a

JOURNAL

OF

MORPHOLOGY:

EDITED BY

C. O. WHITMAN,

With the Cooperation of

EDWARD PHELPS ALLIS, Jr,

MILWAUKEE.

Vien ae

BOS TOW:
GINN & COMPANY.
1889.

II.

|i

IV.

II.

CONTENTSHOP VOLT,

—————— ->-- ——_———
No. 1.— July, 1888.

FREDERICK TUCKERMAN, M.D., Amherst, Mass.
Observations on the Structure of the Gus-

tatory Organs of the Bat (Vespertilio
subulatus) 5

E. D. Cope.
On the Tritubercular Molar in Human
Dentition

C. O. WuiTMaAn, Director of the Lake Labora-
tory, Milwaukee, Wis.
The Seat of Formative and Regenerative
Energy .

Pror. HENRY FAIRFIELD Osporv, Princeton Col-
lege.
A Contribution to the Internal Structure of
the Amphibian Brain

Dr. WILLIAM PaATTEN, Assistant in the Lake
Laboratory, Milwaukee, Wis.
Studies on the Eyes of Arthropods

No. 2. — November, 1888.

Henry V. Witsovn, Fellow of the Johns Hopkins
University.
On the Development of Manicina Areolata,

Joun M. CLARKE.
The Structure and Development of the Vis-
ual Area in the Trilobite, Phacops Rana,

PAGES

I-6

7-26

27-49

51-96

97-190

IQI-252

Green . : 5 : : , » 253-270

{Whi

IV.

fT,

ITy,

CONTENTS.

R. W. SHuFeEtpt, M.D., C.M.Z.S.
Further Studies on Grammicolepis Bra-
chiusculus, Poey .

Eo COPE:
On the Relation of the Hyotd and Otic
Elements of the Skeleton tn the Batra-

chia

R. W. SHuFELDT, M.D., C.M.Z.S.
On the Affinities of Aphriza Virgata

No. 3.— April, 1889.

CHARLES-SEDGWICK Minot, Harvard Medical
School, Boston, Mass.
Uterus and Embryo: 1. Rabbit; I. Man,

EDWARD PHELPS ALLIS, JR.
The Anatomy and Development of the
Lateral Line System in Amita Calva.

Pror. A. E. DotBeEar, College Hill, Mass.
On the Organization of Atoms and Mole-
cules

C. O. WHITMAN.
Some New Facts about the Hirudinea

Dr. WILLIAM PATTEN.
Segmental Sense-Organs of Arthropods .

PAGES

271-296

297-310

311-340

341-462

463-568

569-585

586-599

600-602

Volume II. Fuly, r88s. Number 1.

JOURNAL

OF

MOK PHOROGY.

OBSERVATIONS ON THE STRUCTURE OF WHE
GUSTATORY ORGANS OF THE BAT (Vesper-

tilio subulatus).

FREDERICK TUCKERMAN, M.D.,

' Amuerst, Mass,

THE present paper contains a description of the anatomy of
the taste organs of a single species of Chiroptera. It is highly
probable that further study of these organs in other species of
this interesting group of animals will reveal important varia-
tions, respecting both position and structural characters, from
the results embraced in this short memoir.

It will be of interest first to notice briefly the form and gen-
eral appearance of the tongue of this mammal.

GENERAL DESCRIPTION OF THE TONGUE.

The organ measures 13.5 mm. in length, its greatest transverse
diameter is 5 mm., and at its thickest part it measures 4 mm.
Anteriorly, it is free from the floor of the mouth for 6 mm., or
nearly half its length. The upper posterior surface is slightly
convex, and has a nearly uniform breadth. In the anterior half
of the organ the lateral margins gradually converge, blending at
the tip in a slightly rounded or pointed extremity. The upper
surface of this portion of the tongue is marked by several sub-
parallel, transverse rugze or folds, with corresponding depressions
between them. These folds decrease in size as they approach
the anterior extremity of the organ, and cease altogether at
1.5 mm. from its apex. The dorsal surface is unmarked by any

2 TUCKERMAN. [Vot. II.

median groove or raphé, except at the extreme posterior region.
Here there is a wide and rather deep mesial groove, 2 mm. in
length, beginning in front of the epiglottis and terminating
midway between the two circumvallate papillee.

In one of my specimens, near the line of union of the poste-
rior and middle third of the tongue, is a rounded eminence,
showing a tendency to a raised posterior part, as seen in the
tongue of the Rodentia. This feature, however, is wanting in
other tongues of Vesfertzlio which I examined.

The upper surface, including the lateral margins, is covered
with closely-set tactile and mechanical papilla, the points of
which are directed backwards and inwards.

The fungiform papillz are only fairly numerous, and are dis-
tributed with some degree of uniformity over the dorsal surface
and upon the sides of the tongue. Posteriorly they terminate
in front of the gustatory area, and they cease anteriorly a short
distance from the tip. Those scattered over the anterior third
of the dorsum are usually larger than those occurring elsewhere.

On each lateral half of the tongue, 2 mm. from the base, is
situated a circumvallate papilla. The two papille are placed
quite near the median line, the distance between them being
only 0.6mm. They are oval in form, of nearly equal size, and
are placed obliquely to the long axis of the tongue, their anterior
extremity being directed outwards.

A papilla of similar type to those just mentioned, but less
developed and apparently in a transitional stage, is present at
the posterior limit of each lateral border. Further investigation
will be necessary to determine whether these papille are con-
stant or not. In the specimens which I have examined I have
always found them, although exhibiting striking variations in
form, general appearance, and structure, from normal circum-
vallate papillae. No papilla foliata was found.

The under surface of the tongue is perfectly smooth. Ante-
riorly there is a median ridge, with sloping sides, extending from
the fraenum to the tip.

GUSTATORY STRUCTURES.

The Circumvallate Papille. — These papilla show no indica-
tions of lobation. Their upper surfaces are rounded, and they
measure 0.30 mm. in their transverse diameter, and are 0.22 mm.

No. 1.] GUSTATORY ORGANS OF THE BAT. 3

in height. Where they join the tongue, the transverse diame-
ter is only 0.12 mm. Each papilla is encircled by a rather shal-
low and very wide trench. In some sections this extreme width
of the trench (as shown in Fig. 1) is confined to its upper part,
the lower portion curving beneath the papilla and becoming
quite narrow. The ridge surrounding the trench, and forming
its outer wall, has elongated tactile papillae projecting from its
surface (Fig. 1). The general surface adjoining this gustatory
area is covered with large and small papillz, quite symmetrical
in arrangement, but presenting a great variety of forms. Serous
glands are fairly numerous in the gustatory area, but none were
found within the papillary body itself. The ducts of the serous
glands open into the trench at its base and sides. The papilla
at its upper part bears many secondary papilla, the depressions
between which are filled by the epithelium. The nerves are
chiefly non-medullated and ramify throughout the papilla, but I
was unable to trace their terminal branches with any distinct-
ness. The large ganglion described by Poulton! in the circum-
vallate papilla of Pevameles, and observed by me? in the cir-
cumvallate papilla of F7der, I failed to detect any indications of
here. -

The two lateral circumvallate papillz are asymmetrical, the
right one being much less developed than the left. The latter,
as seen in vertical section, is elliptical in shape, and joins the
tongue by a narrow pedicel. The trench which surrounds this —
papilla is very wide at its upper part, and narrow and of uni-
form breadth at its lower. Serous glands are sparingly scattered
through this region, and are entirely wanting within the papil-
lary body.

The taste-bulbs are not very numerous in the circumvallate
papilla of Vespfertzlio. They are disposed at the sides in a girdle
of seven or eight tiers, the uppermost tier being nearly on a
level with the top of the trench. From horizontal sections,
made at different levels, I estimated the average number of
bulbs in a tier at fifty. If we allow for eight tiers, we shall
have four hundred bulbs for each papilla. I did not succeed in
finding bulbs in the epithelium investing the upper surface of
the papilla, nor was I able to detect them in the outer wall of

1 Quart. Journ. Micr. Sci., Vol. XXIII., 1883, p. 73.
2 Journ. of Anat. and Physiol., Vol. XXII., 1888, p. 136.

4 TUCKERMAN. [Vot. II.

the trench. The bulbs vary somewhat in shape, and in point
of size they are the smallest I have yet observed, the nearest
approach to them in this respect being those of the circumval-
late papilla of the mouse. They vary in length from 0.025 to
0.030 mm., and their breadth is about 0.015 mm. Usually in a
bulb of this area, the diameter of the peripheral end of the bulb
exceeds that of the central. The latter is also curved slightly
downwards. This form of bulb I have not observed before,
although it is seen in those figured by Loven in the circumval-
late papilla of the calf. I did not succeed in finding a bulb
with the peripheral processes of its gustatory cells projecting
beyond the pore. One bulb (in vertical section) shows a fissure,
0.015 mm. long and 0.0015 mm. wide, caused by a separation of
the edges of two adjoining peripheral cells.

I was unable to isolate the central or gustatory cells of the bulbs
sufficiently well for study, but the peripheral cells do not differ
materially from those already described in the taste organs of
other mammals. They are elongated, slightly flattened, nucle-
ated cells, with their two extremities tapering gradually to a
point.

The number of bulbs in the left lateral circumvallate papilla
could not be estimated from my sections with any degree of
accuracy. The most noteworthy thing about them in this
region is their very unusual arrangement (Fig. 3). They occur
only on one side of the papilla; but here they form a continu-
ous chain, seventeen tiers deep, extending from the base of the
papilla nearly to its summit. Bulbs are likewise present in the
lower half of the outer wall of the trench. Here I counted
eight tiers. The bulbs of this region measure 0.024 mm. in
length and 0.015 mm. in breadth, being thus a little smaller than
those of the normal circumvallate papilla.

The Fungiform Papille. — These papille are distributed quite
regularly over the dorsum and sides of the tongue, from the
gustatory area nearly to the tip. Interspersed among those of
the posterior part of the dorsum are a few which appear to
be undergoing transition to the circumvallate type of papilla
(Fig. 6).

In several instances taste-bulbs were present in the epithe-
lium at the upper part of these papillae. They are usually
placed vertically, directly in the long axis of the papilla. By

Non: ] GUSTATORY ORGANS OF THE BAT. 5

far the most interesting specimens (which are shown in Fig. 6)
were found in a papilla from the posterior region of the tongue.
In this papilla there are two well-formed bulbs, and placed
between them is a third, which is either of a low order or unde-
veloped. The largest bulb of the three measures 0.036 mm. in
length and 0.016 mm. in breadth, and its apex appears to reach
the free surface of the epithelium, its base penetrating the
mucosa. Some of the isolated bulbs met with elsewhere in
these papillae, particularly those of the anterior dorsal surface,
are even larger than those shown in Fig. 6. Neither serous nor
- mucous glands were observed near the fungiform papillz.

The entire upper surface of the tongue is covered with papillz
of mechanical and tactile (?) function. They are quite closely
set, except at the basal region, are largest at the posterior part
of the dorsum, and gradually decrease in size as they approach
the anterior extremity. These papilla, when near the tip, en-
large slightly again. One from the posterior third of the tongue
measured 0.11 mm. in height and 0.04 mm. in breadth. Behind
the circumvallate papilla, and also about the tip, are numerous
rather coarse, retroverted, conical papillae. Each papilla is
seated upon a single papillary upgrowth of the mucous mem-
brane, and is invested by epithelium of a uniform thickness.
The outer layers of epithelium covering the upper surface and
sides are usually partly, and occasionally wholly, cornified.
These papillae vary much in shape and general appearance.
Many of them are cone-shaped, while others resemble, in ex-
ternal structure, minute fungiform papillae. The upper surface
is now and then flat or slightly convex, but usually the papilla
terminates in a retroverted, horny spinule.

1 Figure 7 represents a vertical section through a fungiform papilla, from the ante-
rior dorsal surface of the tongue of a pig, containing eight taste-bulbs.

6 TUCKERMAN. [VoL. Il.

EXPLANATION OF PLATE I.
List OF REFERENCE LETTERS.

c.e. Columnar epithelium. g.. Gustatory pore. g/. ad. Duct of serous gland.
m.m. Mucous membrane. Z. Elongated papilla. f. e. Pavement epithelium. 2. £.
Papillary processes of mucous membrane. ». Ridge. s. e. Stratified epithelium.
s. p. Secondary papillz. ¢. Trench. 7. 4. Taste-bulb. 7. 6’. Taste-bulb of outer wall
of trench. 7¢. 4.’ Taste-bulb undeveloped or of low type.

Fic. 1.— Vertical section through one of the circumvallate papillz. (x 100
diam.)

Fic. 2. — Vertical section through the base of the same papilla, showing over-
hanging side with four lowermost tiers of taste-bulbs. (Xx 480 diam.)

Fic. 3. — Vertical section through the left lateral circumvallate papilla. (xX 125
diam.)

Fic. 4.— Horizontal section through the lower part of one of the circumvallate
papillz, representing the taste-bulbs arranged ina zone. /. d. Ducts of the serous
glands which open into the trench at this level. (xX 160 diam.)

Fic. 5.— Vertical section through a fungiform papilla of the mid-dorsal surface of
the tongue, showing a single taste-bulb at its upper part. (XX 400 diam.)

Fic. 6.— Vertical section through a fungiform papilla of the posterior dorsal sur-
face of the tongue, which is probably undergoing transition to the circumvallate type.
(X 480 diam.)

Fic. 7.— Vertical section through a fungiform papilla of the anterior lateral dor-
sal surface of the tongue of a pig. (X 200 diam.)

Journ. Morph. Vol.It.

Cf Hall, del

”

sahil

Pik

Pe Nee
PAL an .
ft

bil
he

ON THE TRITUBERCULAR MOLAR. IN| HUMAN
DENTITION.

E. D: COPE:

Descriptions of the molar teeth of man, given by anato-
mists, differ in important respects. Thus, F. Cuvier (‘ Dents
des Mammifers’’) states that, while the crown of the first
superior true molar consists of four tubercles, those of the
second and third superior true molars consist of but three
tubercles. In the American edition of ‘“Sharpey and Quain’s
Anatomy” it is stated that the crowns of the superior true
molars of man consist of four tubercles; and the same state-
ment is made in Allen’s late work on human anatomy.

My observations having shown me that both of these descrip-
tions apply correctly to certain types of dentition, I determined
to examine for myself, to ascertain, if possible, the extent and
value of the variations thus indicated. My interest in the sub-
ject had been especially stimulated by the researches among
the extinct mammalia, and the results which I had derived
from them. These are, in brief, as follows: first, the quad-
ritubercular type of molar crown, illustrated by the first supe-
rior true molar of man, belongs to the primitive form from
which all the crest-crowned (lophodont) molars of the hoofed
placental mammals have been derived; and second, this quad-
ritubercular type of molar has itself been derived from’a still
earlier, tritubercular crown, by the addition of a cusp at the
posterior internal part of it. This tritubercular molar in the
upper series has given origin directly to the superior secto-
rial teeth of the creodonta and carnivora. In the inferior
series, I have shown that in known placental mammalia at
least, the primitive molar crown is quinquetubercular, or tritu-
bercular with a posterior heel; that this form gave origin to
the inferior sectorial tooth of carnivora by modification, and to
the quadritubercular type — corresponding to the superior quad-
ritubercular crown —by a loss of the anterior inner cusp and

8 COPE. [Vo. II.

connecting crest. And from the quinque- and quadrituber-
cular types of molar crown, the various specialized types of
the ungulates have been derived.

Considerable significance, therefore, attaches to the question
as to whether the superior true molars of Homo sapiens are
quadritubercular or tritubercular. The inferior molars are
also either quadritubercular or quinquetubercular; but less
significance attaches to this modification than to that of the
superior true molars. This is owing to two facts; viz., the
fifth tubercle is not the anterior inner which completes
the anterior triangle of the primitive inferior molar, but is
a median posterior, such as is not uncommon in mammalia
of Puerco and Eocene age; and second, because this tuber-
‘ cle is of quite small size, and is therefore more liable to
variation from insignificant causes.

In the nearest allies of man, the anthropoid apes, the supe-
rior true molars are quadritubercular, the posterior internal
tubercle of the last or third molar being usually smaller than
in the other molars in the chimpanzee. The inferior molars
are quinquetubercular, in the human sense, the gorilla not
infrequently adding a sixth lobe on the external posterior
margin of the crown. The molars of both series are quad-
ritubercular, with an occasional posterior fifth in the inferior
molars in the Cercopithecidz and Cebidz, excepting the
genus Pithecia of the latter, where the superior molars are
tritubercular. The superior molars of the Hapalidz are tri-
tubercular. In the Lemuridz the second and third, and fre-
quently the first, superior true molars are tritubercular. In the
Tarsiidze the superior true molars are tritubercular throughout.
The superior molars of the extinct lemuroids differ, like those
of the recent forms. Thus, in Adapis and its allies they are
quadritubercular, but in Necrolemur they are tritubercular. In
Chriacus (whose reference to the Lemuroidea is uncertain) they
are tritubercular, as is the case, also, with Indrodon. In Anap,
tomophus they are of the true tritubercular type. This is the
genus of Lemuroidea, which in its dental character most nearly
approaches the anthropoid apes and man. I have elsewhere?
pointed out that the formula is I. - Cc. ; Pm. =; M. ; The
canines are small, and there is no diastema in either jaw.

1 Report U. S. Geol. Survey, Terrs., F. V. Hayden, Vol. II1., 1885, p. 245, Pl.
xxv. fig. 10, and Pl. xxive. fig. 1.

No. 1.] TRITUBERCULAR MOLAR. 9

It may be readily seen, in consideration of these facts, that
the appearance of tritubercular superior molars in the genus
Homo constitutes a reversion to the lemurs, and not to the
anthropoid apes or to the monkeys proper. And among lemurs
the reversion is most probably to that type which presents the
closest resemblance to Homo in other parts of the dentition.
The genus which answers most nearly to this requirement
among those at present known, is Anaptomorphus.

Figure 1.—Two species of Anaptomorphus. Fig. a, A. evulus, lower jaw from
above X2. Figs. 4, c, d, A. homunculus; 6, c, natural size; d, 3 natural size. Both
Po

4

from Eocenes of the Rocky Mountains.

In studying the dentition of man, I have examined the crania
contained in the following six collections: those of the Academy
of Natural Sciences of Philadelphia; of the Army Medical Mu-
seum of Washington; of the College of Physicians of Philadel-
phia; of the University of Pennsylvania; of the Boston Society
of Natural History; and of my own museum. The first of these
is especially valuable on account of the negro, Egyptian, and
Hindu crania it contains. My acknowledgments are due to the
Board of Curators, of which Professor Leidy is chairman, for the
opportunity of studying it. I am also indebted to the Boston
Society of Natural History, and its learned curator, Professor

10 CORE. PVOL. Hie

Hyatt, for the opportunity of examining Hindu and Chinese
crania in their museum. The collection of the Army Medical
Museum at Washington is especially important on account of
the Kanakas, Esquimaux, Peruvians, and North American In-
dians which it possesses. I am under great obligations to its
distinguished director, Dr. J. S. Billings, for the facilities which
he placed at my disposal. The museum of the Philadelphia
College of Physicians contains the collection made by the late
Professor Hyrtl of Vienna, of crania of Eastern and Mediterra-
nean Europeans. In this department it is unrivalled, and I am
greatly indebted to the council of the college, and its curator,
Dr. Guy Hinsdale, for the opportunity of examining it. Some
French skulls in the University of Pennsylvania were of value
in the investigation. My own collection, though small, contains
a number of Maoris, Australians, Tahitians,! and North Ameri-
can Indians, which have proved to be of importance. Of Eng-
lish and Europeo-American crania, I have been able to examine
but few of what might be termed the thoroughly amalgamated
race. Of the latter there are probably many crania in the war
collection of the Army Medical Museum, but how free the race
of each may be from foreign intermixture, of course it is impos-
sible to know. In selecting such as are supposed to be “stock
Americans,” those of persons with English names have been
preferred, although many now true Americans are of German
ancestry. In order to increase the list of this class of examina-
tions, I have imposed on the forbearance of my friends by fre-
quent inspections of their dentitions in ove aperto.

I suspect that the characters thus obtained will prove of im-
portance in a zodlogical and ethnological sense. They have
been already found to be of great fixity, and hence significance,
in the lower mammalia. The only reason why they should be
less so in man is, that the modification in reverting to the
tritubercular molar is a process of degeneracy, and may be hence
supposed to be less regular in its action than was the opposite
process of building up, or addition of the posterior internal
cusp. Some justification for a light estimate of its value may

1 For the Maori and Australian skulls, I am indebted to Mr. Speechey Gotch of
Melbourne; and for the Tahitians to Dr. Chassaniol, Chef de la departement de Santé
de Taiti, of Paris. My best acknowledgments to these gentlemen are hereby ex-
pressed.

No. 1.] TRITUBERCULAR MOLAR. II

be found in the following tables. But it must be remembered
that it is not always possible to determine exactly the race of
the person represented by a skull, even when care in its identi-
fication has been exercised. Emigration and war have con-
stantly rendered races impure, and transplantation on a large
scale has in some parts of the earth produced hybrid races. The
results of a study of human crania are sure to be more or less
vitiated by these circumstances. We obtain averages rather
than exact definitions. Nevertheless, the extremes of the series
of variations are likely to be found to be characteristic of estab-
lished forms of man, and will thus justify my belief in the value
of the characters presented. To ascertain the relation of these
variations to the races is the object of the present inquiry.

The cause of the tritubercular reversion belongs to the class
of agencies active in evolution of organic types, of whose real
nature we know little. It cannot be said to be due to a con-
traction of the maxillary arcade, for the Esquimaux and some
other peoples which display the tritubercular dentition are not
deficient in this respect. Nor do tritubercular molars require
less space than the quadritubercular, for the external width of
the crown is the same in both cases. They generally require
less material however than a quadritubercular crown, since a
triangle is smaller than a square drawn on the same base line;
however, in some men of the lower races who present the tritu-
bercular molars, their outline is nearly square. The hypothesis
advanced to account for the reduction of the number and quality
of human teeth observed in the higher races, as well as for the
replacement of the prognathous jaw by the orthognathous, is
that such changes are due to a transference of material and of
growth energy from these parts to the superior part of the skull
and its contents. The relative superiority of the dimensions of
these parts in the higher races is thus accounted for.

In the following tables the tubercular formule are represented
by numbers. Only the last three, or the true molars, in each
jaw are considered. Tubercles of reduced size are represented

by fractions. Thus eae indicates that each superior molar
is quadritubercular, and each inferior molar quinquetubercular.
This represents the extreme of the series represented by the
4a 3
A 44

lowest races. The formula

indicates that the true molars

12 COPE. [VoL. lI.

have four, three, and three, tubercles respectively, and that the
inferior true molars have four each. This represents the ex-
treme common among the higher races. In the table which
follows, the numbers attached to crania in the respective collec-
tions are appended, and initials indicating the collection follow.
Thus A. M. M. refers to the Army Medical Museum, Washing-
ton; C. P., the College of Physicians of Philadelphia; U. P.,
the University of Pennsylvania; B. S., the Boston Society of
Natural History; E. D. C., my private collection; no initials
follow the numbers of the Academy of Natural Sciences of
Philadelphia.

4-4-4

Meg re

Malay! of Madura, *1339; Malay, 425 ; Negroes, 63 and 258, C. P. ;

S. Sea Islander, 86, A. M. M.

4-4-4
5 a ara
Malays, 47 and 433 (latter of Sumbawa) ; Negroid Egyptians, 43,
798, 852*, 869.

4-4-4
4-4-4
Malay, 1338 (of Amboyna).
4-4-4
is

Tahitian, E. D. C.; Kanakas, 143 and 1308, C. P.; Malay, 425
(Java) ; Negro, 963; Hindu, 1070, B.S.

dices
paeie roy)
Marquesas Ids., 1531, C. P.; Greek of the Morea, 55, C. P.
I ory Sa Si)
Si our ee
Peruvian, 932 (Arica).
A Aa ee
ama an

Malay, 430 (Amboyna) ; Italian, 114, C. P. (Elba) ; Peruvian, 2300,
A. M. M.

1 Just what is meant by the “ Malays” of the Philadelphia Academy collection
I do not know.

No. I.] TRITUBERCULAR MOLAR. 13

Yeni ea 3
Broan ©
Negro, 4122, C. P.; Kaffir, 13585 Pessahs, 1095-*7; Gipsy, 31,
C. P.; Montenegrin, 29, C. P.; Tablunka, 106, C. P. ; Germans, 1063-4
(Tiibingen) ; Feejees, 292-3, A. M. M.

4—4— 3%
?

Australian, E. D. C.; Tahitian, E. D. C.; Negroes, 901, 903, 914,
920, 921, 927, 964; American Negro, 980, A. M. M.; Chatham Ako
1557, A. M. M.; Peruvians, 68, 452; 2 N. Amer. Indians, E. D. Cxs
Ponka India, 487, A. M. M.; Comanche, 6563, A. M. M. ; Sicilian,
110, C. P.; Esquimaux, 1859, A. M. M.; French, 1579, A. M. M.;
Anglo-Americans (Wilderness Battle-Field, Va.), 6305-6-7, A. M. M.;
Kanakas, 286, 434, and 584, A. M. M.; Hottentot, Be Ss

A Aer
Die core
Madagascar, two (Hovas) ; Samoan Id.; N. Amer. Indians, 1345
(Lipan), and Hudson’s Bay Ind.; Mexican, 714 (Ancient) ; Peruvians,
72, 1373, 1465 ; Italian, 118, C. P.; Lombard, 117, C. P.; Czech, 131,
C. P.; German, 239, C. P.

roa Seg)
ew arghe NG
N. Amer. Indians, 530 and 1804 (Pawnees), A. M. M.
A483
aaa. O

Italians, 2 (Giurgevo and Piedmont), C. P. ; Gipsy, 18, C. P.; Ural,
33, C. P.; Bulgar, 94, C. P.; Slav, 84, CyB:

4 Sie 3
5 ena
N. Amer. Indian (Spokane), E. D. C.; Italians, 46 and 47 (Terra-
cina and Ragusa), C. P.; Albanian, 123, C. P.; Viennese, 9 59, Cre:

Aa Aes
4—4—4
Negroid Egyptian, 885 ; Swede, 1549.
A= AS 8
?

2 Tahitians, E. D. C.; Kanakas, 291, 451, 455, 570, 588, 844, 1057,
A. M. M.; Chatham Id., 5721, A. M.M.; Esquimaux, 1232, A.M. M.;
N. Amer. Indian, 380 (Chippewa), A. M.M.; ? Anglo-Americans, 5721,

14 COPE. [VonvIL

32654, 6785, A. M. M.; Jew, 3, C: P.; Rouman, 96, C.PoeiChinese,
Sagi. Os) (EO, Te 7e BS.
oe maa
f

Kanakas, 79, 280, 283, 421, 423, 427, 431, 457, 463, 599, 709, 862,
A. M. M.; Chinese, 958, 5130, 5139, A. M. M.; Peruvian, 1765 (An-
con), A. M. M.; Peruvian, 2302, A. M. M.; S. Sea Islander, 344,
A. M. M.; Indian of Yucatan, 629, A. M. M.; Mojave, 209, A. M. M.;
Hindu, 123, B. S.

A Ota
A Aur
Circassian, 762.
4 — 33 — 33
STE Gate
Negro, 1343 (Archipelago) ; American Negro; S. German, 1289.
Mama Bagh
Dh 4 Fic

- N. Amer. Indian, 1794 (Ute), A. M. M.; Hindu, *1344, Bengal ;
Gipsy, 98, C. P.; S. German, 1158, Italians, 2, 8, and 109 (Tessino
and Roveredo), C. P.; Greek, 53 (Cephalonia), C. P.; Bosniak, 100,
CoP:; Cossackienh Don; cor, ©.50.

A 3h = 35
OSS od
Patagonian, 1232 (last infer. mol. 44) ; Negro lunatic, 55.
Weephis Aue
=)

African Negroes, 580, 685, 902, 917; Kanaka, 861, A.M. M.; Ameri-
can Negro, 411, A. M. M.; Peruvian, 1326; 2 N. Amer. Indians,
E. D. C.; Mound Builders, 1049-1123, A. M. M.; Piegan, 6486,
A. M.M.; Cheyenne, 5560, A. M.M.; ? Anglo-Americans, 2, A. M. M. ;
Esquimaux, 1182, 1194,1250; Hollander, 9 10,C. P.; Hindu, 124, B.S.

Mises ee
DONS
Malay, 1340 (Macassar), 1341 (Java) ; Finn, 1539 ; Czech, 79, C. P. ;
Wirennese,/61,)\C.P. 3 French. Ws Ps

/ pemesr
aa inh
Algerine, 3900, C. P.; Uskoke of Banjaluka, 90, C. P.; Styrian, 85,
C.'P. ;’ Hindu, 432; Latin, 115, 'C. P.; Albanian, \o7,"C. Rae nGermean
of Siebenbiirgen, 76, C. P.

NO.;1-] TRITUBERCULAR MOLAR. 15

Ai Brr3
bo 4a A
Hungarian, 14,C. P.; Russian, 35,C. P.; Australian, (1327) ; Negroes
(Benguela), 421, (Mozambique), 423; Hottentot, 1351; Aztec; Cir-
cassian ; Moravia, 9 135, C. P.; Croat, § 134, C. P.; Galician, 139,
COPS; Serb;.96, iC. P..s * Pizgau? Go C.P. > Saltzbure, 65, C..P.

4 aais 3

ee ae
Swedes, 1487-50.

43h = 3

? ? ?

Negro (Dey), 1100; Peruvian; Kanaka, 576, A. M.M.; Dutch, 434;
Malay, 39; Bengal, 20, A. N.S.; Hindu, 1330; Fellah, 999; Kabar-
dine Caucasus, 38, C. P.; Ital. Piedmont, 45, C. P.; N. Amer. Indians
(Flathead), E.D.C., (Cheyenne), 6525, A.M. M., (Ponka), 486, A.M.M.,
(Sioux), 9 2049, A. M. M.; Mound Builders, 169, A. M. M.; Esqui-
maux, 1183, 1189, 1245, A. M. M.; ? Anglo-Americans, 6847, 5922,
A. M. M.; German, 1066; Chinese, 879, B. S.

de Se
?
Kanakas, 564, 569, 571, 591, A. M. M.; Peruvian, 2308, A. M. M.;
Arucanian, 970, A. M. M.; Chuktchi, 277, A.M. M.; Esquimaux, 1779,
A. M. M.

AS 3h
?
Chukchi, 263, A. M. M.
Ae Se 3a
?
? German-American, 6445, A. M. M.
ATONE SO.
Bee ame

Dalmatian, 132, C. P.: Greek (Trieste), 56, C. P.; Indians (Santa
Barbara, Cal.), 3.

‘ire OS
Sea ae
Gipsy, 130, C. P.; Trieste; 120,,C..P.; Apache, 1168, A. M. M-
Aly) onan
5 4p 4s

Modoc, E. D. C.

16 COPE. [VoL. II.

1 Rep & RAS)
Sra eater
Druse, 122, °C. P.; Idria, 89, C. P.; ‘Carniola, $7,,1C. Pees. siyrol
121, C. P.; Paris, 3916, U. P.; 4 Anglo-Americans, E. D. C.; French,
867 (Paris), U. P., 1620, A.M.M. Kurd, 28, C. P.; Thug Hindu,
128 (A. N. S.); \ Esquimaux, 676 (trace of 5 on 2 and 3) ; Italian
(Calabria), 48, C. P.; Greeks (Candia), 54 and 51, C. P.; Slovak,
v2. C. P.; Czech, 4,:C. P.; ‘Lithuania,/9 25, Cooke bokovina. 90 ae,
CG. Ps Tyrol,"9'67, CC. P. 5. Upp: Austria, 625. B) ivorayia, Goi e
Hollander, 9, C. P.

4 Saree
Yay aaa) =
“Krakuse” ((Czech or Pole, large), $2,0C. P. 3) * Kumanie!” i(riiaun-
gary), 71, C. P.; Pole, 24, C. P. 5. Volhyman p26, C2. Me odolanve
C. P.; Hindu (Bengal), 1344; Tatra (large), 83, C. P.; Wallach, 95,
Ge Ps. French; 105 55U.P-

A ai nea
4-4-4

Tchuktchi; Zagrebin, 126, C. P:; Croat, 77, C. P.; Mixed German
and Croat, 17, C. P.; French, 1082; do., 1801, A. M. M.; Anglo-
American, 1108.

Coe Ieee)
?

Peruvian, 1478; do., 2299, /A: ‘M. M:; Turkish ‘grave; a2%) 1G. Pos
Crimean, 34, C: P.; \Cossack, 132.4) Ruthenian, 103, /C. P.; Armeman
99, C. P.; Esquimaux, 675, 679, .A..N. S.; Esquimaux, 12r1,\ 1258,
L219, 1206, 1221, 1225, 1226, 1230, T2321, 124%, 1244, F250, L278, E7or,
1782, 2113, A.M. M.; Chuktchis, 256-7, A. M. M.; N. Amer. Indians,
5550 (Pawnee), 6561, 6565 (Comanches), 7023 (Cheyenne), 170,
(Mound Builder), A. M. M.; Kanakas, 580, 841, A. M. M.; Indians
of Yucatan, 626-628, A. M. M.; American Negroes, 981-983 (Rich-
mond, Va.), 6615 °(S. Carolina; m. 2 on one side is 33); 6 Anglo-
Americans, E. D. C.; ? Anglo-Americans, 95, 6305—6—7-8, 6640, 739,
2699, 1768, 5116, 5145, 5708 9, 5940, 6550, A. M. M.; Hindu, 425,
leASe

hase Span

44 a
Hungarian, 15, C. P.

No. I.] TRITUBERCULAR MOLAR. 17

Neolithic Man.

Through the kindness of Mr. Thomas Wilson, honorary
Curator of the Department of Prehistoric Anthropology in the
United States National Museum, I have had the opportunity
of examining a number of dentitions of men of the Neolithic
period of France. The best preserved of these includes both
series in place in both jaws, the last two inferior molars of one
side and the last inferior of one side being absent. This man
was disinterred from a cemetery on the island of Thinic, on the
coast of Brittany. Teeth of a considerable number of men, in
a separate condition, were obtained by Mr. Wilson from the
dolmen of Poulzongue, near the town of Gramat, in the depart-
ment of Lot, Central France, and have also been examined
by me.

Ai) 3,
445
The second superior molar is a perfect quadritubercular, while

the third is an equally perfect tritubercular, of somewhat
reduced size. This dentition is, then, exactly intermediate
between extremes. It is further advanced than that of the
lowest existing races, but has not reached the final modification
of the most specialized. The dental characters of the men of
Poulzongue vary between the type of the man of Thinic and
43 3,
444
molar plainly tritubercular, and perhaps as many have the

fourth tubercle imperfectly developed. But no indication of a
tritubercular first superior molar is observed, such as occurs in
a few Esquimaux. The resemblance of perhaps half of the
superior molars of Poulzongue to those of Esquimaux and
the more specialized Indo-Europeans is distinct. Pointing in
the direction of the latter, are the small size of the teeth and the
frequent occurrence of caries.

The dental tubercular formula of the man of Thinic is

the formula Several of them have the second superior

The Accessory Anterior Internal Tubercle.

This tubercle is characteristic of the genus Lemur (Fig. 11)
and some of its extinct allies. Such are the Chriacus pelvidens
and C. truncatus Cope, the former figured in Tertiary Vertebrata
(Report U. S.-Geol. Survey Terrs. III), Vol. XXIII, d, Fig. 7.

13 COPE. [Vot. Il.

I have found it well developed in the Malay (Fig. 2, aaz), No.
1339. It is present in three Tahitian crania in my collection,
and I have observed it in another Micronesian cranium, and
in some others. This character is decidedly lemurine, but
whether to be properly termed a reversion or not may be ques-
tioned in view of the fact that it always occurs, so far as yet
known, in dentitions most remote from that type in other
respects. It might be rather regarded as a survival or as a
character which has persisted from the “‘ protanthropos”’ which
was itself immediately derived from lemurine ancestors.

Anomalous dentitions.

I have observed the following examples of aberrant molars. In
an Esquimaux (A. M. M.) the formula of the superior molars of
one size is 3—4—0; in another (B. S.) it is 3—-3—4. Ina
French skull (A. M. M.) we observe on one side 4—4—3; on
the other side, 33—3—33. The posterior superior molar is, by
reason of its late and retarded development, the most liable
to exhibit abnormalities. Ina Tahitian skull in my collection,
it is tritubercular on one side and obtusely haplodont (conic)
on the other.

General Conclusions.

For clearer understanding of these characters, they are
arranged in the form of a table. Only the principal races are
represented, and hybrids, when determinable, are omitted.
The characters of the superior molar teeth only are referred to.
These are classified under four heads, viz.: first, tubercles
4—4—4); second, tubercles 4—4—34 or 4—34—34; third,
tubercles 4—34—3; fourth, tubercles 4—3—3. As already
remarked, the extreme types of the series give the most precise
‘indications of race, while the intermediate conditions have a
various range.

In the first table the most obvious results are, that only the
three lowest races present four tubercles on all the superior
molars, and that of those with tritubercular second and third
molars, Europeans and their American descendants greatly
predominate. Also that of uncivilized races, the Malays and

1 Mulattoes, Mestizoes, Half-breed Indians, Gipsies, etc., are omitted.

NOW i] TRITUBERCULAR MOLAR. 19

Negroes never, and Micronesians very rarely, present this type
of dentition, while in the Esquimaux it considerably predomi-
nates, examples of tritubercular first molars even occurring.

& P a
A |e uo) ros
Pe | telaee 3 I ae
a. ers [il aS) bl 45) cS S38
| STS AS A a iI * un .g
= Br | a fs Sy Bea | ok
a) = tata estas a |S] o 2 ut leas anced: Ih
me le 6 los |) oe ae1g2| Ss / 82 aa| a
A = a tare (aa cei Wee Sa ya laoreet
She UP ices Ee Batis pega tinge (lee etal ees lanier (pea) ees
alte (20) ae |4e/OS! B eo le aie
Doi ae A Oh aaa I 18
(4-4 —?) 13 2 Eig I 20
1
4—4 — 32)
Mesias Stic Te 28. \0 274). .Oy 2a Ee le Sui inOr (eae pees
4-4-3 J
1
5 Soe ames. 3 = 5 r ced labios z 3 | 24 | 45
Las eNom 2 2 3 | 19 | 56 | 90
Motaligaih: EON A429 MIA eat | RS rx) Zou EnGi son

I now give a table of the characters of the superior molars
in the Europeans and Europeo-Americans examined. The
number is not sufficient for final conclusions; nevertheless
there are some indications of value. Some of the one hundred
and nineteen dentitions examined are referred with doubt to
their respective races. Thus the Europeo-Americans may have
been in many instances immigrants, as many such left their
bones on the battle-fields of the American civil war, where
many of the crania were picked up. The supposed Germans
are largely Austrians, so that some of them may be more or
less Slavic or Magyar. Allowance for these would reduce the
number of tritubercular molars.

1Ten crania in the Museum of the Cincinnati Soc. Nat. History, mostly Mound-
Builders, have the formula 4—4— 3.

20 COPE, [ VoL: If

Ee

Z S .

ao] S oS 7)

a i Gi | ea Bae $5
D yi ae O24 | ME | SB as, ass a
ag BB g jas | eS | Es 5 Sa Nes
S.S Ss is} O° aes ole — 3 8 a)
ete | SO | Ba eee ea eames
Be, 2 3 2 I 3 II
A 35 3% Z 2 3 3 2 ro
Neon eee 5 Pa es 35) me
4—3+—-3 I I 6 2 3 8 I 2 24
4—3 —3 2 ged 4 7 6 6 20 56
otal ior I 3 25 7 23 22 8/320 119

As results we have the following: the tritubercular dentition
appears in II out of 25 Slavs; in 7 out of 23 Greeks and Ital-
ians ; in 6 out of 22 Germans and Scandinavians; in 6 out of 8
French; and in 20 out of 30 Europeo-Americans. The only
great race which presents a similar high percentage of trituber-
cular molars is the Esquimaux, where they occur in 21 out of
30 dentitions. The tendency is most marked in Slavs, French,
and Europeo-Americans, and is least marked in Greeks and
Italians and in Germans. The former subrace stands in the
series between the intermediate type of the North American
Indians and the other Europeans. In the Germans the number
with tubercles 4—34—3 is large. If these be added to the
number with 4 — 3 — 3, we have 16 out of 22.

It is important to remember in this connection that the dis-
tinguished ethnologist and archzologist, W. Boyd Dawkins,
affirms that the earliest inhabitants of Britain and some other
parts of Europe were Esquimaux. He refers especially to the
men of the caves, whose implements and arts he declares to be
identical with those used by the Esquimaux of the present day.?
As it is evident that the lemurine or tritubercular reversion
commenced with the Esquimaux, it may be that in some in-
stances at least its appearance in men of Anglo-Saxon and other
European races is due to inheritance alone. But it is also rea-
sonable to suppose that in this case as in other evolutions, the

1 Perhaps improperly included in this table.
2 Early Man in Britain, 1880, p. 233.

No. 1.] TRITUBERCULAR MOLAR. 21

cause which produced this modification of the Esquimaux den-
tition is still active, and its recent appearance in the most civil-
ized races must be due to this unknown cause. The progressive
character of the French dentition in this respect is in broad
contrast with the primitive character of that of Italians and
Greeks. The characters seen in the latter go far towards sus-
taining Professor Huxley’s hypothesis, that the dark Mediterra-
nean sub-races consist of a mixture of Egyptian with the Indo-
European stock.

In conclusion it may be stated, that the tritubercular superior
molars of man constitute a reversion to the dentition of the
Lemuridz of the Eocene period of the family of Anaptomorphi-
dz. And second, that this reversion is principally seen among
the Esquimaux and the Slavic, French, and American branches
of the European race. Observations on some of the races of
the Indo-Europeans are yet so imperfect that some additions to
the above list yet remain to be made, as for instance, probably,
the English sub-race. The neolithic dentitions examined are
intermediate between the two extremes, thus showing an ad-
vance over the lowest existing races.

The Origin of the Quadritubercular Molar.

This question has an interest beyond the history of human
dentition. I will now inquire whether any mechanical cause
can be assigned for the retention of the quadritubercular
structure.

It may be recalled ‘that I have shown that the development
of a fourth tubercle on the posterior side of the internal tubercle
of the tritubercular superior molar has been the origin of the
dentition of the non-carnivorous types, which are principally
Ungulata. The mechanical action of the inferior against the
superior molars cannot have been very different in the early
Ungulates from what it was in the early flesh-eaters, since the
canine teeth, which partly direct this motion,! are equally de-
veloped in both. But the history of the canines in the develop-
ment of the Ungulates is exactly the reverse of what it has been
in the flesh-eaters. In the former the canine has grown suc-
cessively smaller, and has been in most of the lines completely

1 See mechanical origin of the dentition of the carnivora, Proceedings American
Association Advanced Science, 1887.

22 COPE. [VoL. II.

aborted. Whence, then, has come this different history? It
has been probably partly due to the substances used as food.
The softer and often tougher animal tissues permitted the
shearing motion through their elasticity and extensibility carry-
ing the friction beyond the opposing transverse edges of the
crowns, vertically along their sides. The grains and vegeta-
ble substances, on the other hand, possess no such elastic
qualities, and are cut or broken by the approach of the edges
themselves. The pressure would be direct and brief, and not
a continued shear. Just how this would result in the devel-
opment of the fold on the posterior side of the crown of the
superior molar is a question of nutrition not yet explained by
actual observation; but it is generally observable, however,
that in dentition, folds of the surface have resulted from ordi-
nary use, not too severe. In the case of the shearing which
developed the carnivorous dentition, the animal used force to
cut the meat in the manner necessary to do it. This shearing
force is so great as to wear the crown, rather than to encour-
age growth. The temporary force required by the act of
crushing vegetable matters (excepting such as approach flesh in
their characters) is more of the nature of impact, and is of
very brief duration. The fourth tubercle has been the result,
and I have described its various complex derivatives elsewhere.!

Can it be possible that a largely, or exclusively meat diet has
been the mechanical cause of the development of the trituber-
cular molar in man? Its great predominance in the Esquimaux
suggests this explanation. The lower and quadritubercular
races are largely granivorous and frugivorous, but whether so
predominantly so as to restrain the modification in question, I do
not know. It is probable that the tritubercular molar expresses
a change which is both phylogenetic and physiological.?

1 In 1874, in the Journal of the Philadelphia Academy of Natural Sciences, I
homologized the various parts of the mammalian tooth-crown structures and traced
their phylogeny. The same was done about the same time by Kowalevsky. Not
being then familiar with the capacity of dense substances, as dentine and enamel,
to yield their form to continued strains, I did not pursue the question of the origin
of these forms through use in mastication, although I suspected such origin. This
was done in 1878 by Prof. J. A. Ryder, in an able paper on “The Mechanical Gene-
sis of Tooth-Forms,” Proceedings Acad. Phila., p. 45. With minor exceptions, I
have adopted the views there set forth.

? After I had nearly completed this investigation, I received during October of this
year (1886) the admirable monograph of Dr. Wortman on the dentition of the ver-

No. 1.] TRITUBERCULAR MOLAR. 23

tebrata. He describes human dentition more thoroughly than previous authors, and
refers to the tritubercular modification in the following language (p. 444): “The
superior molars, like those in the lower jaw, are three in number, and have quadritu-
bercular crowns normally, but many examples can be found in which the postero-
internal cusp, the last one added in the quadritubercular molar, is little more than a
cingulum, and is scarcely entitled to the appellation of a cusp.” And in a footnote
he observes, “It is probable that this condition, of which I have seen a number of
examples in the higher races, is a degenerate one, and is an effort to return to the
tritubercular stage.”

Dr. Wortman has, at my suggestion, examined a large number of Esquimaux crania
contained in the Army Medical Museum at Washington, which were not accessible
at the time of my visit to it. He confirms the value of the tritubercular second supe-
rior true molar as a race character.

The conclusions described in this paper are mostly embraced in a preliminary one
which appeared in the American Naturalist for November, 1886,

NoTre.—The discussion of the functional relation of the tritubercular to the
quadritubercular molar dentition on a preceding page, has reference to the early
mammalian types, and to the question of origin of the quadritubercular at that
period. The relations cf the parts of opposite jaws are different in the trituber-

cular races of men, since the interaction of the crowns in mastication is no longer
alternate but opposite.

24 COPE. [Vou. II.

EXPLANATION OF PLATE II.
FIGURES NATURAL SIZE.

Fic. 1. Chimpanzee, @ superior, 4 inferior molars. Mus. Academy Philadelphia.

Fic. 2. Malay of Madura, No. 1339, Mus. Academy Philadelphia. Superior
molars all quadritubercular, and m! with the lemurine (Fig. 13) accessory anterior
internal tubercle (badly represented by artist).

Fic. 3. Negroid-Egyptian (Morton), No. 852, Mus. Academy Philadelphia.

Fic. 4. Tahitian, without lower jaw. From Dr. Chassaniol, the colonial physi-
cian of Tahiti. Mus. E. D. Cope.
4 4 33
ae

Fic. 6. Neolithic man from Isle Thinic, Brittany; from collection of Thos. Wil-
son, Esq.

Fic. 5. Pessah, No. 1097, Mus. Academy Philadelphia. Formula

Journ. Morph.Vol. Il. Plate II.

ai aaj P!

TSINGLAIR & SON, LITH PHILA

1.SIMIA NIGRA. 2-6.HOMO SAPIENS

26 COPE. [Vou. II.

EXPLANATION OF PLATE III.

Fic. 7. Spokane from Rock Lake, Witman County, Washington Territory, of the
4 4 3
544

4 32 3
5 4 ot
Fic. 9. Swede, No. 1487, Mus. Academy Philadelphia. From Professor Retzius;

Kamaka tribe; collected by C. H. Sternberg. Mus. E. D. Cope;

bo

Fic. 8. Hindu of Bengal, No. 1344, Mus. Academy Philadelphia;

Fic. 10. Esquimaux of Greenland, No. 1221, A.M.M.

Fic. 11. Alaskan Esquimaux, No. 2669, A.M.M.

433
444
Fic. 13. Lemur collaris, Madagascar. Mus. E. D. Cope. Superior molars tritu-

Fic. 12. Europeo-American, No. 1108, Mus. Academy Philadelphia;

bercular with accessory anterior internal tubercle.

LETTERING.

ae, anterior external tubercle; fz, posterior external; az, anterior internal; 2,
posterior internal; aaé, accessory (lemurine) anterior internal tubercle.

Journ. Morph.Vol. Il. Plate Ill.

Be Be pe

pe Uae rh

T.SINCLAIR & SON, LITH. PHILA,

7-12.HOMO SAPIENS.13.LEMUR COLLARIS

rea b
Y ruta? *;

- ” eh. =
7 ee ad
». ‘ i.
‘
- **
: cae
ha
' i
ay
.
j
* +
y

THE SEAT OF FORMATIVE AND REGENERATIVE
ENERGY.

Cc. O. WHITMAN.

THE question as to the role of the cytoplasm, presents itself
under two forms:

1. Is the cytoplasm a passive body, moving only as it is acted
upon by external forces, or in response to influences emanating
from the nucleus?

2. Or does it behave rather like an organized body, endowed
with subtle powers of its own, and capable of automatic as well
as responsive action ?

There is a strong tendency at the present time to refer all
kinetic changes in the cytoplasm to the agency of the nucleus,
and to ascribe to the former the passive role of a nutritive sub-
stance. The kinetic phenomena of the egg during maturation
and impregnation have already been considered in their bearing
on this important question.!. A number of decisive proofs of
pure nuclear action were pointed out, and at the same time an
attempt was made to support the opinion that the cytoplasm is
capable of automatic as well as responsive action. The present
paper is chiefly devoted to the consideration of phenomena dis-
played in the cytoplasm, and to the discussion of the question,
whether the regenerative and formative power of the cell resides
in the nucleus or in the cytoplasm, or in both taken as a highly
complex physiological unit.

The Doctrine of Isotropy. — Pfliiger’s interesting experiments ?
with the amphibian egg to determine the influence of gravitation
upon the direction of cleavage-planes, led him to conclude that
the entire egg is “zsotropic.” In other words, to quote from the

1O6kinesis. Yourn. Morph., 1., 2, p. 227, December, 1887.
2 Ueber den Einfluss der Schwerkraft auf die Theilung der Zellen. Arch. f. d. ges.
Physiologie, XXXI., pp. 311-318, and XXXII, pp. 1-79. 1883.

28 WHITMAN. [Vot. II.

author, “the fertilized egg possesses absolutely no essential rela-
tion to the later organization of the animal, no more than a snow-
flake stands in any essential relation to the size and form of the
avalanche which under certain conditions develops from it.
That the germ always gives rise to the same form, is due to the
fact that it is always brought under the same external condi-
tions.” Immediately after the appearance of Pfliiger’s papers,
it was pointed out by Agassiz and Whitman & that, “if gravita-
tion were the sole guiding agency in cleavage, its effect ought
to be zustantaneous, and it should be possible to change the
direction of a cleavage-plane already in progress.” It was also
shown that the /zme required to bring about a transposition
of the third cleavage-plane, suggested a corresponding internal
transposition of the active protoplasmic matrix of the ovum, tn-
cluding of course the nucletz, “If a body constituted like the
ovum is restrained by artificial means from taking its normal
position, a redistribution of material must immediately set in and
continue until the equilibrium is restored. The active portion
of the ovum, having a lower specific gravity than the passive
nutritive elements, would eventually recover its normal position,
and thus the virtual axis of the ovum would inevitably right
itself in spite of the inability of the ovum to rotate bodtly.”
Later observations have fully verified these suggestions.

As now maintained by Born,* Hertwig,® Weismann,® Kolliker,?
and others, the cytoplasm alone is isotropic, while the nucleus is
the seat of the directive and form-giving power in development.

In this modified form, the doctrine of isotropy makes a much
nearer approach to truth, but I believe that it is far from correct
in its estimate of the functional importance of the cytoplasm.

The logical consequences of this view are clearly presented
by Oscar Hertwig® (p. 306) in the following words: “Az dite
Kernsubstanz also sind die Krifte gebunden, durch welche die

3 On the Development of some Pelagic Fish Eggs. Proc. Amer. Acad. Arts &
Sciences, XX., p. 40, 1884.

4 Biolog. Untersuch. Arch. f. mik. Anat., XXIV., 1885.

5 Das Problem der Befruchtung und der Isotropie des Eies. Yenatsche Zeitschrift,
XVIIL., 1885.

§ Die Continuitat des Keimplasma’s als Grundlage einer Theorie der Vererbung.
1885.

7 Die Bedeutung der Zellenkerne fiir die Vorginge der Vererbung. Zedéschr. f.
wiss. Zool.. XLII., 1885.

No. 1.] REGENERATIVE ENERGY. 29

organisation des Thieres bestimmt wird.... Es erscheint
gleichgiiltig, ob bei der ersten Thetlung der eine Kern sich mit der
sogenannien avtmalen, der andere mit der vegetativen Dottersub-
stanz umhiillt oder ob betde Kerne sich in vegetative und animale

Dottersubstanz in dieser oder gener Weise theilen.... Der
Dotter ist nicht so organtsirt, dass aus einer bestimmten Portion
desselben cin bestimmtes Organ hervorgehen miisste.”’ It is con-

ceded (p. 304) that the cytoplasm may have a low grade of
organization; but it is an organization that changes from
moment to moment (p. 309), not a “feste Organisation’ bear-
ing fixed relations to the future organism.

The opposing view finds the differentiating and formative
principle either in preformed elements of the cytoplasm (“ Ahysz-
ological molecules’”’ Lankester, “polarized molecules” Pfliiger,
“7dioplasma’’ Nageli), or in a definite organization of the
cytoplasm itself (Van Beneden and others). “Though the
substance of a cell,” says Lankester® (p. 14) “may appear
homogeneous under the most powerful microscope, excepting
for the fine granular matter suspended in it, it is quite possible,
indeed certain, that it may contain already formed and individ-
walized, various kinds of physiological molecules.” And again,
“The development of one kind of cell from another kind is
dependent on internal movements of the physiological molecules
of the protoplasm of such cells.”

Van Beneden® has made a thorough study of the struc-
ture of the egg of Ascaris megalocephala with a view to
ascertaining if “les plans de symétrie de l’embryon ne se
trouvent pas déja préformés dans ]’ceuf lui-méme et si l’un des
traits les plus caractéristiques de l’organisation de l’espéce,
la symetrie qui la distingue, ne se trouve pas déja indiquée
dans l’ceuf. L’ceuf d’un animal a symétrie bilatérale au-
rait-il, comme l’animal dont il provient et qu’il doit devenir,
une extrémité antérieure, une extrémité postérieure, une face
ventrale, une face dorsale, une droite et une gauche? les
matériaux qui doivent servir a édifier la moitié droite du
corps siégent-ils dans la moitié droite de l’ceuf et la substance

® Notes on Embryology and Classification. London, 1877.
® Recherches sur la maturation de l’ceuf et la Fécondation. Arch. de Biologie, IV.,
2 & 3, 1883.

30 WHITMAN. [ VoL. II.

de la téte ne se trouve-t-elle pas concentrée en un point deéter-
miné du corps ovulaire ?”

Both views recognize the necessity of assuming that the
course of ontogenetic development is in some way predeter-
mined in the egg; but while one finds the force motrice in the
nucleus, the other would locate it in the cytoplasm. The ad-
vocates of the former appeal to the so-called isotropy of the
cytoplasm, to the conspicuous part played by nuclear bodies in
fecundation and cleavage, to the incapacity for regeneration
shown by enucleate fragments of infusoria, etc. ; while the sup-
porters of the latter insist on the constancy of premorphologi-
cal relations (axial relations, relation of first cleavage-plane to
the median plane of the future embryo), the remarkable struc-
tural features exhibited in some eggs, cleavage in planes not
previously marked by karyokinetic division, etc. The truth
appears to me to lie on both sides, the error consisting only in
unduly exaggerating the relative importance of one or the other
factor. Just now the weight of authority seems to be turning
in favor of the first view, a result which must be attributed very
largely to the influence of recent discoveries and theories re-
specting the nature of fecundation. The question is one of
such fundamental importance, that it seems desirable to analyze
closely the facts bearing on the subject. It is for this reason
that I have dwelt more at length on the movements of the
germinal vesicle and the pronuclei.

Especially important is the study of the structure of the egg,
and the modifications which it undergoes during the period of
maturation. One of the most important contributions in this
direction is unquestionably Van Beneden’s great work on Asca-
ris. No other biologist has yet gone so deeply and thoroughly
into the subject, nor has any one discussed it with a keener
appreciation of its theoretical importance. Such well-marked
structural features as are claimed to exist in this egg are incon-
sistent with the idea that the cytoplasm is isotropic.

Polar Rings. — Among the more extraordinary examples of
cytokinesis may be mentioned the polar rings in the egg of Clep-
sine, first described by Grube” (pp. 15-16), and recently more in
detail by Robin # (pp. 97-105) and Whitman ® (pp. 20-29, 39-41).

19 Untersuchungen ueber die Entwicklung der Clepsinen. Kénigsberg, 1844.

1 Mémoire sur le Développement embryogénique des Hirudinées. Paris, 1875.
12 The Embryology of Clepsine. Quart. Your. Mic. Sci., July, 1878.

No. I.] REGENERATIVE ENERGY. at

Although it is by no means certain that the hyaline protoplasm
of these rings is not in part derived from the germinal vesi-
cle, it is quite clear that the phenomena are very different
from the polar phenomena attending the division of the first
cleavage-nucleus. These remarkable exhibitions of polarity in
the cytoplasm appear early in the pronuclear stage, and con-
tinue not only during the centripetal march of the pronuclei but
even after the first cleavage-nucleus has entered upon its
kinetic phases of division. Thus we have two distinct series of
polar phenomena in progress at the same time, one displaying
ttself in the cytoplasm, the other in the nucleus. We cannot
suppose that the cytokinetic series is dependent upon the karyo-
kinetic series for two reasons: first, because the former begins
earlier than the latter ; and second, because such cytokinetic dis-
plays are unknown in other eggs. The second ground would
also hold against referring them to pronuclear influences. AI-
lowing that it may yet be possible to demonstrate that these move-
ments originate in response to pronuclear influence, it would
still be very difficult to believe that they are sustained through-
out by the continuous action of the same agency. It would be
altogether more probable, as a little reflection will show, that
the movements once started are capable of maintaining them-
selves, independently of the inciting cause.*

Cytokinetic Phenomena. — The cytoplasm exhibits a great vari-
ety of changes and conditions, variously described as ‘polar
concentration,’ ‘radiating bands,’ ‘ waves of contraction,’ ‘zonal
constrictions,’ ‘automatic cortical layer,’ ‘amoeboid movements,’
‘phases of segregation,’ ‘astral radiations,’ ‘rhythmic contrac-
tility,’ ‘migratory movements,’ ‘crown of folds’ (Faltenkranz),
‘autonomic movements’ (rotation, circulation, pulsation), etc.

While some of these phenomena might, with considerable
reason, be claimed as purely cytokinetic, most of them are so
intimately associated with karyokinetic activity that they must
be explained, either as the direct result of the latter, or as the
effect of impulses generated by the interaction of nucleus and

* The polar and parapolar circles described by Van Beneden (No. g) in the egg of
Ascaris, are not comparable with the polar rings of Clepsine. For the ‘ disque
polaire’ arises before, and disappears with, the penetration of the spermatozoon;
the polar rings (Clepsine), on the contrary, appear after the penetration of the
spermatozoon, and are not wholly dissipated until after the completion of the first
cleavage.

32 WHITMAN. [ Vou. II.

cytoplasm. The hypothesis of reciprocal action is not incom-
patible with the opinion that the conditions of this action are
furnished, in the first instance, if not continuously, by changes
of a chemical or molecular nature, which arise quite indepen-
dently, either in one factor alone, or in both. The source of
the initiatory impulse would still be an open question. Our
knowledge of the phenomena above designated is too incom-
plete to furnish a key to the solution of this problem. For
the purpose we have in view, it will be sufficient, therefore, to
refer to a few of the more important examples, in which each
factor may be supposed to play a more or less important part,
deferring the discussion of the main question until we come to
consider phenomena of a more decisive nature.

Following the penetration of the spermatozoon into the
ovum, various forms of contraction in the vitellus have been
observed; and these are generally regarded as the effect of
impulses generated by the spermatic element. The usual
sequence of events certainly accords very well with this view,
but there are one or two facts which should make us hesitate to
accept it. In some aquatic animals, in which the sexual cells
unite before ovipositing, the time of these contractions bears
no constant relation to the time of union, but does bear such a
relation to the time of contact of the egg with water, whether
this contact be brought about artificially or in the natural
course of events. Still another cogent reason for not ascribing
these contractions to the zwdependent action of the male pro-
nucleus is found in the fact that similar, though more sluggish,
movements may, in some well ascertained cases, be induced by
placing unfertilized eggs in water. The most general of these
movements is the flattening of the pole, and the gradual con-
traction of the whole vitelline sphere, resulting in the forma-
tion of a perivitelline space.

The Constriction Attending the Exit of the Polar Globules. —
The flattening of the pole is attended, or followed, in some cases,
with a very remarkable constriction, which, beginning in the
equatorial zone, travels towards the animal pole, finishing up with
a nipple-like protuberance, from which the first polar globule is
expelled. The exit of the second polar globule is sometimes pre-
ceded by a similar but weaker constriction. This constriction
has been observed (No. 12, p. 18) in the eggs of different species

No. 1I.] REGENERATIVE ENERGY. 33

of Clepsine ; and the same, or a closely analogous constriction,
has been described by Kupffer and Benecke! (p. 19) in the egg
of Petromyzon, and by Ransom !* (pp. 463, 464, 477, 479) in the
egg of the Stickleback and some other fresh-water teleosts.

This constriction has been confounded by the last mentioned
authors with yolk-contraction, and brought into connection with
the formation of the perivitelline space (‘ breathing-chamber ’ of
Ransom, ‘ Eiraum’ of Kupffer and Benecke). This space prob-
ably results from contraction of the vitellus as well as from
expansion of the egg membrane, but the constriction is a
special act of the vitellus to expel the polar globule. The elim-
ination of polar globules is thus a process involving co-op-
erant actions of both factors; and if the part performed by
the polar amphiaster is karyokinetic, the associated act of the
vitellus may be characterized as cytokinetic. I have before
referred to the centrifugal movement of the germinal vesicle
as an instance of repellant action, and I regard this constriction
as a part of the same action. Jf zs thus a phenomenon of
maturation, not of impregnation.

Ransom, as well as Kupffer and Benecke, explains the phe-
nomenon as a result of the penetration of the spermatozoon,
and hence has failed to distinguish it from other phenomena of
a similar, though not identical, nature. Bearing this fact in
mind, we are enabled to find in their descriptions — especially
that of Ransom — an exact parallel of the special constriction
which always accompanies the formation of polar globules in
Clepsine. Ransom’s account is extremely interesting, and has
attracted so little: attention from later embryologists, that it
seems worth while to introduce a portion of it here. After
stating that slow contractions begin from the first moment of
entry of the spermatozoa, causing first a flattening of the ger-
minal pole, and afterwards slight changes of outline due to
‘travelling waves’ at other parts of the surface, he proceeds as
follows : —

“Gradually more vivid contractions commence, at various
times after fecundation, according to the temperature. In warm
weather they have been noted in six minutes, in cooler weather

18 Der Vorgang der Befruchtung am Eie der Neunaugen. Kénigsberg, 1878.
14 Observations on the Ovum of Osseous Fishes. Proc. Roy. Soc. London,
VII., 1856.

34 WHITMAN. [Vou. II.

in fifteen or twenty minutes after impregnation. They cause a
flattening of one side of the yolk-ball, to see which it is often
necessary to roll the egg over. The flat surface gradually be-
comes a sulcus, giving a rentform outline to the yolk. It then
extends all round, giving rise toa dumbbell shape. This sulcus,
which may be termed equatorial, travels with considerable but
variable rapidity towards the germinal pole, producing as it passes
on, the flask form. The sulcus ts lost by passing forwards to the
germinal pole, not by relaxation. It ts seen for a brief space
affecting the thickness of the germinal disc only, to which it gives
a nipple-like form, while the food-yolk 1s round. When effaced,
the whole yolk-ball is globular and at rest, the germinal disc being
no longer prominent. This sertes of forms recurs with more or
less of vegularity, and with some variations both of time and
form, about fifteen or twenty times, each series being the result
of a travelling wave” (No. 14, pp. 463-464).

Had Ransom succeeded in connecting the formation of polar
globules with the more regular and prominent ‘wave,’ which he
has so vividly described, he would doubtless have seen the neces-
sity of distinguishing this wave from the movements which
follow it, precisely as Kupffer and Benecke distinguished in
the egg of Petromyzon a ‘zonal constriction’ which invariably
accompanies the appearance of the second polar globule. They
did not succeed in tracing the origin of the first polar globule;
but they have described a constriction (p. 15) around the ger-
minal pole (Fig. 7, 7), which appears immediately after the sper-
matozoa come into contact with the egg; and this, I would
suggest, may have the same relation to the first polar globule
that the ‘zonal constriction’ has to the second.

Polar Aggregation. — In the formation of the germinal disc
of many pelagic fish ova, we meet with very remarkable cyto-
plasmic movements. In the fresh-laid egg, the germinal proto-
plasm forms a cortical layer of uniform thickness around the yolk.
But this condition lasts only for a few seconds, during which the
spermatozoon finds an entrance into the egg. This event is
followed at once by a polar concentration of the peripheral layer
of protoplasm, which results in the gradual formation of the
germinal disc with its centrally placed pronuclei.

Is it in one or both of the pronuclear bodies that we are to
look for the cause of the polar aggregation of protoplasm? Is

ING. tT.) REGENERATIVE ENERGY. 35

the protoplasm a passive mass, moved at the expense of nuclear
energy alone, or has it motor energy of its own? In the latter
case, are the conditions necessary to action supplied by the
nuclei or by the protoplasm, or by both? Although we are yet
a long way from a solution of these questions, it may be possi-
ble to show that the protoplasm is an active rather than a pas-
sive factor in the movements we are considering. Any view
which represents the germinal protoplasm as a passive body,
moving only as it is impelled by nuclear forces, appears to me
irreconcilable with the following facts : —

1. In most meroblastic vertebrate ova (including those of
many teleostei), the germinal disc is already formed before fec-
undation takes place. The ma/e pronucleus cannot therefore
be a necessary factor in the formation of this disc.

2. In many pelagic fish ova, where the disc forms after fecun-
dation, the polar amphiaster is formed before polar concentra-
tion begins. The cause of concentration cannot therefore, in
this case, be referred to the centrifugal movement of the
germinal vesicle, nor to any changes which this body undergoes
prior to the formation of the polar amphiaster.

If this conclusion holds equally in the first class of eggs, we
are fully warranted+in affirming that the germinal disc forms
independently, not only of the male pronucleus, but also of the
germinal vesicle and its derivatives, since in these eggs the disc
is formed before fecundation and before the polar amphiaster
divides.

The validity of these conclusions may be disputed by those
who hold with Weismann (No. 6, pp. 90-122) that the two pronu-
clei are identical in their molecular structure, and that both act
alike upon the protoplasm, but in proportion to their mass. It
might be argued that a definite guantity of karyoplasm (‘ Keim-
plasm’) is requisite in order to concentrate the protoplasm in
the form of a polar disc. If the mass of the germinal vesicle,
or of its pronuclear elements, be large enough, it would form a
germinal disc without the aid of the male pronucleus; if it fall
short of the requisite mass-measure, it would have to be reinforced
by the male pronucleus before it could accomplish the work. It
will be time to accept this view when it has been shown that
there ave such quantitative relations as the theory postulates.
Such an explanation of the disc-formation would take no account

36 WHITMAN. [VoL. Il.

of the polarity of the egg, and would leave inexplicable the differ-
ence between telolecithal and controlecithal eggs. Besides, this
view assumes that the pronuclei are homodynamous, a point
which cannot be conceded, since male pronuclei do not behave
towards one another as they do towards female pronuclei.

A special feature in the polarity of the fish egg, noticed by
Kupffer and by Hoffman? (p. 88), is the formation of a tem-
porary discoidal thickening (‘Gegenhiigel,’ Kupffer) at the veg-
etal pole. Here, then, is a disc-formation at the point farthest
removed from the nuclear bodies, and this fact appears to be
fatal to the above theory. We are reminded of the rings in the
egg of Clepsine, and their concentration into two polar discs.
It appears not improbable that the two sets of phenomena are
similar in nature, and determined by like forces. In the fish
egg the disc-formation is not preceded by a ring-formation ; and
the nearest approach to the ring-rays are the ‘radiating bands’
or ‘beaded streams’ described by Ryder! (p. 17).

Raffaele (Mitth. d. Zool. Station z. Neapel, VIII., 1, 1888) has
recently described a very singular phenomenon in the egg of
Labrax. The egg has a single large oil globule at the pole op-
posite the germinal disc. This oil globule is enveloped with
protoplasm, which, on the side facing the germ, thickens up
until it takes the form of a long club-shaped body. This body
elongates in an axial direction, and the distal portion, which is
gradually constricted off, eventually assumes a globular form
and rests on the inner face of the germ. Ryder has noticed
protoplasmic bodies in the egg of Gadus (‘segmenting corpus-
cles’) which, as Raffaele suggests, may have a similar mode of
origin. It occurs to me that this body of protoplasm may cor-
respond to Kupffer’s ‘Gegenhiigel,’ and that it is diverted
from its usual peripheral track by the presence of the oil globule.

The Artificial Division of Infusoria. — The artificial divis-
ion of infusoria has been resorted to as a. means of decid-
ing, experimentally, the question of the relative importance
of the nucleus. M. Nussbaum!® was the first to establish

15 Die Entwickelung des Herings im Ei. Fahresh. d. Comm. z. wiss. Unter-
suchung der deutschen Meere in Kiel, 1V.—V1., 1874-1876.

16 Zur Ontogenie der Knochenfische. Amsterdam, 188t.

17 The Embryography of Osseous Fishes. Report of the Commissioner of Fish
and Fisheries for 1882.

18 Die spontane und kiinstliche Theilung der Infusorien. Arch. f. mik. Anat.,

No. 1] REGENERATIVE ENERGY. 37

the general fact, that enucleate pieces of an infusorium are
incapable of regenerating lost parts, while nucleate pieces soon
regain the specific form. “ The nucleus is thus indispensa-
ble to the preservation of the formative energy of the cell.” Gru-
ber,!® whose experiments were begun at about the same time as
those of Nussbaum, has reached the same general result. But
one of Gruber’s experiments, which was at first supposed to
show that regeneration is possible without the presence of a
nucleus, brings out a fact of considerable importance. A Stentor
ceruleus was selected, in which spontaneous fission had already
begun, as indicated by the concentration of the rosary-formed
nucleus into a simple oval form, and by the beginning of a new
peristome at the middle of the body. A transverse section was
made just in front of the new peristome, and so close upon the
nucleus that it nearly all escaped from the cut surface of the
posterior half of the Stentor. The anterior portion retained
no part of the nucleus. The two parts were isolated, and on the
following day each was found to have become a complete Sten-
tor. As the plane of division was nearly the same as that which
would have been followed if the process of spontaneous fission
had not been interfered with, Gruber (No. 19, p. 13) finally con-
cludes, contrary to his first interpretation, that this was not a case
of regeneration, but of reproduction. The process of reproduc-
tion once initiated by nuclear action may go on, so he thinks, to
completion without further assistance from the nucleus. He
insists, however, that the first impulse to division is given by
the nucleus, since in all cases where artificial division is executed
before the process of spontaneous fission begins, enucleate parts
are incapable of regeneration. While finding no reason to doubt
the accuracy of Gruber’s observations, I must contend that they
do not warrant the conclusion so forcibly stated in the following
words: “ Auf rein empirischen Wege werden wir hier vor die
unumstéssliche Thatsache gestellt, dass der Kern der wich-
tigste, dass er der arterhaltende Bestandtheil der Zelle ist” (No.
19, p. 16). Allowing that regeneration is impossible in the ab-
sence of a nucleus, that is no proof that the nucleus is the sole
seat of regenerative power, nor is it a proof that the nucleus is
XXVI., January, 1886, p. 485. Cf. also Sitz-Ber. d. Niederrh. Ges. f. Natur- u.
FHleilkunde, 1884, p. 262.

19 Beitrige zur Kenntniss der Physiologie und Biologie der Protozoen. Berichte
a. Naturforsch. Ges. 2u Freiburg, 1.,H. 2, 1886. Also Biolog. Centraltl., 1V., p.
717, and V., p. 137.

38 WHITMAN. [ Vow. Tie

a more important factor than the cytoplasm. There is not a
single observation to prove what is so confidently asserted, that
the nucleus gives the ‘Anstoss’ to division. This may be so
and it may not. The observations prove, (I) that, in some of
the higher Protozoa, the whole process of reproduction by fission,
with exception of the initiatory steps, may be accomplished inde-
pendently of nuclear action; and (2) that the tnttiatory steps
cannot take place tf the nucleus and the cytoplasm are artificially
separated. The whole truth is well stated by Nussbaum (No. 18,
p. 516): “Kern und Protoplasma sind nur vereint lebensfahig:
beide sterben isolirt nach kurzerer oder langerer Zeit ab.” It
is clearly impossible therefore, by any such experiments as
Gruber has carried out, to settle the question of the precise
locus of the regenerative energy.

On general theoretical grounds, as well as by the fact that
enucleate forms are found among the Protista, we are compelled
to accept the generally received view, that the nucleus is sec-
ondary in origin. It may be true, as suggested by Gruber”
(p. 151), that these so-called enucleate forms contain nuclear
substance in solution, and that the first step in the phylogeny
of the nucleus consisted in the formation of scattered granules,
the coalescence of which would give rise to the single nucleus.
But it is hardly necessary to add that we do not see how this
(or any other) mode of explaining the origin of the nucleus as a
secondary body can be brought into harmony with the idea that
it embodies the whole regenerative energy of the cell.

Interesting and instructive as are these experiments in the
artificial division of the higher Protozoa, they do not alone fur-
nish a satisfactory basis for general conclusions. They require
to be supplemented by similar experiments on the simpler forms
of Protozoa, and by much more complete observations than have
yet appeared on the normal processes of fission and coalescence
exhibited in the Heliozoa. In proof of this we have only to
refer to Gruber’s own observations on Actinophrys sol™ (pp. 63-
67) and Actinospherium eichhornit™ (pp. 381-382). Actinophrys

20 Ueber Kern und Kerntheilung bei den Protozoen. Zetéschr. f. wiss. Zool.,
eS ae peeb2 1.

21 Untersuchunge nueber einige Protozoen. Zezéschr. f. wiss. Zool.. XXXVIIL.,
P- 45, 1883. Also Zool. Anzeiger, No. 118, 1882, p. 423.

22 Ueber Kerntheilungsvorgange bei einigen Protozoen. Zeztschr. f. wtss. Zool.
XXXVIIL., p. 372, 1883.

No. I.] REGENERATIVE ENERGY. 39

is capable of breaking up into parts without the concurrence of
any visible changes in the nucleus. The enucleate individuals —
if such they are entitled to be called — may agree perfectly with
the nucleate individual in outward form and behavior. They
live and grow, and coalesce not only with one another, but with
the nucleate form. Whether they are capable of generating a
nucleus or not was not ascertained. The multinucleate Actzn-
ospherium breaks up in a similar manner without the inter-
vention of the karyokinetic process; but here the individual
parts generally contain one or more of the original nuclei. Two
or more individuals may coalesce, but the coalescence extends
only to the cytoplasm, the number of nuclei being the sum of
those contained in the separate individuals before fusion. These
remarkable facts appear to bear out Gruber’s conclusion: ‘‘ That
the nucleus has no importance for those functions of the cell
which do not stand in direct relation to reproduction ; such as
locomotion (pseudopod-formation), inception of food, excretion
(pulsation of contractile vacuoles), and growth. Even on the ex-
ternal form it may be without influence” (No. 21, p. 66). Gruber
(No. 19, p. 12) still maintains the accuracy of this view in every
particular except that relating to the influence of the nucleus on
the form of the cytoplasm. He now holds, in common with
Weismann, Hertwig, Kolliker, Strasburger, and many other
German biologists, that the form-creating and form-conserving
principle is confined to the nucleus. How, when, or where the
nucleus manifests its form-moulding power remains a mystery ;
but that it gives the first impulse to the regenerative act must be
inferred —so the argument runs— from the fact that the
violent separation of nucleus and cytoplasm destroys the re-
generative power in all cases, except where the process of
reproduction is begun before separation is executed. This is
the focal point of the question with which we set out.

Aside from experiments in the artificial separation of nucleus
and protoplasm, the principal arguments in support of this view
are drawn from the phenomena of fecundation and cleavage, and
are involved with certain theories of heredity which cannot be
dealt with here. The observations of Gruber on Actiénophrys
and Actinospherium, if the phenomena are not of a pathological
nature, —and such an interpretation seems to be precluded, —
should certainly make us hesitate to ascribe all the form-regu-

40 WHITMAN. [VoL. II.

lating power ot the cell to the nucleus. This reserve is ren-
dered imperative by other facts yet to be mentioned, for one of
which we are again indebted to Gruber”? (p. 221). In summing
up the results of his “Studies on Amcebe,” he states, “ that
two very closely related species of Amoeba may have quite unlike-
formed nuclei; while species differing widely in external form
may have quite similar nuclei.” Plainly this is the contrary of
what might be expected if the formative power lay exclusively
in the nucleus.

No Form-Correlation between Nucleus and Cytoplasm.—It
may be put down as an indisputable fact that no form-
correlation exists between nucleus and cytoplasm. Except dur-
ing the process of division, the nucleus seldom departs from its
typical spherical form. It divides and subdivides, ever repeat-
ing the same steps and ever returning to the same round or oval
form. So far as can be seen, its influence upon the cytoplasm
is equal in all directions; and hence it would seem that its
formative power, if it have any, could only contribute to the
maintenance of the spherical form of the cytoplasm. How dif-
ferent with the cell! It preserves the spherical form as rarely
as the nucleus departs from it. Variation in form marks the
beginning and the end of every important chapter in its history.
While the nucleus repeats over and over again its little cycle
of form-changes with mechanical regularity, the cell marches
straight on from form to form, never returning, and never re-
peating, differentiating, developing, and adapting itself at every
step to its environment and to the work it is destined to per-
form. From the egg onward through all the stages of histo-
genesis and form-evolution, we search in vain for a single inti-
mation anywhere that either the form of the organism or the
forms of the individual cells are moulded by direct nuclear in-
fluence. At the beginning of any ontogenetic series, when we
get the most rapid and vivid displays of nuclear energy, we
see that the environment of each cell is much more potent in
determining its form than the nucleus. True, certain conditions
of the environment may be said to be largely the result of
nuclear activity ; and to this extent the nucleus may be said to
determine, indirectly, the form of the cell. But this is very dif-
ferent from saying that the nucleus has a direct controlling

23 «Studien iiber Amoeben.” Zeitschr. f. wiss. Zool., XLI., p. 186, 1884.

No. 1.]J REGENERATIVE ENERGY. AI

power over the specific form of the cell, as claimed by Gruber,
Weismann, and others. When the end of the ontogenetic series
is reached, we find the reproductive power of the nucleus greatly
diminished, and its influence over the form of the cell propor-
tionally reduced. Indeed, in the majority of cases the form of
the cell now appears to be maintained entirely independently of
the nucleus, and whatever modification of form the latter ex-
hibits appears to be the result of mechanical pressure. The
form of the nucleus is now determined by that of the cell rather
than the reverse.

If we study the more varied form-changes of the nucleus
which occur in the life-cycle of one of the higher Protozoa, we
are struck with the fact that the external form of the infusorium
is, to all appearance, completely independent of what transpires
in the nucleus. A single nucleus may divide a hundred times
or more without the slightest effect on the form of the infuso-
rium. The products of these many divisions may undergo vari-
ous changes of form, and ultimately coalesce to form a single
nucleus, and yet no change of form in the cytoplasm. The
multinucleated form may break up into parts, some without,
others with one or more nuclei, and the enucleate, uninucleate,
and plurinucleate individuals all agree in presenting the same
specific form. The nucleus may pass from the oval form to
that of a long rosary; then, after a period of vegetative life on
the part of the cytoplasm, return to the original oval form, and
undergo the regular changes of division, the whole cycle of
transformations coming to a conclusion without producing any
discernible effect on the cytoplasm beyond that of simple fis-,
sion. Each part carries with it the power to resume at once
the form which characterized the original whole. The nucleus
gives no evidence at any time of holding the formative power ;
but we have seen from Gruber’s experiment on Stentor, above
referred to, that the cytoplasm does exercise this power, and
that z¢ does so even in the absence of a nucleus.

Gruber does not attempt to deny this; but he thinks it nec-
essary to assume that the power exhibited by the cytoplasm in
the case mentioned, was communicated to it in the form of
molecular motion, the original impulse being given by the nu-
cleus. As we have seen, there is nothing in his experiments
which makes such a conclusion necessary, and the burden of
proof properly falls to him who makes the assumption.

42 WHITMAN. [VoL. Il.
One needs only reverse the case to see the illogical nature of
the position. Let us suppose that it has been ascertained by
numerous experiments that the nucleus of an infusorium is in-
capable of karyokinetic division when separated from the cyto-
plasm, except in those cases where the division is already in
progress at the time of separation. Would there be anything
either in the general rule or in these exceptional cases, from
which to conclude that the performances of the nucleus are first
set in motion by some impulse from the cytoplasm? Would
the incapacity of the nucleus to divide when placed in abnor-
mal conditions demonstrate its inability to divide autonomically
under normal conditions? If artificial isolation were found
insufficient to arrest a series of complex movements already |
begun in the nucleus, would the death of the nucleus, shortly
after the completion of these movements, furnish any ground for
denying that they were automatic? These questions appear to
present the matter in a just light, and to carry with them their
own answers. The point would hardly seem to deserve the
attention given it, were it not for the great importance of
the question under consideration, and the fact that we are
dealing with the opinion of a high authority, — an opinion for
which experimental evidence of a crucial nature is claimed,
and an opinion fully indorsed by so eminent a thinker as Weis-
mann.

Schneider's Experiment. — Schneider’s 24 (p. 509) experiment
with Thalassicolla, although not affording any decisive evidence
as to the precise location of the formative power, is yet of some
interest in this connection. The extracapsular or cortical pro-
toplasm was removed, leaving the central capsule free. At the
end of twelve hours the whole surface of the capsule showed
delicate pseudopodial extensions, and soon after appeared a dis-
tinct extra-capsular layer (“ matrix” of the pseudopodial rays),
which gradually grew to normal thickness. The experiment was
repeated three times in succession on the same individual, and
each time with the same result. The extra-capsular envelope
gave no evidence of sharing the regenerative power, but died
shortly after isolation. This envelope, according to Brandt ?°

4 Zur Kenntniss des Baues der Radiolarien. AZ#l. Arch. 1867, p. 509.
© Koloniebildende Radiolarien (Sphaerozoéen). Fauna und Florad es Golfes
von Neapel. XIII. Monographie, 1885.

NO. T. | REGENERATIVE ENERGY. 43

(p. 84) takes no share whatever in the production of spores ;
and thus it appears that the central capsule is the seat of the
reproductive as well as the regenerative energy. During ‘‘ vege-
tative life” the various functions (digestion, locomotion, sensa-
tion, etc.) all appear to be performed by the extra-capsular
cytoplasm ; but the whole functional activity, as supposed by
Brandt, is under the vegz/ative influence of the central capsule.
In the Sphzerozoa colonies the division of labor is carried still
farther ; for while the pseudopodial rays have their special func-
tions, certain definite areas of the matrix (“ Klumpen von As-
similationsplasma’’) provide for the digestion of the starch
granules which are produced by symbiotic algae; and different
layers or zones are distinguishable even in the central capsule.
That there should be such a complete separation of functions
between the central core and the cortical layer of the same body
of cytoplasm is no less instructive than it is remarkable. It isa
capital illustration of the possibilities of organization and the
physiological division of labor without any corresponding divis-
ion into distinct morphological units.

Recent studies tend to show that the only important sub-
stance conveyed into the egg by the spermatozoon is that which
takes the form of the male pronucleus. The unavoidable con-
clusion would appear to be that the pronuclei are the sole
bearers of hereditary tendencies. This is unquestionably a
point of cardinal importance, and it furnishes the strongest
argument that has yet been advanced in favor of regarding the
nucleus as the seat of the formative power. This side of the
question could not be fairly dealt with within the limits of
the present paper, as it would lead to a consideration of the
whole problem of heredity. It is my purpose, however, to re-
turn to this subject at no very distant date.

The Idea of a Formative Power.— Let us now consider
whether any rational basis can be found for the idea of a
formative power as a resultant from, and an expression of,
physiological unity. I am fully conscious that the subject is
one of profound mystery, the solution of which appears to
lie as far beyond our grasp to-day as at any time in the
past. We draw nearer to the problem, but the effect is rather
to enhance than to reduce its apparent magnitude. Every step
in advance only brings us to a keener sense of the subtle and

44 WHITMAN. [Vou. Ii.

incomprehensible nature of the force or forces contemplated.
We see the effects only imperfectly, and are baffled in every
attempt to understand the mode of action. For the present we
must be content to search for the advection in which answers
lie; and herein is found the chief value of theories.

The more important speculations on this subject have
taken the form of theories of heredity. In most of these
theories, at least those of recent date, we find a fundamental
idea which must be accepted as true ; namely, that the sexual
cells reflect in some way in their chemico-physiological con-
stitution all the typical structural features of the parent-
organism. How all the hereditary tendencies can be contained
in a single cell, and with such completeness that the developing
organism repeats step for step the chief form-phases of a genea-
logical history stretching through countless myriads of genera-
tions, back from the present into the very dawn of life, and
ultimately unfolds every detail of structure and feature of the
parent-organism, is a mystery that transcends our understand-
ing. The preformationists of last century took refuge in the
celebrated inclusion (Einschachtelung, emboitement) theory,
which made the real mystery unapproachable by hiding it be-
hind an endless series of miracles. The triumph of the epigene-
sists brought with it the reclamation of the problem, but left
us with the indefinable ws essentialis of Wolff, the xzsus forma-
tivus of Blumenbach. In more recent times we have seen vari-
ous metaphysical hypotheses of extra-organic agents or forces
supplanted” by physiological hypotheses which seek the cause of
the phenomena in intra-organic forces. But the reaction which
followed the fierce struggles with vitalism has left its impression
on most of the theories now in vogue. Biologica] problems
have been brought more and more under the influence of
mechanical conceptions, which regard all phenomena from an
objective standpoint. Science has vindicated this method, and
as a method it is unassailable. It is no less indispensable to
research in the organic than in the inorganic world; but the
biologist is reminded at every turn that the method is not ex-
haustive, and from the nature of the case it never can be. The
biologist does not hesitate to follow the shibboleth of “ molecu-
lar motion” to its final goal, but he must beware of being
blinded by any artifice of method to distinctions which lie

No.1] REGENERATIVE ENERGY. 45

beyond it. He accepts the authority of the chemist and the
physicist for the fact that the primary elements of the organism
are identical with those found in inorganic matter, and with
them repudiates the notion that life is “a force having no con-
nection with primary energy or motion.” But no one disputes
the fact that the living organism represents special combinations
of matter and force, and displays phenomena which find no
parallel in non-living matter. Hence it does not appear at all
irrational to conclude that vital phenomena are the manifesta-
tions of special forces, resultants of course, and yet guzte unlike
the elementary forces from which they are derived.

If from the same elements by different chemical combina-
tions, we get new substances, differing widely zz¢er se in their
chemico-physical constitution, and totally unlike their primary
constituents, then why not new forces in the same way? The
chemist and the physicist agree in referring the differences of
substances to a dynamical cause, and their mechanical concep-
tions do not prevent, but compel them to ascribe a specific
energy to each different atom and molecule. Im spite of the
tendency of physical thought to regard “all matter as one and
all energy as one,’’ chemistry and physics are built up on the
assumption that chemical elements are unlike, and that in dif-
ferent modes of combination is given the basis for that infinite
variety of substances with which we meet. If the primary
energy is in each case called by the same name, “ polarity,” it
is nevertheless understood that these polarities are as unlike as
the elements which manifest them. It is just here that we see
the foundation for those gwalztative distinctions which, in the
mind of the biologist, must ever overshadow in importance the
physicist’s factors of quantity and motion.

All physical explanations, no less than biological, lead ulti-
mately to the conception of intrinsic forces. The chemist’s
unit, like the physicist’s, is the embodiment of energy. From
a comparatively few atom-energies an endless number of mole-
cule-energies are built up; these aggregate in units of a higher
order, some statical, others dynamical ; and so on through what
Nageli calls mzcelle and micellar aggregates, until we arrive
at the living cell. In this ascending series each new aggregate
represents a unit, the individuality of the parts being merged
in that of the whole. The grounds for distinguishing various

46 WHITMAN. [Vot. Il.

organic, physiological, and biological units, are thus of the same
general nature as those which compel us to discriminate be-
tween physical and chemical units. Of course these higher
units combine both atomic and molecular structure; but they
have superadded to, and including this, a structure as a whole,
which is entirely ignored in the expression “ molecular aggre-
gates.” As they result from the union, not of simple or com-
plex molecules, but of complex molecular groups, their structure
may be said to be at least as widely separated from the mole-
cule as this is from the atom. The power which such a unit
represents as a whole is not the same as the powers represented
by its constituent elements when uncombined, nor is it the sum
of these several powers. Derived from them, and yet wholly
unlike them, as water is something totally unlike its chemical
elements or any simple mechanical addition of these elements.

It is precisely this point which is so persistently ignored in
all so-called physico-chemical theories of heredity. And yet
all analysis and all observation leads to the conclusion, that
molecular structure is not directly responsible for vital phe-
nomena. In claiming that ‘physiological units” have some-
thing higher than molecular structure and power, I am not
treading on ultra-scientific ground, but following the course
already sanctioned by chemistry and physics, and the only
one which can ever reconcile physico-chemical and _ biological
conceptions.

Admit — what no one denies —that a molecule is totally
unlike its constituent elements, that its energy is unlike that of
its atoms, taken individually or collectively ; and further, that
simple molecules, without losing their structural integrity, may
unite to form complex molecules, and we have only to carry the
same process a few steps farther to reach those units whose in-
tegral structure is no longer adequately described as molecular.
If analysis fails to discover a physiological bond which is capable
of binding molecular aggregates into units of the vital order,
its failure must be attributed to imperfection of methods, for
observation bears constant and unvarying testimony to its ex-
istence. If analysis and observation combine to show that
whatever force an organism expends is the correlate and equiva-
‘lent of force taken into it, and if chemical and physical pro-
cesses underlie all vital phenomena, it does not by any means

WoO: T j REGENERATIVE ENERGY. 47

follow that there is any identity between vital activity and
physico-chemical forces. The power which causes chemical
elements to combine is not identical with the power which
vesults from their combination ; nor is the power which breaks
down a chemical compound identical with the powers of its
separate elements.

The views here enunciated are not contradicted by the long-
established fact, that the laws which regulate the formation of
chemical compounds are the same for both organic and inor-
ganic bodies. The position taken does not affirm that organic
compounds differ from inorganic either in material constituents,
or in the forces which hold these constituents together. What
we do affirm is this: We cannot stop with the most complex
molecules revealed or revealable by chemical or physical re-
search ; we must pass from organic to living, organized matter,
not by the supervention of new laws, but by ultra-chemico-
physical, or chemico-organic combinations, which are absolutely
beyond the highest possibilities of chemical analysis. Inability
to define these higher modes of combination is no reason for
doubting the testimony of all our senses to their existence.
And why should we expect chemical research to bring any
positive confirmation of their reality, when all chemical analysis
presupposes conditions which are the absolute negation of vital
conditions? Does self-stultification ever become more complete
than in the assumption that vital forces and conditions are dis-
coverable precisely there where they confessedly do not exist ?
Or is it rational to conclude that, because vital conditions have
arisen from non-vital, the exclusive study of the latter will reveal
the former? So long as the chemist’s methods debar him from
the study of physiological modes of aggregation will he be im-
potent to divine the links which connect molecular motion with
sensibility, and just so long will “physiological chemistry”
remain a delusive misnomer.

A complex aggregate of atoms, so bound together by mutual
affinities as to represent a physical unit, possessing, as a whole,
properties and powers derived from but unlike those of its con-
stituent elements, and existing by virtue of, and only during the
maintenance of, the chemical connexus of these elements, is a
conception which may be carried straight forward up to the
cell. The living cell may be regarded as a system of very com-

48 WHITMAN. [VoL. II.

plex chemico-organic units, bound together by subtle chemico-
physiological bonds, and displaying in their collective capacity
functions and powers which are entirely foreign to them as
individual and isolated elements, and which are therefore indis-
solubly identified with the physiological connexus or consensus.

Vague and unsatisfactory as such a view may appear, and
as the best possible view must be from the limitations of our
knowledge, it may yet contribute something towards a clearer
conception of what we have called the formative power of the
cell. It will be sufficiently clear now that we have not in mind
a phantom-form which, like a mould, impresses its shape upon
plastic material; but a power which represents the resultant of
the consentient reactions of indwelling forces. Such a power
declares itself in every living organism and in every developing
germ.

The action of the formative power has often been likened to
the architectural power displayed in crystallization ; and if the
essential distinctions are kept in view, such a comparison is
justified by one or two very instructive analogies. If the physi-
cist is not compelled to recognize a special crystallizing force,
he is at least unable to deny that a crystalline aggregate reacts
upon the parts in such a manner as to determine the direction
of that marvellous “constructive power” with which the mole-
cules are endowed. When we see a crystal reproduce its lost
apex ; or, as in the oft-cited experiment of Lavalle, an angle of
an octohedral crystal spontaneously replaced by a surface, as
the result of an artificially produced surface at the correspond-
ing angle, we have no alternative but to infer a physzcal correla-
tion of parts, under the influence of which the drectzon of forces
is determined. So in the development of a germ, in the repair
of injured parts, and in the regeneration of lost parts, the fact
is irresistibly forced upon us, that the organism as a whole con-
trols the formative processes going on in each part. The forma-
tive power then belongs only to the organism as a physiological
whole ; and it does not represent a sum or aggregate of atomic,
molecular, or other forces, but results from special combinations
of ultra-molecular units, and disappears as such the moment the
physiological connexus is destroyed.

This idea may appear, at first sight, to stand in contradiction
with the fact that parts of an organism, resulting from sponta-

No. I.] REGENERATIVE ENERGY. 49

neous or artificial division, possess the same formative power as
did the undivided organism. But it must be remembered that
most organisms do not admit of such division, and that in those
that do admit of it, everything depends on how the division is
made. The extra-capsular portion of a Radiolarian does not
reproduce the central capsule, nor does the non-nucleated frag-
ment of an infusorian regain its lost parts. Even here, then, it
is not permissible to disregard the physiological correlation of
parts, since both nuclear and cytoplasmic elements are indis-
pensable to the preservation of the formative power. We still
have to regard such organisms as physiological wholes, although
the physiological connexus may be representable in aliquot
parts.

The principle holds true of every organism, irrespective of
whether the mass is divided into cells or not. The fact that
physiological unity is not broken by cell-boundaries is confirmed
in so many ways that it must be accepted as one of the funda-
mental truths of biology.

on ne i A

A CONTRIBUTION), TO) THESINEERNAL. STRUC-=
TURE OF THE AMPHISIAN) BRAIN.

PROF. HENRY FAIRFIELD OSBORN,

PRINCETON COLLEGE.

INTRODUCTION.

Tuis contribution to the structure of the Amphibian brain is
the result of observations which began in 1879 and have ex-
tended at wide intervals over several years. The most syste-
matic of these studies, beginning in Munich in 1886, were
directed to the nerve-fibre courses, and interrupted by the dis-
covery of the corpus callosum, which naturally led off to the
comparative study of the encephalic commissures in the verte-
brata. They form the chief portion of the present paper, and
have long been withheld from publication in the hope that an
opportunity would arise to make them more thorough. As this
seems now more distant than ever, it appeared to me best to
publish them in their present shape, with the intention of attach-
ing to each new point the degree of certainty to which the evi-
dence entitles it. Only by carefully distinguishing between
fully and partially established facts can a contribution of this
unfinished character acquire any permanent value. The most
carefully observed region is the medulla oblongata of C7rypto-
branchus, with reference especially to the cranial nerve tracts and
nuclei. The structure of the cerebellum in the Uvodela has been
well worked out, also the region of the optic lobes, thalami, and
posterior portion of the hemispheres in the Urodela and Anura.
Much remains to be done in respect to the peripheral distribu-
tion of the component parts of the several cranial nerves. Only
after this has been thoroughly worked out can we certainly deter-
mine the homologies of the cranial nerves and their segmental
relations in the Amphibia. The present results go far enough
to show that the determination of definite nuclei corresponding
to definite peripheral sensory and motor areas is well within the
range of possibility. In fact, the provisional character which I
have given to some of the conclusions here reached is chiefly

52 OSBORN. [Voe. II.

due to the close connection between several of the cranial nerves
at, or close to, their exit, which makes it necessary to follow
each component bundle in continuous sections peripherad to a
point where their further distribution can be traced macroscopi-
cally. This I believe is possible with several of the nerves, but
has not as yet been successfully accomplished.

The genera studied include Amphiuma, Cryptobranchus, Nec-
turus, Siredon, Proteus, Rana, and Szren.

The following are some of the most important results ar-
rived at :—

1. The determination of the chief motor and sensory nuclei
of the 5th to 10th pairs, which enables me in some degree to
homologize the intra-axial elements of the Vagus and Trigemi-
nal systems, and demonstrate the independence of the Auditory
system and system of the motor nerves of the eyeball.

2. The discovery of a new sensory tract and nucleus, the fas-
ciculus communis, common to the 1oth, oth, and 7th (or
8th) pairs.

3. The determination of the relations of the posterior lon-
gitudinal fasciculus (uncrossed Miillerian fibres), to the
8th, 6th, 4th, and 3d nerve tracts, and of the nucleus of the
latter nerve with the fibres of the posterior commissure.

4. The passage of a portion of the descending trigemi-
nal tract through the cerebellum and the direct connections of
this bundle with the large mesencephalic nucleus.

5. In the encephalon, the determination of the direct mo-
tor tract to the prosencephalon, and of direct sensory
tracts to the mesen- and diencephalon.

The principal characteristics of the Amphibian brain, as
compared with that of the Sauropsida and of the Fishes, ex-
cluding the Dipnoi, are the following: The olfactory lobes are
not sharply defined from the cerebral hemispheres. The corpora
striata are not prominently developed. The cerebellum is always
small, and is either in a primitive or degenerate condition in
the Uvodela. The pineal eye pierces the skull, but does not
develop further! Finally, an important distinction is that the

! According to Spencer it is more rudimentary in the Urodela than Anura and
in the latter forms a vesicle which subsequently degenerates.

No. I.] AMPHIBIAN BRAIN STUDIES. 53

gray matter of the brain immediately surrounds the ventricles,
the central gray, and with the exception of the layers of cells
in the optic lobes of the Azwura, there is nothing developed in
the nature of the cortical gray matter. The Uvode/a are further
distinguished from the Azura by the small size of the optic
lobes, which are barely marked off from the thalami, by the
frequently extensive development of the superior commissure,
and by the primitive condition of the ventriculus communis or
unpaired cavity of the prosencephalon.

I. THE DIVISIONS AND CAVITIES OF THE ADULT BRAIN.

The division of the brain into five large segments is invaria-
bly well marked. The olfactory lobes do not appear as fully
distinct segments, but form the anterior portion of the prosen-
cephalon, sometimes separated from the hemispheres by a
prominent lateral swelling or median indentation. The line of
separation is much more clearly indicated in horizontal sections.
The olfactory nerves arise either from the edge or base of the
lobes. The lobes are broad and truncate anteriorly in the Uvo-
dela,! but taper in Proteus as in the Frog. The diencepha-
lon and mesencephalon are subequal in size in the genera
with small functional eyes, such as Szvedon, Necturus, and Stren,
these two segments presenting the appearance of an elongate
cylinder slightly compressed opposite the posterior commissure.
In the blind Proteus the mesencephalon is smaller than the

' The classification adopted is from Baur’s valuable memoir, “ Beitrage zur Mor-
phogenie des Carpus und Tarsus der Vertebraten, I Theil, Batrachia,” Jena, 1888.
The recent Amphibia are arranged in three orders : —

PROTEIDA. URODELA. ANURA.
Fam. Proteide. Proteus. Fam. Cryptobranchide, Cryptobranchus.
Necturus. Sirenide, Siren.
Pseudobranchus.
Amphiumide, Amphiuma.

Amblystomatine, Amblystoma

(Axolotl), etc.
Also the Cecilitde, Plethodontide.
Desmognathide, Salamandride.
Pleurodelide.

Baur considers the Cryftobranchid@ the most central family of the Urodela, from
which the Strentde, Amphiumide, and Amblystomide may have sprung, p. 55. I
find that the brain structure fully supports this conclusion.

54 OSBORN. [VoL. I.

diencephalon. In the Salamandride the mesencephalon is
larger than the diencephalon, and it is of much greater propor-
tionate size in the Azura, owing to the large optic nerve nuclei.
The size of the roof of the jmesencephalonms aim
direct proportion to the functional perfection yar
the eyes. The cerebellum is invariably small in the Uvodela
and Protezda, but attains a segmental size and importance in the
Anura. The metencephalon, or Medulla oblongata, forms
the fifth, and invariably the largest segment.

The proportions of these segments are very similar to those
observed in the Dzpfuoz (see Fulliquet, ’86), but differ widely
from those in the lower fishes. The great relative size of the
prosencephalon in the Amphibia is, however, deceptive, since
the walls are comparatively thin and the ventricles much larger
than in the two mid-segments.

Surface characters of the brain, Plate IV. In carefully pre-
pared specimens many of the more important structures of the
superficial encephalic walls may be seen upon the surface.

In the hemispheres of Szvez, Fig. 5, are observed nerve tracts
from the postero-lateral regions. Between the hemispheres pos-
teriorly lies the large supraplexus which covers the roof of
the ventriculus communis, Fig. 8, and in most of the Uvodela
extends far forwards. The inner surfaces of the hemispheres
are in close contact with each other in the Uvodela and Proteida,
but I have observed no actual union of the olfactory lobes such
as is found in the Azura. The lamina terminalis, 4, Fig. 3,
extends well forwards, and is sharply defined in the ventral
aspect.

The characters of the roof of the Diencephalon are very
well marked. Just behind the supraplexus are two oval or round
swellings, which represent the ganglia habenarum with
distinct median contours, but closely applied to each other in
forms in which the supracommissura is-well developed,
such as Menopoma, Amphiuma (Osborn, ’83 and ’84, Fig. 4),
and Axolotl/, Fig. 1. Arching between them and spreading be-
yond, into the thalami, is a grayish band which probably repre-
sents the supracommissura. This commissure underlies
the pineal process, and is not seen upon the surface in Wecturus,
Figs. 2 and 8, but is apparently present in Proteus. Immediately
behind this the whitish plates connected with the ganglia diverge,

No. 1.] AMPHIBIAN BRAIN STUDIES. 55

leaving a slit-like, oval or triangular space, in the centre of
which lies the proximal portion of the pineal stalk or proces-
sus pinealis, fz. Close behind this a white or grayish streak
represents the postcommissura. Upon the floor of this
segment is an oval space, bounded by a whitish area which rep-
resents the recessus opticus, or proximal portion of the
primitive optic stalk, which recess in WVecturus and Proteus ex-
tends directly into the centre of rudimentary optic nerve. There
is a striking similarity, which may be merely superficial, between
this area and that surrounding the processus pinealis. The
most prominent features of the floor are the infundibular lobes,
probably homologous with the lobi inferiores of the Tele-
osts, which terminate in the large hypophysis. These lobes
extend anteriorly into the flattened floor of the 3d ventricle,
and laterally into the sides of the thalami. Above them, the
cerebral peduncles diverge around the infundibulum into the
lower portions of the thalami.

The roof of the Mesencephalon is distinguished by a
longitudinal grayish line, probably caused by the thinning of
the wall; on either side of this is a whitish tract the meaning
of which is unknown. Posteriorly the roof thins out into the
valvula, a triangular area from which arises the 4th nerve.
This nerve is apparently atrophied in Proteus. The slender
band representing the cerebellum extends across behind this,
continuous at the sides with the lateral fold of the medulla.

The figures do not represent the actual condition of the
Metencephalon, since the metaplexus has been removed.
The metacoele, or 4th ventricle, is shallow and widely open
in the Uvodela, and varies considerably in shape. In Proteus
the lateral edges are approximated opposite the roth nerve.
On either side of the longitudinal sulcus, in the centre of the
floor, are observed two long white tracts shining through and
giving off lateral branches opposite the exit of the VII., VIII.
nerves. This tract is the posterior longitudinal fasci-
culus, and can be very clearly seen in well-preserved speci-
mens. On the ventral surface is seen the anterior sulcus con-
tinuous with the fissure of the cord. It diverges at two points
in the medulla of Proteus, the meaning of which is not known.
I have not observed in the floor of the 4th ventricle of the
Urodela any trace of the foldings seen in the medulla of Rana

56 OSBORN. [VoL. II.

(Osborn, ’86, Fig. 2, text), which I have suggested may be
remnants of the embryonic neuromeres. The origin of the
cranial nerves is described elsewhere.

The Ventricles of the Brain. A comparison of the encephalic
ventricles of these genera, in longitudinal section, brings out
some interesting facts, Figs. 7, 8,9. Cryptobranchus approaches
the piscine type, and Rava the Sauropidan type: they are at
opposite ends of a series. The roof of the C7yptobranchus brain
is nearly straight in the mid-region ; in Rana it is much folded,
so that the cerebellum and postcommissura are brought to-
gether; these folds and the lateral outgrowth of the optic lobes
produce the diverticulum of the mesoccele, the optocoele
(Wilder), and the tori-semiculares in the walls. The position of
the trigeminal nucleus affords a means of comparing the optic
lobes of the Uvodela and Anura (see below). A still more im-
portant difference is in the fore-brain. In Raza the cerebral com-
missures lie in the lamina terminalis proper; there is no extended
ventriculus communis. In the lower Uvodela (the Sala-
mandridé have not been examined), the commissures trav-
erse a fold ‘of the dloonr and “there 1s a largevvem
triculus communis in ’front-of this, 2, Fie. 7 Was
vus shows a remarkable development of the ventricular plexuses,
which extend well into the lateral ventricles and backwards
nearly to the cerebellum. The elevation of the floor which con-
tains the corpus callosum and anterior commissure is very
similar in position to the commissural band between the cor-
pora striata in the Teleosts. (See Appendix, Note 7.)

SEGMENTATION OF THE BRAIN.

Under this head we may consider the larger encephalic seg-
ments and pass by the neuromeres, which, as recently de-
monstrated by Orr ('87, p. 335), have a special significance with
relation to the origin of the cranial nerves, exclusive of the first
and second pairs. The neuromeres and central nuclei, when
fully investigated, will undoubtedly enable us to establish a
closer comparison between the brain and spinal cord segments
than can ever be drawn from the peripheral distribution of the
cranial nerves.

As above pointed out, the chief points of contrast between
the brains of the Azuwra and Urodela are the large optic lobes

No. I.] AMPHIBIAN BRAIN STUDIES. 57

and cerebellum of the former. The cerebellum is generally
found to have a direct relation to the size and activity of the
limbs; it is extremely small in the limbless forms, intermedi-
ate in the Salamanders, and so on, increasing to the Avzra.
Are we-to consider the Urodele cerebellum.as in a
degenerate orina primitive condition? The limbs
of Cryptobranchus (Menopoma) are well developed and fully func-
tional; they are, moreover, in the most primitive condition
known among the Amphibia (Baur, ’88, p. 55). If the relation
above mentioned holds good here, we may infer that the cere-
bellum is also in a primitive condition in the central Uvrodela
phylum. It may be considered in a degenerate condition in
some of the limbless types.

This correlation has a direct bearing not only upon the ques-
tion of the number of the larger encephalic segments in the
Amphibia, but upon the origin of this segment. By many au-
thors the cerebellum is considered a distinct segment equiva-
lent, for example, to the mid-brain. By others it is considered
as a portion of the roof of the hind-brain. The hypothesis I
ofer 1s that the cerebellum is primitively interseg-
mental, and secondarily acquires a functional im-
portamce equivalent to that of the other secments,
(Osborn, ’87, p. 940).

The cerebellum of C7yptobranchus (see also p. _) is chiefly
composed of decussating tracts, passing on the one side into the
lateral regions of the medulla, on the other into the mesenceph-
alon. It may even be questioned whether we have here the
essential elements of the cerebellum, the structure is so ex-
tremely simple. It has been stated that the posterior com-
missure, which invariably marks the dorsal boundary between
the dien- and mesencephalon, is not a commissure in the strict
sense of the word, but consists of fibres from the two tegmental
tracts 1 decussating to the opposite side of the brain. Similarly,
the superior commissure, described independently by Bel-
lonci (81) and myself (’84, p. 268), consists of fibres passing
across the roof of the third ventricle from the diencephalon
to the opposite prosencephalic segment (see secs in all the fig-

1 With special relations to the tegmental tracts (Pawlowsky) and the nucleus of
the third nerve (Darkschewitz).

58 OSBORN. [Vor. II.

ures). There is thus a striking similarity in the fibre courses
of these three dorsally decussating tracts. In Cryptobranchus,
in which we have the most primitive type of brain thus far
observed among the Amphibia (Plate IV., Fig. 7), these three
tracts are nearly subequal, the superior commissure containing
the largest proportion of fibres.

This anatomical evidence for the serial homology of these
commissures is supported by the facts of their embryological
development. I have followed these stages in the frog, in which
the superior commissure is extremely reduced ; it would probably
be much more clearly shown in C7yptobranchus embryos. These
commissures develop nearly, if not quite, simultaneously with
the anterior commissure, at the period immediately following the
constriction of the neural tube into four vesicles. In the dorsal
median line this constriction is clearer between the two posterior
segments than between the first and second (compare co/ and
pem in Cut 1 with scm).4 But in horizontal sections these three
constrictions are equally great, Cut 2. It is noteworthy that
the floor of the neural tube, which evidently has no relation to
these dorsal commissures, is also the only region in which from
the first there is no constriction between these vesicles, the
constrictions occurring, first, at the point of the cranial flexure ;
second, opposite the anterior commissure, acm.

The inference to be drawn from these facts depends largely
upon the question whether there is really a serial homology be-
tween these commissures in their primitive condition. If not,
there remains considerable ground for the supposition that the
intersegmental folds are lines of retarded growth in the sides
and roof of the neural tube to be traversed at an early period by
the commissures.

In the last number of this Journal, Orr (87, p. 347) has
contributed valuable observations on the lizard’s brain, which
certainly support, and possibly extend, this hypothesis to em-
brace also the anterior commissure. He finds, what I had not
observed, that the fibres of these commissures are possibly con-
tinuations of the primitive lateral longitudinal fibres, although
not positively observed to enter them, concluding as follows:
“The superficial position of these three commissures, anterior,
superior, and posterior, their similar connections with the lateral

1See Appendix. Note 1.

No. I.] AMPHIBIAN BRAIN STUDIES. ; 59

bands, and their relation to the constrictions of thé brain, sug-
gest at this period a striking homology between them.” (See
Plate XVI., Fig. 62, F.) This does not include the cerebellum,
the tracts of which he has not followed. It is true that the
fibres beneath the fore-brain branch from the lateral longitudinal
band in much the same manner as do those passing to the re-
gion of the other commissures; but I cannot at present adopt
his view that they represent the anterior commissure, because
the development of this commissure, as I have found it in the
Amphibia and Mammalia, indicates that it is strictly commis-
sural, and not the decussation of a longitudinal tract, as must
be inferred if its fibres pass directly into such a tract. Immedi-
ately beneath the anterior commissure in the Amphibian fore-
brain, I have observed fibres decussating from longitudinal bun-
dles to the opposite hemisphere (op. cit., Fig. 11, Plate XIV.),
which probably represent those attributed to the anterior com-
missures by Orr (op. cit., p. 346).

Upon these grounds, pro and con, the hypothesis may be
restated as originally: that the early constriction of
tieworaim roof which gives rise to the sfour wesi-
cles is for the accommodation of three nerve-fibre
tacts decussating dorsally, viz, the superionvand
posterior commissures and the cerebellum, which
in their primitive condition have a serial homology.

If in some of the lower vertebrates, ¢.g., the Uvodela, the
cerebellum is intersegmental, and in other vertebrates, lower
and higher, it becomes equivalent to the other segments, it
merely accords with what we may conjecture as to the prob-
able evolution of the encephalic segments, that they were not
primary features of the vertebrate brain, but were defined
secondarily, with the concentration of certain groups of func-
tional centres at certain points. The neuromeres are probably
remnants of the true primitive segmentation.

II. THE CRANIAL NERVES.

EXIT FROM THE BRAIN.

I. The olfactory nerves arise from the lateral or infero-lateral
portion of the olfactory lobes and are distributed in the usual
manner in the olfactory sac, as shown in the figures of Proteus.
They vary little in size throughout the Amphibia.

60 OSBORN. EVormit:

II. The optic nerves are, as a rule, very much reduced in the
Urodela, and are in a degenerate condition in the Pvotezda.
Both in the Proteus and Necturus the primitive epiblastic
stalk of the optic vesicles is persisent. In Proteus
and in some examples of Vecturus the lumen of the stalk is
persistent in the adult condition.! This lumen opens into the
i-like expansion of the bottom of the 3d ventricle, which is
almost invariably found just in front of the chiasma, and demon-
strates that this recessus opticus is the proximal portion
of the primitive optic stalk.

III., IV., VI. These nerves require no special comment.
Their development is naturally parallel with that of the 2d pair.
I have made a doubtful observation of the presence of the
3d pair in Proteus, but have seen no trace of the 4th and 6th,
although it is quite possible that their rudiments will be found
in sections. The 3d and 4th pairs pass off independently.
The 6th pair, according to Fischer (64, p. 125), unites with
the Trigeminus. I have not been able to determine whether
this passes into or through the Gasserian ganglion or unites
with the 5th beyond it. The more difficult problems arise with.
regard to the homologies of the Trigeminal, Facial, and Acous-
tic nerves, which can only be settled by obtaining serial sections
through the nerves, brain, and skull zz sztw. This arises from
the fact that the Trigeminus is always reinforced by a branch of
the Facial, and that the latter and Acoustic are given off so
close together that it is difficult to determine into what bundle
the minor roots of each pass. A clear idea of the exit of these
nerves, as found in Cryptobranchus, is given in Fig. 6, which is
reconstructed from the sections, while the relation of the nerves
to the encephalic tracts is given in Fig. 21; see also Figs. 15
to 18.

V., VII. The main division of the Trigeminus is given off as
a single root from the antero-lateral region of the medulla, V. 1,
2, and it is reinforced by two smaller roots, V. 3.2. The Facial

1 This fact when observed was communicated to Professor Kupffer, who made use
of it in a paper upon the relation of the growth of the optic nerve to the stalk. The
epithelial stalk in long sections extends outwards from the recessus opticus as far as
the nerve can be followed, and is peripheral, the fibres lying at the side.

2 Fischer described four branches from the Gasserian ganglion, instead of the usual
three, in Siredon (op. cit., p. 128): 1. To the skin of the nose region; this he be-

No. 1.] AMPHIBIAN BRAIN STUDIES. ey

arises from two closely applied roots, V.-VII. # and /, which may
be described as the upper and lower roots. The upper root
apparently passes directly forwards as the reinforcing branch of
the Trigeminus. I may anticipate by saying that this is proba-
bly to be regarded as a detached sensory root of the 5th, and
not as properly a part of the 7th. But it is, thus far, somewhat
uncertain whether some of the fibres of the lower root do not
also join the 5th. The lower root passes directly outwards,
and either wholly or for the most part unites with the 8th. For
a short distance these roots form a single trunk, and it is at this
point that the chief uncertainty arises as to their distribution.
A short distance outwards the 8th turns back into the auditory
capsule, and the 7th extends and divides into two branches,
R. mentalis and R. alveolaris, then into four (Fischer, op. cit.,
p- 135)."

VIII. The 8th springs from four roots. _The most anterior
root, VIII. 1, is small, and is given off immediately below and
behind the lower root of the 7th. Behind this is the large root
of the 8th, VIII. 2, and this is reinforced by another small root,
arising somewhat internal and posterior to it, VIII. 3 and 4, by
two small branches. This root may possibly join the lower
division of the 7th, this uncertainty being expressed in Fig. 21
by its double designation, VII.-VIII.

IX., X. The Glossopharyngeus arises by three roots,
IX. 1, 2, 3, which unite to form a single branch, passing back
into the ganglion of the Vagus. Behind these, two more roots,
X. a and 4, unite to form a single branch, also passing back to
the ganglion. Somewhat internal to these two roots, and ex-
tending at about equal intervals backwards, arise five small
roots, which unite to form the third main branch of the Vagus,
system, X. 1-5. Some distance behind these is given off the
12th pair, on either side of the anterior fissure, much nearer the
median line than any of the preceding nerves.

The above description of the exit of the 5th to 1oth pairs,
applies especially to Cryptobranchus, but so far as the main
branches are concerned holds good of the other genera as well.

lieved is formed from the fibres coming from the 7th. 2, Ramus nasalis. 3. Ramus
maxil. superior. And 4. Ramus max. inferior. I have observed but three main
branches from the ganglion. See Appendix, Note 2.

1 See Appendix, Note 2,

62 OSBORN. (Voi. II.

Proteus presents the widest departure from the common type,
inasmuch as the Trigeminus and upper root of the Facial are
given off very close together, and, so far as observed, but two
branches spring from the Gasserian ganglion. The oth and roth
pairs arise some distance behind and are followed by the 12th,
which springs from two small roots and has the same position as
the succeeding nerve, as an anterior spinal nerve root (Fig. 3).

THE MEDULLA OBLONGATA OF CRYPTOBRANCHUS.

General Structure. I have not made a close examination of
the entire section of the medulla at different levels, having
devoted most attention to the lateral regions, which are espe-
cially connected with the tracts and nuclei of the cranial nerves.
As we would naturally anticipate, in an animal of such low
organization as Cryptobranchus, the transition from the spinal
cord to the medulla is a gradual one, but it by no means follows
that we can readily homologize the medulla and spinal cord
sections.

As we ascend from the level of the roth pair (Fig. 10), at
which the general arrangement of the gray and white matter of
the cord is fully preserved, we find the tracts and nuclei of the
posterior nerves, and the deep ascending tracts, which are at the
extreme lateral limits of the medulla, are gradually thrust down-
wards by the nuclei and tracts of the more anterior nerves.
Thus the nuclei of one pair of nerves are overlapped from above,
and then replaced by the nuclei of the pair in front of them,
and so on. This superposition of the posterior by the anterior
nuclei is exclusively in the lateral portions of the medulla, and
none of the nerves between the 12th and 6th pairs
arise from the region corresponding to the an-
terior horn of the gray matter of the cord,

The central region of the medulla is in general composed of
five main areas. 1. At the floor of the ventricle on each side is a
mass of sensory cells. 2. Below these, scattered along the whole
medulla, are multipolar ganglion cells, which are especially
large and numerous opposite the exit of the Acusticus. 3. On
either side of the sulcus are the large fibres of the posterior
longitudinal fasciculus, and below these are the Miillerian fibres.
4. Below this, in the median line, are decussating fibres and the

1Nucleus centralis, Stieda.

No. 1.] AMPHIBIAN BRAIN STUDIES. 63

decussating processes of the ganglion cells! 5. The remaining
area, which makes up the main central region of the medulla, is
composed of the sensory and motor tracts.

The area of large ganglion cells, as shown in Figs. 10, 11, and
12, is continuous with the cells of the anterior horn. It is also
clear that the main motor and sensory tracts which occupy the
anterior and lateral columns, at the level of Fig. 10, are thrust
down, with the ascending Trigeminal tract, to form the area 5.
With the exception of the posterior longitudinal fasciculus, none
of the nuclei or tracts of the cranial nerves below the 6th pair
occupy the central region of the medulla. It follows that the
lateral region of the medulla is exclusively com-
posed of the eranial nerve tracts and nuclei and
the central region is composed of the main sen-
sory and motor tracts of the cord and special sen-
sory and motor centres. These regions are pretty sharply
defined from each other. The lateral region above the level of
the Vagus is bounded by the ascending Trigeminus tracts.

The Tracts and Nuclet, Plate V. A general description
of the fibre tracts and nuclei is necessary to introduce the
special study of the origin of each nerve. In the section
opposite the 12th nerve, we find the columns of the cord and
horns of gray matter well defined. Between the posterior and
lateral columns, at the extreme periphery of the cord, is a small
bundle, the trigeminus ascendens, 5¢/ On the posterior
horn is another small round bundle, not hitherto to my knowl-
edge described, which from its common relations to a number of
the cranial nerves we may call the fasciculus communis.
Opposite this, upon the lower side of the posterior horn, is
another round bundle, which from its relation to the Vagus is
believed to represent the fasciculus solitarius of Len-
hossek, fs. Above this section, Fig. 11, opposite the exit of
X. 4 and 5, is seen a small nucleus contributing to the fibres
of the fasciculus communis, fcz.; then the nucleus and
ascending bundle of the goth, then the ascending trigeminal
tract; below this is the exit of a portion of the fasciculus
communis, and the nucleus and a root of X. 4. In the centre
of the medulla is the posterior longitudinal fasciculus,
which is now a more compact and well-defined tract than in

1 Connected with the crossing Miillerian fibres, (Ahlborn).

64 OSBORN. [Vot. II.

the lower levels, and increases in distinctness as we ascend.
The nucleus and bundle of the Glossopharyngeus increases in
size, and the large ascending bundle of the Trigeminus is thrust
downwards, Figs. 11 and 12; at the level of the exit of the
oth pair, the sensory nucleus and upper and lower roots of the
7th come into view, as well as a third nucleus of the goth, gz,
which takes the place of the internal nucleus of the roth.
The fasciculus solitarius has entered the tIoth, also a
large bundle of the fasciculus communis, fc’, and a fresh
bundle of this fasciculus is now forming, fc'’. It is noteworthy
that although the two bundles of the Facial and the Trigeminal
root are well formed, there is apparently no trace of the Audi-
tory. Above this level, however, the auditory tract, 8¢, forms
rapidly between the ascending 5th and the lower 7th tracts.
It has apparently two nuclei, Fig. 14, and encloses the fas-
ciculus communis. The Auditory is given off by the
union of four tracts, and above this the 7th arises by its
two roots. The upper and lower nuclei of the 7th are then
replaced by the large sensory nucleus of the 5th, which rapidly
reinforces the already large ascending tract. A glance at the
series of figures will show how the sensory nuclei of the gth,
7th, and 5th pairs replace each other in regular succession, while
the 8th, so far as observed at present, belongs to a separate
system. A schematic arrangement of these nuclei is shown in
Fig. 21, the level at which each transection is taken being
indicated at the side.

Glossopharyngeus and Vagus. These nerves are closely related
to each other; the glossopharyngeus arises dorsally,
contributing mixed fibres, and the vagus ventrally,
also contributing mixed fibres. The definite homol-
ogy of these roots with the 9th and Ioth pairs of the higher
vertebrates is uncertain.

The posterior roots of the Vagus, X. ab, 1-5, of this system,
arise from at least three sources. 1. The fasciculus soli-
tarius. 2. The fasciculus communis.) 3). A spear
nucleus in the floor of the 4th ventricle. The two ascending
fasciculi are both found in the region of the posterior horn.
(1) The fasciculus solitarius! appears to arise from the

1 This bundle in the human medulla contributes also to the 9th pair, and extends
to the level of the 8th Cervical (Krause). Hoffmann-Rauber, Lehr. d. Anat., 1886, p.
397-

No. 1.] AMPHIBIAN BRAIN STUDIES. 65

lateral columns of the cord; at least, no special group of nerve
cells has been observed contributing to it. The fasciculus
communis, however, is closely applied to a nucleus of small
sensory cells, fcz., from which it appears to be reinforced. The
fasciculus solitarius enters the two posterior roots. (3)
The three middle roots arise from the nucleus in the floor of
the ventricle, 10 x, which is apparently composed of sotor
cells. (2) The two anterior roots, a, 4, arise from the fasci-
culus communis, which is thereby reduced to a small bundle.

The Glossopharyngeus arises from four sources. 1. The fas-
ciculus communis. 2. A large sensory nucleus. 3. A
nucleus of doubtful motor cells. 4. A motor nucleus in the
floor of the 4th ventricle. (2) The sensory nucleus and tract
is found at a low level opposite the exit of the posterior roots
of the 1oth. This tract 9 ¢ rapidly increases in size from the
nucleus in the dorsal folds of the medulla, which is undoubtedly
sensory. Anteriorly, this nucleus is replaced by the sensory
nucleus of the 7th, and below it, in the angle of the medulla,
(3) is a small nucleus of cells of different character which are
probably motor, 9 mz. These doubtful cells have the same
position as the nucleus of the lower root of the 7th pair,
which is unquestionably motor. The fibres from these two
nuclei constitute a single tract, and form the anterior root of
the oth nerve. (4) The motor nucleus in the floor of the
ventricle, gz, is in exactly the same position as that of the
1oth pair, and is composed of spindle-shaped, probably motor,
cells. The fibres from this nucleus form the posterior root.
(1) The fasciculus communis forms the middle root.

The oth and roth pairs have in common, first, the continuous
and closely similar sensory nuclei and tracts arising from them
which constitute the main sensory supply of the former nerve;
second, the special motor nuclei in the floor of the ventricle;
third, the fibres of the fasciculus communis, also sensory.
The element of doubtful motor cells which is present in the
oth and absent in the roth, may subsequently be found in the
latter. The goth, however, apparently lacks the fasciculus
solitarius. The special motor nuclei, 9 z and 10 %, are seen to
correspond in position to the lateral portions of the anterior horn,
z.e. to the region dorsal to the extremity of the anterior horn.

The Acusticus. The nuclei and tracts of the 8th pair,

66 OSBORN. [Vou. II.

as a nerve of special sense, do not in any degree repeat the
features of the gth and 1oth, which to a certain extent are wit-
nessed in the 5th and 7th. Of the four distinct roots of the
8th, I am in some doubt whether the first and last may not be
given off out of place and ultimately join the 7th. The last of
these roots may, however, at present be described as a portion
of the 8th. (4) The fibres of the fourth, or posterior root, are
received from the posterior longitudinal fasciculus,
as beautifully shown in the floor of the ventricle of Szvex and
in sections of this level, Fig. 15. They suddenly turn out
from the ascending bundle of the fasciculus and traverse the
medulla at an oblique angle to join the nerve by two small roots.
Whether studied in transverse or horizontal sections, this is
clearly an ascending fasciculus, and connects the nerve with the
lower regions of the medulla or spinal cord, not with the enceph-
alon. This isanimportant point. (3) Shortly above the exit of
the oth pair, Fig. 14, a nucleus of large pale ganglion cells
appears, which is quite distinct from the underlying motor
nucleus of the 5th. This is the second source of supply
of the auditory fibres, and probably corresponds to Dezters nu-
cleus; it is sharply defined from the surrounding cells. (2) In
the lower angle of the medulla is also seen a group of small
cells which appears to contribute to this tract of the 8th, 8 sz,
but cannot be positively determined. (1) On the dorsal side of
this tract is the bundle of the fasciculus communis, which
is here double, one-half, VIII., passing outwards to form the
anterior root of the 8th. (5) As the nerve is given off, a large
tract is seen which rises external to the sensory nucleus of the
Trigeminus and constitutes the 8th encephalic tract, which
is indicated by a contour above fc’’’ in Fig. 17, and by dotted
lines in Fig. 21. It is possible that this tract sends fibres
to the mesencephalic sensory cells which may thus form a
superior nucleus.!

It is seen that, whatever may prove to be the peripheral
distribution of the fibres of the fasciculus communis and post-
erior longitudinal fasciculus, whether to the 7th or 8th, two
facts remain: first, that the 8th arises ventral to the
7th, although a purely sensory nerve; second, it
is inserted in the centre of the Facial-Trigem-

1It ascends to the midbrain, see Cerebellum

No. 1.] AMPHIBIAN BRAIN STUDIES. 67

inal system, with no apparent homology in the
arrangement of its nuclei to either.}

There is a strong ground for supposing that the fasciculus
communis, although primarily given off with the Auditory,
subsequently joins the Facial, since, first, it adjoins the lower
motor bundle of the Facial, and second, it also joins the motor
bundles of the roth, 9th, and probably of the 5th, nerves, which
fall into the same general category as the 7th. Still, this ques-
tion can only be settled by following this tract peripherad beyond
the passage of the 8th into the auditory capsule.

The posterior longitudinal fasciculus is stated by
some authors to send a bundle to the 7th; I do not know
that this has been positively determined. Spitzka regards it as
highly improbable that this bundle enters the Auditory proper.
It forms aclose union with this nerve, VII.-VIII., 3-4, soon after
its exit, at which point the two facial and four auditory roots
have the relations, shown in Fig. 16, to each other and to the
large Auditory ganglion. It seems improbable, from these rela-
tions, that this inferior bundle should unite with the facial bun-
dle, and further, both Ahlborn? (83, p. 262) and Fulliquet
(86, p. 81) have followed portions of these large fibres into the
Auditory so that this tract is almost without doubt a portion
of this nerve. There is also much similarity between the
disposition of the 7th, 8th, and 5th tracts in Cryptobranchus and
Petromyzon (op. cit., Taf XIV.).

Facialis and Trigeminus. As already stated, the nuclei and
tracts of the upper and lower /aczal bundles arise at a low level,
opposite the exit of the 9th pair, somewhat lower, in fact, than
represented in the scheme, Fig. 21. There is no difficulty in
recognizing the upper tract as sensory, since it springs from
the outer fold of the medulla in precisely the same manner as

1 Dr. E. C. Spitzka, to whom I am indebted for some valuable suggestions as to
the identification of these tracts, questions the determination of the upper bundles,
7 u-l, in Fig. 15, as parts of the Facial, on the ground that the ventral position of
the Auditory reverses the usual order. There can, however, be no doubt that these
belong to the Trigeminal system, from the fact that 7 « passes directly to the Gasse-
rian ganglion (see Fig. 5).

2 Ahlborn distinguishes three groups of Miillerian fibres in Petromyzon, viz.,
lateral uncrossed, median crossed, and median uncrossed. The
same groups are apparently present in Cryftobranchus. The first named corresponds
in position with the posterior longitudinal fasciculus, and alone enters
the Auditory root. See Appendix, Note 3.

68 OSBORN. [Vot. II.

the dorsal roots of the 9th, and from similar sensory cells, 7 sz.
The lower tract begins at about the same level, and is dis-
tinguished from the upper by its larger fibres and by a distinct
contour, but there is some doubt whether it is a motor tract.
The nucleus, 7 1, is at the angle of the medulla in the same
position as the supposed motor nucleus of the oth, and is com-
posed of slightly larger cells than the sensory nucleus, but they
are not distinctly of the motor character. As represented in
Figs. 15 and 16, some of them are bipolar; but they have not
the characteristic multipolar shape and large nuclei which are
seen in the motor nuclei of the 5th, 5 mz, and 1oth. There
can be little question, however, from the peripheral distribu-
tion of this tract that itis motor. The Facial is thus compar-
atively simple in its origin : unless it is reinforced by the fasciculus
communis or posterior longitudinal fasciculus, or both, it has, so
far as observed, no ascending bundle, and in this respect differs
from the oth, roth, and 5th. It has, however, a small descend-
ing tract, rising towards the cerebellum above the descending 8th.

The Trigeminus. Five, or possibly six, tracts are observed
to enter the Trigeminus, as follows: 1. The ascending tract
from the cervical region, reinforced by, 2, fibres from the deep
motor nucleus, representing two tracts. 3. Fibres from the sen-
sory nucleus. 4. The descending tract from the mesencephalic
nucleus. 5. The direct encephalic tract.

(1) The ascending trigeminus is first observed at the
periphery of the cord, between the lateral and posterior columns,
and increases rapidly in size, probably by accession of fibres
from the lateral columns, so that at the exit of the oth pair it is
the largest of the tracts. (2) At this point we first observe
fibres entering this tract from the motor nucleus, 5 mz,
which immediately adjoins the motor nucleus of the gth pair,
and is external to the group of large ganglion cells which are
coritinuous with those of the anterior horn. This nucleus in-
creases in size to the level of the exit of this tract. (3) No sen-
sory nuclear fibres enter the tract below the level of the exit of
the 7th pair ; at this point the sensory nucleus appears, 5 sz,
continuous with that of the 7th, Fig. 17, and the mgtor nucleus,
which is throughout composed of typical motor cells, immedi-
ately adjoins it ventrally. The sensory nucleus is very large,

1 See Appendix, Note 2.

No. I.] AMPHIBIAN BRAIN STUDIES. 69

and extends forwards beyond the level of the cerebellum. At
this upper level, Fig. 18, the motor nucleus extends towards the
centre, and sends fibres directly into the nerve root. (4) The
descending tract is a large bundle from the more central
region of the medulla. It rises obliquely, 5 4,4 from the root,
Figs. 17 and 21, marked by its large, darkly stained axis cylin-
ders, and is joined by another tract of similar fibres, the origin
of which I have not observed, Fig. 21. The joint tract, thus
formed, is very conspicuous and is followed without much diffi-
culty. Opposite the cerebellum it splits into two bundles (see
Figs. 23 and 24,5 7*). One of these passes into the cerebellum,
Fig. 19, and, without crossing, enters the roof of the optic lobe
at one side of the median line. The second bundle, 5 ¢4’, passes
forwards, and scatters into rays over the whole wall of the optic
lobe, nearly as far forwards as the posterior commissure. These
two bundles undoubtedly arise in the same manner from the
large cells which constitute the nucleus.

The trigeminal mesencephalic nucleus has a re-
markable extent in /Vecturus, reaching in two large masses of
solidly packed cells, on either side of the median line of the
roof, from the cerebellum to the posterior commissure. The
posterior portion of this nucleus is shown, in Fig. 19, in which
the cells lie, two or three deep, above the central gray of the
ventricle. The cells are multipolar and spindle-shaped, Fig.
19 a, with large nuclei, the main processes being directed up-
wards into the tectum opticum. The actual connection of these
processes with the cerebellar bundle of the descending trigemi-
nal can be observed. It is also probable that these fibres are
reinforced from other cells of the roof of the optic lobes, a point
which is discussed later. This trigeminal nucleus is found in all
the Amphibia, but is much larger in WVectwrus than in the other
Urodela, and larger in the latter than in the Anzura. It does
not, therefore, appear to be directly correlated with the power
of sight, although it appears to have an indirect connection with
the mesencephalic roots of the optic nerve.

(5) In horizontal sections a large portion, 5 7°, of the Tri-
geminus is observed passing forwards into the lateral portion of
the medulla, but cannot be followed any great distance, owing
to the similarity of its fibres with those of the main sensory

70 OSBORN: [Vor. II.
tract adjoining. This encephalic tract underlies the similar
bundles from the Auditory and Facial, Fig. 18.

Abducens, Trochlearis, and Oculo-motorius. The most inter-
esting facts observed in connection with these nerves is the
close relation of their nuclei to the posterior lon-
gitudinal fasciculus and the relation of the oculo-
motor nucleus to the posterior commissure. Both
of these observations have been made before, but in the Am-
phibian brain they stand out with unusual clearness. In ver-
tical and longitudinal sections, Figs. 20 and 20 a, some of the
large fibres of this fasciculus seem to pass directly into the
larger processes of the cells of the oculo-motor nucleus, 3 2!.
The larger processes seem to lie in the direction of these
fibres; the smaller processes are partly directed towards the
fibres of the posterior commissure, and actually extend into
the lower portion of this commissure; they are partly directed
towards the exit of the nerve. This group is figured with
the camera as observed in Cryptobranchus ; the posterior com-
missure also descends close to this nucleus in Wecturus and
Rana, as seen in vertical and transverse sections, Fig. 25.

The posterior longitudinal fasciculus also has close
relations with the Abducens nucleus, as shown in Fig. 18,
although I have not observed either in this or in the Troch-
learis? the actual continuity of its fibres with any of the
cell processes. The Abducens nucleus is directly opposite
the exit of the 5th pair, but unlike all the posterior nerves
of the medulla, it passes out close to the middle line, more in
the manner of an anterior spinal nerve root.

The Oculo-motor nucleus is double, consisting of two
small groups of typical motor cells, 3 2 and 3 x’, the fibres of
the posterior commissure descending between them. As found
in Wecturus, Fig. 25, the fibres all arise upon the same side of
the brain, and the nucleus is placed at the edge of the central
gray substance.

1 It is difficult to follow the Trochlearis from its nucleus to its exit. It is
stated to contain sensory fibres in the Selachians and Amphibia. Gegenbaur, op.
cit. p. 49. I have only observed a motor nucleus.

No. 1.] AMPHIBIAN BRAIN STUDIES. 71

GENERAL CONCLUSIONS.

A general survey of the distribution of the nuclei, shown in
Fig. 21, as described in the preceding sections, points to the
natural division of the cranial nerves into three groups: Group
A embraces the Vagus, Glossopharyngeus, Facialis, and Trige-
minus. Group B embraces the Abducens, Trochlearis, and
Oculo-motorius. Group C embraces the Acusticus.

The known tracts and nuclei possessed in common by each of
these groups are distributed below : —

Group A. Group B. Group C,
X.-IX., VIL.-V. VI., IV., IH. VIII.
1. Dorsal! sensory nuclei 1. Special ventral motor 1. Special sensory nuclei.
(? wanting in the roth). nuclei. 2. (Fasciculus communis
2. Lateral motor nuclei 2. Posterior longitudinal from sensory nuclei ?.)
(? wanting in the roth). fasciculus. 3. Posterior longitudinal
3. Fasciculus communis? fasciculus.

from sensory nuclei
(not observed in the

5th).
4. Ventral! motor nuclei
(wanting in the 7th).

The nerves of Group A are apparently closely homologous, in
so far as their mode of origin is concerned. The dorsal sen-
sory nucleus of the t1oth, 9th, 7th, and 5th pairs shows the
most marked continuity, and the nerve bundles are seen to issue
directly from it. The ventral motor nuclei of the 9th and
and roth (10 z and 9 z') are continuous, and occupy the same
region as the great ventral motor nucleus of the 5th. The fas-
ciculus communis, first appearing in the posterior horn, and
all along in close contact with a small group of sensory cells, is
given off to the 10th, gth, probably to the 7th, and possibly to
the 5th. The lateral motor nucleus, consisting of the
cells in the angle of the medulla, contributes to the goth, 7th,
and probably to the 5th.

The absence of the ventral motor nucleus from the 7th nerve,
and the large motor element in the 5th, may indicate that some

1 These adjectives, dorsal and ventral, are retained, since these nuclei are simply
thrust laterad by the opening of the 4th ventricle.

2 This is upon the probability considered on p. 00, that the fasciculus com-
munis joins the 7th instead of the 8th.

72 OSBORN. [Vot. II.

of the motor portion of the 7th, as found in the higher verte-
brates, takes its exit with the 5th in the Uvodela, while some of
the sensory portion of the 5th takes its exit with the 7th, proba-
bly as the upper or sensory bundle which immediately joins the
5th.

The roots of the Glossopharyngeus seem to be in a simi-
lar manner complementary to those of the Vagus, since the
former nerve receives a large bundle from the dorsal sensory
nucleus, as well as from the lateral motor nucleus, neither of
which bundles, so far as I have observed, enter into the 1oth.

Group B. The exit of the Abducens from the central re-
gion of the medulla, and the special connection of its nucleus and
those of the other eyeball muscles with the posterior longitudi-
nal fasciculus, seems to separate these three nerves sharply from
the Vagus or Trigeminus system, and unite them closely into
a group of their own. Iam well aware that some grounds are
found in the development and peripheral distribution of these
nerves for considering the 4th or 6th as vagrant portions of the
Trigeminal or Facial motor roots, but the internal origin cer-
tainly does not support this hypothesis; at the same time it
cannot be said to disprove it.

Group C. The Auditory has been shown to differ widely
from the oth, 5th and 7th nerves by deriving no fibres from the
dorsal sensory nucleus, although a purely sensory nerve. This
can be stated with considerable certainty. One of its special
nuclei is also composed of cells of a unique character, viz.,
pale ganglion cells. The reception of fibres from the ascending
tract adjoining the posterior longitudinal fasciculus further
distinguishes it from the nerves of group A.}

These considerations lead to the following provisional con-
clusions in regard to the zztra-axial origin of the cranial nerves
in the Amphibia.

1°, That there is a close similarity Detween thie
disposition of the nuclei and tracts of the IX.—
X. and V.-VII. groups, the nerves of these groups
being complementary to each other, and together
apparently containing fibres from two sensory nu-
clei and from two motor nuclei. The extreme dor-

1 See Appendix, Note 3.

No. 1.] AMPHIBIAN BRAIN STUDIES. 73

sal and ventral nuclei are composed respectively
of unmistakable sensory and motor cells. While
one of the lateral or intermediate nuclei is composed of less
distinctively motor cells of smaller size (e.g. 9m, 7mm), the
other (fasciculus and nucleus communis) is clearly
sensory.

2, The nérves of the ILL—1Vi=V. E pairs: forma
special system with no apparent homology or con-
nection with the motor elements of the Vagus or
Trigeminus systems.

a7) Lhe VII. as a nerve ofespecial sense, Mas
either no homology or an incomplete homology in
the arrangement of its sensory nuclei and tracts
with the sensory elements of the Vagus and Tri-
geminus systems.

If the fasciculus communis is found to enter the 8th
instead of the 7th, this section must be modified to an incom-
plete homology.

I do not consider that these observations are sufficiently well
tested to give sure support to theoretical deductions as to the
homologies of the cranial and spinal nerve elements. It is
clear that the Vagus and Trigeminus systems approach nearest
the typical spinal nerve arrangement, and the apparent presence
of two sets of sensory and two sets of motor nuclei in these
systems is of great interest in its bearing upon Gaskell’s theory
of the compound nature, somatic and splanchnic, of the anterior
and posterior roots. As frequently stated above, the motor or
sensory character of some of the nuclei and tracts can only be
determined by the study of their peripheral distribution, since
the character and position of the cells themselves, as shown in
the pale ganglion cells of the 8th and the small cells of the
lower nucleus of the 7th, is an uncertain guide as to the nature
of the fibres which spring from them. Even with this precau-
tion it is a great advance to determine the presence of these
two sets of nuclei for each of these systems.

Ill. THE ENCEPHALON.
THE CEREBELLUM.

As already observed, the cerebellum in the Uvodela is
widely different from that in the Azura in its size and internal

74. OSBORN. [Vov. I.

structure. My observations relate principally to the former.
The latter has recently been thoroughly investigated by Wlas-
sak, in a memoir which I have not had an aidan: of study-
ing, and independently by Koppen.

In an earlier paper upon the Cerebellum of Gurbiohwenae I
showed that it receives two lateral systems of fibres on each
side, one from the medulla, one from the mesencephalon. Also
a central system entering the mesencephalon. The latter,
which I mistakenly compared (84, p. 266, Plate VI., Fig. 7)
with the superior peduncles of the mammalian cerebellum, I now
find is composed of the cerebellar branch of the descending
Trigeminus tract. The cerebellum of Asphiuma consists
exclusively of these lateral and central tracts, containing no
cells except the lining of ependyma (83, Plate VIIL, Fig. 3).
The Cryptobranchus cerebellum contains, in addition, a small
mass of round cells of the same description as those composing
the central gray substance of the optic lobes. It thus consists
of the following elements, as shown 1 in Figs. 19, 23 and 28.

1. Fine fibres from the’ c oe lateral portions
of the medulla. It is clear that these fibres, cé/.¢', as shown
in Fig. 18, do not arise from the central region of the medulla.
They ean in part be followed to the point of exit of the 7th and
8th pairs of nerves. Of these the larger portion seem tc come
from the 8th pair.

2°. Coarse fibres from the descending trigeminus
tract. The course of these fibres has already been described
on page 153, 5 7.

3. Fine fibres passing laterally into the mesen-
cephalon, co/.t; these can be followed some distance into the
lateral area of the central gray of the mesencephalon.

4. A nucleus of small rounded cells, cb/.n, in the
ventral area.

The passage of the fibres from the 8th pair through the cere-
bellum has also been observed by Ahlborn. It is somewhat diffi-
cult to determine positively, owing to the close similarity between
the adjoining trigeminal and facial fine fibre bundles. In hori-
zontal sections the fine fibres of the Trigeminus, 5 2°, are, how-
ever, seen to pass directly forward into the lateral region of the
.mesencephalon. It is thus probable that the fibres entering
from the medulla are mostly sensory fibres from the Auditory

No. 1.] AMPHIBIAN BRAIN STUDIES. 75

nerve which decussate to the opposite side of the brain through
the cerebellum, and either enter the main sensory tract or ter-
minate in some of the cells of the mesencephalon. The de-
scending Trigeminus tract does not decussate, but enters the
-medulla on the same side.

The fine fibres of the Urodele cerebellum are
in part decussating tracts of the Auditory nerve,
and the coarse fibres are non-decussating descend-
ing tracts of the Trigeminus nerve.

This conclusion as to the connection with the Auditory
nerve is supported by Ko6ppen’s observations upon Raza (op.
cit., p. 13), and Ahlborn (p. 261). Ahlborn, however, considers
that the fibres entering the cerebellum are commissural between
the Auditory nuclei of opposite sides. This hypothesis is not
supported by the fact that the superior and inferior tracts are
subequal in diameter.

The passage from the medulla into the mesencephalon is
accompanied by the compact disposition of the gray substance
immediately surrounding the ventricle, Fig. 25. The fine fibres
descending to the trigeminus and the great mass of fibres
from the central region of the medulla become indistinguish-
able, and the only fibres which can be readily followed forwards
in transverse sections are those of the descending trigeminal
tract and the posterior longitudinal fasciculus. Anteriorly, in
the region of the diencephalon, the so-called round bundle is
sharply differentiated from the remaining fibres. In vertical
sections, however, the tracts from the central region of the me-
dulla can be followed with great ease, especially in the brains of
Amphiuma, Necturus, and Cryptobranchus, in which the mid-
segments are only slightly swollen and the sections fall in the
plane of large bundles of fibres (see Fig. 30). These tracts have
been carefully studied in Mecturus, Cryptobranchus, and Rana,
the former genera agreeing closely in all essential features.

Tue NuUCLEI OF THE ANTERIOR SEGMENTS.

The main masses of fibres from the spinal cord and central
region of the medulla sweep forwards either directly into the
central gray of the mesencephalon, diencephalon, or prosen-

76 OSBORN. [VoL. II.

cephalon, while the secondary or more local tracts of the enceph-
alon can in most cases be followed directly to certain nuclei.
The latter are more numerous in the Azwra than in the Uvodela,
at least they are much more sharply defined. The following
nuclei have been observed in the brains of both classes (see
Fig. 31).

A. The nuclei of) tiie, cranialymerves:

1°.. The nuclei of the 3d, 4th, and 6th pairs, 37, 47, and 6m,
are nearly upon the same horizontal level in the Uvrodela.

2°. The great mesencephalic trigeminal nucleus extends along
either side of the entire roof of the segment in many of the
Urodela, but in the Aura is much smaller and is mainly con-
fined to the antero-lateral region (Fig. 26).

3°. Two special well-defined centres of the optic nerve fibres
are observed: a. the roof of the mesencephalon on either side
of the median line in the Uvodela; in the Anuva this extends
into the widely expanding optic lobes. 9. A distinct nucleus in
the middle region of the walls of the diencephalon (corpus
geniculatum).

B. The nuclei of the encephalic tracts

1°. The most distinct of these are the ganglia habenarum,
gh, just anterior to and partly traversed by the superior com-
missure. They are composed of small, rounded cells, like those
of the central gray at the dorsal anterior angle of the thalami.

2°. In the floor of the mesencephalon, just posterior to the
oculo-motor nucleus, is the ganglion interpedunculare,
gi, composed of very small triangular cells.

3°. Just posterior to the posterior commissure is a small dor-
sal nucleus, in the course of the optic tract (see Fig. 24), the
connections of which are undetermined.

4. The corpus striatum is not well defined in the Am-
phibia ; it consists of a mass of scattered cells, slightly anterior
and ventral to the anterior commissure, Fig. 28, cs.

5°. Slightly posterior to the oculo-motor nucleus, on the same
horizontal level, is a nucleus of pale bipolar ganglion cells quite
distinct in character from the nucleus of the third pair, which
consists of triangular deeply stained cells. This is figured, but
not lettered, in Fig. 23, and is seen both in Rana and C7ypio-
branchus (? red nucleus).

6°. The most conspicuous nucleus in Rava is the nucleus

No. 1.] AMPHIBIAN BRAIN STUDIES. vii

magnus of Stieda. This is slightly below and in front of the
cerebellum, 7772.

7°. Another smaller but conspicuous nucleus in Raza is in
the wall of the diencephalon, behind the corpus callosum, 7’,
Fig. 29.

The homologies of some of these nuclei are rather uncertain.
The nucleus in the wall of the diencephalon which gives rise to
the fibres of the optic nerve corresponds probably to the mid-
dle or lateral geniculate body.

The nucleus just behind the oculo-motor ganglion corresponds
closely in position to the red nucleus of the tegmentum.
Stieda and K6éppen have suggested that the nucleus magnus
corresponds to the dentate nucleus of the cerebellum, but
this is also in the position of the red nucleus and presents
many points of agreement with it in its relations to the sur-
rounding tracts; its relations to the cerebellum are, however,
by no means well ascertained.

THe Main SENSory AND Motor ENCEPHALIC TRACTS.

There is no certain means of distinguishing the sensory from
the motor tracts. In the ascending series of sections of the
medulla oblongata, it has been shown that the posterior columns,
which presumably contain unmixed sensory fibres, and the lat-
eral columns of mixed fibres are thrust downwards by the super-
position of the cranial nerve nuclei. As a result of this, we
should expect to find the sensory tracts occupying the lateral
portion and the motor tracts the median portion of the central
region of the medulla, corresponding to the anterior columns of
the lower levels of the cord. That such is actually the case is
supported by two facts. First, it is found in Cryptobranchus
that the median region consists of slightly larger and deeply
stained fibres, more of the nature of motor fibres than those of
the lateral region; and second, the fibres of the lateral region
mostly terminate in the mesencephalon and diencephalon, while
those of the median region, in large part at least, extend di-
rectly forwards into the prosencephalon. With this evidence I
may at all events describe these lateral tracts as sezsory and the
median tracts as mo‘¢or.

The Sensory Tracts. In successive sagittal sections of
the brains of Cxyptobranchus, Necturus, and Rana, we first pass

78. OSBORN. [Vou. II.

through the fibres of the extreme lateral portions of the me-
dulla, entering the cerebellum, cé/¢; then we observe large
bundles of fibres from the lateral regions of the medulla,
mst, ascending and spreading over the outer surface of the mes-
encephalon, Figs. 24 and 30. In sections slightly internal to
these, the central gray of the mesencephalon comes into
view, with rows of cells and bands of fibres alternating, and the
continuation of the same medullary tract is observed spreading
over the outer surface of the diencephalon in precisely the same
manner, dst. These direct diencephalic and mesence-
phalic sensory tracts are beautifully shown in vertical sec-
tions of the brain of Amphzuma, in which these segments are
very slightly differentiated from each other. In succeeding.
sections, still approaching the median line, the direction of the
fibres is reversed; from the postero-lateral region of the mesen-
cephalon and the lateral region of the diencephalon, the main
trend of the fibres is downwards and forwards, mst! and dsz.!
The latter fibres pass directly forwards into the basal portion
of the prosencephalon. The former, ms¢’, turn downwards, but
their forward continuation into the prosencephalon cannot be so
distinctly followed. The simplicity of these ascending and
descending systems in the Uvodela is interfered with in the
Anura by the expansion of the optic lobes, but the arrangement
is the same.}

In transverse sections of the optic thalami, the dorsal portion
of the cerebral peduncles is composed of a compact round bun- ©
dle of fibres, (Osborn, ’84, Fig. 8,2). The origin of this is
somewhat uncertain. From the fact that it is first differen-
tiated in the anterior portion of the mesencephalon and becomes
more distinct in the thalami, we may infer that this bundle is
composed of the prosencephalic sensory tracts formed
from these segmenits:

In Rana, in which the corpus callosum and-anterior commis-
sure are somewhat separated, a portion of this bundle seems to
pass between them (Fig. 29). There is room for error here in
the fact that the basal fore-brain bundle from the medulla is
reinforced by fibres both from the ascending diencephalic and
mesencephalic tracts and from the infundibular tract.

1 See Képpen, op. cit., Taf. III., Figs. 27, 28.

No. 1.] AMPHIBIAN BRAIN STUDIES. 79

The Motor Tracts. As the sections extend inwards
the mass of fibres from the medulla does not ascend, but passes
forwards directly into the basal portion of the prosencephalon
as the basal prosencephalic tract (basal fore-brain bundle,
Edinger). This is best followed in the Uvodela, but is also
readily followed in successive sections in the Anwra, Figs. 28, 29.
Upon reaching the corpus striatum, some of the fibres of this
tract enter this body, as described recently by Edinger (Fig. 28),
while others pass directly into the inferior portion of the mantle
of the hemispheres; a third portion seems to terminate imme-
diately below the anterior commissure: but in horizontal sec-
tions it is seen to pass to the other side.!

The tract thus consists of three parts: a, a direct bundle
from the hemispheres; 4, a bundle from the corpus striatum ;
c, a decussating bundle from the hemispheres. Two of these
divisions were incidentally described and figured in my paper
upon the Corpus Callosum (loc. cit., Taf. XIV., Fig. 8, pm, p/).

THE SECONDARY ENCEPHALIC TRACTS.

Under this head may be considered the tracts which, so far
as observed, have no direct connection with the spinal cord or
medulla.

Meynert’s Bundle. This is a conspicuous tract in the
brains of all the Amphibia, 7d. It arises, in the usual manner,
from the ganglia habenulz and descends beneath the superior
commissure as a compact bundle of darkly stained fibres, to the
ganglion interpedunculare. I have followed it slightly beyond
this point in Raza, Fig. 29, but not into the medulla, as Ahlborn
has succeeded in doing, in Petromyzon.

The Infundibular Tract. From the infundibular lobes
this large tract of fibres ascends, z¢, beneath the basal prosence-
phalic tract, towards the hemispheres. Koppen has described it
as entering the thalami. It has this appearance in Rana, but not
in the Uvodela, where it appears to pass directly forwards and
not upwards.

The Posterior Commissure. The relations of this com-
missure are threefold ; first, to the oculo-motor nucleus and prob-
ably to the main sensory tract; second, to the pale ganglion

1 This decussation is described by many authors as a portion of the anterior
commissure, but in my opinion should be considered as entirely distinct,

80 OSBORN. [Vot. II.

cells behind this nucleus; third, to the tectum opticum. As
it descends, the fibres divide into two bundles (Fig. 25),
of which the anterior surrounds the superior processes of
the ganglion cells of the oculo-motor nucleus (Fig. 20, pcs):
this connection is so close that some of these fibres seem to
be actually continuous with the cells. The posterior bundle
has a similar connection with the cell processes of the pale
ganglion, which may in fact also belong to the oculo-motor
nerve. None of the fibres of this commissure can be traced
directly into the main (sensory) tracts adjoining these nuclei,
as observed by Pawlowsky, although such a connection seems
highly probable (tractus cruciatus tegmenti). Dor-
sally, the fibres of this commissure in Rana can be clearly
followed into the peripheral white substance of the tectum
opticum, as shown in horizontal sections.

The Superior Commissure. This is much less constant
in size and development than the foregoing. It is extremely
small in the Azwra and apparently so in the Proteida,! but is
large in Cryptobranchus and Amphiuma. It divides into two
distinct bundles, one of which descends into the inner mantle
of the hemispheres, secs, and finally disappears, after bending
around into the outer portion of the mantle. The second bundle
descends directly along the outer wall of the thalami. These
bundles are clearly seen where the commissure is well developed,
and I have fully described them elsewhere (84, p. 268, Fig. 8).
One fact militates against our considering the commissure as a
purely decussational system ; that is, the bundle entering the
hemispheres is much larger than that entering the thalami. It
forms either partly a commissural system between the poste-
rior portions of the hemispheres and between the thalami, or
partly a decussational system between the hemispheres and
thalami.

Cerebral Commissures. I have seen reason to partly
alter my views as to the nature of the commissures of the
hemispheres which were described in detail in my paper on
the corpus callosum. The more recent researches of Bellonci,
with the aid of the Golgi method, upon these commissures,
should be consulted.2- They show that with the purely commis-

1 Necturus.
21 regret that I have not the opportunity at present to investigate thoroughly the
interesting questions which Bellonci has raised in this valuable memoir in regard to

No. 1.] AMPHIBIAN BRAIN STUDIES. 81

sural fibres, decussational fibres are intermingled. I have
myself discovered that in the upper bundle or corpus callosum
of Menobranchus there enter fibres from the diencephalon.
Proteus agrees with JMenobranchus in the entire separation of
this bundle from the anterior commissure. I have seen no trace
in the Amphibia of the fornix columns which I have found
in the Ophidia (86, p. 533, Fig. 20), and Bellonci has figured in
the Lacertilia, (87).

Other important commissures are the infundibular com-
missures which connect the infundibular lobes, dorsally and
ventrally, and the extensive commissure of the tectum opticum.

THE ORIGIN OF THE Optic NERVES.

It has recently occurred to me that the presence of the
two whitish bands seen upon the external dorsal surface of the
optic lobes in many of the Uvodela is partly due to the under-
lying optic tracts. It is certain that these tracts in the Uvodela
are principally confined to the median portions of the tectum
opticum. They can be followed as far forwards as the cerebel-
lum, II. ¢ 1, Figs. 23, 24, and descend obliquely from this region
to the nerve. In the Uvode/a there is no differentiation of cells
into distinct layers.

The character of the cells of this region is shown in Fig.
25a, which illustrates an interesting observation upon the ap-
parent connection of the fibres either of the optic nerve or
of the direct sensory mesencephalic tract with the fibres of
the descending Trigeminus tract. The peripheral cells of the
central gray substance, II. x, have long single processes.
These processes branch, one of the finer branches en-
tering the coarse fibres of the descending Trigeminus, the
other passing outwards into the fine layer of fibres of the
tectum opticum. This observation has been confirmed at
several points. It shows first that the fibres of the Trigemi-
nus may have a compound origin, partly from the large cells,
5, partly from the small cells; second, that here is a possi-
ble centre between the optic and trigeminus nerves.

The second optic tract, II. #2, arises from a mass of cells im-

the complete structure of these commissures. I do not therefore at present feel in
a position to reply to his courteous criticism of my paper.

82 OSBORN. [VoL. II.

bedded in the central gray of the thalamus, and not clearly
differentiated as a distinct nucleus from the surrounding cells.

The third tract, II. ¢ 3, enters the hemispheres directly. This
observation, although made in both the Uvodela and Anura, re-
quires to be confirmed. The optic tracts have other sources
of origin ;1 the above are the main centres contributing the prin-
cipal portion of the nerve, and are the only ones which can be
clearly made out by the carmine method.? !

In Rana the roof of the optic lobes is divided into eight
distinct layers, the fibres of the superior portion of the optic
tract entering the outermost layer, 1 Fig. 26, and ramifying
to the interior cells. The inferior portion of the optic tract
enters the second fibre layer, 3. The tracts surround the whole
circumference of each of the lobes.

The relations of the encephalic tracts in the general architec-
ture of the amphibian brain is shown in Fig. 21, in which only
the well-determined tracts are introduced. The designation
of the tracts expresses my present views; as I have already
stated, the efferent or afferent character of the main tracts is
not by any means settled.

COMPARISON OF THE DIPNOAN AND AMPHIBIAN BRAIN.?

The recent memoir of Fulliquet upon the brain of Protopterus
is the first contribution to the histology of the Dipnoan brain,
and enables us to make some interesting comparisons. In the
first place, as observed by this author and others, the general
external resemblance between the Dipnoan and Urodele brains
is very striking. The principal external features in common
are as follows: the olfactory lobes are not well distinguished
from the hemispheres ; this is even more marked in Protopterus
than in the Urodela. The mesencephalon of Protopterus passes
imperceptibly into the diencephalon, as in Amphiuma, only a
faint lateral constriction between these segments being evident.*

1 See the papers of Bellonci, Blaschko and Edinger.

2 In my paper upon AZenofoma (84, p. 267, Fig. 8), I described a portion of the
optic nerve as non-decussating. I am now inclined to consider these supposed
uncrossed tracts, 6, as the mesencephalic tracts which cross at a different level, or the
basal optic root of Edinger. The sections at this point are deceptive.

8 See also Appendix, Note 4.

4 In distinguishing between these segments internally, Fulliquet has failed to take

No. 1.] AMPHIBIAN BRAIN STUDIES. 83

The optic lobes form single, unpaired bodies, as in many of the
Urodela. The infundibular lobes in both orders are large and
functional. The cerebellum is small! and partly overhung by
the mesencephalon.

In a few respects the brain of Protopterus differs: the gan-
glia habenarum are much larger than in the Urodela, resembling
those of Petromyzon. The anterior portion of the metencephalon
is greatly expanded by the hypertrophied nuclei of the 5th—8th
nerves and a diverticulum of the 4th ventricle. The olfactory
nerves arise from the dorsal aspect of the rhinencephalon.

The similarity in the internal structure is very significant.
The general arrangement of the encephalic gray substance, as
the central gray, immediately surrounding the ventricles, is the
same ; the dipnoan efendyma has the peculiarity, first observed
by Stieda in Rama, of the thread-like extensions of its cells
through the central gray into the white substance; we also ob-
serve the peculiarly modified elongate ependymal cells (Fulli-
quet, Pl. IV. Fig. 17, cde), in the region of the posterior com-
missure, so characteristic of the Uvodele brain. As these ob-
servations were prior to the discovery of the true nature of the
pineal gland, the author has naturally failed to identify this
structure, mistaking the ganglia habenarum for it (Fig. 19).
The relation of the dia- and procceliz seem to resemble those
of Rava more closely than those of the Urodeles, since, as far
as I can judge from Figs. 19 and 20, the prosencephalic com-
missures are in the /amina terminalis proper, and not in a pro-
jection of the floor of the ventriculus communis, as in the
Urodela. The space marked TM in Fig. 19 represents this
ventricle.

The encephalic commissures of Protopterus? apparently agree

advantage of the anterior and posterior boundaries of the Diencephalon (Entrencé-
phale), as defined by the posterior and superior commissures.

1 As there is no sagittal section of the Protopterus brain given, it is somewhat
difficult to determine the limits of the cerebellum. A portion of the brain desig-
nated Cervelet (Plate I.) is apparently a portion of the hypertrophied nucleus of the
trigeminal nerve.

2 Fulliquet has not distinguished the posterior or superior commissures as such;
nor has he identified the upper bundle in the lamina terminalis with the corpus
callosum, as seems highly probable. It follows that my determination of these com-
missures is largely inferential from a comparison with similar sections of the Urodele
brain.

84 OSBORN. (Vou. II.

closely with those of Cryptobranchus. We first observe that
the lobes of the infundibulum (Fig. 14) are united dorsally and
ventrally by commissural fibres as in the Uvodela (Osborn, ’84,
Plate IV., Fig. 4, scm, icm). The two sides of the tectum opti-
cum are also united by an almost continuous band of transverse
fibres, Fig. 11, fem, as in the Amphibia, terminating anteriorly
in a special enlargement, fce, Fig. 17, which I identify as the
posterior commissure. The bande fibrillaire laterale of Fig. 15,
fl, is probably either the posterior commissure or Mey-
nert’s bundle. The bundle connecting the ganglia habe-
narum, in Fig. 18, fgf, is probably the superior commissure.
The upper bundle 7%, Fig. 19, and ff, Fig. 20, in the lamina
terminalis, is probably the corpus callosum; this is an im-
portant fact, if verified, since this commissure has not heretofore
been definitely identified below the Amphibia! This can only
be verified by following the course of its fibres. The lower
bundle, Fig. 19, ca, occupies a somewhat unusual position, upon
the floor of the brain.

Two differences in the internal structure may be noted : first,
the optic chiasma is intra-axial or central, instead of periph-
eral, as in the Amphibia; second, there is a single pair of
large Mauthner fibres in the medulla oblongata, which are
wanting in most of the Uvodela,? although the posterior lon-
gitudinal fasciculus is apparently present, 77, sp, Fig. 1.

I cannot institute any satisfactory comparison in respect to
the origin of the cranial nerves. Many minor points of re-
semblance and difference have been passed by in this resumé,
the general conclusion being that there is a very close
similarity between the Amphibian (Urodele) and
Dipnoan brain, both in the external and internal
structure.

COMPARISON WITH PETROMYZON.

One of the chief features of Ahlborn’s memoir upon the
brain of Petromyzon is the thoroughness with which he has in-

1JIn concluding my paper upon the corpus callosum (Morph. Jahr., Band
XII., p. 539), I had not seen Fulliquet’s memoir, but anticipated from the embry-
ology of the Ceratodus fore-brain, that this commissure would be found in the Dipnoi
2 They have been observed by Stieda in Siredon, see Appendix, Note 5.

No. 1.] AMPHIBIAN BRAIN STUDIES. 85

vestigated the medulla oblongata, especially the origin of the
cranial nerves and the fate of the Miillerian fibres. The ar-
rangement of the latter, I have reason to believe, is very similar
to that in the Amphibia, but this system has not been as yet
well investigated. His conclusions as to the origin of the
cranial nerves are in many details supported and confirmed by
my own, although I have discovered many additional struc-
tures which either do not exist or have been overlooked in the
lamprey.

An important difference is seen as to the more primitive con-
dition of the medulla in Petromyzon, in that the nerve nuclei
are more central (Fig. 18), and not confined to the lateral regions
of the medulla as in the Urodela. In the latter I have ob-
served the large ganglion cells, gc, opposite the exit of the
8th, but cannot confirm the entrance of their processes into the
Auditory roots as observed by Rohon and partly confirmed by
Ahlborn. He places the 7th and 8th in one group, which I find
cannot be done in the Uvodela, the 7th being closely related to
the 5th.

One chief point of agreement is that in Petromyzon the 7th
nuclei and exit are dorsal to the 8th; this confirms my
observations and undermines the hypothesis that the 8th is the
sensory portion of a typical pair of nerves of which the 7th
forms the motor element. Our observations agree further in
respect to the connection of the posterior longitudinal
fasciculus with the 8th (acusticus haubenbahn, p. 268) ;
also as to the presence of a nucleus of pale ganglion cells near
the exit of the 8th (p. 261), which I have found is one of the
chief Auditory nuclei in the Uvodela; further, the nuclei and
tracts of the 8th have the same relation to those of the 5th, as
I have described in Cryptobranchus; finally, in both genera
the 8th sends a tract into the cerebellum.”

The resemblance of the main Trigeminal system is also close.
I do not find the nucleus of the transverse motor tract as
large as he describes it, but the motor nucleus adjoining the
ascending tract is similar in form and position (Figs. 16-
21). -I do not find an upper and lower nucleus of the 8th,

1 See Appendix, Note 3.
2 This determination of the Auditory nuclei as ventral to those of the Facial is
confirmed by both Stieda’s and K6ppen’s observations upon Rana.

86 OSBORN. [VoL. II:

consisting of small cells such as Ahlborn describes (see Fig.
19). His upper 8th nucleus, VIII., corresponds exactly with
my lower 7th nucleus, 7 #z, this agreement raises a question
whether Ahlborn’s upper 8th root does not pass into the 7th
nerve. If such is the case, the homology with Cryptobranchus
is remarkably close.

In the upper portion of the encephalon in Petromyzon is
found the posterior longitudinal fasciculus, approaching
the Oculo-motor nucleus, and according to Ahlborn, not termi-
nating with it, but decussating at this point to enter the thalami
(p. 274). The descent of Meynert’s bundle to the inter-
peduncular ganglion is also seen The taenia thalami
optici, p. 285, with fibres entering both the hemispheres and
the thalami, is homologous with the superior commissure.

LITERATURE.

AHLBORN. Untersuchungen iiber das Gehirn der Petromyzonten. Zeit. f. wiss. Zodl.,
1883, p. 192.

BELLONCI. Sulle Commissure Cerebrali Anteriori degli Anfibia e dei Rettili. Bologna,
1887. Mem. del. Real. Accad. del. Sci. dell. Istituto di Bologna. Ser. IV.,
Tom. VIII. :

Intorno alla struttura e alle connessioni dei lobi olfattorii negli Artropodi
superiori e nei vertebrati. — Atti della R. Acc. dei Lincei, 1881-82.

EDINGER. Zehn Vorlesungen iiber den Bau der Nervésen Central-organe. Leipzig
1885.

Ueber die Verbindung der sensiblen Nerven mit dem Zwischenhirn. Ana-
tomischer Anzeiger. 1887.

FISCHER. Anatomische Abhandlungen iiber die Perennibranchiaten und Derotre-
men. Hamburg, 1864.

FULLIQUET. Recherches sur le Cerveau du Protopterus Annectens. Genéve. 1886.

GASKELL. Journ. of Phys., 1886, Vol. VII., p. 1.

GEGENBAUR. Die Metamerie des Kopfes und die Wirbeltheorie des Kopfskeletes.
Morpholog. Jahr. Band XIII., pp. 1-112.

HILL. The Grouping of the Cranial Nerves. Brain, Part XXXIX., 1887.

KOpreEN. Zur Anatomie des Froschgehirns. Arch. f. Anat. u. Phys., Anat. Abth.,
1888, pp. I-32.

Orr. The Embryology of the Lizard. Journ. of Morphology, Vol. I., No. 2, Decem-
ber, 1887.

OsBoRN. Preliminary Observations upon the Brain of Amfphiuma. Proc. Phila.
Acad., 1883, p. 177. Preliminary Observations upon the Brain of A/enopoma
and Rana. Proc. Phila. Acad., 1884, p. 262.

The origin of the Corpus Callosum, etc. Morph. Jahrb., Band XII., 1886.
Part I., p. 223; Part IL., p. 530.

1 Ahlborn has followed this bundle, asymmetrical in Pe¢romyzon, into the medulla.

No. 1.] AMPHIBIAN BRAIN STUDIES. 37

The Relation of the Commissures of the Brain to the Formation of the
Encephalic Vesicles. Proc. Amer. Assoc. Adv. Science, August, 1887; published
March, 1888, p. 262. Also, American Naturalist, October, 1887, p. 941.

RAuBER. Die Lehre von dem Nervensystem und den Sinnesorganen, (Anat. des
Menschen). 1886.

SPITZKA. Contributions to Encephalic Anatomy, in nine parts. Journ. of Nerv. and
Mental Disease. New York.

STIEDA. Ueber den Bau des centralen Nervensystems der Amphibien und Rep-
tilien. Zeits. f. wiss. Zod]. Band XX.

Ueber den Bau des centralen Nervensystems des Axolotls. Zeits. f. wiss.
Zool. Band XXV.

WILDER. The Dipnoan Brain. American Naturalist, June, 1887.

“Anatomical Technology; ” also shorter papers upon the structure and nom-
enclature of the Brain.

APPENDIX.

1°. Figure 2. A vertical section of the Brain of a Reva embryo, at the period
of the formation of the encephalic commissures, cé/, pcm, scm. Lettering as in the
Explanation of Plates.

Fig. 3. A horizontal section of the same, composed from two levels, showing the
relation of the commissures to the encephalic vesicles,

2°. Fischer (op. cit. p. 135) upon the distribution of the Facial
and Trigeminal Nervesin Cryptobranchus. The FAcrA divides into
four main branches: R. palatinus; R. mentalis passes the mylohyotdeus
muscle and terminates in the skin of the lower jaw (sensory); R. alveolaris to
the skin above the masseter muscle (sensory); R. jugularis to the mylohyotdeus
posterior and digastricus muscles (motor). The TRIGEMINUs has three branches:
5", a, retractor bulbi, rectus externus and superior, obliguus superior (motor,
including Abducens); 4, skin of forehead, olfactory chamber, snout and superior
maxilla (sensory) ; 5’ to skin over premaxilla; 5/’/’, 2, to masseter and temporal
muscles (motor); 4, skin covering inferior maxilla (sensory). It will be observed
that this distribution of the Facial is largely sensory and is consistent with the
derivation of the main sensory elements of both nerves from the dorsal sensory
nucleus, as I have described them. It also demonstrates that the lower bundle of
the Facial is eertainly motor.

3°. The Miillerian fibres and posterior longitudinal fasciculus.
As shown in Fig. 11 (Plate V.), these two systems are apparently distinct. The
Miillerian fibres are observed at the lowest medulla levels as a compact round

88 OSBORN. [VoL. Il.

bundle immediately below the anterior commissure; as we ascend, they multiply and
form a crescent in the anterior median columns; at the exit of the vagws they sep-
arate into two strands, one, dorsal, below the sulcus centralis, the other, ventral,
in the anterior columns; the ventral strands cross and disappear between the exit of
the oth and 8th nerves, entering large ganglion cells. The dorsal ascend to a higher
level without apparently crossing; they are continuous with and appar-
ently constitute the main portion of the posterior longitudinal
fasciculus.

The Auditory tract of this fasciculus closely adjoins the dorsal Miillerian fibres,
but may be distinguished from them by the slightly smaller diameter of its fibres; it
is clearly distinguished opposite the exit of the roth pair! and on all the higher
levels; this leads me to the conclusion that this portion of the posterior longitudinal
fasciculus is an ascending auditory tract apparently distinct from
the Millerian fibres. This further throws in doubt the supposed connection
between this fasciculus and tract.

4°. Wilder upon the brain of Ceratodus. This description is macro-
scopic. In Ceratodus, like Protopterus, and unlike the lower Urodela, the ventri-
culus communis is very small. As in the Urode/a there is a large supraplexus.
The olfactory lobes, unlike those of Protopterus and the Amphibia, are pedunculated
instead of sessile. The anterior commissure is mentioned, but the corpus callosum is
not observed. Finally, an important distinction is seen in the fact that the extension
of the hemispheres (secondary forebrain) is vedva/ from the primary forebrain both
in Ceratodus and Protopterus, instead of directly anterior, as in the Amphibia.

I may express here my indebtedness to Professor Wilder for much of the termi-
nology which I have adopted from his papers, and my regret that he has found it
necessary to change his former terms in so many instances.

5°. Stieda’s observations upon Axolotl include several points in which,
if correctly described, this genus differs from Crvptobranchus. 1. Opposite the exit
of the 12th nerve, on either side of the sulcus centralis, is a large Mauthner
fibre, exactly as in Petromyzon. I think these fibres are not present in Cryffo-
branchus. 2. The ascending Vagus, or fasciculus solitarius, while arising in
the same manner as in Cryftobranchus, is given off with the exterior roots, the
Glossopharyngeus portion, instead of with the posterior. 3. A portion of the pos-
terior longitudinal fasciculus makes its exit with the 8th pair, but is desig-
nated by Stieda as a portion of the Facial-Trigeminal system. This probably cor-
responds to the bundle which I have finally referred to the 8th nerve, Fig. 15, VII.-
VIII. 3, 4. Another important observation is that a portion of this same fasciculus
enters the Trigeminus. I am inclined to doubt this, as it has no parallel elsewhere,
and it would be easy to mistake this for the posterior bundle which I have observed
uniting with the descending trigeminus (see 54%, Fig. 17). 4. Stieda describes
the ascending trigeminus as sezsory, probably from its relations in human anatomy;
it is true this tract is first found in the sensory column of the cord, but it subsequently
lies in the motor region and is reinforced by motor cells. It probably consists of
mixed fibres.

Stieda’s and Képpen’s observations upon the brain of Rana. It
is difficult to give a critical review of Stieda’s results, first, because from the limitations

1] regret that none of the figures represent the relations of this tract to the Miillerian fibres with
perfect accuracy. I am not sure that this tract can be clearly distinguished at the level of the r2th
pair, as represented in Fig, 11,

No. 1.] AMPHIBIAN BRAIN STUDIES. 89

. of his histological methods his observations were fragmentary; second, because the
brains of Rana and Cryptobranchus differ so widely.

Stieda designates asthe nucleus centralis the group of sensory cells in the
floor of the ventricle on either side of the sulcus centralis. I cannot support his
suggestion that this nucleus is in any way connected with the Vagus roots. As he
has confused the Facial and Auditory nerves and nuclei, his results, so far as these
are concerned, are invalidated.

K6éppen, profiting by the Weigert method, has given a much more precise and
full description of the mzedudla, although his description of the Facial-Trigeminal
system is very incomplete. 1. He recognizes the posterior longitudinal
fasciculus, p. 6, and its probable connection with the Auditory nerve. This
adjoins the dorsal part of the Miillerian fibre system, the ventral part of which,
after crossing, disappears, as in C7yftobranchus, in the great ganglion cells oppo-
site the exit of the Auditory nerve. 2. He describes also, p. 7, a nucleus of
large cells as probably belonging to the Auditory; this corresponds to my pale
ganglion, 8, Fig. 14. At this point he fails to distinguish between the Facial
and Auditory elements, for his dorsal Auditory root, p. 9, is probably the main
portion of the Facial. This error, if error it be, arises from the fact that he expects
to find the facial a purely motor nerve, p. 10. 3. The Trigeminus, p. 10, is traced to
two ascending bundles, and a large motor nucleus. No sensory nucleus or mesen-
cephalic descending bundle is described. 4. Képpen makes many important addi-
tions to the higher encephalic tracts and nuclei in Rava, among which are the
Auditory tract to the cerebellum, p. 13; the interpeduncular ganglion, p. 16; the
posterior longitudinal fasciculus to the region of the III nucleus, p. 17; the infundi-
bular tract to the hemispheres; the mesencephalic and diencephalic tracts from the
medulla, and the tracts from these segments to the hemispheres, pp. 30-31; the
ganglion habenulz and Meynert’s bundle. The hemispheres receive no direct sen-
sory tracts from the medulla; these tracts first enter the optic lobes and thalami,
from which fresh tracts rise to the hemispheres. With this conclusion, p. 31, I am
inclined to agree, although I do not think it is absolutely demonstrated. 5. I differ
from Képpen in his attempt to homologize the encephalic with the lower segments,
p- 26; also, as I understand him, p. 30, he does not describe any direct motor tract,
(basal forebrain bundle), to the anterior columns of the medulla. The agreement, in
respect to the tracts mentioned above, is strongly confirmatory, since my observations
were made independently, and the conclusions reached before the receipt of his
paper.

6°. Methods. The methods of hardening and staining have been fully de-
scribed in previous papers. The best staining results have been obtained with long
zz toto immersion in Ammonia Carmine. I have had the advantage, for purposes
of comparison, of a full series of the brain of Sa/amandra, prepared after Weigert’s
Method by my assistant, Mr. J. Warne Phillips, in Dr, Edinger’s laboratory. I
find that brilliant as these preparations are, the carmine series give a fuller and more
reliable field of observation. The late Professor Gudden, of Munich, told me, after
long experience, that he had reached the same conclusion, and this is also the
opinion of Dr. Spitzka of New York.

90 OSBORN. [Vot. II.

EXPLANATION OF PLATES IV.-VI.
INDEX LETTERS TO ALL FIGURES.

The Encephalic Segments. — Rh, rhinencephalon, olfactory lobes. Pr, prosence-
phalon, cerebral hemispheres. Dz, diencephalon, optic thalami. Ze, mesencepha-
lon, optic lobes. J/¢, metencephalon, medulla oblongata.

Ventricles. — a, aula, ventriculus communis. /rc, prosoceele. Z, porta, foramen
of Monro. a, diaccele. msc, mesoccele. wfc, metaccele. zx/f, infundibulum.

The Commissures. — cto, commissure of the tectum opticum. ca@/, corpus callosum;
cal', posterior division of same, (?comm. cornu ammonis). 2c, inferior infundibu-
lar commissure. cs, posterior commissure. rcs, anterior commissure. scm, superior
infundibular. scs, superior commissure.

Cranial Nerves. —I1.-IV., as usual. V./, opthalmic; V.!, superior maxillary;
V.'"", inferior maxillary, divisions of the Trigeminal. VII, Facial, upper bun-
dle, joining the Gasserian Ganglion; VII.", lower bundle joining the Auditory and
sending off the 2. mentalis and R. jugularis. VIII., Auditory. IX., Glosso-
pharyngeus. X., Vagus. XI. (XII.), Hypoglossal.

The Encephalic Nerve Tracts. —bpt, basal prosencephalic tract. 6/f, same.
chit, cerebellar tract entering optic lobes. cé/¢, cerebellar tract from medulla oblon-
gata. dst, sensory (?) tract to optic thalamus. ds¢’, sensory tract from optic thala-
mus to hemispheres. /<, fasciculus communis. /%, fasciculus solitarius. 7¢, tract
from infundibular lobes to hemispheres. st, sensory (?) tract to mesencephalon.
mst!, sensory tract from mesencephalon to hemispheres. md, Meynert’s bundle.
PF, posterior longitudinal fasciculus.

Cranial Nerve Tracts. Trigeminus.—s5?, the ascending tract. 5 4%, the
ascending tract reinforced by the tract from the great motor nucleus. 5 ¢%, the sen-
sory tract. 5 ¢4, the descending (mesencephalic) tract. 5 75, the encephalic tract.

Facialis. — 7 tl, lower, motor (?) tract. 7 ¢#, upper, sensory tract. 7 ?, ence-
phalic tract.

Acusticus. —§8 ¢, tract from the pale nucleus, and special sensory nucleus. 8?,
cerebellar tract.

Glossopharyngeus. — 9 ¢, sensory tract.

The Encephalic and Cranial Nerve Nuclei. — 3, 3 ', upper and lower Oculo-
motor nuclei. 4, Trochlearis, motor nucleus. 557, dorsal sensory nucleus of
Trigeminus. 5 #7, ventral motor ditto. 5, mesencephalic nucleus of Trigeminus.
6, Abducens nucleus. 75”, and mm, dorsal sensory and lateral motor nuclei of
Facialis. 8, Auditory nucleus of pale ganglion cells. 8s, Auditory nucleus of
small sensory cells. 9 mm, lateral motor nucleus ot Glossopharyngeus. 9 sz, dorsal
sensory nucleus of same. 9, ventral motor nucleus of same. 10, ventral motor
nucleus of Vagus. cé/.m, cerebellar nucleus. cs, corpus striatum. dn, superior
diencephalic nucleus. dz’, inferior diencephalic nucleus. fev, nucleus of fasciculus
communis. gc, nucleus of large ganglion cells opposite Auditory root. gh, ganglion
habenule. 7, interpeduncular ganglion. mc, nucleus centralis. #2, nucleus mag:
nus. #/, pale nucleus,

Ban ibs
re ”

ay

92 OSBORN. (Vou. II.

EXPLANATION OF PLATE IV.

The figures of the brains were outlined with a Nachét camera lucida, and the sur-
face details inserted as studied in different lights. The vertical sections (Figs. 7-9)
are reconstructions of the actual median plane by composition of a number of sec-
tions.

FicurE 1. Brain of Sivredon (Axolotl) mexicanus. The species is somewhat
uncertain. Viewed from above. Enlarged 4} diameters.

Fic. 2. Brain of Mecturus (Aenobranchus) maculosus. Viewed from above.
Enlarged 45 diameters.

Fics. 3 AND 4. Brain of Proteus anguineus. Viewed from below and above.
Enlarged 43 diameters.

Fic. 5. Brain of Siren lacertina. Viewed from above. Enlarged 4} diameters.

Fic. 6. Medulla oblongata of Cryptobranchus alleghaniensis. Viewed upon the
ventral surface, showing the exit of the cranial nerves, as reconstructed from trans-
verse sections.

Fic. 7. Sagittal section of the brain of Cryptobranchus, through an ideal median
plane, as reconstructed from sagittal sections.

Fic. 8. Sagittal section of the brain of Mectwrus, drawn as above.

Fic. 9. Sagittal section of the brain of ana, drawn as above.

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94 OSBORN. [Vor. I.

EXPLANATION OF PLATE V.

Fics. 10 To 18. A series of transverse sections through the medulla oblongata of
Cryptobranchus alleghaniensis, from the exit of the 12th pair (XI.) to the exit of
the 6th pair, enlarged about forty diameters. For the sake of clearness only a few
cells of each nucleus are represented, and these are drawn to scale. Most of the
sensory and motor cells of the Cez¢ra/ region are also omitted. The cell area is
represented in dark gray. The contours of the tracts are usually well defined, but
have been exaggerated in several figures. The level of the transaction represented
by each of these figures is indicated in the diagram, Fig. 21 (— f. 10— f. 18).

Fic. 19. Sagittal section through the tectum opticum (of/) and cerebellum of
Cryptobranchus. This shows the posterior portion of the great trigeminal nucleus;
the small nucleus of cells in the cerebellum, cd/z; the decussating cerebellar tracts,
chit; and the descending trigeminus, 574. 19a represents the cells of the tri-
geminal nucleus enlarged.

Fics. 20 AND 20a. Vertical and horizontal sections through the oculo-motor
nucleus, as seen under a Zeiss D; camera drawing.

Fic. 21. Diagram of the cranial nerve nuclei of Cryptobranchus, as reconstructed
from transverse and horizontal sections. The relative location of the 3d—6th nuclei,
posterior commissure, Meynert’s bundle, the main exits of the nerves and the pos-
terior longitudinal fasciculus are all determined with the camera. The nuclei of the
5th-10th pairs are reconstructed from transverse sections. They overlap each other
less closely than in nature. The sezsorvy nuclei are distinguished by oblique lines;
the ofoy nuclei by transverse lines; the pale ganglion nucleus of the Auditory by
crossed lines. The external row, 5, 7,9, are the dorsal sensory nuclei. The
internal row, 5, 9, 10, are the ventral motor nuclei. The external intermediate,
7, 9, are the doubtful lateral motor nuclei, adjoining 8 and f the lateral
sensory nuclei.

The fasciculus communis /,//”’ is represented in gray to indicate that it is
apparently forming new bundles from a continuous sensory nucleus.

The dotted lines represent the descending, 7.e. encephalic, tracts. The heavy lines,
the descending trigeminus and the posterior longitudinal fasciculus. The pale lines,
the tracts springing from the special nuclei.

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96 OSBORN. [Vou. II.

EXPLANATION OF PLATE VI.

The figures, with the exception of Fig. 30, are composites of three or four sections,
and thus present a larger number of fibres than are in view in any single plane.

Fics. 24 AND 25. Sections of Cryftobranchus. The former is through the outer
regions of the encephalic segments; the latter is just external to the mass of central
gray matter.

Fic. 25. Transverse section of the mesencephalon of Vecturus at the exit of the
3d pair of nerves, 25a. An enlarged actual section of the roof showing the connec-
tion of the descending trigeminal fibres with the cells of the optic tract. Camera
drawing.

Fic. 26. Sagittal section through the outer portion of the left optic lobe of Rana.
Eight layers may be distinguished as follows: 1, the outer fibre layer which contains
the superior portion of the optic tract; 2, the layer of scattered nerve cells; 3, the
second fibre layer penetrated by the inferior portion of the optic tract; 4, the second
layer of compact nerve cells; 5, the third fibre layer; 6, the third fine layer of com-
pact nerve cells; 7, the fourth fibre layer; 8, the ependyma. The outer fibre layer
is mostly homogeneous. The second and third fibre layers are traversed by radiating
fibres which connect the three cell-layers.

Fics. 27 TO 29. Outer, median, and inner sagittal sections of the brain of Rana.
The latter is slightly external to the central gray substance.

Fic. 30. Sagittal section of the brain of Amphiuma. The dotted lines represent
the actual contours in the lateral plane of this section. The plain lines represent
the contours of the median plane.

Fic. 31. A diagram of the main encephalic tracts and nuclei as observed in the
Urodele Amphibia, a composite of the figures upon Plates V. and VI. The distribu-
tion of the tracts is a matter of actual observation. The sensory or motor character
of the tractsis in a measure inferential. .S, main sensory tract. JZ, main motor
tract.

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STUDIES ON THE EVES. OF ARTHROPODS:

WILLIAM PATTEN, Pu.D.

II. Eyes of Acilius.

A COMPARATIVE study of the eyes offers, in my opinion, a
promising field for the determination of the relationship be-
tween the different groups of Arthropods. To determine
these relationships it is necessary to understand, (1) variations
in the structure of the eyes, (2) their topography, and (3) the
position and structure of the optic ganglia.

It is necessary first of all to obtain a thorough knowledge of
some typical form. Comparison is then easy, for the problems
solved in one case are already solved in others, while those
left unsolved will torment the investigator in every succeeding
study.

In following the development of the eyes of Acz/ius I was
forced to consider their relation, and that of the optic ganglia,
to the brain. This required a careful examination of the de-
velopment of the whole head. But finding it impossible to
treat of the head without considering the rest of the body, I
decided to confine my attention to the eyes and optic ganglia.
Some of the figures, however, will also serve to illustrate
certain points in the “Development of Acilius,” which will be
the title of the paper I hope to publish in one of the next num-
bers of this Journal. I shall reserve till then a discussion of
the relations which the eyes and optic ganglia bear to the head
of Arthropods.

I. ToPOGRAPHICAL RELATIONS OF OpTic PLATE AND OPTIC
GANGLION TO CEPHALIC LOBES AND BRAIN.

The earliest stages of the eyes and optic ganglia are found
before the appendages have made their appearance. The distal
edge of each cephalic lobe is thickened to form the semicircular
optic plate, distinguished on surface views by its opacity and the
small size of its nuclei. The large ectoderm cells, on the inner

98 PALTEN. [Vo.. II.

edge of the plate, are infolded, forming an almost semicircular
depression, the beginning of the invagination which subsequently
gives rise to a large part of the optic ganglion.

The optic plate is soon divided into three segments (Pl. VII.,
Fig. 1). The anterior, or first segment, forms a kind of corner to
the anterior, lateral edge of the cephalic lobe; the second occu-
pies the median and larger part of the optic plate, with which its
long axis is parallel; and the third forms the posterior edge of
the cephalic lobes, its long axis being nearly at right angles to
that of the second segment. The distal edge, and in some
cases the whole, of the plate is buried in the yolk; it is then
necessary, if one desires to obtain surface views, to cautiously
pick the yolk away from the lobes with needles.

The ganglionic invagination soon deepens, and also shows
traces of a differentiation into three parts, one of which lies on
the inner edge of each segment of the optic plate (Fig. 1 0.¢.)°).

From the median part of the cephalic lobes rise three pairs of
thickenings, one pair opposite each ganglionic segment. They
form the rudiments of the brain (Figs. 1-3, 41%), and appear to
be direct continuations of the segments of the ventral chord.

The embryo is divided by transverse folds into a certain
number of post-oral terga, the first three of which are grad-
wally drawn towards, and united with, the cephalic lobes. The
line surrounding the optic plate, after the rupture of the embry-
onic membranes, is not the old boundary of the cephalic lobes,
but a new formation, which includes the cephalic lobes and the
terga of the first three post-oral segments (Pl. VIII., Fig. 8).
The indentation; zg.>", appears in surface views like a newly
developed eye. It was quite enigmatical until a more careful
study showed it to be the boundary between the posterior edge
of the cephalic lobes and the terga of the first three post-oral
segments. The last trace of this fold disappears soon after the
stage shown in Fig. 8.

While the optic plate is still in its semicircular form, two
areas in each segment become visible in surface views, on
account of the peculiar arrangement of their nuclei. From
each of these areas is developed an ocellus, which I have
numbered in the way shown in the plates. The growth of the
embryo gradually forces the median, ventral part of the germ
band forwards, leaving, as it were, the distal ends of the cephalic

No. 1.] EYES OF ARTHROPODS. 99

lobes behind, so that they are turned first posteriorly and then
ventrally. This makes the ventral row of eyes assume an ante-
rior and then a dorsal position, and also brings the first seg-
ment behind the other two (Figs. 1, 4, 8, 9, 10).

After the revolution of the embryo, eyes II. and IV. come to
lie close together behind eye I., and eye VI. is wedged in be-
tween eyes I. and III. A comparison of the figures will show
better than any description how the embryonic eyes develop
into those of the larvae. The reader who would follow the
rather confusing changes in the optic ganglion and its nerves
must have a clear mental picture of the way in which the
eyes shift their position.

When the optic plate first appears, it is conspicuous on
account of its dark color. Sections show that at this period
it is composed of a single layer of closely packed cells, whose
small, darkly stained nuclei are crowded together several rows
deep. The nuclei in the brain and optic ganglion are large and
spherical, and do not stain deeply. The optic plate is every-
where sharply demarked from the surrounding tissues, except
on its distal, inner edge, where there is a gradual transition to
the wall of the optic invagination (Pl. IX., Fig. 20, £.z.).

Occasionally one finds a large nucleus near certain clear areas
of which we shall speak later. They are homogeneous and
deeply stained, and, in some cases, contain a nuclear spindle
(Pl. IX., Figs. 20 and 21; Pl. XI., Figs.60 and 61). They often
appeared like naked nuclei projecting above the level surface of
the optic plate. I do not remember seeing them anywhere
except in those parts of the optic plate that give rise to the
eyes.

Eye V.

We shall now describe, by means of sections and surface
views, the development of each eye. It is only with the aid of
these surface views that the earliest stages can be understood.

While the optic plate is but a semicircular thickening of the
lateral edges of the cephalic lobes, eye V. appears as a round,
dark spot, surrounded by a clear area, on the inner edge of the
third segment (Figs. 1-3, V.). During the earliest stages, the
central area is conspicuous on account of its size and dark color.
Later, it is reduced to a narrow band composed of a double row
of darkly stained nuclei.

100 PATTEN. [Vou. II.

A large nucleus appears in the central area, which in-
creases in size as the latter becomes more and more elongated.
It finally lies in about the middle of the dark area, between the
two rows of nuclei (Fig. 6a).

The explanation of the surface views will be found on ex-
amining Pl. XI., Figs. 61-63, which represent sections through
the eye while in the stages shown in Figs. 2, 4, and 6.
It will be seen that the median, dark area corresponds to a
broad elevation of the ectoderm, in which the nuclei are
crowded toward the surface, the superficial ones being slightly
stained by my method of preparing surface views. On either
side of the ridge the nuclei are deeply situated and unstained,
hence the clear area surrounding the ridge. In order to save
time and expense I have, in most instances, indicated the surface
nuclei by shading. The elevation gradually narrows and sinks
to the level of the surrounding ectoderm, or even below it, until
it is reduced to a narrow ridge with a shallow furrow along its
summit. On either side of this furrow a single layer of nuclei
extends to the surface of the ridge (Fig. 63). The most super-
ficial of these nuclei are the ones which appear as a double row
in surface views.

The clear band surrounding the dark area soon loses its regu-
lar outline and becomes distinctly four-lobed (Figs. 6 and 6a),
each lobe being a depression in the ectoderm, beneath which
the nuclei are arranged much like those in the whole ocellus at
a later period (compare Figs. 62 and 64), or like those found in
separate sense organs. Each depression represents, in fact, a
distinct sense organ, or eye. They form the greater part of
the retina of the future ocellus. The two posterior pits are
deeper and larger than the anterior ones, hence the whole
clear area is somewhat conical.

There is a dark spot, with a clear area surrounding it, on
the anterior dorsal edge, and one on the median ventral edge
of the clear area (Fig. 6a, 5 and 6). These clear spots resem-
ble the main clear area, with which they are continuous, in
structure and general appearance.

All these clear areas and dark spots form one thickened patch
of ectoderm, which soon becomes more regularly oval, and the
pits and the dark streak disappear. The whole organ is being
invaginated to form the floor of the deep depression seen in

No. I.] EYES OF ARTHROPODS. IOI

Figs. 7, 7a,and 8a. The opening of the depression, or optic
cup, 1s pear-shaped, the broad, posterior end indicating the
position of the two posterior pits, which are the last to be en-
closed on account of their greater size.

During the earliest stages a striated cuticular thickening ap-
pears over each pit of the clear area, the striations being appar-
ently continuations of those in the clear space beneath (Pl. XL,
Fig. 61, cz.). It terminates abruptly at the periphery of the
central dark area, and as the latter decreases in width the edges
of the cuticular thickening on either side of it come closer to-
gether, until only a narrow space, the median furrow, is left
between them (Fig. 63, #. f.). When the whole sensory patch
begins to invaginate, these edges unite, and the cuticula forms a
continuous layer over the floor of the optic cup (Fig. 64).

From this cuticular layer the retinal rods are developed. In
the stage shown in Figs. 62 and 63 it is apparently com-
posed of stiff cilia, each of which has a minute, bead-like swell-
ing at its base, while their outer ends are covered with a delicate
membrane, which, in Fig. 64, is detached from the fibrous cuti-
cula to form a delicate cover over the mouth of the optic cup.

The only evidence of the compound nature of the optic cup,
after the disappearance of the median dark area, and the sepa-
rate pits and cuticular thickenings, is to be seen in the optic
nerve. In Figs. 62 and 64, the sections are at right angles to
the line along which was developed the median ridge; conse-
quently one part of the nerve goes to the ventral, and the
other to the dorsal half of the clear area (Fig. 6a). A longi-
tudinal, horizontal section would show that each half of the
optic nerve was divided into two much less distinct parts, one
going to the anterior pit, and one to the posterior. Hence the
optic nerve 1s composed of four, and perhaps more, nerve bundles.
This fact, together with the presence of four pits tn the clear area,
the cuticular thickenings over each ptt, and finally the constant
and remarkable arrangement of the nuclet beneath each thicken-
ing, shows clearly that this ocellus ts composed of at least four
primitive optic pits. The two clear areas, each with a dark spot
in the centre, found on the dorsal and ventral side of the eye
in Fig. 6a, form the two bands of inverted cells in the future
ocellus. These patches resemble, both in sections and ‘in
surface views, the clear and dark areas in the centre of the

102 PATTEN. [Vo.. II.

eye, and there is the same absence of nuclei beneath their
cuticular thickenings. I have not been able, however, to de-
tect any evidence that they are supplied with separate bun-
dles of nerve fibres, but this will not seem strange, when we
consider their small size and transitory nature. I see no
reason why they, like the sensory patches composing the cen-
tre of the eye, should not be regarded as remnants of dis-
tinct sense organs. This supposition will appear in a more
favorable light, perhaps, when we consider similar patches
connected with the rudiments of the remaining eyes.

The sensory spots, or primitive eyes, of which the clear area is
composed, are comparable with those on the mantle edge of Avca,
as described by me in “ Eyes of Molluscs and Arthropods” (PI.
30, Fig. 42). It was there shown that some of the eyes arose as
simple, pit-like depressions covered by cuticular thickenings, into
which the everywhere-present intercellular nerve fibres extended,
producing the appearance of vertical striations. Such eyes con-
tain the lowest stages in the development of visual rods. In more
specialized eyes it was shown that the cuticula had broken up
into blocks, one overlying each cell. The nerve fibres arrange
themselves around these blocks in various ways, and a true
retinal rod is the result.

In the embryos of Acz/ius, the eye passes through the stages
permanently represented on the mantle edge of Molluscs, for
the cuticular thickening over each optic pit, at first fuzzy and
non-refractive, soon changes into a layer of stiff and refractive
cilia-like bodies, which finally form a dense and almost homo-
geneous cuticular layer. As soon as the retinal cells become
distinctly outlined, this cuticula breaks up into a number of
minute rods, two being formed over each retinophora. The
arrangement of the nerve fibres about the rods will be de-
scribed later. It is sufficient for the present to state that it
corresponds in almost every particular with that found in the
more highly developed rods of Molluscs. Moreover, in Acz/zus
as in Molluscs the cuticula overlying the sensory cells is divided
into two layers: a thin outer membrane devoid of nerve fibres,
the corneal cuticula ; and a thicker, inner one, the retenzdial cute-
cula, so called because it contains nerve ramifications, and gives
rise to the rods. The development of the rods in Acilius, there-
fore, is in perfect harmony with the view concerning the phylo-

No. T.] EYES OF ARTHROPODS. 103

genetic development of visual rods, which I formulated from a
study of the eyes of Molluscs. The harmony will be more per-
fect, when we consider the nerve endings, and compare the
theory advanced to explain the intercellular nature of these
nerve-ends with the origin of ganglion-cells.

THe Larce Nuc eus of eye V., which is wedge-shaped and
filled with dark granules, is at first situated very near the surface,
and usually projects some distance above it. It remains in
this position until the dark area begins to disappear (Fig. 6).
Sections of the eye after this period show that as the sensory
patch is invaginated, the large nucleus withdraws from the
surface and takes up a position among the other nuclei in the
middle of the optic cup. I have not been able to find it
after the stage represented in Fig. 65, but I presume it re-
mains practically unchanged throughout larval life. Such is
undoubtedly the case with similar nuclei in eyes I. and IV.

The mouth of the optic cup is gradually reduced to a narrow
slit, the long axis of which is parallel with the median ridge,
above which the thickened lips finally unite (Fig. 66). Al-
though there is no duplication to form separate layers, there
are three regions that can be identified as the three layers of
the future eye. The closed lips of the optic cup are composed
of radiating cells with deeply situated nuclei. Those over the
centre of the eye are bent at right angles, their attenuated
inner ends extending as far as the basement membrane on the
sides of the eye. These bent cells, which give rise to the
corneagen, are connected by intermediate forms,with the short,
straight ones of the surrounding ectoderm.

THE CORNEAGEN increases rapidly in thickness, and at the
same time all its nuclei, except those on the periphery, be-
come so indistinct that they seem to have disappeared. Even
in very successful preparations it is only here and there that one
can see, at the inner ends of the corneagen cells, the small, round
nuclei with sufficient clearness to preclude all doubt as to their
identity. In most cases, they are reduced to clear, colorless sacs,
which can be recognized as nuclei only by a careful study of
their position and the transitional stages by which they are con-
nected with the undoubted nuclei of the periphery. In the full-
grown larva, the corneagen cells are large and wedge-shaped,

104 PATTEN. [VoL. Il.

with distinct walls surrounding the coarsely granular, some-
times flocculent, cell contents.

Tue Iris contains pigment granules, varying in size from
minute specks to large spherules, as large, or larger than the
neighboring nuclei. The spherules are usually brown and con-
tain a minute black dot in the centre. They are most abundant
on the inner edge of the iris. The small granules are usually
dull black.

When the pigment is dissolved by acids or alkalies, the iris-
cells are left quite empty and colorless, so that even after the
removal of the pigment it is easy to distinguish them from
the adjacent non-pigmentiferous cells of the corneagen, for the
latter are filled with deeply stained granular protoplasm.

Tue Lens. —Immediately after the rupture of the embryonic
membranes, and while the optic cups are still wide open, a deli-
cate pellicle is formed on the outer surface of the hypoderm.
This pellicle, which gives rise to the cuticula, usually covers the
mouth of the optic cup (Fig. 65), but no part of the membrane
is enclosed in the cavity of the eye, at least I have never
been able to discover any traces of it in the newly formed
vesicles. After the optic cups close, the pellicle is thrown into
loose folds over the whole body, and is then cast off. At the
same time, a new pellicle is formed beneath the old one, which
is still present but widely separated from the surface of the
embryo. The new skin is first visible above the unmodified
hypodermis. Over the surface of the newly formed corneagen,
it first appears as a thick, vertically striated layer much like that
which gives rise to the rods (Fig. 67).

Soon after this stage, the corneagen cells increase in height
and form an elevated cap to the optic vesicle, with a circular
depression around it. The second pellicle becomes refringent
and is thrown into minute folds everywhere except over the eye.
There the non-refringent layer is transformed into a disc of
clear, refractive cuticula (Fig. 68).

After hatching, the dome-shaped layer of cuticula over the
eye increases in density and thickness until it forms the strongly
biconvex lens of the adult, the curvature of the inner surface
being much greater than that of the outer.

In the full-grown larve the cuticula surrounding the lens is
composed of two layers: a dark brown, or quite black, outer one;

No. 1.] EVES OF ARTHROPODS. 105

and a clear, transparent, tangentially striated inner one. The
whole layer is divided into thick, imbricating scales, the tips of
which are raised a little above the surface, producing accord-
ing to the location either a notched, wavy, or serrated outline.
The lens is composed of the same kind of scales, but they are
thinner and higher, and concave like the leaves of an onion.
In most cases they overlie one another so closely, and their
outer surfaces conform so accurately with the general curvature
of the lens, that it is difficult to distinguish their boundaries.
But it sometimes happens that their outer edges curl upwards,
producing a serrated outline to the lens, like that in Fig. 7o.

THE Retina.—The thick cuticular layer upon the floor of
the optic cup is finally interrupted by a second median ridge,
which appears in exactly the same place as that occupied by the
first. It is formed by two rows of cells, the enlarged, projecting
ends of which are bent so that the tips of all the cells in one row
face the tips of those in the other (Figs. 66-70). At the tip of
each cell is a minute rod, which at first sight might appear to be
a product of the lateral wall of the cell; but this is not the case.
These rods are terminal and horizontal, as we can see from the
shape of the cells, and from a comparison with other eyes, where
the homologous cells and their rods are much larger and can be
more conveniently studied.

After the closure of the optic vesicle, some of the cells near
the inner surface of the corneagen are distinguished by their
large, deeply stained nuclei. The horizontal ends of these
cells, which ultimately give rise to the outer wall of the optic
vesicle, are frequently broken into loose, ill-defined, granular
masses (Fig. 67, 0. w.).

The innermost portion of the optic cup ts composed of retinal
cells, the greater number of which are placed so that their outer
ends are at right angles to the median, vertical plane of the eye.
Their rods ave therefore horizontal, and those on opposite halves
of the eye face one another. Only a few retinal cells on etther
side of the ridge are upright and parallel with the optic axis.
The free ends of the cells which form the outer wall of the optic
vesicle are finally bent tnwards, and thus completely inverted
(Figs. 68 and 60, 0. w.); at the same time they become more
sharply outlined, and well-defined rods are formed at their tips.

The ends of the peripheral retinal cells soon begin to draw

106 PATTEN. [Vot. II.

away from the median plane of the eye, the cavity of the optic
vesicle disappears (Figs. 67-70), the layer of rods becomes
flattened out, and all the retinal cells and rods assume an up-
right position, except those of the median ridge.

THE RETINOPHORH.—I have shown that in Molluscs, the
essential elements of the retina were colorless cells, bearing
double rods, and containing two nuclei and an axial nerve
fibre. These cells, or retinophorz, I maintained were formed
by the fusion of two rod-bearing cells, in one of which the
nucleus degenerates. The nerve fibres between the two cells
come to lie in the centre of the double one, to form its axial
nerve. Each cell retains its own rod, hence the double rods
of the retinophore. Resting on these facts, and upon the
supposition that the primitive nerve fibres were intercellular,
I maintained that when sensory cells were found with axial
nerves and traces of two nuclei, they should be classed as
retinophorz, and must have arisen in the manner described
above. In the Arthropods, I found the crystalline-cone cells
had characteristics which led me to consider them as modified
retinophore. My supposition was based on the expectation
of finding in the ocelli of Arthropods, retinal cells, either very
similar to the retinophorze of Molluscs or intermediate between
them and the crystalline-cone cells. A comparison of the text,
and the diagrammatic figures in Plate 32 of “Eyes of Mol-
luscs and Arthropods,” will show that I expected to find the
intermediate forms of retinophorz in the posterior eyes of
Spiders, and in the eyes of Scorpions and Limulus, while the
Molluscan type might be looked for in the ocelli of Insects and
Myriapods, and in the anterior eyes of Spiders.

The retinophorze now to be described, show that these ex-
pectations have been realized, at least, as far as the ocelli
of larval Insects are concerned.

The first stages in the formation of the retinophore are found
during the open-cup period of the eye. In Figs. 63 and 64, we
see that the inner wall of the optic cup is closely packed with
five or six rows of deeply stained nuclei; all of which are alike
except the median one already described, and those belonging
to a few large ganglionic ones, to be described later. In the
next stage (Fig. 65), they appear to be greatly reduced in num-
bers. This change is due to the fact that the cells are uniting

No. I.] EVES OF ARTHROPODS. 107

in twos to form retinophore ; one half of the nuclet have degen-
erated into the non-stainable, apical nuclet of the retinophore, the
other half form the deeply stained basal ones. ‘The first stages
of this process are necessarily difficult to follow, since both
kinds of nuclei are mingled in one confused mass, where one
can distinguish only uncertain differences in the color and size of
the nuclei. But during, and after, the stage shown in Fig. 65,
they begin to arrange themselves in two layers, most of the non-
stainable nuclei lying above the normal ones. I fully expected
to find in the embryos and young larve, that the second nuclei
would be, if not readily visible, at least much more distinct
than in the adult. But my observations on Acilius do not
support this expectation. Even as early as the stage shown
in Fig. 65, the second nuclei are as faintly stained, and as diffi-
cult to see in section, as those of the adult eye. TZhzs fact may
indicate that the double cells are not the result of specialization tn
highly developed eyes, but that they are very ancient structures
which we should expect to find tn the simplest, as well as in the
most spectalized, sense organs.

The large nuclei of the retinophorz arrange themselves in a
single row on the inner surface of the retina. The position of
the smaller nuclei varies somewhat; sometimes they are just
above the large ones, sometimes just below the inner ends of
the rods, but usually about half way between these two points.

During the stage shown in Fig. 64, and in younger stages it is
impossible to distinguish the shape of the retinophore as the
cell walls are indistinct or absent, owing to the rapid division that
is going on. In Fig. 65 the tissues are less dense, and the re-
tinophoree can be seen as spindle-shaped cells drawn out to a
point at either end. The clear striated area beneath the cu-
ticular thickening is composed of the rod-like, or fibrous, outer
ends of the retinal cells mixed with nerve fibres. They are
soon transformed into strongly bent columnar cells.

Although it is sometimes possible to see the secondary nuclet
of the retinophore in sections, it is much easier to study their
position and structure in isolated cells. It is also in this way
that one obtains the most conclusive evidence of the double
nature of the retinophore, for by carefully turning and rolling
them, either before or after the removal of the pigment, one
always obtains one view which shows that they are composed of

108 PATHIEN. [ Vor.aik

two twisted cells (Pl. X., Fig. 58, a. d.). The inner end of one
of the component cells is swollen, and contains a round, fairly
well-stained nucleus; the outer end is quite small, and its con-
tracted tip terminates in a flattened rod. The second cell is
perhaps a little smaller; its broad outer end contains a very
faintly stained nucleus, and also terminates in a flattened rod.
Its opposite extremity fuses with the first cell to form the in-
ward prolongation of the retinophora. Both cells supplement
each other’s irregularities so perfectly that a symmetrical and
apparently single cell is the result (Figs. 57a and 58a).

When the cells are pigmented, the position of the second
nucleus is often plainly indicated by a clear spot, but it would
not be possible to identify it as a nucleus until the pigment had
been removed.

The outer ends of the two component cells of the retinophorze
are widely divergent (Fig. 58, ¢). A similar condition occasion-
ally obtains in Avca and Haliotis, and this fact affords excellent
proof of the double nature of the retinophore.

PIGMENT. — Just after the rupture of the embryonic mem-
branes, one can readily distinguish with the naked eye the
bright red ocelli of the living embryos. The pigment of these
stages is readily soluble in alcohol, the reddish-brown pigment
found in the succeeding stages, much less so. It is the latter
pigment that is first seen in sections, distributed in coarse gran-
ules through the iris. At about the same time, the outer ends
of the retinal cells assume a diffuse reddish-brown color. This
coloring matter was probably in distinct granules, and became
diffuse through the action of the alcohol.

In the next stages, thin sections show a row of minute, pig-
mented blocks, arranged in pairs (Fig. 69). The blocks are
cross sections of a pigmented collar surrounding the outer end
of each cell.

In the fully developed eye, the pigment varies in color from
brown to jet black, according to the method of preparation.
Chromic acid, bichromate of potash, and Muller’s fluid, partly
dissolve the pigment, leaving it a light brown color. Picro-sul-
phuric acid has a similar, but much less effect. Eyes treated
with alcohol alone contain great quantities of intensely black
pigment, which in all stages is most abundant around the outer
ends of the retinal cells,

No. I.] EYES OF ARTHROPODS. 109

A careful study of sections and isolated cells shows that the
pigment is distributed in granules along the nerve fibres that
cling to the walls of the retinophore. Toward the inner ends
of the latter, the course of the external nerve fibres is often
distinctly marked out by the pigment granules deposited upon
them. (Pl. X.; Fig, 58). "At the jouter ends voit the cells, the
external nerves are straight and close together. Where
there is little pigment, one can see that the granules are ar-
ranged in rows around each of these nerve fibres (Figs. 56 and
57). Usually, however, the pigment forms a continuous and
uniform envelop around the outer ends of the cells, where it
terminates abruptly, while the nerve fibres are continued on-
wards over the outer surface of the rods. If there is any
pigment at all inside the cells, it must be deposited in a very
thin layer in, or just beneath, the cell wall.

Just below the inner ends of the rods, cross sections show a
mosaic of deeply pigmented, hexagonal blocks, from which we-
might conclude that here pigment was lodged inside the cell
walls. But isolated cells show that pigment is deposited between
the flattened and diverging ends of the two cells composing each
retinophora ; consequently we may not conclude from these solid
blocks that the pigment is necessarily inside the retinophore.
Again, when the larva had died a so-called natural death, or
perhaps owing to other conditions of which I was ignorant, the
pigment dissolved, staining the retinal cells dark brown through-
out. Of course, in cross sections of such material, pigment
would appear to be deposited inside the cell wall.

There is proof in the optic nerves, that some of the pigment,
at least, is an intercellular product. or in sections and in
loosened or isolated fibres, it is evident that the pigment gran-
ules are scattered about between the fibres, and not in them or
in any distinct cells.

In the peripheral cells of the retina, and in those which con-
stitute the outer wall of the optic vesicle, the pigment is
coarser and less regularly arranged, resembling in general ap-
pearance that found in the iris. This fact enhances the decep-
tive appearance, already mentioned, that might lead one to think
the retina was directly continuous with the iris and surround-
ing ectoderm. In the iris, the pigment is undoubtedly depos-
ited inside the cell walls.

110 PAITEN. [Vot. II.

THE RETINAL Rops AND NERVE EnpiNGs. — Since the retin-
ophore are closely packed in the retina and the rods are on the
periphery of their outer ends, it follows chat the rods of two
neighboring retinophore are placed side by side so that they often
appear like one vod, while those of the same retinophore are sepa-
rated by a wide space.

In eye V. (Fig. 54a) there is a beautiful mosaic of brilliantly
refractive rods which form regular hexagonal figures, in the
centre of which are the axial nerve fibres, and on opposite sides,
the two rods belonging to the same retinophora. On two of
the sides no rods are developed; only a thin membrane sep-
arates the adjoining hexagonal spaces at those points. Hence
under a low magnifying power, the rods appear to be arranged
in nearly parallel, zigzag lines.

It is impossible to see the axial nerves in the isolated retin-
ophore, owing to the twisting of their component cells. But
they are visible in cross sections as a single bundle in each
retinophora. In the clear space between the two rods, the
nerve breaks up into three or four fibres arranged in a plane
parallel with the sides of the rods. In one of the spaces in Fig.
54a, they are at right angles to the normal position. Minute
cross fibrillae arise from these axial fibres, which probably pene-
trate the rods and unite with the external nerves. The cross
fibrillaze constitute a vetzzzdzum similar to that of Pecten. Inthe
latter, each pair of rods has completely fused to form a hollow
cylinder containing a single axial nerve, from which arise radiat-
ing cross fibrillz. In Acilius, the two rods are separate and
flat, and the axial nerve is broken into smaller fibres placed in a
row, so that a perfect radial arrangement of the fibrillze is impos-
sible.

The clear space between the rods is apparently filled with a
non-refractive fluid in which the retinidial fibrillz are suspended.
It often contains fine granules, produced, I believe, by the coagu-
lation or varicosities of the fibrille. The space is exactly like
that in the centre of the rods of Pecten, and is undoubtedly an
entercellular one.

That the cross fibrillae penetrate the rods, I do not doubt, for
they are marked with cross striae continuous with the fibrillze in
the clear space. Neither do I see any reason to doubt that the
fibrillz in the clear space, as well as those in the rods, are

No. I.] EYES OF ARTHROPODS. BIE

equally essential elements. In Pecten, Acilius and Cephalo-
pods, both the clear and the refractive parts of the rods are pres-
ent. In the latter group, each retinal cell is probably double and
has two rods separated by a clear space containing an axial nerve
fibre. The rods are arranged in such a manner that four of
them, each one from a different retinophora, come together to
form compact groups, which Grenacher calls rhabdoms. Such
rhabdoms, however, are different from those of the compound
eye. They are more like the pairs of rodsin Acilius. Jz nezther
Acilius or Cephalopods have these groups of rods any morphological
significance, for they are incidental results of the arrangement of
rods tn pairs, and this arrangement varies greatly in the different
eyes of the same individual. The tmportant fact to be borne in
mind 1s that the patrs of rods belonging to one double cell are the
anits composing the layer of rods, and that the clear spaces contatn-
ing the axial nerves form the centres of these units.

In the rods of the convex eyes of Avca, in the crystalline cones
of Arthropods, and in the rods of the Vertebrate eye, if I am
right in my interpretation of these structures, there is no clear
space between the two rods of the same retinophora. On the
other hand, in J/antis and probably in most Dzpzera, the hard
refractive part of the rods has disappeared, and the retinidial
fibrillaze are suspended in a clear fluid. I think it is fair to con-
clude from these facts that the essential element of the rods ts the
system of cross fibrille, or the retinidium, which may be suspended,
in whole, or in part, etther in a clear fluid or tn a refractive and
cuticula-like substance.

In Acilius, the clear space between the rods is not covered by
a cap of cuticular substance, as in Pecten, although in some
cases I have clearly seen that it is covered by an extremely deli-
cate, arched membrane, through which one of the axial nerve
fibres projects, and, bending at right angles, unites with a simi
lar fibre from an adjacent pair of rods (Figs. 57a and 59). Thus
axtal-nerve loops are formed much like those described in Pec-
ten. In the latter case, the direction of the loops is more
uniform than in Acilius, where they may be bent in any way,
although there is a tendency to turn in some directions more
than in others.

In Acilius, as in Molluscs, the retinophorz are supplied with
numerous pigmented nerve fibres that extend along the surface

i12 PATTEN. [VoL. II.

of the cells. At the outer ends of the cells, the fibres are
straighter and slightly enlarged. The pigment stops at this
place, but the fibres are continued onward, nearly parallel with
one another, over the outer surface of the rods (Figs. 54 and 57).

The inner ends of the retinophorz are continuous with coarse
fibres composed of the inward prolongations cf the external
and axial nerves. There are in rare cases smaller bundles
which, on their way to the more peripheral portion of the ret-
ina, pass over the inner third of some of the retinal cells at a
sharp angle. Some of these fibres impinge upon a retinal cell
near the primary nucleus and join the other external nerve
fibres belonging to that cell. Such nerve fibres occasionally
cling to isolated cells, and one might erroneously infer that
they entered the cell opposite the nucleus.

About the time the clear area begins to be invaginated a
number of deeply stained granules appear on the periphery of
each ocellar thickening. They increase in size from the surface
of the ectoderm inwards, and each one is surrounded by a clear
area (Pl. XI., Figs. 63-66, and Pl. XIII., Figs. 32, 33, ad. 2).
I have found similar products in the optic ganglia and in the
ventral nerve chord. The manner in which they absorb color-
ing matter and their general appearance, together with the fact
that they seem to be most abundant in tissues undergoing ret-
rogressive changes, suggest that they may be degenerating
nuclei.

Eye VI.

Eye VI. first appears in the posterior part of the third segment
of the optic plate as a triangular depression, or clear area, the
apex of which is directed dorsally and slightly forwards. On its
ventral and posterior side, is a round dark area with a small clear
spot in the centre. The depression soon becomes sickle-shaped,
and finally circular, completely surrounding the dark area (Fig.
5a). Ina little later stage (Fig. 6a) the furrows separating
the eyes from each other have disappeared. The clear space is
divided into two parts by a dark ridge, on the dorsal side of
which is that part of the clear area that appeared first; it is
now somewhat rhomboidal, contains a dark ridge composed of
a double row of nuclei, and is divided into four pits, 1, 2, 3, 4.
The ventral part of the eye is composed of an irregular clear

No. 1.] EVES OF ARTHROPODS. 113

area or depression, 6, deepest at the anterior end; it is con-
nected with the dorsal part by a narrow furrow. The interpre-
tation of these surface views is the same as that in eye V.
The clear spaces represent slight surface depressions above a
cup-shaped layer of deeply situated nuclei; the deeper the de-
pression, the lighter it is in surface views; the darker parts are
elevations where the nuclei come close to the surface (Pl. IX.,
Figs. 33 and 34, V/.). Jt zs evident that the structure of eye VI.
ts much like that of eye V, for besides the two peripheral spots tt
contains four separate pits, or sense organs, divided by a trans-
verse ridge, containing a large median nucleus, into two parts.

The whole sensory patch is soon changed into one uniformly
clear area, which finally sinks below the surface to form the floor
of a deep, circular-mouthed pit, or optic cup (PI. X., Fig. 47).
The nuclei no longer show by their arrangement that the patch
is composed of separate groups of cells; the cuticular thicken-
ings have united to form a uniform layer over the floor of tne
optic cup, and the median ridge has disappeared. I have not
represented many sections of the earlier stages of eye VI., since
with the exception of certain modifications readily understood
from an examination of surface views, they are exactly like those
of eye V.

There are considerable differences, however. between the later
stages of the two eyes.

Just before, and during, the rupture of the embryonic mem-
branes, the circular opening of the optic cup is converted into a
transverse slit (Fig. 8a). As soon as the lips meet, their cells,
by assuming different curvatures, form the corneagen, and
the outer wall of the optic vesicle. On the anterior, dorsal
side of the eye, the retina is curled over in such a way that it
forms a part of the middle layer of the eye, although it does not
extend far enough to meet a similar, but larger fold on the
opposite side (Pl. XII., Figs. 72 and 73, 0.w.). In the still later
stages, it is folded down on to the rods, and is apparently con-
tinuous with a very delicate membrane,—in which I believe
I have seen nuclei, but so small and indistinct as to leave me in
some doubt, —that extends over the outer surface of the retina
till it meets the mass of inverted cells on the opposite side (Fig.
74, 0. W.).

When the sensory patch which formed the rudiment of eye

114 PATTEN. [Vot. II.

VI. was invaginated, the large clear spot, 6, (Fig. 62) came to
lie on the ventral and posterior edge of the optic cup (Figs. 8
and 9, 6). The cells of this sense organ become more and more
bent and elongated as the cup closes, until they finally form a
great tongue of cells projecting into the space between the cor-
neagen and the retina (Figs. 71 and 72, ¢ z.c.). As it increases
in length, it reduces the optic cavity to an oval space in the
dorsal and anterior portion of the eye. The cavity is finally
completely obliterated by the increase in length of the corneagen
cells (Fig. 73).

The free ends of the cells belonging to the sixth sense organ
bear inverted retinal rods, the same as those belonging to the
upright ones, except that they are less regular in shape. Cross
sections show that they are cylindrical with a clear central
portion in which runs an axial nerve. The nuclei are at first sit-
uated near the free ends of the inverted cells, and are somewhat
larger and differently stained from those in the remainder of the
retina. When the pigment, which is scattered through these cells
in coarse granules like that in the iris, is removed, they appear
almost colorless, with here and there a few coarse granules.

Figs. 71-74, represent semi-transverse sections of the head,
at right angles to the nerve z VI., Fig. 9, and parallel to
the dark area of eyes III. and I, Fig. 8. When the sections
are cut in most other cross planes, the retina appears per-
fectly symmetrical, its periphery being bent over and contin-
uous with a very thin membrane in the same way that the
left-hand edge is in Fig. 73. But if any of these cross sections
should pass a little posterior to the median plane of the eye,
the tongue of inverted retinophorz would be seen, which might
readily be mistaken for the cut end of a large number of nerve
fibres, such as one finds in retinas with inverted cells, as in
Pecten for example.

That we should have eyes with both upright and inverted
retinophore, as in eye V., is remarkable and, so far as I know,
without parallel. The condition in eye VI. is still more ex-
traordinary, for there only a comparatively small cluster of rod-
bearing cells is inverted, while all the rest are upright.

The sense organ, 5, has either united with 1-4 to form the
floor of the optic cup or disappeared; at any rate after invagina-
tion it is no longer distinguishable.

No. I.] EYES OF ARTHROPODS. 115

In eye V., the two groups of inverted cells arise from the
dorsal and ventral sense organs, 5 and 6, in the same way that
the tongue of cells in eye VI. is derived from its ventral sense
organ, 6.

In the full-grown larva, the group of inverted cells is propor-
tionally as well developed and conspicuous as in the younger
stages. It is not shown in Fig. 75, since the section is a semi-
transverse one passing through the optic nerve z VI. (Fig.
toa). The direction of the cells in the inverted sense organ is
at right angles to that of the optic nerve, consequently it is im-
possible to cut a longitudinal section of both structures at once.

THE CORNEAGEN forms a thick cap to the eye, above which a
lens is formed, as in eye V., from a striated layer of non-refrac-
tive cuticula.

In Fig. 73 there is a temporary indentation in the corneagen
which seems to mark the place where the lips of the optic cup
came together.

Tue Retina. — Just before the closure of the cup, the reti-
nal nuclei suddenly appear to decrease in number, owing to the
formation, in the manner already explained, of the retinophore,
which soon arrange themselves in a single layer, with all their
primary nuclei at about the same level. The retinophore are
the sanie as those in eye V., except that they are a little
shorter, and the primary and secondary nuclei are often situated
so close together as to appear like one nucleus.

In the full-grown larva the retina is almost a hollow hemi-
sphere, and consequently the rods on the periphery are very
nearly at right angles with those in the centre.

Tue Rops are remarkably uniform in structure. On the pos-
terior edce of the retina they are not quite so long as elsewhere.
Each pair forms a thin-walled, hexagonal tube, which when iso-
lated shows distinctly its two component rods. Cross sections
show a mosaic of closely packed, hexagonal figures without the
regularly arranged thin places so conspicuous in the rod-mosaic
of eye V. (Fig. 450).

Eye III.

Eye III. appears very early as an oval, dark area in the middle
of the second segment of the optic plate. It is soon surrounded
by a circular clear space, and then both parts become consider-

116 PATTEN. [VoL. II.

ably elongated, the latter assuming a figure-8 shape, and the
former being reduced to an elongated ridge composed of a
double row of nuclei (Figs. 1-6). The explanation of surface
views given in the description of eye V. will serve equally well
here.

In both eyes I. and III. there are two broad and poorly de-
fined light areas, one on the dorsal and the other on the ventral
side of the eyes, which extend almost their whole length. These
areas are well developed in the stages shown in Figs. 5 @ and 4.
But they soon disappear, and the eye assumes the appearance
shown in Fig. 6a.

Although this eye is considerably longer and larger than eye
V., it is evidently constructed on the same plan. The figure-8
shaped clear area is composed, as in eye V., of four sensory
pits. In the centre is the elongated ridge, and on either side
of its anterior end is a small, round, dark spot, surrounded by a
faint depression. In surface views we see that the dark area is
bent in the middle, and at the apex of the bend, which is directed
dorsally, is situated the large nucleus. In some cases this con-
figuration of the dark area is more conspicuous than that shown
in Fig. 6a, which represents about the average condition. This
bend is similar to that in the retinal furrow of eye IV., to be
described later, but it does not, as in this last case, remain
throughout life. The invagination and general structure of the
eye is almost exactly like that of eye I’, only it has no dorsal
appendage or vertical retina. See zufra.

Eve L.

The early stages of this eye, which arises from the first
segment of the optic plate, are much like those of eye III.
After the light area has assumed a figure-8 shaped contour, it
increases in extent at the anterior end until a large oval patch,
in reality a shallow depression, is formed. This depression is
' finally separated from the remainder of the clear area by a dark
ridge, leaving only a narrow connecting streak on the ventral
side of the eye. Figs. 11-16 represent surface views of the first
segment as seen from the anterior dorsal side of the embryo.
In Fig. 13 a light streak, or furrow, is seen on the ventral side
of the eye, united at its anterior end with the main clear area.
At this point appears a round dark area (d. a.* Fig. 14).

No. 1.] EVES OF ARTHROPODS. LEZ,

The main dark area, d@. a.1, which at first was very broad and
surrounded by a narrow furrow, formed by the abrupt termina-
tion of the cuticular thickening overlying each sensory area
(Figs. 11, 12), is gradually reduced to a narrow ridge composed
of two rows of nuclei, between which is the large median
one, zc.}

The dark area becomes strongly bent at the anterior end,
and at the angle appears a second large nucleus, wc.2, Fig. 14.
Finally a third smaller and much less distinct nucleus appears
where the area 7-8 joins the main eye.

After this stage, the round spot, d. a.4, and the ventral clear
area, 10, together with the nucleus, zc.3, disappear. The dorsal
appendage grows smaller but more conspicuous, and contains
an oblong dark area divided in halves by a narrow light streak,
in the centre of which I thought I could detect a nucleus like
that found in the dark areas of the other eyes (Fig. 18). The
main part of the eye is reduced to a narrow, bent band, with a
light or dark streak, according to the method of preparation, in
the middle.

The main part of eye I. differs from all others in containing at
least two large nuclet and eight sensory pits. The dorsal appen-
dage represents at least one more pit, perhaps two, tf we can place
any reliance upon the indication of a retinal furrow as shown in
the fatnt, light streak seen tn surface views. As in eye V., the
large nuclei are situated in the centre of a group of four sen-
sory pits. The structure of the sensory area is seen from sec-
tions (Pl. XIII., Figs. 82 and 83) to be like that of eye V. The
former section corresponds with Fig. 63, in which the cuticular
thickenings are still separate; and the latter, to Fig. 64, where
they have united and the median furrow has disappeared. In
describing the invagination, we will leave out of consideration
the dorsal appendage c. e., of which we shall speak separately by
and by.

Nothing like an optic cup is formed by the invagination. As
fast as the median ridge sinks below the surface, the outer faces
of the clear areas om either side are brought together like the
leaves of a book, and the distal ends of the sensory cells meet
one another in the median longitudinal plane of the eye.

But this is not the only direction in which invagination takes
place. In Fig. 8 the sensory area is still seen lying lengthwise

118 PATTEN. [Vou. IL.

on the surface; but during the succeeding stage, its anterior
end is pushed into the tissues of the head, as though the whole
plate swung on a pivot at the posterior end, through an angle of
ninety degrees. The long axis of the retina then lies at right
angles to the surface, and in a semi-transparent preparation,
like that shown in Fig. 9, we look along the retinal furrow, not
down into it as in Fig. 8. It is not easy to form a clear mental
picture of the way in which the retinas of eyes I. and III. are
invaginated. To make matters clearer, let us suppose the head
to be made of soft india-rubber. Then if a slender but inflexi-
ble rod be laid between the two rows of nuclei of the median
ridge, as fast as it is pushed below the surface, the lips of the
indentation that will tend to form, come together, conceal the
rod, and prevent the formation of any cavity. If this process
is continued until all the sensory cells on either side of the
rod are invaginated, a long narrow pocket will be formed, com-
posed of two thick walls, whose originally outer surfaces touch
each other, bringing their cells end to end and at right angles
to the opening of the pit (Fig. 85). There are no transitional
cells connecting the inner edges of the two walls, so that, strictly
speaking, there is no floor to the pocket. This completes the
first stage of the invagination. Now, in eye III., suppose the
posterior end of the rod is fixed and the opposite extremity
swung inwards through an arc of ninety degrees; the retina
will then be brought with its long axis at right angles to the
surface, and the second stage will be finished. Finally carry
the rod in this position backwards a distance equal to the height
of the future corneagen, and, without considering minor details,
the third and last stage is completed.

In eye I. the pocket has a bend like that of the dark area
(Figs. 14-16) which divides the retina into two unequal parts.
Between the lateral walls of the posterior portion, or that which
gives rise to the horizontal retina, is situated the first large
nucleus (zc’., Figs. 17 and 85), and in a corresponding. position
in the anterior part, which gives rise to the vertical retina, is the
second large nucleus, #c.2 The whole pocket is of nearly uni-
form depth, as shown in Fig. 17, which represents a digram-
matic outline of the whole eye seen as a transparent object. In
order to continue the invagination by means of our rod, it must
be cut at a point a little back of the second nucleus, zc.%, and

No. 1.] EVES OF ARTHROPODS. 119

that part of the rod lying in the future vertical furrow, removed.
Now if, as in eye III., the posterior end of the rod is fixed, and
its anterior extremity swung inwards through an angle of about
ninety degrees, and then carried backwards a distance equal to
the height of the future corneagen, the invagination of eye I.
will have been completed, and a condition obtained like that in
Fig. 18, Pl. VIII. When we began to carry the posterior part
of the furrow inwards and backwards, of course the anterior
part was gradually pulled into a vertical position and extended
along the inner lateral edge of the flattened optic cup, where
it remains through life as the vertical retina.

Figs. 79-81, Pl. VII., represent longitudinal vertical sections
of eye I. (semi-transverse sections of the head, parallel with the
long axis of the retinal furrow, see Fig. 8), showing three suc-
cessive stages in the invagination of the retina.

CoRNEAGEN. —As soon as the early stages of invagination
have carried all the clear area below the surface, the surround
ing ectoderm cells are drawn in, in the same way, to form the
corneagen. But these cells, instead of meeting end to end
above the retinal furrow, take an outward curve, so that their
long axes are parallel with the plane of invagination. The first
direction of the invagination is towards the brain, and as the
long axes of the corneagen cells are parallel with the direction
of invagination, they naturally point inward and are at right
angles to the long axis of the vertical and horizontal retinas
(Fig. 79). But when the invagination is directed backward, the
inner ends of the corneagen cells are pulled backward also, so
that they finally have their long axes at right angles to the hori-
zontal retina, and parallel with the vertical one (Figs. 80 and 81).

The shape of the corneagen cells shows the way in which
they were formed. In all cross sections of the horizontal retina,
—sagittal sections of the head,—the nucleated ends of the
corneagen cells bend away from the median plane to either side,
and in such a way as to leave no conspicuous boundary between
them and the retinal cells. For some time after the closure of
the flattened optic vesicle there is a line in the middle of the
corneagen marking the place where the lips of the invagi-
nation united. The difference in curvature between the cells
belonging to the corneagen and to the retina gives rise tempo-
rarily to a small triangular space between these two struct

120 PATTEN. [Vor Tk

ures (Fig. 85). After the lens has appeared, and even in the
fully developed eye, the ends of the cells lying in the middle of
the corneagen are so compressed and filled with fine granular
protoplasm as to form a distinct, deeply stained core.

The nuclei of the corneagen are at first arranged in two great
lateral masses (Fig. 85), but as it increases in depth, they form
a single layer that at first sight appears to be a direct continua-
tion of that formed by the retinal nuclei. But the inner ends
of the median corneagen cells, although slightly bent away from
the median plane, do not reach the periphery of the eye. One can
see the nuclei at their expanded inner ends almost over the cen-
tre of the retina (Pl. XIII. Figs. 90, 91). The inner ends of
the remaining corneagen cells are situated at the periphery of
the eye, and are filled with a dense layer of black or dark brown
pigment granules which completely envelop and conceal the
nuciei. In stained, depigmented sections, the formerly pig-
mented ends of the corneagen cells are quite colorless and
empty, with the exception of a few coarse granules and the
deeply stained nuclei.

Retina. — As we have already said, the horizontal retina is
composed of two long strips of thickened ectoderm with their
originally outer surfaces brought face to face (Fig. 85). In the
early stages, the cells nearest the corneagen are indistinctly
defined, and contain large oval nuclei with a few coarse, deeply
stained granules. The position and general character of these
cells is much like that of the inverted ones in eye V., and I
believe them to be of the same nature. However that may be,
they soon disappear. There is no evidence that, in the later
stages, they form an outer wall to the optic vesicle.

Throughout the greater part of embryonic life the free ends
of all the retinal cells are at right angles with the optic axis
(Fig. 85); but the outermost cells finally draw away from the
middle line and assume a more upright position. This process
goes on until only a few rows of small horizontal cells are left
overlying the gigantic ones which form the innermost walls of
the furrow. In cross sections the layers of rods now form a Y,
the diverging arms being composed of nearly upright rods, and
the stalk, of the double rows of horizontal ones (Fig. 86).

In the full-grown larva the anterior wall of eye III. is quite
straight, and most of the retinal cells of that side are horizontal

No. 1.] EYES OF ARTHROPODS. 121

(Fig. 90). The posterior wall, however, is strongly convex, and
the retina on that side is composed of a broad layer of nearly
upright cells, whose short rods decrease in length from the fur-
row toward the posterior periphery of the retina. This remark-
able asymmetry is correlated with the position and inclination
of the lens, which looks upwards, inwards, and forwards, so that
its optic axis falls about in the middle of this posterior layer
of horizontal rods, and not, as one might expect, upon the
retinal furrow. In eye I. the horizontal retina is also asymmet-
rical, but to a less degree, and in an exactly reversed manner,
for the greatest expanse of horizontal rods is on the anterior
side of the furrow instead of the posterior (Fig. 91). There
is a similar asymmetry in the retinas of eyes II. and IV.

The gigantic retinal cells, arranged with great regularity in
two rows, one on either side of the retinal furrow, are very
broad and thin at their freeends. At their opposite extremities,
there is a slight swelling containing a large oval nucleus.
These cells are similar in nature and arrangement to those
at the bottom of eyes II, IV., and V. (Figs. 70-78), except
that they are much larger, and, owing to the way in which
they receive their nerve supply, somewhat differently shaped.
Those on the side of the furrow with the greatest number
of upright rods are longer than those in the opposite part
of the retina. The important point is, that, except in size
and shape, they do not differ from the remaining retinal
cells. They must be regarded as horizontal retinal cells with
very wide and short rods; compare the isolated cells d, e, and 2,
Fig. 58, Pl. X. When these cells first become distinctly out-
lined (Fig. 85), there is only a small space between the pri-
mary nucleus and the rod, while the outer edge of the cell
shelves steeply inwards to the level of the almost horizontal inner
edge. They are also much darker than the smaller cells, and
their free ends being concave, a space is formed between the
two rows of rods. But the latter are soon brought more closely
together, their terminal edges become as straight and ridged as
though crystallized, and the narrow space is filled with a mass
of densely pigmented nerve fibres.

In order to economize space without disturbing the arrange-
ment of the rod-bearing portion, the thick nuclear ends of the
cells are turned alternately toward and away from the median

122 PATTEN. [Vom iat

plane. Hence it happens that in vertical cross-sections of the
eye, four or five rows of large nuclei are seen near the middle of
the retina, although the outer ends of the cells to which these
nuclei belong are arranged with the utmost precision in two
rows.

The giant cells have, in the early stages (Fig. 76), short rods
extending the whole length of their distal ends. In the full-
grown larva these rods are longer but narrower, the proto-
plasm of the cells having pushed its way under the inner edge of
the rod to form a deeply pigmented heel that excludes the rays
of light from the underlying nerve fibres (PI. X., Fig. 56).

The large nucleus, nc, conspicuous in surface views, remains
throughout life unaltered, except that it is perhaps a little larger
and flatter in the older stages. It lies a little inside the middle
of the horizontal retina, between the deep edges of the two rows
of large cells (Figs. 81 and 86).

The vertical retina differs principally in size from the horizon-
tal one. It is deeply buried in the pigment at the periphery of
the corneagen, and might be easily overlooked. It arises, as
already pointed out, from the short bent portion of the dark
area (Figs. 14, 15, 16). There is a second: larce ‘nuclens
that marks, in surface views, about the point where the hori-
zontal and vertical retinas are continuous ; but when the eye is
well invaginated, this nucleus has changed its position to
about the middle of the vertical retina. In the next stage (Fig.
80), the vertical retina is reduced in size at the angle of the
bend, so that it has apparently lost its connection with the hori-
zontal one. At its outer end the retinal cells are well developed,
and form a projecting mass that shelves off abruptly toward the
dorsal appendage (PI. XIII., Fig. 80).

In the still later stages the furrow is relatively smaller and
more uniform in size. At the bottom of the furrow is a double
row of large, flat cells, bearing short, broad rods placed end to end
against those on the opposite side (Fig. 84). Outside-of them
is a single row of smaller, cylindrical ones, bent in the form of
a semi-circle and bearing short terminal rods. These retinal
cells are filled with coarse, black pigment granules, so that only
a narrow slit is left through which the light can pass to the cir-
cular space containing the large rods (Fig. 84).

Longitudinal vertical sections of the eye expose the arrange

No. 1.] EVES OF ARTHROPODS. 123

ment of the cells on one side of the furrow (Fig. 81). It is there
seen that the terminal edges of the broad rods trend toward the
centre of the newly developed lens. The latter is placed so as
to throw light upon the vertical furrow. But this condition is
not permanent; in the adult, the lens is horizontal, and its
axis is directed toward the bottom of the eye. By this change,
the amount of light that falls upon the vertical furrow is very
much reduced.

The nucleated ends of the corneagen cells never lie in front
of the furrow, but always to one side of it.

The vetinophore of eyes I. and III. are like those of eye V.:
The secondary nucleus is always situated beyond the primary
one, in the terminal quarter of the cell.

It is not so easy to detect the secondary nucleus in the gigan-
tic cells as one might suppose. Their flattened ends make
it difficult to roll them when isolated, so that one cannot view
the same cell from different points. Moreover, they have a ten-
dency to stick together in great flakes that appear, owing to the
excessive thinness of the cells, to consist of but one retinophora,
when they may contain half a dozen or more. But in spite of
these difficulties, I have seen enough to convince me that they
are double cells and that the secondary nucleus is situated in
their expanded and flattened ends about half way between the
primary nucleus and the rod.

Although I have not made any extended observation on the
structure of the retinophorz in the vertical furrow, their intimate
connection with those of the horizontal retina, as shown by the
early stages of development, and the presence of the double
rods, leave no room to doubt that they have the same structure
as the other retinophore.

In only one instance have I seen anything like ganglion-cells
in the retina. It was a small tripolar cell, with an outward pro-
longation extending along the sides of a retinal cell. Both cells
were firmly united with each other, and were found among a
great many isolated ones from all the eyes, so that it was impos-
sible to determine to which retina it belonged. It was (Pl. X.,
Fig. 58, 2) very much like the tripolar cells found by me in the
retina of Haliotis. :

I have looked for these cells in sections, but have never
found any trustworthy evidence of their presence. I regard

124 PATTEN. [Vou. II.

them as half-formed ganglion-cells which have not succeeded
in separating themselves from among the sensory cells, by
transformation of which they arose.

NERVE Enps.— The manner in which the nerves terminate in
the retina is practically the same as in eye V., while owing to
the large size of the inner retinal cells, some points are brought
out with great clearness. But the layer of pigmented nerve
fibres between the rows of gigantic cells is a fedture only
found where these cells are especially well developed.

In Fig. 56, Pl. X., is represented a section through the hori-
zontal furrow of eye I. The sides of the cells are thickly cov-
ered with nerve fibres that converge toward the inner end of
the cell to form a large bundle that might readily be mistaken
for a continuation of the cell substance. The fibres follow, as
nearly as possible, the contours of the outer and inner edges of
the cell. This point is of importance, for it furnishes additional
evidence that the rods belonging to these cells are terminal, and
consequently developed at what is morphologically the free end
of the cell; for in the smaller retinal cells the nerve fibres always
run parallel with the longitudinal axis; hence the direction of
the fibres shows in which way the cells have been bent.

At the distal end of the cell all the nerve fibres become
roughly parallel, and develop refractive, spindle-shaped swell-
ings, densely coated with pigment, the granules of which often
form distinct lines, showing clearly the position and direction of
the nerve fibres around which they are arranged; or the gran-
ules may be collected in shapeless masses near the inner end of
the rod, showing no traces of the arrangement of the nerve
fibres they so effectually conceal.

At the opposite extremities of the cells the pigment granules
are arranged in lines similar in direction to the nerve fibres ;
they are also found on the nerve fibres after they have left the
cell to form the optic nerve.

Beyond the spindle layer described above, the nerve fibres
emerge from the pigment and extend over the surface of the
rods in nearly parallel lines. At certain intervals these fibres
expand into spindles, which were a sore puzzle to me before I
had made a careful study of depigmented sections. They
seemed to indicate quite clearly the division of the broad rods
into segments, about the width of the smaller rods, a condition

No. 1.] EVES OF ARTHROPODS. 125

that it was of course impossible to reconcile with the great size
of the cells to which they belonged, unless we assumed that
each of these cells possessed many rods.

In the smaller cells, the nerve fibres and pigment granules are
also distributed in the manner just described, but their course
ana arrangement is less easily followed.

The small retinal cells contain an axial nerve which, between
the two rods of each retinophora, breaks up into a fan-shaped
bundle of fibres, that in cross sections appear like a row of dots
midway between each pair of rods, and usually parallel with
their broad surfaces (Fig. 55).

In the gigantic retinophoree, the axial nerves are arranged ina
sheet as broad as the ends of the cells. In longitudinal vertical
sections, they are consequently seen as a row of dots between
each pair of rods (Fig. 55).

Most of the nerve fibres supplying the retinal cells come from
two bundles that extend along the edges of the horizontal retina
(Figs. 90 and 91). A third group extends along the middle of
the under surface of the retina. From it arise two sheets of
densely pigmented nerve fibres which extend upward into the
Space between the two rows of gigantic cells (Pl. X., Fig. 56, v. 7.).
These fibres are very straight and arranged with almost as
much regularity as the large rods, with whose terminal edges
they are parallel. I suspect that the number of these nerve fibres.
bears a pretty constant relation to the number of large rods. In
some of my preparations I could see that a single nerve fibre lay
in or near a shallow furrow which marked the point of union of
each pair. From this I judge that in the living, normal condi-
tion, one of these vertical fibres extends along the terminal
edge of each pair of large rods. But evidence of this condition
is not often found in sections, owing to the action of the re-
agents, which cause a contraction that draws the fibres away
from the rods towards the middle of the furrow. Hence in hori-
zontal sections, these nerve fibres are seen in cross sections as
two rows of dots, a little distance from the terminal edges of the
rods (PI. Xi, Figs 50, v7).

From the vertical nerve fibres arise a great many fine fibrillze
which extend at right angles to the main fibres towards the rods
and apparently become continuous with the external nerve fibres.
Others extend in an opposite direction where, detween the two

126 PATTEM. [Vot. II.

sheets of vertical fibres, they form amass of the finest, interwoven
fibrille, that presents the same appearance as the medullary sub-
stance in the optic gangla. It cannot be that this enigmatical
mass of nerve fibres is nothing but a flake of coagulated serum.
The latter is frequently present and is especially abundant after
some modes of treatment, filling all the cavities of the head
with a finely granular substance. At other times it is altogether
absent, or at any rate the cavities appear quite empty. But
under both these conditions, this mass of nerve fibres, unen-
closed by any membrane and devoid of nuclei, maintains such a
constant shape and uniform appearance as to preclude all thought
of its being a product of coagulation. It may be remarked, also,
that the coarse pigment granules, so abundant about this fibrous
mass, are completely dissolved by acids, and consequently leave
no granular residue that might be mistaken for nerve fibrille.
We have already pointed out that in the iris the pigment is also
completely dissolved by these reagents.

One occasionally finds, among the fragments of cells isolated
by maceration, what appear to be large flakes of pigment with
parallel striations. They are fragments of the sheets of ver-
tical nerve fibres covered with pigment, the fibres being united
with one another by the innumerable fibrille that arise from
them.

Between the outer ends of the vertical nerve fibres is an oval
space devoid of pigment, quite constant in shape and size (Figs.
go and of, Pl. XIII). I have no suggestion to make concerning
its significance.

The vertical fibres, and the pigment surrounding them, do not
extend beyond the outer edges of the large rods.

The Rods in eyes I. and III. develop in the same way as those
of eyes V. and VI.; and although their arrangement in the fully
developed eye differs in some important and interesting particu-
lars from that in the last-mentioned eyes, their general struct-
ure is the same in both cases. ¢

The horizontal rods are arranged with great precision and
regularity edge to edge in vertical rows. The broad sides of
two rods belonging to adjacent retinophore lie so close together
as to look like one rod with a faint vertical line in the middle.
The rods belonging to the same retinophore are separated
by a clear space, a little smaller in diameter than that of the

No. 1.] EYES OF ARTHROPODS. 127

retinophorze to which they belong. In the centre of the clear
space is the vertical row of axial nerve fibres (Pl. X., Fig. 55).
At the lower end of each double row of rods are two pairs of
much larger ones belonging to the large retinophorze at the
bottom of the retinal furrow. They are arranged in pairs like
those of the small retinal cells, except that the clear space
between each pair is alternately wide and narrow.

The rods in the rows just above the gigantic ones differ from
all others in that their free ends are united in pairs opposite the
centre of the retinophore (Fig. 60).

Toward the periphery of the retina, where the rods are up-
right, the rod-mosaic is Hae of zigzag lines like those in
Bare (Fig. 54a).

DorsaL APPENDAGE. — Pesce the vertical, and horizontal
retinas of eye I. there is a third part that up to this time we have
left out of consideration. It is what in a former paper I have
called the dorsal outgrowth of the large posterior ocellus. The
observations recorded in this paper throw new light on that
remarkable organ.

We have already described how the changes seen in surface
views gave rise to an oval sensory patch constricted off from
the anterior, dorsal end of eye I., but with which it was still con-
nected by means of a narrow furrow (Pl. VIII, Figs. 14-16).
While the main portion of eye I. is being invaginated, the dor-
sal appendage is depressed, forming a deep pit, at first round,
then oval, and finally slit-shaped, the long axis of the depression
being at right angles with that of the main eye (comp. Figs.
8 and 14-16). In Fig. 79 is shown a longitudinal section of the
main eye with a cross section through the middle of the dorsal
appendage, during a stage corresponding to that shown in Fig.
16. Ina similar section of a later stage, the pit is closed and
three layers of cells are formed very much like those in eye V.
(Fig. 80). The outer ends of the retinal cells soon lie close
against the corneagen. The outer wall of the vesicle is flat-
tened and probably forms an imperfect middle layer; at least I
have seen in several cases one or two nuclei just beneath the
corneagen, which, I believe, must be referred to the outer wall of
the vesicle. Fig. 16 shows that the sensory cells connecting
the ocellus with its dorsal appendage are joined to the latter at
its anterior edge, consequently only those sections that pass

128 PATTEN. [VoL. II.

through the anterior edge of both these structures—and not
those shown in Figs. 79-81, which pass through the middle of
the appendage — will show the continuity of their retinal cells.
After the stage shown in Fig. 81, I have not been able to detect
evidence of this continuity, although the vertical furrow contains
retinal cells up to the very outermost edge of the eye.

Surface views indicate that the peculiar structures found in
all the other eyes, such as the median rows of cells and the large
nucleus, are probably present in the dorsal appendage, although
imperfectly developed. My failure to detect them in sections
may be due to the difficulties of observation.

In longitudinal vertical sections of eye I., the dorsal append-
age is seen to be somewhat thickened in the middle, the rod-
bearing ends of the retinal cells converging toward an imagine
centre some distance above the corneagen.

The appendage is never sharply limited from the surrounding
ectoderm; it is less so in the older stages than during the period
when it is an open cup or newly closed vesicle (Figs. 80 and
81). The basement membrane is continued without interrup-
tion from the surrounding ectoderm, over the inner surface of
the appendage, and this tends to obscure still more the limits
of the parts in question.

The retinophorz of the appendage are much like those of the
other eyes. They are long, spindle-shaped cells with double
rods, and hence probably contain two nuclei and an axial nerve
fibre.

The observations recorded in this paper were made entirely
upon material collected in a small pool near Milwaukee. In all
these specimens the appendage was entirely devoid of pigment.}
In the larve that formed the basis of my preliminary note on
the ‘Eyes of Acilius,” in the first number of this Journal, and
which were collected near Boston, Mass., the retinophorz of _
the appendage contained large blotches of pigment just below
the rods.

Grenacher has described, without figures, the dorsal appen-
dage in the larva of Acilius sulcata as being pigmented. He
failed to recognize that it was composed of two distinct
layers; and while he thought it was in all probability some kind

1In some of my sections I have noticed, since this was written, mere traces of
pigment at the base of the rods in the Milwaukee species.

No. 1.] EYES OF ARTHROPODS. 129

of a sense organ, perhaps one in course of development, he
apparently had grave doubts about its being a visual organ ; at
any rate he is careful not to call it such.

Eves II. ann IV.

Eyes II. and IV. arise from the distal edge of the first and
second segments of the optic plate. They are so much alike
that it will not be necessary to describe them separately. I
have not been able to follow the very earliest stages in the
development of these eyes, owing partly to their small size and
partly to the fact that during these stages they are situated on
the infolded edge of the optic plate, so that it is almost impossi-
ble to study them in surface views. Nothing in the sections
indicates that they differ in any important points from the cor-
responding stages of eyes V. and VI.

The eyes are first seen in surface views (Figs. 5a and 50),
as round clear spaces containing an elongated dark area com-
posed of a double row of nuclei nearly parallel with those of
eyes I. and II. Between the rows of nuclei is a single large
nucleus. The similarity between the structure of these eyes
and the remaining ones makes it probable that the large nu-
cleus, as in all the other eyes, is situated in the centre of four
sense organs.

Eyes II. and IV. are not invaginated to form either optic cups
or vesicles. Just as in eyes I. and III., as fast as the sensory
areas on either side of the median ridge are tipped over, the
ends of their cells meet in a vertical plane above the median
ridge, and thus obliterate the cavity that tends to be formed.

Toward the close of invagination the cells on the outer edges
of the sensory area curve outward and their sides meet in the
median plane of the eyes to form the corneagen (Pl. XIL., Fig.
76), whose nuclei form a row continuous with those of the
retina, so that the latter appears to be directly continuous with
the unmodified hyperdermis. This deceptive appearance is due
to the fact that the nuclei of the corneagen cells over the
centre of the eye stain very faintly, so that, in most cases, they
escape, or even defy detection. In Fig. 76 there is no trace of
a middle layer of cells between the retina and corneagen. But
in two cases, one or two cells were seen, with rather large and
deeply stained nuclei, wedged in between the periphery of the

130 PATTEN. [Vor. IL.

retina and corneagen. They were like the similarly placed
cells described in eyes I. and III. (Pl. XIII, Fig. 85, 0, w), and
I do not doubt they are of the same nature, z.e. cells that have
been pushed between the retina, and the corneagen, forming the
rudiments of a middle layer. They never form groups of in-
verted sensory cells, as in eyes V. and VI., or a continuous layer
of non-sensory ones, as in a part of eye VI.

The retinas ot both eyes are asymmetrical, as in eyes I. and
III., in that there are more upright rods on the dorsal side of
the retina than on the ventral (Figs. 77, 78).

Eye II. contains a greater number of horizontal rods than eye
IV., and the median space in which they lie is considerably
deeper.

The outer retinophore are long and semi-circular, and nearly
uniform in size throughout. The innermost ones are broad, scim-
etar-shaped cells, arranged with great regularity in two rows that
extend the whole length of the longitudinal axis of the retina.
Their free ends, which are bent at right angles, are almost as
broad as the remainder of the overlying retina. In the younger
stages, the terminal edges of the large rods are concave, and a
considerable space is left between the two rows (Fig. 76). In
the later stages they are rigidly straight, and the space is
filled with a layer of densely pigmented, vertical nerve fibres,
like those in eyes I. and III. (Fig. 78).

In all essential particulars, the finer structure and arrange-
ment of the retinophore and their rods, and the distribution of
nerve fibres, is the same as in eyes I. and III.

After the corneagen has formed a continuous layer over
the retina, the Jarge nucleus lies just below and between the
inner edges of the two rows of giant retinophorae. It stains
deeply on the periphery, and contains a few coarse, deeply
stained granules. It is always oval, with its long axis parallel
with the long axis of the retina, and is somewhat compressed,
‘as though forceably flattened between the two rows of cells.
It remains in this position, unaltered, through larval life.

Eyes II. and IV. are somewhat canoe-shaped, the retinal
furrow being at first nearly parallel with that of eyes I. and III,
below which they lie in the earlier stages; but they finally
change their position for one behind the deep end of eye I.
During this change, they rotate on their optical axis through an

No. 1.] EVES OF ARTHROPODS. 131

angle of about ninety degrees, so that by the time the embryo
is ready to hatch, their retinal furrows are at right angles with
those of eyes I. and III. (compare Figs. 54, 8, and 10a). Sur-
face views of eye IV., in its younger stages, show that its
retinal furrow is bent, a condition which is retained through
life (Fig. 8a).

The Lens of eye Il. (Fig. 77) is asymmetrical, in that the
radius of curvature of its strongly convex inner surface is
greater on the dorsal, than on the ventral side. The axis of
the lens falls upon the layer of short, nearly upright rods
on the dorsal side of the retinal furrow. The latter, which
is the most specialized part of the retina, lies, therefore, very
much to one side of the apparent optical axis of the eye.
The same fact was observed in eyes I. and III. This extra-
ordinary condition is difficult to account for satisfactorily.
There is every reason to believe that the retina has not been
moved by shrinkage from its normal position in relation to
the lens. The greater depth of the iris on the dorsal side,
the extension of the rods in that direction, the slight flat-
tening of the dorsal, inner surface of the lens, and the whole
history of development, show too clearly that these diverse parts
are modified in this manner in order that the optical axis might
have the direction indicated.

Although in eye IV. the lens is more symmetrical, its axis
falls upon the retina some distance above the furrow.

In the larva, the optical axis of eye II. is directed upward
and backward, that of eye IV. downward and backward.

II. THE Optic GANGLION.

As soon as the cephalic lobes have assumed their character-
istic shape, a slight depression, the future mouth, appears in
the median line between them. On either side of this depres-
sion are three ectodermic thickenings from which the brain is
subsequently developed; they appear to be direct combinations
of the segmental thickenings of the ventral nerve chord (Fig.
2, 6%), On the lateral edge of the third pair of thickenings, 0°,
are the antennae, a* On the inner edge of the second pair
are two appendage-like outgrowths of the ectoderm, that finally
unite in the middle line above the mouth to form the labrum, a.

132 PATTEN. [VoL. II.

Between the brain and the optic plate (Fig. I.) is a broad
expanse of ectoderm composed of faintly stained cells contain-
ing coarsely granular, or even flocculent, protoplasm and large
spherical nuclei.

In Pl. IX., Fig. 19, which represents a cross section through
the middle of the cephalic lobes of an embryo considerably
younger than that shown in Fig. 1, there is no thickening to form
the brain, although the distal edges of the lobes have already
given rise to the optic plate, on the inner edge of which is a
depression, containing large wedge-shaped cells quite different
in appearance from those on either side of them (0. g.). This
depression, the beginning of the invagination of the optic gan-
glion, is fairly uniform in depth, and in surface views appears
like a semi-circular furrow on the inner edge of the optic plate.

The ectoderm that gives rise to the optic ganglion divides into
three segments, or lobes, each of which ts united on the one hand
with a segment of the brain, and on the other, with a segment of
the optic plate (Fig. 1, 0. g.*").

The semi-circular groove is soon deepened to form two distinct
pits with slit-like openings (Fig. 1, g. v.t*). There is no infold-
ing between the third segment of the optic plate and the third
segment of the optic ganglion, but there is, as shown in sections,
a distinct inward proliferation of ganglion-cells at this point.
Each segment appears in some cases to be divided by a faint
line into two parts, a condition that may have some connection
with the fact that it belongs toa part of the optic plate provided
with two eyes.

Figs. 20-23, Pl. IX., represent four cross sections of the
cephalic lobes during the stage shown in Fig. 1. The first
section passes through the first ganglionic invagination, g. v.},
the lateral wall of which is composed of a single layer of loosely
connected cells, continuous, at the opening of the pit, with the
edge of the optic plate. There is no infolding between the
anterior edges of the optic plate and first ganglionic segment
(Fig. 1). The invagination appears just behind this point as a
slight furrow that increases in depth backwards as far as the
anterior end of the second segment of the optic plate.

The section shown in Fig. 21 passes through the bridge of
ectoderm separating the first invagination from the second.
Beneath the uninfolded layer is a V-shaped mass of ganglionic

No. 1.] EVES OF ARTHROPODS. 133

cells, the cavity of which is continuous with that of the first
ganglionic invagination.

In the next two sections there is a solid chord of cells in the
place of the V-shaped mass of Fig. 21. It connects the cells of
the first ganglionic invagination with those of the second.

The succeeding section (Fig. 22) passes through the second
pit; e.oF

That shown in Fig. 23 passes through the base of the antenna
and the point marked g. v.3, Fig. 1. It shows at g. v.? a cross
section of a thick chord of ganglion-cells extending from the
third ganglionic segment to the under surface of the third
ocular plate. It is produced by an inward proliferation the
direction of which is parallel with the long axis of the antenna.

The invaginated part of the optic ganglion now forms a con-
tinuous semi-circular mass of cells tucked beneath the optic
plate. J¢ zs directly continuous along its inner edge with the
distal inner edge of the optic plate, p. n.

This fact may possibly throw some light on the inexplicable
presence of an optic, and ganglionic invagination side by side.
My studies on Molluscs and Arthropods led me to suppose that
ganglion-cells were derived from sensory cells that had wandered
into the underlying tissues, leaving their outer ends, transformed
into nerve fibres, sticking in the epidermis. Confirmation of
this supposition was found in Pecten. Much better evidence will
be given in describing the origin of the large tripolar cells in
the optic ganglion of Acilius.

But the point I wish to emphasize now, is, that from the ear-
liest stages, the inner surface of the optic plate is continuous
with the optic ganglion (Figs. 20-23, f. z.), and from what takes
place later, it is highly probable that ganglion-cells are formed
at this period by an inward proliferation of the optic plate.

My idea is that an increase in the width of the optic plate,
since its distal edge is fixed, would produce a fold like that
in Fig. 20. The main part of the optic ganglion of this period
may be regarded as a formerly sensory area with an underlying
plexus of ganglionic cells continuous with a similar plexus under-
lying the eyes. With the great development of the latter,
all the cells of the sensory area were converted into gan-
glionic ones, which were then overgrown by the optic plate
and added to the plexus arising directly from the eyes. The

134 PATTEN. [Vot. II.

general character of the invagination points to this conclusion,
and it seems hardly possible to reconcile, by an explanation
along any other line, the independent development of such de-
pendent structures as the eye and the optic ganglion.

The sections shown in Figs. 24-27 belong to a little younger
stage than those shown in Figs. 20-23. They were cut from an
embryo somewhat abnormal, the antenne being lodged in a
great depression, on the floor of which was the mouth. There
was nothing abnormal about the parts belonging to the eyes.
The first and second ganglionic invaginations are shown particu-
larly well.

All these sections and those described above are instructive
from the fact that there cannot be a shade of doubt that the
ganglionic invaginations have nothing whatever to do with the
formation of optic vesicles, for the peculiar way in which the
eyes develop makes it possible to determine, even at this period,
just what parts develop into the eyes and what into the optic
ganglion.

These two series of sections show pretty clearly that chere
are two distinct, and onze obscure, invaginations to form the optic
ganglion. This fact ts of especial interest when we consider that
there are three segments to the brain and three to the optic plate,
and three distinct parts to the optic ganglion of the convex eye.

In Fig. 3 a the three ganglionic segments, o. ¢.¥? are still visi-
ble in surface views, and at the anterior ends of the first two are
seen the openings of the ganglionic invaginations, g. v.t and g. v.2

In a later stage (Fig. 4), nearly all the eyes, as well as the
mouths of the two invaginations, are visible. Still later (Figs.
5 a and 6) the invaginations have disappeared, and all but a small
part of the optic ganglion is concealed by the optic plate.

Just after the rupture of the embryonic membranes, the optic
ganglion is completely shut off from the surface, and the ecto-
derm of the optic plate becomes continuous with that over the
brain. é
Figs. 28-34, Pl. IX., represent seven sections of an embryo
about the age of that in Fig. 4.

The optic ganglion now forms a great, complex mass of cells, |
the most of which is not yet overgrown by the optic plate. It
requires careful attention, not only to recognize its parts, but to
distinguish them from the brain.

No. I.] EVES OF ARTHROPODS. 135

The first section (Fig. 28) passes just above the anterior edge
of the plate, and shows the proximal ends of each ganglionic
segment, a. g.t%

The next (Fig. 29), passes through the first invagination,
g.v., and the anterior end of eye V.; compare Fig. 4. At this
niveau, the third ganglionic segment, o. ¢.°, is separated from the
third lobe of the brain by the cephalic infolding, z.

In Fig. 30, the section passes through the centre of the third
segment, which is not separated by any epithelial layer from the
exterior. At x.y. is a section of the second segment of the
optic plate, where it dips down towards the second ganglionic
invagination. The underlying cells, o. g.1 and o. g.2, connect
the main part of each ganglion with the segment of the optic
plate to which it belongs.

In Fig. 31, the section passes through the upper edge of eyes
V. and IIL. and in Fig. 32, through about the middle of these
eyes. The scattering fibres uniting the eyes with the optic
ganglion indicate the position of the future nerves.

In Figs. 33 and 34, the sections pass through the upper and
lower edges of eye VI., and show how the optic ganglion is here
reduced to a chord of cells continuous with the retinal cells of
the eye.

After the rather confusing condition shown in the last series
of sections, it will be a relief to find in the next (Figs. 37-39),
a simpler arrangement. These sections are taken from a head
a little older than that shown in Fig. 4. The first section (Fig.
37) passes through the site of the first ganglionic invagination.
It is now closed, but there is a depression above an inwardly
projecting core of cells, which marks its former position, g. v.}
It also cuts the anterior edge of the first ocular plate, showing
a small part of the first ganglionic segment, o. 1 Two or three
sections below this we find one (Fig. 38) which passes through
the point ¢. v.2, Fig. 4, and consequently through about the mid-
dle of eye I. and the anterior edge of the second ocular seg-
ment. The third segment of the optic ganglion is still exposed
to the exterior, 0. g.3 The outer wall of the ganglionic invagi-
nation has completely disappeared by this time, and the edge of
the optic plate comes squarely against the outer surface of the
third ganglionic segment. The only part of the brain seen at
this niveau is a section of the anterior end of the antennary lobe.

136 PATTEN. (Vou. II.

it is separated from the optic ganglion by the invaginated ecto-
derm, z. After three or four more sections, we come to one
(Fig. 39) that passes through the middle of the fifth eye and the
lower end of the first. It should be remembered that the sec-
tions are cut from an embryo a little older than that in Fig. 4,
and that the posterior end of eye I. is on a level with eye V.
We see that the continuity of the optic plate with the optic gan-
glion is now interrupted everywhere except along three lines
directly beneath, and parallel with, the median furrow of the
eyes. These three connectives are short and nearly as broad
as the optic plate. Compare Figs. 4 and 5a. They are the
rudiments of the optic nerves, and are composed of a mixture of
nerve fibres and ganglionic cells.

If we refer to Fig. 1, and the sections of that age, Figs. 20-
23, we shall see that the first cross section passes through the
first ganglionic invagination, with whose direction of ingrowth
it is nearly parallel. Now if we suppose a section to be cut
through the long axis of the optic plate at that stage, we should
then see three bands of cells—the optic plate, the middle wall
of the ganglionic fold, and the optic ganglion itself. Owing to
the way the cephalic lobes have developed, a cross section of the
head shown in Fig. 4 will give a picture something like our
imaginary one, only the middle wall of the fold has disappeared,
and the inner one, the optic ganglion, is bent so as to appear
like a thick, imperfect ring (Fig. 39).

The brain at this period consists of a medullary core enclosed
in a thick layer of ganglion-cells. The latter are continued,
without any perceptible modification or break, into those which
constitute the optic ganglion, which, up to this time, contains
no medullary core. From this time up to the latest stages,
there is no way of distinguishing the parts of the optic ganglion
except by their position, and the nerves which go from them to |
their respective ocular segments.

I have represented two more sections from a head a little
younger than that in Fig. 6. The first (Fig. 35) passes through
the upper edges of the first and second ocular segments, and
shows, besides eyes I. and III., the anterior edge of the optic
ganglion. In the next section below, not represented in the
plate, the optic ganglion is seen in section as a circular mass of
cells, apparently cut off from the brain by the invaginated ecto-

No. 1.] EVES OF ARTHROPODS. 137

derm, z. It contains in the centre a round medulla, the down-
ward continuation of the fibrous mass, m. d. in Fig. 35. The
second section (Fig. 36) passes through about the middle of the
first and second ocular segment, and just above the third. The
ring of ganglion cells is now interrupted on its median edge,
forming a narrow inlet into a central space lined with the
cut ends of medullary fibrillae. The whole cavity is soon
filled with a mass of fibres which develop into the medullary
stalk of the optic ganglion, s. 0. ¢., which afterwards serves to
connect the different ganglionic centres with the brain.

In all sections of the optic ganglion during the younger
stages, its inner face is sharply defined, as though bounded by a
delicate membrane, something like the basement membrane on
the inner surface of ectodermic layers. In the older stages this
membrane disappears, and the optic ganglion becomes a mass of
loosely connected cells.

In the section shown in Fig. 36, and in those of the same
series below it, the short bundles of nerve fibres connect-
ing the optic ganglion with the eyes, pass completely through
the ganglionic layer, at the inner surface of which they bend
upwards, and pass through the centre of the ganglion into the
brain.

MEDULL# OF THE OpTic GANGLION. —It is necessary to
understand the position and arrangement of the larval medullz
in order to comprehend the structure of the optic ganglion of the
imago. They become definitely established soon after or during
the rupture of the embryonic membranes, and may be studied
in a series of sections (Figs. 42-47) cut from a head like that in
Fig. 8.

The first section (Fig. 42) passes through the upper ends of
eyes I. and III. and cuts through the optic ganglion at its
junction with the brain, showing the cut ends of the medullary
fibres as they bend from the brain down into the centre of the
optic ganglion. After four more sections, we come to one (Fig.
43) passing through the upper end of the optic ganglion, in
the centre of which is a circular mass of medullary substance
bounded by a layer of minute dark cells, continuous with those
surrounding the medulla of the brain.

In the fourth next section (Fig. 44) the optic ganglion appears
as an oval mass of cells close beneath the optic plate. The

138 PATTEN. [VoL. II.

roots of nerves I. and III., seen in longitudinal sections, are
somewhat swollen and divided into two parts.

The fibres at the ends of the nerve roots turn upwards and
pass into the stalk of the optic ganglion. Their cut ends do
not lie on the inner surface of the ganglion, as during the earlier
stage (Fig. 39), but in the centre. On the ventral side are seen
medulla 3 and sections of the roots of the nerves supplying eyes
V. and VI.

The next section (Fig. 45) passes through eye V., and shows
its double nerve in longitudinal, and that of eye VI. in cross
section. It is below the level of eyes I. and III., but shows eye
II. and its minute nerve root with its adjacent large ganglion
cell. ,

Fig. 47 represents a section passing through eye VI. and its
nerve just as the latter bends at right angles. It is clothed with
nerve cells up to the very base of the eye.

This series of sections shows the principal features of the
optic ganglion at this stage. The parts are lettered in a way to
show at once their relations to the eyes. They should be care-
fully examined and compared with Fig. 8, for a better under-
standing of the parts will be obtained in this way than by a
long and tedious description.

Toward the close of embryonic life most of the nerve cells are
situated on the dorsal surface of the ganglion, where the latter
joins the brain.

In Fig. 48 is represented the optic ganglion as seen in a
cross section of an embryo about ready to hatch. The section
passed through the head between eyes II. and IV. showing a
little of both. Fig. 8 represents a younger embryo than the one
we have in mind, but it serves perfectly well to show the level
of the section. As the head is bent at right angles to the body
in such embryos, the section would be the same as a longi-
tudinal, horizontal one of the larval head, Fig. 10. Again, the
section we are about to describe would cut that shown. in Fig.
49, taken, however, from an older head, just below the crown of
ganglionic cells on its dorsal surface. At this period, the shape
of the medulla and the characteristic arrangement of the fibres
in them can be studied to best advantage.

Suppose the side of the head to which belongs the optic gan-
glion we are describing, laid flat on the paper, opposite the

No. 1.] EVES OF ARTHROPODS. 139

section of the optic ganglion. An outline drawing of the eyes
in this position would then be almost the exact mirror-image or
“Spiegelbild,” as the Germans call it, of the medulla of the
optic ganglion (Fig. 1, wood-cut).

Figure z.— A. Projection of the retinas just affer the rupture of the embryonic
membranes. B. Horizontal section of the optic ganglion during the same period.
I.-VII.=eyes. 6= cluster of inverted cells derived from sixth sense organ of eye
VI.; d.a.= dorsal appendage; %. r. = horizontal retina; v. 7. = vertical retina;
uv. f.= vertical fibre; 1 = plate of medullary substance between the vertical fibres,
corresponding to a similar plate in the retina. mm. III. = medulla of eye III.; and
m.d.a.= medulla of dorsal appendage, etc. The two cuts illustrate the corre-
spondence between the structure of the medullz and that of the retinas.

Medulla 3 (Fig. 48) is long and flat in section and somewhat
pointed at the outermost end. It is divided into two unequal
parts by a double row of coarse fibres. Between them is a clear
space containing a long line of extremely fine medullary sub-
stance, which I have not succeeded in dissolving into fibrilla,
although I do not doubt it has such a structure from its great
similarity to the medullary substance on either side of it. If we
compare this part of the medulla with a horizontal section of the
retinal furrow of eye III., we shall see (Fig. 59) that in both,
there is a double row of coarse fibres seen in cross sections;
the rows are separated by about the same distance, and between
them is a thin layer of interwoven fibrillaz which in the retinal
furrow are deeply pigmented.

On either side of the double row of cut fibres, there is a layer

140 PATTEN. [Vot. II.

of felted fibrilla, that on the posterior outer side being much
thicker than the other. If we turn again to the retina of eye
III., it will be seen that the part on the posterior side of the
furrow is much broader than that on the opposite, and exceeds
it in width by about as much as the posterior layer of fibrillae
in the medulla exceeds that on the anterior side. That this
extraordinary correspondence between the structure of the eye
and its medulla is no fanciful one, may be proved by referring
to any other medulla. In each case, we shall find that she
structure of the medulla is like that of the retina to which it
belongs. For instance, in eye V. there are remnants of a me-
dian row of peculiar cells which undoubtedly represent the
gigantic cells, such as those in eyes I. and III. In the embryos
just ready to hatch, the medulla of eye V. is divided in the
middle by a layer of coarse fibres, the cut ends of which are
distinctly visible in cross sections, so that the outline of the
medulla, with its median row of cross fibres, is the mirror-image
of eye V. with its median row of cells. In the full-grown larva,
the latter are much smaller and less conspicuous, and we find
on turning to a section of the medulla that the median row of
coarse fibres has degenerated in a corresponding degree.

In eye VI. the upright retinal cells are uniform in structure
throughout, the median ridge seen in surface views of the
younger stages having disappeared. But there is a remarkable
bundle of inverted cells on the ventral side of the retina, and
this peculiarity is expressed in the medulla of that eye by a
small bundle of fibres in a corresponding position. Still again
medulla I. shows by its configuration that it belongs to eye I.
There is the narrow bent portion belonging to the vertical
furrow, the broad inner part to the horizgntal retina, and at the
outermost end of the medulla is a small bundle of fibres belong-
ing to the appendage. To complete the correspondence there
are the three rows of fibres in the middle, just as described in
medulla III., and on either side a layer of medullary substance,
the thicker layer being on the anterior edge, corresponding to
the greater width of the retina on that side of the furrow.

All the optic nerves are composed of coarse fibres arising
from the medullz. So far as it is possible to determine, each
fibre is composed of the prolongation of the external and inter-
nal fibrillee of the cell with which it is united. The latter are

No. I.] EVES OF ARTHROPODS. I4I

probably continued into the medulla without losing their iden-
tity. There is reason to believe, from the similarity in structure
of the retina and the medulla, that the fibrille of the latter are
rearranged in a manner corresponding with that of the fibrille in
the retinal cells. Now if my supposition is correct, we ought to
find in the medullz of eye I., for example, systems of fibrillae
similar in number and arrangement to the retinidia of the retina.
We find indications of such a condition, for there is a furrow in
the medulla containing a double row of fibres, between which is
a layer of very fine medullary substance. To make the compari-
son complete, the cross fibrillae arising from the fibres ought to
unite with distinct clusters of fibrillz corresponding in compo-
sition and number with the retinidia on either side of the retinal
furrow. But although we cannot distinguish these medullary
vetinidia, since all are united to form one continuous mass, there
is reason to suppose they really exist, for, as we have shown
above, where there is a break or any marked peculiarity in the
arrangement of the retinal retinidia, we find a corresponding
change in the structure of the medullz. For example, if there
are more rods and consequently more retinidia on one side of
the retina, there is an increase in the thickness of the medulla
on its corresponding side. If there is a bend in the retina,
there is a similar one in the medulla. If there is a furrow in
the retina, containing a double row of coarse fibres, there is a
space in the medulla that also contains a double row of coarse
fibres, and if the furrow is absent, the space is absent also;
and we might enumerate a number of other peculiarities in
the structure of the retina that had their counterpart in the
medulla.

I am not prepared to discuss the conflicting hypotheses
that have been advanced concerning the significance of the
medullary substauce, but I desire to call attention to the fact
that its peculiar structure in Acz/zws may throw some light upon
its function.

I venture to suggest the idea that occurred to me. The
medullze may be regarded as the retinas of the mind, the inner
eyes, in which are reacted the nerve changes produced in the
external ones. The whole apparatus may be compared to a
telephone in which a vibration of the air produces a movement
of the receiver, an intermittent flow of electricity follows, and

142 PATTEN. [Vot. II.

finally, at some distant point, perhaps, a second vibration is
produced exactly like the first. We may suppose that in the
eye, light causes some change—it may be vibrations of the
retinidial fibrille which are transmitted, not as vibrations, but
as chemical changes, along the fibres of the optic nerve to the
medullz, where they give rise to other vibrations exactly like
those produced in the eye. The changes aroused in each
retinal cell are transmitted along a bundle of wires to the
medullz, where they are united in a proper sequence of time and
place, which if we could see or hear, we should recognize as the
same symphony of activities produced in the eye. An essential
feature of the telephone is the similarity in structure and action
of the two ends. It was the similarity in structure between
the retina and the medullz which led me to infer that the
activities aroused in one must produce similar activities in the
other.

The fibrilla at the proximal ends of the medullz unite to
form the medullary stalk to the optic ganglion, which is con-
tinuous with the medullary substance of the brain. The me-
dullz of those eyes belonging to the same segment unite first,
that is, medulla I. with II., III. with IV., and V. with VI., so
that three stalks are formed, which almost immediately unite
with one another to form the common stalk of the whole optic
ganglion. Thus another intimation of the threefold structure
of the optic ganglion is given.

On the dorsal surface of the young larval optic ganglion are
some small, deeply stained cells, crowded together to form
three ill-defined clusters, one on the side and dorsal surface of
each of the three branches of the medullary stalk. The nerve
cells send downwards single fibrous prolongations, which, after
uniting with one another to form ill-defined bundles (Fig. 48,
p.n. fy, pass to the sides of the medullze where they appear to
break up into fine fibrilla. The latter issue from the distal
end of the medulla and immediately unite to form coarse
fibres about the size of those which arise directly from the
ganglionic cells. These fibres then unite in large bundles to
form the optic nerves.

Between the medulle are scattered cells, which in the
younger stages cannot be distinguished from other cells in
the brain and optic ganglion.

No. 1.] EYES OF ARTHROPODS. 143

In the larvze, however, after some modes of treatment, they
appear to be much smaller and stain more deeply. They then
resemble the small dark cells which immediately surround the
medulla of the brain and the ventral nerve cord.

The optic ganglion of the late embryonic, or early larval, stages
does not undergo any noteworthy change until toward the be-
ginning of the pupal period. I never succeeded in finding or
raising pupe, but feel confident that the oldest larvae obtained
had about reached that stage. A view of the dorsal surface of
part of the brain and optic ganglion at this period is shown
in “Pl. LX, Fig; 40; and sections of itm shila, Pigs. 49
and 53.

In Fig. 40 we see beneath the crown of ganglion cells the
faint outline of the medulla, and still further below, the con-
tinuation of their distal ends into the optic nerves. The
ganglion cells of the second segment, o. g.2, now form a semi-
circular band that almost encloses the other two. They are
recognized in sections by the clear protoplasm of their colum-
nar cells (Figs. 49 and 50).

The cells of the third segment are crowded toward the brain,
where they form a narrow collar around the stalk of the optic
ganglion. Above the middle of the stalk, the band lies at the
bottom of a cavity, the roof of which is formed by over-arching
ganglion cells (Fig. 50, o. g.8). Towards its anterior end it is
wider and folded double (Fig. 49, 0. g.3). It is directly continu-
ous on the one hand with the cells of the second segment, and
on the other, with a broad layer of large scattering cells that
fill up the space between it and the third segment (Figs. 40, 49
and 50).

Horizontal sections below the crown of nerve cells have a
wedge-shaped outline in which the medullze have much the
same arrangement as in Fig. 48. Fig. 51 represents such a
section at the posterior edge of which is shown a part of the
second ganglion segment. A section a little above this (Fig.
52) shows part of the second and first segments, and finally a
still more dorsal section (Fig. 53) shows the second and
third.

In Figs. 49 and 50 the optic ganglion is seen in two vertical
sections, the first, near the anterior edge, the second, near the
middle. By comparing these sections with the surface view

144 PATTEN. [ VoL. II.

in Figs. 40 and 41, a fair idea will be obtained of the structure
of the optic ganglion at the close of the larval period.

Optic Nerves. —In the younger embryonic stages, the fibres
connecting the eyes with the optic ganglia are so intermingled
with ganglion-cells that it is not easy to distinguish them from
the optic ganglion. Even in the larval stages, when the optic
ganglion is situated behind and some distance away from the
eyes, the optic nerves are in places so ill-defined that it is
difficult to follow them to the medullz from which they arise.

The nerve to eye V. descends from the outer anterior edge of
the optic ganglion, and after reaching the inner lower edge of
eye III. turns nearly at right angles and runs forward to join
the eye on its posterior dorsal face.

Nerve 6 is the most compact of all. Its root lies on the
inside of that belonging to eye V. The two nerve roots extend
downwards nearly parallel with each other to the lower edge of
the ganglion; and then nerve 6 bends backwards, and sweeping
around the lower posterior edge of eye I., terminates on the
posterior edge of eye VI.

Nerves I and 3 extend downward and forward from the lower
anterior edges of their respective medullz as two great sheets
of loose fibres. At the lower, inner edge of eye I., those of
nerve I unite to form a more compact mass which suddenly
bends outward and divides into five bundles, two of which run
along the under side of the eye on either side of the retinal
furrow. Two other bundles extend upward on either side of
the vertical furrow. The fifth bundle extends upward to the
dorsal appendage (Fig. 18).

The nerve to eye III. is similar to that of eye I. in shape
and in the direction it follows. On reaching the eye it divides
into two branches which extend parallel with each other along
the under side of the retina.

In both eyes I. and III., fibres extend along the median under
surface of the horizontal retinas, and finally bend upward to
form, between the rows of gigantic cells, the vertical fibres.

There is nothing noteworthy about the course of nerves 2
and 4.

The relative positions, in the full-grown larva, of the nerves,
the medullz, and the eyes, throw some light on the relation of
the eyes to one another.

No. 1.] EYES OF ARTHROPODS. 145

It will be seen that in the later stages the medullz show
more clearly their primitive relations to one another than do the
eyes. At this period, it is impossible to recognize which eyes
belong to the same segment, or that there is any paired arrange-
ment at all.

NEvuRILEMMA. — The brain, optic ganglion, nerves, and eyes
are suspended or enclosed.in a common envelope continuous
with the basement membranes and derived from the ectoderm.
During the youngest embryonic stages, the inner surface of the
ectoderm, especially of the thickenings that give rise either to the
eyes or nervous system, is covered by a delicate membrane
which in the majority of cases is quite devoid of nuclei. When
the eyes are invaginated, the membrane is pushed in likewise,
but it is unaffected by the shifting of the cells to form the
corneagen and the outer wall of the optic vesicle, and is con-
tinued from the indifferent ectoderm over the bulb of the eye
to the optic nerve.

The neurilemma of the brain and optic ganglion is formed in
a similar manner. As the ectodermic thickenings that give
rise to these organs separate from the parent layer, they are
suspended in a sort of sling formed by the basement membrane,
which is distinctly nucleated where it surrounds the developing
organs. As the latter separate from the ectoderm, the mem-
brane surrounds, but does not completely enclose them, for
at quite late periods one sees at certain places the two limbs
of the membrane close together, suspending the brain, as
the intestine in its mesentery, to the wall of the head (Pl. X.,
Figs. 43 and 44). Wherever the membrane is still attached to
the surface ectoderm, the cells are drawn out into long fibres
with nuclei at various heights. Some cells are entirely sepa-
rated from the others, taking up a position on the outer surface
of the membrane, in the formation of which they seem to take
a part. As the outer surface of the basement membrane be-
comes the inner one of the neurilemma, we find that the nuclei
of the latter, during embryonic life at least, are on its inner sur-
face (Figs. 42 and 47).

In the adult larvze, the suspending membranes are reduced to
cords of fibres mixed with nuclei extending from the posterior,
median edge of each brain lobe to the roof of the head.

In Figs. 42-47, are shown different stages in the formation of

146 PATTEN. [Vot. II.

the neurilemma as seen in different parts of the head. In Figs.
42 and 43, its continuity with the basement membrane, and the
drawn-out ectoderm cells are well shown, and in Fig. 45, the
double membranes suspending each lobe of the brain.

The same membrane forms a common envelop for the distal
end of the optic ganglion and the roots of the nerves, but be-
yond this point each nerve has a separate sheath.

In the full-grown larve, the neurilemma is thicker and lami-
nated, with small flattened nuclei in the middle of the layer. I
have seen some cases when it appears to be composed of two
thin membranes with nuclei between.

ORIGIN OF GANGLION-CELLS.

During the earliest embryonic stages, the whole inner, dis-
tal edge of the optic plate is connected with the optic gan-
glion by a mass of tissue composed of fibres mixed with ganglion-
cells. The connection is gradually broken everywhere except
beneath each eye, where broad bands of tissue remain forming
the rudiments of the optic nerves. It will be more convenient
to follow the development of the ganglion-cells in eye V., since
the different stages of this eye have been described and illus-
trated in most detail.

Near the connecting bridge of cells in Pl. XL, Fig. 61, 2. g.c.,
the ganglionic nuclei are smaller, cell boundaries have disap-
peared, and the tissue assumes an appearance more like that in
the optic thickening. In fact, there is a gradual transition from
the retinal cells to those of the optic ganglion. A careful exam-
ination shows that among the half-ganglion, half-retinal cells,
are many fibres of varying size, some large enough to be parts
of slender cells, others so minute that they are seen with diffi-
culty. The larger fibres are the outer ends of newly formed
ganglion-cells; the minute ones are similar parts of cells whose
outer ends have been converted into true nerve fibres. Sucha
condition as this may be seen in sections of eyes from the stage
shown in Fig. 4, Pl. VII., down to that in Fig. 1. In the older
stages the tissue connecting the eyes and optic ganglion has
become almost devoid of cells and is composed of closely packed
fibres. The migration of sensory cells from the eye has nearly
ceased, but one or two cells may still be seen, which, owing to
their enormous size, offer special facilities for following the pro-

No. 1.] EVES OF ARTHROPODS. 147

cess in detail. In Fig. 62 is shown. one of these cells just as it
has reached the inner surface of the eye. It arose from one
of the large nuclei found among the closely packed retinal
ones, from which they are distinguished by their large size and
coarsely granular contents. As these nuclei descend into
the clear space at the inner surface of the eye they in-
crease rapidly in size, and a great mass of finely granular
protoplasm collects around them so that they become very
conspicuous objects in sections of the eye at this period.
The cells are distinctly tripolar. One of the prolongations is
always directed outwards. Its base, which is broad and filled
with protoplasm like that in the cell, is continuous with a tube-
like prolongation. Owing to its wavy course and to its clear
contents, which cause it to stand out clearly against the dark
protoplasm of the retinal cells, it is not difficult to follow this
tube a considerable distance into the tissues of the eye, where it
is finally reduced to a thin refractive fibre that disappears be-
tween the retinal cells. The two inner prolongations do not
become visible until the cell has reached the innermost part of
the eye. They are less conspicuous than the one just described,
for they are smaller, and the dark protoplasm extends into them
a short distance only. They usually arise from opposite sides of
the inner surface of the cell and extend in opposite directions at
right angles to the outer fibre. But there is considerable irregu-
larity in the position of the fibres. In some cases it looks as
though the nucleus moved inward faster than the rest of the cell,
leaving the inner fibres behind. It frequently happens that the
latter are directed at right angles to the section plane; the cell
then assumes a shape like that in Fig. 82. One often sees a
cluster of four or five enormous cells midway between the eye
and the optic ganglion (Fig. 63, z. g.c.). Most of these cells are
converted by rapid division into small pear-shaped ones which
gradually move inwards along the optic nerve, forcing a way for
themselves between the fibres, until they are finally lost among
the similar cells of the optic ganglion. But one of the cells
retains its great size. When it reaches the optic ganglion, it is
pushed to one side, out of the nerve root; its inner end is swung
outward toward the periphery of the ganglion and the outer
prolongation, which is now more conspicuous than ever, is bent
almost double. Between the bend and the cell itself, the pro-

148 PATTEN. [Vot. II.

longation is filled with dark granular protoplasm. Beyond the
bend it is reduced to a coarse, colorless, and refractive fibre that
may be followed outward into the eye. As development goes
on, the bend of the fibre is carried more and more into the optic
ganglion until it reaches the medulla, where it becomes hyaline
and refractive and breaks up into a tuft of a dozen or more
fibrille that extend along the sides of the medulla and then
turning inward, disappear (Fig. 48).

The outer end of the cell is somewhat flattened, and on either
side is continued into a tube-like prolongation with clear, homo-
geneous contents. In the centre of the tube, I have seen on
several occasions what appeared to be a small fibre, but cannot
say positively that it was such. The protoplasm of the cell pro-
trudes a little near the mouth of the tube, but is not continued
into it.

These tubes, or fibres, are difficult to follow, and I have only
succeeded in doing so in a few cases, and then not very far.
They extend, at right angles to the great inner stalk, in opposite
directions along the under surface of the neurilemma, and I
should judge they served to connect the ganglion-cells with one
another. I see no reason to suppose they extend into the
medulle; they do not run in that direction, and no fibres were
seen running into the medullz that could not be referred to the
stalk-like prolongations of the ganglion-cells.

The gigantic ganglion-cells continue to divide, but with
decreasing frequency, up to about the time of hatching. At
that period, there is usually but one cell of enormous dimensions
on the side of each medulla. Their position, size, and shape, as
shown in Fig. 48, are very constant. In rare cases, there may
be in the larve two large cells side by side, one a little smaller
than the other. In the full-grown larve, the cells are propor-
tionally smaller and less conspicuous.

In Fig. 48 is shown a pair of ganglion-cells placed end to end,
and easily distinguishable from the surrounding ones by their
peculiar shape. There was an exactly similar pair in the optic
ganglion on the other side of the head, and I have also seen them
in one or two other cases, so that I do not doubt that they are
usually present during these stages.

There is a singular modification of the sixth gigantic ganglion-
cell, in that its inward prolongation is divided into two branches,

NO. 1.) EYES OF ARTHROPODS. 149

one of which is continued half way across the optic ganglion to
the fifth medulla.

There are some minute fibres scattered about among the cells
of the cortical layer, that I cannot trace to distinct cells. They
are seen running in an irregular manner from one cell to an
other, or from the cortical layer to the neurilemma. They
often extend over the surface of the large cells branching in all
directions (Pl. X., Fig. 48). They are not numerous enough to
form a sheath or envelop about the cells, such as that so fre-
quently described in the Annelids, although it is not improbable
that they belong to the same category. They may possibly
arise from the small, dark cells, sometimes called the inner neu-
rilemma, that form an investment for the medulla, and which are
specially well developed in the brain and ventral nerve chord.

The fact that a not inconsiderable number of the ganglion-
cells arise directly from the gigantic, tripolar ones might lead
one to suppose that all the cells of the optic ganglion were tripo-
lar and differed from the large ones only in size. All that one
can actually observe points towards this conclusion.

In my paper on the eyes of Vespa, page 198, attention was
called to certain conical or pear-shaped ganglion-cells at the inner
edge of the middle lobe of the optic ganglion, and it was stated
that some of the conical ones were possibly tripolar, for indica-
tions of two prolongations at the broad distal ends of such cells
had occasionally been seen. A re-examination has led me to
believe that all of them are tripolar, like the large ones in
Acilius. Their deceptive, unipolar habitus is due to the great
size of the inner prolongation as compared with the very delicate
outer ones.

As there is no reason to suppose that more than one kind of
cell is present in the cortical layer of the optic ganglion, — we
do not include the minute, dark cells surrounding the medulla,
or those interspersed among the fibres of the optic nerves, con-
cerning whose minute structure we are ignorant, —and in con-
sideration of the facts we have presented concerning the origin
of ganglion-cells, we have arrived at the following conclusion:
The cortical layers of the optic ganglia are composed of large and
small tripolar ganglion-cells. The large, inward prolongation of
cach of these cells ts filled with granular protoplasm continuous
with that in the cell body, and represents a part of the outer end

150 PATTEN. [Vot. II.

of a formerly sensory cell lodged in the ectoderm, or of one derived
by division from such acell. In passing through the medulla this
prolongation breaks up into a bundle of fibrille. The other two
prolongations are small, and contain no granular protoplasm ;
they arise from the opposite sides of the broad end of the pear-
shaped cells and, extending tn opposite directions, probably serve to
unite the ganglion-cells with one another.

COMPARATIVE ANATOMY OF THE OpTiIc GANGLION.

Although some work has recently been done on the develop-
ment of the Arthropod eyes, the optic ganglion, both of the con-
vex eyes and ocelli, has received little notice. It has been stated
that it arises either as an invagination of the ectoderm near the
eyes, or as an outgrowth of the brain. Both Bobretzsky and
Reichenbach have failed to produce satisfactory evidence to
show that what they regarded as the developing optic ganglion
really was such. Reichenbach made the fatal mistake of neglect-
ing to follow his optic invagination up to a point where its real
nature would be apparent. Had he done so, he would not have
mistaken the retinal ganglion for the layer of rhabdoms and re-
tinulz, and he would have seen that his crystalline-cone layer was
the whole ommateum. In my paper upon the eyes of Vespa, I
maintained that Reichenbach had misinterpreted the facts. I
have recently examined, by means of sections and ‘surface views,
the head of Astacus, and find my objections sustained.

It is not my intention to enter here into a long account of the
comparative anatomy of the optic ganglion of Arthropods, for
the subject is worthy of separate consideration. I merely de-
sire to state the main conclusions to which I have been led by a
study of the development of the optic ganglion in such groups
of Arthropods as the Isopods, Decapods, Hymenoptera, Lepidop-
tera, and Coleoptera.

In Vespa, it was shown that on the dorsal edge of the optic
thickening a great mass of cells was pushed inward to form the
rudiment of the optic ganglion. This mass of cells, which from
the very earliest stages is connected with the ventral edge of the
optic thickening, after invagination divides into three lobes, which
immediately arrange themselves in a line connecting the eye and
brain. The middle lobe develops into the optic ganglion of the

No. 1.] EVES OF ARTHROPODS. ISI

adult ; the outer, into a layer of cells which, during the earlier
stages, form, around the outer edge of the median lobe, a semi-
circular band, conspicuous on account of the peculiar character
of its cells (Fig. 2, wood-cut). The inner lobe, which likewise
disappears during the later stages, forms a characteristically
shaped layer of dark cells on the proximal side of the median
one. It is over-arched by the cells of the brain in such a way
that it appears to form the floor of an oblong cavity. Each lobe,
except the outer one, contains a great medullary core.

FU, 2.

Figure 2.— Semi-diagrammatic views of the optic ganglion of:

(A) Vespa, towards the close of the larval stage, (2) Astacus, (C) Cecropia, be-
ginning of pupal stage; (D) Acilius, close of larval stage, — showing the position of
the retinal ganglion and the three lobes of the imaginal optic ganglion.

E. Eye I. of Acilius; c. e. ventral half, c. e.1 dorsal half of convex eye; g1® lobes
of optic ganglion; 1-3 medulle of same; 7. g. retinal ganglion.

The retinal ganglion arises at a comparatively late period, not
by invagination, but by the formation of a layer of ganglion-
cells among the fibres connecting the optic ganglion with the
eye.

In Astacus (Fig. 2, B.), the optic ganglion, after invagination,
breaks up into three lobes. The outer one is formed of a folded

152 PATTEN. [Vot. II.

layer of clear cells, Reichenbach’s “ Augenfalte.” The shape,
position, and structure of this fold, and the manner in which it
degenerates and disappears, leave little room to doubt that it is
homologous with the outer lobe of the optic ganglion of Vespa.
The fact that in Astacus this layer is folded as if formed by
invagination is an incidental and secondary condition. In Vespa,
Cecropia, and Acilius the direction of the infolding is reversed.

The middle lobe is relatively smaller in Astacus than in
Vespa; from it arises the epiopticon of Hickson, or the second
optic ganglion of Carriere. This lobe contains an oval medulla,
from the outer end of which arise decussating fibres that extend
into the retinal ganglion, The inner lobe of Astacus, unlike that
of Vespa, develops into a distinct ganglion, with a medulla and
cortical layer of ganglion-cells like those in the median lobe, but
darker colored. It is over-arched by a thick layer of cells aris-
ing from the cortical layer of the stalk of the optic ganglion.

The distal end of the stalk is enlarged, and apparently forms
a third medulla, the minute structure of which is quite different
from that of the other two.

On the outer side of the first lobe is a layer of small, dark
ganglion-cells, which Reichenbach regarded as the outer wall of
his “Augenfalte,’ and which he maintained gave rise to the layer
of retinula and rhabdoms. But this layer of cells is really the
retinal ganglion, and is formed, as in Vespa, by the development,
some time after the ganglionic invagination, of a layer of cells
among the fibres connecting the optic ganglion with the eye.

Among /sopods I have examined the optic ganglion of Cymo-
thoa, and find that in development and structure it does not
differ from that of Astacus in any particulars that concern us at
present.

No extended observations were made on the optic ganglion of
the larvee of Cecropia. I can only say that it has a superficial
resemblance to that of Acilius, but it is much smaller and less
perfectly developed. Toward the beginning of pupal life, the
optic ganglion increases enormously in size and assumes a
structure very much like that of Vespa (Fig. 2, C.). The resem-
blance between the optie ganglion of Vespa and Cecropia is suf-
ficiently evident to render a detailed description unnecessary. In
the later stages both the inner and outer lobes disappear or are
reduced to mere insignificant appendages, and the cells at the

No. 1.] EYES OF ARTHROPODS. 153

base of the optic nerve develop into a large retinal ganglion.
The main portion of the optic ganglion arises from the middle
lobe.

The similarity in the structure of the optic ganglion of these
distantly related genera shows that the optic ganglion of the
convex eye of Insects is homologous with that of Crustacea, and
that in both groups its structure may be reduced to the same
plan. Zhe variations in the structure of the optic ganglion of
Arthropods may be referred to the modification, development, or
suppression of one or more of three lobes, to which may be subse-
quently added the retinal ganglion. What is the meaning of the
three lobes so constantly present, at one stage or another, in the
optic ganglion of Arthropods? It would be difficult to form a
fruitful hypothesis of their significance from a study of forms
that do not pass through an active larval existence, for we now
know that the optic ganglion of the imago is derived from a larval
ganglion, which in some cases is highly complicated, and has
itself a long story to tell. In Astacus, Cymothoa, etc., the con-
vex eye and its optic ganglion appear at a period corresponding
with the end of the larval stage. Hence we must look for the
preliminary stages of the optic ganglion in the larva and em-
bryos of such forms as Acilius; and there we may expect to
find a solution of the three-lobed structure of the ganglion of
the convex eye.

We have already seen how, in the earliest stages of Acilius,
the optic plate is composed of three segments, each bearing a
pair of eyes, and on the dorsal side of each segment there is a
ganglionic invagination.

The three masses of ganglion-cells thus produced unite to
form the larval ganglion. Toward the close of larval life, each
segment increases rapidly in size; the third segment grows
around the proximal side of the ganglion to form the inner lobe,
the second forms the fold around the anterior edge of the gan-
glion, or the outer lobe, and the first forms the posterior inner
mass of the ganglion, or the middle lobe of the future ganglion
of the convex eye.

At the beginning of pupal life, the ocelli are drawn towards
the brain, and are replaced by the convex eye, which unites
with the larval ganglion in a way that I do not yet understand.

From these facts we may infer that the three-lobed optic gan-

154 PATTEN. (VoL. II.
glion of the convex eye of Arthropods ts derived from a three-seg-
mented, larval ganglion, each segment of which belongs toa pair
of larval ocell.

III. SumMMAry AND COMPARISON.

The great nucleus that figures so prominently in the early
stages is not the least remarkable feature of the eyes of Acilius.
So far as my knowledge goes, it is without parallel and inex-
plicable.

In eyes II., III., IV., and V., there is a single nucleus in the
middle of the retina, between the two rows of gigantic cells,
that remains unaltered through life. In eye I. there are at least
two of these nuclei, one in the horizontal, and one in the vertical
furrow. In eye VI. the nucleus is only present a short time
during the earliest stages. In all the eyes the large nucleus
seems to be situated in the centre of a group of four sensory
pits.

Kleinenberg has described in Asterope a gigantic, flask-shaped
cell that secretes the vitreous substance filling the cavity of the
optic vesicle. But there is probably only a superficial resem-
blance between this cell and that in the eye of Acilius.

The reader has no doubt been impressed by the presence of
horizontal rods in the eyes of Acilius, as well as by the fact that
the rod mosaic varies tn a constant manner, according to the inclt-
nation of the retinal cells. All the horizontal rods, large or
small, are flat, and arranged in long, parallel rows. The semi-
upright ones form, in cross sections, zigzag lines, and the up-
right rods are bent so as to form the sides of regular hexagonal
figures. Why are the horizontal rods invariably arranged in
parallel lines? As the rods are mere frames for the support of
nerve fibrilla, it must be, no doubt, because in this way the
fibrilla are most advantageously arranged for the reception of
light stimuli. In my paper upon the “Eyes of Molluscs and
Arthropods,” page 652, the statement was made that the perfec-
tion of a visual organ was dependent, among other things, upon
the degree to which the retinidial fibrille have become perpen-
dicular to the rays of light. At that time I did not think it
probable that there were horizontal rods, as stated by Grenacher,
in the eyes of Myriapods. It must be evident now from my
description of horizontal rods in Acilius that there is no longer

No. 1.] EVES OF ARTHROPODS. 155

any reason for me to doubt the accuracy of that part of Grena-
cher’s account.

When I became convinced that most of the rods of Acilius
were horizontal, it seemed at first as though the above-mentioned
view concerning the direction of the retinidial fibrillae would have
to be abandoned, for here were undoubtedly highly specialized
eyes in which as many retinidial fibrillae were parallel with the
rays of light as at right angles to them, provided they radiated
in all directions from an axial nerve. In Pecten, e.g., (Fig. 5,
A.), we have cylindrical vertical rods containing axial nerves,
from which radiate nerve fibrillz in all directions. All the
fibrilla are consequently at right angles to the rays of light.
But put the rod in a horizontal position, and just as many
fibrillze will be vertical as horizontal. In order to bring these
horizontal rods into harmony with my theory of nerve end-
ings, it is requisite that the rods should be flattened, and of
course so that the long diameter is vertical. Then if the
axial fibres, instead of forming a single bundle, as in the
cylindrical rods, should form a transverse row (Fig. 5, B.),
fibrillae could arise from them, nearly all of which would be at
right angles to the rays of light. If the rod were broad and
very much flattened, and the upper and lower sides disap-
peared, then all the fibrilla would be at right angles to the
rays of light (Fig. 5, C.). In Aczlius all the horizontal rods
fulfil the above requirements; they have exactly the structure
they ought to have, and the only one they could have, to bring
their retinidial fibrille at right angles to the rays of light;
therefore, instead of horizontal rods being fatal to my theory
of nerve endings, they afford by thetr arrangement convine-
ing evidence in favor of it. For those who believe that the
nerve fibres described by me are the product of coagulation, or,
perhaps of the imagination, may not be so ready to push lightly
aside the evidence which the structure of the horizontal rods
affords. It certainly is remarkable that in Acilius, whose eyes
show as wide differences in structure as we could expect to find
between any larval ocelli of Insects, the horizontal rods should
invariably assume the only shape that would permit all the reti-
nidial fibrillze to be at right angles to the rays of light.

A vertical section of a pair of broad horizontal rods would
give an outline exactly like that formed by a similar section of

156 PATLIEN: [VoL. II.

upright ones, except that in the first case between each pair
would be the cut ends of a row of axial nerves, and in the sec-
ond, a bundle of vertical nerve fibres (Fig. 5, C. and D.).

Some observations have been made upon the eyes of other
insect larvz. With one or two exceptions, nothing was found
that I care to speak of here. When enough material has been
obtained, it is possible that I may be able to give a more ex-
tended comparative account of the larval ocelli of insects than
I desire, or am able, to do now.

Figure 3.— Vertical (4) and horizontal (2) section of a Hydrophilus larva about
7mm.long. cg. corneagen; o. w. outer wall of the optic vesicle; 7d. rods.

The eyes in the young larvze of both Hydrophilus and Dytiscus
are much alike. In the woodcut (Fig. 3) is represented a sec-
tion of the eye of a Hydrophilus larva about 8 mm. long. We
perceive at once the fundamental differences in the construction
of this eye and that shown in Grenacher’s well-known figure of
the young larval ocellus of Dytiscus. First, there are three
distinct layers in my figure produced by the invagination of an
optic vesicle. The outer wall of the vesicle is represented by a
cluster of small, deeply stained nuclei over the centre of the
retina. The latter is composed, not of upright cells, as Gren-
acher has it, but of horizontal ones, bearing short horizontal rods.
The latter form a thin oblong and vertical plate in the middle

No. 1.] EVES OF ARTHROPODS. rSy

of the retina. In this respect also, Grenacher’s figure is incor-
rect, since it represents a broad layer of long upright rods,
whereas no such structures are present.

The eye of Hydrophilus, as shown in the woodcut, is much
like that of eyes II. and IV. of Acilius, even to the presence of
the large retinal cells at the bottom of the furrow.

OEE ae
LICHT TT

Figure 4.—Uorizontal (4) and vertical (2) section of the larval eye of a
neuropterous larva, Chauliodes (?). cg. corneagen; /1, 72, inner and outer lenses;
o. w. outer wall of the optic vesicle; +d. rods.

Figure 5.— Diagrammatic views of the retinidial fibrille in upright and horizon-
tal rods. A. cross section of rods of Pecten,; B&B. same of small horizontal rods of
Acilius ; C. same of large rods, and D. longitudinal section of upright rods in eye V.
The arrows indicate the direction of the light.

In Fig. 4 is shown a section through the eye of what I took
to be a full-grown larva of Chauliodes, but I am by no means
certain that it is such. Expecting to obtain more material,
all but the heads were thrown away, and now I have no means
of identifying the larvee.

I have represented a section of the eye because it showed an
interesting modification of the three-layered ocellus. There
seem to have been present both upright and inverted retinal
cells, as in eyes V. and VI. of Acilius, but the latter, instead of
retaining their inverted rods have converted them into a cuticu-
lar, nerveless mass that has assumed the function of an inner

158 PATTEN. [Vot. II.

lens something like that in Peripatus. On the inner surface of
the lens, we can still see some of the inverted rods that have
not quite lost their identity. The outer surface of the lens is
surrounded by a membrane, between which and the lens area
few scattered nuclei. The latter are continuous with those of
the retina. In vertical sections, the rods appear to be upright,
but cross sections show that they are horizontal and arranged
in a double row in a nearly circular space surrounded by the
pigmented ends of the retinal cells.

The optic vesicle is covered by a corneagen composed of a
thick layer of colorless, columnar cells with distinctly stained
nuclei. On the periphery of the corneagen is a thin layer of
pigment.

Myrtapops. — There are many important points in which the
larval ocelli of Insects resemble those of Myriapods, and I ven-
ture to assert we shall find a still greater resemblance when a
better knowledge of the structure and arrangement of the rods
in the latter group has been obtained.

The material upon which Grenacher made his observations
had been hardened in alcohol only, and as he himself had occa-
sion to repeat, there was much to be desired, especially in the
preservation of the rods. In only two instances was a clear
picture of the rod mosaic obtained: in Cormocephalus, where
they were cylindrical tubes; and in Scutigera, where they were
flattened much like those of Acilius. If, after re-examination
of properly prepared material, the first case should still stand, it
would offset the significance that I attached to the flattened
rods in Acilius. But there are not inconsiderable reasons for
doubting that it will stand, for in Acilius the flattened rods
when hardened in alcohol sometimes appear like cylindrical
tubes. In other cases the rods were so poorly outlined that
Grenacher was always in doubt as to their structure; indeed, in
some instances he could go no farther than to assert that they
were rods.

Besides the similarity in the possession of horizontal rods, one
that is all the more striking since these remarkable structures
are at present only known in the two groups we are discussing,
there are many minor points in which the ocelli of Insects re-
semble those of Myriapods. The resemblance is striking when

NO. 3.) EYES OF ARTHROPODS. I59

we compare eyes ITI. and IV. of Acilius with those of Iulus or of
Heterostoma.

The retinal pigment is in both cases most abundant at the
outer ends of the retinophore, and is confined to the outside of
the cell. At least on p. 437 Grenacher states that in the Scolo-
pendriden, if we may regard the condition in Cormocephalus
as normal, the pigment appears “in der Mantelflache der Zellen
abgelagert zu sein, und die innern Theile derselben freizulassen.”
My sections show just such figures as he represents in Fig. 6,
except that in my judgment the pigment in Acilius and Dy-
tiscus is outside the cell wall instead of inside.

A peculiar feature of Acilius is that in the younger stages all
the eyes are elongated in the direction of the retinal furrow, and
this condition is more or less conspicuous in the larvee of Dytis-
cus, Hydrophilus, Colymbetes, Psephenus, and Gyrinnus. There
is a similar elongation of the retina in Iulus.

One of the most striking points in the less specialized eyes of
Acilius is the great notch at the bottom of the eye containing
the broad rods of the gigantic cells. Grenacher has shown in
Scolopendra a similar notch, and there are strong reasons for
believing that it contains a double row of large cells. I think it
probable that in Scolopendra, as in the first four eyes of Acil-
ius, all the originally horizontal retinal cells, except the large
ones at the bottom, have gradually withdrawn from the median
plane of the eye to form a concave layer of nearly upright
rods.

When it is urged that Grenacher saw no such gigantic cells,
and that there is no indication of them in his drawings, we shall
answer that the same thing might be said of his description of
the eyes of Acilius, and yet a casual examination of depigmented
sections will show at once that such cells are there.

When we compare the retina of Heterostoma (Fig. 4) with
that of eyes IT. and IV., we cannot withhold the suspicion that
in the retina of this Myriapod there is also a double row of large
cells, and that their gigantic rods were provided with horizontal
external nerve fibres which had been mistaken for the dividing
lines between many small superimposed rods.! If this be so,
then Grenacher’s “ Haargellen”’ are probably ordinary retinal

1 At one time I also regarded these markings in Acilius as the divisions between
small rods,

160 PATTEN. [VoL. II.

cells with double horizontal rods, and the so-called hairs are the
external nerves of these rods. In sections parallel with the broad
surface of the rods of Acilius, the external nerves are conspic-
uous, and in alcoholic material they appear like hairs, or at any
rate might give rise to the impression that each cell was provided
with a number of slender rods. That these external nerves are
probably present in Myriapods is shown by the fact that Gren-
acher, p. 456, has himself described in the large flat rods of
Scrutigera a set of cross striations which he says recall the
“ Plaittchenstructur’”’ so frequently described in the rods of
Arthropods, and he even hints that there may be some connec-
tion between this fact and the hair-like rods in the eyes of
Myriapods.

Finally, in his Fig. 14, is shown a semi-transverse section of the
retina of Glomeris, where the hair-like rods are united in groups
that would correspond very closely to the flattened rods of
Acilius, and even in his vertical sections we see indications of
the same thing.

The bodies projecting beyond the pigment layer in his Fig.
1, look more like a layer of short rods than the ends of cells,
as he calls them. There is no other instance to my knowl-
edge where only the outer ends of retinal cells are free from
pigment. I regard them as rods, and support this interpreta-
tion mainly on the fact that Grenacher represents them as
extending into the notch at the bettom of the eye.

But what shall be done with the layer of rods in his first
figure? I should regard it as a corneagen, which like that in
Acilius had lost its nuclei, if in Fig. 2 both a corneagen and
this striated layer were not present. If we do not accept
Grenacher’s interpretation, no course appears to be open except
to consider the outer layer of Fig. 2 as a corneagen, and the
middle one, if it is really a separate layer, as the outer wall of
an optic vesicle, which forms in this case a vitreous, striated
body comparable to that in Chauliodes (Fig. 3) or with that in
the cavity of the optic vesicle of Peripatus.

That there is a tendency to form two kinds of rods in Myria-
pods is clearly shown in Grenacher’s drawing of the eye of
Heterostoma (Fig. 4). We might expect to find the outer rods
short and upright as in the eyes II. and IV. of Acilius, although

No. I.] EVES OF ARTHROPODS. 161

Grenacher maintains that they are horizontal like the others,
but much longer.

Eye I. of Acilius is the largest and most complicated, and as
there are several instances in which the posterior dorsal ocellus
of other Insect larvze is conspicuous on account of its greater
size, it may be well to mention that a similar condition is to be
found in Lithobius, for Grenacher says, p. 441, “ Die Einselau-
gen sind unter sich nicht vollig gleich gross ; auffallig ist freilich
nur die uberwiegenden Grdsse der jenseite am meisten nach
hinten gelegenen.”

We have tried to show above: That there ts a striking resem-
blance between the eyes of Myriapods and those of larval Insects,
(1) 22 the pigmentation of the retinal cells ; (2) in the shape of the
retina; (3) 2x the presence of a retinal furrow, and (4) and (5) in
the probable presence of dimorphic retinal cells and rods, some of
which are horizontal and others upright. This similarity is all
the more important since we seek in vain for any special points of
resemblance between the larval ocelli of Insects and those of Crius-
tacea or Arachnids. Even if it should be shown that the retinal
cells in Spiders and Scorpions are upright, there would still be
a great difference between the ocelli of Insects and those of
these groups, for the presence of upright rods in both instances
is in itself too general a feature to be of much importance in
determining affinities, and there is no trace whatever in Scor-
pions, Crustacea, or Spiders of those peculiar features, such as
horizontal rods, retinal furrow, and dimorphic retinal cells, that
are common to Insect larvze and Myriapods.

SPIDERS AND Scorpions. — Although both Graber and
Sograff maintain that the eyes of Myriapods and the ocelli of
Insects and Spiders have essentially the same structure, it is
probable that both writers based their opinions solely on the
fact that in all these cases the eyes were composed of two
layers. But granting that such a condition prevails, very little
is gained thereby, for it leaves out of account altogether the
fundamental differences in the structure of the retinas.

In spite of the recent contributions to our knowledge of the
eyes of Arachnids, by Schwemkewitz, Bertkau, Locy, Mark,
and Parker, we are still much in the dark concerning the struc-
ture and development of these eyes.

162 PATTEN. [Vot. II.

Locy maintained that the ocelli of Spiders were formed of in-
vaginated vesicles, the outer walls of which became the retinas.

Mark, in discussing the various theories that had been ad-
vanced to account for the origin of the retina and its method of
formation, says, p. 54, that Locy’s observations ‘seem adequate
to settle these conflicting views— so far at least as regards
the spider-like type.’ Great stress is laid upon the inversion
of the retina in Spiders, for he says (p. 54), “The inversion of the
retina proper is a fact of broader significance than would at first
sight appear, and it affords a satisfactory explanation of some
of the points in the anatomy and histology of simple eyes which
have been so earnestly discussed during the past few years.”
And a little farther on he intimates that it is doubtful if any
Monomeniscus Arthropod eyes contain upright retinas. In fact,
the main purpose of his paper is to show that the Arthropod
ocelli are constructed on the “ Spider-like type,” that is; of three
layers, the inverted middle one forming the retina. Wherever
in the ocelli of Arachnids, Myriapods, and Insects there is evi-
dence of a post-retinal layer and a “dentigen” with a retina
between, Professor Mark would infer that the eye originated as
in Spiders, and he seems to have found evidence of one or more
of these structures in the eyes of Myriapods and Scorpions and
in the larval and frontal ocelli of Insects.

In the present state of our knowledge, the larval and frontal
ocelli of Insects cannot be made to fit this theory; certainly
not in Acilius and Vespa, the two cases to which Professor
Mark gives especial attention. In Vespa, I have shown since
his paper was published that the frontal ocelli were derived
from open-mouthed pits, the inner wall of which gave rise to
the retina.

The eyes of Myriapods are so much like those of Coleopterous
larvee that there is every reason to suppose they develop in the
same way.

It would not be safe to conclude from Parker’s observations
that the retina of the median eyes of Scorpions is inverted,
since they do not extend to sufficiently young stages. But,
according to his observations, the lateral eyes are single-layered,
and consequently the retinal cells are upright. Professor Mark
regards the retinal cells in the median eyes as inverted, and
since the rods and nerve fibres do not indicate any such inver-

Wo. 1.] EYES OF ARTHROPODS. 163

sion, he is forced to assume not only that the nerve fibres have
shifted their attachment from one end of the cell to the other,
but that new rods have been developed at those ends of the
cells where, according to all experience, rods are never found.
His supposition, which implies that inverted rods are not favora-
ble to perfect vision, which pretends that, in some unexplained
manner, upright rods get into an unfavorable position, and
then forces us to-assume a fundamental upheaval of primitive
relations in order to bring them back to what is practically their
original condition, is, in my opinion, at present unnecessary.
Even after making this sacrifice of preconceived ideas, the way
is no clearer than before, since we have imposed upon ourselves
the difficult task of explaining why these supposed inverted
retinal cells are exactly like the upright ones of the lateral
eye!

I may be permitted to call attention to one or two facts that
will perhaps be of service to those who think it necessary to
make further observations on the eyes of Spiders. My observa-
tions on the eyes of Astacus, Cymothoa, Vespa, and Acilius
leave no room to doubt that there are two invaginations con-
nected with the eyes: one to form the optic vesicle; another,
the optic ganglion. The presence of two such invaginations in
types so widely separated suggest that a similar condition prevails
in Arachnids. If this be so, where is the ganglionic invagina-
tion? Is it possible that the ganglionic and optic invaginations
have been confused as in Astacus and Crangon, and the con-
clusions vitiated thereby?

The second point I wish to mention is more of a theoretical
nature, and has to do with the causes of inversion. Professor
Mark has suggested that the primitive eye was a laterally flat-
tened cup, with a lens over the slit-like opening, and that either
the cup was bent to one side, so that the broad surface of one
wall was folded against the lens, or a second lens had been
formed, bringing light to the retina from a new direction, and
this led to the development of the retina from that wall of the
pit next the new lens. In either case the final result would be
the formation of a three-layered eye, the middle layer of which
developed into the retina. A simpler explanation is suggested
by the condition in eye V. of Acilius, where there are both
inverted and upright rods; in such an eye it would be a simple

164 PATTEN. [Vou. IL.

matter to develop the inverted cells at the expense of the
upright ones. The degenerated retinal cells could then be
transformed into the tapetal matrix, the retinal cells producing
tapetal scales instead of rods, as the inverted retinal cells in
Chauliodes give rise to the inner lens. If this be true, then
the tapetal slit might be compared to the median furrow in the
retinas of Acilius.

A probable instance of such a method of inversion is found
in Pecten, whose inverted rods I derived from the outer wall of
an optic vesicle, by supposing that partially inverted and upright
rods existed at the same time; eye V. of Acilius furnishes
us with a needed example of such an eye. Moreover, in Pecten
there is evidence that the inner wall was derived from a retina,
the retinophore of which were transformed into the argentea or
reflector, and the ganglion-cells into the red pigment layer.
Such a transformation of the optic vesicle of Spiders would
harmonize with Bertkau’s description of the tapetal eyes, or
“ Nebenaugen.’ The anatomy of the non-tapetal ones, as far
as known, would lead one to believe the retina is composed of
upright cells, while embryology says they are inverted.1

In the earliest stages of Acilius, the eyes are composed of
several sensory pits, each with its cuticular thickening and nerve.
It is possible that in the Arachnids the numerous nerve bundles
supplying the eyes, such as figured by Grenacher for Lycosa
(Pl. III., Fig. 22), might owe their existence to the fact that
these eyes also were formed by the fusion of several sense
organs.

We might change the eyes of Acilius into the Aranean type
by suppressing the eyes of the third segment and inverting the
retinas in all but the large posterior pair. The latter would
then become the “ Hauptaugen” of Spiders, and the smaller
ones with inverted retinas the “ Vebenaugen.”

The failure to form, either by speculation or observation, an
adequate notion of the origin of the retina in Arthropods has
long stood in the way of a satisfactory explanation of the various
structural forms these eyes assume. It was not possible to treat
the subject comprehensively and systematically while still in

1Jt is difficult to understand Bertkau’s statement that his observations confirm

those of Grenacher. There certainly is a great difference between his drawings of
the tapetal eyes and those of Grenacher.

No. FS} EYES OF ARTHROPODS. 165

doubt as to whether the retina arose from the hypodermis or
from the brain, or from neither; or while that organ sometimes
called the optic ganglion, in the absence of all evidence, might
be regarded as a retina, a retinal ganglion, the brain, an out-
growth of the brain, or an optic nerve, or whatever else might
commend itself to the imagination of the investigator.

There were the one-layered, the two-layered, and the three-
layered eyes, one with upright, another with inverted, another
with horizontal rods. The structure of one eye was as intel-
ligible as that of another; no more, no less. There was no unit
of measure.

It was inferred in “Eyes of Molluscs and Arthropods”’
that the ground plan in all these confusing variations of
structure was a three-layered eye, an invaginated optic vesi-
cle, the inner wall of which became the retina, and an over-
lying layer of hypodermis the corneagen. Such an eye would
be much like that of Peripatus; flatten the vesicle vertically,
reduce the outer wall to a thin membrane, and you have
the ocelli of some Insects and Spiders. The observations re-
corded in this paper confirm the supposition mentioned above.
We may now go still farther and say that a lateral flattening
would produce the larval Insect, and Myriapod eyes, with hori-
zontal rods; that the outer wall of the vesicle may, in some
cases, develop inverted retinal cells side by side with the up-
right ones of the inner layer; and that the rods of these
inverted cells may be converted into a lens inside of the optic
vesicle, as in Chauliodes and perhaps Peripatus, or they may
take the place altogether of the upright ones, as in the tapetal
eyes of Spiders.

It can no longer be affirmed that there is a wide difference
between the so-called Molluscan and Arthropod eye; both belong
to the same type, as I formerly maintained. This difference it
has been urged was due to the presence in the former of an optic
cavity filled with an inspissated, refractive substance. But there
is just such a cavity in the early stages of eyes V. and VI. of
Acilius and one in Chauliodes which is filled with a lens like
that in Peripatus and some Molluscs and Worms.

Professor Mark maintains that “none of Locy’s predecessors
have in the least foreseen the true course of events’’ concerning
the origin and method of formation of the retina of Arthropods.

166 PATTEN. [Vot. II.

But it cannot be denied that I foresaw in my paper on the “ Eyes
of Molluscs and Arthropods”’ not only the origin of the retina
and its method of formation, but, to a great extent, that of the
optic ganglion as well. The observations on the development
of Vespa and Acilius now furnish a substantial support for the
theoretical views advanced in that paper, and this confirmation
does not lose any of its value in consideration of the inversion of
the retina in the tapetal eyes of Spiders, for that can most readily
be explained, as already shown, by referring to the condition in
eyes V. and VI. of Acilius; or by the fact that Reichenbach’s
and Kingsley’s observations point to the conclusion that the
sensory part of the convex eye is inverted, for in both instances
the misconception undoubtedly arises from a confusion of gan-
glionic and optic invaginations; and finally the inference lies
close at hand that the supposed inversion of the retina in the
eyes of Scorpions and in the non-tapetal ones of Spiders is due
to a similar confusion of the two invaginations.

Convex Eyre.—In my paper on the “Eyes of Vespa,” an
attempt was made to throw some light in the phylogeny of the
“convex eye.” It seemed to me that a solution of the problem
might be obtained by explaining its double nature; for as
shown by the embryology of Vespa and by the permanent
condition in such forms as the Libelluliden, Ephemeriden,
Gyrinnus, Astacus, Phronima, Schizopods, and others, it is prob-
ably composed throughout the Arthropods of a distinct ventral
and dorsal part.

I attempted to explain this double condition by supposing
that it was a modified larval ocellus like the posterior dorsal
one of Acilius and Dytiscus, which I maintained was also
composed of a dorsal and ventral part: the latter was the ocellus
‘proper; the former, an appendage whose structure and general
appearance indicated that it was a secondary and younger part
subsequently added to the ocellus; and it was maintained that if
such an ocellus developed into the compound eye, a needed expla-
nation would then be furnished of its double nature. But there
was no evidence to show that the posterior ocellus with its dorsal
appendage really did develop into the convex eye. I deter-
mined to obtain such evidence, if possible, by studying the
history of the eye of Acilius during the larval and pupal stages.
But all my efforts to obtain pupze were unsuccessful. I have

No. I.] EYES OF ARTHROPODS. 167

shown, however, that the appendage is not, strictly speaking,
an outgrowth of the posterior dorsal ocellus, as I formerly sup-
posed, and I do not now see any reason to suppose that the
ocellus proper develops into any part of the compound eye. The
appendage is, I now believe, one or two of the primitive sense
organs of which the ocellus is composed, that have not com-
pletely united with the others, and have undergone a special
modification in the direction we have already explained.

Toward the close of larval life, the convex eye appears as a
thickening of the ectoderm immediately around the appendage.
At this time it is difficult to distinguish any line of demarkation
between the appendage and the thickening. In the latest stages
I possess, it forms an enormous, thickened band that almost en-
circles the six ocelli. The band is narrow in the middle, but
expanded and rounded at either end. Its ventral edge is deeply
invaginated, especially near the appendage where the invagina-
tion first appears, and is connected with the adjacent ectoderm
by a thin vertical layer of cells (Fig. 1, wood-cut). At first it
seemed probable that the appendage developed into the ventral
half of the convex eye, and the thickened band into the dorsal
half. If the band itself should be divided into two parts, this
interpretation would be, so far as I can see, untenable, and I
must admit that there is an indication of such a division, though
so indistinct and unaccompanied by any difference in the de-
velopment of the ommatidia on either side of it, that I am still
in doubt as to its meaning.

It is difficult to believe that the appendage of the posterior
ocellus has nothing to do with the convex eye, since the lat-
ter is, in the early stages, so intimately connected with the
former. One thing is certain, that a great part of the com-
pound eye arises suddenly at the close of larval life as a thick-
ening in a previously indifferent layer of hypodermis; hence
that part at least cannot be considered a modification of any
functional larval organ.

The development of the frontal ocelli points to the conclusion
that they are widely different from the larval ones, and perhaps
closely related to the compound eyes.

One of the things that impressed itself most deeply upon me,
after studying the embryology of Acilius, was the threefold
structure of the head as shown in the three segments of the

168 PATTEN. [Vor. II.

optic plate, optic ganglion, and brain. The same feature is also
shown in the arrangement of the eyes in the imagines of those
insects supplied with frontal ocelli, for in such cases it is evi-
dent, since I have shown in Vespa that the median unpaired
ocellus is double, that the imagines have three pairs of eyes,
and it at once suggests itself that there is some intimate connec-
tion between this fact and the presence of the three larval seg-
ments. It is possible that the solution of the problem, to which
I shall return in my next paper on the “ Development of Acilius,”
may lie in an explanation of the pupal stage.

NEUROEPITHEL CELLS. — My studies on the “ Eyes of Mol-
luscs and Arthropods” led me to believe that ganglion-cells were
modifications of sensory ones. This belief was based upon the
presence of intermediate stages between sensory and ganglionic
cells, upon the constant occurrence of intercellular nerve ends,
and upon the embryological evidence afforded by the fact that
in Pecten the ganglionic cells of the eye and sensory papillz
were derived from the cells of the hypodermic thickening that
gave rise to these sense organs. This supposition further led
to the conclusion that the optic ganglion of Arthropods could
not be an outgrowth from the brain toward the eye, but one
from the eye toward the brain. This conclusion is now in a
measure confirmed by the history of the development of the
optic ganglion of Acilius.

When we review the semi-ganglionic cells described by me in
Haliotis, “Eyes of Molluscs and Arthropods,” Pl. 30, Fig. 68,
and in Acilius, Pl. X., Fig. 58, 4, and the myoepithelial cells of
Ccelenterates as described by Hertwig, we perceive that nearly
all these cells have three prolongations, one of which is di-
rected outwards, and terminates between, the cells of the ecto-
derm; the other two extend, from the opposite pole of the cell,
inwards, and probably unite with similar prolongations from
other ganglionic cells. There is no sharp line of demarkation
between the tripolar cells described by me in the retina of Halio-
tis and the neuroepithelial cells of Coelenterates as figured by
the Hertwigs. In the case of Haliotis and Pecten, the origin
of some, at least, of the ganglion-cells is beyond question, for
they still form a part of the ectodermic thickening that gave
rise to the sensory part of the eye. In Acilius we have tempo-
rarily represented the condition that prevails in the sense organs

No. 1.] EVES OF ARTHROPODS. 169

of Coelenterates and Molluscs; for, while many ganglion-cells
arise from the invagination on the side of the eye, others wander
inward from the optic thickening itself. The details of the lat-
ter process are best studied in the great cells that are the last
to form. While these cells are still in the optic thickening
they are distinctly tripolar, one prolongation being directed out-
ward to form the rudiment of a nerve end. Such cells would
correspond to the tripolar neuroepithelial cells of Coelenterates,
or those tripolar ones already mentioned in Haliotis and Acilius.

In Acilius there is no reason to suppose that a ganglion-cell
once established in the above manner ever loses its direct con-
nection with the ectoderm. According to Hertwig, those con-
nected by an outward prolongation with the ectoderm are
intermediate between fully developed ganglion-cells and sen-
sory ones, and we are to infer that they are intermediate
because of this outward prolongation. I fail to see the neces-
sity for this conclusion, for there is reason to suppose that
most, if not all, ganglion-cells, have some connection with the
outer world, consequently the existence of such a connection
would not indicate the age of the ganglion-cells.

The history of the giant ganglion-cells of Acilius, together
with a consideration of the neuroepithelial cells of other groups,
it seems to me, warrant the conclusion that the primitive gang-
lion-cells were tripolar, and were derived from tripolar neuroept-
thelial cells. The outer extremities of these neuroepithelial cells
were reduced to intercellular nerve ends, the bases of which, in
Actlius, became the protoplasmic prolongations of the ganglion-
cells, and are probably homologous with the axts-cylinders of
Vertebrates.

SUMMARY.

The more important results of the foregoing study are as follows : —

(1) The larval optic ganglion is composed of three segments, each
of which is united on the one hand with a segment of the brain, and on
the other, with a segment of the optic plate.

(2) Each segment of the optic plate bears a pair of eyes.

(3) The ocelli are composed of four or more sensory spots, or pits,
each pit being supplied with a separate cuticular thickening and nerve.

170 PATTEN. [Vot. II.

In the centre of each group of four sensory pits, is a single large nucleus
of doubtful significance.

(4) The pits of each eye finally unite to form a thickened patch of
ectoderm, with a median double row of gigantic cells and a common
cuticular thickening.

(5) The thickened ectoderm is invaginated to form an optic vesicle,
the inner walls of which form the retina, while the surrounding indiffer-
ent ectoderm forms a third layer of cells over each vesicle, thus produc-
ing a typical three-layered eye.

(6) In the embryonic stages of eyes I.-IV., the retinas of which are
invaginated without the formation of a cavity in the optic vesicle (unless
the space between the median row of gigantic cells can be called one),
all the rods are horizontal.

(7) In the full-grown larvz, the smaller outermost rods become up-
right ; the larger and deeper ones remain in a horizontal position.

(8) In eye V., there is at first a strong tendency to form horizontal
rods. But the laterally flattened optic vesicle expands, forming a
spacious cavity in the vesicle, and all the rods become upright except
those of the median row of gigantic cells.

(9) In eye VI., which has no median row of giant cells, no horizontal
rods are formed.

(10) The outer wall of the optic vesicle in eyes I-IV. seems to be
absent. In the embryos, its presence is indicated only by a few char-
acteristic nuclei between the retina and the corneagen.

(11) In eye V., the outer wall of the optic vesicle is represented by
two great masses of inverted, rod-bearing cells, probably derived from
the two sensory spots, 5 and 6, seen in surface views of the eye before
invagination.

(12) In eye VI., the outer wall is composed of a thin nucleated
membrane, and a cluster of inverted retinal cells, derived from sense
organ number 6.

(13) Eye I. is composed of at least nine sensory spots, four of which
with their central nucleus and median row of giant cells give rise to the
horizontal retina ; four more, exactly like the first, to the vertical retina ;
and the ninth, to the appendage. All these sense spots unite to form a
single homogeneous organ ; but, during the later stages, the three groups
of sensory spots become greatly modified, so that in the adult eye the
parts they give rise to, the vertical, and horizontal retinas, and the ap-
pendage, are widely different in structure.

(14) All the retinas are composed of retinophore, formed by the
union of two cells. They contain two nuclei and two rods, and are
supplied with axial, and external nerve fibres.

No. I.] EVES OF ARTHROPODS. 171

(15) In very rare cases one finds ganglionic cells in the retina of
Acilius.

(16) The rods are arranged in pairs, which form a mosaic of hex-
agonal figures when upright, and straight vertical lines when horizontal.

(17) In the horizontal, as well as in the vertical rods, the retinidial
fibrillae are at right angles to the rays of light.

(18) All the larval ocelli of Acilius and Dytiscus contain more or
less distinct dimorphic, retinal cells. The giant cells always form a
double row along the bottom of the furrow. Their free ends are bent
at right angles, and bear short but broad horizontal rods.

(19) The ends of the smaller retinal cells, and consequently their
rods, may be horizontal, upright, or inverted.

(20) Between the two rows of giant rods are two sheets of coarse,
vertical nerve fibres and a layer of medulla-like substance.

(21) The pigment granules are deposited on the surface of the retino-
phoree and around the external nerve fibres.

(22) All the eyes are developed from the optic plate, the thickened
distal edge of the cephalic lobes. On the proximal edge of this optic
plate is a semi-circular furrow, which gives rise to the optic ganglion.
The furrow is deepened to form two distinct pockets, that give rise to
the first and second segments of the optic ganglion ; the third segment
is formed by an inward proliferation on the proximal side of the third
segment of the optic plate.

(23) The innermost walls of the ganglionic segments are from
the earliest stages connected with the inner face of the optic plate.

(24) Numerous ganglionic cells arise from the optic thickening, and
wander along the optic nerves into the optic ganglion.

(25) Toward the close of this process, about the time when the in-
vagination of the sensory areas begins, enormous, tripolar cells are
formed in each eye, which pass along the optic nerve, from the eye to the
optic ganglion, dividing rapidly on the way, and producing small, tripolar
ganglion-cells. But one of the proliferating cells retains its great size
throughout life, and finally takes up its position on one side of the
medulla belonging to the eye from which it arose.

(26) The history of these cells affords excellent evidence in proof of
the theory which explains the presence of intercellular nerve fibres, by
supposing them to be the outer ends of sensory cells, now converted
into ganglionic ones.

(27) The optic ganglion of the convex eye of Arthropods is com-
posed of three lobes: the first always, and the third sometimes, disap-
pears ; the second gives rise to the optic ganglion proper. The retinal
ganglion is a secondary product, and is not formed by invagination.

172 PATTEN. [ Vio‘. Woh

(28) The three-lobed optic ganglion of the convex eye of Arthro-
pods is derived from a three-segmented larval ganglion, each segment
of the latter belonging to a pair of larval ocelli.

(29) The first, second, and third segments of the optic ganglion of
Acilius larvee are respectively homologous with the second, first, and
third lobes of the optic ganglion of the compound eye.

(30) Hence, from the first segment of the larval ganglion, or that
segment which is united with the large, posterior, dorsal ocellus, is
developed the optic ganglion proper of the compound eye.

(31) The optic ganglion contains six medullz, each of which corre-
sponds in structure to that of the retina to which it belongs, and this
indicates that the arrangement of the medullary fibrillz is as near like
that of the retinidial fibrille of the retina, as the existing condition will
allow. .

(32) The structure of the retina in the larval ocelli of Insects is much
like that of Myriapods, and the whole eye is constructed on the same
plan as that of Perzpatus and most Molluscs.

MILWAUKEE, June 1, 1888.

No. t.] EVES OF ARTHROPODS. 173

CONTENTS:

Introduction . 5 : : - : : ; : 4 7 : Oy,
Topographical relation of optic plate and ganglion to cephalic lobes and brain, 97

PART I.—EYES.
EYE V.

Position; explanation of surface views; sense organs; optic cup; optic vesi-
cles; cuticular thickenings; median ridge; median furrow; comparison
of sensory pits with eyes on mantle of Molluscs; corneal and retini-
dial cuticula; the eye composed of a collection of sensory spots; large
nucleus; closure of optic cup, and formation of the three layers; cor-
neagen; iris; pigment; cuticular pellicle; lens; the retina; second me-
dian ridge; double row of cells with horizontal ends; retinophore;
pigment; retinal rods and nerve endings; rods in Cephalopods; in Arca,
etc.; nerve bundles . : E 3 ; : ; : 5 : Q9Q-I12

EYE VI.

Position; surface views; sensory pits; closure of optic cup; sixth sensory

spot forms tongue of inverted cells; corneagen retina; rods . - 12-115
EYE III.

Position; surface views . : ; : : 6 : ° - - II5-116
: EYE I.

Position; surface views; contain two large nuclei and nine sensory pits; invag-
ination of eyes I. and III.; corneagen; retina; retinophorz; nerve ends;
rods; dorsal appendage . - . é ; : : < . 116-129

EYES II. AND IV.

Position; invagination; retina; shape; lens; asymmetry 5 : . 129-131

PART II.—OPTIC GANGLION.

ORIGIN OF OpTIC GANGLION. — Topography; three segments; invagination of
first two segments and inward proliferation of the third; connection of
inner surface of optic plate with the segments of: the optic ganglion;
proliferation of ganglion cells; theory of invagination of optic ganglion;
inclosing of ganglionic segments by growth of optic plate; optic ganglion
before rupture of embryonic membranes. : : : : - 131-137

MEDULL& OF OpTic GANGLION.— Position; shape; structure; structure is
similar to that of retina to which it belongs; signification of this similarity;

174 PATTEN. [Vou. Il.

branches of medullary stalk; crown of ganglion cells; primary nerve
fibres; optic ganglion of late larval stage; origin of the three lobes of

imaginal ganglion from three segments of larval one é : + 137-144
Optic NERVES. — Position; course . : : . . . . - 144-145
NEURILEMMA. — Origin from basement membrane; structure . i . 145-146

ORIGIN OF GANGLION CELLS. — Modified tripolar sensory cells; position and
structure; passage from eye to optic ganglion; structure of outer prolon-
gation; gigantic ganglion cells of larve; position near medullz; connect-
ing fibres; small ganglion cells, probably tripolar; Vespa . - . 146-150

COMPARATIVE ANATOMY OF OpTic GANGLION.— Optic ganglion of Vespa;
of Astacus; Cymothoa; Cecropia; homology of optic ganglion of insects
with that of Crustacea; the three lobes of optic ganglion of convex eye of
Arthropods homologous with the three-segmented ganglion of the larvee, 150-154

PART III.—SUMMARY AND COMPARISON.

Large nucleus; horizontal rods; mosaic of upright and horizontal rods; struc-
ture of horizontal rods supports the theory that retinidial fibrille are at
right angles to the rays of light; eyes of Hydrophilus; comparison with
Grenacher’s figure of larval eye of Dytiscus; eye of Chauliodes . 154-158
Comparison of Myriapod eyes with those of Acilius . ; c . 158-161
Eyes of Scorpions and SprpERS; absence of ganglionic saaatintion, in Arach-
nids; possible explanation of inversion of retina in anterior eyes of

Spiders. : ; : : : : : - 5 : - 161-166
Convex Eye; origin; frontal ocelli ofimagines’ . ; : ; . 166-168
NEUROEPITHEL CELLS . : : - : . : é 4 - 168-169
SUMMARY : : : : - ; : : : : A - 169-173
CONTENTS ; : - - : 2 , c - : - 173-174

EXPLANATION OF PLATES : , : : : : ; : . 178-190

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175

EXPLANATION OF LETTERS USED IN THE PLATES.

first pair of antennz; labrum.
second pair of antennz.
nuclear-like bodies.
antennary lobe.

amnion.

nerve to second antenna.
appendage to eye I.

. nerve to appendage of eye I.

axial nerve.

brain.

bridge over ganglionic invagina-
tion.

basement membrane = outer
‘neurilemma.

clear area.

1 convex eye.

. corneagen.

corneagen; median part with
faint nuclei.

corneagen of appendage.

cuticula that gives rise to lens.

cavity of ganglionic invagina-
tion.

corneal cuticula.

cavity of the optic vesicle.

cuticula thickening = retinidial
cuticula.

dark areas.

dividing nuclei.

eyes.

endoderm.

cavity in endoderm.

external nerve fibres.

frontal ganglion.

great ganglion cells of optic gan-
glion.

double ganglion cell of optic
ganglion.

ganglion cell of retina.

great rods.

ganglionic invagination.

heel of great retinal cells.

medulla of the horizontal retina.

horizontal retina of eye I.

. horizontal rods.

iris.
inner neurilemma.
infra-cesophageal ganglion.

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inverted rods of outer wall of
optic vesicle.

lens.

loops of axial nerve.

. lateral nerve of horizontal retina.

mouth.

medulla of the appendage to
eye I.

muscles.

median chord.

medulla of the brain.

mandibles.

mandibular nerve.

medulla to horizontal retina.

medulla to inverted cells.

median furrow.

median row of giant cells.

median row of giant rods.

cesophageal muscles.

median ridge.

mesoderm.

medulla of vertical retina.

maxillee.

nerves to the eyes.

nerves to the sense organs in
eyes.

large nuclei.

nerve fibres.

nerve fibrillze.

newly formed ganglion cells.

outer ends of ganglion cells that
have passed inwards.

primary nuclei of retinophore.

secondary nuclei of retinophorze.

nerve spindles.

cesophagus.

cesophageal commissures.

optic ganglion.

outer neurilemma.

opening of optic cavity.

optic plate.

outer wall of optic vesicle.

outer wall of optic ganglion.

. pigmented nerve fibres.
. place where optic ganglion is

continuous with the optic
plate.

176 PATTEN. [Vot. II.

p.n.f. primitive nerve fibres. z.z.¢. tongue of inverted cells.
rd. rods. tm. tentorium.
rd.' & rd.'! rods of primary and second- v.#. vertical nerve fibres.
ary cells of the retinophorz. v.r. vertical retina.
rn. retinidium. x. dark nuclei in young eyes.
s. segments of nerve chord. y. yolk.
s.o. segments of optic plate. y.c. yolk cells.
s.o0.g. stalk of optic ganglion. z. first cephalic invagination.
s.r.c. small retinal cells. z. second cephalic invagination.
s. rd. small rods. _ I-10. sense organs of the eyes.
z1-3 tentorium. x.y. upper edge of eye III.

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EXPLANATION OF PLATE VII.

Fic. 1. Surface view of the head of a young Acilius embryo. X 110.
Fic. 2. The same. X I10.
Fic. 3. The same. Dea ito):
Fic. 3a. Side view of the same. : xXeamte:
Fic. 4. Side view of the head. <auros
Fic. 5. Ventral view of head. X 110.
Fic. 5a. Side view of same head. x ie:
Fic. 54. Dorsal view of dorsal edge of optic plate of same head. Xnles
Fic. 6. Ventral view of head. X IIo.
Fic. 6a. Side view of optic plate of the embryo in Fig. 6, showing arrangement of
surface nuclei around the sense organ of each eye. X 190.

Fic. 7. Ventral view of head just before rupture of embryonic membranes.
Fic. 7a. Side view of same. X 110.

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180 PATIEN. [VoL. Il.

EXPLANATION OF PLATE VIII.

Fics. 8 AND 8a. Ventral and side view of head just after rupture of embryonic

membranes. x 86.
Fic. 9. Side view of head of an embryo almost ready to hatch. Semi-transparent.
X 96.

Fics. 10 AXD Ioa. Dorsal and side view of the head of a full-grown larva.

Fics. 11-16. Surface views of the dorsal, anterior edge of the optic plate, show-
ing successive stages in the formation of the first eye. In order to economize time
and labor, the surface nuclei are shown only in Figs. 14 and 16. X 260.

Fic. 17. Semi-diagrammatic and transparent side view of eye I., in the stage
shown in surface view in Fig. 16.

Fic. 18. The same, in a later stage, showing the bend in the middle of the sensi-
tive area, to form the vertical and horizontal retinas, and the sense organs and nerves
to each part.

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182 PATTEN. [Vot. II.

EXPLANATION OF PLATE IX.

Fic. 19. Cross section of the cephalic lobes of an embryo somewhat younger than

that in Fig. 1, Pl. VII. X 360.
Fics. 20-23. A series of cross sections through the cephalic lobes of an embryo
like that in Fig. 1; showing the three ganglionic invaginations. X 360.

Fics. 24-27. Cross sections of an embryonic head about same age, perhaps
younger, as that in Fig. 1. This head was abnormally shaped. It was deeply invag-
inated along the median line; on the sides of the invagination were the antenne, and

at the bottom, the mouth. X 360.
Fics. 28-34. A series of cross sections through the head represented in Fig. 5.
They show the structure of the brain, optic ganglion, and optic plate. X 360.
FIGs. 35, 36. Cross sections of a head like that in Fig. 6, just after the optic gan-
glion is completely shut off from the exterior. X 190.
Fics. 37-39. Cross sections of a younger stage than that in the preceding figures,
showing the last stages in the enclosure of the optic ganglion, etc. X 138.

Fic. 40. Semi-transparent surface view of the optic ganglion and one side of the
brain; showing the three lobes of the optic ganglion, the medullz, and the nerves.

Fic. 41. Semi-diagrammatic horizontal section through the medullary portion of
the optic ganglion; showing the position and shape of the medullz and the nerves
that unite them with their respective eyes.

c

184 PATTEN. [VoL. II.

EXPLANATION OF PLATE X.

Fics. 42-47. A series of sections through the head of an embryo just after the
rupture of the embryonic membranes. See Fig. 8. They show the structure of the
brain and its envelop, optic ganglion and eyes, as well as the tracheal invagina-
tions of the head. For explanation of last-named structures, see my next paper on
the “ Development of Acilius.” Ka383

Fic. 48. Horizontal section of the optic ganglion, from an embryo just ready to
hatch. The break in the outer neurilemma is on the side next the eyes. It is im-
portant to notice the remarkable similarity between the structure of the medulle and
the retinas to which they belong.

Fics. 49, 50. Two vertical sections through the optic ganglion of a full-grown
larva; showing the medullz and nerves, and the three lobes of the ganglion. X 170.

Fics. 51-53. Three horizontal sections of the optic ganglion of a full-grown
larva. Shows same as preceding sections. X 170.

Fic. 54a. Cross section of the rods in the fifth Eye; showing axial nerves, retini-
dia, etc.

Fic. 544. Same from the sixth eye; showing loops of axial nerves, etc.

Fic. 55. A vertical section through the furrow of eye I.; showing the ends of the
giant, and small rods. Compare Fig. 56.

Fic. 56. Vertical section of the horizontal retina of the first eye; showing the
double row of giant cells with their external nerve fibres, the layer of vertical fibres,
with their fibrillee, and the ends of the small horizontal cells, etc.

Fic. 57a. Semi-diagrammatic view of a retinal cell from the fifth eye; showing the
double retinophorze, and the position and shape of the rods belonging to each cell of
the retinophora, etc.

Fic. 574. Same, in side view.

Fic. 58. Retinophorz isolated by maceration.

a. A double cell, decolorized, from the fifth eye.

4, Isolated cell from the sixth eye. The primary and secondary nuclei are
situated close together.

c. Two double cells, depigmented, from the sixth eye; showing the nerve
fibres and the deceptive shape of the inner ends of the retinal cells.

d, Same.

e.f. Two views of a small retinal cell with horizontal rods, probably from the

second or fourth eye.

g. Decolorized retinophora that showed especially well the shape of its com-
ponent cells.

A. A fragment of a retinal cell with a tripolar ganglionic cell attached to it.

z. Two giant cells from the first eye; showing how the light and dark cells
overlap.

Fic. 59. Horizontal section of the first eye; showing one of the rows of giant
cells and the two layers of vertical fibres with the medulla-like substance between.
Compare Fig. 56.

Fic, 60. Horizontal section of the row of small retinal cells just above the giant
cells in the horizontal retina of the first eye. It shows how the rods of each retino-
phora unite with each other above the centre of the cells, and not with the rods of
neighboring cells, as in all other cases. See Fig. 57a.

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186 PATTEN. [VoL. II.

EXPLANATION OF PLATE XI.

Development and Structure of: the Fifth Eye.

Fic. 61. Cross section of the head in Fig. 3; showing the large median nuclei

and two of the sensory pits of which the eye is composed, etc. X 430.
Fic. 62. Same, in a little older stage ; showing formation of a large ganglion cell.
X 560.

Fic. 63. Section of the eye in the stage shown in Fig. 6a. It shows a large clus-
ter of newly formed tripolar ganglion cells, wandering from the retina to the optic
ganglion. X 560.

Fic. 64. Section of the eye before the rupture of the embryonic membranes. The
pits and their cuticular thickenings have united to form a single sensory layer, and
the large nucleus has sunk into the retina. The formation of ganglionic cells from
the retina has ceased. The last one formed is now seen in the optic ganglion on one
side of the optic nerve. X 560.

Fic. 65. Section of the eye just after the rupture of the embryonic membranes.

Fic. 66. Section of the eye just after the closure of the optic cup. The median
row of giant cells, although small compared with those in the other eyes, is very
conspicuous on account of the manner in which it protrudes above the level of the
surrounding cells. X 560.

Fic. 67. Section of the eye in a later stage, showing the first steps in the differen-
tiation of the corneagen, and the outer wall of the optic vesicle.

Fic. 68. Section from an embryo about ready to hatch. The outer wall of the
optic vesicle is formed by two great masses of inverted rod-bearing cells, derived
from the sense organs 5 and 6. See Fig. 62. We can now see the minute rods of
which the cuticular thickening is composed. Most of the reddish brown pigment
has been dissolved by the alcohol. X 560.

Fic. 69. Section of the eye one or two days after hatching ; showing the distribu-
tion of pigment, and the well-developed inverted rods of the outer wall of the optic
vesicle. X 520.

Fic. 70. The eye as shown in a longitudinal horizontal section of a fully devel-
oped larva. X 220.

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EXPLANATION OF PLATE XII.

Structure and Development of Eyes If., IV., and VI.

Fic. 71. Eye VI. as seen in a cross section of the head just after the closure of the
optic cup. X 430.
Fic. 72. Same in a little later stage. X 430.
Fic. 73. Eye VI. of an embryo about ready to hatch. Compare Fig. 9. The
section is semi-transverse, cutting through the inverted sense organ 6=¢. i. c., and
the longitudinal vertical axis of eve III. X 430.
Fic. 74. A similar section through the same eye of a one-day-old larva. X 430.
Fic. 75. Eye VI. of a full-grown larva, as seen in semi-transverse section. Com-
pare Fig. 10a. The section passes through the optic nerve of this eye, but does not
show the tongue of inverted cells. It passes just on the dorsal side of it. X 350.
Fic. 76. Eyes Il. and IV.=4 and 8, as seen in a longitudinal horizontal section
of an embryo, some time after the rupture of the embryonic membranes. Compare
Fig. 9. X 430.
Fics. 77 AND 78. Eyes II. and IV. of a fully developed larva, as seen in a semi-
transverse section, nearly parallel with the vertical axis of the first and third eyes.
X 430.

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190 PATTEN. [VoL. Il.

EXPLANATION OF PLATE XIII.

Fic. 79. Eye I. as seen in a semi-transverse section of an embryo just after the
rupture of the embryonic membranes. Compare Figs. 8 and 16. X 520.

Fic. 80. The same, after the sensory area is differentiated into the vertical and
horizontal retinas.

Fic. 81. The same, from an embryo some time before hatching.

Fic. 82. Transverse section of the sensory area of Eye I. in the stage shown in
Fig. 14. X 560.

Fic. 83. Same, of Eye III. in a later stage. The median furrow has disappeared
and the invagination of the sensory area has commenced. X 560.

Fic. 84. Cross section of the vertical retina of Eye I. in the full-grown larva.

X 430.

Fic. 85. Eye I. as seen in a tangential section of the side of the head. The sec-

tion is at right angles, and from an eye in the same stage, to that shown in Fig. 8o.

X 415.
Fic. 86. Section, in same direction as the preceding, of Eye I. just before hatch-
ing. X 260.

Fic. 87. Transverse section of Eye I. in same stage as shown in Fig. 79. The
section passes through the large nucleus of the horizontal retina.

Fic. 88. Section similar to the preceding one, through the vertical retina of the
same eye. X 430.

Fic. 89. Horizontal section through the horizontal retina of Eye I. during a little
earlier stage than that shown in Fig. 85. X 430.

Fic. 90. Eye III. as seen in a tangential section of the head of a full-grown larva;
partly depigmented. X 240.

Fic. 91, Eye I, in same section as the preceding. X 240.

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Volume II. November, 1888. Number 2.

JOURNAL

OF

MORPHOLOGY

ON THE DEVELOPMENT OF MANICINA AREO-
LATA.

A thesis for the degree of Ph.D., accepted by the Board of University Studies of the Johns Hopkins
University, May, 1888.

HENRY V. WILSON,

FELLOW OF THE JoHNS Hopkins UNIVERSITY.

DurineG the spring of 1887 the Marine Laboratory of the
Johns Hopkins University was stationed on the island of New
’ Providence, Bahamas. As soon as possible after my arrival,
March 10, I endeavored to find out what corals were breeding.
Of half a dozen species examined only one was with eggs. This
was the so-called Chenille stone, or Mantcina areolata, one of
the commonest corals in the Bahama waters. The breeding
continued to be very active until the middle of April, when it
began to decline, coming to a close before the first of May.

The coral is found in large numbers in water of easy wading
depth, lying with its pedicel buried in the sand. It lives very
well in small aquaria, if care be taken to change the water twice
a day. In rearing the larve I was compelled to employ the
same tedious method as Lucaze Duthiers: every morning and
evening I transferred them, one or two at a time, by means of
a pipette, to a dish of fresh water. When once the larve had
become attached, the matter was simplified by transferring the
entire dish to a bucket of fresh water. For preserving the
larvze, Perenyi’s fluid proved the most generally useful reagent.
Osmic acid specimens were also of very considerable value in
elucidating special points. For the anatomy of the adult, abso-

192 WILSON. [VoL. II.

lute alcohol gave the most satisfactory results. I take this
opportunity of thanking Professor Brooks, the director of the
Marine Laboratory, for his advice and constant suggestions, which
have been of the greatest value to me during the course of this
work, both at the seaside and in the Baltimore laboratory. I
am also indebted to Mr. C. S. Hodge, of this laboratory, who
very kindly took upon himself a part of the task of cutting the
sections.

J. SysTEMATIC DESCRIPTION OF MANICINA.

Milne Edwards makes Manicina the sixty-fourth genus in the
family Astreide. Like Meandrina, this coral grows by incom-
plete fission, the calicles remaining connected so as to form
meandering valleys, in which the limits of a calicle are not dis-
tinguishable. The shape of the colony ordinarily met with is
subturbinate (see figures on Plate I), there being a well-marked
pedicel. With increasing age the pedicel becomes less and less
evident, until the corallum finally assumes the shape of a convex
mass with a flat basal surface. The basal surface has two diam-
eters, the longer about three inches, the shorter two inches, and »
the vertical height of the corallum is about equal to the shorter
diameter. The distinguishing features of the genus, besides its
growth from a pedicel, are as follows: The columella is spongy
and very well developed. The septa are thin, closely set, and
have strongly marked granulations on their sides. The edges
of the septa, both within and over the exterior of the calicles
(costze), are finely and regularly toothed. “The genus was in-
stituted by Ehrenberg for certain of Lamarck’s Meandrinez,
characterized by growing from a pedicel or central point of
attachment”’ (Dana). In the species Manicina areolata, the
septa can be divided into three cycles, and each septum has in
the neighborhood of the columella a large and rounded lobe.’

The animal is of a brownish color, and when expanded, extends
high above the skeleton. In this condition the tentacles are
moderately long, and are closely set round the periphery of the
oral surface. Inthe pedunculate forms, both in the expanded and
contracted condition of the animal, the upper part of the lateral
surface of the skeleton is covered by the polyp. The pedicel,

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 193

which includes the skeleton below this region, is usually disfig-
ured by small annelid tubes and other incrustations.

The young, after the swarming life is over, affix themselves
to some solid substratum, such as a piece of rock or a shell.
To this they remain attached until they have reached a diameter
of about half an inch. Until the diameter is one-third of an
inch, the animal remains a single polyp, circular or oval in trans-
verse section, and with a flat or irregular surface of attachment.
The multiplication by fission then begins, and with it the forma-
tion of the pedicel. When the latter has become apparent, the
coral is broken off from the rock to which it was attached, and
henceforth lives free in the sand.

II. GENERAL SKETCH OF THE DEVELOPMENT FROM SURFACE
VIEWS.

Lacaze Duthier’s figures of Astroides (1) apply so well to
Manicina, that I have thought it unnecessary to give a series of
such views. The chief point of difference is that the larve are
red in the former genus, but colorless in the latter.

Manicina is hermaphrodite. Normally, it would appear, the
mother gives birth to larvae, which pass out by the mouth. But
the first two batches of corals I kept poured out an abundance
of eggs and semen. Each batch numbered eight corals, was
distributed into four aquaria, and was kept for only a day. The
first set laid on the night of the 15th, the second, on the
17th of March. I was not able to try a third batch until the
20th, when I was surprised to find that all the corals had given
birth to larvee a little more advanced than the planula stage.
The throwing out of eggs and spermatozoa was probably abnor-
mal, as the eggs which I watched underwent very irregular
changes, and finally broke up. In connection with this ejection
of eggs and semen, it may be interesting to note that though
after March 20 the corals always ejected larvee when kept in
aquaria, the stage of development in which the larve were
born became much more advanced as the season grew older.
The larvz born March 20 and 21 were without cilia, and at the
stage represented in Fig. 4, Pl. II. Those born April 5 were
ciliated and as far advanced as Fig. 20, Pl. IV.

The larve I obtained during March lay, for a day or two after

194 WILSON. [Vot. II.

birth, motionless on the surface of the water. They then ac-
quired cilia, and began to swim feebly about at the surface, often
collecting in rows at the sides of the vessel or in groups away
from the sides. Lucaze Duthiers noticed the same habit in
Astroides. At the end of a week the larvz are rapid swimmers,
now spending most of their time below the surface of the water.
Often they creep along the bottom and sides of the dish like
little worms. Though they are constantly lengthening or
shortening their bodies, the general shape is that of a pear,
with the mouth at the small end. The broad end is usually,
though not invariably, directed forwards in swimming. While
creeping over the glass they frequently fasten themselves by
their broad ends for from one to ten minutes, becoming free again
of theirown accord. The larve continued to swim about without
any change in form until the middle of April. By this time, as
subsequent examination showed, they had acquired six mesenter-
ies (three pairs) and two long mesentrial filaments (Fig. 19, Pl.
III.). A large number now began to attach themselves. Sup-
ported on the broad end, they stood nearly erect, spinning slowly
around. The long axis began to shorten, and by the time they
had assumed the shape of an oblate spheroid, eight meridional
constrictions had appeared, marking the number of mesenteries.
The long or, rather, oral-aboral axis continued to shorten until
the little coral had assumed a disk-like shape with a flat basal
surface and a convex upper surface, the latter marked with the
meridional constrictions (a transverse section of this stage is
shown in Fig. 34, Pl. V., and a longitudinal in Fig. 38). The
whole process of fixation occupied several hours. All the larvee
did not become attached at the same time. On the contrary,
many continued to lead a free life until the first part of May.
The lot of larvze I got on the fifth of April were born in a
more advanced state than their predecessors, and developed
after birth more rapidly. So much so, that by the middle of
April as many of this batch became attached as of the larvee
born March 20. Indeed, the first fixed larvze I obtained, April
9, were from this lot, and had taken only four days to go through
the metamorphosis, which in all the other larve required from
two to four weeks. This great amount of difference amongst
the larvae, as to the time required to reach a certain stage of
development, made it a matter of some trouble to pick out a

No. 2.| DEVELOPMENT OF MANICINA AREOLATA. 195

consecutive series of stages. When I began to section, I found
that inferences based on the length of the larva’s life were only
true within wide limits.

The stage with eight mesenteries is followed in a day or two
by the stage with twelve. At this period the first deposition of
the skeleton makes its appearance as a circular patch of calcare-
ous matter on the basal surface of the attached polyp. I was
not able to rear the young corals beyond this point; though I
kept a few alive until the first of June. The death rate increased
very much as soon as the larvz became attached.

III]. Earty STAGES, INCLUDING THE FORMATION OF LAYERS.

The diameter of the unsegmented egg was about two-thirds the
long diameter of the blastosphere (Fig. 2, Pl. II.). There was
a very large centrally-placed nucleus, and the body of the egg
was filled with vesicles, resembling in this respect the endoderm
of the subsequent planula. The only observations on the seg-
mentation were made on the eggs accidentally (?) discharged
March 21. The spermatozoa played round each egg in large
numbers. After fertilization the spherical egg became oval,
and then divided into two equal blastomeres, which remained
connected by a bridge of tissue. The division into four then
followed. So far the segmentation was quite regular, but irreg-
ularities now began to crowd in, which led to the production of
a grotesquely shaped mass comparable with the irregular planula
described by Metschnikoff for Oceania (2). (I have observed a
precisely similar segmentation and planula in an allied medusa,
Turritopsis.) The irregular mass did not develop any further.

The normal segmentation which goes on in the body of the
parent results in the formation of a blastosphere with a very
large cavity (Fig. 1). The blastosphere is markedly bilateral,
and is without cilia. The cells contain a large number of very
distinct vacuoles, pretty evenly distributed through the cell
body. In older blastospheres, Figs. 2 and 3, the formation of
the larval or primitive endoderm has begun. The blastosphere
cells are columnar, the nucleus is peripherally placed, and the
vacuoles are concentrated in the central end of the cell. The
cells are evidently delaminating, the inner vacuolated ends
being split off to form the endoderm. The nuclei of the endo-

196 WILSON. [Vou. II.

derm segments are very hard to make out. The delamination
takes place irregularly over the general surface of the blasto-
sphere, and is of a peculiarly complex character in certain spots.
In the cell groups # and m!, Fig. 2, for instance, the lines of
the transverse divisions of the several cells are continuous, and
seem to indicate that the whole group must have divided trans-
versely while it was yet a single cell: before it had been split
up by the longitudinal divisions. But the latter show that the
transverse divisions did not precede them. Such a cell as x,
Fig. 3, throws light on the matter. This cell has begun to
divide longitudinally, but even in the peripheral part of the cell,
though the longitudinal constrictions are evident enough, the
segments are far more intimately connected than are, say 7, and
the adjacent cells. In another cell, z', the longitudinal division
is apparently perfect ; but on comparing the close apposition of
the new segments with the marked space between z' and the
adjacent cells, I am inclined to believe that the halves of z' are
still connected by bridges of tissue, much as the blastomeres in
many segmenting eggs remain connected after they are clearly
marked off. In the group m!', then, Fig. 2, it is probable that
the longitudinal constrictions were the first to appear in the
mother cell, but that before they became complete divisions a
general transverse constriction took place.

Delamination appears to be the exclusive means by which the
endoderm is formed. I looked in vain for cells migrating from
the surface. Whenever there appeared to be such, examination
of the next sections showed that the cells in question had been
cut obliquely, the peripheral end with the nucleus having been
severed from the rest of the cell body. The cell a, Fig. 2, for
instance, is merely the central portion of a constricted cell like
6 in the same figure. The delamination and accompanying
longitudinal division often give rise to spheroidal cells, such as
x, Fig. 3. These cells are always at the surface of the blasto-
spheres. Whether their fate is different from that of the
general ectoderm cells, I do not know.

The cavity of the blastosphere having been filled up by the
endoderm segments, a solid planula, Fig, 4, is formed. On
studying this figure, a median longitudinal section, we see that
the longitudinal division of the superficial cells, which was
active in the blastosphere, has given rise to a layer of columnar

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 197

cells, the ectoderm. The inner ends of these cells are not dis-
tinctly marked off from the solid endoderm. The endoderm,
when the living larva is compressed or when pretty thick
sections are examined, appears made up of a quantity of vesicles,
which look something like fat cells. When thin sections are
examined (Fig. 4), it is found there exists a continuous proto-
plasmic matrix binding the vesicles together, which are now
seen to be identical with the vacuoles present in the endoderm
segments of the blastosphere cells. There is, however, a differ-
ence in their appearance, which is best shown in Figs. 9 and Io.
In the blastosphere cell, the protoplasm in which lie the vacu-
oles is pretty uniform ; but in the endoderm of the planula, the
protoplasm immediately round each vacuole is denser than the
intervening stroma, and forms a more or less differentiated shell
for the vacuole. The shell stains much more deeply than the
stroma. What the contents of the vesicle is, I cannot say.
Carmine and hematoxylin do not affect it, and in these young
stages I did not try osmic acid.

The endoderm contains, besides the vacuoles just mentioned,
a number of “yellow cells” and scattered nuclei. No cell
boundaries can be made out, and there is every indication that
the layer is a plasmodium. A stage between Figs. 2 and 4
would go far towards elucidating the intricate structure of the
solid endoderm, but I did not succeed in obtaining such.

While the embryo is still solid, the cesophageal invagination
makes its appearance, Fig. 4. The larva is very narrow except
at its base, where it is slightly dilated. At this stage it swims
feebly about, the cilia having commenced to develop.

The formation of the permanent layers is illustrated in Fig. 5.
In the region @ the layers are in the condition characteristic of
the earlier larva. But in the neighborhood of ¢ the ectoderm
cells have become much more clearly marked off from the
endoderm. Their inner ends forma ragged line which gradu-
ally becomes more uniform, until the ectoderm is bounded
internally by a smooth limiting surface, as at a. Though the
bounding surface is smooth in this region, the supporting
lamella has not yet formed. A little later it appears as a
delicate membrane between the two layers (from @ towards the
mouth). While it is still very thin it resembles an ordinary
cuticle. It appears between the layers, and is not formed by

198 WILSON. [Vot. II.

the direct metamorphosis of the ends of ectoderm or endoderm
cells. As tothe much-discussed question of which layer secretes
the membranes; in early stage, such as Fig. 5, it is impossible
to decide whether the secretion is the peculiar property of either
layer. But in later stages, it is found in places where it can
only be endodermic, and in others where it is evidently ecto-
dermic. I shall return to this point further on. The various
steps in the formation of the permanent layers can often be
observed, with but few gaps, in a single section. Fig. 5 is such
a section, with a few additions from another.

The permanent endoderm is formed from the larval endoderm
by a differentiation of a peripheral layer from the central por-
tion, Fig. 5. The peripheral layer is not formed continuously
over the whole surface, but in spots here and there. It is at
first marked off from the central portion only by its somewhat
greater density, but it gradually breaks its connection with the
latter by the acquisition of a smooth limiting surface, Figs. 5
and 10. Cell boundaries soon appear. The permanent endo-
derm as thus formed is a single layer of vacuolated cubical cells,
except in the immediate neighborhood of the cesophagus, round
the sides of which the cells are massed so as to fill up, more or
less completely, the space between it and the body wall. This
is especially noticeable on the left side of Fig. 5.

The cesophageal invagination as seen in Fig. 5 is much
dilated at its base. Here the ectoderm has preserved its
intimate connection with the endoderm, the ectoderm cells not
even having acquired a smooth bounding surface. In Fig. 6
this even surface has been acquired, but at no time is a support-
ing lamella secreted over this area. The absence of the lamella
clearly facilitates the absorption by the endoderm (or yolk) of
the base of the invagination. The details of the absorption are
as follows. The dilated bottom of the invagination, shown in
transverse section in Fig. 10, is broken through at one point.
Through this breach the yoke passes into the lumen, Figs. 8-10,
and the base of the cesophagus thus enclosed above and below
by yolk is absorbed. It is, I think, possible to recognize the
base after it has passed into the yolk, though of course the
histological structure is gone. In Fig. 8 is seen a curved mass
of tissue extending from the left side of the cesophagus nearly
to the right. Though in structure like the yolk, it stains a much

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 199

deeper hue, and is therefore well defined. On comparing this
figure with Figs. 6 and 10, there seems to be no doubt that the
mass in question really represents the ectoderm base of the
cesophagus.

The central portion of the larval endoderm remains as a food-
yolk. In Fig. 5 it still exists as a continuous structure, but as
more and more of the protoplasm is drawn into the layer of per-
manent endoderm, the vesicles lose their connection with each
other. By the time the layers are definitely established, Figs.
6 and 8, the yolk is a loose mass of vesicles, the shells of which
have begun to disintegrate. The shell is extremely dense, and
in this and subsequent stages seems to be fatty, as it stains very
dark with osmic. Remnants of the yolk are found in stages as
late as Fig. I9.

Though the formation of the supporting lamella and the dif-
ferentiation of the permanent endoderm very often take place
at about the same time, this is not always the case. In many
larve the supporting lamella is entirely formed, and the cesoph-
agus has opened centrally, while the endoderm is still solid,
Figs. 10 and 12.

The “yellow cells,” which later are found in such abundance,
appear for the first time in the planula, Fig. 4. I have not
seen them actually entering the planula, but in this and slightly
older stages, Fig. 5, a few occur in the surface ectoderm,
whereas in older larve and in the adult they are confined to
the inner layer of the body.

COMPARISONS.

a. Germinal Layers.

Among the many ways in which the germinal layers are
formed within the Ccelenterates, Metschnikoff (2) has decided
that one represents the manner in which the earliest metazoa
were formed. In this so-called “mixed delamination” a solid
endoderm is built up both by delamination and by the migration
of superficial cells into the interior. Polyxenta (Metschnikoff)
and, better, Aurelia (Gotte) are good examples of this process.
Accepting this type as ancestral, JZanzcina has diverged along
the same path as certain Trachomedusze (Geryonia, Liriope) ;

200 WILSON. [Vot. Il.

i.e, none of the blastosphere cells migrate into the interior, but
the endoderm is formed exclusively by delamination.

Though the way in which the solid larva was originally
formed seems preserved in but a few species, the solid larva
itself may fairly be considered as typical for the Ccelenterates.
It is especially well preserved in the Hydroids and Anthozoa.
In the latter group it is nearly universal among Alcyonarians,
and occurs in the majority of the Zoantheria. The Alcyonarian
which comes nearest to J/anzcina in the formation of its layers
is Renilla (3). In this genus, though the blastosphere has a very
small cavity, the endoderm is formed by delamination, as in the
coral. As regards the structure of its larval endoderm, how-
ever, Renilla differs from Manicina. In the former the endo-
derm is made up of a mass of cells, of which the peripheral layer
becomes the permanent endoderm, while the central cells go to
pieces, and are probably eaten, amoeboid fashion, by the periph-
eral cells. In Manicina, on the other hand, the larval endoderm
is a plasmodium, and in the entire process which leads up to the
formation of the adult endoderm it would seem that a prominent
physiological part is played by the “ vesicles,’ which in all proba-
bility contain some kind of yolk. Owing to the plasmodial nature
of the solid endoderm, the complete transformation of the latter
into the permanent layer must require less time in Manicina than
in Renilla. For in Manicina there is no large accumulation of
yolk cells which must slowly be devoured, amoeba fashion, by the
peripheral cells. On the contrary, when the time for the forma-
tion of the permanent endoderm has arrived, the general proto-
plasm is merely drawn towards the periphery, and after it has
there broken up into cells, there remains but little nutriment
in the loose yolk mass. Just how the yolk is ingested after the
cellular endoderm is formed, Iam unable to say. It is not de-
voured, amoeba fashion, by the endoderm cells at large, though
in the region of the cesophagus, Figs. 6 and 8, connection is
maintained for a considerable time between the yolk and the
endoderm, which elsewhere is completely formed.

Amongst the corals and actinias, two or three forms have
been described as undergoing invagination, notably Cerzanthus
(Kowalevsky 4) and Actznza (Jourdan 5). While the mere recur-
rence of invagination in a ccelenterate group can scarcely be
said any longer to have a phylogenetic significance, these two

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 201

forms are especially interesting, as E. B. Wilson has remarked
(3), because in each of them a yolk mass appears after the layers
have been completely formed. I have not seen Kowalevsky’s
figures, but the yolk shown in Jourdan’s figure 11g is precisely
like the yolk of a young Manicina (making allowance for differ-
ence in thickness of the sections). The @ gréorz improbability
that the endoderm would first secrete a yolk (Kowalevsky) and
then swallow it again, taken together with the similarity of the
yolk in question to that of Manicina, might tempt one to believe
that both authors had mistaken a stage like Fig. 12, Pl. I., fora
true gastrula. But Kowalevsky’s statements on this head are
so definite as to preclude this supposition.

b. Supporting Lamella.

The only two authors who have described in detail the forma-
tion of the supporting lamella are Jourdan (/c.) and Wilson (Z.c.).
Jourdan’s observations were made on a coral, Balanophyllia, and
an actinia, Actinia equina. He draws a sharp distinction be-
tween the ‘membrana propria” and the jelly.

The former answers to the German Stutzmembran. It isa
firm limiting membrane which appears between the two layers
and extends into the mesenteries to form their axial bands.
This is what I have spoken of as the supporting lamella (comp.
any of figures on Pl. IV.). Its origin Jourdan was unable to
trace with any certainty. The jelly, on the other hand, which
eventually becomes fibrous, is formed outside the membrana
by the superficial ectoderm cells. The inner ends of these
cells break off and fuse together to form a granular mass, in
which fibres subsequently appear (/.c. Figs. 119 and 129).

The supporting lamella described by Wilson is evidently the
same thing as Jourdon’s membrana. Its origin according to Wil-
son is double. In the mesenteries it isa simple cuticular secre-
tion of the ectoderm cells. But in the body wall it is formed
in a manner similar to that just described for the jelly: the
inner ends of the ectoderm cells become swollen, constrict off,
and form a granular layer which condenses to a smooth mem-
brane.

In Manicina there is first formed a very distinct membrane
as described. In later larval stages, at various spots, especially
in angles, a thin fluid jelly accumulates. This is noticeable in

202 WILSON. [VoL. II.

Figs. 16 and 17, beneath the right-hand mesenteric filament,
and in Figs. 44 and 45 at the angles of the cesophagus. It is
always to be found in the axis of the larval filament, Fig. 26.
The distinction between the supporting membrane and the
more fluid jelly, which is noticeable in larval stages, is lost later
in life. In the older larve, Fig. 39 for instance, the supporting
membrane throughout its whole extent has become consider-
ably thicker than in younger stages, though the jelly in the axis
of the filament is still to be distinguished from the more mem-
brane-like band of the mesentery. In the adult the axial band
of the mesentery is so much wider, while the jelly in the axis
of the filament is at the same time denser than in larval stages,
that all distinction between the two structures is lost. Com-
pared with an actinia the whole mesodermic skeleton of the
adult Manicina is very scanty and membrane-like, but in certain
places it reaches a more generous jelly-like condition, for exam-
ple, in parts of the mesenteries, Fig. 51. Here the supporting
substance is merely the thickened primitive membrane.

There indeed seems to be no difference between the support-
ing membrane proper and the jelly, except in the mere quantity
of the secreted substance and in the percentage of water. What
applies to the origin of one should explain the origin of the other.
Now as regards the membrane proper, I am quite sure that in
Manicina it is formed as a cuticular secretion, and not by the
direct conversion of the ends of ectoderm cells into granular
matter, which subsequently condenses to a membrane. Turn-
ing now to the question as to which layer secretes the membrane,
we see from the figures (14, 17, 26, 45) that after the mesenteries
are formed, the lamella is much more intimately connected with
the endoderm than with the ectoderm: where the layers are
forced apart, it always sticks to the endoderm. But even here
the ectoderm is provided with a well-defined limiting membrane,
which if thinner than the lamella, is essentially like it. I con-
clude from this and other facts to follow that when the lamella
lies between the two layers, both layers share in secreting it.
That the endoderm cells can secrete the lamella, is plain from |
its occurrence in the axis of the mesenteries, and in the axis of
the genital bands of a Cubomedusa (6). On the other hand, the
same argument can be used to prove the ability of the ectodermal
cells to secrete this substance, for in the velum of Hydromedu-

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 203

see there is a well-defined lamella, which is formed zz sztu. In
Cunocantha (7) I have pointed out that when the velum is
developing, the ectoderm cells range themselves so that their
bases will secrete a continuous membrane.

IV. FoRMATION OF THE First Parr oF MESENTERIES AND
FILAMENTS.

I was led to pay especial attention to the filaments by E. B.
Wilson’s interesting discovery that the dorsal pair of filaments
in the Alcyonarian polyps are ectodermal lobes (8). Relying on
the histological similarity between this pair of filaments and the
flimmerstretfen of an actinian filament, Wilson suggested that
perhaps in the latter the /@mmerstreifen were ectodermal, and
only the median xesseldrusenstretf was endodermal. I find, how-
ever, that the filaments of Maniciva are as to origin like the
dorsal pair in the Alcyonaria. They are simple ectoderm lobes
which grow down from the cesophagus.

The cesophageal invagination in the earliest stages is symmet-
rically placed, Figs. 4 and 5. It very soon, however, begins to
travel towards one side of the larva. This is shown in the
transverse section, Fig. 7, and still better in the longitudinal
section, Fig. 6 (the endoderm in these two larve is in different
stages of development). The lateral motion of the cesophagus
has compressed the endoderm on its left into a compact mass,
which completely fills the space between the cesophagus and
body ectoderm. On the right hand the endoderm has been
stretched, until it forms a single layer of cells. The narrow
lumen of the cesophagus is bilateral (it is doubtful whether this
is true in all larvee at this stage), and its dilated extremity has
no longer the symmetrical bulb-like shape of Fig. 5. In Fig. 8
the lateral movement has gone a step farther, and meanwhile
the cesophagus has opened centrally. The movement of the
cesophagus is continued until in one meridian there is nothing
left between the cesophageal and superficial ectoderm but the
supporting lamella, Figs. 11 and 12. (In Fig. 11 the lamella
has not yet appeared, but both stomadoeal and body ectoderm
have smooth, limiting surfaces.) The intermediate stages show
that the lateral movement of the cesophagus travels from above
downwards, and that the endoderm has consequently been pushed

204 WILSON. (VoL. II.

down in this meridian. This is proved by Figs. 9 and Io,
transverse sections from a larva in which the cesophageal move-
ment had gone farther than in Fig. 8. Fig. g is about at the
level a in Fig. 8, and Fig. 10 is at the level 4. In this larva
then the cesophagus was closely pressed against the ectoderm at
the level a, but was separated from it by endoderm at a lower
level 6. In the later stage, Fig. 11, the lowest part of the
cesophagus has completed the journey. The meridian in which
the oesophagus is thus pressed against the ectoderm, is that of
the first mesentery. (Though Figs. 9 and 10 are from the same
larva, both the supporting lamella and endoderm are much
farther advanced in the lower section than in the upper.)

The larva from which the longitudinal sections, Figs. 12 and
13, were cut, was very backward in forming the permanent
endoderm. Fig. 12 is taken through the line a and 6 in Fig.
II, and is in the plane of the first pair of mesenteries. It is
only on the left side that the cesophagus is in contact with the
body ectoderm. But the right side is following suit, and in a
slightly older stage, Fig. 12, is in the same manner applied to
the surface ectoderm over a narrow tract. Fig. 13 is to one side
of aand 6 in Fig. 11, and is consequently out of the plane of
the mesenteries.

My next stage after Fig. 12, is the larva from which the
series of transverse sections, Figs. 14 to 17, was taken. It is
this stage which proves the meridians, along which the cesophagus
is applied to the body ectoderm, to be really those of the first
pair of mesenteries. Fig. 14 is the uppermost of the series, and
is through the body of the cesophagus, the lumen of which is
exceptionally large. On the right side the cesophagus is sepa-
rated by jelly alone from the surface ectoderm. Following down
the series of sections, we see that in this meridian the cesopha-
geal ectoderm sends down a slender lobe, which, like the cesoph-
agus above it, divides the endoderm and rests on an accu-
mulation of jelly (right side of Figs. 15, 17). This lobe is a
mesenterial filament. It is considerably shorter than the fila-
ment on the opposite side, Fig. 17, and is probably the second
one of the first pair. The right side of this larva is practically
in the condition shown in Fig. 12, except that the cesophagus
has formed a filament.

On the left side of the larva, Fig. 14, matters are more

No.2.] DEVELOPMENT OF MANICINA AREOLATA. 205

advanced. On comparing this side with Fig. 12, we see the
cesophagus has moved away from the surface ectoderm, but
while doing so has remained connected with it by a band of
supporting lamella. Running through the series of sections, it
is found that in this meridian also an ectoderm lobe has grown
down from the cesophagus. This lobe is the primary filament.
It is much wider at its start, near the cesophagus, than its fellow
on the opposite side, but soon dwindles to about the same size.
Like the cesophagus above it, this filament is in a more advanced
condition than the filament on the right side. Since we know
that the left side of the cesophagus itself has passed through the
condition which exists on the right side, we are pretty safe in
believing that the left filament has likewise passed through the
condition in which the right filament is found. The lack of a
fairly intermediate stage between Fig. 12 and the larva we are
studying, is to a certain extent supplied by the larva from which
Fig. 11 was taken. In this individual, which was sectioned
transversely, the cesophagus extended so much farther down in
the meridian of the first mesentery than round its general lip,
that in this meridian it formed a very evident though not a very
long lobe. This lobe, which becomes the primary filament, is
shown in Fig. 11, and is to be found in the sections immediately
below the one figured, growing smaller towards its end.

On comparing the first and second filaments in Fig. 17, it is
clear that the endoderm, which at a higher level grew in between
the cesophagus and body ectoderm, has likewise forced its way
beneath the primary filament, and thus given rise to the first
mesentery. The mesentery is continued from the level of Fig.
17 downwards, as a very slight endodermic ridge on which rests
the filament. The axial band of supporting lamella is continu-
ous with a thinner lamella, separating the filament from the
endoderm. Immediately beneath the opening of the cesophagus
the mesentery is much more elevated than at a lower level.
The elevation of the mesentery in this region is connected with
the first appearance of an intermesenterial chamber.

In the larva we have been studying the first pair of intermes-
enterial chambers has been marked off. Round the cesophagus,
however, they are still solid, Fig. 14, though at a lower level
the hollowing out of the solid endoderm has begun. At this
level, Fig. 15, which is just beneath the opening of the cesopha-

206 WILSON. [Vot. II.

gus, the endoderm on one side of the first mesentery exhibits a
small cavity. The cavity, when traced through the series of
sections, is found to open into the ccelom in Fig. 16, forming,
as it does so, the cave or bay which underlies one-half the
primary filament in the figure. It is thus (comp. Figs. 14 and
15) in the larger of the two primary chambers that the excava-
tion of the solid endoderm begins, and, as I learn from other
series, the excavation of this chamber is nearly completed
before that of the smaller begins. The excavation starts, as we
have just seen, in the immediate neighborhood of the first mes-
entery. From this spot it gradually extends across the chamber
to the second mesentery, travelling all the while from the lip of
the cesophagus upwards.

The second mesentery, which exists in its embryonic condition
in Fig. 14, follows the example of the first. In Fig. 18 it is
completely formed, and in the series of longitudinal sections,
Figs. 20-23, which I shall describe later, the second mesentery
is in the condition in which the primary is in Fig. 14; z.e., in the
immediate neighborhood of the second mesentery the larger of
the two intermesenteric chambers is solid, while the smaller
chamber is entirely solid.

In the larva from which the transverse section, Fig. 18, was
made, the various processes which have been described are now
completed. The cesophagus is swung by two complete mesen-
teries. Both intermesenteric chambers—the larger on the
left, the smaller on the right — have been hollowed out. Below
the cesophagus, the mesenteric ridges extend the whole length
of the larva, and the first pair of filaments about half the length.
The section is slightly complicated by other features, of which I
shall now speak.

In the larger of the two chambers, Fig. 18, the second pair of
mesenteries, 3 and 4, has appeared. The axial bands of sup-
porting lamella as yet cause no elevation of the endoderm, and
at a level slightly below the cesophagus are entirely lost. In
Fig. 18 a, above Fig. 18, the axial band numbered 4 stretches
across to the cesophagus, and still higher up 3 does likewise.
In this section the position of the cesophagus is eccentric. This
is very often the case at the extreme upper limit (the appearance
is not due to oblique sections), and hence one mesentery usually
runs out before its fellow (2 before 1). The mode of origin of

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 207

the second pair of mesenteries is thus entirely different from
that of the first pair. All the subsequent mesenteries are
formed after the fashion of the second pair.

The outer wall of the larger intermesenterial chamber in Fig.
18 is made up of unmistakable endoderm, but the inner or
cesophageal wall has an ephithelium precisely like that of the
cesophagus. Both are composed of very slender elongated cells
with a median thickening, in which lies the nucleus ; the periph-
eral end is enlarged and flattened, so that by the juxtaposition
of many such cells a continuous cuticle can be formed. The
cells in question resemble the well-known “supporting cells ”’ of
the Hertwigs (9). Besides the supporting cells, glandular cells
are found. These are slender and full of granules, the latter
staining very deeply with hzmatoxylin. The epithelium of the
oesophageal wall of this chamber is, moreover, sharply marked off
from the rest of the epithelium. It is directly continuous with
the cesophageal ectoderm round the lip of the cesophagus, and is
evidently a tract of ectoderm. Any doubt which might cloud
this point is removed by later stages, such as Figs. 44 and 45,
where the epithelium, which is claimed as ectoderm, overlaps, at
its upper limit, the endoderm. It is clear that in this stage, Fig.
18, the cesophageal ectoderm has been reflected round that por-
tion of the lip (free edge of cesophagus) which belongs to the
larger chamber, and has then run up along the outer surface of
the cesophageal tube, driving the endoderm before it. The
direction of growth is reversed, but otherwise the ectoderm is
acting in precisely the way which it chose in forming the first
pair of filaments. In the smaller chamber of Fig. 18, the
epithelium forming the cesophageal wall does not differ from the
rest of the endoderm. Ina later stage, when the third pair of
mesenteries has appeared, the ectoderm is also reflected round
the lips of this chamber, and runs up along the cesophageal
wall, Figs. 36 and 39.

The reflection of ectoderm, which leads to the condition
shown in Fig. 18, commences as soon as the excavation of the
primary (larger) chamber begins, and follows close on the heels
of the latter process. The object of the reflection of ectoderm,
as will be shown later, is to provide filaments for the young
mesenteries before the latter are complete; ze., continuous
from body wall to cesophagus. Bearing this in mind, it is prob-

208 WILSON. [Vot. II.

able that the reason why the ectoderm is reflected into the
primary chamber at such an early date, is that the second pair
of mesenteries will be formed in this chamber. The series of
longitudinal sections, Figs. 20-23, illustrates the early reflection
of ectoderm round the lip of the larger chamber. The larva
from which this series was made was at a stage intermediate
between Figs. 14 and 18. The supporting lamella of both of
the first pair of mesenteries were complete, as in Fig. 18; but
the intermesenterial chambers were far from perfect. The
smaller chamber was entirely solid, and the cavity of the larger
was only partially forméd. In spite of the difference in age, it
will do to refer the planes of the longitudinal sections to Fig. 18.
The section, Fig. 20, thus is taken through the mesenteries 1 and
2, and the corresponding filaments. The next three figures
represent a series of sections to the left of this plane, the one
farthest to the left lying in the plane a—é of Fig. 18. Finally,
the left-hand mesentery in Fig. 20 is the primary mesentery,
I in Fig. 18. With this orientation it is seen, on glancing
through the series 20-23, that only in the neighborhood of the
primary mesentery has the intermesenteric chamber been hol-
lowed out. In all the sections the endoderm is solid on the
right side of the cesophagus. Now, in Fig. 23, the intermesen-
teric chamber (to the left of cesophagus) is in the state in which
it was formed. The ectoderm has not yet been reflected round
the cesophageal lip. But in the sections nearer to the mesen-
tery, Figs. 21 and 22, the ectoderm as been reflected, and has
driven the endoderm before it. The reflection of ectoderm, as I
have said, follows very closely the excavation of this chamber.
As the latter proceeds from mesentery 1 to mesentery 2 (Fig.
18), so does the former; and by the time the chamber is com-
pletely established, the ectoderm is reflected all the way from I
to 2, as Is seen in Fig. 18.

In the larva which was used to show the earliest appearance
of the primary intermesenteric chamber, Figs. 14-16, the re-
flection of ectoderm had already begun to take place round one
edge of the primary oesophageal lobe (Fig. 16, left).

To sum up the more important events described in this
section :

To form the first mesentery the whole cesophagus moves lat-
erally, until in the meridian of the mesentery there is only sup-

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 209

porting lamella between the cesophageal and surface ectoderm,
The cesophagus now grows downward in this meridian as a lobe
of ectoderm, which represents the primary filament, and which
pushes the endoderm before it. On the opposite side of the ani-
mal, along the line of the second mesentery, the cesophagus be-
comes applied to the body ectoderm in the same manner, and a
lobe grows down from it to form the second filament. The
mesenteries as such are formed by the ingrowth of the endoderm
between the body ectoderm and cesophagus above, and between
the body ectoderm and the filaments below. The primary pair
of intermesenterial chambers are at first solid. The larger cham-
ber acquires its cavity before the smaller, the excavation travel-
ling from the lip of the cesophagus upward, and from the first
toward the second mesentery. The excavation of the primary
chamber is closely followed by the reflection of ectoderm into
this chamber, the reflected ectoderm running up the cesophageal
wall, and driving the endoderm before it. The second pair of
mesenteries appear in the larger chamber as longitudinal ridges
of the supporting lamella, which cause no elevation of the endo-
derm.

V. HIsTOLoGY OF THE LARVA.

It may now be advisable to describe the histology of the
larve, going when necessary beyond the stages already studied.

a. The Surface Ectoderm.

The ectoderm at the time when the supporting lamella is
formed, Figs. 5 and 6, consists of columnar cells, the protoplasm
of which shows a great tendency to break into small polygonal
balls. While the ectoderm is in this condition the mucus cells
appear (m, Fig. 6, Figs. 7, 8), as pear-shaped bodies in the
peripheral ends of the columnar cells. The contents of the
pear-shaped body stains a deep blue with haematoxylin, and is
thus distinctly marked off from the surrounding cells. It ap-
pears to be fluid from the start, as even in such young stages as
Fig. 7, many of the mucus cells have poured out their contents,
which adheres to the mouth of the cell as a little mass of a blue
color. This tendency of the mucus cells to eject their contents,
presumably when the killing fluid touches the larva, is very

210 WILSON. (VoL. II.

noticeable in older stages such as Fig. 27, which are often com-
pletely covered by a thin layer of mucus. The mucus cells in-
crease in size and number, until they become the prominent
feature of the ectoderm (Figs. 7, 20, 27). In their final condi-
tion, Fig. 27, they are large, clear sacs, in which a few strands of
protoplasm may be seen in carefully prepared osmic specimens.
The nucleus of the original cell in which the sac developed can-
not be made out in sections.

The mucus cells develop over the general surface of the larva,
but are not found at the aboral end. Here their place is taken
by a slender elongated cell, full of granules which stain even
deeper with hamatoxylin than does the mucus cell. The gran-
ular gland cell is easily recognized in its earliest stage, and is
formed from the embryonic ectoderm cell by a deposition of
granules throughout the length of the cell. The granular cells,
though especially grouped at the aboral end of the larva, are
found here and there over the general surface.

The remaining cells of the embryonic ectoderm become for
the most part transformed into slender ‘supporting cells.”
Thread cells, 7.c., are first noticed in larvz at about the stage
of Fig. 14. Whether the ectoderm contains any muscle cells, I
do not know. The larvz can alter their shape to a great ex-
tent, but the fibres are probably all endodermal.

For the study of nervous elements, J/anzczna in all stages is a
very unfavorable subject. Even the ganglion cells which show
so plainly in sections of actinian larva, I was not able to make
out in the coral. There is, however, a finely granular stratum at
the base of the ectoderm, which is very thin over the general
surface, Fig. 26, but at the aboral end of the swimming larva is
thick and easily seen, Fig. 20. When the living larva is com-
pressed, this accumulation of granular substance is very noticea-
ble. It is perfectly clear, and until I began to section I thought
it was jelly. When carefully examined, the granular layer in
this region is found to consist of a mass of fine fibrils. It is
very probably nervous. The fact that the ccelenterate planula in
general swims with its aboral end in front, taken together with
the occurrence of a bunch of long cilia on this end of many
actinian larve, suggests the existence of some such primitive
nervous centre as I take this accumulation of granular matter
to be.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 211

When the various elements of the ectoderm have been com-
pletely differentiated, Fig. 26 (from a stage a trifle older than
Fig. 29), a finely striated cuticle is secreted, in all respects like
that described by the Hertwigs for the actinias (g. Taf. III.).
The cilia with which the body ectoderm is completely covered,
and with which the cesophagus and filaments are likewise pro-
vided, I have not represented in the figures.

b. Esophagus and Filaments.

The cesophagus and young filaments, Fig. 20, have the same
structure as the superficial ectoderm, except that mucus cells
are absent, and the granular gland cells more abundant than
over the general surface. Asarule it is only in the youngest
stages that the reflected ectoderm, Fig. 18, contains gland cells,
and even then they are rare. In later stages, Fig. 24, mucus
cells are found in the upper part of the cesophagus immediately
round the mouth, and very large thread cells, Figs. 24 and 27,
appear in considerable numbers in the cesophageal epithelium,
extending down into the filaments. The histology of the fila-
ments will be treated in detail in a special section.

c. Endoderm.

The endoderm, after it has once formed, remains about the
same during larval life. I am not sure whether it is ciliated.
The cells are cubical or columnar, and contain one or more large
and distinct vacuoles. The protoplasm is granular and coarsely
reticular. The cell outlines can only be distinguished with a
little care. The number of yellow cells steadily increases with
age. A few very fine muscle fibres can be made out here and
there, especially in the mesenteries, and a continuous layer
probably exists.

In closing, the general similarity between the ectoderm of
the coral larva (practically the same in the adult Manicina) and
the actinian ectoderm, as described by the Hertwigs, may be
noticed. In particular, the two kinds of gland cells in the ac-
tinias are exactly represented in the coral. The Hertwigs sug-
gested that possibly the granular gland cell was but a stage in
the development of the mucus cell; but this appears not to be
the case, as the two are distinguishable from the start, and have
also a different distribution.

212 WILSON. [Vot. II.

VI. MESENTERIES AND FILAMENTS FROM THE SECOND TO THE
SrxtTH PArr.

Before proceeding to the detailed description of the reflection
of ectoderm, which, as I conclude, leads to the formation of all
the filaments except the first pair, it will be convenient to give
an account of the order in which the mesenteries appear.

The first appearance of the second pair of mesenteries has
already been described, Fig. 18. In a later stage, Fig. 27 (trans-
verse section) this pair is complete at the level of the figure.
At a lower level, just above the lip, Fig. 28, one of the pair, 3,
is still complete, while the other, 4, is incomplete. The dif-
ference in growth between the two mesenteries of the second
pair is an exception; they usually develop at the same rate.
Below the cesophagus, Fig. 29, both mesenteries exist as slight
ridges, which extend the length of the larva.

The third pair of mesenteries have appeared in Fig. 27. They
remain insignificant during the swimming life of the larva.
After the larva has become attached, the third pair is promi-
nent ; and the fourth pair is also found, in the position shown in
Fig. 34 (a transverse section taken below the cesophagus — the
primary mesenteries are supplied with large and coiled filaments).
According to Lacaze Duthiers, the fourth pair appears between
the first and second pairs. The Hertwigs suggested (?) on gen-
eral grounds of symmetry that the order of appearance was as I
have figured. As regards the fifth and sixth pairs, however, the
old account of Lacaze Duthiers holds for JJanicina as against
the figures given by the Hertwigs for Adamsia (Taf. 1, f. 3).
This is seen on referring to Fig. 39, a transverse section through
the cesophagus of a stage with twelve mesenteries. The fifth
and sixth pairs develop simultaneously on opposite sides of the
primary mesenteries. In Adamsza, according to the Hertwigs,
the two pairs of mesenteries appear on opposite sides of the
long axis of the cesophagus, in the chambers between the first
and second pairs.

Fig. 39 represents my oldest larval stage, and I was conse-
quently not able to trace the development of the muscle plates
and the rearrangement of the twelve primary mesenteries.
According to the accepted account, the pairs 3 and 4, in Fig.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 213

39, become the directive pairs, and on each side of the long
axis of the cesophagus, 5 and 1 unite to form one pair, and 6
and 2 another pair.

In this connection it may be observed that after the larve
became attached, the lumen of the cesophagus was decidedly
bilateral in the living animal, and bore the relations to the
mesenteries shown in Fig. 39. The shape of the lumen is,
however, susceptible of great changes, and in many of the
sections through attached larve the typical shape is not re-
tained (Fig. 36), or the cesophagus is compressed in the (nor-
mally) long axis, and drawn out in the short (Fig. 45). In the
swimming larva the small size of the mouth will not permit one
to decide as to the shape of the cesophagus in the living animal.
After examining a large number of sections I conclude that in
stages as old as Fig. 27, the arrangements are as in the attached
larva: the lumen is bilateral and has one of the first pair of
mesenteries on each side of its long axis. In earlier stages,
such as Figs. 7, 14, 18, I could not decide whether the cesopha-
gus had acquired its ultimate shape.

We now come to the formation of filaments for the second
and subsequent pairs of mesenteries. In Fig. 18 the reflected
ectoderm which forms the cesophageal wall of the larger cham-
ber extends horizontally from 1 to 2. The mesenteries of the
second pair, 3 and 4, are extremely incomplete. In Fig. 27 these
mesenteries are complete, and now the reflected ectoderm does
not extend from I to 6, but is represented by the patch &.£.
between 3 and 4. In sections of the same larva (Figs. 28 and
29, below the level of Fig. 27) a certain irregularity makes its
appearance, which is connected with the formation of the third
mesentery, and of which I shall speak later. In the typical
larva of this stage the sections below Fig. 27, between it and
the lip of the cesophagus, are precisely like Fig. 27. This
means that the mesenteries 3 and 4 are both complete through-
out the length of the cesophagus, and that the cesophageal wall
of the chambers inclosed between 2 and 4, and 3 and I respec-
tively, is endodermal. At the very lip of the cesophagus in
some larve the cesophageal walls of these chambers are ecto-
dermic. ’ In a section just below the cesophagus it is found
that the mesenteries 3 and 4 have short filaments. Further,
the tract of ectoderm &.£. only extends upwards for about

214 WILSON. [Vo. Il.

one-third the length of the cesophagus, while it will be remem-
bered that in this stage (Fig. 18) the reflected ectoderm extends
nearly the whole length of the cesophagus. Now what has
taken place in the transition of the stage Fig. 18 into the stage
Fig. 27? Plainly it is that the mesenteries 3 and 4, as they
grew down and gradually became complete, carried along with
them the reflected ectoderm, part of which came to lie along
the mesenteries as short filaments, while the remainder was
divided into three portions. Of these, the two lateral, which
originally extended from 2 to 4 on the one side, and from 1 to 3
on the other (Fig. 27), were carried all the way down to the lip
of the oesophagus, while the middle portion &.Z. was not car-
ried the whole way down.

A couple of longitudinal sections will further elucidate the
series of changes which separate Fig. 18 from Fig. 27. The
sections given in Fig. 25 were made from a larva at about the
same stage as Fig. 27. The two mesenteries of the first pair
had long filaments, and the mesenteries of the second pair were
complete and equally advanced. The section @ is a radial half-
section through one of the second pair of mesenteries, say 4 in
Fig. 27. The mesentery is complete, and to its edge clings a
short filament. The other mesentery of the second pair, with
its filament, is the exact counterpart of the one figured (in cut-
ting the larva, radial sections of one mesentery and equally
true transverse sections of the other were obtained). The pre-
cisely horizontal plane in which the filament of 0 lies, is prob-
ably due to the sudden expansion of the larva, on being killed,
in the direction of the shorter transverse axis of the cesophagus
(the transverse section would be elongated in a direction at
right angles to the long axis of Fig. 27). The half-section ¢ in
Fig. 25 is reversed so as to complete the cesophageal lumen.
It is the second section to one side of 4, and a is the second or
third on the other side. Comparing all these figures with Fig.
27, 6 is through mesentery 4, a is on the far side of 4, and con-
sequently cuts the reflected ectoderm #.Z.; ¢ is on the near
side of 4, and the ectoderm is not reflected round the free edge
of the cesophagus.

Fig. 24 is a single longitudinal section from a stage slightly
older than the one just described. On the right it is through
one of the second pair of filaments, and on the left through an

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 218

intermesenteric chamber. Referring the section to Fig. 27,
the right half is through mesentery 4, and the left through the
chamber opposite at about the point x.

Having now described the ordinary way in which the first
and second pairs of mesenteries and filaments are formed, I
will take up an exception, which has more bearing on the rela-
tionship between the Anthozoa and Scyphomeduse. Figs.
30-33 are transverse sections, numbered from above down, of
a larva in which the first pair of filaments extended about half
the length of the body. The cesophagus throughout its verti-
cal extent is apposed to the surface ectoderm over a wide tract,
ato 6in Fig. 30. On running through the series of sections it
becomes evident that the tract a—d is not the meridian of a sin-
gle mesentery, as it would be in a normal larva like Fig, 14,
but is the space between two mesenteries. The first section
below the cesophagus, Fig. 31, shows that a rather wide lobe of
ectoderm is growing down, and also that between a and @ this
lobe has been forced apart from the body ectoderm. In Fig. 32
(two sections omitted between 31 and 32) a lobe of endoderm
‘has grown in between a and 4, and has thus given rise to two
mesenteries, which are provided with a common filament. In
the section below, Fig. 33, the lobe of endoderm is hollowed
out, and the two mesenteries definitely established. In a sec-
tion (not figured) below Fig. 33, the mesenteries @ and 0 exist as
separate ridges, and the common filament has split into its con-
stituent parts, 1 and 3. The filament 3 extends a very short
distance down, and the mesentery 6 only reaches the equator of
the larva. The mesentery a, with its filament 1, is the fellow of
2, on the opposite side of Fig. 32. These two mesenteries
belong to the first pair. I have assumed that a is the primary
mesentery, since its filament is larger than that of 2.

Bearing in mind the normal development as illustrated in
Figs. 12 and 14, the exceptional character of this larva is due
to the fact that one of the second pair of mesenteries is formed
at the same time and in the same manner as the mesenteries of
the first pair. This aberrant member of the second pair, 4, Fig.
30, etc., may be called the third mesentery. We may suppose
that the cesophagus, applying itself to the body ectoderm along
the line not only of the first a, but also of the third mesentery 4,
was unable to force down the endoderm in these lines without

216 WILSON. (Vou. II.

carrying down at the same time the endoderm between a and 4.
Thus came the condition shown in Figs. 30 and 31. When the
time came for the mesenteries as such to be formed, the endo-
derm which had been pushed down between a and 6 was com-
pelled to grow up again, becoming excavated so as to form the
intermesenteric chamber. It is in this process that we see the
endoderm in Figs. 32 and 33. The irregularity of the larva, it
will be noticed, is confined to one side: the right side of the
sections is normal, and doubtless the other member of the sec-
ond pair of mesenteries would have developed in the usual way.

The larva just described was the only young specimen I
observed, which exhibited this peculiar variation. I found a
few older individuals, however, in which one of the filaments of
the first pair was so intimately connected with one of the sec-
ond pair, as to render it probable that the two were simulta-
neously formed from a common lobe in the manner shown in
Figs. 30-33. The larva, Figs. 27-29, to which I have already
referred several times, comes under this head. Though the
section, Fig. 29, is an appreciable distance below the cesopha-
gus, the filaments 1 and 3 are still united, and bear evidence of
their common origin. The other mesentery of the second pair,
4 in Fig. 28, has itself been formed, and is gaining its filament,
in the normal manner. The reflected ectoderm only extends
from 2 to 3, and if the latter mesentery has been formed in the
manner suggested, the ectoderm never was reflected between
3 and I.

Returning to the normal development we have now to trace
the origin of the filaments for the third pair of mesenteries.
These filaments are derived from a lobe of ectoderm, which is
reflected into the smaller of the two primary chambers. The
reflection takes place after the larvee have become attached. In
a stage with twelve mesenteries, Fig. 39, the lobe is marked ~.
The section is taken at a level higher than that reached by the
lobe belonging to the chamber c (marked #.Z. in Fig. 27). In
a section just above Fig. 39 the third pair of mesenteries bury
themselves in the lobe z, much as 4 does in Fig. 28. In the
uppermost sections, where the mesenteries are complete, x is
not found. After a great many trials I succeeded in getting a
radial section through one of this pair of mesenteries, which
had forced down the reflected ectoderm so that the latter lay

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 217

along its free edge as a tiny filament (Fig. 38, left half; the
right half is through chamber c¢, Fig. 39). The lobe for the
third pair of filaments is almost always present in larvze with
eight mesenteries: in Fig. 36, a section just above the lip, it is
marked ¢. In this larva the mesenteries of the second pair are
backward in development ; they are not yet perfectly complete,
though on one of them a very small filament is seen.

As the fourth pair of mesenteries continue to increase in
size, the tract of ectoderm, which belongs to the chamber «¢, in
Fig. 39, extends farther upwards. In Fig. 39 it reaches about
the same level as in Fig. 27 (R.£.). In a slightly more ad-
vanced stage, Fig. 38 (right half), it extends nearly the whole
length of the cesophagus ; and in the series of transverse sec-
tions, Figs. 43-45, it likewise extends to nearly the uppermost.
limit of the chamber. The latter series is a very good one, as
the polyp was killed in its natural shape. In life, when the
young coral is expanded, there is a very distinct oral cone, in-
dicated by the line m-m in Fig. 38. In dying, the oral surface
is almost always retracted, and the median longitudinal section
is then as in Figs. 37 and 38. The transverse section, Fig. 43,
is taken through the line z-y, in Fig. 38. Figs. 44 and 45 lie
above it. In the larva from which the series was taken, both
the third and fourth pairs of mesenteries were very well devel-
oped below the level of z#-y, but above this level they were not
perceptible. Judging from all my other sections I should say
that this rapid development of the mesenteries along the side-
wall of the polyp, as contrasted with their backwardness in
the upper cesophageal region, was exceptional. In the sections
figured the first and second pairs of mesenteries are complete.
The chambers a and 8, together with c, represent the larger
of the two primary chambers. The walls of @ and @ are endo-
dermal except for a short distance above the cesophageal lip, but
in ¢ and in d (the smaller of the two primary chambers) the re-
flected ectoderm extends very far up. As the third pair of
mesenteries lie in chamber ad, the ectoderm of this chamber, as
might be expected, extends farther up than in ¢, in which lie
the fourth pair. In the ectoderm of d there are a few large
nettle cells, a rare occurrence. At the upper limit of each tract
of ectoderm, the overlapping of the layers, previously referred
to, is shown. This overlapping of the layers, while uncommon,

218 WILSON. [Vot. Il.

is noticed in a good many specimens. In Fig. 37 the left half
of the section, through an intermesenteric chamber, exhibits
this phenomenon. The right half of the section is through one
of the second pair of mesenteries.

The fifth and sixth pairs of mesenteries appear simultaneously,
but it is convenient to speak of one pair as the fifth and the
other as the sixth. They are still very small in my oldest larval
stage. The filaments for the fifth pair are probably formed
from the lateral portions of the lobe x, Fig. 39, after it has been
divided by the completion of the third pair of mesenteries.
The filaments for the sixth pair, it seems, will be formed from
the tracts of ectoderm, which belong to the chambers a and 4,
Fig. 39. These tracts, it will be remembered, were in most
larvee pushed completely back to the free edge of the cesopha-
gus, where the second pair of mesenteries become complete.
In stages with twelve mesenteries, however, such as Fig. 39,
they have again appeared, though they usually extend but a
very short distance above the lip. In a couple of larve as old
as Fig. 39, they were unusually well developed, reaching as far
up as the tract for the chamber c.

In summing up the facts of the reflection of ectoderm it will
be convenient to refer to Fig. 39.

The ectoderm reflected into the larger of the two primary
chambers is pushed down by the growth of the second pair of
mesenteries. From it are formed the filaments for these mesen-
teries, while the remainder of the original tract splits into three
divisions. The middle division, chamber c, is not pushed en-
, tirely to the edge of the cesophagus ; later in life, when the
fourth pair of mesenteries is well developed, this tract grows
once more nearly to the upper limit of the cesophagus. The
lateral divisions a and 6 are pushed to the edge, but after the
sixth pair of mesenteries has appeared they begin to grow up
again. When the mesenteries of the third pair are well ad-
vanced, the ectoderm is reflected into the smaller of the two
primary chambers, and runs up the cesophageal wall nearly to
the top of the chamber. The mesenteries, when they begin to
grow down, carry a part of the ectoderm along their free edges
as very slender filaments. The growth of the various tracts of
reflected ectoderm is thus seen to follow in general the order
of development of the mesenteries.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 219

VII. OriciIn OF THE FILAMENTS IN THE ADULT.

After studying the larval development it seems very sure that
the filaments of the first twelve mesenteries are ectodermal.
Further, I think the stage with twelve mesenteries holds the
key to the condition in the adult. In this stage, Fig. 39, etc.,
there are complete (first and second pairs) and incomplete mes-
enteries (third pair), both provided with ectodermal filaments.
Both kinds of mesenteries are exactly comparable with the two
kinds in the adult, and if the incomplete mesenteries of the
larva are successively supplied with filaments by the reflection
and upward growth of the ectoderm, it seems probable that the
incomplete mesenteries of the adult are supplied in the same
manner.

The gap between my series of larval stages and the adult is
partially bridged over by the transverse sections, Figs. 41 and
42. The young Manicina from which these sections were made
was one-eighth inch diameter. I found a couple of about the
same size on a piece of coral rock. In hardening these two
specimens I was not fortunate, and they were consequently of
no value for the study of such fine points as the reflection of
ectoderm. Fig. 41 is through the cesophagus, and disregarding
the skeleton, shows six pairs of complete and six pairs of in-
complete mesenteries. The twelve complete mesenteries repre-
sent the mesenteries present in the larva, now rearranged in
pairs and with simple muscle plates (only shown in the directive
mesenteries). The incomplete mesenteries have appeared ac-
cording to the general law governing the mesenteries above
twelve.

Manicina remains a single polyp until it has reached a diam-
eter of about one-third of an inch. In this condition it has all
the characters of the adult, except those dependent on asexual
multiplication. It is, moreover, not sexually mature. Such a
coral has, disregarding local irregularities, twelve pairs of mes-
enteries of the first order (complete), twelve of the second order
(incomplete), and twenty-four pairs of the third order (much
more incomplete). Fig. 50 gives a median longitudinal section
of the coral at this age. The polyp was in a state of complete
contraction, the oral surface or peristome, Py, pulled down, the
mouth, Mo, widely open, and the tentacles, 7, retracted. The

220 WILSON. [VoL. II.

section on the right is through a mesentery of the first order, on
the left through one of the second order. The line 3 marks the
position of the free edges of the tertiary mesenteries. The
latter are not provided with filaments. On each side of the
section, the mesentery is divided into a central and peripheral
part (R.P.) by the calcareous theca, 7%. (When the animal is
expanded, the peristome is lifted high above the level of the
skeleton. It then embraces the whole width of the animal,
the tentacles forming a dense ring round its edge, while the
mouth is narrowed to a slit-like opening.)

On the right side of Fig. 50 the epithelium of the cesophagus,
cz, is directly continuous with the filament 1, the mesentery
being complete. On the left side the mesentery being incom-
plete, the cesophagus has a free edge. Now if my view is cor-
rect, not only the lining epithelium of the cesophagus is ecto-
dermal, but the epithelium x, which forms the gastric covering
of the cesophagus and peristome between the complete mesen-
teries, is likewise ectodermal: the ectoderm here, as in the
larva, is reflected round the lip of the cesophagus, and extends
upwards until it reaches the secondary mesentery, down which
it courses as the filaments. Fig. 55 is a more highly magnified
view of the lower part of the cesophagus, as shown in the left
half of Fig. 50. The lining epithelium of this part of the
cesophagus, the Jower third, is composed of slender supporting
cells. The upper two thirds contain large nettle cells, and in
the region of the mouth mucus cells. The epithelium on the
outer surface of the cesophagus, is for some-distance (compare
Fig. 55 with Fig. 50) exactly like the lining epithelium, except
that it contains a few yellow cells. Then comes a region of
vacuolated cells, which is followed by a very low epithelium made
up of exceedingly small cells, the exact shape of which I could
not determine. The low epithelium is continued up the cesopha-
gus and over the peristome, and is continuous with the filaments
on the secondary mesenteries. These filaments, though of large
size at a lower level, gradually become very small as they ap-
proach their upper limit, and by this means run without any
break into the low epithelium covering the peristome. The fila-
ments on the third pair of mesenteries in the larva were like-
wise very small in the upper part of their course, though, to be
sure, in my oldest larval stage they as yet only existed in this
part.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 221

The view that the gastric lining of the cesophagus and peris-
tome is ectoderm can only be held by supposing the epithelium
in question to have suffered a great histological change. (It is
possible that a very careful histological examination of the epi-
thelium, x, would show that it does not differ so much from the
ectoderm as appears to be the case.) But though this tract of
epithelium cannot be said to resemble the ectoderm, it differs
quite as much from the undoubted endoderm. The endoderm
of the adult, Figs. 51 and 52, is made up of large irregularly
columnar cells, packed with ‘yellow cells,” the vacuoles present
in the larval endoderm being confined to special localities. The
only apparent alternative to the view offered is that while the
first twelve mesenteries are provided with ectodermal filaments,
the filaments of all subsequent mesenteries are endoderm.
Since the several orders of filaments in the adult differ only
as regards size, and since even this difference is a transient
one, owing to the constant transformation of incomplete into
complete mesenteries during the growth of the coral, it seems
improbable that such precisely similar organs should be formed
by both layers.

On the other hand, E. B. Wilson (8) came to the conclusion
that the dorsal pair of filaments in the Alcyonaria were ectoder-
mal lobes, but that the remaining six filaments were purely
endodermal. The two kinds of filaments in these polyps have,
however, a very different histological structure, with which is
associated a division of labor.

Von Heider (11) several years ago decided that the filaments
of Cerzanthus were ectodermal. He reached his decision by a
histological study of the adult, and though this method is incon-
clusive, I am not surprised after studying myself some immature
specimens of Cerianthus, that he came to this view. The
Hertwigs-in their classical work on the actiniz pointed out that
embryological deductions based on adult histology are not very
reliable, and also brought forward as an objection to von Heider’s
view, the existence of filaments in the actiniz generally on
incomplete mesenteries,

222 WILSON. [Vot. II.

VIII. HisToLoGicAL STRUCTURE OF THE FILAMENTS.

The very young mesenteric filament is shown in cross-section
in Fig. 17. In this larva, the first pair extend about half the
length of the body. In Fig. 29, though the mesentery is ele-
vated above the general endoderm, the filament retains its simple
character. It is roughly hemispherical in section, and is sepa-
rated from the mesentery by a thin sheet of supporting mem-
brane. Besides supporting cells, there are present granular
gland cells. In most larve in which the first pair of filaments
reach the aboral end of the body, the filament is no longer
separated from the mesentery by supporting lamella. Fig. 19
gives a surface view of such a larva, and Fig. 26, a cross-section
of one of the long filaments. In the latter figure the sheet of
supporting lamella, on which the filament formerly rested, has
given place to an accumulation of jelly at the apex of the mes-
entery. Though the cells of the filament are practically con-
tinuous round this gelatinous axis with the cells of the mesen-
tery, the line of demarcation is very evident on each side owing
to the different histological characters of the endoderm and
ectoderm cells. In the filament there are now numbers of large
nettle cells, and the gland cells are far more numerous than in
earlier stages. Nervous elements are very probably present, as
there is a granular stratum in the deepest part of the filament.
As is shown in Fig. 19, the filament increases in size towards
its lower end. Near the close of the swimming life the first
pair of filaments begin to get slightly curved and twisted in the
lower part of their course. The young filament before its cells
become continuous with those of the mesentery, is very loosely
attached to the latter; in a number of cases I observed that the
mesentery and filament had entirely separated from each other
(Fig. 29, Mes. 3), owing, no doubt, to the contraction caused by
the killing fluid.

Fig. 35 is through one of the first pair of filaments, and its
mesentery, of an attached larva with eight mesenteries. In the
attached larva these filaments pursue a straight course for a
short distance below the cesophagus. In the lower part of their
extent, they are curved and twisted as in the adult, and in this
region sections like Fig. 34 are obtained. Fig. 35 is through the
straight portion of the filament. On comparing this figure

No. 2.]| DEVELOPMENT OF MANICINA AREOLATA. 223

with Fig. 26 (magnified to the same degree) it is seen that the
mesentery has become more elevated, and at the same time
thinner ; also, that where the endoderm cells end and the filament
cells begin there has been a pinching in, which, added to the
actual bulging out of the filament, has very distinctly worked
off the latter from the mesentery. The bulging out of the fila-
ment is due to the lateral expansion of the axial jelly shown in
Fig. 26. The expansion of the jelly has so taken place that the
filament, Fig. 35, is divided into three portions: the main body
to which are confined the nettle and gland cells ; and two tracts,
v./, which may be called the ventro-lateral tracts. The latter
are composed exclusively of slender supporting cells. As in
the swimming larva, the filament cells are sharply marked off
from the cells of the mesentery. In spite of the twisted con-
dition of the lower part of the filament, sections show that the
structure is the same as in the upper part.

In the adult the upper portion of the filament on a complete
mesentery is comparatively straight, but the main portion is
twisted, Fig. 50. The filaments of the incomplete, are less
twisted than those of the complete mesenteries. The filaments
are attached their whole length to the mesenteries, there being
no free acontium ; they are, however, capable of extrusion both
through the mouth and (though I could not find the apertures)
through pores (cynclides) in the body wall.

Unlike the larval filament, that of the adult has a different
structure at different levels. Figs. 52, 53, and 54-are sections
through the different parts of a filament on a complete mesen-
tery. Fig. 52 is through the upper third. The filament itself
has almost exactly the shape shown in Fig. 35, but the mesen-
tery is swollen out and forms two lateral lobes, ./., between
which the filament rests. The ventro-lateral tracts are much
better marked in the adult than in the larval filament. This is
due to the continuation of the pinching in process which had
already gone some distance in Fig. 35, and to the outgrowth
of the mesenteric lobes, m./. By these means the slender
“waist” is produced, which indicates the separation of filament
and mesentery.

The ventro-lateral tracts of the filament, both in the upper
portion of its course, Fig. 52, and lower down, Figs. 53 and 54,
are made up exclusively of supporting cells. The main body of

224 WILSON. [Vot. II.

the filament in Fig. 52 contains a large number of granular
gland cells and numerous nettle cells. The mesenteric lobes
are composed of cells which do not differ essentially from the
rest of the endoderm; they are only much elongated and con-
tain a number of very large vacuoles. The passage of the fila-
ment into the cesophageal epithelium is effected in the following
manner. Immediately below the cesophagus, the “ waist” in
Fig. 52 becomes gradually wider until the ventro-lateral tracts
no longer exist, and the filament cells are continuous with the
mesentery cells round the horns, 4, of the supporting lamella of
the filament. At this level, the filament or cesophageal lobe is
much flatter and wider than it is below (Fig. 52), and the sup-
porting lamella of the filament is also nearly flat. The latter
passes directly into the supporting lamella of the cesophagus,
and the filament into the lining epithelium of the cesophagus.

Fig. 53 is through the middle third of the filament. The
gland cells are absent in this region, but the nettle cells are
very large and exceedingly abundant. The mesenterial lobes
are not so well developed as in the region above..

The lower third of the filament, Fig. 54, contains neither
nettle cells nor the typical gland cells. The body of the fila-
ment is here made up of very large granular cells, between
which are scattered a few supporting cells. The granules are
much more numerous in the peripheral than in the central halves
of the large cells, and at the sides of the filament where the
main body passes into the ventro-lateral tracts, they become
gradually restricted to the peripheral ends of the cells. The
granules are chemically different from those in the ordinary
granular gland cell: they do not stain especially well with heze-
matoxylin, but become dark brown with osmic acid. In a
number of filaments these peculiar granular cells contained
large, irregular concretions, which stained dark red with
borax carmine, while the cell body stained but faintly. The
mesenteric lobes in this region are slightly less pronounced
than in the rest of the filament. In a transverse section through
the filament of Sagartia, Von Heider (10) has figured the lat-
eral parts of the simple filament (according to the Hertwigs, the
section is through the acontium) as composed of just such large
granular cells as I have described. The Hertwigs do not speak
of these tracts.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 228

From Fowler’s brief description (15, II.) it would seem that
the filaments of Wadrepora are essentially like those of Manz-
cina. The condition of the specimens, however, as the author
states, did not permit a detailed study.

The filaments on the secondary are somewhat smaller than
those on the primary mesenteries. The mesenteric lobes, too,
are less pronounced, not reaching a development greater than
is shown in Fig. 54. It has been mentioned that in the upper
part of their course the secondary filaments become very small.
Though the diminution in size is so great in this region, that it
was impossible for me to make out the histological structure, I
was able to trace the filament as a darkly staining and compact
mass of tissue into the epithelium of the peristome. The fila-
ments of the young coral, from which Figs. 41 and 42 were
made, were like those of the adult, except that the mesenterial
lobes were less developed.

I did not study the living filaments, but from the histology it
is evident that the function of the ventro-lateral tracts is that of
ciliated bands, while the digestive functions and nettle cells
are distributed over the three portions of the main body of the
filament. The mesenteric lobes I regard merely as a device to
support the filament.

Before comparing the mesenteric filaments of Mancina with
the actinian filament as described by the Hertwigs, I will give
a brief account of the filaments of Cerianthus, this being the
only actinia I have been able to study by way of comparison.
In Nassau harbor the larval or free-swimming Cerianthus
was common. All the individuals I obtained were at about the
same stage of development. They were oval light brown bodies
about one-fourth inch long, and had eight or nine very short,
stubby tentacles. On sectioning the larve, I found they con-
firmed the theory advanced by the Hertwigs (/c.) as to the
mode of origin of the mesenteries. Fig. 49 is a section through
the upper part of the cesophagus. The number of complete mes-
enteries is fifteen. At one end of the cesophagus is the ventral
or directive pair of mesenteries, D.JZ, At the other or dorsal
end are two incomplete mesenteries, 1 and 2, of which the
former is the younger. The mesentery 3 becomes incomplete
not far above the cesophageal lip, and 4 follows its example just
above the lip. From these four mesenteries it may be gathered

226 WILSON. [Vot. II.

that each new mesentery appears along the dorsal meridian
between the two last formed, and in such a way that the suc-
cessive mesenteries come to lie on opposite sides of the dorso-
ventral plane. The directive pair, D.JZ, corresponds to the
directive pair which the Hertwigs have figured (Taf. I., Fig. 8).
These authors state, however, that this pair is the longest of
all, extending to the anal pore. In the young specimens I have
studied, this pair disappears some distance above the pore, and
is exceeded in length by two or three. mesenteries on each side
of the dorso-ventral plane. Von Heider (11) made the discovery,
which the Hertwigs confirmed, that in the adult there is a much
shorter pair enclosed between the two directive mesenteries.
This short pair only extends the length of the cesophagus. It
must appear in stages later than Fig. 49, so that besides the
formation of mesenteries which takes place dorsally, at least
one pair is formed ventrally.

Filaments were found only on the complete mesenteries.
Fig. 47 is from a section just below the cesophagus. The mes-
entery is composed of very large cells with immense vacuoles.

At the edge of the mesentery, just beneath the filament, the
tissue is becoming more compact. This process has gone much
farther in Fig. 48 (from the same mesentery at a lower level).
The whole mesentery, as may be seen by comparing my fig-
ures with Hertwigs’ Taf. VIII., gradually suffers this change as
the animal becomes adult. In Fig. 47 the filament has a cen-
tral body provided with gland and nettle cells, and two lateral
ciliated tracts 7, composed of supporting cells, which are grad-
ually assuming the shape of distinct lobes owing to the subjacent
growth of the jelly. The central body passes directly into the
epithelium of the cesophagus, the lateral tracts becoming indis-
tinguishable from the body of the filament just before the transi-
tion. This figure is but slightly different from the section of
the adult filament given by the Hertwigs. At a lower level,
Fig. 48, the ciliated tracts are no longer found. On many mes-
enteries the filament has almost no connection with the endo.
derm, as in the figure. In such figures as Fig. 48, it need hardly
be said that violent contraction has had much to do with pro-
ducing such complete separation of filament and mesentery;
but this only shows how loose the connection is in early life.
On other mesenteries the filament is continuous at its sides

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 227

with the cells of the mesentery. None of the filaments in these
young specimens of Cerzanthus ran the whole length of the
mesentery. Most of them stopped at about the equator of the
body.

In the actinias, studied by the Hertwigs, the mesenterial fila-
ment in the upper part of its course is in section tri-lobed. There
is a median secretory tract and two lateral ciliated tracts. The
mesoderm extends into each lobe. On all the mesenteries the
ciliated tracts are lost in the lower portion of the filament. On
the incomplete mesenteries the median tract disappears towards
the upper limit of the mesentery, the lateral ciliated bands
remaining. On the complete mesenteries the median tract
merely gets smaller towards the cesophageal end, but does not
disappear.

The description I have given of the filaments of Cerianthus
is, barring slight differences due to age, like the account the
Hertwigs give for this actinia. From this description it is seen
that the filament of Cerzanthus corresponds in the main to a
typical Hertwig filament, such as is on a complete mesentery.
But the lateral lobes, #, Fig. 47, are very small even in the
adult when compared with the lateral wings of the Sagartza
Mament (Fi, Tat. V., Fig. 10).

The filament of M/anicina is a much simpler structure. It is
not trifid, though the mesenteric lobes, m./, Fig. 52, give such
an appearance to the edge of the mesentery. But on referring
to Hertwig’s figure of Sagartia (Taf. V., Fig. 10), it is evident
that the mesenterial lobes of Manzcina do not represent the
ciliated bands of Sagartia. They are totally different histologi-
cally, and do not contain prolongations of the mesoderm. On
the other hand, the ventro-lateral tracts of Manzcina do cor-
respond histologically with the ciliated bands in the Hertwig
filament, and the glandular lobe of the latter is in general
similar to the median stripe of the M/anzcina filament. As I
take it, all three tracts of the Hertwig filament, taken together,
are homologous with the simple filament of J/anzcina. They
must all, therefore, be ectodermal: in the young Cerzanthus,
Fig. 47, the lateral lobes evidently belong to the median lobe,
and are not modified parts of the mesentery; and since the
median lobe at a lower level, Fig. 48, shows its independence of
the mesentery, the conclusion seems to be that the whole fila-

228 WILSON. [Vot. II.

ment is ectodermal. Though the filament of the adult coral is
a much simpler form than the trifid filament, it would be diffi-
cult to derive the latter from the former, owing to the presence
of mesenteric lobes in the coral. It is easy, however, to derive
the trifid from the larval filament, Fig. 35. In this form the
ciliated tracts, v./, and the median secretory tract, are already
differentiated ; to produce the trifid filament it is only necessary
for these tracts to become separated by the division of the
mesoderm into three lobes. By this division, while the median
stripe gains but little, the ventro-lateral tracts are put in a
position where it is possible for them to reach a high develop-
ment.

The number of Actinozoa in which the mesenterial filaments
have been carefully studied is very limited, but from the data at
hand it seems probable that the ancestral filament, like the
filament of the larval M/anzcina, was a simple undivided body,
in which, however, the originally uniform ectoderm had become
split up into three physiologically distinct tracts : a median tract,
in which were concentrated the nettle and glandular elements,
and which embraced most of the filament; and two lateral
ciliated portions which were but slightly developed. The belief
that the division of labor in the Zoanthorian filament dates very
far back, is supported by the existence of a similar division of
labor in the Alcyonaria. But in these polyps, as Wilson (8) has
shown, the functions are not distributed over different parts of
the same filament, but amongst the several filaments. The
dorsal pair are ciliated bands, having no gland or nettle cells,
while the remaining six filaments contain gland and nettle cells,
but have no ciliated tracts.

IX. Tue SKELETON.

Until the time of. Von Koch’s researches the skeleton of the
Madreporaria was regarded as calcified mesoderm. The theca,
or coral wall, according to this view, represented the supporting
lamella of the lateral body wall of an actinia; and where, as in
most corals, the theca was largely uncovered by animal sub-
stance, the explanation was that the ectoderm had atrophied.
In 1879 Von Koch (12) showed that the theca is independent of
the lateral body-wall, and projects into the ccelenteron of the

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 229

polyp in such a way as to divide the cavity and mesenteries into
central and peripheral parts. This conclusion, though not uni-
versally accepted, is, I think, now incontestable. Von Heider
in 1882 (14) published the important observation that the skele-
ton is not only covered by supporting lamella and endoderm,
but that between the calcareous matter and the supporting
lamella is another layer of cells, to which was given the name
of calycoblasts. Von Koch in 1883 (13) made the whole matter
clear by showing that in the young Asteroides the skeleton is
secreted by the ectoderm and is at first entirely outside the
body. The ectoderm of the basal surface of the attached
larva secretes a calcareous basal plate. Radial folds of the
basal ectoderm then grow up between the mesenteries into
the cavity of the polyp, lifting up, as they grow, the supporting
lamella and endoderm. The cavity of the fold is filled with
calcareous matter, which is the septum. The secreting ecto-
derm becomes the calycoblast layer of Von Heider. The origin
of the basal plate and septa is thus clear enough, but Von
Koch’s account of the development of the theca is not satis-
factory. As far as his observations went they appear to have
confirmed his belief, gathered from a study of adult corals, that
the theca is formed secondarily from the septa; the originally
simple septa become bifurcate at their peripheral ends; the
lateral processes of adjacent septa grow towards each other,
pierce the mesentery, and, fusing, form the theca. Von Koch’s
account of the relation of the skeleton to the soft parts in the
adult has recently been confirmed on a number of genera by
Fowler (15) and Bourne (16), though as regards the extra-thecal
part of the ccelenteron Fowler differs from Von Koch in the
interpretation of his sections. From these papers it is also
evident that the Madreporaria exhibit great variety in the
details of the relation between the soft parts and skeleton.
My own very incomplete observations on the skeleton of Manz-
cima are for the most part a confirmation of Von Koch’s state-
ments.

In the newly attached larva, Fig. 37, the ectoderm of the
basal surface is made up exclusively of supporting cells. The
granular cells present at the aboral end of the swimming larva
have all disappeared. Some time after attachment a small patch
of calcareous matter is found on the basal surface, and sections

230 WILSON. [Vou. IL.

through such larve, after the lime has been removed by acid,
give figures like Fig. 38, though in many individuals the ecto-
derm was torn in freeing the larva from the bottom of the dish.
In Fig. 38 the cells of the basal ectoderm radiate toward a com-
mon centre. There seems to be an effort on the part of the
more peripheral cells to share in the secretior. of the central
patch of homogeneous substance shown in the figure. This
homogeneous substance is the animal basis of the nascent basal
plate. It exhibits no structure, but stains deeply with hzema-
toxylin, and in its general appearance impresses one as a very
much thickened cuticle. I was not able to trace the develop-
ment of the skeleton any further.

The fully formed skeleton may very conveniently be studied
in young polyps, which have not begun to multiply asexually.
Ground sections of the skeleton are of some use, but witha
little care the polyps may be decalcified so that the skeletal
layer of tissue retains with great exactness the shape of the
skeleton. Figs. 46, 50, and 56 are from young J/anzcznas about
one-third inch in diameter. Fig. 46 is part of a transverse section
through the line a in Fig. 50 (oe. ec. is the ectoderm of the peris-
tome ; ec. that of the lateral body wall). Were the section complete,
it would show twelve primary, twelve secondary, and twenty-four
tertiary pairs of mesenteries. At this level the secondary mes-
enteries are complete ; a little lower down they are incomplete.

In going down through a series of sections, the tertiaries run
out before the lip of the cesophagus is reached. In Fig. 50 the
line 3 marks the free edge of a tertiary mesentery. The theca,
7h., divides the mesenteries and ccelenteron into peripheral and
central portions. The septa, S., are all entoccelic; 2.2, lie be-
tween the two mesenteries of one pair, and not between two
adjacent pairs. The size of the septa varies with the rank of
the mesenteries between which they lie. On the outer surface
of the theca are the longitudinal ridges, C., or costa, which
appear to be merely the peripheral prolongations of the septa.
The edges of the septa are finely and regularly toothed. This
is shown in the radial section, Fig. 56, which is taken through
one of the coral septa. In Figs. 50 and 56 the relations of the
columella, Co/., to the theca and septa are shown. In the
former figure, through a mesentery on each side and conse-
quently between two septa, a deep depression separates the

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 231

columella from the theca. The primary mesenteries extend to
the floor of the depression ; the secondaries end some distance
above it. The columella is circular in section, and the depres-
sion surrounds it asa trench. But the trench is not continu-
ous, being completely divided in the radius of each primary
septum, as is gathered from Fig. 56, which is taken through
such a septum. In this figure the septum and columella are
directly continuous with each other. The columella in reality
is not solid, as it is drawn in the figure, but is spongy, being
full of portions of the body cavity which it has cut off during its
growth. Whether an originally simple and solid columella is
formed as a central elevation of the basal plate, is an open ques-
tion. But the subsequent growth of the columella takes place
by the constant incorporation in it of the lower portions of the
inner edges of the primary septa. The teeth on the edge of
the septa, and the granulations found on their sides, sufficiently
explain the spongy nature of the columella.

The skeleton inside the polyp is everywhere covered by the
three layers of the body wall, of which the skeletogenous ecto-
derm or calycoblast layer is next the skeleton. In Fig. 46 and
the radial sections these layers are not represented, but they
are shown in Fig. 51, a more highly magnified portion of one of
the peripheral entocoelic chambers of Fig. 46. The superficial
ectoderm is marked ec.; the peripheral parts of the mesenteries
mes. The calycoblast layer covering the costa, or, more ex-
actly, the costal tooth, is as elsewhere a layer of flattened cells.
The skeletal endoderm is likewise very flat, and markedly dif-
ferent from the endoderm of the body wall and mesenteries.
In radial sections the calycoblast layer is found to be continuous
with the superficial ectoderm round the edge of the extra-thecal
part of the polyp, or vandplatte, R.P. in Fig. 50.

That portion of the polyp, &.P., that lies outside the theca,
has been called by Von Heider the randplatte. It has been
claimed (Moseley, 18; Fowler, 15) that this part of the polyp
ought not to be regarded as normally on the outer surface of
the skeleton ; but that when the expanded polyp, which extends
high above the skeleton, contracts, while most of the body is
drawn into the interior of the theca, a portion is pulled down
over the outer surface of the skeleton. However plausible this
belief may be in the case of those adults in which the extra-

232 WILSON. (VoL. II.

thecal part of the polyp is confined to the upper edge of the
theca, it is at once found to be untenable on examining a small
number of young JZanicinae of the size of Fig. 50. In the
polyp, for instance, from which this section was made, the rand-
platte covered more than one-half of the lateral surface of the
skeleton, and this was true both in the expanded and contracted
condition of the animal. Further, in every dozen such young
Manicinas, one or two asymmetrical ones will be found, in
which, while the randplatte is confined to the upper half of the
lateral surface on one side of the polyp, on the other side it
covers the whole wall down to the surface of attachment. What
puts the matter beyond dispute, in this genus at least, is that in
the very young Manzicina, Figs. 41 and 42, the whole skeleton
is practically inside the polyp. I also found two or three older
specimens (single polyps) in which the entire lateral surface of
the skeleton was covered by the randplatte. One of these which
I sectioned, was oval in transverse section, long axis about ? in.;
short axis 1in. The skeleton had a flat surface of attachment,
and was } in. in height. The randplatte (on rather extra-thecal
polyp) in this individual was unbroken, down to the piece of
rock to which the coral was fastened; here its ectoderm turned
in to form the calycoblast layer.

It appears, then, that up to a certain age, which varies much
in individuals, the lateral surface of the skeleton is entirely cov-
ered by the polyp. The transformation of the originally large
extra-thecal part of the polyp into the relatively small rand
platte may possibly take place in many cases gradually, by the
constant dying off of this part of the polyp at its free edge, and
subsequent disappearance of the dead tissue. But in some in-
stances this is not the case. I found a number of small single
polyps in which I first thought the randplatte covered the en-
tire lateral wall of the skeleton, but on looking again, I saw that
a very definite line extended all round the lateral surface at
about the level of the edge of the randplatte in Fig. 50.
Above this line the soft parts looked perfectly healthy, but be-
low it dull and sickly. On sectioning I found that above the
line the randplatte was normal, but that the tissue below it was
a membrane with scarcely a trace of cellular structure and
made up for the most part of plant filaments. In some asym-
metrical specimens the portion of the skeleton left uncovered by

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 233

the randplatte was covered by a precisely similar membrane,
which was marked off from the randplatte by a deep furrow. In
all such specimens the ectoderm of the randplatte was continu-
ous at the edge of the latter with the calycoblast layer. These
peculiar membranes gave every indication of having been origi-
nally continuations of the randplatte; and I conclude that in
the individuals possessing them, the extra-thecal part of the
polyp had remained intact up to a certain time, but that then
the whole lower portion of this part of the animal was cut off
from the general gastric cavity. Deprived of its nutriment, this
portion became membranous, and was infested by plant filaments.
As the coral increases in size, the membranes are shed, leaving
a large part of the theca bare. After the randplatte once be-
comes restricted to the upper part of the skeleton, there is no
more shedding of large pieces of tissue. But as the skeleton is
constantly growing in height, we have to suppose that the rand-
platte as constantly dies at its free edge, unless, indeed, we
assume that the connection between the calycoblast layer and
the skeleton is so slight that the randplatte is merely carried up
with the growing skeleton.

In the young Manicina, Figs. 41, 42 (4 in. diam.), the skele-
ton is very immature, though the various parts of the adult
skeleton can all be recognized. In this specimen there was a
thin, flat, basal plate, uncovered at its periphery by the body
wall. The skeleton above the plate was internal except at the
points a and a‘, where the lower edge of the extra-thecal part of
the polyp was notched, so that at these points the skeleton was
bare for a short distance above the basal plate. Fig. 41 is
through the cesophagus, Fig. 42 is below, and strikes the apex
of the columella. Though some of the septa are still independ-
ent at as low a level as Fig. 42, at a still lower level they all
unite to form a theca, which on the right side of the directive
mesenteries is very slightly developed, but on the left side is
prominent. Two or three of the septa in the region where the
theca is so slightly developed, exhibit the bifurcation of their
peripheral ends which Lacaze Duthiers and Von Koch have
described. In Fig. 42 indications of six primary septa are more
or less evident, and in lower sections where the septa fuse with
the columella they are easily distinguished. There are also six
secondary septa to be made out in Fig. 42. These twelve septa,

234 WILSON. [Vor. II.

which are entoccelic, extend as high and higher than Fig. 41.
Further, in Fig. 42 it is evident that twelve tertiary septa have
started to develop, though only a few of them extend an appre-
ciable distance above the theca. As only twelve pairs of mes-
enteries have been formed, the tertiary septa are temporarily
exoceelic. Transverse and longitudinal sections through such a
polyp as this show very clearly that the growth of the theca is
continuous and from below upwards. Nowhere are two septa
found which actually pierce a mesentery to form the theca, but
everywhere the growing theca pushes the tissues of the mesen-
teries upwards. Where the theca is formed in such a manner
as this, it is out of the question to believe, after Von Koch, that
the radial cracks found in ground sections of the theca are due
to the existence in these radii of the atrophied remains of the
lower portions of the mesenteries.

The costz in Figs. 41 and 42 are very feebly and irregularly
developed. Each septum has, however, three or four teeth
along its outer edge, and also a few on its inner edge. All the
teeth on the outer edge of the septa open directly to the exte-
rior over the side wall of the coral. In Fig. 41 the septum in-
cluded between the near pair of directive mesenteries is cut
just below the point at which it thus opens. Fig. 40 givesa
more highly magnified view of the same septum cut at the level
of its opening. In Fig. 42 a tooth has opened at mm, and another
at z is sectioned just beyond its opening. The apertures are
of good size, and through them the external ectoderm is contin-
uous with the calycoblast layer. This peculiarity of the teeth
is no longer found in JZanzcina after asexual multiplication has
begun, and only a few teeth open to the exterior in single polyps
with the full complement of septa. In one such polyp, however,
all the teeth opened in this way. From this it would seem that
the connection of the calycoblast layer with the surface ecto-
derm at these points is a characteristic of youth which is gradu-
ally lost. It is possible that this peculiarity may have been ac-
quired in order to bind the little polyp and its simple skeleton
firmly together.

X. ORIGIN OF THE ANTHOZOA.

As is well known, the reigning view as to the origin of the
Anthozoa is that advanced by Claus and Haeckel, according to

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 235

which the Anthozoa are descended from hydropolyps with gas-
tric ridges. This hypothesis, which considers the distinguishing
feature of the Anthozoa (and Scyphomedusz) to be the posses-
sion of taenioles, or endodermal ridges (mesenteric ridges), has
recently been attacked by Professor Gotte in a very interesting
paper (17) on the development of the Scyphomedusze (Aurelia).
The author conclusively proves the Anthozoan nature of the
Scyphostoma larva, showing it to possess four complete mesen-
teries and an ectodermal cesophagus. Unfortunately, no obser-
vations were made on the origin of the mesenterial filaments,
which in all probability are ectodermal lobes. Regarding, then,
the Scyphomedusz as an offshoot from the older Anthozoan

Fig. b

Ectoderm represented as made of columnar cells. Endoderm is dotted. Support-
ing lamella left untouched. After Gédtte, Pl. II., Figs. 20 and 24.

stem, Gotte argues that the manner in which the mesenteries
and intermesenterial chambers are formed in the larva of the
former, is directly opposed to the old view of the hydroid origin
of the Anthozoa. The mesenteries and chambers are formed in
the following manner: the planula is bilateral, and the perma-
nent layers are formed before the invagination of the cesophagus
takes place. The latter is invaginated in such a shape that in
the shorter transverse axis of the larva the endoderm is pushed
down, while in the other transverse axis two endoderm sacs are
formed. The woodcut, Fig. 1, is a transverse section of this
stage, through the cesophagus, and Fig. 2 is a longitudinal section
through the shorter transverse axis. In a subsequent stage,

236 WILSON. [VoL. II.

two endoderm sacs grow up from the ceelenteron in the shorter
axis, and the cesophagus is then surrounded by four sacs. The
sacs are the intermesenteric chambers, and their partition walls
form the mesenteries. Gétte concludes that in this develop-
ment there is no stage which corresponds to the hypothetical
hydropolyp ancestor. The young Scyphostoma itself, which
has hitherto been regarded as a hydropolyp with tzenioles, is in
reality an Anthozoan with four complete mesenteries ; and the
development previous to the Scyphostoma does not pass through
a hydroid stage, but, on the contrary, jumps directly from a
hollow planula to the larva provided with two (later four) endo-
dermal sacs. This larva is called the Scyphula, and from Kow-
alevsky’s account of the development of Cerzanthus (4), Godtte
believes it to be common to both the Scyphomedusze and An-
thozoa, and consequently an ancestral form. In Cerzanthus
according to the abstract given by Hoffman and Schwalbe of
Kowalevsky’s paper, the cesophageal invagination does push
down the endoderm along two opposite meridians; but though
the abstract is not definite on this point, the implication is that
the meridians are those of future mesenteries. If this is so,
Cerianthus agrees essentially with Manicina, and not with
Aurelia.

The ancestral Scyphula form was derived, according to Gotte,
directly from the hollow planula, the invagination of the cesoph-
agus necessitating the simultaneous formation of endoderm
sacs. The infra-cesophageal mesenteric ridges, from this point of
view, are not of any phylogenetic importance, and have nothing
to do with the endoderm ridges of Tubularian or Siphonophore
polyps; they have come into existence merely as the after-result
of the formation of endodermal sacs. This theory contains in
itself an obvious difficulty: the sudden and direct transforma-
tion of such a simple form as the planula into such a complex
form as the Scyphula. What could have caused this complex
group of changes, Gétte does not suggest. But aside from this
objection it seems clear that the development of Aurelia is a
highly modified form of the development of Manzcina, and the
manner in which this peculiarly symmetrical modification was
brought about is suggested by the variations shown in Figs.
30-33.

If Fig. 30 is compared with the woodcut Fig. 1, it is seen that

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 237

as far as the left halves of the sections are concerned, they are
identical in all essential respects. In each the cesophagus is
opposed to the surface ectoderm along -the meridians of two
adjacent mesenteries (a and 4, I and 3), and also over the interven-
ing tract. In a later stage an endoderm lobe grows up between
aand 6 in Fig. 30, and between I and 3 in the woodcut, and in
each this lobe becomes an intermesenteric chamber. If, now,
in the larva, Figs. 30-33, the right side had followed the exam-
ple of the left, that is, if the second and fourth mesenteries had
been formed in the same manner as the first and third (@ and 8),
there would have resulted an exact counterpart of the condition
in the Aurela larva.

The four mesenteries of Scyphostoma would thus seem to
correspond to the first and second pairs of mesenteries in
Manicina. We may suppose that in the primitive Scyphostoma
the mesenteries were usually formed in the gradual way which
is normal in Manzczna, but that the Scyphostoma had inherited
from the parent stock (probably Anthozoa with a large number
of mesenteries) a tendency towards the variation illustrated in
Figs. 30-33, and that this variation gained ground and finally
became the normal process. There is, of course, an alternative
to this hypothesis, namely, to regard the variation found in
Manicina as a case of partial reversion to the ancestral condition
as presented by Aurelia. But the derivation of the Anthozoa
from such an ancestor as the young Scyphostoma (or Scyphula
with four endoderm lobes) is beset with the greatest difficulties ;
for instance, the formation of the first before the second mes-
entery, and the very general occurrence of a primary tentacle
in actinia larvae and in the Scyphostoma itself. Moreover, the
Scyphula larva has not been found in any Anthozoa, unless,
indeed, the case of Cerianthus be really, as Professor Géotte
seems to have considered it, similar to Aurelia.

Having shown that it is possible to derive the so-called Scy-
phula larva from the larva of Manicina, and that it is conse-
quently in all probability an instance of secondarily acquired
symmetry, I consider Gétte’s objection, based on the existence
of this larva, to the hydropolyp ancestry of the Anthozoa, as no
longer valid. The question whether or not the Anthozoa are
descended from hydropolyps must be argued out on the ground
of some more primitive Anthozoan development, such as that

238 WILSON. [Vot. II.

of Manicina. And here it is at once seen that, contrary to
Gotte’s idea, the invagination of the cesophagus does not
necessitate the formation of endodermal sacs. In Figs. 5
and 7 the cesophagus is already formed, but is still surrounded
on all sides by endoderm. The apposition of the cesophagus to
the surface ectoderm along the lines of the first and second
mesenteries takes place later; and though, since this process
occurs in the Scyphomedusz as well as the Zoantharia, it must
date very far back. Iam inclined to believe it was secondarily
acquired and was not a peculiarity of the primitive Anthozoa.
This belief is supported by the entire absence of the process
in the Alcyonaria (Wilson, 3). The explanation of the process
is possibly connected with the early development of the first
pair of filaments.

BALTIMORE, March 25, 1888.

No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 239

LIST OF REFERENCES.

. Lacaze Duthiers. Developpement des Coralliaires. Arch. de Zodl. Exp. T., II.

1873.

. Metschnikoff. Embr. Studien an Medusen. Wien, 1886.
. Wilson, E. B. Development of Renilla. Phil. Trans., 1883.
. Kowalevsky. Unters. ii. Entwick. d. Coelenteraten. Nachrichten d. kais. Gesell.

d. Freunde, etc., Moskau. Vol. X. (Russian.) Abstract in Hoffman &
Schwalbe, 1873.

. Jourdan. Zoanthaires du Golfe de Marseille. Ann. des Sc. Nat. T., X. 1879-

1880.

. Claus. Unters. ii. Charybdea marsupialis. Arb. aus dem Zool. Inst. Wien, 1878.
. Wilson, H. V. Structure of Cunoctantha oct. in Adult and Larval Stages.

Studies fr. Biol. Lab. Johns Hopkins Univ. 1887.

. Wilson, E. B. Mesenterial Filaments of the Alcyonaria. Mitt. Zool. Sta.

Neapel. Bd. V. 1884.

. Hertwig. Die Actinien. Jena, 1879.

Von Heider. Sagartia troglodytes. Sitzungsber. d. kais. Akad. zu Wien. Bd.
75, Abth. 1. 1877.

. Von Heider. Cerianthus mem. Sitz. kais. Akad. Wien. Bd. 79, Abth.1. 1879.
. Von Koch, Bemerk. ii. das Skelet d. Korallen. Morph. Jahrb. Bd. V. 1879.
. Von Koch. Entwick. d. Kalkskelettes von Astroides calycularis. Mitt. Zool.

Sta. Neapel. Bd. 3. 1882.

. Von Heider. Die Gattung Cladocora. Sitz. kais. Akad. Wien, 1882.
. Fowler. Anatomy of the Madreporaria, I., II., II]. Quar. Jour. Micr. Sc.

1885, 1886, 1887.

. Bourne. Anatomy of Fungia. Anatomy of Mussa and Euphyllia. Q. J. Micr.

Sc. 1887.

. Gétte. Entwick. d. Aurelia aurita und Cotylorhiza tuberculata (Abh. z. Entw.

d. Th., 1V.). Hamburg and Leipzig, 1887.

. Mosely. Remarks upon Some Specimens of Sections of Coral. Proc. Zodl. Soc.

London, 1880.

240 WILSON.

DESCRIPTION OF THE FIGURES.

In the larvze, the supporting membrane is represented as a heavy black line; the
jelly, where present, as light brown. In the adult, and in the complete section of
Cerianthus, the supporting substance is uncolored. All the sections were drawn with
the camera. Zeiss lenses are referred to, and the figures are reduced to one-half the
size of the original drawings.

The following letters have been used uniformly in the figures : —

c.b, Calycoblast Layer. Oe. (Esophagus.

C. Costa. Py, Peristome.

Col. Columella. RP. Randplatte or Extra-thecal Part of
D.M. Directive Mesenteries. Polyp.

ec. Ectoderm. S. Septum.

en. Endoderm. T. Tentacle.

Mo. Mouth. dT Aeenbneca:

Mes. Mesentery. Ud, Ventro-lateral Ciliated Tracts.

Ml. Mesenterial Lobes.

DESCRIPTION OF PLATE I.

Fic. A. Corallum of a Manicina colony, viewed from above. Natural size.

Fic. B. Side view of same, to show the pedicel. The randplatte extends but a
short distance below the rim of the theca; its lower limit is marked by a slight accu-
mulation of irregular lamine.

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242 WILSON.

DESCRIPTION OF PLATE II.

Fic. 1. Section through a blastosphere. C, 4.

Fic. 2. Section through delaminating blastosphere. C, 4.

Fic. 3. Part of another blastosphere such as Fig. 2. D, 4.

Fic. 4. Median long. sec. through a solid planula with commencing cesophagus.
Cia: ;

Fic. 5. Long. sec. through a larva in which the permanent layers are forming.
Core
Fic. 6. Long. sec. of slightly older stage. Position of cesophagus is eccentric.
Cra:

Fic. 7. Trans. sec., through cesophagus, of larva at about the stage of Fig.5. The
formation of the permanent layers is not so far advanced as in the latter figure. D, 4.

Fic. 8. Long. sec. through a larva in which the cesophagus has opened cen-
trally. D, 4.

Fic. 9. Trans. sec. through a larva in which the cesophagus is still more eccentric
than in Fig. 8. The section is through line @ in Fig. 8. D, 4.

Fic. 10. Trans. sec. of same larva at lower level, through line 4 in Fig. 8. D, 4.

v 7?

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244 WILSON.

DESCRIPTION OF PLATE III.

Fic. 11. Trans. sec., through lowest part of cesophagus, of a larva in which the
cesophagus along its whole length is apposed to the surface ectoderm. D, 4.

Fic. 12. Long. sec. of larva at about the same stage as Fig. 11 in the plane of the
first two mesenteries. D, 4.

Fic. 12’. Median long. sec. of a larva, in which the cesophagus is applied to the
surface ectoderm along the lines of the first and second mesenteries. An older stage
than Fig. 12. D, 4.

Fic. 13. A section to one side of Fig. 12, through future intermesenteric cham-
bers:, (D) 4.

Fics. 14, 15, 16,17. Series of transverse sections, numbered from above down
(Fig. 14 is through the cesophagus), from a larva in which the first pair of filaments
and the first mesenteric ridge are present. Along the line of mesentery 2, the cesoph-
agus is still applied to the surface ectoderm. D, 4.

Fics. 18, 18@. Trans. sec., through cesophagus, of a larva with two complete
mesenteries and a pair of filaments. Fig. 18 @ is the upper of the two. D., 4.

Fic. 19. Surface view of balsam preparation. The larva has two long, and one
(possibly two) short filaments. C, 2.

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246 WILSON.

DESCRIPTION OF PLATE IV.

FIGs. 20, 21, 22, 23. Series of long. sec. from a stage somewhat younger than
Fig. 18. Fig. 20 is through the first pair of mesenteries and filaments; Fig. 23 is
through the line a, 4 in Fig. 18; and the other sections fall between. C, 4.

Fic. 24. Long. sec. through a larva such as Fig. 19; on the right, through one of
second pair of filaments, on the left through an intermesenteric chamber. D, 4.

Fic. 25. From a larva with two long and two very short filaments, a, 4, c, are
three half-sections from the same side of the larva. 4 is through one of second pair
of mesenteries with its filament; @ and 4 are on opposite sides of this mesentery. D, 4.

Fic, 26. Trans. sec. through one of primary pair of filaments and mesenteries of
a stage like Fig. 19. F, 4.

Fics. 27, 28, 29. Series of trans. sec. from a larva like Fig. 19. Fig. 27 is through
the cesophagus, 28 is just above the lip, and 29 is below the cesophagus. The sec-
tions are very slightly oblique. The third pair of mesenteries exist as longitudinal
ridges of the supporting lamella. .Z. is the reflected ectoderm. D, 4.

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248 WILSON.

DESCRIPTION OF PLATE V.

Fics. 30, 31, 32, 33. Series of trans. sec., numbered from above down, from a
larva with two pretty long (half the length of larva) and one very short filament.
The first and third filaments have been formed from a common lobe, and the third
mesentery (4) has been formed at the same time and in the same way as the first (a),
1D Ae

Fic. 34. Trans. sec., below cesophagus, of attached larva with eight mesenteries.
185

Fic. 35. Trans. sec. through upper part of one of the primary filaments of an
attached larva. The large clear cells are nettle cells. F, 4.

Fic. 36. Trans. sec., through cesophagus, of attached larva with eight mesenteries.
The second pair of mesenteries is not quite complete, and consequently at this level
(just above the lip) the reflected ectoderm is found all round the cesophagus. B, 4.

Fic. 37. Long. sec. through attached larva; on the right through one of second
pair of mesenteries, on the left through an intermesenteric chamber. C, 2.

Fic. 38. Long. sec. through attached larva in which the basal plate has appeared;
on the left through one of third pair of mesenteries with its filament, on the right
through an intermesenteric chamber. The line m, m indicates the outline of the
polyp when expanded. C, 2.

Fic. 39. Trans. sec., through cesophagus, of attached larva with twelve mesen-
teries. B, 4.

Fic. 40. A more highly magnified view of one of the septa of Fig. 41 (that lying
in the near “directive” chamber), sectioned at the level of its opening. ¢.d. is the
calycoblast layer.

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DESCRIPTION OF PLATE VI.

Fic. 41. Trans. sec. through cesophagus of young Manicina, iin. diam. D.JZ,
the directive mesenteries. X, 60.

Fic. 42. Section of same specimen, below cesophagus. Skeleton is bare at a and
a’. The tip of the columella lies in the ccelenteron. X, 68.

Fics. 43, 44, 45. Series of trans. sec., numbered from below upwards, through
the oval cone of a larva like Fig. 38. Fig. 43 is through the line x, y in Fig. 38.
Only the first two pairs of mesenteries extend into the uppermost part of the ccelen-
teron. The overlapping of the reflected ectoderm and endoderm is well shown. D, 4.

Fic. 46. Part of a trans. sec. of adult single polyp, through line a in Fig. 50. The
ectoderm of the peristome is marked oe.ec.; that of the lateral body wall, ec. X, 30.

Fic. 47. Trans. sec. of filament and mesentery of a larval Cerianthus. Level of
section is just below the cesophagus. m is the commencing ciliated band (flimmer-
streif). F, 2.

Fic. 48. Section of same filament lower down. The violent contraction has
caused the halves of the mesentery to spring apart, leaving the coagulated supporting
lamella partially free. F, 2.

Fic. 49. Trans. sec., through cesophagus, of a larval Certianthus. D.M., the
(larval) directive mesenteries. The numbers 1, 2, 3, 4, mark the four youngest mes-
enteries, in the order of their age, I being the youngest. X, 60.

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252 WILSON.

DESCRIPTION OF PLATE VII.

Fic. 50. Median long. sec. through an adult single polyp; on the right through a
primary, on the left through a secondary mesentery. The line 3 marks the position
of the free edge of a tertiary mesentery. The surface of attachment was irregular,
but the corallum extended only a very short distance below the limit of the skeleton
in the figure. X, 30.

Fic. 51. One of the extra-thecal entoccelic chambers of Fig. 49 more highly mag-
nified. Jes. is the peripheral portion of a mesentery.

Fics. 52, 53, 54. ‘Trans. sec. of an adult primary filament. Fig. 52 is through the
upper, 53 through the middle, and 54 through the lower portion. The large clear
cells in Fig. 53 are nettle cells. D, 4.

Fic. 55. A more highly magnified figure of the lower portion of the cesophagus,
as shown in the left halfof Fig. 50. Oe.ec. is the lining epithelium of the cesophagus.

Fic. 56. One-half of a median long. sec. of an adult single polyp. The section is
through one of the primary septa. X, 30.

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mie STRUCTURE. AND. DEVELOPMENT OF) THE
VISUAL. AREA IN THE TRILOBITE,
PHACOPS RANA, GREEN.

By JOHN M. CLARKE.

To students of the fossil Arthropoda it should be a matter
of congratulation that so great success has been achieved by
paleontologists in solving the problem of anatomy and develop-
ment in the extinct crustacean order, the Trilobita. Though
much may remain to be done, too great esteem cannot be
accorded to those who have contributed to what has been ac-
complished ; Eichwald, Burmeister, Volborth, Quenstedt, Rich-
ter,! Barrande, Hall, Billings, Ford, Walcott, Woodward, Mickle-
borough, Matthew, Packard. To the labors of these men is due
our knowledge of the development of the trilobite from the
ovum to maturity; of its delicate locomotive and respiratory
apparatus ; and somewhat of its reproductive, alimentary, and
muscular anatomy.

The present paper endeavors to throw some light upon the
structure and development of the eye in atypical representative
of an extensive group of trilobites, Phacops rana, Green. In
the study of this organ abundant material consisting of several
thousand specimens has been accessible, in the majority of in-
stances only those being utilizable in which the lenses of the eye

1 It may be well to call attention to the fact that Richter’s single observation upon
the ventral anatomy of Phacofs, which has been overlooked by later investigators, is
of much greater significance than the author himself accorded it. In the Beitrag zur
Paléontologie des Thiiringer Waldes, 1848, Pl. 2, Fig. 32, is given an enlarged view
of a transverse section through one-half the thorax of a De-
vonian Phacops (species not given). As this work may not ley oi x
be generally accessible, the figure is here reproduced; and -
although the author states (of. cit. p. 20) that the section
serves to establish Burmeister’s conception of the ventral anatomy of the trilobite,
in the light of Walcott’s demonstration of the spiral branchiz in Calymene senaria
it appears that what is represented here is a section of one of these appendages. I
may add that I have also detected evidence of these spiral branchiz in Phacops rana,

254 CLARKE. [ VoL. II.

have been so perfectly retained as to allow of enumeration.
These specimens have been derived from the shales and lime-
stones of the Hamilton group at various localities in Western
New York, those best adapted for the purpose of sectioning
being from the basal limestones near Centerfield, Ontario
County.

THE CHARACTER OF THE VISUAL AREA in the trilobites is
twofold; (a) it may be covered by a smooth, continuous epi-
thelial film or cornea, through which the lenses of the ommatidia
are visible by translucence, and (6) the cornea may be transected
by the protrusion of the sclera! and limited to the surfaces of the
ommatidia. To the first group belong species of the genera
Asaphus, Ilenus, Calymene,* Homalonotus, Proétus, Cyphaspis,
Acidaspis, Lichas, and others; to the second, the single exten-
sive family, Phacopide, with its genera, Phacops and Dalma-
nites (? Harpes,; vide conclusion). The first group may be des-
ignated by the term /olochroal ; the second group by the term
Schizochroal,

PHACOPS RANA is one of the most abundant and characteristic
species of the Hamilton faunas. Though widely distributed in
the formations of this age throughout the United States and
Canada, it is not known with certainty to have been present in
faunas older than those of the Hamilton, and it does not appear
to have continued its existence after the displacement of the
Hamilton faunas. A detailed and very complete description of
the species, accompanied by copious illustration, is given in the

1] have found the term ommatidium, proposed by Carriére for the little eyes or
ocular elements in the compound eyes of Arthropods and Mollusks, a very convenient
and significant term, but may use it with a little license, as I do not regard the eyes
included in the second of the above groups as properly compound. ‘The term
sclera as here used may be open to some objection. It is applied to the interstitial
test between the ommatidia, and is preferable to the expression cornée opaque of Bar-
rande.

2 Professor Edward Orton, of Columbus, Ohio, has allowed me to examine a very
young individual of Calymene senaria in which the lenses are relatively very large,
and are strongly suggestive of the character of the lenses in Piacops, although in the
adult of this species they are so small as scarcely to be detected. This specimen
suggests the query whether in the holochroal eyes the lenses may, with the advanc-
ing growth of the animal, become apparently smaller, from close juxtaposition or
other cause, and also indicates the possibility that the difference in the holo- and
schizochroal eyes is not as great as it now appears.

No. 2.] EYES OF ARTHROPODS. 255

monograph of North American Devonian crustacea, constituting
Volume VII. of the Palaeontology of New York. In this place
are also to be found satisfactory figures of the eye in various
modes of preservation.

COMPOSITION OF THE VISUAL NODE.

The eye is composed of the visual surface, which is normally
a lunate segment of the surface of a cone, but often in senile
individuals is inclined to sphericity; this surface is buttressed
on the glabellar side by a strong palpebral lobe, which is pro-
duced to and slightly beyond the upper edge of the visual sur-
face, forming a distinct palpebrum. The lower edge of the visual
surface is bordered by a ridge, which becomes broader and more
conspicuous outwardly, and may be called the orbital ridge.

The lenses as seen from the upper surface are convex, some-
times being translucent, especially when they have been filled
with crystalline calcite, or have been slightly separated from the
matrix; they are circular in outline, although the cavities in
which they lie (/ensal pits) appear in old individuals to be hex-
agonal. This appearance is due to the undiminished growth
beyond maturity of the sclera, which crowds upon and overlaps
the edges of the lenses on all sides, deepening the lensal pits.
The general arrangement of the lenses is in alternating vertical
rows or quincunx. For convenience, however, in the accom-
panying statements of enumeration, the lenses are regarded as
arranged in diagonal rows parallel to the lower posterior margin
of the visual surface, and are numbered from this line consecu-
tively. It appears probable that this is also the order followed
by nature in increments to the number of lenses, from the time
of the formation of the primary row of ommatidia (vide seq.)
onward to maturity. Under this arrangement the last row in
enumeration is that ending in the upper anterior angle of the
visual surface.

Lhe number of these rows 1s variable, in the majority of cases
being zzve, in comparatively few individuals of average size and
richly supplied with lenses, being ¢ez, in extremely rare instances
eleven, only a single example of average size showing so many;
in very young individuals the number of rows is but e¢gz. The
youngest specimens observed show no less than this number,
and it seems probable from other considerations that in still

256 CLARKE. [VoL. II.

<

earlier stages of growth the number of diagonal rows was not
much less than eight.

The number of lenses constituting the visual surface of each
eye ts variable, but not trregularly so. The smallest number
noted is thirty-three, in a very young individual having but ezgh¢
rows; the greatest is eighty-eight, occurring in the single
example mentioned, which bears e/even rows.

Again, the number of lenses in successive rows is variable,
but only so within certain well-defined limits. . In order to make
this point clear, the following ten enumerations are presented,
taken at random from a list of above three hundred tabulated
eyes.

ef
3
<
tal
a
1
2
3
4
5
6
7
8
9

Oo woDwnwno wad 6 ©
Cor Go’ Oi, Ov Gy Oo Ox Co => ON
NaF PHB DTH DA VF
bh BN NHN N fF NY HH WN

=
i)
x
[o)

It appears from this table that whatever may be the total
number of rows in any eye, in the last four rows of lenses, and
generally in the fourth from the last, the number of lenses is
subject to very little variation, while the number in the first two
or three rows may vary greatly. This variation is partially
explained by the following fact: It will be found upon examina-
tion of an average eye that the anterior edge is normally nearly
vertical ; the vertical row following this edge is composed of
four lenses. It is impossible for any lenses to be added to the
anterior extremities of the diagonal rows terminating at this
anterior margin, for new lenses are added only from the lower
and upper margins of the visual surface (see further on). In

ee

a

No. 2.] EYES OF ARTHROPODS. 257

immature eyes a greater variation is noticeable in the last rows,
as seen in the following examples of surfaces bearing but ezght
rows of lenses.

Gi st 4 De hep idea See aie a 35
(2) Ay! Me ae he) Se eee Ve 33
(C) Re PR MR BR ie) ie Tea 41
(4) COIN. See Ce CR OP NS RR Cee 42

In these instances the eye has not attained its full growth in
height, which would preclude variations in the last rows. ,

Conversely, as the first four or five rows of lenses terminate
on the lower margin of the visual surface, and as additions to
the number of lenses are made most abundantly from this area,
the number in these rows is constantly varying. It may be
here stated, that with the exception of the right and left eyes of
the same individual, no two eyes in all the specimens enumerated
have shown the same number of lenses in all corresponding
rows.

A definite relation exists between the number of lenses of the
eyes and the size (t.e. age) of the animal, This fact has been
established by recording with each enumeration of lenses a
single measurement which would serve as an index of the stage
of development attained by the animal. The measurement
taken is the basal width of the cephalon. Phacops rana is rarely
found with all the parts in articulation, and still retaining the
lenses with sufficient distinctness for enumeration. Detached
cephala are abundant, and it serves every purpose to take the
indicial dimension from this part of the animal; it is, moreover,
found that the peculiar form of the cheek renders this dimen-
sion of the head less liable to variation from flattening in the
shales than the longitudinal measurement. Comparison of all
the specimens enumerated gives the following results :—

The average number of lenses in individuals having a cephalic
width less than

TO mm. is 44
Between 5 and 15 mm. is 56.5
“ 10 and 20 mm. is 69.5
ft and\or mim is 92
20 and 30 mm. is 71
« 25 and 35 mm. is 66

258 CLARKE. [VoL. II.

Between 30 and 40 mm. is 62.5
Vee and’ 45 ina. s G2r6
From 40 mm. upwards, 58

The calculated average basal cephalic width in this species,
deduced from measurement of 1518 cephala, is 22.8mm. The
material from which this average is derived was unselected,
much of it collected without reference to quality or size, and is
fairly representative. I therefore venture the statement that
the average Phacops rana has a width across the posterior
margin of the cephalon of approximately 22.8 mm.

It is, moreover, probable that 22.8 mm. is approximately the
dimensional index for the average normal adult of this species.
In all specimens of the entire animal which have passed under
observation, varying in axial length from Io mm. to 100 mm., no
evidence has appeared of any developmental change in the suc-
cessive stages of growth, except in the increase and diminution
of the number of corneal lenses. Save in this one respect the
species assumed all the features of maturity at a very early
point in its history; and the data given above conclusively
indicate that in this feature, also, maturity was attained with
this stage of growth. The important conclusion here drawn is
that the number of lenses increases from youth to maturity (di-
mensional index approximately 22.8 mm.), axd decreases from
maturity to senility.

Two questions immediately arise from this inference; (2) how
is the number of lenses increased? and (4) how is it diminished ?
These points will be adverted to in a following section.

STRUCTURE OF THE LENS.

Sections across the visual surface show that the lenses are
unequally bi-convex, the curvature being greatest on the proxi-
mal surface. This inferior surface is perforated by a central
circular aperture. Vertical sections of the lens when favorably
preserved, also show this envelope as a simple, thin, distinctly
black or brown corneous film; and in natural casts of the inter-
nal surface of the visual area, the ommatidial cavities are repre-
sented by a series of shallow cups standing on short pillars, and
each bearing at its centre a little ball, which is the filling of the
interior of the lens. These lenses are consequently corneal and

No. 2.] EYES OF ARTHROPODS. 259
hollow. It appears, also, in sections that zz the mature lens the
cornea is discrete from the sclera, lying in juxtaposition with
and held in place by it, but in nowise continuous with it. This
fact is also frequentiy apparent in specimens from which the
sclera has been removed by solution, leaving the corneal lenses
standing on little pillars of the matrix, which has filled the
ommatidial cavities. Other specimens just as frequently show
the converse, the lenses being removed, while the sclera is
retained. There is evidence which I deem worthy of considera-
tion, that these corneal lenses, during the life of the animal,
were not empty, but filled possibly with some viscid or spissate
humor. This evidence is of the following character :—

The cornea itself is thin, and of even calibre throughout its
extent. The casts of the corneal cavities, such as are shown in
Figs. 25 and 26, as little balls lying in cups, are not of sufficient
size to have occupied all the space within the cornea. A speci-
men of Phacops of a species closely allied to vana (Ph. cristata
var. pzpa Hall), from the decomposed phtanite of the Cornifer-
ous limestone, seems to demonstrate this fact. This fossil
was evidently originally preserved in calcic carbonate, which
not only replaced the entire crust, but filled the ommatidial
cavities, and the posterior cavity of the corneze as well. This
calcic carbonate was subsequently removed from within, and
its place partially taken by silica, and when exposed to more
rapid decomposing agencies, the remainder of the calcic car-
bonate was removed, leaving the fossil so preserved that
the cornea and a thin film over the entire external surface
of the sclera has been taken away, the remainder of the test
being replaced by silica. The external surface of each lensal cast
remains convex, but on carefully removing a little of the decom-
posed rock from beneath the position of the cornea a vacant
space appears, which corresponds to the corneal cavity as repre-
sented by the ball-in-cup casts. To elucidate this point, see
Plate XXI., Fig. 5, and explanation thereof.

Again, certain well-preserved sections from the limestone
show a distinct difference in the character of the matrix fill-
ing the outer and inner cavities of the cornea, that in the outer
being of lighter color, and more translucent (? subcrystalline),
while that in the inner is the opaque mud of the sediment.
More evidence upon this point is very desirable, but enough

260 CLARKE. [Vot. II.

has been seen to indicate the fact that the cavity of the cornea
was not szmple, but compound. (May the posterior cavity-fillings
represent the position of the anterior extremities of crystalline
cones ?)

MULTIPLICATION AND DIMINUTION IN THE NUMBER OF
LENSES.

The lenses of the visual surface are not all of the same size
in any of the stages of growth observed. The size of the fully:
developed lens varies according to the individual development
of the animal; z.¢., the larger the animal, the larger the lenses ;
but in any given subject some lenses are to be found which are
below the average of size for that eye. These small lenses are
found at the extremities of the diagonal rows which terminate
on the posterior portions of the upper and lower margins of the
visual surface.

The inferior size of these lenses is due in part to unlike causes.
Of these the principal cause is (a) that they are new and imma-
ture lenses added in regular order to the ends of the rows of
older lenses. It has not been as yet satisfactorily determined
whether the increment of new lenses may take place at either
upper or lower extremity of the diagonal rows, although the
small lenses occur indifferently at either end. There is no
reason to doubt that this addition does take place at the lower
extremities, but on account of the close juxtaposition of the
palpebrum to the upper margin of the visual surface, it may be
questioned if at any period of growth sufficient room is allowed
in this region for additional lenses.

A secondary reason for the small size of the lenses is (4) the
constantly increasing size of the interlensar sclera after matu-
rity, which gradually envelops the lenses especially along the
upper margin of the visual surface, where, by coming into con-
tact with the increasingly prominent palpebrum, the lenses are
often nearly concealed.

To what degree the small size of the lenses along this upper
margin may be due to the overgrowth of the sclera, and how
much to the possibility of their being newly developed, it has
been impossible to ascertain, but that it is due to acertain degree
to both causes, is shown by the following facts: (1) immature

No. 2.] EVES OF ARTHROPODS. 261

eyes, in which the sclera has attained no excessive growth, very
often show these small lenses along the upper margin, and they
would, therefore, appear to be developed there; (2) it has
already been shown that after the average normal mature growth
of the animal has been reached, the number of the lenses
becomes less with advancing senility. This fact must be
explained either by the gradual envelopment of the lenses of
the upper margin by the sclera and palpebrum, and their entire
concealment within the substance of the latter, unless it is pos-
sible that atrophy of the ommatidial nerve branches and con-
comitant reabsorption of the lenses takes place with advancing
old age.

From the examination of eyes limited to ezg/¢ rows of lenses,
it appears that with this number of rows there may be consid-
erable variation in the number of lenses, as seen on the plate
(Fig. 9, thirty-one lenses; Fig. 10, forty lenses). These figures
also indicate the fact, that with a constant diminution in the
number of lenses from the upper and lower extremities of the
rows, the eight diagonal rows would ultimately be reduced to a
single or double longitudinal row parallel to the margins of the
visual surface. Hence, without overmuch hypothesis, the pri-
mary lenses probably appeared in a single or double row, a
visual line parallel to the margins of the orbital node.

DEVELOPMENT OF THE LENS.

There is sufficient evidence at hand for the statement that
that portion of the ommatidial cavity which penetrates the
test arises from an evagination from the internal surface of the
test accompanied by a corresponding but very shallow invagi-
nation from the upper surface. Natural casts of the internal sur-
face of the visual area not infrequently show minute lensar cav-
ities at the ends of the rows of lenses, which appear not to have
penetrated to the upper surface, and bear at their summits no
impression of a corneal surface or corneal cavity, as do the other
lenses in the same eye. It would be inferentially true that the
cornea is developed from the attenuated integument (cuticular
epithelium), and is the specialized film of the test left between
the depressions from its lower and upper surfaces, eventually
becoming discrete.

262 CLARKE. [Vot. II.

STRUCTURE OF THE SCLERA.

The interlensar sclera is continuous with the test, and its
structure is in all points identical with that of the test.

The vertical tubules and smaller tubulipores, with which
nearly every part of the test of Phacops rana is densely perfo-
rated, are plainly visible in every section of the sclera, no dif-
ference in the structure of the parts being discernible, although
the thickness of the sclera is somewhat less than that of the
adjoining portions of the test; however, the thickness of the
test is of necessity very variable in different parts of the ani-
mal. Not infrequently eyes have been observed, preserved as
casts in decomposed chert, in which the tubules of the sclera
are represented by delicate rods traversing the vacant space left
by the removal of the integument.

ABNORMALITIES in the arrangement of the corneal lenses are
of comparatively rare occurrence. They appear to be due, in
every instance observed, to the failure of a lens to develop at
the proper time and place in its own row, but in no case has a
lens appeared so out of place as to be intercalated between
rows. Marked abnormalities, such as that represented in Figs.
II and 12, are usually confined to one of the two eyes. It is,
however, not uncommon to find the right and left eye differing
in the number of lenses in the corresponding rows, either with
or without affecting the total number of lenses. In the follow-
ing example the total is the same, although the arrangement
differs : —

Right eye. 6.
6.

9. 60
Left eye. O. 60

8.
8.1

9590 716;4. 2
9.10. 7:,0,\A. 2

In another example both the number in the corresponding
rows and the sum total differ :—

Right eyes 5.7. 8. 7. 77.,0- 42 ee Ay
Left eyes 0) 5-19.09. 10.9.1 7-..0- 4a 2 — 55

These instances of irregular development may be due to
pathologic or other organic conditions of the animal; perhaps,
also, in part to external influences.

No. 2.] EVES OF ARTHROPODS. 263

NoTE. — No satisfactory evidence of crystalline cones within the ommatidial cav-
ities has been ascertained, and it is not surprising that these bodies, which undoubtedly
existed, were removed with the soft parts of the visual organ. With respect to this
feature the sections of the eye of Phacopfs given by Barrande (Systéme Silurien du
Centre de la Bohéme, Vol. I., Pl. 3, Figs. 15 and 16), and reproduced by Zittel
(Handbuch der Palewontologie, 1885), are misleading. The fillings of the ommati-
dial cavities are so shaded as “to indicate prisms” (compound) “ corresponding ~
with each lens,” and extending very far inward without diminution in width. Such
structure finds no correspondence in the eye of the living Arthropod, and is prob-
ably to a large degree schematic and imaginary. The structure of the lens, as we have
found it, is also essentially different from that represented by Barrande.

MopES OF PRESERVATION OF THE VISUAL SURFACE.

a) The cornea and sclera are normally preserved. (Fig. 1.)
This is the usual mode of preservation in the limestones
where the original substance of the test has been preserved in
calcic carbonate, though leaving so considerable a portion of the
organic matter as to give a black and lustrous surface. Such
specimens retain the minute structure of the test most perfectly
and are most satisfactory for sectioning.

b) The cornea ts removed and the sclera retained. (Fig. 2.)
This is a rare mode of occurrence noticed only in specimens
from the shales.

c) The sclera 1s removed and the cornea retained. (Fig. 3.)
In these examples, which occur in the shales and weathered
limestones, the corneal lenses stand supported on the summits
of pillars of matrix. It is not an uncommon mode of occurrence.

ad) Both cornea and sclera ave removed (Fig. 4), leaving pillars
of the matrix with cup-shaped upper surfaces, each bearing a
little ball at the centre. This condition is often observed in the
decomposed limestones and phtanites.

e) An external film ts removed from the entire visual area,
destroying the cornea (Fig. 5). A single example has been
observed in which the entire test was apparently originally pre-
served in calcic carbonate. Subsequently this was removed
from within and gradually replaced by silica, with the exception
of the thin outer film, which afterward was entirely removed,
leaving the space it occupied vacant.

J) Silica deposited as a thin film upon, or replacing a thin film
of the external and internal surfaces of the test, and all the rest of
the substance of the test and the matrix removed (Figs. 6 and 7).
In this condition the visual surface is a mere shell appearing as

264 CLARKE. (VoL. II.

when normally preserved, but the corneal lenses are hollow, and
the sclera represented by a thin wall of silica. This condition
is sometimes modified by the removal of the entire upper sur-
face of the visual area, generally by its adherence to the outer
part of the matrix, leaving only vertical tubes representing the
ommatidial cavities.

While the foregoing observations and the essential conclu-
sions therefrom in regard to the structure of this phase of the
trilobite eye, agree in some respects with the opinions of earlier
writers upon this topic, there are many important points of dif-
ference and various features of structure which have not before -
been noticed. I therefore give a brief historical review of the
observations upon the subject.

Quenstedt, 1837 (Wiegmann’s Archiv fiir Naturgeschtchte,
Vol. I., p. 340), was the first to recognize two distinct types of
structure in the eyes of trilobite, and divided them into

1. * Aggregated eyes having a facetted cornea.

2. Aggregated eyes having a smooth cornea.

In both groups the cornea was regarded as the direct continu-
ation of the superficial layer of the test of the cheek. The
first type of structure was represented by the eye of Phacops
latifrons, Bronn (z.e., the Phacopidz). The second type was
exemplified by ///e@nus crassicauda, Dalman (z.e., holochroal
eyes), in which the facets are said to be in relief upon the
internal surface of the general corneal (visual) area, each facet
being formed by a lens or crystalline body, behind which lies a
vitreous body, penetrating deeply into the organ. In these the
cornea was regarded as composed of two distinct layers, of
which the outer is quite smooth, the inner very finely reticulate.

Burmeister, 1843 (Organization der Trilobiten, p. 19), regarded
the structure of the holochroal eye as directly comparable in all
respects to that of the eye in Branchipus stagnalis, and indorsed
Quenstedt’s view of the compound corneal layer, while admit-
ting but a single type of structure. He assumes with respect
to Phacops that the cornea must have been more destructible
than in the other trilobites, and by its removal the facetted sur-
face exposed.

* As I have not had access to this work, I am compelled to take the summary of
these observations as given by Barrande (Syst. sz/., p. 133).

No. 2.] EVES OF ARTHROPODS. 265

Barrande, 1852 (Systéme stlurien du centre Bohéme, Vol. L., p.
185), recognizes three distinct types of structure, two of which
are similar in breadth to those of Quenstedt, though differently
interpreted. The third type of structure is exemplified in the
genus Hares, the eye of which is considered as an aggregation
of ocelli (two or three in each eye). For the schizochroal eyes
Barrande establishes the fact that the sclera (cornée opaque) of
the visual surface is identical with that of the test of the head,
and continuous with it. He also regards the existence of a
transparent cornea covering the entire surface as suggested by
Burmeister, as probable, but admits that he has been unable to
assure himself upon this point. For the holochroal eyes the en-
velope of the visual surface is shown to be of different character
than that of the test, and consists of a general cornea covering
the entire visual area. His observations do not seem to have
led to a decisive conclusion in regard to the simple or compound
character of this cornea.

Packard, 1880 (The Structure of the Eye of Trilobites: Amert-
can Naturalist, p. 503), quotes a resumé of the status of the dis-
cussion as given by Gerstiacker in Bronn’s Classen und Ordnungen
des Thierreichs, which is virtually a reiteration of Barrande’s
opinions. The “‘ocelli” of Hares are regarded as aggregate
eyes, not comparable with the simple eyes or ocelli of Lzmulus
and the Merostomata. The eyes of Barrande’s first and second
groups are considered as true compound eyes and not aggre-
gated eyes; no essential difference is recognized in the form
and arrangement of the corneal lenses of Phacops and Asaphus,
and the distinctions pointed out by Quenstedt and Barrande are
considered artificial.

The sections used by Professor Packard in the comparative
study of the trilobite eye appear to have been altogether of
holochroal forms. A close correspondence in structure is de-
monstrated between the eye of Asaphus and that of Limulus.
In the Lzmulus eye the lenses are covered by a continuous cor-
neal layer, which does not make itself apparent in Professor
Packard’s sections of Asaphus, although it undoubtedly exists.
It may be questioned whether the conclusion drawn from this
comparative study is not too broad, viz., that the trilobite eye is
organized on the same plan as that of Lzmudlus.1

1 Professor Packard’s observations upon the eye of Asaphus show no indication
of the existence of interstitial epithelium between the lenses, an extremely important

266 CLARKE. [VoL. II.

CONCLUSION.

The study of the eye in Phacops rana as here presented al-
lows the statement of the following points : —

1) The schizochroal eyes of the Trilobites are aggregated
and not properly compound eyes. ‘The visual organs of Harpes
may prove to be of similar character.

2) The scleral portion of the visual surface is of the same
structure as the test, and is a direct continuation of it.

3) No evidence appears of any continuous corneal layer cov-
ering the entire surface.

4) The corneal lenses are wholly discrete from the epidermis,
but are of epidermal origin. In the addition of new lenses to
the visual surface, they appear to arise from a thinning of both
surfaces of the integument.

5) The corneal lenses were hollow or filled with some matter
not homogeneous with the cornea itself.

6) The corneal lenses, and therefore the ommatidia, are
added to the visual surface with advancing age until the mature
growth of the individual is attained; thereafter they diminish
in number with increasing senility.

7) The addition of corneal lenses occurs regularly at the ex-
tremities of the diagonal rows.

8) No evidence is preserved of crystalline cones in the om-
matidial cavities, though they may have been removed in the
decomposition of the soft parts of the eye.

In conclusion I wish to call attention to the primitive struc-
ture of the eye exhibited in a Devonian subtype which is provis-
ionally referred to the order of the Phyllocarida. Dr. J. S.
Kingsley in the final paragraph of a valuable paper on the
“Development of the compound eye in Crangon”’ (/ournal of
Morphology, Vol. 1., p. 63), has written: “The observations as
yet recorded are not sufficient to throw any great light on the
phyllogeny of the Arthropod eye; still one or two points may be

feature of difference from the schizochroal eyes. My own study of the holochroal
eyes has not been as careful as I hope to have the opportunity of making it, but it
may be observed that sections of the eye in Proé‘us Rowi seem to indicate a very
tenuous interlensar sclera; moreover, the immature Calymene senaria referred to in
a previous footnote shows evidence of such interlensar integument.

No. 2.] EVES OF ARTHROPODS. 267

spoken of. The mere fact of invagination! must be regarded
as indicating an ancestral condition, but what this condition was
is uncertain. The pit or groove must have had sensory func-
tions and either wall” (retinogen and gangliogen) “must for a
time have been like its fellow, as is shown by its having similar
nuclei, and by the similar development of rows of nuclei.”

In the species Mesothyra Oceant, Hall, a member of one of the
faunas of the Portage group, and one of the largest known repre-
sentatives of the Phyllocarida, the eye consists of a simple deep
pit at the summit of the optic node. There is no evidence that
this pit contained a series of lenses, but it is highly probable that
it is an otherwise embryonic character retained at maturity, and
may serve as the ancestral condition of the Decapod eye sug-
gested by Dr. Kingsley. That there is Decapod blood in the
Phyllocarida has been disputed by Packard, the author of the
group term, but Decapod affinities are strongly indicated by the
recently described Devonian genus of Phyllocarida, Rhinocaris,
(Paleontology of New York, Vol. VIL, 1888).

1 This refers to the primary optic invagination in the embryo, for the formation of
the entire visual surface, first pointed out by Locy (Bud/. Mus. Comp. Zodl. 1886),
and verified by Kingsley (of. cz¢.). The term is not used in a sense similar to that
in which it has been employed in this paper in referring to the formation of the
corneal lenses.

268 CLARKE. [Vou. II.

EXPLANATION OF PLATES.

Fics. 1-7. Schematic representations showing the different modes of preservation
observed in the visual surface of Phacops. Each figure represents a single lens with
the lensal or ommatidial cavity, and the adjoining sclera or its equivalent space.

1. The cornea and sclera normally retained, the lensal and corneal cavities being
filled with matrix. The lens is represented with its posterior cavity having the rela-
tive size indicated by the specimens figured elsewhere on the plate, and the anterior
corneal cavity is characterized by radiating lines which are intended to show the
difference often apparent in the character of the matrix filling the cornea.

2. The cornea removed and the sclera retained, the matrix showing the position
and size of the posterior corneal cavity, but retaining no indication of the anterior
cavity filling, which is removed with the cornea.

3. The cornea retained and the sclera removed, the lens standing at the summit
of a pillar of matrix which represents the ommatidial cavity.

4. Both cornea and sclera removed, \eaving pillars of matrix with a cup-shaped
summit, in the bottom of which lies a little ball. The pillar represents the ommati-
dial cavity; the concave summit, the lower surface of the lens, and the little ball, the
posterior corneal cavity.

5. An external film is removed from both cornea and sclera, destroying the for-
mer and leaving the filling of the anterior corneal cavity standing out prominently
with almost the full size of the lens. In the single instance observed of an eye in
this condition, the posterior corneal cavity is empty in all the ommatidia that were
opened. The reason for this is not well understood. The sclera has been silicified,
and subsequently decomposed, so that it is indistinguishable from the matrix.

6. The outer and inner wails of the visual area have been replaced by a film of
silica, and the rest of the calcareous matter subsequently removed, leaving both cornea
and sclera preserved as a mere shell.

7. The same condition of preservation, modified by the adherence of the cornea
and outer wall of the sclera to the matrix outside the eye, leaving the walls of the
ommatidial cavities adhering to the internal matrix as a series of short tubes. This
mode of fossilization has not been observed in Phacofs rana, but is not uncommon in
specimens of Phacops cristata, var. pipa, from the decomposed Upper Helderberg
phtanite.

Fics. 8-22. Schematic representations of the lenses of the visual surface. The
curved surface is projected upon a plane, and the relative size and position of the
lenses is retained. Whether the representation is from a right or left eye, the
lower posterior margin is at the right of the figure, the diagonal rows being enumer-
ated from this side, obliquely downward from right to left. All the figures are drawn
to the same scale.

8. The visual surface of an extremely young individual measuring 6 mm. across the
base of the cephalon; composed of 31 lenses in 8 rows, nearly all the terminal lenses
being immature. The older lenses show a tendency to arrangement along a single
or double transverse row, parallel to the margins of the visual surface.

g. An older eye, bearing 35 lenses in 8 rows, belonging to a young Phacops, hav-
ing a cephalic width of 7 mm. At the upper extremities of the rows the lenses are
all full-grown, and all immature at the lower extremities.

Io. An eye composed of 40 lenses in 8 rows, and belonging to a young individ-
ual with a cephalic width of 9 mm.

No. 2.] EYES OF ARTHROPODS. 269

11. An eye with 42 lenses in 8 rows, belonging to a large individual, having a
width across the cephalon of 34 mm. The lenses are nearly all mature, but are abnor-
mal in their arrangement, showing a failure to develop properly at the upper extremi-
ties of the rows after the third.

12. An eye of Phacops cristata, var. pipa, composed of 50 lenses, and showing
an abnormal arrangement, a single mature lens in the last row being situated high up
in the base of the palpebrum. Had it developed in the vacant space in the last row
but one, the arrangement of the lenses would have been normal for this variety.

13. An eye of the same variety bearing 52 lenses in 8 rows. Eight appears to be
the normal number of rows in the mature eye of this form, the anterior vertical row,
and the last diagonal row, consisting of three lenses. In the other diagonal rows
there is apparently much greater variation than in the eye of Phacofs rana.

14. Aneye of Phacops rana composed of 57 lenses in 9 rows, the head having a
basal width of 52mm. This is the eye of a senile individual, and all the lenses are of
mature size with the exception of those on the palpebral margin. The number of
lenses in the anterior vertical row is three instead of four, as in the normal adult.

15. Another senile eye, with 60 lenses in 9 rows, belonging to a very large speci-
men, with a cephalic width of 7omm. Here again the lenses are all of full size with
the exception of those on the upper margin of the visual surface; the lenses of the
anterior vertical row are also three in number.

16. An eye composed of 60 lenses in 9 rows belonging to an individual slightly
above normal adult size, having a cephalic width of 28mm. In the first row one
interval has been skipped in the addition of the last lens.

17. An eye of normal size and development, bearing 70 lenses in 10 rows, the
cephalon having a width of 24mm. The first row consists of a single full-grown lens
at a considerable distance from the posterior extremity.

18. An eye from an individual of the same size, having 70 lenses in 9 rows.

19. An eye composed of 71 lenses in 10 rows, the cephalon to which it belongs
having a width of 27 mm. It essentially differs from the preceding only in the pres-
ence of the single lens constituting the first row.

20. An eye with 75 lenses in 10 rows, from an individual having a cephalon 28 mm.
in width.

21. An eye composed of 88 lenses in II rows, from an individual measuring
17 mm. in cephalic width. This is the greatest number of lenses and rows of lenses
noticed in this species.

22. An average eye of Dalmanites Boothi, var. Calliteles, Green, consisting of 206
lenses in 29 rows.

Fic. 23. A left eye of Phacops rana, enlarged to 3 diameters, showing the arrange-
ment of the lenses, the smaller size of several of the terminal lenses, and the tuber-
cles on the integument of the palpebrum and orbital ridge. The lensar cavities are
represented as much too sharply hexagonal; they should be more rounded and exca-
vate. The figure is copied from the Palzontology of New York, Vol. VIL., Pl. 8, Fig. 6.

Fic. 24. A portion of the visual surface of a very old eye, taken from an individ-
ual measuring 70 mm. across the base of the cephalon; showing the thick and deeply
excavate sclera, the full-grown lenses along the lower margin, and the small lenses at
the upper margin of the area. Enlarged to 3 diameters.

Fic. 25. A natural cast of the internal surface of a portion of the visual area in
Phacops cristata, var. ipa, enlarged to 6 diameters. The specimen shows very beau-
tifully the cup-shaped casts of the ommatidial cavities, each with a little ball at its cen-
tre representing the posterior corneal cavity. At the upper extremities of the last

270 CLARKE. (Vou. He

two vertical rows at the left, are two casts of immature lenses, in one of which the
filling of the corneal cavity is just discernible; in the other the ommatidial cavity
appears not to have penetrated to the upper surface. Several features of similar
character are to be seen on parts of the specimen not represented in the figure. The
portion of the eye represented is the posterior one-third of the right eye.

Fic. 26. Two cavity-fillings from the same specimen enlarged to 15 diameters,
showing the small size of the balls compared with the probable size of the entire
cavity of the cornea.

Fic. 27. A section through the eye and adjoining parts of Phacops rana, showing
the lenses and the interlensar sclera. Enlarged to 3 diameters.

Fic. 28. The same enlarged to 6 diameters, showing the continuity of the porifer-
ous integument of the head with the interlensar sclera, the double convexity of the
lenses, and the depth of the ommatidial cavities in the sclera. At the right of the
first lens in the series is an internal depression on the integument which appears to
indicate the position of a newly developing ommatidium. No evidence of a lens was
visible at this point before the section was made.

Fic. 29. Three lenses with their interstitial integument, from the same specimen,
enlarged to 10 diameters. There is a slight difference in the character of the matrix
filling the cavity of the cornea, it being possible to distinguish the line between the
anterior and posterior divisions of the space. The dark color of the lower portion
of the sclera is due to an increase of pigment.

Fic. 30. A portion of the eye of Phacops rana, from which the sclera has been
removed by natural causes, leaving the cornez standing on pillars of matrix. En-
larged to 12 diameters.

Fic. 31. A natural section of the eye of Phacops cristata, var. pipa, enlarged to 8
diameters. The sclera has been removed, and the doubly convex surface of the len-
ses is well shown.

Fic. 32. The eye of Mesothyra Oceani, Hall, enlarged to 3 diameters, showing
the strong optic node with a simple, deep pit at its summit. The figure is taken from
the Paleontology of New York, Vol. VIL., Pl. 32, Fig. 2.

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FURTHER STUDIES ON GRAMMICOLEPIS BRACHI-
GOSCULCS; ~ POE

By R. W. SHUFELDT, M.D., C.M.Z.S.

Durinc the spring of 1872, Professor Poey of Havana, Cuba,
came into possession of a very remarkable form of fish, which
presumably was taken in Cuban waters.

Fortunate it was for science that it fell into such excellent
hands, as that eminent ichthyologist promptly presented us
(Anal. de la Soc. Esp. de Hist. Nat., Tom. 11, 1873) with a very
excellent account of this more than rare type, the duplicate of
which, so far as I am aware, has yet to be found by natural-
ists.

This account of Professor Poey’s, as will be seen, was pub-
lished in the Spanish language, and it has given me much
pleasure to make a translation of it, and present it here as an
introduction to some subsequent examinations which I had the
rare opportunity of undertaking upon the skeleton of the speci-
men in question. The osteology of this fish is very interesting,
not only from the fact that it is the only specimen in the
hands of science, but from its extraordinary peculiarities, and
from the fact that it may some day be found upon our own
coasts.

My translation of the original description just referred to
reads as follows :—

“GRAMMICOLEPIS BRACHIUSCULUS.

DYPE OF ANEW FAMILY IN] DHE CLASS: PICES:

By Don FELIPE POoeEy,

PROFESSOR IN THE UNIVERSITY OF HAVANA, AND CORRESPONDING MEMBER OF THE ACADEMY
oF Exact, PuysicaL, AND NATURAL SCIENCES OF MAprID.

The length of this extraordinary fish is 470 millimetres. The
head enters five times into the total length of the body, and two

272 SHUFELDT. [Vot. II.

and two-thirds times into its greatest depth. The body is much
compressed, and quite deep. The very large eye is contained
two and a third times in the length of the head, and lacks the
membrana adiposa.

The branchial apertures are deeply cleft, but I fail to find
more than four branchiostegal rays, without ‘being able to assert
that there may be a greater number of them. The snout is
short. The prefrontal, the turbinal, and the anterior suborbital,
are extremely hard, and covered with spiny rugosities. The
preoperculum and interoperculum have rugose borders, while the
remaining opercular bones are entirely so. The mouth is
small, subvertically cleft; the premaxilary process is large,
and is lodged in a fossa of the cranium. The maxillary is com-
plicated. The teeth are simply a narrow row of minute pric-
kles ; they do not occur upon the vomer, nor the palatines.

D. 6-34; A. 2-33; V. 1,6; P. 15; C. 1-13-1. The leading
spine of the first dorsal series is rugose, as is the first ventral,
the two post-anals, and the external ones of the tail, which latter
show the condition equally well in either one.

The rays of the pectoral, second dorsal, and the anal fins are
compressed, and do not ramify at their extremities. The pecto-
rals are very short and rounded. On the other hand, the vertical
fins, the dorsal, and anal are well developed.

The tail was injured, and apparently cut; the membrane
which unites its rays had disappeared; the peduncle which
supports it is large, and capable of communicating a powerful
impulse to the act of progression. The thoracic pectorals un-
questionably possess a rugose spine and six flexible ones that
are branched.

Aside from the frontal bones and the suborbitals where the
skin abruptly terminates, and the nasal portion of the snout, all
the trunk and the head is covered with scales, including the
inferior mandible.

These scales in no way resemble those found among the
acanthopterygean fishes. Their length greatly exceeds their
width; they have the appearance of parchment, — transparent,
brittle when dry, — overlap each other, and are strengthened
longitudinally by a raised lineal ridge.

Their contact with each other is so extremely intimate that it
lends to the skin of either side a very smooth appearance — so

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 273

much so, that the rough borders of the scales would not be
suspected without the aid of the fingers.

Thanks to the length of these scales, four, five, or six of them
are sufficient to span the height of the trunk, one of such a
series being crossed by the lateral line, where its presence is
denoted by a raised ridge.

The leading scales on the body, above as well as below, are
shorter, and where carried on to the head, are doubly as firm as
those found at the base of the fin rays.

Without having done more than counted the scales in a longi-
tudinal line, I calculate that the number is considerably above
two hundred ; those of the head, although shorter, have the
same form as those of the trunk. There are no scales upon the
fins.

The caudal peduncle develops neither a cartilaginous nor an
osseous plate at its sides. Posterior to the arms the ventral
keel is rough.

The cranium is more cartilaginous in structure than it is
osseous, except the frontals, which are rugose in lines in the
supraorbital region, and bristly in front, as are the turbinals and
suborbitals; these latter are four in number, the last three
being very slender. There are two supratemporals.

The inferior mandible is characterized by several rows of
minute spines upon the dentary and articular elements. The
vertebrae number 10-+ 36.

The anterior neural spine is not excavated, being lofty and
smooth ; the five that follow are short and inclined backwards.
The remaining ones are slender, which applies also to their
hemapophyses. The last vertebra is without lateral spines.

The pleurapophyses are inconspicuous, feebly developed, and
have much the same size and shape as the epipleurals. I dis-
cover but one pseudo-interneural spine in front of the one that
supports the first dorsal fin ray.

The specimen I described, when received by me was without

gills and without abdominal viscera. Preserved as it was three
days upon ice, its general color appeared to be white; but we
have reason to suspect that in the fresh condition this fish can
easily assume a violet tint. The hard parts of the head were of
an intense violet shade. The ascending border of the preoper-
culum, violet. The fins were white, changing to violet in cer-

274 SHUFELDT, [ Vou. II.

tain lights; the caudal fin rays were of a reddish tint. Eye
inclining to white.

FamiLy: The characters which are presented us in this fish
are of such an extraordinary nature that they will not permit
us to place their possessor in any of the recognized families of
fishes. Its nearest affinities are with the Beryczde and with the
Carangide, two families widely separated from each other; I
am inclined to believe that its better place is along-side of the last-
named one. Its resemblance to the BLeryctde is seen in the
large eye; the asperity of the cranium; the rugosities upon the
fin rays; the ventrals composed of more than five soft rays,
over and above the spiny one; its resemblance to the Carangide
is seen in the two free spines which precede the anal fin, and
especially to Serzo/as for lacking the bony plate of the lat-
eral line; but in the number of its vertebrz it approaches the
Scombrid@, as the shape of its ventral fins are in pattern analo-
gous to those of the Acanthurid@, and its unramified fin rays
agree with the Balistide.

The character of the scale, to which ichthyologists have
attached so much importance, separates it from all other forms
known to me.

My examination, then, authorizes me in establishing the fam-
ily Grammtcolepide, based upon the following characters: Lat-
eral line unarmed with bony plates; ventral fins composed of
more than five soft rays; two free postanal spines; caudal ver-
tebrze numerous; scales very long and narrow, without fan-like
expansions or denticulations.

Genus: The genus Grammtcolepis has for its etymology ypap-
puxos, line ; Nézris, scale.

The characters, in addition to those I have already pointed
out for the family, are: Body deep, compressed; eye large;
mouth small; head, in part, rugose, which also applies to the
interoperculum and the preoperculum; to all appearances a lim-
ited number of branchiostegal rays; teeth mere asperities, the
palatine arch without them; two dorsals, the first short, the
second very extensive, its height insensibly increasing ; pectoral
short and rounded; the dorsal, anal, and pectoral fin rays do
not ramify at their extremities.

History: I saw this fish for the first time in Havana, on the
5th of April, 1872, and I have not observed it since; neither

No. 2. GRAMMICOLEPIS BRACHIUSCULUS. 275

fishermen nor students of the class have been able to give me
its name, because neither one nor the other have seen it to
know it. It is, then, one of the rarest forms in existence. The
skeleton I have sent to the eminent Professor Gill, who has it
in his possession, though I do not know but that he has pre-
ferred placing it in the collection of the Smithsonian Institution
in Washington.”

This account is completed by a plate and its accompanying
description, showing the fish one-third the size of nature, and
various illustrations of its scales and other parts.

Now about a year ago, Professor Gill did me the great honor to
place in my hands, for a little more extended illustration, not only
the skeleton of this rare type, but a life-size outline drawing of
the fish made by Professor Poey himself. In addition to these
treasures, this eminent zodlogist also placed at my disposal sev-
eral crania of fishes, representing the genus Cavaux and others,
to be used in the present connection. Situated as I now am,
at an outpost in New Mexico, notwithstanding the great value
of these crania for comparison, I can only regret that the material
at my hand is not still more extensive, as it might be, were I
more favorably situated to undertake this kind of a paper. Es-
pecially would I like to examine specimens of Brama Razz,
which, if I have recalled the proper form, possesses vertical
linear scales something like those in Grammacolepis, though, I
believe, very much smaller. ;

In order to give an idea of the external appearance of the
subject of this article, I brought to my aid the two drawings of

1 Since writing the above, a very valuable work upon ichthyology has appeared,
viz.: Zhe Fisheries and Fishery Industries of the United States. By G. Brown Goode,
Asst. Direc. U. S. Nat. Mus. and a staff of Associates. Washington, 1884. On
page 335 of the text of this book, we read of the BRAMID® that “The only member
of this family of interest to us is the Brama Razz, called “ Pomfret” in Bermuda,
where a few individuals were observed by the writer in 1876. In 1880, an individual
was obtained on the Grand Bank of Newfoundland, and more recently the species
has been found to be somewhat abundant on the coast of Washington Territory and
Vancouver’s Island. This species was described from the coast of South America,
under the name 4rama Chilensis.” In the second volume of this work, we find an
excellent figure of Brama Kazi, Plate 112, which shows the fish possesses vertical
linear scales, although they are much shorter than they are in the subject of this
article.

The Pomfret also has its tail more deeply forked, and the dorsal fin is seen to be
continuous. The eye is very much smaller, though otherwise there are some general
external resemblances between the two forms. (R. W.S., 7 Aug., ’86.)

276 SHUFELDT. (VoL. II.

By the author,

One-third size of nature.

assisted by Poey’s outline drawings, and existing material.

Figure r.— Right lateral view of Grammicolepis brachiusculus.

Professor Poey, neither of which profess to be anything more
than the merest outline of Grammicolepis, and the scales, fins,
and other parts that accompanied the skeleton. These, taken in
connection with the lucid description of the fish, and all care-

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 27

<

fully compared, have resulted in my drawing presented in Fig. 1
of this memoir.

Owing to the fact that many parts of the skeleton, from long
keeping and their delicate structure, have warped considerably
out of shape, I propose to devote myself on the present occasion
only to such as seem most important of them, and chief among
these stands the cranium.

As I say, so far as I know, the specimen of the cranium of
Grummicolepis before me is the only one in the hands of
science, and a most extraordinary object it is. Three features
strike us most forcibly when we first came to examine it: the
enormous orbits, the truncate appearance of its anterior part,
and the semi-transparency of its gelatinous-looking bones.

Figure 2.— Left lateral aspect of the cranium of Grammicolepis brachiusculus;
life size, drawn by the author from the specimen. /%, frontal; /a, palatine; S.O.,
supraoccipital; Sg, squamosal; Z/.0., epiotic; P#.0., pterotic; Z.O., exoccipital;
Op.O., opisthotic; B.O., basioccipital; &s, basisphenoid; Pr.O., prodtic; PZ, post-
frontal; As, alisphenoid; Os, orbitosphenoid; £72, ethmoid; Prf, prefrontal; Pr.S.,
parasphenoid; Vo, vomer.

The peculiar rugose condition of a frontal bone, referred to by
Professor Poey, is well shown in Figs. 2 and 3, #7. It will be seen
that these rugosities of the frontal radiate from a common cen-
tre on its superior aspect, this centre being found at about the
middle of the bone, or what would be the middle of its oblong
figure were its anterior internal notch completed, and we do not
regard its postero-lateral prolongation. This latter part of the
bone forms the superior periphery of the orbit, and is produced
backwards as far as the squamosal (Sg). To the inner side of

278 SHUFELDT. [Vor Ue

this process, the posterior border of the frontal shows at least
one conspicuous notch, while its free margin overlaps the supra-
occipital, and is in turn overlapped by the parietal (Pa) more ex-
ternally (Fig. 2). | Mesially, its surface turns upwards, more
particularly behind, where with the fellow of the opposite side
it grasps in the middle line the anterior portion of the supraoc-
cipital crest. Below this point the two frontals have their
straight, free, mesial edges roughly in contact with each other,
and slope gradually downwards to the margin of that concavity
which is found in front (Figs. 2 and 3).

This extraordinary fossa on the anterior aspect of the cranium
of Grammicolepis is entirely open above; its rugose and subcir-
cular margin being formed by the frontals; while below it
becomes conical with its apex in the middle line, and in the eth-
moid. Above, where it is most capacious, it has its posterior
wall formed by descending plates developed on the part of the
frontals, the left one considerably overlapping the right. Below
this, in the middle line, there is an opening of some size, which
leads into a commodious chamber lying between the frontals
above and the mesethmoid below.

A frontal is truncate in front, where it overhangs the corre-
sponding prefrontal, and internally articulates with the curiously
shaped ethmoid. Behind this, and on its under side, it forms the
major share of the roof of the orbit. Then occurs a longitudinal
keel, which separates this from that other part of its under
surface which forms the roof of the mid-chamber described in
the last paragraph. Viewed together from above (Fig. 3), it
will be observed that the rugosities of the frontals are limited
behind by a subparabolic curve with its arc anteriorly directed.

In this dried cranium a farietal (Pa) is represented by a
thin, flake-like, semi-transparent piece of bone, of a form shown
in Fig. 3. To the outer side of its mid-longitudinal line it de-
velops for its entire length quite a prominent, though thin, crest,
which is rugose all along its superior margin.

The anterior three-fifths of the under surface of this element
simply rests upon the frontal and supraoccipital, while the re-
maining portion behind is more firmly attached, and really holds
the bone.in its position. Its outer free margin articulates prin-
cipally with the inner border of the posterior prolongation of
the corresponding frontal, though still more posteriorly it meets

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 279

to some extent the squamosai (Sg). With the epiotic (£.0.)
it is connected simply by a feeble and thin band of bone. The
parietals, then, seem to play the part here of binders, rather
than their presence is at all essential to covering over any siza-
ble vacuity in the cranial vault, that might exist were either of
them removed.

The supraoccipital is a very extensive ossification, and is char-
acterized by a fairly prominent crest.

4
BO.

Figure 3.— Cranium of Grammicolepis brachiusculus, seen from above; life size,
by the author. Lettering as before.

This crest is triangular in outline, with its apex above, and its
base attached in the middle line, to the horizontal portion of
the bone. From the middle point of this base, a narrow, fan-
shaped development springs upon either side, which is incor-
porated with the crest, to strengthen it, being carried nearly as
high as its apex (Fig. 2).

. The broad and spreading horizontal portion of the bone forms
the roof of the brain-case, while posteriorly, just before the ter-
mination of the crest, it is bent abruptly down to meet the
exoccipitals. The flexure, being sharply defined by a transverse
line, the outer end of which, either way, terminates in the apex

280 SHOUFELDT. [Vor2ik

of a pyramid, the lateral and upper sides of each being also
formed by the supraoccipital. The lateral aspect of this pyra-
mid is overlapped by the epiotic (£/.0.), while outwardly its
free margin articulates with the squamosal (Fig. 3).

Regarding one of these epzotics, we find that its fan-like
portion is finished off behind by a semicircular piece, which is
thickened below, where it becomes firmly attached to the neigh-
boring bones. The blade portion is longitudinally fluted, but
no rugosities are found upon it. This does not apply to the
element at its outer side, the sgwamosal (Sq), which element
develops very conspicuous rugosities upon its upper aspect in
direct continuation with the longitudinal ones on the long, back-
ward-extending process of the corresponding frontal (Fig. 3).

At the distal extremity of the squamosal I detect a small,
flake-like piece of bone, thoroughly attached, though individu-
alized by sutural traces, which I take to be the representatives
of the pterotic (Pt.O.). Beneath and beyond, the squamosal
seems to make the usual ichthyic articulations with the post-
frontal (Pzf) and the prootic (P7v.O.). At its under side we
find a small hyomandibular facet (Fig. 4, “/).

A postfrontal of considerable size (P¢/) develops at its outer
side, a sharp, descending, spicula-form process of bone, which is
transversely pierced at its base by a small foramen. The infe-
rior articular sutural trace of the postfrontal, as I make it out,
is subcircular in outline, and closely meets corresponding mar-
ginal concavities offered by the prodtic and alisphenoid.

Each alisphenoid is necessarily a very extensive ossification,
forming, as they conjointly do, the major part of the bony wall
of the posterior aspect of the immense orbit (As).

In front they articulate with far smaller ovbztosphenotds, which
in their turn meet in the median line anteriorly (Os). Now
above the basisphenoid (4s), the alisphenoids and orbitosphe-
noids are separated from each other, mesially, by a vertical
vacuity, broadest below, graduaily tapering to a blunt apex
above, which constitutes a great fenestra for the anterior wall
of the cranial casket (Fig. 4).

As already stated, the hinder portion of the ethmozd (Eth)
forms the mid-roof of the orbital space. This division of the
bone is of an oblong outline, being encroached upon by the
common, circular, anterior margin of the obitosphenoids behind,

INO Ze GRAMMICOLEPIS BRACHIUSCULUS. 281
®

the two elements being completely united. Below, it is convex
from side to side, correspondingly concave above, where it
forms the floor of the interfronto-ethmoidal chamber, already
alluded to above. I have previously described how now the
ethmoid is deflexed, and becomes concaved in front to form
the lower limits of that excavation on the anterior aspect of the
cranium.

This, as we have already seen, terminates in a conical point,
and even beyond this the bone is carried forwards as a median

Figure 4.— Under side of the cranium of Grammicolepis brachiusculus ; life size;
reference letters the same as in former figures, with 2/, hyomandibular facet, and gf,
foramen for the exit of the glossopharyngeal nerve in the opisthotic (O/.0O.).

triangular process, the apex of which rests upon the parasphe-
mold (Figs 3) “i. PFS.).

Upon either side of the ethmoid, the flat anterior aspect of
this cranium is completed by a broad prefrontal (P7f). The
form assumed by one of these elements can best be appreciated
by referring to Fig. 5, which represents the cranium of Gram-
micolepis seen from behind, while the anterior face is in the
horizontal plane. In this position the posterior aspects of the
prefrontals come into view.

Each one essentially consists of a thicker and vertical outer

282 SHUFELDT. [Vot. II.
+.)

column of bone, antero-posteriorly compressed, and an expanded
inner portion, which latter is reénforced by radiating projections
that converge to meet at a point at the lower part of the inner
margin of the columnar portion. It is hardly necessary to state
that these prefrontals form the externo-lateral parts of the ante-
rior orbital wall, the ethmoid completing it mesially.

Coming now to the vomer (Vo), we find it to be a thin scale-
like bone, of a form best shown in Fig. 4. It rests in the
longitudinal excavation of the anterior and lower side of the
parasphenoid, while its firmest attachment to that bone seems
to be by the periphery of its anterior margin.

The parasphenoid (P7.S.) is gently arched as it spans the
orbital space below, having its convex arc downwards. The
lower side of this part of the bone, as I have already intimated,
is longitudinally scooped out, while the upper side presents lat-
eral surfaces, which are inclined so as to meet in a median line.
Posteriorly, the parasphenoid makes the usual teleostean con-
nections with the basioccipital, basisphenoid, and prodtic, being
deeply cleft as it passes to cover the under side of the first-
named element (Fig. 4).

Occupying its usual position, the daszsphenord (Bs) not only
develops the median process (Fig. 2) seen in so many true
teleosts, but furnishes a firm horizontal roof for the three-sided
pyramidal eye-muscle canal, the lateral walls of which are com-
pleted by the prodtic and parasphenoid.

As in the majority of osseous fishes, the fvodtic is a well-
defined and important element at the lateral aspect of the brain-
case (Pr.O.). Its anterior margin is pierced by the foramen for
the trigeminal nerve, from which point faint lines in the tissue
of the bone are seen to radiate.

The basioccipital (4s) has its thickened and longitudinal por-
tion underlying the brain-case, as in most fishes, being com-
pleted behind the facet for the leading vertebra of the spinal
column. This facet is comparatively rather small, with its con-
ical depression very deep.

At either of its sides the basioccipital develops an upturned
and semicircular plate of bone, similar in structure to the other
flat bones of the lateral cranial walls, which articulates with the
lower margin of the opisthotic and the posterior margin of the
prootic (Fig. 2).

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 283

The opisthotic (Op.O.) is large and occupies its usual position,
as generally found, in the cranium of the teleosts. Its posterior
margin is pierced by a conspicuous foramen for the exit of the
glossopharyngeal nerve from the brain-case. The intersutural
traces defining its borders are easily made out in the specimen,
and this element contributes not a little to the lateral wall of
the cranial cavity, —a large vacuity existing after its disarticu-
lation.

Each eroccipital (E.O.) develops at the outer sides of the ver-
tically oval foramen magnum, a fan-shaped, bony thickening
(Fig. 5), which nearly meets at the middle point above.

Figure 5.— Posterior aspect of the cranium of Grammicolepis brachiusculus ; life
size. Letters have the same significance as in former figures. The cranium is repre-
sented as resting upon its anterior face on the horizontal plane, the line of sight
being perpendicular to the latter, and passing through the imaginary centre of the
foramen magnum.

Further, these bones spread out so as to complete the hinder
cranial wall, where the supraoccipital and osseous elements at
the lateral angles have failed to do so.

Now a number of the bones required to complete the skull of
this fish have been lost, and, as I said before, the others in my
possession are too much out of shape, from their fragile nature,
for me to decide, with any degree of certainty, as to their several
proper positions. This is much to be regretted, as I expect a
complete skull of Grammicolepis would prove a very interesting
and instructive object.

284 SHUFELDT. [Vot. II.

To return to the cranium for the purpose of taking a general
glance at it: we are to note especially the almost entire absence
of those parial and lateral crests, developed on the part of the
parietals and squamosals, so manifest in some fishes, as for in-
stance the genus Cavazx ; we are to note, also, the very peculiar
texture of the bone that composes this cranium, being more like
the material that is found in ordinary fish scales rather than
bone ; particularly are we to observe the relation between the
anterior portion of the supraoccipital crest, and the upturned
portions of the frontals.

There are but few striking features within the cranial case of
this strange form of fish. For the most part, surfaces, convex-
ities, and concavities on the outside give rise to similar surfaces
on the inside, the last two being, of course, reversed. The fos-
see for the ofoliths are ample and well defined, but the elements
themselves have been lost.

I have already expressed my regrets at not having at hand
more extensive material wherewith I might compare this extra-
ordinary fish; they only increased as my investigations pro-
ceeded, while the remaining consolation left me, is, that I feel I
have added at least my mite to the labors of Professor Poey ; so
should another specimen of Grammucoleprs fall into the hands of
naturalists, we can, at least, meet it with drawings of its cranium
and other skeletal parts, as well as with similar drawings of
some of the forms to which it is supposed to be related.

Through the courtesy of the Smithsonian Institution, and the
kindness of Dr. Gill for selection, I find before me the cranium
of a specimen of Cavanx hippos, with the spinal column of the
same fish (No. 13,561 S.I. Coll.). There is also the cranium
(No. 11,385) of another and still larger Cavanx, the species
being unknown. This last specimen presents some points of
peculiar interest not so well shown in the first. I have also the
cranium of a specimen of Zeuthis ceruleus, which will be intro-
duced to show certain points; and finally, the cranium of Poma-
canthus paru (No. 12,770 S. I. Coll.) brought forward to illus-
trate still other points.

Professor Poey’s investigations evidently led him to believe
that Grammicolepis was more nearly related to the Carangide@
than any other family of fishes known to him. And in this
opinion, so far as I can see or am able to judge, I must concur.

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 285

The cranium of the Cavanx No. 11,385, which bears a very
close resemblance to C. hzppos, shown in Fig. 6, although, be it
known, it possesses marked differences, is composed of a bone
tissue much more like that seen in the cranium of Grammiico-
/epis than any of the other specimens before me. As much as
it is unlike it, it evidently approaches the semi-transparent and
brittle condition found in our subject. The next thing that
our attention is directed to, is the strikingly large orbit of this
Caranx, and the evident, though distant, similarity of the ele-
ments that go to form its walls. The chief difference we meet
with here is the absence in the Cavanx of the backward-extend-
ing plate of the ethmoid seen in Grammicolepis, while there is
much to support a probable relationship of the forms, in the
parasphenoid, the basisphenoid, and less so in the prefrontals, of
the two. |

Figure 6.— Left lateral view of cranium of Caranx hippos. Spec. No. 13,561, Col-
lection of the Smithsonian Institution; life size, by the author. Letters signify the
same as in the other figures.

Again, in the Carvanx, the ethmoidal mass, and parts, which of
a consequence associate with it, are produced forwards, and we
fail to find anything upon this aspect that in any way reminds
us of the curiously truncate appearance of the front part of the
cranium in Grammtcolcpis.

Another marked difference is seen in the vomerine element ;
this bone, as we have observed, is in our subject merely a kite-
shaped scale, in no way incorporated with the parasphenoid,
being merely attached around its anterior rim. Now our speci-

286 SHUFELDT. [Vou. II.

men of Caranx, No. 11,385, foreshadows in its vomer what even-
tually comes to pass, between this condition in Grammucolepis
and what we find in C. £zppos. In this latter fish, as will be
observed by referring to the figures Fig. 6, e¢ seg., the vomer
is quite a solid bone, and is moulded upon the anterior end of
the parasphenoid, forming a more or less massive termination of
this end of the cranium.

In our unspecified specimen of Cavanx, this general appear-
ance is likewise maintained; but upon a lateral view, we are
enabled to look in between the vomer and parasphenoid, and
the less solid formation of either can at once be appreciated as
well as their less intimate relation to each other. It is a shame
that this species is not known, nor was ever diagnosed when this
specimen of cranium was taken, as this condition is very inter-
esting in the present connection, as are several others, as we
shall presently see.

As representatives of the Cavangid@, neither of these speci-
mens develop a spine-like process descending from the post-
frontal, which is a very marked feature of that bone in Grammz-
colepis. It is, however, present in other teleosteans, as seen in
one crania of Pomacanthus and Teuthis, Figs. 10 and It.

Before leaving this region of the cranium, I would like to
invite attention to the anterior aspect of it, in this very speci-
men of Pomacanthus (Fig. 10). It approaches to some degree
the truncate appearance, so often alluded to in Gvam#miacolepis ;
a closer resemblance, however, is vitiated by the extraordinary
forward and upward projection of the vomer in Pomacanthus.
Posterior to this bone, in the individual in question, an extraor-
dinary concavity is seen, the sides of which are formed by the
prefrontals and parasphenoid, being perforated on either side by
a group of foramina. Its bottom is completed entirely by the
latter bone.

Teuthis ceruleus offers us in its ethmoid and vomer just the
very reverse of this condition, as may seen by a reference to
Bis. 11,

It may be as well to note in passing that in Pomacanthus paru
the parasphenoid is very deep in the vertical direction, being
longitudinally excavated above and continuous with the capa-
cious eye-muscle canal, while anteriorly and below it is sharply
carinated. Posterior to this carination the bone develops a

Wor] GRAMMICOLEPIS BRACHIUSCULUS. 287

rounded and descending prominence, which is bifid, the two
lamina being directed backwards and outwards. The behavior
of the anterior end of the parasphenoid of Pomacanthus has
already been described above.

This bone is also wonderfully developed in our cranium of
Teuthis (Fig. 11). Here the carination in front is exceedingly
deep, while behind it, a distinct descending process is also seen.

figure 7.— Superior view of the cra-
nium of Caranx hippos, same specimen
as in Fig. 6; life size.

figure S.—The same seen from be-
low. Letters as in the former figures.

Further, this elegantly developed element makes another curi-
ous departure from all the specimens thus far examined. It is
this: where it forks over the basioccipital behind, a large fora-
men is found between the diverging limbs; this opening is in
reality the apex of the eye-muscle canal in this fish, and conse-
quently leads through that fossa to its continuation, which again
is the longitudinal excavation on the upper side of the parasphe-
noid or the floor common to the orbits.

But to return to our cranium of the Caranr No. 11,385: we
find that the anterior and horizontal portions of the frontal bone

288 SHUFELDT. [Vo.. II.

are quite transparent at their centres, while raised flutings radiate
from their hinder points, forwards and outwards. The trans-
parent areas are found to be even perforated in my specimen of
Caranx hippos, so thin do they become. Now it will be remem-
bered that in Grammzcolepis, from the horizontal portion of either
frontal, was developed an upturned, scroll-like projection, the
free edges of the two bones meeting in the median line. There
was thus formed sort of a conical prominence, the lower part
and base of which was anterior, being terminated by the trans-
verse rugosity in front, while the apex, or highest part, seized
the free front margin of the supraoccipital crest. In Caranx
hippos these vertical portions of the frontal bones are in close
approximation, so that they appear to be the continuation for-
wards of the supraoccipital crest ; the sutural traces, however,
have entirely disappeared; while in the cranium of our other
Caranx, the method of formation is very evident from the fact
that the vertical frontal plates are not thus coéssified, but plainly
show their individual origin as well as their relation and connec-
tion with the, anterior free margin of the supraoccipital crest,
which is wedged in between them. (Compare Figs. 2 and 6, as
well as 7 and 3.)

Pomacanthus paru has very extensive rugosities upon its
frontal bones, but these latter elements are exceedingly dense
and thick, as is the anterior border of the supraoccipital crest in
this fish, which measures at its widest part nearly five millime-
tres across.

Such forms as Pomacanthus paru do not develop conspicuous
parietal and squamosal crests; they are still less manifest in
Teuthis. On the other hand, in the Carangideé these crests
constitute the most striking feature of the cranium. As already
stated above, they are but feebly produced in Gvammiucolepis,
though they are plainly indicated.

All the lateral parts of the cranium, made up of the hinder
portion of the parasphenoid, the prodtic, opisthotic, exoccipital,
basioccipital, and below the squamosal line, are very much alike
in Cavanx and our unique subject, more particularly in our un-
diagnosed specimen of a Cavanx. But in the latter the basioc-
cipital enters far more extensively into the formation of the eye-
muscle canal than it does in Grammicolepis, as in the Caranx
we find a condition existing, as regards the opening between

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 289

the hinder forks of the parasphenoid, very much the same as
described for Teuthis cwruleus.

Upon comparing the posterior views of the crania of Caranx
hippos and Grammtcolepis (Figs. 5 and 9), we find, indeed, but
few points of resemblance between them. The occipital crest
in the former comes almost down, as it does in Pomacanthus, to
the supero-median point of the foramen magnum. It is far
above it in the latter fish. There the absence of the spreading
lateral crests, seen in the Cavanx, constitute a marked difference.
Professor Poey’s fish also has bony pillars developed by the ex-
occipitals, one being on either side of the foramen magnum.
These are absent in the Carangide.

Figure 9.— Posterior view of the cranium of Caranx hippos, Spec. 13,561, Smithso-
nian Institution Collection. Life size, by the author from the specimen. Letters as
before.

In C. hippos the facets on the exoccipitals for the first verte-
bra of the column meet in the middle line; these parts, how-
ever, in G. brachiusculus have been injured, probably during the
first dissection, so that I am unable to say positively upon this
point in regard tothem. In P. paru the first vertebra of the
column coossifies with the basioccipital, but this condition does
not obtain in Zewthzs. In this latter form the supraoccipital
crest also fails to reach the upper periphery of the foramen mag-
num at its middle point.

We find that both P. parw and Teuthis have the squamosal
curled downwards and forwards in the most extraordinary
manner, best marked in the latter type. This is well shown in
lateral view in Fig. 11, though I am not sure but that the piece
there indicated by sg may not be a separate ossification, in

290 SHUFELDT. [Vor=dil:

which case it would be a pterotic. I would have to dissect a
young fish to decide this point. These processes are very
conspicuous upon posterior view, and of course Grammicolepis
can show nothing like them.

Pomacanthus paru has another condition present, not seen in
any of the other forms alluded to above. Just posterior to the
prootic, and above the basioccipital and parasphenoid in the
cranium of this fish, on either side, we find a subelliptical fora-
men, with its major axis placed longitudinally, of no inconsider-
able size, through which we can easily observe the movable
otolith (Fig. 10, ot?).

Figure ro. — Left lateral view of the cranium of Pomacanthus paru; life size, by
the author, from specimen 12,770 of the Smithsonian Institute. Lettering as before,
with o@/, ofolith, and c.v., first vertebra of the spinal column, which is here codssified
with the basioccipital.

Before concluding our comparison of these crania, we must
note another point in the cranium of Pomacanthus, and this is,
the ossified orbitosphenoids and the ethmoid meet in the middle
and interorbital line, immediately beneath the frontals.

We have already fully described above, the relation of these
several elements in the subject of this paper, and how any such
condition is entirely absent in Caranx. This latter form, how-
ever, may have the ethmoid extended backwards in cartilage,
which material may be missing in these dried preparations.

NO. 2. |] GRAMMICOLEPIS BRACHIUSCULUS. 291

Now my material on this occasion will not admit of such a
thing as an analysis of characters for comparison. In my opin-
ion, without a thorough examination of the entire organization
of not only the forms at my command at the present writing,
but several others, such a tabulated synopsis, made up at the
best from such fragmentary material, would be of but little ser-
vice to us. The structure of Sevzo/a taken in the present con-
nection would come handsomely into play. aucrates ductor
would be another good form to examine.

From a comparison of the crania alone, I should say that the
relation between Grammzicolepis and such a fish as Pomacanthus
paru was very distant, while its affinity with Zeuthzs ceruleus
is still more remote. I should have liked, however, to have ex-
amined some of the Sa/istide, and perhaps glanced at one or
two more of the Chetodonts.

Figure 11.— Left lateral view of the cranium of a specimen of Teuthis ceruleus ;
life size. Kindly loaned the author by Professor Gill. Letters have the same signifi-
cance as in the foregoing figures.

Its relationship with the Carangid@, as Professor Poey pre-
dicted, is far more evident, though this, too, is extremely indi-
rect, and many forms still unknown to us are required to
demonstrate the connection.

These forms must especially show an increased density in the
cranial bones ; a decrease in the size of the eye and orbits; a
gradual disappearance of the rugose condition of some of the
flat bones of the cranium, particularly the frontals; a gradual
protrusion of the snout; and finally the development of the
parial cranial crests.

Of the shoulder girdle. — Although a number of the bones are

292 SHUFELDT, [Vor-iIg

lost, I am enabled at least to present a very good idea of the
shoulder girdle in this fish. This is shown in Fig. 12, illus-
trating this paper, and if the reader happen to have at hand a
copy of my osteology of Amza calva, published in the Annual
Report of the Commissioner of Fish and Fisheries for 1883, it
will be well to compare it with the figure I there gave of the
shoulder girdle of MWicropterus salmoides (Pl. 14, Fig. 35). It
represents these parts as they appear in a typical teleostean
fish. A glance is sufficient to satisfy us that the general form
of the proscapula (Ps) of Grammicolepis is very much like that
element in the Bass, differing principally in being slenderer and
more sloping, and in its relations with some of the other bones.
I am very sorry that I have not at hand the shoulder girdle of a
Caranx, as it would be interesting to compare it in the present
connection.

As is most usual in teleosteans, the hypercoracoid and hypo-
coracoid (Fig. 12, yp.c. and Hyo.c.) are fused together, and in the
present instance, to the proscapula also. The hypercoracoid
(Hyp.c.) is pierced by the usual foramen seen in this element
among typical teleosts. The anterior projection of the hypocor-
acoid (//yo.c.) is long and slender, almost reaching to the extrem-
ity of the proscapula (Ps).

It will be noted in Fig. 12 that each of these elements
develop a backward, extending process, and the letters /Zyp.c.
stand between them. This recess harbors the actznosts of the
pectoral fin, when these parts are zz sztu. These pectoral fins
have been carefully wrapped up by Professor Poey in a separate
little package, and I find three of these actinosts attached to
each fin. It does not appear as though any of them had been
lost, and I am led to expect that that is the correct number in
life. They are composed of rather elementary bone, as is so
much of the rest of the skeleton in this curious fish. Now the
bone marked 7 in Fig. 12 I take to be the ¢eleotemporal, and
designated by the same letter in my drawing of the shoulder
girdle of the Black Bass. On this latter form, however, as it is
also in Amza, the teleotemporal is very loosely attached to the
rest of the girdle by ligament, while here in Grammtcolepis, it is
represented (7) by an exceedingly long and slender bone, which
has its superior extremity moulded upon the side of the pro-
scapula s, and firmly attached thereto. I fail to find in any of

“=

No. 2.] GRAMMICOLEPIS BRACHIUSCULUS. 293

the little packages put up by Professor Poey anything that
might answer for a /ower teleotemporal, T, of my Bass figure.
We would, however, hardly expect to find such an addition,
where the superior element proves to be so very much elongated.

Figure r2.— Outer view of the principal elements of the left side of the shoulder
girdle of Grammicolepis brachiusculus ; life size, fromthe specimen. s, proscapula;
fTyp.c. hypercoracoid; /yo.c. hypocoracoid; 7, teleotemporal. The acéinos¢s are
attached to the vertical border of the recess in which the letters Yy/.c. are contained.

Whatever we may see in the cranium of Gvammtcolepis to
remind us of like parts in any of the Carangid@, such resem-
blances are certainly not borne out when we come to compare
the vertebral column of our subject with the column of a speci-
men of Caranx hippos. Figs. 13 and 14 are presented to show

the extraordinary departures that take place in this part of the
skeleton.

204 SHUFELDT. [VoL. II.

Of all the bizarre structures that pertain to the organization
of fishes which it has been my pleasure to examine, I cannot
recall at this moment one that presents quite so supremely a
fantastic arrangement as the eleven or twelve leading vertebra
in the column of Grammicolepis. These are represented in
Fig. 13, but I have omitted to include the first vertebra, or that
one which is found between the basioccipital and the one shown
in the figure with the enormous neural spine. In it the neural
spine is not developed, and its connections with the skull are
very intimate.

Taken in connection with Professor Poey’s account of these
parts, this figure obviates the necessity of my presenting a
verbal description of any great length, as all the details can be
plainly studied without any such additional assistance.

I am inclined to think that the bony pillars, which I described
in a previous paragraph, found on either side of the foramen
magnum, and completely fused with the exoccipitals, are the
halves of the neural spines of this first vertebra of the spinal
column. To support this view, we find by placing this vertebra
in position, that their pedicles spring from the centrum as in
other vertebre, and that, moreover, the sculpturing on the
external surfaces of these pillars is precisely like that upon the
sides of the neural spine of the second segment of the column.

This last process is very strong, and quite firmly attached to
its centrum: it curves gracefully first backwards, then upwards,
in a gentle curve, as shown in Fig. 13.

The succeeding four neurapophyses are inclined well back-
wards, each one, as we advance in that direction, becoming
shorter, more slender, and with a gradual disposition to assume
the vertical attitude. This is nearly accomplished by the neural
spine of the next segment following, or the seventh vertebra.
Fig. 13 shows, also, the eighth, ninth, tenth, and eleventh ver-
tebrze, and, as will be seen, the neurapophyses of these segments
actually lean forwards. The one on the twelfth, not here
shown, is nearly vertical again, while after that, they gradually
incline backwards. The broken spines on the last two vertebre
of the figure I have restored by dotted lines.

Now a glance at Fig. 14 is enough to convey to us that the
arrangement of these neurapophyses are entirely different in
Caranx hippos. In this latter drawing the first vertebra is

No; 25] GRAMMICOLEPIS BRACHIUSCULUS. 295

<

shown, and it has a vertical neural spine movably articulated
with its centrum. The succeeding spines, firmly fused with
their centra, gradually become slenderer, longer, and more
inclined backwards, to again become nearly vertical in the mid-
series of the column, to incline once more as we approach the
caudal end.

In Grammicolepis the ventral parial apophyses at first support
the freely articulated ribs with their attached epipleural appen-

Figure 13, — Left lateral view of the anterior end of the vertebral column of
Grammicolepis brachiusculus, the first vertebra removed; life size from the specimen.

dages, but in the seventh vertebra the capitulum of the rib
completely fuses with the apophysis, and as the latter lengthens,
the two become indistinguishably blended. The first and sec-
ond vertebre do not support ribs, and in the third pair only,
they articulate high up on the sides of the centrum, at the base
of the neural arch.

296 SHUFELDT. [Vor

The appendages have been lost in my specimen of Caranx
hippos, so I am unable to say anything about them.

When we come to compare the existing differences in the
latter halves of the spinal columns of these two fish, we find
that they are quite as great as those shown in Figs. 13 and 14.
Indeed, I can see there nothing to indicate that the forms in
question have any relationship whatever and were they in the

Figure 14. — Left lateral view of the first eleven vertebrze of the spinal column
of Caranx hippos; specimen 13,561, of the Smithsonian Institution collection; life
size, from the specimen.

class Aves, I should feel justified in placing one at one end of
the system and one at the other. ;

The absence of the hypural spine in Grammicolepis has already
been commented upon by Professor Poey in his memoir at the
head of this article; this apophysis is quite manifest in the
genus Caranx, as in most true teleosteans.

ON THE REVATIONS OF FRE HYOID AND “OTIC
EEE MENTS “OF “THEY SKEEETON: IN THE
leva Mewe(Glalvaye

EH D CORE,

Tue characters of the hyoid bones of many Batrachia have
been described by Dr. Parker? and Professor Wiedersheim,?
and their otic elements have received much attention from the
same authors. In both fields, however, much remained to be
done. The otic elements of the Salientia have been extensively
described by Parker, but no especial attention has been devoted
to those of the Urodela by either author, except incidentally to
other objects. In the present paper I desire to call attention to
these elements in the Urodela, and to contribute thereby to the
general theory of the morphology of the inferior arches of the
skull. Whether light be thrown on the vexed question of
the homologies of the suspensors of the inferior arches of the
skull or not, it is desirable to see what this intermediate group
of vertebrata contributes to its solution. I go over the types
seriatim, commencing with the lowest.

GANOCEPHALA.

In the genus Trimerorhachis (Cope) there appears to be a
distinct opisthotic bone in addition to the intercalare, as in
the fishes. In form it is much like the prootic, but in reversed
position ; its anterior thin edge forming a suture with the pos-
terior thin edge of the latter. The two together form on their
inferior surface a spout-like groove, which extends outwards,

1 Read before the United States National Academy of Sciences, April, 1888. Ab-
stract published in American Naturalist, 1888, p. 464.

2 On the Structure and Development of the Skull of the Common Frog, Transactions
of the Royal Society, London, 1870, p. 137; Ox the Structure and Development of
the Skull in the Batrachia, \oc. cit., 1875, p. 601; On the Structure and Development
of the Skull in the Urodelous Amphibia, loc. cit., 1876, p. 529.

8 Das Kopfskelet der Urodelen ; Morphologisches Fahrbuch, 1877, pp. 352, 459.

298 COPE. [Vo.. II.

terminating at the narrow truncate extremity of the two bones.
At the base of the opisthotic, and between it and the parasphe-
noid, is situated the fenestra ovale. This is closed by the
extremity of a columella auris, whose proximal part at least may
be homologized with the stapes, since no other element corre-
sponding with the latter is visible. The columella is then
directed outwards, backwards, and upwards to the notch which
is formed between the adjacent borders of the intercalars and
suspensorium, where it terminates without having displayed any
segmentation. This notch, which is present in all the Permian
Batrachia known to me except Acheloma, may have been occu-
pied by a membranum tympani, and that the Ganocephala had,
like the Salientia, distinct external organs of hearing, thus dif-
fering from the Proteida and Urodela.

RHACHITOMI.

The only genus in which I have observed ossicula auditus is
Zatrachys (Cope). Here the parts resemble nearly those de-
scribed in Trimerorhachis. The columella! is curved outwards
and backwards, and terminates at the notch external to the os
entercalare, which was, I suspect, covered by a membranum tym-
pani as in the Salientia.

PROTEIDA.

In Necturus (Pl. XXIL, Fig. 1) the stapes is osseous and has its
columella directed abruptly forwards. ‘It articulates with a cor-
responding process of the squamosal bone, which extends pos-
teriorly to meet it from the posterior bone of the latter. The
quadrate part of the suspensorium of the mandible is exten-
sively osseous. The distal extremity of the ceratohyal is not
articulated with anything, but is connected with the quadrate
by the hyosuspensorial ligament, and with the angle of the
mandible by the mandibulo-hyoid ligament, as has been pointed
out by Huxley.?

In Proteus the relation of the stapes to the squamosal is
similar in general to that in Necturus, but the connection

1 Transactions American Philosophical Society, 1886, p. 290.
2 Proceedings Zotlogical Society, London, 1874, p. 192, Pl. XXIX. Professor
Huxley does not describe or figure the relation of the stapes to the squamosal bone.

No. 2.] HYOIDS AND OTICS OF BATRACHIA. 299

=<

between the anterior process of the former and the posterior
process of the latter is accomplished by an intervening bit of
ligament. The quadrate cartilage is little or not ossified in
Froteus. The ceratohyal is not articulated at its distal end, but
the latter is attached to the squamosal by two ligaments, the
superior and inferior hyosuspensorials (Pl. I., Fig. 2). The at-
tachment is higher up than in Necturus, as the ceratohyal is
longer.

URODELA.

Trematodcra.

In Cryptobranchus the columella of the stapes is directed
forwards, and terminates in a cartilaginous stem. This is artic-
ulated with the suspensorium of the mandible at its proximal
part, at the line of junction between the squamosal bone and
the quadrate cartilage. The latter is not ossified. The distal
end of the ceratohyal is not prolonged, and it is connected with
the distal half of the posterior border of the quadrate cartilage
by a wide hyosuspensorial ligament. This ligament is inter-
rupted by a subtriangular cartilage, the hyosuspensorial carti-
lage.

I have not examined the genus Megalobatrachus.

Amphiumotdea.

In Amphiuma the stapes is lateral in position, and its short
columella is directed outwards. It is continued as a cartilage to
the truncate posterior apex of the osseous quadrate bone, with
which it articulates by a suture. The quadrate is extensively
osseous. The distal extremity of the ceratohyal is long and free,
and is connected with the middle of the posterior border of the
quadrate by an elongate hyosuspensorial ligament.

Apoda.

Merrem Pseudophidia De Blainville. Gymnophiona Miill.

In Typhlonectes (compressicaudus) the stapes is osseous,
and is lateral in position. Its columella is short, and is directed
forwards, and is connected by ligament with the posterior
border of the quadrate. The distal end of the ceratohyal is
entirely free from the manibular suspensorium.

300 COPE. [ Von. ite

In Dermophis (mexicanus) the stapes is lateral in position,
and is osseous. Its columella is robust and osseous, and extends
forwards, abutting against the posterior border of the quadrate,
with which it forms a close movable articulation. The quadrate
is completely osseous, and is freely articulated proximally with
the cranium. The ceratohyal is free, and not connected with
the suspensorium.

Pseudosauria.

De Blainville ; IZyctodera, J. Miiller.

This extensive group is most conveniently considered by
families.

In the Amblystomide the columella of the stapes is replaced
by the stapedius muscle. This is directed posteriorly, and away
from the suspensorium. The ceratohyal is short distally, and
its extremity is articulated to the distal part of the posterior
border of the quadrate cartilage. The quadrate cartilage is
ossified distally, but not proximally.

In the Plethodontidz the stapes has the same character as in
the Amblystomidz, except that in some specimens a slender car-
tilaginous process is seen to be directed towards the quadrate car-
tilage in Plethodon glutinosus and Spelerpes ruber. This is
probably the persistence of the larval condition of both this fam-
ily and of the Amblystomidz. In the larva (Pl. I, Figs. 7, 9)
the columella of the stapes is directed forwards, and is con-
nected with the proximal part of the quadrate cartilage by a
short cartilaginous rod. In the larva of Chondrotus tenebrosus
the connection is completed for a short distance by ligament.
Thus the larvee of these two families present the character of
the mature members of the suborders Trematodera, Amphiu-
moidea, and Pseudophidia. The quadrate in the Plethodontidze
is ossified in its proximal part only. The ceratohyal has its
distal extremity curved forwards, and articulated by distinct
suture with the quadrate cartilage or bone; in Plethodon glutt-
nosus it is inserted in a fossa (Pl. I., Fig. 14).

In Desmognathidz the characters are as in Plethodontidez.

In Salamandridz the position of the stapes is as in the
previous families, but the relations of the extremity of the
ceratohyal are as in the larve of those animals, or as in the

No. 2.] HYOIDS AND OTICS OF BATRACHIA. 301

Amphiumoidea. The extremity is connected with the quadrate
bone by a hyosuspensorial ligament. In Salamandra the cera-
tohyal and the ligament are of moderate length.

In the Pleurodelidz the arrangement is as in the Salamandri-
dz. In some of the species the ceratohyal is greatly elongate. In
the Diemyctylus torosus the free extremity of the ceratohyal ex-
tends to the inferior line of the occipital condyle, carrying with
it the hyosuspensorial ligament. This ligament is elongate, and
arises from the proximal part of the posterior border of the quad-
rate cartilage (PI. II., Fig. 3). Inthe D. virtdescens this pecu-
liarity is carried still further. The ceratohyal extends to the
lateral crest of the exoccipital, and is received into a fossa of its
inferior surface, as has been pointed out to me by my friend Dr.
E. E. Galt. The hyosuspensorial ligament extends from the
proximal part of the quadrate cartilage beneath the ridge men-
tioned to the apex of the ceratohyal (Plate II., Fig. 4).

TRACHYSTOMATA.

In Siren the stapes is osseous. Its columella is replaced by
the stapedius muscle, which extends posteriorly. It has no
connection with the suspensorium. The quadrate is cartilagi-
nous. The ceratohyal is large and is much produced distally.
It is connected with the posterior part of the quadrate, the ex-
occipital, and the stapes by a wide hyosuspensorial ligament.
It is inserted on the anterior side of the ceratohyal oppo-
site the quadrate, and is interrupted by a hyosuspensorial
cartilage, as in Cryptobranchus.

SALIENTIA.

Laurenti. Axura Dumeril.

The stapes in this order resembles that of the Urodela. It is
an oval disc without distinct process, and gives insertion to a
stapedius muscle near its centre. But this order differs totally
from the other existing orders, in the presence of a chain of
ossicula auditus, which extends from the border of the stapes to
the dermal membranum tympani. There are three of these,
which have been named the interstapedial, the mesostapedial,
and the epistapedial. The interstapedial is a bony style with a
cartilaginous basis which originates alongside of the anterior

302 COPE. [Vons ik

border of the stapes, in a shallow cup-like expansion which abuts
against the cranial wall. The shaft is cylindric. The meso-
stapedial is a cartilage which is attached to the narrow extremity
of the interstapedial much as an anther of a flower is attached
to its filament. The proximal part of this element is shorter
than the distal, and is connected with the superior part of the
quadrate by a ligament, the mesostapedial. The distal part is
deflected at a strong angle to the interstapedial, and is frequently
somewhat spatulate by reason of an expansion distally. Its ex-
ternal face is flat and is applied to the internal face of the epi-
stapedial. The latter is a cartilaginous disk which closes the
tympanic chamber externally. It fits like a lid on the cartilagi-
nous annulus tympanicus, which extends beyond it all round.
The annulus tympanicus is a thin and wide cartilaginous ring
with a thickened margin, which is not continuous, but is inter-
rupted at its superior outline. This interruption is occupied by
the distal end of the interstapedial, and the proximal part of
the mesostapedial. The distal part of the latter extend verti-
cally across the median foramen. These structures have been
described and figured by Parker (l.c.), who has found them to
be generally similar in all the families of the order. J] have’
examined all the principal types, and give figures of them in
the genera Xenopus, Discoglossus, Stereocyclops, Scaphiopus,
Buto, Hyla, and Rana (PL. IL, Figs. 7-12; FU ies ay

The ceratohyal is slender at the point of connection with the
skull. This is just in front of and external to the cartilaginous
base of the interstapedial. It is continuous with the cranial wall
in some species. It is involved, just distal to its origin, in the
annular igamentum tympani, which forms the posterior wall of
the tympanic chamber; but it has no structural connection with
it.

The development of the Saliential skull has been studied by
various authors, especially by Dugés, Huxley, and Parker. I
have examined series of Rana virescens, R. clamata, and R. cates-
briana for the purpose of determining the homologies of the
auricular bones of this order, by a study of their development.
It has been shown that the ceratohyal cartilage is, for the greater
part of the life of the tadpole, articulated with the quadrate car-
tilage, first on its inferior, and then later on its posterior face.
Professor Parker believes that it is a dismemberment of the dis-

No. 2.] HYOIDS AND OTICS OF BATRACHIA. 303

tal half of the third ventral arch of the skull, and that the supe-
rior half of the same becomes fused later with the second arch,
thus forming the quadrate cartilage as it exists in adult Salientia.
On approaching maturity, the ceratohyal leaves this connection,
and is attached to the base of the skull as above described. My
observations coincide with those of Parker in that the ossicula
auditus do not appear until a later period of larval life in the
genus Rana. But they appear before the ceratohyal has aban-
doned its articulation with the quadrate cartilage. They then
arise as follows: the epistapedial occupies from the first its
normal position as a disk of cartilage at the flexure of the quad-
rate cartilage. The interstapedial, on the other hand, arises as
a bud from the normal position of its base, and gradually extends
itself anteriorly. It early appears as cartilage with a short, free
membranous extremity. The latter becomes the mesostapedial
cartilage. These elements gradually elongate until they reach
the epistapedial. For a time they reach no farther than the
quadrate cartilage, and they rest on it, as in the Proteida and
larvee of Urodela.

CONCLUSIONS.

From what has preceded, the following conclusions may be
derived :—

First. The relations of the stapes to the quadrate cartilage or
bone are of two types in the Urodela. The one is possessed by
the Proteida, Trematodera, Amphuimoidea, and Pseudophidia ;
the other by the Pseudosauria and Trachystomata. The larval
structure in the Pseudosauria, and inferentially in the Trachy-
stomata, is identical with the structure characterizing the adults
of the other division. This is confirmatory of the opinion which
I have expressed 1 as to the origin of the genus Siren. This is to
the effect that Siren is an animal which is descended from a
land salamander, and that its immediate ancestor became
aquatic again at a comparatively late period of geological time.
My opinion was at first suggested by the condition of the bran-
chize in very young animals, where they are functionally abor-
tive, and do not become respiratory organs until later in life, the
largest animals having the best developed gills. The characters

1 American Naturalist, 1885, p. 1226.

304. COPE. [Vou. IL.

of the stapes confirm this view, since they are those of land
salamanders, as distinguished from those of aquatic habitat.

Second. There are also three types of relation between the
ceratohyal arch and the skull. In the one there is no connection
between the two, as in the Pseudophidia. Secondly, the con-
nection is by ligament. This is seen in Proteida, Trachysto-
mata, and all Pseudosauria except the Amblystomidz and Pletho-
dontide. The last two families embrace the third type, in
which the ceratohyal is articulated by suture with the quadrate.
This last type is the most specialized, since the larve of those
families display the connection between the ceratohyal and the
skull similar to that seen in the types first and second. Thus
the Salamandridz, which are superior to the Plethodontidze
in their osseous carpus and tarsus, and opisthoccelous vertebree,
have the hyoid connected with the skull, as in the larvze of the
latter.

Third. Ata stage in the history of the development of the
Salientia, the relations of the stapes and of the ceratohyal to
the skull are the same as in a transitional stage of the Urodele
family of Plethodontidz ; or, taken separately, the relations of
the stapes are those of Proteida, Trematodera, and larval Pseu-
dosauria, while the relation of the ceratohyal is as in adult Pletho-
dontidz and Amblystomide. This is when the interstapedial
cartilage connects the stapes with the posterior face of the
quadrate cartilage, and where the ceratohyal articulates with the
posterior face of the quadrate at its distal part.

Fourth. It is not probable that the epistapedial forms an
integral part of a single primitive element, which includes
the other osstcula auditus, as it originates independently of
the interstapedial and mesostapedial.

Fifth. The interstapedial and mesostapedial do not, at any
time in the history of the development of the genus Rana, form
any part of the ceratohyal or meckelian ventral arches. As the
incus and malleus of the Mammalian ossicula auditus are seg-
mented from the proximal parts of these arches, embryology
indicates that they are not homologous with the ossicula of the
Salientia. From this point of view, the latter form a special
line of development, distinct from that displayed by the Mam-
malia, unless the developmental record has been greatly falsi-
fied by caznogeny. From the embryological standpoint, it

No. 2.] HYOIDS AND OTICS OF BATRACHTA. 305

follows that the osszcula auditus of the Batrachia Salientia must
be excluded from the discussion of the homologies of the Mam-
malian ossicula.

Sixth. But the characters of the Ganocephala and Rhachi-
tomi permit the following reflections, since the latter order is
the one from which the Salientia derive their descent. The
existence of a well-developed columella auris, which is unseg-
mented, in the former orders, apparently like that of the Lacer-
tilia, suggests that the segmentation seen in the Salentia is a
specialization of later origin. This columella has also the posi-
tion of the proximal part of the ceratohyal in the adult frog and
the larval salamander. As the position of this element in all
but the youngest tadpoles is a result of coenogeny, it may be
inferred that the osszcula auditus of both the Rhachitomi and
the Salientia represent the separated proximal end of that arch,
and hence be truly homologous with the incus of the Mam-
mal. The probability that this is the case is increased by the
character of this element in the Pelycosaurian genus Clepsy-
drops,! — where the columella extends to the cranial wall, leav-
ing the stapes to one side. This is exactly comparable to the
relation between the interstapedial and the stapes seen in the
Salientia, except that the two elements are not actually con-
nected, as in Clepsydrops. Palaeontology then modifies the evi-
dence from embryology, and renders it probable that the
columella auris of the Permian genera, the interstapedial, and
the incus are homologous elements, and originated by segmen-
tation from the proximal end of a ventral cranial arch, probably
the ceratohyal.

Seventh. It follows from what has preceded, that the con-
dition of the representatives of the osstcula auditus in the
Urodela is one of degeneration.

Liighth. It becomes probable, but not certain, from the posi-
tion of the tympanic disk in the Rhachitomi, at the proximal base
of the quadrate bone, that the epistapedial cartilage has originated
as a segmentation from the proximal extremity of the quadrate
cartilage, and is therefore truly homologous with the Mammalian
malleus. This is, however, nothing more thana probability. For
a considerable part of the material described in the preceding
pages I am indebted to the United States National Museum.

1 See Proceedings American Philosophical Society, 1884, p. 41, Pl. I., Fig. 2.

306 COPE.

EXPLANATION OF PLATE XXII.

The relations of the quadrate, stapedial, and hyoid apparatus. In Figs. f, 3, 9,
14, 15, and 76, the squamosal bone has been removed.

Figures twice natural size, excepting I, 3, 4, 7, and 8, which are natural size, and
10, II, and 12, which are three times natural size.

Fic. 1. Mecturus maculatus ; squamosal removed.

Fic. 2. Proteus anguinus.

Fic. 3. Cryptobranchus allegheniensis; the middle of the squamosal removed,
the extremities remaining.

Fic. 4. Amphiuma means; a, from behind.

Fic. 5. Zyphlonectes compressicaudus; from the Belize.

Fic. 6. Dermophis mexicanus; with the quadrate bone turned up, exposing its
inferior face, and that of the quadrato jugal; 4a, the same with the quadrate in
normal position. From Mexico.

Fic. 7. Chondrotus tenebrosus ; larva 250 mm.

Fic. 8. Chondrotus tenebrosus; adult.

Fic. 9. Amblystoma tigrinum,; \arva; squamosal removed.

Fic. 10. Amblystoma punctatum; adult.

Fic. 11. Hemidactylium scutatum.

Fic. 12. Batrachoseps attenuatus.

Fic. 13. Gyrinophilus porphyriticus.

Fic. 14. Plethodon glutinosus ; squamosal removed.

Fic. 15. Autodax lugubris; squamosal removed.

Fic. 16, Spelerpes ruber ; squamosal removed.

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308 COPE.

EXPLANATION OF PLATE XXIII.

The relations of the quadrate, stapedial, and hyoid apparatus in Urodela and Sali-
entia. Figures twice natural size, with separate details larger.

Fic. 1. Desmognathus nigra; a, stapes separate and enlarged, the squamosal
in place.

Fic. 2. Salamandra maculata 2; the squamosal separated.

Fic. 3. Diéemyctylus torosus, squamosal removed; a, separate squamosal.

Fic. 4. Diemyctylus viridescens, three times natural size; the squamosal removed.
2a, the squamosal, external side; 4, apex of ceratohyal, with hyoquadrate ligament.

Fic. 5. Siren lacertina +; squamosal in place.

Fic. 6. Discoglossus pictus, partly posterior view; @, ear bones, and origin of
ceratohyal, enlarged.

Fic. 7. Bufo lentiginosus americanus, the squamosal removed; a, the squamo-
sal separate.

Fic. 8. Scaphiopus hammondii, the squamosal removed; a, the squamosal; 4,
the ear bones.

Fic. 9. Ayla gratiosa, the squamosal removed; a, the squamosal; 4, the ear
bones and cartilages in profile, the cartilages of the tympanum divided by vertical
section; c, the ear bones and cartilages undivided, external view.

Fic. 10. Xenopus calcaratus, partly from behind, with squamosal in place.

Fic. 11. Stereocyclops incrassatus, squamosal in place; @, stapes and ear bones
and cartilages.

Fic. 12. Rana pretiosa, squamosal in place; @, ear bones and vertically divided
cartilages,

Journ. Morph.Voli.

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310 COPE.

EXPLANATION OF PLATE XXIV.

Fic. 1. Rana virescens, adult, X 2; @, squamosal bone; 4, ear bones without
epistapedial.

Fic. 2. Rana virescens, larva with hind legs, and developed fore legs concealed,
the skull X 2; a, the hyoid apparatus from below, X 4.

Fic. 3. Rana catesbeyana, larva further advanced than that represented in Fig. 2;
showing the first appearance of the auditory cartilages at ST and AT.

Fic. 4. Zrimerorhachis insignis of the Permian bed of Texas; part of skull from
below, showing columella at s¢.; natural size.

Fic. 5. Zvrimerorhachis insignis basicranial axis from below, without stapes;
natural size.

Fic. 6. Zatrachys serratus, wpper posterior part of skull from above; natural
size.

Fic. 7. Zatrachys serratus, inferior view of external part of posterior part of
skull of individual represented in Fig. 6; showing columella.

EXPLANATION OF LETTERING.

A.T., Annulus tympanicus; B.0., basioccipital; C.Br., Ceratobranchial; C.Z.,
Ceratohyal; C.77.,Cornutrabeculi; £.5., Epistapedial; £7z., Ethmoid; 4£x.0., Ex-
occipital; #.P., Frontoparietal; A7., Hyomandibular; .Q., Hyosuspensorial liga-
ment; /zz., Intercalare; /.S¢., Interstapedial; ¥. Jugal; Z/, Lower labial cartilage;
Mk., Meckel’s cartilage; JZx., Maxillary; J/z., Mandible; J7.S., Mesostapedial;
0.C., Occipital condyle; P., Parietal; Parv., Parasphenoid; /g., Pterygoid; Pm.,
Premaxillary ; Pod., Postorbital arch; @Q., Quadrate; Q.C., Quadrate cartilage; S., Sz,
Stapes; Sg., Squamosal; .S/., Superior labial cartilage; 7., Trabeculum; 7Z7y., Posi-
tion of Membranum tympani.

Cartilage, blue; ligament and membrane, yellow; bone, white.

Journ. Morph. Voli

ED. Cone del

PLXXIV.

ON THE AFFINITIES OF APHRIZA VIRGATA.
[Based upon a comparative study of its skeleton. |

R. W SHUFELDT, M.D., C.M.Z.S.

DurinG the latter part of November, 1885, Surgeon Thomas
H. Streets of the United States Navy, then naturalist of the
United States Exploring Steamer “ Patterson,” kindly sent me
a skeleton of the Surf-bird, the subject of the present memoir;
and again in August, 1886, the same distinguished officer for-
warded me a fine pair of skeletons of this species, represent-
ing both sexes, adult. All of this material was collected by
Dr. Streets in Alaska, and I am indebted to him also for skele-
tons of Charadrius squatarola and Arenaria melanocephala, the
former taken in San Francisco Bay, the latter at Port Townsend,
Washington Territory, and placed at my disposal for comparison
with the skeletons of Aphriza.

As additional material for the osteological comparisons the
writer here proposes to make, I find I have at my command two
skeletons of adult specimens of Hematopus bachmani (Nos.
13,636 and 13,637), belonging to the Smithsonian Institution of
Washington; and finally, in my own cabinet several skeletal
preparations of the Charadritde and Tringee, all of which will
be of assistance in the work now in hand.

Aphriza virgata constitutes but another one of those forms
around which centres so much that is of interest to the sys-
tematic ornithologist, owing to the fact that even after more
than a mere superficial examination we discover not a little in
its anatomy that is inclined to puzzle one, when called upon to
pronounce as to its kinship with more or less nearly related
groups or types,

Of the first skin that he ever examined, Audubon wrote:
“The remarkable bird here represented, which in form and
size bears a considerable resemblance to the Knot [Zvinga ca-
nutus|, was procured by Mr. Townsend on the shore of Cape

312 SHUFELDT. [Vot. II.

Disappointment, and proved to be a female.”? And Dr.
Coues remarks, in defining the genus, — “ General character
of plumage, in its pattern of coloration and seasonal changes, as
in Tringe@. One species, a remarkable, isolated form, perhaps
a plover, and connecting this family with the next by close
relationships with Strepsz/as, but with hind toe as well devel-
oped as usual in Sandpipers, and general appearance rather
sandpiper-like than plover-like. <Aphrizine might go under
Hematopodide next to Strepsilas ; or, perhaps better, Aphriza
and Strepsilas might together constitute a family APHRIZIDA,
next to, but apart from, Hematopodide.” *

Two years after the publication of the doubts here candidly
expressed by this eminent authority, the American Ornithologi-
cal Union issued its official Check-List, wherein the arrangement
proposed was adopted; and we find the Aphriz7de@ with its one
species, A. virgata, including the sub-family Avenariine, the
Turnstones, standing between the Plovers on the one hand, and
the Oyster-catchers on the other,? an arrangement which proba-
bly meets with the views of the majority of avian taxonomists of
the present time.

Believing that under these circumstances a full account of
the skeleton of Aphriza will prove an acceptable contribution to
the literature of the family, as well as a useful work to the better
understanding of the osteology of the Lzmzcole generally, it was
in view of this that I undertook the task. So far as my mate-
rial at hand will admit of it, the study will be made thoroughly
comparative, and in the end it may go to show that, for osteolog-
ical considerations at least, the position selected in the system
by ornithologists may be the most natural one to create for our
Surf-bird, or a somewhat different light may be cast upon the
problem ; in any event we are satisfied that more light in such
matters is a thing most to be desired, and this alone morphology
has the power of affording.

The Skull.—When we come to submit the skulls of adult
specimens of certain true 77izgee to moderately prolonged ma-
ceration in water, we invariably find that the premaxillary bone
detaches itself, as does the dentary of the mandible, leaving in

1 Birds of America, Vol. V., pl. 228.
2 Coues, E, Key to North American Birds, 2d. ed., p. 605. 1884.
8 Check-List of North American Birds, pp. 160-166. New York, 1886.

No.2.) APHRIZA VIRGATA. 313

the first case the long, thread-like extremities of the palatines and
median processes of the nasals freely projecting forwards, and
in the latter instance, a similar condition of the mid-ramal
elements of the lower jaw. TZyvinga, Actitis, and others have
their skulls behave in this manner, under similar circumstances,
and it is quite characteristic of them; whereas, on the other
hand, macerate the skulls as long as we may, no such detach-
ment ever takes place in the Surf-bird, nor in Turnstones and
Oyster-catchers, nor in such forms as Gallinago and Philohela.
Indeed, this peculiar feature seems to be restricted to the more
typical Sandpipers, and it is worthy of our notice that in Aphriza
it never happens, and I may add that one never observes it to
be the case in any of the Plovers.

Aside from this fact, the general faczes of the form of the
superior osseous mandible in Aphviza, carried back as far as the
rhinal chamber and frontal region, is more as we find it in such
a species as Acéz¢zs, for example, or some of the genus 77inga,
than it has any semblance to either Avenaria, or much less
flematopus. Even when we come to compare the individual
parts, this assertion holds true, including in the observation the
extensive outline of the triangular aperture, on either side, of
the external nares ; and the superior ends of the fronto-maxil-
lary processes of the nasals not overlapping, mesiad, the outer
and juxtaposed margins of their premaxillary processes ; which
latter condition obtains both in the Turnstones and in Oyster-
catchers. Again, in Aphriza we note that the extremity of the
superior mandible in the skull is somewhat tumefied, and marked
over with minute pits, as we find it to be in Gallinago. This
character is absent in such a form as Actztzs and other Sand-
pipers, nor do we find it to be present in Charadrius, Arenaria,
and Hematopus.

In Bachman’s Oyster-catcher (4. bachmanz) the superior
osseous mandible is about seven centimetres long, the remainder
of the cranium being something over 3.5 cm. long, measured
along the median line. Taking these same distances in the
Black Turnstone, we find the first to be 2.5 cm., and the latter
2.3 cm.; but barring this difference in proportion between beak
and cranium in these two species, the superior osseous mandible
in the Turnstone is almost the perfect miniature of that part of
the skull in an Oyster-catcher. We are to note, however, one

314 SHUFELDT. [Vor t8

other difference, and that is, in @matopus the anterior extrem-
ities of the palatines fuse across the median interspace much
further back than they do in the Turnstone, but essentially, as
I say, the plan of these parts in the two birds in question is the
same, and quite different from the corresponding structure in
Aphriza. Plovers in this particular seem to stand between the
Surf-bird and Avenaria.

Taking next these several skulls upon their superior aspects,
and comparing them with the same view in JA. virgata (Fig. 1),
we find that the latter bird again agrees with such a Sandpiper
as Actitis macularia, or with such a species as 7. mzinutzlla.
The cranium being very narrow in the frontal region between
the superior orbital margins, while the vault of the brain-case is
externally rounded, smooth, and ample, being occasionally
marked in some of the Sandpipers by a median, longitudinal
furrow.

In both, the lacrymals jut out about in the same proportion,
and much in the same manner, as they do in a Turnstone.
Aphriza and Actitis show scarcely any tilting upwards of the
superior orbital peripheries, a feature so very conspicuous in
Charadrius squatarola; \ess so in Hematopus, and again quite
absent in Avenaria.

Oyster-catchers exhibit their strong larine affinities in their
prominent out-jutting lacrymal bones, and still more in their
deep and sharply defined glandular fossze over the orbital roofs.
These latter depressions are but fairly well marked in Turn-
stones, while in A. virgata, again agreeing in this respect with
most, if not all true 77zzge@, they are entirely absent.

Passing to the basi-posterior aspect of the cranium, the Surf-
bird is seen to possess, in common with all North American
Limicole, a well-marked supraoccipital prominence, which shows
one on either side, the supraoccipital vacuities being larger in
this species than they chance to be in any Sandpiper at my
hand. Plovers have them next largest, they being very minute
in Avenaria, and not present in any of the skulls of the genus
Hematopus before me, although these latter have large supra-
occipital prominences.

In this last-named genus, too, the “occipital area”’ is sharply
defined by a very strong and raised crest, of a subcircular out-
line. This crest is very much mellowed down in Charadrius ;

No. 2.] APHRIZA VIRGATA. 315

more manifest again in the Turnstones, in which genus the
occipital area is proportionately much smaller; and finally, in
Sandpipers and Aphrviza the crest is present only as a raised
line, which in them also bounds an occipital area of a subcircu-
lar outline, the extremities of the boundary line terminating, on
either side, at the apex of a paroccipital process.

Most limicoline types have the plane of the foramen magnum
nearly coincident with the horizontal plane; and so it is in all
the skulls of the species now before me. But the outline of
this great foramen of the occiput differs considerably in the
several genera, being perfectly cordate in the Surf-bird, with
the prominent posterior apex standing well in between the pair
of vacuities of the supraoccipital prominence, which condition
is enjoyed by most Z7imgee; while in Avenaria and the Plov-
ers there is a slight’ tendency for this aperture to become
rounder, its circularity becoming quite evident in Hematopus.
In all these species, the condyle of the occiput is proportion-
ately very small in each and every species, it being of a hemi-
spherical form, and unnotched.

So in general pattern, taken as a whole, the basi-posterior
aspect of the cranium is more nearly alike in Aphriza and any
true tringine form; while in Turnstones the approach is
towards the Oyster-catchers. And Plovers in this particular
seem to maintain sort of a mid-position between the two latter
groups. H@matopus is notorious for the restricted confines of
its basi-temporal area at the base of the cranium,! and this space
is never very wide and deep in any of the Lzmzcole.

Figure 3 of my drawings in the plate shows the skull of A.
virgata upon direct lateral view, and here we have a number of
points to examine. First, it will be observed that the pars plana
is of a quadrilateral outline, thoroughly ossified, and with its
superior and inferior borders not in contact with either the
orbital roof above or the maxillary bar below. The out-jutting
lacrymal sends down a spicula of bone, which diminutive process
turns backwards to have its lower end anchylose with the pars

1 Had not the writer already fully figured the skeleton of the Black Oyster-catcher
(which figure and its description has been accepted for publication by the Yournal of
Anatomy of London), I should have taken pleasure in presenting drawings of it in
the present connection, as it constitutes a wonderfully interesting form for comparison
in this way with species now under consideration.

316 SHUFELDT. [VoL. II.

plana, on its anterior aspect at a point below, and to the inner
side of its externo-superior angle. I am thus particular in de-
scribing in detail the point of attachment of this extremity of
the descending process of the lacrymal, for the reason that in
some Sandpipers it is found to be attached to the very angle
above referred to, while just before arriving there it sends for-
wards another small, pointed spine, the extremity of which
latter is free, and directed somewhat inwards towards the
rhinal chamber. No little variety, however, is to be met with
in this particular among the 77zzge@, and in such a form as the
solitary Sandpiper (2. solitarius) the free end of the lacrymal is
attached at a point corresponding to the site of its attachment
in Afhriza. With the true Plovers the case is still different, for
in them the gars plana is quite small and with rounded angles,
while the lacrymal has a long, slender, descending process ter-
minating in a free point below, and likewise has the anterior-
projecting spine coming off from a mid-point of its continuity.?

Arenaria has a large square pars plana, and in this form the
lacrymal soon fuses at its lower end with the supero-external
angle of the osseous lamina in question; while in Hematopus
the pars plana is again found to be small, and the lacrymals
very large, with their descending processes thick and strong,
being fully anchylosed with the outer border of the pars plana,
and projecting a short distance below that plate, though not arriv-
ing at the maxillary bar.

From all this I should say, then, that in Aphviza, Arenaria,
and most true Sandpipers the gars plana and the lacrymal bones
were more or less alike, having much the same relation to each
other; but in Plovers and Oyster-catchers these structures are
essentially very different; not only do they differ with each
other, but with the aforesaid mentioned types, and in a manner
set forth in the last paragraph.

Limicoline birds are notorious for the large vacuities that occur
in their interorbital septa, rendering that osseous partition in the
vast majority, if in not all the species, a very deficient bulwark
between the-orbits. Mematopus has it most entire, while in
Aphriza, the Turnstones, Sandpipers, and Plovers, it commonly

1 For an excellent figure of this arrangement of the lacrymal, see Huxley’s figure
of the enlarged skull of C. p/uvialis in his paper, “On the Classification of Birds.”
P.Z.S., 1867, p. 427, Fig. 7, L.

No. 2.] APHRIZA VIRGATA. 317

presents two large deficiencies, or often one imperfectly divided
by a backward-extending remnant of the septum springing from
the mesethmoid (Fig. 3).

In the Sandpipers (Ac¢z¢7s) the entire anterior wall of the
brain-case is, mesiad, wonderfully lacking in bony support; on
the other hand, in the black Oyster-catcher the foramina for the
first pair, as well as for the optic nerves, are entire and com-
pletely encircled by bone. All the species that we have thus far
mentioned in this memoir possess a straight and slender zxzfra-
orbito maxillary bar of nearly uniform calibre throughout.

Figure 1 of the plate will show the peculiar orbital processes
of the guadrates in the Surf-bird, and indeed they are nothing
less than unusually enlarged, thin, and compressed lamina of
bone, which in no small degree contribute to the floor of the
orbit on either side. We also find the two remaining apophyses
of a quadrate to be more than commonly large and stout, and
each of these bones has a double mastoidal facet ; two mandib-
ular facets, the inner one being as good as two in Aphriza,
though less markedly divided in Turnstones, Oyster-catchers,
or Sandpipers; and finally, a proportionately large pterygoidal
facet situated upon the internal aspect of the bone, just above
mandibular articulation. Few departures are to be detected
from this almost common pattern of the quadrate among the
Limicole; where, too, I may add, this bone is always found to
be perfectly pneumatic, as is the greater share of the skull itself
among these shore-birds. Still confining ourselves to the lateral
aspect of the skull, we are to note the long, spicula-form, sphe-
notic process possessed by Aphriza, and the less conspicuous and
bifurcated squamosal apophysis ; both of which features are far
better marked in this species than they are in any of its allies
now beforeme. Turnstones show quite deeply marked temporal
foss@ that lack something less than a centimetre of meeting
posteriorly over the supraoccipital prominence. Hematopus also
show these, but here they are strictly confined on either side to
the squamosal region, and do not encroach in the slightest
degree upon the posterior aspect of the cranium. Charadrius
likewise faintly displays the same feature, a feature which is
so prominently seen in any of the skulls of the Lavide and
their kin.

Careful search through my material fails to detect the presence

318 SHUFELDT. [VoL. II.

of such fossze, either in the Surf-bird or among the Sandpipers.
Actitus has a skull as free from any such depressions in its tem-
poral region as the veriest Thrush that ever lived, and the same
remark fully applies to our least Sandpiper and others of its
genus. Another interesting point to notice in the cranium of
A. virgata is the marvellous degree to which a tympanic cavity is
exposed, as well as the external opening of the Eustachian tube
within it. These parts seem to depend upon the large quadrate
anteriorly, and the somewhat arching paroccipital process be-
hind, for their protection, in so far as any osseous surrounding
defence is concerned.

This condition obtains in varying degree in the allied forms
we have under consideration ; it being notably the case in Turn-
stones and in Yematopus, though Plovers and Zringee are but
little better off in this respect, perhaps the former of these last
being the better provided of them all.

And now, finally, turning to the nether aspect of the skull in
Aphriza, we are at first struck with the diminutive size of its
pair of pterygoid bones. These are short, compressed from
above downwards, sharpened all along their anterior margins ;
while behind they are characterized by strong basipterygoid
processes, which articulate in the usual fashion with the facettes
designed for them at the base of the sphenoidal rostrum.

In the black Oyster-catcher, a pterygoid is no longer than the
mandibular aspect of the corresponding quadrate is wide, and
this statement holds true for the other skulls we have been ex-
amining in connection with Aphriza.

For the Plovers the pterygoids are well shown in Professor
Huxley’s figure of Charadrius pluvialis,| although they are com-
paratively much smaller in such a species, for instance, as C.
squatarola, or others of our North American Charadriide.

Upon comparing the palatines of A. virgata with those bones
in the allied forms before us, we meet with several excellent dis-
tinctive characters, especially when we include in this compari-
son the maxillo-palatines. In Plovers, Sandpipers, Turnstones,
and Oyster-catchers, the postero-internal angles or heads of the

1 Ibid. P. Z. S., 1867, p. 427, Fig. 6. These bones are also represented in my figure
of the base of the skull in the Mountain Plover (4. montana); Your. of Anat. and
Phys. London, October, 1883, Pl. V., Fig. 3, Ag., where their relatively small size can
at once be appreciated.

——

No. 2.] APHRIZA VIRGATA. 319

palatines, each turns outward as it articulates with the anterior
end of the corresponding pterygoid ; nor do these palatine heads
meet each other in the medium plane. With this common fea-
ture, Afhriza agrees ; but when we come to examine the postero-
external angles of these bones, we find them obliquely truncated
in our subject, or at least the hinder ends of the palatines them-
selves thus obliquely truncated, forming obtuse postero-external
angles, which angles are rounded off in Actztus, Charadrius, and
in Avenaria, while in Hematopus a moderate, backward-extend-
ing and rounded process is found at their site. In this latter
species, too, the internal and external laminz of a palatine bone
are very conspicuous, as they are, though less so, in the Surf-
bird, Spotted Sandpiper, and the Black Turnstone. Plovers have
this character much subdued. Mesiad, the superior and at the
same time, internal borders of the palatines, beyond the “ptery-
goidal processes,” along the rostrum, come in contact with each
other in all of the enumerated species; and in all completely
fuse anteriorly with the hinder limbs of the vomerine bifurca-
tion. Coalescence, again, is most thorough in all these forms
among the anterior ends of the palatines and those parts of the
maxillaries and premaxillaries with which they come in contact,
upon either side (Fig. 2). From this description, then, of the
palatines, it is clear that A. virgata possesses them in a form
essentially its own, and further that the pattern varies in all the
allied groups or species.

Not so, however, is this altogether the case with the maxzllo-
palatines. One of these in Aphriza virgata is seen to be a
shell-like process; extending backwards, concave externally ;
the reverse being the case upon its mesial aspect ; perforated by
a few foramina; and finally, xot unzted along its inferior border
with the palatine of the same side which extends beneath it.
Charadrius also possesses a maxillo-palatine almost identical
with this, and in the last-named feature, the true Sandpipers
also agree, but in these latter birds the bone is much narrower
and more curved.

Passing to the Oyster-catchers and Turnstones, a very different
state of affairs is to be met with; for in Hematopus, for instance,
we find a maxillo-palatine to be quite a thick, laterally compressed
and unperforated lamina of bone, which completely fuses with
the corresponding palatine for the entire length of tts inferior

320 SHUFELDT. [Vot. II.

margin, appearing in the adult to be a part of the palatine itself.
A similar arrangement is to be found in Avexaria, — so that in
this character, Turnstones and Oyster-catchers agree, while the
Surf-bird, Plovers, and 77mge@ are fundamentally alike; in
the first, the maxillo-palatines have, in the adult individual,
coalesced with the palatines, each on its own side; while in the
three last-mentioned families the maxillo-palatines are indepen-
dent and freely projecting processes.

Aphriza agrees with all the allied types before us, in having a
long, slender vomer, its posterior limbs anchylosing with the
palatines behind, and a median carination extending for its en-
tire length along its nether aspect. With the exception of
Hematopus, the bone in all is pointed anteriorly, and in the ex-
cepted genus it is at that end distinctly bifurcated.}

In the form of its mandzble, A. virgata substantially agrees
with the Plovers and Sandpipers. The upturned, slender
process at the angle is well developed, and the inturned ends
of the articular cups are quite prominent, showing the usual
single pneumatic foramen at each extremity. Two vacuities
occur in either ramus, a small surangular one, and a long, semi-
closed, splenial one, the sides of the jaw in this region being verti-
cal and rather deep. The symphysis is rounded beneath, concaved
above, and equals in length about one-fifth the length of a ramus.
In the Black Oyster-catcher the symphysis equals more than a
third of the ramus, and is scarcely at all excavated above, while
it is decidedly wedge-shaped below. Avenaria also has a deep
symphysis to its mandible, but here again it is concaved above
and rounded beneath, and the larger of the two ramal vacuities
is represented by a very open, subelliptical foramen.

Among the more ordinary types of existing birds, the Zyotdean
apparatus, as we know, presents but few differences when we
come to compare it for the various families. Our subject forms
no exception to this statement, and little need be said here in
reference to this part of the skeleton in Aphviza. We find the
arches alluded to to be very delicately constructed, and have
the basibranchials in two separate pieces, the second one being
very short and finished off behind in cartilage. The cerato-

1 Here we have a departure from the rule laid down by Huxley, who has said
that in Schizognathous birds, “ the vomer, sometimes large and sometimes very small,
always tapers to a point anteriorly.” P. Z. S., 1867, p. 426.

No. 2.] APHRIZA VIRGATA. 321

hyals largely coalesce, but the ossification proceeds but a lim-
ited distance into the glosso-hyal, which latter element in the
adult is found to be in cartilage only. Thyro-hyals are notably
slender and of considerable length ; they, too, being posteriorly
tipped with cartilage throughout the life of the individual.
Most Sandpipers possess a hyoidean apparatus similar to the
one I have just described for Aphriza ; and, indeed, no material
difference can be detected for the allied species from other
groups.!

Upon carefully examining the special ossifications of the ear
in a skull of A. wrgata, I fail to detect anything worthy of
detailed record ; the form of the stapedial plate and the coéssi-
fied shaft of the columella have much the same pattern as
we find these parts in the Fowl, and so clearly drawn for us
by Parker.2. Dr. Streets, in preparing my skeletons of Aphriza
for me, threw away the eye-balls, so I am unable to make any
observations here upon the sclerotal plates in this species ; they
have also been lost from my skeletons of Hematopus, the Turn-
stones, and Plovers.

This completes what I have to say here in reference to the
comparative osteology of the skull and its associate parts of the
skeleton in Afhriza virgata, and such deductions as may be
drawn from the study the writer proposes to defer making until
the closing paragraphs of the memoir are arrived at, when the
skeleton as a whole, in this species, will be passed in review, and
the proper comparisons made with the others we have been
considering.

Remainder of the Axial Skeleton. — Since the days that
anatomists first took to counting the total number of vertebrz
in the spinal column of any of our existing Carinate, there
have been difficulties and differences upon that point; and
as to the differences, these have been but multiplied by the
many attempts that have been made to state exactly the num-

1 Unfortunately the hyoid arches of both my specimens of Hematopus bachmani
have been lost, and I am unable to add, by way of comparison, anything about them
here. I am inclined to believe, however, that if any essential difference is to be
hereafter detected in these arches for adult specimens of various representations of
the Zimicole, it may be that some form will show a fusion of the first and second
basibranchials ; but I look for nothing more than some such a difference as this, and
even it may never be found to exist.

* Parker, W. K., Morphology of the Skull, p. 258, Fig. 74, m.st. and st.

322 SHUFELDT. [Vot. II.

ber of cervical vertebra, and the number of true dorsals, in any
particular species. In the case of the total count for the verte-
bree in any adult bird of the kind alluded to, the trouble is with
the pelvic sacrum, and the skeleton of the tail. In nearly
every example it is almost impossible to decide with certainty
as to the number of vertebrz that have been incorporated in
its fusion; while in the case of the tail, the pygostyle is the
stumbling-block, for sometimes in representatives of the same
species this bone in one individual will thoroughly appropriate
to itself a terminal caudal vertebra, that will perhaps remain
free in the other, thus making an additional segment for a bird
of the same species. Then, again, it is pretty well agreed that
when we come to define the line between cervical and dorsal
divisions of the column, we look chiefly to the ribs for assist-
ance; yet these are by no means to be always relied upon; as
sometimes, in the same species, an additional pair may remain
free at the further end of the cervical region, or an additional
pair (always at the anterior part of the dorsal division) may
connect with the sternum by a pair of hamapophyses. So
that one observer might state that the first pair of free ribs
in a certain species of bird were to be found upon the 13th
cervical vertebrze, while another observer, equally careful, finds
an individual of the same species wherein it is the 14th cer-
vical that has the leading pair of free ribs. Thus it is that
confusion and doubt creeps into the work.

After having paid no little attention to the osteology of birds
for more than ten years, now, I am fairly convinced that there
is but one safe or very nearly safe method of arriving at the
total number of vertebrae in the spinal column of any particular
species of the class, and to do it we should have the prepared
skeletons of the young of the species, two, or, better, three, of
them, made just at the time when fusion is about to take place
among the vertebrz, which eventually go to form the pygostyle
in the adult, and when the vertebre composing the pelvic
sacrum are all still individualized. Then the count can be made
with certainty, and we should not fail to have by us at the time
several skeletons of the adult of the same species for compari-
son. Finally, our remaining difficulty, it is evident, cannot be
settled in any such manner, and the only course left to pursue
here, is to state, if possible, the general rule and the noted

NO. 2.) APHRIZA VIRGATA. 323

exceptions. For instance, we may say in a certain species, it
has been found as a general rule that free ribs occur upon the
13th and 14th vertebree, and that upon the 15th, the ribs connect
with the sternum by costal ribs, but examples have been found
in the same species where free ribs were found upon the 12th,
13th, and 14th vertebrz; or again, a specimen of the same
species showed free ribs on the 12th and 13th vertebre, while
the ribs on the 14th connected with the sternum. This is by
no means a fanciful description, as I have studied cases quite
like it, and it only goes to show the utter hopelessness of laying
down hard and fast lines in describing the cervical and dorsal
divisions of the vertebral column in existing birds. On the
other hand, I am inclined to believe that if the zotal number of
vertebrze be counted in the skeleton of the chick of any par-
ticular species, the number will be found to be quite constant.
Now I believe, after carefully re-counting the vertebrz in the
skeleton of the tail in the Mountain Plover (4. montanus),
there should be a quzre placed after the number I have given
in my memoir upon the osteology of that species, as I believe
it should be seven, zo¢ counting the pygostyle ; further, I am
inclined to think I made another miscount, for some reason, in
my specimen of He@matopus, and too many vertebra have been
mentioned as forming the skeleton of its tail in another paper
of mine.”

At the present writing I have not at hand the immature skel-
etons of any of the species we have here under consideration,
and consequently am unable to carry out the suggestions made
in the foregoing paragraphs, so I can candidly admit that the
number of vertebree given below as found in the sacra of the
birds there enumerated must be taken cum grano salts ; although
I will add that I counted them to the best of my ability: the
process can often be assisted by holding the pelvis up to a strong
light, with the dorsal aspect towards you.

In my female specimen of A. vixgata, the ‘“ epipleural appen-
dages”’ are present upon the pair of free ribs on the 15th
vertebra, the reverse being the case in the skeleton of two males

1 [bid., p. 97.

2 Shufeldt, R. W., “Osteology of Mumenius longirostris, with notes upon the
Skeletons of other American Limicole.” Fourn. of Anat. and Phys. London. Vol.
XIX., October, 1884, pp. 71, 72.

324 SHOUFELDT. [Verne

of the same species. Charadrius squatarola seems to have the
usual cervical vertebrz (6th to 9th inclusive) modified beneath for
the carotid canal; while in a Killdeer before me, the series so
modified includes the fifth cervical. Only the free caudal verte-
bree have been counted in the subjoined “ Table,” omitting in
every case to include the pygostyle; a bone that may include
several more, and perhaps vary for the species here given.

TABLE.

Number of vertebrae that possess ribs

Pairs of sacral ribs (they do not reach

sternum).

SPECIES.

Total number of free prepelvic verte-

brae.

ra
te
°
<s
B=]
2
R
a
Be)
vo
=
-
o
>
_
fe
>
~
7)
=)
-
°
ra
vo
a
E
A

The first cervical vertebra that has

free ribs.

which reach the sternum by costal ribs.

The second cervical vertebra that has

free ribs.
Total number of vertebrae in column

exclusive of pygostyle.
Carotid canal in following cervical ver-

Number of vertebrz in pelvic sacrum.
tebrz: (inclusive).

The first vertebra that has ribs which

The third cervical vertebra that has
reach the sternum by costal ribs.

free ribs.
free ribs.

Aphriza virgata

cl
iS)
_

| 6th to oth
| 6th to oth
| 6th to oth
6th to 9th
6th to 9th
| 6th to oth

—
2
-_ -_
- -

Charadrius squatarola .

Los)
ot
wm unum
— mo
fopi plone (on)

ms

t

toy
_

Actitis macularia....

_
ios)

-_
ty
_
aS
_
oO’
to
Land

Heematopus bachmani .

No
al

Arenaria melanocephala|

“SI CN SI “1 © | Number of free caudal vertebrz.

CNS Oie (ON ON Oy ON
-

G2
_ _
on om
_

ion)

i)
OV
No
i

Rhyacophilus solitarius

rl
ios)

We find nothing especially noteworthy in the vertebre of
Aphriza virgata, as they in a general way are fashioned upon
the usual ornithic pattern of those bones among ordinary birds.
The axis, and the three cervical vertebre that follow it, are
especially conspicuous for their prominent neural and hzemal
spines, and their postzygapophyses, which latter extend upwards,
outwards, and backwards, as strong processes in the second and
third cervicals. This last feature is not so manifest in Aphriza
but becomes more so in Avenaria, and in Hematopus arrives at
its maximum development, for in this species the postzyga-
pophyses of the axis and the vertebra next behind it are nearly
as lofty as the great neural spines upon these vertebra, giving
them the appearance of being tricornuted upon their dorsal
aspects. Oyster-catchers have comparatively short parapophy-

No. 2.] APHRIZA VIRGATA. 325

ses in the cervicals, while in both the Surf-bird and in Turn-
stones these are quite long and spicula-form in the fourth, fifth,
sixth, and seventh vertebra; and these last species differ with
Flematopus, in that in this bird the vertebrze of the entire col-
umn are unusually large in proportion to the size of their owner.
Free ribs in all the species before us possess both capitula and
tubercula ; the leading pair being of diminutive size, and gradu-
ally increasing as they near the ribs of the dorsal region. The
last pair usually do not develop unciform appendages, though
they may do so, as in the skeleton of my female Surf-bird, and
an Oyster-catcher before me. In the dorsal region only the first
two, or at the most, three, leading vertebrze possess hzema- °
pophyses, while ossified metapophyses link their transverse pro-
cesses together above. <Aphriza has the neural spines of its
dorsals very low, they being more lofty in the Turnstone, and
still more so in Hematopus. Plovers and 7Tringee have them of
a medium height. We find few or no especial distinctive differ-
ences in the true dorsal ribs of the several species before us, to
render any aid as pointing to near or remote kinship in the case
of any two species compared. Agreeing with the majority of
limicoline birds, these parts are for the most slender, curved as
usual, and rather long, with uncinate processes that do not
completely anchylose with the several ribs to which they belong.

Elsewhere, as I have already said above, I have presented
figures of the pelvis of the Black Oyster-catcher, and it can be
said here now that this bone in Hematopus very markedly dif-
fers from the pelvis either of Aphriza or of Arvenaria. Indeed,
in some respects, the pelvis of an Oyster-catcher reminds us not
a little of the pelvis in Gallus bankiva, it lacks, however, the
propubic spine, and the antero-median borders of the ilia do not
fuse with the sacral crista. Further, it is noted for having a
certain solidity and thickness of the several bones that com-
pose it, quite in keeping with the other parts of the skeleton of
this powerfully built bird. It differs with the general plan of
the pelvis in Aphriza (Fig. 21), and in the Turnstones, in that
in Hematopus the ilium forms a ledge, overhanging to some
extent the ischium and the ischiadic foramen; the postpubis is
far separated from the lower ischiadic margin, and is truncated
almost immediately after passing the ischium behind; finally,
anchylosis is very strong between all the several bones making

326 SHUFELDT. [Vo. II.

up the pelvis in the Oyster-catcher, so that prolonged macera-
tion does not tend to separate them.

One skeleton of Hematopus at my hand shows a curious dila-
tation of the latter third, or less, of the postpubis of the /eft side,
not present in any other specimen, nor upon the opposite side
of the same individual. All these points and characters are
very different in the pelvis of the Surf-bird, wherein this bone
is remarkable for its breadth, and for being, as it were, flattened
out in the vertical direction, — shallowed ; its sides narrow, and
ilia more or less spread. As among Plovers, and most or all
Sandpipers, it shows a double row of interapophysial foramina
down the sacrum (Fig. 21); and the anterior ends of the ilia are
subtruncated and embellished with a delicately raised rim,
nearly always to be seen in limicoline birds. Between the
hinder ends of ilium and ischium, a rounded notch occupies the
entire margin of the bone, which notch in Hematopus is angu-
lated. Postpubis is in contact, more or less, for its entire
length with the lower border of the ischium above it; and is
carried beyond for some little distance to a pointed extremity,
much the same being the case in the Turnstones.

The ischiadic foramen is of considerable size, and of a subel-
liptical outline; this vacuity being unusually large in an Oyster-
catcher, and such a species as the Killdeer Plover.

Without, then, further entering upon a fuller discussion of
minor details, although they have all been carefully noted and
weighed by the writer, I would state that in so far as the Hema-
topodide@ are concerned, the pattern of the pelvis in that group,
as represented by the bone from the skeleton of A. bachmant,
is of quite a different style from the pelvis of either Aphrzza or
Arenaria. That when we come to study the pelvis of A. var
gata, and compare it with the bone in allied types, we discover
that notwithstanding the fact that it exhibits many characters
held in common by the limicoline forms generally, still it is
impressed with a character of its own, being proportionately
broader and shallower than the generality of either charadrine
or tringine pelves. It is most nearly approached by the pelvis
of a Turnstone, while this latter bird shows in its pelvis a marked
shading towards the style of the bone in the Plovers.

Again, Actztis and Afgialitis vocifera possess pelves almost
identically alike in their general form; and in both these

No. 2.] APHRIZA VIRGATA. 327

species the postpubis is separated by more or less of an interval
from the lower margin of the ischium of the same side, along
the middle of its continuity.

Figure 20 of the Plate shows the form upon lateral view of
the pygostyle in A. vzrgata, and that is not far departed from
by the representatives of nearly affined Lzmzcole. In Oyster-
catchers it varies, because in them the ultimate caudal vertebra
usually is coalesced with the bone, giving it the different shape.
The Surf-bird and its allies show the diapophyses of the caudal
vertebrze to be spreading in the first few leading ones; then in
mid-course they become shorter and bend downwards; then long
and more flaring again, to terminate by an aborted one just
before coming to the pygostyle. The ultimate two or three
may develop bifid hamapophyses, which anteriorly stand be-
tween the joints of the centra as chevron bones ; this feature is
well marked in 7. dbachmant.

Oyster-catchers have the neural spines of the caudal verte-
bre notched in front, while Aphriza, Charadrius, and the major-
ity of the Z7zxgee possess these apophyses as plain points.

That time-honored standby of avian skeletologists, the ster-
num, presents among the birds we have been noticing in this
memoir but few insignificant departures from a common pat-
tern, except in the cases of R. solztarius and Actttzs.

Aphriza has the bone (Figs 12 and 15) doubly notched on
each side posteriorly, the outer notches being fully twice the
dimensions of the inner ones, —the outer pair of xiphoidal pro-
cesses thus formed having a tendency to flare outwards;
otherwise, the outline of the sternal body is quadrilateral, being
much concaved above and correspondingly convexed upon its
pectoral aspect. Either costal border shows six hamapophysi-
cal facettes for the costal ribs, while extensive ‘ eostal pro-
cesses’”’ of a triangular outline rear above these in front.

The manubrium is small and sessile, being sharp beneath and
blunt above, and directly between coracoidal grooves, thus pre-
venting the coracoids in the articulated skeleton from infringing
upon each other ; the reverse being the case in Oyster-catchers
and Avenaria, wherein these bones are in contact posterior to
the manubrium, when the former are zz sz¢u. Returning to the
sternum of Apfriza, we are to note its ample carina, which ex-
tends the entire length of the sternal body, being thickened for

328 SHUFELDT. (Vou. II.

the upper two-thirds of its anterior border, sharpened below, and
concaved throughout. Along its lower margin a thickened rim
defines its edge, which is outlined by a long, gentle convexity
from carinal angle in front to mid-xiphoidal process behind
(Fig. 12).

Viewing the bone upon its pectoral aspect, a muscular line —
the zuterpectoral muscular line we will call it here — extends,
on either side, from the boundary of the costal fossa beneath,
to the inner of the pair of xiphoidal notches behind, to the
mesial edge of the same. This line occurs sharply defined
in both Plovers and Oyster-catchers, where it is similarly drawn,
as it is likewise in a Turnstone.

Arenaria has a sternum, which, excepting the fact of its being
a size smaller, is the perfect counterpart of the bone in A. vir-
gata, though in the latter species the sternal keel seems to be
comparatively a trifle deeper in proportion.

When I published my Osteology of Numenius longirostris, I
therein stated that the sternum to a skeleton of the Spotted
Sandpiper (A. macularia) possessed two notches upon either
side, a large outer pair and a very small inner pair. Those
skeletons were prepared and the species diagnosed by a very
incompetent man, and at the present writing I am not prepared
to vouch for the correctness of the statement. I have had to
regret many times since, the confidence I placed in the identifi-
cation of the skeletons which went to make up the collection
of the vertebrate series in the Museum and Library of the
Surgeon General’s Office of the Army at Washington; they
were the cause of a number of oversights creeping into my
avian osteology in early days, which now are being corrected
in my more recent papers. So I am inclined to believe that the
Jfour-notched sternum of Actitis may be a specimen from the
same category; it was “on file” in the same institution. At
any rate, we have before us now an excellent skeleton of Actzézs
of my own collecting, and it possesses but a pazr of notches in
its sternum, otherwise the bone has the general pattern of the
Limicole at large.

In afew days The Auk for July (1888) will be issued, and in
there, in a letter to its distinguished editors, I point out the
fact that the Solitary Sandpiper is another species which has
but a pair of notches in its sternum, and suggest that its old

No. 2.] APHRIZA VIRGATA. 3209

genus, Ryacophilus, be restored for it (at the present writing it is
a subgenus of Zofanus). But the majority of 77zzgee, as for
example, all the true representatives of the genus Z7yinga, have
the “four-notched”’ sternum, and the fact that Actt7s and Rya-
cophtlus have each only a pair of notches, may be of more signi-
ficance in so far as the true affinity of those two species is
concerned, than some of their external characters (that are so
very subject to change from minor causes), but which have alone
been relied upon thus far by the systematist, to classify them.

Finally, then, the fact may be broadly stated, that with respect
to the sterna of Aphriza and Arenaria, they are to all intents
and purposes the miniatures of that bone as we find it in Hema-
topus bachmani ,; and although this is very interesting, the cir-
cumstance goes to prove, in the light of other skeletal characters
of these species, we would utterly fail were we to rely upon this
bone alone as any indication of family, or much less, generic,
affinities.

All the sterna that the writer has examined from the skele-
tons of North American Lzmzco/e were non-pneumatic bones,
and if it is ever found to be otherwise, we must believe that it
is the exception. Ina specimen of 77ixga minutilla in my col-
lection, the bone is so thin that a large perforation occurs on
either side of the keel in the sternal body, and one through the
keel itself, high up in front.

Speaking of the pneumaticity of the skeletons of the several
species we are here considering, I am strongly inclined to be-
lieve that the skull is the only part in any of them where air
gains access to the interior of the bones, and as a rule to no
_ very great extent, comparatively, there.

Turning our attention next to the shoulder girdle (Figs. 11,
16, and 17) in Aphriza virgata, we meet with a scapula having
much the form that that bone assumes among the Shore Birds,
generally, being shaped a good deal like the blade of a miniature
cimeter, and when zz sz¢u in the articulated skeleton bearing the
usual relations to the clavicle and coracoid of its own side. A
coracoid is conspicuous for its short, sub-cylindrical shaft ; its
head being tuberous and much crooked over towards the median
plane, while the sternal extremity of the bone is not only thick-
ened from before, backwards, but much expanded lateral-wise,
showing at its outer angle a prominent lamelliform process, com-

330 SHUFELDT. [Vou. II.

pressed in the antero-posterior direction, and curved somewhat
upwards. Os furcula typifies the U-shape form of the bone, and
has in al] Lzmzcole, that the writer has ever studied, the merest
apology for a hypocleidium, below. Its limbs are of nearly
uniform calibre throughout, being slightly heavier above than
below, and-moderately compressed transversely for their entire
lengths. Their heads, that is, the free ends of the clavicular
limbs, are much elongated, and when articulated zz sztu, reach
far back to the heads of the scapulaz. Viewed upon direct lat-
eral aspect, it will be noticed that the os furcula is very con-
siderably, though gracefully, curved in the antero-posterior
direction, the convexity of the curvature being to the front.

In Hematopus the shaft of a coracoid is pierced by a small
oval foramen, from before, backwards, and just below the scap-
ular process, that does not occur in either the Surf-bird or among
Turnstones.

Now, aside from the exceptions of this foramen, and differen-
ces as to the method of articulation of the coracoids with the
sternum, already alluded to, and finally, the mere matter of size,
—the description of the shoulder girdle here rendered for
Aphriza, will apply almost equally well to the shoulder girdles of
the Zvinge@, the Turnstones, and the Plovers, and no doubt to
many other Shore Birds. Were we to depend for characters,
upon which to base distinctive differences, on the shoulder gir-
dle alone in Aphriza, Arenaria, and a true Plover of a correspond-
ing size, we should surely be disappointed, for the bones of this
arch do not offer them in the genera enumerated.

OF THE APPENDICULAR SKELETON.

The Pectoral Limb. — The majority of the bones of this part
of the skeleton in Aphriza are shown by my drawings in the
Plate, as already stated above. The corresponding parts for
Hlematopus and Plovers have been given in other connections.

It will be seen that in the humerus of our Surf-bird, both
“radial crest’ and “ulnar tuberosity”’ are strikingly well devel-
oped, while the articular humeral head between them is rather
small (Figs. 18 and 19). The pneumatic fossa is an extensive
excavation, although the bone itself is not pneumatic. As to
the shaft, it shows but little curvature, is smooth, and subcylin-
drical in form. At the distal extremity of the bone, a conspicu-

No. 2.] APHRIZA VIRGATA. 331

ous “ectocondyloid process” is to be observed; and at the
extreme end, the oblique and radial tubercles, or condyles, stand
out with more than their usual boldness, a condition which is
enhanced by the fact that just above them there exists a fossa
of some considerable depth. When the bones of this limb are
articulated, and the arm tightly closed, the head of the radius
accommodates itself to this latter depression at the distal end of
humerus. Upon the anconal aspect of this extremity of the
bone, we also find strong and powerfully impressed grooves for
the passage of the tendons of muscles inserted upon it, and at
the shoulder joint, during the life of the individual.

Neither vadzus nor ulna exhibit any very great degree of cur-
vature, and as a consequence the interosseous space in the
articulated arm is not very wide. The latter bone develops
down its shaft a row of some eight or nine papillz, for the quill
butts of the secondaries of the wing, a feature common to so
many of our Shore Birds. Comparatively speaking, the distal
extremities of these bones of the antibrachium in Aphriza, as in
all Lzmzcole which the writer has examined, are small, though
to this fact the Oyster-catcher seems to offer an exception.

The carpal segments are two in number, as usual, and present
nothing, either in their size, form, or method of articulation, in
any way different from what we usually find.

In the pinion (Figs. 13 and 14), the carpo-metacarpal bone is
long, large-headed, and with its coalesced shafts straight, and
more than commonly close together. As a negative character,
we miss the overlapping process at the proximal end of the mid-
metacarpal, —an apophysis which characterizes this bone in all
true Galling. Prominent and upturned, the pollex metacarpal
supports a phalangeal joint that is clawless; the same being
the case with the distal phalanx of the digit of the succeeding
finger.

Regarding the expanded and proximal phalanx of this last
digit, it is to be noted that its somewhat narrow blade, although
more or less scooped out upon either aspect, is never perforated
as we find it in some of the Lavzd@. Att its further end a little
process protrudes, against which, in life, the head of its follow-
ing phalanx plays ; this latter joint being very long and slender,
as in some Plovers and Sandpipers. The little phalangeal joint
of the remaining digit is crooked so as to accommodate itself to

332 SHUFELDT. [Vou. II.

the outline of the posterior border of the blade of the proximal
joint of index finger.

Equal correspondence of characters in the pectoral limbs of
Plovers, Sandpipers, and Turnstones, as compared with the
bones of the skeleton of the arm, in Aphrzza seem to prevail,
as they were found to prevail among the shoulder girdles and
sterna of the same species. Practically, the description I have
just given for the arm bones of the Surf-bird will answer all
purposes of exactness for the representatives of the genera
Tringa, Arenaria, and most, if not all, true pluvialine types.
This, of course, does not apply to the mere question of the
difference of size, but to the salient features only. Our engag-
ing little 7: mznutzlla has a pectoral limb, the skeleton of which
corresponds, in so far as its available taxonomic points are con-
cerned, with the same parts in the Surf-bird, to a degree of
nearness most exasperating to the comparative anatomist, and
discouraging to one eagerly searching for strong diagnostic dis-
tinctions in the structure of such types. Turning to the skele-
ton of the black Oyster-catcher we find but one sure point of
difference that can be relied upon, apart from its size, as distin-
guishing the fundamental plan of the structure of the skeleton
of its arm from the above species. In this bird we find a claw
upon the end of the pollex phalanx, which, by the way, is also
found in some Curlews.

Aside from this character, then, we might, were it possible,
reduce the arm bones of this Oyster-catcher until they equalled
in size those of a Surf-bird, and it would puzzle the best of us
to correctly decide to which species either belonged, after such
a hypothetical reduction.

These limicoline birds all seem to lack the os humero scapu-
Jare at the shoulder joint, and I have yet to find in any of
them the sesmoidal ossicles at the elbow, such as we do find,
for instance, in some of the Puffins.

Of the Skeleton of the Pelvic Limb. —In Aphriza virgata the
Jemur possesses only a moderately sized, semi-globular head,
with barely any depression on the top of it for the insertion of
the teres ligament. The trochanter is lofty and thick, reaching
conspicuously above the articular summit of the bone, which
latter is broad and smooth. Little or no curvature is met with
as we descend the shaft, and this is quite cylindrical for its

No. 2.] APHRIZA VIRGATA. 333

middle third. As to the condyles, we find nothing worthy of
special note, as they are fashioned much as we generally find
them in ordinary birds; the external one being the larger and
lower, while it shows behind the usual vertical groove for the
head of the fibula.

In the leg the fbu/a is free, not anchylosing with the tibio-
tarsus, being but a trifle longer than the half of this latter bone.
Its lower two-thirds are almost hair-like in proportion, and as
for that matter it would seem that this delicate osseous fila-
ment can add next to nothing to the skeletal support for the
structures of the limb (Fig. 8).

Tibi0-tarsus also has very nearly a straight shaft, but com-
monly shows, as in Hematopus, a curvature in the transverse
plane, being gently bowed outwards towards the fibular side.
Its procnemial process is much the larger of the two laminar
crests in front of the head of the bone, and it is pointed almost
directly forwards, while the ectocnemial process is turned out-
wards, and curves downwards, as a pointed hook.

They both rear slightly above the articular summit of the
proximal end of the shaft. Occupying the middle part of the
upper third, the fibular ridge stands out quite boldly at the
outer aspect, as in all birds. Proceeding to the distal ex-
tremity of the shaft we find a marked difference in the form of
the two condyles, the outer one being decidedly uniform in out-
line, and the inner one more elongated and showing compres-
sion in the vertical direction. Between, and at the same time
above them, in front, we detect the usual little osseous bar for
tendinal confinement. A /ate//a is absent in the Surf-bird, the
case, I believe, in all Lzszco/e—at least the writer is not aware
of any exception to the rule.

Having a length just equal to that of the femur, the Zarso-
metatarsus exhibits at its usual site at the upper end and back
part of its shaft a stumpy hypotarsus, that appears to be both
pierced and grooved, for the guidance of tendons. Two minute
foramina in this locality also perforate the bone in the antero-
posterior direction, which is also the case in an Oyster-catcher.
A mid-section of the shaft of tarso-metatarsus would show a
quadrilateral outline, but the calibre increases, and this form
changes as we pass to its distal extremity, where we find three
large and prominent trochlez, the middle one of which is the

334 SHUFELDT. [Vow. II.

biggest and placed the lowest on the bone. The ones upon
either side of it are directed to the rear. At its usual site,
above the innermost one, is faintly to be discerned the facette
for the articulation of the os metatarsale accessorius, of hallux
phalanx. Already the ornithologist has placed at our command
the fact that the arrangement of the joints of pes in this spe-
cies, as in Avenaria and many Tringe@, is upon the most com-
mon plan of 2, 3, 4,and 5 bones from hind toe to outermost
digit, respectively, and a study of these in the skeleton reveals
nothing peculiar in them.

The Black Turnstone being a somewhat smaller bird than
Aphriza, it has a correspondingly smaller pelvic limb and skele-
ton ; aside from this fact, however, the several bones of that
extremity are fashioned quite as they are in our Surf-bird, and
present no decided differences in any particular. This state-
ment applies with equal truth to various Sandpipers, and would
to Charadrius were it not that in the latter genus a dispropor-
tion, and a disproportion merely, exists in the hallux, — that
toe being much smaller in the Plover, though all the other
bones of the limb are remarkably similar in all their essential
features, bone for bone, as we have described and figured them
for Aphriza virgata. Hallux is also missing in Hematopus,
where we sometimes find a process of bone anchylosed to the
shaft of tarso-metatarsus, at a point where the accessory meta-
tarsal is commonly attached by ligament. In a specimen of
HT. bachmant before me, such a process is to be found upon the
shaft of the tarso-metatarsus of the right pelvic limb, but is
missing from the corresponding bone in the opposite limb of
the same individual. Strange to say, this is precisely the state
of affairs in the skeleton of a second specimen at my hand, —
the process is present in the right, absent in the left. It may
prove of interest to look further into this point with additional
specimens. Returning to our comparison between the pelvic
limb of this Oyster-catcher, then, with the same part of the
skeleton in Aphriza, we may say in brief that beyond the few
exceptions mentioned the limb in the former is simply an ampli-
fication of the limb in the latter species, — its bone for bone,
character for character, the same thing over again, only the
mould happened to be several sizes larger wherein the skeleton
of these parts in our Oyster-caicher were cast.

No. 2.] APHRIZA VIRGATA. 335

Having now briefly passed over the more salient characters
to be found in the skeletons of Aphriza, Arenaria, Hematopus,
and several representative Plovers and Sandpipers, we are, I
think, in a position to offer our conclusions upon the affinities
of the Surf-bird, in so far as they seem to be indicated through
this study of its osteology.

CONCLUSIONS.

Taking the skull as the part of the skeleton, I would invite
attention to the peculiar form of the superior osseous mandible
in Hematopus,; and in the cranium of the same bird to the deeply
sculpt, supra-orbital, glandular depressions ; to its bold, outstand-
ing lacrymal bones, and their mode of meeting the pars plana on
either side; to its vomer, which is forked at its anterior ex-
tremity ; to the absence of the supra-occipital foramina; to the
complete coalescence of the maxillo-palatine, with the palatine
of the same side; to its cranial foramina in front for exit of
the first and second pair, they being completely surrounded by
bone; and, finally, to the subelliptical outline of its foramen
magnum. All these points, and many minor ones in its skull,
are totally different in Aphriza, and alone are sufficient to war-
rant us in at least drawing strong lines of family distinc-
tion between these two types. Equally clear is the differ-
ence between the skull in Hematopus and Charadrius, but
when we come to compare it in the former with the skull
of Avenaria, a faint indication of affinity may be made out,
which indication is principally seen in the Turnstone, having
similarly formed nasals; feebly developed supra-orbital glandu-
lar depressions ; a somewhat similar superior osseous mandible ;
and, lastly, in that its maxillo-palatines unite along their entire
lower margins with the corresponding palatine on either side
below them.

The differences presented to us, however, in the skulls of
Hematopus and Arenaria, amount at least to family distinction.
So, too, when we come to compare the skulls of Avenaria and
Charadrius, they are very different, and undoubtedly belong to
representatives of distinct families.

Comparing next the skull of a Turnstone with that of the
Surf-bird, we are at first struca with the radical differences

336 SHUFELDT. [Vou. II.

exhibited in the superior osseous mandibles of the two species.
Then in the former the maxillo-palatine fuses, in a manner
already described, with the palatine, and finally, the “ croto-
phyte fosse”’ are pretty well defined in Avenaria, whereas in
Aphriza not a vestige of them is to be seen. The posterior
external angles of the palatines are obliquely truncated in A.
virgata, rounded in the Turnstone ; and finally, the mandibles
of these two types are essentially very different, both as to
form and structure, as in the Turnstone a large vacuity persists
between the forks of the dentary, which is nearly absent in the
Surf-bird.

Taking it all and all, the skull, mandible, and associated parts
of the skeleton of the head in Aphriza agree more nearly with
the corresponding structures in the skeleton of the head of some
of the larger Zrimgee than with any other class of limicoline
birds. I have arrived at this point by carefully comparing this
part of the skeleton in the numerous species at my hand, end I
am fully convinced of the truth of the assertion.

Passing next to the remainder of the axial skeleton, and with-
out enumerating the differences that have been dwelt upon
quite at length when under review, it is evident from the ar-
rangement and number of the ribs that Hemazopus differs es-
sentially from the several types we have been examining, and
agrees only with Avenaria in the number of its free caudal
vertebrae. If we were to be guided in this matter by the Zo¢al
number of vertebrz, as shown by these several species of birds,
providing our count is correct, it would seem that in this respect
Hematopus, Arenaria, and Aphriza fall together, while some
Plovers and some Sandpipers are thus associated. MHematopus
has a very different style of pelvis from the other species we
have enumerated, while the pattern of this bone is not a little
different when compared in Aphriza and Arenaria. Were we
allowed the expression, it might be said that in so far as the
pelvis goes in the genera Aphriza, Charadrius, Actitis, Are-
maria, and some few others, the pluvialine design seems to be
impressed with more or less strength upon them all. This
statement will not apply to the pelvis in an Oyster-catcher.

The sternum and shoulder girdle do not materially assist us
in this matter; we found it with but ¢wo notches in such

No. 2. ] APHRIZA VIRGATA. 337

species as Acéztis macularia and R. solitarius, and in the other
forms it is of a markedly pluvialine stripe throughout.

As to the appendicular skeleton, a marvellous sameness of
style—barring the question of mere difference in size—seems
to pertain to the skeleton of the limbs in Surf-birds, Turnstones,
Sandpipers, Plovers, and others. Hematopus, as we saw, pos-
sesses a claw upon its pollex phalanx, while some of the species
possess but three toes, as in the last-named genus and in Hzman-
zopus and others.

To sum up, then: my comparative studies of the osteology
of Aphriza virgata lead me to believe that in the first place
its affinity with H@matopus is by no means a close one, the
Oyster-catchers forming a very well-marked and distinct family
of limicoline birds by themselves, showing by the structure of
certain parts of their skeletons strong larine derivation.

Secondly, the skull in Avexarza is in some respects more upon
the plan of the skull in H@matopus than it in any way ap-
proaches the structure of that part of the skeleton in Aphriza ;
indeed, so far as the skulls are concerned, the skulls in Chara-
adrius, Arenaria, and Aphriza might be represented as each
occupying the angle of an equilateral triangle, each sharing cer-
tain characters in common and each removed from the other,
equally distant by an equal set of others, not possessed by
either of the other species. Were the skulls of Hematopus and
an average 7vinga introduced into this hypothetical figure, the
skull of the Oyster-catcher would be, as far as the characters
they hold in common are concerned and for no other reason,
on the line joining the skulls of the Turnstone and Surf-bird,
and considerably nearer the first species than the last. The
Sandpiper’s skull would be on the line joining the skulls of
Aphriza and the pluvialine type, and considerably nearer the
former species than the latter. Aside from the skull, the re-
mainder of the skeleton of Avexarza would answer fully for the
skeleton of an equal-sized Plover, but hardly so for A. vzrgata.

To conclude: the sum total of the skeletal characters of
Aphriza virgata place this species nearer the 7ringe@—say some
typical large-sized 77zmga, with a four-notched sternum — than it
does to the Plovers; less so to Avenaria, and far less so to
Hematopus. Some pluvialine forms, however, are not so dis-

338 SHOREEDR:

tantly removed from Aphriza, if we may be allowed to judge
from osteological premises.

There is not the slightest doubt in my mind that had such a
form as Charadrius squatarola been the sole representative of
the Charadritde in the entire world’s avifauna, and been found
taking the place, the habitat, of Aphriza, modern systematists
of the class would surely have grouped it with the Turnstones
as forming a family APHRizID&. We must believe that the
fashion is far too prevalent, that when an isolated form like
Aphriza is met with, to lay about and endeavor to hit upon a
family, a corner, where best to stow it away, without creating,
as in the majority of cases should be done, a separate family
fOnae:

Now Aphriza is no more nearly related to Avexarza than is
Charadrius related to Arenaria, and as at present classified by
American Ornithologists, by no means indicates its true posi-
tion in the system. I would propose then, in view of the ana-
tomical facts brought out in the present memoir, that the family
APHRIZIDA be made to contain the sole representative of it,
Aphriza virgata ; and that another family, the ARENARIDA, be
created to contain the Turnstones.

It would seem that Aphriza in some way connects the Plovers
with such 7yzzge@ as may possess the hallax and a four-notched
sternum ; while Avexaria links the Plovers with Hematopus,
albeit that the Turnstone is much nearer the Plover than the
far more remotely affined Oyster-catcher would in any way
appear to be.

340 SHUFELDT.

EXPLANATION OF PLATE XXV.

Norte. — The figures in this Plate were all drawn by the author from the skeleton
of a single individual, an adult male, and are all of natural size.

Fic. 1, The skull of A. virgata, seen directly from above; mandible removed.

Fic. 2. The skull of 4. virgata, seen upon basal aspect; mandible removed.

Fic. 3. The skull of 4. vixgaza, seen upon direct lateral view ; right side, includ-
ing the mandible.

Fic. 4. The mandible of 4. vivgaza, direct superior view.

Fic. 5. The right tarso-metatarsus of 4. vivgaza, anterior view.
Fic. 6. The right radius of 4. virgata, palmar aspect.

Fic. 7. The right ulna of 4. virgata, palmar aspect.

Fic. 8. The right fibula of 4. virgada, inner side.

Fic. 9. The right tibio-tarsus of A. virgata, mesial aspect.
Fic. 10. The right femur of 4. vzvgata, anterior surface.

Fic. 11. The os furcula of 4. virgata, seen obliquely from the right side.

Fic. 12. The sternum of 4. vixgata, seen upon right lateral aspect.

Fic. 13. The right carpo-metacarpus of A. virgata, anconal surface; pollex pha-
lanx 272 s2¢z. ;

Fic. 14. The right proximal phalanx of the index digit of 4. virgata, anconal
side.

Fic. 15. The sternum of 4. vzrgata, seen upon direct anterior view.

Fic. 16. The left coracoid and scapula of 4. virgata, outer aspect, and articula-
ted 27 sttu.

Fic. 17. The right coracoid of A. vi~ga¢a, seen upon direct anterior view.

Fic. 18. The left humerus of 4. vivgaza, palmar aspect.

Fic. 19. The left humerus of 4. virgata, anconal aspect.

Fic. 20. The four last vertebra of the skeleton of the tail of 4. vixgata, and the
pygostyle, seen upon the right lateral aspect.

Fic. 21. The pelvis of 4. virgata, dorsal view.

Journ. Mornh. Vol.II PUXXV.

# W Shufeldt,ad nat. del. EB. Meisel, Jith. Boston.

Anhriza virgata, ad.c,x J.

Volume Ll.

April, 17889.

Number 3.

JOURNAL

OF

MOK? EPC ©) Gare

UTERUS AND EMBRYO:—I. RABBIT; II. MAN.

CHARLES-SEDGWICK MINOT,

Harvarp Mepicat Scuoot, Boston, Mass.

TABLE OF
INTRODUCTION
I. RABBIT.
PAGE
§ 1. Uterus at six days 343
§ 2. Uterus at seven days » 343
§ 3. Uterus at eight days. « 345
§ 4. Uterus at nine days . - 348
§ 5. Embryo at nine days 5 Be
§ 6. Uterus at nine days and seven-
feen Honise ey 6. ost ce 1 357
§ 7. Uterus at eleven days . » 359
§ 8. Embryo at eleven days . - 365
§ 9. Uterus at thirteen days . . 369
§ 10. Uterus and embryo at fifteen
GENS aeG ae a6 5 BP
11, Summary .. . 370
12. Comparison with other rodents 378

CONTENTS.
+ « « PAGE 341
II. MAN.

PAGE

§ 13. Allantois and umbilical cord . 380
§ 14. Amnion . - 385
§ 15. Chorion . : » 389
§ 16. Uterus during menstruation . 413
§ 17. Uterus one month pregnant . 416
§ 18. Uterus seven months pregnant 421
§ 19. Uterus after abortion - 428
§ 20. Origin of decidual cells . » 429
§ 21. General considerations - - 431
S227) SUMMary) 7-7 ml esis » 435
§ 23. Bibliography . .. . - 438

THIS paper arose not as the result of a special investigation,
but as the outcome of general studies undertaken in connection
with the preparation of a 7reatise on Human Embryology. For

342 MINOT. [VoL. II.
such a work, knowledge of the foetal envelopes seemed espe-
cially important. I was thus led to examine them, and found
in so doing that the structure of the parts differed in many re-
spects from what had been assumed. The rabbit’s uterus was
examined in the hope of obtaining light as to some of the
changes in the human uterus, but the differences are so great
that little help was gotten ; but on the other hand I was brought
to a conception of the changes in the rabbit’s uterus so funda-
mentally different from the views of previous writers that I was
induced to carry my observations far enough to make sure of
the essential alterations. The following communication is there-
fore in no sense monographic, but only supplementary to the
work of others. My own work has been accomplished by the
aid of a grant from the American Association for the Advance-
ment of Science, without which it could not have been carried
out. The recipient of such aid naturally wishes to publish what
he has accomplished, since such a publication is the most fitting
acknowledgment of the assistance enjoyed. I feel my obliga-
tions to the Association the more deeply because the grant is the
first made from its Research Fund. May I express the hope
that that fund will be largely increased, and the Association en-
abled to make numerous grants to other workers, for in so doing
it will do more for the promotion of science than, I believe, by
any other means whatsoever.

I. RABBIT.

The observations here recorded were made upon pregnant
uteri of the rabbit at various intervals from the sixth to the
fifteenth day of gestation, both inclusive: The uteri were cut
out carefully, stretched very slightly, and the ends of each uterus
tied to an iron rod; the specimens were then hardened in
Kleinenberg’s picrosulphuric acid, according to the directions
given in Foster and Balfour’s Embryology, 2d ed. pp. 425, 426.
Although this reagent worked fairly well, and preserved the
histological elements of the uterus and of the older embryos
satisfactorily, it failed to preserve the blastodermic vesicles in
uteri of six and seven days; and in the older specimens, after
hardening, the extra-embryonic foetal membranes were somewhat
rumpled. Owing to the great difficulty of obtaining doe-rabbits

No. 3.] UTERUS AND EMBRYO. 343

in Boston, and their consequent high price, I have been unable
to experiment with other methods of hardening. The speci-
mens after hardening were for the most part stained zx ¢oto with
alum cochineal and eosine, imbedded in paraffine and cut into
serial sections with an automatic microtome, made by Herr G.
Baltzar of Leipzig.

§ 1. Uterus at six days and three hours. — The position of
the ova is recognizable externally, being marked by a very slight
protuberance on the free side of the tubular uterus. Transverse
sections show that there is a considerable dilatation of the uter-
ine cavity, corresponding to the swelling ; the walls are consid-
erably thinned out by stretching. The glands are much altered,
otherwise there is no striking change in the uterine structure.
The shape of the glands varies, but everywhere their cavities
are very much expanded, and the epithelial linings of adjacent
glands are separated only by very thin connective tissue parti-
tions; on the side of the mesentery the glands are distinctly
tubular, and grouped on folds of the mucosa; the relations of
these folds are described in the next section. On the opposite
side of the uterus, that is, away from the mesentery, the glands
are short, with wide cavities, constituting a series of irregular
ampulla with wide mouths. The epithelium is thickened every-
where ; it stains deeply, and has enlarged nuclei; it has many
intercellular vertical fissures, and therefore a good many of the
cells are separated from their neighbors ; adjacent cells project
unequally, rendering the surface of the epithelium irregular.
The change in the epithelium is greatest opposite and least
near the mesentery, but is everywhere similar in kind, though
varying in degree.

I am unfortunately unable to state anything in regard to the
relations of the ovum, owing to the failure of its attempted
preservation in my specimens.

§ 2. Uterus of seven days and three hours. — The placental
swellings are well marked as smooth, rounded bulbs only a little
larger in diameter than the unaltered uterus between the swell-
ings, and not projecting at all on the mesenterial side of the
uterus. Transverse sections show at once the changes which
have taken place. As is well known, the rabbit’s uterus has six
longitudinal folds, symmetrically disposed ; the line of insertion
of the mesentery (mesometrium or broad ligament) corresponds

344 MINOT. [ Vou. IL

to the space between two folds, which alone participate in the
formation of the placenta; accordingly we may designate them
as the placental folds. In the region of the swellings the
placental folds are already hypertrophied, and form a marked
contrast to the opposite side, where the folds have completely
disappeared, and their glands have become shorter and some-
what contorted; the two lateral folds are intermediate in ap-
pearance. In the placental folds there is a great increase in
the connective tissue, which consists solely of anastomosing
cells, forming a loose meshwork of very granular protoplasm, of
which only a small amount is accumulated around each nucleus.
Described in other words, the cells are small, granular, with long
processes continuous with those of adjacent cells. The glands
extend only a short and nearly uniform distance down from the
surface of the folds; the glands themselves are somewhat
dilated ; their epithelium stains deeply ; its free surface is quite
irregular; the nuclei are greatly increased in number, and lie
crowded throughout the whole thickness of the layer; the nu-
clei are round or oval in outline, with a well-marked reticulum
densest superficially. In many places the nuclei are grouped,
three, four, or five together, and sometimes one can distinguish
a distinct outline around the group. These appearances I in-
terpret as evidence that the nucleus of each cell proliferates,
rendering the cell multinucleate. The blood-vessels are like-
wise hypertrophied in the placental folds, and to a less extent
in the adjacent folds, but not at all in the folds opposite the
placenta. In the placental folds there are larger blood-vessels
running for the most part longitudinally, and all situated in the
zone next the muscularis ; between this zone and the glandular
layer, the blood-vessels are, on the contrary, all of small calibre,
most of them taking a more or less radial course, and lying ap-
proximately in the plane of the transverse sections. All the
blood-vessels of the mucosa have, so far as I have observed, the
character of capillaries, for they consist of merely an endothe-
lium without adventitial or muscular envelope, although some
of them are many times the diameter of ordinary capillaries.
The blood-vessels of the placenta of the Guinea pig are stated
by Creighton, 77a, p. 544, to have the same character. There
is a single layer of connective tissue cells condensed around the
vessels, and representing the commencement of the perivascu-

No. 3.] UTERUS AND EMBRYO. 345

lar decidua] cells, though the cells themselves scarcely differ
yet from the ordinary connective tissue cells between the
vessels.

We find at this stage all the regions of the placental swell-
ings, to be found in later stages, already definitely marked out.

These regions are as follows :—

1, PLACENTAL: subdivided into

A, glandular zone.

B, sub-glandular vascular zone with (a), sub-glandular
zone with small vessels (4), outer zone with
large vessels.

2, PERI-PLACENTAL.
3, OB-PLACENTAL.

Each of these regions comprises two folds of the mucosa,
viz.: the placental, the two folds next the mesentery ;! the perz-
placental, the two lateral folds; and the 0b-placental region, the
two folds opposite the mesentery. The three zones of the
placental area persist and become much more marked in later
stages, owing to the great divergence of the processes of his-
tological differentiation in each zone. Of the two vascular
zones, the szb-glandiular is characterized later by its very large
multinucleate cells, while the outer zone is characterized by its
crowded uninucleate decidual cells. All the regions and their
subdivisions will be perhaps better understood by the descrip-
tions and figures of the nine days’ uterus. (See below.)

In my specimens, although the uterus seemed to be very well
preserved, the blastodermic vesicles were completely shrivelled
up; hence I could make no observations as to the relations of
the embryo to the uterine wall.

§ 3. Uterus of eight days and three hours. — It is un-
necessary to describe the appearances at this age in detail,
as they have been described already with admirable clearness
and exactitude by Masquelin and Swaen, 114, 25-30. I have
therefore only to confirm their account and refer to certain
points on which my observations extend or differ from theirs ;
it is also necessary to describe the extra-placental structures,
which are left out of consideration by Masquelin and Swaen.

1 Although this use of the term mesentery is etymologically indefensible, it seems
permissible, and not likely to lead to misunderstanding any more than the etymologi-
cally indefensible terms cell, endothelium, terminology, etc., etc.

346 MINOT. (Vou. Il.

The connective tissue is but little altered from the condition
at seven days ; it has the same adenoid character; the cells are
elongated in directions more or less parallel to one another, and
the appearance of the protoplasmic reticulum therefore varies
according as the section passes at right angles or parallel with
the long axes of the cells; in the former case the meshes are
smaller, in the latter larger and longer. The perivascular cells
have grown ; Masquelin and Swaen trace their origin to a meta-
morphosis of the connective tissue cells, in doing which I en-
tirely agree with them; these authors likewise describe fibrillze
in the connective tissue, but in my preparation I can find none,
nor from what we know of the structure of the mammalian
uterus is it probable that any are present; in regard to this
point I think that Masquelin and Swaen’s account needs recti-
fication.

The placental blood-vessels have increased in size, and, I
think, in number; their epithelium, particularly in the larger
vessels, is decidedly thickened.

The uterine epithelium has entered upon its complex degen-
erative metamorphosis — most of the changes have been seen
and correctly described by Masquelin and Swaen for the pla-
cental area. They conclude that the changes lead to a new
formation of blood corpuscles out of the substance of the epi-
thelium. My own observations oblige me to regard the changes
as phases of a hyaline degeneration with hyperplasia of the
degenerating elements, and having nothing to do, therefore,
with blood formation. In all parts of the uterine dilatations the
epithelium is considerably thickened (Plate XXVI., Fig. 1). The
thickening is due to the enlargement and fusion of the epithelial
cells, and this enlargement of the cells is due to the prolifera-
tion of the nuclei and to the growth of the protoplasm, which
begins later and continues longer (as later stages show) than
the multiplication of the nuclei. That the nuclei multiply
within each cell can be distinctly seen in my specimens of this
age; the same fact has been observed by Masquelin and Swaen.
The growth of the protoplasm is more properly described as an
enlargement, due to degenerative metamorphosis. As to the
nature of this metamorphosis I am unable to speak with much
precision. The substance presents a very granular appearance, |
and possesses a slightly greater affinity for coloring-matters

No. 3.] UTERUS AND EMBRYO. 347

than the unaltered protoplasm. Examination with an apochro-
matic oil immersion shows in some parts of the degenerated
epithelium a distinct network, the threads of which are rather
coarse and hyaline in appearance. In default of chemical and
further microscopic examination we may accept the hypothesis
that the degeneration consists in direct change of the pro-
toplasmic reticulum into hyaline substance, accompanied by
thickening of the reticular threads. The degeneration of the
epithelium has progressed much further over the non-placental
area than elsewhere, and much less over the placental area:
the peri-placental regions are in an intermediate stage.

It is also important to note that the deep portions of the
glands are nowhere degenerated. The glandular layer may be
divided accordingly into an upper degenerated zone and a lower
not degenerated zone.

In the placental area there is no stretching of the tissues, and
accordingly the glands retain their tubular character. The
nuclei fill up most of the epithelial layer; there are three, four,
or even five, in each cell in the upper part of the gland; the cells
of the fundi are but slightly altered from their usual appearance.
The embryo is attached to the maternal placental surface only
by the ectoderm, without any participation of the other germ
layers, direct or indirect, so far as I can observe. That portion
of the ectoderm which is soldered to the uterus is very much
thickened, in marked contrast to all other parts of the layer. As
shown in Fig. 1., Pl. XXVI., the placental ectoderm runs over
the surface only of the placenta, and stretches straight across
the mouths of the glands, shutting them completely; it
does not dip down into the glands at all, and possesses no villi
whatsoever. On the surface, between the glandular orifices,
the uterine epithelium, already degenerated, is clearly distin-
guishable.

In the other regions the stretching of the walls stretches the
glands also, and of course proportionately to the extent of the
strain ; hence, in the non-placental area the glands become slits
running parallel to the surface, and in the peri-placental part
become wide cavities. The upper zone of the peri-placental
glandular layer has its epithelium changed into a very thick
layer, and beginning to undergo resorption, as evidenced by the
presence of cavities. As we follow round towards the non-pla-

348 MINOT. (Vou. IL.

cental area, the evidences of resorption are greater, and over the
area itself a large part of the upper glandular zone has disap-
peared altogether. Similar relations are found in the uterus of
nine days, from which the drawings have been taken. For the
sake of greater clearness, and to avoid repetition, we pass at
once to the next stage. The fact that I have found the uterus
at eight days so much nearer in its stage of development to that
of nine than to that of seven days, may be attributed to acci-
dental variations.

§ 4. Uterus at nine days and three hours. — Fig. 2, PI.
XXVI., represents a transverse section through a swelling. The
attenuation of the walls everywhere, except in the placenta, is
very marked, and affects both the outer and inner muscular
layers, 4m, cm, and the mucosa, muc. In the placental region,
P/, on the contrary, the walls are thickened ; the placenta itself
is formed chiefly by the hypertrophy of the connective tissue of
the two longitudinal folds nearest the mesentery, mes: the
superficial glandular layer, g/, owing to its deeper staining, is
readily distinguished even by the naked eye; each lobe of the
placenta is imperfectly subdivided into two lobules; the em-
bryo, in the specimen figured, appears in transverse section over
the right-hand lobe, directly above the furrow separating its lob-
ules; the actual disposition is shown in Cut 1; in Fig. 2 the
embryonic structures are purposely omitted on account of the
small scale; to the consideration of the foetal membranes the
next section (§ 5) is devoted.

The connective tissue of the placenta is already far advanced
in its metamorphosis, which progresses as described by Masque-
lin and Swaen. It consists of a rich cellular network, Fig. 3,
conn, of which the cell bodies are much larger than in previous
stages ; these bodies are for the most part elongated, with very
irregular surfaces, and are, therefore, perhaps best characterized
as roughly spindle-shaped ; their long axes are more or less par-
allel with the blood-vessels ; the nuclei are round, oval, or ellip-
tical, granular, but with a clearer cortical layer, as is usually
the case in young connective tissue cells: compare Rollett’s
Figs. 4 and 5 in Stricker’s Handbuch der Lehre von den Gewe-
ben, 1., pp. 63 and 65. The processes of the cells are numerous
and very fine, forming a meshwork, between the cells, of such
delicacy that it can be followed out only with high powers

No. 3.] OTERUS AND EMBRYO. 349

(400-500 diams.). The observation of the threads of this net-
work has led certain investigators to assume the presence of
connective tissue fibrilla. Scattered about in the connective
tissue are a not inconsiderable number of leucocytes, 4, 4 /,
easily recognized by their size and shape, their granular appear-
ance, deep staining and characteristic nuclei. Around the
blood-vessels is the perivascular layer of decidual cells, per v,
which have already been amply described by Masquelin and
Swaen, Ercolani, Godet, Creighton, and others. Ercolani’s
descriptions, of which the most important to us is that of the
rabbit at fifteen days,! 89, p. 278, is far from sufficient. Go-
det’s paper I know only from an unsatisfactory abstract.
Creighton’s account of the perivascular layer in the Guinea pig,
77a, 544, is also good, and he agrees with the Belgian authors
in tracing the origin of the cells to the metamorphosis of the
connective tissue. Ercolani opposed this view and maintained
that the uterine mucosa is completely destroyed, leaving the
whole placental tissue of the mother to arise as a new formation.
My preparations render it impossible to agree with Ercolani,
since they show all the phases of the metamorphosis. It is only
necessary to follow, in Fig. 3, the three series of cells numbered
I, 2, 3, 4, each, and to find in all parts of the placenta the same
appearances; to see the perivascular layer at six and seven
days, before it is much differentiated; and finally to see the
perivascular accretions at later stages, to render inevitable the
conviction that the perivascular layer is modified connective
tissue. Neither at this stage nor at any earlier or later one
have I been able to detect any evidence whatsoever of the re-
sorption of the connective tissue affirmed by Ercolani, $9.
Masquelin and Swaen describe multinucleate cells, but I fail
to find them until later stages.

The blood-vessels have their endothelial lining code
thickened, each cell for itself, and to its individual degree, Fig. 3,
Endo; they are stained by alum-cochineal and eosine more
deeply than the adjacent decidual cells, from which they are
sharply distinguished. I am unable to recognize any cells which
might be interpreted as intermediate stages between the endo-
thelial and decidual cells, as we should anticipate, were Erco-

1 The specimen described by Ercolani I consider to have been probably really only
about thirteen days.

350 MINOT. [Vot. II.

lani’s suggestion correct that the decidual cells arise from the
blood-vessels. The contents of the blood-vessels are blood cor-
puscles and coagulum ; the blood corpuscles resemble the ordi-
nary red globules of the rabbit, a point deserving notice in view
of the change occurring later. There are occasional leucocytes,
but they are nowhere numerous.

The two layers of the vascular zone are now distinguishable
not only by the size of the vessels (not well illustrated in the
section drawn as Fig. 2), but also by the much greater develop-
ment of the perivascular cells in the outer zone; in the sub-
glandular zone the cells are now not far from their maximum
development, forming a coat one or two cells thick around the
vessels ; on the outer zone, on the contrary, the number of lay-
ers of cells has still to increase very much; consequently as
development progresses, the difference between the subglandu-
lar and outer zone becomes more conspicuous.

The epithelium and glands repay careful study at this stage.
The degenerative processes are similar in certain essential re-
spects in all parts of the uterine swelling. The likeness con-
cerns five chief points: 1°, the deep portions of the glands
show little change in the epithelium; 2°, the upper portions are
very far degenerated; 3°, the protoplasm of the degenerated
epithelial cells is fused into a continuous thick hyaline mass, the
growth of which ultimately obliterates the cavity of the glands ;
4°, the nuclei of the degenerated epithelium multiply enor-
mously; 5°, the degenerated tissue is absorbed by progressive
vacuolization.

But although these resemblances are dominant, each of the
three principal regions, the placental, peri-placental, and ob-pla-
cental, presents now a very distinctive appearance, and has its
distinctive further history.

In the peri-placental region, with which we begin, because the
relations are more obvious there than elsewhere, we find the
appearances shown in Fig. 4. The line of demarcation from
the placenta, though not definite or sharp, can be approximately
determined, but the passage into the ob-placental region is very
gradual. The most striking feature of the section is the de-
generated and enormously thickened epithelium, /.¢, deeply
tinctured by the eosine, and remarkable for the crowded band
of nuclei. Within the area of the degeneration the former

INO: 3; ] UTERUS AND EMBRYO. 351

gland cavities are closed; the diameter of the glands has enor-
mously increased, and in some places two adjacent glands have
swollen until they have come in contact and fused, the glands
then forming a network; in the placental region the conversion
of the glands into a network goes very far. The distribution of
the nuclei as at @ and 6 preserves in some parts the original
grouping in opposite walls of the gland tube; at other points
they lie in irregular patches. Secondary cavities, vac, appear
at various points; they are irregular in size, shape, and position,
and arise by the resorption of the degenerated tissue. There is
probably a certain amount of resorption carried on upon the
surface against the connective tissue, for that surface becomes
jagged and irregular, presenting a corroded appearance, as can
be seen at various parts of Fig. 4. The vacuolization is, how-
ever, the principal factor of destruction. As to the manner in
which the spaces are produced in the heart of the very compact
layer, my observations give no satisfactory information. There
are no accumulations of leucocytes either in the epithelial layer
nor even in the connective tissue (see Fig. 4), in which all the
cells are copied with approximately entire accuracy from the
preparation. The only material I have ever noticed in the vacu-
oles is broken-down fragments of the surrounding hyaline tissue
(epithelium) itself. The hypothesis may be suggested that the
resorption vacuoles are produced by liquefaction, but the sug-
gestion calls for no further discussion since there are no direct
observations to test the validity of the hypothesis.

The deep portions of the peri-placental glands, Fig. 4, ¢/, are
dilated transversely to an extent which has converted them from
tubes into wide vesicles. Towards the ob-placental region the
transverse stretching gradually increases. The epithelium differs
but little from that of the resting utricular glands; it is com-
posed of cylinder cells with basally placed oval nuclei.

In the ob-placental region the mucosa is much thinner than
elsewhere. As we proceed from the edge of the peri-placental
region towards the pole furthest from the placenta we find that
the layer thins out and is more advanced in its degeneration.
Near the peri-placental thickening there is a wide superficial
layer of degenerated epithelium with the characteristic central
band of nuclei, but the prolongations corresponding to the
degenerated gland ducts are short; the deep portions of the

352 MINOT. [Vor. II.

glands are oval slits parallel with the muscularis, Fig. 5, ¢7 <A
little further along, the resorptive vacuolization begins, producing
a curious irregular layer, Fig. 5. The degeneration and vacuo-
lization is found still further along to have involved the inner
adjacent wall of the gland vesicles, thus producing the appear-
ances shown in the left-hand part of Fig. 5, where there are
shallow cups, g/, of epithelium, each entirely separate from its
fellows, and all overlaid by the hyaline stratum, /.ef. There is
usually a dome-like hollow in the degenerated stratum above
each cup. Since the processes described vary in rapidity, there
is not a uniform, but only a general, progression of stages towards
the centre of the ob-placental region. Moreover, the variability
is great, and the images from different sections and different
parts of the same section are correspondingly multifarious, but
the general succession of changes is everywhere the same; hence
it would be profitless to expand the descriptions.

The placental glands have preserved their tubular character;
they are less degenerated than the uterine glands of the non-
placental parts; their walls are less thickened and in most parts
the glandular cavity is still present. The deep portion of the
glands are tubes lined by columnar epithelium. For the rest, I
may refer to the satisfactory description of Masquelin and Swaen,
114, 30-31, except as to one point.’ As shown in Cut 1, p. 355, the
ectoderm of the embryo is firmly soldered to the placental surface
over certain. areas. The nature of this connection and the accom-
panying structural changes in the uterus are illustrated in Fig. 7,
which has been copied with great care from one of the sections.
For the sake of clearness, only the nuclei of the connective tissue
have been drawn in; the perivascular cells are represented by
their nuclei and outlines, and the nuclei and cells of the foetal
ectederm are given in outline; but there is nothing diagrammatic
in the drawing; of course in the figure the distinction between
the foetal and maternal tissues is more marked, though not more
real than in the section; in fact there is scarcely a cell even on
the line of junction of the ectoderm with the uterus about the
assignment of which one could have any doubt, so distinct is the
texture and the staining of the foetal and maternal tissues.
This is a matter of importance, as it renders it possible to ascer-
tain beyond question that there are no villi; nevertheless their
presence has been assumed not infrequently. To pass on:

No. 3.] UTERUS AND EMBRYO. 353

where the ectoderm, Fig. 7, Ecto, touches the placenta, the active
resorption of the degenerated glands is going on (see the part of
Fig. 7, above bracket C); whereas in other parts the glands pre-
sent: the appearance shown in Fig. 7, A, gz, and described by
Masquelin and Swaen. There is also an intermediate zone
shown in Fig. 7, above bracket B, where the transition phases
between the two states are found; the zone of transition lies
immediately underneath the point where the ectoderm, £céo,
joins the uterine epithelium, /.ef; here the glands are thick-
ened and hypertrophied ; the lumen is obliterated, but the cylin-
drical shape is irregularly preserved; where the distal end of the
ectoderm leaves the placenta, there is again a similar transi-
tion: in other words, the resorption is less advanced around
the periphery than in the centre of the area of ectodermal
attachment. The resorptive process is essentially the same
as outside the placenta, — superficial corrosion and internal
vacuolization, — but the vacuoles formed are relatively small
and consequently more numerous: moreover, the space left by
the disappearing epithelium is at once occupied by connective
tissue cells, so that there are no cavities. The resorption goes
on principally in the superficial layers of the placenta, where it
results, as later stages show, in the complete disappearance of the
glands immediately underneath the ectoderm; deeper down the
glands at the present age are hypertrophied and without lumina,
but even in the region of bracket C of Fig. 7 (Pl. XX VII.) most
of the glands show very few or no vacuoles.

§ 5. Embryo at nine days and three hours. — It is not pro-
posed to consider here anything but a few points bearing on the
relations of the embryo to the uterine walls.

First, as to the fosztion of the embryo: the dorsal surface of
the embryo is turned towards the placenta; the embryo may be
situated over one or the other lobe of the placenta or across
both; its long axis may be either parallel or oblique or at right
angles, to the long axis of the uterus. In the specimen repre-
sented in Cut 1, both the uterus and embryo appear in trans-
verse section. Similar variability appears in my specimens of
uteri of eight days, and of nine days and seventeen hours. The
statements of Van Beneden and Julin, 44, and other authors,!

1 Compare Bischoff, Entwickelungsgesch. d. Kaninchens, p. 138, and von Baer,
Entwickelungsgesch. i1., 232.

354 MINOT. [VoL. II.

lead rather to the supposition that the embryo normally lies
across the uterus; but this is true in my experience only of the
later stages after the embryo is suspended more freely.

Next as to the extra-embryonic portions of the germ layers:
my observations compel me to differ as to the composition of the
walls of the blastodermic vesicle or yolk sack. Sections through
the middle region of the embryo, Cut 1, show an open medul-
lary groove, JZd, the thickened notochordal band, zch, of the
entoderm; the mesoderm of the Stammzone is undivided ; that
of the parietal zone is split to form the ccelom, Coe, which may
be followed a considerable distance from the axis of the embryo,
when the two leaves of the mesoderm again unite into a single
distal plate, mes, in which the two layers can be distinguished
for a certain distance; the distal edge of the mesoderm is
sharply marked; the mesoderm is thickened around its margin.
Beyond the margin the ectoderm and entoderm come into con-
tact, a; the former is the thicker layer, being composed of cubical
cells, while the entoderm consists of very thin broad cells; the
two layers continue outwards until, having passed over the peri-
placental thickening, they reach the region of transition from the
peri-placental to the ob-placental area, where the ectoderm chang-
ing to a thin flat-celled membrane is intimately conjoined to the
degenerated epithelium of the uterus. Where the concrescence
takes place, the union of the two layers becomes very intimate,
so that it is difficult to satisfy one’s self how much farther the
ectoderm extends, but apparently it goes completely around,
forming a closed vesicle, as is generally stated and as is found
later. Apparently the ectoderm is not involved in the resorption
of the uterine epithelium, which disappears — but further inves-
tigation is required. The entoderm of the other hand is readily
followed, and although somewhat crumpled and torn in the ob-
placental region of my specimens, there is to my mind very little
doubt that it forms a closed sack, corresponding to the ento-
dermic lining of the yolk sack of other mammals. From the
observations above recorded it is evident that two germ layers
are readily traced for some distance from the embryo, but that
beyond a certain line only one layer, the entoderm, is readily
followed. Now this fact is carefully represented in van Bene-
den’s and Julin’s diagram, 44, Pl. XXIV., but the membrane
which stops is there given as entoderm, which, as seen in my

355

UTERUS AND EMBRYO.

No. 3.]

Ecto

PN

Pe SN
= OSs a

pe now ea
CEG

é R ees SS.
ry _ . ! .° > '
OW ate AS Ares

G
.

:)
/

«)
&

SS

Cut r.— Transverse section of a rabbit embryo, z# sé¢w, of nine days and three hours. @, wall of yolk-sack composed of ecto-

derm and endoderm only; v/, vena terminalis; mes, mesoderm; sf/, splanchnopleure; coe, ccelom; ch, notochord; JZd, medullary
groove; my,myotome; Endo, endoderm; Lcéo, ectoderm; g/, glands; v, blood-vessel; Ae, hyaline uterine epithelium.

356 MINOT. [Vou. IL.
specimens, is continued around. It is probable that when
embryos of nine days are removed, that a portion of the ecto-
derm remains attached to the uterine wall, and consequently the
inferior portion of the vesicle is without any ectoderm. Being
unaware of such a possibility, van Beneden and Julin have
perhaps represented the single layer left as ectoderm on
account of the theoretical necessity of an ectodermal cover-
ing on the external or apparently external surface of the ovum.
The question, therefore, is to be posed: Have not observers
found two layers up to a certain limit beyond the vena termin-
alis, and only one layer over the remaining inferior portion of
the embryonic vesicle, and assumed the single layer to be ecto-
derm, whereas it is entoderm, and the true ectoderm is left upon
the uterus, to which it is indissolubly attached? The view I
advocate brings the further question whether a portion of the
embryonic ectoderm disappears by being involved in the resorp-
tion of the ob-placental uterine epithelium. This I think is not
the case. The intimate adherence of the extra-embryonic por-
tions of the germ layers to the uterine walls has been carefully
recorded by Bischoff, Extwzckelungs gesch. Kantnchens, p. 131,
“Vom dem Umkreise der Vena terminalis an ist das Ei [of ten
days] in die in dieser Lage, etc... . und von hier an sind auch alle
Eihaute so innig unter einander und durch den Uterus vereinigt,
dass es nicht gelingt sie zu lésen.”

The attachment of the embryo takes place as described by
van Beneden and Julin, p. 402, 403, by an area of thickened ecto-
derm; the general arrangement is well shown in Cut 1, while
the fitting together of the foetal and maternal surface is better
illustrated by Fig. 7, Pl. XXVII. The foetal mesoderm does not
participate even indirectly in this attachment, but runs along
free from the outer germ layer. The ectoderm, as it nears its
attachment (see Fig. 7), gradually thickens. Just where it joins
the uterine surface there are several large cells with very large
nuclei; appearances which are probably connected with the
growth of the layer, for beyond the line of the large cells the
ectoderm is very much thicker. Extremely distended nuclei
also occur very strikingly in the developing supra-renal capsules,
and are also there connected presumably with cell proliferation.
If these suppositions are correct, there is a modified form of cell
division characterized by dilatation of the nuclei and which

Se

No. 3.] UTERUS AND EMBRYO. 357

deserves special study. Over the area of attachment the uterine
epithelium, Fig. 7, 4.ef, is degenerated as before described, its
surface is extremely irregular, but the ectoderm, Lcéo, is per-
fectly fitted to every irregularity, but the free surface (towards
the mesoderm) is comparatively smooth; the layer consists of
two, three, or four strata of cells. Beyond the area of attach-
ment the ectoderm again thins out.

As to how the tissues are held together, my observations
afford no explanation. It seems to me possible that the two
tissues actually grow together asa grafting unites with a bough;
but for aught we know it may be by some other process, perhaps
simple agglutination. The thickening of the ectoderm I am in-
clined to regard as degenerative, and therefore somewhat com-
parable to the degenerative thickening of the uterine epithelium.
I am brought to this view by no conclusive observations, but
chiefly by two facts: 1°, that in later stages the ectoderm seems
to have disappeared over the greater part of the placenta (see §
7. Uterus of eleven days); 2°, hyperplasia is often the com-
mencement of degeneration, as is familiarly known to patholo-
gists. To this evidence may be added the appearance of the
ectoderm at nine days and seventeen hours, which I interpret
as indicative of degeneration.

§ 6. Uterus of nine days and seventeen hours. — In my
specimen there are not many changes from the previous stage
last described, but of these changes the following deserve special
mention: 1°, the commencing formation of perivascular decid-
ual cells in the peri-placenta ; 2°, the reconstitution of the ob-pla-
cental epithelium; 3°, the formation of the true chorion; 4°,
changes in the extra-embryonic ectoderm; 5°, the contents of
the placental blood-vessels.

1°. The peri-placenta is still only a small bolster at the side of
the placenta ; its glands are still recognizable and its blood-ves-
sels are more conspicuous; the connective tissue cells are en-
larged and have begun to form more or less distinct coats around
the blood-vessels. I feel assured that the decidual cells arise
here in the same way as those of the outer zone of the placenta ;
the cells in the two parts appear to me identical in character as
soon as they attain their full development, and to differ only
in the period during which their development takes place ; later
on, Fig. 8, Pl. XXVIII., the peri-placenta forms, together with

358 MINOT. [ Vou. IL

the outer zone of the placenta, a continuous layer of uninucleate
decidual cells, extending over half the uterus.

2°. In the ob-placental region the degenerated portion of the
uterine epithelium is almost completely resorbed around the
pole opposite the placenta, (compare Figs. 4, 5, and 6). Fig. 6,
taken from an older stage, in which the phase existing at nine
days and seventeen hours at the pole is found near the peri-pla-
centa, illustrates the manner in which the patches of unaltered
epithelium, g/, of Fig. 5, grew together by the union of their
edges into a continuous sheet of epithelium, Fig. 6, g/, forming
a series of shallow cups, widely open.

3°. The chorion of mammals, as I have defined it elsewhere, is
“the whole of that portion of the extra-embryonic somatopleure
which is not concerned in the formation of the amnion.”! The
term is not applicable until the mesoderm has united with the
ectoderm in the region outside the embryo to forma single mem-
brane: such a union has now taken place; the thickened pla-
cental ectoderm is coated by a thin layer of flat cells, epithelial
in character and with bulging nuclei. These cells represent the
lining of the body cavity, or, as this lining is conveniently called,
mesothelium. The mesothelium, and consequently the ccelom,
extend a slight distance beyond the edge of the placenta; the
mesothelium then bends over onto the yolk sack, of which it
becomes the vascular coat, and then runs ¢owards the embryo;
the vascular coat has a large vessel, szzus terminalis, near the
end of the ccelomatic space, and the mesoderm stretches a short
distance beyond away from the embryo. The ectoderm, on the
contrary, extends beyond the end of the mesoderm away from
the embryo over the rest of the yolk sack. Thus the yolk
sack, as is well known, comprises two parts, one near the em-
bryo with walls composed of entoderm covered by mesoderm,
and away from or opposite the embryo, with walls composed of
entoderm covered by ectoderm ; compare the clearly expressed
summary of the relations in the rabbit given by Balfour in his
Comparative Embryology, 11., 199, 200.

4°. The ectoderm of the embryo presents the same general
arrangement as at nine days. The area of thickened entoderm,
however, which is attached to the placenta has changed in ap-
pearance ; at nine days and three hours each cell outline was

1 Wood's Reference Handbook of the Medical Sciences, I1., 143; article, Chorion.

No. 3.] UTERUS AND EMBRYO. 359

distinct, and the protoplasm around each nucleus dense and
finely granular ; now the cell outlines are hard to follow and the
picture is confused by broader lines of hyaline matter, which is
colored by the eosine; the nuclei are enlarged, the protoplasm
is more coarsely and more irregularly granular, and somewhat
vacuolated. The characteristics enumerated concord with the
idea that degeneration is going on, —an idea suggested, also, as
before stated, by the failure to find this part of the ectoderm in
later stages.

5°. The blood-vessels show increased hypertrophy of their
epithelium, and the perivascular cells form two or three layers
around them; they are especially remarkable for containing a
very large number of multinucleate leucocytes and comparatively
few red corpuscles. The excessive abundance of white globules
continues up to the oldest stage I have examined (sixteenth
day). The predominance of nucleated corpuscles causes the
contents of the maternal vessels to resemble foetal blood when
examined with a low power; with high magnifications the dif-
ference is evident. To the foetal blood in the placenta we shall
have to recur.

§ 7. Uterus at eleven days and three hours. — Very great
changes have taken place — so great that they cannot be under-
stood completely until some of the intermediate phases are
studied. Want of suitable material has hitherto prevented my
doing this. At the present stage—the beginning of the
twelfth day —the placenta is distinctly pedunculate, and there
is consequently a circular cleft between its sides and the closely
adjacent peri-placenta; in the middle of the placenta a deep
fissure corresponds, of course, to the space between the two
folds of the uterus, out of which the placenta is developed, and
therefore runs lengthwise of the uterus. The allantois has ac-
quired considerable size and is attached to the surface of the
placenta, from which the ectoderm has disappeared. The
glands of the placenta are very far degenerated and altered; in
the sub-glandular zone the multinucleate cells have appeared,
and in the outer zone the perivascular cells have increased so as
to occupy nearly all the space between the vessels. In the peri-
placental and ob-placental regions, the modifications are equally
noteworthy. Such, in brief, are the more striking changes.
Let us consider them with greater detail.

360 MINOT. [Vot. II.

The diagram on Pl]. X XIX. will enable the reader to follow the
ensuing descriptions. The general explanation of the diagram
is given in the next section.

The placenta is shaped somewhat like a mushroom: it has
a very thick stalk, with a somewhat broader top. The top is
bilobate, there being a deep fissure between the two lobes; this
fissure persists at thirteen days (Fig. 8, 7) ; its fundus is the sub-
placenta (Ercolani’s cotyledonary organ). The sides of the
fissure are, of course, part of the surface of the placenta, mor-
phologically speaking, and bear glands. The three zones of the
placenta are well marked. In the outer zone the blood-vessels
are very wide, with thickened degenerated epithelium ; the peri-
vascular cells occupy the entire space between the vessels in all
that part of the zone towards the muscularis and most of the
space in the part towards the glands. Next to the sub-glandular
zone, therefore, we see the vessels surrounded, each by its sep-
arate thick perivascular coat, while the intervening tissue still
consists of anastomosing cells, like those which in earlier stages
occupied more of the space and which formed the only packing
between the vessels at six days. The blood-vessels convert the
layer, by their enlargement, into a spongy tissue, which has been
described not only in the rabbit, but in other rodents; the ves-
sels themselves have been generally described as glands, but
the study of their development renders doubt as to their true
character impossible. The vessels are partially empty in my
preparations, but they contain very numerous leucocytes, nearly
all of which have several nuclei apiece, which are conspicuous
from their dark staining: there are a few red globules and here
and there a little coagulum. As the corpuscles of the embryo
are large nucleated bodies, there is no difficulty in distinguishing
the foetal from the maternal blood, even in the upper part of
the placenta, where the two circulations are juxtaposed. The
middle or sub-glandular zone has undergone greater changes still.
In it, as likewise in the glandular zone, the perivascular cells have
almost entirely disappeared,! but they are, as it were, replaced

1 This statement is perhaps not correct. There are certain spaces surrounded by
epithelial or epithelioid cells to be seen in the upper part of the sub-glandular and in
the lower part of the glandular zone; these spaces I have interpreted as parts of the
glandular system, but they are perhaps maternal vessels with perivascular cells. The

uncertainty as to their character could be probably removed by the examination of
the ten days’ placenta, which presumably offers the intermediate stages.

No. 3-] UTERUS AND EMBRYO. 361
by multinucleate cells (compare Fig. 14, Pl. XXVIIL, of these
cells from an older placenta) ; their origin appears to be due to
the development of clusters of connective tissue cells, which lie
scattered about between the blood-vessels ; each cluster consists
of from three to six cells lying together and connected on the
one hand by short processes with one another, and on the other
by longer processes with the cells of adjacent clusters. The
larger clusters are separated by membranes from one another,
and thus every cluster becomes enclosed in a membrane and ap-
pears as a multinucleate cell. The development of these cells
would doubtless repay more accurate investigation. The multi-
nucleate cells do not yet form a continuous bed under the
placenta, but are divided into parts by masses of very loose
connective tissue. At the base of the fissure between the two
lobes of the placenta the glands have almost entirely disap-
peared, but we still find a few unresorbed fragments of their
degenerated epithelium; these fragments are conspicuous by
their very deep staining, both of the hyaline substance and of
the nuclei: the neighboring tissues are less colored. The fissure
itself is like an inverted L; that is, it is transversely expanded
at the base; the floor of the expansion is thrown up into folds
and covered by a cylinder epithelium, which I feel some hesita-
tion in designating as the regenerated uterine epithelium, al-
though it resembles the epithelium on the peri-placenta, where
the glands are resorbed and the epithelium reconstituted from
its degenerated self. On the other hand, as shown in the next
section, there is some proof that the foetal ectoderm penetrates,
by villous growths, far into the placenta. It seems possible that
the fissure is filled by villous excrescence of foetal origin and
that the epithelium of the sub-placenta belongs to the villus.
This view does not commend itself to me. Neither upon the
upper wall of the expansion nor on the sides of the fissure have
I recognized any epithelium. The upper part of the fissure is
closed by an ingrowth of connective tissue. Hence the lower
part is changed into a shut cavity in the centre of the placenta,
and into this cavity the folds covered with epithelium project.

So far as I am informed, this curious structure has not been
described hitherto, but what appears to be clearly its homologue
has been observed by Ercolani, 89, pp. 290, 291, Tav. IV., Fig.
I., O, and specially studied by Creighton, 77b. Both of these

362 MINOT. [Vou. II.

authors examined late stages when the fissure is completely
filled by connective tissue, so that there is no space —a condi-
tion found in the rabbit at thirteen days. It will be convenient
to designate the structure as the swb-placenta. Its occurrence is
confined to rodents so far as at present known. Finally, we
have to note that at the edge of the placenta, toward the peri-pla-
centa, the sub-glandular layer, which we are now considering, is
characterized by the presence of deeply stained fragments of
glandular epithelium irregularly scattered through the other
tissues and similar in appearance to the remnants of the glands
about the sub-placenta. These fragments appear to have been
seen by Ercolani, Creighton, Masquelin, Swaen, and others, and
variously interpreted, their true nature not being recognized.
The disappearance of the glands at the centre and at the
_ periphery of the placenta virtually increases the domain of
the sub-glandular layer. The greatest changes have occurred
in the glandular layer. Scarcely a trace of the perivascular cells
can be found; the space they formerly occupied is taken up by
a very loose embryonic tissue; the glands are completely altered ;
they have lost their special affinity for eosine and cochineal,
neither the hyaline substance of which they are composed nor
the nuclei they contain being more stained than other tissues
(compare Fig. 8); they are irregularly cylindrical in shape, very
much contorted, and united with one another at irregular inter-
vals, so as to constitute an actual network: they are very much
vacuolated; their deep portions (fundi) are somewhat wider than
the upper parts; here and there one sees a remnant of the origi-
nal central lumen. The contorted masses, which I consider
glands, are apparently the same as have been seen by Mauthner
in the placenta at term, 115, p. 121. He describes these cords
as consisting of the fused epithelium of adjacent foetal villi, and
the spaces I have designated as vacuoles he describes as maternal
blood-channels; he states explicitly that he has injected them
from the maternal vessels, and in other cases found them gorged
with maternal blood. These statements are irreconcilable with
my own views, detailed in the present article. The uterine epi-
thelium has entirely disappeared both from the top and the sides
of the placenta. The top surface is covered by a very thin layer
of flat epithelium, Fig. 8, sth, which is found, when followed
out, to be continuous with the lining of the body cavity of the

No. 3.] UTERUS AND EMBRYO. 363

embryo; it is therefore mesothelium. Underneath this covering,
and above the glands, there is a layer of varying thickness con-
taining some large and a few small blood-vessels with embryonic
blood in them, and consisting otherwise only of scattered anasto-
mosing connective tissue cells,! which can be followed without
the slightest break on the one part until they pass directly into
the mesoderm of the superjacent embryo; on the other part,
down between the glands, Fig. 8, wes ; compare, also, later stages,
Figs. 10 and 11. Between the glands, also, are blood-vessels con-
taining embryonic blood. On the top surface of the placenta I
can find nothing recognizable as even a trace of the foetal ecto-
derm, which formed a thick and conspicuous covering in the
latest previous stage examined (nine days and seventeen hours).
At the edge of the top of the placenta, Fig. 8, the relations
change: the mesothelium, ms¢, bends up and leaves the placenta,
and together with a few subjacent mesodermic cells joins a sheet
of cylinder epithelium, cto, which is shown by its connections
to be foetal ectoderm. The ectoderm from the point where the
mesothelium, mst, bends on to the top of the placenta con-
tinues downward, c/o, to clothe the side of the placenta which
faces the peri-placenta. Between the placenta and peri-placenta,
as shown in Fig. 9, there is a fissure; the ectoderm can be fol-
lowed to the bottom of this, and from there extends, —not on to
the peri-placenta, — but turns abruptly back on to the side of the
placenta, up which it stretches a minute distance and thereupon
ends abruptly. The disappearance of the ectoderm is discussed
in the next section.

The peri-placenta is now characterized by the enormous
increase of the perivascular decidual cells and the accompany-
ing expansion of the blood-vessels; by the disappearance of its
glands and by the reconstitution, in part, of its superficial epi-
thelium. The peri-placenta appears like the continuation of the
outer zone of the placenta, for it directly adjoins it, is of about
the same thickness, and is histologically similar. The blood-
vessels are wide with hypertrophied endothelium; the peri-
vascular cells are disposed as in the sub-glandular zone of the
placenta; that is, in the half towards the uterine muscularis they
completely fill the intervascular room, but in the half towards

1A layer closely similar to this, and presumably homologous with it, exists in the
Guinea pig (Creighton, 77a, p. 558), in the rat (Ercolani), and other rodents.

364 MINOT. [Vou. II.

the interior of the uterus they form a discrete envelope around
each vessel, the spaces between the perivascular coats being
occupied by simple connective tissue cells. The glands which
at nine days, Fig. 4, were so bulky and conspicuous, have almost
completely disappeared, being now represented only by remnants
of multinucleate hyaline matter scattered superficially, and easily
recognized by their distinctive and conspicuous coloration:
some of these remnants are still united with the surface. The
epithelium is in two forms: on the half of the peri-placental sur-
face towards the placenta it is entirely in the phase of degenera-
tion, while over the other half it is already reconstituted as irreg-
ular cylinder epithelium, the cells of which are more or less
separated from one another, and somewhat variable in height ;
this epithelium stops abruptly near the middle of the peri-
placenta and is replaced towards the placenta by a hyaline
nucleated layer occasionally thickened into a lump, where the
nuclei are clustered; the cylinder epithelium is deeply stained
by the cochineal; the hyaline epithelium has a marked color from
the eosine, and its nuclei are dark with cochineal. The glands
are further resorbed under the cylinder epithelium than nearer
the placenta.

The ob-placenta is now characterized by the disappearance of
its degenerated epithelium, by the fusion of the epithelium of
the deep portions of its glands into a new continuous layer, and
by the development of peculfir monster cells in its central area
facing the placenta. The resorption of the epithelium by vacu-
olization has already been described in the account of the nine
days’ uterus, § 3. The epithelium, Fig. 6, g/, is everywhere
re-formed as a continuous layer; portions, Fig. 6, 4.e, of the
degenerated layer remain especially near the peri-placenta, but
for the most part the new epithelium is entirely uncovered, and
in the central region it has grown, so that the glands are already
deepened. But the most remarkable feature is the accumulation,
opposite the placenta, where the mucosa is much thickened, of
the curious bodies, to which I apply the term monster cells. They
are round or oval masses many times the size of any other histo-
logical element of the uterus or embryo, and possess huge nuclei.
They are shown in Fig. 17, which represents them at a later stage,
when they are further enlarged. I regard these bodies as de-
tached epithelial cells, undergoing degenerative hypertrophy. In

No. 3.] UTERUS AND EMBRYO. 365

spite of long searching for the phases representing their early
history, I have failed to ascertain positively their origin. In the
next section the question is recurred to. The monster cells vary
in size: the smallest ones lienear the epithelium; the larger ones,
for the most part, deeper down and even among the muscular
fibres, but a few large cells lie next the surface. The body of
the cell is evenly and coarsely granular and resembles the hya-
line degenerated protoplasm of the epithelium ; its external out-
line is distinct, well-rounded, and without processes; the nucleus,
which often has a slight space around it, as if it had shrunk a
little, has a clear regular outline, being apparently provided with
a membrane; it is well colored by cochineal, and contains an
indistinct network with imbedded granules of various sizes; in
the smaller cells the nuclei have one or two granules much larger
than the rest, and which may be spoken of as nucleoli; the size
of the nucleus increases with that of the cell, and at the same
time the granulation becomes coarser.

The description of the placenta at ten and eleven days given
by Masquelin and Swaen I have not been able to follow in all
respects. Owing to their conclusion that the epithelium of the
uterus gives rise to blood, they apply the term cavités hemato-
blastiques to apparently all the cavities of the placenta except
those of the maternal blood-vessels. I have compared their
description very carefully with my own preparations: so far as
this enables me to judge, their “cavités hamatoblastiques ”
include the foetal blood-vessels, the vacuoles in the: degenerated
glands, the spaces included within the epithelial U’s described in
the next section, and which are supposed to be the tips of foetal
villi, the multinucleate cells and perhaps also the sub-placenta.
Why the multinucleate cells are included among the blood-
forming organs the authors do not render clear. Their failure
to recognize the variety of constituents in the glandular layer
of the placenta must be ascribed to the want of the perfected
methods at present at our disposal. With the means now at
command there is no difficulty in obtaining preparations which
show indisputably that the glands though degenerated persist
intact, and do not give rise to blood cavities nor blood corpuscles
as Masquelin and Swaen have erroneously believed.

§ 8. Embryo at eleven to thirteen days. — As known already,
the embryo is completely separated from the yolk sack, and the

366 MINOT. [Vor. II.

allantois has grown forth and attached itself to the placenta.
The relations of the extra-embryonic structures have been repre-
sented by Bischoff in the diagrams of Pl. XVI. of his classical
memoir on the development of the rabbit. These diagrams have
since been reproduced again and again, sometimes with modifi-
cations as notably by Kolliker in his manual, and by Van Bene-
den and Julin. Guided by these and by my own preparations I
venture to construct a new diagram, Pl. XXIX., which I hope
will approximate more nearly to the actual relations of the parts,
with which we are now concerned.

In the first place it is to be noted that most of the section is
occupied by uterine tissue:—compare Fig. 9, Pl. XXVIII.
The largest space is occupied by the placenta, on the surface of
which is situated the embryo, lying upon its side. Opposite
(above in the figure) the embryo is the ob-placenta, 06-p/, with
its central area, containing the monster cells, zo c/; the inferior
wall of the yolk sack is fitted upon, but not attached to, the ob-
placental surface. The peri-placenta, PP, appears as the con-
tinuation of the outer zone, oz, of the placenta; it has no
glands: its blood-vessels are enlarged, and all the space between
them is filled with uninucleate decidual cells. This description
of the peri-placental structure applies also to the outer zone, az,
of the placenta. A narrow space separates the surface of the
peri-placenta from the side of the glandular zone, ¢/, of the pla-
centa: the letters a and 4 lie in this space. The placenta con-
sists of three zones: 1°, the upper glandular zone, g7/, divided
by a fissure, #, into two lobes. This fissure is partly filled with
an ingrowth of embryonic mesoderm, mes; the transversely
expanded bottom of the fissure forms the sub-placenta, sd.p/;
the glandular zone as a whole constitutes a protuberant mass
with top and sides clearly distinguishable. Below the sub-pla-
centa is the sub-glandular zone, s.-g/z, with dilated blood-vessels
and multinucleate decidual cells.

The embryo lies upon the surface of the placenta. From its
ventral side spring the allantois, a//, and the stalk of the yolk
sack ; for the sake of clearness the amnion and pro-amnion are
entirely omitted, since they have no direct relation to the
uterus.! The allantois expands upon the placenta; the yolk

1 For diagrams of the pro-amnion, etc., see Van Beneden et Julin. Copies of
their figures are given in Buck’s Reference Handbook of the Medical Science, V1., 32.

No. 3.] UTERUS AND EMBRYO. 367

sack expands over the ob-placenta. The cavity of the allantois,
all, is of course lined by entoderm; it is, however, quite small,
and in my preparations by no means the spacious vesicle com-
monly represented, for instance, by Kolliker in his Grundriss
(2te Aufl. Fig. 88), or by Balfour (Comparative Embryology,
II., Fig. 148). The allantoic mesoderm, mes; on the other
hand, spreads out, over the surface of the placenta, down its
sides, down into the fissure, 4, between the two lobes, and pene-
trates between the glands, g/, of the placenta; wherever it goes,
the mesoderm carries foetal blood-vessels. The free, z.¢., inner
or ccelomatic, surface of the mesoderm bears the mesothelium,
msth; as the extra-embryonic ccelom does not extend beyond
the top of the placenta, there is, of course, no mesothelium
upon the sides of the glandular zone (between a and 8), but at
the edge of the top of the placenta the mesothelium is re-
flected back, and after a short course joins the wall of the yolk
sack near the szzus terminalis, v.t.

The yolk sack, as has been long known, consists of two parts :}
Ist, the avea vasculosa bounded approximately by the szxus
terminalis, vt; within this area the entoderm is united with
the mesoderm, which passes only a very short distance further
out ; 2d, the remaining portion without mesoderm, excepting
always the pro-amnion, which is included in the avea vasculosa ;
over this second region the entoderm, ez, rests directly upon
the outer germ-layer, ec/o.

If we follow the ectoderm around, we find that it leaves the
yolk sack, just before the szzus terminalis, vt, is reached, and
being joined by the mesodermic lining of the coelom passes
down 6 on to the lateral surface between the peri-placenta, P,
and the glandular placenta, g/, where, as already described, it
bends inwards, and turning back runs a minute distance up-
wards ; according to my hypothesis it continued earlier over the
surface of the placenta, as indicated by the broad dotted line, @.
The layer of embryonic epithelium upon the side wall of the
rodent placenta has been seen by other observers, among whom
may be mentioned Ercolani and Creighton ; the latter, 77b, 560,
directs especial attention to it, in the Guinea pig, but refers it
to the entoderm. I consider it probable that it is really ecto-
dermal in the Guinea pig, as in the rabbit. Underneath the

1 Leaving the pro-amnion out of consideration.

368 MINOT. [Vou. II.

ectoderm, 4, to be seen at eleven to thirteen days at the sides on
the placenta, is a layer of mesoderm without any ccelom. Now, if
my suppositions are correct, then the ectoderm forms at first an
independent fold, da, beyond the terminal vein, vt; the meso-
derm, but not the mesothelium, extends into this fold, which
covers the sides of the placenta. The disappearance of the
foetal ectoderm from the surface of the placenta, and the pene-
tration of the foetal blood-vessels between the glands, are
changes which take place during the eleventh day. How those
changes occur, observations on the development at that age
must decide. Meanwhile let us make shift with two hypothe-
ses. The first is: The whole of the ectoderm attached to the
placenta degenerates and is resorbed. Since the uterine epithe-
lium, as observation indicates, has likewise disappeared from the
placenta, the mesoderm, mes, of the allantois, a//, is brought into
direct and free contact with the connective tissue and degener-
ated glands of the placenta, and is thus enabled to carry by its
own ingrowth the foetal blood-vessels into the very substance of
the placenta. The second hypothesis is that the ectoderm and
mesoderm have produced villi, which have grown into the pla-
centa. In favor of this latter hypothesis there is certain evi-
dence which I have not yet alluded to. In the deep portions of
the glandular layer of the placentas of both eleven and thirteen
one finds narrow loops of epithelium like a tuning-fork in shape ;
the open ends of the U-loops are towards the top of the pla-
centa; the epithelium composing them is a cylinder epithelium,
which gradually thins out towards the upper end of the legs of
the U;; it differs altogether in appearance from the degenerate
gland epithelium, the interiors of the U’s contain vessels with
foetal blood ; so far, then, these structures might be longitudinal
sections of the ends of foetal villi. Towards the surface of the
placenta the epithelium of the loops thins out, and I have not
been able to follow them. If we have to do with villi, we must
assume that the ectoderm has become exceedingly thin over
their basal portions, but is preserved as a thicker layer over
their tips, and my failure to trace the villi would be attributable
to the imperfection of my preparations and observations. Bal-
ancing the pros and cons leads me to favor the second hypoth-
esis. Let me add that the mesoderm of the embryo is continu-
ous without a break with the interglandular connective tissue ;

No. 3.] UTERUS AND EMBRYO. 369

this statement is correct beyond any doubt, for I have several
sections, in each of which the direct passage is observable under
the microscope without even displacing the slide. By hypothe-
sis this mesoderm is, however, really separated by a very thin
covering of foetal ectoderm from the uterine tissue, and the
whole constitutes a system of villi which have grown down like
roots into the placental soil.

That there is no communication between the foetal and ma-
ternal circulations must be deduced from the fact that the two
bloods are never mingled in one vessel, although found side by
side in adjacent vessels. The separation of the foetal and ma-
ternal blood has already been insisted upon. The full elucida-
tion of the double placental circulation must be left for injec-
tions to bring.

In brief: The rabbit embryo is attached to the placenta by
the ectoderm, which disappears from the surface of the placenta
during the eleventh day ; the vascular connective tissue of the
allantois grows probably by forming true villi into the placenta,
and so comes close to the maternal circulation.

In other rodents the placenta contains foetal vessels; its sur-
face is covered after a certain stage by a thin epithelium like the
mesothelial layer of the rabbit, and by a layer of vascular con-
nective tissue. Hence it seems probable that the structure in
the rabbit is typical of the class — compare § 12.

§ 9. Uterus at thirteen days and three hours. — The pla-
centa and embryo are considerably bigger than at eleven days,
but the structure of the parts is comparatively little changed.

A complete section is drawn in Fig.9. The longitudinal
muscles, Z.7z., and the circular muscles c.m., form the external
covering. They differ in microscopical appearance from the mus-
cles of the resting uterus, but I have not investigated the
change in them.

The placenta is very bulky. Its two lobes have begun to
form separate protuberances, so that the top of the placenta is
no longer a nearly plane surface. The placental surface is cov-
ered by the mesothelium, which is a little thicker than in the
previous stage, the cells having a greater vertical diameter.
Between the mesothelium and the glandular layer, g/, is the
vascular mesoderm, several of the large vessels of which are
shown in Fig. 9. The central fissure, f, of the placenta is very

370 MINOT. [Vou. II.

deep; it is completely filled with the ingrowth of mesoderm and
its accompanying large vessels. At the bottom of the fissure
next the outer placental zone, 0.2, is situated the sub-placenta,
sb.~l. The section drawn in Fig. 9 does not show the connec-
tion between the fissure and sub-placenta, which appears in sec-
tions 208-214 of the same series. The thickness of the meso-
dermic covering of the placenta has increased very considerably,
and the larger vessels are now provided with well-marked mus-
cular as well as endothelial walls. Many of the foetal vessels
run in spaces which stretch down nearly vertically from the
placental surface; in some cases the vascular columns can be
followed until they enter a cap of epithelium which forms a sort
of U. These relations suggest the presence of a series of foetal
villi covered in part by a very thin epithelium, and covered at
their tips by a relatively thick epithelium. This interpretation
has been discussed in the previous section. Beside the normal-
looking epithelium, we find the degenerated glands not much
changed from eleven days. The sub-glandular zone, sgZz,
shows further enlargement of the blood-vessels, so that they are
now larger than those of the outer zone, 0.2, thus reversing the
earlier relative proportions; the multinucleate cells have in-
creased in number and size, and contain more nuclei than at
eleven days; they occupy all, or nearly all, the room between the
vessels. Towards the outer zone the vessels are surrounded by
the uninucleate perivascular cells, but the intervening tissue
consists of multinucleate cells, so that there is a boundary re-
gion which cannot be assigned strictly either to the subglandu-
lar or to the outer zone. The outer zone, 0.2, is solidly packed
with perivascular cells.

The sub-placenta, s0.p/, lies still deeper than before, being
now close to the outer zone. Its epithelium is undergoing
hyaline degeneration, and accordingly is irregularly thickened,
and its nuclei are multiplied: the substance of the layer stains
deeply with eosine.

The peri-placenta, P, differs from that at eleven days, princi-
pally in having the perivascular cells as a solid packing through-
out the whole of its extent, except just where it adjoins the
glandular layer of the placenta. As at eleven days, its covering
epithelium is reconstituted on the part towards the sub-placenta,
and is in the phase of degeneration towards the placenta.

No. 3-] UTERUS AND EMBRYO. I
37

The ob-placenta, 04.p/, shows everywhere a marked growth of
its glands; as illustrated by Fig. 10, the glands are follicular ;
their cavities wide. The glands are not branched or pouched,
as the appearances in the sections suggest; they are broad
tubes closely packed, and are necessarily cut obliquely in most
cases. The rather ragged-looking epithelium is composed of
long cylinder cells (Fig. 10), with the nuclei at various heights,
and the protoplasm a good deal colored by the cochineal. The
connective tissue of the mucosa has also grown, and forms both
thin inter-glandular dissepiments and a thickened sub-glandular
stratum. In the centre of the ob-placenta the mucosa is still
further thickened to make room for the monster cells, which lie
for the most part below the glands, but are found also between
the glands and in the superficial portion of the muscularis. At
one point the ob-placenta is interrupted by a protuberant mass,
4, resembling the peri-placenta in structure; it consists of
crowded perivascular cells with dilated blood-vessels, and is cov-
ered by epithelium. As I have seen nothing analogous to this
mass in any other specimen of any age, it must be regarded as
a singular sporadic variation from the normal processes of devel-
opment.

The origin of the monster cells I am inclined to seek in the
uterine epithelium, as stated in § 7. The appearance of their
cell bodies, and of their nuclei at once suggest this origin on
account of the similarity with the appearance of the degenerated
epithelium elsewhere. We find, also, the smallest monster cells
near the epithelium. In Fig. 11 portions of the epithelium of
the peri-placenta are represented. The cells are all multinucleate,
as seen both in vertical section, A, and surface views, B; occa-
sionally, but very rarely, there is a cell with the nuclei gathered
together in a central mass, with an indistinct line enclosing the
bunch, Fig. 11, ¢. These cells are larger than the rest, and their
protoplasm is somewhat degenerated. If such acell were to de-
tach itself, and hypertrophy and the bunch of nuclei to break
down, it would resemble a monster cell. Yet I can find no evi-
dence that such a metamorphosis actually takes place in the
ob-placenta. In the ob-placenta itself there appear a few epithe-
lial cells with a single nucleus which are slightly enlarged, and
are possibly the initial stages of monster cells, but between
them and the youngest monster cells observed I have failed te

372 * MINOT. [Vou. IL.

discover any intermediate stages. The difficulty of finding the
first stages of the monster cells indicates that their develop-
ment must be extremely rapid, almost sudden.

§ 10. Uterus and embryo at fifteen days and four hours.
— The swelling of the uterus has considerably increased ; the
placenta is larger ; the cavity containing the embryo is very much
larger; the peri-placenta has grown but little. We notice now
that of the six folds of the uterus, the two placental have ex-
panded both in width and thickness to a far greater extent than
the remaining four folds, except that the lateral expansion of the
two ob-placental folds, by attenuation of their walls, has enabled
the ob-placenta to occupy an extent of the circumference of the
uterus which is about equal to that taken up by the placenta
proper; only about one-sixth of the whole circumference is
allotted to the peri-placenta. With the naked eye one can see
that the fissure of the placenta has opened so that the surfaces
of the two lobes of the placenta now face each other like the
sides of a V; the surface of each lobe, though somewhat irregu-
lar, is as a whole arched. The glandular zone is perhaps slightly
thicker than at thirteen days, but the diameter of the sub-glan-
dular zone is markedly lessened, owing apparently to the open-
ing of the interlobal fissure and the consequent flattening of
the surfaces of the lobes. With a hand-lens one easily recog-
nizes that the blood-vessels of the vascular zone of the placenta
are of much greater diameter than at thirteen days, while the
dissepiments between the vessels are not only relatively but ab-
solutely thinner than before: this observation does not necessa-
rily involve the conclusion that there has been an actual loss of
tissue, for the placenta as a whole has increase in bulk. Let us
turn now to the microscopical examination.

The placenta differs but little, except in the respects above
mentioned, from the stage last described. The mesodermic
covering of the placenta is well marked, Fig. 12, mes, and the
foetal mesothelium, mszh, is perfectly distinct ; it leaves the pla-
centa at its edge to curl over on to the yolk sack, just as at an
earlier stage, Fig. 8, msth. The side of the lobe next the peri-
placenta is clothed by ectoderm essentially as described at eleven
days and partially shown in Fig. 8, ecto; but the ectoderm is
now more irregular than at earlier periods and is thrown into
small folds near the point where it is reflected back on the pla-

No. 3.] UTERUS AND EMBRYO. 373

centa; similar appearances are clearly indicated in Ercolani’s
memoir, 89, Tav. IV, Fig. 1, z, 2, for the Guinea pig. It is quite
possible that the folds are more developed in the rabbit later.
The placental glands are very much contorted, Fig. 12, g/, g/;
very coarsely grandular, with numerous irregular vacuoles and
with the nuclei lying for the most part against or near the outer
surface of the gland, Fig. 13, g/: the nuclei no longer stain
deeply as they do during the first stage of the gland degenera-
tion, Fig. 7, In the upper part of the placenta the glands are
much narrower and more widely separated than in the deep part
of the layer, as can be seen in Fig. 12, which takes in about
half of the glandular layer from the surface down ; towards the
surface the glands often form wide loops, Fig. 12, and join one
another, making a network with closed meshes. As regards
the supposed foetal villi, I find the columns of the foetal meso-
derm running down more distinctly than at thirteen days, but as
before, the only epithelium which I clearly distinguished, is
that in the deepest part of the glandular layer disposed as if
covering the tips of the villi. The blood-vessels are very num-
erous, and some of those above the glands in the foetal meso-
derm are very large, Fig. 12, v. It will be remembered that
these vessels belong to the foetal system and that the plexus of
vessels, which is so conspicuous upon the surface of a freshly
excised placenta, pertains therefore to the embryo. At certain
points there rise thin membranes from the surface of the pla-
centa, which carry good-sized vessels: whether these are acci-
dental or constant, I am unable to say. Examined with a still
higher power, Fig. 12, the glandular layer shows the peculiarities
of its structure still more clearly; the mesothelium, mst, upon
the surface, though composed of flat cells, has considerable
thickness; the mesodermic cells, mes, are for the most part
spindle-shaped and their processes anastomose; the foetal blood-
vessels, v, v, come close against the glands, g/; if, therefore,
there is a layer of foetal ectoderm separating the foetal mesoderm
from the uterine tissues, it must be very inconspicuous from
extreme thinness.

As to the relations of the sub-placenta, my preparations are
unsatisfactory.

The sub-glandular layer shows the vascular endothelium ad-
vanced in degeneration, the cells projecting far from the surface.

374 MINOT. [ Vou. te

Many parts of the vessels are filled with coagulum, suggesting
thrombi formed during life, as has been asserted to occur nor-
mally in the human placenta. For the most part, the vessels
contain normal blood, save that there is an excess of leucocytes ;
in some vessels, however, there are large clear refringent bodies
which look like vesicles. What these bodies are I am unable
to say — possibly they come from breaking down of the endo-
thelium. The multinucleate cells, Fig. 14, are large and very
much crowded ; they contain each a dozen nuclei, more or less.
I have nothing of importance to add to the previous descriptions.

In the outer zone we notice at once that the expansion of the
blood-vessels is far less active near the muscularis than further
in; indeed, we might subdivide the zone into an outer compact
and an inner cavernous layer. The vascular epithelium is far
degenerated, Fig. 16; A is a surface view; B and C vertical
sections; each cell forms a more or less independent projection ;
the cells vary extremely in size; the nuclei are either single or
multiple; in the former case they may be small and compara-
tively regular, or large and very irregular in shape; in the latter
case they are of unequal sizes. The perivascular cells are in-
numerable; their appearance is indicated by Fig. 15; but where
the blood-vessels are wider, or, in other words, towards the glan-
dular zone, they exhibit signs of breaking down; the signs in
question are indistinctness of outline, granular appearance of
the protoplasm, and the difficulty of staining the nuclei. As
the changes are slight, they are perhaps accidental. It must be
left for future examination of later stages to show whether they
do break down or not. I also think that there is a tendency for
the multinucleate cells to invade the territory of their uninu-
cleate neighbors.

The peri-placenta agrees with the outer zone of the placenta
in its parenchymal structure, except as to two points: I°, it is
now invaded to a slight extent by the multinucleate cells, at
the spot nearest the placental glands; I have no reason to sup-
pose that these cells actually migrate into the peri-placenta, but
presume that they arise zz sztz,; 2°, near the ob-placenta there
are in some parts young monster cells lying close under the
epithelium ; the evidence is better here than anywhere else I
have observed that the monster cells arise from the epithelium.

The ob-placenta now has monster cells throughout almost its

No. 3.] UTERUS AND EMBRYO. ae

entire extent, but the greatest accumulation is where they first
are developed, directly opposite the placenta. In this region
(Fig. 17) they occupy not only the connective tissue of the
mucosa, a, 6, but also the territory of the circular muscular coat,
where they lie, c, between the bundles, msc, of muscular fibres,
which they have forced apart to make room for themselves.
The smallest monster cells, a, are found nearest the lining epi-
thelium, ef; those at the base of the mucosa, 4, are bigger, but
the biggest of all are those which lie in the outer part of the
muscularis, c; if, therefore, the cells arise from the epithelium
and migrate outwards, they must grow while they move. My
preparations show in the nuclei of the monster cells certain
large, deeply stained fragments which are perhaps chromatine,
Fig. 18. Owing to the stretching of the uterine walls, the
regenerated glands of the ob-placenta are no longer follicular as
at thirteen days (Fig. 10), but are again stretched out, so as to
approximate a second time to the form of shallow, open cups,
which they had at eleven days (Fig. 6); but where the monster
cells have accumulated most (Fig. 17), the only distinct trace of
the glands is the irregularity of the free surface covered by
epithelium, ef.

The embryo and its appendages do not show much alteration
in the parts concerning us in the present article. We may,
however, note especially two changes in the outer germ layer.
1°. On the strip of ectoderm between the vena terminalis of the
yolk sack and the points where the ectoderm joins the placenta,
there are a number of thickenings, which form small papillz
upon the outer surface of the layer. These outgrowths are
solid ectoderm, and like the buds of the villi of the human cho-
rion contain no mesoderm. Whether these structures do
become actual villi in later stages, 1am unable to say. 2°. Over
the yolk sack the ectoderm has become a cylinder epithelium, of
which the outer surface is irregular, each cell projecting a little
more or less than its neighbors. A similar modification occurs
in the opossum according to H. F. Osborn, 61 A, 378-379,
Pl. XVIL, Fig. 4, and Selenka (Eutwickelungsges. d. Thiere,
Taf. XXVIIL, Fig. 5). It is probable that the ectoderm
assumes this modification in other mammals, where it remains
attached to the yolk sack owing to failure to form a complete
chorion.

376 MINOT. [VoL. II.

§ 11. Summary.!— In the resting uterus of the rabbit there
are six longitudinal folds. The ovum attaches itself on or
between the two folds nearest the mesentery, and the placenta
is there developed ; the two adjacent lateral folds form a cushion
(the peri-placenta) about the placenta, but the two folds oppo-
site the mesentery are flattened out by the stretching of the
walls to form the swelling to contain the embryo; they consti-
tute the ob-placenta. In the region of the placenta the mucosa
undergoes an enormous hypertrophy: there is likewise an
enlargement, but much slighter, of the peri-placenta.

The entire epithelium lining the uterine swelling degener-
ates; its nuclei proliferate, and its protoplasm hypertrophies,
becoming at the same time hyaline and granular. The degen-
eration affects the glands also. The degenerated epithelium
becomes vacuolated and in large part resorbed. The process
goes on with distinctive features in each of the three primary
divisions of the swellings.

The connective tissue increases by hyperplasia in the peri-pla-
centa and to a still greater degree in the placenta, and is trans-
formed for the most part into uninucleate perivascular decidual
cells, but also in part, — namely, immediately below the glandular
layer of the placenta, —into large multinucleate cells. In the
placenta, and to a less extent in the peri-placenta, there is a new
formation of blood-vessels, which subsequently enlarge to great
size, although their only walls are an endothelium which under-
goes rapid hypertrophic degeneration.

In the placental region the uterine epithelium degenerates
and disappears, but the glands are preserved as irregular anasto-
mosing rows of coarse granular matter, with numerous vacuoles
and scattered nuclei, but without central lumina. Below the
glands is a zone containing wide vessels and large multinucleate
cells. The outer layer has wide blood-vessels, with numerous
uninucleate decidual cells, which arise from the connective tissue
cells and arrange themselves in successive coats around the
blood-vessels until they occupy the entire room between the
vessels.

The embryo is attached at first to the surface of the placenta

1 It will be remembered that the observations cover the period of from six to fif-
teen days ony, and do not include the eleventh day, when several important develop-
ments occur.

No. 3.-] UTERUS AND EMBRYO. 377

only by the ectoderm, to which the mesoderm soon joins itself.
As soon as the coelomatic fissure appears, we can speak of a
foetal chorion adhering to the placenta. When the allantois
grows out, it forms the stalk of connection between the embryo
and the placental chorion. After the development of the cho-
rion, the free surface of the placenta is, of course, covered by
mesothelium (the epithelium of the coelom). Outgrowths of
the chorion penetrate the glandular layer of the placenta;
whether these outgrowths are in the form of villi in the sense
that they preserve a covering of foetal ectoderm was not ascer-
tained, although the tips of the outgrowths appear to have such
a covering, and there is no mingling of the foetal with the ma-
ternal circulation. The ccelom of the embryo does not extend
to the edge of the placenta next the peri-placenta, but the meso-
derm does, and is covered by ectoderm.

In the peri-placenta, the glands degenerate and disappear com-
pletely, but the covering epithelium is reconstituted except on
the part near the placenta. The blood-vessels and connective
tissue change as in the outer zone of the placenta, though later.
At the fifteenth day a few young monster cells were found near
the surface.

In the ob-placenta the degeneration and resorption affect only
the surface epithelium and the upper part of the glands; the
deep portions remain as a series of shallow cups, having been
stretched transversely by the expansion of the ob-placenta; the
epithelium of the cups unites into a new continuous layer ;
the glands grow up into follicles and are again stretched out by
the expansion of the walls. Meanwhile there appear monster
cells, which probably arise by the hypertrophy and migration of
single cells of the epithelium; they are characterized by the
granular hyaline appearance of their bodies, by the coarse gran-
ulation and large scattered fragments of chromatine of their
nuclei, and by their hugeness. The monster cells continue to
enlarge and subsequently invade the whole thickness of the
annular muscularis. They appear first and are always most
numerous directly opposite the placenta, but they are ultimately
present throughout the ob-placenta.

The relations of the embryo having been outlined in § 8, with
the aid of Plate XXIX., it is not necessary to recapitulate them
again.

378 MINOT. [Vot. II.

§ 12, Comparison with other rodents.— The history of the
rabbit’s placenta elucidates also that of the Guinea pig, of which
we possess descriptions by Bischoff, Ercolani, $9, Creighton,
77a, 77b, Tafani, 134, and others. These authors being un-
aware of the nature of the metamorphoses of the uterine glands,
and not knowing the disappearance of the foetal ectoderm over
the placenta, but, on the contrary, seeking for foetal placental
villi, lacked the necessary basis for a correct interpretation.
Ercolani was further misled by his erroneous belief that the pla-
cental tissues of the mother arise as new formations, not as
metamorphosed constituents of the uterine mucosa, but coming
after the assumed but non-occurrent complete destruction of
the mucosa. Tafani’s work betrays gross inaccuracy, for he
based his figures and descriptions upon schematic notions, based
in their turn upon very superficial, and often entirely false, ob-
servations. To justify a judgment so severely unfavorable, it is
necessary only to direct examination to some of Tafani’s plates.
His drawings of the human placenta, for instance, /c. Tav.
VII., leave a great deal to be desired; in Fig. 1 the sections of
the villi are altogether too large and too few; the separate
triangle of tissue at the edge of the placenta does not exist; the
decidua is represented without any compact layer, and its gland
cavities are made into blood-vessels. The section of the rabbit’s
placenta (Fig. 2, Tav. IV.) is even more open to criticism, since
it is impossible to determine the foundation of observation.
Ercolani, on the other hand, was an observer of considerable
ability, and his numerous memoirs on the placenta are valuable,
although his hypothesis of xeoformaztone led him to adopt an
unfortunate terminology which makes it difficult to follow him.
Creighton observed with more impartial objectivity. That Bis-
choff was a first-class observer every one knows; he never
leaves any confusion between what he saw and what he in-
ferred; for us he has the disadvantage of having written before
the developments of recent histology. On the whole, we prob-
ably do best to turn to Ercolani, who figures 89, Tav. IV., Fig. I.,
a section of a placenta of a Guinea pig near full term. Let us
compare it with the rabbit’s placenta.

It is discoidal, pedunculate, and bilobed. The upper surface is
covered by a thin epithelium beneath which is a layer of vascu-
lar connective tissue, Z, extending over the sides of the pla-

No. 3.] UTERUS AND EMBRYO. 379

centa, g, f, f, and down between the lobes, g: the epithelium
therefore corresponds entirely with the placental mesothelium
of the rabbit. The upper portion of the placenta, /, corresponds
to the meshwork of degenerated glands in the rabbit’s placenta.
The layer of epithelium, 2, z, #, covering the side of the placenta,
corresponds to the foetal ectoderm in a similar position in the
rabbit ; at an earlier stage it resembles very closely in appear-
ance what I find in the rabbit (Creighton, 77a, p. 560, Pl. XIX.,
Fig. 0, ¢, c, c,). Deep down under the space between the lobes of
the placenta comes the sub-placenta, Ercolani’s cotyledonary
organ, O, which was compared above with the sub-placenta of
the rabbit ; the thick pedicle of the placenta, e, x, x, corresponds
to the sub-glandular layers of multinucleate decidual cells, which
has encroached upon and apparently replaced the outer zone
of uninucleate decidual cells, which is present earlier, as it is in
the rabbit. At the side of the placenta is the peri-placental
thickening, ¢.d, and springing from it the so-called reflexa, c,
which is probably only the peri-placenta hypertrophied. The
reflexa is entirely absent in the rabbit. In regard to what I
suppose to be the glands, P, neither the descriptions nor the
figures of Ercolani suffice to indicate their character.

The interpretation offered differs in nearly every respect from
Ercolani’s own; and yet though I have no preparations of the
Guinea pig’s placenta, and am acquainted with the organ only
through the publications of others, I think the homologies drawn
may be accepted with considerable security; but let me add
that I am well aware that their actual justification can come
only from the specimens.

Sections of the rat’s placenta near full term show that the
structure in that species is strictly comparable to what exists in
the rabbit. The surface is covered by a thin epithelium over-
laying a vascular connective tissue layer ; the vacuolated tubular
glands, very much degenerated, occupy the greater part of the
placenta, leaving only a thin vascular zone from which the outer
zone is lost, and which is therefore occupied solely by the much
altered sub-glandular zone of multinucleate cells. There are
many differences in details of structure from the rabbit, but the
fundamental likeness is self-evident.

As the similarity of the placentz of various rodents has been
noted by previous authors, it is probable that the type of
placental organization is the same throughout the class.

380 MINOT. [VoL. II.

II. MAN.

The following observations are of a fragmentary character,
but may serve to round out our information in certain respects.
Some of the facts have already been recorded in the series of
numerous embryological articles contributed to Dr. Buck’s Ref
evence Handbook of the Medical Sciences ; but as that work is
for consultation rather than the publication of original observa-
tions, it will hardly seem a mistaken repetition if I include here
some things already published there.

§ 13. Allantois and umbilical cord.— Prof. W. His has
shown that the entodermal cavity of the allantois is the termi-
nal stretch of the entodermal canal; the posterior end of the
body is prolonged into a mass to which he gives the name of
“ Bauchstiel” (Anatomie menschlicher Embryonen, IIl., 222-
226), and which develops in the same general manner as the

Cut 2.— Diagrammatic section of the Bauchstiel of a human embryo, modified
from W. His. Am, amnion; md, medullary groove; v, v, veins; A, A, umbilical
arteries; A//, allantois; coe, coelom.

body proper, having a rudimentary medullary groove, a somato-
pleure and splanchnopleure, Cut 2. It is morphologically the
hind portion of the body. After its closure and separation from
the amnion it appears as the umbilical cord. Its development
requires that the umbilical cord should be covered, not by the
amnion, as it is almost universally stated, but by an extension
of the foetal epidermis. Histological examination shows that
this is the case. The amnion is characterized by the ectoderm
remaining a single layer of cuboidal or low cylinder cells, and by
the matrix of mesoderm being distinct, owing to its high refran-

No. 3. ] UTERUS AND EMBRYO. 381

gibility. The foetal skin is characterized by the ectoderm be-
coming many layered, while the cutis remains for a long time
undifferentiated from the mesoderm below, and the matrix is of
low refrangibility. In comparing the ectoderm of the umbilical
cord with the skin, therefore, we do not expect to find any differ-
entiated cutis. The epithelium of the cord is at first, of course,
single layered, the condition which is permanent over the am-
nion. In the cord of a three-months embryo, Cut 3, I find the
two-layer stage. The outer layer is granular, and in some parts
each cell protrudes like a dome. Dome cells also appear on the
young epidermis, and as I learn from Dr. J. T. Bowen, who has

Cut 3. — Epithelial covering of the umbilical cord of an embryo of three months.
X 545 diams.

been investigating the subject in my laboratory, are probably
the precursors of the epitrichium. The cells of the inner layer
are larger and clearer than those outside. By the fifth month
the epithelium is distinctly stratified, and the superficial layers
consist of flattened cells similar to those of the horny layer of
the skin at an early stage. The ectoderm of the cord agrees
therefore entirely with that of the embryo proper in its general
development, but the differentiation proceeds more slowly, so
that at any given age the ectoderm of the cord is at a less
advanced stage than that of the embryo.

The appearance of the cord in cross-sections is instructive.
Cut 4, A, is a section through a cord of sixty days; the right
umbilical vein is already aborted; the caelom, coe, is a large
cavity, and contains the yolk stalk, Y.S, with its two vessels,

382 MINOT. (VoL. II.

Ar All

Cut 4.—Two sections of umbilical cord. A, at sixty days; B, at three months;
V, vein; Ar, artery; Ad/, allantois cavity; Coe, celom; Y, yolk sack; X 22 diams.

and its entodermic cavity entirely obliterated. Near the em-
bryo the ccelom may become much enlarged, and is often found
during the second month and even later to contain a few coils
of the intestine, as has been long known. Above the body cav- *

Cut 5.— Connective tissue of the umbilical cord of an embryo of 21™™; x 540
diams., stained with alum-cochineal, and eosine.

No. 3.] UTERUS AND EMBRVO. 383

ity is the duct of the allantois, A//, lined by entodermal epithe-
lium ; and in this region are situated the two arteries and single
vein ; the section is bounded by ectoderm.! The further devel-
opment of the cord depends upon three factors: 1°, the growth
of the connective tissue and blood-vessels; 2°, the abortion of
the ccelom, yolk stalk, and allantoic duct in the order named ; 3°,
differentiation of the connective tissue and of the ectoderm.

Cut6.— Connective tissue of the umbilical cord of a human embryo of about
three months, X 511 diams. Stained with alum-cochineal, and eosine.

The growth and differentiation of the mesoderm proceeds rap-
idly, encroaching upon the ccelom, which is obliterated (early in
the fourth month). At first the connective tissue, Cut 5, is ¢om-
posed merely of numerous cells embedded in a clear substance ;
the cells form a complex network, of which the filaments and
meshes are extremely variable in size; the nuclei are oval, gran-
ular, and do not have always accumulations of protoplasm about

1 The ectoderm is often wanting, owing to its frequent destruction post mortem.

384, MINOT. (Vou. II.

them, forming main cell bodies. I notice, also, a few cells which
I suppose to be leucocytes, but see no other structures. By the
end of the third month the cells have assumed nearly their defi-
nite form; the protoplasm has increased in amount, and forms a
large cell body around each nucleus, Cut 6. The network has
become simpler and coarser, the meshes bigger, and the fila-
ments fewer and thicker; in the matrix are numerous connec-
tive tissue fibrils, not yet disposed in bundles, except here and
there ; as they curl in all directions many of them are cut trans-
versely, and therefore appear as dots. In older cords there is an
obvious increase in the number of fibrils, and they form many
bundles. In the cord at term the matrix contains mucin, and
may be stained by alum hamatoxylin; at what period this re-

Cut 7.— Section of the allantois from the umbilical cord of an embryo of three
months; e¢, entoderm; es, mesoderm. X 340 diams.

action is first developed I have not ascertained. I have ob-
served nothing to indicate the presence of special lymph chan-
nels in the cord at any period, but I have not investigated the
point. Tait’s lymph channels are merely the intercellular spaces.

The tube of allantoic entoderm increases very little in diame-
ter after the second month; compare A and B, Cut 4. It is
very persistent, appearing usually even in the cord at full term,
at least in the proximal end, according to Kdlliker (Extwick-
lungsges. 2te Aufl, p. 34). After the second month it is a small
group of epithelioid cells, with distinct walls, irregularly granu-
lar contents, and round nuclei; around the cells, ez¢, which may
or may not show a remnant of the central cavity, there is a

No. 3.] UTERUS AND EMBRYO. 385

slight condensation, mes, of the connective tissue to form, as it
were, an envelope. This structure has been regarded by Ahl-
feld and others as the persistent yolk sack. I think the correct
interpretation was first suggested by Kolliker.

§ 14. Amnion. — The tissues of the amnion do not progress
beyond an early embryonic stage; the ectoderm remaining at
the one-layered stage, the mesoderm preserving much of the
primitive matrix. Emery (Arch. [tal. Biol., III., 37) has directed
attention to the primitive homogeneous matrix of the vertebrate
mesoderm, and especially to the separate sub-epidermal layer of
the embryo, which contains no cells at first. In the human

Cut 8.— Two sections of the placental amnion: A, from an embryo of the eighth
month; B, at term; ec¢, ectoderm; #zes, mesoderm; a, layer of mesodermic cells.
X 340.

amnion there is a non-cellular layer under the epithelium, as is
well shown in Cut 8, A and B. Sometimes this layer is in-
vaded to a certain extent by connective tissue cells, B ; in other
cases the portion of the matrix towards the chorion acquires a
fibrillar character, A, as if partially resorbed, but in no case
have I seen the matrix entirely altered from its primitive char-
acter. The cells of the mesoderm lie in lacunz ; they are flat-
tened in the plane parallel to the surface, and hence in vertical
sections, Cut 8, appear more or less fusiform. They present no
special features, so far as I have observed, to distinguish them

386 MINOT. [Vot. II.

from other embryonic connective tissue cells. Their bodies
have little affinity for coloring-matters, hence it is difficult to
follow the processes by which the cells are united. Their
nuclei are at first round or oval. After the third month they
often show a great variety of alterations in shape and size, Cuts
g, 10; some of the nuclei are then very large, with a distinct
net-work, d; others are smaller and differ but slightly from the
normal; some are very irregular, 6, and others again strangely
elongated, @; many other forms beside those represented in
Cut g are to be found. The changes indicated I consider of
a degenerative character, and in fact many of the nuclei are

Cut 9. — A natural group of nuclei from the mesoderm of the amnion of a foetus
of the fifth month. XX 1225 diams.

breaking down, for one finds in some specimens every stage be-
tween a nucleus and scattered granules, — nuclei, nuclei with in-
distinct membranes, nuclei without membranes, masses of gran-
ular matter, clusters of granules crowded together, and finally
other clusters more or less scattered. This degenerative pro-
cess may be compared with that described by Phisalix (Arch.
Zool. Expt., Sér. Il., T. III., 382) as occurring in the blood cells
of the spleen of teleosts. Compare also the chromatine degen-
eration observed by Flemming to occur in ova of the vertebrate
ovary (Hzs and Braune’s Archiv. 1885, 221-244). In the human
amnion the nuclear degeneration described is not always to be
recognized so clearly, although the nuclei in all amnia older
than three months, which I have observed, are more or less

No. 3-] UTERUS AND EMBRYO. 387

irregular and distorted. Finally it is to be added that not in-
_ frequently the cells form a distinct epithelioid layer upon the

surface of the amnion next the chorion, as represented in Cut 8,
'B; a.

Cut ro.— Mesodermic nuclei of the amnion of an embryo of about four months.
X 713 diam.

The epithelium of the amnion varies in appearance, as seen in
transverse sections. Usually the cells are cuboidal or low cyl-

Cut 11. — Surface view of the amniotic epithelium of an embryo of 144 days;
stained with alum — hzematoxyline, and eogine. £/, protoplasm; #7, intercellular pro-
cesses; 2, nucleus. X 1225 diams.

388 MINOT. [Vou. II.

inders, Cut 8, A, each one with a rounded top, in which is sit-
uated the more or less nearly spherical nucleus; sometimes,
however, the nuclei lie deeper down. Less frequently the
epithelium is thin, Cut 8, B, and its nuclei, which are trans-
versely elongated, lie further apart. It is probable that these
differences are not structural, but conditional upon the greater
or less degree to which the amnion is stretched. I have ob-
served no constant differences between the placental and the
remaining amnion. The most interesting peculiarity of the
epithelium is best seen in surface views; namely, the inter-
cellular bridges. They display themselves with a clearness
which I have never seen in other epithelia; see Cut 11.

The nuclei, z#, are relatively large, rounded with distinct out-
lines; they have a more or less well marked intra-nuclear net-
work, with thickened nodes, and a small number of deeply
stained granules, which are probably chromatine. Each nucleus
is surrounded by a cell body, f/; and the adjacent cell bodies
are separated from one another by clear spaces. With high
powers, as represented in the cut, one sees that these spaces are
separated from one another by threads of material, pv, stretch-
ing across as bridges, connecting neighboring cells. Examined
attentively, the protoplasm of the cells exhibits a vacuolated
appearance. One is thus led to view the epithelium as a sponge
work of protoplasm somewhat condensed around each nucleus ;
according to this interpretation the intercellular spaces are large
meshes of the sponge work, and the intercellular bridges are
protoplasmic. A recent paper! by M. Manille Ide, which I owe
to the kindness of the author, brings a series of interesting ob-
servations to show that the intercellular bridges of the Rete
Malpighi of the mammalian epidermis are not protoplasmic, but
processes of the cell membranes. This paper has led me to re-
examine my preparations of the amniotic epithelium, but I have
been unable to find in them any indications of membranes
around the cells or reasons for considering the intercellular
bridges as other than protoplasmatic in constitution. Whether
this result is due to the imperfection of my preparations, or is
in accordance with the truth, must be decided by further inves-
tigation.

1 Manille Ide, La membrane des cellples du corps muqueux de Malpighi. Za
Cellule, 1V., 2me fasc., 1888.

No. 3.] UTERUS AND EMBRYO. 389

Meola, 59, ascribes a much more complex structure to the
amnion than his predecessors, in which he is followed by Viti,
21. Both of these authors subdivide the mesodermic stratum
into three layers: a lamina connetivale, next the ectoderm, a
sostanza intermedia, and a membrana limttante. As to the his-
tological details, Viti differs somewhat from Meola, but agrees
with him in finding a histological distinction between the three
layers enumerated. The extent to which I can distinguish three
layers is indicated by the description of the mesoderm given
above: I have been unable to find the marked structural dif-
ferences affirmed by Viti. Viti’s paper is to be commended for
its excellent historical reviews, particularly for his summary of
the various theories as to the origin of the amniotic fluid.

§ 15. Chorion.— The human chorion has been the object of
greater misconception than perhaps any other organ of the
body. Even at the present time there prevail numerous false
conceptions concerning it, nor do I know of any text-book which
gives a satisfactory or even tolerably correct account of its
structure. This singular confusion is not due to deficiency of
observations, for from the vast literature of the subject (by
trusting the accurate observers, such as Coste, Farre, Kolliker,
Turner, Langhans, Waldeyer, etc.), we may cull a fairly com-
plete and exact history of the development of the chorion. But
the literature of the chorion consists chiefly of papers of little
value, and often remarkable for the gross crudeness of the ob-
servations they record, and for the proofs they are of their
author’s ignorance of other and better investigations. It ap-
pears that the anatomists and physiologists, by a species of
tacit understanding much to be regretted, have regarded the
uterus and placenta outside of their province, and have left the
investigation of the anatomy and functions of these organs to
gynecologists and others, whose capacities have lain rather in
the direction of medical practice than of original research, al-
though among them are some notable exceptions. The major-
ity of the practitioners who have written on the uterus and
foetal appendages have done at least as much harm as good. It
would be a sheer waste of time to subject this mass of literature
to a critical revision in order to extract from it what little there
may be of value. I have, however, read a large number of the
articles, and studied those which seemed worthy of it. Upon

390 MINOT. (Vou. II.

this course of reading and a study of my own extensive mate-
rial I have based the following history of the chorion, which
passes briefly over what is known, and dwells upon what is
founded on my own observations.

The human chorion as I have defined it} is “the whole of
that portion of the extra-embryonic somatopleure, which is not
concerned in the formation of the amnion.’”’ The human cho-
rion is remarkable for its very early complete separation from
the yolk sack, and for its precocious development of villi. Both
of these developments had already taken place in His’ youngest
embryo, and in Reichert’s ovum, which is supposed to be nor-
mal and the youngest known, there were chorionic villi, though
no embryo was distinguished. Reichert’s description is not
satisfactory, his long memoir? being principally concerned with
speculations.

The villi of the chorion, as shown long ago by the obser-
vations of Coste, are formed at first only
by the ectoderm. I reproduce here Fig.
6; of Pl. IL, ‘xeferring to the “human
species from Coste’s great work. The
hollowness of the villi and their clumsy
shape are to be especially noted. The
mesoderm grows into the villi subse-
quently. The branches of the villi grow
out in a similar manner, the process
being led, as it were, by the ectoderm.
Orth, in a special paper, 118, has used
these facts to argue against Boll’s Prz-
cip des Wachsthums. Kollman’s obser-
chorion of ‘an-embryo sup-) “ations ©) on the (prom the ar jvalln dinens
posed to be about eighteen the fourth week are particularly instruc-
days; mes, mesoderm; ec, tive. The outgrowth of the branches
peaeyaet aL mpeg BT very rapid and occurs with every de-

gree of participation of the connective
tissue. The two extremes are: 1°, a bud consisting wholly
of epithelium, which may become a process with a long, thin
pedicle, and a thickened free end remaining entirely with-

Cut 72. — Portions of the

1 Buck’s Reference Handbook, Medical Sciences, — Art. Chorion.
2 Reichert, Berlin Akad. Abhandlungen, 1873.
3 Kollman, Arch. Anat. Physiol. Anat. Abth., 1879, 297.

No. 3.] UTERUS AND EMBRYO. 391

out mesoderm; 2°, a thick bud with a well-developed core of
connective tissue, and having a nearly cylindrical form. Between
these extremes every intermediate state can be found. Other
observers have noted this peculiar manner of growth, which I
have found still going on in the placental chorion during
the fourth month. Robin, 125, appears also to have crudely
observed both the young hollow villi, and the solid epithelial
buds. The blood-vessels he traces to the division of the cavity
of the villi into an artery and a vein; from the nature of things
he offers no observations in support of this assertion.

Only the tips of the villi touch
the surface of the decidua,
either at first or subsequently,
except of course, over the cho-
rion lave during the abortion of
the vill. ~ The tips’ of the villi
are attached to the uterine sur-
face; they penetrate the decidua
for a short distance, but even in
the placental area at the close
of gestation, the penetration is
slight, and the villi make their
way only into the surface stratum
of the decidua serotina. There

is no evidence of any sort that ae 2 .
. . :. yy i]
the villi penetrate the glands she
at any period. The relation of Cut 73.—Isolated terminal branch

of a villus from the chorion of an em-

the villi to the decidua has now iyo afl twelve ween

been so accurately ascertained,

that there can be, I think, no longer any question whatso-
ever on this point. The best discussion is by Langhans, 110,
Py 2o tik.

The shape of the villi varies according to the part of the
chorion and the age of the embryo. They gradually abort over
the chorion leve, and gradually grow over the chorion frondo-
sum. Let us begin with the placental villi: At first they are
short, thick-set bodies of irregular shape, as shown in Cut 12; at
twelve weeks their form is extremely characteristic, Cut 13; the
main stem gives off numerous branches at more or less acute
angles, and these again, other branches, until at last the termi-

392

MINOT. [Von i

nal twigs are reached; the whole of the space between the
chorion and decidua is occupied by these ramifications; the

Cut rg.—Villous stem from a
placenta of the fifth month. xX 9
diams.

branches and twigs, as the illus-
tration shows, are extremely irregu-
lar and variable, although in gen-
eral they may be described as
club-shaped, being more or less
constricted at their bases. The
branches may be bigger than the
trunk which bears them, or of any
less size; some of the smallest are
merely slender outgrowths of the
epithelial covering of the villus,
such as have already been alluded
to. Gradually there is a change.
During the fifth month we find
the irregularity, though still very
marked, decidedly less exaggerated,
Cut 14; the branches tend to go
off at more nearly right angles;
one finds very numerous free ends,
as of course only a small proportion

of the branches touch the decidual surface; the branches, too,
are less out of proportion to the stems, less constricted at
their bases, or, in other words, less remote from the cylin-
drical form; the awkward cucumber shapes of the twelfth
week are no longer found except here and there. The
change continues in the same direction; that is, is towards

Cut 15.— Terminal villi of a placenta at full term. The little spots represent the
proliferation islands of the covering epithelium.

No. 3.] UTERUS AND EMBRYO. 393

greater regularity of configuration. It is hardly necessary
to describe the intermediate phases that have been exam-
ined, but it will suffice to describe the form at full term, Cut 15,
when the branches are long, slender, and less closely set, as well
as less subdivided, than at earlier stages; they have nodular
projections, like brapches arrested at the beginning of their de-
velopment ; there are numerous spots upon the surfaces of the
villi; microscopical examination shows that these spots are
proliferation islands, as we may call them, or little thickenings
of the ectoderm with crowded nuclei. It appears that not all
the villi change to the slender form; for some villi, having still
the earlier, thicker form, are found even in the mature placenta,
a fact already noticed by Jassinsky, 105, 346. These thick villi

Cut 16.— Section of the chorion at three weeks. a, layer of coagulum; 4, meso-
derm of chorion; £4, epithelium, also extending over the villi; /z and Vz',; the meso-
derm, 4, contains a number of blood-vessels, nearly all in transverse section. X 65.

usually show also a distinct “cellular layer” in their ectoderm,
a peculiarity to be considered below again. Seiler, 131a,
has given figures of the villi at various ages, but fails to show
the characteristic forms. Langhans has observed the altera-
tion in the villi, 110, 199, and even justly remarks that many
of the villi in so-called “moulds” are not pathological, as they
have been frequently considered, but normal young villi. The
differences in the villi, according to age, are very conspicuous
in sections. The sections should of course be made so that the
fragments of the villi will remain 27 sz¢w, imbedding in celloi-
dine is convenient for this purpose; if this end be attained, one

394 MINOT. [Vox if

finds below the chorionic membrane numerous sections of villi;
if the specimen be a young chorion, —first to third month, —
the villi are large, with a good deal of room between them ; their
outlines are very irregular, and there are relatively few small
branches (Cut 16). The older the specimen, the larger the
proportion of small branches.
In an old chorion—seventh to
ninth month—the number of
small villi of nearly uniform size
is very striking (see the figure
of a section through a placenta
im sttu, given in Cut 35).

The abortion of the villi of
the chorion lave takes place by
an arrest of development and =
a subsequent slow degeneration
of the tissues, which lose all recognizable organization in the pro-
toplasm, and to a large extent of the nuclei; at the same time
they alter their shape (Cut 17), becoming more and more filamen-
tous; by the fourth month only a few tapering threads, with
very few branches, remain. The villi disappear almost com-
pletely from the lzve, except near the edge of the placenta,
where they are to be found, even in the after-birth, imbedded in

Cut 17. — Aborting villus from a
chorion of the second month.

Cut 18.—Section of the chorionic membrane of an embryo of three weeks;
stained with osmic acid; mes, mesoderm; ect, ectoderm; a, outer, 4, inner layer of
ectoderm. From a section prepared by Prof. Theodor Langhans. X 445 diams.

No. 3.] UTERUS AND EMBRYO. 395

the degenerated epithelium of the chorion and the upper layers
of the decidua, as shown in Cut 25, wv, the epithelium and
decidua being so fused at this point that it is impossible to
determine any line of demarcation between them.

The chorion, being a portion of the somatopleure, consists, of
course, of two primary layers, the mesoderm and ectoderm.
During the second half of the first month, the earliest period
concerning which we have any accurate knowledge, the meso-
derm is already a vascular layer of considerable thickness
(Cuts 16 and 18, mes), and the epithelium (ectoderm) has two
layers of cells (Cut 18, aand 4) ; of which the outer is the darker
in specimens stained with osmic acid, carmine, cochineal, or
haematoxyline, and has also smaller and more granular nuclei.
The same distinction exists in the two-layered stage of the ecto-
derm of the umbilical cord (Cut 3), and of the foetal skin.
Hitherto most authors have entirely overlooked the inner layer
at early stages. It was first clearly recognized by Langhans,
who directed attention to it in a special memoir, 111, he having
already described its later history, 110. In some earlier writers
are allusions to the layer. Kastschenko, in his paper on the
chorionic epithelium, has also described it, although he has not
followed its history very far. The interpretation to be offered
seems to me clearly to be, that the chorionic epithelium advan-
ces in its differentiation to a stage equivalent to the two-layered
stage of the epidermis and there stops ; whatever further change
occurs is degenerative.

The two primitive layers of the chorionic epithelium have
been more or less clearly observed at later stages by several
anatomists, and have been variously interpreted. Ercolani and
Turner regard them as absolutely distinct, assigning the deep
layer to the chorion as its true and only epithelium, and the
outer layer to the uterus, thus enabling themselves to conceive
the villi as covered by a maternal as well as a foetal epithelium,
so that maternal blood found between the villi is still within the
maternal tissue. After accepting the outer layer as maternal,
the question as to its origin still remained. Some authors
affirmed it to be the uterine epithelium, others to be the lining
of expanded uterine blood sinuses. So far as I am aware, no
one has made observations to show by the developmental history
of the layer, that one or the other of the last mentioned hy-

306 MINOT. [Vot. II.

potheses is correct. When we consider the precision and exacti-
tude of Kastschenko’s observations, which actual specimens
enable one to verify, there is in my judgment no reason left for
differing from the conclusion that both layers are parts of the
foetal ectoderm. |

Governed by the difficulty of accounting for the presence of
maternal blood in the intervillous spaces, and therefore appar-
ently outside the maternal tissues, several investigators have
been led to seek for at least an endothelium outside the chori-
onic epithelium. Some authors, as for instance Winkler, have
asserted the existence of such an endothelium, but after a pro-
longed and careful search, I fail to find anything of the kind,
and in this result it seems to me the best observers are agreed.

The conclusion, I think, may now be safely formulated that
the chorion is covered externally by the foetal ectoderm, and
has no other covering in any part except, of course, where the
chorion lzve rests upon the surface of the decidua, and where
the tips of the villi touch the serotina; but the morphological
distinction holds, and the decidua is no more the covering of
the chorion, than are clothes morphologically the covering of the
body. I believe further, on grounds stated below, that the con-
clusion just formulated holds true of the chorion at all periods.

The further history of the chorionic mesoderm is so fully
given by Langhans in his invaluable memoir, 110, and Kast-
schenko, 107, that there is little to be added. In the earliest
stage I have been able to examine, an ovum of the third week,
the matrix of the chorionic connective tissue, in a preparation
stained with cochineal or hematoxyline, and imbedded in paraf-
fine for cutting, appeared hyaline and glistening, owing to its
refrangibility (Cut 19); it has lacunze in which the cells lie; the
cell bodies are either shrunken or colorless, so that lacune,
except for the staining of their contained nuclei, are clear and
light. This appearance I find again in specimens a little older.
The image is entirely distinct from that of the same layer later,
for then the cells are stained darker than the matrix, which at
the same time has lost its homogeneous character, and acquired
a fibrillated look. Very different from my own sections are
several which I owe to the kindness of Professor Langhans of
Bern, and which that distinguished investigator informs me are
from a three-weeks ovum, which had been preserved in osmic

No. 3.] UTERUS AND EMBRYO. 397

acid (see azte, Cut 18). In Professor Langhans’ preparations
the cells are all stained much deeper than the matrix; they have
an elongated form, and run in various directions more or less par-
allel to the epithelium ecto; hence many of them are cut trans-
versely or obliquely. Whether the differences noted are due to
the methods of preparation must be decided by preserving the
same chorion in part with osmic acid, in part with Miiller’s fluid
or picrosulphuric acid, the latter being the reagents I have used.
In specimens of the tenth week, the matrix of the chorionic meso-
derm has quite altered in character, being no longer homo-

Cut 1g. — Section of the chorionic membrane of an ovum supposed to belong to
the third week; ec¢, ectoderm; es, mesoderm; a, outer, 4, inner layer of ectoderm;
stained with alum-cochineal. * 445 diams.

geneous, and at the same time it has increased in thickness.
For the most part the matrix stains lightly, and where it is
lighter it contains fibrils of extreme fineness, and running curly
courses ; there are also streaks of lightly stained matrix, giving
the impression of fibres resulting from portions of the primitive
colorable matrix being left. In other parts of the layer the
primitive matrix is still present, and we find a homogeneous
well-colored basal substance, the cell lacunae of which appear
light by contrast, as in Cut 19. One can distinguish also the

398 MINOT. [Vou. II.

commencement of the perivascular coats, at least of the larger
vessels, the matrix being quite dense around them, and the cells
elongated almost into fibres, and possessing a slightly increased
affinity for coloring-matters. The larger blood-vessels and
unmetamorphosed part of the layer occupy a middle portion be-
tween the two surfaces, but the smaller blood-vessels lie near
the ectoderm (compare Cut 19, v), thus presaging the formation
of Langhans’ vascular layer (Gefassschicht). The development
of the mesoderm of the chorion leve stops at about this stage,
or at the stage when the matrix has completely changed from
its first state; in the region of the frondosum, however, develop-

—s 2 oy; = SS i! ass SD Oeecn
SE ons eNOS if BS fang Gh
ny NS A f a\h I, is aes

as

Cut 20.— Section of the amnion and placental chorion of the fifth month. £9,
amniotic epithelium; Am, amnion; Str, stroma; /70, fibrille layer; /ér, fibrine
layer; c, cellular layer; Vz, villi. (From a section cut in celloidine, and stained
with Weigert’s Hzmatoxyline. The drawing is only approximately correct as to
details. XX 71 diams.).

ment proceeds much further by the production of fibres throug

out the whole of the layer; usually, but not invariably, the fibres
become much more numerous near the ectoderm than in the
inner part of the mesoderm, thus differentiating a well-marked
sub-epithelial fibrillar layer, Cut 20, 76, from the deeper and
wider stroma, S¢v. The fibrillar layer is that commonly spoken
of as the connective tissue layer of the chorion: for details of
its structure, including the “‘ Gefassschicht,’ see Langhans and

No. 3.] UTERUS AND EMBRYO. 399

Kastschenko. The inner layer, S¢v, is called the Gallertschicht
by many German writers, and seems to be what Kolliker (Zvt-
wickelungsgeschichte, 2te Aufl., p. 322) designates as “ Gallert-
gewebe zwischen Chorion und Amnion”’; it usually contains a
considerable number of large granular wandering cells. Jung-
bluth, 106a, describes a network of capillaries, which exist
during the first half of pregnancy, apparently in the upper part of
the stroma, —z.e. next the amnion — but I fail to findany. Where
the amnion comes into contact with the chorion the adjacent parts
of the two membranes are more or less loosened, forming a net-
work of strands by which the membranes are united: most of
the uniting strands appear to belong rather to the chorion than
to the amnion. This loose tissue is perhaps that which Kolliker
designates as a Gaclertgewebe distinct from the chorion.

Although the chorion bounds the ccelom, I have observed no
mesothelium upon its mesodermic surface; but I have not made
search for it by any special methods. In the rabbit, it will be
remembered, the mesothelium is very evident over the placenta,
but the rabbit differs from man by the absence of union between
the amnion andchorion. Nor have I been able to find any base-
ment membrane, properly so called, under the chorionic ecto-
derm. As to the appearance which suggests it, I accept Kast-
schenko’s explanation, 107, 455.

The mesoderm in the villi is differentiated otherwise than
that of the membrane of the chorion. In the youngest stage
I have examined there is some of the primitive matrix present
in the villi; and I presume that earlier the whole mesoderm has
the same character. In my specimen (three weeks) the change
is progressing.» I have not succeeded in satisfying myself as to
the process of change which takes place, but I think it probably
essentially as follows: The cells gradually develop large bodies
and acquire a more decided affinity for coloring-matters; mean-
while vacuoles appear in the matrix, presumably by its modifica-
tion into a new substance; the vacuoles increase in size and
number, transforming the matrix into a network and ultimately
causing its total disappearance, leaving the intercellular spaces
filled entirely with the new substance, which has come from a
metamorphosis of the original matrix; probably this new sub-
stance is more or less fluid, since wandering cells are scattered
freely through it. Leaving this half-hypothetical history, let us

400 MINOT. [VoL. II.

pass on to direct observations. In the placental villi of embryos
of four months and older, the mesoderm exists in two principal
forms, —adenoid tissue and fibre-cell tissue around the blood-
vessels. The adenoid tissue, Cut 21, is that of which the sup-
posed development has just been sketched ; it may be considered
as the proper tissue of the villus. It consists of a network of
protoplasmic threads, which start from nucleated masses (cells).
There are many large meshes, which are partly occupied by the
coarsely granular wandering cells, /, 4, which are scattered about,
and are usually present in large numbers. About the capilla-

Cut 21.— Adenoid tissue of a villus from a placenta of four months. /,4,/
wandering cells; wv, v, capillary blood-vessels; a, finer meshwork from near a
capillary. X 352 diams.

ries the network is much more finely spun. Kastschenko, 107,
454, found the wandering cells most abundant near the epithe-
lium, but I have noticed no such peculiarity, except that they do
not often enter the dense perivascular tissue; and as the blood-
vessels are centrally situated, the adenoid tissue and the wander-
ing cells in it are of course more peripheral. It seems to me
that the leucocytes are distributed more or less evenly through-
out the adenoid tissue. I fail to recognize any intercellular sub-
stance. The abundance of nuclei deserves special mention.
Around all the non-capillary vessels the mesoderm is very dif-
ferent, for it exhibits distinct intercellular substance, with a ten-

No. 3.] UTERUS AND EMBRYO. 401

dency to fibrillar differentiation in quite a wide zone around the
blood-vessels; in this zone the cells become elongated and
irregularly fusiform; around the larger vessels the cells are
grouped in lamina, making the structure similar to that already
described in the walls of the vessels of the umbilical cord; after
the perivascular coats acquire a certain thickness, the cells of
the inner layers are more elongated, more regularly fusiform,
and more closely packed than those of the outer layer; the
transition from the denser to the looser tissue is gradual. We
are perhaps entitled to recognize in the denser inner layer the
media, in the outer looser layer the adventitia, although neither
of the layers has by any means the full histological differentia-
tion characteristic of the like-named layers of the blood-vessels
of the adult.

The epithelium of the chorion becomes differentiated in three
different ways: 1°, upon the chorion frondosum; 2°, upon the
chorion lave; 3°, upon the villi. For a correct knowledge of
the remarkable changes which the epithelium undergoes, partic-
ularly in the placenta, we are indebted to the remarkably exact
investigations of Langhans, 110 and 111. This author left two
points of importance unsettled; namely, the origin of his
“ Zellschicht,’ and of the “canalisirtes Fibrin.’ Kastschenko
has traced the cellular layer (Zel/schicht) to the epithelium, as
already stated: compare pp. 463-469 of his memoir, 107. My
own observations show, I think conclusively, that the canalized
fibrine arises through a degenerative metamorphosis of the epi-
thelium, which begins in the outer layer and may invade the
inner layer (Langhans’ Ze//schicht). Let us consider separately
the three series of modifications of the chorionic. ectoderm.

In the region of the chorion frondosum the inner layer of the
ectoderm (the cellular layer of Langhans) becomes irregularly
thickened in patches, which present every possible degree of
variation as to number and as to their breadth and thickness.
Although at first the cellular layer is more or less continuous
and composed of uniform cells, this is not the case in later
stages. We must assume that with the growth of the mem-
brane the epithelium increases in area, but remains in many
places single layered, developing no “ Zellschicht.” The patches
of cells have been well described by Langhans, 110, and Kast-
schenko, 107, 466, and are represented with lower power in

402 MINOT. (Vo. II.

Cut 20, c, and with a higher power in Cut 22, c. They vary
much in appearance: the cells are more distinct in the small
patches, but are less individual in the large patches, owing to
the spread of the process of degeneration into the layer, Cut 22, ¢.
The cell bodies are lightly stained, and the granular nuclei are
not very sharply defined and vary in size and shape. The cellu-

MES

Cut 22,— Placental chorion of an embryo of seven months; vertical section
through the ectoderm and portion of the adjacent stroma. mes, mesodermic stroma;
¢, cell layer; /%, fibrine layer; ef, remnant of epithelium. X 445 diams.

lar layer is always sharply defined against the stroma, although
there is no true basement membrane, but towards the outer
layer of the ectoderm its boundary is sometimes distinct, some-
times lost in a gradual transition.

The outer layer of the ectoderm of the frondosum is even
more variable. As stated by Kastschenko, it is primitively a
dense protoplasmic reticulum, with nuclei in a single layer and

No. 3.] UTERUS AND EMBRYO. 403

without any cell boundaries. In the chorion frondosum at four
months and after I find spots where this structure still prevails,
either with or without an underlying cellular layer; in other
spots the layer is thickened and contains an increased number
of nuclei, which are sometimes crowded in a bunch; elsewhere
the layer is thinned out and has no nuclei; in still other spots
the thickening has gone on much further, and usually, but not
always, where the outer layer is much thickened the cellular
layer under it is also thickened; whérever it is thickened, and
occasionally where it is thin, the outer layer of the ectoderm
shows a marked tendency to degenerate into canalized fibrine,
Cut 20, fo, and Cut 22, fd. It is not difficult to assure one’s
self that the fibrine arises by direct metamorphosis of the ecto-
derm. I now think that its formation begins in the outer layer
and thence spreads into the cellular layer; for, in fact, when
both layers are distinguishable, as in Cut 22, the fibrine layer,
fo, is always external, and the external layer of nucleated proto-
plasm has either totally disappeared or is represented by mere
remnants, as in Cut 22, ef. The fibrine layer consists of a
hyaline, very refringent substance permeated by numerous
channels, Cut 22, 76; the substance has a violent affinity for
carmine and hzmatoxyline, and is always the most deeply
colored part of a stained section; the channels tend to run
more or less parallel to the surface of the chorion and are con-
nected by numerous cross-channels ; some of the channels con-
tain cells or nuclei. This complex system of canals is by no
means of uniform appearance in all parts of the placenta, both
the spaces and dissepiments varying in size and shape. The
fibrine often sends, as shown in Cut 22, long outshoots into the
cellular layers upon which it seems to encroach. The frequency
of these images in my preparations led me to the opinion? that
the fibrine arises from the cellular layer only, and I concluded
that the ectoderm was first transformed into the so-called cel-
lular layer, which was then transformed into fibrine. It still
appears to me that much of the degeneration goes by these
stages; but, on the other hand, it seems clear that the degenera-
tion begins, as above stated, in the outer layer. Another appear-
ance is presented by the ectoderm where it is thickened and
wholly transformed into the cellular layer. In brief: the ecto-

1 Anatom. Anzeiger, ii. 23.

404 MINOT. [Vou. Il.

derm of the placental chorionic mesoderm undergoes patchwise
manifold changes ; it exists in three chief forms: 1°, the nucleated
protoplasm ; 2°, the cellular layer; 3°, canalized fibrine. A patch
of the ectoderm may consist of any one of these modifications,
of any two or of all three, but they have fixed relative positions,
for when the nucleated protoplasm is present, it always covers
the free surface of the chorion; when the cellular layer is
present, it always lies next the mesoderm; and when all three
forms are present over the same part, the fibrine is always the
middle stratum. In general terms it may be said that the
amount of canalized fibrine increases with the age of the
placenta, but it is very variable in its degree of development.
The peculiar layer into which the ectoderm is transformed has
long puzzled anatomists. E. H. Weber recognized the fibrine
layer and described its appearance correctly; it has probably
been often seen, but generally regarded as either pathological
or a blood coagulum. Robin, for instance, may be cited, 125,
70-71, as one who saw, without observing correctly and under-
standingly, the tissue in question. An important gain was
made when Winkler recognized the modified ectoderm as a
constant layer, and in 1872 directed especial attention to it
under the name of “ Schlussplatte,’ 152. Kolliker (Entwicke-
lungsgeschichte, 2te Aufl., 337) added essentially to our knowl-
edge of its structure, but it is to Langhans that we owe the first
clear light. Meanwhile, other writers, following the lead of
Ercolani and Turner, 146, 551-553, have been influenced chiefly
by the presence of the cellular layer, in the large size of the ele-
ments of which they found a resemblance to the decidual cells,
which has guided them to the conclusion that the cellular layer
is derived from the wall of the uterus. This error has been
definitely corrected by Kastschenko, as already stated. In
further support of the conclusion that the chorionic cellular
layer is not decidual, may be brought forward the fact that
there is a certain immigration of decidual cells into the placenta
at its margin; but they remain entirely distinct from the cells
of the cellular layer. This is readily seen in radial sections
through the margin of a placenta from a normal after-birth —
compare below, the account of the ectoderm of the chorion
leve. The origin of the canalized fibrine from blood, which
Langhans left in his first paper as an open possibility, and which

No. 3.] UTERUS AND EMBRYO. 405

even so recent a writer as Ruge, 129a, 123 and 130, has advo-
cated, cannot be maintained. Of course, there may be a deposit
of blood fibrine (coagulum), but it would be pathological, and
therefore to be distinguished from the normal fibrine of ecto-
dermal origin. Moreover, the microscopic appearance of a blood
clot or thrombus is so extremely characteristic that one can
readily distinguish it from the placental canalized fibrine.

The ectoderm of the villi of the placenta differs from that of
the chorionic membrane in several respects: 1°, the cellular
layer after the first month becomes less and less conspicuous,
and after the fourth month E
is present only in a few iso-
lated patches, known as the
Zellknoten, and carefully de-
scribed by Langhans and
Kastschenko; both of these
authors were impressed by
the resemblance of the cells
to those of the decidua
serotina; Langhans con-
cludes that the Zel/knoten
arise from the serotina, but
Kastschenko, having traced
their development from the Cut 23. — Cross-section of a villus from a
chorionic epithelium, denies placenta of seven months; three blood-vessels
his predecessor’s conclu- are shown; a,a, thickenings of the ectoderm;
sion, but still clinging to ane We a thickening transformed into canalized
, i ; fibrine. X 222 diams.
idea of a genetic connection
between the Ze//knoten and the decidua, reverses the reasoning,
and concludes that the decidual cells arise in part at least from
the Knotenx. Neither of these authors have found the intermedi-
ate forms between the two types of cells, and when we examine
their descriptions critically we find that they have really no
evidence except the likeness of the cells to offer in favor of
their genetic relationship, and accordingly Langhans expresses
himself with characteristic caution. To me the resemblance
appears altogether superficial; hence my conclusion that the
Zellknoten are remnants of the cellular layer. 2°, For the most
part the villi remain covered by the nucleated protoplasm, which
in many places is thickened. In the later stages these thicken-

406 MINOT. (Vou. II.

ings are small and numerous, constituting the so-called “ Prolif-
evations-inseln”’:; compare Cut 15. Many of the little thicken-
ings appear in sections of the villi, Cut 23, a, a, and here and
there are converted into fibrine, # I have interpreted them
(Wood's Reference Handbook of the Medical Sciences, V., 695)
as commencing buds, and consider that in earlier stages they
grow into branches, but in later stages are in part at least
arrested in their development. 3°, The proliferation islands are
converted into canalized fibrine, and at the same time grow and
fuse, forming larger patches, particularly on the larger stems: in
this manner are produced the large areas and columns of fibrine
found in the placenta at four months and after; they have been
well described by Langhans, and form a striking feature in sec-
tions of placente. Some of the columns, as stated by Lang-
hans, stretch along the villi from the chorionic membrane to the
surface of the serotina as if to act as supports. Ercolani appears,
if I understand his account, to have seen the fibrine columns,
without, however, ascertaining either their structure or their
origin. 4°, Over the tips of the villi, which are bent considera-
bly where they are imbedded in the decidua serotina, the rela-
tions are not clear; the epithelium is certainly not present in its
original form over the imbedded ends of the villi, which are,
however, surrounded by a hyaline tissue of the character of the
canalized fibrine, except that the canals are often indistinct or
even wanting; the hyaline tissue forms an almost continuous
coat over the decidual surface ; in earlier stages the ectoderm of
the terminal villi is often considerably expanded. The natural
interpretation of these facts is that the ectoderm of the villi ex-
pands over the decidua serotina and degenerates. In this
manner we account for both the absence of any cellular ecto-
derm over the ends of the villi and the presence of canalized
fibrine upon the serotinal surface — but the hypothesis must
await the final test by observation.

The ectoderm of the chorion lzve loses by the seventh month
all traces of the protoplasmic layer, and is without any canalized
fibrine, except near the placenta; cf zzfra. It is transformed
into a Zellschicht. In a section of the leve zm sztu at seven
months, Cut 33, the chorionic ectoderm, c, rests directly upon
the decidua, which has no epithelium of its own. The ecto-
dermal cells lie two or three deep; they are described by Kolli-

No. 3-] UTERUS AND EMBRYO. 407

ker and Langhans, the former designating them as the chorionic
epithelium, while the latter doubtfully traces their origin to
the uterus. That Kolliker (Entwickelungsgeschichte, 2te Aufl.,
p. 322) is right, I am confident. It is easy to follow the layer
of cells in question at the edge of the placenta, and see that it
is directly continuous with the cellular layer of the frondosum,
which it resembles in character. On the other hand, the ecto-

Cut 24. — Placenta at full term. A, vertical radial section through the margin;
D, decidua; v2, aborted villi outside the placenta; Cho, chorion; .Sz, circular sinus;
V2, placental villi; 724, canalized fibrine. B, portion of A more magnified to show
the decidual tissue near 4; wv, blood-vessel; ad’, decidual cells; d@, with one, @’,
with several nuclei.

dermal cells of the lave are distinct in character from the decid-
ual cells next to them, Cut 34, having smaller and more darkly
stained nuclei, and much more coarsely granular protoplasm ;
the ectodermal cells are much smaller than the decidual. The
ectoderm is sharply marked off from the decidua, but its surface

408 MINOT. [Vot. II.

is often corrugated, and then the line of separation between the
tissues is irregular, and in sections it may even appear that
there is a true interpenetration and mingling of the decidual and
ectodermal cells; but it is only apparent, and the demarcation is
always preserved.

At the edge of the placenta, as shown by examination of after-
births, the relations of the layers are somewhat different. I
reproduce with a few additions the descriptions given in my
article on the Placenta’ of a radial section through the
margin of a normal placenta discharged at full term, Cut 24,
A, from which the amnion had been removed. The chorion,
Cho, and decidua, D, are in immediate contact at the left of

Cut 25. — After-birth at full term; vertical section of the amnion, chorion, and
decidua in their natural relations near the placenta. am, amnion; cho, chorion;
¢, cellular layer or ectoderm; 7, fibrine and decidual tissue, degenerated; D’, decid-
ual tissue. XX 125 diams.

the figure; that is, outside of the placenta, though remnants of
the aborted villi, vz, are still plainly recognizable; but, as stated
previously, they occur only in the immediate neighborhood of
the placenta. These villi are surrounded by hyaline matter which
resembles and can be followed into continuity with the canalized
fibrine layer, /26, covering the surface of the decidua serotina
and the fibrine layer of the chorion frondosum. Below the
aborted villi, vz, of the chorion lave, the fibrine layer is broken
down and penetrated by the decidual tissue, so that the demar-

1 Wood’s Reference Handbook Medical Science, V., 694, 695.

No. 3.] UTERUS AND EMBRYO. 409

cation between the foetal and maternal tissues is here lost, and
in fact, at the edge of the placenta the decidual cells make their
way into the chorionic tissue, and for a certain distance towards
the centre of the placenta they are found lying chiefly in the
ectoderm. In other placentz the fibrine layer and the decidual
tissue around the margin of the placenta have not only inter-
grown, but also undergone a common degeneration, Cut 25, in
consequence of which all distinct structure is obliterated, and we
find the villi, vz, imbedded in a stratum, 7, of more or less
colored substance, without definite organization except irregu-
larly scattered nuclei. Attentive examination shows that this
layer, f, has unmistakable remains, c, of the cellular layer next
the mesoderm of the chorion, and that it passes into an outer
layer, D', in which the traces of decidual structure are unmistak-
able ; the dark line at the lower edge of the decidua, D’, is merely
detritus and coagulum, as is often found on after-births. If we
follow the layers in this, or a similar specimen, in the direction
away from the placenta, the layers gradually alter, losing their
degenerated character, until we reach a point where the
chorionic ectoderm and the uterine decidua both exhibit their
normal features. Returning now to the placenta we were pre-
viously considering, Cut 24: The placental chorion begins to
exhibit its characteristic stratification a short distance within
the margin. I have found, however, that the distinctness of
that stratification varies considerably, not only in different
placentze, but also in different parts of the same placenta. The
decidua, D, outside the placenta is very thick, but at the edge
of the placenta it begins to thin out, and as it passes over the
under side of the placenta, rapidly becomes so much reduced as
to be even less in thickness than the chorion, cho. The decidua
is everywhere crowded with an immense number of decidual
cells, but in some other specimens they are less crowded. The
surface of the decidua serotina is covered by a layer of fibrine,
easily recognized by its deep staining ; this coat of degenerated
material has not yet received the attention it deserves, as a fea-
ture of the human placenta, which is quite constant, so far as
my observations go; as stated previously, I consider its origin
to be the epithelium of the ends of the villi imbedded in mucosa.
Up to the edge of the placenta the chorion leve and decidua
are united; at the edge they separate, to make room for the

410 MINOT. [Vot. II.

villi, Vz, Vz, of the frondosum. In the angle, Sz, where the two
membranes first separate there are very few villi, so that there
is a comparatively clear space left, which is known as the cir-
cular sinus. It is not, as some of the older writers have believed,
a distinct vessel, nor does it extend as a clear space completely

Cut 26.— Placenta at full term, doubly injected by Dr. H. P. Quincy, to show
the distribution of blood-vessels upon the surface; the arteries are drawn light; the
veins dark. XX 0.7 diams.

around the placenta ; but, on the contrary, it is interrupted here
and there by an ingrowth of villi. In the cut, the spaces oc-
cupied of maternal blood are left white; the foetal blood-vessels
are drawn black.

The chorionic circulation is complete in itself. The single
vein and the two arteries of the umbilical cord spread out over

No. 3-] UTERUS AND EMBRYO. II
3 4

the surface of the chorion, marking their course by projecting
ridges. The insertion of the cord is always, so far as I have
observed, obviously eccentric ; the degree of eccentricity varies
from a nearly central position to the so-called velamentous in-
sertion,—compare B. S. Schultze, 159; the degree of eccen-
tricity is easily seen to be related to the distribution of the
vessels, —a point not mentioned in current text-books. The
arteries come down together from the cord, and are usually
connected, but not invariably, by a short transverse vessel,
situated about half an inch above the surface of the placenta,
and which has been noted by many observers. I have never
noticed any arterial or venous anastomoses on the surface of the
placenta. The two kinds of vessels do not run together; the
arteries lie nearer the surface, the veins deeper, Cut 26;
the arteries fork separately until they are represented only by
small branches and fine vessels; some of the small branches
disappear by dipping down suddenly into the villi below; the
veins are considerably larger than the arteries, and some of the
larger branches disappear from the surface in the same abrupt
manner as do the smaller arteries. There is the greatest possi-
ble variability in the vessels of the placenta; I have never seen
two placentz with the vessels alike. The more eccentric the
insertion of the cord, the more do the vessels tend to distribute
themselves symmetrically ; the more central the position of the
cord, the less can any vascular symmetry be made out.

The two following paragraphs are copied without change
from my article on the placenta (Buck’s Reference Handbook of
the Medical Sciences, V., 696, 697) : —

“To follow the course of the foetal blood-vessels within the
placenta, the best method is by corrosion injections. These
may be made either with fusible metal, wax, or celloidine. The
first is specially suited for the study of the large trunks; the
latter, for that of the smaller vessels also. I have a very beauti-
ful celloidine injection by Dr. S. J. Mixter, which, with others of
wax and metals, has served as the basis of the following descrip-
tion: The veins leave the surface somewhat more abruptly than
do the arteries, which gives off more small branches to the sur-
face than do the veins, Cut 26. Both kinds of vessels leave
the surface by curving downward for a short distance into the
trunk of a villus; the vessels then divide, and their branches

412 MINOT. [Vot. II.

again take a more horizontal course; the branches then curl
over downward, and, after a second short descent toward the
decidua, again send out horizontal branches. The result of this
arrangement is a terrace-like appearance in the course of the
vessels ; they approach the uterine side of the placenta in this
very characteristic manner. The number of terraces is variable ;
usually there are two or three, but sometimes there is only one,
or they may number four or even five. Arrived at the end of
its terraces, the main vessel takes a more nearly perpendicular
course, and rapidly subdi-
vides. Immediately after
entering the villi, the ar-
teries and veins give off
but few capillaries, but
after a short course in the
main stalk of the villus,
the vessels give rise to
many branchlets, and grad-
ually the character of the
circulation changes, until
in the smallest villous
twigs there are capilla-
ries only, ‘Gat’ 27-7 ine

, oe , vascular trunks have
Cut 27.— Portion of an injected villus

from a placenta of about five months; magni- a marked tendency to di-
fied 210 diams. chotomous division, which

is maintained within the
villi to a certain extent; the arterioles and veinlets in the
mature placenta go from their trunks at wide angles for the
most part, and subdivide in the same manner, so that they
spread out through the whole substance of the placenta. The
vessels next the decidua take a more horizontal trend, like the
top branches of a wind-swept tree. As the vessels run in the
villi, of course the way in which the latter branch out deter-
mines the paths of the former ; hence by following the distri-
bution of the vessels we inform ourselves as to the ramifica-
tions of the villi. Thus the horizontal course of the vessels
on the uterine side of the placenta corresponds to the well-
known fact that the ends of the villi attached to the uterus
become bent and adhere by their sides to the decidual surface.”

No. 3. ] UTERUS AND EMBRYO. 413

“The capillaries of the villi are remarkable for their large
size, and on this account have been described as arteries or
veins by E. H. Weber, Goodsir, and other writers. Their calibre
is often sufficient for from four to six blood-disks abreast. They
are very variable in diameter, and also peculiar in exhibiting
sudden restrictions and dilatations, Cut
27, In the short bud-like branches
there is often only a single capillary
loop, but as the branch becomes larger,
the number of loops increases, and
they form anastomoses. In branches
large enough to serve as a stem, some
one or two of the vessels may be en-
larged, as may be seen in Cut 27; in
the branches large enough to admit of
it, there are two (or sometimes only
one) longitudinal central vessels, an ar-
tery and vein, and a superficial network
of capillaries, Cut 27@. Goodsir and
other early writers laid great stress on
the formation of the capillary loops, but
this feature is a common one in the de-
velopment of the foetal vascular system,
as is also the width of the capillaries.
In my opinion these peculiarities are
characteristic rather of the foetus than

: Cut 27a. Placenta of about
specifically of the placenta. In some of gy months; ay cone? Seal
the older writers (Goodsir, Farre, e¢ a/.) villus, to show the central ves-
it is asserted that the true capillary sys- sels and superficial capillaries.
tem disappears toward the end of ges- * 105 diams.
tation. I am unable to confirm this, but find instead that in
the slender terminal villi of the placenta at term there is often
only a single, sometimes long, capillary loop; the capillary is
very wide, and its width is probably the reason of its having
been held formerly to be a vein or an artery.”

§ 16. Uterus during menstruation. — I have little to add to
the descriptions of previous authors, particularly those of
Leopold, 36, and Kolliker.t It is, however, worth while to pre-
sent the accompanying illustration, Cut 28, since there is a lack

1 K6lliker’s Handbuch der Gewebelehre, 5te Aufl., p. 563.

(Vou. II.

MINOT.

frake] poyeasojutsip

furntpayyide ‘Za

‘suivip Sg K ‘strepNosnur 9sv2 {spossaa-pooyq ‘2 ‘2
‘uolenaysuow jo Aep jsiy oy} SULINP sN19jN UISITA B JO sULIqUIOUT SNOONI — ‘92 7729

V.
= ISNut

ba 3

“IRE SMa ST NENT,

No. 3.] UTERUS AND EMBRYO. 41s

of figures. The cut represents a transverse section of the
corpus utert of a fine specimen, for which I am indebted to Dr.
W. W. Gannett. The woman died from acute miliary tuber-
culosis ; the autopsy was made almost immediately after death,
and within four hours from death the complete genitalia were
placed in Miiller’s fluid, the uterus having been first carefully
opened by a single median ventral incision. Death is said to
have occurred on the day of the regular period. The hymen
was intact. There was no sign of pathological change in any
of the genitalia. In one ovary, the right, there was a fresh
corpus hemorrhagicum. These data afford a sufficient basis for
the belief that the uterus was well preserved in a perfectly
normal condition.

The mucous membrane is from 1I.I-1I.3 mm. thick; its sur-
face is irregularly tumefied ; the gland openings lie for the most
part in the depressions. In the cavity of the uterus there was
a small blood-clot. The mucosa is sharply limited against the
muscularis, Cut 28. In transverse sections one sees that the
upper fourth of the mucosa is very much broken down and dis-
integrated, Cut 28, d; the cells stain less than those of the
deep portions of the membrane ; as represented in the cut the
tissue is divided into numerous more or less separate small
masses; some of the blood-vessels appear torn through, but it
is difficult to make sure observation: Overlach, 39, considers
it probable that the infiltration of blood takes place by diapede-
sin, not by rupture of the capillaries. The superficial epithe-
lium, ¢, is loosened everywhere ; in places fragments of it have
fallen off, and in some parts it is gone altogether; it stains
readily with cochineal and its nuclei color well, the epithelium
differing in this respect from the underlying connective tissue,
which does not stain well; the blood-vessels in the disintegrated
layer are for the most part small.

The deeper layer of the mucosa is dense with crowded well-
stained cells, which lie in groups separated by clearer lines; in
the cut this grouping shows less plainly than in the preparation ;
the lighter channels are perhaps lymph-vessels, a suggestion
which occurs to me, because in so-called “moulds” one some-
times finds similar channels crowded with leucocytes. The cells
appear to be the proliferated interglandular tissue; there are
very few leucocytes, so far as I can distinguish ; the cells have

416 MINOT. [VoL. Il.

small, oval, or elongated, darkly stained nuclei, with a very small
granular protoplasmatic body each ; there is certainly no noticea-
ble enlargement of the cells, but only a remarkable multiplica-
tion. The point is important; I see nothing to suggest the
presence of decidual cells, nothing even like definite enlarge-
ment of any of the cells. The image of the tissue is compara-
ble to that of the connective tissue of the rabbit’s placenta at
six days, except that there the cells are widely separated, here
closely crowded, but in each case the cells are small, with little
protoplasm, and connected by their processes. In another
specimen in my possession of a normal uterus at the close of
menstruation, the condition of the mucous membrane agrees
with that of the specimen we have considered, except, of course,
that the disintegrated superficial layer is lost, and that the super-
ficial layers stain poorly. In this second specimen, also, the
interglandular cells are small and very crowded; there are few
leucocytes and no decidual cells. The two specimens further
agree in having the glands distended and contorted; each gland
is surrounded by a distinct basement membrane or layer of con-
nective tissue cells closely investing the epithelium, as has been
observed by Leopold, 36. In my article on the decidua in the
Reference Handbook, I1., p. 390, is a summary of the changes
occurring during menstruation, and stress is there laid upon two
points emphasized by previous writers ; namely, the increase in
the number of leucocytes and the presence of decidual cells.
Since my own observations have failed to confirm these state-
ments, I can no longer accept them. The proliferated connec-
tive tissue cells are those, probably, which become decidual cells
when the decidua menstrualis is changed into the decidua gravt-
ditatis — compare the account of the one month’s uterus in the
next section.

§ 17. Uterus one month pregnant.— The specimen to be
described came from a woman who committed suicide by vio-
lence, not by poison, and I was informed that she was known to
be about one month pregnant. Further information was not
- obtained, and I was requested not to seek it. The specimen
was received in very fresh condition, but it had been opened,
the reflexa was torn and pretty much gone; the embryo had
been removed, and I was therefore unable to verify the age, or
investigate the attachment of the villi of the chorion to the

No. 3.] UTERUS AND EMBRYO. 417

uterus. There was a beautiful corpus lutewm in one ovary, quite
similar to that figured by Dalton in his Report on the corpus
/uteum in the transactions of the American Gynzecological
Society for 1877, Fig. 9. The surface of the uterus seemed
uninjured. The specimen was hardened in Miiller’s fluid, and
found subsequently to be well preserved. It may be considered,
I think, perfectly normal.

Cut 29. — Uterus one month pregnant; outlines of the glands from a vertical sec-
tion: to show the divisjon of the mucosa into an upper compact layer, D’, anda
lower cavernous layer, D!’; g/', g/!', glands; art, spiral artery; mzazsc, muscularis.

My specimen enables me to confirm in most respects Turner’s
accurate description of two uteri of about the same age, 146,
546-548. The inner surface shows the hillocks (/zseln) de-

418 MINOT. [ Vox. If

scribed by Reichert in the uterus of two weeks, studied by him,
which have been figured by Coste in slightly older specimens,
and found by Turner also, 146, 540.

The three illustrations given herewith are all from sections
through what I suppose to be the placental region.

There is an upper compact layer, Cut 29, D’, and a lower
cavernous layer, D"; the caverns, being gland cavities, which
appear as rounded areolz lined with epithelium, are filled with
broken-down epithelial cells. The drawing, reproduced in Cut
29, was obtained by drawing the outlines very carefully, stip-
pling the areas occupied by the connective tissue, representing
the blood-vessels by double outlines, and omitting the glandular

ys Ail Oe ppm

coagl.
Be eae ta

Cut 30. — Uterus one month pregnant; portion of the compact layer of the de-
cidua seen in vertical section; coag/, coagulum upon the surface; d, a’, decidual
cells. XX 445 diams.
epithelium altogether. It will be noticed that about three-
fourths of the diameter of the mucosa is occupied by the
cavernous layer, D".

The upper or compact layer is shown in Cut 30. The surface

No. 3.] UTERUS AND EMBRYO. 419

is without any trace of epithelium, but is covered only by a thin
fibrous and granular coagulum, coag/; the tissue itself consists
almost exclusively of young decidual cells, d, @', with a clear
homogeneous matrix; here and there are leucocytes, but they
are nowhere numerous; the decidual cells are all quite large,
with their bodies deeply stained by the eosine; the nuclei are
round, oval, or slightly irregular in shape, coarsely granular, and
sharp in outline; the cells themselves, though irregular and
variable in shape, are all more or less rounded with processes
running off in various directions; scattered between the cells
are many sections of their processes; occasionally it can be
seen that two cells are connected; in fact, we have in this
tissue evidently a modified embryonic or so-called anastomosing
connective tissue. Now, as we know through the observations
of Leopold, 36, which I have verified, the connective tissue of
the uterine mucosa consists of anastomosing cells, and as stated
in the previous section, the cells are found proliferated in the
menstruating uterus; we have therefore only to imagine the
cells enlarged with certain accompanying modifications, to obtain
the tissue figured in Cut 30. There is no special formation of
cells around the blood-vessels, where, according to Ercolani, the
decidual tissue arises by new formation. In Turner’s specimens
the upper part of the compact layer was imperfectly preserved,
but according to his description there appears to have been a
coagulum similar to that which I have found, but thicker. In
the deep part of the layer the cells are less enlarged, and when
the cavernous layer is reached, there occurs a rapid transition
in the character of the cells, which become smaller and more
fusiform, and their nuclei more elongate, smaller, and deeper
stained by alum-cochineal. The gland openings upon the sur-
face of the uterus lead into tubes, Cut 30, g/’, which run slightly
obliquely through the compact layer, taking a more or less
nearly straight course and joining the contorted gland tubes,
Cut 30, ¢/", of the cavernous layer. The gland ducts are com-
pletely devoid of lining epithelium, which has disappeared
except for a very few loose cells, occasionally found lying free
in the ducts; the cells have not fallen out from the sections,
but were lost before the tissue was imbedded.!_ The ducts then

1 The blocks to be cut were stained zz fofo with alum-cochineal and eosine, im-

bedded in paraffine, etc. The sections were fastened on the slide with celloidine, to
keep the parts in place.

420 MINOT. [ VoL. ie

are wide tubes running nearly straight through the upper part
of the decidua and bounded directly by the decidual tissue ;
they communicate below with a contorted cavity. Similar tubes
appear in later stages and have been described as blood-vessels
—see the next section.

The cavernous layer contains numerous spaces, the areolz of
Turner, 146, 547, who was uncertain as to their character,
though he ascertained
that many of them be-
longed to the glandular
system. In my specimen
it is perfectly clear that
all the larger areole be-
long to the glands, which
must be extremely dis-
torted and distended to
give the shapes shown
in Cut 29. The thin dis-

sepiments between the
Cut 31.— Uterus one month pregnant; sec-

tion of gland from cavernous layer, with the epi- areola are composed of
thelium partly adherent to the walls. x 445 Connective tissue, the

diams. long dark nuclei of which,
Cut 31, are strikingly different from those of the cells of the
compact layer, Cut 30. The areole present two extreme modifi-
cations and all intermediate phases between these two. The
smaller areolz are lined by a well-preserved cylinder epithe-
Tium; or by one in which the cells are separated by small fis-
sures; in other areolz the cells are a little larger, Cut 31, each
for the most part cleft from its fellows, and some of them loos-
ened from the wall and lying free in the cavity. The other
extreme is represented in Cut 32; the size of the areolz is
much increased,—compare Cuts 31 and 32,—both drawn on
the same scale; the epithelium is entirely loosened from the
wall, and the cells lie separately in the cavity which they fill;
the cells are greatly enlarged, their bodies having three or four
times the diameter of the cells in the small areolz; they have
not the cylinder shape, but are irregular in outline: their proto-
plasm is finely granular and stains rather lightly ; the nuclei are
large, rounded, glandular, and with sharp outlines; they are less
darkly stained than the nuclei of the epithelium of Cut 31.

The obvious interpretation of the appearances described is,
that the glandular epithelium is breaking down, that it is lost
altogether from the ducts, but is still present in the deep por-
tions of the glands; in breaking down the cells separate from

Cut 32. — Uterus one month pregnant; section of gland from cavernous layer,
with the epithelium loosened from the walls; > 445 diams.

one another, and then from the wall, and falling into the gland
cavity, there enlarge, the cavity enlarging also. Similar appear-
ances are also found in “moulds’’ of the second month; very
likely they have been often observed and mistaken for patholog-
ical changes.

The blood-vessels of course lie in the dissepiments between
the glands. I observed nothing to correspond with the “ colos-
sal capillaries dilated into small sinuses,” mentioned by Turner
146, 548. Were not these supposed capillaries gland cavities,
from which the epithelium had fallen out? Occasionally the
sections pass through a spiral artery, Cut 209, av¢, which is cut
again and again as it twists around in its characteristic separate
column of connective tissue.

§ 18. Uterus seven months pregnant, with the foetal mem-
branes in place. — The specimen to be described was obtained
for me through the kindness of Dr. W. W. Gannett. It is an
apparently normal uterus, which contained a normal embryo
weighing 1150 grammes and having an umbilical cord §8 centi-
metres long, — probably about seven months old, or a little

422 MINOT. [Vot. II.

more: there were no data as to the duration of gestation.
The uterus was opened, and preserved in Miiller’s fluid without
disturbing the membranes.

A section through the amnion, chorion leve, and uterine

°
e
)
s
°
ra’
°,

os

Sano
28 \ o's.4

s8 fers ¢
A hae

3 vertical section through the decidua vera, with the chorion

; Cho, chorion; c, epithelium (cellular layer of chorion); wv, blood-ves-
avities; “sc, muscularis: the blood-vessels are represented dark. X 40

'‘@o@
vrai Saent-’
Am, amnion

Cut 33. — Uterus about seven months pregnant

zve and amnion 77 sz/z.

sel; g/, spaces supposed to be gland c

diams.

]

mucosa, stained with hzmatoxyline, and viewed with a low
power, is represented in Cut 33; the dark spots are maternal
blood-vessels, which have been shaded for the sake of clearness.
The amnion, am, and chorion, cho, present the characteristics

No. 3.] UTERUS AND EMBRYO. 423

previously described, §§ 14, 15; the chorion is bounded against
the decidua by an epithelium c, which I interpret as the chori-
onic ectoderm; there is no trace of a second layer of epithe-
lium; so that the uterine epithelium must be considered lost, a
conclusion agreeing with the observations of Kolliker, Turner,
and myself upon earlier stages, and the statements of Ercolani.
The decidua has eight or nine times the thickness of the cho-
rion ; it has an upper compact and a lower cavernous layer; the
former contains numerous decidual cells, most of which are a
little larger than those nearer the muscularis; the compact
layer contains a few blood-vessels of moderate calibre, and occa-

Cut 34.— Uterus about seven months pregnant; upper portion of decidua vera,
with the chorion leve zz sztu. mes, mesodermic layer of chorion; ef, epithelial
layer of chorion; D', decidua. X 340 diams.

sionally a large vessel, v, surrounded by connective tissue contain-
ing no decidual cells. Examined witha higher power, the decid-
ual cells —compare Cut 34, D!—are found to resemble quite
closely those at one month, Cut 30, but they are much more
numerous and closer together, and their processes are fewer ;
they vary also more in size; some of the larger ones are multi-
nucleate; it is probable that the cells are multiplying by divis-
ion; the matrix presents a fibrous look, but whether it contains
actual fibres, I am not sure; between the decidual cells are a

; Vou. Ie
424 UINOT. [

Wns Rocione P:
Won Pe,

= @ .)
Sheek

J
Se
mS
iy

Sa,
es

ox

my

Oso
1S sre

at Ogee
ye

As

Cut 35.— Section through a normal placenta of seven months, in situ. Am,
amnion; Cho, chorion; V2, villus trunk; 77, sections of villi in the substance of the
placenta; D, decidua; A/c, muscularis; D’, compact layer of decidua; Ve, uterine
blood-vessel (or gland?) opening into the placenta. The fcetal blood-vessels are
drawn black; the maternal blood spaces are left white; the chorionic tissue 1s
stippled, except the canalized fibrine, which is shaded by lines; the remnants of the
gland cavities in D! are stippled dark. (Drawn from nature by J. H. Emerton. )

INOS 31 UTERUS AND EMBRYO. 425
certain number of nuclei, some of which belong to leucocytes,
others to blood capillaries, and still others, which I am uncer-
tain about, which are few in number, and possibly belong to
connective tissue corpuscles. The cavernous layer resembles
now, in contrast to the first month, the upper layer of the de-
cidua in histological constitution, but the decidual cells are
smaller and at little wider intervals from one another; the cav-
ernous layer is especially characterized by the slit-like spaces in
it; some of these spaces, as indicated by the drawing, Cut 33,
are undoubtedly blood-vessels or sinuses, but still others contain
no blood, or at most three or four isolated corpuscles, although
close to them are capillaries gorged with blood; once in a while
a few epithelioid cells can be seen adhering to the walls of the
spaces. These spaces can hardly be assigned to the vascular
system ; they have been held by Kundrat and Engelmann, 180,
and various subsequent writers, to be the gland cavities; we
have not sufficient observations to establish the actual meta-
morphosis of the areole of the one month’s uterus into the
slits, 27, of Cuts 33 and 35, D’, but there is no ground to ques-
tion the occurrence of the change, which appears to be a neces-
sary consequence of the stretching of the decidua due to the
expansion of the uterus during pregnancy.

A complete section through the placenta zz sz¢z and uterus is
represented in Cut 35, which has already appeared in my arti-
cle, “ Placenta” (Buck’s Handbook, V., 696), and been sufficiently
described. The chorion is separated by a dense forest of villi
from the decidua, 1; the ends of some of the villi touch and
are imbedded in the decidual tissue; these imbedded ends are
without epithelium, but their connective tissue is immediately
surrounded by hyaline substance. The decidua is_ plainly
divided into two strata—cf. zxfra. The section passes through
a wide tube, Ve, which opens directly into the interior of the
placenta and contains blood; in my article, Zc., this opening is
referred to as that of a vein, the identification being in accord-
ance with my understanding of the descriptions of Waldeyer,!
149. Professor Langhans has since informed me, that accord-
ing to his own observations the opening of the arteries are char-
acterized by the absence of villi projecting into their openings.

1 T am under much obligation to Professor Waldeyer for an opportunity to examine

some of the injected specimens upon which his very important researches were con-
ducted.

426 MINOT. [Vo. II.

His pupil, Raissa Nitabuch, has since published a dissertation,
117, confirming this opinion, according to which the vessel
shown in Cut 35, Ve, is not venous, but arterial. Another pos-
sibility has occurred to me, viz.: that it is a gland duct; in
fact, it resembles very closely the undoubted gland ducts of the
one month’s decidua: there is no reason apparent why the gland
ducts, which pass nearly vertically through the compact layer,
should be obliterated; on the contrary, one might expect to
find them widened by the stretching of the uterus; as there is

Cut 36. — Uterus of seven months, vertical section of the decidua serotina from
near the margin of the placenta. mc, muscularis; D!, D!’, decidua serotina; D’,
cavernous or spongy layer; D!’, compact layer; V7, scattered chorionic villi. The
intervillous spaces were filled with blood, which ts not represented in the figure,
X 50 diams.

blood in the intervillous spaces, it could easily make its way
into the distended glands, and its presence there would not
prove the glands to be blood-vessels. While, therefore, I ac-
cept Waldeyer’s researches, 149, as well as those of Langhans
and Nitabuch, 117, as verifying Farre’s neglected account,
172, 722, of the placental circulation, I venture to express a
note of caution as to the danger of mistaking glandular for vas-
cular openings.

No. 3.] UTERUS AND EMBRYO. 427

The following additional points deserve notice: The serotina
is about 1.5 mm. thick, and contains an enormous number of
decidual cells, Cut 36. The cavernous, D’, and compact layers,
D", are very clearly separated; the mucosa is sharply marked
off from the muscularis, mc, although scattered decidual cells
have penetrated between the muscular fibres. The muscularis
is about 10 mm. thick, and is characterized by the presence
of quite large and numerous venous thrombi, especially in the
part towards the decidua. The decidua contains few blood-
vessels. Upon the surface of the decidua can be distinguished
a special layer of mingled hyaline and decidual tissue, which in
many places is interrupted by the ends of the chorionic villi, as
is well shown in Cut 36. The supposed gland cavities of the
spongy layer, D’, are long and slit-like; they are filled for the
most part with fine granular matter, which colors light blue
with haematoxyline ; they also contain a little blood, sometimes
a few decidual cells.
I have seen in them
also a few oval bod-
ies several times
larger than any of
the decidual cells,
and presenting a
vacuolated appear-
anee’; what these
bodies are, I have
not ascertained. In
places the glandu-
lar epithelium is
distinct ; its: cells
enSy greatly in aes Cut 37. — Decidual cells from the section represented
pearance, neighbor- in part in Cut 36. a, 4, d, f, various forms of cells from
ing cells being serotina; c, giant cell from the margin of the placenta;

eé, clear cells from chorion; at a, seven blood globules
have been drawn in to scale. X 545 diams.

often quite dissimi-
lar; nearly all are
cuboidal, but some are flattened out; of the former there are
some with darkly stained nuclei, but the majority of the cells are
enlarged, with greatly enlarged hyaline, very refringent nuclei.
The decidual cells are smaller and more crowded in the cav-
ernous layer, and mostly larger in the compact layer — compare

428 MINOT. [Vot. IIL.

Cut 36. The largest cells are scattered through the compact
layer, but are most numerous towards the surface. The decid-
ual cells exhibit great variety in their features, Cut 37; they are
nearly all oval disks, so that their outlines vary according as they
happen to lie in the tissue ; they vary greatly in size; the larger
they are, the more nuclei they contain; but I observe no cells
with more than ten nuclei. The nuclei are usually more or less
elongated; the contents of the cells granular. Some of the
cells present another type ; these are more nearly round, clear,
and transparent, ¢; the nucleus is round, stained lightly, and
contains relatively few and small granules; such cells are most
numerous about the placental margin.1

§ 19. Uterus twelve hours after abortion at six months. —
For this specimen, also, I am indebted to Dr. W. W. Gannett.
The woman was brought into the Boston City Hospital in a
comatose condition ; the foetus, estimated to be about six months,
was removed by the forceps ; the mother died twelve hours later ;
the autopsy by Dr. Gannett showed death to have been caused
by tubercular meningitis. The uterus is apparently normal; I
received it in a fresh state, and hardened it in Miiller’s fluid. It
was already very much contracted; the mucosa measured about
2mm. in thickness ; its surface was ragged and more or less cov-
ered with clotted blood, presenting very much the appearance
so superbly figured by Coste (Développement des Corps organisés,
Pl. X., Espéce humaine).

Vertical sections, Cut 38, show that the surfaces of the mu-
cosa are very uneven ; on the free surface there is a thin layer
of clotted blood, coag/; the upper or compact layer of the
decidua has entirely disappeared, leaving only the deep portion,
D, permeated by numerous large empty spaces, which I take to
be in part gland cavities, in part blood sinuses, both changed
from their slit-like form by the contraction of the uterus during
and since the delivery of the child. Between the spaces are the
brownish and hyaline cells, and a great many blood-corpuscles,
which lie throughout the tissue itself as well as in the blood-ves-
sels. In short, the conditions found agree with those described
by Leopold as present in the uterus a short time after normal
delivery at full term, 36, and accordingly, further details con-
cerning my specimen may be omitted.

1This and the preceding paragraph are taken with sundry alterations from my
article on the placenta, /.s.c.

No. 3.] UTERUS AND EMBRYO. 429

§ 20. Origin of decidual cells. — Besides the erroneous hy-
pothesis of Ercolani, there are three views as to the origin of
the decidual cells known to me, to wit: 1°, they are modified
leucocytes (Hennig, Langhans, e¢ a/); 2°, they arise from the
connective tissue cells of the mucosa (Leopold, 36) ; 3°, they

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are produced by the epithelium (Overlach, 39). The first view
is not supported by observation, even by its advocates, and may
be dismissed. Overlach’s observations certainly favor the third
view, but inasmuch as he has studied only ome uterus with
pseudo-menstruation from acute phosphorus poisoning, his the-

430 MINOT. [Vo. II.

ory cannot be accepted definitely until verified by further obser-
vations on normal uteri. Overlach found in the cervix of the
uterus in question, the lining epithelial cells to contain an en-
dogenous brood of small cells, one to fifteen in each parent-cell ;
the daughter-cells begin as nuclei, around which there gathers
a protoplasmatic body for each. The cells are like the young
decidual cells just below, so that the latter may be assumed to
have wandered forth from the epithelium. I may recall that in
the normal menstruating uterus I find no true decidual cells,
and consequently I must regard Overlach’s find as pathological.

The observations of Creighton, of Masquelin and Swaen, and
of myself may be fairly considered to establish the fact that in
rodents, at least, the decidual cells arise from the connective
tissue cells of the mucosa. That they arise from the same cells
in man is rendered extremely probable by the investigations of
Leopold, which have been confirmed and extended by the obser-
vations recorded in §§ 16, 17, and 18, of the present article.
Accordingly I assent to the second of the views above enumer-
ated.

Ercolani erroneously regarded the decidual tissue as a new
formation, arising after the total destruction of the mucosa. He
observed the degenerative processes of the uterine epithelium,
and the arrangement of the decidual cells around the vessels of
the placenta in rodents and other mammals; he inferred that
the whole mucosa was degenerated and lost, but he never estab-
lished the inference by observation; he also inferred that the
perivascular cells, being different from the surrounding tissues,
were a new formation, but he never traced the actual genesis of
the cells. In spite, however, of the absence of the observations
necessary to establish his double thesis of the total destruction
of the mucosa and the new formation of the decidua, he advo-
cated his doctrine with the greatest earnestness, even to the
last — see 91, 92. The failure of his hypothesis to find accept-
ance has been due not to any unreadiness to bestow merited
acknowledgment upon his researches, but to the incompatibil-
ity of the hypothesis itself with the ascertained facts of the
structure and development of the placenta. While, therefore,
we utilize Ercolani’s numerous and valuable observations, it will
be a distinct gain for science to set aside his theory of the new
formation of the decidua.

No. 3.] UTERUS AND EMBRYO. 431

§ 21. General considerations. — We are nowin a position to
compare the changes in the uterus during menstruation and
gestation. In both cases the processes begin with tumefaction
and hyperemia of the mucosa; they continue with hyperplasia
of the connective tissue (the decidual cells being regarded as
modified connective tissue corpuscles) and with hypertrophy,
accompanied by distention and contortion of the glands ; they
both close with casting off the superficial layers of the mucosa,
after which follows the regeneration of the membrane. The
essential steps, then, are the same in both cases. The difference
is, that during the long life of the dectdua graviditatis, changes
supervene in the tissues which do not take place during the
rapid menstrual cycle; the mucosa of gestation is distinguished
by the loss of both its surface and glandular epithelium, and by
the enlargement of its connective tissue cells into so-called de-
cidual cells. We must accordingly view the changes in the
uterus during gestation as a prolonged and modified menstrual
cycle. The relation in time between menstruation and the com-
mencement of pregnancy is attributable to the menstrual pro-
cess rendering the uterus receptive; that is to say, capable of
receiving and retaining the ovum. We must conceive that the
ovum has no power of initiating the development of a decidua,
but only of modifying the menstrual process ; hence pregnancy
can begin only at a menstrual period. The ovum, too, exercises
this influence at a distance, for in all mammals, the earliest de-
velopment of which is known, the ovum passes through its seg-
mentation in the oviduct (Fallopian tube), and takes from three
to eight days to reach the uterus; but during this period the
change in the womb is going on. The most plausible explana-
tion of this action of the ovum at a distance is a reflex stimulus
passing from the oviduct to the central nervous system of the
mother, and thence back to the uterus; the validity of this hy-
pothesis must be tested by physiological experiment. That the
nerves are able to effect morphological changes is already
abundantly proven, not only by the influence of the secretory
nerves upon gland cells, by the degeneration of muscular and
other tissues, when their nerves are severed, but also by certain
embryological observations tending to show that histological
differentiation does not progress very far until the tissues are
joined by the outgrowing nerves.

432 MINOT. [Vot. II.

When the ovum reaches the uterus, it appears to exert a
more direct influence, for one set of changes occurs in the
placental area, where there is concrescence of foetal and mater-
nal parts; another in the region around the placenta (peri-pla-
centa, decidua reflexa), and still another in the rest of the uterus
(decidua vera, ob-placenta). Whether the three zones enumer-
ated can be distinguished in the pregnant uteri of all placental
mammals, and whether they have more features in common than
appear from a direct comparison between man and the rabbit,
are questions to be decided by increased knowledge. However,
it already seems very probable that the decidua reflexa and
peri-placenta are homologous at least in rodents.

Concerning the evolution of the amnion nothing definite is
known, nor do the speculations of Balfour (Comparative Em-
bryology, I1., 256) nor of van Beneden and Julin, 44, 425, seem
satisfactory, although the view of the latter is suggestive.
They say :—

«Tans notre opinion, la cause determinante de la formation de
Venvellope amniotique réside dans la descente de l’embryon, déter-
minée elle méme par le pois du corps. C’est par une accélération du
développement que la cavité amniotique en est venu a se former quand
lembryon ne possede encore qu’un pois insignifiant.” The chief ob-
jection to this theory is that it really gives no cause for the expansion of
the somatopleure and chorion; there is no proof that a mere strain of
weight can cause the cells of a membrane to proliferate, and since such
proliferation is the immediate cause of the growth of the amnion, van
Beneden and Julin must assume for their theory that the strain of weight
does cause proliferation ; but this assumption lacks support. Moreover,
they give no evidence to show that the embryo zz w#ero is situated in
the primitive amniota upon the upper side of the ovum, although it is
probable such is the case.”’?

Ryder’s theory, 19, of the origin of the amnion, like that of
van Beneden and Julin, to which he does not refer, is purely
mechanical ; but Ryder seeks the cause in a rigid zona radiata,
forcing the embryo down into the yolk. See his summary, /c.,
p. 184. So far as we know, however, the embryo of the Sau-
ropsida cannot be said to sink into the yolk, and so lead to the
development of an amnion ; but, on the contrary, the amniotic

1 Quoted from Buck’s Reference Handbook, I., 140.

Now| UTERUS AND EMBRYO. 433

folds rise up clear above the yolk. Moreover, the formation of
the amnion is really a very complex process, part arising from
the pro-amnion, part by a dilation of the pericardial cavity
(Parietalhohle), and part as the extra-embryonic tail folds.
These facts speak, in my judgment, unequivocally against the
amnion having arisen by the sinking of the embryo into the
yolk sack. Nor is there any justification, I think, for seeking
these simple mechanical explanations, which are worthy of
Herbert Spencer, since the formation of the amnion depends
upon inequalities in the growth power of the germ layers, and
only such explanation can be valid as explains that inequality —
which Ryder’s hypothesis fails to do, so far as I can see.

As regards the evolution of the placenta, we are in the dark.
Contrary to prevalent opinion, it is not an organ of the allantois,
nor is it an organ of the yolk sack. On the contrary, it is
always, so far as we know, an organ of the chorion, and begins
its development by a differentiation of that membrane. The
allantois is a secondary and later structure. Its primitive réle —
is apparently only that of a stalk of connection between the
chorion and embryo. There is no evidence to show that the
tissue of the allantois spreads out over the chorion to form the
mesodermic layer thereof, but the mesoderm of the chorion is
proper to it as much as to any part of the somatopleure the
mesoderm thereof. When the allantois becomes a large sack,
we have a subsidiary change, so that we are brought squarely to
the conclusion that the foetal placenta is chorionic. From this
premise phylogenetic speculation must start. Further, we know
through the discovery of fundamental importance by His that
the allantois cavity is at first a small entodermal tube lying ina
posterior prolongation of the body (Bauchstzel), and that at this
time the so-called allantoic vessels run to and branch out upon
the chorion; the placental differentiation of the chorion has
already begun, without participation of the allantois, the en-
largement of which, when it occurs at all, occurs at a later
stage. To speak, therefore, of an allantoic chorion as do Bal-
four and Selenka (Studien iiber Entwichelungsges., p. 135) 1s
unjustifiable. Nor can we trace the origin of the placenta to
the yolk sack, since in most mammals the mesoderm does not
spread over the yolk until quite late, so that the yolk sack
consists, as in the rabbit and opossum, in large part of ectoderm

434 MINOT. [Vot. II.

and entoderm only, and is without vessels, and therefore unable
to form a placenta, which, however, is developing meanwhile
from the chorion.

We seek nowadays, following the lead of Professor Cope, to
deduce mammalia from the reptilia. Since the reptilia have a
free allantois, it is a temptation for embryologists to seek to
trace the placenta to a modification of the allantois; but the
placenta of mammals appears in the embryo before the allantois
becomes free, and the great size of the allantoic vessels is con-
nected primitively not with the allantois, but with the already
important chorionic circulation. The placenta is interpolated
in the ontogeny of mammals before the specialization of the
allantois, which functions as the vascular pathway between the
embryo and the chorion, both primitively and permanently.
The enlargement of the allantois, which takes place in certain
mammals, is a supervening change, probably a survival of rep-
tilian ontogeny. The question is, not how is the connection of
the allantois with the placenta (chorion) established in mammals,
for it exists from the start,! but what becomes of it in reptiles
and birds.

Ryder’s theory, 128a, of the origin of the discoidal pla-
centa? by constriction of the villous area of the zonary placenta,
is difficult to accept. The placenta, being chorionic, cannot of
course develop, except so far as the chorion is differentiated ;
that is to say, so far as the ectoderm (exochorion) is underlaid
by mesoderm. Now, in mammals, the chorion, as mentioned
above, does not go at first but part way over the yolk sack, even
at the period when the development of the placenta has begun.
Accordingly, so far as our present knowledge enables us to
judge, the discoidal is probably the primitive placental type.
If the chorion is completed by the further extension of the
mesoderm around the yolk sack, then the placental formation
also may spread, and a diffuse type arise. At present, the
whole subject is very obscure, but there is certainly no suffi-
cient evidence to prove that the diffuse placenta is the primi-
tive type.

In conclusion, let me point out that we have no satisfactory

1 This is beautifully shown by Selenka’s investigations on the opossum, cited in the

text.
2 The human placenta is of discoidal, but metadiscoidal.

No. 3.] UTERUS AND EMBRYO. 435

knowledge of the nutrition of the embryo. We know positively
scarcely more than that the maternal and fcetal circulations are
brought very close together in the placenta. We infer that
there must be a transfer of nutritive material from one blood to
the other. As to wat material is transferred and how, we have
only theories, but of them an abundance. Under these circum-
stances, the best beginning is undoubtedly a frank acknowledg-
ment of our ignorance.

§ 22. Summary.— The following paragraphs attempt to give
the more important of the conclusions reached in the second
part of this paper.

§ 13. The umbilical cord is not covered by the amnion, but
by an extension of the foetal epidermis. Its caelomatic cavity
is completely obliterated during the third month, and a little
later the stalk of the yolk sack is resorbed. The allantoic epi-
thelium persists as a tube or cord of cells for a long period.
The blood-vessels have specialized walls derived from the sur-
rounding mesoderm, but have no true adventitia. Connective
tissue fibres begin to develop during the third month.

§ 14. The amnion is covered by a single layer of ectodermal
cells, which are connected by conspicuous intercellular bridges.
It has no true stomata. -Its mesoderm consists of anastomosing
cells, with a dense matrix; it is imperfectly divided into three
strata, of which that next the ectoderm is without cells, that
furthest from the ectoderm is often of a loose texture.

§ 15. The chorion consists of two layers, mesoderm and ecto-
derm, both of which are present over all parts of the chorion
throughout the entire period of pregnancy. The mesoderm has
at first a dense colorable matrix, with cells, which color very
slightly. During the second month the matrix loses its coloring
property, and subsequently the cells acquire a greater affinity
for coloring-matters ; the matrix assumes a fibrous appearance,
and ultimately in the region of the chorion frondosum connec-
tive tissue fibrils appear in it, most numerously next the ecto-
derm, so that the mesoderm is differentiated there into an outer
fibrillar layer and an inner and thicker stroma layer. The ecto-
derm during the first month divides into two strata, an outer
dense protoplasmic layer and an inner less dense cellular layer.
In the latter part of pregnancy the whole ectoderm of the chorion
lave has acquired the character of the cellular layer, except close

436 MINOT. [Vou. II.

to the margin of the placenta; at the same period the cellular
layer forms a number of irregular patches over the chorion lzeve,
while the protoplasmic layer remains over the entire surface,
both where the cellular is present and where it is absent; the
protoplasmic layer may undergo complete or partial degenera-
tion into canalized fibrine, which is developed in irregular
patches. The cellular layer remains on the villi only in a few
patches (Ze//knoten) and over the tips of certain villi; the pro-
toplasmic layer of the villi remains everywhere and develops
numerous nodular thickenings; it changes partially into canal-
ized fibrine. It is probable that the fibrine covering the surface
of the decidua serotina is derived from the ectoderm of the ends
of the villi imbedded in the decidua. The villi are at first of
awkward and irregular forms, but their branching gradually
becomes more regular, and the twigs acquire a slender and
more uniform shape.

§ 16. The menstruating uterus is characterized by hyperzemia,
by hyperplasia of the connective tissue of the mucosa, and by
hypertrophy of the uterine glands; the upper fourth of the
mucosa is loosened and breaks off: there are no decidual cells.

§ 17. The uterus one month pregnant has lost its epithelium
from its surface, and from the ducts of its glands; owing to the
dilatation and contortion of the deep parts of the glands, it is
divided into a lower cavernous or spongy layer and an upper
compact layer; the connective tissue of the upper layer is
transformed into decidual cells; in sections the glands of the
lower layer appear as crowded areolz, which are lined by a
cylinder epithelium more or less disintegrated, or else filled
with isolated enlarged epithelial cells.

§ 18. The uterus seven months pregnant is without epithe-
lium either on its surface or in the glands, except a few isolated
patches in the deep parts of the latter; there is no trace of the
decidua reflexa; the decidua vera is covered by the epithelium
of the adherent chorion leve; the decidual serotina is covered
for the most part bya layer of fibrine, which is probably derived
from the degeneration of the chorionic ectoderm covering the
imbedded ends of the villi; the decidua is divisible into an
upper compact and a lower cavernous layer, in which latter the
gland cavities are reduced to slits; the decidual cells are very
numerous and crowded ; the larger ones lie near the chorion ;

No. 3.] UTERUS AND EMBRYO. 437

the multinucleate decidual cells are found chiefly in the serotina;
at the edge of the placenta decidual cells are found in the
chorion.

§ 20. The decidual cells arise by direct enlargement of the
connective tissue cells of the mucosa. All parts of the decidua
and placenta arise in place by metamorphosis of the tissue; the
mucosa is preserved, and there is no production of placental
tissues by new formation.

§ 21. The changes of the uterus during menstruation and
gestation are homologous, the menstrual cycle being prolonged
and modified by pregnancy; hence it is that conception takes
place only at the menstrual period, for the ovum can only
modify the menstrual change, not initiate the formation of a
decidua. No satisfactory explanation of the origin of the am-
nion has yet been offered. The placenta is an organ of the
chorion; its evolution cannot be traced to modifications of
either the allantois or the yolk sack; the allantois is originally
the intestinal canal of the Bauchstiel, which serves as the means
of vascular communication between the chorion and embryo;
the enlargement of the allantois is secondary. We possess no
positive information as to how the placenta performs its nutri-
tive functions.

Boston, Aug. 3, 1888.

438

MINOT.

[ VoL. II.

§ 23. Preliminary Bibliography of Works and Articles
specially relating to the foetal envelopes of mammals,
exclusive of general works.

*,* I shall be much obliged to any who will inform me of errors in and omissions

from this list.

verify.

10.

11.

12.

13.

14.

15.

. Ablfeld, F.

. Beddard, F.

E.

. Budge, A.

. Cadiat.

. Dastre, A.

- Dobrynin, P.

. Krause, W.

Kuppfer, C.

Lieberkiihn,
N.

Olivette,
Marco.

Preuschen,

Franz von.

Strahl, H.

“e “

ALLANTOIS.

(See also F@TAL MEMBRANES,)

Die Allantois des Menschen und
ihr Verhaltniss zur Nabelschnur.

Note on the presence of an Allan-
toic (Anterior Abdominal) Vein
in Echidna.

Ueber die Harnblase bei Vogel-
embryonen.

L’allantoide.

Recherches sur l’allantoide et le
chorion de quelques mammifeéres.

Ueber die erste Anlage der Allan-
tois.

Ueber die Allantois des Menschen.

Ueber die Allantois des Menschen.
Ueber die Allantois des Menschen.

Die Entstehung der Allantois und
die Gastrula der Wirbelthiere.

Querschmitte von der AnJage der
Allantois und der Harnblase von
Meerschweinchen Embryonen.

Ein Beitrag zur Kenntniss der
ersten Allantoisbildung.

Die Allantois des Menschen, eine
entwickelungsgeschichtliche Stu-
die auf Grund eigner Beobach-
tung.

Ueber die Entwicklung der Allan-
tois der Eidechse.

Die Allantois von Lacerta vividis.

Areh, ifGynalks, ox,
81-117. Taf. III.
Zool. Anz., VII., 653-

654.

Deutsche med. Woch-
enschrift, VII., 69-
70.

Gaz. med. Paris, 4
Sér., VI., 97-98.

Ann. Sci. Nat., 6 Sér.,
Til, pp. 118: Pls;
VII-X.

Wiener Akad. Sitzb.,
LXIV., 185-192.
Taf:

Arch. f. Anat. u. Phys.,
LO7G i 2L5) sho Os
204-207.

Zool. Anz., IV., 185.

Z. Z., XXXVI., 175-
179. Taf. IX.

Zool. Anz., II., 520-
522; 593-5973 O12-
617.

Marburger Sitz., 70-
Wt

Wiener med. Jahrb.
447-450. Taf. XIII.
Wiesbaden, pp. 195.
Taf. I.-X.

Marburger Sitz., 47-
49.

Sitz. Marburger Ges.,
25-27.

I have other titles, but the following are all I have been able hitherto to

1876.

1884.
1881.

1887.

1876.
1871.
1876.

1881.
1881.

1879.

1882.

1874.

1877.

1880.

1883.

No 3.]

AMNION.

UTERUS AND EMBRYO.

(See also F@:TAL MEMBRANES.)

16. Ahfeld, F.
(Antwort zur Wienkler, F. N.

24).
17. Hoffmann, C.}| Ueber das Amnion des zweitblat-
K. trigen Keimes.

18. Hotz, Anna. | Das Epithel des Amnions.

19. Ryder, J. A. | The Origin of the Amnion.

20. Schenk, L. | Beitrage zur Lehre vom Amnion.

21. Viti, Arnaldo.; L’ amnois umano nella sua genesi
e struttura ed in rapporto all’
origine del liquido amniotico.

22. Winkler, F. | Die Zotten des menschlichen Am-

N. nions.

Textur, Structur und Zellleben in
der Adnexen des menschlichen
Eies.

Erwiderung und Berichtigung zu
“Ueber die Zotten des Amnion”
(Arch. f. Gynak., VI., 358).

DECIDUA.

Zur Genese der Amnion-zotten | Arch. f. Gynak., VIL.,

567-570.

Arch. f. mikr. Anat.,
XXIII., 530-536.
Taf. XXV.

Bern (Inaug. Diss.).

Am. Nat., XX., 179-
185.

Arch. f. mikr. Anat.,
VII., 192-201. Taf.
XVIII.

Siena, pp. 59. Pl. I.

Jenaischr. Z. Med. u.
Naturu., IV., 535-
549.

Jena (Hermann Da-
bis), pp. 56. Taf.
I.-IL.

Arch. f. Gynak., VIL.,

325-330-

(See also PLACENTA and UTERUS.)

25. Ahlfeld, F.

vera und reflexa reifer Eier.

mG acer Die Beschaffenheit der Decidua
des Eies ein Zeichen der Reife

oder Friihreife der Frucht.
27. Duncan, J. | Notes on the history of the mu-
Matthews. cous membrane of the body of

the uterus.

The mucous membrane of the
uterus, with especial reference
to the development and structure
of the decidua. (This is a trans-
lation, with some changes of
Kundrat and Engelmann, 180).

29. Ercolani, G.| Delle glandole otricolari dell’

B. utero e dell’ organo glandulare
di nuova formazione, etc.

28. Engelmann,
Geo. J.

Ueber Befunde an der Decidua | Arch. f.Gynak., XIIL.,

290-292.
Centralbl. f. Gynec.,
217-220.

Edinburg Med. Journ.,
III., 688-697.

Amer. Journ. Obst.,
VIII., 30-87. Pl. I.

Mem. Accad. Sci. Ist.
Bologna. 4to. Sér.
2 VILES
Tav. I.-X.

133-207.

439

1875.

1884.

1878.
1886.

1871.

1886.

1868.

1870.

1875.

1878.

1878.

1858.

1875.

1868.

440

MINOT.

30. Ercolani, G. | The utricular glands of the uterus,

31. Friedlander,

32.

335.

34.
35.

36.

37.

38.

39.

40.

41.

42.

43.

B. etc., translated from the Italian
under the direction of H. O.
Marcy.

Physiologisch-anatomische Unter-

Carl. suchungen iiber den Uterus,
I., Die Innenflache des Uterus
frisch nach der Geburt und
die Neugestaltung der Uterus-
schleimhaut wahrend des Wo-
chenbetts, II., Die Uterinsinus-
Thrombose an der Placentar-
stelle.

Gervais, H. | Sur un uterus gravide de Ponto-

P. poria Blainvillei.

Haussmann. | Lehre von Decidua Menstrualis.

Heintze. Ueber den feineren Bau der De-
cidua.

Langhans. | Die Lésung der miitterlichen
Eihaute.

Leopold, Studien ueber die Uterusschleim-

Gerhard. haut wahrend Menstruation

Schwangerschaft und Wochen-
bett.

Moricke. Die Uteruschleimhaut in den ver-

< schiedenen Alters-Perioden und
zur Zeit der Menstruation.

Oliver, Menstruation — its nerve origin —

James. not a shedding of mucous mem-
brane.

Overlach, Die pseudo-menstruirende muco-

Martin. sa uteri nach akuter Phosphor-
vergiftung.

Pfliiger, Ueber die Bedeutung und Ur-
sache der Menstruation.

Robin, Ch. | Sur quelques points de l’anato-
mie et de la physiologie de la
muqueuse et de l’epithélium de
Puterus pendant la grossesse.

Rouvier, Recherches sur la menstruation

Jules. en Syrie.

Sutton, J. |,On menstruation in monkeys.

Bland.

[VoL. II.

Boston, 8vo, pp. 305.
Atlas, pp. 21. Pl. 1-
XV. 4to.

1880.

Leipzig, pp-57- Tafn.| gvo.
ei

C. R. Paris, XCVIL.,
760-762.

Beitr. z. Geb. u. Gy-
nak., Berlin, I., 155-
277.

Centralbl. f. med.
Wiss., XIII., 33-35.
Arch. f. Gynak., VIII.,
287-297. Taf. IX.
Arch. f. Gynak., XI.,
110-144. Tafn. I.-
III. Cont. X1.,443-
500. Tafn., XII-

VEL Con7: Xai,
169-210. Tafn. III.—
NV;

Zeitschr. f. Geburtsk.
u. Gynadk., VII., 84-
137.

J. Anat. and Physiol.,
AL nes. iL, Pe Eads:
pp. 378-384.

A. fm. A, XXV.,
191-235. Tafn. X.-
XI.

Journ. Phys., I., 46—-
71.

Ann. Gynec., XXVIL.,
Mars, pp. 178-201.
British Gynec. Journ.,
VII., pp. 285-292.
Med. Press and Cir-
cular, London, n.s.

XLIIL., pp. 259-261.

1883.

1872,

1875.

1876.

1877.

1882,

1887.

1885.

1865.

1858.

1887.

1886.

No.

44.

45.
46.

| AT,

48.

3]

Beneden, E.
v. and
Julin, Chas.
Bischoff, Th.
LW:
Blacher, K.

“ “

Caldwell,
W. iH.

49. Chabry, L., et

50.

51.

Boulart, R.

Chapman,
Henry C.

a“ ac

Dohrn, H.

52. Edwards,

A. Milne.
53. “ “ce
54. Hennig, C.
55. Hart, B. D.,
and
Carter; J.
56. Klaatsch,
Hermann.
57. Kyburg,
Bernhard.

UTERUS AND EMBRYO.

FO:TAL MEMBRANES.

(See also ALLANTOIS, AMNION, and PLACENTA.)

Recherches sur la formation des
annexes foetales chez les mammi-
féres (Lapin et Cheiroptéres).

Beitrage zur Lehre von den Eihiil-
len des menschlichen Foetus.

Ein Beitrag zum Bau der mensch-
lichen Eihiillen.

Noch ein Beitrag zum Baue der
menschlichen Ejhiillen.

On the arrangement of the em-
bryonic membranes in marsupial
animals.

Note sur un foetus de dauphin et
ses membranes.

On a foetal Kangaroo and its mem-
branes.

Ein Beitrag zur mikroskopischen
Anatomie der reifen menschli-
chen Eihiillen.

Recherches sur les envellopes foe-
tales du Tatou a neuf bands.

Sur la disposition des envellopes
foetales de l’Aye-Aye.

Ueber die Eihiillen einiger Sange-
thiere.

A contribution to the sectional
Anatomy of advanced extra-
uterine Gestation.

Die Ejihiillen von Phoczena com-
munis, Cuv.

Beschreibung von Feeten und peri-
pheren Eitheilen einer Vierlings-
geburt nebst Musterung der An-
gaben iiber die Geschlechtsver-
haltnisse der einem Ei entstam-
menden Fceten.

Arch. Biol.,V., fasc. 3,
pp. 369-434. PI.
XX.-XXIV.

Bonn, pp.112. Tafn.
I-II.

Arch, f. Gynak., X.,
459-469. Taf. XI.

Arch. f. Gynak., XIV.,
121-126. Tafn. I-
Ue

OF Jo Miss! Xex DV.
pp- 655-658. ‘Pi.
XLIII.

Journ. Anat. et Phys.
Robin et Pouchet,
XIX., 572-575. Pl.
XXXIV.

Proc. Acad. Sci., Phil-
adelphia, pp. 468-
AWTo) HEXEN

Ann. and Mag. N.H.,
Ser. 5, IX., 338-
340.

Monatschr. f.
burtsk., XXVL.,
114-127. Tafn. I.-
IV.

CRS Paris:
LXXXVIII., 406-
408.

GIRS Parish XCiIoe.
265-267.

Sitzb. nat.forsch Ges.
Leipzig, I., 9-12.

Edinburgh Med.
Journ., XXXIIL.,
332-343. Pls. I-III.

Arch. f. mikrosk.
Anat., XXVI., I-50.
Taf. I.-II.

4to (Diss.), pp. 27.
1 Taf. Halle:

Ge-

44I

1884.

1834.

1876.

1879.

1884.

1883.

1881.

1882.

1865.

1879.

1884.

1875.
1887.

1885.

1887.

442
58. Lowe, L.

59. Meola, F.

60. Osborn, H.

F,
61. ‘ce “
Gla. “ “e
62. Owen, R
68. “ “
64. Ravn, Ed-
ward.

65. Ruge, Carl.

66. Turner, Wm.

67. “ce “
68. “ec “
69. Walker, A.

MINOT.

In Sachen der Eihaute jiingster
menschlichen Fier.

Sulla struttura degli involucri del
feto umano.

Observations upon the foetal mem-
branes of the Opossum marsu-
pials.

Upon the fcetal membranes of the
marsupials.

The fcetal “membranes of the
marsupials: the yolk-sac pla-
centa in Didelphys.

Description of the membranes of
the uterine foetus of the Kanga-
roo.

Description of the foetal mem-
branes and placenta of the Ele-
phant (Elephas Indicus, Cur.),
with remarks on the value of
placentary characters in the
classification of the mammalia.

Ueber die mesodermfrie Stelle in
der Keimscheibe des Hiihner-
embryos.

Die Eihiillen in der Geburt befind-
lichen Uterus. Bemerkungen
ueber den Ort und die Art der
Ernahrung des Kindes in dem-
selben.

On the gravid uterus and on the
arrangement of the foetal mem-
branes in the Cetacea.

Note on the foetal membranes of
the Reindeer (Rangifer taran-
dus).

On the foetal membranes of the
eland (Oreas canna).

Der Bau der Eihaute bei Gravidi-
tatis abdominalis.

[Vou. II.

Arch. f. Gynak., XIV.,
190-196.

Riv. Internaz di Med.
e Chir., I., 505-502;
582-609. = Tav. I.
Abstr. Cbl. Gynak.,

pp. 584.

Q. J. M. S. XXIIL,
473-484.
Pl. XXXIII.

Zool. Anz., VI., 418-
419.

Journal of Morphol.,
I., 373-382. Pl
XVII.

Mag. Nat. Hist., L,,
481-484.

Philos. Trans.,
CXLVIL., 347-353.

His u. Braune, Arch.,

Ppp- 412-421. Taf.
XXI.
In Schréder, 129a,
pp. 113-151.
Trans. ‘Roy. :'Soc;,

Edinburgh, XXVL,
467-504. Pl. XVIL-
XVIII.

Journ. Anat. and
Phys., XII., 601-
603.
Journ. Anat. and
Phys., XIV., 241-
243:

Virchow’s Arch.,
CXVIL., 72-99. Taf.
II.

1879.

1884.

1883.

1883.

1887.

1837.

1857.

1886.

1886.

1872.

1878.

1879.

1887.

No.

70.

71.

72.

73.

74.

75.

76.

77.

3-]

UTERUS AND EMBRYO.

PLACENTA.

(See also F@TAL MEMBRANES, AMNION, ALLANTOIS, and DECIDUA.)

Baer, €. E.

von.

Balfour, F.

M.

Bassett, J.

Beauregard

et Boulart.

Cainven-
berghe,

Charles van.

Chapman,
H.C.

Chatellier,
HH.

77a. Creighton,

Ch.

Z7b. “e “cc

78.

79.

8o.

81.

Dastre.

Delore.

Dugés, A.

Duncan, J.
M.

Untersuchungen iiber die Gefass-
verbindungen zwischen Mutter
und Frucht in den Saiigethieren.
Ein Gliickwunsch zur Jubelfeier.
Samuel Thomas von Sdémmer-
ings.

On the evolution of the placenta
and on the possibility of employ-
ing the characters of the pla-
centa in the classification of the
mammalia.

Utersuchungen der Placenta bei
Drillinger.

Note sur la placentation des Ru-
minants (cites some earlier liter-
ature).

Sur L’Anatomie Physiologique
and la Pathologie du Placenta.

Placenta of Macacus cynomolgus.

The placenta and generative ap-
paratus of the Elephant.

Etude sur un point de l’anato-
mie du placenta chez les fe-
melles du rat blanc.

On the formation of the placenta
in the Guinea Pig.

Further observations on the for-
mation of the placenta in the
Guinea Pig.

Du placenta foetal des Pachy-
dermes.

Etude de la circulation mater-
nelle dans le placenta.

Lettre relative 4 la placentation
du Dasypus novemcinctus.

Note of a proof of the free inter-
communication near the cho-
rionic surface, between different
parts of the system of maternal

Leipzig, pp. 30, L.,
col. pl. folio.

Proc. Zool. Soc., Lon-
don, 210-212.

Obstetr. Trans.,
XXIII., 129-130.
Robin’s Journ., XXI.,

93-99. Pl. V.

Gand (Diss. ), pp. 203.

Proc. Acad. Nat. Sci.,

Philadelphia, 146-
147.

J. Acad. Nat. Sci.,
Philadelphia, to,

Ser: IT.-VIIL., 413-

422. Pl. XLVIII.-L.

Nouv. Arch. d’ obstetr.
et de gynéc., Paris,
I, pp. 488-491.

Journ. Anat. and Phy-
siol., XII., 534-590.
Pl. XIX.-XX.

Journ. Anat. and Phy-

siol., XIII., 173-182.

PIEENEVAS

Ann. Gynéc., V., 66-
67.

Ann. Gynéc. Juin. Pls.
I.-II.

Ann. Sci. Nat. Zool.,
Sér. IX., VI., Art. 3,
pp. 2.

Edinburgh Obstr.
Soc., III., 116-121.

443

1828.

1881.

1882.

1885.

1871.

1880.

1881.

1875.

444

82. Edwards,
A. Milne.

83. Ercolani, G.

84.

85.

86.

87.

88.

89.

90.

91.

92.

B.

ec

“

MINOT.

cells or blood caverns of the
placenta, in the same and in
different cotyledons.
Observations sur la conformation
du placenta chez le Tamandua.

Sul processo formativo della por-
zione glandulare o materna
della placenta.

Delle malattie della placenta.

De la portion maternelle du pla-
centa chez les mammiféres.

Sulla parti che hanno le glandule
otricolari dell’ utero nella forma-
zione della porzione materna
della placenta.

Della struttura anatomica della
caduca uterina nei casi di gravi-
danza extrauterina nella donna.

Della placenta nei mostri per in-
clusione e nei casi di gravidanza
extrauterina nella donna e in
alcuni animale.

Sulla unita del tipo anatomico
della placenta nei mammiferi e
nella umana specie e sull’ unita
fisiologica della nutrizione dei
fete in tutti vertebrate.

Nuove Ricerche sulla placenta
nei pesci cartilaginosi e nei
mammiferi e delle sue applica-

zioni alla tassonomia zoologica

e all’antropogenia.

Nuove Ricerche di anatomia nor-
male e patologica sulla placenta
dei mammiferi e della donna
(Tre Lettere al chiarissimo sig-
nore Prof. Alberto Kolliker).

Resumé francais par l’auteur de
91.

93. Fleischmann, | Ueber die erste Anlage der Pla-
Albert.
94. Garrod, A.| The gravid uterus and placenta of

H., and
Turner, Wm.

centa bei den Raubtieren.

Hyomoschus aquaticus.

[Vou. II.

Ann. Sci. Nat., Sér.
V., XV., Art. 16, pp.
API WV.

Mem. Accad. Sci. Ist.,
Bolonga, 4to, Sér.
TUX ikascans))s
363-432. Tav. I-
VI.

Mem. Accad. Sci.
Ist., Bolonga, 4to,
Sér IL, X., 4g1-

554. Tav. VII.
Journ. Zool., I., 472-
480. Pl. XXIV.

Mem. Accad. Sci. Ist.,
Bolonga, 4to, Sér,
3, Ill, 264-312.
Tav. I-IV.

Mem. Accad. Sci. Ist.,
Bolonga, 4to, Sér.
3, IV., 397-414.
Tav., 1.

Mem. Accad. Sci. Ist.,
Bolonga, 4to, Sér.
3, V-, 527-541.

Mem. Accad. Sci. Ist.,
Bolonga, 4to, Sér.
3, VII., 271-346.
Tav. I-V.

Mem. Accad. Sci. Ist.,
Bolonga, Sér. 3, X.,
601-982. Tav. I-
XI.

| Mem. Accad. Sci. Ist.,
Bolonga, Sér. 4, IV.,
707-782. Tav. I-
III.

Arch, Ital. Biol., IV.,

179-192.
Sitzb. d. Phys.-Med.

Soc., Erlangen, pp. 3.

Proc. Zool. Soc. Lon-
don, 682-686. Pls.
XLIV.

1872.

1870.

1870.

1872.

1873.

1874.

1875.

1877.

1880.

1883.

1883.
1886.

1878.

No.

97.

98.

99.

3-]

. Gervais, P.

. Godet, R.

Goodsir, J.

Hegar.

Hening, C.

100. Hicks, J.

101. Harting, P.

Braxton.

102. Holl, M.

103. Homberger.

104. Hyrtl, J.

105. Jassinsky,

184

106. Joly, N.

106a. Jungbluth.

107. Kastschen-

108. KGlliker, A.

ko, N.

UTERUS AND EMBRYO.

Addition au mémoire de M. Turner,
(185).

Recherches sur la structure in-
time de placenta du lapin.

Structure of the human placenta.

Die Placenta materna am Ende
der Schwangerschaft.

Studien ueber den Bau der
menschlichen Placenta und iiber
ihr Erkranken.

Some remarks on the anatomy of
the human placenta.

On the ovum and placenta of the
Dugong (Abstract by Prof.
Turner).

Ueber die Blutgefasse der
menschlichen Nachgeburt.

Die nachtragliche Diagnose der
Lagerung des Eies im Uterus
aus den ausgestossenen Nach-
geburtstheilen.

Die Blutgefasse der menschlichen
Nachgeburt in normalen und
abnormen Verhiltnissen.

Zur Lehre ueber die Structur der
Placenta.

Etudes sur la placenta de Ai
(Bradypus tridactylus, Linn.).
Place que cet animale occupe
dans la série des Mammiféres.

Beitrige zur Lehre von Frucht-
wasser und seiner iibermdssigen
Vermehrung.

Das menschliche Chorion epithel
und dessen Rolle bei der Pla-
centa.

Ueber die Placenta der Gattung
Tragulus.

Journ. Zool. I., 323-
S24 serie eV LL

Neuveville, pp. 48.
Tav. I.-II. (Berner
Inaug. Diss.).

Goodsir’s Anat. and
Pathol. | Observa-
tions, Edinburgh, pp.
50-54-

Monatschr. f. Ge-
burtsk., XXIX., 1-
Di:

Leipzig, Englemann,

pp. 39. Tafn. I-
VIII.

Journ. Anat. and
Phys.5)) Vile. 1(Ser:
II.), V., 405-410.
Journ. Anat. and
Phys., XIII, 116-
117.

Sitzb. Akad. Wiss.,
LXXXIII., Abth.
3, April, pp. I-4I.
Tafn. I.-II.

Freund Gynak. Klin-
ik, L., pp. 663-676.

Wien, 4to, pp. VIII.,
152. Tafn. 1-XX.

Virchow’s Arch., XL.,
341-352. Taf. III.

C.R. Paris, LXXXII.,
283-287.

Inaug. Diss., Bonn.

His. Arch., 451-480.
Taf. XXI. (also in
Russian, 1884, Char-
kow, pp2)33- Els.
I.-II.)

Verh. Wiirzburg Phys.-

Med. Ges., N. F.,
X., 74-83. Tafn.
IV.-V.

445

1872.

1877.

1845.

1867.

1872.

1872.

1879.

1881.

1885.

1870.

1867.

1878.

1869.

1885.

1879.

446

109

110.

111.

112.

113.

114.

115.

116.

117.

118.

119.

120

121.

122.

. Langhans,
Th.

Laulanié.

Marcy, H.

0.

Masquelin,
H., et

Swaen, A.

Mauthner,

J:

Meyer, L.

Nitabuch,
Raissa.

Orth, J.

Pylejajeee.

Reitz.

“ “

MINOT.

Zur Kenntniss der menschlichen
Placenta.

Untersuchungen ueber die mensch-
liche Placenta.

Ueber die Zellschicht des mensch-
lichen Chorion.

Sur la nature de la néoformation
placentaire et lunité de com-
position du placenta.

The placental development in

“ mammals. A unity of anatomi-
cal and physiological modality
in all vertebrates.

Premiéres phases du _ develop-
ment du placenta maternal chez
le lapin.

Ueber den miitterlichen Kreis-
lauf in der Kaninchenplacenta
mit Riicksicht auf die in der
Menschenplacenta bis jetzt vor-
gefundenen anatomischen Ver-
haltnisse.

Ueber die Blutmenge der Placenta.

Beitrage zur Kenntniss der
menschlichen Placenta.

Das Wachsthum der Placenta
foetalis und Boll’s Prinzip des
Wachsthums.

An experimental research on the
utero-placental circulation.

. Reid, John. | On the anatomical relations of

the blood-vessels of the mother
to those of the foetus in the
human species (also Appendix
to Dr. J. Reid’s paper on the
anatomical relations of the blood
of the mother to those of the
foetus).

Beitraége zur Kenntniss des Baues
der Placenta des Weibes.

Artikel Placenta.

[VoL. II.

Arch. f. Gynak, L.,
317-334. Taf. V.
His. Arch., 188-267.
Tafn. VII.-VIII.
Beitrage z. Anat. u.
Embryol. als Fest-

replay” WH TLCS = "Vc
Henle, 4to, 69-79.
Taf. IX. a.

Gone Paris; 4to, ‘Gi
651-653.

Ann. Anat. and Surg.,
PP-

Arch. Biol., I., 25-
44.

Wien Sitzb., LXVII.,
Abth. 3. 118-124.
Matsak:

Centralbl. f. Gynaec.,
II., 220-222.

Bern. (Diss.), pp. 39.
Pl-vne

|
Zeitschr. f. Geb. h. u.

Gyn., II., 9-23. Taf.
III.

Philadelphia Med.
Times, No. 433,
XIV., June 28, pp.
711-715.

Edinburgh Med. and
Surg. Journ., LV.,
i125) Ply De 35—
136.

Sitzb. K. Akad. Wiss.
Wien, LVII., 1009-
TOMS we laks

Stricker’s Handbuch
der Gewebelehre,
II., 1183-1186.

1870.

1877.

1882.

1885.

1882.

1880.

1873.

1878.
1887.

1878.

1884.

1841.

1868.

1872.

No. 3-]

128. Ribemont-
Dessaignes,
A.
124. Ritgen, F.
A.

125. Robin, Ch.

126. Rolleston.

127. Romiti,
Guglielmo.
128. Ryder, J.A.

28a, 6

129. Schatz, F.

129a. Schréder,
Carl.

180. Schroeder
van der
Kolk, J.
Wa

131. Schultze,
BAS:

131a. Seiler.
132. Sym, A. C.

UTERUS AND EMBRYO.

Des placentas multiples dans les | Ann. Gynéc., XXVIL.,

grossesses simples.
Beitrage zur Aufhellung der
Verbindung der menschlichen

Frucht mit dem Fruchthilter
und der Ernahrung derselben.
Recherches sur les modifications
graduelles des villositiés du cho-

rion et du placenta.

On the placental structures of the
Tenrec (Centeles ecaudatus) and
of those of certain other mam-
malia, with remarks on the
value of the placental system of
classification.

Placenta (Anatomia descriptiva e
struttura).

The placentation of the two-toed
Anteater (Cycloturus didactylus).

A theory of the origin of placental
types, and on certain vestigiary
structures in the placente of the
mouse, rat, and field-mouse.

Die Gefassverbindungen der
Placentakreislaufe eineiger
Zwillinge, ihre Entwicklung und
ihre Folgen.

Fortsezung.

Fortsetzung.

Der schwangere und kreissende
Uterus.

Waarnenungen over het maaksel
van de menschelijke Placenta en
over haren Bloeds-omloop.

Die Placentarrespiration des

Feetus.

Die Gebarmutter, etc.

On a case of vesicular placenta
from a premature birth at the
seventh month, the child being
born alive.

Janvier, pp. 12-52.

Leipzig u. Stuttgart,
pp. 78. Tafn. I.-IIL.,
fol.

Mém. Soc. Biol., Sér.
2, I., 63-75.

Trans. Zool. Soc., 4to,
V., 285-316. Pl. I.

Encicl. Med. Ital.,
Seley Vite bantes:

Proc. Acad. N. 5;
Philadelphia, 115-
120.

American Naturalist,
XXIL., 780-784.

Arch. f. Gynic.,

XXIV., 337-399.
Taf. I.-V.

Arch. f. Gynac.,
XXVIL., 1-72. Tafn.
I-IV.

Arch. f. Gynic.,
XXIX., 419-443.

8vo, Bonn.

Verhand. eerste Klas-
se K. nederl. In-
stitut., Amsterdam.
Derde Reeks, 4to,
4 deel., 69-180.
Tafn. I.-VI.

Jena. Zeitschr. f. Med.
n. Naturu., IV., 541-
552.

Fo., pp. 38. XII. Pls.
Edinburgh Medical
Journal, XXXIIL.,
102-109.

447

1837.

1835.

1854.

1866.

1387.

1887.

1887.

1884.

1885.

1887.
1886.

1851.

1868.

1832.
1887.

448

133. Tafani, A.

134.

135

136.

137.

138.

139.

140.

141.

142.

143.

144.

145.

seburner:

Wm.

146.

147.

MINOT.

Sulle condizione uteroplacentari
della vita fetale.

La circulation dans le Placenta
de quelques mammiféres (Trans-
lated from Lo Sperimentale,
Agosta, 1885).

De la placentation des Cétacés
comparée a celle des autres
mammiféres.

Observations on the structure of

the human placenta.

On the placentation of the Sloths
(Choleopus Hoffmani).

On the placentation of Seals (Ha-
lichcerus gryphus).

Lectures on the Comparative
Anatomy of the Placenta. First
series.

Note on the placentation of Hy-
Tax.

On the placentation of the Le-
murs (see No. 144).

On the placentation of the Cape
Ant-eater (Orcetropus capensis).
Some general observations on the
placenta, with especial refer-
ence to the theory of evolution.

On the placentation of the Le-
murs (see 141).

A further contribution to the pla-
centation of Cetacea (Monodon
monoceros).

On the placentation of the Apes,
with a comparison of the struc-
ture of their placenta with that
of the human female.

On the cotyledonary and diffused
placenta of the Mexican deer
(Cervus Mexicanus).

(Vo. II.

Arch. Scuola d’ Anat.
pathol. diretto dal
Prof. Giorgi Pelli-
zari, Firenze, IV., pp.

53-216. Tav. I.-VIII.

Arch. Ital.
VIII., 49-57.

Biol.,

Journ. Zool., I., 304-
323.) eelexvil.

Journ. Anat. Physiol.,
Sér. 2, VI., 120-
ev ee We

Trans. R. Soc., Edin-
burgh, XXVII., 71-
104. Pls. II-VI.

Trans, “Roy. ‘Soc:,
Edinburgh, XXVILI.,
275-304-

Pls. XVIII.-XXI.
Edinburgh (Black),
pp. 124. Pl. I-III.

Proc. Roy. Soc.,
XXIV., 151-155.
Philos. Trans. Roy.
Soc., London,
CLXVI., 569-587.
Pl. XLIX.-LI.

Proc. Roy. Soc.,
XXIV., 400.

Journ. Anat. and
Phys., X., 693-706.

Journ. Anat. Physiol.,
XI, 33-53.

Journ. Anat. Physiol.,
XII., 147-153.

Proc. Roy. Soc., Ed-
inburgh, IX., 103-
II.

Phil. Trans., LXIX.,
523-562.
Pls. XLVIII.-
XLIX.

Journ. Anat.
Phys., XIII.,
200.

and
toe

1886.

1887.

1872.

1873.

1873.

1875.

1876.

1876.

1876.

1876.

1877.

1877.

1877.

1879.

1879.

No. 3.]

148.

149.

150.

151.

152.

153.

154.

155.

156.

157.

158.

159.

160.

161.

162.

Turner,
Wm.

Waldeyer,
W.

Watson, M.

Weldon,
W. F. H.
Winkler,
F.N.

Koster.

Neugebau-
ery lez “AY
Renaut, J.

Ruge, C.

Schott, J.
A.C.

S.

Stutz, Gus-
tav.

Tait, Law-
son.

Schultze, B.

.OTERUS AND EMBRYO.

On the placenta of the hog-deer
(Cervus porcinus).

Ueber den Placentarkreislauf des
Menschen.

On the female organs and placen-
tation of the Racoon (Procyon
lotor).

Abstract.

Note on the placentation of Tetra-
ceros quadricornis.

Zur Kenntniss der menschlichen
Placenta.

Journ. Anat. and
Phys., XIII., 94-98.

Sitzb. K. Akad. Wiss.
Berlin, VI., 83-93.

Proc. Roy. Soc. Lon-
don, XXXII, 272-
298. Pls. III.-VI.

Proc. Roy. Soc., Lon-
don, XXXI., 325-
326.

Proc. Zool. Soc. Lon-
don, No. I, pp. 2-6.

Arch. f. Gynak., IV.,
238-265. Taf. V.

UMBILICAL CORD.

(See also ALLANTOIS.)

Ueber die feinere Structur der
menschlichen Nabelschnur.

Morphologie der menschlichen
Nabelschnur.

Du tissu muqueux et du cordon
ombilical.

Ueber die Gebilde im Nabel-
strang.

Untersuchungen iiber den Dotter-
gang und iiber die Capillaren
im Nabelstrang.

Die Controverse ueber die Nerven
des Nabelstranges und seine
Gefasse.

Die genetische Bedeutung der ve-
lamentésen Insertion des Nabel-
stranges.

Ueber velamentale und placentale
Insertion der Nabelschnur.

Der Nabelstrang und dessen Ab-
sterbe-process.

Preliminary note on the anatomy
of the umbilical cord.

Abstract.

Wiirzburg, pp. 32, 2,
4to.

Breslau.

Arch. de Physiol.,
Vil 210:

Z. Gebiirtshilfe u. Gyn-
ak., I., 1-21.

Z. f. Geburts. u. Gyn-

ak., I., 253-259. ‘

Jena Zeit., III., 198-
205. Zweiter Arti-
kel, III., 344-358.

Arch. f. Gynak.,
XXX., 47-56.

Arch. f. Gynak., XIIL.,
315-354-

Proc. Roy. Soc., Ion-
don, 417-440. Pls.
XI-XIV.

Proc. Roy. Soc., Lon-
don, XXIII., 498-
50].

Frankfurt a M.

449
1879.
1887.

1881.

1884.

1872.

1868.
1858.
1872,
1877.

1877.

1836.

1867.

1887.
1878.

1876.

1875.

450

163.

164.

165.

166.

167.

168.

169.

170.

171.

172.

173.

174.

175.

176.

177.

Bonnet, R.

Cadiat, O.

Coblenz, H.

Delaunay,
G.

Dohrn, H.

Elisher, J.
Farre, A.
Friedlander,

Carl.
Gasser.

Gottschalk.

Hofmeier,
M.

Imbert,
Gaston.

MINOT.

UTERUS.

(Vou. I.

(See also DECIDUA and PLACENTA.)

Die Uterinmilch und ihre Bedeu-
tung fiir die Frucht.

Mémoire sur l’uterus et les
Trompes.

Zur Entwicklungsgeschichte der
inneren weiblichen Sexual-or-
gane beim Menschen im Zu-
sammenhange mit pathologischen
Vorgangen.

La Fecondité.

Ueber die Miiller’schen Gange
und die Entwicklung des Uterus.

Zur Kenntniss der Miillerschen
Giange und ihrer Verschmelzung.

Ueber des Entwickelung des Hy-
mens.

Ueber die Gartnerschen Kaniale
beim Weibe.

Beitrige zur feineren Anatomie
der Muskelfasern des Uterus.

Article “Uterus and its append-
ages.”

Ueber die Innenflache des Uterus
post partum.

Ueber Entwicklung der Miiller’-

schen Giange.

Ein Uterus gravidus aus der fiinf-
ten Woche der Lebenden ent-
nommen.

Das untere Uterinsegment in an-
atomischer und physiologischer
Beziehung.

Le Col du Segment intérieur de
Vuterus a la fin de la grossesse;
documents anatomiques.

Beitrage zur Biologie
(von Bischoff’s Fest-
gabe, Stuttgart),
221-263, mit einer
Tafel.

Robin’s Journ. Anat.,
409-431.

Pls. XXVI.-XXIX.

Giebel. Z. Naturwiss.,
3 Folge, VI., 313-

320; Tat. IT:

Revue Scientif., 3 Oct.,
433-437, et 10 Oct.,
466-470.

Monatschr. f. Ge-
burtsk, XXXIV.,
382-384.

Marburg Ges., IX.

Schriften. Ges. Nat.
Wiss. Marburg, X.,
Suppl., Heft I., pp.
8. Tafn. L-X.

Arch. f. Gynak., XXL,
328-345:

Arch. f. Gynak., IX.,
10-21. Taf. If.

Todd’s Cyclop. Anat.,
V., Suppl.

Arch. of Gynak., IX.,
22-28.

Sitzb. Ges. Béford
Naturw. Marburg.,
I-3.

Arch. Gynak., XXIX.,
Heft 3, pp. 488-510.
Taf. IX.

In Schréder, 129a,

21-73.

Paris, pp. 79.

1882.

1884.

1881.

1885.

1869.

1871.

1875.

1883.
1876.
1858.
1876.

1872.

1887.

1886.

1887.

No. 3.-]

178.

179.

180.

181.

182.

183.

184.

185.

186.

187.

188.

189.

190.

191.

Johnstone.

Kiistner,
Otto.
Kundrat,
Hanns, u.
Engelmann,
Gone
Leopold, G.

Lowenthal.

Paschen, D.

Patenko, T.

Sinéty, de.

Tourneux,
F., et

Legay, Ch.

Underhill.

Waldeyer,
W.

Williams, J.

UTERUS AND EMBRYO.

On the Menstruation Organ. Dis-
cussion.

Das untere Uterinsegment und
die Decidua cervicalis.

Untersuchungen ueber die Ute-
ruschleimhaut. (Translation, see
Engelmann, 28).

Die Lymphgefiisse des normalen
nicht schwangeren Uterus (III.
Die Lymphlamen der Schleim-
haut, 30-48).

Eine neue Deutung des Men-
strual-processes.

Beschreibung eines graviden Uter-
us aus dem fiinften Monat der
Schwangerschaft.

Uber die Nervenendigungen in der
Uteruschleimhaut des Menschen
(Vorlainfige Mittheilung).

Sur Vhistologie normale de la
cavité utérine quelques heures
aprés l’accouchment.

Etude histologique sur la cavité
utérine aprés la parturition.

Mémoire sur le developpement de
Puterus et du vagin envisagé
principalment chez le fcetus hu-
main. ;

Note on the uterine mucous mem-
brane of a woman who died im-
mediately after menstruation.

Medianschmitt einer Hochschwan-
geren bei Steisslage des Fcetus
nebst Bemerkungen iiber die
Lage und _ Formverhaltnisse
des Uterus gravidus nach Langs-
und Querschmitten.

On the structure of the mucous
membrane of the uterus and its
periodical changes.

The mucous membrane of the
body of the uterus.

British Gynec. J., Pt.
VII, S., pp. 292-
301; 301-307.

8vo, 2 Tafin.

Stricker’s Med. Jahrb.,
135-177. Taf. I.

Arch. f. Gyn., VL. 1-
54. Tafn. I-III.

Arch. Gyn., XXIV.,
168-261. Abstr. Cbl.
Gyn., 306-312.

Marburg (Diss.), pp.
19.

Centralb. Gynak., IV.,
442-444.

Ann. Gynécol., VI.,
217-220.

Arch. Physiol. Norm.
et Path., Sér. 2, III.,
342-352.

Robin’s Journ. Anat.,
330-386. Pls. XX.—
XXV.

Edinburgh Med.
Journ., XXI., 132-
naa

Bonn. (Cohens Ver-
lag) Atlas, 5 Tafin.

Obstet. Journ. Gt.
Brit. and Ireland,
II., 681-696. Pl. 1.;
753-767. Pl. I1-
Ill.

Obstet. Journ. Gt.

Brit. and Ireland,
III., 496-504.

451

1886.

1882.

1873.

1874.

1885.

1887.

1880.

1876.

1876.

1884.

1875.

1886.

1875.

1875.

452 MINOT. [Vot. II.

192. Wyder, Beitrage zur nomalen und pathol- | Arch. f. Gyn., XIIL., | 1878.
Aloys ogischen Histologie der mensch- | 1-55. Taf. I.

Theodor. lichen Uteruschleimhaut (I. Die

mucosa uteri der Kinder. II.

Menstruation Endometritis. III. .

Dyemenorrhea membranosa). |

YOLE-SACK.

193. Ahlfeld, F.| Ueber die Persistenz des Dotter- | Arch. f. Gynak., IX.,| 1876.
strangs in der Nabelschnur. 325. Only four lines.

14. GI Ueber die Persistenz der Dotter- | Arch. f. Gynak., XI.,| 1877.
gefasse nebst Bemerkungen iiber | 184-197.

die Anatomie des Dotterstranges.

195. Allen, W. | Omphalo-mesenteric remains in| J. Anat. and Phys.,| 1883.

mammals. XVIL., 59-61.
196. Kleimwach-| Ein Beitrag zur Anatomie des | Arch. f. Gynak., X.,| 1876.
ter, L. Ductus omphalo-mesentericus. 238-247. Taf. I-
Vil,
197. Schenk, S.| Der Dotterstrang der Plagiosto- |} Sitzb. K. K. Akad.| 1874.
men. Wien., LXIX., 301-
308. Taf. I.
198. Schultze, | Das Nabelblaschen ein constantes | Leipzig, pp. 1861.
B.S. Gebilde in der Nachgeburt des

ausgetragenen Kindes.

MINOT. 453

EXPLANATION OF PLATES.

Nearly all the figures were drawn by Mr. E. Stanley Abbot under my supervision.
The outlines were drawn with the camera lucida, and the details added free-hand.
The drawings are all accurate representations of the preparations, and though of
course not photographically exact, are not diagrammatic, except in the case of a few
figures expressly specified below. I owe much to Mr. Abbot’s patient skill.

Reference Letters.

all, allantois.
cm, circular muscles.
conn, connective tissue.
ecto, foetal ectoderm.
emé, embryo.
en, entoderm.
endo, endothelium.
ep, epithelium.
J; placental fissure.
Sv, foetal blood-vessel.

gt, gland; glandular layer.

h.ep, hyaline epithelium.
Z, leucocytes.
/m, longitudinal muscles.

mes, mesoderm.
mo.cl, monster cells.
misth, mesothelium.
miuc, mucosa.
musc, muscularis.
ob.pl, ob-placenta.
0.2, outer zone of placenta.
P, periplacenta.
perv, perivascular cells.
sp.pl, sub-placenta.
Sel.z, subglandular zone.
V, blood-vessel.
vac, vacuole.

EXPLANATION OF PLATE XXVI.

Fic. 1. Placenta of rabbit at eight days, with dilated glands, 2/7, and superjacent
foetal ectoderm, ecto (X 125 diams.).

Fic. 2. Rabbit’s uterus at nine days, transverse section of a swelling (X 7 diams.).

Fic. 3. Portion of the placenta of Fig. 2 (X 445 diams.), to show the connective
tissue, conn, the perivascular cells, ev.v, and the thickened endothelium, exdo, of the
blood capillaries.

Fic. 4. Portion of the periplacenta of Fig. 2 (X 175 diams.), to show the degen-
eration of the epithelium, /.e/.

me ea |

Endo

conn perv

=
‘

a
=~ —
ar ste Oe

logy. Vol.

Lith Anse v Wormer § Winer, Frankf 8

,
im

: 4 i of ial |
mo “J nv

hae

‘*

j 4 a } ‘AINeA | |

Piglet) } x | : i 1 pill Da peer. ey
' / ; | § ay Ae a ‘A 4 (ties yy
if 7 anit Ws , 1) 1A ad Od | Oe y

: | i ' i ae \ ae
‘ vi ; yh) 1 Ticw het te) iat ee oat aii We ut
Ba An kiy | | at a
0 ae tre tp I Aa ah mi
Me a
. hin Anne i? Ve), ;
> pre ey} waite od A CN ‘i y . a

Par? | i : 4 zs va 1h ; ay Ae r , ' peat

; hy tgs ; } ek ee] Wages ab

it Lae un she: ie i
y {
7 \
‘
Ke
| +7 i ;
if
ees
J. M \
. Nak +
Ph f
Ay j .
re, 1
} : q -

458 MINOT.

EXPLANATION OF PLATE XXVII.

Fic. 5. Portion of the ob-placenta of Fig. 2 ( X 175 diams.), to show the degen-
erated epithelium, 4.e/, and the saucer-shaped glands, <7, 27’.

Fic. 6. Rabbit’s uterus of eleven days; portion of the ob-placenta to show the
degenerated epithelium, /.ef, and the regenerated glands, ¢/ ( X 175 diams.).

Fic. 7. Portion of the placenta of Fig. 2 ( X 175 diams.), to show the degenera-
tion of the uterine tissue and the relations of the foetal ectoderm to the piacental
surface.

Fic. 10. Rabbit’s uterus of thirteen days; portion of the ob-placenta (x 175
diams.), to show the regenerated glands.

Fic. 11. Portions of the epithelium of the periplacenta at thirteen days. A, ver-
tical section (X 175 diams.). B, surface view (X 175 diams.). C, single cell
( X 445 diams.).

eel

Z
3
7S
ny

+
1

erg

—~ == conn

= muse
2 :

Anst.v Wercera WinterFrankfet 9M

-

to

460 MINOT.

EXPLANATION OF PLATE XXVIII.

Fic. 8. Portion of a vertical section of the placenta at eleven days of a rabbit, to
show the relations of the mesothelium, ms¢h, to the top, and of the ectoderm, ecéo,
to the side of the placenta ( X 175 diams.).

Fic. 9. Complete transverse section of a rabbit’s uterus at thirteen days, with the
embryo, ed, in place ( X 7 diams.) ; the details are only approximately accurate ;
x, mass of perivascular decidual cells, developed in the region of the ob-placenta.

Fic. 12. Rabbit’s uterus at fifteen days; portion of a section through the placenta
(X 90 diams.), to show the degenerated glands, ¢/, and the mesoderm, 7es, and meso-
thelium, mst, covering the surface of the placenta; the blood-vessels are drawn
dark.

Fic. 13. Portion of upper part of a rabbit’s placenta at fifteen days ( Xx 340
diams.), to show the histological structure of the glandular layer of the placenta.

Fic. 14. Multinucleate decidual cells from the subglandular zone of a rabbit’s
placenta at fifteen days ( X 540 diams.).

Fic. 15. Uninucleate perivascular decidual cells from the outer zone of a rabbit’s
placenta at fifteen days ( X 540 diams.).

Fic. 16. Endothelium from the blood-vessels of the periplacenta of a rabbit at
fifteen days ( X 240 diams.). A, surface view; B, C, in section.

Fic. 17. Ob-placenta of a rabbit at fifteen days ( X 125 diams.), to show the
monster cells, a, 4, c, and the uterine epithelium, ¢/.

Fic. 18. Nucleus of a monster cell from the ob-placenta of a rabbit at fifteen
days ( X 445 diams.).

ED ~

b=

ITHUSC «

Lith. Anst v Werner «Winter Frankf OM

| AP Ng | }

~~

EXPLANATION OF PLATE XXIX.

Diagram to show the relations of the embryo and uterus in the rabbit from the
eleventh to the thirteenth day of gestation.

PULXXIX.

=
&
8
IXJOOo
LO s COSC 3 SS
PEL SE S ‘
OF SSF OED s S 8
PSX: Ss 5 E
8 Nios 2
~ mn i
2 cas es
GS Ss 8
ele nee i awe s
RUSS Says eS 38 ES
LS se = Ss 8 ast
SSS SS Se Ste S
Se eS Vo eos
SS, ESS
cae Se is =
Se Soo ck ts as
POR IR oasoie feos
S ~
Bee eo, eae
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s
g
SoHel hae
segs
i SS
= See No) aS
Roy eae
Y io heaet FS
¢ FO ak S
TGS ee > a
a ~s 6k $ » YY
= = S ESS
2.6 5 pole “S 5
SoS ea Ss + i oe
S S So Sk 4s) oases
mw SSS ese
S48) Bos) Shai
Gy SSIs SS
FYsEsssK HEE
ms
~ S SS
SS ew fw ~~
Sys 8 Ss SEE

THE ANATOMY AND DEVELOPMENT OF THE
LATERAL LINE SYSTEM IN’ AMIA CALVA

EDWARD PHELPS ALLIS, Junr.

CONTENTS.
PAGE
INTRODUCEION co <ibiss aoe) as) acca ie 0 an) soon afi diem ie et eet nmi me mmr OFS
PAGE
I. ADULT FORM. 3. Supra-orbital Line . . . . 491
se ae . Operculo-mandibular Line. .
General Description. . . . . . 465 ae ae
Courselot the'Canals; = 2. . ~ 470 II. Post-LARVAL Forms.
1. Infra-orbital Canal. . . . 471 | 1, Primary Pores. . . AGA.
2. Supra-orbital Canal . . . - 472 | 2. Number and Position of ‘Carta
3. Operculo-mandibular Canal. . 473 Organs. . . . 499
4. Supratemporal Cross-commis- 3. Sense-organs of the Suirucilas
SUES o/s : 473 Canali ot 5.1%5, Garde SON
Topography of the Peripheral Canal- 4. Lines of Pit Organs...) 2. 7=) . 502
systems . . oe to Sis Ae @...-Head, Lanesy sti. Satan ee ee505
1. Infra-orbital Canal) i oe elf 6; Body’ Bines) in) et gay
2. Lateral Line of the Body . ~ 483 | 5. Surface Sense-organs . . . . 509
3. Supratemporal Cross-commis- 6. Innervation. . . . . 510
sure. . . - + «+ + 483 | 7. Review of Nerves and Oars S20
4. Supra-orbital ties Sowa rt PASS
5. Operculo-mandibular Line . . 485 III. Larvar Forms.
G Summary. «+ . - . = » 4686 | x. Formationiof the Canals 4.7.) 523
Surface’ Pores 2 . << . . - «|. 487 | 2. Originvot the Canal/@rpans. 4 0. ge
i Intea-orbital’ Line. 2. |). 487 General Summary . . . . 535
2. Lateral Line of the Body . . 490 |

THE general course and position of the lateral canals in fishes
have long been known, and short descriptions and diagrams,
showing what is commonly accepted as the typical arrangement
of the main canals, are given in nearly all modern text-books
of vertebrate anatomy. More complete descriptions are given
in numerous special works, most of which deal more particularly
with other subjects, such as the structure of the skull, the

464 ALLIS. (Vou. II.

development and distribution of the cranial nerves, or the his-
tology and function of the sense-organs.

With a few exceptions, all these descriptions, so far as they
relate to the cranial part of the lateral system, are of a general
character only, giving little more than the course of the main
canals. The development of the canals, the number and posi-
tion of the organs, and their innervation, receive but scant
attention. This has doubtless been largely due, as Merkel sug-
gests, to the difficulties attending this part of the investigation
before the introduction and perfection of modern methods of
research ; but this cannot have been the only reason, for most
of the work could easily have been done by any of the earlier
writers. The purely descriptive part of the subject seems
simply to have been neglected in the greater interest attaching
to the histological and physiological sides, so that it is only
within the last five or six years that the constant relations of
the cranial canals to the dermal bones of the head, and their
importance in determining these bones in doubtful cases, have
been recognized. Both Sagemehl and Van Wijhe have called
special attention to this, and Sagemehl further says (No. 12,
p. 182, note) that the lateral canals seem to deserve a more
careful study than has hitherto been given them.

In Amia calva the cranial canals have been oftener and more
fully described than in any other form. Franque (No. 6), in 1847,
in a dorsal view of the dermal bones of the head, shows some of
the surface openings of these canals, but in the text he does not
refer to them, these four words only being found, “ Linea lateralis
fere recta” (No. 14, p. 368). Bridge (No. 4, p. 620), thirty years
afterward, in describing the skull, gave the course and position
of the main canals, the connections they form with one another,
and the bones they traverse, and the arrangement given by
him agrees closely with that more fully detailed in the present
paper. His work was mainly confirmed in 1882 by Van Wijhe
(No. 17, p. 288), and in 1883 and 1884 by Sagemehl (No. 12, p.
183, and No. 13, p. 36); still later by Shufeldt (No. 15), in con-
nection with his translation of Sagemehl’s paper; and finally
Wright (No. 18) has called attention to the sensory tissue lying
in the upper end of the spiracular canal, and belonging, by its
innervation, to the general lateral canal system, though classed
by him as hypodermal and exceptional.

No. 3.] LATERAL LINE OF AMIA. 465

Sagemehl’s description is much the best and most complete
of all; but he does not give the smaller branches of the sys-
tem, simply saying of them that the main canals have numer-
ous branches, arranged in many longitudinal rows and leading
to minute openings on the outer surface of the head. These
small branches are similarly disposed of in his description of the
cranial canals in the Characinidz, where he says they are too
variable and irregular to have any morphological significance
whatever.

A closer examination of Amia has shown that these small
branches have as constant relations to the dermal bones as the
main canals have, and hence may have as great significance.
They also have constant relations to the sense-organs found
in the canals, agreeing in this with the conditions described by
Bodenstein in Cottus gobio (No. 3) and by Emory in Fierasfer
(No. 5, p. 39).

The drawings for this paper have been made by Mr. Nomura,
to whose patience and skill the plates bear witness.

I. ADULT FORM.
General Description.

If an adult specimen of Amia calva be examined, many hun-
dreds of minute pores will be found, scattered to all appearance
most irregularly over a large portion of the head (Figs. 20, 21,
and 22, Pl. XXXVI.). Most of them lie directly superficial to
the dermal bones ; and they are found in greater or less num-
ber external to all these bones, excepting the prefrontal, max-
illary and jugal, operculum, sub- and interoperculum, branchi-
ostegal rays, and gular plate. They are also found in certain
places beyond the limits of the dermal bones; as, for instance,
near the posterior nasal aperture, in the fold of dermis imme-
diately behind the pre-operculum, and in the thick dermis
between the pre-operculum and the hinder and lower margins
of the postorbitals. In these places they lie mostly near the
edges of the bones, and are particularly numerous along the
anterior edge of the pre-operculum.

Each pore, as is well known, is the external opening of a
small epidermal tube which leads inward through the dermis

466 ALLIS. [Vor 28,

into some one of the dermal bones. In its course it unites with
similar canals from other pores, and increasing continually in
size, finally becomes a trunk canal, which opens into one of the
main lateral canals of the head. This trunk canal and its
branches form what has been called a dendritic system, of which
the surface pores are the external openings.

The arrangement of these pores varies greatly in different parts
of the head. They are found either single or in pairs, in more
or less irregular lines, or in irregular groups, the number and
arrangement of them differing somewhat in every specimen, and
even on opposite sides of the head in the same specimen. As
many as thirty-seven hundred were counted on the head of a
single large specimen, and the number apparently increases
indefinitely with the age of the fish. This great multiplication
is the result of a repeated dichtomous division of the pores
formed in younger stages. The impulse leading to this division
acts with much greater intensity in certain parts of the head
than in others, but is felt in all parts; for, with the exception
of the large pore at the hind edge of the supraclavicula (Fig.
39, Pl. XXXIX., 2722/19), which marks the limit of the cranial
system, there is not a pore on the head of the young fish that
is not double in later stages.

In both fresh and alcoholic specimens, the pores have a well-
marked whitish border, due mainly to the absence of inter-epi-
thelial pigment cells; and when fully formed they are approxi-
mately round. When about to divide, the sides of the oblong
and continually lengthening pore grow rapidly upward and toward
each other, and the pore becomes hour-glass or dumb-bell-shaped.
The projecting sides or lips finally meet and coalesce, and the
pore is divided into two pear-shaped portions which lie in a
small unpigmented oval space. In this process the canal lead-
ing to the pore is also divided into two portions, for an arch
is formed across the end of it, and it becomes Y-shaped form
as shown in the accompanying diagrammatic figure (Cut 1, d,
é, f). The two newly formed pores are at first connected by
a whitish cicatrice (Fig. 17, Pl. XXXV.); but the impulse which
led to their formation continuing to act, they travel apart, the
cicatrice disappears, and they become distinct and perfect pores.
One or both of them may again divide in the same manner,
and nearly in the same direction as at first, thus giving rise

No. 3.] LATERAL LINE OF AMIA. 467

to a line of pores usually somewhat curved, and to a canal of
the form shown in Cut 1, g. The division of the terminal pores
of such a line may then proceed more rapidly than that of the in-
termediate ones, thus producing creeper-like canals of the form
shown in /; or later, divisions may take place at an angle to
the original direction of division as shown in z, the angle being
usually a right one, or nearly so, and then again in the same
direction, or in the original direction, thus giving rise to a series
of intersecting, or parallel lines, and to a more or less compli-
cated arrangement of pores in groups of different sizes and
shapes. There is in this process of multiplication a strong ten-
dency to keep the pores of the different lines and groups at

BERR OO

Bee

g h )
CuERT.

Cut 1.— Diagrammatic representation of the formation and subsequent division
of a primary pore or tube: a, 4 and ¢, two half-pores approaching each other and
fusing; d@, primary pore and tube; ¢, the same, undergoing its first division, which in
f is completed; g, dentritic system after second regular division; 4 and 2, forms of
creeper-like branches.

about the same distance apart, so that when the groups become
large, somewhat geometrical designs are formed, and any particu-
lar pore may appear to belong to one of two or more intersecting
surface lines, either one of which might be taken, from surface
indications alone, to be the line of formation of the series.

This is the regular method of multiplication and formation of
the pores and branch canals in Amia, none of them being formed
by growth from beneath; that is, by the canals first forming
there as diverticula, or prolongations of existing canals, and
then forcing their way through to the upper surface. Not a

468 ALLIS. [Vou. Il.

single instance was found of such a growth from below, and
but one of the reverse condition,—that of a tube leading
blindly inward from the external surface toward a canal; and
the conditions in this case seemed to indicate that the tube,
after its regular formation, had been closed secondarily below
the surface. The specimen in which this was found was taken
in winter, through the ice, and having been frozen and fre-
quently handled, the epidermis was so injured before the pit
was discovered that it was impossible to tell whether there had
originally been a regular surface pore or not.

The formation of the more or less complicated groups of
pores resulting from this method of division is well shown in Fig.
17, Pl. XXXV., which represents the head of an Amia about
fifteen months old and 114 inches long. This specimen, which
was raised in an aquarium, was much larger than other speci-
mens two years old living in the same aquarium, and probably
larger than fishes of the same age found in their native waters ;
for, according to Dr. Estes (No. 7, p. 659), Amia one year old,
taken in the sloughs tributary to Lake Pepin, are only from
three to six inches long. All stages in the division of a pore
are shown in this figure. In some instances the pore is appar-
ently dividing into three portions instead of two, but this is due
to the accelerated re-division of one of the portions before the
regular division has been completed. Nothing of this kind was
found in any of the several adult fishes examined, but in the
skeletons prepared, the openings of the canals on the upper sur-
face of the frontal often presented a tri-lobate appearance, indi-
cating that they had arisen in this manner (Pl. XL., Fig. 40,
Ce ca)

The different groups of pores, although varying greatly in
size and shape in different individuals, or even in the same
individual on opposite sides of the head, are normally definite
in number and general position. Each group when small is con-
fined strictly to some particular region of the head; but in its
growth it extends beyond this region, and becomes continuous
with neighboring groups. It is necessary, therefore, in order
to arrive at the proper number and arrangement of the groups
in large and well-developed specimens, to trace the canal lead-
ing from each pore to the particular trunk or stem from which
it arises.

No. 3.] LATERAL LINE OF AMIA. 469

The system of canals leading from the pores of any one
group forms, as already stated, a dendritic structure, the trunk
of which is the common connection of the group with some
one of the main canals of the head. These main canals lie
almost exclusively in the deeper, more porous layer of the
dermal bones, near their under surface, and often project
in the form of a ridge below the general level of this surface.
Bridge (No. 4, pp. 607 and 608) considers this part of the bone in
Amia an “adherent parostosis,” resulting from the later ossifi-
cation of the subcutaneous tissues lying immediately under the
original ganoid plate, which is represented in the superficial,
thinner, and denser layer of the bone. The development, how-
ever, shows that the dermal bones grow mainly by accretions to
their upper surfaces, and that the deeper portion is the one
formed first, the canals in young specimens lying in it or above
it, and in no case below it.

In their passage from one bone to another, where the bones
are not suturally connected, the canals lie in a dense connective
tissue, which forms the deeper part of the cutis. This occurs
particularly between the frontal and nasal on either side, and
between the upper and lower ends of “he pre-operculum and the
squamosal and angular respectively.

The trunks of most of the dendritic systems and the proxi-
mal parts of their branches lie in the dermal bones, but in their
upper denser layer. The openings of the branches on the upper
surface of the bone present all the various stages between the
single opening and two openings about to become separate that
the pores do on the external surface of the head. The number
of openings on the upper surface of the bone does not, however,
usually correspond with the number of external pores; for where
the dermis is thick, as on the end of the nose, around the pos-
terior nares, and along the edges of the pre-operculum, there
may be one or more series of branches lying in it, entirely above
or beyond the bones; and where the dermis is thin, although
some of the branches pass directly through it to the external
surface, others, of the creeper-like form shown in Cut 1, %, are
continued along the outer surface of the bone in long channelled
lines, the bone not yet fully inclosing them.

470 ALLIS: [Vou. II.

Course of the Canals.

In tracing the canals through the dermal bones, the method
used was the following. The head of a fish was boiled a few
minutes, cleaned as much as possible, and then allowed to
macerate until the tissues were thoroughly softened. The dif-
ferent bones that contained any part of the canals of the lateral
system were then separated and carefully cleaned, the outside
with a brush, and the canals by forcing water through them
with a pipette. They were then heated in water and injected
with a blue gelatine solution, and after a short exposure to the
air, to allow the gelatine to set, cleaned and put in 50 per cent
alcohol. The smaller tubes of the system, that the gelatine
mass had failed to penetrate, were filled by forcing with a
needle little plugs of the cold injection mass into them from
the openings on the surface. Finally, the bones were scraped
on the inner surface below the canals, until under the micro-
scope every branch could be distinctly traced. In bones that
had been simply macerated without boiling, the canals and
branches were so filled with a chalk-like deposit that they could
not be successfully injected.

All the dermal bones containing any part of the canals of the
lateral system are shown in Figs. 40-43, Pl. XL. They are
enlarged two diameters, and all, excepting the suprascapula and
supraclavicula, placed in serial order as they occur in the fish.
In these figures the canals and dendritic systems lying in the
dermal tissues between the frontal and nasal, and at either end
of the pre-operculum, are shown, as well as all the ramifications
of the osseous canals, and the openings and channelled lines on
the outer surfaces of the bones. In Figs. 45, 46, and 47, Pl.
XLI., three views are given of the skull, natural size, with the
dermal bones in place. In Figs. 46 and 47 the canals are, for
fuller illustration, shown’ on both sides of the head, but the
dissections were made on one side only, and the perfect bilateral
symmetry shown in the drawing does not exist in nature.

The arrangement of the canals and dendritic systems shown
in these figures is the normal one, from which there are, how-
ever, frequent variations. There are on each side of the head
the three well-known canals: the infra-orbital, supra-orbital, and
operculo-mandibular, and in addition a supratemporal or occipital
cross-commissure.

No. 3.] LATERAL LINE OF AMIA. 471

1. /nfra-orbttal Canal.— The infra-orbital is the main canal of
the system, and is directly continuous with the lateral canal of
the body. It has four parts or regions, which develop some-
what independently: an antorbital, a suborbital, a squamosal
or temporal, and a post-temporal, —all continuous in the adult.
The antorbital part of the canal begins at a sharp bend in the
suborbital portion, immediately in front of the eye and below
the posterior nasal aperture. It runs forward and downward,
and partly encircles the nasal tube (which in Amia is the ante-
rior nasal aperture), running below and in front of it, and unit-
ing, on the top of the snout between the nasal tubes, with the
corresponding canal of the opposite side of the head. This ant-
orbital portion, which is more properly an anterior cross-com-
missure connecting the two main infra-orbital lines, seems to be
found in some other ganoids; for Traquair (No. 18, p. 181)
describes a similar connection in Polypterus bichir, and Leydig
(No. 9, p. 249) three of them in Chzmcera monstrosa,; but it is
not found in the teleostei, so far as can be judged from the
descriptions I have been able to find. According to Sagemehl
(No. 14, p. 36), it does not exist in the Characinidz, nor is it
found in Amzurus catus (No. 21, p. 265), and from my own exami-
nations I know it is not found in Salvelinus namaycush, Microp-
terus dolomieu, E:sox luctus, or Stizostedium vitreum. In Salve-
linus, a line of organs lying wholly in the external epidermis,
occupies about the position of the canal in Amia. These organs
belong to the same class as the canal organs. There are several
other lines on the head of Salvelinus, and corresponding ones
on that of Amia.

The suborbital part of the infra-orbital part is, in the adult,
connected at its anterior end, immediately in front of the pos-
terior nasal aperture, with the supra-orbital canal. There is no
direct union of the two lines here, the connection being of the
nature of a commissure formed by the anastomosis of two
dendritic systems, one of which is the terminal system of the
suborbital, and the other the fourth regular system of the supra-
orbital canal. Starting from this point, the suborbital canal
runs forward and downward to a point above the anterior end
of the maxillary, where it is joined by the antorbital canal or
anterior commissure; it then turns sharply backward, and lying
above the upper edge of the maxillary and jugal and below the

472 ALLELES. {Vou.H:
eye, it somewhat more than half encircles the orbit, extending
to a point above and behind it, and a little in front of the blind
upper end of the spiracular canal. The canal here turns sharply
backward, and, as the squamosal or temporal portion, is continued
backward and upward above the pre-opercular fold, to a point
between this fold and the upper end of the opercular opening,
where it gives off the supratemporal cross-commissure. The
post-temporal portion lies behind this commissure, continuing
at first in the line of the squamosal canal upward and backward,
above the upper end of the opercular opening, and then down-
ward and backward under the upper and posterior margin of
the operculum, to the hind edge of the supraclavicula, where
it joins the anterior end of the lateral canal of the body.

2. Supra-orbital Canal.— The supra-orbital canal begins a
little median to and behind the nasal tube. It runs at first
toward the median line, and then almost directly backward
above the eye, ending near the hind margin of the frontal,
and sending its posterior branches into the anterior part of
the parietal and squamosal. Behind the eye it is deflected
somewhat laterally, and anastomoses with the infra-orbital canal
at the bend in that line where the suborbital portion joins
the squamosal. The arrangement of the canals in the adult
at this point is such that the supra-orbital has always been
considered the direct continuation forward of the squamosal
or temporal portion of the infra-orbital, the two together being
described as the main lateral canal of the head, and the suborbi-
tal as one of its branches. The development of the canals
in Amia shows conclusively that this interpretation is wrong,
for the supra-orbital develops independently, its innervation is
different, and it only acquires its connection with the main
infra-orbital as an anastomosis after both canals have been fully
inclosed.

That this independence of the supra-orbital canal is not
peculiar to Amia is shown by the arrangement in the Chara-
cinidz as given by Sagemehl (No. 14, p. 36). In these fishes
the supra-orbital has, in the adult, the condition found in the
larva of Amia; that is, it is separate and distinct from the main
infra-orbital, broken off from it, as Sagemehl says, by the in-
trusion of the anterior end of the dilator operculi muscle,
which has in this fish an unusual insertion on the upper sur-

No. 3-] LATERAL LINE OF AMIA. 473

face of the post-orbital process. His description of the canal
in the Characinide shows that it agrees closely in general
course and position with that of Amia, beginning in both
forms at the anterior end of the nasal, median to the nasal
openings, and ending at the hind margin of the frontal,
where one or more branches are sent backward into the parietal.
The main canal in the Characinidz also agrees closely with
that in Amia, but Sagemehl describes the suborbital part of it
as a branch given off downward behind the eye, from the
extreme anterior end of what he considers to be the main tem-
poral or posterior division of the supra-orbital.

3. Operculo-mandibular Canal.— The operculo-mandibular
canal begins at the anterior end of the lower jaw, close to the
middle line of the head and close to the anterior end of the
canal of the opposite side, but without any connection what-
ever with it. Bridge (No. 4, p. 620), Sagemehl ( No. 13, p. 183),
Van Wijhe (No. Io, p. 288), and Shufeldt ( No. 16) all agree in’
stating that here the two canals are continuous; but this was
not the case in any of the many specimens I have examined.

Starting here as an independent line on each side of the
head, the mandibular part of the canal runs backward along
the lower inner margin of the ramus of the mandible, nearly to
its hind end, where it turns upward and passes out of the man-
dible immediately in front of and above the articular process for
the symplectic. It then turns sharply backward and is contin-
ued as the opercular part of the canal upward and backward
through the pre-operculum in the curved line of that bone,
Leaving the bone at its upper end it passes through a narrow
strip of dermis, and joins the infra-orbital canal, near the hind
end of the squamosal, turning forward at the point of union.
The mandibular and opercular portions of the canal develop as
two distinct canals, uniting later with each other to form a
continuous line and then uniting with the main infra-orbital.
These later connections in Amia are not always formed in other
fishes. In Fsoxr /uctus for example, the two portions always
remain, even in the adult, separate from each other and from
the infra-orbital ; and in Polypterus bichir, Amturus catus, and
Cottus gobio, although they unite to form a continuous line, they
do not unite with the main canal.

4. Supratemporal Cross-commissure. — The supratemporal

474 ALLIS. (VoL. II.

cross-commissure lies in the temporal region. Leaving the
main infra-orbital canal in the extrascapula it runs slightly for-
ward toward the top of the head, and meets there the end of
the corresponding canal of the opposite side, thus forming a
second connection between the two main lines, the first or
anterior one lying on the top of the snout, as already described.
These two are the only connections that are formed in Amia
between the lateral systems of the opposite sides of the head.

Leaving the several canals at irregular intervals, but at
definite places, are the trunks of the different peripheral canal
systems, each of which is represented on the outer surface of the
bone by a distinct group of openings.

Topography of the Peripheral Canal Systems.

1. Infra-orbital Canal. — The infra-orbital canal, which is the
direct continuation of the lateral line of the body, traverses in
succession the supraclavicula, suprascapula, extrascapula, squa-
mosal, postfrontal, post- and suborbitals, lachrymal, antorbital,
and ethmoid, joining in this last bone the canal of the opposite
side. Beginning at this point, in the middle line of the head,
the canal first runs forward, outward, and downward to the outer
anterior end of the arm of the V-shaped ethmoid, giving off at
about two-thirds its course through the bone a branch which
runs straight forward and upward to the surface of the bone,
and has there a single large opening. This branch canal repre-
sents the second peripheral system of the line, the first system
having disappeared at the middle line of the head, as will be
described later. It may be designated as trunk 2 (Fig. 41,
Pl. XL.), and the corresponding pore or group of pores on the
external surface as group 2.

Leaving the ethmoid, the main canal turns sharply backward
and upward, and entering the antorbital at its extreme anterior
end, runs upward and backward along the middle line of the
bone for about two-thirds its length. At this point, which is
approximately above the articular end of the maxillary, it turns
backward and leaves the bone at its hind margin. In the ant-
orbital the canal gives off the trunks of four peripheral systems:
trunk 3 at the beginning, trunk 4 at about one-third, and trunks
5 and 6 close together at about two-thirds its course through

No. 3.] LATERAL LINE OF AMIA. 475

the bone. Trunk 3 runs forward and outward, and lies so far for-
ward that it is not entirely inclosed in bone, leaving the canal
between the ethmoid and antorbital, giving off no branches
in the bone. Trunk 4 is directed downward, forward, and
outward, and has a single large opening at the surface of the
bone. Trunks 5 and 6 are given off almost at the same point,
but on opposite sides of the canal, just before or at the horizontal
bend in it. Trunk 5 is short, and is directed outward and down-
ward, It sends one long branch forward with two single and
one double opening, and one branch outward and downward
which has two short branches with five openings, making in all
seven single and one double opening in the system, all lying
along the lower outer edge of the bone. Trunk 6 is a direct
continuation upward and backward of the antorbital part of
the main canal, and is comparatively long, extending from the
bend in the canal to a point beyond the upper posterior margin
of the bone and a little in front of the posterior nasal aperture.
Here it runs directly into, and is continuous with, trunk 4
supra-orbital, the two trunks or some of their branches meeting
and anastomosing, and so forming a direct connection between
the two canals.

Trunk 6, infra-orbital, after leaving the antorbital bone at its
hind end, enters the little strip of dermal tissue (near the lateral
edge of which the posterior naris lies), which extends across the
top of the head between the lachrymals, and between the frontals
behind and the nasals and antorbitals in front. The canals that
traverse this strip of dermis lie in a deeper, denser stratum
of the corium, which corresponds in position to that of the
dermal bones in other places. Trunk 4 supra-orbital lies en-
tirely in this tissue, as does also 6 infra-orbital after leaving the
antorbital bone at its upper end. This latter trunk usually
sends one or more creeper-like branches forward, toward or into
the hind margin of the nasal, and one or more backward,
toward the median or anterior edge of the posterior nasal aper-
ture; but these branches are given off so near the point of
anastomosis that it is often difficult to determine to which one
of the systems they belong. In the two systems combined, in
the specimen used for illustration, there were on one side of the
head twenty-six pores, and on the other twenty-seven, three on
one side and five on the other being in the nasal.

476 ALLIS. [Vou. II.

The anastomosis of these two peripheral systems is not formed
until the fish is well advanced in age. In the large 15-month
specimen shown in Fig. 17, it is just forming. It is brought
about in the following way: trunk 4 supra-orbital, which leaves
its canal immediately in front of the frontal, runs forward and
laterally until it reaches a point median to the anterior edge
of the posterior nasal aperture. Here it turns backward, and
runs toward the anterior edge of the frontal, often extending
beyond this edge onto the upper surface of the bone. Trunk 6,
infra-orbital, lies almost exactly in the line of the main part of
trunk 4, supra-orbital, the two trunks and their system of pores
and branches growing directly toward each other until either
the trunks or some of their branches come squarely together
and unite at or near the bend in trunk 4, enlargements being
usually formed at the points of union. A remnant of the divid-
ing wall remains, indicating the line where the two systems
came together. Zzzs zs the only place in the entire lateral system
of Amia where an anastomosts below the surface occurs; for, even
where terminal branches of the same or neighboring systems are
united below the surface, as shown in Fig. 4o, Pl. XL., z%, the
union, so far as I have been able to determine, is always first
formed at the surface by the fusion of two pores in a manner to
be fully described in treating of the development of the system.

Leaving the antorbital at its hind edge, at about two-thirds
the length of the bone, the main canal enters the upper anterior
edge of the lachrymal, and, running backward along its middle
line, gives off the trunks of three peripheral systems, — trunk
7, immediately on entering the bone, trunk 8, about half-way
through it, and trunk 9, just before leaving it. All these trunks
run outward, downward, and forward. Trunk 7, which is short,
lies just above a small notch in the lower anterior corner of the
lachrymal. Its system has three large openings along the upper
edge of the notch, and five along a slender branch directed
backward from it, making eight in all.

The openings of the next two systems, 8 and 9, are arranged
along the entire lower, lateral edge of the lachrymal. No. 8
has three double and two single openings, and No. 9 two double
and seven single ones. One of the double openings in this last
system is formed by the anastomosis of two branches at their
outer ends, an instance of the fusion of two pores in adult life

No. 3.] LATERAL LINE OF AMIA. 477

already referred to. The posterior branch of this system is
continued as a groove onto the outer surface of the first sub-
orbital.

Leaving the lachrymal, the canal passes through the middle
of the two suborbitals, and enters the lower postorbital near its
lower anterior angle. Running upward and backward in this
bone, to about one-quarter its length, the canal turns directly
upward, traverses the rest of the bone, and enters the upper
postorbital at the anterior quarter of its lower edge. Turning
somewhat forward here, it passes through this bone, turning
directly upward again and then backward, just as it leaves it,
to enter the postfrontal.

In its course through the sub- and postorbitals, the canal
gives off the trunks of seven peripheral systems. The first one,
trunk 10, leaves the main canal near the hind end of the first
suborbital. Dividing immediately, it sends one branch forward,
with five large openings near the lower edge of the bone, and
one backward, ending in a groove on the anterior end of the
outer surface of the second suborbital, making six openings in
all, three of which at least are double. Trunk 11 is given off
upward and outward near the hind end of the second suborbital.
It sends one branch forward along the outer edge of this bone
toward the end of the branch from trunk 10, and another
backward into the lower postorbital, the two branches having
sixteen openings in all, five, three of which are double, being
in the suborbital, and eleven single ones in the postorbital.
Trunk 12 leaves the canal where it turns directly upward at
about the middle of its course through the lower postorbital.
It is directed downward and backward, and gives off several
branches, each of which divides again one or more times, the
longer branches lying mostly parallel to the main trunk. It has
in all thirty-seven openings, which lie in a group a little in front
of and below the middle point of the bone. Trunk 13 is short,
and is given off just as the main canal enters the upper post-
orbital. It divides immediately, sending one branch, with eight
openings, downward and backward into the lower postorbital,
and another, with twelve openings, upward and backward into
the upper postorbital, making twenty openings in this system.
Trunk 14 is given off at about three-quarters of the course of
the canal through the upper postorbital, the bone here being

478 ALLIS. [Vot. II.

very thick, and is directed backward and outward. It sends a
large branch backward to about the middle of the bone, and
another forward toward the eye, in front of the main canal,
both of them branching several times, and having in all thirty-
seven openings, all lying in front of the middle point of the
bone, and extending almost to its extreme anterior edge.

The canal, after leaving the upper postorbital, enters the
postfrontal, where it has a curved course, turning gradually
backward till it reaches the median edge of the bone at about
its middle point. Here it turns directly backward, and, running
between the frontal and postfrontal, enters the squamosal at
about the middle of its anterior end. It traverses this bone
from end to end, running directly backward with a slight lateral
bend near the hind end, where it is joined by the opercular
canal.

In the postfrontal, the canal lies entirely in what Sagemehl
(No. 13, pp. 184 and 185) considers merely the outer, denser,
and harder part of the primary ossification of the postorbital
process. This ossification, which is traversed by a canal of the
lateral system, and the prefrontal, which is not, are both con-
sidered by him as exceptional instances of primary ossifica-
tions that have acquired secondarily the surface characteristics
of true dermal bones. He calls attention to the earlier work
of Bridge (No. 4, p. 607), who describes each of these bones
as having an outer dermal component wholly separate from the
underlying primary ossification; but he nevertheless strongly
asserts that this separation can only be made by fracture.

In the several specimens which I have examined with special
reference to this point, I have always found the prefrontal a
single bone and the postfrontal in two parts. The prefrontal
(Cut 2, gvf) lies under the outer anterior corner of the frontal,
projecting slightly beyond it, but in no place rising above the
level of its under surface. The projecting edge is continuous
with the edge of the frontal, which in this place is bevelled, and,
although roughened, it has neither the character nor appearance
of the outer surface of the dermal bones. In the unprepared
head it is covered by thick dermis, and its roughened edge gives
attachment to strong membranes. It lies deep and is not
traversed by the main cranial canals or any of their branches.

The dermal portion of the postfrontal (Cut 2, psf) is a small

NO. 3] LATERAL LINE OF AMIA. 479

bone, somewhat triangular in shape, exactly filling a large notch
extending from the middle of the lateral edge of the frontal to
the hind edge of the bone. Its small posterior end usually fits
into a notch in the anterior end of the squamosal, which over-
laps somewhat its lateral edge. It rests directly upon the deeper
postorbital ossification, and is so closely connected with it, that
in attempting to remove it in fresh specimens, one of the bones
is usually broken, and a fractured surface obtained; but in skel-
etons properly prepared,— by maceration or by boiling, — the

ag 2a out

we wwe
Pi Ae al
Lat

Ee

Cut 2.— A, top view of frontal, postfrontal, prefrontal, and squamosal bones,
showing the postorbital ossification in place; 4, side view of same; C, top view of
postorbital ossification after removing the dermal bones; ZY, top view of prefrontal
after removing the frontal; /*, frontal; zf c, infra-orbital canal; om. c, operculo-
mandibular canal; vf, prefrontal; psf, postfrontal; /s¢, postorbital ossification;
spc, spiracular canal; sg, squamosal.

two bones are easily parted, leaving a clean and perfect surface
of separation. The postfrontal projects beyond the postorbital
ossification in front, and forms part of the roof of the orbit.
The lateral edge of this part of the bone is thickened, frequently
having a rib-like projection along its under surface, as if the
edge of the bone had been turned down and a little under.
The upper corner of this thickened edge and the corners of

480 ALLIS. [Vo. II.

the bones immediately behind it are slightly bevelled, thus form-
ing a shelving surface which looks upward and outward, and,
when the cheeks are distended, serves as an articular surface for
the overlapping edge of the upper postorbital. This lateral rib
or thickening only extends one-half the length of the bone,
which behind it is much smaller and narrower, the lateral edge
and under surface being cut away by the postorbital process, a
small portion of which here comes to the level of the outer
surface of the dermal bones (Cut 2).

The postorbital ossification has roughly the shape of an
inverted pyramid, one edge of which projects laterally and forms
the hind boundary of the orbit. The upper outer angle of the
ossification expands into an elongate cap-like piece, which over-
hangs the pyramid in front, behind, and laterally. Its outer
surface is divided into two portions by a strong longitudinal
line, which is continuous in front with the lower outer edge
of the postfrontal, and behind with the corresponding edge of
the squamosal. The part above this line is the small portion
that forms a part of the external surface of the dermal bones,
and it has in every particular the characteristic appearance of
these bones. The part below the line lies at a deeper level and
gives attachment to portions of the levator arcus palatini and
adductor mandibule muscles. The line separating these two
surfaces is sharp and strong, while that separating the upper
surface from the dermal postfrontal is faint and indistinct, and
might easily be overlooked.

The postorbital ossification gives support on its upper surface
to the frontal and squamosal as well as to the postfrontal, but
neither of these bones are closely attached to it. The squamosal
projects slightly under the frontal and postfrontal, and separates
the main lateral canal from the spiracular canal, which opens
widely on the upper surface of the skull immediately below it.
The spiracular canal has been fully described by Sagemehl
(No. 13, p. 200) and by Wright (No. 20, p. 492).

The infra-orbital canal enters the postfrontal in front of the
lateral edge of the postorbital ossification (Cut 2, zzf. c.), and
no branch is given off in its course through it. At the median
edge of the bone it forms an anastomosis with the supra-orbital
canal, and a double system is given off; that is, one formed by
the complete fusion of two systems, one belonging to each of

No. 3.] LATERAL LINE OF AMIA. 481

two anastomosing lines. There are seven such systems on the
head of Amia, all of them essentially similar. Their pores
multiply exactly as do those of a simple system, but the double
trunk increases greatly in width along the canal, and the primary
division of it is so deep that the trunk becomes practically a
part of the canal (Cut 3, e. fg), its two primary branches ap-
pearing as the trunks of separate systems. This is the con-
dition found at the point of anastomosis of the infra-orbital and
supra-orbital canals. The two systems that have fused here are
Nos. 15 infra-orbital and 7 supra-orbital, and that part of the
main canal lying between the frontal and postfrontal and extend-
ing as far as the anterior edge of the squamosal is in reality the

2 a

Cut 3.— Diagrammatic representation of the formation of a double pore and
system: a@, 0, and c, two pores approaching and fusing; d, double pore and tube; e
and 7, the same, undergoing its first division; g, double system after second division
of pore and tube.

trunk of the double system. The anterior primary branch of
this system (Fig. 40. Pl. XL.) runs forward and outward into
the postfrontal, sending one branch medianward into the lateral
edge of the frontal, and having thirty openings in all, three of
them in the frontal. The other issues at the anterior edge of
the squamosal, sending one branch forward and another back-
ward, with ten openings in the postfrontal and thirteen in the
squamosal.

Trunk 16, the next regular one, is given off in the squamosal
beyond the middle line of the bone, and is a short trunk directed
laterally. It sends one long branch forward, overlapping the
posterior branch of trunk 15, and a shorter one backward. It
has twenty-nine openings, all lying near the lateral edge of the
bone. Behind this trunk the main infra-orbital is joined by the

482 ALLIS. [Vou I.

operculo-mandibular canal which comes up through the pre-oper-
culum. At the point of union a double system is formed by
the fusion of system 17 infra-orbital with 17 operculo-mandibu-
lar; but the trunk of this system has been pushed out of its
proper place down into the opercular line, and les with all its
branches in the dermal tissue between the upper end of the pre-
operculum and the lateral edge of the squamosal. Its primary
branches are not so widely separated as those of the double
trunk 15-7. They are directed one forward and the other
backward, with all their branches running downward and with
eighteen openings in all.

Leaving the squamosal at its hind end on the short shelving
surface which is overlapped by the extrascapula, the main
canal passes through a strongly raised portion on the under
surface of the latter. It then traverses the suprascapula, enter-
ing it on its upper surface near its lateral edge, where it is
overlapped by the extrascapula, and leaving it on its under sur-
face, where it, in turn, overlaps the supraclavicula. Entering
the supraclavicula on its upper surface at its upper end, it
passes downward and backward through this bone, leaving it
on its under surface to enter the first scale of the lateral line
of the body.

The extrascapula overlaps the squamosal in front and the
suprascapula behind, so that the canal only passes through the
middle third of the bone, giving off trunk 18, with thirty-six
openings, near its entrance, and trunk 19, with twenty-two open-
ings, near its exit from the bone. Trunk 20 is given off in the
suprascapula just as the canal leaves the bone. It runs back-
ward and outward, and has thirty-nine openings, some of them
double or triple. Trunk 21, given off soon after the canal
enters the supraclavicula, runs backward, and, branching once,
has two openings only at the hind edge of the bone. Trunk
22, the last one of the cranial system, is also trunk 1 of the
lateral line. The supraclavicula overlaps the first scale of the
lateral line, and the double trunk 22-1 is given off at the point
where the main canal leaves the supraclavicula and turns inward
to enter the scale. It is a long, open channel on the under sur-
face of the bone, running downward and backward as a direct
continuation of the main canal, and having a single large open-
ing at the hind edge of the bone.

No. 3.] LATERAL LINE OF AMIA. 483

2. Lateral Line of the Body.— The first scale of the lateral
line (Fig. 44, Pl. XL.) is always an irregular one. It is smaller
than those immediately following it, much thickened, and
roughly triangular in shape. It extends under the supraclavi-
cula and lies in the direction of trunk 22-1, at an angle to the
following scales of the line. The lateral canal enters it near its
front edge, and leaves it on its inner surface, entering the next
scale on its outer surface, and leaving it on the inner after trav-
ersing approximately its middle third. It passes in the same
way through the other scales of the line normally, giving off in
each a peripheral canal system, similar to those found on the
head. The trunk of each of these systems is given off at the
extreme posterior end of the section of canal contained in the
scale to which the system belongs. It lies in the direction of
the canal and soon branches dichotomously, sending one branch
upward and one downward, each with one or more openings
on the outer surface of the scale. These openings lie near the
hind edge of the scale, and are approximately concentric with
it. The system of the first scale of the line is very irregular.
It always has fewer surface openings than that of the next
following scale, or no openings at all; the trunk is present, but
in a more or less aborted condition.

3. Supratemporal Cross-commissure. — The supratemporal
cross-commissure is given off medianward from the main canal,
between trunks 18 and 19, in the extrascapula ; it traverses the
length of this bone in about its middle line and joins, on the top
of the head, the corresponding canal of the other side. In the
full commissure there are two peripheral systems on each side
and a double one in the middle. The two primary branches of
this median system have become so widely separated in the
adult that there are apparently three systems on each side of
the head, the trunks of all of which run backward and laterally,
with most of their branches directed backward and medianward.
The median one of these three systems, although only a half-
system, may be called No. 1, and it has in the specimen figured
eight osseous openings. The next system, No. 2, has nineteen,
and the lateral one, No. 3, twenty-five.

4. Supra-orbital Line.— The supra-orbital canal begins near
the anterior end of the nasal. It runs for a short distance
backward and medianward, and then, turning sharply backward,

484 ALLIS. [Vot. II.

continues in about the middle line of the bone to its hind edge,
and then passing through the strip of dermal tissue, lying be-
tween the frontal and nasal, enters the frontal at about the
middle of its anterior edge. It traverses this bone along its
middle line for about half its length and then curves gradually
outward until it reaches the lateral edge of the bone, where it
meets and anastomoses with the infra-orbital canal, as already
described. Leaving this canal immediately, it runs medianward
and backward to the hind edge of the frontal, and then into the
anterior and lateral part of the parietal, where it comes to the
surface and ends.

Trunk 1 of this line leaves the canal at its extreme anterior
end, and, running forward and laterally, has two openings at
the outer edge of the nasal, immediately behind the notch
made in this bone for the passage of the anterior naris. Trunk
2 leaves the canal exactly at the bend, and runs forward toward
the anterior edge of the nasal, where it branches regularly, and
has four openings on the surface of the bone, three single and
one double. Trunk 3, given off near the middle of the bone,
runs medianward and forward, and has eight single and six
double openings arranged along the median edge of the bone.
Trunk 4 is given off nearly opposite the posterior nasal aper-
ture from that part of the canal lying in the dermal tissue
between the nasal and frontal. It runs forward and outward,
turning backward along the median edge of the nasal aper-
ture, and anastomosing with trunk 6 infra-orbital, as already
described. Trunk 5 is given off laterally at about one-third
the length of the frontal, and trunk 6 medianward at about
the middle of it: both are short and stout. No. § sends a
long branch backward, overlapping the anterior branches of No.
6, and another forward almost to the anterior edge of the
frontal. In front of this last branch, and also in front of several
of the smaller branches, there are deeply channelled lines in
which the epidermal canals of the system are continued onward
along the upper surface of the bone, partly imbedded in it, and
extending in some cases into the strip of tissue in front of it,
reaching even tothe hind edge of the posterior nasal aperture.
System 5 has twenty single openings and eleven double or
channelled ones, and system 6, thirty-three single and ten double
or triple ones. Trunk 8 is a direct continuation backward of that

No. 3.] LATERAL LINE OF AMIA. 485

part of the canal lying beyond the point of its anastomosis with
the infra-orbital line ; two of its branches lie in the frontal, both
directed backward and laterally, one reaching to the extreme
hind edge of the bone, and the other sending a short branch
beyond this bone into the squamosal. The two branches have
six single and three double openings in the frontal and two in
the squamosal. A third and principal branch is sent backward,
directly in the line of the trunk, into the parietal, near its
anterior and lateral corner. It runs straight backward in this
bone, sending six branches to the surface, making seventeen
openings in the entire system.

5. Operculo-mandibular Line.— Close to the anterior end
of each ramus of the mandible there is a single large opening
which marks the beginning of the mandibular line. The tube
from this opening leads backward and outward laterally into the
anterior end of the mandibular canal, which, starting here, runs
backward along the lower inner edge of the dentary. Leaving
this bone, it enters the angular, and, turning upward near its
hind end, passes out of it, and out of the upper surface of the
mandible immediately in front of and above the articular pro-
cess for the sympletic. It then turns sharply backward, and
passing through the thick dermis between the angular and pre-
operculum, enters this last bone on the dorsal surface of its
lower anterior end. It passes through the entire length of this
bone, lying near its inner deeper edge, and then passing again
through a strip of dermis it enters the squamosal and unites
with the infra-orbital canal.

Along the mandibular part of the canal there are ten and a
half peripheral systems, seven in the dentary and three and a
half in the angular, most of them branching several times.
Trunk 1 is a direct continuation forward of the main canal,
which begins here, and has no connection whatever with the
corresponding canal on the other side of the head. It has a
large single opening at the front end of the dentary near the
symphysis. Trunks 1 to 10 lie along the anterior horizontal
part of the canal. No. 10 leaves it at the. point where it turns
upward near the hind end of the angular, and has one branch
running straight backward as a direct continuation of the main
canal. In these ten systems there are seventy-four openings,
twenty-eight of them plainly double.

486 ALLIS. [Vou. II.

System II. is a double one formed at the point where the
mandibular and opercular parts of the canal unite. Its primary
branches are widely separated, one of them lying in the angu-
lar, near the upper end of the bone, and the other in the thick
dermis between the angular and pre-operculum. The former
has twenty-eight openings, eighteen in the angular and two in
the supra-angular; and the latter, seven, all in the dermis,
making twenty-seven in all for the entire system.

In the opercular part of the canal, the trunks of five peripheral
systems are given off, Nos. 12 to 16, all of them running out-
ward, and backward or downward, toward the outer edge of the
bone, where each has several large irregular openings, approxi-
mately thirty-four in all. Trunk 17, the last one of the line,
has united with 17 infra-orbital, as already described, to form a
double trunk and system which lies wholly in the dermis be-
tween the pre-operculum and squamosal.

The mandibular canal in Micropterus dolomeus and in Salve-
linus namaycush passes through the articular, and not through
the angular, as in Amia and in Polypterus (No. 18, p. 182). In
those two teleosts the angular is a small bone lying below or
behind the articular, which is large and has the same position
relative to the dentary that the angular has in the two ganoids.
The articular in Polypterus is small, and lies below and behind
the angular; and in Amia, what Bridge has called ossicle holds
a corresponding position. This ossicle is, according to him,
formed by the ossification of the hind end of Meckle’s cartilage.
It is covered by a small ganoid plate; and Bridge suggests that
it may represent, at least in part, the articular of teleosts. But
neither it nor the overlying dermal plate is traversed by a lateral
canal, while the angular is. This last bone in the ganoids has
doubtless been so called because it is entirely dermal, agreeing
in this respect with the angular in teleosts, and differing from
the articular, which has been supposed to be always pre-formed
in cartilage. As the teleostean articular is in some forms trav-
ersed by a lateral canal, this distinction does not hald good, and
the names now used for the bones in the ganoids should proba-
bly be changed.

6. Summary.—In this specimen, which is strictly a normal
one, there are in all xznety-three peripheral canal-systems, forty-six
on each side of the head, and a median one in the supratemporal

No. 3.] LATERAL LINE OF AMIA. 487

cross-commissure. This median system ts a double one (Cut 3,
g:), and there are on each side of the head three other similar
systems, making seven in all. One is formed by the fusion of
systems 15 infra-orbital and 7 supra-orbital; a second one by
the fusion of 17 infra-orbital and 17 operculo-mandibular, and
the third by the union of the two portions of the operculo-
mandibular canal. This last system, being formed in the line
of its canal, is called No. 11 of that line. The other two
being formed at the points of anastomosis of two different
lines, have each been given a double number which indicates
the position of the system on each of the lines to which it
belongs. Counting it this way, there are three peripheral
systems along the supratemporal cross-commissure, eight along
the supra-orbital line, seventeen along the operculo-mandibular,
and twenty-one along the infra-orbital; but as a median double
system has disappeared at the point where the two infra-orbital
lines unite on the top of the snout, there are properly twenty-
two systems along this line, seventeen of them up to the point
where it is joined by the operculo-mandibular.

Surface Pores.

The peripheral canal systems are represented on the surface
of the head by more or less distinct groups of pores. The
number of pores in some of these groups can be easily de-
termined by surface examination; but in many cases several
groups are so run together that only the general position of
each group and the total number of pores in the series can be
ascertained.

For the following description three specimens were used :
two males, one 17 in. and the other 20} in. in length, and a
female 27 in. long. The number of pores given in the different
groups, unless otherwise specified, applies only to the left side
of the head, a comparison being made in every case with the
number of openings in the skeleton. The arrangement of the
surface pores in the larger male is shown in Figs. 20, 21, and
22, Pie XVI.

1. Lnfra-orbital Line. — The first group of the infra-orbital
line, group 2, lies near the base of the nasal tube, a little in
front of and median to it. It has usually one or two pores

488 ALLIS. [Vor. Il.

only, arranged, where there are two, across the top of the snout.
In the 17-inch specimen, which seemed an exceptional one in
many ways, there were three pores in this group on each side
of the head, the third pore lying a little in front of, and lateral
to, the two regular ones. In no other specimen were more than
two pores found. In the skull there was but one opening in the
ethmoid corresponding to this group, showing that the division
of the trunk lies in the dermis entirely above the bone.

Group 3 lies near the edge of the upper lip, below and in front
of the nasal tube, and has but one pore, or two lying parallel
to the edge of the lip. As the trunk of this system issues in
the dermis between the ethmoid and antorbital, there is no cor-
responding opening in the skull.

Group 4 lies near the edge of the upper lip, lateral to and
below the nasal tube, and usually has two pores in the adult.
In the 17-inch male there were two pores in the group on each
side of the head; in the 20}-inch male, two on one side, and
four, arranged in a square, on the other; and in the 27-inch
female, three, lying in a line parallel to the edge of the lip. In
the skull there was a single opening only.

Group 5 lies back of and lateral to the nasal tube, and below
the dermal crease which extends from the base of the tube
toward the posterior nasal aperture. The number of pores in
this group varies, as does also their arrangement, and they are
nearly, if not quite, continuous with those of group 7. In the
17-inch specimen there were eight pores in the group; in the
204-Inch one, nine; and in the 27-inch one, nineteen. One or
more of the anterior pores of the group lie close to the dermal
crease before mentioned, and directly opposite the pores of
group I, supra-orbital. In the skull there were eight openings
in this system.

Group 6 belongs in position to the supra-orbital line, and will
be described with group 4 of that line, with which it is con-
tinuous.

Group 7 lies behind, and lateral to, group 5, considerably
below the posterior nasal aperture, and immediately above
group 8. ,

Groups 8 to 11 lie along the upper edge of a deep furrow
which separates the maxilla from the side of the head. The
maxilla, when the mouth is closed, shuts under the overhanging

No. 3.] LATERAL LINE OF AMIA. 489

edges of the lachrymal and first suborbital, and over the lower
edge of the second suborbital and the lower anterior corner of
the lower postorbital, fitting into a depression on the outer sur-
face of these two bones. The lower edges of the lachrymal and
first suborbital, and the upper edge of this depression from the
upper edge of the furrow, which is continued a short distance
downward and backward behind the maxilla along the hind
edge of the mandible. In young specimens the edge of this
furrow, which may be called the supramaxillary furrow, is
straight, and the pores of groups 8 to 11 are closely arranged in
a line along it; but in the adult it is strongly ogee-shaped, and
many pores may lie above the marginal row, especially immedi-
ately below or just in front of the eye. Group 12, which is
usually continuous with group 11, lies immediately behind the
maxilla, near the lower edge of the lower postorbital, and often
extending beyond it. It is usually continuous with groups 13
and 14, which lie above and before it, directly behind the eye,
superficial to the postorbitals and below the lateral edges of the
postfrontal and squamosal. In these eight groups, Nos. 7 to 14
inclusive, there were in the 17-inch specimen one hundred and
two pores, and in the 27-inch one, three hundred and thirty-
three. In the 20}-inch male, either system 13 or 14 was want-
ing (probably No. 13), a condition frequently found, and there
were accordingly only one hundred and one pores in groups 7
to 14, while in the skull, where the number of groups was nor-
mal, there were one hundred and forty-nine openings.

The pores of the double system, infra-orbital 15, supra-orbital
7, and those of group 16 infra-orbital, form a continuous line,
extending from immediately above and behind the eye, nearly
to the front edge of the extrascapula, which edge lies in line
with the upper end of the pre-opercular fold. Some of the
pores of these two groups extend laterally beyond the edges of
the postfrontal and squamosal. In the 17-inch specimen there
were eighty-nine pores in the two groups; in the 201-inch one,
seventy-eight ; and in the 27-inch one, two hundred and eighty-
eight. In the skull there were eighty-two openings.

Groups 18 and 19, and group 3 of the supratemporal commis-
sure, form one large surface group. Groups Ig and 20, and 20
and 21, are also more or less continuous, but easily distinguish-
able, as seen in the figures. Groups 18 and Ig infra-orbital

490 ALLIS. [VoL. II.

and the three groups of the supratemporal line all lie superfi-
cial to the extrascapula. They extend slightly beyond its mar-
gins, and form, with the same groups on the other side of the
head, a nearly continuous series which lies behind the line of
the pre-opercular fold and in front of the first row of scales.
In the 17-inch specimen there were ninety-four pores in these
five groups on one side of the head; in the 20}-inch one, one
hundred and two; and in the 27-inch one, two hundred and
fourteen. In the skull there were one hundred and ten open-
ings.

Group 20 lies ona fleshy pad above, and immediately in front
of, the upper end of the opercular opening, behind the extra-
scapula and opposite the first two or three scales behind that
bone.

Group 21 is much smaller than No. 20, and lies on a similar
but smaller pad above and behind the upper end of the opercular
opening, above the upper edge of the supraclavicula and oppo-
site the third and fourth, fourth and fifth, or fourth, fifth, and
sixth scales, behind the extrascapula. The pores of this group
often extend onto the bases of the scales, but when this occurs,
the canals leading to them lie entirely in the dermis or epider-
mis, not entering the bony part of the scale at all. There were
in groups 20 and 21, in the 17-inch specimen, thirty-nine pores ;
in the 20}-inch one, fifty ; in the 27-inch one, ninety-one; and
in the skull forty-one openings.

Groups 20 and 21 and those found on the first five scales of
the lateral line in the 27-inch specimen-are shown in Fig. 39, PI.
XXXIX. The hind edge of the gill cover is cut off in order to
show the position of the supraclavicula and the arrangement of
the scales immediately behind it. In this specimen, the pores
of group 21 extended onto the base of the sixth scale, counting
always from the hind edge of the extrascapula, and the lateral
line began on the eighth. In the 17 and 203 inch ones, group
21 only extended to the level of the fifth scale; and the lateral
line began on the seventh.

2. Lateral Line of the Body.—The first scale of the lateral
line is always irregular, and without the thin portion which
extends beyond the bone in the other scales, and which gives
them their rounded outline. Between it and the hind edge of
the supraclavicula there is a single large opening (Fig. 39, PI.

No. 3-] LATERAL LINE OF AMIA. 491

XL., p. 22, z, 7), which is the undivided original double pore
formed by the fusion of the posterior peripheral system of the
head with the anterior one of the lateral line. Although com-
pressed and flattened and hidden from view under an overhang-
ing fold of dermis, this pore is the largest one in the entire
lateral system of Amia.

The peripheral system of the first scale is always more or
less aborted. In the 27-inch specimen it had but two pores on
one side of the body and four on the other, and in the 17 and
201 inch specimens but one pore on each side. In several
other specimens there were no pores at all in this system, the
scale projected but little beyond the hind edge of the supracla-
vicula, the end of it being cut squarely off across the line of the
canal so that the exposed portion was triangular in shape, with
a straight edge behind.

There were, in the several specimens in which they were
counted, sixty-seven or sixty-eight full scales in the lateral line.
In the second scale of the line there were, in the 17-inch
specimen, seven openings; in the third, six ; and in the fourth,
seven. In the 27-inch one (Fig. 39) there were eight in the
second scale, twelve in the third, and eleven in the fourth. In
the following scales, for about half the length of the line,
the peripheral systems are fairly constant and regular; but
behind that there is great irregularity, some of the scales, and
often several in succession, having no pores at all, and nearly all
of them having a much smaller number than those in the first
half of the line. Toward the tail there are usually but one or
two pores in a scale (Fig 3, b, Pl. XXX.), and the development
here is often so greatly arrested that the lateral canal, through
one or more scales, is an open channel.

Behind the last full scale of the line the canal turns slightly
downward, and enters the tail fin between two of its rays. It
then runs straight backward about three-fourths the length of
the fin, and ends in a single terminal pore, which is usually
closed secondarily. Along this part of the canal there is only
a single row of pores, those toward the end of the line being
small, and often closed.

3. Supra-orbital Line. — Group 1 of the supra-orbital line lies
near the base of the nasal tube, close to the dorsal edge of the
dermal crease, which extends backward from it. There are

492 ALTERS: [ VOL. Te

usually only one or two pores in this group; but in the 27-inch
specimen there were six on one side and five on the other, all
lying along the edge of the crease. As already stated, this
group lies close to group 5 infra-orbital, the two being separated
by the crease. There were two openings in the nasal bone
corresponding to this group.

Group 2 has usually four pores, which form a slightly curved
line, extending backward and medianward from the anterior
edge of the nasal tube, and lying nearly in the line of the
hind edge of the ethmoid. The group is a prominent one,
and is most regular and constant in shape and position. In
the 27-inch specimen it contained seven pores on each side of
the head, all arranged in line as usual; but on the left side the
median pore of the group, which approached closely the ante-
rior pore of group 3, was dividing at right angles to the line of
the group, the new pore lying in front of the line of the rest of
the pores. In the 17-inch specimen the lateral pore of the
group, on the right side, had undergone a complete division at
right angles to the line of the group. These two instances
were the only ones noted of a pore lying out of the regular line.

Group 3 lies near the middle line of the head, directly above
the nasal sack. In the 17-inch specimen it had nineteen pores ;
in the 20-inch one, twenty-four ; and in the 27-inch one a still
greater number; but in this specimen the group was so continu-
ous with groups 4 supra-orbital and 6 infra-orbital that the exact
number of pores in each could not be determined.

The double group, 4 supra-orbital and 6 infra-orbital, lies close
to the posterior naris. A part of the pores lie in a half-circle
along the median edge of the aperture, and the rest of them
form two groups, one lying in front of and median to the aper-
ture, and the other behind and median to it, or directly behind
it. This last group belongs entirely to system 4 supra-orbital,
and the other entirely to system 6 infra-orbital ; while the half
circle of pores belongs partly to each of these systems. The
group is usually continuous with group 5 supra-orbital. In the
17-inch specimen it had twenty-eight pores; in the 201-inch ©
one, twenty-four ; and in the 27-inch one, a much larger number,
but it was so continuous with groups 3 and 5 that the number
of pores could not be determined. The two systems lie almost
entirely in the dermis, so that in the skull there were only five

No. 3.] LATERAL LINE OF AMIA. 493

openings, all in the nasal, and all belonging to group 6 infra-
orbital.

Groups 5 and 6 are almost always continuous, both lying be-
tween the eyes on top of the head, No. 5 almost directly behind
the posterior nasal aperture, and No. 6 much nearer the middle
line of the head, and extending somewhat behind the eye. In
the 17-inch specimen there were in these two groups one hun-
dred and nine pores; in the 20}-inch one, one hundred and six-
teen, and in the skull eighty-two openings. In the 27-inch
specimen these groups were continuous with 3 and 4 supra-
orbital and 6 infra-orbital. The total number of pores in the
five groups in this specimen was three hundred and fifty-four ;
in the 17-inch one, one hundred and fifty-six, and in the 20}-
inch one, one hundred and seventy-four.

Group 8 lies behind group 6, not so near the middle line of
the head, and about half way between that group and the supra-
temporal cross-commissure. It had in the 17-inch specimen
twenty-nine pores; in the 20}-inch one, thirty-two; in the 27-
inch one, ninety-three ; and in the skull, seventeen openings.

4. Operculo-mandibular Line. — Group 1 of the operculo-man-
dibular line in all the numerous specimens examined, excepting
only the unusually large 27-inch one, had only a single large
pore belonging to it; the two pores, one on each side, lying
directly in front of the gular plate, near the tip of the lower
jaw and close to its middle line. In the 27-inch specimen there
were two pores on each side of the head, lying in a line trans-
verse to the direction of the trunk of the system as seen from
below.

The pores of group 2 and those of the succeeding groups to
No. 10 are arranged in regular lines, approximately parallel to the
inner edge of the mandible, but the lines of the different groups
are broken, and overlap, or are continuous with each other, so
that the number of pores belonging to each cannot be deter-
mined. In groups I to 10 inclusive, in the 17-inch specimen,
there were sixty-six pores; in the 20}-inch one, seventy-two ;
and in the 27-inch one, one hundred and twenty-five. In the
skull there were seventy-four openings, many of them double.

Group 11 lies at the hind end of the mandible, in front of and
above group 10, and about half way between the maxilla and
the lower end of the pre-opercular fold. It lies on both sides

494 ALLIS. [Vot. II.

of the posterior prolongation of the supramaxillary furrow. The
part below the furrow lies superficial to the angular element of
the mandible, and is much larger than the other part which lies
wholly in the dermis. In the 17-inch specimen there were
sixteen pores in this group, thirteen of them in the lower por-
tion of it; in the 20}-inch one, twenty-four, eighteen below the
furrow ; and in the 27-inch one, sixty-four, with fifty-eight below
the furrow. In the skull there were twenty-seven openings in
the angular and supra-angular, corresponding to the lower por-
tion of this group.

Groups 12 to 17 extend from the lower end of the pre-opercu-
lar fold almost to the lateral edge of the dermal bones of the
top of the head. The pre-operculum lies just in front of the
surface fold, and the pores of the different groups lie mostly in
lines transverse to and extending on both sides of it. Some of
them extend to the very edge of the fold, and others, at the
upper end of the series, reach onto the surface of the upper
postorbital. In this series of groups, in the 17-inch specimen
there were one-hundred and fifty-two pores; in the 20}-inch
one, one hundred and fifty-five; and in the 27-inch one, two
hundred and five; while in the skull there were only eighty-four
large and irregular openings, showing that the branches of the
different systems lie mostly in the dermis.

The total number of pores on one-half of the head of the
17-inch specimen was seven hundred and sixty-two; of the
201-inch one, seven hundred and twelve; and of the 27-inch
one, eighteen hundred and thirty-one. Other adult specimens
examined had intermediate numbers, showing that the pores
continue to divide, the canals leading to them increasing corre-
spondingly in number and extent, up to a late period, if not
throughout life.

il. , POSTLABVAL. FORMS.
1. Primary Pores.

As all the pores and branches of the peripheral canal-systems
arise by the repeated dichotomous division of previously exist-
ing pores and branches, it is evident that at some stage of
growth each system must have been represented by a single

No. 3.] LATERAL LINE OF AMIA. 495

primary pore with a single unbranching tube leading to it from
one of the central canals. This condition is found in fishes
about one month old, or from 40 to 60 millimetres long; but as
the different systems pass through it at slightly different times,
no single specimen or age fully represents it.

There are normally at this stage ninety-three primary pores
and tubes on the entire head, — forty-six on each side and a me-
dian one in the supratemporal cross-commissure. This median
pore is the last one developed, and its formation marks the end
of a first period, in which the canals and the primary tubes
and pores are developed, and the beginning of a second and last
in which the tubes and pores begin the dividing, shifting, and
multiplying which result in the complicated arrangements found
in the adult. Fig. 49, Pl. XLII., is a diagrammatic representation
of this stage, showing the course of the canals and the position
of the primary pores and tubes. Fig. 13, Pl. XX XIV., shows the
arrangement of the pores on the head of a fish 30% millimetres
long, in which the lateral system is in a somewhat earlier stage
of development; and Figs. 14, 15, and 16, Pl. XXXV., that on
the head of a fish 78 millimetres long, in a more advanced con-
dition.

At the stage represented in the diagram, pores I and 2 supra-
orbital, and 2, 3, 4, and § infra-orbital, are arranged nearly in a
circle around the nasal tube, No. 5 infra-orbital lying somewhat
out of the circle, directly in line with pores 1 and 2 supra-orbital
in front, and 7 and 8 infra-orbital behind. A dermal depression
separates pores I supra-orbital and 5 infra-orbital as in the adult.
Pore 8 infra-orbital lies in a well-marked corner formed by the
anterior end of the supramaxillary furrow, which turns sharply
upward in a curved line. Pores 9 to 12 lie below the eye, form-
ing with No. 8 a straight line extending directly backward. Pores
13 and 14 lie behind the eye, and above and behind it is the
double pore, 15 infra-orbital and 7 supra-orbital, which, in the
674-millimetre specimen has undergone its first division. Pore 16
is in process of division in this specimen, lying about mid-way
between the double pores, 15-7 and 17-17, formed at the point
where the infra-orbital and operculo-mandibular canals unite.
Then follow pores 18 and Ig as a pair a little in front of the
upper end of the opercular opening, and pores 20, 21, and 22-1
above this opening.

496 ALELS: [ VOL. Tr:

Pore 3 of the supra-orbital line and the corresponding one of
the opposite side form a prominent pair about half way between
the nasal apertures. Pores 6 infra-orbital and 4 supra-orbital
lie close together near the posterior nasal aperture, No. 6 in
front of, and No. 4 median to, it. No. 5 supra-orbital lies imme-
diately behind No. 4, about on a level with the anterior edge of
the eye; No. 6 nearer the middle line on the top of the head,
between the eyes; and No. 8 behind and median to the double
pore 15-7.

Pores 1 to 10 of the operculo-mandibular line lie along the
lower edge of the jaw, No. 1 markedly in front of the curved
line of the others. No. 11 lies almost directly above No. Io,
and has in the 674-millimetre specimen undergone its first divis-
ion, the two secondary pores lying, as in the adult, one on
either side of the end of the supramaxillary furrow. Pores 12
to 16 lie along the edge of the pre-operculum, Nos. 13 and 14
already double in the larger specimen.

In the supratemporal cross-commissure there are two pores
on either side, and one in the middle line of the head.

The central canals at this age are inclosed in thin, bony tubes
which in certain places, as in the suborbital series (Cut 9),
represent the entire bone of the adult. In others, as in the
squamosal and frontal, the tube lies along the edge or toward
the middle of a thin, bony plate of the same thickness as the
wall of the tube, and the tube and plate together form the bone.
In young larve, where the bones are just beginning to develop,
they are represented by short, semi-cylindrical pieces lying im-
mediately below each organ. At this stage they correspond to
the short, bony scales which, according to Bodenstein (No. 3,
p. 131), partly inclose each organ of the lateral line in the adult
of Cottus, and to the bony half-rings which, according to Leydig
(No. 9, p. 251) and Solger (No. 14, p. 111), support the walls and
protect the organs in the cranial canals of Chimzera monstrosa.
These semi-cylindrical pieces in Amia increase in length and
soon become open gutters or channels. The plate then appears
along the sides or toward the bottom of the channel, always
continuous with it and growing from it on either side. The
canal and the gutter in which it lies are always at this stage on
the upper surface of the bone, thus corresponding to the con-
ditions described by Bodenstein (No. 3, pp. 132 and 143) in the

No. 3.] LATERAL LINE OF AMIA. 497

os mastotdeum of the adult Cottus. The gutters then become
tubes, lying at first on the upper surface of the bony plates, and
corresponding to the conditions found in the adult of some of
the bony fishes.

The relations of the primary tubes to the various dermal
bones in Amia are easily determined in a series of sections.
They differ slightly from the relations of the trunks of the
corresponding systems to the bones in the adult.

Trunk No. 2 infra-orbital enters its canal through the eth-
moid; No. 3 between the ethmoid and the antorbital; Nos. 4
and 5 through the antorbital, and No. 6 at its upper posterior
edge; No. 7 between the antorbital and lachrymal; No. 8
through the lachrymal; No. 9 between the lachrymal and first
suborbital; No. 10 between the first and second suborbitals ;
No. 11 between the second suborbital and lower postorbital ;
No. 12 through the lower postorbital ; No. 13 between the post-
orbitals ; No. 14 between the upper postorbital and the post-
frontal.

The double trunk 15-7 lies between the frontal and postfrontal
and between the two anastomosing canals, which, at this point,
change sharply their direction. The infra-orbital lies entirely
in the postfrontal, and the supra-orbital entirely in the frontal ;
both of them along the open edges of the bones. The trunk of
the system at this age is a large shallow pit into which the two
canals open. In the further development of the system it
deepens, becomes narrower, and lies over the point of anastomo-
sis of the two canals instead of between them as at first. In
the first division of the system the trunk divides after the man-
ner shown in Cut 3, p. 18, fand g. One of the primary branches
resulting from this division retains its position at the point of
anastomosis of the two canals. The other travels backward
along the infra-orbital canal till it reaches the anterior edge of
the squamosal, where it is found in the adult (Fig. 40). The
trunk of the system disappears.

Trunk 16 infra-orbital enters its canal through the squamosal.
Immediately behind it is the double opening, 17-17, which lies
at the lateral edge of the squamosal, between it and the upper
end of the pre-operculum, and resembles closely the double pore
15-7. The upper end of the opercular line opens directly into
the pit on its lower wall, and on the upper wall a small opening,

498 ALLIS, [VoL. II.

much smaller than the openings of the other pores, leads into
the infra-orbital canal, which at this point is deflected toward
the lateral edge of the squamosal. In the first division of this
double system the trunk disappears, and the two primary
branches travel downward along the opercular canal, at the
‘same time separating somewhat along the line of that canal.
The two secondary pores formed by this division also separate
antero-posteriorly. From one of them arises the half-system
lying in the adult in front of the canal (Fig. 40), and from the
other that lying behind it.

Trunks 18 and Ig enter the main canal on either side of the
extrascapula, between it and the squamosal and suprascapula
respectively ; No. 20 enters it between the suprascapula and
supraclavicula ; No. 21 through the supraclavicula, and No. 22-1
between the supraclavicula and the first scale of the lateral line.

In the supra-orbital line trunks 1, 2, and 3 all enter the canal
through the nasal; No. 1 on its lateral edge; No. 2 on the ante-
rior edge; and No. 3 through the top of the bone. Trunk 4
enters the canal between the nasal and frontal; Nos. 5 and 6
through the frontal; No. 7, as already described, between the
frontal and postfrontal; and No. 8 between the frontal and
parietal.

In the operculo-mandibular line, trunks 1 to 7 enter the canal
through the dentary; No. 8 between the dentary and nasal;
Nos. 9 and 10 through the angular; No. 11, a compound or
double trunk, between the angular and pre-operculum; Nos.
12 to 16 through the pre-operculum ; and No. 17 between the
upper end of this bone and the lateral edge of the squamosal.

In the supratemporal cross-commissure the two lateral trunks
on each side enter the canal through the extrascapulz, and the
large double median one between the two bones. By the first
division of this median pore the two primary branches are
formed, which, in the adult, become the trunks of the half-
systems lying one on each side of the middle line of the head.

The conditions existing at this age and a little earlier show that
a primary tube originally leaves each of the main lateral canals
along its entire length between cach two consecutive dermal bones,
and that at every point of union of two canals, whether of the
same or of opposite sides of the head, a double pore and trunk ts
formed, which give rise at this point to a double dendritic system.

No. 3.] LATERAL LINE OF AMIA. 499

If the bones containing the two anastomosing canals have anchy-
losed, or the two canals lie in the same bone, then both the pore
and the trunk belonging to it entirely disappear.

The ethmoid in Amia is formed by the union of the two bones
usually found in other fishes. At the line of union of these
two bones, where the main infra-orbital canals of opposite sides
unite, a single median pore and trunk have been formed and
disappeared, as younger stages show. In like manner a pore
and trunk have disappeared on either side at the point where
the supratemporal commissure joins the main infra-orbital, these
two canals here lying in the same bone, the extrascapula.
These two are the only trunks and pores that have disappeared
in the entire system in Amia. In the adult, with two exceptions
only, all of the primary tubes, which at younger ages issue from the
main canals between consecutive bones, become partly or entirely
wnclosed tn one or the other of these bones. The two exceptions
are trunk 4, supra-orbital, and the double trunk 17—17, which,
even in the adult, lie wholly in the dermis.

2. Number and Position of the Canal Organs.

Between every two consecutive trunks, along the entire length
of each canal, counting the double trunks twice, once along each
of the anastomosing lines, and also counting the trunks that
have disappeared, there is a single sensory spot or patch con-
taining either a single well-developed organ of the kind called
by Merkel (No. 12, p. 5) nerve-hillocks, and by Wright (No. 20,
p. 480, note) neuromasts, or such an organ with one or more
smaller ones developing at either end of it (Fig. 48, Pl. XLI.).

These sensory patches always lie inside the dermal bones,
and there are along the infra-orbital line two in the ethmoid,
four in the antorbital, two in the lachrymal, one in each sub-
orbital, two in the lower postorbital, one in the upper postorbi-
tal, one in the postfrontal, three in the squamosal, one in the
extrascapula, one in the suprascapula, and two in the supra-
clavicula. Along the supra-orbital line there are three in the
nasal, and four in the frontal; along the operculo-mandibular,
seven in the dentary, three in the angular, and six in the pre-
operculum ; and in each half of the supratemporal cross-com-
missure three, all in the extrascapula, making forty in all on
each side of the head.

500 ALLIS. [Vou. II.

The position of these organs in the canals, and their method
of innervation, is shown in the diagrammatic drawing, Fig. 49,
Plate XL:

In this diagram two sense-organs, or groups of organs, are
shown between the first trunks of the supra-orbital line on either
side of the head, and one in this same line between trunks 18
and 19, directly opposite the point where the supratemporal
cross-commissure joins it, with no trunk system between it and
the first group of organs in this commissure. These two trunks
and pores have disappeared, the position of the organs and the
development of the system alone showing that they at one time
existed, There is but one group of organs in the infra-orbital
canal on each side of the double trunk 17-17, and only one
between it and trunk 16 operculo-mandibular, showing that the
double trunk, although displaced in the adult, belongs primarily
at the point of union of the two canals. There is one group of
organs on each side of the double trunk 15-7, between it and
the next trunk, in the infra-orbital and supra-orbital canals,
showing that the displaced primary branch, which in the adult
issues between the squamosal and postfrontal, is in reality a
part of the double trunk, and not a separate system. There is
also but one group on each side of the compound trunk 11 of
the operculo-mandibular line, between it and the next trunks
of that line, and but one on each side of the median system of
the supratemporal cross-commissure.

The fifth group of the infra-orbital line is appacedly out of
place, lying in what seems to be the trunk of system 6, above
the point where the anterior commissure joins the suborbital
part of the main canal. This is due to the fact that the end of
the suborbital canal, beyond the point where the commissure
joins it, has taken the direction of the commissure instead of
retaining that of its own canal; so that what appears as the
trunk of system 6 is in reality this trunk and the extreme ante-
rior end of the main canal, and it is in this anterior end, and not
in trunk 6, that group 5 lies. Moreover, system 6 being prop-
erly a terminal system in which the trunk continues the line of
the main canal, there is nothing to indicate where it begins and
the canal ends. Organs 1 and 7 supra-orbital and 1 operculo-
mandibular occupy strictly analogous positions, apparently lying
in the trunks of the neighboring terminal systems.

No. 3. ] LATERAL LINE OF AMIA. 501

3. Sense-organs of the Spiracular Canal.

Wright (No. 20, pp. 481 and 489) has described a patch of
neuro-epithelium at the upper end of the spiracular canal in
both Amia and Lepidosteus. It is supposed by him to have
developed in this canal, and hence to be of hypodermal origin.
In the young of Amia this sensory patch is a group of organs
exactly like the regular organs of the lateral canals, consisting,
as they do, of a large central organ and two or more smaller
terminal ones. The group lies in the median wall of the mem-
branous spiracular canal near its blind upper end.

The spiracular canal in Amia (No. 20, p. 492) opens widely
on the upper surface of the cartilaginous cranium, at the
extreme anterior end of what is rather a diverticulum of the
temporal groove of Sagemehl (No. 13, p. 188) than a part of
the groove itself. The main groove lodges the anterior end of
the trunk muscles, while the diverticulum, which lies wholly
lateral to it, connected with it along its edge, lodges no muscles
whatever. It contains only loose, fatty tissues, vessels, and
nerves. The squamosal portion of the infra-orbital canal lies
directly above this diverticulum, and that branch of the R.
oticus facialts that supplies organs 15 and 16 of that line lies in
it, running backward from the point where the nerve issues
through the roof of the cranium median to and about on a
level with the opening of the spiracular canal. A branch of
this same nerve, given off just as it leaves its foramen, turns
outward and downward into the upper end of the spiracular
canal, and is distributed to the group of organs there in the
same way that the nerves of the lateral canals are distributed
to the organs they supply.

When it is remembered in connection with the innervation
and position of this group of organs, that all the sense-organs
which at this stage lie inside the canals of the lateral system,
are in earlier stages found on the external surface of the head,
it seems reasonable to suppose that this particular group in
Amia, apparently so anomalous in position, was regularly devel-
oped in the epidermal covering of the head along with the other
organs of the infra-orbital line, but, lying near the edge of the
spiracular cleft, it wandered into this cleft as it was closed, and
so acquired its present position. If this be so, the lining mem-

502 ALLIS. [VoL. Il.

brane at the upper end of the spiracular canal must be ectodermal
rather than entodermal in origin. No positive evidence of this
method of development has yet been found, for in none of the
postembryonic forms to which the present work has so far been
confined has the spiracle been open. In some of the youngest
specimens, however, certain appearances seemed to indicate that
it had only recently been closed. In specimens from one to five
days old there is always a strong depression immediately above
the upper end of the opercular line (Figs. 1 and 3, Pl. XXX,,
spr). The developing infra-orbital line crosses this depression,
and organs 15 and 16 lie in it. In freshly prepared one-day-
old specimens there is in the bottom of the depression, imme-
diately below these organs, a dark spot indicating the position
of the blind upper end of the spiracular canal. This spot in
some specimens is strongly marked, and if the tissues are fresh
and somewhat transparent, has the appearance of being an
opening with a part of the sensory tissue of the infra-orbital
line extending into it or across its edge.

4. Lines of Pit Organs.

There are in Amia, in addition to the sense-organs found in
the lateral and spiracular canals, several surface lines of some-
what similar organs, which, although belonging to the same
general class of nerve-hillocks (Merkel), differ greatly from the
canal organs in shape, arrangement, and method of multiplica-
tion. These organs are somewhat conical in shape, and, like
the canal organs, represent the entire thickness of the epidermis
at the points where they occur. In young fishes, and on the
body in the adult, they project slightly beyond, or come nearly
to the level of, the outer surface; but on the head of the
adult they lie at the bottom of little pits, and therefore they
may be called pit organs. They are found close together, in
regular lines on slight dermal papillz, and are connected by a
special cord of cells which extends beyond the end of the line,
and is lost among the general epidermal cells. They appear to
develop independently along this cord.

Cut 5 represents a section through one of these surface lines
in an adult; and Cut 4, one in a fish 45 millimetres long. Cuts
4 to 9 are semi-diagrammatic, but the outlines are taken from

No. 3.] LATERAL LINE OF AMIA. 503

actual sections. In Cut 4 is seen the cord along which the
organs lie, and an organ developing in it. The organ at this

Cut s. Cut 6.

Cut 4.— Longitudinal section through a line of pit organs in a fish 45 millimetres
long, showing four organs, one of which is just forming, all connected by a cord of
cells in the deeper layers of the epidermis.

Cut 5.— Longitudinal section through a line of pit organs in the adult, showing
three organs and the connecting cord.

Cut 6.— Section through a developing organ of the suborbital line in a fish 114
millimetres long, showing large vacuolar space at top of organ.

Cut 7,—Thesameina fish millimetres long, where the organ has reached the
other surface.

Cut 8.—The same ina fish millimetres long, where the organ is beginning to
sink below the surface and the osseous canal is forming.

Cut 9.—The same in a fish millimetres long, where the canal is just closing
over the organ, showing the nearly formed osseous canal and the nerve leading

through it to the organ.

504 ALLIS. [ VoL. Id:

stage of its development has the appearance of a flat dome
with a large, vesicle-like space, set like a keystone at the
top of the structure. Toward this space the cells of the organ
are directed, and as they increase in length, and the organ in
height, the latter pushes its way, wedge-like, through epidermal
cells, crowding them to either side, until it reaches the outer
surface, where its upper central portion becomes exposed. It
has now the shape of a cone with rounded summit (Cut 4); and
its exposed upper end, which contains the compressed outer
ends of all the sensory cells, reaches to the general level of the
outer surface, or even projects beyond it. On the body, and
particularly toward the tail, the organs retain nearly this con-
dition even in the adult; but on the head they are later so much
withdrawn from the surface that only a series of minute holes
indicates their position (Cut 5).

Cut 6 is a section through the suborbital line in a fish 113
millimetres long. It shows one of the canal organs in a stage
corresponding to that of the young pit organ in Cut 4, and also
to that of the organs of the lateral line in Salmon embryos
before the organs have reached the outer surface, as shown by
Hoffman (No. 8, Pl. V., Fig. 29). There is at the top-of this
canal organ the same vacuolar space that is found in the develop-
ing pit organ, and there are apparently no support cells. These
appear later, after the organ has reached the outer surface, as
shown in Cut 7.

In these early stages the different organs of a canal line are
connected by a special cord of cells similar to that connecting
the organs of a pit line. In Cut 8 the organ has begun to sink
below the surface, and in Cut 9 the canal is just closing over it.
As development progresses, the connecting cord of cells disap-
pears, except immediately adjoining the organ, where it was
present in the oldest specimen in which it was examined, one
about 80 millimetres long. Along this remnant of the cord,
and immediately adjoining the primary organ, the other organs
of the group appear, at first as small bud-like organs, inclined
away from the larger central one (Fig. 48, Pl. XLI). These
new organs grow rapidly, and others soon appear in succession
along the cord beyond them, all at first in contact at their bases,
but separated above by projecting ridges of indifferent cells, ex-
actly as figured and described by Blaue (No. 2), in the olfactory

No. 3.] LATERAL LINE OF AMIA. 505

epithelium of Exoccetus and other forms. The groups which
thus arise are doubtless the beginnings of what Merkel has
called nerve-ridges (No. 12, p. 20), for under this name he in-
cludes all organs found in the adult inside the canals of the
lateral system (No. 12, p. 23). He also finds nerve-ridges on
the surface in some fishes that have no canals, as Petromyzon,
Squatina, etc., and describes them as simply an elongated form
of the regular conical nerve-hillock, containing exactly the same
histological elements, but with a larger proportion of support-
cells. He further says, that in the teleosts the conical hillocks
are always found on the surface or in slight depressions ; that
they may either be arranged in lines and groups, or scattered
irregularly over the whole body; that they are most numerous
in those forms that have but few openings to the lateral canals,
‘or have no canals at all; and that where the canals branch
freely, and there are many pores, the conical hillocks may
entirely disappear, as on the head of Mullus. In the Sela-
chians they are, according to him, found only on two species,
Mustelus and Squatina, being entirely replaced in other forms
by another kind of sense-organ, the nerve-ampulla (No. 12, p. 39) ;
and in the Ganoids, he says, they are not found at all, being
entirely replaced by still another kind of organ, the nerve-sack
(No. 12, p. 36). This certainly is not true of all the Ganoids,
for in Amia I have not been able to find any of the nerve-sacks
which he considers peculiar to the Ganoids, and I have always
found seven different lines of pit organs (his conical hillocks)
on each side of the head, and two series of lines of organs on
each side of the body.

Of the seven lines found on the head, three lie on top of it,
two on the cheek, one on the side of the mandible, and one on the
gular plate (Figs. 21, 22, and 23, Pls. XXXVI. and XXXVII_).
Of the two on the body, one lies parallel to the lateral line, and
the other on the top of the body close to the dorsal fin. Each
of the lines on the head is a continuous series of organs, while
those on the body in the adult are each made up of a series
of such lines, one approximately to each segment of the body.
No ventral body line could be found.

a. Head Lines. — The first or anterior one (Fig. 21, a/) of
the three dorsal lines of the head runs backward and median-
ward from group 8 supra-orbital; and the third or posterior one

506 ALIAS. [Vou. II.

(Fig. 21, p/) forward and medianward from group 2 supra-
temporal. The second or middle one (Fig. 21, #/) lies between
the other two, and extends almost direct medianward from near
the double group 17-17. The first line lies superficial to the
parietal. It begins close to, or among, the pores of group 8
supra-orbital, sometimes starting in or running across the edge
of a pore so that one of its organs lies partly inside it. The
second one lies superficial to the squamosal and parietal, just in
front of the anterior edge of the extrascapula. It often ends
close to the posterior end of the first line, the two almost meet-
ing to form an angle. The third one lies superficial to the
parietal and extrascapula, and usually extends much nearer
the middle line of the head than the other two. In many speci-
mens these six lines, three on each side, seem to radiate from a
clear space directly on the crown of the head. This appearance
is most marked in young specimens (Figs. 14, 15, and 16, Pl.
XXXV.), in which the anterior line begins close to pore 8 supra-
orbital, and 1s a direct continuation of the line of that canal. The
first organ of the pit line often lies partly inside the tube of pore 8,
and in one set of sections was entirely inside it, somewhat modified
in shape and about midway between the next following pit organ
and the regular terminal organ No. 7 of the canal. This organ
No. 7 is inclosed in its canal much later than the other organs
of the line, and is in specimens up to 45 millimetres in length
much smaller, being still single while they are represented by
groups of three or five.

The horizontal line on the cheek (Fig. 22, 7) begins among
the pores of groups 14 or 15 of the opercular line, and ends
among those of group 12 infra-orbital. It lies partly superficial
to the lower postorbital, somewhat behind the centre of the
bone, and frequently runs directly into a pore of group 12, just
as the anterior dorsal line does tnto the pores of group 8 supra-
orbital. These two lines are the only ones tn which this occurs, the
other lines beginning at some little distance from the pores of the
groups near which they arise. The vertical line (Fig. 22, v/)
begins behind or among the pores of group 12 infra-orbital, near
the anterior end of the horizontal line, and, lying partly superfi-
cial to the lower postorbital, runs downward toward the pores
of group II operculo-mandibular, or a little behind them. The
mandibular line (Fig. 22, md/) lies superficial to the angular,

INO. 3-.] LATERAL LINE OF AMIA. 507

and runs, in the shape of a letter S, from the anterior part of
group II toward group 9 operculo-mandibular. The gular line
(Fig. 23, g7) runs transversely across the gular plate between
groups 7 and 8 on either side.

In the adult the bones immediately beneath these pit lines are
slightly furrowed, and the lines are often broken.

Body Lines. —In the adult there is, on nearly every scale of
the first two-thirds of the lateral line, a line of pit organs run-
ning across the scale immediately in front of the group of pores
(Fig. 39, Pl. XX XIX., a//). In young specimens these lines are
each represented by a single organ lying immediately above the
corresponding organ of the lateral line. In the development of
the pit line these single organs are apparently connected by a
cord of cells, not only with each other, but also with the corre-
sponding organs of the lateral line. The line grows backward in
the same way that the main line does, and may be called the acces-
sory lateral line, a name already used by Solger (No. 17, p. 380)
and others. In the adult the first series of pit organs is found
on the third, fourth, or fifth scale of the line; in one specimen
which was examined for this purpose no organ could be found
behind the forty-fifth scale, there being in all sixty-seven scales
in the lateral line. Toward the head there are always more
organs in each series or line, some of them having as many as
eight.

The first series of organs of the dorsal body line is usually
found on the second row of scales, above and behind group 21
infra-orbital (Figs. 15, 16, and 17). This row of scales is the
second or third row of the body, counting backward along the
middle line of the back, or the second row, counting along
the lateral line. Considering the rows transverse to this, —
that is, those that run upward and backward, — the dorsal body
line begins on the sixth or seventh row of scales and on the
second row in front of the first scale of the lateral line. Still
considering these transverse rows, the second series of organs
lies on the row following that on which the first series is found,
and on the second scale dorsalward along that row. The third
series lies on the next row, usually four scales dorsalward from
the second series, and on the second scale from the middle line
of the body. It lies in the same row as the first scale of the
lateral line. From this point the pit line runs directly back-

508 ALLIS. [Vou. II.

ward, and ends about opposite the anus. The different’ series
of organs, after the third, lie one behind the other on the second
or third scale from the middle line of the body, or on the sec-
ond scale from the base of the dorsal fin ; and there is normally
a series on each row of scales, the rows corresponding to the
scales of the lateral line. The series or lines in front of the
dorsal fin are transverse to the body, while those along either
side of it are longitudinal.

In 55-millimetre specimens the different lines or series of the
dorsal line, as well as those of the accessory lateral line, are stil}
represented by single organs (Figs. 12 and 13, Pl. XXXIV.).

In both Lepidosteus and Polypterus the canal of the lateral
line extends to the tail fin; and in both there seem to be, from
the descriptions given by Solger (No. 14, pp. 368 and 369),
series of organs corresponding to the pit lines of the body in
Amia. In neither form are the organs themselves described,
but their distribution, as indicated by well-marked furrows, is
fully given. In Lepidosteus the furrows are transverse, as they
are in Amia; and there are only two series, one on the back
extending as far as the dorsal fin, and the other accompanying
the lateral canal, and extending as far as the tail fin. The fur-
rows of this last line lie, as in Amia, just in front of the pores
of the lateral canal, and they are found on about one-half the
scales of the line.

In Polypterus the furrows are longitudinal. The dorsal series
extends as far as the tail fin, and a number of irregularly scat-
tered furrows lying below the lateral line and immediately be-
hind the pectoral fin represent what Solger considers a ventral
series, not found in Amia. A third series of furrows is found
on the scales of the lateral lines, but it is impossible to tell from
Solger’s description whether they represent lines of pit organs
or the lateral canal itself not fully inclosed. Each furrow cuts
through the hind edge of the scale on which it lies, and they
are found on nearly every scale of the line. Immediately above
them there is a series of depressions, which differ somewhat in
appearance from the furrows of the lateral line while they closely
resemble the transverse furrows in Lepidosteus. They doubt-
less represent the accessory lateral line of Amia.

In Fierasfer also there are several lines of organs which seem,
from the descriptions given by Emory (No. 5, p. 40), to corre-

LATERAL LINE OF AMIA. 509

spond to the pit organs in Amia. They lie at the bottoms of
flask-shaped epidermal pits, each of which contains a single
organ. The external opening of the pit is about the size of the
exposed upper end of the organ, and the organ which is smaller
than, but similar to, those found in the lateral canals does not
come in contact with the sides of the pit. They are found in
lines or irregular groups on the head, and on the body in four
lines or series of lines, a dorsal line, two accessory lateral lines,
one immediately above and one immediately below the lateral
canal, and a ventral line. The pits of the ventral line and those
of the dorsal accessory line are all connected by small longi-
tudinal canals formed in the deeper layers of the epidermis, and
those of the ventral accessory line that are formed on a single
segment of the body are similarly connected. The organs of
the dorsal body line are not so connected; but canals extend
transversely on either side of them, and end blindly in the
epidermis, often branching toward the end. These epidermal
canals have not been described in other fishes. They agree
exactly in position with the cords of cells connecting the pit
organs in Amia; and if these cords should be replaced by
canals, or canals should be formed in them by deliquescence
or otherwise, as the lateral canals themselves are formed in
Selachians, the arrangement described by Emory would arise.
The artificial separation of the cord from the overlying epidermal
cells would probably produce a somewhat similar appearance.

5. Surface Sense-organs.

Under the name Terminal Buds Merkel includes a large class
of organs, which, in Amia, always come to a level with or pro-
ject slightly beyond the outer surface of the membrane in which
they lie. They are found in great numbers on the external
surface of the head, including the operculum, gular plate, and
branchiostegal rays. They also extend on the top of the body
as far as the dorsal fin; but behind this, and along the sides and
belly, none could be found by surface examinations of the adult
or by sections in young specimens, and none were found on any
of the fins. They are also found in the mouth and branchial

cavities.
In the adult they are scattered irregularly over the surfaces

510 ALELS. [Vo.. II.

where they occur; but in young specimens they are found in
lines or series, connected more or less distinctly in hardened
specimens by a whitish cord similar to that connecting the pit
and canal organs at this age. They are first seen in specimens
of from one to two days old as faint whitish spots adjoining a
canal line, as shown in Fig. 4, median to the line of the supra-
orbital canal. This spot soon breaks up into, or is replaced by,
a series of spots, as shown in the four-day-old specimen repre-
sented in Fig. 5. In this specimen similar rows are also seen
on the other side of the supra-orbital and on each side of the
infra-orbital line, while faint markings on the cheeks, median to
the squamosal and post-temporal part of infra-orbital, indicate
still other places where they will soon appear. After this age
the organs develop rapidly, and in specimens five days old
(Figs. 6 and 7, Pl. XXXI.) they are already numerous on the
anterior half of the head. In specimens ten or twelve days old
(Figs. 8 to 11, Pls. XXXII. and XXXIII.) they appear on the
operculum ; and when the fish is from three to four weeks old
(Fig. 13, Pl. XXXIV.), they have spread over the entire head
and part of the body. In these older specimens the serial
arrangement of the organs has disappeared, except in those parts
of the head where they are just beginning to appear. In such
places (Fig. 9, Pl. XXXII.) they are still found in rows, and
more or less distinctly connected by a cord.

6. Innervation.

It is now well known that all the sense-organs belonging to
the canals of the lateral system are innervated by dorsal branches
of the cranial nerves. For these organs Beard has recently pro-
posed the name branchial sense-organs, because of their develop-
ment in early embryos from thickenings of the epiblast over
each branchial cleft, and for the nerves the name suprabranchial
nerves (No. I, pp. 171 and 174).

According to his general scheme of development in Elasmo-
branchs, based largely on the researches of Balfour, Marshall,
and Van Wijhe, the dorsal root of a cranial nerve grows out-
ward and downward from the neural crest, toward a local thicken-
ing of epiblast already formed over the cleft of its segment.
At the level of the notochord, it fuses with the epiblastic thick-

No. 3.] LATERAL LINE OF AMIA. STI

ening, a part of it, however, passing on as the future postbran-
chial nerve to the lateral muscle-plate of the segment. At the
point of fusion, cells are rapidly proliferated. The deeper part
of the mass which thus arises is the rudiment of the ganglion
of the dorsal root, and the superficial portion, the rudiment of a
branchial sense-organ. The deeper portion soon separates from
the rest of the mass, leaving a nerve strand connecting it with
sensory portion, and, lying deeper in the mesoblast on the root
of the nerve, apparently at first distal to the point of separation
of the post-branchial branch, becomes the ganglion of the nerve.

The superficial sensory part of the thickening may remain
very small, or it may increase to a very considerable length,
pushing its way either backward or forward, as the case may
be, between the general epiblast cells, and connected in every
case with the ganglion of the segment by the supra-branchial
nerve, which is split off from under side of the thickening
simultaneously with its growth. Along this thickening, con-
comitantly with the splitting off of the nerve, different organs
arise, according to Beard, by the simple and repeated division
of the single organ formed over the cleft, each organ so formed
being connected by a separate branch with the main supra-
branchial nerve.

This method of origin differs somewhat from that of the
lateral line of Salmo, where, according to Hoffman (No. 8, p.
88), the different sense-organs arise independently after the
lateral nerve has been split off from the under part of the
epiblastic thickening which represents the line. As the nerve
separates, a strand is left at each intermuscular septum con-
necting the nerve with the cells of the deeper part of the epi-
dermis where later the organ will arise.

Beard’s work was mainly confined to Torpedo ocellata, but he
confirmed the results obtained in this form by comparison with
the embryos of Mustelus and Pristiurus, and of certain Teleostei
and Amphibia. In all these forms he finds seven supra-bran-
chial nerves and seven corresponding lines of branchial sense-
organs ; but the position of these organs in the embryos is not
fully detailed, and the adult conditions are not noticed at all, so
that it is impossible to tell what becomes of the seven thicken-
ings, and where, in the adult, the organs developed from each
are to be found.

wT ALLIS. [ Vor, Ee

The seven supra-branchial nerves, as given by Beard, are the
following :—
1. Ophthalmicus profundus,
belonging to the ciliary ganglion and hypophysis cleft.

2. Ophthalmicus superficialis less portio facialis,
of the gasserion ganglion and mouth cleft.

3. Portio facialis of Ophthalmicus superficialis.

4. Ramus buccalis,
of the facial ganglion and two clefts, the hyoid and an absent
one.

5. Supratemporal branch of the glossopharyngeal,
of the glossopharyngeal ganglion and the first branchial cleft.

6. Supratemporal branch,
of the first vagus ganglion and second branchial cleft.

7. Lateral nerve,
of the second, third, and fourth vagus ganglia, and the third and
following visceral clefts.

Of these seven nerves, the ophthalmicus profundus and
ophthalmicus superficialis less portio facialis innervate, according
to him, sense-organs lying over the snout; the portio facialis
and ramus buccalis, the organs of the supra- and infra-orbital
lines respectively ; the glossopharyngeal and first vagus branches,
the supratemporal organs; and the rest of the vagus, or nervus
lineze lateralis, the organs of the lateral line of the body.

The arrangement of the organs of the lateral system in
Amia calva and their method of innervation, as determined by
the examination of larval stages by sections, does not agree with
Beard’s scheme, for the trigeminal and ophthalmicus profundus
take no part with any of their branches in the innervation either
of the canal or pit organs. Moreover, there is the large and
important operculo-mandibular line of organs, which Beard seems
to have overlooked, for he does not mention it, and none of the
suprabranchial branches given in his scheme of the sensory
nerves could take any part in its innervation, unless the con-
ditions in Torpedo and the other forms used by him for com-
parison are markedly different from those found in Amia.

In Amia the trigeminal, although it takes no part in the
innervation of the regular canal or pit organs, has a large and

No. 3-] LATERAL LINE OF AMIA. 513

important part in innervating the surface sense-organs, or ter-
minal buds. Its ophthalmic and superior maxillary branches are
largely devoted to this purpose. They supply no muscles, and
numerous branches can be traced in sections from each of them
directly to the surface organs which they supply. The inferior
maxillary is partly sensory and partly motor, several important
branches of it being distributed entirely to the surface sense-
organs and other non-muscular tissues.

The ophthalmicus profundus is also entirely sensory. A
small branch pierces the choroid coat of the eye, accompanied
by a branch of the external carotoid artery, while the rest of
the nerve fuses completely with the ophthalmic division of the
trigeminal, so that its special distribution cannot be determined.
In one set of sections only of all those examined did there
seem to be a separation of these two nerves on the top of the
snout, the ophthalmicus profundus being lost in the general
tissues above the nasal sacks, and doubtless taking part there,
along with the trigeminal, in the innervation of the surface
organs.

The facial is the first one of the cranial nerves that takes any
part in supplying the regular organs of the lateral canals, and
it has a large and important part not only in their innervation,
but also in that of the different lines of pit organs. Four of its
branches, the ophthalmicus superfacialis, buccalis, oticus, and
mandibularis externus, are entirely devoted to this purpose.

The R. ophthalmicus superfacialis facialis supplies all the
organs of the supra-orbital canal, a separate branch being sent
from the main nerve to each group of organs. This branch
pierces the bony canal of the line immediately below the cen-
tral organ of the group, and after entering the canal sends a
branch to each organ. This is the method of innervation in
all the canals. Posterior to all the branches sent to the different
groups of supra-orbital organs, still another branch —the most
posterior one of the R. ophthalmicus — is sent to the organs of
the anterior dorsal pit line, a separate, smaller branch being sent
from it to each organ of the line. This nerve alone, or together
with the branch to organ 7 supra-orbital, which Jeaves the main
nerve close to it, probably represents the branch which, accord-
ing to Wright (No. 26, p. 483), supplies the organs of the trans-
verse commissure in Mustelus. Wright is inclined to consider

514 ALLIS. [VoL. II.

this most posterior of the dorsal twigs of the seventh in Mus-
telus as homologous with the ramus oticus in Ganoids and Tel-
eosts (No. 20, p. 490).

The ophthalmic branch of the facial is closely associated
throughout most of its course with the ophthalmic branch of the
trigeminal, but there is apparently no interchange of fibres be-
tween them; and in the youngest specimens examined, the two
nerves were wholly separate, although lying close together.

The R. buccalis facialis supplies the first thirteen organs of
the infra-orbital line, and the R. oticus facialis the next three,
making sixteen organs in all of this line supplied by the facial,
or all those in front of the line of the opercular canal. The
remaining organs of the infra-orbital line are innervated by the
glossopharyngeal and vagus.

The sixteen infra-orbital organs supplied by the facial are
separated by their innervation into four distinct groups. The
first four, all belonging to the anterior commissure, form the
first of these groups. They are supplied regularly by separate,
consecutive branches given off from the anterior portion of the
R. buccalis, which ends in the first one of them. The next six
organs, from 5 to 10 inclusive, form the second group of the
line, and they are also supplied by separate branches of the
R. buccalis; but the branches to organs 5 and 6 are given off
close together, the one to No. 6 passing outward behind the fifth
division of the M. levator arcus palatini (McMurrich, No. 10,
p. 122), and the other to No. 5, internal to, and in front of,
this muscle. The origin of these two nerves close together
from the main R. buccalis is easily explained by supposing the
first four organs of the canal in Amia to have belonged to a
line of pit organs in some earlier form. As the separate organs
of such a line are always much smaller than those found in the
canals, and as the nerve that supplies a whole line of them,
where still found in Amia, is no larger, or not so large, as the
branch sent to a single canal organ, the main part of the ramus
buccalis would, in such an earlier form, have ended in the termi-
nal organ of the canal; that is, in organ 5 of the line in Amia ;
and what is the anterior part of the nerve in Amia would, in
that form, have been simply a smaller branch sent to the organs
of the pit line, and given off beyond and rather close to the
branch to organ 6, just as a similar branch, destined to supply

No. 3.] LATERAL LINE OF AMIA. PRRs

the organs of the dorsal pit line, is still given off in Amia from
the end of the nerve supplying the organs of the supratem-
poral commissure. As this anterior branch became larger and
more important, concomitantly with the change of the pit line
to a canal, it would become the anterior part of the main
nerve, and the branches to organs 5 and 6 would arise close
together from it, as they do in Amia.

Organs 11, 12, and 13 form the third group of the line. They
are innervated in different specimens by one or by two branches
of the R. buccalis, the branches, where there are two of them,
arising close together and close to the origin of the main nerve
from its ganglion, and one of them supplies organs 11 and 12;
where there is but one, the branch to organ 13 arises close to
the origin of the nerve from the main R. buccalis ; thus repre-
senting a stage in which the division of the nerve has not
proceeded far enough to give rise toa separate branch. The
branches to the different organs enter the bony canal of the
suborbital line by separate passages, immediately below the
proper organ.

The next three organs, Nos. 14, 15, and 16, form the fourth
group of the line, and vary somewhat in their method of inner-
vation. Organs 15 and 16 are always supplied by branches of
the R. oticus facialis. This nerve arises directly from the
facial ganglion. It runs upward and outward without entering
the orbit, and, piercing the cranial cartilage, issues on the top
of the chondrocranium at the extreme anterior end of the
diverticulum of the temporal groove. It here separates into
three branches, two of which supply organs 15 and 16, and one
the organ at the upper end of the spiracular canal.

Organ 14 is sometimes supplied by a branch given off by the
ramus oticus after it makes its exit on top of the cranium;
but oftener, in the specimens examined, it was innervated by a
branch which left the nerve close to its origin, or even from the
facial ganglion itself, near the root of the oticus, but a little in
front of it. This branch, after making its exit into the orbit
through the regular foramen for the ophthalmic nerves, turns
upward and reaches its proper organ without piercing the
cranium at all, or passes through a special perforation in the
overhanging cartilaginous roof of the orbit.

In young specimens the buccal and ophthalmic branches of

516, ALLIS. [Vot. II.

the facial arise from a Y-shaped mass of ganglion cells, formed
on the dorsal root of the facial nerve, and lying on top of the
rest of the trigemino-facial ganglionic complex, closely applied
to it, but quite separate from it. The ophthalmic branch of the
facial arises from the inner and upper arm of the Y, and the
buccal from the lower and outer one. The otic and the branches
to organs I1 to 14 infra-orbital, when they are not given off by
the buccal, arise from the external side of the Y, and hence
seem properly a part of the buccal. If this be so, and Beard’s
theory is to be accepted, then the original epiblastic thickening
from which the infra-orbital line to organ 16 is developed, must
have grown both forward and backward, the buccal being split
off concomitantly with the growth of the anterior part, and the
otic with that of the posterior, a few uncertain branches lying
between them.

Organ 17 is supplied by the dorsal branch of the glosso-
pharyngeal. This branch arises by a separate root, which
passes out of the cranial cavity immediately behind the root of
the main nerve, and often at this age by a separate foramen, or
through a special part of the main foramen. On this root a
separate ganglion is formed close to, and more or less intimately
connected with, the main ganglion, and from it the dorsal nerve
mentioned by Wright arises (No. 17, p. 489). This nerve runs
upward through a special perforation of the chondrocranium,
and, issuing on the bottom of the temporal groove, sends one
branch to organ 17, the only canal organ supplied by it, and
another to the middle dorsal pit line. This last branch runs
medianward to about one-third the length of the pit line. It
then turns upward and outward through the dermal bone, and
dividing somewhat dichtomously, sends one branch medianward
and another outward, both of them lying immediately under-
neath the line. From these branches smaller ones are given
off directly to the separate organs. The innervation of this line
indicates that it has grown in both directions from the original
sensory spot found in younger specimens, and also that, although
supplied by the same dorsal nerve that supplies canal organ 17,
it is not a continuous growth from the epithelial thickening
which was the rudiment of that organ. In this it differs from
the other two dorsal head-lines, which grow from, and are
directly continuous with, the rudiments of the canal organs
from which they start.

No. 3.] LATERAL LINE OF AMIA. S17

The remaining organs of the infra-orbital canal, and those of
the supratemporal cross-commissure, as well as the organs of
the lateral line, are all supplied by branches arising from the
ganglion formed on the root of the N. linez lateralis, or from
that nerve itself. The arrangement here apparently departs
somewhat from that given by Beard. The root of the N. linez
lateralis receives its most anterior fibres at this age close to and
a little above and behind the root of the N. acousticus. Pierc-
ing the membranes that separate the cranial cavity from the
labyrinth, it runs directly backward, close to their outer surface
and just above the posterior branch of the N. acousticus, in
which there are numerous ganglion cells. It passes through
the upper part of the main root of the glossopharyngeal, receiv-
ing there an important addition to its fibres, and, continuing
backward immediately external to the origins of the anterior
roots of the vagus, it issues through the main foramen of that
nerve. In its passage through this foramen, it runs backward
and outward, crossing the main root of the vagus at a consider-
able angle, and lying immediately above and closely applied to
it. It probably receives here also an important addition to its
fibres, but this could not be traced.

Immediately outside the foramen it forms a large, well-rounded
ganglion, which lies directly above, and partly embedded in, the
first vagus ganglion, but has no commissural connection with it,
the line separating the ganglia in sections being perfectly sharp
and distinct. From the proximal part of this ganglion, at its
extreme anterior end, and almost from the root itself of the
nerve, a large nerve is given off upward and outward. From it
a branch is sent to organ 19 infra-orbital, and another, arising
close to it, to organ 18, the rest of the nerve passing upward
and medianward to supply the organs of the supratemporal
commissure and those of the posterior dorsal pit line. The
branch supplying the pit line is given off immediately beyond
the. branch to organ 2 of the commissure, thus agreeing in its
relation to the other branches with that of the large branch sent
by the R. buccalis to supply the organs of the anterior commis-
sure, which branch is given off immediately beyond the branch
to organ 6 infra-orbital, the second one of the suborbital line.

This dorsal nerve is described by Beard as the supra-branchial
nerve of the first vagus ganglion. In Amia it is the first dorsal

518 ALLIS. (Vou. II.

or supratemporal branch of the lateral nerve. It is joined soon
after leaving its ganglion by a branch arising inside the cranial
cavity, either from the root of the lateral nerve or from the root
of the vagus, which here contains numerous ganglion cells.
This branch, although closely applied to the regular dorsal
nerve, is wholly separate from it. It is distributed entirely to
the general tissues of this part of the head, including doubtless
the surface organs, although the direct connection with any of
them was not determined.

The next or second regular dorsal branch of the lateral nerve
is given off near the base of the nerve, and not from the gan-
glion. It supplies organ 20 infra-orbital and the dorsal pit line
of the body, branches being sent in succession to each organ
or series of organs of that line. Other dorsal branches of the
lateral nerve are then sent in succession to organ 21 infra-orbital
and the organs of the lateral line of the body.

The lateral nerve has an undulating course, as shown
by longitudinal horizontal sections (Fig. 48, Pl. XLI.). Each
full undulation of the nerve corresponds to a muscle segment,
and from the outer crests of each the branches sent to the
organs of the lateral line arise. Running outward along the
intermuscular septa, they pass through the corium, and then
backward along the under surface of the scale they supply.
Reaching the anterior end of the section of canal contained in
this scale, the nerve enters it through a special passage, and
supplies the single organ or groups of organs found there in the
same way that the organs of the head are supplied. Each of
these nerves, before reaching the under surface of the dermis,
sends a branch upward and outward through the corium, a little
dorsal to the point where the main nerve pierces it. Arriving
under the same scale, this branch runs backward, dorsal to and
parallel to the main nerve, and, piercing the scale about opposite
the regular canal organ, supplies the corresponding series of pit
organs.

The organs of the operculo-mandibular line are all innervated
by branches of the R. mandibularis facialis externus. The first
one of these branches is given off before the externus has
separated from the main truncus hyoideo-mandibularis facialis.
Leaving the truncus immediately after its passage from the
facial canal through the hyomandibular, or even while still in

No. 3.] LATERAL LINE OF AMIA. 519

that canal, it runs outward, backward, and upward, and enters
the bony canal of the opercular line immediately under organ I5.
It sends a branch to this organ, and then continuing upward
inside the bony canal, immediately underneath the epidermal
lining, ends in organ 16, the last one of the line. Organs 14
and 13 are supplied by separate branches, given off either
from the mandibularis externus or from the main ramus man-
dibularis before it has separated into an external and internal
portion, Organs 12 and 11 are supplied by a single branch,
which, as in the case of the branch to organs 15 and 16, enters
the bony canal under the first organ supplied, No. 12, and then
passes on inside the canal to the second one, No. 11. Where
these branches are given off from the main ramus mandibularis
or the main truncus, it is from that part of the nerve that
contains the fibres which afterward separate as the externus.
Beyond the branch to organs 12 and I1, separate branches are
sent in succession to each organ up to No. 4. The nerve then
enters the bony canal, and running forward inside it, supplies
in succession organs 3, 2, and I.

Between the single branch that supplies organs 15 and 16,
and the next regular one to organ 14, a branch is sent out-
ward through the adductor mandibulz muscle and then forward
along its outer surface, immediately underneath the horizontal
cheek line, branches being sent in succession to each organ of
the line. A similar nerve is given off between the branch to
organ 13 and the one to organs 12 and 11. This nerve also
passes outward through the adductor muscle, and then for-
ward along its outer surface, but it soon separates into two
parts, one of which goes to supply the vertical cheek line, and
the other the pit line on the mandible. In both cases the
nerve arrives near the middle of the line it supplies, and there
separates into two parts which run toward either end of the
line, sending separate branches to each organ. In one specimen
the nerve supplying these two pit lines was not given off as a
separate nerve from the externus, but as a branch from the
nerve supplying organs 12 and II.

The innervation of the line of the gular plate could not be
fully determined. Branches can be traced from the different
organs of the line to a single nerve which runs backward in-
ternal to the plate. At the hind edge of the bone the nerve

520 ALLIS. [Vou. II. +

turns dorsalward, and, lying close beneath the epidermal lining
of the dorsal side of the gular plate, runs forward dorsal to the
hind edge of the geniohyoid muscle. Here it turns upward and
backward, and then immediately upward and forward toward
the front edge of the hyohyoideus muscle, round which it turns
upward and backward, and, passing external to the front end
of the sternohyoid muscle, enters the first branchial arch, and
joins a part of the main nerve of that arch. This main nerve, so
far as could be determined, is formed by the union of the post-
branchial branch of the glossopharyngeal and the prebranchial
branch of the first vagus ganglion. At the point where it is
joined by the nerve of the gular line it has just separated into
two parts, one of which runs downward and inward, and the
other upward and inward, to be distributed to the tissues on the
upper surface of the hyoid apparatus. It is this last branch that
is joined by the nerve of the gular line.

7. Review of Nerves and Organs.

Reviewing briefly the arrangement of the nerves and organs,
there are in front of the double pore 17-17, where the opercu-
lar and infra-orbital lines unite, sixteen separate canal organs
or groups of organs along each line. The last two organs
on each line, Nos. 15 and 16, are supplied by branches of a
single nerve, which is directed posteriorly along the canal.
Organs 11 and 12 of each line are also supplied by branches,
directed anteriorly, of a single nerve; while the intermediate
organs, Nos. 13 and 14, are in most cases supplied by in-
dependent branches. On the infra-orbital line a branch of
the otic, anterior to organ 15, supplies the organ or group of
organs of the spiracular cleft; while on the opercular line a
branch of the mandibularis given off next in front of the single
nerve to organs 1§ and 16, and hence in a corresponding posi-
tion, supplies the organs of one of the surface lines of the cheek.
The other cheek line and the surface line on the mandible are
supplied by a single nerve, which, in one of the two sets of
sections in which it was traced, arose as a branch of a nerve
supplying a regular canal organ. The possible significance of
this will appear in considering the arrangement of the dorsal
nerves behind the facial. The horizontal cheek line ends close

‘ No. 3.] LATERAL LINE OF AMIA. 521

to organ 11 infra-orbital; and the vertical cheek line, close to
organ II operculo-mandibular. In front of this the canal organs
on both lines are innervated by separate branches from the
main nerve of the line.

Behind the point where the infra-orbital and opercular lines
unite, organ 17 is supplied by the dorsal branch of the glosso-
pharyngeal, which also supplies a line of surface organs lying
dorsal to it. The next dorsal nerve, the first branch of the
lateral line nerve, supplies organs 19 and 18, the organs of
the supratemporal commissure, and a line of pit organs dorsal
in their innervation to all of these. The second branch of
the lateral nerve supplies organ 20 and the dorsal body line of
pit organs. The next branch, so far as could be determined,
supplies organ 21 alone; but each of the following branches
for nearly the full length of the line normally supplies an
organ of the lateral line and a corresponding line of pit organs.

The supratemporal cross-commissure, in the Characinidz
(No. 13, p. 36), lies in the parietals, and according to Sagemehl
is an independent formation not to be compared with the com-
missure in Amia. So far as can be determined from his descrip-
tion, it occupies about the position of the middle dorsal pit line
on the head of Amia. If it has the same innervation as this pit
line, that is by the glossopharyngeal, a not improbable supposi-
tion, its exceptional position can easily be explained ; for a canal
line in one form is often represented by a pit line in another, as
for instance, the anterior commissure in Amia and the corre-
sponding pit line in Esox or Salvelinus ; and probably also the
anterior dorsal pit line in Amia and the cross-commissure in
Mustelus, which has a corresponding position and apparently
the same innervation.

In Fierasfer (No. 5, p. 38) the arrangement of the canals in
this part of the head is markedly different from that in Amia.
The cross-commissure leaves the main canal near the hind end
of the squamosal directly opposite the upper end of the opercu-
lar canal, apparently as a direct continuation of that canal. It
is innervated by the “ramus ascendente”’ of the lateral nerve,
a branch which corresponds to or comprehends, according to
Emory, both the supratemporal (probably of vagus) and opercular
branches in other fishes. The “ramus ascendente”’ innervates
not only the organs of the commissure, but also those in the

522 ALLE ES. [VOL. II.

temporal part of the main canal and in the upper end of the
operculo-mandibular. The glossopharyngeal, which in Amia
supplies a canal organ and line of pit organs lying almost
directly above the end of the opercular canal, is in Fierasfer
distributed entirely to the first branchial arch, and takes no
part in the innervation of the lateral system.

Variations. — The arrangement of the canals and organs of
the lateral system given in the preceding descriptions is the one
most commonly found; but there are frequent variations, due
either to the complete disappearance, or to the addition, of one
or more peripheral systems. A group of sense-organs and its
nerve appear or disappear with the addition or disappearance
of a system. No exception to this rule was found in Amia;
but in one specimen of Amiurus, a primary tube was missing
in the mandibular line without the disappearance of a corre-
sponding nerve and organ, thus leaving two separate organs or
groups of organs between two consecutive tubes. This was
doubtless due to the abnormal closing of a tube after its regular
formation.

In Amia the most frequent variation from the normal type
was the disappearance of one sense-organ and corresponding
primary tube in the mandibular canal, leaving nine organs,
tubes, and pores along the lower edge of the mandible in-
stead of ten. The missing system was always one of those
normally found in the angular. Less frequently there was the
addition of one system, or the disappearance of two, along this
same canal, the number along the opercular part of the line
always remaining constant.

Other variations were the addition or disappearance of a single
system along that part of the suborbital canal that lies in the
postorbital bones, and the addition or disappearance of one in
the one-half of the supratemporal cross-commissure, the other
half of the commissure often varying inversely, so that the total
number of systems in the full commissure remained the same.
The organ that is missing when there is one system short in
the suborbital line is either No. 11 or No. 12, both of which
normally lie in the lower postorbital, and are innervated by a
single branch of the R. buccalis. No variations were found in
the supra-orbital line.

Van Wijhe (No. Io, p. 285) has called attention to the regular

No. 3.] LATERAL LINE OF AMIA. 523

correspondence of each scale of the lateral line in Amia to a
segment of the body, and has suggested the possibility of some
sort of relation between the dermal bones of the head and the
cranial segments. The arrangement of the sense-organs and
nerves of the lateral system, the regular occurrence of primary
tubes between consecutive dermal bones of the head, as well
as between consecutive scales of the lateral line, and the singu-
lar correspondence between the infra-orbital and opercular canals
is further evidence in this same direction.

Hi eLARVAL FORMS.

1. Formation of the Canals.

The inclosing of the lateral canals and the formation of the
ninety-three normal primary pores and tubes is essentially a
simple and regular process, but in most parts of the head marked
abbreviations take place, which greatly obscure it. Where the
process is regularly and fully carried out, the canals arise in
separate sections, each of which contains a single sense-organ,
and hence corresponds to the part between two primary tubes
in the developed canal. This has already been described by
Bodenstein in the lateral line of Cottus (No. 3, p. 142) and
by both Schulze (No. 16, p. 69) and Solger (No. 18, p. 386) in
Plateria.

If young Amia, in which the canals have not yet begun to
develop, are hardened in chromic or picro-sulphuric acid, the
organs of the lateral system, still below the surface, appear as
whitish spots, with indistinct outlines, strung along more or
less continuous whitish lines. These lines mark general and
extensive surface depressions. After a developing canal organ
has reached the surface at the bottom of one of these depres-
sions, it begins to sink, carrying with it the surrounding tissues,
thus forming a small pit, at the bottom of which the organ lies.
A series of changes now begin, which, on an exaggerated scale,
are a repetition of those which lead to the division of a pore.
Lips grow upward and inward from the edges of the pit, and,
meeting above the organ, form a short section of canal, the
openings of which are inclined to the general surface, and give
to the canal a tunnel-like appearance. A narrow shallow chan-
nel, pigmented like the rest of the outer surface, has meantime

524 ALLIS. [Vou. II.

formed between the organs along the bottom of the general
depression. It is deepest near the newly formed section of
canal; and into it the canal opens, the sides of the openings
passing gradually into the walls of the channel. The limits of
the canal are clearly defined by a sharp change in direction of
the bottom of the channel, the canal leading inward at some-
thing of an angle, the walls of the canals and pits always being
much lighter in color than the outer surface.

The openings of these short sections of canal may be called
half-pores because, with a few exceptions, all the primary pores
in the developed system are formed by the fusion of two of
them. After its formation the short canal increases in length
by the continued coalescing of the edges of the channel im-
mediately beyond it, and the two half-pores are pushed apart
along the line of the canal toward other pores which are in a
similar way approaching them from adjoining sections. This
process in Amia is continued until the pores meet and unite,
thus forming a continuous canal with a primary pore and tube
between every two consecutive organs; but it may be arrested,
in which case an interrupted canal will be formed, as in the
post-temporal part of the infra-orbital in Esox lucius and along
the canal of the lateral line in Ophidium (No. 5, p. 39). At
each end of a continuous canal formed in this manner it is evi-
dent there must be a pore, which, if it cannot unite with a pore
of some other line to form a double system, must always remain
a half-pore or terminal opening. Such terminal openings are
retained in Amia in pores 1 and 8 supra-orbital and 1 operculo-
mandibular. The other terminal opening of the opercular line,
pore 17, unites with pore 17 infra-orbital to form a double sys-
tem. In the infra-orbital line pore 6 is a terminal one, and pore
22-1 a double one, formed at the other end of the line where it
joins the lateral canal of the body. In the anterior commissure
one terminal opening has disappeared on the top of the snout
where the two lines meet, and the other has fused with the sec-
ond pore of the main canal to form what has been called pore 5
infra-orbital.

Cut Io is a diagrammatic representation of the formation and
' subsequent subdivision of a primary pore. These two processes
are continuous and essentially similar; for even in the adult,
two pores if forced together from want of space fuse, as fre-

No. 3-] LATERAL LINE OF AMIA. 525

quently happens along the lower edge of the lachrymal. Double
pores of this kind, formed in the adult, usually undergo no fur-
ther division; but the conditions shown at omg’! in group 11
operculo-mandibular (Fig. 20, Pl. XX XVI.) can only be explained
on the supposition that this pore has afterward subdivided and
multiplied exactly as do the simple pores.

lieu 1S ang Boley ‘i
eur pr
MG eee vi pacers a)

ee (oO aa, aot: Mal
: aera oo [OSes 0

Cut ro. — Diagrammatic representation of the formation of pores and groups of
pores. The small black spots indicate organs, and the curved outlines openings
of pits or pores in different stages of formation and division.

All phases in the formation of half-pores, as well as of the
primary ones, are shown in Figs. 23 to 34, which fully illustrate
the development of that part of the infra-orbital canal lying
immediately behind the eye. The formation of the first few
pores of the lateral line and the last three pores of the infra-
orbital are shown in Figs. 35 to 38.

In Fig. 23, which represents a specimen 19 millimetres long,
and from twelve to fifteen days old, organ 16 infra-orbital is just
inclosed, an unpigmented line still marking where the sides of
the canal have come together above it. Organ 15 lies in a deep
groove continuous with the canal at organ 16, and is about to
be inclosed. The inclosing of these two organs is an abbrevia-

526 ALLIS. [Vou. II.

tion of the regular method. They lie relatively close together,
and the pits in which they lie become a continuous groove, as
shown in Fig. 12, before the canal closes over either of them.
The canal is formed as usual, but a relatively long section of it
is inclosed at once so that the two half-pores which go to make
pore 16 are formed facing each other and already partly fused.
The different steps in this process are shown in Figs. 23, 24,
and 25, in the last of which pore 16 is fully developed. This
abbreviated method occurs wherever the organs lie close to-
gether, or where the canals are relatively large, as in young
larvee.

In Figs. 23 and 24, organ 8 supra-orbital lies on the surface,
and is hardly to be distinguished except by position from the
following organs of the anterior dorsal pit line. In Fig. 25, —
which represents a 234-millimetre specimen, it is just being
inclosed, and in Fig. 27, a 29-millimetre one, is entirely so, pore
8 appearing as a small terminal opening immediately in front of
the first organ of the pit line.

In Fig. 23, organs 14 and 15 infra-orbital can both be seen;
in Fig. 24 they are just inclosed ; and in the succeeding figures
up to 28 the principal phases in the formation of pore 15 are
shown. This pore lies at a sharp bend in the infra-orbital line
close to pore 7 supra-orbital, which also lies at a bend in its line.
The two lines are approaching each other at these bends, and
the surface between them is strongly depressed, just as it is be-
tween successive organs on a regularly developing line. Along
this depression pores 15 and 7, once formed, approach each
other and coalesce, exactly as half-pores do along the line of a
canal. In Figs. 29 and 30 they are shown partly united, and in
Fig. 31, a 40-millimetre specimen, they have already united and
begun their primary division, which is completed in Fig. 33, a
54-millimetre specimen. In Fig. 34, a specimen 135 millimetres
long, the double pore has undergone its secondary division, and
is represented by a group of four.

In Figs. 23 and 24, organ 16 operculo-mandibular and all the
organs of the infra-orbital line behind organ 16, lie on the sur-
face or in small pits along the strong channels which mark the
course of the canal. In Fig. 25 the canal is closing over organs
17, 19,and 20. In Fig. 26 it has fully closed over organs 17 and
19, but organ 20 is still visible in a large double pit common to

No. 3.] LATERAL LINE OF AMIA. 527
it and to organ 21. In Fig. 27 the canal has closed over organ
20 and is about to close over organ 21, the process being so
greatly abbreviated that pore 21 is formed at once in place.
The two halves of pore 20 are always formed at some distance
apart, as shown in Figs. 26, 27, and 28.

In Fig. 26 the two half-pores that go to form pore 17 infra-
orbital are some distance apart. In Fig. 27 they are nearing
each other, and in Fig. 30 they have united. The pore so
formed is also beginning, in this figure, to travel down the oper-
cular canal toward the terminal pore 17, which is formed by the
closing of the canal over organ 16. In Fig: 33 the double pore
17-17 is nearly formed, and in Fig. 34 it has undergone its first
division.

The formation of pores 18 and 1g infra-orbital is somewhat
irregular. Organs 2 and 3 of the supratemporal commissure
are usually the first ones inclosed, but in Fig. 27 the canal has
formed over organs I and 3, and not over organ 2. The lateral
terminal opening of the commissure, pore 4, lies directly oppo-
site organ 18 infra-orbital, and a little in front of and behind
this organ are the anterior and posterior halves of pores 18 and
19. In Figs. 28 and 35, which represent the same specimen,
the canal is beginning to close over organ 18, the upper lip of
the canal forming at the end of the commissure directly above
its terminal opening. In Figs. 29 and 36, which also represent
the same specimen, the canal has nearly closed over organ 18,
and in Figs. 30 and 31 the process is completed, the terminal
opening of the commissure being entirely shut off from the
exterior, —transferred, in fact, from the exterior to the inner wall
of the infra-orbital canal. In two of the specimens examined
by section there was an extra pore and tube at this point, both
small, the tube leading forward and medianward from the point
where the commissure joined the main canal.

In Fig. 34 pores 18 infra-orbital and 3 supra-orbital have
undergone their first division. In this figure the median termi-
nal openings of the half-commissure of each side have united
and undergone their first division. This division frequently takes
place before the two terminal pores have fully united, and in
such cases the median pore never gets beyond the oblong shape
shown in Figs. 32 and 33. The same thing often occurs in
pore 17 infra-orbital, which may undergo its first division before

528 ALLIS. [Vor. II.

it is fully formed and before it has united with pore 17 operculo-
mandibular, as shown in Fig. 13. In this case only the anterior
one of the secondary pores takes part in the fusion with the
opercular line.

The canal of the lateral line, like the canals of the head, is
first formed in short sections, which afterward become continu-
ous. The rudiments of the different organs of the line are
formed on the intermuscular septa, as described by Bodenstein
and others in the bony fishes; but as the organ develops, it
travels backward, and before being inclosed lies in the middle
of the segment, as shown in Figs. 35 and 36, and as found by
Malbranc in the Amphibia (No. 11). The organ then sinks
into a little pit, and on its dorsal and ventral sides lips are
formed which coalesce, forming a short canal about the length
of a body segment, as seen in Figs. 36 and 37. The pri-
mary pores formed by the union of the terminal openings of
these short sections lie at first opposite the intermuscular septa
and between consecutive scales, which at this age have only the
length of a body segment and no free edge (Fig. 37, /p! and //’).
As the scale grows its free hind edge pushes backward on
either side of the primary tube and, uniting beyond it, leaves
the pore on its outer surface (Fig. 38) and the tube at the point
where the canal passes from one scale to the next (Fig. 48).
The tube at first runs directly outward through the scale, but
later it acquires a longitudinal position, extending backward
almost as a prolongation of the short canal, and having on the
outer surface of the scale one or more pores (Fig. 44).

Toward the front of the head and along the mandibular line
the canals are inclosed much earlier than in the parts behind
the eye. The process in this part of the head is always greatly
abbreviated after the manner detailed in describing the forma-
tion of that part of the infra-orbital canal containing organs 15
and 16. The development also proceeds so rapidly here that
the canals in this anterior part of the system are fully formed
before those behind it have much more than begun to develop.
This anterior part includes the first six organs of the supra-orbi-
tal line, the first ten of the infra-orbital, and the first nine of
the operculo-mandibular. The canals inclosing these organs
appear in specimens only five or six days old, and when the
fish is from twelve to fifteen days old they are fully formed.

No. 3.] LATERAL LINE OF AMIA. 529

Figures 6 to 12 show the formation of these canals in three
specimens, —one 114 millimetres long (Figs. 6 and 7), one 14
millimetres long (Figs. 8 to 11), and one 18 millimetres (Fig.
12). As shown in these figures, the supra-orbital canal in front
of organ 7 is inclosed in two sections containing three organs
each, and the mandibular canal in a single section containing
the first nine organs of the line. In the infra-orbital line organs
3 to 7 are inclosed together in a Y-shaped section of canal, and
then organs I and 2, and 8, 9, 10. The median pore No. 1
formed in this process is shown in Fig. 11. It afterwards
entirely disappears.

Organ 5 infra-orbital is normally the first one in the whole
lateral system to be inclosed, and the formation of that part of
the canal in which it lies is closely associated with the develop-
ment of the nose. In Fig. 1 the nose is shown as a simple pit
lying beyond the line of the infra-orbital canal. It is at first
round and deep, but it soon becomes oblong, as shown in Fig.
4, and is then inclosed exactly as the canals of the lateral sys-
tem are, a short section of canal being formed open at both ends
and continuous behind with the Y-shaped open depression of
the infra-orbital line. This stage is shown in Fig. 6, an unpig-
mented surface line still showing where the canal has closed
over the nasal pit. The whitish cord of the infra-orbital line
extends beyond organ 5 toward and partly into the posterior
one of the two openings. In the 14-millimetre specimen, Fig.
8, organ 5 has been inclosed, and the half-opening, destined to
become pore 6, stands facing the posterior naris, connected with
it by a deep depression. At this stage these two openings
appear like two half-pores about to fuse, but this resemblance
soon disappears. In the 18-millimetre specimen, Fig. 12, the
two pores still open into a large common depression, but it is
becoming shallower; in Fig. 13, a 31-millimetre specimen, it has
nearly disappeared ; and in Fig. 14, entirely so, pore 6 now hav-
ing a position in front of the naris instead of below it as at
first. The formation of pore 5 infra-orbital from three half-
pores is shown in Fig. 8.

In the opercular line the central part of the canal is formed
at an early age. Organs 13 and 14 are the first to be inclosed
(Fig. 12), then organs 12 and 15, and finally, at a much later
period, organs 11 and 16. During this stage of its development

530 ALLIS. (VoL. II.

the opercular canal is an independent canal not connected with
the mandibular portion, or with the main line, a condition which
is permanent in Esox lucius.

The lateral canals of Amia present a more highly developed
arrangement than those of the bony fishes. Lepidosteus, judg-
ing from a most cursory examination, resembles Amia; Polyp-
terus, except in the possession of large dermal plates, has essen-
tially the arrangement found in Amia immediately after the
formation of the primary pores and tubes, and before the opercu-
lar line has joined the main canal. This larval arrangement in
Amia also corresponds to that found in the adult of most bony
fishes, but in many teleostean forms still more primitive condi-
tions exist.

Sagemehl has advanced the theory that the teleostean condi-
tion is derived directly from that found in the adult of Amia by
the gradual growth of a thicker cutis from the edges of the der-
mal bones toward their centres. As a result of this growth, the
bones lose their superficial position, and finally lie beneath a
thick dermis. The lateral canals, however, in order to maintain
their communication with the exterior, do not sink in a corre-
sponding degree, and they are accordingly found in the Teleosts
much nearer the upper surface of the bone than in Amia. In
many species they project in ridges above it, and in Gymnotus,
many of the Murzenidz, some Cyprinoids and others, they lie
entirely above the bones of the head inclosed in bony tubes
and forming the ‘“nervenskelet”’ of Stannius. In Polyodon
Spathula, also, clearly a more primitive form in this respect
than Amia, a somewhat similar arrangement exists ; for, accord-
ing to Van Wijhe, the canals lie in the flesh in open, bony
channels. These different conditions both in the Teleosts and
in the Ganoids would also be obtained if the development, as
shown in Amia, was simply arrested instead of undergoing
retrogression ; that is, by supposing that the Teleosts had never .
attained the Amia condition instead of having passed through
it as indicated by Sagemehl.

In Salvelinus the canal of the lateral line is never developed,
and the peripheral systems of the cranial canals have, in most
cases, only a single surface opening corresponding to the pri-
mary pores of Amia; but in one very large specimen, two of
these systems had undergone a primary division similar to that

No. 3-] LATERAL LINE OF AMIA. 531

which takes place in Amia, and the two pores, always found single
in other specimens, were each represented by a group of two.

2. Origin of the Canal Organs.

The discussion of the origin and growth of the sensory
thickenings from which the different lines of the lateral system
arise, and the origin of the sense-organs along these lines, lies
wholly beyond the scope of the present paper, but the order
and manner of their appearance, as determined from surface
examinations, lies fairly within it. Most of the specimens used
in this part of the work were killed in picro-sulphuric acid or
chromic acid, with, or without, a trace of osmic, or in the vapor
of osmic acid, and then transferred to chromic. Chromic acid
was found to emphasize the continuity of the whitish lines which
represent the sensory tissues, while picro-sulphuric produced a
somewhat opposite effect, making evident a want of continuity,
or at least a difference in the composition of the lines in those
places where the innervation changes. Freshly killed speci-
mens were found to give much the best results, for the use
of alcohol obscured the markings which in certain places are
indistinct even in the best preparations.

In fishes just hatched, the lines of the infra-orbital, supra-orbi-
tal, and lateral line canals are the only ones that can be distin-
guished. They are all represented by short, straight, raised

lines of about the same length. That of the lateral canal _

starts immediately above the opercular opening, and those of the
other two close together (if not from a common point), imme-
diately behind the eye and directed, like the arms of a letter V,
one above and the other below it. In somewhat older speci-
mens the infra-orbital line extends under the eye to the level
of the hind edge of the nasal pit, where it ends in an enlargement,
from which later (Fig. 1, Pl. XXX.) the anterior commissure
is given off downward and forward, the main line continuing
upward toward the nasal pit. Behind the infra-orbital line, and
immediately above the opercular opening, there are at this age
two short, curved, comma-like lines directed upward and back-
ward with their enlarged ends behind. The anterior one is the
rudiment of organ 17 and the middle dorsal pit line, and the
other the rudiment of the supratemporal and posterior dorsal
pit lines. They both lie on the anterior end of a raised surface
which is continuous with the dorsal part of the body muscles,

532 ALLIS. (Vou. II.

and is faintly indicated in Fig. 1. The dorsal outline of this
raised portion curves downward, leaving a semi-transparent space
in front of it, between it and the hind edge of the cerebellum.
Its curved surface forms an angle behind with the curved sur-
face of the yolk, the line of the angle extending backward and
upward from the hind edge of the opercular opening to the
anterior end of the line of depression between the dorsal and
ventral muscle segments of the body. At the angle formed by
these two lines of depression, at some distance behind the
supratemporal line, the lateral line begins, as does also the
accessory lateral line.

In specimens less than a day old, or even in those a little
older, the lines or regions supplied by different nerves are dis-
tinctly separate in picro-sulphuric preparations, but in chro-
mic acid ones much less so, particularly when first killed in
the vapor of osmic. In such specimens the infra-orbital line
is somewhat continuous throughout its length. In fishes two
and one-half days old this appearance is still more marked,
as shown in Fig. 1, which is drawn from a chromic acid
preparation. The sense-organs of the different lines in this
specimen are not yet sufficiently developed to show on the
surface; but the raised whitish lines, which indicate the
positions of the cords of cells along which they arise, are
strongly marked. The line of the supra-orbital canal is con-
tinuous with that of the anterior dorsal pit line, and widely
separated from the infra-orbital at the point where later the
anastomosis with it will take place. Both ends of the line are
enlarged where, according to the theory of Beard and others, it
is pushing its way through the surrounding indifferent epithelial
cells. The infra-orbital line is continuous throughout its length,
and continuous with the lateral line which extends beyond the
pectoral fin nearly to the level of the hind edge of the yolk.
The accessory lateral line, which has just begun to develop,
starts from the lateral line immediately behind the line of
the supratemporal commissure, and is pushing backward
through the surrounding cells exactly as the lateral line does.
The ends of both these lines are enlarged, that of the lateral
line sometimes forming a large and prominent swelling. The
dorsal body line has not yet appeared. The posterior dorsal
pit line of the head is continuous at an angle with the line

No. 3.] LATERAL LINE OF AMIA. 533

of the supratemporal commissure, which is represented by a
single whitish spot connected by a cord with the infra-orbital
line. These two lines are short and indistinct. They lie be-
hind the upper end of the opercular opening and immediately
behind the slight prominence of the auditory vesicle. The
middle dorsal pit line is represented by a large spot lying imme-
diately superficial to the auditory vesicle, and connected by a
faint cord with the line of the infra-orbital.

Just in front of the auditory vesicle, the infra-orbital line runs
across a depression, in the bottom of which, immediately below
the line, is a dark spot marking the blind upper end of the
spiracular canal. Above and in front of this point the line is
enlarged; and from this enlargement organs 14, 15, and 16 arise.
No opening into the spiracular canal could be found at this age
or in one-day-old specimens. Behind and below the eye, the
infra-orbital line is small; but in front of it, where organs 7
and 6 arise, it is enlarged again. In front of this enlargement
it again narrows; and the line of the anterior commissure is
given off, the main line continuing on toward the nasal pit,
and ending there in an enlargement which is indistinctly con-
tinuous with the whitish border of the pit.

The operculo-mandibular line is a slender and faint but con-
tinuous line, lying along the anterior edge of a depression which
marks the boundary between the operculum and branchiostegal
rays on one side and the pre-operculum and mandible on the
other. Its upper end lies in line with the spiracle, but is sepa-
rated from it and from the infra-orbital by a strong prominence.
A slight depression indicates the position of the horizontal
cheek line, and another that of the vertical one.

The raised whitish lines which in these early specimens rep-
resent the growing sensory tissues disappear as the separate
organs of the line develop, and there is left a slender white cord
connecting them. This cord is doubtless the one found by
Bodenstein in the adult of Cottus gobio (No. 3, p. 136), where
it must be much more strongly developed than in Amia, for
even in specimens only 40 millimetres long (or from twenty
to thirty days old) it is traced with difficulty in sections. It
is apparently the remnant of the cord along which the organs
develop. In the four-day-old specimens, shown in Figs. 4 and 5,
these cords are well defined, and most of the canal organs rec-

534 ALLIS. [Vou. II.

ognizable. The organs of the supra-orbital line are well devel-
oped, the first six being widely separated from the seventh and
last, which cannot be distinguished in outward appearance from
the pit organs lying immediately behind it. The cord connect-
ing the canal organs is continuous with that connecting the
organs of the pit line. On the infra-orbital line all of the organs
up to No. 16 have appeared; and all, excepting Nos. I, 6, 11,
12, and 13, which are always the last ones in this section of
canal to be fully developed, have reached the outer surface.
Organ 5 lies above the point where the anterior commissure and
suborbital canal unite, and may from its position belong to either
line. Up to No. 16 the cord of the line is continuous, but
behind this it is broken or very faint. At the spiracular depres-
sion it begins again, and is continued back into the lateral line.
Organ 17 is the only one in this length of canal that can be
distinctly recognized. The lateral line extends beyond the anus,
and the accessory lateral line not quite to it, as shown in Fig.
2. The dorsal body line begins opposite a bend in the main
line a little in front of the point where the first organ of the
lateral line will appear, and has already reached the top of the
body, and turned backward along the edge of the dorsal fin.
The end of the line is strongly swollen. Neither this line nor
the supratemporal or middle dorsal pit lines are continuous at
this age with the main lateral line. The supratemporal line
shows two enlargements, from the median one of which the
posterior pit line starts at a sharp angle. The middle dorsal pit
line has a single well-developed organ, with the cord of the line
extending on either side of it. The line of the mandibular
canal is regularly developed to organ 10, the first two or three
organs still being indistinct. The opercular part of the line is
broken. Organ 15 and the rudiment of organ 16 le above the
horizontal cheek line, and separated from it and from organs 12,
13, and 14, none of which are fully developed. Organ 11 has
not yet appeared. The vertical cheek line and mandibular sur-
face line form a nearly continuous line, extending between organ
8 mandibular and 12 infra-orbital. The gular line could not be
found.

In the 114-millimetre specimen (Fig. 6, Pl. XX XI.) the cord of
the infra-orbital line extends the whole length of the line, and
is continuous with that of the lateral line. In this specimen

No. 3.] LATERAL LINE OF AMITA. 535

the dorsal body line is also continuous with the cord of the
lateral line; the cord of the supratemporal line, with organ 18;
and the cords of the three dorsal pit lines and the lines on the
cheek, with the canal organs, near which they arise. In slightly
older specimens these connections disappear, and in still older
ones even the cord connecting the organs of each line is traced
with difficulty. In the 114-millimetre specimen there are, be-
hind organ 18 infra-orbital, five faint transverse markings, as
shown in Fig. 6. The first one marks the hind edge of the
extrascapula, and the others the lines of intermuscular septa.
Between the fourth and fifth lies the first regular organ of
the lateral line. Between the others, organs I9, 20, and 21
will doubtless appear; but this could not be established, for
when these organs are first seen, the intersegmental markings
have disappeared.

General Summary.

The sense-organs of the lateral system in Amia are separated
by their position and by their innervation into distinct groups.
Each group develops from a special cord of cells lying in the
deeper layers of the epidermis, and each cord from a special
sensory thickening, which when first seen from the surface in
specimens hardened in chromic or picro-sulphuric acid, appears
as a large, whitish, and slightly raised spot. These spots are the
rudiments, not only of the different groups of organs, but also,
according to the theory of Beard and others, of the nerves
supplying them. They are all distinctly recognizable before the
close of the first day after hatching. From them are developed
the following groups of organs :—

1. The first sixteen organs of the infra-orbital canal, and
the one organ of the spiracular canal, all innervated by the RX.
buccalis facialis, and its posterior division, the R. ofzcus.

2. The seven organs of the supra-orbital canal and those of
the anterior dorsal pit line, all innervated by the R. ophthal-
micus factalis.

3.. The sixteen organs of the operculo-mandibular line and
those of the two pit lines on the cheek and the one on the
mandible, all innervated by the R. mandtbularis externus.

4. Organ 17 infra-orbital and those of the middle dorsal pit line,
all innervated by the dorsal branch of the WV. glossopharyngeus.

536 ALLIS. [VoL. II.

5. Organs 19 and 18 infra-orbital, the three organs of the
supratemporal cross-commissure, and those of the posterior
dorsal pit line, all innervated by a dorsal nerve arising from the
ganglion or root of the WV. /¢xe@e lateralis.

6. The organs of the lateral line of the body, organs 20 and
21 infra-orbital, and those of the accessory lateral and dorsal
pit lines of the body, all innervated by branches of the V. linee
lateralts.

All these organs in the early stages of their development lie
below the surface, but they soon push through the overlying
epidermal cells, and their upper central portions become exposed.
Each pit organ subsequently sinks slightly below the surface,
and a little epidermal pit is formed above its central portion.
The canal organs also sink below the surface, but they carry
with them the surrounding tissues and by a process of infolding
become inclosed in short canals, each containing a single organ.
These short canals then become continuous, a single surface
opening being left between every two consecutive organs along
each line. These simple openings, or primary pores, may be
retained in the adult, but most of them undergo a repeated
dichotomous division, thus giving rise to groups of surface pores
and to corresponding dendritic systems of canals.

By the union of the primary groups of short canals three
principal canals are formed and two cross-commissures ; namely,
the infra-orbital or main canal, which is continuous with the
canal of the lateral line of the body, the supra-orbital and
operculo-mandibular canals, and the anterior and supratemporal
cross-commissures. The anterior commissure has, following
the terminology of other writers, been considered as a part of
the infra-orbital canal. It lies over the snout, and connects the
infra-orbital lines between organs 5 and 6, which are properly
the first two organs of the line. The supratemporal commis-
sure lies in the temporal region, and connects the main lines
between organs 18 and 19, or directly opposite organ 18. The
supra-orbital and operculo-mandibular canals have no connection
with the corresponding canals of the opposite side. They arise as
independent canals, but the supra-orbital, soon after its regular
formation, anastomoses between organs 6 and 7 with the main
canal between organs 14 and 15; and the operculo-mandibular,
by its terminal opening, with the main canal between organs

No. 3-] LATERAL LINE OF AMIA. 537

16 and 17. These two anastomoses, and those of the anterior
commissure with the infra-orbital, and the supratemporal com-
missure with the corresponding canal of the other side, are the
result of the fusion of two primary pores which coalesce to
form double pores, in the same way that two half-pores unite
to form the primary ones. Double pores are formed in this
way, and then disappear at the point where the anterior com-
missure joins the canal of the other side, and where the supra-
temporal commissure joins the main infra-orbital. One other
anastomosis, formed in a somewhat different way between
systems 6 infra-orbital and 4 supra-orbital, establishes a second
connection between these two canals, and completes the circuit
of the orbit.

There are on each side three lines of pit organs on top of the
head, besides two on the cheek, one on the mandible, and one
on the gular plate. The anterior and middle pit lines on top of
the head lie nearly above the anterior and posterior semicircular
canals. On the body there are two series of pit lines, one on
the back and one accompanying the lateral canal.

In the adult the main canals lie in the deeper layers of the
dermal bones. In larval stages they lie in open channels, or in
bony tubes on the upper surface of these bones. Although
some of the primary tubes issue through the bone, one always
issues between every two consecutive bones along each line.

The sense-organs always lie inside the bones. They are at
first single, but by the formation of bud-like organs at each
end of the original one, large groups are formed, which in
certain stages resemble the nasal epithelium of Exocetus and
other forms, as given by Blaue.

The nasal pits are inclosed in the same way that the lateral
canals are, and the short canal so formed is at first continuous
with the canal inclosing organ 5 infra-orbital.

The head, gill-covers, and gular plate are thickly covered with
the surface sense-organs called by Merkel terminal buds, which
extend also onto the body. They are innervated in large part
by the trigeminal, but probably also by the ophthalmicus pro-
fundus, facialis, glossopharyngeus, and vagus.

538 ALLIS. (Vou. II.

20.

2I.

BIBLIOGRAPHY.

. BEARD, JOHN. “The System of Branchial Sense-Organs and their Associated

Ganglia in Ichthyopsida. A contribution to the ancestral History of Verte-
brates.” Studies from the Biological Laboratories of The Owens College.
Vol. I., p. 170. 1886.

. BLAUE, JuLIus. “ Untersuchungen iiber den Bau der Nasenschleimhaut bei

Fischen und Amphibien, namentlich iiber Endknospen als Endapparate des
Nervus olfactorius.” Archiv. f. Anat. und Phys. Hft. 3 u. 4, p. 231. 1884.

. BODENSTEIN, Dr. Emit. “Der Seitenkanal von Cottus gobio.” Zeitschr. f.

wiss. Zodl. Bd. XXXVIL., Hft. 1., p. 121. August, 1882.

. BRIDGE, T. W. “The Cranial Osteology of Amia calva.” The Jour. of Anat.

and Phys. Vol. XI., Part IV., p. 605. July, 1877.

. Emory, Dr. Carto. “Le Specie del Genere Fierasfer nei Golfo di Napoli e

Regimi limitrofe.” Fauna und Flora des Golfes von Neapel. II. Mono-
graphie. 1880.

. FRANQUE, HENRICUS. Amiz calve Anatomia. Berlin, 1847.
. GOODE, G. BRown. The Fisheries and Fishery Industries of the United States.

Sect. 1. Natural History of Useful Aquatic Animals. Washington, 1884.

. HorrMan, Dr. C. K. “Zur Autogonie der Knochenfische.” Archiv. f. Mik.

Anat., Bd. XXIII., Hft. 1, p. 45. October, 1883.

. Leypic, Dr. Franz. “Zur Anatomie und Histologie der Chimera monstrosa.”

Miiller’s Archiv. f. Anat. u. Phys., p. 241. 1851.

. McMourricu, J. PLAYFAIR. “The Cranial Muscles of Amia calva.” Studies

from the Biological Laboratory of Johns Hopkins University, p. 121. Balti-
more, June, 1885.

. MALBRANC, M. “Von der Seitenlinie und ihren Sinnesorganen bei Amphibien.”

Zeit. f. wiss. Zodl., p. 24, Vol. XXVI. September, 1875.

. MERKEL, Fr. ‘ Ueber die Endigungen die Sensiblen Nerven in der Haut der

Wirbelthiere.” Rostock, 1880.

. SAGEMEHL, M. “ Beitrage zur Vergleichenden Anatomie der Fische.” I. “Das

Cranium von Amia calva. I.” Morph. Jahrb., p. 177, Bd. IX., Hft. 2. 1883.

. SAGEMEHL, M. “III. Das Cranium der Characiniden,” etc., p. 1. Morph.

Jahrb., Bd. X., Hft. 1. 1884.

. SCHULZE, F. E. “Ueber die Sinnesorgane der Seitenlinie bei Fischen und

Amphibien.” Archiv. f. mikr. Anat., Bd. VI., Hft. 1, p. 62. 1870.

. SHUFELDT, R. W. “The Osteology of Amia calva.” Extracted from the

Annual Report of the Commissioner’of Fish and Fisheries for 1883. Wash-
ington, 1885.

. SOLGER, Dr. B. “Neue Untersuchungen zur Anatomie der Seitenorgane der

Fische.” Archiv. f. mikr. Anat., Bd. XVIL., Hft. 1, p. 95 u. Bd. XVII., Hft.
4, p. 458, und Bd. XVIII., Hft. 3, p. 364.

. TRAQUAIR, RAMSEY H. “On the Cranial Osteology of Polypterus.” Jour. of

Anat. and Phys., p. 166, No. 7, 2d series. November, 1870.

. VAN WIJHE, Dr. J. W. “Ueber das Visceralskelett und die Nerven des Kopfes

der Ganoiden und von Ceratodus.” Neiderland. Archiv. f. Zodl., p. 207,
Bd. V., Hft. 3. July, 1882.

WRIGHT, Prof. R. RAMSEY. ‘On the Hyomandibular Clefts and Pseudobranchs
of Lepidosteus and Amia.” Jour. of Anat. and Phys., p. 476, Vol. XIX.
July, 1885.

Idem. “On the Skin and Cutaneous Sense-Organs of Amiurus.” Proceedings
of the Canadian Institute. Vol. II. Fasciculus, No. 3, p. 252. Toronto,
October, 1884,

No. 3-]

LATERAL LINE OF AMIA.

539

EXPLANATION OF PLATES.

INDEX LETTERS.

a, anal fin.

a/, anterior dorsal pit lineof head.

. accessory lateral line.

. sense-organ of lateral line.

. anterior nasal aperture.

. angular.

. antorbital.

av, auditory vesicle.

ramus buccalis facialis.

¢. caudal fin.

canal of lateral line.

mandibular canal.

D. dentary.

dl. dorsal pit line of body.

. sense-organ of dorsal pit line.

cp. epiphysis.

ethmoid.

. extrascapula.

facial ganglion.

. frontal.

G. gular.

. glossopharyngeal ganglion.

gf. gular pit line.

. gular plate.

Af. ramus hyoideus facialis.

truncus hyoideo-mandibularis

facialis.

Ai. horizontal line pit of cheek.

. interoperculum.

zg. infra-orbital groups of pores.
zo. infra-orbital sense-organs.
zp. infra-orbital primary pores.
217 om\' g. double pore at union of in-
fra-orbital and operculo-
mandibular canals.

217 om1 g. double group of pores at union
of infra-orbital and oper-
culo-mandibular canals.

72 7/1 ~. double pore at union of infra-
orbital and lateral line ca-
nals.

215 si », double pore at union of infra-
orbital and supra - orbital
canals.

215 s7 ¢, double group at union of infra-
orbital and supra - orbital
canals.

® st g.

7G.

LA,

1b.
li.
d.md.
dom.

double group at union of infra-
orbital and supra - orbital
canals,

jugal.

lachrymal.

surface organs.

line of infra-orbital canal.

mandibular line of pit organs.

line of operculo-mandibular
canal.

. line of antorbital cross-com-

missure.

. line of supra-orbital canal.

line of supra-temporal cross-
commissure.

. lateral line.
. lateral line group of pores.

lateral line sense-organs.

. lateral line primary pores.

line of mandibular canal.

ramus mandibularis externus
facialis.

ramus mandibularis internus
facialis.

ramus mandibularis facialis.

middle dorsal pit line of head.

. maxilla.

- maxillar”.

= Masale

. nervus linez lateralis.
. nasal pit.

. nasal tube.

operculo-mandibular group of
pores.

operculo-mandibular sense-or-
gans.

operculo-mandibular primary
pores.

. operculum.

; ramus opthalmicus facialis.

. pectoral fin.

. parietal.

. posterior dorsal pit line of

head.
posterior nasal aperture.
pre-opercular fold.
pre-operculum.

540 ALLIS.

POR. first postorbital. spr. spiracle.
POR? second postorbital. sf.o. spiracular sense-organ. ~
PSF. postfrontal. SQ. squamosal.
513, scales of lateral line. s¢g. supratemporal group of pores.
S.ANG. supra-angular. sto. supratemporal sense-organs.
SC. suprascapular. stp. supratemporal primary pores.
SCZ. supraclavicula. st.gl. supratemporal branch of glos-
sg. supra-orbital group of pores. sopharyngeal.
so. supra-orbital sense-organs. st.v', supratemporal branch of vagus.
sp. supra-orbital primary pores. v. ventral fin.
smf. supramaxillary furrow. vd. vertical pit line of cheek.
SOP. suboperculum. x. nerve to gular line of pit
SOR. first suborbital. organs.

SOR. second suborbital.

The numerals affixed to the index letters g, 7, and /, along the infra-orbital line,
should be increased by one, except in Pl. XXXVI., where the correction has been
made by the lithographer.

For sp tread 2g7 ar
‘“ igh « p22,
«tsi pandg “ 21657 » and g.
“ om pandg “ tom" p and g.

af ip and zg@t 2727/1 » and g.

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on : iv ae 2 ) eT ag Lagi Neu » i Serbia i

we ot} a ih@' ae : one Mee ttrd j Pwe Gu) sich) Gale A 7 TA. ‘ ? ry
Pia y My Gu) joed wir 03 - tant Lids ae, : wall be § gly tele eine

i 4
ir Tia r y we A per ¢ get ph oi cal 4
iia! yi tigd tr wre wy U4 @ are, fet ees Ot. | : eh Nea y ae a §
} jet ra - RTE Ay pe Ci’ BS pes - PA ead Bs ee ue
, . i Pe
i eyed Ur i ian ‘th ' vA im Ariki es ‘
, + -
r ay ‘
J 4 ‘
‘ { =? } tae ‘a iar rut j
, if ue Ares '
wh » A } tal ve 2
i 6
~ i
*
i
wh
/ “xX :
| |
i
f
i
4d gf
hi ~
L*, 1
4 4 by
}
|
| 4 rs if - wy
' = LU 7 5
re 4
yi f pe A ’
' ‘ A
} aT) fama Lv A ,

542 ALLIS.

EXPLANATION OF PLATE, XXX.

Fic. 1. Larval Amia, one day old, showing a stage in the development of the
lateral line, preceding the appearance of definite sense-organs. X 40.
Fic. 2. Larva four days old. Sense-organs beginning to appear along the sen-
sory lines of the head. The double line of the body has not yet completed its growth
backward. Length 10o™™, Ong:
Fic. 3a. Larva 40"™ long. Lateral line has reached the rays of the caudal fin;
and while the formation of sense-organs now begins to advance along the body lines,
the more anterior organs of the head have already disappeared by inclusion in their

respective canals. 15;
Fic. 3. Tail of a larva 21™™ long, showing the extension of the lateral-line organs
onto the caudal rays. X15.

Fic. 3c. Tail of an adult Q 22% inches long. Half natural size.

Litt Anse elena dieter Prachi ae

v's ee ea Wii ates
a Wibere nen i) Pete if bine eth, W), Ans aa be
a ne uf iy in i, f i ; p i ie i
: ae (ot Waa Ba Alig h
; 4 ati,
Ad ALLIS.
-
.

Sul,

EXPLANATION OF PLATE XXxXI
Fic. 4. Side view of larva four days old (10™™ lone). The surface organs appear
X 40.

in a line above and below the eye.
Fic. 5. Front view of same larva.
Fic. 6. Side view of larva six days old (11%™™ long). Lateral-line organs of
Surface organs multiplying X 40.

head lying in half-closed canals.
Fic. 7. Front view of same larva.

Journal of Morphology. Vol.I.

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546 ALLIS.

EXPLANATION OF PLATE XXXII.

Fic. 8. Side view of larva 14™™ long, showing canals of head in various stages
of formation. Surface organs have become numerous. X 40.
Fic. 9. Dorsal view of same larva.

&.€

Wy (ibaa; pity Muhoch 4)S Lahn Ab,

PANY ean

fm ¥ , y :

548

EXPLANATION OF PLATE XXXIIL.

Fics. to and 11. Ventral and front views of the same larva.

—— a

Journal of Morphology. Vol IL A :
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cmd

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EXPLANATION OF PLATE XXXIV.

Fic. 12. Larva 18m long, showing the primary pores in various stages of forma- _
tion. = X 30. :
Fig. 13. Larva 31™™ long, showing the primary pores of the head. 30:00

’ )
a we aN Ae

A

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Cae

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af

ay

i
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4
5
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552 ALLIS.

EXPLANATION OF PLATE XXXV.

Fics. 14-16. Three views of a young Amia 78™™ long. The pores have begun
to multiply by division. x 5:
Fic. 17. Young Amia 25°™ long. The primary pores are now represented by
irregular groups of pores in different stages of division. > ey

554 ALLIS.

EXPLANATION OF PLATE XXXVI.

Fics. 18 and 19. Young Amia, 13.6°™ long, shows most of the pores of the head
divided into two, a few pores (/?) of the lateral line still single, and the surface organs
of the dorsal line (a7). <2:

Fics. 21 and 22. Three views of the adult head. Natural size.

sty

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endl mg” omg" ig?

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LD RAD. ® RAS

SAC aie

556

ALETS,

EXPLANATION OF PLATE XXXVII.

Surface views of the area between the eye and the first scales of the lateral line,
taken at different ages, to illustrate the formation of the canal in sections, and the
establishment of continuity between the sections by bringing two openings together
to form one pore.

Fic.
FIc.
Fic.
Fic.
FIG:
Fic.

23%
24.
25.
26.
2A
28.

From a specimen 19™™ long.
From a specimen 201%4™™ long.
From a specimen 23%4™™ long.
From a specimen 26™™ long.
From a specimen 29™™ long.
From a specimen 30%4™™ long.

x 40.
X 40.
X 40.
X 40.
X 40.
X 20.

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aed wiihie shai Sree ta, cn

RAE ERK erik fied ts gina Np! Wide
fy Se shy RAL Tee hy he heey: > ih

558

ALLIS.

EXPLANATION OF PLATE XXXVIII.

Fics. 29-33 illustrate still later stages in the formation of the primary pores; and
Fig. 34, the first division of these pores.

Fic.
FIG,
Fic.
Fie.
Fic.
FIc.

20.
30.
31.
32.
33-
34.

From a young Amia 35™™ long.
From a young Amia 37™™ long.
From a young Amia 40™™ long.
From a young Amia 50™™ long.
From a young Amia 54™™ long.
From a young Amia 134™™ long.
In Fig. 33, read 528 for 18.

X 20.
X 20.
X 20.
X 20.
X 20.
x 8.

Journal of Morphology. Voll.

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560

ALLIS.

EXPLANATION OF PLATE XXXIXx.

Fics. 35-38, illustrate the formation of the Jateral-line canal; and Fig. 39 shows

the primary pores replaced by a group of pores in each scale.
Fic.
FIc.
Fic,
Fic.
Fic.

35:
36.

37:
38.

39:

From a specimen 30%4™™ long.

From a specimen 35™™ long.
From a specimen 40™™ long.

From a specimen 60™™ Jong.
From a specimen 69°™ long.

Natural size.

X 40.
X 40.
X 40.
X 20.

dlo ia

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COT Aad,

562 ALLIS.

EXPLANATION OF PLATE XL.

Illustrating the osseous canals and pores in the adult. Xie:
Fic. 40. Bones of the head separated, but in serial order.

Fics. 41-43. Scapular arch.

Fic. 44. First four scales of lateral line.

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564 ALLIS.

EXPLANATION OF PLATE XLI.

Fics. 45-47. Three views of the skull with the bones 7» sttu, showing the course
of the laterai canals and the dendritic systems of peripheral canals. Natural size.
Fic. 48. A longitudinal section of a portion of the lateral line. X 140.

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s

; EXPLANATION OF PLATE XLII.

Fic. 49. A diagram showing the innervation of the lateral-line organs. i

ON THE ORGANIZATION OF ATOMS AND MOLE-
CULES.

PROF. A. E. DOLBEAR,

CoLLeGE Hitt, Mass.

In his dialogues on The Plurality of Worlds, Fontenelle rep-
resents the sages of antiquity as being spectators at the opera,
watching the play of the Universe. The subject is supposed
to be Phaeton carried away by the winds. The dancer who rep-
resents Phaeton is made to fly away through the upper part of
the scenes, much to the admiration of the lookers-on. The
wise ones now begin to speculate, and attempt to explain the
extraordinary movement of Phaeton. An Aristotelian says,
“Phaeton has an occult quality which carries him away.” <A
Pythagorean says, “Phaeton is composed of certain numbers
that make him move upwards.’”’ Another one says, ‘‘ Phaeton
has a longing for the top of the theatre, and is not easy until
he gets there.” He explains the universe by love and hate.
Another one says, “ Phaeton has not a natural tendency to fly,
but he prefers flying to leaving the top of the theatre empty,”
—which is the doctrine of Nature’s abhorrence of a vacuum.
After all these come Descartes and some other modern philoso-
phers ; and they say, “ Phaeton goes up because he is pulled up
by a weight that goes down behind the scenes.”

This is the mechanical philosophy that has been employed so
successfully im the unravelling of phenomena once thought to
be altogether occult. It is the philosophy that explains every
phenomenon of vzsz/e motion as due to some antecedent mo-
tion, which may or may not itself be visible. Since the time
of Sir Isaac Newton and the discovery of the laws of motion,
there has been no room for mysterious forces operating to give
movements to matter of visible magnitude. Guiding spirits
like Kepler’s are no more thought of as being necessary to
account for them than are Arabian genii.

When, however, we come to the phenomena manifested by
atoms and molecules, it is plain that the mechanical philosophy

570 DOLBEAR. [VOL. II..

has not only not been applied, it has not even-been assumed :
and all sorts of visionary entities and special forces have been
summoned to explain their behavior. Phlogiston and Caloric
for heat, fluids for electricity ; crystallizing force and vital
force for the phenomena of organization in crystals and living
things, —a continuation of the philosophies of the pre-New-
tonian period, which proved to be inappropriate, inadequate,
and unnecessary when applied to larger masses. The assumed
explanation was more mysterious, and needed explanation more
than the phenomenon to be explained by it; for the latter are
admitted to be mechanical, while the assumed explanations are
of a super-mechanical sort, for which there is no evidence apart
from its implied necessity for accounting for the special move-
ments observed.

Another Fontenelle might fairly make game of modern philos-
ophers who offer such inappropriate explanations of the move-
ments of matter, whether they be large or small, and who refuse,
in any case, to assume a mechanical cause for any mechanical
operation. To be sure, Caloric and Phlogiston and electric fluids
are no longer serviceable in physics, for it is conceded that heat
7s a mode of motion; and as for electricity, it is also conceded
that, whatever it may be, it is certainly not a fluid; and many
are not ashamed to admit being electrical agnostics, and say
they don’t know what it is.

It is certainly the business of physical science to explain phys-
ical phenomena; and there are certain fundamental principles
sufficiently well attested which may be assumed at the outset of
every investigation ; namely, the laws of motion, and that these
laws are always operative and quantitatively never change.
Hence every change in the position or collocation of a mass of
matter of any magnitude is referable to the laws of motion
of matter, is purely mechanical, and is to be explained solely
upon the assumption of antecedent motion.

Even the so-called properties of matter are amenable to this
principle. Physical terminology is, perhaps, to blame for not a
little of the incoherence, as is the case when the expansibility
of a gas or its pressure upon the walls of a containing vessel are
explained as due to molecular repulsion, seeming to endow the
molecules with an unmechanical property. When a base-ball
rebounds from the side of a house against which it has been

No. 3.] ATOMS AND MOLECULES. 571

thrown, no one thinks of saying that the house and ball repel
each other ; instead, it is recognized as the result of the impact
of elastic bodies. In like manner, the impact of elastic mole-
cules upon the sides of the containing vessel produce a pressure
upon it proportional to the momentum of the molecules; and
when molecules collide, they have their direction of movement
changed, and they separate.

Chemical affinity is another term that seems to imply that
atoms are endowed with essential selective properties by which
they are enabled to combine in definite ratios. In late years
chemists have adopted the term Chemzsm in place of chemical
affinity, and have given to it a greater range of proclivities,
finding no difference but one of degree between it and cohesion.
It makes but little difference to one who uses it who is con-
cerned solely with chemical reactions ; but it makes a good deal
of difference to one who is to explain the relations of chemical
changes to other physical changes, whether or not, as soon as
he touches atomic phenomena, he has to import into his discus-
sion a factor which has no physical antecedent that can move
and arrange atoms and molecules thus and thus, and yet itself
not be subject to the laws that obtain among larger masses.
As chemists no longer contend for a chemical force that is not
derived from antecedent physical conditions, it is alluded to
here for the double purpose of calling attention to the positive
mischief that often comes from inappropriate terminology, and
to the fact that, so far as my knowledge goes, chemists have
not attempted to give a physical explanation of the cohesion of
atoms into molecules, but have stopped with chemism, as if it
were an ultimate fact or property.

To give such a physical explanation of chemism or atomic
cohesion, and to extend it to the building up of geometrical
crystalline forms, is the object of this paper. It is not claimed
to be demonstrated, but as a hypothesis having a good degree
of probability in its favor. But even if it be inadequate, at least
it gives one a mechanical idea of how such forms necessarily
result from mechanical conditions.

Investigations into the relations of chemical reactions to heat
have developed the fact that all chemical changes involve
definite quantities of heat, either absorbed or evolved. That all
such changes are absolutely dependent upon the exchanges in

B72 DOLBEAR. (VoL. II.

<

motion that constitute what is called heat, and are therefore
measurable in heat units. As a heat unit can do a definite
amount of mechanical work, namely, raise 426 kilograms a metre
high, this latter quantity is called the mechanical equivalent of
heat. Chemical work is therefore expressible in mechanical
units. For example, when a kilogram of hydrogen combines
with oxygen to form water, there are given out in the operation
34,000 heat units, capable of doing 426 X 34,000 = 14,484,000
kilogrammetres of work. A kilogram of coal when burnt gives
out 8080 such units, and the elements thus combined can only
be separated again by the expenditure of as much energy upon
them as they gave out when combining. This department
of chemistry is known as Thermo-Chemistry. The relation
between heat and work, as explained above, is known as the
first law of Thermodynamics.

Again, from the second law of Thermodynamics it may be
shown that the total heat energy of a body, or its ability to do
work, is proportional to its absolute temperature. Hence at
absolute zero no chemical work could be done; that is, chemism
does not exist, and no work would be spent against cohesion to
separate the elements in a molecule. From this it may be
inferred that chemism is a derived property, and is the result
of heat; and also that Chemistry itself is a department of
Thermodynamics.

In order to understand more definitely how heat can bring
about such phenomena as selective combinations and the organ-
ization of atoms into molecules and crystalline forms, it becomes
necessary to know more precisely what the nature of heat
motions is that enables it to produce such mechanical effects.

If one turns to the text-books for a definition of heat, he will
quite likely be perplexed by the different statements to be found
in them. One may say that heat is energy; another, that it
consists of ether waves; a third, that it is a mode of motion;
and still others treat it in all three senses. The trouble comes
from the failure to distinguish between heat and some of the
effects of heat. Really they all agree that heat is a kind of
atomic and molecular vibration, as distinguished from oscillatory,
rotary, or free-path motions, and that is the meaning of it as
applied here. It is a necessary change of form of the atoms
or molecules, and will be easily understood by considering the
diagram, Fig. 1.

No. 3-] ATOMS AND MOLECULES. 573

The heavy-lined circle represents the atom, which is certainly
an elastic body, whatever may be its dimensions; and if it be .
subjected to pressure or impact, will yield like
the prong of a tuning-fork or the mouth of a
bell; and if spherical or circular, will assume
an elliptical outline; and if free to move, will
execute a series of elliptical phases at right
angles to each other, as represented by the dot-
ted lines in the figure. This change of form
is a mechanical necessity when bodies are elastic, and that
quite independent of what the form of the body may be. The
evidence for the statement that this is the real character of the
motion that constitutes what is called heat comes from Spec-
troscopy, especially that of heated gases, where molecules have
time to execute vibrations between impacts, in which case they
give out radiations of definite wave lengths, and in harmonic
series, which of course must be derived from the harmonic
vibrations of the particles of matter that are heated. It has
been demonstrated that the ultimate particles of matter, atoms,
cannot be spherical in shape; and to-day the only theory of the
constitution of matter we have is the Vortex Ring Theory of Sir
William Thomson. One must either adopt that or be without
any ; but evidence for its being a true theory is fast accumu-
lating, and there has as yet no serious objection been offered to
it from either physics, chemistry, or mathematics.

It will be adopted for the purposes of this paper, and hence
the diagram, Fig. 1, may be considered as a vortex ring capable
of changing its form and vibrating with an amplitude determined
by its size, thickness of ring, etc. Such an atom has a definite
fundamental rate of vibration, and a series of harmonic rates
which are 2, 3, 4... # times the fundamental rate, which is the
one represented. It is to be noted that where such vibrations
are taking place there are certain places upon the vibrating body
where the motion is at a maximum, called the /oops, and also
intermediate places where the motion is least, called xodes.
In the diagram there are four of each. If the body has a series
of harmonic vibrations, there will then be 2, 3, 4, and so on,
number of times the nodes of the fundamental. The number
of times such vibrations can occur among the atoms of matter
is determined by dividing the velocity of light by the wave

574 DOLBEAR. [Vou. II.

length of any particular ray that is produced by the vibration.
Thus, if the red hydrogen rays have a wave length of 0.000656
of a millimetre, the frequency of vibration of the hydrogen atom
that produces it is 457,000,000,000,000 times per second. This
particular vibration is the 20th harmonic of hydrogen. What
is of most moment here is to bear in mind that waves of so-called
light, having definite and constant wave lengths, are the result
of the heat vibrations of the atoms and of molecules, which must
therefore be vibrating at a constant rate, not irregularly ; and to
vibrate thus is one of the fundamental mechanical properties of
atoms as elastic bodies.

In order now to see what must follow from such motions, it
will be best to consider some of the phenomena of vibrations as
manifested in bodies of visible magnitude, say a tuning-fork.
If a light body like a pith ball be brought near the prong of a
vibrating tuning-fork, it will move towards the prong as if the
latter attracted it, and this is explained as being due to the fact
that a vibrating body reduces the air pressure adjacent to it.
How a vibrating body can reduce the pressure of the medium
about it may be understood by remembering that the pressure
is proportional to the density. If the vibration lessens the
density, it lessens the pressure. Let the inner circle of the dia-
gram, Fig. 2, represent an elastic sphere capa-
ble of extension to the dimension of the outer
circle. When it is thus expanded, of course it
excludes the air from the space it occupies.
When it contracts again, the air must follow.
Suppose the contraction should take place at a
rate greater than the air could move; then
there would be a vacuum between the surface and the advanc-
ing air, and that would be the condition all about the sphere ;
but at whatever rate the contraction took place there would still
be a partial vacuum next the surface of the sphere, else there
would be no movement of the air towards it; that is to say, the
pressure is less next to the sphere than at a distance from it.
Suppose the sphere to contract and dilate between the limits of
the lines in the figure, say one hundred times per second; then
the density would be less between those limits than it would be
beyond the outer one, with the consequence that the lessened
density would lessen the pressure upon the sphere in every

Fic. 2.

No. 3.] ATOMS AND MOLECULES. 575

direction about it, and this condition would be maintained as
long as the vibration was maintained. Another body near the
vibrating sphere would be subject to a pressure on its further
side greater than on the side adjacent to it, and as a conse-
quence would be pushed towards the sphere. It would appear
as if the latter attracted it. The space about the vibrating
body within which such lessening of pressure occurs, may be
called its mechanical field, because the effects noted are mechan-
ical effects. This expression is in accordance with usage in
electrical and magnetic phenomena. The magnetic field is that
space about a magnet within which magnetic effects take place.
In the case of the sphere the shape of the field would be spheri-
cal; but if the vibrating body was a rod or fork or disk or ring,
the shape of the field would be different, and evidently would
depend upon the shape of the body as well as upon its charac-
teristic vibrations. A tuning-fork does not have such a uniform
field as the imagined sphere, but presents two nodes, radiating
from the outer edge of each prong. These nodes, or spaces of
no vibration, may easily be detected by holding the fork near
the ear and rotating it with the fingers while it is vibrating.
As the lessening of density depends upon the amplitude of
vibration, it is plain that the greatest disturbance and least
pressure will be in the plane of vibration of the fork and near
the ends of the prongs, and here is where it makes itself
obvious by its apparent attraction of other bodies. If a paper
wind-mill three or four inches in diameter be held by a thread
near to a vibrating Chladni plate, it will be made to rapidly
rotate by the difference in pressure above and below the arms
of the mill. A smaller one that may be moved to different
parts of the plate will be found to be but little affected at the
nodal points and lines. This mechanical field of the Chladni
plate extends an inch or more from its surface both above and
below, and its form, of course, varies with the number of vibra-
tions the plate is making and the energy of the components of
the sound.

It is here assumed that vibrating atoms must have a fe/d in
the same sense as larger bodies, and that mechanical effects
must be produced in them not dissimilar to what takes place in
larger masses. The atoms, however, vibrate in the ether; but
we know from various other phenomena presented by atoms,

576 DOLBEAR. [Vou. II.

molecules, and ether, that the latter is affected by motions of
the former because they spend their energy upon it in some
cases, and in others receive energy from it. This is true for
light, for magnetism and electricity, and these are explained as
setting up undulations or special stresses in the ether. If one
considers the space affected by a heat vibration of an atom as
its field, it appears to be as large as the universe, for the undu-
lation travels on in straight lines to an indefinite distance, as do
sound vibrations in the air; but the maximum displacement or
change in the density or stress in the medium must necessarily
be greatest where the amplitude of motion is greatest ; namely,
immediately adjacent to the vibrating body itself. Assume that
the vibrating atom lessens the density of the ether adjacent to
it, and at once it is seen that other atoms near by will be
crowded towards the one thus vibrating —there is an apparent
attraction within its field. But the heat vibrations of an atom,
as represented in Fig. 1, will have a field somewhat like
that of a tuning-fork ; for, as
shown, there are four nodes
: 5 \ where there would be no les-
sening of the pressure, and
four parts where such les-
sening would be at its max-
imum. Consider, then, two
atoms adjacent to each other,
but not in contact; and
one of them vibrating in its
fundamental rate, Fig. 3.
The modés” are’ ata, 2304
and 4; and if the spaces marked 5, 6, 7, and 8 represent the
variable pressure spaces or the field of the atom, it is shown
that the other atom will be in a space of less pressure at 6 than
at 9, and consequently will be crowded towards 6, where the
amplitude is greatest; but because it is greatest, it will be in
unstable position, and will move to one or the other nodes, I or
2, where it will be held while the vibration is kept up. If the
second atom vibrates also, that will only double the strength
of the field at 6 and make the pressure towards each other
stronger than before, and the two will join nodes at I or 2.
But there are four nodes, and consequently as many places

No. 3.] ATOMS AND MOLECULES. 577

where other atoms can join, in which case, if all were vibrating
similarly, there might be a conjunction, as shown in Fig. 4, —an
atom at each one of the nodes; but
such an arrangement in one plane would
not be a stable arrangement. The point |
of attachment of any one might be con-
sidered as a kind of hinge, allowing a
swing to and fro. Imagine two oppo-
site ones, as 2 and 4, to swing upwards ,
so as to touch each other. If these ‘
be vibrating, their points of contact
will be nodes. They will, therefore,
cohere by another bond, and such an atomic arrangement will
be a stable one. If the rings have equal dimensions, an edge
view would show them as an equilateral triangle with nodes at
the apices, Fig. 5. We might call such a combination a mole-
cule, and say it was held together by chemism. Each molecule
thus constituted must have a mechanical fe/d, which will be the
resultant of all the atomic fields that compose it ; and indeed this
will be true for such molecules of every degree of complexity.
Molecules having similar fields fit together for obvious mechani-
cal reasons, and cohere because they are pressed together by
the medium they vibrate in. If similar triangular forms to the
one above unite, they may form hexagonal prisms, as Fig. 6
shows, in cross-section, and such as is the crystalline forms
assumed by water, silica, and some other minerals having three
atoms in the molecule.

Fic. 5 Fic. 6.

Now let 2, 3, 4, and 5 of Fig. 4 swing upwards; they too will
touch each other at their sides and at nodes, so as to form a
stable figure held by eight bonds, —an atomic box without a
lid, — yet having four nodes on the open end to which another

578 DOLBEAR. [VoL. II.

similar atom could be attached by its four bonds, forming a cubi-
cal box having a high degree of mechanical stability. It will
have a symmetrical, but not a uniform, field; the corners be-
ing the places having maximum displacements, and the middle
of each edge the minimum, as the nodes are all in such posi-
tions. Hence other similar cubes would be moved to assume
symmetrical positions when in contact, and thus a cubical struc-
ture, or prismatic form, would be built by aggregation of similar
molecules. This is on the supposition that all the atoms com-
bining thus together are equal in size as well as uniform in their
vibrations; and this cubical form is one in which not a few of
the elements crystallize ; for example, gold, iron, copper.

If one would see more clearly how these nodes and loops fit
together in such structures, let him make paper models, drawing
a set of circles with their peripheries touching at one point, as
shown in Fig. 4. Make points upon each circle to indicate the
nodes, and then bend them up as described. If another one
similar to 3 be made hinged at 6, it will form the cover to the
cube, and all the nodes will be adjacent.

So far such vortex atoms have been considered as being all
of one magnitude, or as all having a similar rate of vibration ;
but the different elements have different masses, and therefore
vibrate with different rates; the greater the mass, the slower
the rate, according to the laws of motion. When two elemen-
tary atoms come into contact with each other while vibrating
at their individual rates, whether they can cohere or not will
depend upon whether the vibratory rates are commensurate or
not. If they are not, there will be what is called interference
in their respective fields, and each will tend to destroy the
other’s field. When the vibrations of two tuning-forks not in
unison or ina harmonic series are heard together, their inter-
ferences are audible, and are called deats. They are in oppo-
site phases a portion of the time. Vibrating atoms must be
subject to the same conditions. One ought, therefore, to expect
that elements with different masses would show different degrees
of coherence, as indeed they do. There are all degrees of these
incompatible movements from that exhibited by oxygen and
fluorine, which have never been made to combine at all, through
the slight cohesions shown by gold, platinum, etc., for other ele-
ments, up to that exhibited by carbon for itself in the diamond,

No. 3.] ATOMS AND MOLECULES. 579

and oxygen and aluminium in the ruby. Furthermore, an ele-
ment having but a small mass like hydrogen could produce a field
of slight strength compared to that of an element moving with
the same velocity, yet having decidedly a greater mass, so that
when it combined with any other element, it would be because
of the greater energy of the other’s field; that is to say, oxygen
holds on to hydrogen rather than hydrogen to oxygen, and one
would expect that hydrogen could be replaced by some other
element in a compound more readily than any other element.
Hence, whatever might be the relative rates of vibration when
compared with other elements, one might infer it could be asso-
ciated with them. One might explain its weak affinities by its
small mass and consequent small vibrating energy. With larger
masses, however, the case would be different. If one made five
vibrations while the other made but one, they would be in the
same phase but one-fifth of the time, and in more or less interfer-
ence the other four-fifths ; and unless there was a considerable
disparity in their masses, there would apparently be but slight
cohesion. If one made four while the other made one, they
would be in similar phases three-fourths of the time, and could
thus form a more stable alliance.

As has already been said, atoms vibrate in harmonic series,
and this must frequently modify the position of the nodes when
adhesions can occur. Now the harmonic series is 2, 3, 4, and
so on, times the fundamental rate. If one will imagine such a
vibrating ring to be cut at one of the nodes, and the two ends
straightened out, it will be seen that there are really two vibra-
tions, or stationary waves, as they sometimes are called, in the
ring, and the harmonics are the fractional parts of one wave.
Suppose each of these waves to be divided into three parts, —
that is, to be accompanied by the second harmonic; then the cir-
cumference of the ring would have twelve nodes, —an arrange-
ment that would permit three other rings to be hinged at angles of
120° apart ; and if these were swung upwards until they touched
each other, they would form a stable combination, but the angle
made between the base and the side of this pyramidal structure
would depend upon the relative diameters of the ring composing
the base and sides. The smaller the latter, the greater the
inclination. With similar structure there could grow up an-
other hexagonal system, having a differently distributed field

580 DOLBEAR. [VoL. II.

from the other, but still symmetrical, and therefore capable of
growing a symmetrical shape.

This has probably been carried far enough to show what was
intended ; namely, that because the atoms of matter are vibrating,
and for all matter within our experience a long way above abso-
lute zero, and because the motions of matter are known to affect
the ether in a manner that depends upon the character of the
motion, it follows that each atom has a field the shape of which,
and the strength of which, must depend upon the kind of motion
it has and the energy involved; that vibrating motions affect
the density of the ether in different directions about the atom,
and result in a pressure towards it, and on account of the
harmonic motions, there are stationary nodes where atoms may
cohere together, forming symmetrical figures of molecules and
larger masses of crystals, each of which in its turn has a field
which is the resultant of the combined fields of its constituents.
It is the reaction of this field upon other molecules that organizes
them into the larger geometrical shapes, and tends to replace
upon imperfect crystals the parts that have been removed or
which are not symmetrical with the rest—a phenomenon that
has been observed.

The reaction of a field upon a body within it is recognized in
the familiar phenomena of heat ; for the ether waves that have
been produced by a hot body compel other molecules, which
these waves meet, to vibrate like those that produced the waves.
The earth is heated by the sun for this reason.

Whenever the ether is put into a condition of motion or of an
abnormal stress through the motions of atoms and molecules,
other atoms and molecules must adapt themselves to the abnor-
mal condition by adopting the motions, or changing their posi-
tion, or both, the tendency always being to assume the condition
of the original disturbing body. This explains why it is that a
certain molecular combination possesses the ability to aid in the
formation of other similar molecules, a property exhibited by
the simplest as well as the most complex molecules, in non-
living as well as living organisms.

The foregoing explanation of the organization of atoms into
molecules, and molecules into crystalline forms, is made to
depend upon the freedom of such bodies to assume their geo-
metrical positions, such as gases and liquids permit; but it must

No. 3-] ATOMS AND MOLECULES. 581

not be inferred that molecules could not cohere except at such
nodal points. So long as the atoms vibrate, they produce fields ;
and this compels the molecules to assume a degree of compact-
ness that depends upon the strength of the fields, and this may
take place in the most irregular manner and without any special
order. A piece of wrought iron may be made crystalline by
repeated jarring, as it gives to the molecules a transient degree
of freedom to assume any new position they have any tendency
to take. In like manner, a bar of iron held in the proper posi-
tion in a magnetic field will, if jarred by the stroke of a hammer,
assume polarity; for the jar assists the molecules to rotate to
the magnetic position induced by the field. But the strength
of cohesion in crystals is generally less than in amorphous
bodies, probably from the fact that when the molecules have
moved to the vibratory nodes, forming geometrical figures, they
have moved somewhat away from the place of greatest pressure,
which is where the amount of motion is greatest, the atomic
impacts at such places tending to move them towards less dis-
turbed points. When molecules are very compact, such change
of position is mechanically difficult, and vigorous jarring aids
somewhat to the rearrangement. Hence the crystallization
that often takes place in solids like iron.

Perhaps most who have read this so far have already foreseen
the bearing it has upon organization as manifested in living
things, rendering it unnecessary to do more than briefly to
apply it.

Chemically, protoplasm is made up of complex molecules, not
of so great a variety of elements, yet a thousand or more atoms
in one molecule. As molecules increase in complexity, they
become less stable, the interior atoms being in a much more
uniform field than the outer ones, and therefore more easily dis-
placed; but every such protoplasmic molecule, whether with or
without a cell structure, must have a mechanical field, and there-
fore must compel other matter in proximity to it to assume the
same arrangement as its own. If all the elements necessary
are available, it will be done; that is to say, the protoplasmic
mass grows. But this process is called life, or the results of
life.

As the mechanical relation to the fed is different for an atom
deeply imbedded in a molecule from that of one on the surface,

582 DOLBEAR. [Vot. II.

as was pointed out a little way back, it follows that a greater
degree of stability would be looked for in the materials upon
the outside than upon the inside; and hence the cellular struc-
ture itself is a result of the mechanical relations between the
molecules and their field.

The field of a given cell must depend upon the elements of
its composition, their number and arrangement; and for any
one of visible magnitude must be so complex that, at any rate,
now it would be quite a hopeless task to attempt to describe it,
yet there does not appear to be a good reason for not having a
well-grounded conviction that in fact there must be such a field,
and some sort of a mental picture of what it must be like.

As its source is purely mechanical, its properties must also
be purely mechanical, the form assumed and the order exhibited
being but an extension to complex molecules of the form and
order displayed among relatively simpler bodies called crystals.

Now, vital force as an entity has been quite given up by all,
except a few of the old school of biologists who have not yet, and
probably never will learn that such a view is incompatible with
almost everything we do know, as science, about the matter.
The foregoing presentation shows that such an assumption is
an unnecessary one, as fundamental mechanics will explain the
phenomena without its aid. Its bearings upon some of the
problems of biology must be apparent, as a prime factor in
evolution, in explaining heredity, and in giving a very distinct
answer to the question as to the cause of variation; for an extra
molecule, even accidentally imbedded in a mass of other mole-
cules, must change the configuration of the field, and hence the
direction of growth. One does not need to go further than the
formation of a cell that can organize a similar one, animal or
vegetable, for the purposes of this article; but the next ques-
tion to be asked by every one interested in the problems of life
is, What is to be said of mind, consciousness? Has that, too,
a mechanical antecedent, a mechanical equivalent, and does it
depend solely upon mechanical conditions? Not long ago it was
the custom to speak of Azgher and lower forces. These were
mechanical forces on the lowest plane, then chemical, then vital
and mental forces highest of all. Now two of these, the chemi-
cal and vital, have absolutely been absorbed into the mechanical
one. In fact, it now seems absurd to speak of higher and lower

No. 3.] ATOMS AND MOLECULES. 583

in physical phenomena in any philosophical sense. There is
matter and its motions, rectilinear, rotary, vibratory, and vorti-
cal, each kind changeable into the other under proper mechanical
conditions ; and there is no sense in speaking of one of them as
being higher than another. Each one of them has mechanical
possibilities that do not belong to the others, and no one of
them can be treated as first in order.

When it is ascertained that heat is a vibration, that light is
an undulation, that electricity is a rotation, that is, that they are
only conditions, it is seen that the questions what zs heat, what
7s light, what ts electricity, are philosophically improper ques-
tions, and the whole scheme of the universe mechanically con-
sidered is on one plane, and there is nothing common or unclean
in it. This is to meet the objections of those who think that
matter and its phenomena are of a low grade. As a matter of
fact, mind is in some way associated with matter, and depends
for its development upon matter and its properties. As it is
associated with a certain cell structure, there is at the outset a
presumption that the mechanical relations are not so different
as they seem to be, and the explanation is to be found sooner or
later in entire accordance with all other physical phenomena.
If one is to attempt an explanation, it must be in accordance
with what we do know, and not in accordance with what we
don’t know.

Suppose, then, there be in the universe a mental field, no
matter how that was produced. Wherever there should chance
to be a collocation of matter, with a field upon which the first
could react, the second would be mechanically endowed with
the property that maintained the field; that is to say, mental
phenomena would manifest themselves for precisely the same
reason that other properties manifest themselves. The char-
acter of the mental manifestations would in such a case depend
upon the character and complexity of the material structure that
was acted upon, giving scope for all the degrees of intelligence
exhibited by the animal creation including man.

Perhaps most persons would say I have now invoked the
deity, to which I do not object; but as my purpose is to show
how things can be so and so in accordance with mechanics,
I have spoken of the mental field without regard to other than
its mechanical relations to such matter as makes up the nervous

584 DOLBEAR. [ Vo. II.

matter of animals. When the needle of a compass turns from
its normal position, we know that a new magnetic field is acting
upon it, and we do not need to know whether that was produced
by a permanent magnet or a current of electricity in a neigh-
boring conductor. Its behavior is explained without regard to
the antecedents of the field.

REMARKS.

As the foregoing article cannot be said to come strictly within the
scope of this JOURNAL, a note of explanation is here appended. The
nature of formative energy was briefly adverted to in a previous number,
and the views there presented elicited some critical comments by letter
from Professor Dolbear. The outcome of the correspondence was that
Professor Dolbear prepared, at my solicitation, a paper for the JOURNAL,
in which the question is treated from the physicist’s standpoint. An
article of such exceptional interest, bearing directly on a problem under-
lying all animal and vegetable morphology, can hardly be regarded as
out of place in these pages, and I am confident that its perusal will not
leave the reader over-solicitous on such a point.

It is not my purpose here to discuss the bearings of the mechanical
hypothesis presented by Professor Dolbear, but a brief comment or two
may not be amiss.

According to this hypothesis, the formative agency is ether-pressure,
acting under conditions induced and maintained, not by unit-action
of the organism, but by vibratory motions of its constituent elements
mechanically associated. Attraction is banished from the universe.
Chemism and cohesion, and presumably gravitation too, are but dif-
ferent degrees of ether-pressure. Crystallization, development, growth,
are all mere expressions of the interaction of atomic vibration and
ether-pressure.

Now consider the elements out of which the organic world is to be
evolved: Azoms, absolutely inert, and utterly destitute of all guahtatve
distinctions ; impressed, vibratory motions, measured and timed by the
magnitude of the atoms ; and e¢her-pressure, compelling purely mechan-
ical associations. Then we have the mechanical field, and with this
captivating conception, we rise to that of an automaton in the form of
man. But alas! the all-important psychical qualities are missing. We
have just what we started with — unconscious, inert atoms, played
upon by ether-impressions. Of course we had no right to expect more;

No. 3.] REMARKS. 585

for if qualities are left out at the beginning, they will not turn up at the
end. £x nihilo nihil fit. Now I may be mistaken, but I think there are
few biologists to-day who will object to an hypothesis because it is
mechanical ; but there are at least some who find it difficult to accept
any hypothesis that ignores qualities. The evolution of function pro-
ceeds pari passu with that of structure, and the basis for both must be
postulated at the outset. There is no place anywhere for the sudden
apparition of qualities for which no basis previously existed. And here
the question forces itself upon us: If it be inadmissible for a physicist
to import into his discussion of atomic phenomena anything which has
no physical antecedent, how much has he lessened the difficulty by post-
poning the forbidden act till after his automaton has been constructed ?
And yet we are told that the psychical factor, once introduced, trans-
forms the machine into a microcosm, and henceforth exhibits itself in
vibrations that do not upset the previous mechanical harmony. If the
mechanical field be the avenue of admission for the psychical factor,
then why may not our mechanical hypotheses endure its presence at one
stage with as much composure as at another? If the doctrine of the
conservation of energy allows a “ mental field,” impressing itself upon
a mechanical field, then it surely will not break down under the burden
of a few qualitative distinctions imported into our atoms and molecules.
Then, too, I am tempted to ask, is not the “ mental field’ a needless
invention? It claims to add nothing to the organism except motion,
and if qualitative distinctions need no other basis, why seek an unknown
source for what is furnished in the elements with which we have to deal?

But there is no end to questions, and my interest in Professor Dol-
bear’s admirable exposition has already carried me beyond the first
intention of my comments, and perhaps beyond the forbearance of the
reader.

C. O. WHITMAN.

SOME NEW FACTS ABOUT THE HIRUDINEA.
C. O. WHITMAN.

A FEw facts and conclusions are here briefly stated in advance
of several papers on the Azrudinea, which are now nearly com-
pleted, and which I hope to see published in the third volume of
this JOURNAL.

1. The Hirudinea, as a group, are characterized by the posses-
sion of segmental sense-organs on the first ring of every somite.
The plan of arrangement is everywhere essentially the same as
I have already described in detail for the ten-eyed leeches. The
statement by Mr. Apathy that such organs do not mark the
somites in Az/astoma is incorrect ; and inexcusably so, as their
topography has already been made known. I do not deny that
some forms are found, like Vephelts, Clepsine bioculata, and Pon-
tobdella, in which the segmental arrangement has been much
obscured, or perhaps entirely obliterated. It is plain that such
conditions might be reached in two ways: either by the loss or
the multiplication of organs.

2. As the metameric arrangement of these sense-organs charac-
terizes marine as well as fresh-water and land leeches, and as they
everywhere agree in certain remarkable details of number, topog-
raphy, and structure, I am led to believe that the diffuse, or non.
metameric arrangement, exemplified in Mephelzs and some other
forms, has been secondarily acquired. Vephelis is an instructive
example, for it shows an analogous departure from the typical
arrangement in the multiplication of its testicular organs. The
lateral-line organs of some fishes and amphibia illustrate the
same point. Obscuration of the metamerism of organs through
multiplication is too well known to require further illustration
here. The presence of well-developed eyes in (Wephelis, seg-
mentally disposed, points unmistakably to the former possession
of the ordinary segmental sense-organs.

3. I have brought together a large amount of evidence to
prove that in all ten-eyed leeches, including many widely scat-

No. 3.]| SOME NEW FACTS ABOUT THE HIRUDINEA. 587

tered species of both land and fresh-water forms, the eyes
represent enlarged and more or less modified segmental sense-
organs. The question remains to be answered, whether the
same holds true of other leeches. If this be conceded, then I
see no easy escape from the conclusion that the metameric
sense-organs are earlier in origin than the non-metameric ones.
If the scattered organs were first in order of development, we
ought at least to find some cases in which the eyes are not seg-
mentally arranged. There are some cases in which the serial
homology of the eyes with the segmental sense-organs is not at
first sight apparent. This is true of some species of Clepszne.
The development of the eyes in these cases, as will be shown in
one of my papers, settles, beyond dispute, the fact that the eyes
are segmental in origin, and strictly homologous with the seg-
mental sense-organs.

4. In the case of Clepsine parasitica and C. chelydre (n.sp.), I
- have satisfied myself that the segmental sense-organs appear
very early in the embryo, before the time of hatching, while the
scattered organs arise later. Another evidence in support of
the above-stated conclusion.

5. In Hementeria (commonly, but incorrectly, Hementaria),
and in several species of C/epseve from Japan and America, there
is one somite clearly marked by segmental sense-organs in front
of the eyes. This makes twenty-six somites in front of the
acetabulum, not counting the narrow tip of the cephalic lobe.
Mr. Apathy insists on counting this tip as the first somite, but
he has not yet produced any satisfactory grounds for so doing.
The difference between us is, not that I deny the possibility of
finding one, or even more than one somite in the “ prostomial,”’
but that I question the propriety of calling it oe, while it still
remains undetermined whether it represents one, two, three, or
none at all. The argument from the number of segments in
the brain will be worth considering when we know precisely
how many somites are there represented. The question is beset
with some difficulties, which are not likely to be removed by
anything less than thorough embryological research. The argu-
ment from the labial sense-organs, as will be seen in the next
paragraph, is likewise premature.

6. The labial sense-organs — prostomial sense-organs of
Apathy — are serially homologous with vextval segmental sense-

588 WHITMAN. [Vou. II.

organs, as I shall be able to show very clearly in C. chelydre
and in a Japanese species. They do not therefore represent
one somite, as supposed by Mr. Apathy, but merely the ventral
organs of as many somites as belong to the cephalic lobe. Their
dorsal counterparts have preserved their segmental arrangement.
If any dorsal organs are represented in these labial organs, the
development ought to show it. I once thought I had found
some evidence of this nature, but I have since followed the
history of these organs farther, and find reason to modify my
view.

7. Systematists have usually concluded that where no eyes
could be recognized by surface examination, none were present.
My experience leads me to suspect that most of our reputed
blind leeches will yet be made to bear testimony to the blind-
ness of their observers. To all outward appearance, Branchel-
liopsis (gen. nov.), a Japanese marine leech, has no eyes. I
made a careful examination of the head, first in a fresh and
then in a hardened state, and finally by sections, but found
no eyes. Returning to the study of this leech recently, after
having learned in what the eye of a leech consists, I suc-
ceeded in finding at least two pairs of eyes. These eyes have
so little pigment that they cannot be seen from the surface;
and any one in search of pigment-spots would find little in sec-
tions to arrest the eye. The visual cells, however, are there ;
and their form and relation to a thin, open background of pig-
ment would, on close examination, entitle them to rank as eyes
in the ordinary acceptation of that term as applied to leeches.
In form they remind one of the eyes of Pzsczco/a,; in structure,
the eyes of Clepsine,; and in position, the eyes of Wephelts.
They are in fact so little removed in general make-up and
appearance from the ordinary segmental sense-organ, that I
had to examine sections made in the three principal planes
before fully satisfying myself that they would pass as veritable
leech eyes.

8. Piscicolaria (gen. nov.), a parasite of fishes in the smaller
lakes of Wisconsin, about the size of Pzsczcola, and intermediate
in form and structure between Piscicola and Branchelliopsis,
* comes nearer to being blind than any other leech I have yet
examined. The only evidence of an eye is a single large
visual cell, on either side of the head, without a trace of a pig-

No. 3.] SOME NEW FACTS ABOUT THE HIRUDINEA. 589

ment investment. In view of these facts, and others yet to be
noticed, we can no longer regard pigment as an essential ele-
ment of the leech eye. It will not do to fall back on the
hypothesis of degeneration, and assume that these eyes sup-
plied with little or no pigment are functionless rudiments. The
visual cells are here as perfectly developed as in the pigmented
eyes, and the same is true of the optic nerves.

g. The test of a leech eye, then, is the presence of visual cells.
Now what are the visual cells, and how are they to be recog-
nized? After spending a good deal of time in the study of the
structure and development of the sense-organs of the leech,
I feel quite confident of having reached a point in the inves-
tigation where I can safely answer these questions. The visual
cells are the “/arge clear cells” of Leydig, the so-called “ Glas-
korper.’ The proof of this lies in a variety of facts, only a few
of which can here be presented in a summary way. The leading
points are as follows: 1. These cells always make up the bulk
of the eye, and in the Hirudo pattern they are the only cells
supplied by the optic nerve. 2. The main axis of these cells —
that passing through the centre of the cell and the eccentric
nucleus — is generally, though not invariably, parallel with the
axis of the eye. This is most clearly seen in some species of
Clepsine, and is very evident in Branchelliopsis. 3. In these
genera, the nucleus lies on the side exposed to the light, the
clear rod-like part of the cell being directed towards the pig-
ment. The cells are practically inverted, the nerve-fibres enter-
ing at the nucleated pole. 4. A comparison of the different
patterns of eye represented in Hzrudo, Nephelis, Clepsine, and
Branchetliopsis, with the typical segmental sense-organ, shows
that the chief distinction between the two classes of organs
lies in the relative abundance of the clear cells.

10. The segmental sense-organs are double organs, both in
structure and in function. There is an axial cluster of elon-
gated cells, terminating at the surface in minute hairs, and
representing most likely a tactile organ. Around and beneath
the factile cells, are the large, clear visual cells, so characteristic
of the eye. Thus we have a visual and a tactile organ combined,
both derived from a common mass of indifferent epidermal cells,
and both supplied by fibres from a common nerve branch.

11. Incredible as the double nature of these organs may at

590 WHITMAN. [Vou, II.

first appear, there is no escape from the fact, when we once
understand the structure of the eye in Clepsive. A vertical
section in the plane of the optical axis reveals the com-
pound nature of the eye, and the identity of its structure with
that of the segmental sense-organs. Here stands the tactile
part of the organ, an exact copy of every feature seen in the
corresponding part of a segmental sense-organ; and below and
behind, but in continuity with the tactile portion, lies the mass
of visual cells. The common nerve runs up in front of the
visual cells, dwindling gradually in size as its fibres pass to the
cells, and at length it is lost in the tactile cells. The main
features of this eye have been known to me for about two years,
but it did not seem best to hasten the communication of the
facts before giving the whole subject careful study. The sense-
hairs were first clearly demonstrated in WVephelis, and next in
both the young and adult of Clepszme. The nerves supplying
the eyes and sense-organs of the head arise in Branchelliopsis
and C/lepszne from the five sub-cesophageal ganglia.

12. In Azrudo, the visual cells are symmetrically placed
around the axza/ nerve fibres, and no tactile cells are developed;
in Clepsine and Hementeria, the visual cells are developed only
on the posterior side of the nerve, while the tactile cells are
grouped above and in front. In Wephelis the nerve is again
axial; in Branchelliopsis it is eccentric, as in Clepsine, and there
are comparatively few visual cells.

13. Both the eyes and the segmental sense-organs develop
as local thickenings of the epidermis. At first the cells are
alike in form, size, and structure. About the time the pigment
begins to appear, the two sorts of sense-cells begin to show
a difference in size, and an indistinct boundary line appears
between them.

14. The metameric arrangement of the sense-organs of the
fTirudinea is a matter of more importance than the latest writer
on the subject, Mr. Apathy, appears to realize. The limits of
this paper do not permit me to review the arguments which this
young naturalist has entombed in a preliminary report of about
eighty pages (portentous dimensions !). I am compelled to re-
mark, however, that this author has not been sufficiently careful
in presenting the views of others. As one out of many instances
that might be cited, the following is characteristic. I am rep-

No. 3-] SOME NEW FACTS ABOUT THE HIRUDINEA. 591

resented as having made the supremely ridiculous mistake of
taking the wart-like protuberances found on many species of
Clepsine for sense-organs. In C. marginata —to cite one more
case —I reported four anal ganglia. My statement was made
with reference to a single species, and is perfectly accurate ;
but Mr. A. charges me with an error, because, forsooth, my
statement is not true for a// leaches. This is the style of criti-
cism indulged in throughout this preliminary monograph. What
I have called visual cells are put down, er cathedra, for “ fat-
cells,” “gland-cells,” etc. Charity and necessity alike commend
us in taking immediate leave of such oracular wisdom. It is to
be hoped that before that impending final monograph is launched,
our author will have discovered the unregenerate source of his
present afflatus.

15. The key to the analytical study of the external form is to
be found in the metameric disposition of the sense-organs. Of
course internal structure is to be taken into account, and a fair
critic would hardly have fallen into the mistake of supposing
that I had neglected this side of the subject. I have had con-
siderable opportunity to learn the practical value of this key for
systematic purposes, and the longer I use it the more indispen-
sable it proves. The terminal somites are of the highest impor-

tance for specific diagnosis, and their annular composition, which
offers so much of theoretical interest, cannot be deciphered
without the aid of the segmental sense-organs. What clearer
demonstration of all this could be desired than has already been
furnished in the case of the ten-eyed Hirudinea? I am now
prepared to show that the same holds true of both fresh-water
and marine Rhyucobdellide, although the application of the
method is, as a rule, more difficult here than in the Guathob-
dellide. The number of ventral ganglia is generally supposed
to be the same for all the different species, genera, families,
and so on for the entire class. While we may be sure that the
number of somites represented in the rings does not exceed the
number of ganglia, is it not perfectly clear that the latter can-
not serve as a guide in determining the aznular limits of somi-
tes, particularly at the ends of the body? Then it must be
remembered that the number of ganglia in the cephalic group
has never been satisfactorily determined, and even the number

592 WHITMAN. [VoL. Il.

=<

in the caudal group has been variously estimated at six, seven,
and eight.

16. The importance of the segmental character of the sense-
organs is not to be measured by its usefulness in systematic
determinations. Leydig showed long ago, in A/zrudo, how the
same nerve supplies successive sets of eyes. How, then, could
the ganglia or nerves of the so-called brain be made to reveal
the metameric character of the eyes? And how could the im-
portant serial homology of the eyes ever have been determined
except through the discovery of their relations to sense-organs
known to have a metameric arrangement? It is by virtue of
this arrangement that I have succeeded in getting such a com-
plete and convincing picture of the origin and history of the
leech eye. Segmental sense-organs are found in other annelids
and in vertebrates, but nowhere is the transition from lower
to higher sense-organs so pérfectly illustrated as in the leech.
Branchelliopsis, Clepsine and Hirudo reveal all the intermediate
steps, beginning with the purely tactile organ; then advancing
to the compound organ, in which a few of the cells have been
modified to serve the purpose of vision, while the rest have
retained their primitive character ; and finally, culminating after
a long series of progressive encroachments, —the visual elements
increasing gradually at the expense of the tactile, — in an organ
in which the original function has been entirely suppressed and
a new one substituted for it. Here is a chapter in the evolu-
tion of sense-organs so perfectly preserved in all its details as
to leave no room for scepticism.

17. Without entering into the discussion of the point, I desire
to repeat here the suggestion made on another occasion, that
the segmental sense-organs of the leech are identical with the
lateral-line organs of vertebrates. I do not venture to express
such an opinion without having duly reflected on the objections
that might be raised. Having spent considerable time in the
study of the lateral-line organs in the larval stages of amphibia
and marine fishes, and having followed closely the work of my
colleague on Amia, Lepidosteus, and various teleostei, I know,
at first hand, where the difficulties lie, and I do not think I
underestimate their importance.

18. Perhaps it will not be venturing too far on speculative
ground if, in this connection, another suggestion be offered ;

No. 3.] SOME NEW FACTS ABOUT THE HIRUDINEA. 593

namely, that the segmental sense-organs of annelids have formed
the starting-point for the development of the organs of special
sense tn the higher animals, not excepting even the eyes of ver-
tebrates. The evidence is rapidly growing stronger in favor
of the origin of the olfactory and auditory organs from lateral-
line organs; and the gustatory organs are certainly destined
to fall into the same line. Mr. Allis’ observations show
how lateral-line organs may travel through gill-slits, and the
mode of growth of the surface bulbs shows how they may
spread to new areas. In regard to the vertebrate eye, we can
never expect, of course, to determine its identity with lateral-
line organs by such direct evidence as is available in tracing the
origin of the leech eye. Assuming that vertebrates and anne-
lids have had common ancestors with segmental sense-organs,
the fact that such organs have been converted into eyes in
at least one large group of annelids, raises the suspicion that
nature may have practised the same economy in all branches
from the common stock. And when we find strong grounds
for thinking that the lateral-line organs have served as the point
of departure for the formation of gustatory, olfactory, and audi-
tory organs, our suspicion in regard to the eyes no longer
appears incredible. I am not at all unmindful of what might
now appear to be an almost insurmountable objection to regard-
ing the vertebrate eye as a segmental organ. As one of my
laboratory colleagues is soon to bring some new facts to bear
on this subject, and as further discussion might lead to the
expression of views that have certainly been corroborated by
his observations, I drop the question for the present. I would,
however, mention one observation of mine with reference to the
eye of Wecturus. The basis for the eye is already discernible as
a circular area—after treatment with osmic acid followed by
Merkel’s fluid —long before the closure of the medullary folds
of the brain, at a stage corresponding closely with Goette’s Fig.
12, Pl. IIL, of Bombinator igneus.

But we have an wxpaired vertebrate eye, of recent discovery,
but possibly of very ancient origin. How is it possible to
apply the hypothesis of segmental derivation here? As seg-
mental sense-organs are always paired, it is not easy to account
for the origin of an azygous organ from them except through
the fusion of at least one pair. We are not able to point to

594 WHITMAN. [Vot. II.

many indications of a double origin, but the two vesicles in
Petromyzon (Ahlborn, Beard), and the double pineal stalk of
Varanus giganteus (Spencer), are facts that certainly favor such
a view. Moreover, the position of the organ is such that we
must suppose it to be derived from two sources, namely, the
lateral (sutural) edges of the medullary plate. The fusion of
segmental sense-organs has nothing improbable in it, as can be
shown by more than one example from the Hzrudinea. On the
other hand, the origin of organs by division, although claimed
by a number of authors of high repute, has not a single verified
fact in its favor. I am quite confident that such a process does
not underlie the multiplication of lateral-line organs, and I have
found nothing of the kind in the development of the segmental
sense-organs of the Hzrudinea.

The origin of the pineal eye from the lateral eyes, as held by
Beard, is open to more serious objections. In the first place, it
is difficult to believe that this organ is of later origin than the
lateral eyes ; and in the second place, the idea that the entire
optic vesicles (before and during the closure of the neural plate)
represented retinal epithelium does not appear probable.

Professor Cope has recently brought some new paleontological
evidence to bear on this question, and suggests that the lateral
eyes may have arisen from the pineal eye. The condition rep-
resented in J/ycterops is not claimed to necessitate such a view,
and there is another interpretation which seems to me admis-
sible, and more in accordance with what we know of the genesis
of sense-organs. If the whole median orifice is not to be re-
garded as a parietal foramen, and if its lateral portions are really
orbits as pointed out by Professor Cope, then there seems to be
nothing in the way of interpreting the pair of orifices in the
plate that divides the orbits as parietal foramina, if the possibil-
ity of the double origin of the pineal eye be conceded. Beard
has already called attention to the possible existence of a pari-
etal foramen in a corresponding position in Asterolepis ornatus.

Leydig’s interpretation of the pineal eye is the only one that
approaches my view, but it does not carry the origin directly
back to invertebrate segmental sense-organs. It must be re-
membered, however, that Leydig! identifies the lateral-line

1 Since the above was written, Professor Leydig has published a paper, in which
he contends that the pineal organ is not an eye nor a sense-organ of any kind, but a

No. 3.] SOME NEW FACTS ABOUT THE HIRUDINEA. 595

organs with the sense-organs of the annelids. If an authority
of Professor Leydig’s standing can be presumed to stand in
need of instruction on the differences that divide cerebral from
peripheral sense-organs, it is not of course to be expected that
my suggestion will meet with a less patronizing reception.
These differences have been insisted on so often that they
have become common property, and it indicates no small meas-
ure of audacity in a critic to assume the role of instructor in
regard to them. Take what are now incontestable facts in the
phylogeny of annelid and arthropod sense-organs, and add to
them the evidences in favor of the common derivation of the
vertebrate organs of special sense, and is it not enough to
awaken a very strong suspicion that the visual organs of verte-
brates will not be able much longer to hold the position of
isolation so long conceded to them?

In the study of this question the following points seem to me
of first importance: 1. Vertebrate sense-organs must be assumed
to be derived from invertebrate sense-organs, and the history of
the latter must furnish clues to the genesis of the former. 2. In
the development of special senses, visual cells have made the
widest departure from the primitive tactile cells. As the deri-
vation of visual cells from cells of the tactile order is now, as
I maintain, clearly established by the facts announced in this
paper, it follows that structural and functional differences in
sensory organs cannot be accepted as proof of diversity of
origin. 3. The medullary plate of the vertebrate is undoubt-
edly an enormous extension of the ancestral invertebrate plate.
4. Sense-organs lying originally outside the neural plate have
probably, in consequence of this extension in width, been
brought within the medullary area. 5. The ancestral seg-
mental sense-organs were not limited to a single pair of lateral
lines, but to several paired lines symmetrically placed on the
dorso-lateral and ventro-lateral surface.

19. The caudal ganglia are seven in number, with perhaps a
rudimentary eighth. Sometimes from ¢wo to four ganglia in
front of the caudal group are approximated, and the group thus
formed constitutes the anal ganglia. In several American
species of C/epsine, however, no such group exists, all the

lymph-sac. This startling announcement is evidently based on extended and careful
observations, and it will make it necessary to re-examine the whole ground.

596 WAITMAN. (Vor. ar

ganglia standing at regular intervals apart. There are gener-
ally seven pairs of distinct spinal nerves arising from the caudal
ganglia, and sometimes eight.

20. The postoral (infra-pharyngeal) ganglia represent five
somites, as can be shown in Clepsine parasitica and Branchelli-
opsts. Whether one or more somites are represented in the
pre-oral (supra-pharyngeal) ganglia, I am not prepared to say.
As there are always twenty-one ganglia between the pharyngeal
and caudal groups, we have thirty-three somites represented in the
ventral chain (exclusive of the pre-oral ganglia).

21. A careful analysis of the annular composition of the body
of Clepsine has enabled me to find just ¢zwenty-szx somites in
front of the caudal sucker. Adding seven for the sucker, we
have thirty-three, which makes the number of somites deter-
mined by the external rings agree precisely with the number of
ganglia in the ventral chain.

22. The assertion by Mr. Apathy that there are szr caudal
ganglia lacks ove of being true; and his statement that there
are always three anal ganglia would hit the mark in very few
cases indeed. Mr. A. boldly asserts that there are szx somites
represented in the pharyngeal ganglia. This author does not
appear to be aware that the nice balance which he strikes be-
tween the head and the tail of a leech is open to any serious
objection. For the present I pursue the criticism no further.

23. The nervous system of Branchelliopsis presents one fea-
ture of exceptional interest. This leech possesses veritable spzxal
ganglia. These ganglia are lodged in the anterior (sensory) of
the two spinal nerves of each somite, at a short distance from
the ventral cord. The two nerves issue side by side, but di-
verge after passing the ganglia of the ventral cord, and then are
re-united by a commissure, at the level of the spinal ganglion.
Passing the spinal ganglion, the nerves at once subdivide into
several branches. One of the main sensory branches runs out-
ward in the anterior wall of the segmental sinus, while another
large branch (motor ?) runs in the dorsal and posterior wall of
the sinus. The pre-sinal branch divides just before reaching
the longitudinal muscles, into three branches, the smallest of
which appears to end in the muscles, while the two remaining
pass on, one to the anterior, the other to the posterior side of
the lateral heart, and eventually end in segmental sense-organs.

No. 3.] SOME NEW FACTS ABOUT THE. HIRUDINEA. 597

24. A pair of colossal axial nerve-cells are found between
every two consecutive ganglia in the ventral cord of Branchel-
fiopsts. The nuclei are very large, and placed about midway
between the ganglia. The cells stretch from ganglion to gan-
glion, but do not pass these limits. Between the brain and the
caudal ganglia there are twenty-two pairs, and in both these
groups of ganglia the same cells probably occur, for a nucleus,
resembling in general appearance the nuclei of the axial cells,
is found imbedded close to the root of each nerve. These axial
cells undoubtedly correspond to the neurochord cells of other an-
nelids, and probably to the colossal nerve-fibres of Amphioxus,
Miiller’s fibres in Petromyzon, and Manthner’s fibres in Ze/eostez.
Faivre’s intermediate nerve terminates here in the manner de-
scribed by Hermann for Hzvudo, and has nothing whatever to
do with the axial cells. Hermann’s “median ganglion-cells”’
are also found in this leech.

25. In Clepsine chelydre, the spinal nerves issue from the
ventral cord as ¢hvee distinct roots. The anterior, smaller root
unites with the middle root, at the lateral edge of the ganglia,
and the two then pass on as one nerve, corresponding to the
anterior nerve of other leeches.

26. The agreement in form and structure between Piscicolaria
and the Japanese Branchelliopsis, is remarkable, for it is much
closer than that between the fresh-water Pzscicola of Europe
and marine leeches. Each has ¢hrvee rings to the somite, five
pairs of testes, and e/even pairs of nephridia. The testes and
nephridia are in corresponding somites in the two forms. I
have not thus far succeeded in finding segmental sense-organs
in Pzscicolarta, but fresh material may bring them to light.

27. The nephridial organs of Branchelliopsis resemble those
of Clepsine. Each pair appears to be entirely distinct, and thus
to present conditions quite unlike the nephridial net-work de-
scribed by Bourne in Pontobdella and Branchellion. For each
pair of organs there is a pair of funnels and a pair of external
pores. The funnel lies in a diverticulum from the posterior
wall of the segmental sinus, in the angle formed by the junction
of the segmental with the lateral sinus. A vertical plane cut-
ting a pair of funnels would divide the first ring of the somite
into two unequal parts, the posterior of which would be the
smaller. A horizontal plane would cut the ventral wall of the

598 WHAITMAN. [Vou. II.

lateral hearts and the dorsal sides of the testes. Its position is
thus a little behind the nephridial pore, which opens on the ventral
surface a little below the lateral heart, in the anterior half of
the first ring.

28. There are four longitudinal vessels and as many sinuses,
one dorsal, one ventral, and two lateral. The dorsal vessel is
inclosed for the greater part of its length in the dorsal sinus ;
the ventral vessel lies mostly outside the ventral sinus ; the lat-
eral vessels lie just above the lateral sinuses, and run parallel
with them. In the post-clitellar region, a pair of branchial ves-
sels are given off in each somite from the lateral vessels. Each
branchial vessel divides into two branches, after passing through
the muscular strata of the body, one of which passes forward to
meet a posterior branch coming from the preceding branchial
vessel, while the other passes backward to meet an anterior
branch coming from the succeeding branchial vessel. The two
branches do not actually meet, but rather each enters separately
the base of the auricular chamber of the heart, where the two
inflowing currents mingle and ascend to pass through a wide
common opening into the main chamber. This opening is on
the dorso-lateral face of the chamber, while the efferent opening
lies on the ventro-median surface, and leads into the branchial
sinus, which opens in turn into the lateral sinus, opposite the
junction of the latter with the segmental sinus. The four sinal
ostia thus brought together are guarded by peculiar pluriramous
muscles. The dorso-ventral sinus communicates with the tes-
ticular sinus, and passes into the segmental sinus just before
the latter unites with the lateral sinus. The connections be-
tween the vessels and sinuses at the ends of the body have not
yet been completely traced.

29. All the Hzrudinea may be derived from a form in which
the somite consists of three rings. The 5-ring type of Mephelis
and Hzrudo has been derived, not from a 6-ring or 12-ring type,
but from a 3-ring type, by the acquisition of two new rings.
The position of the nephridial pores in the posterior edge of the
last ring of the somite, can be accounted for more readily as
the result of shifting than of a loss of rings. How three rings
can become 4, 5, 6, or 12, I can promise to make clear in an
early paper.

30. Copulation in Clepsine is never direct, z.¢, by union of

No. 3.] SOME NEW FACTS ABOUT THE HIRUDINEA. 599

the sexual pores. The spermatozoa are transmitted in spermato-
phores, which are planted on any part of the exterior, preferably
on the back. The gradual contraction of the sperm-case forces
the contents through the skin in a steady stream that can be
seen under a magnifying power of 20 diameters. By means
of sections, I have traced the spermatozoa from the place of
entrance to within a few millimetres of the ovaries. The same
mode of copulation occurs in Nephelis, and in Peripatus (Sedg-
wick).

THE LAKE LABorATOoRY, Milwaukee.
Dec. 25, 1888,

SEGMENTAL SENSE-ORGANS OF ARTHROPODS.
WILLIAM PATTEN.

THE cephalic lobes of Acilius are composed of three seg-
ments, each of which contains a segment of the brain, optic
ganglion, and optic plate, the latter bearing two pairs of
segmental sense-organs, or eyes. That these characters are
common to all insects is very probable since the larve of many
Coleoptera, Neuroptera, and Lepidoptera agree with those of
Acilius in having six pairs of ocelli and three optic ganglia,
while in the adult the ganglion of the convex eye is generally
composed of three lobes probably derived from three inde-
pendent ganglia.

The segmental nature of the eyes is more clearly seen in the
embryos of Scorpions, Spiders, and Limulus, where it can be
shown that they are serially homologous, with one or more pairs
of sense-organs on each segment of the thorax.

In Scorpions, whose cephalic lobes are composed of three
segments similar to those of Acilius, the ganglionic invagina-
tions of the first segment, which has no eyes, unite to form a
transverse furrow that is soon converted into a closed sac, the
walls .of which are formed by the He segment of the optic
plate, optic ganglion, and brain.

The second ganglionic invagination is at first like that of
Acilius ; but the optic plate itself is soon infolded, forming the
outer wall of the ganglionic sac, the inner wall being the optic
ganglion. The two cavities finally unite in the median line, and
the median eyes appear as a pair of thickenings on the inverted
optic plates. A small group of upright cells soon appears on the
posterior edge of each eye, and pushing its way over the inverted
cells, gives rise to the permanent retina. The primitive retin-
ophore are finally converted into the irregular pigment cells,
filling the inner portion of the eye, some of which Lankester
supposed to be of mesodermic origin. A thin part of the inner
wall of the ganglionic sac, belonging neither to the optic plate
nor the optic ganglion, forms the capsule of the eye.

No. 3.] SEGMENTAL SENSE-ORGANS OF ARTHROPODS. 601

The ganglionic invagination of the third segment is not as
extensive as the preceding ones, and the optic plate which bears
the lateral eyes is not involved in the infolding. If the cephalic
lobes of Scorpions could be stretched out, the eyes would lie, as
in Acilius, on the thickened outer edge of each segment. This
thickened edge is represented in the post-oral region by the
pleurze of the thoracic segments, each of which bears two large
sense-organs, close together near the outer edge of the base of
the legs. It is clear that the eyes are serially homologous with
these thoracic sense-organs. The latter contain a cavity, shaped
like the bowl and stalk of a goblet, lined with striated cuticula
similar to that found at an early stage over the eyes of Acilius.

In Spiders the structure of the cephalic lobes is the same as
those of Scorpions. The two anterior median eyes belong to
the second segment, and are homologous with the median eyes
of Scorpions, the development being the same in both cases.

The three remaining pairs belong to the third segment, and
are homologous with the lateral eyes of Scorpions. They are
invaginated to form optic cups in the same way as those of
Acilius. The retina is apparently cut into two separate layers
by the tapetum; but the tapetum is really pierced by regularly
arranged holes, through each of which passes a pair of retino-
phore. Above the narrow openings, each cell expands into an
oblong body containing two rods like those of Acilius. Beyond
the rods the cell terminates in a short, rounded swelling, con-
taining the primary nucleus of the retinophora. The secondary
nucleus lies at the opposite extremity, where the cell is continu-
ous with a bundle of nerve fibres. The segmental sense-organs
at the base of the legs are smaller than in Scorpions and easily
overlooked.

In Limulus the cephalic lobes are composed of three highly
modified segments, the first and second being invaginated to
form two sacs. An evagination of that part of each sac formed
by the optic plate then gives rise to a tube, at the end of which
is formed an eye. A pair of these tubes from the first segment
unites with a similar pair from the second to form the stalk of
the median eye, the eye itself being formed by the union of the
four eyes at the ends of these tubes. The two posterior eyes
are therefore homologous with the median eyes of Scorpions
and Spiders.

602 PATTEN. [Vou. II.

Before the segments just described are invaginated, the optic
plate extends backward, almost the whole length of the body,
as a thickened ridge which in every thoracic segment gives
rise to a large sense-organ. On the median edge of the plate is
formed a segmentally deepened furrow that gives rise to a longi-
tudinal cord of ganglion cells. The three optic ganglia are
segmental thickenings of this cord. The convex eye arises
from three small sense-organs near the third thoracic segment,
its nerve being derived from a part of the lateral cord of gan-
glion cells. The sense-organ of the third cephalic segment
developed into a pigmented body connected by a nerve with the
ganglion of the convex eyes. The remaining sense-organs soon
disappear. That of the fourth thoracic segment is very large,
and has been erroneously described as giving rise to the convex
eyes.

The ventral cord and brain of Arthropods is at first composed
entirely of minute sense-organs, which in Scorpions have the
same structure as the segmental ones at the base of the legs.

On the lateral edge of each ganglion of the ventral cord of
Scorpions are two of these sense-organs, conspicuous on account
of their size and dark color. In each segment of the brain are
similar but still larger ones. All these sense-organs are con-
verted into the ganglion cells of the brain and ventral cord.

The above-mentioned facts and others will be fully discussed
and illustrated in one of the following numbers of this Journal.

MILWAUKEE, Feb. Ig.

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