ERRATA.

Page 12, lines 16 and 17, for one hundred read three hundred and for

one thousand read six hundred.

Page 17, line 2, dele first letter in the line.

Page 168, line 12, page 177, lines 13 and 14, and page 271, line 10, for

Lemna tnsulca read Spirodela polyrMza.

Page 209, line 2 of foot-note, after hut insert represents.

Page 2;'56, line 7, and page 266, line 19: snoioi n. s. has been shown to

be hieroghjijhka, (^.

Page 257, insert as line 8 as follows: -ken to the office produced young
in ten days. The

Page 272, line 13, for P. higuUatus read Pompiliis higuttatus.

Page 278, Plate Y., 16, after view insert as follows: a, mentum; 6,

labial rudiment; c, maxillary palpi; d, maxilla; e, labrum; /, antenna; g,

eye; h, mandible.

Page 286, line 11, drop initial the one line.

Page 386, line 1, for Comstocki read Comstock.

Page 399, line 17, for specimens read specimen.

Page 411, line 10, for Michaelson read Michaelsen.

Page 441, line 3 from bottom, for 66 read 68.

Page 445, line 10 from bottom, for 57 read 5S.

Page 466, line 1 from bottom, for Cyima read Oypris.



Article l'X..—Some Notes on the Brain and Pineal Struo

tares of Polyodon folium. By H. Gakman, Lexing-

ton, Ky.

Some time about 1888 the writer of these uotes made
several dissections of the brain of this interesting- fish

and drawings of them were made by Magnus Westergren,

at that time Artist of the Illinois State Laboratory of

Natural History. Other duties have until recently pre-

vented further prosecution of the study, but I have

now to present some of the results of a reexamination

of these dissections, kindly placed in my hands by Pro-

fessor Forbes, together with some facts gained by a
study of fresh material obtained by me from the Ohio

River. For purposes of comparison I have dissected out

the brain of our common sturgeon {Acipenser rubicuiv-

ckis).

As in other sturgeons, the brain of Polyodon folium is

enclosed by a thick cartilaginous cranium. It rests on
the floor of a cavity which it only partly fills, the space

above being partly occupied by fatty tissue, but that

part dorsal to the mid-brain being almost entirely

empty. As if to make up for the deficiency of padding

about the brain, the fore- and raid-brains are enclosed

in a tough whitish fatty tissue of considerable thick-

ness, which can only be removed by the exercise of great

care, so closely and tenaciously does it adhere. A
peculiar feature of the brain when first exposed is a
dense black fat which encloses the hind-brain and fills a
large space surrounding the base of the spinal cord

where it leaves the medulla. I have seen nothing just

like it in other fresh-water fishes.

The olfactory nerves are very large, indicating that

the sense of smell is an important one to the shovel-

fish. Each nerve is separated, from its origin on the



Brain and Plu'^il Structures of Polyodon folium. 299

walls of the olfactory lobe, into two divisions, with

some eliiiht iutermiuolins; of fibers at the base. The

divisions lie parallel at first, but separate completely

at about the middle of their course, and before reach-

ing the nasal sac each divides into a number (seven

were counted) of small diverging branches passing into

the walls of the sac. One can see in the olfactory nerve

of Acipenser ruljicundus an indication of doubleness, but

in Polyodon it is carried much further, the divisions

being independent except for the slender fibers which

cross from one to the other at the base. The nerves

have a very slight upward turn as they pass out to the

fiac.

The olfactory lobe is well developed in both Poh'^odon

and A. rubicundu^, but is not a conspicuous part of the

brain in either fish. To ordinary inspection it looks

like a slight enlargement of the base of the olfactory

nerve. It contains a ventricle of large relative size

which communicates with the ventricle of the fore-brain.

The fore-brain presents no outward trace of double-

ness. When viewed from above it is oval in general

shape, widest at about the middle, and is obtusely

angulate medially in front. Viewed from the side it is

seen to rise above the level of the olfactory lobes. It

appears not to be so well developed in Polyodon as in

Acipenser. The division commonly termed the thala-

raencephalon can hardly be said to exist, though the

constriction of the brain at this region and the positions

of the epiphysis and hypophysis definitely locate it.

The ventral wall of the fore-brain bears two large, lobed,

white, basal ganglia which encroach a good deal upon

the ventricle. The front extremity of each lies opposite

the opening into the ventricle of the olfactory lobe. A
membranous dorsal sac is present which communicates

freely posteriorly with the cavity of the fore-brain. It

is not as conspicuous in Polyodon as in our sturgeon,

and is not perceptible from without except as its out-



300 Illinois State Lahyratorij <>f Natural Ilhtory.

line is roughly inrlicatod in alcoholic specimens by col-

lapse of its dorsal wall, which usually gives rise to a«

depressed area on the posterior dorsal surface of the fore-

brain. In frout of the dorsal sac the dorsal wall of the

fore-brain, viewed from within, pi-esents a slight median
ridge, while anteriorly, between the olfactory lobes, is a
sliglit membranous fold, these being the only indication

of separation of the cavity of the fore-brain into two
ventricles. The fore-brain of A. ruhlcimdus shows a sim-

ilar but, I think, somewhat larger trace of a septum
between the halves of this division of the brain. The
lateral wall of the fore-brain of Polyodon is provid-

ed within with thin vertical plicae, resembling those on
the inside of the dorsal membrane of the fourth ventricle.

Arising from the dorsal wall of the brain at the junc-

tion of the fore- with the mid-brain is a slender white

filament having the appearance, to ordinary inspection,,

of a nerve. At first it is concealed by the dorsal wall of

the dorsal sac. By reflecting this wall it appears run-

ning along the ventral side of the wall as a whitish line.

It emerges to the exterior near the anterior extremity

of the dorsal sac and extends thence obliquely upward
and forward to the cartilaginous cranium, where it passes

into a special channel, along the middle of which it ex-

tends in a direct course nearly to the surface. In a fish

which must have been about 3% feet long, the end organ

to which this filament passes lies about 1.66 mm. from

the outer surface. The stalk expands as it enters the

end organ. It is enclosed throughout its course in a
membranous sheath, which gives it an appearance of

being larger than it really is. It is accompanied by small

blood vessels which supply the walls of the passage and
eventually give small capillary vessels to the end organ.

The end organ is also enclosed in a sheath continuous

with that surrounding the stalk. From the surface of

the sheath radiate numerous small slender fibers (mus-

cular?) which pass to the walls of the cavity in whicli



Brain and Flneal Structures of Polyodon folium. 301

the organ lies, and thus serve to keep it in place. Some of

the fibers arise from the dorsal face of the sheath of the

end organ. The essential part of the organ, within the

sheath, looks, on ordinary examination with a low-power

objective, like a small whitish nervous ganglion. It is

somewhat slipper-shaped viewed from the side, but a
dorsal view shows it to be a little depressed, with the^

dorsal side slightly convex. The outline is roughly oval

in shape, viewed from above. In the specimen studied

most carefully there was a slight rounded anterior

projection. From my recollection of some sections pre-

pared by me at the Illinois Laboratory, and of a draw-

ing of one of them made by Mr. Westergren, I can say

that the organ contains a cavity, but presents nothing

which could be regarded as a lens. The stalk and end

organ are sometimes accompanied by pigment, but

may show only a slight trace of it. as indicated in my
outline figure (Fig. 9) of these structures. In one exam-
ple studied pigment was much more abundant than in

the rest, and was accumulated beneath the end organ

somewhat as it is back of the e^-es of Vermes and
Crustacea.

The channel in which the stalk and end organ lie is in

one of the shovel-fish* examined 18.5 mm. in length,

and has an average diameter of about two millimeters.

Distally it enlarges somewhat, and is rounded at its ex-

tremity. A system of smaller passages ramifying in the

cartilage of the cranium is in communication with it.

In one of my specimens the cavity about the end organ

is more enlarged than in the others and a small passage

leads through the cartilage above to the exterior. The
passage was plugged with connective tissue similar to

that constituting the skin which overlies the cartilage

above the end organ. In another example studied I

found no trace of an opening to the exterior. Unfortu-

nately I neglected to examine thoroughly, wit^h reference

• This fish was not less than threo feet Jong.



302 Illinois State Laljoratory of Natural History.

to this point, two other examples dissected, but I am
disposed to think such passage could not have been pres-

ent in them, else it would have caught my attention.

From the outside the position of the end organ can be

made out at once in Polyodon by the presence of an
elliptical foramen* in the bony exoskeleton which covers

the cartilage of the head. It shows as a depressed area

when undisturbed, and is occupied by skin in which one

can see with a magnifier uniformly distributed pigment

specks. In one of my specimens the foramen measures

7 mm. in diameter and 19 mm. in length. It extends

lengthwise with the cranium, and lies between the eyes.

I can see no change in the character of the skin imme-

diately over the end organ, which lies beneath or a trifle

posterior to the center of the foramen. When the skin

occupying the foramen is removed the cartilage under

it is seen to be gently convex; and when the surround-

ing bony exoskeleton is also taken away the region is

still perceptible, owing to this convexity and to the dif-

ferent color and greater translucency of its cartilage,

through which, by close looking, one can see the end

organ. The adjoining cartilage is of a more opaque

whitish cast. The thickness of the cartilage and skin

together just above the end organ measures in one of my
examples 1.75 mm., of which each tissue constitutes

about one half. The end organ in this specimen lies 0.50

mm. beneath the cartilage, and measures about one

millimeter in diameter, excluding the enclosing sheath.

In Acipenser rubicundus the pineal structures are in gen-

eral much like those of Polyodon. In this fish the stalk

is concealed at first beneath the wall of the dorsal sac and
reaches the roof of the brain proper at the same point

a.s in Polyodon. It is accompanied into the channel in

*The foramen is completely surrounded by the "frontal" bones of Collinge
(Quar. Jour. Mier. Science, Vol. 36, 1894, pp 499-537). These bones are not sep-
arate at the middle line, as represented by this author, but moet both in
front and behind the foramen, so that the median bone, the "dermo-
ethmoid," is excluded from the foramen in front. Collinge may have described
the bones of an immature example; otherwise the difference between his ac-
count and my own indicates considerable variation.



Brain and Pineal Structures of Pohjodon folium. 303

tlic caniUigp bv an exteiKsion of the dorsal sac, which

<aii be followed rather more than half the distance to

the end organ. The stalk is, however, throughout its

course an entirely independent .structure, and is made
conspicuous by the blood vessels accompanying it, the

blood supply here being apparently greater than in

Pol3'odon. The end organ lies close under the carti-

lage, but not quite so near the surface as in Polyodon.

The cartilage over it, in one example studied, is 1.50 mm.
thick. I found no opening through the cartilage, and

the bony exoskeleton of the head, which is here about

2 ram. thick, is without a foramen.

The end organ in A. ruhicundus is somewhat different

from that of Polyodon. The stalk in its sheath expands

gradually at its distal extremity and forms an elongate-

obovate or club-shaped organ which is not firmly sus-

pended like that of Polyodon by elastic bands. It meas-

ures 2 mm. in length and has a diameter of 0.66 mm.
near its extremity. A system of minute blood vessels

ramifies over the surface of its sheath in such profusion

that one cannot help thinking that the organ must be

functional. No pigment is apparent about it.

Whether these end organs are to be considered eyes or

not they certainly are entirely independent not only of the

lateral line system, but of all other nervous structures.

In both of these fishes the slender stalk has a very

direct and evident course from its origin on the roof of

the brain to its end organ, and without receiving or

giving off branches expands in the substance of this

terminal enlargement. If its present condition is taken

into account one must conclude that the structure is,

or has r-ecently been, an important sense organ to the

sturgeons.

The infundibulum is very large in both Polyodon and

jI. rubicundu.'i. It opens freely above into the posterior

part of the fore-brain. The cavity extends well down
into the organ, but the hypophysis itself, though



304 Illinois State Laboratory of Natural History.

somewhat hollowed out within, is a compact, solid, whit-

ish body. The saccus vascidosns, also of large size, is

noticeable from its dark color. It is completely hollo\^

,

and its cavity communicates with that of the infundi-

bulum. In A. mhicundus there is on each side of the in-

fuudibulum a conspicuous oval swelling, which dissection

shows to be a thin-walled sac or pouch opening widely

into the cavity of the infundibulum. In Polyodon this

swelling is scarcely evident.

The optic nerves are small in Polyodon, as would be

expected from the small size of the eyes. They are of

larger relative size in our sturgeon.

The mid-brain is a compact rounded mass of small

size, whitish in color when the pigmented connective

tissue is all removed, and without any decided outward

trace of separation into two lobes. There is a very

slight median impression in front, but beyond this the

mid-brain shows little appearance of doubleness, either

inside or out. In A. ruhicimdus this division of the

brain is more extensively and deeply impressed along

the dorsal middle line, but even in this fish the mid-

brain is a single structure with one undivided cavity.

Its ventricle is occupied in part by an extension of the

cerebellum, called by Goronowitsch the valvula cerehelli.

The oculo-motor nerve arises on the ventral side of

the mid-brain close to its junction with the hind-brain.

The trochlear nerves are exceedingly small and slender,

and their origin is so concealed by the adjacent struc-

tures and so covered up by connective tissue that one

must follow them up with care in order to find where

they leave the roof of the brain. Both nerves, in both

Polyodon and A. ruhicundus, seem to arise at the dorsal

middle line, and originate so close together that they

look like a single nerve passing over the roof of the

brain and joined to the latter at the middle line. In the

sturgeon there is a small whitish lunate swelling just in.

front of the point where they leave the brain.



Brain and Pineal Structures of Polyodon folium. 305

The hind-brain is the largest division of the brain in

Polyodon. It is large also in Acipenser ruhicundus, but

the disproportion is not so groat in the latter. In the

shovel-fish it is, in front, more than twice the width of

the mid-brain. The extensive fourth ventricle is com-

pletely covered dorsally by a thick, tough, black epi-

thelial membrane, with strongly plicate inner surface.

When this membrane is removed the ventricle is seen to

be widely open and bounded largely by the conspicuous

restiform tract. The lobe of the cerebellum, already

mentioned as the valvida cerebelli., can be seen extending

into the ventricle from the front, its forward extension,

already noted, occupying the posterior part of the ven-

tricle of the mid-brain.

The trigeminal group of nerves, arising from the lateral

wall of the medulla, is made up of three well-defined parts

in Polyodon. The most anterior division is a slender

nerve* about as large as the oculo-motor, which extends

obliquely outward and forward, crossing over the oculo-

motor and pasting out towards the snout. It seems to

be throughout entirely independent of the other divisions

of the fifth nerve. The second division is much larger

and, arising just behind the first, extends outward and

forward, parallel with the first, until it joins the third

division. The latter is the largest division of the three,

and arises from the restiform tract, some distance be-

hind the second division and well up on the side wall of

the medulla. At first it extends downward and forward,

then outward over the large second division.

The seventh nerve (facial) looks in Polyodon like a
posteriorly directed branch of the trigeminal. It arises

from the side of the medulla beneath the third division

of the fifth, with which it is at first very closely bound

up, extends forward and outward, and then turns ab-

ruptly backward, leaving the fifth at once.

*llamu5 opihalmicus superflcialis, according to Collinge.



306 Illinois State Lahoratory of JSatural Ilhtory.

The auditor^' (eighth) is a strong nerve \vhi(.'h arises^

just behind the facial and on a level with it, but is com-
pletely independent. It divides into two branches at

once, and these subdivide before being distributed to the

ear.

A considerable space separates the ninth nerve (glosso-

pharyngeal) from the eighth. It is slender in Polyodon,

and extends backward parallel with the spinal cord at

first, lying beneath the tenth nerve (vagus), so that it is

not visible from above. A short distance posterior to

the medulla it turns outward and then becomes distin-

guishable.

A slender nerve arises above the ninth and extends

back over it to the side of the tenth with which it joins

and merges, though not entirely losing its identity as

far as followed. I take this to be the lateral line nerve.

Near its origin it exchanges fibers with the ninth.

One of the largest cranial nerves in Polyodon is the

vagus, although it is not as large as in A. i^hicundnis.

It arises well back on the side of the medulla, on a level

with the nerves just mentioned. Its fibers separate into

bundles where it joins the medulla, of which I count

eleven, the two hindmost being smallest and turning-

abruptly out of the general course to join the medulla.

The sixth nerve (abdueens) I have not studied in Poly-

odon. In A. rubicundus it is very small, and arises by
two roots near the ventral middle line, about midway
between the eighth and ninth nerves.

Further explanation may be left to the figures accom-

panying these notes.

Looking at the brain of Polyodon as a whole, and as

compared with that of the sturgeon and other fishes,

it may be said that it impresses one as that of a fish

of inferior rank, although the peculiar snout and other

features of the anatomy speak of a somewhat special de-

velopment. The large relative size of the medulla oblon-

gata and the undivided and poorly developed fore- and



Brain and Pineal Stiiictures of Polyodon folium. 307

mid-brains justify this impression, as do the condition

of the pineal structures and their relation to the exterior.

The brain of A. rvhicundus is certainly that of a more

active and intelligent fish. The corresponding nerves are

larger in the sturgeon; its fore-brain is larger relatively;

the mid-brain is larger and with an evident suggestion

of doubleness; the medulla is smaller relatively; and,

finally, the pineal end organ is less evidently placed and

surrounded to receive impressions from without.

EXPLANATION OF FIGURES.

Plate I.

Fig. 1. Side view of brain and pineal structures of

Polyodon as they appear when the cartilage is cut away
from one side. Natural size, Magnus Westergren del.

Plate II.

Fig. 2. Dorsal view of brain of Polyodon, with the

connective tissue and fat removed from the fore- and

mid-brains and the cerebellum, but with membrane roof

of 4th ventricle left in place. A, nasal sac ; B, olfactory

lobe; C, pineal stalk; D, fore-brain; I, mid-brain; J, cere-

bellum; M, medulla oblongata; O, spinal cord; 1, olfac-

tory nerve; 3, oculo-motor nerve; 10, vagus nerve.

From a photograph.

Plate III.

Fig. 3. Dorsal view of brain of Polyodon. B, olfac-

tory lobe; C, pineal stalk; D, fore-brain; I, mid-brain;

J, cerebellum ; K, valvula cerebelli ; L, restiform tract

;

0, spinal cord; P, part of membrane roof of medulla

oblongata, turned aside; 1, olfactory nerve; 2, optic

nerve; 3, oculo-motor nerve; 4, trochlear nerve; 5, 5, tri-

geminal nerves; 7, facial nerve; 8, auditory nerve; 9,

glosso-pharyngeal nerve; 10, vagus nerve. H. Ga/rmmh

del.



308 JJlinois State Lahoratory of Natural History.

Fig-. 4. The glosso-pharyugeal and vagus nerves, com-

pletely uncovered and drawn apart so as to show the

lateral line nerve at E. JI. Garman del.

Fig. 5. Side view of brain of Polyodon turned so as

to show the infundibulutn. F, hypophysis cerebri; G,

saccus vasculosus. Other letters and figures as in Fig. 3,

H. Oarman del.

Plate IV.

Fig. 6. Side view of brain of Acipenser rubicundus. B,

olfactory lobe ; C, C, pineal stalk terminating distally in

the pineal end organ ; D, fore-brain ; E, infundibulum

;

F, hypophysis cerebri ; G, saccus vasculosus ; H, swelling

on side of infundibulum; I, mid-brain; J, cerebellum; M,

medulla oblongata; 0, spinal cord: 1, olfactory nerve; 2,

optic nerve; 3, oculo-motor nerve; 4, 4, trochlear nerves;

5. 5, origin of trigeminal nerve; 7, origin of faciahnerve;

8, origin of auditory nerve; 9, origin of glosso-pharyngeal

nerve; 10, origin of vagus nerve. The small enclosed

area connected with 10 by an arrow, marks the origin

of the lateral line nerve, a part of 10. II. Garman del.

Plate Y.

Fig. 7. The exposed channel in which the pineal end

organ and its stalk lie in Polyodon. A, aperture to the

exterior. (The skin covering the cartilage has been re-

moved.) B, end organ; C, cut end of stalk. 11. Gar-

onan del.

Fig. 8. Pineal end organ and a part of its stalk in

Polyodon, removed from the channel in cartilage, and

the end organ turned so as to show the surface presented

to the exterior. A, end organ enclosed in sheath and
with part of the elastic bands remaining attached; B,

cut end of stalk. H. Garman del.

Fig. 9. Pineal end organ and stalk of Polyodon shown
in place. A, end organ; B, cut end of stalk; C, sheath



Bi'dln and Pineal Structures of Polyodon folkim. 309

enelosing stalk; D, line representino- boundary of channel.

II. Garman del.

Fio-. 10. Pineal end organ and stalk oiAcipeiuer rubi-

curulu^. Letters as in Fig. 9. //. Garman del.

Plate >^X1.

Fig. 11. Part of the bony exoskeleton of head of

Polyodon, with the elliptical foramen under which the

pineal end organ lies. Natural size. From a photograph.