Mr. Spencer's physiological units, inasmuch as a
certain number, or mass of them, are, as we shall see, requisite for the
development of each cell or part. Nevertheless I should have concluded that
Mr. Spencer's views were fundamentally the same with mine, had it not been
for several passages which, as far as I understand them, indicate something
quite different. I will quote some of these passages from pp. 254-256. "In
the fertilised germ we have two groups of physiological units, slightly
different in their structures."... "It is not obvious that change in the
form of the part, caused by changed action, involves such change in the
physiological units throughout the organism, that these, when groups of
them are thrown off in the shape of reproductive centres, will unfold into
organisms that have this part similarly changed in form. Indeed, when
treating of Adaptation, we saw that an organ modified by increase or
decrease of function can but slowly so react on the system at large as to
bring about those correlative changes required to produce a new
equilibrium; and yet only when such new equilibrium has been established,
can we expect it to be _fully_ expressed in the modified physiological
units of which the organism is built--only then can we count on a complete
transfer of the modification to descendants."... "That the change in the
offspring must, other things equal, be in the same direction as the change
in the parent, we may dimly see is implied by the fact, that the change
propagated throughout the parental system is a change towards a new state
of equilibrium--a change tending to bring the actions of all organs,
reproductive included, into harmony with these new actions."

[903] M. Philipeaux ('Comptes Rendus,' Oct. 1, 1866, p. 576, and June,
1867) has lately shown that when the entire fore-limb, including the
scapula, is extirpated, the power of regrowth is lost. From this he
concludes that it is necessary for regrowth that a small portion of the
limb should be left. But as in the lower animals the whole body may be
bisected and both halves be reproduced, this belief does not seem probable.
May not the early closing of a deep wound, as in the case of the
extirpation of the scapula, prevent the formation or protrusion of the
nascent limb?

[904] 'Annal. des Sc. Nat.,' 3rd series, Bot., tom. xiv., 1850, p. 244.

[905] _See_ some very interesting papers on this subject by Prof. Lionel
Beale, in 'Medical Times and Gazette,' Sept. 9th, 1865, pp. 273, 330.

[906] Third Report of the R. Comm. on the Cattle Plague, as quoted in
'Gard. Chronicle,' 1866, p. 446.

[907] In a cod-fish, weighing 20 lb., Mr. F. Buckland ('Land and Water,'
1867, p. 57) calculated the above number of eggs. In another instance,
Harmer ('Phil. Transact.,' 1767, p. 280) found 3,681,760 eggs. For the
Ascaris, _see_ Carpenter's 'Comp. Phys.,' 1854, p. 590. Mr. J. Scott, of
the Royal Botanic Garden of Edinburgh, calculated, in the same manner as I
have done for some British orchids ('Fertilisation of Orchids,' p. 344),
the number of seeds in a capsule of an Acropera, and found the number to be
371,250. Now this plant produces several flowers on a raceme and many
racemes during a season. In an allied genus, Gongora, Mr. Scott has seen
twenty capsules produced on a single raceme: ten such racemes on the
Acropera would yield above seventy-four millions of seed. I may add that
Fritz Müller informs me that he found in a capsule of a Maxillaria, in
South Brazil, that the seed weighed 42½ grains: he then arranged half a
grain of seed in a narrow line, and by counting a measured length found the
number in the half-grain to be 20,667, so that in the capsule there must
have been 1,756,440 seeds! The same plant sometimes produces half-a-dozen
capsules.

[908] 'Annals and Mag. of Nat. Hist.,' 3rd series, vol. viii., 1861, p.
490.

[909] Paget, 'Lectures on Pathology,' p. 27; Virchow, 'Cellular Pathology,'
translat. by Dr. Chance, pp. 123, 126, 294; Claude Bernard, 'Des Tissus
Vivants,' pp. 177, 210, 337; Müller's 'Physiology,' Eng. translat., p. 290.

[910] Virchow, 'Cellular Pathology,' trans. by Dr. Chance, 1860, pp. 60,
162, 245, 441, 454.

[911] Idem, pp. 412-426.

[912] _See_ Rev. J. M. Berkeley, in 'Gard. Chron.,' April 28th, 1866, on a
bud developed on the petal of the Clarkia. _See_ also H. Schacht, 'Lehrbuch
der Anat.,' &c., 1859, Theile ii. s. 12, on adventitious buds.

[913] Mr. Herbert Spencer ('Principles of Biology,' vol. ii. p. 430) has
fully discussed the antagonism between growth and reproduction.

[914] The male salmon is known to breed at a very early age. The Triton and
Siredon, whilst retaining their larval branchiæ, according to Filippi and
Duméril ('Annals and Mag. of Nat. Hist.,' 3rd series, 1866, p. 157), are
capable of reproduction. Ernst Häckel has recently ('Monatsbericht Akad.
Wiss. Berlin,' Feb. 2nd, 1865) observed the surprising case of a medusa,
with its reproductive organs active, which produces by budding a widely
different form of medusa; and this latter also has the power of sexual
reproduction. Krohn has shown ('Annals and Mag. of Nat. Hist.,' 3rd series,
vol. xix., 1862, p. 6) that certain other medusæ, whilst sexually mature,
propagate by gemmæ.

[915] _See_ his excellent discussion on this subject in 'Nouvelles Archives
du Muséum,' tom. i. p. 151.

[916] Various physiologists have insisted on this distinction between
growth and development. Prof. Marshall ('Phil. Transact.,' 1864, p. 544)
gives a good instance in microcephalous idiots, in which the brain
continues to grow after having been arrested in its development.

[917] 'Compte Rendu,' Nov. 14, 1864, p. 800.

[918] As previously remarked by Quatrefages, in his 'Metamorphoses de
l'Homme,' &c., 1862, p. 129.

[919] Günther's 'Zoological Record,' 1864, p. 279.

[920] Sedgwick, in 'Medico-Chirurg. Review,' April 1863, p. 454.

[921] Isid. Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. i., 1832, pp.
435, 657; and tom. ii. p. 560.

[922] Virchow, 'Cellular Pathology,' 1860, p. 66.

[923] Moquin-Tandon, 'Tératologie Veg.,' 1841, pp. 218, 220, 353. For the
case of the pea, _see_ 'Gardener's Chron.,' 1866, p. 897.

[924] Müller's 'Physiology,' Eng. translat., vol. i. p. 407.

[925] _See_ some remarks to this effect by Sir H. Holland in his 'Medical
Notes,' 1839, p. 32.

[926] This is the view taken by Prof. Häckel, in his 'Generelle
Morphologie' (B. ii. s. 171), who says: "Lediglich die partielle Identität
der specifischconstituirten Materie im elterlichen und im kindlichen
Organismus, die Theilung dieser Materie bei der Fortpflanzung, ist die
Ursache der Erblichkeit."

[927] In these remarks I, in fact, follow Naudin, who speaks of the
elements or essences of the two species which are crossed. See his
excellent memoir in the 'Nouvelles Archives du Muséum,' tom. i. p. 151.

[928] Godron, 'De l'Espèce,' 1859, tom. ii. p. 44, &c.

[929] Journal Proc. Linn. Soc., 1858, vol. iii. p. 60.

[930] 'The Quarterly Journal of Science,' Oct. 1867, p. 486.

[931] M. Rufz de Lavison, in 'Bull. Soc. Imp. d'Acclimat.,' Dec. 1862, p.
1009.

[932] 'Races of Man,' 1850, p. 315.

[933] 'Travels in Peru,' Eng. translat., p. 177.

[934] Youatt on Cattle, 1834, p 200: on Pigs; _see_ 'Gard. Chronicle,'
1854, p. 410.

[935] 'Die Pflanzen der Pfahlbauten,' 1865.

[936] Morlot, 'Soc. Vaud. des Scien. Nat,' Mars 1860, p. 298.

[937] Rütimeyer, 'Die Fauna der Pfahlbauten,' 1861, s. 30.

[938] Godron, 'De l'Espèce,' tom. i., 1859, p. 368.

[939] 'Géographie Botan.,' 1855, p. 989.

[940] Pickering, 'Races of Man,' 1850, p. 318.

[941] 'Journal of a Horticultural Tour,' by a Deputation of the Caledonian
Hist. Soc., 1823, p. 293.





       *       *       *       *       *





Corrections made to printed original.

p. iii. "APPEARANCE WITH ADVANCING AGE": 'ARPEARANCE' in original.

p. vi. "SLIGHT CHANGES SUFFICIENT": 'SUFFICENT' in original.

p. 61. "bearing in mind what has been said": 'bearnig' in original.

p. 78. "not attached to any particular period": 'particuliar' in original.

p. 243. "it permits innumerable individuals to be born": 'permitts' in
original.

p. 294. "liable to complete absorption": 'absortion' in original.

p. 297. "found that when the animal was compelled ...": 'found than ...' in
original.

p. 318. "branches in a rudimentary condition": 'rudimentry' in original.

p. 384. "force themselves into a minute orifice": 'into' was printed on
next line in original, after 'must'.




