GIFT OF
WILLIAM DILLER MATTHEW

WILLIAM DILLER MATTHEW

CHIMMOID FISHES AND THEIR
DEVELOPMENT

BY

BASHFORD DEAN
PROFESSOR OF VERTEBRATE ZOOLOGY, COLUMBIA UNIVERSITY

WASHINGTON, D. C.

PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON

1906

CHIM^ROID FISHES AND THEIR
DEVELOPMENT

BY

BASHFORD DEAN
o>

PROFESSOR OF VERTEBRATE ZOOLOGY, COLUMBIA UNIVERSITY

WASHINGTON, D. C.

PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON

1906

EARTH

SCIENCES

LIBRARY

:ARNEGIE INSTITUTION OF WASHINGTON
PUBLICATION No. 32

FROM THE PRESS OF

THE WILKENS-SHEIRY PRINTING CO.

WASHINGTON, 0. C.

TABLE OF CONTENTS.

Introduction 3

Paleontological evidence as to the position of Chimseroids 3

Anatomical evidence as to their position 4-9

Taxonomy of living forms 6-7

Collecting notes 7-10

Habits of Chimsera colliei; color, size, distribution, movements.. . 11-18

Sexual differences, food 19-21

Breeding 23-25

Mode of depositing eggs 25-27

Rate of embryonic development 27

Egg and its capsule 27-40

General plan of development 41

Primary egg membranes 42-45

Yolk 45-46

Germinal vesicle 47

Fertilization 48-52

Segmentation 52-63

Gastrulation 63-92

Early embryos , 75-101

Late embryos 102-109

Comparison with other Chimseroids 109-1 1 1

"Larval" Chimsera 111-114

Organogeny 1 14-132

Relationships of fossil Chimseroids 133-155

Summary of evidence bearing upon the position of Chimseroids . . . 155-156

Bibliography 159-172

Description of plates 174-194

ERRATA.

Page ii, for Regne read Regne.

Page 30, second column, after Rhinochimaera pacifica, for 3 read 33.

Page 36, fig. 20, for Rhinochimsera read Harriotta (?).

73464,3

A day's catch of Rat-fish, Chimsera colliei, on the beach at Pacific Grove

(near Monterey), California. Beside the fish are the float-lines

and baskets with trawl.

CHIA/LEROID FISHES AND THEIR DEVELOPMENT.

BY BASHFORD DEAN,

Professor of Vertebrate Zoology, Columbia University.

CHIA/LEROID FISHES AND THEIR DEVELOPMENT.

INTRODUCTION. ; ^ .-*• • •;": ".•/. :

Chimaeroid fishes, a group representing some of the oldest and simplest of
backboned animals, are considered in the present memoir with especial regard to
their relationship and descent. To this end, attention has now been paid to the
plan of their embryonic development, and upon this side evidence has been obtained
which, whether of major or minor importance in the study of descent, has at least
the interest of newness. For to the embryologist Chimaeroids have until recently
remained practically unknown, and they are thus the only vertebrate group of their
anatomical importance— if ranked as a subclass — to have escaped investigation.

On the other hand, from the standpoints of comparative anatomy and paleon-
tology these shark-like fishes have received considerable notice, and they have
figured in publications of the past half-century as the "most primitive vertebrates,"
or, more precisely, as the least modified descendants of the ancestral cranium- and
jaw-bearing vertebrate. And in such a role (which I now believe is only partially
deserved) they have been given especial importance in problems of descent.

The evidence which has been brought forward to demonstrate the primitive
nature of Chimaeroids is based in part upon the findings of paleontology ; it is,
moreover, as one frankly admits, supported by anatomical facts which are broad
in range and which have in many instances been provided by masters in morph-
ology. The substance of this evidence is that Chimaeroids, although shark-like,
are nevertheless widely distinct from the shark, and that they represent a lower
plane in piscine evolution. As an aid to subsequent reference, the grounds for this
conclusion may now be summarized.

PALEONTOLOGICAL.

Chimaeroids are believed by some to be older than sharks. Their fossils, as
Walcott maintains, occur among fragments of ' ' fish " plates in the Ordovician
(Lower Silurian) sandstones. Sharks, on the other hand, do not occur — that is,
unquestionably — before the Upper Silurian. Probable it is that Chimaeroids lived
during the Lower Devonian and, judging from their dental plates, these forms, if
Chimaeroid, were highly differentiated, even at this early period. Moreover, according
to the studies of Jaekel, paleozoic Chimaeroids provide the evolutional stages from
certain archaic armored "fishes" to the shagreened sharks.

4 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

RECENT.

Many characteristic structures of living Chimaeroids have been referred to as
indicating the primitive nature of the group. The following may be cited :

Dentition and dermal defenses, by Jaekel (1901), who maintains that the dental
plates are primitive or "statodont," i. c., the ancestral condition of the "lyodont, "
or successional teeth of the later sharks. They have thus, if I understand
Jacket's view correctly, become greatly subdivided, so as to produce the cuspid
teeth of sharks. So, -top, the larger integumental plates of ancient Chimaeroids
are believed to have given rise to cuspid scales, and a somewhat similar view was
expressed by Pollard (1891). According to Schauinsland (1902), the scales of Callo-
rhynchus are of so primitive a nature as to be directly compared to those of the
earliest Silurian "sharks." Finally, Reis (1895) suggests that the curious unpaired
tooth of mesozoic Chimaeroids finds its homologue only in the ancient Acanthodia.

Vertebral column, with delicate ring "vertebrae," characteristic of Chimseroids,
is, according to Schultze (1817), but the next stage above the notochordal con-
dition of the lamprey; to Hasse (1879) it represents a polyspondylous condition
ancestral to the diplospondyly of the simplest living sharks; to Gegenbaur (1901)
"less differentiated"; to Howes (1902) a purely "chordal type"; to Meyer (1886)
"possibly primitive"; to Rabl (1901) a column which has "not developed centra."

Cranium and arches. — According to Cope (1870), the autostylism of Chim-
aeroids is in itself primitive, in spite of the evidence of its secondary character, which
has been assumed on comparative anatomical grounds from the time of Johannes
Miiller (1838). So, too, Kitchen Parker (1883) inclines, though doubtfully, to its
primitive autostyly; and Gadow (1886) appears to have a similar view in stating
that dipnoans were descended from a "simple autostylic form." The curious
labial cartilages are regarded by Howes (1891) and others as homologous with those
of hag-fishes. And connected with these the levator anguli oris, according to Reis
(1896), suggests closely the condition in Acanthodian sharks. Allis (1898) also
suggests that the jaw muscle (adductor) is of a primitive type (i. e., interbranchial),
and in this he follows distinctly the more general conclusions of Vetter (1878),
which are, indeed, in the latest time confirmed by K. Fiirbringer. The second
branchial arch, • it may here be mentioned, has been referred to several times
(v. infra] as retaining archaic features. The labial cartilages, furthermore, are
said to be primitive, inasmuch as they represent the most perfect condition of
preoral gill-arches known among recent gnathostomes (K. Fiirbringer, 1903, and
Schauinsland, 1903); and a presymphyseal cartilaginous element is regarded as a
primitive copula between the mandibular and a premandibular arch. In fact, the
entire series of copulae is archaic (Gegenbaur, 1901).

Ribs are absent, a primitive character, according to Goeppert (1895).

Fin structures are of peculiar interest. According to Jeffrey Parker (1886),
the Chimaeroid is the only vertebrate to retain rudiments of a third pair of limbs. Its
paired limbs furnish, according to Gegenbaur, M. Fiirbringer, and Braus, evidence
of the origin of the paired limbs from gill-arches. In this connection Howes (1886)

EVIDENCE OF PRIMITIVE CHARACTERS. 5

maintains that the paired fins of Chimaera are ancestral to those of sharks and
dipnoans. Rabl (1901) also refers, but in a different aspect, to the primitive nature
of the fins of Chimaera. By several writers the unpaired fins are regarded as
primitive. The fin spine, as Reis (1896) maintains, shows the granular calcification
of the mesozoic Ischyodus. The mixipterygia are "of less compound construc-
tion" (Jungersen, 1898) than those of sharks.

Brain, nerves, and sense organs have received considerable attention. Valentin
(1842) states that in its brain Chimaera is intermediate between cyclostomes and
plagiostomes, and his view is shared, more or less distinctly, by Johannes Muller,
Mikloucho-Macleay, Gegenbaur, Wilder, and M. Fiirbringer. To Burckhardt (i 893)
the Chimaeroid brain suggests characters allied on the one hand to the primitive
sharks, on the other to the lower ganoids, and according to Studnicka (1895) the
forebrain is nearer the primitive form of the selachian brain than even that of
Notidanid. Jaekel (1902) holds also that in Chimaera, alone among fishes, there
appears an epiphyseal opening in the cranial roof. In the matter of cranial nerves
Cole (1896) states that " Chimaera is unrivalled among vertebrates, first, for the ease
with which its nerves may be dissected and, second, for the almost ideal results
that may be attained, " as well as for the peculiarity of independent nerve roots,
"archaic and perhaps primitive in type." Similarly, Fiirbringer (1897) comments
upon the peculiar conditions of the nerves of the occiput. Collinge (1896) notes
also the simplicity of the mucous-canal system, which, he believes, separates widely
Chimaeroids and sharks. From the standpoint of the auditory organ Retzius (1884)
places Chimaeroids in the ancestral line of the modern elasmobranchs. Gegenbaur
(1901), finally, notes that the flattened cord is primitive, like that of cyclostomes.

Visceral peculiarities have also been given considerable notice. Thus Huxley
(1872) refers to the "almost undeveloped gastric division of the alimentary canal,
[and] the relatively small and simple heart." Gegenbaur (1901) is inclined to regard
the few turns of the spiral intestinal valve as the ancestral condition of the gut of
Lepidosteus and Ceratodus. Leydig(i85i), followed by Mazza and Perugia (1894),
suggests that the many small brown glands of the rectum represent the ancestral
condition of the digitiform appendix of sharks. Redeke (1899) maintains that in the
structure of the kidney Chimaeroids are primitive, since, among other features, they
retain a remarkable metamerism and have not the modified Geschlechtsniere of sharks.

The foregoing are the principal lines of argument in favor of the primitive
position of Chimaeroids. Whether they can be maintained in the light of additional
evidence, notably on the side of embryology, is a question which will be discussed
in the present memoir.

To summarize the problem : Are the Chimaeroid fishes the least modified
descendants of the primitive gnathostome? Or are they, on the contrary, degen-
erate, specialized, or widely modified? Are they, in other words, close to ancestral
forms which gave rise to sharks, with which they are obviously associated — or are
they but modifications of the shark-like form? In spite of the formidable list

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

of citations as to their phyletic position, every investigator will admit that Chim-
aeroids have been but little studied — surprisingly little studied, if we consider the
morphological problems which they have trenched upon And in this regard we
may safely conclude that the obstacle in the way of the investigator has often
been a simple one — lack of material for research. For, until recently, good material
of Chimsera was relatively rare. As a deep-water form, it was taken only by special
fishermen in special localities, and even then, since it was not a food-fish, it found its
way rarely to a market and still more rarely to a laboratory. This, then, has been
an obvious reason why embryological material was not early described. It may
finally be mentioned that fossil Chimaeroids, so important to the general discussion,
are rare, and, with very few exceptions, fragmentary.

Recent Chimaeroids are included in 4 genera and about 25 species. An idea of
their distribution and size may be had by reference to the following table :

TABLE A.— Kinds, Localities, and Approximate Sizes of Recent Chimferoids.

Genus and species.

Reference.

IvOcality.

Size (±).

Gronovius, 1754, Mus. Ichthyol., I, p. 59,
plate iv, figs, i and 2. Linn., as spe-
cies, Syst. Nat., Zoophylae, ioed.,p.
236. (Followed by Swainson, Guiche-
not, and others.)
Lacepede, 1799, Hist. Poiss., I, p. 400,
plate xii. ( Followed by Swainson,
Guichenot, and others. )
Hobson ( 1840 ), Tasmanian Jour. Science,
vol. i.
Shaw, Gen. Zool.,V, Pt. II, 368, pls.cLVii
and CLVIII. ? Immature specimen.
Dumeril, 1865, Hist. Nat. Poiss. I. Elas-
mobranchs, 694-695. Immature speci-
mens.

Meters.
o .85

•75

S Africa

.85
•95

Richardson, 1841, Proc. Zool. Soc. and
Trans. Zool. Soc., Ill, 174.
Bory St. Vincent, Diet. Class. Hist. Nat.,
vol. in, p. 62, plate v.
Bennett, Fishes of Capt. Beechey's Voy-
age, p. 75, plate xxn, fig. 3.
Colenso, 1878, Trans. N. Z. Inst, vol. XL,
pp. 299-300, plate xvn.
Philippi,i892, An. Mus. Nac. Chile, Zool.,
p. ii, tab. v, fig. i. Immature specimen
( 39 cm. ).
Goode & Bean (1894), Proc. U. S. Nat.
Mus., vol. xvn, pp. 471-472.

( ? — C milii)

1. 10

y

Chile

N Atlantic

.70

Garman (1901), P. N. Eng. Zool. Club,
vol. i, ii, pp. 75-77.
Mitsukuri (1895), Zool. Mag. Tokyo,
vol. vii, p. 2.

Tanan

1.30

dicus), Mem. M. C. Z., vol. xxiv, pp.
20-21. Named from egg-case only.

*By any remote possibility could this have been CallorhyncJtus centrina, which Gronow described from a speci-
men which he saw " in museo cl. Gaubii, Lugd. Batav. " ? (Syst.,ed. Gray, 1854, pp. 15-16.) His description suggests
Harriotta rather than Rhinochimaera, since "habitat in Oceano Americano." It is hardly conceivable, however,
that Gronow should have happened across this rare form, and from the general vagueness of the description and
in view of the absence of the type specimen the name CaUorkynchus centrina should be cast out of the systematic list.

DATA REGARDING COLLECTING.
TABLE A. — A'l/iifs, Localities, and Approximate Sizes of Recent Chimccroids — Continued.

7

Genus and species.

Reference.

Locality.

Size(±).

Chimaera

Linnaeus, Mus. Regis Adolph. Frid., vol.
i, p. 53. Syst. Nat., ed. x, 1758, vol. i,
p. 236.
Capello(i868), Jour. Math. Phys. e Nat.
Lisb., vol. LV, p. 314, plate HI.
Gill (1884), Proc. U. S. Nat. Mus., vol.
vi. p. 254.
Bennett (1839), Fishes, in- Zoology of
Capt. Beechey's Voyage, p. 71, plate

XXIII.

Gill (1862), Proc. Acad. Nat. Sci. Phila.,
p. 331; cf. Dean, J. Sci. Coll. Tokyo
(1904), vol. xix, art. 3, p. 8.
Waite (1898), Ref. in "Thetis," N. S.
Wales Fisheries, p. 56.
Dean ( 1904 ), Jour, of Sci. College,
Tokyo, Japan, vol. xix, art. 3, pp. 6-9.
Gunner (1763), Det. Trondhiemske Sel-
skabs Skrifter, vol. 11, p. 270, plates

V, VI.

Ascan., Icones rerum natur., plate xv. .
Gronow 1854, Syst., ed. Gray, pp. 16-17. •
Shaw, Gen. Zool. , vol. v, pt. 2, p. 365,
plate 157.
Faber, Naturgesch. Fische Islands, p. 45.
Based on abnormal specimens.
Risso, 1826. No. 151. Nat. Eur. Merid.,
t. in, p. 168.
Collett, 1904. Chr. Videnkabs-Selskabs
Forh., No. 9, pp. 5-6. Based on young
specimens.
Waite (1899), Austr. Museum Mem.,
IV, p. 48, plate vi.
Jordan & Fowler, 1903, Proc. U. S. Nat.
Mus., vol. xxvi, p. 669 (nee Jordan &
Snyder, 1900, Proc. U. S. Nat. Mus.,
vol. xxin, p. 338 ( 1901)).
Gill ( 1878), Bull. Phil. Soc. Washington,
vol. ii, p. 182.
Gilbert MS

Meters.

(0.70)

( ? — abbreviata )

Pacific Coast of U. S..

.70

( =Hydrolagus colliei ) . ...
( — neglecta )

.60

.80

North Atlantic and
Mediterranean.
( ? Cape of Good
Hope.)
North Atlantic

( — Cal. atlanticus)

( — borealis )

North Atlantic

( ? C. Bathyalopex) mirabilis.

Faroe

•85

I.OO
I.OO

i-75
•75

phantasma

plumbea

Hawaii and Japan
Cape of Good Hope. . .

vaillanti

Dean, MS. (type in Jardin des Plantes,
No. 2557.)

(Since the above was in type the writer has seen in Japan two new species of Chimaera. These will shortly be
described by Mr. Tanaka in the Jour. Sci. Coll.)

DATA REGARDING COLLECTING.

It has long been known that Chimaeroids deposit large eggs, and that these
are inclosed in dart-shaped capsules, brown, heavy, somewhat after the fashion of
sharks, and resembling outwardly a frond of a giant Fucus. But further than this
nothing appears to have been ascertained as to their habits in breeding. At the
most, it was understood, from the complicated character of the capsule, that the
eggs were carried in the oviducts for a considerable time.

This inference is clearly important to one who seeks to collect embryonic stages.
For, given unlimited time and a locality yielding numerous specimens of Chimaera,
one could evidently secure gravid females, and from these the requisite number of
mature egg-capsules. Thereafter one would have merely to incubate the eggs,

g CHIM^ROID FISHES AND THEIR DEVELOPMENT.

either in aquaria or in cases floating or sunken, and then, from time to time, select
the developmental stages.* This mode of procedure, however, was not without prac-
tical difficulties, as the present writer found to his cost. In the first place, he was
for several years unable to locate a region in which Chimsera could be taken con-
stantly and plentifully. To this end several points along the European coast were
considered in vain. In the bay of Naples Chimsera is uncommon, contrary to what
one is led to infer from the notes given by Costa (1854); for it was found (1891) that
but few specimens could there be obtained, even through the excellent collecting
facilities offered by the Stazione. Messina is said to be a favorable locality, but
upon inquiry it was ascertained through Cav. LoBianco that even there Chimaera
was erratic in its appearance, and that months might elapse before many specimens
could be collected. At Nice, also, inquiry showed that similar conditions prevailed.
The coast of Portugal gave the best promise of abundant material, but the writer
found, during a visit in 1891, that collecting facilities were unattainable. There
were still to be considered the collecting possibilities of the coast of Norway,
where, indeed, Collett (1875) had already obtained an egg of Chimsera, when it was
learned that a species of Chimsera, C. colliei, was taken in considerable numbers
on the Pacific coast of the United States. It was next ascertained from Dr. Tarle-
ton H. Bean that this form could be taken in the waters of Puget Sound, and that
it was especially abundant in the neighborhood of Port Townsend. Here, more-
over, it occurred in relatively shallow water, and Dr. Bean had seen specimens of
these "rat-fish," as they are locally known, swimming about near the wharves.
Puget Sound was accordingly visited, Columbia University sending out a partyf
with a view to collect, among other desiderata, embryonic material of Chimera ;
and during a summer (1896) efforts were made to secure both the eggs and the
living fish. The latter were abundant. About a score of females were examined,
but in no case were eggs obtained. From the condition of the ovaries it was
inferred that the spawning season had passed.

Efforts were next made to secure eggs by dredging, but this means also proved
in the end fruitless. It resulted, nevertheless, in collecting egg-capsules, and in sev-
eral localities. At one point in Discovery Bay as many as sixty capsules were dredged
(6 fathoms) during a single morning, but these, as in other instances, were found
to be empty. The majority of the capsules were broken and frayed, and bore
evidence of having been in the water many months. Every effort, however, failed
to secure capsules containing eggs. Possibly they might have been secured if
dredging in deeper water could have bee,n carried on, for in no case was material
obtained from deeper than 10 fathoms. But it was remarkable that so many
empty cases should be taken close together, and in shallow water, if they had not

* Since these pages were written Prof. Schauinsland has published an extremely valuable memoir on the devel-
opment of Callorhynchus, but he has given no notes regarding the manner in which eggs were secured at Chatham
Island, or how these embryos were reared. They appear to have been collected separately, since he describes no
stage earlier than gastrula.

fin this, as in similar cases, the University was indebted to the fund donated by Charles H. Senff, Esq.

DATA REGARDING COLLECTING. g

been deposited in the neighborhood. It was still, of course, possible that they had
been sifted into the present position, perhaps by currents, from a greater depth,
or that the egg-bearing capsules were actually close to the empty ones and had
not been dredged. The latter alternative would clearly be suggested if the eggs,
like those of certain species of rays, were deposited in beds, thrust into sand or
mud deeper than the reach of the dredge — a possibility which, a priori, seemed
favored by the dart-like shape of the Chimseroid egg-case. But even this suggestion
proved in the end valueless, for experiments showed that no eggs were to be taken
by the use of a weighted dredge (one which cut deep into the muddy bottom), even
when used in the especial spot which had yielded the greatest number of empty
capsules.

The first eggs of Chimaera were obtained on the California coast during the
latter part of the same summer (1896). The writer is greatly indebted to President
Jordan for his invitation to visit the Hopkins Marine Laboratory at Monterey, and
for his suggestion as to the value of the Chinese fisher-people as zoological collectors.
Among the fishermen Ah Tack Lee was found to be of the utmost service, skilful,
persevering, accurate in locating Chimaera grounds, and keen in observing. He had
even noticed that Chimsera has the curious habit of carrying temporarily its pair of
eggs hung freely in the water attached only by elastic threads, and that the terminal
filament of the egg-case is provided with an end-bulb which secures its attachment.

A few words further regarding collecting. During the first summer, between
July 22 and September 12, there were collected 300 males and 139 females. Of
the latter 1 5 carried eggs. Each gravid female was found to contain two eggs in
practically the same stage of development. The plan pursued was to take those
eggs in which the capsule was sufficiently formed (18 out of 30 eggs) and place them
in a case, which was then sunk, attached to a buoy, in water of about 30 feet. Of the
number of eggs thus incubated, half were opened for the earlier stages; the rest,
unfortunately, were lost, a storm having carried away buoy and hatching-case. It
was none the less clear, however, that the method was successful, and it was evi-
dently but a matter of time before a fairly complete series of embryos could be
collected. A new and stronger buoy was therefore established off the Chinese
village, and from that time to the present, allowing always for periods of laxity,
the fisher-people, influenced by Ah Tack, have been collecting eggs. The only
practical difficulty was found to be the suitable fastening of the hatching-cases, for
at various times about 1 50 eggs have been lost.

The writer is particularly indebted to Dr. Ray L. Wilbur, of the department
of physiology of Leland Stanford University, for his kind cooperation in the col-
lecting work. Dr. Wilbur paid a number of visits to Monterey for the purpose
of opening and preserving the eggs, and incidentally prepared a number of notes
which are referred to in subsequent pages. Thanks to his care, about a dozen
embryos of various stages were secured. There was still lacking, however, a series
of segmentation and gastrulation stages, and to obtain these the writer paid a

I0 CHHVUEROID FISHES AND THEIR DEVELOPMENT.

second visit to the Californian coast during the summer of 1899. This visit resulted
in the taking of 179 female Chimaera, from which 20 eggs were secured. In addition
to the latter, a single egg containing a late embryo was obtained, which had become
attached (65 fathoms) to one of the hooks of a trawl line. It is upon these stages,
accordingly, that the writer has had to depend for his review of the development of
Chimsera. He may add that he was able to secure several notes regarding the
eggs of Chimcera phantasma and of Chimcera -mitsukurii during a stay in Japan,
and that he has further had the opportunity, thanks to his European colleagues,
of examining Chima^roid eggs and young in several museums, notably in Paris,
London, Berlin, Bergen, and Tromsoe.

The present introduction would be seriously incomplete without reference to
the generous aid which has been given the writer at various stages of his work.
Especially helpful were the suggestions of Dr. Tarleton H. Bean and President
Jordan, and the many courtesies received from Professors Gilbert and Jenkins,
Directors of the Hopkins Laboratory, and from other members of the staff of Leland
Stanford University, notably Professor Wilbur. Grateful acknowledgment should
be made to Professor Theodore N. Gill, who very generously examined the proof
of the present paper. In Japan, also, while a guest of the Imperial University's
laboratories, both at Tokyo and Misaki, the writer acknowledges the valued aid
of Dean Mitsukuri and his associates. Finally, especial thanks are due to Dr.
Naohide Yatsu, Rigakushi, for his assistance both in Japan and in New York,
preparing many text-figures, and aiding notably in the section of the present
memoir dealing with the fertilization of the egg. During the latter study Mr.
Yatsu's comments, it need hardly be added, were especially valuable in view of
similar studies which he had undertaken in the case of invertebrates.

The present memoir includes the following themes :

I. Chimsra and its characteristics. Appearance, movements, sexual differences, feeding.

II. Development:

Breeding habits, mode of depositing eggs, and rate of embryonic development.
The capsule and its formation.
The egg and its membranes.
Fertilization.
Segmentation.
Gastrulation.

Early embryos, i. <?•, prior to appearance of gill-openings.
Late embryos, i.e., from appearance of gill-openings to time of hatching.
Immature 3roung.

Morphology. Reference to: (a) integument and dentition; (£) skeleton; (f) viscera;
(tf) nervous system.

III. Fossil Chimseroids and their significance in the study of recent forms.

IV. Chimseroids in the problem of vertebrate descent.
V. Literature of Chimaeroids.

I. CHIM/ERA AND ITS CHARACTERISTICS.

THE LIVING FISH: COLOR, SIZE, DISTRIBUTION, HABITS.

This section was suggested as a beginning_fqr the present memoir, since, in
spite of many references, no observations have hitherto been published describing
the living fish. In fact, the impression which the rank and file of zoologists have of
Chimera is, I believe, derived from the figure* given by Valenciennes in the illus-
trated edition of Cuvier's Regne Animal, which has been copied trustfully by text-
books, even by those which have appeared during recent years. This figure was
evidently taken from a stuffed specimen, and gives the grotesque appearance of one
of Aldrovandus's monsters, thus well meriting the name of "Chimsera. " It is a sur-

Fig. I. — Chimaera colliei. One- fifth actual size.

The upper specimen, a male, shows the frontal clasping organ everted, a position which was only retained by fastening the organ in
this position. The mixipterygia were turned somewhat sideways, so as to make them more apparent. The antero-venlral clasping organ
is not conspicuous, hut its lip is seen to protrude from the vertical slit immediately in front of the pelvic fin. The figure indicates the
translucency of the snout region.

The lower, larger specimen, a well-grown female, shows immediately above the base of the ventral fin the tumid eminence at the
opening of an oviduct. It illustrates, as secondary sexual characters, the narrower pectoral fin and first dorsal.
The photographs illustrate the translucency of the fins and delicate sheen of the newly-caaght specimens.

prise, therefore, to find that the fish is, in point of fact, remarkably beautiful, its
contours well rounded, its fins delicate, and its colors almost herring-like in bril-
liancy. Instead of ' 'Chimsera" it deserves rather its popular Norwegian name, ' 'king
of the herrings," or, better still, its Japanese name, "gin-same" (silver shark).
On the other hand, it can not be denied that there is a suspicion of grotesqueness

*This is scarcely more satisfactory than the "fantastic figures of Clusius and Aldrovandus," to which this
author refers.

12

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

in Chimsera. In the water the moving fish gives one the impression that its pec-
toral fins are too large for its body ; they stand out prominently, and from their
transparency they remind one strongly of those of some specialized teleost, such as
a gurnet or a flying-fish. In figures (figs, i and 2), reproduced from photographs,
the transparency of the pectoral fins is indicated, though we gain little idea of their
delicacy and beauty. They are well supplied with blood, which passes through the
transparent fins in delicate vessels arranged parallel with the fin rays and sometimes
gives the fin a rosy tinge.

COLORS.

Chimara collici, of which an immature specimen is pictured in plate xi, shows
lustrous colors when taken from the water. Its ground tone is silver, but at every
movement it reflects metallic hues — brass, copper, and gold. Its snout is trans-

Fig. 2. — Photograph of living Chimaera colliei.

This shows the pectoral fins extended on either side of the body at the time of the down stroke of the fin. The pelvic fins stand out on either
side apron-like, showing clearly their light-colored anterior border, la this position the spotting of the back is conspicuous. In lateral view (cf. fig. I )
the spots can scarcely be seen.

lucent, its optic cup is luminous, refracting pale greenish-blue, its iris brassy, and
on head and trunk are tinges of rose, cobalt, pale-green, and madder. Out of
water, however, its brilliant tones soon fade, and its delicate, scaleless skin blotches
and dries. In the aquarium, as one could naturally expect, the fish fails to show
much of its metallic luster, but, on the other hand, its pigments appear to greater
advantage. Its back region is dark umber, through which pass, as the fish changes
position, shades of olive and rose-madder. Its ventral region and fin bases are
white, the fins themselves translucent and even transparent. In the adult the
paired fins show little pigment ; they stand out from the body prominently, their
anterior rims white, and their constant movement adds greatly to the fish's beauty.
It may be added that the dorsal spine shows brightly in the water, forming a

CHIMERA AND ITS CHARACTERISTICS. ^

conspicuous anterior rim to the dorsal fin, whose remaining margin, in reality of a
dark umber, now appears jet-black. In side view the body of the fish exhibits white
spots, but they are not noticed in many positions. From above, however (fig. 2), they
are conspicuous, and the general ground tone of the fish appears much darker, a
change in coloration which is probably of value for protection.

In the matter of color Chimcera colliei is not far from the mean of recent
Chimseroids ; for some of these have but little pigment, while others are dusky
and even black. This range in color might be expressed in somewhat the following
way : With least pigment are the Callorhynchids, with clear silvery sides, obscured
only by several large lateral blotches, and Chimara phantasma, with silvery sides
marked with longitudinal dark stripes. With increase of pigment come the series
C. monstrosa, C. affinis,* C. colliei, C. mitsukurii, C. purpiirascens, and C. ogilbyi,
the last almost entirely black. The distinctly abyssal types, unshaded, uniformly
plumbeous, with pigmented lateral line, are Rhinochimaera, Harriotta, and C.plumbea.

SIZE.

The general relations of size in Chimseroids will be referred to on a later page.
The recent forms present a range of length from about 60 to 200 cm. C. mitsu-
kurii, even including its long opisthure, is the smallest species, and the gradation
in size extends somewhat as follows through the series : C. colliei, C. affinis, C.
monstrosa, C. ogilbyi, and C. phantasma; and in the neighborhood of a meter in length
are all other forms except C. purprtrascens. Following the general rule among
other fishes, males are smaller than females; in length less by about one-twelfth, and
in weight by about one-seventh. In this connection a few comments may be added
regarding the general shape of the fish. In Callorhynchids and in C. phantasma
the modeling of the head, trunk, and tail is compact and suggests that of Cestra-
ciont sharks. In general, males are more slender than females. This relation is
shown in fig. i, taken from a photograph of the freshly caught fish.

OCCURRENCE, HABITAT.

Chimaeroids are widely distributed (cf. species list, pp. 6, 7). Callorhynchus,
however, is limited to the south seas, and Chimera largely to the north. The
distribution of Chimsera is clearly the more general, for C. vaillanti occurs at Cape of
Good Hope and C. ogilbyi in Australia. It is the general belief that all Chimaeroids
are obtained from deep water, since the majority of the species occur at a greater
depth than the loo-fathom line, while some indeed are abyssal. It is stated, for
example, that C. monstrosa occurs in water as deep as 1,000 fathoms, C. affinis^ in
depths from 200 to 1,300, Callorhynchus up to 600, Harriotta from 700 to 1,000, and
Rhinochimsera at about 700. On the other hand, it must be admitted that C.
colliei occurs in relatively shallow water. Dr. Bean records (Oceanic Ichthyology,
p. 32) that "it swims at the surface," and states further that "there is no evidence

*It is probable that the C. aflinis recorded from great depths represents a new species.
fC. affinis is the most abyssal of elasmobranchs.

CHIMJGROID FISHES AND THEIR DEVELOPMENT.

that it descends to very considerable depths." The writer has taken it in water of
less than 5 fathoms in Puget Sound, and he obtained a specimen caught from
the Monterey wharf in water of about 3 fathoms. He also secured over a score of
immature specimens (measuring about 30 cm.) from a single haul of a seine along a
shore reach near Port Townsend, at a depth not greater than 2 fathoms. It is
known, furthermore, that egg-cases of this species are plentiful in shallow water.
C. -phantasma and C. ogilbyi also occur in relatively shallow water, /. e. , respectively
from 10 to 50 and from 22 to 150 fathoms. It appears, further, that Callorhyn-
chus is sometimes taken in water of no great depth. (Thus Plate records having
dredged off the coast of Chile an egg-capsule in water of 10 fathoms.) It follows,
therefore, that in the matter of vertical distribution Chimaeroids are not widely
different from sharks.

36 ,j 13

Whistling Buoy,, is 15

K0 .-• ?-::.'-'-'--'-'."'-i6-.

BDELLOSTOMA
GROUND

27 a

Fig. 3. — Sketch of the region of Monterey, Cal., showing the location of the fishing-ground for Chimaera.

Returning to the habitat of C. colliei : It can safely be said that this species
is more abundant in shallow water in Puget Sound than at similar depths on the
California coast — in this regard paralleling several other fishes as well as inverte-
brates. It is nevertheless true that in the region of Monterey specimens were often
taken in water shallower than 1 5 fathoms ; but experience demonstrated that the
greatest number of individuals could be fished in water of 60 fathoms. It was also
found that in somewhat deeper water, 60 to 120 fathoms, females, although less

CHIMERA AND ITS CHARACTERISTICS. !$

abundant, were more apt to yield eggs, and that in water of less than 40 fathoms
females were usually eggless. Collecting notes show that of 48 females taken in water
shallower than 40 fathoms there was but a single specimen that yielded eggs, and
in this instance the egg-capsules were quite immature. One concludes, accordingly,
that near Monterey this Chimseroid occurs generally and at various depths, but that
it is usually found at the time of spawning at a depth of somewhat over 60 fathoms.
This conclusion is interestingly confirmed by the accidental taking of a naturally
deposited egg-capsule on a hook of a trawl-line in water of 65 fathoms.

The best collecting-ground known to the writer is about 3 miles NNE. of Pinos
buoy, as indicated on the map (fig. 3). Here about 500 were taken, and it is to
this region that the following notes apply. A trawl-line,* baited with squid or
herring, can be laid in any direction with a reasonable prospect of securing fish; in
fact, rarely less than 6 Chimsera are taken in a day's catch; on one memorable
occasion 7 1 were taken. Tabulation of results shows that males are taken over five
times as often as females, f and that of the latter (taken during the summer months)
but i in 13 bears eggs which can be incubated. It is an interesting fact that in
trawling the fish are often caught close together. The writer has seen as many as
ten drawn into the boat attached to adjoining hooks. One infers from this that the
line has fallen over a restricted feeding-ground, where the fish occur in great number.
And it is found, furthermore, that if a fresh line is set over the same course more
fish are usually forthcoming, and at the same stretch of the line. If, however, a
line is set parallel to the first, and but about 200 feet distant, one is apt to find that
no fish are taken. From the above observations one may naturally conclude that
the especial feeding-grounds of Chimsera are sometimes small in size. Material
brought up by the trawl-line indicates, further, that such a favorable feeding-ground
is closely strewn with very small rock fragments. Where large rocks occur Chimsera
is less common, and it is relatively rare on a sandy bottom. There is also evidence
for the belief that Chimsera occurs in schools; and this view, it may be remarked, is
prevalent among fisher-people in widely separate localities, as in Lisbon, Messina,
Bergen, Monterey, and Misaki.

Chimsera is plentiful near Monterey. According to Ah Tack, however, an even
more favorable fishing-ground occurs about 10 miles to the southward, near Point
Lobos, and it is said to be well known to the Chinese fishermen of the neighboring
Pescaderos. From this neighborhood eggs were collected during the winter season.

In the region of Monterey the temperature of the water during the summer
months ranges between 50° and 60° F., and the specific gravity is about 1.028.

*Six or seven baskets (/'. c., lines) were usually set, having altogether about 5,000 hooks. The boat employed was
a Chinese fishing skiff.

•(•This result agrees with the observations of Grieg and Olsson for Chimicra monstrosa. Costa, on the other
hand, states that in the Gulf of Naples no less than 14 were females out of 16 specimens examined (between 1830 and
1851), and in Norwegian waters Malm notes that 26 out of 33 specimens were females.

i6

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

MOVEMENTS.

Chimcera colliei is essentially a delicate fish. When taken from the water it
struggles but little and soon dies (about 15 minutes). It makes no sound, save on
rare occasions, when it clicks its dental plates together ; and it shows no effort to
erect its dorsal spine. In handling it the fishermen take less account of the formi-
dable spine than of the jaws, which are capable of inflicting a painful wound, in one
case snapping out at a single stroke a bit of skin and flesh. It is a difficult fish to
keep alive, even under favorable conditions. In the aquarium of the Hopkins Sta-
tion it lived rarely longer than two days.*

Fig. 4. — Chimaera colliei. Sketches of the living fish.

A. Swimming fish shown from in front. This indicates particularly the position of the pectoral fins ; from the point marked with an asterisk (*)
undulations arise which pass out over the tip of the fin as indicated by the arrows and end at the fin's posterior margin.

B. Fish shown in resting position. The tail droops somewhat and the weight of the trunk is apt to fall upon the fleshy pad which is present on
the ventral side of the body immediately behind the mixipterygia. The opening of the operculum and the position of the mouth in this, as in the pre-
ceding figure, are indicated in their normal position.

C. Mouth region, showing the extent to which the jaws open during the process of breathing. As here shown, the opening is even greater than
usual. Behind the mandibular plates can be seen the wide breathing valve b l', and the prominent anterior nostrils. The latter serve to pass water
lateralward under the large labial folds into the mouth.

The moving fish is conspicuous in the use of its paired fins. The pectorals are
in constant motion, like delicate translucent fansf moving to and from the body,
and passing undulations one after another along their delicate rims, somewhat
as in the pectorals of skates. Thus, in the sketch given in fig. 4 A, these fins are
seen in a characteristic position. They are supposed to be moving dorso-ventrad,
the path of their flexible tips describing an arc of about 90°. At the ventralmost

*Mr. C. F. Holder, the director of the aquarium at Avalon, Santa Catalina Islands, informs the writer that he
has been able to keep C. colliei alive for a longer time, although no definite time was recalled.

fThe translucency of the pectoral fins is seen in the photograph reproduced in fig. i, page n.

CHIMERA AND ITS CHARACTERISTICS. 17

point of their movement they appear in the position shown in fig. 4 B. A large part
of the movement takes place in the dermal web of the fin. Starting from the point
marked with an asterisk (*) a wave of movement passes out to the apex of the fin,
where its greatest height is shown; then it passes rapidly around the ventral rim and
dies out in the axil. This wave is followed by another, more or less rapidly, accord-
ing to the effort of the fish. As the dermal rays are parallel to one another, their
fall and rise suggest the movement of the keys of a piano when a finger is drawn
across the keyboard. As so much of the conspicuous movement is accomplished
by dermal rays, the muscular bases of the fins show to full advantage as balancing
organs (cf. fig. 2), almost as in Polypterus. It may be mentioned, in connection with
this constant movement, that the dermal margin of the fin is so delicate that it soon
becomes ragged by wearing against the sides and bottom of the tank.

Chimsera is deliberate in its general movements, suggesting somewhat a shark,
but occasionally it shows great activity. On one occasion a fish which had been
balancing quietly for some minutes suddenly dashed about the aquarium and
then shot up over the side. Quick movements of the pectoral fins greatly aid the
fish's forward propulsion; and in the undulation of the body the dorsals are far
more important as swimming organs than the caudal. The ventrals serve rather
passively as balancing organs, preserving a horizontal plane and hanging behind
like an apron, their median edges overlapping (fig. 4 A). It may be noted that the
mixipterygia, which are so conspicuous a feature in museum specimens, are hardlv
seen in the swimming fish (fig. 43). They are neatly tucked together behind the
ventral fins in the median line and can little impede movement. In slow forward
movement Chimaera rocks somewhat from side to side, the dorsal fin functioning
imperfectly as a keel, its spine, by the way, rarely more erect than shown in the
figure. In resting the tail droops noticeably* and the fish balances by slow move-
ments of the pectorals. The hinder trunk sometimes rests on the prominent pad
of the postanal region. (PI. i, fig. 2, c.)

In further detail: The fish sometimes swims about freely, with a movement
described by an observer as "butterfly-like," from the conspicuous flapping of its
large pectoral fins. It is more active at night; if placed in a large tank it is apt
to swim restlessly from one end of the tank to the other. In daytime it is quieter,
and appears to avoid strong light. Occasionally it "sails" or "flutters" to the
surface, thrusts its snout out of water, and then, suspending all movements, sinks
to the bottom. Here it sometimes rests, balanced on the tips of its fins, like a
dipnoan, or Squatina, or even a ray. In this position, when otherwise quiet, its
brilliant eyes often show active movements. One receives the impression that
captivity is irksome to the fish, an impression often strengthened by its subsequent
behavior, for it will suddenly advance, then retreat, advance again, and sometimes
thrust itself out of the water in its attempt to escape.

*This condition has been recorded in weak, aquarium-bred fishes (e. g., Lepidosteus), but in Chimaera it is
probably normal, since it was observed in freshly caught specimens. There is, nevertheless, the possibility of its
being due to change of pressure.

i8

CHIM/EROID FISHES AND THEIR DEVELOPMENT.

B

C

G

The mode of breathing of the fish is somewhat
remarkable. The mouth is very small, and its rims are
motionless or almost motionless, scarcely parted in breath-
ing; so nearly closed, in fact, that the movement of
the breathing-valve can hardly be seen. A portion,
probably a large portion, of the water — as in the case
also of dipnoans — is breathed through the prominent
nasal openings (fig. 4 A and c), whose cartilaginous marginal
flap is specialized to this end ; and since the mouth is motion-
less, it follows that the branchio-opercular muscles are the
efficient means of introducing water to the gills. In point
of fact, in the living fish one readily observes an extensive
dilation and contraction of the opercular flaps. In spite,
however, of this extensive movement, the excurrent open-
ing is remarkably small, and at this point the opercular
fold puffs out conspicuously, like an opened valve, a small
one at that, forming a slit about three-sixteenths of an
inch in diameter. The rhythmic opening and closing of
this slit gives a further suggestion of its valvular nature.
The breathing, moreover, as in the case of other fishes,
is rendered more effective by the presence of oral breath-
ing-valves, operating so as to close not merely the open-
ing of the mouth, but the nasal passage also. The respi-
ratory movements are rapid, at least in captive fish. In
such specimens there are counted as many as 100 respi-
rations a minute, a number evidently abnormal. Occa-
sionally, when the fish is swimming, the mouth will open
two or three times spasmodically. This occurs too rarely,
however, to be of especial respiratory value ; and it is
also to be observed, if the fish is a male, that the
frontal clasping spine will at the same time be elevated
and depressed.

This correlated movement of clasping spine and jaw
has already been suggested by Reis on anatomical grounds.
In this connection it was once observed that both mixip-
terygia were suddenly dropped from their position close to
the trunk, rotating downward together from their bases,
their tips rotating through an arc of 90°, just as rigid fingers
might be bent downward from the plane of the hand, but
no details of this process were seen, for they at once rotated backward into their
closed position.

I

J

K

V 5— MandibuUr dental plates of

Chimaera colhei, shown in outer lat-
eral aspect, and indicating variation
in these structures. A I, specimens

from females ; j L, from males.

CHIMERA AND ITS CHARACTERISTICS.

SEXUAL DIFFERENCES.

In living specimens it is surprisingly difficult to distinguish the sexes (C colliei}.
The secondary sexual characters of the male are then inconspicuous, and one is apt
to identify it rather by its smaller size and by its slightly darker tone. Breeding

colors are not marked, but at the time of spawning the
female shows considerable color in the anal and caudal
regions, the fins especially being suffused with blood.
In males, those, it appears, are in breeding colors in
which the anterior rim ~of~ the pelvic fins and the ante-
rior region of the pectoral fins are the whitest. It is
difficult to distinguish the claspers. The frontal organ is
folded neatly away below the surface of the head ; the
mixipterygia are closely apposed to the trunk, hardly mod-
ifying the contour of this region ; the anteropelvic claspers
are tucked into their dermal pouch, and the mouth of the
pouch is nearly closed. In the female a fleshy pad lies in
the median ventral line behind the pelvic fins, and pro-
duces a contour not unlike that of the combined mixipte-
rygia. Closer examination shows slight differences in the
proportions of male and female; thus (cf. fig. i)in the male
the eye is relatively of larger size, the snout more obtuse,
the fins shorter and wider, the dental plates smaller and
often distinguishable in shape.

Dental plates. — In C. colliei the mandibular dental
plates of the female do not usually exhibit as marked a
prong in the "canine" region as the males. Nine such
plates are shown in fig. 5 A-I, sketched from jaws of adult
females selected at random, and these may be contrasted
with the common type of the mandibular plate of the male
outlined in fig. 5 j and L. Great variation is, however,
apparent in both cases. Of the nine plates figured, four
(A, c, E, i) have no conspicuous "canine" prong, two have
the prong well marked (D, c), the rest are intermediate. In
the males seven plates out of ten were found to be conspic-
uous in the "canine" prong, quite similar to the specimen
figured (j, L). One specimen (ic)only was remarkable for
the evenness of its edge. Variation was also marked in the
number, arrangement, and distinctness of the tritors, and
in the general thickness of the dental plates. These characters, however, are partly
dependent upon the age of the fish. In the young the plates are more delicate
and regular, and when viewed against the light they are less apt to show tritoral
lines. When the latter appear they are slender and translucent. In large specimens

D

Fig. 6. — Dental plates of Chimaera

A, front view of dental plates of large
specimen ( female ) .

B, dental plates of same specimen, viewed
in visceral aspect.

C, front view of dental plates of male.
Observe especially the asymmetry of the right
mandibular plate.

D, dental plates of same specimen, viewed
in visceral aspect.

20 CHIM^iROID FISHES AND THEIR DEVELOPMENT.

the plates are stouter and show irregularly worn margins. In somewhat rare cases
asymmetry results. Two instances of this kind are shown in fig. 6. In the first
(A and B) the upper "incisor" plates are quite different in shape (a female) ; in the
second (a male, c and D) the mandibular plates are irregular, one having the typical
"canine" prong, the other a fairly straight margin. In visceral aspect one (D) car-
ries the median tritors of the palatine plates far forward ; the other (B) is prac-
tically without a median tritor. In one (D) the mandibular plates form a symphyseal
beak-like prominence ; in the symphysis of the other (B) there is a noticeable
notch. In general, there is considerable variation in the number of tritors in indi-
viduals of apparently the same age.

The foregoing peculiarities are commented upon, since they show that consider-
able judgment is necessary to determine accurately species of Chimseroids when
dental plates alone can be studied, e. g. , in the case of many fossil forms. Indeed,
with so wide a range of variation, it is quite conceivable that C. colliei, if known only
by its dental plates, might be described under several species, and possibly two
genera. The general relations of the dental plates in both living and fossil forms
are considered on a later page.

FEEDING AND FOOD.

In view of the special character of the dentition of Chimera, one would nat-
urally expect its food supply to be definite in character. The examination of the
contents of its gut, however, showed (C colliei) singularly omnivorous habits. It
is true that the broken shells of mollusks are commonly found, as well as fragments
of good-sized crustaceans, as indeed the scanty literature records. Thus, in the gut
of C. monstrosa Faber finds crustacean and shell-fish fragments ; Monticelli, quoting
Liitken, Cyprina islandica; and Olsson, broken shells (Leda and Venus} and bits of
large decapods. Olsson finds also (and his observations are the most detailed
hitherto published on the feeding of Chimsera) chsetopods, amphipods, echinoids,
and polyps.

In C. colliei observations on about a score of individuals showed a singular
mixture of foods. Most numerous were vertebral columns of small isospondylous
fishes, a few mollusk shells, usually greatly crushed, a quantity of sand and fine
gravel, squid, nudibranchs and opisthobranchs, bits of cases, jaws, and seta? of
annelids, and occasionally a fragment of a crustacean. In one instance the gut was
filled with seaweed. One is not surprised, therefore, that this species is taken
readily with various baits. In Puget Sound it is fished with mussel, clam, prawn,
sandworms, and even salt pork. At Monterey the greatest numbers were taken
with squid; failing this, trawls were baited with herring, fresh or salted.

A curious feature in connection with the feeding conditions of Chimaera is that
in so many specimens examined the gut is found entirely empty, even at the time
the fish is taken from the water. This condition has been commented upon by
several authors, among others by P. J. Van Beneden and Olsson, the latter finding

CHIMERA AND ITS CHARACTERISTICS. 21

the gut empty in as many as 5 examples out of 16. The explanation of this is,
however, we believe, not necessarily due to cessation of feeding, for it is found that
the fish does not cease to feed even while in the act of depositing eggs. On the
other hand, from the simplicity of the valve of the gut* it is quite probable, as
experiments on living fish have convinced the writer, that the food material is voided
between the times of hooking the fish and of drawing it into the boat.

Another curious feature connected with feeding is that Chimera, in spite of
the small size of its mouth, can ingest objects of large size. Thus it was found that
a specimen of C. collici of moderate size, one whose mouth appeared too small to
admit a finger tip, had ingested a fish 6 or 7 inches in length. Whether it had
swallowed it in a single piece is doubtful, but judging from a section of vertebral
column, a fragment 2 or 3 inches long had been taken. Another specimen had swal-
lowed a portion of a crab's carapace nearly an inch in length. Indeed, the usual
baits taken measure over an inch in diameter, and it is found that they are easily
bolted, not cut or crushed by the dental plates. No observations are recorded as to
the way in which the small and delicately shaped mouth behaves while feeding. As
far as the experience of the writer goes, a fish will not feed in captivity, and it can
rarely be induced to notice a bait. In one instance the mouth opened rather widely
and the jaws snapped together with an audible click. It was evident, however, even
from a single observation, that the mouth is accurately adjusted and can focus
its stroke with precision, somewhat after the fashion of the beak of a bird; and
there can be no doubt that the dental plates of this species form together a powerful
instrument for cutting, rather than crushing. On one occasion the writer saw them
part the line of a trawl.

In spite of formidable dentition and erectile dorsal spine, Chimaera is preyed
upon by other fish. According to Olsson it is eaten by Somniosus microcephalus , and
small specimens have been found in the stomach contents of cod.

*The stomach is broadly continuous with the intestine ; when food is found it usually occurs in the first turn of the
intestinal valve.

II. DEVELOPMENT.

BREEDING HABITS.

Chim&ra colliei, to which the following notes refer unless otherwise stated,
spawns at all seasons of the year. The writer has himself collected eggs from June
till September. On another occasion he received in June a gathering of eggs which,
judging from their stages of development, were deposited during March, April, and
May. In April (1898) Dr. Wilbur opened a number of eggs, one of which was
evidently deposited in January or late in December. Dr. Wilbur's collecting notes
remark further that in December (1898) there was lost a hatching-case containing
eggs (about two dozen) collected between September and December. While
eggs can thus be secured throughout the year, a season of maximum spawning
probably occurs. In Californian waters this appears to be during the late summer
and early fall.

The place of spawning in this species is known in a general way. A naturally
deposited egg was taken, as above noted, in water of 65 fathoms on gravelly bottom.
There is good evidence that the capsules are attached to rocks or heavy sea-weed,
since a definite organ of attachment is present at the filamentous end of the
egg-case. It is even possible that the eggs are deposited on favorite spawning-
grounds. Thus it was found that in an area of about 2 acres (Discovery Bay,
Puget Sound, 200 yards off Tukey's Point, in water of 6 fathoms) as many as 85
capsules were dredged in a single day, while in neighboring regions they were only
occasionally noticed.

From the habits of Chimera it is very doubtful whether its copulation and
spawning will ever be observed. By indirect evidence, however, the mode of
copulation appears to be distinct!}' shark-like. The accessory claspers, i. e., the
male's frontal spine and anterior appendage of the pelvic fin, are evidently of use in
securing the female and retaining her in copulo.

Garman long ago (1877) suggested that the frontal "holder" functioned in
securing the pectoral fin of the female and in "turning her," thus serving like the
hooks on the pectoral fins of the male ray; and he further maintained that the pelvic
claspers were used for holding the mixipterygia when erected. As far as the frontal
spine is concerned, a more probable interpretation is that the male Chimera (cf.
the position in shark) wraps its body about the female and secures final attachment
in copulo by attaching the spine near the female's dorsal fin ; for it was found, in an
examination of specimens which were about to deposit eggs, that well-marked scars
were present, indicating the point of attachment. The region of the dorsal fin in such
examples is shown in figs. 7 to 1 1 ; and there can be no question, from a closer
examination of the scars, each of which is shown enlarged on the same page

23

24

CHIM/EROID FISHES AND THEIR DEVELOPMENT.

according to corresponding numbers, that these were caused by the frontal organ,
for each shows a number of small punctures, usually 8 to 12, corresponding in
arrangement to the cusps of the frontal spine, as one may demonstrate by experi-

12

,/

f

10

10

,11

Figs. 7 to 1 1. — Region of dorsal fin in (emale specimens of Chimaera colliei, showing marks of frontal clasping organ of male. The
smaller numbers, i to 14, and (at the left) enlargements with corresponding numbers, show positions and details of scars made by frontal
clasping organ.

ments with the spine itself. The majority of these scars occur, moreover, in the
position where they would be expected if the male assumed in copulo the same
position as the shark. With few exceptions they are situated in the region of the

BREEDING HABITS. 25

first dorsal fin. In some instances the presence of several scars indicates that a
number of attachments were attempted. The most posterior scars (figs. 10 and 1 1,
scars 13 and 14) are rather scratches than points of attachment. In spite of this
evidence, however, the writer must remark that one gravid specimen examined
failed to show a scar in the region referred to. On the other hand, there was little
doubt that the marks referred to were made on the fish prior to capture, and that
in those specimens no other marks were noticeable.

The antero-pelvic clasping organs are distinctly erectile and probably serve as
an additional means of attachment in copula. Thcycan hardly function as Garman
has indicated (i. e. , to hold the erected mixipterygia), if for no other reason than
that if thus held the mixipterygia not only diverge widely, but are so closely
fastened to the side of the male that they can not well be made to enter an oviducal
opening.

It may be noted that Parker (1897) states that spermatophores are present in
Callorhynchus.*

MODE OF DEPOSITING EGGS.

Two eggs are deposited almost simultaneously; and it is more than probable
that, just as in sharks, considerable time is taken in the actual process of extruding the
eggs. In fig. 12 is shown the anal region of a specimen (C phantasma) in which the
egg-capsules were protruding. This specimen, it may be said, had been rather
carelessly handled and had been in the well of a fishing-boat nearly half a day, but
the eggs showed no tendency to become detached. The capsules in this instance
are still deeply inserted in the oviducts; even at a later stage they remain firmly
attached. In the condition shown in plate i, fig. 4, the capsules protruded as far
as the base of their terminal filament, yet they remained attached to the fish for
several hours and were thus brought to the Hopkins laboratory. It was then found,
as the figure indicates, that the terminal filament passed throughout the length of
the thickened portion of the oviduct and terminated in an expanded tract in the
crease at the lower end of the capsular gland. At this stage the walls of the lower
oviducts were contracted and embraced tightly the capsular filament. At a still
later stage the filament hardens into a dark-colored string, and the capsules then
hang freely into the water, 2 or 3 inches distant from the body.f Such a condition
was once observed by the writer, and he found that even thus the eggs were firmly
attached. In removing them the connecting strings were observed to possess con-
siderable elasticity. They could even be lengthened and shortened several inches.
When detached from the fish they showed that the terminal was still immature,
soft, and pale in color. It is to be regretted that in this specimen no dissection of

*Doubt has been expressed as to the presence of a receptaculum seminis. (Hyrtl in Sb. Akad. , Wien, 1853, XI,
pp. 1078-1087, and Redecke, Tydschr. d. nederl. Dierkund. Ver, zd ser., Decl. vi, 1899, p. 125.) In this connection
ff. Howes as to a "rudiraental vesicula seminis" in Chimaera ( ? ). (J. Linn. Soc., vol. xxm, p. 405.)

fProf. Einar Lonnberg, in a recent letter, which I am permitted to quote, states that he has observed (in July,
1898, in the market of Bergen), a specimen of Chimcera monstrosa in which egg-capsules were protruding from
the oviducts, somewhat in the condition shown in the present fig. 12.

26

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

the oviducts was made, for the filaments were so perfectly formed that they might
well have yielded some interesting notes as to their terminal. That this is finally
a bulbous organ there can now be no doubt. Ah Tack early made a drawing
of it, but the writer's skepticism* continued until word was received from Dr.
Wilbur (May i, 1899) that he had himself seen the terminal organ, describing it
as a "sort of disc," and figuring it (plate i, fig. 3) very much as Ah Tack had
done.f From all this it follows that the ovulation of this Chimseroid is highly
specialized. The elaborate egg-case is not shot out quickly nor festooned on fixed
objects by its terminal filament, as in the case of recent selachians, but is carried

Fig. 12. — Region of ventral fins ol a specimen of Chimera phantasms, in which egg-capsules protruded from oviducts. This
specimen was taken (Misalci, Japan) in water of about 1 50 fathoms and shows the intestine everted, a condition usual in a fish
taken from such a depth.

about for a longer time, protruding from the oviducts before it is made fast to a
suitable object. This is possibly a stone, % and if the eggs are thus attached near
or among rock masses, we have a suggestion why embryo-bearing capsules have
never been dredged.

"Pains were taken to observe the process of depositing the eggs. To this end a fish was secured in which egg-
capsules were just protruding. This specimen was closely watched, but succeeded, nevertheless, in depositing the eggs
unobserved. The process could not have taken more than 10 minutes. The capsules were immature, possessing
scarcely more than a stump of the filament (plate n, fig. 10).

fUnfortunately this capsule was lost in a hatching-case swept away by a storm.

|Ah Tack states that several times his trawl lines have brought to the surface capsules which still retained small
stones attached to the terminal organ of the filament.

DEVELOPMENT.

It is observed that after the eggs are deposited the oviducal openings are everted,
tumid, suffused with blood (plate i, fig. 2; cf. also Costa, p. 23, plate n, andGaimard,
plate xx, in Voy. en Islande et au Groenland); in fact, the entire anal region is
bloodshot, including the fin margins.

In many instances (August and September) the fish may soon spawn again.
This is evident from the mature condition of a pair of ovarian eggs which were
found in specimens having tumid oviducal openings.

RATE OF EMBRYONIC DEVELOPMENT.

The young Chimaera spends the greater part of a year in its capsule, probably
not less than nine months, and possibly as long as twelve. The duration of the
younger stages is known with reasonable accuracy. In the following table, show-
ing the rate of development of C. colliet, the results are based upon eggs in hatch-
ing-cases (water temperature between 50° and 60° F.).

TABLE B. — Kate of Embryonic Development.

Stage.

Fertilization.
Cleavage. .

First. . .

Second .

Sixth...

Blastula

Gastrula ..

Embryo.

Estimated

duration of

entire process.

36 to 60 hours
3 days.

4 days .
14 days .

Approximate age of specimen in material studied, time of
fertilization included.*

2 days 3 hours.

2 days 5 hours.

3 days.

5 to 9 days.

10 days.

12 days, corresponding to Balfour's shark embryo stage C.

19 days, corresponding to Balfour's shark embryo stage D.

21 days, corresponding to Balfour's shark embryo stage E.

24 days, corresponding to Balfour's shark embryo stage F.

28 days, corresponding to Balfour's shark embryo stage G.

33 days, corresponding to Balfour's shark embryo stage I.

90 days, f corresponding to Balfour's shark embryo stage L.
130 days, f corresponding to Balfour's shark embryo stage N.
180 days, \ corresponding to Balfour's shark embryo stage O.

*A re-examination of the writer's collecting notes leads him to estimate that fertilization takes place
in about two days. This time has therefore been added in assigning ages to the various stages.

tThese figures are based upon notes given by the fishermau Ah Tack, recording months when eggs were
placed in the hatching-cases. If these are accurate, and I believe they are reasonably so, Chimoera does not
differ notably from a shark in its rate of later embryonic growth.

THE EGG.

The egg of C. colliei measures in its capsule about 2.9 by 1.9 by 1.3 cm.
(average). It is inclosed in a delicate vitellina; when this is ruptured, the egg breaks
into a syrupy mass, very much as the egg of a typical selachian. Especially
soft is the egg about the time of its passage into the oviduct. At such a stage

28

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

(plate n, fig. 5), if placed on a flat surface, it spreads out circu-
larly, measuring in this way over 5 cm. in diameter. It is pinkish
(it is earlier yellow, and later creamy white), although its tint
is probably due to the capillaries in the enveloping membrane.
These capillaries, it may be noted in passing, become focused
around a well-marked stigma.

In the disposition of yolk the egg differs slightly from that of
typical selachians (e. g., as shown by Riickert in Torpedo). (Cf.
p. 47.) In the matter of fertilization, sperms have been found in
the uppermost portion of the oviduct, and there can be little ques-
tion that the earliest stages of fertilization here take place. It is
further evident that the eggs are received in the oviducts one after
another, for there is but a single funnel present, and it is prob-
able, from the condition of the ovaries examined, that the eggs
are shed from both right and left sides at almost the same time.
By this inference we can also best explain the passage of the
eggs, one to the right oviduct and one to the left, since if the first
egg were blocking the upper portion of one oviduct, the second
egg would naturally pass to the other. The fluidity of the egg
at this stage unquestionably aids it in passing through the narrow
opening of the oviduct in the zone of the capsular gland (plate n,
fig. 6), granting even that this opening is greatly enlarged at the
time of the egg's descent

THE EGG-CAPSULE.

The egg-capsules of Chimseroids* are illustrated in figs.
13-23, and a list of those hitherto described, together with notes
as to the depth at which they were collected, is given in Table C
on page 29.

An examination of the capsules indicates that they may be
grouped according to the genera and species which they repre-

Fig. 1 3. — Spirangium (egg-
capsule of Chimaeroid?).
From lithographic stone
of Lerida (Spain). Ju-
rassic. After Sauvage.

*In the instance of C. colliei, the parts of the young fish are found to have a definite relation to the egg-capsule,
and these relations are probably constant in other Chimaeroids. The capsule may therefore be referred to as containing
a case for the embryo, which is always subdivided into snout sheath, trunk sheath, and tail sheath. The case has
also a dorsal side, which bears anteriorly an opercular flap, which provides for the ultimate escape of the young, and
a ventral side, which is (usually) the more convex. Other descriptive terms are: Lateral zuebs, which are flanges of the
capsule extending outward from the case. These are sometimes strengthened transversely by stout undulating thick-
enings, rugfe, of the web; and these often pass over into, or are .associated with, more delicate and more numerous
distal rugulce, or both rugae and rugulae may become close-set, rib-like thickenings passing from case to web margin,
costie ; these terms will be found useful in description. Opercular ridges, overlapping, form together the rims of the
opercular flap. In their specialization these rims have sometimes protruding serrulcc, which interlock and form a close-
set grating, which admits water for the respiration of the embryo and which later breaks open to permit the young fish
to escape from the capsule. These grating-like fenestrulae are collectively homologous with the (pair or several pairs of)
lateral slits which appear near the rims of the egg-capsule of the shark or ray. Continuing the line of the fenestrulae,
ventilating apertures are also present at the sides of the tail-sheath, and these may be termed caudal fores. They are
typically furnished with "tongue-bars," which double the number of simple openings. A dorsal keel is present in the
capsules of Chimaera.

THE EGG-CAPSULE.

sent. In further detail, the capsules may be classified on somewhat the basis shown
by Table E on page 30. (Cf. this table for proportional measurements.)

TABLE C. — Egg-Capsules of Chimceroids.

Approximate
depth at which
deposited.

Species.

Reference.
(For detailed reference
c/. Literature List . )

Fathoms.

10-f

Callorhynchus*

1842 Miiller, J.

1865 "THrmeril, A

1871 Cunningham, R. O.

1880 Gunther, A.

1897 Parker and Haswell.

1899 Garman, S.

1901 Vavra.

^ to 6^

1901 Jaekel, O.
1903 Dean, Bashford.

J HJ \JJ

?3OO

mitsukurii

1904 Dean, Bashford.

• j""*

?2OO

monstrosa ....

1855 Nilsson, S.

1858 Lutken, C. F.

1874 Collett, R.

1877 Malm, A. W.

1889 Gunther, A.

1892 Alcock, A. (C. monstrosa?).

1896)
and > Grieg, J. A.
1899)

1896 Olsson, P.

phantasma

1901 Jaekel, O.
1889 Gunther, A.

ISO

375

Harriotta raleighana

1904 Dean, Bashford.
(v. infra)

3 1 J
3OO-6OO

Rhinochiniasra pacifica

1904 Dean, Bashford.

c6i

indica

1891 Wood Mason, J., and Alcock, A.

j

*Referenceis made in the present paper (pp. 30, et scq. and figs. 15 B-F) to several "species" of capsules
of Cattorhynchus ; e. g., Specimen 7983, Zool. Mus. Jardin des Plantes, Cape of Good Hope (Quoy and
Gaimard); Specimen 7982, Zool. Mus. Jardin des Plantes, Cape of Good Hope (Voyage Peron);
Specimen 7984, Zool. Mus. Jardin des Plantes, Chile (Martinez) ; Specimen 8823 A, Zool. Mus. Jardin des
Plantes, Straits of Magellan (Savatier). Also to specimens from Australia in the British Museum.

TABLE D. — Egg-Capsules of Fossil Chimceroids.

fschyodus ( = Alclodus) fcrrugineus :
(Upper Jurassic) 1901, Jaekel, O.

The fossils Spirangium, Palasoxyris, Fayolia, and similar forms may prove to be the egg-
capsules of Chimseroids or of cestraciont sharks. From their imperfect preservation,
however, they may equally well be coprolites of fishes having spiral intestinal valves. To
a somewhat more definite category, however, belongs the following "Spirangium" :
Spirangium:

1903, Sauvage, H. E.

Cf. fig. 13. If this prove to be a Chimaeroid egg-capsule it is remarkable in a feature suggest-
ing the capsule of a cestraciont — marginal webs arranged in spiral.

CHIMJEROID FISHES AND THEIR DEVELOPMENT.

TASL* E. — £gf-Cmses of Otimaroids Compared. (Cf. figs. 13-16.)

---"

M m LI

f!::ti

1 i = *f-l9

If I

j! j

a £ si £

— —
3 = C

M

L

J

14

"

XI

«3

--

13-17

'-
--

RB- is»

Fag-iy

£'*•

Kg. 150

i «5

33

"""""""

.-

36

(So—).-...

12

'

*»•-. _ t

.-•-. •_

«3

—

35 do do

33
33

3»

20
20

:- --

75

^

:•

37

n

53 4*

-.-'--
• -

•fc'i

i«t *

-

THE EGG-CAPSULE.

CLASSIFICATION OF CAFSVLES.

Fig. 14. Egg-capsulr oj lossil Chimirroid, I«chyoA»(AI*«odu»),
from Dogger bcd$ (Jurassic), Germany. Alter Jaekcl. Actual

From the materials provided in the
present table and figures the egg-capsules
of Chimaeroids may be classified on some-
what the following basis :

Callorhynchus. (Fig. 15 A-F.)

Capsules with case spindle-shaped; snout-sheath
subequal in length to the tail-sheath; lateral web
broad, exhibiting stout rugae; of these a conspicu-
ous pair proceeds outward from hinge of opercular
valve. No serrulse present, the opercular ridges
merely separating to admit water, as in related
structures in sharks. No caudal pores; in their
place a slit on each side of tail-sheath opening on
the ventral side in the angle between web and case.
Anterior lip of operculum transverse, situated on
dorsal side at a considerable distance from anterior
margin of capsule. No dorsal keel. Heavy cap
sules, leathery and glabrous.

No capsules of Callorhynchus are
known to be definitely associated with par-
ticular species, although many of the speci-
mens preserved in museums are ascribed
to " C. MAmtftec." From a study of
the capsules of the species of Chimaera, *
however, it is clear that the differences
between the capsules described are such
that we can not believe that they belonged
to the same species. Thus the Chilean
capsule (fig. 15), described by Jaekel as
"Ca/. ariJarf/ictis" (a synonym of C, caJ-
lorhynthHS of Valenciennes) is probably of
a different species from the similar egg-
case (fig. 1 5 A) figured by Dumeril, and
this in turn is notably different from sev-
eral specimens in the zoological museum of
the Jardin des Plantes, which the writer
was recently permitted to examine through
the courtesy of Professor Yaillant. The
latter capsules are accordingly figured

* Variation of the capsules within the range of the species was studied by the writer in the instance of Ckima-ra
About eighty capsules were examined, but the variations were found different in character from those
referred to in the present pages.

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

(fig. 1 5 B-F) from tracings of the specimens, and they will be seen to present a
considerable range, both in proportional measurements and in the number and
character of the rugse and rugulse.

Fig. 1 5.— Egg-capsule of Callorhynchus. From specimen collected in Chile by Plate. After Jaekel. Actual size.
Fig. 1 5A. — Egg-capsule of Callorhynchus. Locality unknown. After Dumeril. About two-thirds actual size.

In further detail, the capsule, fig. 153 (Cape of Good Hope), resembles most
closely that of fig. 1 5 E (Magellan). It differs, on the other hand, in having the walls
of the case more delicate and transparent, in spite of the fact that the Magellan speci-

THE EGG-CAPSULE.

33

men (or specimens) is much smaller in size. This difference, therefore, could hardly
prove a matter merely of age. Another capsule (Chilean), fig. 150, is again quite
unlike the specimen figured by Jaekel. It is almost a third larger in size, but nar-

\

Fig. 15 B. — Egg-capsule of Callorhynchus. (Quoy and Caimard.) From Cape of Good Hope.

(Ventral aspect.) One-half actual size.
Fig. ISC. — Egg-capsule of Callorhynchus. (Peron.) From Australia. (Ventral aspect.)

One-half actual size.

rower proportionately. Its emphasized rugae arising from the opercular hinge are
more nearly transverse, and, unlike any other capsule of Callorhynchus known to the
writer, it presents a thick, opaque case, margined by a thin, transparent web. In

34

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

the last regard it differs again from the capsule of fig. 1 5 E, in which the portion of
the web in front of the opercular hinge is far more transparent than the posterior
portion. Again, the capsule of fig. 1 5 c, although somewhat resembling that of fig.
1 5 B, differs notably in proportions ; thus, the tail-sheath is relatively longer. The
capsule is also much lighter in substance. A sixth and final capsule, fig. 1 5 F
(Australian), one of several specimens in the British Museum, presents additional
differences. It is much broader than the rest, and is notably deficient in rugulae.*

I5D

Fig. 15 D.— Egg-capsule of Callorhynchus. (Martinez.) From Chile. (Ventral aspect.) One-half actual size.

Fig. 15 E. — Egg-capsule of Callorhynchus. (Savatier.) From Magellan. (Ventral aspect.) One-half actual size.

Fig. 15 F. — Egg-capsule of Callorhynchus. (British Museum.) From Australia. ( Dorsal aspect.) One-half actual size.

Specimens similar to the last mentioned appear in the museums of Copenhagen
and of Harvard University.

Other Callorhynchid capsules include a fossil one, ' 'Aletodus" (Ischyodus), and
one of the curious elongated forms from the middle Pacific, which has recently
been described by Carman. The first (fig. 13), lately discussed by Jaekel,
proves so similar to the foregoing recent capsules that one may doubt the propriety
of regarding it as having belonged to a separate genus. The second, Carman's cap-

*The specimens, four in number, in the British Museum, are essentially alike ; two were collected near Dunedin,
two near Hobart (mem, kindly furnished by Mr. Boulenger).

THE EGG-CAPSULE.

35

Fig. 16. — Chimaeroid egg-cap-
sule. Mid-Pacific. (Ventral
aspect.) After Garman.
About two-thirds natural size.

Fig. 17. — Egg-capsule of Chi-
maera monstrosa. Norway.

sule (fig. 1 6), differs widely from other
recent forms. It has thus a remark-
ably long tail-sheath; is provided with
a distinct type of lateral web, for its
rugae are few in number and restricted
to the region of the trunk-case, and
there are no conspicuous rugae arising
from the hinge of the opercular flap,
dividing a precardinal from a post-
cardinal lateral web, as in the other
forms.

These differences are so striking that
I am quite convinced that this capsule
represents a new genus.* Garman
himself tells us nothing of its antece-
dents, and as he on one page refers
to it as belonging to Callorhynchtts
antarcticus and on another to Callo-
rhynchus callorhynchus, I infer that he
attributes it to the latter species and
that he regards these terms as synony-
mous.
Chimaera.

Capsules somewhat tadpole-shaped, with
large trunk-sheath, short snout-, and long,
tapering tail-sheath; lateral web narrow, with
rugae faint, if present at all. Opercular flap
extends forward to end of case; serrulae pres-
ent, beginning far forward, a part of the
complicated apparatus of opercular ridges
(cf. pi. ni, fig. 17, A, B, c) ; caudal pores
many, opening on both dorsal and ventral
sides. A dorsal keel present. Capsules thin,
parchment-like, smooth or slightly ridged.
The species differ in well-marked details, e-g.,
in width of lateral web, length of tail-sheath,
modeling of trunk- and snout-case, texture,
number of serrulae, etc. If arranged in a com-
parative series (cf. table, p. 30, and figs- 17, 18,
21, 22), C. colliei stands closest to the type of
Carman's capsule, and C. mitsukurii is ob-

(Ventral aspect.) Natural size. viously the most specialized.

*This might be christened and specified by a systematist who does not hesitate
ultimatelylto complicate Chimaeroid literature in the matter of synonyms. It may be
long before a new Chimaeroid is fished from the mid- Pacific and it may be a century
before this can be satisfactorily fitted to "Carman's capsule." Let us therefore pro-
visionally refer to such capsules according to the names associated with them — thus
under Callorhynchids we may refer to the " Martinez capsule, " " P^ron capsule, "etc.

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

Harriotts (?).

Capsule (fig. 19) with case outlined like a short-handled spoon; lateral web wide and evenly
transparent, strengthened by an even series of thickened costal ridges. Dorsal valve terminates in
a broad transverse lip subterminal; its lateral rims have ruffle-like serrulae, which are most marked
midway between hinge and anterior lip, and fade away anteriorly and posteriorly. No dorsal keel;
on the contrary, a shallow groove extends along the dorsal wall of caudal sheath. Caudal pores in
a series of decided slits; the largest, in the middle of the series, open ventrad, although they appear
also on the dorsal side as a marked surf ace feature of the capsule. Capsule smooth, parchment-like, pale.
iS i 20

Fig. 18. — Egg-capsule of Chimaera colliei. Puget Sound. (Ventral aspect.) Natural size.

pig. |9.— Egg-capsule of Harriotta (?) . North Atlantic. After specimen preserved in U. S. National

Museum. (Ventral aspect.) Natural size.
Fig. 20. — Egg-capsule of Rhinochimaera indica (" Callorhynchus indicus "). Indian Ocean. After Alcock.

(Ventral aspect.) Three-quarters natural size.

This interesting specimen is preserved in the National Museum at Washington,
where it bears the number 22793. The present writer is indebted to the Curator
of the Department of Fishes, Mr. Barton A. Bean, for his courtesy in bringing it
to his attention, and to the Museum for the privilege of describing it. Its
history is briefly as follows: It was taken, 1879 (on trawl line), by the Gloucester
fishing vessel of Capt. G. A. Johnson, in water of 375 fathoms, lat. 42° 47', long.
63° 10'. It obviously does not belong to the foregoing genera, but from its resem-

THE EGG-CAPSULE.

37

21

22

Fig. 21. — Egg-capsule of Chimaera phan-

tasma. Misaki, Japan. (Ventral aspect.}

Natural size.
Fig. 22. — Egg-capsule of Chimaera mit-

sukurii. Misaki, Japan. (Ventral aspect.)

Natural size.

blance to Rhinochimsera it evidently
belonged to a similar fish. It is thus to
be attributed, with strong probability, to
the only Chimseroid of this character
known from the region in which it was
taken, i. e., Harriotta.*

A second capsule (fig. 20), hitherto
associated with Callorhynchus, should
provisionally be placed with the present
genus. Although collected in the Indian
ocean, it .resembles closely the capsule
from the Atlantic, having the same type
of lateral web, costae, and subterminal
opercular margin, f

Rhinochimaera.

Capsule with case spindle-shaped; snout-sheath
stouter and thicker than tail-sheath; lateral web
wide, its outer margin transparent, strengthened
by a regular series of tapering costse. Lip of
dorsal valve ends in a narrow, delicate lip, sub-
terminal. Serrulse low and faint. No dorsal keel;
in its place a shallow groove extends along the
dorsal wall of the caudal sheath. Caudal pores
similar to those in Harriotta (?). Capsules
smooth, dark-colored, hornlike.

The capsule shown in fig. 23 has been
definitely associated with the species
R. pacifica. It differs notably from
the Indian capsule in proportions, in the
number and character of its costae, and
in its operculum.

On the foregoing pages the egg-cap-
sules of Chimgeroids have been referred
to in considerable detail, since by a com-
parison of their characters light is thrown
upon the problem of Chimseroid descent.
For it is clear that the different species
of Chimasroids produce capsules specific-
ally distinct; and it follows, therefore,
in the light of evolutional analogies, that
the fishes which produced the more
differentiated capsules are the descend-
ants of those in which simpler capsular
structures prevailed. It follows, also,
conversely, that the forms which have
the simpler capsules are apt, in this and
other regards, to represent more closely
the common ancestor. This evidence,

* Harriotta has been taken between lat. 36° and 40°, long. 70° and 75°; from greater depth, however — 700 to 1,100

fathoms. The latter difference is not all-important, as by many analogies spawning might well occur at a lesser depth.

fThe writer recently examined this specimen in the Calcutta museum, through the courtesy of Major Alcock.

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

Fig. 23. — Egg-capsule of Rliinorliimaera pacifica. Misaki.
(Ventral aspect.) Natural size.

however, may best be considered subse-
quently in correlation with similar facts.

The capsules may also be referred to
at the present time in the evidence they
present regarding the factors of evolution ;
for it is clear that such highly specialized
capsules provide a valuable check upon
the evolutional process from the standpoint
of the obvious "prevision" which they
demonstrate. The capsule is, in short,
adapted not so much to the egg as to
the young fish which it will later contain.
Thus it is specialized in accord with the
shape of the young fish, its position, and
its late physiological needs, all to a de-
gree which is, indeed, probably unequaled
in the secondary embryonic membranes of
other animals. * This degree of special-
ization becomes clearer, moreover, when
we take into consideration the formation
of the capsule.

FORMATION OF THE CAPSULE.

At the time the egg is about to leave
the ovary the oviduct is flaccid and is
richly suffused with blood ; in fact, from
this time onward the oviducal sinus f in
which they lie is dilated (plate i, fig. 4,
and plate n, fig. 5, ovd. s.\ forming a

* ' Cf. Dean, 1904, Biol. Bulletin, vol. vn, pp. 105-112.

t These sinuses arise in the mesovaria, the walls of which
do not become apposed. They are thus longitudinal sacs of
blood in which the oviducts lie more or less freely, depend-
ing upon the degree of development of the egg-capsule
(cf. plate 11, fig. 5, and plate i, fig. 4, left oviduct). In the
former figure, however, this condition is not seen favorably,
since the oviduct is purposely pushed against the wall
of its sinus, thus dislodging the opaque blood, so that the
structures of the oviduct can be better described. In
the latest stage in the formation of the capsule, on the other
hand, the sinus is so filled with the enlarged oviduct that in
ventral view it can hardly be seen ; thus in the figure the
oviducts appear to lie freely in the body-cavity. The blood
supply in the sinus, it may be remarked, is maintained by
direct communication with the cardinal (not to complicate
the problem as to the relations with the renal portal ) blood-
cavities. Between the lines where the mesovarial folds are
attached to the dorsal body wall a row of ostia is present
( pi. i, fig. 4, o). This method of increasing enormously the
oviducts' blood (venous) supply is evidently correlated with
the rapid formation of the highly complicated egg-capsule.
It can hardly be regarded as evidence of a primitive gon-
adial sinus, and we are led to conclude that morphologically
the veins of the mesovarium have coalesced, leaving ostia
as vestiges of the gonadial veins, e. g., of sharks.

THE EGG-CAPSULE. 39

remarkable venous outlet, and the arterial supply is also highly developed, branches
of the oviducal artery passing backward along the oviduct and dividing into an
elaborate series of transverse branchlets. *

The oviduct itself undergoes striking changes to accomplish step by step the
stages in the formation of the capsule. To follow these briefly, the oviduct con-
tracts cephalad when the egg is received, and holds it in the cavity dilated in the
posterior region of the capsular gland. Here it is that the walls of the oviduct
form folds and ridges and by these are able to model the secretion of the gland
into the beginnings of the capsule. From such a position the early capsule was
obtained which is figured in plate in, figure 12. Jts shell was papery, whitish (with
but a trace of color), and so frail that it could not be removed unbroken with the
contained egg.

The exact mode of folding of the walls of the oviduct to produce the details of
the capsule need not be given in detail. The growth in the capsule continues, as
shown in plate in, figs. 13, 14, 15, and 16, the tail-sheath and its appendage of
the case being the last portions formed. The fact that the anterior part of the
case is finished before the tail-sheath was often taken advantage of by the writer in
his effort to secure embryological material, for he found that such an egg as shown
in plate n, fig. 8, could be safely incubated for earlier stages if the base of the tail-
sheath was kept closed, e. g., by a ligature.

In comparing the foregoing figures one observes a number of details as to the
modeling of the capsule from stage to stage. The earliest condition (plate in, fig. 1 2),
shows that the tip of the capsule, although delicate, is almost complete, with
opercular folds, serrulae, apex, lateral ridges, and the beginnings of the dorsal
keel. In the stage of plate in, fig. 16, the capsule is practically complete, save for
the tail-sheath, and in this stage the lateral webs are widest, suggesting the con-
ditions of Callorhynchus.

The oviduct from which such a stage is taken as that shown opened in plate n,
fig. 6, forms, as we could naturally expect, an exact mold for the capsule. Thus we
find a cervix, c, with sphincter (for apex of the case) ; distinct creases, /. w. (for lateral
webs) ; a thickened tract, with folded margins and with median groove, d. k. (for
dorsal wall of case, opercular folds, and dorsal keel). As the tail-sheath was not
yet developed in this capsule, the corresponding region of the oviduct, /. s., is still
contracted ; but at the sides we note the broader folds, r, in which the ruga=: are
laid down ; also at t. o. the deep recesses below the capsular gland in which the
terminal organ comes to be formed. At a subsequent stage the lateral webs are
strengthened by a process of folding, which causes them to become narrower (cf.
plate 11, fig. 10, and plate in, fig. 16) ; and at the same time the tail-sheath is laid
down (plate i, fig. i).

In the latter process the sheath itself, with the beginnings of its caudal pores,
is formed before the adjacent web (plate 11, fig. 7), and when this is completed there
remains to be formed only the capsular filament and adhesive organ. By this time,
however, the capsule has acquired such a phenomenal length that it extends from
the oviducal (i. e. retroanal) opening forward to the anterior wall of the body-cavity

* The oviducal artery divides into four branches when it reaches the anterior end of the capsular gland, two beccm-
ing dorsal, two ventral, and thus they proceed, bilaterally arranged, as far as the posterior portion of the oviduct (cf.
plate i, fig. i ; plate n, figs. 5 and 7 ).

40 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

terminating near the cardiac region. To add, therefore, a couple of inches to the
length of the capsule involves a serious problem in the matter of space. This has
been solved as follows : The capsule is gradually released, so that it comes to project
from the fish's body ; at first the apex appears at the mouth of the oviduct, then
the trunk-sheath, then the tail-sheath (fig. 1 2). If at this time the egg is dislodged,
an abortive terminal results, as in plate n, fig. 10. If it remains, the process in the
formation of the capsular filament and terminal organ progresses as seen in plate i,
fig. 4. The capsule now protrudes as far as the base of the filament, and with this

26

Figs. 24-26. — Egg-capsules of Chimaera colliei, partly opened, so as to show egg and young. Natural size.
24. Late blastula (about 9 days). 25. Early gattrula (about 19 days). 26. Late gastrula (about 24 days).

protrusion occur many changes in the oviduct (cf. plate u, fig 4, and plate n, fig. 6),
e. g. , its diameter becomes greatly constricted and its dorsoventral characters and
web creases obsolescent ; it also loses its earlier differentiation into trunk-sheath
and tail-sheath forming portions, and its vaginal region is extended headward, the
remaining part of the oviduct becoming correspondingly reduced. All these changes
are to the obvious end of molding the long capsular filament and the bulbous terminal
organ (plate i, fig. 4, c. f. , and c. o. ). For the formation of the latter serves a special
region of the capsular gland, i. e., its hindmost zone, a portion pinkish in color,
provided with the recesses into which the terminal organ has been traced. *

* Finally, a note may be given as to the probable mode of attachment of the capsule (cf, pp. 26, 27.) It is evident
that the oviduct can be greatly evaginated at the time the egg is deposited (plate i, fig. 2\ and with this phenomenon
is evidently connected the forward extension of the cervix (cf. plate i, fig. 4, and plate n, fig. 6). We may thus
conclude that at the cervix, then, the bulbous organ of attachment can be held by the fish even when the oviducts have
been greatly everted ; and it would naturally be by such elongated, even finger-like, processes that the fish could press
the filamentous ends of the capsules against the object of attachment, e. g-., a. rock fragment, and thus secure their
adhesion.

THE EGG-CAPSULE. 4-1

Before describing the various stages of Chimsera (C. colliei) a brief survey of
the general plan of development might be given (cf. Biol. Bulletin, 1903, vol. iv,
No. 5, pp. 270-286):

The development is shark-like (figs. 24-29). In early stages a small germinal
area is present. In this polyspermy occurs, then a cleavage, in which, however,
surface furrows are retarded. The early gastrula suggests somewhat closely the
condition in shark, or rather in ray, but the blastopore appears near instead of at
the margin of the blastoderm. The embryo develops a long, delicate tail, external
gills, and a head terminating in a conspicuous frontal -"lobe." It absorbs the yolk-

29

28

Figs. 27-29. — Egg-capsules of Chimaera colliei, partly opened, so as to show egg and young. Natural size.

27. Early embryo (about 32 days), showing subdivision of yolk material.

28. Late embryo (about 5 months), showing external gills and miniature sac. At this rime the embryo is bathed in a heavy milky fluid resulting

from continued subdivision of yolk masses.

29. Young Chimaera at about the time of hatching ? eight months). The capsule at this period is greatly weathered and develops a tension

which probably aids the operculum in springing open and permitting the young to escape.

sac, and before hatching becomes large in size and has many features of the adult,
e. g. , mixipterygia in the case of the male. By far the most remarkable feature
during this process of development is the behavior of the yolk. This undergoes
vacuolization, followed by fragmentation. Of the yolk a small portion only is
inclosed within the sac of the young ; the remainder continues to fragment, form-
ing a creamy mass which nourishes the embryo via external gills and gut. The
fragmentation, we have reason to believe, is an extreme modification of the process
of cleavage.

42 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

THE EGG AND ITS MEMBRANES.

In the newly deposited capsule the egg measures 35 by 20 by 12 mm., but it is
smaller, together with the capsule, if taken from young fish (cf. the size of the
capsules shown in plate n, fig. 10, and plate in, fig. 17), as is also the case in sela-
chians (Riickert). Its consistency becomes less fluid-like as development advances;
thus, shortly before breaking from the ovarian membrane, the egg has so little con-
sistency that it will flatten out to the diameter of about 45 mm. (plate n, fig. 5).
Its ellipsoidal outline is assumed when inclosed in the capsule. It will, however,

32

Fig. 30. — Early ovarian egg of Chimaera colliei. Section through major axis of egg. ffs, Gonadial sinus; £-<', germinative vesicle —
around it the extent of the space indicates the size of vesicle before fixation ; o, stalk attaching egg to ovary and inclosing the
arterial blood supply; /, peritoneum; /, tunic (= granulosa).

Figs. 31 and 32. — Sections of the marginal region of ovarian eggs (the first measuring about 5 mm. in diameter, the second about 15 mm.),
indicating changes in the tunic and the development of yolk, bm. Basement membrane ( between the tunic and the egg ) ;
by, botryoidal yolk masses developed in vacuoles in germinal yolk ; c, layers of connective and vascular tissue theca in ovarian
membrane surrounding egg; ffx, gonadial sinus; p, peritoneum; /.tunic of ovarian tissue inclosing egg (follicular epithelium);
/, inmost layer ; »;, middle layer ; o, outmost layer ; zr, zona radiata. X 585.

present an almost spherical form (horizontal outline 25 by 20 mm.) if the constricting
capsule be opened (plate n, fig. 8). In later stages it has the consistency of thick
cream.

THE OVARIAN MEMBRANES.

Comparison with corresponding stages in shark (Pristiurus) shows that the
wrappings of the ovarian eggs of Chimaera are the more complex. In early stages of
the latter the ovarian tunic is thicker and its nuclear elements more abundant and
more evidently specialized. Thus in fig. 30, which shows in section an egg of about
5 mm. , one notes the thickness of the tunic ; this (greatly enlarged) is shown in

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43

:ial in character, is clearly
middle, and inmost. In
essed — oblong, therefore,
ley are large and diffuse ;
he basement membrane,
lial sinus, gs, the tissue of
interspersed with plasma
issed through the special-
ay be assumed that the
us the closely compacted
plasma spaces (and capil-
hese again transfer their
1 the egg.

33C

) mm. in diameter), gy. Germinal
oup of chromosomes ; mgT, limiting

region of the zona radiata. In this

. vesicle recedes from surface of egg.
c, showing large vacuoles ; :, zona
•n the vesicle and the adjacent tunic

rently physiological, since
:leus of the inmost layer
is clearly connected with a nucleus ot the middle layer. ~In some cases such a rela-
tionship is demonstrated by dividing nuclei, which, it may be remarked, exhibit
sometimes direct, sometimes indirect division. At the surface of the egg is a sharply
marked membrana limitans ; below this, irregular in thickness, a zona radiata, prob-
ably homologous with the well-known layer in eggs of other fishes. Below this the
egg shows an outer finer layer and an inner coarser or reticular layer, in which
large vacuoles frequently occur. At a somewhat later stage (egg measuring about

CHIM/ER(

In the newly deposite
smaller, together with th<
capsules shown in plate n,
chians (Riickert). Its con
thus, shortly before breakii
sistency that it will flatte
Its ellipsoidal outline is a

Fig. 30. — Early ovarian egg of Chimaera co
around it the extent of the space intlii
arterial blood supply; />, peritoneum;

Figs. 3 1 and 32. — Sections of the marginal
indicating changes in the tunic and I
by, botryoidal yolk masses developei
membrane surrounding egg; gs, gona
i, inmost layer; m, middle layer; o,

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THE OVARIAN MEMBRANES.

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43

rtial in character, is clearly
, middle, and inmost. In
ressed — oblong, therefore,

hey are large and diffuse ;
the basement membrane,
dial sinus, gs, the tissue of

interspersed with plasma
•assed through the special-
aay be assumed that the
lus the closely compacted

plasma spaces (and capil-
These again transfer their
o the egg.

33 D y

W' .

10 mm. in diameter). <• v, Germinal
;roup of chromosomes ; mgT, limiting

s region of the zona radial a. In this

11 vesicle recedes from surface of egg.
tic, showing large vacuolcs ; : , zona
:en the vesicle and the adjacent tunic

irently physiological, since
icleus of the inmost layer

is clearly connected with a nucleus ot tne middle layer. In some cases such a rela-
tionship is demonstrated by dividing nuclei, which, it may be remarked, exhibit
sometimes direct, sometimes indirect division. At the surface of the egg is a sharply
marked membrana limitans ; below this, irregular in thickness, a zona radiata, prob-
ably homologous with the well-known layer in eggs of other fishes. Below this the
egg shows an outer finer layer and an inner coarser or reticular layer, in which
large vacuoles frequently occur. At a somewhat later stage (egg measuring about

CHIM^RC

In the newly depositec
smaller, together with the
capsules shown in plate u,
chians (Riickert). Its cons
thus, shortly before breakir
sistency that it will flattei
Its ellipsoidal outline is a;

Fig. 30. — F.arly ovarian egg of Chimaera col
around it the extent of the space indie
arterial blood supply ; /, peritoneum ; i

Figs. 3 1 and 32. — Sections of the marginal
indicating changes in the tunic and t
by, botryoidal yolk masses developec
membrane surrounding egg; g-x, gona
/. inmost layer ; /;; , middle layer ; o,

present an almost spherica
capsule be opened (plate i .
cream.

No.

No.

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No. 71. Atlas of Absorption Spectra. By H. S. Uhler and R. W.

Wood. Quarto. In press.
No. 72. Investigation of Inequalities in the Motion of the Moon

Produced by the Action of the Planets. By Simon Newcomb.

Quarto. In press.
No. 73. Explorations in Turkestan: ArcheologicalandPhysiograph-

ical Results of Expedition of 1904, under direction of Raphael

Pumpelly. Reports by Raphael Pumpelly, Herbert Schmidt, J.

E. Durst and R. W. Pumpelly, with contributions by F. A.

Gooch, Langdon Warner, Ellsworth Huntington, and Homer

Kidder. Quarto. In press.
No. 74. The Vulgate Version of the Arthurian Romances — A

faithful reproduction of Mss. in the British Museum, by

H. Oskar Souimer. Quarto. In press.

November 17, 1906.

THE OVARIAN MEMBRANES.

Comparison with corresponding stages in shark (Pristiurus) shows that the
wrappings of the ovarian eggs of Chimxra are the more complex. In early stages of
the latter the ovarian tunic is thicker and its nuclear elements more abundant and
more evidently specialized. Thus in fig. 30, which shows in section an egg of about
5 mm. , one notes the thickness of the tunic ; this (greatly enlarged) is shown in

THE EGG AND ITS MEMBRANES.

43

fig 3 1 ; here it will be seen that the tunic, although syncytial in character, is clearly
divided according to its nuclei into three layers — outmost, middle, and inmost. In
the outmost layer the nuclei are small and closely compressed — oblong, therefore,
in form — and directed ecto-entad ; in the middle layer they are large and diffuse ;
in the inmost, small, irregular, and closely apposed to the basement membrane.
Between the outmost layer of the tunic, o, and the gonadial sinus, gs, the tissue of
the ovary contains numerous strands of connective tissue interspersed with plasma
spaces, c; it is from these, doubtless, that nutriment is passed through the special-
ized tunic to the inclosed egg. During this process it may be assumed that the
various types of nuclei of the tunic play definite parts ; thus the closely compacted
nuclei of the outmost layer purvey nutriment from the plasma spaces (and capil-
laries) to the dilated elements of the middle layer. These again transfer their
nutriment to the small nuclei which are closely apposed to the egg.

.33*

Fig. 33. — Section of region of germinative vesicle of well-grown ovarian egg (about 20 mm. in diameter), gy. Germinal
yolk; gs, gonadial sinus; gv, large germinal vesicle containing near its center a group of chromosomes; mgv, limiting
membrane of germinal vesicle ; t, tunic ; zr, zona radiata.

Fig. 33A. — Detail of preceding section from point at side of egg, showing absence in this region of the zona radiata. In this
region yolk granules are developed in numerous minute vacuoles.

Fig. 33B. — Detail of section of fig. 33, taken at a point where the side of the germinal vesicle recedes from surface of egg.
gy, Germinative yolk ; mgi', membrane forming wall of germinal vesicle ; /, tunic, showing large vacuoles ; z, zona
radiata. This will be seen to extend only over the margin of the vesicle. Between the vesicle and the adjacent tunic
there extends only a thin peripheral layer of germinative yolk.

Figs. 33C and 33D. — Detail of chromosomes shown in fig. 33 (two sections). X 385.

The differences in the nuclei of the tunics are apparently physiological, since
intergrading forms occur ; thus in the figure cited a nucleus of the inmost layer
is clearly connected with a nucleus of the middle layer. In some cases such a rela-
tionship is demonstrated by dividing nuclei, which, it may be remarked, exhibit
sometimes direct, sometimes indirect division. At the surface of the egg is a sharply
marked membrana limitans ; below this, irregular in thickness, a zona radiata, prob-
ably homologous with the well-known layer in eggs of other fishes. Below this the
egg shows an outer finer layer and an inner coarser or reticular layer, in which
large vacuoles frequently occur. At a somewhat later stage (egg measuring about

44

CHIM^JROID FISHES AND THEIR DEVELOPMENT.

15 mm.) the conditions of the tunic have changed. It has become thinner (fig. 32)
and has modified its structures considerably. In place of the differentiated inmost,
middle, and outmost layers, an outer layer is alone conspicuous and even here the
nuclei have not the crowded character of the earlier stage ; the inmost and middle
layers have merged, forming a somewhat indefinite layer, poor in nuclei. In some
cases markings in the (partial) syncytium indicate that the tunic is in places but one
cell thick. Indirect divisions sometimes occur. The entire structure of the tunic
suggests that closer physiological relations exist between the vascular supply, on
the one hand — plasma spaces, as in c, having now extensively drawn together into

d

•cy

•Sf

Fig. 34. — Section of germinal region of egg of Chimeera colliei during stage of early fertilization. cy. Coarse
yolk ; li, dendritic lines marking paths of sperms ; fy, fine yolk ; gp, germinal area extending as a
plug-shaped mass deep into the egg ; n, nuclei, sperm, and egg fusing. Under the points marked with
asterisks (*) vacuoles occur which separate masses of fine germinal yolk and are usually found to contain
sperm nuclei.

capillaries — and the egg on the other. This physiological process is doubtless aided
by the thinning of the membrana limitans, bm, and of the zona radiata. And as
an indication that the nutriment is being passed rapidly into the yolk we observe
that even close to the surface of the egg large yolk masses are appearing.

In a final stage of the ovarian egg the tunic is still further diminished in thickness
(figs. 33, 33 A). It is reduced, in fact, to a single-celled layer, of which the nuclei
are usually disposed nearer the outer wall in the same niveau. Sometimes, however,
they are closely apposed to the inner wall, but in all cases they are of the same
general character (fig. 33 B), i. e., spherical nuclei, with sharply marked mem-
brane, showing but faint traces of chromatin meshwork, but with one or two con-

THE EGG AND ITS MEMBRANES. 45

spicuous nucleoles. Cell boundaries are sometimes better seen than in earlier
stages, and large vacuoles are present near the tunic's outer wall ; surrounding this
the ovarian stroma is reduced to practically a single-celled layer, which now alone
separates the tunic from the blood in the large gonadial sinus ( fig. 33, gs). Com-
parison with earlier stages thus indicates — paradoxical as the statement reads — that
the arterial supply of the developing egg is progressively diminished and the venous
supply progressively increased.*

The foregoing details are given, since they indicate the complexness of the
problem of the growth of the egg in Chimaera. There here exist at various stages
not a tunic of an almost unvarying character, as apparently is the case in sharks,
but one which in earlier stages is shark-like, but which later changes progressively,
diminishing its thickness and reducing the number of its component elements, to
the end that each cell of this membrane comes in immediate contact on the one
hand with the egg and on the other with the nutritive fluid. It is further clear that
the elements of the tunic acquire changed physiological characters as development
proceeds — witness the changes which occur in size, shape, and disposition of the
nuclei, the appearance of vacuoles in the late stage — pari passu with changes in the
arrangement of the blood supply.

YOLK.

The yolk masses at first occur in the granular ooplasm close to the zona; next
they appear in vacuoles, cavities which are noted before the appearance of the yolk
masses, and are later seen to become greatly enlarged and to be drawn together
around the masses of yolk. The yolk itself increases in bulk, its masses now often
presenting irregular protuberances, resulting apparently from a process of accretion.
In surface view many of the yolk masses appear botryoidal (in eggs preserved in
sublimate, acetic-sublimate, picro-sulphuric, picro-formalin). And this condition
persists while the egg is attaining its mature size. In stages as late as gastrulation
the coarse yolk differs little outwardly from the foregoing conditions. The grains
show only a smoother surface and a possible tendency to coalesce ; but it is
evident that the vacuoles are now more closely adjusted to the yolk. The fine
yolk, on the other hand, is, as Riickert's figures indicate in sharks, derived from
the coarse yolk by a process of subdivision. Comparing the earlier stage (fig. 32)
with one at fertilization (fig. 35), we observe that the substance of the former grains
has become subdivided into morula-like masses of minute deutoplasmic elements,
these, as before, lying in large vacuoles. In each of these masses one notes that
there has usually been produced a globule of a highly refringent substance analo-
gous to the oil-drop of the teleostean egg. In a later stage the corresponding por-
tion of the egg has become a well-defined region of germinal yolk (Riickert's Keim-
dotter), and we are led to conclude that the later condition, with fine grains of yolk,
is the result of a continued process of subdivision of the morula-like masses and
their subsequent confluence. (The general character of the germinal yolk is shown
in figs. 33 A and 33 B aigy.)

* In its latest stage the ovarian egg shows a series of capillaries (plate n, fig. 5), converging to an elliptical stigma.
Unfortunately, the relations of the tunic in this stage were not examined.

46 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

The grouping of the yolk elements in the mature egg is somewhat irregular.
Sometimes "drifts" of germinal yolk underlie the coarse yolk; sometimes they
extend obliquely, admitting between them inbursts of coarser yolk. In general, at
the time of fertilization, the germinal yolk dips deeply down into the coarse yolk,

36

35

Fig, 35. — Section of fertilization stage, showing near the surface and at the side of the germinal area a sperm which has just gained
entrance. This is shown at .•>•, surrounded by a lighter area of germinal material. In the depression above the sperm is a mucus,
like mass which may represent in part the tail of the sperm. «/, Middle piece. X 575.

Fig. 36. — Section of fertilization stage, showing deep entrance pit of a sperm. From the lowermost point arise branching rays.

Fig. 37. — Detail of section of specimen shown in fig. 34. From the path of a sperm astral rays branch in many directions, and at
various points (indicated by the dark points) new centers of radiation appear.

Fig. 38. — Detail of fertilization stage shown in fig. 34. The present section follows almost exactly the entrance path of a sperm. The
latter appears at .v, and it is seen that the entrance pit is a delicate tube extending downward in the direction of a sperm. Around
the latter appears a well-marked aster, and in this neighborhood, strung along a prominent ray of the aster, are a number of deeply
stained " centrosomes." A similar " centrosome " occurs near the lowermost point of the entrance tube of the sperm.

forming a plug-shaped mass twice as deep as wide (fig. 34). This is possibly the
homologue of the Panderian nucleus figured in the shark egg ; certain it is, how-
ever, that the egg of Chimaera has not as clearly a marked series of tunics in its
yolk arrangement.

THE EGG AND ITS MEMBRANES.

47

THE GERMINAL VESICLE.

This is eccentric in eggs even as small as' 3 mm. (cf. fig. 30). In the section of a
well-grown ovarian egg shown in fig. 33 it lies close to the side of the egg. The
spireme has here contracted into a minute mass and has given rise to (about) twelve
pairs of chromosomes. * These are of remarkably small size, smaller by about
one-half than those of a corresponding stage of shark (Pristiurus); and they are
also smaller in terms of the germinative vesicle. In Pristiuris (Riickert) the mass of
chromosomes at this stage measures 36 p in width and the vesicle 296 ; in Chimaera

40

39

&£&?yi :-:S3sjS

'M

Fig. 39. — Detail of sperm nucleus from section of late fertilization stage. The sperm head is surrounded by a conspicuous aster,

in some of whose dendritic rays appear the nodes referred to below. The sperm nucleus itself is undergoing amitotic

division. X 475.
Fig. 40. — Detail of section of late fertilization stage. Throughout the germinal yolk occur asters which have no apparent

reference to nuclear structures. At / many of these asters appear around a large granule of yolk. It will be seen that

the rays are formed as lines in the thickened walls of alveoles.
Fig. 41. — Detail of section of late fertilization stage, showing asters in germinal yolk.
Fig. 42. — Detail of section of late fertilization stage. At n the egg-nucleus is shown surrounded by a number of asters.

The asters appear to lack centrosomes and centrosphere. Note as before rays formed from rims of alveoles.
Fig. 43. — Section similar to the foregoing. A sperm nucleus, however (n). is shown surrounded by asters.

the same mass measures 16 and the vesicle 570. In other words, with a germinal
vesicle twice the size, the size of the chromatin mass in Chimaera is but one-half
that of the shark. In the shark the chromatin mass measures about one-ninth the
diameter of the vesicle; in Chimsera, on the other hand, about one thirty-eighth.
This condition indicates again the greater specialization in the egg of Chimsera.
The chromosomes themselves, it will be remarked (figs. 33 c, 33 D), vary considerably
in length ; thus the pair shown at x are apparently longer than those at y and at 2,
and a detailed examination has convinced the writer that this difference is a real
one, i, c. , not due to the oblique position of the objects. This observation may be
mentioned, since it affords an additional suggestion as to the individuality of the
chromosomes, recently discussed, e. g., by Sutton, Wilson, and Moenkhaus.

*Preliminary to first polar division. The number of chromosomes is clearly much smaller than in sharks ( 36 in
Pristiurus and Torpedo).

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

FERTILIZATION.

Fertilization begins, as in sharks, in the uppermost portion of the oviduct and
continues throughout the period of the formation of the capsule.* The earliest
stage in the writer's material was obtained from a capsule like that shown in plate in,
fig. 1 3, earlier stages not having been handled successfully. Late stages were secured

4.6 A

45

454

46

••:-.'• .-

91

-• "• . u-' v
• v. ''

Fig. 44. — Detail of late fertilization stage, showing male nucleus in the process of approaching the egg nucleus. A club-shaped centrosome

surrounded by astral rays appears at (right) side of nuclear membrane. X 475.

Fig. 45. — Detail of section similar to the last. A well-marked vacuole (artifact?) appears at one end of nucleus.
Fig. 45A. — Sperm nucleus with aster from section similar to the preceding.

Fig 45B. — Sperm nucleus from stage similar to foregoing. The center of aster is to be found in the section below present one.
Fig. 46. — Detail of section shown in fig. 34. Sperm nucleus has divided amitotically. This at first suggests a stage of copulating

pronuclei.

Fig. 46A. — Egg and sperm nuclei in apposition. Rays not conspicuous.

Fig. 47. — Early prophase of segmentation nucleus. Two asters are present, one of which (the right) contains two centrosomes.
Fig. 47 A. — Early segmentation stage. Section passing through segmentation nuclei. No surface furrows are as yet present. X 190.

from capsules about as shown in plate in, fig. 16. In the present account the
stages may conveniently be referred to as early, middle, and late.

An early stage is shown in surface view in plate iv, fig. 18, magnified about
15 diameters. This was drawn from a living egg and shows the germinal area
somewhat misshapen, due to rupture of the vitelline membrane, f The germinal
area is not sharply outlined ; it is the same color as the remainder of the egg, and

* The egg at deposition is undergoing the first stage of segmentation.
\ This is conspicuous at this stage, glossy and tense.

FERTILIZATION STAGES. 49

is only demarked by a slight furrow. Under a dissecting lens a number of minute
depressions indicate the points of entrance of sperms. Seven of such points appear
in the present instance, and all of them are peripheral; four are close together. In
this case sections show that no sperms have entered the middle of the germ.

A middle stage in fertilization (plate iv, fig. 19), also examined in the living egg,
showed 23 entrance pits. Of these half a dozen are of large diameter and several
are minute, a condition which, in comparison with the preceding stage, suggests
that the small pits are the early phases of the large ones, and we query, accord-
ingly, whether in point of time the entrance of sperms in Chimsera may not prove an
extended process (v. infra, heading /). In the present specimen it will be seen
that the sperms have entered not only the germinal substance but the bottom and
even the outer wall of the germinal fosse.

Study of sections leads us to conclude:

(a) That the tail of the spermatozoon does not enter the egg. In fig. 35 a
sperm is shown which has just entered the egg ; the middle piece, mp, ends
abruptly, and there is no trace of the tail. The entrance pit is not yet sharply
formed.

(b) That the head of the spermatozoon rotates as it travels inward. Even at
the early period above figured, the filamentous character of the sperm head has
been lost ; it is now spheroidal, surrounded by a light-colored area of the germ.
Although hardly within the egg, its axis inclines 45° to the surface, and its middle
piece is parallel with the surface, a condition which by analogy with other forms
leads us to conclude that it has already begun a process of rotation. In a later
stage in the entrance of the sperm (fig. 38) the lighter-colored portion of the " head "
points toward the surface of the germ and thus indicates that the rotation has been
carried through an angle of 180°.

(c) A state of remarkable kinetic activity exists in these stages. In fig. 36 a
series of "astral rays" are seen diverging downward from the entrance pit of a
spermatozoon (cf. the observations of Miss Foote in Allolobophora). And from paths
traversed by a sperm "astral rays" arise, sometimes radiating regularly, but usually
branching irregularly and forming new groups of radiation. At such points of
reradiation darkly staining bodies occasionally appear which remind one of centro-
somes. In the present fig. 34 branching astral rays are seen. These, it is found,
have arisen around a sperm path. A similar series greatly enlarged is shown
in fig. 37, a series of considerable interest, since it shows many "centrosomes"
surrounded by bending and irregularly branching rays. The "centrosomes" some-
times appear at centers of reradiating rays in sperm asters (figs. 38, 39); at other
times they arise without any apparent relation to sperm asters or sperm paths, as
around an unusually large yolk granule (fig. 40, the group at the right). As shown
in the last figure, more than half a dozen centers of radiation appear around the
yolk granule. On the other hand, the two large "asters" shown at the left in the
present figure have no apparent relation with the former series, nor are they in the

-0 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

neighborhood of sperm asters. A similar pair of "asters" are shown in fig. 41,
On the other hand, the asters shown in fig. 42 are arranged around the male
pronucleus, but how they are related to one another can not safely be inferred. In
the following section (fig. 43), drawn from the same specimen, a similar radiation
occurs around a supplemental sperm head, n. In the four preceding cases it is
interesting to observe how perfectly the rays fulfil the alveolar conditions for aster
formation as explained by Biitschli. Note in this connection the large size of the
alveoli in the immediate neighborhood of the aster.

(ct) The behavior of the germ nuclei in fertilization is similar to that in shark.
The sperm which enters the germ in the region nearest to the egg nucleus is the one
which accomplishes fertilization; it undergoes the customary form changes while
traveling through the germ. In the stage shown in fig. 44 its chromatic material
is becoming resolved, and the aster which appears beside it radiates from a
centrosome, which is in this case somewhat elongated, situated close to the
nuclear membrane. A stage somewhat earlier than the foregoing is shown in fig.
45 ; this, however, represents a stage in the development of a supplemental sperm
head. The foregoing figures are taken largely from late stages in fertilization. A
stage from a nearly finished capsule (fig. 46) pictures the union of the germ nuclei,
i. e., corresponding to Ruckert's fifth stage in the fertilization of the ray (Torpedo),
as figured in the Kupffer Festschrift (fig. 53 B). On the other hand, fig. 46 A,
which at first sight suggests copulating pronuclei, must be construed as picturing a
(sperm) merocyte dividing amitotically; for here a third nucleus is found to be pres-
ent, above the niveau of the other two. The figure indicates, further, the retention
of the aster and an extensive pale-colored area surrounding the nuclei.

(e) The behavior of the supplemental sperm heads is also notably shark-like. In
even the middle stage of fertilization they can not readily be distinguished from the
early sperm nucleus. Indeed, the nearer they are in a position to the egg nucleus
the more difficult they become to distinguish from one another. And conversely
those undergo the least conspicuous changes which occur in the margins of the
germ. We have already referred, in fig. 45, to a structure which from its position
is apparently the early sperm nucleus. In this phase, at the margin of the nucleus
is a vesicular area, at one end of which an aster radiates from a minute centrosome.
A somewhat similar appearance occurs in what, from its eccentric position, is
undoubtedly a supplemental sperm head (fig. 45 A). Here the vesicular area of
the nucleus is less perfectly developed, strands of karyoplasm passing from the
nuclear membrane to the large and deeply staining mass of chromatin, a stage,
indeed, which may be looked upon as the earlier condition of that of fig. 45.
Another sperm head (fig. 45 B) from the same series of sections is intermediate
between those of figs. 45 and 45 A. The vacuolated margin is now broken into
several discrete areas, and the chromatin is collected into a diffuse mass, irregular
in outline.* From this stage the transition is not wide to that of fig. 34, in

*The aster lies below the plane of the section.

FERTILIZATION STAGES. cr

which is pictured a (sperm) merocyte occurring eccentrically (n) in the germinal
area of an egg twin to the preceding. In this the vacuolar area has been practically
lost, the aster increased in size, and the nucleus subdivided into a number, probably
five or six, of smaller merocytes. Division of this kind has been observed in many
instances; and on the other hand no case has been found in which a sperm nucleus
divides indirectly. This condition is noteworthy, since it emphasizes on still
another line the specialization of the Chimaeroid. For in the shark the sperm
nuclei may undergo indirect division throughout practically the entire process of
cleavage; and when early direct divisions do appear, e. g., in the third cleavage
(Riickert in Torpedo), they still show traces of their mitotic ancestry. Indeed, the
nearest condition to the presegmentation division of the sperm head in Chimsera
(fig. 39) occurs in shark only in the period of later segmentation (cf. Riickert, op.
cit., pi. in, fig. 1 8). In other words, the morphological (or the physiological)
result which in the shark is effected only at the end of a series of graduated stages
is accomplished by Chimsera at a single stroke — a condition worthy of comment,
since it affords a palpable case of "precocious segregation."

(_/) The sperms enter the germ not simultaneously, but during a relatively
extended period. The pits formed by the sperms when entering the germ, as already
noted, are different in size, and we accordingly infer that, as the sperms themselves
do not differ materially in size, nor in all probability in individual activity, the dif-
ference in the pits is due to their having been formed at successive periods. This
suggestion is borne out by examination of sections. Thus, in fig. 36 an entrance
pit is shown, pointing down in the direction of, but not actually connected with, a
sperm head lying deep in the germ. And here the pit or funnel has a wide mouth.
On the other hand, in fig. 38, a funnel is pictured whose apex is still connected
with a sperm head, and its mouth is narrow. The sperm head, in this case, lies
in a shallower layer of the germ, and from its structure, also, is clearly a younger
stage in development. It follows, therefore, that the former sperm entered
the germ at an earlier period than the latter, and that the process of semina-
tion is a relatively extended one — relatively, since in sharks all sperms appear
to enter simultaneously. The suggestion may, on the other hand, be made that
the difference in the behavior of the sperms in the germ might be due rather to
their location than to their time of entrance; or, in other words, that the rapidity
of their development might be influenced by their proximity to the egg nucleus.
This suggestion, however, is not tenable in view of the condition of the fertilization
stage (middle stage) shown in plate iv, fig. 19, for here small pits occur side by side
with large ones, both in the middle of the germinal area and on the sides.

Finally, to contrast Chimsera and shark in stages of fertilization: In Chi-
msera the entrance of the sperms is a protracted process; but as soon as the sperms
(other of course than the one which fertilizes the egg) enter the germ they divide
promptly by amitosis, with the very probable result of producing a greater number

tj2 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

of merocytes in a shorter time. * It thus appears that the early divided merocytes
are equivalent morphologically, and probably, therefore, physiologically, to late
merocytes in sharks. Furthermore, at the time of fertilization the number of sperms
entering the egg of Chimsera appears to be greater than in sharks. The average
number reckoned by Riickert in Pristiurus is about 16; in Chimsera it is at least
24, judging from the number of entrance funnels in late stages of fertilization.
Again, in Chimera the sperms form and long retain definite paths in the germ which
are unknown in other forms; so also are their entrance funnels more conspicuous.
The sperm nuclei, furthermore, as well as the segmentation nuclei, are the more
special in terms of the entire egg, since they are smaller than in sharks (in diameter
about one-half). Also, as evidence of specialization — for these structures have
clearly a special physiological value — witness the great number of asters and their
ready mode of appearance, e. g., around vagrant yolk granules of extraordinary
size. In point of histological differentiation of the germinal cytoplasm, finally, we
observe in Chimsera conditions unparalleled in the shark. We recall here the differ-
entiation of typical Schaumplasma, the light areas surrounding the nuclei, and the
extensive development of astral rays.

SEGMENTATION.

Drawings of the living germ, plate iv, figs. 20-29, give a general idea of the
process of segmentation. And in surface view this resembles distinctly the usual
conditions in shark. There is the same type of germinal area in which cleavage lines
appear, and a marginal zone which apparently circumscribes the area of cleavage.

In the first of these figures the germinal area appears convex, although some-
what flattened above, and is separated from the surrounding germinal yolk by a
narrow fosse. The furrow which appears to traverse it is sharpest and deepest in
the middle of the germ and fades away at the margins. The surrounding zone of
germinal yolk, however, extends widely over the surface of the egg and lacks a
sharply marked outer boundary line. Its inner boundary, i. e. , at the fosse, shows
a number of small eminences These, as sections also show, correspond to the
eminences formed in the shark blastoderm by peripheral (sperm) merocytes; they
are more numerous at the corresponding stage and are more regularly disposed
around the germ.

In further detail: Sections of the present specimen demonstrate that in spite
of the single apparent furrow the present stage represents not the first, but the
third cleavage, two cleavage furrows having been retarded (? suppressed), for there
are found to be present six segmentation nuclei. This condition, it may be
remarked, occurs in certain specialized sharks (Torpedo).

The first division of the segmentation nuclei is accompanied by no trace of a
surface furrow. Such a stage is shown in fig. 47 A. The nuclei are here somewhat
widely separated from one another and are in the resting stage ; the only indication

*Recent examinations of the sections of the fertilization stage which yielded fig. 46 A (Chimaera Emb. 12, in my
cabinet) show that no less than 88 (sperm) merocytes are present. Thus in Chimaera as many merocytes are present
in a presegmentation stage as in Torpedo (Ruckert) in a stage of fourth cleavage.

SEGMENTATION STAGES, 53

of cleavage is in the arrangement of the germinal cytoplasm afotind the nuclei.
This is expressed in such a way that the germinal yolk rises between them like a walL
The second stage in which cleavage is seen at the surface is shown in plate iv,
fig. 21, from the egg companion to the one shown in plate iv, fig. 20, but incubated
longer (about forty minutes). Here a second furrow is noticeable. The
resulting " blastomeres " are unequal in size, one of them being as large as two of

Fig. 48. — Section passing between the point 1 and 1 of the segmentation stage shown in PI. IV, fig. 20. In the present section the

line which appeared to indicate first cleavage lies below the point f; below this a vacuole is present whose lateral extent gives one

the impression of the width of the furrow noted in surface view. X 35.
Fig. 49. — Section through a segmentation stage corresponding to PI. IV, fig. 22. It will be observed that some of the cleavage lines

do not open to the surface, as at c. On the other hand, one of the spaces between the blastomeres opens into a fissure-like

vacuole, a.
Fig. 50. — Similar section of early segmentation stage, in which, as at n, a nucleus appears without any neighboring cleavage furrow.

A line of thicker germinal yolk appears in its place.
Fig. 51. — Section of early cleavage stage in which, when viewed from the surface, deep, fissure-like vacuoles appear as cleavage lines.

the others. As in the companion stage the furrows fade away at the margin of the
germinal area, and this is again surrounded by a somewhat regular ring of merocyte
eminences. It may be mentioned that these characters are materially modified,
i. e., as far as surface view is concerned, when the egg is hardened, e. g., in acetic
sublimate. And in sections it is found that the circumgerminal fosse and merocyte
eminences disappear and what was interpreted as surface furrows in the living egg
appear as long and wide vacuoles. Thus in fig. 48, a section transverse to the

e A CHIMjEROID FISHES AND THEIR DEVELOPMENT.

first cleavage line of the stage of plate iv, fig. 20, the fosse will be seen to have dis-
appeared, and the line which indicated cleavage, so conspicuous in surface view,
now appears under the point / as a vacuole triangular in section, its apex touching the
surface of a germ.* Vacuoles, we note, are abundant in early stages; several
are present in the section of the germ just referred to, and from their arrange-
ment they suggest the division of the germ into blastomeres.

Three stages of early cleavage are shown in surface view in plate iv, figs. 22,
23, and 24, the first as an opaque object, drawn from the living egg, the second and
third as translucent objects, in the last cases the germ having been removed, placed
in a watch glass, and examined by transmitted light during the process of fixation.
In these three preparations there is considerable irregularity in the surface charac-
ters; in the first the margins of the blastomeres are rounded, in the others angular;
outwardly they appear to represent fourth and fifth cleavages; in section, how-
ever, single ' ' blastomeres " are sometimes found to contain several segmentation
nuclei. It was observed that the resting and dividing nuclei were sometimes found
in the same section, and it follows accordingly that in Chimaera the synchrony of
cleavage is early lost.

Four later stages of segmentation appear in plate iv, figs. 25, 26, 27, and 28, all
drawn under conditions of transmitted light, the living specimens having been
removed and examined in watch glasses. In the first of these the germ is well
marked off from its circumgerminal zone; in the rest some of the marginal cleav-
age lines were traced half-way across the circumgerminal zone, and in a few
instances these lines could be followed quite across it. In these stages continued
subdivision of the "blastomeres" has taken place, those in the central position
becoming divided oftener than those near the periphery. As in earlier stages, some
of the cleavage lines are probably not expressed at the surface, and are due only to
vacuoles; the latter are lineal in surface view, sometimes wide, sometimes narrow,
occasionally almost attaining the surface, at other times lying fairly deep in the
germ. (Cf.fi.gs. 49, 50,51.) Sometimes, as in fig. 49, they are actually continuous
with cleavage furrows, as at a, and considering the relation which they often bear
to nuclei (e.g., infra, under the heading "gastrulation"), we conclude that in
some cases — even, indeed, in many cases — they are homologous to cleavage spaces,
i. e., that they are cleavage spaces which fail to become expressed at the surface
of the germ. This conception appears to be applicable even when the vacuoles
appear in the peripheral region of the germ in fertilization stages. Thus in fig. 34
the masses of germinal yolk separated by the vacuoles (under the points marked
with an asterisk [*]) usually bear sperm nuclei which, as we know by analogy, will
cause ' ' segmentation. " Accordingly, even in this position vacuoles may be compared
to intercellular spaces, at least from the standpoint of developmental mechanics.

In fig. 52 a section of a segmentation stage corresponding to plate iv, fig. 26,
shows that cleavage has by this time extended deep into the germinal area. Hori-
zontal divisions have occurred, irregularly however, for in some places the blastoderm

*There is thus a possibility of there having been an open furrow in the living egg.

CLEAVAGE STAGES.

55

varies in thickness from one to five cells. Noteworthy is the irregularity of the yolk
wall out of which blastomeres are segmenting, as at x, and into which deep inter-
cellular spaces are continued, becoming confluent below, as at v, v, v, with vacu-
oles like those described in earlier stages. It may be remarked that in this stage
the vacuoles pass deeply into the yolk.

Another stage of late segmentation (or blastula), corresponding in general with
plate iv, fig. 27, is shown in the series of sections, figs. 53-56. In the section, fig. 53,
which passes near the center of the germ, the conditions differ little from the
preceding stage. We observe that continued divisions have taken place and that
there is still the same outcropping of blastomeres from the yolk wall, as at .a: and x,
following mitoses. An advancing character in this stage is the general flattening of
the germinal wall, as at the point y, a preliminary step toward the formation of the
floor of the segmentation cavity, and possibly indicating fore and aft differentiation
of the germ. It may be remarked that this is the first stage in which a conspicuous
zone of merocytes was seen. These are numerous under the central blastomeres,
most numerous under the peripheral blastomeres, and then rapidly decrease in

^V. :•;;:

Fig. 52. — Section of late cleavage stage (corresponding to PI. IV, fig. 26). x. Mass of germinal yolk from which a
blastomere is being budded out ; ?', vacuoles which are continuous with intercellular spaces.

number peripherad. The three sections, figs. 54-56, illustrate such a series. The
first of them, fig. 54, indicates the relation of the above-mentioned vacuoles to
intercellular spaces, as at the points marked with an asterisk (*) ; the second and
third, figs. 55, 56, are instructive as showing the extension of a nest of cells, n
(it is the same group in both sections — it appears, however, at the left in the lower
section, since this has been turned over on the slide), beyond the margin of the
circular mass of blastomeres — instructive, since it suggests that the outlying
region of the germ (circumgerminal zone) is still little different from the germ
itself in its cell-forming nature. It is also to be observed that deep fissures
representing intercellular spaces (fig. 56, 2), extend peripherad through the
germinal yolk, corresponding to the marginal furrows described in the eggs of
ganoids and dipnoi, of Heterodontus, even of amphibia. There is here accord-
ingly a region in which, side by side, occur small blastomeres, large yolk masses
(bearing nuclei), and undivided yolk ; there is no gradual transition from the yolk
to the large blastomeres and from these in turn to the small ones, which, as
we have seen, correspond in size with blastomeres of the center of the germinal
area. We observe, furthermore, that the small blastomeres arise in any

FISHES AND THEIR DEVELOPMENT.

neighboring position, as in figure 55, at a, b, or c, budding out directly from
the yolk. In such cases the important question remains whether the nuclei
which pass into the blastomeres are derived from segmentation nuclei or from

53

%*&%$•?'$&*.

55

.SSSa^.

-\ c

J .-• -"55, -gffi;^^?SB^

Figs. 53-56.— Sections of late segmentation or early blastula stage (corresponding to PI. IV, fig. 27). The first section traverses the
mid-region of the segmented area, the others progress marginalward. x, Blastomeres which have recently budded out of the yolk ;
y, wall of sub-germinal yolk ; z, cleavage line passing deep into the sub-germinal yolk ; *. vacuoles which come to the surface of the
germ and form intercellular spaces. X 35.

sperm-nuclei. In the latter event, judging by analogy, they would show amitoses
only; in the former they should multiply by mitosis. Examined in this light it
is found that the nuclei which here pass into the blastomeres show amitoses, and

THE DIVISION OF THE YOLK. 57

they might thus be regarded as of sperm-head origin. On the other hand, it
might still be claimed that the nuclei of such blastomeres were derived from the
segmentation nuclei, fora more careful examination shows (i) that amitoses exist
in the blastomeres in the central region of the germ, and (2) that no mitoses are
found in the zone of the merocytes, where we may reasonably expect that some
nuclei are present which are derived from segmentation nuclei. The problem is,
nevertheless, a difficult one, and hardly to be answered in the present outline of
Chimsroid development. We point out, however, that two criteria which have been
given a prominent place in the discussions of sEafk development can not be
employed in the present instance, viz. (i) the number of the chromosomes which
would naturally give a clue as to the origin of the nuclei can not be estimated in the
merocytes, since they are here undergoing only amitotic division ; (2) the size of the
present merocytes can not prove an important element for comparison, since they
range from minute to large, and in shape from spherical to greatly elongated and
irregular.

An important phase of the cleavage in Chimaera has naturally been introduced
by the foregoing discussion, i. e., as to the segmentation of the egg in its extra-
germinal region. We have seen that as segmentation progresses nuclei (whether
segmentation or sperm-merocyte) spread peripherad. Their presence can be
determined in sections ; and in surface view, in the later stages, e. g., plate iv,
fig. 28, cleavage lines can be seen passing outward in the region of the circum-
germinal zone. That these lines are actual furrows is shown in such a section as
that of fig. 56 (at the right). Such marginal furrows, however, are usually minute
in size, and are often, in surface view at least, difficult to follow, a difficulty which
may be due either to the blending of these delicate lines with the color of the
circumgerminal zone, or to the partial or total confluence of the adjacent rims of
the cleavage furrows, e. g., as in the marginal blastomeres of Cryptobranchus
(according to Ishikawa). The distinctness of these lines, however, increases after
the circumgerminal zone is passed, and they later give rise to what we must regard
as the most remarkable feature of the segmenting egg.

To follow this process: In fig. 57 a late stage of segmentation is shown; the
germ is atg; nearby are nests of blastomeres (cf. fig. 56, «), two of which are of
such size as to appear in the figure, as at.^'; from the germ radiate furrows, two of
which, a and a', have become conspicuous at the periphery of the egg, where they
may have merged with similar furrows, or indeed, on the other hand, there is a
possibility that the long furrow passing between the points marked with an asterisk
(*) may be the deflected continuation of the lines a and a'.

In figs. 58 and 59 furrows are seen arising from or near the circumgerminal
zone, and examination shows they deepen as they proceed peripherad. In the egg
shown in fig. 59 the outgoing line subdivides and marks out superficially a narrow
segment of yolk. In the same egg, but in the anterior region, we note another
marginal line, b. Examined from below this stage is of considerable interest

_8 CHIM;EROID FISHES AND THEIR DEVELOPMENT.

(fig. 60), for it shows that while the cleavage lines have failed to express themselves
on the dorsal side of the egg, they yet appear conspicuously on the vegetal side. Thus
the line in fig. 59 at a passes sharply inward (fig. 60), subdividing into a series of

57 58

Figs. 57-61.— Eggs showing progressive cleavage of the yolk mass. In a blastula (57) a conspicuous fissure

it noted between the points * and *.

cleavage lines which in turn merge with other cleavage lines (b-g)
passing downward and inward from the equatorial zone of the egg.
In some cases well-marked yolk masses are outlined, as at the point
marked with an asterisk (*), suggesting large yolk-filled blasto-
meres on the ventral wall of an amphibian blastula. It may be
remarked that the lines here described are not mere surface mark-
ings, for during the process of hardening an egg, e. g., in acetic-
sublimate, one may separate the yolk masses by aid of dissecting
needles, and in this process it becomes clear that the lines are in
reality fissures dipping deeply into the substance of the egg.
Indeed, in the former specimen it was found that the mass marked
with an asterisk (*) could be removed en bloc from the remaining
mass of yolk. It is evident, accordingly, that in this stage the egg
is being divided up on its ventral side into a number of large yolk
masses; that these masses stand in relation to the entire egg very much as do,
e. £-., in the frog's egg, the blastomeres of the lower pole to this entire holoblastic
egg ; further, that the fissures which accomplish this result, like cleavage lines on
the vegetal side of the holoblastic egg, are interconnected with a series (a-g, in
fig. 60) of cleavage lines which pass downward and inward from different points in
the equatorial region of the egg. Between the stages shown in figs. 59 and 60, and
those in figs. 61 and 27, which are older by about nine days, observations are
lacking. It is nevertheless clear, by comparison of these stages, that the yolk
masses shown in fig. 60 have separated from one another widely as the fissures
deepened, and that, as the masses became more distinct, their condition of surface
tension — in view always of the syrupy consistency of the egg — caused them to
round out their contours to the degree shown in fig. 61.

THE DIVISION OF THE YOLK. 59

*

In dorsal view the latter stage shows few large yolk masses, and these are
distinct from one another, although closely pressed together. The yolk masses,
it may be mentioned, were removed separately (in the living condition) without
causing their rupture, and it was then seen that the fragmentation of the yolk mass
had progressed further than was at first evident, for, lying below and on either
side, against the ventral wall of the capsule, were many small masses of yolk (cf.
fig. 61, at the right, and fig. 27, somewhat behind the embryo), their contours
rounded out for the most part; but a thick, creamy or syrupy fluid in which they lay
made it further evident that in some cases the yolk masses had broken down.
This fluid, we remark, was observed in specimens of this stage only when the
larger masses were separated; but if sea-water was injected (by pipette) between
the larger masses as they lay in the open capsule, it would dissolve the underlying
creamy yolk and the entire contents of the capsule would become hidden from
sight in the resulting milky fluid.

One might conveniently digress at this point to follow the fate of the yolk
masses above mentioned. The blastoderm appropriates only a small portion
(which has been estimated as about one-tenth of the volume) of the entire egg.
This separate yolk mass is shown slightly shaded in figs. 27 and 61, and the blasto-
derm, with its attached embryo, has as yet inclosed only a small portion of it. A
similar stage is figured in plate vin, fig. 47, and a somewhat later one in plate viu,
fig. 48. In the latter the blastoderm is seen to have almost inclosed the yolk.
It completely incloses the yolk and forms a diminutive yolk sac in the embryo
shown in plate vin, fig. 49, and a similar condition occurred in the embryo of
plate ix, fig. 50. These features are dwelt upon in order to show that the
behavior of the blastoderm in appropriating but a portion of the yolk is a normal
phenomenon. And I note that the condition shown in fig. 61 has been observed
on three occasions by myself, and that similar conditions were recorded by
Dr. Wilbur.* In supplementary evidence upon this point we may again refer to
the embryo of plate vin, fig. 49, for in this the yolk sac, although of miniature size,
is evidently normal, since it exhibits a well-developed vitelline circulation, f

The yolk-masses other than that appropriated by the blastoderm undergo con
tinued subdivision. This is in progress in fig. 61, where the large yolk mass shown
in the lower part of the figure is being divided into three smaller ones. We have
already referred to the pasty fluid present among the lowermost yolk masses in this
stage. In the egg capsule from which the embryo of plate vin, fig. 49, was taken,
no extra embryonic yolk masses were found, but the egg capsule contained a fluid so
cream-like as to conceal completely the embryo and lead me to infer that the egg
was addled, almost causing me to throw away this valuable stage. We can only
conclude, therefore, that the creamy fluid was due to the continued breaking down

*In his early letters Dr. Wilbur referred to these conditions doubtfully; he was then "not sure whether they
represented normal appearances."

fTheyolk sac measured about half an inch in length and a quarter of an inch in breadth; accordingly at this
stage of development it represents but about one-tenth the volume of the egg of an Elasmobranch of similar size
(e. g., Spinax niger}.

60 CHIM;EROID FISHES AND THEIR DEVELOPMENT.

of the yolk masses of the earlier stage.* That this fluid was nutritive to the
embryo was also evident, since the external gills were dilated at various points
with brilliantly colored blood knots, and in these, as I later found, numerous
erythrocytes were undergoing division. And this condition in the gill filaments
is the more clearly correlated with the presence of the milky fluid, since in similar
egg capsules (sharks and rays), where this milky fluid mass is lacking, blood knots
on the external gills are also absent. One infers, moreover, that the milky fluid,
which from its included yolk is highly nutritive, may also be passed as food into
the mouth of the embryo and assimilated in the gut. But to this I will refer at a
later point.

The entire process of the fragmentation of the egg of Chimaera, it will be seen,
is worthy of especial comment. Unlike the eggs of other vertebrates, and unlike,
indeed, those of invertebrates, unless we include a somewhat generic resemblance
in certain mollusks (e. g., Neritina, Blochmann, 1887) and in certain digenetic
trematodes, the present egg follows in its development two distinct paths, i. e., a
small portion of the egg develops in the direction of producing the embryo with
its complete though diminutive yolk sac; the remaining portion, about nine-tenths
of the bulk of the egg, proceeds to undergo a process of repeated fragmentation to
the end that it may be appropriated by the embryo secondarily.

To account on phyletic grounds for this extraordinary and "unnatural" plan of
development, one must, I believe, start with the premise that the fragmentation
of the egg is a process comparable with total cleavage. This premise we may
accept on the following evidence:

(1) The fragmentation, like cleavage, is progressive.

(2) Although the cleavage lines have never been followed conclusively from
the rim of the blastoderm into the deep fissures which initiate the fragmentation,
they have at least been observed in late stages of segmentation to pass out over the
circumgerminal zone in the direction of the peripheral fissures (cf. in this regard
the evidence of Heterodontus).f

(3) The yolk masses give evidence of being nucleated. There is in the first
place evidence that the nuclei travel peripherad. In the stages of plate iv, figs.
25-27, nuclei are found to have occupied the circumgerminal zone, i. e., they have
traveled outward a distance equal to about three-quarters of the diameter of the
blastoderm. In an early gastrula, furthermore (plate v, fig. 31), and in section,
fig. 63, they have proceeded outward a distance equal to twice the diameter of the
blastoderm. Now, on the evidence of progressive centrifugal movement of the

*The reader may reasonably query at this point how it happens that the creamy nutritive material is not washed
out through the openings of the capsule during the respiration of the young. This result has, I take it, been avoided
in the course of the evolution of this process in two ways : (i) By retarding the appearance and growth of the capsular
openings until the nutritive material is partly consumed ; (n) by the great density of the creamy fluid, for if the
nutritive fluid be heavy (and experiments with the living eggs have convinced me that this is the fact), a moderate
current of sea-water could be passed over it without causing it to be washed away.

tAnnot. Zool. Jap., 1901, vol. iv, pt. I, pp. 1-7.

THE REDUCED SIZE OF THE YOLK SAC. 6 1

nuclei, and as this nucleated area (in diameter) is measurably greater than that
of the yolk mass which the blastoderm comes to inclose, it follows that nuclei are
present in some of the outlying yolk masses. Of this, however, we must none the less
admit that no direct proof is at hand, since no sections of these outlying yolk masses
were made. In this connection I observe that if the embryo-bearing yolk mass
be examined even under a low power (plate viu, fig. 480) one obtains a fairly con-
vincing picture of its holoblastic character.

(4) The foregoing evidence is none the less_strong if, conversely, we consider
that on no other morphological ground, save that of cleavage, using the word in a
broad sense, can this progressive and normal fragmentation be explained.

Accepting, then, the premise that these divergent paths in the development
of the egg of Chimera took their origin in a holoblastic egg, the present con-
ditions may well have been developed on somewhat the following lines : In
the primitive Chimseroid the egg resembled that of Cestraciont; it was probably,
however, not as large as that of the recent Heterodontus, but its cleavage fissures
were deeper and more numerous. The embryo at that stage had the usual
external gills of the selachian. The next stage would be attained when the
gill filaments, passing beyond the stage of the well-known trophonemata, came to
appropriate the white of the egg which was contained in the deep cleavage fissures,
a process which in time caused or accompanied («) the deepening of the fissures,
and in further time (fr) a rupture at the bottom of the fissures. Through such a
process yolk material came to escape and mingle with the albuminous contents of
the deep fissures. Such a process, we may now assume, was naturally followed by
adaptative changes in the trophonemata, which in the end accelerated the growth
and differentiation of the embryo. In short, at this evolutional stage the embryo
was receiving through a (morphologically) indirect channel an amount of nutri-
ment which rivaled that derived from the vitelline circulation. The result was
what one would have anticipated, i. e., the down growth of the vascular blastoderm
was retarded, while the fissuring of the yolk-mass became deepened and the
trophonemata further modified. The line of evolution thus carried on in the egg
will be seen to involve the fate of the yolk sac, viz. , in determining how great an
amount of the yolk could be diverted from it. In the present species (C. colliei)
about nine-tenths of the egg has been diverted, while in the Callorhynchids, where
the yolk sac is known to be larger, possibly not more than half.

In the foregoing process it is suggested that the first steps in the disinte-
gration of the yolk mass were found in cleavage phenomena. It should, however,
be admitted that the cleavage may not have been equivalent to that of the usual
holoblastic type. The nuclei which spread peripherad may have been sperm-nuclei ;
and in this event the peripheral furrows are special phenomena, unconnected,
possibly, in phylogeny with the cleavage lines in the holoblastic egg. Certainly
in favor of such an interpretation is the fate of the disintegrating yolk masses,
since such a fate is paralleled somewhat by the sperm-nuclei in the shark egg. It

62 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

is opposed, on the other hand, by the conditions in the egg of Cestracion, where
the peripheral furrows, similar in general regards, are known to be continuous with
those of true cleavage. The question, therefore, can not be answered finally until
evidence is forthcoming to distinguish the kinds of nuclei present in the extra-
embryonic yolk masses. Meanwhile, judging at least from the behavior of the
nuclei in the circumgerminal ring, I think it is not at all improbable (cf. Gastru-
lation) that in these masses both sperm and segmentation nuclei are present.

Returning again to the development proceeding at the animal pole of the egg:
We recall that in the sections figs. 53-56 there was shown a stage of late seg-
mentation, or an early blastula, such, for example, as pictured in plate iv, fig. 27.
In a slightly later stage (plate iv, fig. 28) an increased number of blastomeres are
present, and there is still an indefinite condition in the periphery of the germ,
blastomeres being continued irregularly over the ring-like circumgerminal zone.
On the other hand, in plate iv, fig. 29, a stage is figured earlier than the preceding,

Fig. 62. — Section of blastula. sc, Segmentation cavity.

but showing a well-marked line of demarcation between the blastomeres and the cir-
cumgerminal zone. It seems evident, accordingly, from this and similar instances,
that considerable variation occurs as to the time at which the marginal relations of
the germ are established. Thus in the stage first referred to (figs. 53-56) the
circumgerminal zone was traversed by radial fissures and invaded by nests of cells;
in a similar stage (plate iv, fig. 29, sectioned in fig. 62) the same region is solid and
yolk-filled, forming a compact border to the germ.

In contrasting these two stages one observes that, while they can differ little in
point of age, judging from the number of blastomeres in the cross section of the
middle of the germ, they yet have marked differences in their relation to the yolk ; the
former has around it and under it "fine yolk" (Ruckert); the latter has its fine yolk
contracted into a thick mass lying immediately below the germ, a condition which
may be the immediate cause of the failure of marginal blastomeres to express
themselves in a peripheral direction. We observe that in fig. 62 the fine yolk is
pervaded with vacuoles which, from their shape and relations, are evidently equiv-
alent to inter-blastomeral spaces, a conclusion which is supported both by the
nucleated character of the masses of fine yolk thus outlined and by the continua-
tion of the inter-blastomeral spaces with the distal ends of the vacuoles. The fine
yolk, in short, is already coming to be formed into blastomeres, and it is interesting
to note that a blastomere, which is found on the boundary line between the fine

GASTRULATION. g,

and coarse yolk is composed half of fine and half of coarse yolk. It is quite prob-
able, therefore, even from this single observation (cf. also infra), that the region of
the coarse yolk is not as inert as one is at first inclined to believe, an induction
which suggests at once that the fewer and larger fissure-like vacuoles in this region
are equivalent to the vacuoles of the fine yolk, or in other words, to intercellular
spaces.

A final point of contrast between the foregoing stages: In the former the
blastomeres are relatively compact; in the latter there-is a general inter-blastomeral
space which marks an early state of the definite cleavage cavity. It is probable,
as noted for the former stage, that the anterior end of the germ can now be

distinguished.

GASTRULATION.

The stage shown in surface view in plate v, fig. 30, and in sagittal section in
fig. 63, is probably the most valuable of the author's early Chimaeroid embryos.
For it may be accepted as providing a key to the problem of gastrulation not only
in this form but in sharks as well. Its discovery is none the less a fortunate one,
since it is a stage which has every appearance of being brief, and therefore easily
overlooked. In diameter it differs little from the blastula above described (fig. 62),
but its depth is notably greater. Comparing these two stages, we conclude that
the deep subgerminal region of the earlier stage (fig. 62), which was traversed
by vacuoles, has been replaced by the deep-lying mass of cells of fig. 63. We
observe that this thickening of the cellular mass has not yet been accompanied by
an extension over the surrounding region; the mass is at present compact, sub-
spherical, lying in a smooth depression of the germinal wall. At one end of the
cellular mass the segmentation cavity, below the letters sc, represents all that
remains of the intercellular spaces of earlier stages. Near the opposite end is a
small archenteric cavity, a, communicating with the surface through the opening
bp. The archenteron is regular in outline, its marginal cells forming a somewhat
epithelial lining (fig. 63 B). It has probably arisen by an invagination in pre-
existing cells, since the cells lining its outer half are slightly pigmented and closely
resemble those of the surface of the blastoderm. Especially noteworthy is this—
that behind the archenteron, i. e. , between it and the germinal wall, are several
rows of cells.

We have, therefore, evidence that in Chimera a gastrula is formed whose
blastopore is located not at the rim of the early blastoderm but near it. It
is thus a condition in which the merging of the cells of the blastoderm with the
surrounding yolk does not yet take place in that zone of the blastoderm in which the
archenteron is forming. We have here, accordingly, a condition which throws
light upon the origin of the gastrula of sharks, confirming in a striking way the
interpretations of C. K. Hoffman (1896, Morph. JB., p. 210).

64 CHIMjEROID FISHES AND THEIR DEVELOPMENT.

Continuing our examination of the present specimen, it will be observed that
the growth of the cell mass is taking place at both anterior and posterior margins.
Cells are still being contributed to the cellular wall behind the archenteron, judging
at least from their relations to the yolk — such a blastomere, for example, as that
near 2 having become detached from the germinal wall. And at the extreme
anterior region of the blastoderm many cells are being budded out of the germinal
wall. Thus, as shown in the detail (fig. 63 A), it will be seen that in an overhanging
portion of the germinal wall, as below and between the points marked with aster-
isks (*), a row of half a dozen cells are clearly outlined in the wall — a condition which
indicates strongly a similar origin for the adjacent cells. At lower points of the

Fig. 63. — Sagittal section of earliest gastrula. a, Archenteric cavity, bp, Blastopore. sc, Segmentation cavity. I-V indicate

position of nuclei in yolk region.
Figs. 63 A and B. — Details of foregoing section at anteriormost and posteriormost margins respectively.

germinal wall, finally, cellular additions to the blastoderm are being made. Note-
worthy in the present section are the vacuoles which pass deeply into the yolk and
suggest, as we have already noted, modified or suppressed lines of cleavage; espe-
cially well marked are those occurring in the fine yolk on either side of the blasto-
derm, since they form a series of vertical fissures and mark off masses of fine yolk
containing nuclei. The vacuoles also occur throughout the neighboring coarse yolk,
and in connection with their appearance there we note the presence of merocytes
which have traveled, as at iv, in, n or i, far out over the yolk. We note, lastly,
the way in which the fine yolk passes down in rifts into the coarse yolk, for this
suggests again the modified holoblastic condition of the egg.

The next stages in gastrulation deal with the extension of the blastoderm over
the yolk. Thus in fig. 64 is given 'a sagittal section of a stage in which the diameter

GASTRULATION.

of the blastoderm has doubled and during this growth it has lost the compact char-
acter of the earlier stage. We recognize, however, in the cellular mass (at the left
in the figure, p-nt) the group of cells which formed the ventral lip of the blastopore,
and from a detail of this region, fig. 64*, we conclude that the blastopore, bp, has

64"

Fig. 64. — Sagittal section of gastrula slightly older than the preceding. X 35. a, Archenteron ; bp, position of

former blastopore ; ptn. Cells of posterior lip of blastopore ; .sv, Segmentation cavity.
Fig. 64'. — Detail of preceding section showing the region of the blastopore.
Fig. 64". — Lateral section from the series from which fig. 64 was drawn.

become closed, owing probably to stress arising from the rapid extension backward
of the entire blastoderm; and we note in this connection the greatly compressed
character of the cells. Parenthetically, we may also call attention in another

66 CHIM.EROID FISHES AND THEIR DEVELOPMENT.

section (fig. 64 A) to the great number of amitoses occurring throughout the germinal
wall, and on the other hand, the absence of mitoses in this region. Referring again
to fig. 64, we interpret the cavity a as the archenteron of the earlier stage which
has deepened and reached the germinal wall, still preserving its smooth posterior
boundary, but dilated anteriorly and fading into a mass of detached cells. And we
identify the cavity sc as the segmentation cavity now enlarged and with irregular
offshoots. Another section of the present specimen shows, near the side, fig. 64",
the marginal extent of the dilated archenteron and the obliteration in this region
of the segmentation cavity. Its major interest, however, is in contributing data
concerning the relation of the blastoderm to the yolk. Especially at the anterior
end we observe that the cellular elements, of great size, have recently become
detached from the yolk.

The details in the study of this specimen deserve especial comment, for they
indicate an intimate functional relationship between mitosis and amitosis.* To
illustrate these conditions a number of details are given in figs. 64 A-N, all drawn
from the foregoing specimen, but from selected sections. We may first refer to the
character of the merocytes. In a detail of the anterior end of this specimen,
fig. 64 A, over fifty merocytes are present, most occurring in the fine yolk, but some
in a superficial rift of coarse yolk which spreads inward toward the blastoderm. We
observe: numerous amitoses; the masses of fine yolk whose distinct outlines suggest
poly nuclear blastomeres; at one point (near i)a nucleus surrounded with fine yolk,
altogether suggesting a single blastomere ; blastomeres formed out of the yolk (2 and
3); a large clear blastomere (4) which appears to have budded out of the germinal
wall; and (5) a small clear blastomere, which has undoubtedly been derived from
the adjacent yolk. At the opposite end of the blastoderm (fig. 64 B), and within it,
is a large cell containing many nuclei, some of which are in amitotic division, and
similar appearances are observed further along in the same section, fig. 64 i and j.
In the first of these, i, a large blastomere has broken up into three smaller cells, in
the largest of which the nucleus has subdivided amitotically into at least half a
dozen smaller ones; in the second, j, a blastomere has divided and in each resulting

*The merocytes here considered are regarded as products of the segmentation nuclei. The difficulty, however,
in distinguishing finally between the merocytes derived from the segmentation nuclei or from the sperm-heads has
already been commented on (p. 57).

Figs. 64 A-N. Details of sections of preceding stage. (See page 67.)
A. Detail of germinal wall at extreme anterior end of blastoderm. I -5, cells which are arising, or have recently arisen from the germinal wall. There can be

little question from the yolk-filled character of some of these that they have recently arisen from the germinal wall (i. e., they can not be cells which are

being passed into the germinal wall, as His suggests). Such a cell as that indicated at 5, although destitute of yolk material, is so far from the remaining

cells of the blastoderm that it could only have been budded off from the germinal wall.
li. Detail of the posterior rim of blastoderm showing the origin of blastomeres from the yolk wall. Observe that some of the cells are Blled with coarse yolk ;

others, 3, have relatively little. The cell, 2, just separated from the germinal wall, contains a number of (amitotic) nuclei.
G Detail of wall of germinal yolk. 1 , 2, 3, Nuclei arising amitotically. passing in the direction of the floor of the subgerminal cavity. 4. Blastomere arising

from the germinal wall. 5, Blastomere undergoing amitosis. 6, Blastomere arising from the germinal wall, and showing aster.

D. Origin of blistomtres from the germinal wall. 4 and 5, Blastomeres recently separated. 1 , 2, and 3, Nuclei about to be passed into blastomeres.

E. Yolk-filled cell arising from the germinal wall, and exhibiting typical mitosis. Adjacent is a blastomere whose nucleus is dividing amitotically.
f- Blastomeres newly arisen from the germinal wall.

'•'• Vesicular nuclei in region near surface of germinal wall.

' /• Vesicular nucleus, undergoing amitotic division, with adjacent vacuolar spaces.
/ . I • A . and L. Cells of blastoderms in some of which amitosis is taking place.
M and A. Cells of blastoderm dividing by atypical multiple mitosis.

MITOSIS AND AMITOSIS.

67

Of

N

Figs. 64 A-N. Details of sections of preceding stage. (See bottom of opposite page.)

68 CHIMvEROID FISHES AND THEIR DEVELOPMENT.

blastomere the nucleus has undergone, or is undergoing, amitosis. Now in these
instances there can be no question that the amitotic divisions are taking place within
the blastoderm itself, in a region where, by analogy, mitosis alone should occur,
and where later, indeed, in the same form, mitoses alone are found. And we are
thus constrained to conclude either that amitosis and mitosis are processes not as
immutably different in fate as is generally assumed, or that at a later period the
amitotic blastomeres undergo disintegration within the blastoderm.

But to continue: In fig. 64 c, from a neighboring section, we observe as before
amitosis occurring within the germinal wall, and this type of nuclear multiplication
appears active to an extraordinary degree, as the detail, i, indicates. Moreover,
with this activity, there is evidence from the greatly elongated character of some
of the nuclei, 2, 2, and from the evident trails which occur, e. g., at 3, that these
nuclei are passing rapidly in the direction of the surface of the yolk. We note also
that cellular increments, e. g., in such a cell as 4, are arising from the germinal
wall, and, as in the former specimen, amitotic division is present, 5, in the blasto-
derm proper. Adjacent to this, and in as close relation with the germinal wall,
there is also evidence of mitotic division, 6. We have seen that in this section the
cell 4 is arising out of the germinal wall ; if any doubt exists as to possibility of
cells to arise from the germinal wall at this late stage, we may refer to the detail
shown from a neighboring section in fig. 64 D. Here is present a row of cells
arising in this manner: in the wall itself occur the nuclei 2 and 3, of which the
latter is passing into a lobe-shaped process budding outward from the germinal
wall. From their position we may safely conclude that 4 and 5 have arisen in a
similar way. We observe, finally, that the nucleus in cell 5 is undergoing changes
in the direction of amitotic division.

Another interesting detail is given in fig. 64 E. We have here two cells which
appear to have arisen side by side from the germinal wall; the cytoplasm of one is
clearer, more differentiated apparently than its neighbor, which contains fine yolk,
yet the nucleus of the cell lacking in yolk is undergoing amitotic division, while
that of its neighbor is dividing mitotically. In other sections in this series we note
the following details: Fig. 64 F, a cell half budded from the germinal wall, also a
pair of cells evidently in stage of telophase, of which the lower appears to have just
budded out from the germinal wall; fig. 640, two reticular nuclei in the germinal
wall, products of amitotic division (cf. fig. 640), in one of which are two large
chromatin masses; fig. 64 H, nucleus undergoing a complicated series of amitotic
divisions; this occurs near the surface of the germinal wall, and we note the
presence of vacuoles, three in number, lying immediately above the main masses
of the dividing nuclei ; fig. 64 i, within the outline of a single large blastomere occur-
ring in the blastoderm proper, three cells appear, and two of these appear to
have been derived from the largest, in which we observe as many as half a dozen
nuclei; fig. 64;, a cell in a late stage of division which shows three nuclei already

GASTRULATION.

69

separate in one of its daughter cells, and the nucleus in the other about to undergo
amitotic division; fig. 64 K, a nucleus similar to the last occurs in a cell high up in
the blastoderm, and near it a cell which has undergone amitosis; fig. 64 M and N,
two cells which are undergoing an extraordinary type of division; they contain
many asters, conspicuous centrosomes, but no chromosomes; in N the cell is sub-
dividing into three daughter cells.

The significance of these phenomena is commented upon on a later page, in
the discussion of megaspheres and yolk nuclei in their relation to germ layers.

To resume the question of gastrulation :

The third stage in the writer's material is represented in surface view in plate v,
fig. 31. It differs from the earlier stage shown in this way, plate v, fig. 30, in the
following regards: (i) The circumgerminal ring, which had gradually been
extending and carrying its nuclei peripherad, has faded out over the surface of the
yolk, its proximal zone now alone noteworthy. (2) There is a conspicuous antero-
posterior differentiation. The region of the blastopore is indicated by a short
transverse shadow, marking the cavity of the archenteron, and the segmentation
cavity is denoted by a broad transverse area, the ends of which as they approach
the rim of the blastoderm bend backward, giving a somewhat crescentic shape.
Three sections of this blastoderm are figured, the first, fig. 65, is sagittal, the
second, fig. 65 A, passes between the points A- A, shown in the surface view, the
third, fig. 65 B, between the points B-B. Comparing the sagittal section fig. 65,
with that of the earlier stage, fig. 64, we observe increased growth at the posterior
rim of the blastoderm; the germinal wall instead of shelving forward, now shelves
backward, especially near the surface of the egg, still having below a sharp
shoulder* against which lies the remains of the posterior lip of the blastopore, pm<
of earlier stages, — this region, in short, is being overgrown by the blastoderm as it
progresses hindward. The archenteron thus remains, as at a, separated only
imperfectly from the segmentation cavity, sc, which is now of great size. This
condition, indeed, is well shown in the more lateral sections, figs. 65 A and B, and
they indicate as well the narrow limits of the archenteron; the sides of which, it
will here be seen, are practically confluent with the sides of the segmentation cavity.
As in the preceding stage, noteworthy relations exist between the blastoderm and
the yolk. We observe, for example, that in the more lateral section a tongue of
coarse yolk passes inward close to the surface of the germinal wall, and we obtain
evidence that the row of neighboring cells has been formed by actual outbudding.
In these cells amitosis occurs, as in the previous stage. These cells, it may be
remarked, do not long remain in their subjacent position, for, identified by the
coarse yolk they contain, they can be traced into the blastoderm and are found
widely scattered among other cells.

* I'is-ti-i'fs is a second shoulder which corresponds to the anterior germinal wall of the stage shown in fig. 63. In
both regions, then, the blastoderm has overgrown the surface of the egg.

70 CHIlvLEROID FISHES AND THEIR DEVELOPMENT.

The fourth stage in gastrulation appears in surface view in plate v, fig. 32, and
is but two days older than the preceding, plate v, fig. 31. It shows the following
advances: (i) The embryo proper makes its appearance in a small depression, and
is conspicuous on account of the dark adjacent shadows; (2) the center of the
blastoderm rises as a circular plateau, leaving at its base a well-marked flattened
rim; surrounding this the circumgerminal ring has largely faded away, its nuclei

Fig. 65. — Sagittal section of gastrula slightly older than the preceding,
a, Archenteron. sc, Segmentation cavity.
put, Posterior mass of cells (in region of ventral lip of blastopore).

Fig. 65 A. — Section parallel to preceding, but situated further at the side.
Fig. 65 B. — Section parallel to preceding, but more nearly marginal.
Fig. 65 C. — Detail showing coarse yolk.

now having passed far out over and into the yolk;* (3) anteriorly the segmentation
cavity is becoming restricted to a small area, appearing in surface view as a light-
colored tract near the rim of the blastoderm. Two sections of this blastoderm are
figured, one sagittal (fig. 66), the other (fig. 66 A) passing between the points A- A
shown in surface view. Contrasting the sagittal section (fig. 66) with that of the

* The figure represents the circumgerminal zone as too wide and conspicuous, an inaccuracy which was noticed
too late for correction.

GASTRULATION. 7 1

earlier stage (fig. 65), we notice that (a) almost the entire flattened rim of the
blastoderm has been added ; that (b) in the posterior portion of this rim the ectoderm
is already differentiating the medullary plate of the embryo, m ; that (c) the major
growth has taken place backward — in witness of this, contrast the distance between
the anterior end of the archenteron and the posterior rim of the blastopore in these
two stages; that (cT) in this connection the main cell-mass extends itself dorsalward
and becomes the plateau-like region of the blastoderm ; that (<?) the germinal wall
rising abruptly beside the archenteron in the ear-tier stage becomes excavated in

bf

Fig. 66. — Sagittal section of gastrula in which ihe embryo is appearing.

«i Archenleron.

'> Region of outermost margin of ventral lip of blastopore.

jnn, Posterior mass of cells (in position of ventral lip of blastopore).

/(/'t Region of blastopore.

"'. Thickening in medullary plate of embryo.

*'', Segmentation cavity.

Fig. 66 A. — Section (lateral) parallel to the preceding.

the later, a portion of its material, at least, being represented by the spongy mass
of cells which now forms the floor of the archenteron, a; that finally (/) there is
evidence that the posterior rim of the blastoderm is rolling inward, the surface of
the blastoderm growing more rapidly in this region than the lower layer with which
it is connected. Detailed examination of the sections, however, leads us to the
belief that the process of inrolling extends only as far as the point i (fig. 66) ; just
above this the inrolled rim of the blastoderm merges with the cells arising from
the germinal wall, and from this point inward openings occur between the cells
and communicate with the archenteron. The section (fig. 66 A) already referred

72 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

to as passing slightly to one side of the sagittal plane shows favorably the
thickening of the ectoderm at the side of the medullary plate and its inbending.
We here observe also the reduced size of the segmentation cavity, the thickening
of the cell mass roofing the archenteron, and the thinning out of the mass of cells,
pm, forming its floor.

We may at this point consider conveniently the general bearing of the process of
early gastrulation in the Chimseroid. We have seen that:

(a) In an early stage an archenteron was present (fig. 63), whose ventral wall
was composed of cells and whose axis was at right angles to the surface of the
blastoderm.

(<$) In a second stage, the area of the blastoderm had increased, and the blasto-
pore was closed (fig. 64); its position (fig. 64 A), however, accurately located, but
more posterior than in the first stage; also the archenteron has greatly increased
in size.

(c) At a third stage (fig. 65), the location of the blastopore can not be
accurately determined, although it is certainly near the hindmost point of the
blastoderm ; the archenteron is less definite, and its long axis, which remains parallel
to the neighboring germinal wall, becomes tilted backward, as indicated by the
arrow in the figure: and the cells, pm, which correspond to the ventral (posterior)
wall of the archenteron, now occupy a position further under and further forward
than in earlier stages, in consequence of the hindward extension of the blastoderm.

(cf) Finally (fig. 66), this hindward extension is so expressed that the position
of the early blastopore shifts under the rim of the blastoderm and comes to appear
at the point bp; concomitantly the archenteron increases in size, its axis lying
nearly parallel to the surface and its ventral wall developing extensively both in
thickness and in (anterior) extension. From these conditions it follows that in the
later gastrulation of Chimsera we are dealing with a reopening of the blastopore of
an earlier stage. Accordingly, in contrast with gastrulation in sharks, Chimaera
preserves the primitive blastopore within the blastoderm itself. This stage,
however, is an evanescent one. In connection probably with a change in nutritive
values, whereby the yolk is passed to the archenteron from a source more and
more postero-ventral there is a constant tendency for the cells of the archenteron
to be drawn, both in ontogeny and in phylogeny, closer to the source of nutriment.
For this reason the cells of the archenteron multiply more rapidly from below than
from above (/'. e. , the region where primitively they were invaginated from the
ectoderm) with a result that the blastopore becomes of less and less importance in
early stages. It is suggested, also, that during this growth there is a constant
convection of the cells of the blastoderm, in the process of which elements formed
in the region of the posterior wall of the archenteron pass downward and forward.
Part passu, the posterior rim of the blastoderm, including the region of the blasto-
pore, extends first backward, then downward and inward; it thus comes finally to
lie under the rim (i. e., the later rim) of the blastoderm.

GASTRULA OF SHARK AND CHIMERA.

73

We have emphasized these conditions of growth in Chimsera, since they serve,
I conclude, to explain the gastrulation of the shark, a process so puzzling that
Samassa (1895) has even gone so far as to deny its presence, sensu stricto, in this
group. According to the present interpretation the primitive shark had, like Chi-
maera, a blastopore which opened near but not at the rim of the blastoderm; in
this position it next became a rudimentary organ, since, apparently, the conditions
governing the increase of cells in the archenteron suffered a change — inasmuch as
they came to receive their nutriment directly front the neighboring germinal wall
instead of indirectly, i. e., through a process of continued invagination at the
blastopore. Accordingly, in the development of modern sharks the blastopore

Fig. 67. Diagrams comparing gastrulae of Chimaera and Selachian. A and B, Earlier and later stages in gastrula of Chimeera
colliei. C and 1~>, Earlier and later gastrulae of shark (mainly after Riickert).

O, Archenteron. dl, Dorsal lip of blastopore. sc, Segmentation cavity, vl. Ventral lip of blastopore.

fails to appear within the blastodermal disc, since here it has long been functionless.
But obviously the blastopore would again become important in the economy of
gastrulation, if nutritive material were brought into its neighborhood by any process
in the growth of the blastoderm or in the encroachment of the germinal wall.
Thus we may infer that it would again become a functional organ when its position
was transferred to the rim of the blastoderm. In this position it still occurs
exceptionally, as C. K. Hoffman has shown in Acanthias, * or it may indeed reopen
deeper under the rim of the blastoderm, as the majority of investigators maintain.

*In a letter, which I am permitted to quote (July, 1903), from Professor Hoffman, the comparison is accepted as
follows: "In Chimaera the blastopore is located near and in Acanthias at the rim of the early blastoderm. For the
rest the archenteron and the open blastopore of Acanthias agree entirely with those of Chimgera. Acanthias forms
the bridge (in this regard) between Chimaera and other sharks and furnishes us the key to the problem of gastrulation
of the other sharks."

74

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

To make the comparison of the gastrulae of Chimaera and Shark more concrete
we have figured two stages side by side (fig. 67, A and c, B and D). We need
only add to the foregoing text the remark that the archenteron and segmentation
cavity are more distinct in Chimaera, and that the differentiation of the embryo
takes place in a more restricted area. We append also (fig. 68, A, B, c) a scheme
expressing our interpretation of the mode of origin of the meroblastic gastrula in
this form. In A is pictured a sagittal section of an early gastrula of a holoblastic
type, and between the points marked with asterisks is indicated the narrow zone
below which the amount of yolk is supposed to have notably increased. In B, the
second stage in this evolution, is a condition not unlike the late gastrula in Chimaera:
The yolk mass still segments, and the ventral lip, vl, passes inward and forward as
the dorsal lip rolls backward and inward. In c, finally, is attained the condition in
sharks: Archenteron and segmentation cavity merge; segmentation is lost in the

Fig. 68. — -Diagrams suggesting origin of meroblaslic character of egg of shaik.

A. Sagittal section of early gastrula of holoblastic egg (e. g., Petromyzon). />. Section showing conditions similar
to those in Chimaera colliei (cf. fig. 66). C. Section of gastrula of shark, arch, Archenteron; v!, ventral
lip of blastopore ; sc, segmentation cavity.

yolk mass, and the latter comes to pass its nutriment into the blastoderm indirectly,
i. e., as nourishment for the growth and multiplication of the cells already formed,
instead of directly, i. e., in the form of new yolk-filled blastomeres, and from this
process there results a smooth germinal wall. This interpretation agrees in general
with that lately restated by Ziegler (Lehrbuch Entwicklungsgeschichte, 1901, pp.
352-353); it differs in the interpretation of the fate of the ventral lip of the
blastopore. According to the older view the ventral lip remains more or less
passive, in the present interpretation it has undergone a marked change; the cells
which primitively formed the ventral lip of the blastopore are to be sought in the
region vl, on the floor of the archenteron. The de facto ventral lip of the
blastopore (i. e. , in all stages but the earliest) is accordingly a secondary structure,
which arises from the new conditions attending the overgrowth of the blastoderm.

LATER G A STROLL. 75

LATER GASTRUL^E.

Surface views of three later gastrulse are pictured in plate v, figs. 33-35, a
series in which the body of the embryo becomes distinctly differentiated. In the
first it occurs as a lip-like thickening, the blastoderm itself having become some-
what larger in diameter and flatter than in the previous stage. In the present
specimen, which was examined after my interest was aroused in the matter of the
peripherad migration of the yolk-nuclei, these structures could be seen* spread out
widely over the neighboring surface of the yolk. Tlfe second stage, plate v, fig. 34,
resembles outwardly a shark embryo at Balfour's stage B; the light area in the
anterior and median portion of the blastoderm, which marks the cleavage cavity, is,
however, larger than in any selachian hitherto described. In the third stage, plate v,
fig. 35, the embryo arises as a knob-like eminence, its tail end projecting some-
what over the edge of the blastoderm; anteriorly the surface of the blastoderm
becomes thin and transparent, and it here assumes a peculiar vesicular character.

DETAILS OF THE LATER GASTRULA OF PLATE V, FIG. 35.

This stage, although scarcely later than Balfour's stage B in shark nomencla-
ture, is remarkable for the concentration of its elements. Thus, if we compare it
in point of size with a similar stage in Pristiurus, measuring it always in terms of its
blastoderm, it is of much smaller size. At this stage the length of an embryo of
Torpedo measures about one-third the diameter of its blastoderm, that of Pristiurus
about one-eighth, and that of Chimsera not more than one-twelfth. Moreover,
its component parts are already more highly differentiated.

A number of details of this stage are given in plate vi, fig. 39, and figs. 39 A-E.
In the first of these (fig. 39) the embryo with its adjacent blastoderm is viewed as
an opaque object; it appears next in similar position (A) but as a transparent object,
showing ectoderm, entoderm, and archenteron. Behind the embryo the surface of
the yolk shows a series of lines representing either surface fissures or vacuoles,
related, as we have concluded, to lines of cleavage. In the following figures the
embryo is viewed from an antero-dorsal direction (B), postero-dorsal (c), postero-
median (D), and postero-ventral (E). The mesoblast is well indicated in plate vi,
fig- 39 n> also the extent of the thickening of the ectoblast forming the posterior
margin of the embryonic body. In connection with these figures we may refer to
the series, fig. 69 A-M, drawn from sections of this embryo cut parallel to the
neighboring rim of the blastoderm (i. e., transverse, although slightly oblique to
the axis of the embryo), and point out the following features: (i) The size and
definiteness of the gut, an important factor in establishing the contour of the
embryonic body; the gut acquires the cavity, gc (which communicates with the
yolk region only for a short space near the rim of the blastoderm, c, and accumu-
lates around its anterior end the bulk of the mesoblast, mes). (2) The fusion of
ecto- and entoblast occurring not merely at the tail end of the embryonic body but

*The circumgerminal zone is, however, shown too distinctly in the present figure; its color should resemble rather
that in plate v, fig. 34.

76 CHIMyEROID FISHES AND THEIR DEVELOPMENT.

far forward, almost to the end of the embryonic gut, the band of fusion extending
in a narrow zone as denoted at x, fig. 69 n. (3) The concentration of the yolk-
entoblast under the embryonic body; this becomes conspicuous quite in front of the
embryonic gut, then merges with the gut, then separates from it, and, as the lumen
of the gut opens out ventrally, it proceeds backward in a layer finally rounding

H

D

F

Fig. 69 A-M. — Transverse sections through early embryo and neighboring blastoderm of stage corresponding to that of plate V,

fig. 35. The series passes from in front backward.

C, Yolk region intruding between caudal folds ; <!<*, gut cavity; '", mesoblast; :V, yolk lying in cavity of gut ;
X, fold near posterior end of embryo where ectoderm and entoderm merge.

outward on either side. (4) The presence in the cavity of the embryonic gut of
small masses of the disintegrating segments of the egg (fig. 69 G, gc), which serve
probably as food, interesting in connection with the fate of the yolk in Chimsera
(cf. in stages of Plate vm). Contrasting the foregoing conditions with those in an
elasmobranch in stage B (e. g., as shown by the Zieglers, Archiv f. mikr. Anatomic,

PRECOCIOUS DEVELOPMENT IN EARLY EMBRYO.

77

6

N.

Bd. xxxix, Taf. in), we note that the Chimse-
roid although smaller is much less flattened
out; that the gut which is flattened against the
yolk in the elasmobranch is in Chimaera defi-
nitely formed and provided with a distinct
lumen; that the lateral contour of the embryo's
body in Chimsera is already developed, the
ectoderm in the Jiinder region fusing with the
entoderm; that the yolk entoblast thickens in
the median axial line, a feature lacking in the
shark, but important doubtless in the early
assimilation of the yolk.

From the foregoing details one is led to
conclude that in Chimsera ' ' precocious segre-
gation" has been developed to a noteworthy
degree. In spite of the small size of the
embryo, both relatively and actually, it has
already made strides in the direction
of attaining its definite form, outstrip-
ping in these regards the elasmo-
branch ; thus it has already developed
gut outline, definitely arranged the
mesoblast, separated practically the
sides of the embryo from the blasto-
derm, and has specially concentrated
the yolk entoblast in the axial region.
Accordingly, in these regards, Chi-
msera stands separate from the elas-
mobranchs; transitional, however, is
Callorhynchus, judging from figures
recently given by Schauinsland (c. g. ,
in his plate xn).

An idea of the complicated
nature of the blastoderm at this stage
(plate v, fig. 35), both in itself and in
its relation to the yolk, may be had by
examination of fig. 70. This repre-
sents part of a section which passes
through the blastoderm transversely,
somewhat in front of the embryo.

Fig. 70. — Detail ol section of preceding embryo. The section is transverse and passes near
middle of blastoderm. It shows particularly the early differentiation of the vacuolar area.
,ili. Peripheral zone of blaslod erro ; b-c, central region of blastoderm ; 1-5, centers of proliferation of ecto-
derm into mesoderm ; 6-7, Lower ends of these proliferations in their relation to entoderm ; 8, amitosis in
spongy trabeculae ; 9, grouping of mesoderra cells to form vessels; 10-1 I, centers, large and small, of
germinal-yolk in which or near which nuclear elements are dividing amilotically.

/. . •"

-g CH1MJEROID FISHES AND THEIR DEVELOPMENT.

We notice, first of all, that the peripheral zone of the blastoderm (between the
points a-fr) is less complicated than its central portion (between b-c). The periph-
eral zone is, however, more highly differentiated than in a similar region in an
elasmobranch (cf. Riickert's memoir in Kupffer's Festschrift, plate vn, fig. 75);
witness the definite character of the ectoblast and yolk entoblast, and the gigantic
size of many of the mesoblast cells. But it is in the central region of the blasto-
derm where the conditions are most extraordinary; we observe, that at many
points, 1-5, masses of cells extend downward from the ectoderm, proliferating in
ridges, sometimes giving rise to root-like processes. These terminate below either
freely, or they may actually fuse with the entoblast; at various points, 6, they lie
close to the entoblast ; at 7 is shown a point where they become continuous with the
entoblast (the continuity to be traced in the serial sections). They thus form the
spongy meshwork which we have already noted in the surface view of this stage,
a condition of complication, which, as far as I am aware, is unknown in the
extra-embryonal blastoderm of so early a stage in any other vertebrate.

We note in connection with the spongy character of the blastoderm the
presence of many large cells (unshaded in the figure), some of which, like many in
the neighboring spongy trabecute, are undergoing numerous divisions (amitotic) as
at 8.* To understand the meaning of this spongy blastoderm one should first
consider it in its prospective value. Later specimens show that in this region
appear blood-vessels, and in the present early preparation — and even indeed in
earlier ones, we are evidently dealing with the beginnings of vascular structures.
In fact in the trabeculs themselves we find at various points (9) the cells already
grouped together so as to form cavities, and in the latter large granular cells are
undergoing subdivision, in the direction evidently of blood-building. In this character
again, it will be remarked there is given an important instance of the precocious
mode of development of Chimera. In other words, in this form at a period which
outwardly suggests stage B of the shark the vascular development in the extra-
embryonal blastoderm is (approximately) equivalent to the shark's in stage E.

*We have here again evidence against the commonly accepted view (of Flemming, Ziegler, and von Rath) as to
the significance of amitosis. Admitting that these cells come to form blood and blood-vessels, it must also be granted,
as the following evidence shows, that the blastoderm becomes part of the young fish, and therefore the behavior of its
cellular components is not to be compared with that of the vitellophagous periblast nuclei in the teleost. Of course
it will be seen, on the other hand, that the adherent of the Flemmingian view might object that although the blastoderm
itself was a permanent structure of the embryo it might none the less contain provisional cellular elements (nutritive) .
He will admit, however, that this rarified view as to the fate of component elements of the blastoderm receives little
support from the examination of related elasmobranchian structures.

The present evidence, it seems to me, favors the view that amitosis is but a symptom of early and rapid cell-
multiplication. Such a need for rapid division often occurs in evanescent structures, and hence it may happen that
this type of division has been given less consideration than it is justly entitled to, from the standpoints both of cell
physiology and cell philosophy. In this matter I need merely mention, in view of the scope of the present paper, that
there is rapidly accumulating a mass of evidence against the decadent character of amitosis. In the nature of such
evidence are the observations of Conklin (Am. Nat., Oct., 1903) on the egg follicle cells of Gryllus ; Kellogg 's results on
similar structures in Hydrophilus (Science, Mar. 4, 1904); also H. L. Osborn's observations on Fasciolaria (Science,
Feb. 5, 1904) in which amitosis occurs in stages of gastrulation ; Boeke's statements that in teleosts mitotic may
arise from amitotic nuclei (Petrus Camper, vol. n, Afl. 2, pp. 161, 1902); finally, Child's "Amitosis in Moniezia" (Anat.
Anz., vol. xxv, 1904).

EXTRA-EMBRYONIC BLASTODERM.

79

The complexity of the foregoing conditions (fig. 70) applies as
well to the yolk region as to the blastoderm itself. Without enter-
ing into undue detail we may note the following: Extreme vacuo-
lization of the subgerminal region (the vacuoles at the right in
the figure are indicated by dotted lines); they usually occur

in or in association with the lighter areas
of the germinal yolk. If we regard the
vacuoles in the earlier stage as retaining
the character of intercellular spaces, they
have by this time undergone, in part at
least, change of function, serving now as
nutriment purveyors to the yolk ento-
blast. In this connection we find that at
various points, 10, the coarse yolk is
traversed by fine yolk in rifts, whose
shape suggests that of the vacuoles of
earlier stages. In this fine yolk, more-
over, many nuclei are present, and, judg-
ing from numerous amitoses, dividing
rapidly. In addition to these rifts of fine
yolk, we note that there occur at many
places throughout the coarse yolk small
areas of fine yolk, 1 1 ; these have in nearly
every case nuclei in or near them, and
we have thus ground for regarding the
yolk region of the egg not as a syncytium
pur, but rather as a mass of yolk-filled
cells whose boundaries have broken down,
but whose individuality as cells has not
yet been wholly lost.

A second section of the extra-embry-
onic blastoderm of this stage is shown in
fig. 70 A, a detail of a section passing
through the blastoderm considerably in
front of the preceding section. Here is indicated even better
than before the presence of giant cells which have arisen from
the yolk, migrated outward, and are undergoing division in the
region immediately below the ectoderm. At one point (a) a
yolk cell of gigantic size is shown (unshaded); at other points
(b, b, b} similar yolk cells are undergoing division by amitosis.

Figs. 70 A and B. -Sections of stage of early embryo figured in fig. 69.

A. Portion of extra-embryonic region in section corresponding to fig. 69 B.

B. Embryonic and extra-embryonic regions in section similar to fig. 69 C.

80 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

Into this region extends a delicate layer of mesoblast (W); and here and there
groupings of cells of this layer, as at v, suggest the formation of blood vessels.
Under the gigantic cell, one notes that the cells of the mesoblast layer are of
remarkable size.

Another section, given in fig. 70 B, pictures details of a section similar to fig.
69 G. This illustrates particularly a subgerminal zone containing large yolk nuclei ;
of these some are situated close to the surface of the subgerminal wall, and one (W)
has passed into the entoderm. This obviously cannot be confused with the adja-
cent entoderm cells, if only on account of its greater size. In this section a special
area of formative yolk is shown underlying the periphery of the blastoderm. Under
the embryo itself the formative yolk attains the surface notably at the sides of the
embryonic body, and it is from this region that the cells appear to be passed into
the embryo. Less activity is probably present in the ventral median line, on
account of the quantity of coarse yolk which is here present.

LATER GASTRULA. EMBRYO WITH OPEN MEDULLARY FOLDS.

This stage, figured in surface view, plate v, fig. 36, and in detail, plate vi, fig. 40,
may be compared with Balfour's stage D in elasmobranch. In spite of the conspicu-
ous growth of the embryo, the blastoderm, it may be noted, remains remarkably
small in size. In this stage the blastoderm of Chimaera shows a well-marked
central area, which on closer examination is found to be made up of spongy mesh-
work ; there is also a somewhat thickened rim, and a marginal zone, the latter
shown in sections to be formed of peristomial mesoblast. Beyond the limits of the
blastoderm the surface of the yolk showed faintly diverging lines which suggested
cleavage planes. (Cf. plate vi, fig. 39 A.) The embryo itself, when viewed as a
transparent object, plate vi, fig. 40, shows shark-like medullary folds, more delicate,
however, and narrower in proportions. The tail folds are less conspicuous ; the
mesoblast concentrating in this region shows on each side a dark area, the rela-
tions of which are referred to later.

DETAILS OF STAGE D.

Transverse sections of the embryo and the neighboring blastoderm in this
stage are pictured in fig. 71, A-i. Thus beginning with a section through the tail
folds, we see in B, ectoderm and entoderm continuous in the chordal region. In
this section the mesoderm merges with the entoderm not at the sides of the chordal
region, but near the margin of the blastoderm, thus suggesting the theoretical condi-
tion in the origin of the mesoblast advocated by Graham Kerr. In section c (at the
left side, the plane being slightly oblique) the side of the blastoderm is coming into
functional connection with the yolk; the notochord is here being folded off from
the entoderm ; the latter is now a thick, flattened layer, its outer half lying apposed
to the yolk wall. In D the section shows the beginning of the neural folds ; below
them is a well formed layer of mesoblast, also the dorsal wall of the gut; the gut
lumen appears at g ; at its side the dorsal wall of the gut shows a wide contact with

DETAILS OF EARLY EMBRYO.

8l

B

Figs. 71 A-E and continued F-I on page 82. — Transverse sections of late gastrula shown in Plate V, fig. 36. The sections pass
forward ; the first of the series, A, traverses the tail folds ; the last, I, the head region of the early embryo.

fli Tongue of mesoblast cells representing the urogenital anlage ; &, megaspheres in process of passing through the yolk-entoblast ; be, body cavity;
c. points in extra-embryonic region where the ectoderm cells arc being proliferated into the blastoderm ; a, gut cavity ; m, megasphere appearing
in peristomial mesoblast.

82

CHIM;EROID FISHES AND THEIR DEVELOPMENT.

the yolk, and here at various points yolk nuclei are clustered, having evidently an
important physiological relation with the overlying blastoderm ; we note at a a
tongue of mesoblast cells which projects medianward; this occurs but in a few
sections, and evidently corresponds to the dark area noted in surface view; it
resembles, however, so closely the "lame intermediate" (Swaen and Brachet)

H: WVT. -r^*^.-

\i/ y • .» » •'-. ^b

Figs. 71 F-I. (For description and lettering see page 81, A-E.)

in the teleost, that, if for no other reason, we are led to suggest that it represents
the precocious beginnings of the excretory system. In E the notochord has sepa-
rated from the yolk, the gut lumen becomes narrowed, and lateralward the first
trace of a body cavity (be) appears. We observe that the margin of the gut
passes directly into yolk-entoderm, the distinctness of its lower boundary having

DETAILS OF EARLY EMBRYO. 83

faded away, and, part passu, the yolk nuclei have greatly increased in number. In
the region where the yolk-entoderm approaches the lumen of the gut it thickens
and sinks downward, leaving as the floor of the gut cavity a wedge-shaped mass of ger-
minal yolk. At the outer rim of the yolk-entoderm we observe that it becomes con-
tinuous with the mesoblast; in other words, recalling sections D and G, the peristomial
mesoblast of Chimaera which now arises is not continuous with the gastral mesoblast.
We have thus a reason for inquiring whether gastral and peristomial mesoblast

Figs. 71 J-N.— Details in sections of foregoing embryo (figs. 71 A-I).
/. Region of peristomial mesoblast.

e, ectoderm; e', cells recently derived from e ; entt entodcrm ; m, perutomiat mesobiast.
K. Detail of subgerminal yolk region showing cellular arrangement of merocyte elements.
L. Lying in the subgerminal yolk is a megasphere, which, on the evidence of the overlying vacuoles, is in the process of rising

towards the yolk entoderm.

M. Similar megasphere passing into the yolk entoderm.
N. Megaspheres similar to preceding, but representing a somewhat later stage of passage into the blastoderm.

are as intimately related as we have generally assumed.* A condition of the
peristomial mesoblast is figured in detail in j, and it proves of considerable interest,
since the region of mesoblast proliferation is of wide extent. Not only are cells
budded out from the marginal mass m, but we observe also that cells are added to
the mesoblast from the neighboring ectoderm ; thus at e' is a cell which has been
derived from the ectoderm e, where, by the way, a syncytium is now present ; and

*Cf. the current view as to the secondary confluence of blastopore and yolk " blastopore, " as summarized in
Ziegler's Handbuch der Embryologie, pp. 352 and 353.

CHIlvLEROID FISHES AND THEIR DEVELOPMENT.

at the point e a mitosis is taking place preliminary to budding off another mesoblast
cell. We conclude that the cell e' has been derived from the layer e, and not from
the cell mass m, when we consider (i) that its granular contents agree in character
with the layer e rather than with the mass m ; (2) that a continuous boundary line sepa-
rates the mass m from e'; and finally (3) that the cell e' is connected with the layer
by a protoplasmic process, above which a nucleus in mitosis is present. Less
evident, from this section at least, is the question whether cells are added to the

0

:o .

r V?S~''"'i >TjUf"'. V A

v I ' -"• x / J

(H 1

\i SV\ •••:-:• ;-'\v^7*£jfer"*.

m '"

BB

HH

II

DD

JE.E

FF

GG

o.

p.

Q-

Figs. 71 O-II. — Details in sections of foregoing embryo (continued from page 83).

Detail showing transition between yolk region and the cells of the blastoderm.

m. Yolk nucleus lying against the wall of the vacuole «'. "• Zone of large vacuoles.

m'. Yolk nucleus now lying within a vacuole, and transformed into V. Zone of small vacuoles and fine germinal yolk.

a yolk-surrounded blastomerc. 3/C- Yolk enloderm.

Detail of blastoderm, showing at y the division by mitosis of a megasphere lying in the yolk entoderm.
Detail of section near the marginal region of the blastoderm, showing single megasphere, y, lying free in the space between
ectoderm and yolk entoderm.
.'/«• Yolk nuclei undergoing division by atypical mitosis and by amitosis.
R—II. Details showing various phases of division in yolk nuclei.

peristomial mesoblast from the entoderm more proximal in position. At some
points one is inclined to admit that such a cell as shown in j, ent, is being budded off
into the tongue of mesoblast. (Cf. the condition shown in the section N.)

In the section F, the notochord is again continuous with the entoderm; the
gut region rises, and its lumen is now walled with cells save in its median-ventral
line. Here a thin wedge of yolk intrudes. Especially noteworthy is the relation
of the yolk to the yolk-entoderm in this region. The latter has again a more

MEROCYTES AND BLASTODERM. 85

distinct ventral line of boundary, broken only at points, as at b and b, where cells
from the yolk are entering. There can be no question in this regard since the
entering cells are distinguishable as large in size, circular in outline, and granular
in content. (Cf. sections L, M.) Another noteworthy feature in this section is that
some of the ectoderm cells as at c and c, give off amoeboid processes and, I am
led to believe, later become detached, contributing to the growth of the mesoblast.
A detail of this condition is shown in section j. We may finally note that the
body cavity, be, reaches its maximum size in this region of the embryo.

In G the floor of the gut becomes cellular ; the notochord is again separate from
the gut wall ; and as before merocytes contribute directly to the growth of the yolk
entoderm. In n the last-mentioned character is seen even to better advantage,
for not only are the large yolk-cells passed into the lateral yolk entoderm, but they
appear also high up in the central gut wall, as at^-, and in the region of the peristo-
mial mesoblast, as at m.

In i, finally, a section is shown passing through the region of the head tip,
which now projects forward above the blastoderm. On either side of the gut the
mesoblast is distinct, differing in this regard from the condition shown in an
elasmobranch (cf. Ziegler's figure 19, n, Arch. f. mikr. Anat., Bd. xxxix, Taf. iv).
In the neighboring blastoderm, as in the shark, the mesoblast is limited to a small
tongue of peristomial cells.

Before concluding an account of this stage two of its features still deserve
comment, (i) The fissuring of the yolk region. The fissures are usually vertical,
as indicated in all the foregoing sections, and may, as we have already seen, be
regarded as homologous with cleavage spaces. (2) The mode by which merocytes
become cells of the embryo. This heading, however, deserves to be treated in a
more formal way.

THE TRANSFORMATION OF MEROCYTES INTO CELLS OF THE BLASTODERM.

In this connection a number of details of sections of stage D have been figured,
figs. 71 K-II, and in examining the series we find evidence, first of all, that
merocytes move from a lower into a higher zone of the yolk. Thus, in fig. 7 1 o, the
merocytes are elongated in the direction of the yolk-entoderm.* Also in the
three sections L, M, and N we observe a great yolk cell (megasphere)f first deep in

*That this is connected with a migration of these elements in the direction of the surface of the cell mass is
known by analogy — witness the behavior of slime cells in the skin of amphibians and fishes (e. g., Homea).

tThe tnegaspheres can have little to do with primitive ova, since they occur widely scattered throughout the
blastoderm. Thus in fig. 71 H one is arising at the extreme rim of the blastoderm, in F several are seen midway
between the embryo and the rim of the blastoderm, in H one occurs near the middle of the floor of the gut; others
appear in mesoderm and others still in ectoderm. In these several regions they are seen to undergo division, losing
more and more of their appearance as megaspheres (v. fig. 71 p). It can not be believed, therefore, that these elements
are to be regarded as primitive ova, destined to carry the segregated germ plasm into the embryonic genital folds, for
this would involve a conception of primitive ova traveling about extravagantly, from the gut wall to the rim of the blas-
toderm, a conception the more improbable when we consider that the urogenital region, to which primitive eggs
naturally belong, is already indicated by this stage, as at a, fig. 71 G. On the other hand, it follows, I believe, that
the evidence provided by Chimaera strengthens materially the position of Ruckert that the megaspheres in elasmo-
branchs are to be regarded not as primitive ova but as highly specialized bearers of nutriment, capable of carrying
into the midst of embryonic tissues centers of new formative energy. These as single large cells could be passed
through the intervening tissue more effectively than could the many small cells to which they give rise, for the resistance
of an embryonic tissue to the penetration of cells is obviously proportioned to the surface-contact of the invading cells.

g6 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

the germinal wall, next having just emerged from the germinal wall, and finally
having almost passed through the niveau of the yolk-entoderm. We have even
data indicating how the upward migration of such a megasphere takes place. One
sees in L a line of vacuoles appearing between the megasphere and the yolk-
entoderm, and it follows clearly that the vacuoles, by a process of coalescence,
provide a less resisting space into which the megasphere can rise.

Regarding, in the next place, the fate of the megaspheres, I think that there
can be no doubt that they serve to bear nutriment to the tissue which they enter.
In some cases, as in fig. 71 p, at y, they undergo mitotic division (after having divided
only by amitosis in the yolk), and their descendants can not be distinguished from
the neighboring cells. In other cases, M and N, they become closely surrounded
by cells, entoderm in the present case, which form around them a syncytium, and
appear to serve as nutriment distributors; witness for example the grouping of the
cells around the large megasphere in M, and the radiating arrangement of the cells
adjacent to the cluster; even the ectoderm is budding off a cell at the point nearest
the megasphere.

In a word, I think we can fairly conclude that in Chimaera, even in this late
stage, cells are constantly being added to the blastoderm from the germinal wall.
This condition maintains in the case of the megaspheres, as we have just noted,
and it holds equally good for other types of cellular additions to the blastoderm.
We thus observe in o (a detail of section G) that between the yolk-entoderm (yc),
and the wall of fine yolk (y) is a vacuolar zone,* in which merocyte elements are
being ferried over to become cells of the blastoderm; thus at v' is a vacuole into
which the merocyte (m) is about to pass. It is to be noted, however, that cells
may also appear in the finer yolk, and thence by the mediation of an enveloping
vacuole be passed upward into the vacuolar zone, thence to the blastoderm (cf. in
fig. 710, at »/).

That throughout these stages there is a general transformation of the yolk
from coarser elements into finer elements there can be no question. Deep in the
yolk appear nuclei surrounded by spherical masses of finer yolk, in turn surrounded
by masses of coarser yolk, in turn more or less irregularly by a system of vacuoles
(= intercellular spaces) fig. 71 K. There is, to be sure, a greater or less amount
of coalescence of these yolk elements, and in the zone close to the entoderm we
observe that the nuclei with their surrounding fine yolk have come to merge into a
single layer (= the zone of merocytes of the subgerminal wall). It is from the
elements of this layer in turn that some cellular additions to the blastoderm are
made.

The nuclear changes which occur during the process of their "levitation" are
worthy of especial comment, for while the cells of the yolk-entoderm now divide by
mitosis (as in o), the nuclei of the region below the vacuolar zone divide amitotically,

*Similar conditions have been observed in the early stages of teleosts (cf., among others, Hoffmann, Zeit. wiss.
Zool., vol. XLVI (1888), pi. xxxv, a paper, by the way, which is too little referred to in recent work on teleostean
embryology).

MEROCYTES AND BLASTODERM. 87

and under varied and striking forms — albeit in a series more or less gradational
(/. e. , showing more decided mitotic character) as one passes from a lower to a
higher zone in the yolk substance. To illustrate various types of division: In R,
in a sphere of fine yolk is a nucleus about to divide amitotically* ; in s a similar
nucleus has undergone such a division, in this case four nuclei resulting. In a
somewhat similar case, T, noteworthy growth in two of the resultant nuclei has
occurred; they have, in fact, passed out of the sphere of finer into the coarser
yolk. In u three similar and large nuclei result. _In v, which represents a later
stage of the condition shown in T or u, and is drawn similarly from deep in the yolk
region of a section (c. g., as seen at several points in K), continued amitosis occurs;
here one of the larger nuclei, especially, is seen to be budding off a small nucleus,
and it has already apparently budded off several. In w, a similar detail indicates
the great rapidity with which nuclei may arise; a large nucleus at one point has
given off a small one, while at a neighboring point almost simultaneously (judging
from the close position of the small nucleus) it is budding out a long process which
is about to be separated not into a single new nucleus but into two. In x seven
nuclei have arisen from a single center (? sphere substance) in the fine yolk, and of
these one has undergone rearrangement in its chromatin material. Of this a dense
mass occupies the center of the nucleus and is connected with the nuclear wall
by a series of radiating linin strands. In Y a somewhat similar nucleus is shown in
detail; at one side it is apposed to the finer yolk (= ? sphere substance) and here
the mass of chromatin approaches, indeed almost touches the nuclear membrane
(for nutritive reasons?). In another nucleus, z, the chromatin mass shows a doubled
arrangement, preliminary, as it appears, to a stage in division shown in AA, FF, and
possibly in BE. In turn the doubled nucleus in cc is obviously a further stage than
AA, but it shows also around it a series of (five) smaller nuclei which, from their
radiating arrangement around the dividing nucleus in the center of the fine yolk,
are possibly the descendants of a similar type of nuclear division. In DD a nucleus
shows a less distinct doubling of its chromatic elements than AA-CC. And in EE a
distinct threefold division occurs. GG represents a stage in division carried further
than cc, the neighboring nucleus having probably arisen from a similar division.
In IIH are two neighboring nuclei, the products, we conclude, of a division like that
of GG and cc : but, curiously enough, they are undergoing division in different ways.
The upper, near which appears an attraction sphere and centrosome, has arrayed
its chromatin in two masses nearly equal in size, each suggesting a confused series
of chromosomes; the lower is simply passing out a portion of its chromatic substance
into the fine yolk. In n, the last of the series given, two nuclei appear; they are
evidently products of such a division as GG, and each in turn is about to undergo
division. The lower one is noteworthy, since the division of the chromatin material
is practically completed in the middle of the nucleus. It may be said in general
that the nuclear processes which here approximate mitosis (cc or HH) are observed
in the region immediately subjacent to the yolk entoderm.

*A similar condition in the embryonic germ cells of Loligo appears to be due to rapid growth, and is not
followed by fragmentation (Miss Sturges, Science, 1899, Feb. 3, pp. 183-184).

gg CHIM/EROID FISHES AND THEIR DEVELOPMENT.

In summary: The evidence which is thus provided strengthens the conclusion
that in the gastrulation of Chimsera amitosis is not to be interpreted in accordance
with the current view, i. e., as a process of decadent cell division. It is conditioned,
rather, by rapid growth and multiplication of nuclei, since its products may resume
mitosis when the usual rate of cellular division is attained. Moreover, the products of
amitotic division in the blastoderm of Chimsera, are too many and too widely scat-
tered to warrant the belief that their cellular descendants can play no part in
producing permanent organs

LATER GASTRULA. EMBRYO WITH PARTLY CLOSED MEDULLARY FOLDS.

This stage is figured in surface view, plate v, fig. 37, and enlarged, viewed as
a transparent object, in plate vi, fig. 41. It corresponds approximately with Bal-
four's stage F in the shark.

Comparing the blastoderm of this with the preceding stage, we find that it has
increased but little in size. The spongy region, however, which occupies its central
portion appears more prominently, and we observe a noteworthy thickening in the
region of mesoblast (gastral) extending outward on either side of the embryo. The
details of the embryo are well seen in a toto preparation. The medullary folds arch
over and meet in the median line, fusing in the posterior third of the embryo's length.
In front of this, after a slight interruption, the folds meet again, then diverge to a
degree suggesting the corresponding stage of shark. The tail folds are conspicuous
at this stage, and we observe that the gut has arched upward, a transverse line
showing where a neurenteric canal is to open below. On either side in this region
the mesoblast is thickened, fading away laterally. Here are forming the extensive
caudal veins. Other vascular details are shown in the antero-median vessel
(apparently vitelline vein) which appears immediately in front of the head and
spreads out widely over the blood-producing region. We note also transverse larger
vessels, the vitello-intestinal, extending outward on either side to about an equal
distance. Gastral mesoblast is conspicuous in this stage; in this may be traced
about a dozen somites, the anterior ones extending far forward.

DETAILS OF FOREGOING STAGE, CORRESPONDING TO BALFOUR'S STAGE F.

Sections are shown in fig. 72 A-E passing through the blastoderm in a plane
transverse to the axis of the embryo. In the first, which passes through the tail
region of the embryo, we observe that the mesoblast bands (mes) are continuous
with the entoderm not in the region adjacent to the notochord but marginally (cf.
the view of Graham Kerr as to this place of origin in the vertebrate gut pouches);
near by the entoderm (eni) thickens conspicuously, then thins again as it passes
into the notochord. Only at the open notch between the tail folds does the lumen
of the nerve tube pass over into the wide space (cf. fig. 7 1 A) which is coming to
form the cavity of the gut. It will be seen that it is especially the thickening of
the entoderm and the constricted origin of the mesoderm which in the transparent
preparation (plate vi, fig. 41) causes the appearance of a dark band in the region of
the tail folds of the embryo. In fig. 72 B similar conditions in gastral mesoblast and

DETAILS OF EARLY EMBRYO.

89

B

Figs. 72 A E. — Transverse sections and details of the blastoderm shown in fig. 72. The sections pass anteriorward from
the region of the caudal folds, shown in section A, as far as the "neck" region of the embryo, section E.

(I. Beginnings of segmental duct. met. Mesoderm.

ect. Ectoderm at the point where this becomes continuous with the !/. Yollt lying free in the gul cavity.

mesoderm in the tail folds o( the embryo. ' Urogenilal anlage.

'•"'• Enloderm.

90 CHIM^ROID PISHES AND THEIR DEVELOPMENT.

entoderm prevail; the thickened ectoderm at ect marks a point at which this layer
is making cellular additions to the mesoblast; it represents the marginal point
where the tail fold and the margin of the blastoderm meet. At other points also,
the mesoblast is receiving increments ; in addition to the gastral mesoblast we note
cells arising from the wall of the yolk-entoderm midway between the cavity of the
gut and the periphery of the blastoderm, and we see further that an invasion of

Figs. 72 F-K. — Details of the region of the yolk-entoderm of fig. 72. In /•' the region is indicated in detail which lies immediately
below and at the side of the arching wall of the gut. (Cf. fig. 72 E.)

" Large vacuolar nucleus which appears on the point of undergoing reconstitution Wl. Megasphere.

into a cell of the yolk-entoderm. SffZ. Subgerminal zone,

ft. Nucleus similar to foregoing, but in a less advanced condition. V. Vacuolar zone.

r, c', (1. Cells which have recently been differentiated out of the germinal wall. ?/''- Yolk entoderm.

G, H, and I illustrate particularly the zone of reconstruction of yolk-entoblast cells from yolk nuclei. In J a telophase occurs, repre-
senting a rare condition in the subgerminal zone. In K, similarly, a telophase occurs in a megasphere. The latter has, however,
passed through the zone of vacuoles and lies in the yolk-entoderm. In this neighborhood, however, as we note at the left, a
syncytial condition may be present.

cells from the periphery of the blastoderm has occurred, in the form of a crease-
shaped invagination. In c the dorsal wall is sharply distinguished from the sides of
the gut. On the floor of the latter appear small masses of yolk, y, which can only
serve, as already noted, as ingested nutriment. The mesoblast in this region
shows considerable differentiation; myotomes are sharply marked off; the gono-

DETAILS OF EARLY EMBRYO. 91

nephrotomal zone is of notable size; at d and in the adjacent cell-mass (at the left)
are the beginnings of the pronephric tubules; and below at x appears the thickening
of the mesentoderm whence arises the posterior portion of the pronephric duct.

In a section, D, passing through a more anterior region of the embryo, the
urogenital structures are practically undifferentiated; the mesoblast extending
continuously from the notochord to the periphery of the blastoderm. In this
region the mesoblast probably receives little or no increment from the yolk-ento-
derm, judging from the latter 's smooth surface, save only at or near the margin of
the blastoderm. Below the yolk-entoderm in this region the subgerminal zone of
nuclei is more conspicuous and definite than in the early stage, fig. 71 E, and this
zone, indeed, appears with even greater prominence in the more anterior section,
fig. 72 E (to be contrasted with fig. 71 F or G). It will here also be seen that divi-
sion of the mesoblast into splanchno- and somatopleure is occurring, and that the
lateral wall of the gut is more definitely established.

A detail, shown in F, indicates the more special relation of the subgerminal
zone to the marginal cells of the gut cavity. The subgerminal zone is here reduced
to a narrow tongue (cf. also E), which inserts itself under the thickened mass of cells
at the base of the gut wall, in the direction of the lumen of the gut. In the present
detail the base of the gut wall is shown at gw, the yolk-entoderm at ye, the
vacuolar layer at v, and the subgerminal zone at sgz. We note first of all the narrow-
ness of the vacuolar layer, through the intervention of which we have seen (fig. 7 1 o)
yolk nuclei become cells of the embryo, a condition indicating the specialization of
this region. In this zone (v), furthermore, we see large nuclei which are evidently
in transition between yolk and embryo, and at m a megasphere which has just
passed through it, the vacuoles becoming reconstituted below. Most significant in
the region of the rim of the gut wall is the concentration of the elements of the
subgerminal zone, coarse yolk, fine yolk, lacunae, vacuoles and yolk nuclei of different
kinds, the continuation (to the left) of the vacuolar layer, and the compounding of
its vacuoles — characters which are obviously to be interpreted as more special and
complicated than in the earlier stage.

A few additional details may be cited. In G, where nuclei are passing through
the vacuolar zone and becoming cells, we observe that at c a nucleus which has
been taken into a large vacuole (a process forming now a reconstituted cell), is still
dividing amitotically, and that at c' a similar division has recently occurred, indi-
cating in both cases, as we have before remarked, that the difference between ami-
totic and mitotic division is one of degree rather than of kind. In H, a detail from
a section close to fig. 72 E, a point is figured where merocytes and newly constituted
yolk-entoderm cells occur in such confusion that it is difficult to say where the layer
of merocytes terminates and where the cells of the embryo begin. And the same
is true of the detail shown in i. In the last figure, on the other hand, merocytes
are still multiplying, even at a point close to the yolk-entoderm. In j, a detail of
the vacuolar region, cells are arising from merocytes; at b a merocyte, less vesicular
than «, adjoins a vacuole into which it will probably pass, judging from transitional
conditions (cf. the neighboring c). And even in the vacuolar layer such newly

92 CHIM^.ROID FISHES AND THEIR DEVELOPMENT.

constituted cells may divide, and by mitosis, although this is not of the usual type
(cf. at^). In this connection, finally, in K a detail is given showing that megaspheres
as they pass into the yolk-entoderm present more or less evident mitosis, witness
the conditions m and m (cf. also fig. 72 F at m). Parenthetically, just below the
megaspheres here mentioned are vacuoles into which merocytes are passing.

EARLY EMBRYOS FROM THE COMPLETE CLOSURE OF MEDULLARY FOLDS
TO OPENING OF GILL-CLEFTS.

An early embryo attached to its blastoderm is shown in plate v, fig. 38. This
may be contrasted with the stage of closing medullary folds shown in same plate,
fig. 37. In the blastoderm we observe that the spongy central area has increased
notably in size and that it has even extended to the anterior rim of the blastoderm.
We note also that asymmetry has made its appearance, the embryo now lying some-
what on its right side. The present blastoderm has increased more rapidly at its
left, and here a lobe-like eminence is produced hindward over the yolk. The
entire size of the blastoderm is scarcely larger than in the preceding figure. The
embryo is shown in detail, plate vi, as an opaque, fig. 41", and then as a transpar-
ent object, fig. 4ib. In general this stage corresponds with Balfour's stage G in
shark; it differs, however, in the definiteness of its structures, for the anterior region
has already become quite highly differentiated in spite of the fact that the tail region
is still flattened out against the yolk and hardly protrudes beyond the rim of the
blastoderm. About 22 segments are present in this stage. The head rises above
the blastoderm and the divisions of the brain and the optic vesicles are formed, and
it is an evidence of the high specialization in development that the embryo of
this large-eyed form should possess large optic vesicles at this early period, i. e.,
before the tail end of the body is established, — a fact of considerable interest
from the standpoint of embryonic adaptation. In this stage two gill-slits are
appearing, g3, g". The region of the pronephros is marked out at pn, the heart at
h, the anterior cardinal vessels at c, and the vitello-intestinal at o. In the tail region
the neurenteric canal is distinctly seen at n.

DETAILS OF THE PRESENT EMBRYO (STAGE G).

A series of selected transverse sections of this embryo may now be passed in
review to indicate the more prominent advances, figs. 73 A-UU. The anterior
sections A-D pass through the ectoderm inclosing the tip of the head and show a
conspicuous median infolding (recessus olfactorius impar) which in surface view
gives the appearance of separating a "forebrain" from a "right optic vesicle," the
sections having been cut in the plane indicated by the dotted line in plate vi, fig. 4ib.
The next section (E) touches the distinct end of the central nervous system, the wall
of which is more extensively traversed in F and G. In H, i, and j, the lumen of the
forebrain is traversed. In K and L, representing many sections, the cavities of
the optic vesicles appear, and we observe here closely apposed to the ventro-
median wall of the brain a mass of cells which in later sections is seen to constitute
the anterior end of both notochord and gut. In sections M and N this cell mass forms
a conspicuous ventral keel, in N the lumen of the gut first appearing. In o and p

DETAILS OF EARLY EMBRYO.

93

F

H

Figs. 73 AS. — Transverse sections of embryo shown in plate V, fig. 38, and in plate VI, figs. 41 and 41 A. These begin at the
head end of the embryo, section A, and extend through 47 sections to the tip of the tail, section UU (see pages 94 and 95.)
fft Gut cavity; n, notochord; *i somite.

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

cc

DD

be. Body cavity.
(/' . .</"• Evagination of gut wall to form the

first and second sill openings.
/>. Heart.

Figs. 73 T-EE — Continued.

nc. Neural crest,
in. Subnotochordal rod.
y. Yolk lying free in cavity of gut.

DETAILS OF EARLY EMBRYO.

95

r\

HH

Figs. 73 FF-UU.— Continued.
w. Wedge-shaped mast of yolk which cornel to pass into the ventral wall of the gut cavity.

96

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

we distinguish in this ventral cell mass a lower lumen-bearing area and above a
thickened mass, on either side of which, attached but not fused, lies a solid mass of
mesoblast. In Q we distinguish notochord and gut (», g}; on either side of the
notochord the mesoblastic somite (s) bears a cavity. In R the mesoblastic sacs
are well separated from both notochord and gut, and the notochord itself, greatly
reduced in size, shows a compressed and almost longitudinally subdivided appear-
ance. In s, the body of the embryo is becoming flattened on its side; the lumen of
the gut is deep and narrow; closely apposed to its sides are the mesoblastic masses
whose lumen now becomes greatly reduced ; on the dorsal median wall of the gut
appear the beginnings of a subnotochordal rod. From this stage onward the lumen
of the central nervous system becomes notably reduced. In T the section passes
through the embryo in the plane where the neck region flattens out over the yolk.
Here we note the distinct subnotochordal rod (sn) and the flattening mesoblast
which now forms a delicate band almost surrounding the gut. In the surface view of
this region, on the other hand, only the thickened proximal ends of the mesoblast
masses can be distinguished. In u, where the neck is flattened out, the heart
appears at h; and in the upper region of the gut we note the thickening of the wall
of the gill-slit, the cavity of which is seen in the preceding section at^1. In v, as
indeed in some of the earlier sections, a thickened neural crest appears at nc. In
w the body cavity (be) is becoming conspicuous. In x the somato- and splanchno-
pleure spread out widely peripherally; in the gut we notice in the thickening of the
lateral walls an out-bending for the second gill-slit (cf. in z, g11) and in the cavity of
the gut in this and in many sections following we find masses of yolk. These
masses, sometimes small, as in sections z, AA, BB, EE, sometimes large, as in Y, cc,
DD, are unquestionably budded out (as in EE and HH) of the ventro-median wall of
the gut. On account of their abundance and range in size we can not conclude
that they are artifacts, but, on the other hand, if we regard them as normal
structures, it is natural to assume that they serve as food material, and are assimi-
lated by the gut in the usual way. This conclusion, simple as it seems, is none the
less difficult, since it attributes to Chimaera an embryological process which appears
to be unknown in the vertebrata and only remotely paralleled among invertebrates.
If, accordingly, we accept the present evidence, it follows that Chimaera is to be
regarded as the terminal member of an evolutional series, at one end of which were
forms whose yolk-laden cells contributed directly to the growth of the young; next
came those whose yolk-filled cells contributed indirectly to the growth of the young
through various processes, typically through the intervention of merocytes; and
finally, in Chimsera, the mode of nutrition by merocytes is supplemented by a still
more oblique process, i. e., one which passes fragmented yolk material from the
zone of merocytes directly into the lumen of the gut.

Continuing the sections: In GG, and in many sections following, a wedge-shaped
mass of yolk material (w) is converging toward the ventro-median line of the gut
(v. also p. 76); in LL it becomes subdivided, and in MM appears a small recess which
may also contain this nutriment (? anlage of liver). In jj and in following

YOLK AND YOLK-ENTODERM IN EARLY EMBRYO.

97

sections the pronephric duct appears, at first only on the left side, as an ectodermal
keel, beginning about the plane of the 8th somite. Thence, passing backward, it
merges with the somatopleure at about the plane of the 1 2th somite, after MM. In
this section the subnotochordal rod appears for the last time. In oo the notochord
dips into the dorsal wall of the gut; and in PP it forms an evagination of its wall.
QQ and RR are sections through the neurenteric canal, and ss to uu through the
tail end.

Two further details of this stage are shown "in figures 74 and 75. The
former of a section close to that of fig. 73 LL, the latter from a section close to fig.
73 G, representing only a detail of the extra-embryonic blastoderm lying under the
region of the head. Fig. 74 has been given to illustrate the ingress of yolk material
through the ventral wall of the gut, for here is seen the wedge of yolk protruding
through the thickened mass of yolk-entoderm cells, but under conditions which
bespeak the complicated nature of the process. For the rest, there is here not a
mere rupture which admits the yolk into the cavity of the gut, but an attendant

Fig. 74. — Detail of section of early embryo shown in fig. 73 LL.
y. Yolk plug pressing into cavity o( gut ; V'.y",v"', layers of yolk of different consistencies.

series of changes of which the "rupture" itself is, with fair probability, the terminal
member. Thus the wedge-shaped mass of yolk (y) is composed of fine yolk; it
next passes through a transitional zone (_/) into the coarse yolk (y"). And on
either side of the wedge lies a layer of very coarse yolk (j/"), which obviously comes
into close physiological rapport with the neighboring layers, for this thickens as it
approaches the,.yolk-wedge, and here it is filled with nuclei of extraordinary size.
Indeed on one, side (left) we note that this layer of coarse yolk is separated from the
yolk-entoderm by a layer-like offshoot of the fine yolk (j/) from near the point of
the wedge. We observe also the relation which the bordering yolk-entoderm bears
to the point of the yolk-wedge, for this layer is here many times thicker than in
neighboring regions. The yolk-wedge, in short, which passes into the cavity of
the gut stands in specialized relation (i) to the usual mass of yolk, i. e., spreading out
fan-shaped below, thus securing a large surface of contact; (2) to the lateral areas
of coarse yolk; (3) to the lateral masses of yolk-entoblast, and (4) finally, as we

98

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

Fig. 75. — Detail of extra-embryonic region of embryo of fig. 73.
«. Ectoderm; m, maoblut ; meg, meg', gigantic yolk-cells ; », vacuole;
,V< i yolk-entoderm.

have already seen, to the walls of the gut, since it passes to them yolk masses,
large and small, and perhaps also dissolved yolk material. In evidence of the
nutritive value of this material witness numerous mitoses in the adjacent (inmost)
cells of the entoderm — one of which appears in the present section.

In fig. 75 a detail is given of the
process by which yolk-cells are passed
into the tissues of the embryo. In this
portion of the extra-embryonic blasto-
derm the mesoderm occurs only as
detached (mesenchymatous) cells (m);
the ectoderm forms a single-celled
layer, and the entoderm a closely
formed cellular mass (j'e). Between
the entoderm and the yolk is the usual
zone of vacuoles (v). At meg a large
yolk-filled cell (cf. pp. 83 et seq.) pro-
trudes from the yolk into the entoderm,
the cells of the latter affording little bar
to its progress upward. In this connection we note that the huge cell (meg) lies
now within a vacuole in whose wall yolk-nuclei appear; indeed at one point a yolk-
nucleus has actually entered the vacuole. In the same figure at meg' is a large
cell (cut not quite through the middle) which has evidently had a similar origin to
meg; for from its size it can not be confused with a neighboring cell of any germ
layer. It contains coarse yolk, and on account of its irregular outline, judging from
earlier instances, it has probably undergone division by amitosis.

ADDITIONAL EMBRYOS OF THIS PERIOD.

A second embryo of this period, i. e., prior to the breaking through of gills
and mouth, is shown on plate vn, figs. 42, 42" and 42**, and on plate vni, fig. 42°.
The present specimen is badly bent in its trunk region, but in other regards it may
be readily compared with the earlier stage, plate vi, fig. 41. The chief advances
include: (i) the modeling of the trunk, in whose hindmost region only appears the
former flattened condition; (2) the appearance of auditory sacs (««); (3) the model-
ing of optic vesicles (pp)\ the protrusion of the forebrain region into a frontal knob
(£). The general shape of the head, as shown in dorsal view, already suggests the
adult condition, in spite of the small size of the embryo. This noj^ measures only
2. 5 mm. , not allowing for the bent trunk region. The tail at this stage protrudes
beyond the rim of the blastoderm, its tip budding out like a knob beyond the flat-
tened caudal eminence. About 25 somites are present.

A third embryo, plate vn, figs. 43 and 43", shows over sixty somites, and
gives us a picture of the young Chimaera at about the end of the first month of
incubation. In this stage over sixty somites are present, and the tail bud has

EARLY EMBRYOS. 99

grown out conspicuously. The broad flattened trunk terminal of the preceding
embryo is here represented, and at a the anal region, a point anterior to which the
number of somites corresponds in a general way to that in the earlier stage.
Noteworthy advances include:

(1) A more definite modeling of the regions of head and trunk. The latter
has now lifted up above the surrounding blastoderm, and the head (including the
chin region) has separated from the yolk-wall.

(2) The gill-slits are now conspicuous, although, as sections show, they have
not yet broken through; we note that the spiracular slit s, evidently the equivalent
of g1 in the former stage, is of considerable size; behind it occur three prominent
depressions and the trace of fourth and fifth.

(3) The appearance of pronephros and pronephric duct; the pronephros itself is
situated at the plane of the ninth, tenth, eleventh and twelfth somites, as can
better be seen in the transparent preparation in the same embryo, plate vn, fig. 43°.

(4) The knob-like terminal eminence of the head region has greatly increased
in size.

A fourth embryo of this period is shown as a transparent preparation in plate
vir, fig. 44. It contains a greater number of somites than the preceding, over 80
as opposed to over 60, but in many regards it appears to be less advanced in devel-
opment. Thus we note that its head region appears somewhat less mature than in
the former embryo; the chin is less definitely established and so also the gill-slits
are shallower and the optic and auditory vesicles and the pronephros less definite.
The tail, moreover, is less pointed, even bulbous where the terminal growth is taking
place. In this stage we note the presence of a conspicuous postanal gut. The
details of the vascular supply of the gill region are well shown ; the spiracular artery
is conspicuous, and, further hindward, we observe the duct of the pronephros (pnd)
and the postanal gut pag.

A series of characteristic sections of this stage is given in figures 76 A-N.
These show a general correspondence to the conditions of the young shark. In
fig. c the premandibular head cavity (pm) is shown; in D the mandibular (m). In
this section also we observe that the mouth has not yet broken through. In later
sections, as in E, F, H, i, and K, we note that the gill-slits have not been com-
pleted; fusions of the gut wall with the ectoderm have, however, occurred. We
note in section M, passing through the pronephric tubules, that the relation of these
structures corresponds closely to that in the young shark. A subnotochordal rod,
conspicuous in the earlier stage, is here represented only in a rudimentary condition,
as in N ; the gut has separated from the notochord and the main vascular trunks now
appear in the region formerly occupied by the subnotochordal rod. The present
stage corresponds closely with that of the shark in which the mesoblast bounds a
continuous myo-, nephro-, and splanchno-ccele. In Chimera, however, continuity
in these regions is less clearly marked, a feature which evinces greater develop-
mental specialization, i. e. , in masking an archaic condition and preparing the way
for the prompter growth of structures useful to the young fish.

100

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

THE RELATION OF THE BLASTODERM AND YOLK AT THIS STAGE.

As already noted (p. 58), the egg of Chimaera has by this time undergone a
process of fragmentation. The bulk of the egg subdivides in the direction of pro-
ducing for the embryo nutriment to be appropriated via gills and gut; a single mass

Fig*- 76 A-N. — Transverse sections of the embryo shown in plate VII, fig. 44.
Wl, Mandibular head cavity ; /"'* , premandibular head cavity.

YOLK-SAC OF EARLY EMBRYO.

IOI

only, representing about one-tenth the bulk of the unsegmented egg, is reserved
for the yolk-sac of the young fish.

In the stage last described (i. e., of plate vn, fig. 44), in spite of the advanced
characters of the embryo, the blastoderm has not increased vastly in size beyond
that shown in plate v, fig. 38. It has, however, as we see in plate vm, fig. 47,
constricted marginally, becoming cup-shaped, as it continues. to envelop the small
yolk mass. How far it has succeeded in inclosing the yolk 'is: p'erhaps better seen
in the details of the last figure, shown in figs. 47a_and 47b/ ' /, : '•'•'.'•'">'•.',' ':'•''. ''. A

The relation of yolk and blastoderm is pictured in detail" in fig. 77, 'a section
passing through the blastoderm parallel to the long axis of the embryo. At the
points mb and mb', the rim of the blastoderm comes in contact with the yolk ;
above mb the blastoderm is thickened and
spongy; for, as a sign that the body of the
embryo lay adjacent, this region is richly
vascular. Noteworthy here is a deep sub-
marginal sinus (ms) whose posterior wall (c)
is cellular. We have in this condition a
physiological parallel with the submarginal
space in ganoids, and more directly even with
Kupffer's vesicle in teleosts. On the ventral
side of the blastodermic cap (on the left in
the figure) the vascular sponginess is largely
lost ; and the blastoderm is thin, save only at
its rim (mb'). And here in place of a deep
submarginal sinus, a number of distinct blood-
producing vesicles appear (ms) scattered
distally in a narrow zone of finely divided yolk (fy). From another standpoint,
finally, the present section is noteworthy. For it shows that the entire yolk-sac is
divided into masses which are largely separated from one another by a system
of fissure-like vacuoles. Closer inspection shows nuclei scattered irregularly
through these masses of yolk, and, everything considered, I think we can therefore
justly conclude that the yolk-sac at this stage, in spite of its relatively large size, is a
totally segmented structure comparable with the yolk-sac of Amia or Ichthyophis.
In the present case, it is true, the yolk masses (blastomeres) show a condition of
greater or less attachment to their neighbors, and each mass will usually contain
more than a single nucleus. But even in this event, the comparison will, I believe,
hold. In some cases the shape of the yolk masses is distinctly blastomere-like,
as between the vacuoles (v) in the present section. Viewed from this standpoint,
accordingly, Chimsera has retained a primitive embryological character, holoblastic
cleavage; but we can hardly fail to observe that this character has lost much of its
primitiveness inasmuch as the blastomeres are polynuclear and the intercellular
spaces obviously adapted as reservoirs of nutriment.

Fig. 77.— Section of extra-embryonic region and of upper
part of yolk-sac of stage of plate VIII, fig. 47.

c. Cellular area ; mb, mb', margin of blastoderm: ms, marginal
sinus ; /.'/i fluid yolk ; V, vacuoles.

I02 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

LATE EMBRYOS.
EMBRYOS FROM THE APPEARANCE OF GILL-OPENINGS TO THE TIME OF HATCHING.

Four specimens illustrating this period are described on the following pages.
The first of these, shown in toto (plate vn, fig. 45), illustrates a stage in which all
five gill-slits are cle.arly shown, but of these only the first has completely broken
through, tha,t lying immediately below the auditory vesicle. In front of this the
spiracular cleft is faintly outlined. The entire head region is modeled clearly, and
the anterior "end of the -embryo has separated from the blastoderm as far back as
the region immediately behind the heart. The tail has greatly elongated and has
entirely lost the bulbous terminal which we noted in the earlier embryo.

The region immediately adjacent to the embryo is divided up into a spongy
mass by many blood-vessels; we observe also that the blastoderm has almost com-
pletely inclosed the attached yolk mass, a small yolk plug only being visible at the
hinder end of the yolk-sac. This condition is shown in plate vm, fig. 48. Here,
through the rim of the blastoderm one can faintly see the extent of the submarginal
sinus which was noted in the preceding stage. From it now extend many vessels,
as indicated in the figure. The region of the yolk plug is figured in plate vm,
fig. 48", as viewed under a dissecting microscope. It shows an interesting condition
in connection with the holoblastic behavior of the yolk; for a number of irregular
masses are visible, outlined, it appears, by vacuoles, and suggest yolk-filled blasto-
meres. It will be observed, however, that the contours of the yolk masses are less
definite as they approach the irregular rim of the blastoderm. (Cf. fig. 77.)

Sections of this stage are shown in the adjacent figures. In the first (fig. 78)
the mouth (i. e., its hinder portion) and auditory vesicles are traversed; the mouth
has not yet broken through nor has the neighboring gill-slit, the hyomandibular.
We note that the auditory vesicle is now a thick-walled sac opening broadly at the
surface; that a subnotochordal rod is present; that the brain wall in this region (hind-
brain) is remarkably thick and asymmetrical, and that the fifth ventricle is corre-
spondingly reduced in diameter. A section through the mid-trunk (fig. 79) indicates
that in this region the trunk is spread out more widely than in the corresponding
or, in fact, in any stage in the shark. The splanchnocoele (spc) is of great size, and
its walls, both splanchnic and somatic, contain large spaces. The myocoele is
virtually obliterated, although its margining cells have not fused across its earlier
opening into the gononephrocrele. The last region is not clearly demarked; atpn a
pronephric tubule appears in the position usual in elasmobranch. At df the early
condition of the dorsal fin corresponds closely with that of a shark embryo.

A second embryo (plate vn, fig. 46) slightly older than the preceding, was one
of the specimens received from Dr. Wilbur. It had with it only a small fragment
of the blastoderm, and at the time of preservation the embryo appears to have
turned in a position nearly transverse to its usual one. At this stage the tail
protruded widely over the rim of the blastoderm, and it follows, therefore, that,
probably as an individual variation, the blastoderm has not as completely inclosed

DETAILS OF LATER EMBRYO.

103

the yolk as in the former specimen. A more detailed examination of this embryo
shows that two gill-slits have broken through. The mouth, moreover, is more nearly
completed, the mandible appearing and the visceral region having a more advanced
contour. The pronephros is conspicuous. The pectoral fin is present as a longitud-
inal dermal ridge. The tail, judging from its twisted condition, is evidently capable
of active movements. This, however, in its detailed structure, as shown in a trans-
parent preparation (plate vm, fig. 46") is still distinctly immature; its tip retains
a neurenteric canal (nc), and a postanal gut (pag)._ In the latter the irregularity
at the point x is probably artifact. The present embryo measured about 20 mm.
in length.

78

Fig. 78. — Transverse section passing through the posterior head region of embryo of plate VII, fig. 42.

At the right the section traverses an auditory vesicle and the hyomandibular evagination. The latter fuses with

the ectoderm, which here invaginatesi but no opening has as yet been formed.

Fig. 79.— Transverse section through the middle of the trunk region of the preceding embryo.
df. Ectodermal anlage of dorsal fin. P». Pronephros. »J>C. Body cavity.

hb. Hyomandibular evagination. *»• Subnolochordal rod.

A third embryo of this stage is pictured in plate vm, fig. 49" to d. It measured
about 35 mm. in length, and was observed living. It was this embryo whose
capsule was taken accidentally on a trawl line during one of the writer's visits at
Pacific Grove. As already noted, it was found developing in a creamy fluid.
When placed in a watch-glass, its general position and color were as here repre-
sented. It lay for a while on its side, its diminutive yolk-sac extending outward
from the body and the delicate tail region showing constant undulatory movements.
Most conspicuous were the bright-colored vessels on the yolk-sac, which outlined a
vitelline circulation obviously shark-like. The visceral cavity showed red through
the delicate wall, and in the gill region there were prominent bead-like dilatations,
brilliant in color. One notes the bright red spot under the eye, which was later

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

found by sections to represent the spiracle.* Further details of the gill region are
given in fig. 49".

In the various figures given of this embryo we note a number of advancing
structures :

(1) The eyes are now well formed, protrude widely from the head, and are
provided with a conspicuous lens.

(2) The region of the snout shows distinct modeling. Olfactory pits are
present and are separate from the rim of the mouth. The snout region, it will be
seen by reviewing the preceding figures, notably plate vn, figs. 44-46, does not cor-
respond to the greatly dilated eminence which forms the cap-like knob surmounting
the head. This appears rather in the region of the forebrain, and the writer does
not, therefore, agree in the conclusions of Schauinsland (who, however, it will be
borne in mind, examined Callorhynchus, not Chimaera) as to the fate of this singular
organ. It has, we suggest, the function of providing for the growth of the contour
of the antero-dorsal head regionf rather than for the framework of the snout, as
Schauinsland suggests.

(3) The mouth has broken through, and its margins are thickened. It shows
distinct movements, although at irregular intervals, in the living young. Between
the rim of the upper jaw and the eye appears the spiracle, and in a remarkably
anterior position contrasted with that of an elasmobranch.

(4) The five gill-arches (plate vm, fig. 49d) show well-developed lamellae on
their anterior margins, and from these are produced the external gills. The latter
extend outward on either side to a distance equal to about the diameter of the head
between the eyes. The presence of dilated spaces, blood-filled, in the external gills
has already been recorded. It is worthy of note, perhaps, that when the present
specimen was preserved masses of yolk (plate vm, fig. 49b) were found adhering
to the gill-filaments, a fact which may have some significance, since the blood-
dilated spaces appeared at points adjacent to the attached yolk masses. In this
stage, it may be added, the fifth gill-slit has not as yet broken through.

(5) The fins are well established. The lobe of the anterior dorsal fin, however,
shows as yet no trace of a spine. The paired fins are distinct lateral folds, much
as in the young shark; in fact, the pectorals are even precociously large. It may be
added that the metameral elements of the fins were conspicuous in the living
embryo, since blood-vessels were present and appeared in a series of brilliant spots.
The ventral fins are drawn together immediately behind the anus, and no trace
appears of a clasping organ or of a third pair of limbs. % The general arrangement
of the fins is best seen in plate vm, fig. 49.

(6) The yolk-sac, in spite of its small size, was perfect. Its structure is
delicate, for at first its contour was smooth, but after the embryo had been kept
living for several hours in sea-water, it was noticed that the surface of the sac

•This is not in the position in which Solger (Morph. JB., 1876, pp. 219-221) expected it to appear, i. e., behind the
articulation of the mandible.

fPossibly as a larval organ to protect the head when in contact with the wall of the egg-capsule.

\Cf. T. J. Parker, Nature, vol. xxxix, p. 625. With regard to the non-appearance of mixipterygia, which
certainly occur early in Chimseroid ontogeny (cf. infra, plate ix, fig. 50^ also text), it is possible, of course, that the
present embryo was a female.

DETAILS OF LATER EMBRYO.

105

loosened at several points, giving the wavy contour noted in the figure of the
entire embryo. The arrangement of the vessels is clearly shown, and one traces
the posterior umbilical veins and the anterior vitelline arteries. At first sight the
yolk-sac seemed to be attached anteriorly throughout the length of the heart region.
Later examination, however, showed that a single stalk, albeit a very short one,
connected the sac with the trunk in a fashion very much as in the young shark.
(Cf. plate vni, fig. 49b).

(7) The lateral line sys-
tem of organs is already
established. At either side
of the eye sensory pits are
present and the backward

growth of the lateral line /jj&L, / 9/ 0

, , , j c ., M&wSkffltoL A II ' f^J

could be traced as far as the

anal region.

DETAILS OF THE FOREGOING
EMBRYO.

In the sections, figs.
80-83, are shown details of
the foregoing embryo. In
the first of these (fig. 80),
in the eye structures one
observes the proportionally
enormous size of the lens.
Particularly noticeable,
also, are the elaborately
branching vessels lying be-
tween the eye and the mid-
brain (v, v), a symptom again
of the embryo's precocious
growth. In the following
section (fig. 81) the spiracle (s) is seen to be continuous. Sections through an
external gill-filament show, even more conspicuously than in shark, the presence of
both vein and artery (a, v). In the same section we observe one of the blood-filled
dilatations (d\ which have already been commented upon. This appears at or near
the end of the gill-filament.

In fig. 82, a section through the pelvic region just anterior to the anus, we
observe on the right side the opening of a segmental duct at sd. Beside it, at mt,
appears a mesonephric tubule. On the opposite side of the body a corresponding
tubule, ;///, opens directly into the body cavity. One observes in the same section
a dilated caudal vein at cv, and above it the caudal artery. In the section, fig. 83,
we observe that the unpaired fins are already well established and that they are
made up largely of mesoblast. The caudal vein and artery appear as before, and
the section traverses numerous muscle plates.

Fig. 80. — Transverse section through the eye region of the embryo shown in

plate VIII, fig. 49.
V, V, Branches of anterior internal carotid.

io6

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

The latest embryo in the writer's material, one of the specimens secured by
Professor Wilbur, measured 5 1 mm. in length. Its age was said to be six months.
(Plate ix, figs. 50 and 50° to g.) It is decidedly like the adult Chimaera, as can be
seen from the figures; it has well-established snout (in which sensory grooves and

pits appear), paired and
unpaired fins, and
clasping organs, show-
ing that the present
specimen was a male.
On the other hand, two
prominent embryonic
characters still appear,
viz, the yolk-sac (which
in the present specimen
is preserved only in
part) and the external
gills, a tuft of which is
seen protruding from
below the opercular
folds. The external
gills are shown in plate
ix, fig. 50", c, e, and e.
Their degree of differ-
entiation is indicated in
fig. 5og, in which we
note that in each fila-
ment one of the compo-
nent vessels is less con-
Fig. 81— Transverse section passing through the otic vesicles of preceding embryo. At the torted than its neigh-
sides external gills are shown. bor, the filament thus
a, artery ;d, dilated blood knot in external gill; .. -piracle ; «, vein. presenting a Ctinkly

appearance when viewed under a low power. Occasionally a terminal dilatation
is seen. It will be noted that some of the filaments attain great length, although
in general they are fewer in this than in the earlier stage, a process of reduction
having set in at certain points.* In lateral view this embryo shows fragments
of yolk attached to its side and to its paired fins, a condition probably artifact,
although deserving mention, since in the younger stage yolk masses were
observed attached to the gills. Before making the present sketch, a portion of the
opercular fold and the neighboring external filaments were removed. The sensory
canals are well indicated; that of the lateral line has now passed down the side of
the body and has entered the tail region. The mandible is well established. In
plate ix, fig. 50°, we observe the extent to which the opercular folds overlap
the tuft of external filaments; we here observe also that the frontal clasping organ

*Cf. also Schauinsland (op. cit., Taf. xvi).

DETAILS OF LATER EMBRYO.

I07

is long, narrow, and relatively of great size, suggesting its origin from an anterior
fin spine, and interesting in connection with paleontological data(V/i figs. 132-137).
In fig. 5Od, an idea is had of the extent of the overgrowth of the opercular fold on
the ventral side of the head, and here is shown also that the external gill-filaments
arise only from the anterior wall of the gill-slit, and that the external filaments
increase in length as they pass toward the middle of each flap. A detail of the
ventral fin is shown in fig. 5Of. Here the mixipterygium is but a further differen-
tiation of the base of the ventral fin (cf. plate via, fig._ 49b), and the anterior clasping
organ (acl} evidently represents the fin's anterior segmental elements (radialia)
(cf. also fig. 1 1 2). The mouth region

in this stage is noteworthy, since it Q* -*

shows that not only are the anterior ^&™ ^^

and posterior dental plates (adp and
pdp) present, but also a series of other
eminences which are best interpreted
as rudimentary dental plates. Similar
structures are now described in detail
in the work of Schauinsland on Cal-
lorhynchus (u. infra). The present
figure also indicates the early stages
in the curious lip cartilages of the
Chimseroid. They arise at the sides
of the mouth and suggest at this
stage the corresponding structures in
shark. In view of the recent work
of Schauinsland and of the younger
Fiirbringer (Morph. JB., 1903, vol.
xxxi, pp. 360-445), we recognize with interest the unpaired element at the mandib-
ular symphysis which is held to represent the homologue of the basihyal of the
hyoid arch. (Cf. fig. 1 1 1.) In commenting further upon this stage we note that in
the eye the iris is well established, and that in the umbilical sac the yolk material is
arranged in conspicuously concentric lamellae (plate ix, fig. 5od).

The Skull. — The skull at this stage may be compared instructively with that
of a late embryo of Callorhynchus figured by Schauinsland in Taf. xvn, figs. 124,
125, 1 26, op. cit. The present figs. 84 A-D were, like the figures mentioned, prepared
from wax-plate models. The embryo referred to by Schauinsland is more advanced
than the present one, although the difference in age does not appear to be conspic-
uous. On the other hand, the figures of a younger Callorhynchus shown in
Schauinsland's Taf. xvm, figs. 130 and 131, can not be compared satisfactorily
with the present specimen of Chimsera, for its skull was evidently far less mature,
a large part of the model having been based upon outlines of procartilage. A
study of the foregoing figures indicates that the skull of Chimaera is, at a corre-
sponding growth period, the more highly modified; the orbits are larger, the snout

Fig. 82. — Transverse section through the region of the ventral fins of

preceding embryo.

i>c, Body cavity; crt, caudal artery; cv, caudal vein; nit, tubule of meso-
nephros ; 8(1, posterior portion of segmental ducL

Fig. 83. — Transverse section through the tail region of the preceding
embryo.

io8

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

region is wider and more compressed, the palato-quadrate is reduced and trans-
ferred to a more anterior position, nor is it as distinct an element as Schauinsland
figures it in the kindred genus. As further evidence of the more modified character
ol the skull of Chimsera, we observe that the preorbital ridges are curiously
flattened, forming together a transverse brow-plate in the young skull; and that the

A

Figs. 84 A-D. — Reconstruction of skull of CKim&era embryo shown in plate IX, fig. 50. The model is shown in lateral, three-quarters

dorsal, and caudal aspects.

Ot-6, Anterior and posterior points at which the palato-quadrate element has fused with the cranium ; etc, roof of auditory capsule : ch, ceratohyal ; /". fora-
men through which the ophthalmic nerve passes out of the cranium ; fos, foramen through which passes the superficial branch of the ophthalmic nerve;
gh, basihyal ; hch, hypochordal portion of the basis cranii ; /»?«, hyomandibular : pb, pharyngobranchial ; p<lf, palato-quadrale fissure; pro,
preorbital process; pto, poslorbital process; r, median rostral cartilage; s, spiracular cleft later retained as the foramen through which the hyomandibular
branch of the seventh nerve passes to ihe under side of the skull ; V^- VII, foramen for fifth and seventh nerves.

postorbital ridges are reduced in size. We note also the greater width of the
cranium in Chimaera and the lesser development of cartilage in the region between
the orbits. In short, we can justly conclude that at corresponding stages the skull
of Callorhynchus more closely resembles that of a young shark than does the skull
of a young Chimaera. The proportions in the case of Callorhynchus are distinctly

DETAILS OF LATER EMBRYO. 109

shark-like, so also are its early rostral cartilages. In Chimaera, on the other hand,
the developmental processes, evidently abbreviated, produce larger orbits, larger
auditory organs (from this is due the broadening of the skull noted above), coales-
cence of foramina, and altogether a more mature modeling of the head.* In this
form, moreover, we find in the hyoid arch more perfectly developed ceratohyal and
greatly reduced pharyngobranchial elements. It follows, I conclude, in view of
these and other evident specializations^ that one can not reverse the order of
comparison and regard Chimaera as resembling the" more closely the ancestral type
from which in turn Callorhynchus and sharks developed.

COMPARISONS WITH OTHER CHIM/EROIDS.

Before concluding the account of the later embryonic stages of Chimssroid,
which we have hitherto based upon C. colliei, reference should be made to the
conditions known in other genera and species.

In Callorhynchus. — Schauinsland has already given many observations upon
the young of Callorhynchus. It appears from his figures that there are little
outward differences in the development of stages corresponding to those of plate
vii, fig. 45, of Chimara colliei, and that of Callorhynchus in Schauinsland's Taf.
xin, fig. 105. Also there are but minor differences between the present plate vii,
fig. 42, and Schauinsland's Taf. xm, fig. 98. We may thus compare also the
present plate vn, fig. 45, with Taf. xiv, fig. 107, also plate vn, fig. 43*, with Taf.
xiv, fig. 106. In a later stage, contrasting Chimaera in plate vin, fig. 49, with
Schauinsland's Taf. xv, figs. 116 and 117, we can not fail to note the more shark-
like conditions in the Australian species, and this is even more evident if we contrast
the still later stage of C. colliei given in the present plate ix, fig. 50, with Schau-
insland's Taf. xv, fig. 121. Observe in this connection the less tapering tail of
Callorhynchus, a more distinct second dorsal fin and the early appearance of the
row of dorsal scales which suggest closely the conditions shown in Scyllium by Paul
Meyer.

In referring to the latest embryonic stages in Callorhynchus, outline drawings
may be given of specimens preserved in the department of ichthyology in the
British Museum, figs. 86-88, and in the Copenhagen Museum, fig. 89. % And these
may in turn be compared with the outline of the young Callorhynchus, fig. 85,
figured by Parker and Haswell in their Text-book of Zoology. An examination of
these figures shows that the absorption of the yolk-sac takes place, as one would
expect, while the embryo is still inclosed within the capsule. In fig. 85 the yolk-
sac is of irregular shape, rather large, and the embryo still retains its external gills.
In figure 86 the sac, still large, is somewhat bilobed, a condition which becomes

*Cf. also in this connection the more advanced condition of the mixipterygia in Chimaera (plate ix, fig. sof, and
Schauinsland's Taf. xvi, fig. 120).

fin morphological regards cf. the reduction of dermal defenses, great size of head, reduction of caudal region, differ-
entiation of dorsal fin, specialization of clasping organs, modification of brain.

JFor the privilege of examining these valuable specimens the writer is indebted to Mr. Boulenger and to
Dr. Winge.

no

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

Figs. 85-89. — Latest stages in the development of Callorhynchus within the capsule. Nearly actual size.

85. Callorhynchus " antarcticus." Detail of figure given by Parker and Haswell.

86. Callorhynchus sp. Stage in which the yolk-sac is reduced in size.

A. Outline of dorsal fin when unfolded . B, Detail of frontal clasping organ with surrounding row of dermal denticles.
87 and 88. Callorhynchus sp. Late stages in absorption of yolk-sac. The foregoing three figures are after specimens in the

British Museum. (Cf. p. 34.)
89. Callorhynchus " antarcticus," showing very late stage in the absorption of the yolk-sac. After sketch of specimen from New

Brighton, New Zealand, preserved in the Zoological Museum at Copenhagen.

"LARVAE" OF CHIMERA. m

intensified in the later stage, fig. 87. In fig. 88 the sac is still irregularly bilobed
and in figure 89, where it has been almost completely taken into the embryo,
the anterior lobe is still present. Observe in connection with these figures that the
shape of the sac is obviously correlated with the shape of the embryo inclosed
within the capsule.* A further consideration of these figures leads us to conclude
that in the latest stages of development the embryo of Callorhynchus rests on its
side, and in this position the dorsal fin is observed to lie neatly tucked against the
side of the body, the dermal web of the fin being folded under the depressed spine.
So also the paired and unpaired fins are closely apposed to the sides of the body, the
continuous dorsal and anal fins folding closely around the side. The dorsal fin folds
over the trunk towards the left side of the embryo. An outline of its margin,
slightly raised, is shown in fig. 86 A. In this stage the appearance of the frontal
clasping spine is indicated in fig. 86 B. This corresponds obviously to the con-
dition which is figured in a younger stage by Schauinsland in his Taf. xvi, fig. 122.
In Chimcera. — The only late embryonic stage known to the writer is the one
preserved in the Jardin des Plantes and figured by Professor Vaillant in his
" Travailleur " report (1882), a specimen which the writer had the opportunity of
examining through the courtesy of its describer. This specimen (fig. 90 A, B),
probably of C. affinis, was dredged in the Bay of Biscay, together with fragments of
its egg-capsule. A small yolk-sac is adherent; this is of spherical form, and appears
to have been delicately connected with the body of the embryo. It is possible,
of course, that the present spherical form of the yolk-sac may have been the result
of the specimen having been freed from the capsule, for under this condition the
yolk-sac would probably have assumed its present shape. It may be noted that
the surface of the sac was deeply creased with blood-vessels, somewhat as indicated
in fig. 90 A. Noteworthy in this specimen is the great length of the hinder trunk
(and tail) which, it will be seen, is proportionately longer than in Chimara colliei,
and much longer than in Callorhynchus, and it is also to be mentioned that the
long urostyle shows that the continuous dorsal fin could not have extended function-
ally into this posterior region. Clasping organs are developed, and, as shown in
fig. 90 B, they attain even now a considerable size, about one-third their adult
(proportional) length. This condition is noteworthy as indicating again a precocious
type of development, sexual characters having been differentiated, although the
embryo is small in size and provided with a considerable yolk-sac.

IMMATURE YOUNG.

Four stages of "larvae" of Chimcsra colliei are shown in plates x and xi, to
illustrate especially changes in outward form, proportions, and coloration. The
specimens figured in plate x were secured by the Albatross during its work on the
Pacific coast, and were kindly placed at the writer's disposal by the United States
National Museum. The youngest specimen figured (fig. 51 and figs. 51* and b)
was evidently lately hatched. It still shows the scar marking the point of intrusion

*The irregular outline of the yolk-sac would, by analogy, probably be filled out if the living embryo were removed
from the constricting capsule.

I 12

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

of the yolk-sac (plate x, fig. 5ib, ys); its form at this stage is probably modeled
somewhat differently from that of the latest stage of the encapsuled embryo; thus
the membranes of the unpaired fin in the tail region are probably less marked than
in the earlier stage (comparing the embryo of plate ix, fig. 50) in which this mem-
brane serves as an organ for carrying out the water used in the respiration of the

go

Fig. 90. — Late stage of Chimrera affinis (>).

The yolk-sac is largely resorbed. The present is the type specimen of Professor VailUnl, and i> preserved in the ichthyological museum of the Jardin
des Plantes, bearing the number 42392. In spite of its small size (its total length is only about 1 I cm.) it shows a well-developed mixipterygium
(B) . A detail showing the vascular supply of the yolk-sac is indicated at A.
Fig. 91. — Detail of early Chimeera monstrosa, showing larval coloration.

After sketch of specimen in the museum of Tromsoe. Colors are indicated, a, ashen, if, white.
Fig. 92.— Detail of Chimsera monstrosa indicating final larval coloration. After sketch of specimen in the museum in Copenhagen.

encapsuled young. The advancing characters of the earlier young may best be
followed by contrasting figs. 51, 52, and 53. The changes thus observed are:

In proportions. — The head length of the embryo, measured for example anterior
to the base of the dorsal fin, decreases as we ascend the scale ; in the earlier stage it
measures about 20 per cent, of the entire length, in the latest about 16 per cent. ;
the eye alters little in size, but the region of the head lying below the eye increases
notably; the shape of the pectoral fin changes progressively; almost as wide as high
in the first figure, it becomes nearly twice as high as wide in the latest stage. So,

"LARV.E" OF CHIMERA. 113

too, the unpaired fins change proportions notably; in the stage shown in plate x,
fig. 52, their width is much greater proportionately than at other stages.

In shape. — The shape of the trunk undergoes noteworthy changes. In the
stage shown in plate x, fig. 53, it is much longer proportionately than in the earlier
and later stages. We note also that the dorsal fin (or rather that portion of it
posterior to the first dorsal) changes from continuous to lobate and then again later
to a lower and less lobate form, during progressive development.

In color. — Pigmentation appears progressively. In the youngest stage the pig-
mented areas are dorsal. In the stage of plate x, fig. 53, pigmentation is more
marked on the sides of the body than at any other stage. The sharpness in the
coloration of the distal margin of the dorsal fins is most conspicuous in the stage of
plate x, fig. 52; also a distinct larval coloration is noticed in the pectoral fin, a well-
marked color being present along the anterior margin of this fin and in the anterior
portion of its dermal web. Observe also the distinct patch of pigment at the base
of the dermal web in plate x, fig. 53. Noteworthy, further, is the progressive
increase in the number of pigmentless blotches; few in fig. 51", they become
numerous in fig. 53", and small and most numerous in the stage of plate x, fig. 54.
Similar changes in coloration affect the region of the eye.

A late stage in the development of Chimcera colliei may finally be referred to in
plate XT. At this age the young fish has attained nearly mature size (i. e., about
three-quarters of that of the adult), although it is still distinctly "larval." Its
coloration is darker (cf. fig. i), making the small pigmentless spots more con-
spicuous. The margins of the fins, on the other hand, are pigmented, and with
these we may contrast the fin margins in the adult, figs, i and 2, especially in the
latter figure, where we observe that the anterior rim of the paired fins, notably the
ventral, are pigmentless. We observe also distinct changes in proportions from
the earlier stages; the length of the fish anterior to the anal region is now scarcely
more than one-half the total length; in the earlier stage figured it is less than one-
third. In the present specimen, a young male, the ventral fins partly uncover the
mixipterygia ; the ventrals are small in size, surprisingly so when we consider the
length of the entire fish. At this growth period the young of this species occur in
schools and sometimes appear in shallow water. *

In other species similar changes in colors and proportions are probably present
in "larval" young. In one species, Chimcera monstrosa, they are present in even
a more marked condition. In a young specimen preserved in the museum of
Tromsoe, to which the writer's attention was kindly called by Dr. V. Storm, the
coloration was brilliantly marked. Although not larger than the specimen shown
in plate x, fig. 53, it had developed dorsals sharply marked with black, pectorals
with an ashen blotch and with a white anterior rim, a pattern which has been
reproduced from a sketch in the present fig. 91. It is evident, moreover, that
in C. monstrosa this stage is of brief duration; for in a second and equally well-

*The present specimen was taken, together with 22 others, in a water depth of less than 10 feet, near Port Wash-
ington, Puget Sound, June, 1896, in a single haul of a herring seine. In this locality Chimaera is rarely taken in
shallow seines. The specimens measured from 30 to 40 cm.

H4 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

preserved specimen of this species — one which was examined in the Copenhagen
collection — the colors had notably changed. The pigmented margins of caudal
and postdorsal fins had become reduced to a dusky band, and the marking of the
pectoral was limited to a mere fuscous blotch at the fin tip (fig. 92). The length of
this specimen was but about two inches greater than the former one.

From the foregoing notes we may justly conclude that Chimaera undergoes
a series of "larval" changes. That these are adaptive remains still to be proven,
a verdict which, it may be remarked, applies equally well to many if not all the
"larval " changes of teleosts, but the fact that such changes do occur in the hatched
young is noteworthy in its bearing on the specialized nature of Chimaeroid
development. It is also, I believe, significant that the "larval " coloration of the
young of Chimtzra monstrosa occurs at an earlier relative period than in C. colliei
(i. e., that the distinctness of coloration, which in C. colliei — a smaller species by the
way — is shown in a specimen twelve inches in length, is attained in monstrosa by
the time the young measures but about seven inches), for this denotes that the
structures of monstrosa are the more highly differentiated and that this species is
of later origin. In another direction it contributes testimony as to the abbrevia-
tion of developmental processes.

ORGANOGENY.
INTEGUMENT AND DENTITION.

In the major problem of the position of Chimaeroids the evidence of scales and
dentition claims an important place. For the question has been raised repeatedly
whether the dentition of these fishes is fundamentally different from that of sharks,
and whether the characteristic tritoral plates may not have retained primitive gnath-
ostomal characters (Jaekel). And it has similarly been queried (Pollard) whether
the present integumental defenses of Chimaeroids may not prove the rudiments of
a complete body armoring. We may accordingly review at this point the evidence
in the matter of integument and teeth afforded by a study of the recent forms, both
in adult and in embryonic condition.

It has long been known that recent Chimaeroids retain shagreen-like structures.
These occur in greater or less number (a) on either side of the median dorsal line ;
(<$) in connection with sensory canals, especially in the suborbital region; and (c) in
the male as organs of retention in copulo.

(a) Shagreen-like scales on either side of the median line are most numerous in
Callorhynchus, where they form rows, each including about a dozen scales, in three
definite tracts, i. e., in the head, between the first and second dorsals, and between
the second dorsal and the caudal fin (figs. 93 A and B). In Harriotta they are
smaller and less numerous. In Rhinochimaera they are tumid and uncalcified,
occurring along the fleshy anterior margin of the caudal fin, obsolescent elsewhere.
In Chimaera they are rudimentary or absent. These scales occur, therefore, in a
regressive series, at one end of which stands Callorhynchus, at the other Chimaera;
and it is significant, I believe, that a condition closely similar to Callorhynchus
occurs in sharks, e. g., Pristiurus and Scyllium, as figured by Paul Meyer, who,

SHARK-LIKE DERMAL DENTICLES.

D

E

Figs. 93 A-F. — Dermal denticles of Callorhynchus.

The dorsal

A. Dona! aspect of young Callorhynchus " antarcticus" (Chili), measuring 16 cm. in length.

denticles are conspicuous ; their disposition and number is indicated.

B. Dorsal aspect of well-grown Callorhynchus "antarcricus" (Chili), measuring 50 cm. in length. The

dorsal denticles are reduced. In a specimen (Australian) measuring 92 cm. they do not appear.

C. Isolated denticle from the back of a late " embryo." X 42. After Schauinsland.

D. Isolated denticle of a late "embryo" (shown from side). X 42. After Schauinsland.

E. Row of four denticles from the back (in front of second dorsal fin) of a late "embryo." After Schauinsland.

F. Enlarged denticle from similar situation in " adult " specimen. X 21. After Schauinsland.

ng CHIMyEROID FISHES AND THEIR DEVELOPMENT.

however, does not refer to these structures in connection with Chimsera (MT. Zool.
Stat. Neapel, vi, p. 221 et seq.\ In further detail: in the dorsal scales of Callo-
rhynchus, as Dumeril and others have shown, the individual scales are furcate at
their base, and the free points of the base project forward and embrace the pre-
ceding member of the series, thus rendering the row of scales stronger and more
compact (cf. esp. Dumeril, Carman, and Schauinsland). (Figs. 93 C-E.) It has
further been shown by Schauinsland that these scales present notable shark-like
features in their development; they first arise, like shagreen denticles, as an out-
growth of the derma; they then differentiate odontoblasts, by which in a centrifugal
direction dentine is laid down ; and at the end of the process a pulp cavity remains
and a basal plate perforated by small nutrient canals. In Schauinsland's words we
further note that "in the latest embryonal stages the denticles, and especially their
tips, acquire a greater and glassy transparency (vitrodentine), by which they
become more and more differentiated from the substance of the (basal) plate. In
short, developmentally speaking, the dermal denticles of Callorhynchus represent
the most primitive scales which occur among living selachians. Through the
presence of a basal plate perforated by dentine tubules, they suggest the scales of
the oldest palaeozoic selachians. " * Schauinsland illustrates his foregoing remarks
with two excellent figures, one showing in section an early stage (pp. cit., Taf. xix,
fig. 139) in the development of the dermal cusp, the other a late stage in which
the cusp presents a thick cortical layer of vasodentine (ibid., fig. 140), projecting
its tip beyond the epidermis.

On the basis of the foregoing observations, therefore, we may conclude that, as
far as these body scales are concerned, Callorhynchus is distinctly shark-like; there
is not the slightest embryological evidence that this Chimaeroid had ever ganoid-
like scales. We might even, I think, go farther than Schauinsland, and point out
resemblance with more typical selachian conditions; for this author, while main-
taining that "the epidermis takes no part in the formation of the denticle," and
admitting that he "was unable to demonstrate the presence of enamel," shows
nevertheless in his earlier figure that the cells of the epidermis are arranged over
the dermal papilla in a wayf that is more than suggestive of an enamel organ—
an emphatically shark-like character; and we may further conclude that the base
of the denticle perforated with tubules is not merely characteristic of denticles of
Silurian forms but of later sharks as well (cf. Rose, re trabeculo-dentine in Anat.
Anz., 1897, P- S^)- In connection with the presence of scales arranged near the
dorsal line, it has already been commented on (Schauinsland) that these structures
are relatively more prominent in the late embryo than in the adult, although
no explanation of this phenomenon has yet been advanced. I may accord-
ingly hazard the opinion that they have been retained in this position owing to
their importance as larval organs — possibly for the purpose of enabling the well-

*Cf. Rohon, J. O., Ober fossile Fische vom oberen Jenissei, Mem. Acad. St. Petersburg, 1889, and Die ober-
silurischen Fische von Oesel, Mem. Acad. St. Petersburg, 1893. He refers to denticles of Thelodus-like forms which
the recent researches of Traquair have associated with fishes which are in some regards shark-like.

\Cf. e.g., Jentsch, B., Beitr. z. Entwick. u. Struktur d. Selachierzahne. Leip. 1897, fy?- 6.

SHARK-LIKE DERMAL DENTICLES. 117

developed young to maintain its position in the egg-capsule, possibly also for the
purpose of protecting the delicate dorsal fin, i. e. , by keeping it from rubbing against
the walls and the roof of the capsule, during the movements of the young fish.
According to this view the dorsal scales of the young Callorhynchus after the time
of hatching are to be looked upon merely as rudimentary organs.* And it may
be pointed out, in this connection, that when these enlarged dorsal scales are
developed in shark embryos they appear only in those forms in which development
takes place in egg-capsules.^

(£) Small dermal plates have long been known to occur in Chimseroids in
connection with the sensory-canal system. Pollard makes a special reference to
those situated in the suborbital canals, and Schauinsland gives the following notes
upon them (pp. cit. , p. 13):

In the immediate neighborhood of the mucous canals — I have investigated those only situated
on the head — there also occur dermal calcifications. I find there (in transverse section) in the
floor of the canal (in the neighborhood of the skull) a large plate, and in addition at its sides and
bounding it four to six conical caps of dentine. The development of these is like that of the
denticles, save that the plate contains no pulp cavity, while the lateral small hard structures
present such a cavity, if indeed only in a narrow form, and filled with few cells, whereby they
come to resemble a small denticle. These calcifications are also probably only the rudiments of
former dermal denticles which came to sink down at the same time that the epidermis was invag-
inated to form the mucous canals ; in this process they lost their primitive form and underwent
degeneration. In adult, and especially in a number of fossil Holocephali the slime canals are
surrounded by a great number of closely compressed rings formed of calcified and bony material ;
these had their origin through a process of pressing together the single dentine-like bony caps
noted in the embryo.

In the matter, then, of the character of these plates in living forms, we may again
conclude that they are equally derived from solitary dermal denticles, shark-like in
type. There is no evidence, on the side of embryology at least, that these plates
result from a breaking down of larger structures. It is only necessary to note
further that these structures in Callorhynchus are most marked in their likeness to
the selachian condition, and that they are least marked in the case of Chimaera. \

(c) In all recent Chimseroids numerous denticles are present in the male, i. e.,
on the frontal clasping organ, on the mixipterygium, and on the anterior pelvic
clasping organ. These denticles have a transparent, almost glassy character. In
the frontal clasping organ of Callorhynchus, they occur not only at the tip of the
organ itself, but also proximalward and at the front and sides of the depression into
which this clasping organ fits; but in the other genera, the denticles are limited
only to the tip of this organ. It follows, accordingly, that in Callorhynchus appears
again a more shark-like character, i. e., a greater number of denticles spread over
a larger extent both of the clasping organ itself, and of the sheath into which the

*In a specimen of Callorhynchus " antarcticus" (Australia), measuring 92 cm. in length, the dorsal denticles
have disappeared.

fThe tubercles in the encapsuled Scyllium (de Philippi, Paul Meyer) may well have a similar function. By
Paul Meyer they are described (op. cit., p. 224) as rudimentary organs, viz., the remains of the ancestral annelidan
parapods!

$As to the condition of these dermal elements in fossil Chimaeroids, j>. figs. 138 and 139 ; by evidence thus obtained
the conclusion becomes definite, i. e., that the shagreen of recent forms has been greatly reduced from a condition
altogether shark-like.

jjg CHIM^ROID FISHES AND THEIR DEVELOPMENT.

clasping organ is usually depressed. In this connection we call to mind the great size
of the clasping organ in the young Callorhynchus, suggesting its origin from an
anterior fin spine (cf. figs. 132-137); its small size in Chimaera on the other hand
indicates the later derivation of this genus.

This induction is also supported by a study of the clasping organs connected
with the ventral fins in the antero-pelvic clasping organ of Callorhynchus. We
observe that this structure is furnished with many dermal denticles — 40 or there-
abouts in the case of Callorhynchus antarcticus, according to Dumeril, whereas in
the various species of Chimsera and in Rhinochimaera the number is reduced, varying
usually from about six to three.

In the mixipterygium shagreen denticles occur plentifully. In the case of one
arm of this trifid organ in Chimcera colliei the denticles extend proximally as far as
the base of the organ. In the other two arms the shagreen is limited to tracts
near the tips. An abundant supply of these denticles is, however, present, repre-
senting, in fact, tracts of shagreen. In Chimcera monstrosa, on the other hand, the
amount of the shagreen is less, a condition which furnishes another reason for
regarding this species as the more modified. In Rhinochimczra pacifica, as the
writer has already noted (Jour. Sci. Coll. Tokyo, vol. xix, p. 10), the shagreen at
the tip of the mixipterygium is greatly reduced. In Callorhynchus, on the other
hand, it is as abundant as in the case of Chimara colliei.

. DENTAL PLATES.

These have always been the stumbling-block in comparing Chimseroid with
sharks, for by only superficial comparison have the tritoral areas in the dental
plates of Chimseroids been regarded as equivalent to the teeth or clusters of teeth
in the shark. Nor has paleontology as yet been able to elucidate the problem,
even to the degree in which it has thrown light upon the origin of the dental plates
in the lung-fishes. In fact, as we shall later note, the study of the dentition of
fossil Chima^roids leads us at the present time to no decisive results. The develop-
ment of the dental plates might therefore be looked to to furnish evidence as to the
nature of these structures. For it is well known that through embryology a flood of
light has been thrown upon the mode of origin of the dentition of lung fishes.
Accordingly, we conclude that one of the most important sections of Schauinsland's
memoir on Callorhynchus is devoted to the question of the mode of origin of the
dental plates.

Schauinsland's account, indeed, is of such value in the present connection that
I have been led to quote it in freely translated form (pp. tit., pp. 13-16) :

In even their earliest stages the dental plates are laid down as distinct elements, i. e., four
above and two below, and there is at no time a definite indication that these are composed of
simpler elements which have fused together. The upper anterior plates are certainly simple ;
the remaining pairs, however, show along their hinder (caudal) border a somewhat trifid
arrangement. In this region, too, the plates with their three ridges pass into a fold of the skin,
and here their growth takes place. (No trace appears even in earlier stages of the median
(unpaired) mandibular tooth which has been described in fossil Chimseroids.) If we regard the
three ridges as rows of teeth which have become fused together, they would have obviously a
certain similarity to the dental plates of dipnoi or even of teleosts (e. g., Anarrhichas); and we

THE ORIGIN OF THE DENTAL PLATES. 119

might accordingly regard the anterior plates as premaxillary or vomerine, although in the latter
regard, i. e., re premaxillary and vomerine elements, we query whether we can justly introduce
this comparison in the holocephali. On the other hand, if the comparison be a legitimate one, we
might even go farther and regard the more median ridge of the large plates of the mouth-roof
as equivalent to the fused vomerine teeth, and look upon the remainder of these plates as having
arisen from fusion of the elements in a double row of palatine teeth. Of course, however, such
an interpretation would be purely hypothetical.

One is inclined to look upon the anlage of a dental plate as the product of a single and
enormously enlarged dental papilla, circumscribed by a dermal fold, the induplicature of which is
deepest at the posterior margin of the papilla. The first deposition of hard material begins at the
outer surface of the papilla, and takes the form of a thin cap of dentine, soon, however, the tooth-
substance appears below at the points where the plate is to come in contact with the cartilage of
the head. And almost at the same time trabeculse and lamellae appear between, i. e., in the
substance of the plate, and produce a rneshwork of spongy tooth-substance (pulp-dentine). The
mode of origin of the plate resembles closely that of bone when derived from connective tissue
(e. g., in Sphenodon). The mesenchyme cells in the papilla are collected together closely
at certain points and become transformed into odontoblasts, and from these, peripherally, the
dentine takes its origin. It may be remarked that the dentine is sometimes laid down in an
irregular way, with branching processes, its canals ramifying, unlike the parallel canals of true
dentine. Occasionally trabecules of the dental mass, especially in older individuals, show a
somewhat lamellar structure, and those which are first differentiated, that is, those lying inner-
most, are distinguishable from the later lamellae by their capacity to become stained. As
already noted, the entire dental plate is finally formed of a meshwork of dentine-like material,
whose trabecules thicken with age, so that finally the plate attains a high degree of hardness.
The spaces between the meshwork represent collectively a large, greatly branched pulp cavity,
whose cells in part have retained their former reticular arrangement, in part have become odonto-
blasts, as far at least as they become opposed to the trabecules. In the various ramifications
of the pulp cavity blood-vessels are often present. Enamel is not deposited; nevertheless the
epidermis cells must have a certain influence on the character of the dentine, since the dentine
becomes glassy in character when in contact with the epidermis, but remains unchanged when-
ever the epidermis is lacking. The dental plates are fastened to the head cartilage by means of
a firm layer of connective tissue, which indeed here and there may enter the substance of the
plate, and for still stronger attachment claw-like outgrowths arise from the base of the plate,
especially from its anterior and lateral portions.

Finally, I must refer to the presence of remarkable structures in the dental plates, which occur
only within the ridges above referred to. These take the form of a chalky mass, which appears
in cleared preparations and can be traced throughout the entire length of a dental ridge ; it
is partly inclosed within the meshes of the trabecules of the dentine, and by these partly
again broken up into rounded masses and processes. In transverse section this chalky mass
presents the appearance of a section of a many-rooted tooth, while in longitudinal section its
substance appears continuous, although greatly fenestrated. A more detailed examination
shows that we are here dealing with an especial variety of dentine; that is, differentiated from
odontoblast-like embryonic cells, whose processes grow deeply down and develop canals which
from their parallel arrangement recall strikingly those of typical dentine. In any event, the
material in question can more accurately be designated as dentine than can the remaining spongy
substance of the dental plate. From the latter it is also distinguished in remaining colorless
after treatment with the usual stains for bone, and especially in retaining permanently, even in
the grown Callorhynchus, its soft and uncalcified condition. It may be noted that this soft
dentine is not present in the youngest embryonic stages ; it appears shortly after the caudal ends
of the plate are established and extends gradually from a hindward into a more anterior position.

It has nothing to do with the origin of the hard structures of the plate, since it appears after
these have been laid down. It usually appears somewhat deeper than the outer surface of the
plate ; later it often comes to lie in close contact with it, and even extends thence inward, not
infrequently coming to be associated with the remaining meshwork of the dentine. What the
significance of this structure is remains in any event doubtful, and only with reserve do I express
the opinion that these soft masses of dentine represent the rudiments of former rows of single or

I2o CHIM/EROID FISHES AND THEIR DEVELOPMENT.

already fused teeth, which had primitively passed from behind and taken up a position on the
dental ridges. In the case of these teeth (a similar process occurs in the ontogeny of Cerato-
dus) spongy dentine, or bone-like masses, were differentiated in the course of phylogenetic
development, and these became finally of greater value for purposes of nutrition than the separate
teeth ; and they accordingly fused together, overgrew the teeth, and in the end completely
enveloped them. And since the teeth had no longer their primitive function, they came to lose
their limy structure and degenerated, remaining in the condition in which we see them to-day.
While their arrangement in three rows possibly indicates an alliance with the higher forms,
their mode of successional growth suggests the origin of the rows of teeth of selachians.

The results of the foregoing observations of Schauinsland, it will be seen, are
disappointing to those who on a priori grounds anticipated that the dental plates
of Chimaeroids would in the ontogeny of recent species be found to be formed of
the coalesced bases of separate tooth elements, which, in their turn, would of
course be homologous with those of sharks. One may, nevertheless, I believe,
take a somewhat more hopeful view of this problem, in view of the evidence
above provided. In the first place, however, in order that there may be a better
understanding of the terms of the problem, it will be found expedient to review
briefly the characters of dentition known among the more prominent types of
recent Chimaeroids, for there is room for the belief that Callorhynchus, in spite of
its many archaic features, may prove to have modified the conditions of its dental
plates, or at least parts of them (the ' 'tritors ' '), more completely than some of the
other forms.

To this end we may compare the dental characters of Harriotta with those of
Rhinochimaera, as representing extreme types in Chimaeroid dentition. In fig. 94 A
are shown in Harriotta the dental plates and the roof of the mouth; in fig. 943 the
dental plates, tongue region and floor of the mouth, and, in figs. 940 and 940,
corresponding regions are shown in Rhinochimaera. Contrasting these forms, we
notice that in Harriotta the dental plates are studded with peg-like eminences,
some of which, both in the upper and in the lower "jaws," form together tumid
tracts or ridges. These peg-like eminences, "tritors," are found to pass deep
into the substance of the dental plate; thus, where the plate is flattened and
more or less transparent, as at the anterior margin, the peg-like structures are
seen to pass backward, forming long and narrow cores. These are evidently of
hard, bony texture, for they often stand out from the plate-like ridges when
the intervening basal portion of the plate is worn away. We also observe that the
adjacent mucous membrane of the roof, sides, and floor of the mouth is studded
with distinct papillae. These, it will be seen, correspond to the "tritors," in
size, prominence, and closeness in arrangement, and may, I believe, from the evi-
dence of similar structures in the mouth region of various fishes, be looked upon as
homologous with tooth-forming papillae.* It will thus be observed, as in figs. 94 A,
94 B, that they occur within the stomadeal region; they are absent in the dorsal
wall of the pharynx; they are present, however, on the floor of the mouth, and are

*In a recently published paper on the oral and pharyngeal denticles of elasmobranchs (Proc. Zool. Soc., 1905, I,
pp. 41-49), Imms gives reasons for homologizing similar structures in sharks with teeth. He did not, however, find
the papillae present in the specimen of Chimcera monstrosa which he examined.

COMPARISON OF DENTAL PLATES.

121

continued along the floor and sides of the pharynx. In Rhinochimaera, on the
other hand, the dental plates have become thin and have developed hard cutting
edges, giving the mouth an almost beak-like appearance. In the plates tritoral
areas are reduced to thread-like elements, so delicate that they become difficult to

94*

Fig. 94. — Dental plates, and roof and floor of mouth of : A, B, Harriotta raleighana. C, D, RhinocHimaera pacifica.

distinguish even in the hard anterior pair of "vomerine" plates; and in con-
nection with the obsolescence of the tritoral areas, it is now interesting to observe a
great reduction in the number and size of the papillae of the mouth. Thus on the
roof of the mouth there occur no papillae throughout the wide tract immediately
behind the palatine plates.

122

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

(

Figs. 95 to 103. — Dental plates of Chimaeroids.

Fig. 95. Callorhynchus " calloihynctms " ; 96t Harriotta raleighana; 97, Chimnera phantasma ; 98, C. meditcr-
r«nea;99. C. motubou; 100. C. mitsuturii ; 101. C. affinU; 1 02, C. colliei ; 1 03, Rhinochimirra pacifica.

COMPARISON OF DENTAL PLATES. 123

Comparing now a series of the dental plates of Chimaeroids (figs. 95 to 103),
we may first place side by side those of Callorhynchus and Harriotta (figs. 95, 96).
It then becomes clear, I think, that the ridges in the dental plates of the former
genus correspond to the clustered tubercles in Harriotta, a comparison which is
well borne out by the embryological studies of Schauinsland, for it will be recalled
that the separate ridges of Callorhynchus were shown to consist of a mass of chalky
centers in which the lamellae of dentine were parallel to one another, although their
substance, as was noted, remains uncalcified (cf. fig. 105). A similar state of affairs,
it may be remarked, occurs in the posterior part of the large tumid ridges in
Harriotta, for these ridges and their tritors can be readily sectioned. On the other
hand, the anterior eminences of the same tumid ridges are found to be much harder
than the neighboring bony plate, and may with less question, therefore, be regarded
as representing true teeth. Indeed, it is, after all, a matter of minor importance
that these tritoral elements have never hardened in the case of Callorhynchus; for
when we consider the thickness and hardness of the surrounding bony plate, we
are led to conclude that this may well have usurped the function of the separate
denticles, and that these therefore remain undeveloped. The same rudimentary
condition is probably true of the minute tritoral points which one finds along the
anterior margin of the vomerine plates in Callorhynchus.

Continuing the comparison, one can with fair definiteness understand the
relations between the dental plates of such forms as Harriotta and Chimara
phantasma. For, in the latter, the wide tritors at the base of the palatine and
mandibular plates (fig. 97) are evidently homologous with the clustered tubercles
in Harriotta. In C. phantasma, however, the crushing surfaces of the plate are
smoother and less extended. In C. mediterranea (fig. 98) the dental plates have
become more oblique (slanting) in their manner of attachment, the posterior flange
of the plates intruding deeply below the mucous fold in the roof of the mouth. In
C. monstrosa (fig. 99) the tritoral areas of the palatine plates are less numerous,
while in the mandibular plates they are more abundant, but show less clearly
the peculiar banded structure of the foregoing specimen. In C. mitsiikurii
(fig. 100) the conditions are not widely different from those in the species from the
Mediterranean. A peculiar arching appears in the palatine plates, and the ridges
on the posterior face of the mandibular plates, although smaller, are more con-
spicuous. In C. affinis (fig. 101) the proximal tritoral areas were not observed, and
altogether the grinding margin of the palatine and mandibular plates was narrower.
In C. colliei (fig. 102), while the tritoral ridges on the posterior faces of the pala-
tine and mandibular plates are (usually) conspicuous, the grinding edges of these
plates are exceedingly narrow. And in Rhinochimara pacifica (fig. 103), finally,
we attain a condition, as we have already noted, in which the tritoral areas are
reduced to obsolescence, the entire distal margin of the plate functioning as a
cutting edge.

From what has already been said regarding the dental plates in C. colliei
(p. 19), I think we may safely conclude that a wide range of variation occurs in the
dental plates of Chimaeroids. Thus the tritoral structures may vary in number, size,

I24

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

and arrangement; in fact, one might even go so far as to maintain that from a large
series of dental plates of one species of Chimaera one might obtain variants which,
separately considered, would be placed with other species. Moreover, from the
function of these crushing plates, it is not unnatural that marked differences should
appear in specimens of different ages and from different localities (e.g., from those
individuals which have lived upon different food material). In short, we incline to
the belief that changes in the dental plates of Chimaeroids do not predicate as wide
divergences in lines of descent as one would naturally expect. From the standpoint
of adaptation, furthermore, admitting the extreme value of physiological adaptation
in dental plates within the limits of the present group, we obtain a suggestion why

phylogenetic changes
are not recapitulated
favorably in their devel-
opment. In a form, for
example, like Callo-
rhynchus, in which the
basal (trabecular) por-
tion of the plates has
become greatly devel-
oped in the adult, we
naturally expect that
there will be less oppor-
tunity— shall we say
time ? — for the tritors
to recur in develop-
ment in a separate and
finished form. If they
do appear, they appear
regularly only in
form, soon to be remodeled or erased. Thus we find in

Fig. 1 04. — Callorhynchus callorhynchus. Dental plates and neighboring mouth parts of late
embryo (about 1 10 mm. long). After Schauinsland.

Fig. 105. — Callorhynchus. Detail of middle ridge of mandibular dental plate of specimen
slightly younger (about 95 mm. in length) than the preceding. The dental ridge is seen
as a transparent object. After Schauinsland.

Fig. 106. Callorhynchus. Dental plates of " larva " measuring about 16 cm. After spec-
imen in museum of Columbia University.

"family" or in "generic
Callorhynchus, according to the figures of Schauinsland, that these tritors do occur
in later embryonic stages (fig. 105), although this author does not refer distinctly
to the relation of dermal cusps to tritors in Chimaeroid plates. Following briefly
the problem of the dentition of Chimseroids, we may again refer to the presence of
numerous papillae in the mouth region of these forms. For, by analogies in other
fishes, these structures may well represent rudiments of discrete denticles. It is,
therefore, of particular interest that in the case of Callorhynchus, where the dental
plates are heaviest and largest, we find a corresponding increase in the size of the
papillae. For it may be suggested that papillae which have become calcified either
singly or in groups, have retained their dentitional (and ancient) trend in evolution,
while those which remain soft have survived because they have undergone a
change of function. The similarity in dental and non-dental structures is shown
strikingly in the roof of the mouth of Callorhynchus (fig. 104), after Schauinsland.
That shown in the roof of the mouth of Chimaera (plate ix, fig. 5Oe), although not

DENTAL PLATES OF LARVAL CHIM^ROIDS.

125

as conspicuous, is none the less suggestive when we compare it with the strictly
tritoral conditions shown in Harriotta, fig. 94 A.

DENTAL PLATES OF LARVAL CHIM^ROIDS.

Furthermore, if one compares the dental plates in Chimaeroids of different
stages of growth, one is impressed with the evidence of larval adaptations. The
plates of a Chimaeroid recently hatched (C. colliei*) are surprisingly large in size,
but instead of spreading out in
the form of crushing plates, they
protrude marginally, forming
relatively high edges and
function evidently in cutting.
Moreover, the substance of these
juvenile plates is glassy (cf.
Schauinsland, re vitrodentine)
rather than horn-like or chalky,
and their margins are sharp and
brittle. It is clear, therefore,
that the plates grow during
earlier stages, notably at their
outer or secant margins, and it
is a probable conclusion that
this condition of growth is corre-
lated with the special feeding
requirements of the young. In
later stages the plates broaden
and thicken, the secant edges
become less and less conspicu-
ous, and gradually the tritoral
areas appear. The latter, at

Figs. 107-109. — Harriotta raleighana. Dental plates (somewhat diagrammatic)
of three individuals measuring respectively 10, 49, and 64 cm. At A the
lateral aspect of the vomerine and palatine plates is given.

least in the species examined, are developed first vaguely, in extended tracts or
ridges, and in these there later arise discrete eminences. This is the condition
indicated above in Callorhynchus (cf. also with fig. 95 the juvenile plates shown in
fig. 1 06); it is even more marked in Chimcera colliei, and it is to be observed in
such a form as Harriotta. Of the last form we may introduce sketches of three
stages of the dental plates.* In the first (fig. 107) the plates are frail, although
well formed, and with secant prosilient edges; they have already ridges outlined
and their clouded color (especially in the palatines) is probably due to the presence
of vitrodentine. In the second stage (fig. 108) a number of distinct tritoral emi-
nences appear. And in the final stage (fig. 109), the largest specimen of Harriotta
recorded, the tritors are well differentiated.

*For the privilege of examining this unique material the writer is indebted to the United States National Museum.
He wishes especially to express his thanks to its Assistant Secretary, Mr. Richard Rathbun, and to its assistant
curator of Fishes, Mr. Barton A. Bean.

126 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

From the foregoing characters in "larval" dental plates, and they are certainly
in the general line of Carman's observations,* we conclude that among the many
specializations in the young Chimaeroid may be included a larval dentition, i. e.,
preceding the appearance of tritors. It may also be remarked that the tritors
themselves, when they come to appear in the different forms of Chimaeroids, occur
in point of time in interesting sequence. In Callorhynchus they appear in the
embryo (95 mm.), while it is still encapsuled, but they fail to develop into typical
structures; in their place there appear calcined ridges representing collections of
tritors. In Harriotta tritors become functional at a period shortly after hatching,
and from this time onward increase both in size and number. In Chimaera they
occur at a later period, develop slowly, and even in the adult are relatively few, and
the plates themselves early develop secant margins. In Rhinochimsera, finally,
they appear only in the adult, and even then in rudimentary form. In the Chim-
aeroid series, there is thus, I think, such evidence of progression, even in recent
forms, that we can hardly assume with Carman that from a condition like that in
Rhinochimsera arose the dental plates of the other genera. On the contrary, in the
case of Rhinochimaera we are dealing evidently with a terminal form, one in which
the tritors fail to develop perfectly even in the adult, f

CONCLUSIONS CONCERNING THE DENTAL PLATES OF RECENT CHIM^ROIDS.

A comparison of a series of the dental plates of recent Chimseroids, as we
have seen, strengthens the view that these structures are compound, i. e. , formed of
separate denticle-like elements, homologous with the dental plates of certain sharks,
e. £-., Cestracjonts. The tritors, according to this view, represent dental eminences,
simple or compound. But more doubtful is the homologue of the dental plate
itself. It may represent either the fused bases of teeth like the Cestraciont, or
a structure entirely sui generis, i. e., fused by a hardening of the connective tissue
accumulated around the bases of the true dental plates. According to the observa-
tions of Schauinsland the embryological facts support more or less distinctly the
origin of the tritoral ridges from many tooth-like eminences dentinal in structure.
On the other hand, the same evidence tends to regard the substance of the dental
plate itself as independent of the tritors. An examination of the larval dentition of
Chimaeroids throws, I think, a side-light on the foregoing discrepancy, for it is found

*Garman, however, interprets these characters (Proc. New Eng. Zool. Club, 1901, vol. n, pp. 75-76) not as larval-
isms, but as primitive ; thus, according to him " the teeth of Rhinochimsera are of a much less differentiated form than
those of any other of the recent genera of the group ; that is, their later stages are more like the earlier, and presum-
ably more like the teeth of primitive Chimaeroids ; they approach those of the extinct myriacanths and the very early
conditions of the teeth of other living Chimaeroids, Chimaera, Callorhynchus, and Harriotta. In advanced stages the
teeth of Harriotta differ from those of Rhinochimiera in possessing several series of tritors which in superficial aspect
resemble, in shapes and arrangement, certain crowns of placodont teeth. On the teeth of Rhinochimaera there are no
tritors ; the teeth of the very young of the other living genera are similar ; this no doubt is a mutual resemblance to
those of a common ancestor, an index to derivation. ' To this interpretation, on the other hand, there are

two somewhat critical objections : (i) that in Rhinochimaera, as this author has later observed, there are present tritoral
points, small, it is true, but tritors none the less ; and (2) that his conception of the dental plates of fossil Chimasroids
(t. g., Myriacanth) is not valid, for whatever be the puzzles of the dental plates of fossil Chimaeroids they have always
tritoral areas.

fThey may be expected to appear in a more perfect condition in very old individuals, somewhat as they develop in
the late rather than in the young larvae of Chimaera.

SKELETON. 127

that the dental plates of the adult are attained only after a process of metamor-
phosis, during which the marginally high, delicate, glassy, and secant plates of the
young are worn down and give rise to the adult dental plates, broad and thick, studded
with tritors. Obviously, therefore, if we accept the view that a larval dentition is
present, it is clear that the substance of the dental plate can better be regarded
as a "precocious segregation" of the basal elements of teeth, i. e., along the outer
marginal rim of the plates, than as a new and independent accession to the
materials of development. All will admit, however, that the requisite proof of this
conclusion can be presented only by paleontology. On a later page the evidence
in this regard is summarized.

SKELETON.

The vertebrate column of Chimaeroids represents, according to Hasse (1879) a
polyspondyly, which he regards as typifying the ancestral condition in sharks. The
column of Callorhynchus was examined from the standpoint of embryology by
Schauinsland, whose conclusions I summarize as follows :

That the early growth of the chordal sheath resembles that of many sharks,
inasmuch as its substance is invaded gradually, and only at few points, by mesen-
chyme cells. That cartilage appears quite late in development. That in each
segment (metamere) appear both neural and interneural plates, as well as corre-
sponding (i. e., double) haemal arches, especially throughout a greater portion of
the tail region. That these cartilaginous arches do not grow around with their
bases the secondary chordal sheath; this is only overgrown by a stout sheath of
connective tissue; the latter together with the arches on the one hand and the
secondary chordal sheath on the other forms the secondary vertebras, but the
secondary chordal sheath is not divided into separate (primary) vertebras — the
segmentation of the column being indicated only through these parate arches.

Schauinsland, in brief, has been able to find no vertebral centra, in the sense
in which they occur in other fishes ; and my own studies upon Chimssra have been
no more successful in this important quest. No centra are found in either early or
late ' ' larval ' ' stages. Nor do they occur, as I suspected they might, after the
fashion of gerontic structures, in very large individuals. At the most, in the latter
case, there was a fusion of neural and hsemal arches occurring in the region near
the occiput, but nothing which could be interpreted as definite centra. There is
still, none the less, the possibility that some form of centra were represented in the
ancestral Chimssroid, and that they were gradually lost in ontogeny; indeed, as we
shall later note in the Jurassic Squaloraja and Myriacanthus, centra appear to have
been present in the anterior region of the column (figs. 138 and 140 c), where in all
recent Chimaeroids, indeed, the most perfect neural and haemal supports appear.

The development of the skull has already been illustrated in several stages of
Callorhynchus by Schauinsland, and in a single late stage of Chimaera by the
present writer. The results of their observations are briefly these : The chimaeroid
cranium, instead of developing as a uniform trough-like brain-case (shark), appears,
even in early condition, in a wonderfully complete form ; it incloses the hindbrain,

128 CHIM/EROID FISHES AND THEIR DEVELOPMENT.

the forebrain, and the nasal region ; and it early develops conspicuous ridges which
evidently support and protect the eyes. And it is the latter organs, it may safely
be said, which have played the most important part in modifying the growth of the
cranium. For the orbital region is of enormous size, occupying no less than 50 per
cent of the entire length of the cranium;* and, correlated with this, between and
above the huge optic capsules, the growth of cartilaginous structures is retarded.
It follows, accordingly, that while the posterior and anterior parts of the chondro-
cranium are well developed, its mid- or orbital region is largely unformed, and this
is, I take it, the reason, the principal reason, that holocephaly has been developed,
to weld strongly together the anterior and posterior parts of the crani^lm where primi-
tively the orbital walls came to be suppressed as the eyes increased in size. Certain it is
that the wide palato-quadrate elements extend like firm beams between the anterior
and posterior moieties of the skull, and afford at the same time a support for
the great optic capsules. And in this result appears a suggestion why the palato-
quadrates appear so early and are so large in size; in fact, in no stage examined
has it yet been found that these palatine elements are altogether separate from the
cranium. In the earlier stages described (Callorhynchus) they are separate only for
about half their length, and from the details of that stage it is even doubtful whether
greater separateness ever occurs in the development of this element, earlier stages
showing probably a prochondrial continuum — very much as one sees it in the
prochondrium of the paired fins of sharks. The skull of the Chimaeroid, in a word,
is specialized even in early ontogeny ; witness, among other regards, the enormous
size of the posterior clinoid process, the huge fosse for the infundibulum, the exag-
gerated preorbital processes, the median frontal crest, and the interorbital vacuity.

It is true, on the other hand, that certain skeletal structures in the chimaeroid
head retain a primitive character — possibly because they have been spared func-
tional changes by the very fact that the palato-quadrate element has fused with
the cranium. As primitive features we may here mention: (i) The perfect
condition of the copulse of the branchial arches. (2) The presence of a pha-
ryngeal element in the hyoid arch which resembles the pharyngobranchials of the
hinder arches. (3) The relatively large and discrete labial cartilages, as probable
premandibular arches, and finally (4) the presence of a symphyseal cartilage as
(Schauinsland, K. Fiirbringer) the probable serial homologue of a basihyal. These
characters are expressed, slightly schematized, in fig. in, and may be compared
with the corresponding structures in sharks (fig. 110). In these figures serially
homologous parts are indicated by shaded or unshaded areas.

It should be mentioned, in passing, that even the branchial region of Chimaeroid,
in spite of the foregoing primitive characters, is not without convincing evidence
of precocious specialization — witness the early appearance of the supporting extra-
branchials of the hyoid arch, which are prophetic of the opercular flap of the adult.

The problem of rostral cartilages receives no evident solution in Chimseroid
development. The anterior azygous process of selachians, which rises from the

* In the skull of the shark ( e. g., Scyllium ) at a corresponding stage the orbit occupies about 30 per cent of the
entire length of the cranium.

ROSTRUM, BRANCHIAL-ARCHES, FINS.

129

nasal septum (usually its base) is probably represented in the element which
Schauinsland has figured as sp in his plate xvn, figs. 1 24, 1 26. However, in
the Chimaeroid the rostral supports (rl and r2) later developed into long and
separately jointed elements. Quite doubtful, on the other hand, are the homo-
logues of the paired dorsal elements in the selachian rostrum, those figured,
e. g., by Kitchen Parker in Trans. Zool. Soc., vol. x, plate xxxvm, fig. i, as btr;
they are possibly the homologues of Schauinsland's elements ^ in the figures quoted.
Equally doubtful is the more dorsal azygous element (Schauinsland's rV v. the
present fig. in), which folds forward and becomes a main support of the produced
snout in Callorhynchus; it certainly finds no homologue in sharks, and in view of the
history of the frontal clasping organ in Chimaeroids (v. figs. 132-137) I am inclined
to interpret it as an element, i. e., a fin support, transposed from a hinder position, *
a view which is the less difficult to accept when one considers the metamorphosis
to which the head roof has been subjected by the precocious growth of the eyes.

M

Figs. 1 10 and 1 1 1. — Skull and branchial arches of Shark and Chimaeroid compared.

7?1-Z?5, Branchial arches; -B ^f , basihyal ; b tr, basis trabecularum (Kitchen Parker) ; C, copula; C/?, ceratobranchial; Ell, Epibranchial;
H B, hypobranchial ; I' , " anteriormost lip cartilage " (Kitchen Parker); Af, mandible ; PR* pharyngobranchiaL

The history of the fins and their supports, finally, gives additional evidence as
to the modified nature of later Chimaeroid development. We may comment, for
example, upon the appearance of lobate dorsal fins, the anterior with its spine, at
an early period, and the prominence of the paired fins, the pectoral, for example,
having at one time a greater proportional size than in the adult. We observe also
the precocious appearance of the mixipterygia and the antero-pelvic appendages
(note especially plate ix, fig. 5of; also fig. 90, and Schauinsland's Taf. xvi, figs.
120 and 125), a well-marked character which in such earl}' embryos can hardly be
regarded as primitive. Nor is the plan of development of the paired fins to be
looked upon as yielding any evidence in favor of Gegenbaur's archipterygium
theory. Thus, the pectoral, for example, appears not as a lobate organ, contracted,
shortly to bud out radial structures, but as a lappet of a lateral fold which shows in
the early stages distinct metameral elements (cf. especially plate vm, fig. 49, and
Schauinsland's Taf. xxiv, fig. 174).* The paired fins, in short, develop like those of

*This translocation of anterior fin-rays is by no means uncommon, associated, too, with change of function, e. g.,
Lophius, Autennarius, etc. Even the sucking disc of Remora might here be cited.

130

CHIMvEROID FISHES AND THEIR DEVELOPMENT.

young sharks, save that, as in the case of many other chima^roid structures, the rate
of growth is accelerated; the lateral-fold beginnings extend over fewer body segments
and are higher (proximo-distally), leading us to conclude that in this mode of
early fin growth the Chimsroid exhibits the same relation to the shark that the tel-
eost bears to the ganoid. Especially convincing evidence as to the modified nature
of the chimsroid fin is produced by the development of the ventral "claspers"; for
these, the antero-ventral hooks and the mixipterygia, are to be regarded as highly
modified radials. The antero-ventral clasper, it is clear, has not yet been evolved
in the sharks, unless the greatly enlarged anterior lappet of the ventral fin be
regarded as its equivalent ; but there is good foundation for the belief that in
Chimsroids between the antero-ventral organ and the compressed lappet of the

B

Fig. 1 1 2. — Ventral fin and appendages in Chimaera colliei.

A, Fin of young specimen (31 cm. in length) ; ventral aspect showing mixipterygia and antero- ventral clasper, the latter still connected by dermal crease with the
anterior rim of fin ; C, mixipterygium with lips unfolded ; B, skeleton of foregoing fin, showing the arrangement of the supports (radials) of the branches of
the mixipterygium ; C, skeleton of fin, adult : D, skeleton of ventral fin of Cestracion (Heterodontus japomcus), adult, for comparison with foregoing.

pelvic fin there formerly existed a number of radialia ; witness, for example, the
rudiments of the segmentation of the basal plate from which the antero-ventral
organ arises (fig. 112, nerve and vessel openings in B and c),f or better still, the
radials which persist in the anterior reach of the fin of the Jurassic Chima^roid,
Squaloraja (fig. 138, ar). The mixipterygium also bears testimony to having
been closely connected with the radials of the base of the fin; thus in one stage in
development, cf. fig. 1 1 2 B, the base of the mixipterygium bears rudiments of
radialia, and the trifid tip is in itself a relic of a clustering of distal radials. These
observations are clearly in line with Jungersen's, who, while admitting that the
"appendix-skeleton of the Holocephales is of less compound construction than that
of Plagiostomes," calls attention to the "wide separation of the whole organ (i. <?.,)

*In the adult Chimaeroid the basal articular element of the pectoral fin is usually termed (as in Cestracion)
mesopterygium, and it is regarded (Gegenbaur, 1901) as including also the propterygium ; Schauinsland, however,
has shown (op. cit., Taf. xxiv, fig. 174) that the bibasal character of the fin is due to the obsolescence of the
metapterygium. The articular basal is, therefore, the propterygium. With this result the present writer is in accord.

fThis conclusion was originally suggested by Gegenbaur (1901) on the evidence of adult anatomy.

VISCERA.

the mixipterygium) from the fin proper ; the highly specialized form of the primary
skeletal parts — against the simpler form in the Plagiostomes (as the simple rod-
like shape of the terminal joint * * * )," the presence of "particular copulatory
organs," and infers finally that "the Holocephales by no means occupy a primitive
position among the Selachians." (Danish Ingolf Exped., n, pp. 20-21).

VISCERA.

In the development of its viscera, also, Chimsera indicates a high degree of
specialization. This, for example, may be noted in the following structures:

Mesenteries. — No continuous mesentery is observed even in later embryonic
stages of development. Thus, in the embryo shown in plate vn, fig. 45, the
mesentery is clearly reduced to the string-like supports for vessels and ducts which
characterize the adult. In the same stage only a rudiment of a ventral mesentery
is present.

Gut. — In no stage is the gut of the same proportional length as in the shark.
In the latter (Pristiurus) the length of the digestive tract (measured from mouth to
anus) decreases in length between stages K to o from 55 per cent to about 50 per
cent of the total length of the embryo; in Chimaera in similar stages from less than
30 to about 15 per cent. In other words, the gut of Chimsera develops in a much
more restricted body region; and from early stages it appears as a short tube of
wide caliber. The stomach dilatation, we may thus conclude, fails to become
expressed, and the intestinal valve, instead of undergoing the further spiral devel-
opment of sharks, makes but a few turns (about four) and then increases rapidly
in the width of the infolded band.

Gills. — The gills exhibit greater changes in their "metameral" series than
sharks. Thus the hyobranchial cleft, even in as early a stage as K, is notably the
largest and by stage o the opercular fold has attained almost its adult proportion.
On the other hand, the fifth gill-furrow, although clearly indicated, e. g., stages
K, L, M, fails to become a functional gill-slit. And the spiracle, even in a favorable
stage, is little more than a tubular rudiment; it never develops respiratory filaments
and is lost by stage N. Another evidence of precocious development is shown in the
mode of growth of the external gills. These filaments are from the beginning
(about stage K) of large caliber (cf. Schauinsland's Taf. xiv, fig. no), i. e., they at
once assume nearly their functional size. Accordingly they do not arise in a
uniformly developed vertical series, but on account of their extraordinary diameter
bud out one after another as the gill-bar increases in size. Their later specialization
in developing blood-producing dilatations has already been noted (pp. 60, 106).

Kidney. — The restricted length of the visceral cavity is accompanied by modi-
fications of the excretory system. Of the pronephros I am unable at present to
give a detailed account, and will note only that it is smaller and more difficult to
trace than in the shark. The mesonephric tubules, on the other hand, are long and
coiled irregularly ; they appear early and are clustered in a deep stroma along
the dorsal wall of the body cavity. Their early condition, therefore, does not,

132 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

embryologically at least, indicate a primitive segmented condition (Redecke), and
I am led to suggest that the "segmentation" of the kidney of the adult arose
secondarily. The absence of the Geschlechtsniere in Chimseroids, moreover, I also
interpret as a secondary reduction, an accompaniment of the enormous develop-
ment of kidney in a short body cavity, a process which caused an enlargement of
functional nephric tubules, an obliteration of rudimentary ones, and more direct
and special means of carrying out gonadial products. In favor of the last inter-
pretation are the great size and elaborate regional differentiation of Wolffian and
Miillerian ducts.

NERVOUS SYSTEM.

The following features in the development of the system may be mentioned as
indicating that the Chimaeroids have been subject to wider changes than kindred
sharks.

Rcdiiction of Cord. — The cord in the region of tail and hinder trunk, repre-
senting about 60 per cent of its entire length, is greatly modified. Contrast in this
region the diameter of the cord, its histological differentiation, the size, number,
and character of the roots of the spinal nerves. The flattening of the cord in the
hinder trunk and tail region is, therefore, hardly to be compared to the condition
in Cyclostomes.

Flexure of Brain. — In Callorhynchus (cf. Schauinsland's Taf. xxn) the brain
shows extraordinary flexures; in the region of the midbrain its axis changes direc-
tion by almost 180°.

Size of Infundibrihim. — In early stages the infundibulum attains great size;
and concomitantly the dorsal wall of the diencephalon is compressed between the
forebrain and the optic lobes.

Separation of Hemispheres. — In this regard the early condition is more marked
than in any other fish-like vertebrate. Observe also the separation of the entire
forebrain from the midbrain. This in Chimaera begins in early stages and in the
adult attains remarkable proportions.

III. FOSSILCHIM/EROIDS:
THEIR SIGNIFICANCE IN THE STUDY OF RECENT FORMS.

The evidence of paleontology in the problem of Chimseroid descent is import-
ant, although one must frankly admit that it is still lacking in essential details, for
not only are fossil Chimaeroids rare, but they occur with but few exceptions in
fragmentary form.

An outline of the distribution in time of the genera of Chimaeroids is shown
at the bottom of page 134. In this has been omitted reference to the supposed
Silurian Chimseroid Dictyorhabdus prisons Walcott, for reasons which are stated
below. Among the genera given, it will be seen that three, doubtfully Chimseroid,
are Devonian, representing together about 16 species; one, probably a Chimseroid,
is Permian, and four are exclusively Jurassic. From this time onward the greatest
number of genera flourished in the Cretaceous, representing at least 50 species, and
one of these genera, Ischyodus, extends from the Jurassic into the early Miocene.
Another, a Cretaceous genus, Callorhynchus, is, as we have seen, represented by
half a dozen species at the present time.

With this plan of distribution in mind, we may summarize our knowledge of
fossil Chimaeroids with reference especially to their advancing characters.

THE QUESTION OF A SILURIAN CHIMSEROID.

Palaeozoic Chimseroids claim evidently our closest attention, and we should
consider first of all the question of the "fossil Chimseroids" described by Walcott in
1885. At Canon City, Colorado, in the Ordovician (Upper Silurian), the United
States Geological Survey obtained a number of narrow, ribbon-shaped fossils which
were described by Walcott as Dictyorhabdus prisons, and were regarded provision-
ally, on account of their general shape and transverse striation, as vertebral
columns of a chimseroid fish.* In spite of the relative abundance of these fossils,
however, no Chimaera-like dental plates, spines, or kindred structures were found,
a condition the more remarkable since in the matrix there occur innumerable frag-
mentary "fish" remains. It is therefore doubtful whether so delicate a structure as
the vertebral column of a Chimseroid would be preserved if no traces were present
of associated spines, heavier cartilages, and dental plates. The chimaeroid nature
of the fossils, moreover, becomes more doubtful still if they are closely scrutinized.

*Walcott, it should be stated, refers doubtfully to their chimaeroid nature. The "correlation is based entirely
upon the resemblance between the fossil form and the calcined sheath of Chimccra monstrosa. This resemblance is
too striking to be passed over, although there are certain differences that render it of less value in classification than
at first."

133

134

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

In the type specimens (e. g., one shown in fig. 113) we note that the calcified
"rings," which were compared to the "centra" of Chimaera, are not rings at all,
in the sense that they occur in, for example, Squaloraja, but suggest rather a series
of more or less irregular lines of growth. These, indeed, are not transverse to the
long axis of the fossil, but at one side pass obliquely into root-like processes, com-
pared by Walcott to "lateral rib-sockets or supports," structures which, it must be
admitted, are altogether unknown in chima^roid anatomy. The foregoing evidence,
accordingly, seemed inadequate for associating this fossil with Holocephali, and an
examination of the types in Washington did not yield me any more convincing
basis of comparison. Nevertheless the very suspicion of a Silurian Chimaeroid was
of sufficient interest to warrant an attempt to secure more perfectly preserved
material.

Accordingly, in 1896, I took the opportunity of visiting the type locality, and
may now add the following details :

The horizon, the age of which is now generally admitted to be Ordovician, was
readily located, and Dictyorhabdus was found to be fairly abundant. A day's
collecting trip made in company with Mr. Burbadge of Canon City, to whose kind
guidance I am greatly indebted, resulted in obtaining about a dozen "columns" in
lengths averaging between one and two inches, together with numerous fragments;

Distribution of Chimceroids in Time.

j

B
I

C/3

"o

d

55

Devonian.

Carboniferous.

Permian.

Triassic.

1
Jurassic.

Cretaceous.

Eocene.

Miocene.

Pliocene.

(2

Rhynchodus

5

Squaloraja

Chimaeropsis

Ischyodus ( — Aletodus)

27

x

?x

Leptomy lus

Klasmodectes

I

Rhinochimaera

Chimaera

8

DEVONIAN CHIM^ROIDS.

135

and upon a closer examination of these remains, I was more than ever convinced
that they could not be associated with a Chimaeroid. In the first place, in well-
preserved specimens the striae are sometimes continued longitudinally above the
"rib sockets," showing, in other words, that they were absolutely unlike vertebral
centra. (Cf. fig. 114, /.) Furthermore, and this is, I believe, most convincing,
several of the fossils showed a delicate flaring out at one end, like the mouth of a
trumpet, which at once suggested the lip of a molluscan shell ; a character in any
event distinctly non-vertebrate, not to say un-Chimseroid. I am also permitted to
state that it was the view of Professor Cope, to whom my specimens were shown,
that the "columns" could have nothing to do with vertebrates. It is probable, on
the other hand, that they represent fragments of the shells of mollusks, possibly
Cephalopods.*

Figs. 113 and 114. — "Vertebral columns" of "Silurian Chimaeroid," Dictyorhabdus

priscus Walcott. The first figure after Walcott.
t, oblique laminar in the structure of the fossil, suggesting lines of growth.

Fig. 115.— Dental plates of Men-
aspis armata = Chalcodus (permi-
anus). Kupferschiefer. After spec-
imen in Berlin Museum.

DEVONIAN CHIJVL-EROIDS.

Chimaeroid remains, or, more accurately, what are generally accepted as such,
are widely distributed throughout the middle and especially the upper Devonian
rocks of northern Europe and North America. These are referred to the family
Ptyctodontidae, Unfortunately for accurate diagnosis the fossils are fragmentary
and the best results which can be obtained from them are briefly these: That in the
three genera — all at present known — Ptyctodus, Rhynchodus, and Palaeomylus,
dental plates were present which resemble closely those of Chimaeroids. On the
other hand, these plates were only four in number and their tritoral characters are
puzzling. Within the substance of the plate appear not a few tubercular tritors,
but a general series of tritoral points, sometimes arranged in lamellae, which in
turn may form a series of flat or curving surfaces tritoral in function. The tritoral
points are most conspicuous in Ptyctodus (fig. 116), where they form lamellae. In
Palaeomylus (fig. 117) they spread out diffusely, and in Rhynchodus (fig. 118) are
drawn together close to the rim of the plates, forming thus an extended sectorial

*The cephalopod nature of Dictyorhabdus was early commented upon by Hyatt, a reference which I had over-
looked and for which I am recently indebted to my friend, Dr. C. R. Eastman.

136 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

margin. These conditions are shown in lateral (outer) aspect in figures 126-129.
It may be added that there have been found (Eastman) a few detached plates
of Ptyctodus (in the Hamilton limestone) resembling those of Myriacanthus as
figured by Woodward (Cat. Foss. Fishes, vol. 2, pi. 2, fig. 2, a). Also that in
Rhynchodus the shape of the meckelian cartilage is known (fig. 127). These char-
acters, it will be seen, yield strong evidence in favor of their chimseroid nature.
On the other hand, we must admit the possibility they may yet have belonged to
some early specialized offshoot of a selachian stem which may not have given rise
to true Chimseroids. Thus they may have greater affinity with the Sandalodonts,
in which very similar tritoral points occur, or to Deltodonts or Cochliodonts, forms
which on fairly strong evidence are regarded as selachian. As to Ptyctodontids it
must frankly be admitted that there is nothing accurately known as to the form of
body, character of fins, and the possession of spines. In the latter regard, however,
it is fairly probable, as Eastman and others have shown, that the spine Phlyctsena-
canthus is to be regarded as belonging to Ptyctodus. And it is not impossible
that Belemnacanthus and Heteracanthus were associated with members of this
group. Harpacanthus and Cyrtacanthus may also have belonged to a Chimgeroid.
But spines of this character, we must admit, might be associated almost equally
well with cestraciont sharks.

The main virtue in the study of Ptyctodontids is to the writer this — that they
present some evidence (i) that Chimaeroids are of Devonian stock; (2) that at this
early period their dental plates were still but four in number, representing the
dental structures of the jaw halves of sharks; and (3) that the tritors existed as
small points forming together a texture in the dental plates which is well known
among early sharks. The evidence, in short, leads us to conclude with fair proba-
bility that the vomerine plates of Chimseroids were a later acquisition.

In connection with these earliest "Chimseroids" there should be mentioned
the obscure group of Petalodontids, which occur abundantly throughout the Carbo-
Permian and were in some regards Chimsera-like, though it is more probable that
they represented forms of sharks which were not closely related to the ancestral
Chimseroid, but were rather examples of parallelism. It is none the less noteworthy
that in such a form as Janassa the dental arrangement, although still retaining
discrete elements, suggests the formation of tritoral plates. Thus, we find that the
dental elements are crowded into the axial line of the mouth and are here provided
with interlocking ridges, which might well serve as the point of departure for the
evolution of tritors. In this event, the tritoral points would represent not each one
an individual tooth, but only a very small portion of a tooth. It may further be
shown that Janassa was singularly chimseroid in the possession of a stout jaw,
thick and solid at the symphysis, and of remarkably large labial elements. Finally,
referring to Jaekel's reconstruction, it may be pointed out that Janassa possessed
a distinct antero-ventral fin lappet which appears to the writer to correspond more
accurately to the antero-ventral clasping organ of a Chimgeroid than to an enlarged
fin ray of Raja, with which Jaekel compares it. In short, there is at least the
suggestion that in such a form as Janassa was represented a shark which had

FOSSIL CHIM^EROIDS.

137

Figs. 1 16-120.— Association of denial plates of early Chimaeroids.

I 16, Ptyctodus, restored dentition, after specimens in Museum ol Comparative Zoology, Cambridge, Mats.

117, Paleeomylus, after specimens in Newberry collection, American Museum of Natural History.

I 1 8, Rhynchodus, after specimen in Newberry collection, American Museum of Natural History.

I 19, Myriacanthui, after specimens in the British Museum, and in the Jermyn Street collection ; the tritoral areas of the two anterior

pairs of plates in the upper jaw are shown in detail in fig. 119 A.
1 20, Squaloraja, after specimens in the British Museum, and in the Museum of Comparative Zoology, Cambridge, Mass.

138

CHIM^ROID FISHES AND THEIR DEVELOPMENT.

evolved a long way in the direction of the Chimseroid. On the other hand, we
must leave entirely doubtful whether Janassa was still retaining the features of an
ancestor which gave rise to the Chimseroid, or whether it was a form which was
becoming still more Chimsera-like than its ancestor — just as Lepidosiren has
become more like the amphibian than has the more primitive Ceratodus.

Figs. 121-125. — Association of dental plates of late mesozoic Chimeeroids. Tritors represented by shaded areas.

After specimens in British Museum. Partly after Smith Woodward.
121, Ganodui ruaulosus ; 122, Elasmodus hunteri; 123. Edaphodon bucklandi; 124, Uchyodu: egertoni ; 125, Elasmodectcs willetti.

The Permian fossil Menaspis should also be mentioned in this connection.
Whether, however, it can be regarded as Chimseroid has already been considered
by the present writer in a recent number of the American Geologist (vol. xxxiv,
pp. 49-53). It was there shown that the size of the dental plates of Menaspis
(fig. 1 1 5) indicates that the entire region of the fossil inclosed with spines is to be

JURASSIC CHIM^ROIDS.

139

regarded as belonging to the head. It was noted, further, that the peculiar fibro-
cartilage spines, characteristic of Menaspis, may be interpreted as homologous with
the so-called lip cartilages of the later Squaloraja; on the other hand, the paired
head spines of Menaspis correspond with those later seen in Myriacanthus, although,
naturally, they were less highly specialized. If, accordingly, Menaspis proves to
be a Permian Chimseroid, it certainly simplifies the problem of Chimaeroid descent.
It indicates a shark-like form having four dental plates (fig. 115), like Deltodus or
Sandalodus, and a dermal armoring which advanced pari passu with the develop-
ment of the dentition.

Figs. 1 26- 1 3 I . — Associations of dental plates in fossil Chimaeroids. Lateral aspect.

126, Ptyctodus; 127, Rhynchodus secans (attached to the mandibular dental plate is shown the outline of the entire meclcelian cartilage) ;
1 28, Paleeoraylus greenei ; 1 29, Palfcomylus crassus ; 1 30, Myriacanthus paradoxus ; 131, Uchyodus.

JURASSIC CHIM/EROIDS.

Our definite knowledge of early Chimseroids does not, however, begin before
the Lias (Lower Jurassic), when remains of Squaloraja and Myriacanthus occur,
notably in the fine-grained limestones of Lyme Regis. In this favorable matrix
Squaloraja is so perfectly preserved, even in its cartilaginous parts, that we are
enabled to reconstruct its essential characters. As shown in fig. 138, it appears
as a somewhat flattened form; its vertebral column is strengthened with fine,
closely set, ring-shaped thickenings which resemble those of a typical recent Chim-
aeroid ; the cranium is autostylic (Traquair) and bears in the male the frontal
clasping organ, which here is long and spine-shaped (figs. 137, 137 A, 138, and detail
in fig. 139), situated immediately in front of the eyes and folding forward. The
orbits are large, and between them the breadth of the cranium suggests that the,

140 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

brain was shaped like that of a shark. Of dental plates (fig. 120) there are three
pairs; the meckelian and palatines resemble one another closely, thus suggesting
the doubtful Devonian forms. In front of the palatines now occur, for the first
time among Chimaeroids, a pair of "vomerine" plates, oblong and tumid. In these,
as in the other dental plates, tritors occur, in the form of conspicuous lamellae. The
mouth was probably delicate and, judging from the position of the dental plates,
it opened widely, far more shark-like than in any recent Chimaeroid. At either
side of the mouth region appear three conspicuous outgrowths, fibro-cartilaginous in
structure, forming together the marginal framework of this region of the head. These
structures, although shown in many specimens, are none the less too imperfectly
preserved to warrant a definite conclusion as to their relations. By some authors
they have been regarded as spines, by others as direct outgrowths from the trabec-
ular region of the cranium. The anterior pair may represent the paired rostral
cartilages of recent forms. The two posterior pairs are possibly labial cartilages.
A conspicuous rostrum is present, unjointed at its base, and defended on the dorsal
side by marginal rows of stout dermal denticles (fig. 1 39). Adjoining the rostrum
the snout was narrowed, and in this region were apparently areas representing
the pellucid spaces on either side of the rostrum in recent Chimseroids and in such
selachians, for example, as Rhinobatus and many rays. In the occipital region of
the cranium a large, median, elliptical fosse was present, at the base of which there
were probably openings into the otic region. Below this fosse one can sometimes
trace the anterior end of the column, advancing into the floor of the cranium as far
forward as between the orbits, and showing even in this region ring-like peripheral
thickenings. It is interesting in this connection to observe that a well-marked
occipital joint was present between cranium and column, and that in a single
specimen (Harvard Museum No. 1147, Pal. Coll., which through the kindness of
Dr. Eastman was generously loaned me) the anterior portion of the column shows
traces of a coarser segmentation, which indicates, outwardly at least, cyclospondy-
lous vertebrae (fig. 138 A).

In dermal characters Squaloraja was distinctly shark-like. The entire body
was covered more or less thickly with shagreen, and at certain points the denticles
attained considerable size, <?. g. , on the sides of the rostrum, near the base of the
clasping spine (detail in fig. 139), along the sides of the tail, on the dorsal side,
near the base of the paired fins, on the clasping organs, and almost as spines in the
suborbital region. Here they form so firm a mass that the ring below the eye is
preserved as a conspicuous character of the fossil.

Girdles and the cartilaginous supports of the paired fins are distinctly Chimae-
roid, e. g., in location and proportions. The stoutly developed shoulder-girdle is
similar in form to that of a recent genus; it is not known whether the bi-basal
arrangement of the basalia occurs in the pectoral fin, but it is certain that the radial
cartilages, about 30 in number, are arranged in a manner strikingly like those of
Chimaera; their marginal extension was also modern in plan. In the ventral fins, on
the other hand, more conservative conditions prevail, for the radial cartilages were
probably 1 8 to 20 in number (about one-third more numerous than in recent forms),

JURASSIC CHIM^ROIDS.

141

and extended in
their lines of attach-
ment forward as far

as the antero-lateral clasping organ.*
This is of particular interest, since it in-
dicates, as we have already noted, that
the antero-lateral clasping organ was
probably, as Gegenbaur, Carman, and
Agassiz suggested, a modified radial car-
tilage (possibly a number of radial car-
tilages), but up to the present time
there has been no evidence which has
bridged the wide gap between the antero-
ventral clasper and the true radial
cartilages. The condition of the mixip-
terygium is also significant, for it is here
short and wide, its base in one specimen
suggesting clearly its origin in a cluster
of radial cartilages. One observes, also,
that the shagreen which encases this
organ is not limited to its tip, but extends
proximally almost to its base, a condition
which has been retained so completely
in no living Chimseroid. It may be
noted, finally, that a mucous-canal sys-
tem is present whose supports are
arranged in rouleaux of minute rings, a
condition which exists in a somewhat
rudimentary form in recent genera.

Summarizing, then, our knowledge
of Squaloraja, we find that this early
Chimseroid was shark-like in the follow-
ing regards: (i) In dermal defenses,
exhibiting as it does an investiture of
shagreen. (2) In the width of the mouth,
which shows definitely that it had not
yet attained the beak-like character of
the mouth of recent forms. (3) In the
undifferentiated condition of the clasp-
ing organs. The frontal clasper is still a

133

135

Figs. 132-137. — Evolution of frontal clasping spine of Chim-
aeroids.

132, I'm-spmeof Myriacanthus. 133, Frontal clasping spine- of Squalo-
raja. 134, Frontal clasping spine of Myriacanthus. 1 34 A, Base
of clasping spine of Myriacanthus, ventral aspect, to show areas of
attachment of muscles. 135, Frontal clasping spine of Ischyodus,
after specimen in Munich Museum. 136t Frontal clasping spine
of Chimera, after section given by O. M. Reis. 1 37, Frontal
clasping spine of Squaloraja, dorsal aspect. I37A, Ventral view
of base, showing areas of attachment of muscles.

*This wasobserved by the writer in a specimen (P 2276) in the British Museum earlier described by Smith Wood-
ward. Dr. Woodward did not, however, note that these clasping organs were present, although figuring them as
"remarkably strong prepubic processes." Each clasper has appended denticles, of which as many as eleven were prob-
ably present. The same specimen has preserved in outline visceral structures, apparently testes and vasa deferentia.

142

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

s

\

spine, figs. 137 and 137 A, resem-
bling closely the dorsal fin-spine of
many sharks (no second dorsal
spine or even a dorsal fin is known
in Squaloraja, a condition which
suggests that this form may have
been bottom-living and that the
dorsal fin may have become shifted
into the region of the tail). The
antero-pelvic claspers are shown
by the presence of neighboring
radial cartilages to be reasonably
deduced from such elements, and
the short, wide, shagreen-coated
mixipterygia are
~"\ also shark-like in

pattern. Their
derivation from
radial cartilages
is also indicated.
^'' On the other

hand, Squaloraja
gives no positive ground for
the belief that the fine rings
in its vertebral column are the
homologues of selachian
centra. For in this Liassic
form they are nearly as nu-
merous as in the living genera,
and the best evidence that they
are derived from metameral centra is that
the rings become slightly reduced both in
number and in diameter in the region just
behind the occiput.*

Fig. 138. — Squaloraja polyspondyla. Details and partial restoration.
After specimen P 2276 in British Museum, figured by Smith Wood-
ward (1886).

The narrowing of the snout is indicated in specimen No. 1 147 in Harvard Museum and in an undescribed specimen in the Museum of Science and Arts, Edinburgh.
Fin outlines hypothetical. Details of dermal tubercles are shown in A and ^?. In C*the ventral occipital region is figured after the above-noted specimen of
Harvard Museum. Here the condylar region is admirably preserved ; behind it centra appear at the right, neural arches at the left. And "ring " vertebrae
apparently grade into metameral centra. «>'» anterior radial* ; tni.r, mixipterygtum; '"V, antero-ventral clasper ; oc, occipital condyle; r, anterior "ring
vertebrae" ; d, tract of enlarged dermal denticles.

*Since the foregoing was written additional light has been thrown upon the question of metameral segmentation
in the column of Squaloraja; in the Harvard specimen already referred to, a coarse segmentation, which suggests
outwardly cyclospondylous vertebrae, is well shown in the postoccipital region, fig. 138 c. It is not certain, however,
that these coarse segments are serially homologous with the fine rings in other parts of the column : it is possible, as
embryology indicates, that they belong to the outer chordal sheath.

JURASSIC CHIM^ROIDS.

The second Jurassic Chimaeroid, Myriacanthus, is known, unfortunately, in
less detail. Nothing has been definitely ascertained regarding its general shape or
the structures of its trunk. But what is known of its head region shows that it
possessed extraordinary features. The form of the head was, in general, like that
of Callorhynchus, terminating in a long snout. This had a somewhat foliaceous
tip (fig. 140), as in the recent genus, but, on the other hand, was broader, less
acutely pointed, and studded dorsally with shagreen denticles and dermal plates.

The best example of a snout of Myriacanthus belongs probably to a specimen
in the Jermyn Street collection, of which a sketch is given in figure 141. The
figure, which shows the snout in dorsal aspect, indicates also the spine-like nature
of the frontal clasping organ. This organ is shown again, in lateral view in fig. 133.
There can be little question that in this genus the shagreen-like defenses seen
in the head of Squaloraja are replaced by a number of conspicuous pairs of
dermal plates, some of which attain a large size and are furnished with spinous
outgrowths. Thus, for example, on
either side of the jaw (slightly schem-
atized in fig. 142) there is a conspic-
uous "trachyacanthid " spine bearing
a large serrate row of four or five
subspines. These elements, it may
be remarked, are well shown in a
second specimen from Lyme Regis,
in the Jermyn Street collection, and
in Egerton's type specimen of Prog-
nathodus gucntheri {Myriacanthus par-
adoxus), now preserved in the British
Museum, in which one of these
spines is shown in situ, attached to
the broad jaw. The arrangement
of the dental plates of Myriacanthus

•.* f • fc \

With tair aCCUraCy (fig. 1X9).

IS

F;g. l39.-Squalor.ja. Detail of roshal spine of specimen P 4323
in British Museum.

The dermal denticles are grouped closely together, their bases flat and greatly enlarged.
They occasionally become detached. a, the .car, in the .peamen indicate.

The mandibular plates show foldings on the visceral face and in these folded areas
appears the most conspicuous aggregation of tritoral points. A somewhat similar
condition prevails in the palatines. In front of the palatines, as in Squaloraja,
there occurs a pair of "vomerine" plates. These, however, instead of exhibiting
a finely arranged series of tritoral points, present three rows of larger tritors,
somewhat as indicated in the restoration (fig. 1 19 A). Furthermore, in front of the
"vomerines" (and this condition is unique among all other Chimseroids, fossil or
recent) there is a third and still smaller pair of plates, showing faintly a series of
rows of tritors. Another puzzle in the dentition of Myriacanthus is seen in the
region of the mandibular symphysis, for here occurs an azygous chisel-shaped
tooth which is known only in this genus and in the kindred Chimseropsis (cf. also
p. 145). The restoration in lateral view of these dental plates is shown in fig. 130.
On the other hand, Myriacanthus, like recent Chimseroids, was autostylic, and it

144

CHIM^EROID FISHES AND THEIR DEVELOPMENT.

was provided with a well-marked dorsal fin which was supported anteriorly by a
spine. This fin, it may be remarked, is the earliest dorsal known in Chimgeroids,
and its structure, therefore, deserves more than passing mention. Thus, as shown
in fig. 140, and in the series of figures, figs. 143 A, B, c, D, its position is further
hindward than in recent forms, in this regard suggesting interestingly the condition
of shark. It is also noteworthy that the base of the myriacanthid spine is not
articulated to the fused mass of anterior epichordalia, but is still connected with a
hinder independent plate, b, which, we suggest, becomes in recent Chimaeroids the
articular process of the anterior cartilaginous plate. A further correspondence with
a shark-like condition is noticed in the separation of the fin basis into proximal
("basal") and distal ("radial") moieties; in recent Chimseroids these are repre-
sented by but a single plate, c.

It should be finally observed that the vertebral column of Myriacanthus, fig.
143 B, shows anteriorly a segmentation which reasonably indicates the presence
of centra.

Fig. 140. — Head region o( the Jurassic Chimaeroid Myriacanthus. After Egerton's specimen, in British Museum.
C, Centra; 5, Detached ventro-median chisel-shaped "tooth."

Summarizing our knowledge of Myriacanthus, we note that its dermal defenses
are far more highly specialized than in Squaloraja, and that it has evolved an addi-
tional pair of tritoral plates in the upper jaw, as well as a ventro-median element
in the mandible. Furthermore, that its frontal clasping organ, although still spine-
shaped, is less like a spine than in Squaloraja (cf, figs. 131, 132, and 133). On the
other hand, in its dorsal fin and in its fairly evident vertebrae it is more distinctly
shark-like than any other Chimaeroid.

JURASSIC CHIM^EROIDS.

Chimseropsis, a third Jurassic genus, is known only from the lithographic stone
(Kimmeridgian = Upper Jurassic) of Bavaria. It resembles Myriacanthus — as far,
at least, as one can judge from fragmentary remains. It certainly had similar
mandibular plates and the presymphyseal chisel-shaped element. It was provided
with a similar frontal clasping spine and an elongated snout. It had also a series
of dermal plates, as in the former genus, and in addition its trunk was studded
with small, conical, radially-grooved denticles.

Fig. 141. — Myriacanthus granulatus. Detail of snout region.

After specimen presented to Jermyn Street Museum by Captain Ibbetson. As indicated in dorsal aspect, the snout is broad and thickly
studded with dermal tubercles. The frontal clasping spine appears somewhat in its relative position. The dental plates are dissociated.

Fig. 142. — Mandible of Myriacanthus, viewed from in front.
Restoration after one of Egerton's specimens in the British Museum.

Brief mention need only be made of the Jurassic genera Ganodus (fig. 121)
and Brachymylus, since these forms are known only by detached dental plates. It
is possible, however, that a more or less complete skeleton of Ganodus* is preserved
in the Museum at Northampton (Smith Woodward, 1892), and, in this event, its
structures closely resemble Ischyodus. f

*This specimen, a male, lacks the rostrum, but shows the frontal clasping organ ; of the latter the base is expanded
transversely, and shows, as in Myriacanthus and Squaloraja (figs. I34A and 137 A), a faint median crest on its attached
face; its sides are laterally compressed. The column shows ring thickenings. Its dorsal spine is slender and arched
(= Lepracanthus).

fSince the foregoing was written I have reexamined the specimen of " Ganodus " avitus in the Munich Museum,
and am inclined to agree with its determination as Ischyodus by Reiss and Smith Woodward. It is quite possible,
however, that this specimen will be shown to represent a new genus as soon as a more definite knowledge of Ischyodus
is obtained. Thus the present specimen has small orbits, small snout, and large dermal denticles, the latter scattered
widely, especially conspicuous in the region just anterior to the ventral fin. There is also ground for the belief that a
pair of dermal plates were present on or near the posterior rim of the mandible.

146

CHIMyEROID FISHES AND THEIR DEVELOPMENT.

Ischyodus, the final Jurassic Chimseroid, deserves more detailed examination,
since its skeleton has been obtained in a condition of fair preservation in the Bava-
rian lithographic stone. From structural details, accordingly, this genus is known
to be widely separated from Myriacanthus or Squaloraja; and on the other hand it
resembled closely recent forms. It was thus similar in the shape of its head and

D

R

Fig. 143. — Anterior dorsal fin and its supports.
A, Shark, (Squalid); B, Myriacanthus; C, Callorhynchus ; D, Cliiiiurra.

trunk; its snout was fleshy and appears to have
terminated in a flap-like tip. Its dental plates,
however, are stouter (fig. 124) than in Chimera,
and show fewer localized tritoral areas. Its dor-
sal spine was relatively short and robust, and the
frontal clasping organ is not unlike that of recent
Chimseroids, save that (cf. figs. 135 and 136) it
is more prominent and its ventral margin has a
more extended series of smaller denticles. In
the details of its skeleton, it strikingly resem-
bles recent forms. One may also recall that
an egg-capsule, probably of this genus (of a
new genus, Aletodus, according to Jaekel), has
already been referred to in the present paper,
p. 31. It resembles closely the capsule of the
recent Callorhynchus.
It is clear that in Ischyodus is represented the advancing line of Chimaeroids,
for it extends from the upper (probably, indeed, from the lower) Jurassic as far as
the upper Chalk, even possibly into the Miocene (? /. helvetica), and is represented
during this interval by many species of many sizes. Some were probably as small
as the recent Chimczra colliei, others must have exceeded 3 meters in length.

CRETACEOUS CHIMyEROIDS. 147

CRETACEOUS CHIM/EROIDS.

Chimaeroids, it may finally be remarked, were at their maximum evolutional
development during the Cretaceous period; they were then represented by the
greatest number of genera and of species (about 50 species), a result which may
well have proceeded from the acquisition in their line of some new "expression
points"; such, for example, may have been the apposition of meckelian and chisel-
shaped subnasal "vomerine" plates, which must have added vastly to the effective-
ness of this type of dentition; also the greater development of the clasping organs;
also, perhaps, deep-water adaptations which enabled these forms to enter a new and
rich field for development. Certain it is that these Cretaceous Chimaeroids were
of a distinctly modern pattern, and one of them is even assigned to the recent
genus Callorhynchus.

The details of the evolution of recent genera from their Cretaceous ancestors
are unfortunately meager. Dental plates and spines are practically the only
evidence at hand for comparison. If, however, we limit our studies to dental
characters, we can at least conclude that their evolution has been in the line of
producing tritors either in marginal or in centralized arrangement. In Ischyodus,
for example (fig. 1 24), it will be seen that some of the tritoral areas of the palatines
and meckelian plates are becoming localized near the median line. In Edaphodon
(fig. 123) the tritoral areas of even the vomerines are more nearly median; indeed
the only conspicuous appearance of marginal tritors occurs at the tip of the meck-
elian plates. Elasmodus (fig. 122) indicates an interesting combination, since it
has developed both the marginal and the median series of tritors. It has thus a
dentition of a generalized character, and one is not surprised to find that it passes
over from the Cretaceous into the Eocene. In fact, it differs little from the denti-
tion of the recent Harriotta. On the other hand, Elasmodectes (judging from its
meckelian plates, which alone are accurately known) represents a form which is
specializing in the direction of marginal tritors; they are numerous, continuous in
arrangement, and minute in size, and altogether the plates were probably beak-
like in function. This type of dentition appears at first sight too specialized to
have long survived. Nevertheless, granting a continued reduction of these minute
marginal tritors, and more flattened and beak-like arrangement of the plates, a
descendant of Elasmodectes might well be represented in the recent Rhinochimaera.

As far, therefore, as a study of the dental plates alone is concerned, one might
conclude reasonably that the recent genera were descended from Mesozoic forms
in somewhat the following way: Callorhynchus from an ancestor closely related to
Edaphodon, Chimera from Ischyodus, Harriotta from Elasmodus, and Rhinochi-
maera from Elasmodectes. Such genera, for example, as the Cretaceous Lepto-
mylus and the Miocene Mylognathus are apparently already too specialized to have
represented the ancestral condition of the living forms. There can be no question
that, with the exception of the three genera first named, the Mesozoic, Tertiary and
recent Chimaeroids are a single and homogeneous stock. They have none of the

148 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

bizarre features of Myriacanthus, Chimaeropsis, and Squaloraja; no highly special-
ized plates and spines in the head region, no spine-shaped frontal clasping organ,
no presymphyseal element, and no second pair of "vomerine" plates. Among
recent forms, Callorhynchus, a Cretaceous genus, has probably retained in most
regards the striking characters of its Mesozoic kindred. And it is not to be
wondered at, therefore, that its developmental features appear more conservative
than in other genera. On one side of this early genus we may place Chimaera,
which, as we have seen, is in many ways a highly modified form; and on the
other side would be arranged Harriotta and Rhinochimaera, similar to one another
outwardly, but (on the evidence of dental characters) long separated from a common
ancestor.

It yet remains to consider the probable relationships of the earlier forms. It
is clear, first of all, that in the Jurassic epoch there existed three distinct types of
Chimaeroids. One, as we have noted, is that of Ischyodus and its allies, from
which unquestionably all recent Chimaeroids are descended. The second, Squal-
oraja, represents an aberrant and terminal group; it is to its kindred as is Pristi-
ophorus to sharks. On the other hand, one must admit that it shows certain
characters* which ally it to the stock from which Ischyodus-like forms must have
arisen. The third Jurassic type, represented by Myriacanthus and Chimaeropsis,
is the most difficult to interpret. From present data it can hardly have pictured
the ancestral line of modern Chimaeroids, for from what we already know of the
elaborate dermal plates of the head and its "trachyacanthid" spines, we infer that
it was already too highly specialized to have had the evolutional vigor to give rise
to forms in which shagreen-like conditions again occur, for such a series would
present an analogy not as close, e. g. , to the descending line of the sturgeons as
to the line of the Cestracionts, in which the modern form is related only collaterally
to the elaborately spined and heavily plated genera of the late Palaeozoic. Espe-
cially puzzling are the dental characters of Myriacanthids; for how are to be
interpreted the symphyseal chisel-shaped element and the anterior pair of subnasal
plates? One might readily suggest that the former element was developed on the
copula of the mandibular arch — a suggestion which bears with it a greater shade of
probability when we consider the size and importance of the mandibular copula
as recently described by both Schauinsland and the younger Fiirbringer. And
following a similar line of speculation we might maintain that the "vomerine"
plates were developed on the pharyngobranchial element of the jaw arch, just as
the palatine plates were developed on the next lower (epibranchial) element. In
support of this hypothesis we may note that, as in Chimaera a pharyngobranchial
element is present in the hyoid arch, a similar serial element appears also to have
been present in the mandibular arch (cf. figs. 1 10 and 1 1 1). A second hypothesis-
hypothesis may be a little too dignified a term — is that the "vomerine" and "pre-
vomerine" plates of Myriacanthus represent the palatine plates of premandibular

*E. ff., number and disposition of dental plates, clasping organs, integumental defenses.

CRETACEOUS CHIM^ROIDS.

149

gill-arches. This view, it will be seen, finds some support in the remarkable gill-
arch-like character of the labial cartilages, and it becomes less fanciful when one
considers how frequently the labial cartilages, especially in Chimseroids, have been
homologized with premandibular arches. As far as Myriacanthus is concerned,
such interpretations are clearly favored by our knowledge of its evident speciali-
zation in dermal defenses, for in such a light it would be not improbable that addi-
tional dermal elements would be evolved and impressed into the service of the
mouth parts—/, e., plates which may not have been present in the parent stock
from which descended Myriacanthus, Squaloraja, and modern Chimseroids.

Moreover, it is worthy of mention that the forms which are commonly accepted
as the earliest Chimseroids, the Ptyctodontids, have but two pairs of dental plates.
For it might be plausibly suggested that these primitive forms had not reached the
stage in evolution when the "vomerines" (i. e., dermal elements) appeared as
defenses for the anterior arch.

In accordance with the present considerations a scheme of the evolution of the
genera of Chimseroids may be arranged somewhat as on page 150, fig. 144.

150

CHIM^SROID FISHES AND THEIR DEVELOPMENT.

RECENT Rbinochi macro, ffarriolta, Ca/lorhyncbus Chimacra

JURASSIC

.Sharks

TR1ASSIC

\

\\
\\

PERMIAN

Menaspis

CARBONIFEROUS

\ \

N N
Rhynchodus \ N\

Palcpomylus^ ^ \ \

DEVONIAN

Ptyctodus

Fig. 144. — Phylogeny of the Chimseroids. Arrangement according to palcontological data.

IV. CHIM/EROIDS IN THE PROBLEM OF VERTEBRATE DESCENT.

On the basis of the foregoing discussion we may finally consider the critical
question whether Chimseroids are to be regarded "as the most primitive verte-
brates, or more precisely as the least modified descendants of the ancestral cranium-
and jaw-bearing vertebrate?" Are they, in other words, to be looked upon as
more primitive than sharks and as "representing a lower plane in piscine evolu-
tion' ' ? These questions have been touched upon, more or less distinctly, throughout
the present paper and the conclusion has been already indicated. And I think we
may now state confidently that, from the evidence of embryology and paleontology,
Chimseroids represent not the ancestral vertebrate, but rather a highly modified
group descended from selachian ancestors. At the present time the evidence may
be summarized upon which this induction is based.

PALEONTOLOGICAL EVIDENCE THAT CHIM/ERO1DS ARE DERIVED FROM SELACHIAN

ANCESTORS.

(a) Their later origin:

The earliest genera of whose Chimseroid nature there can be no doubt do not
appear before the lower Jurassic, and from this horizon have been described but
two genera. Sharks, on the other hand, appear in ages remotely earlier, and they
are then represented by several orders, many genera, and very many species.
Thus, in the Palaeozoic alone, we may enumerate at least fifteen genera and forty
species whose shark-like anatomical features are definitely known, and we may
reject altogether the testimony of the numberless selachian "species" of spines and
teeth. Into this limbo of indeterminata may provisionally be cast Ptyctodonts,
together with Cochliodonts, Deltodonts, and similar forms. And we may in like
manner regard the Permian Menaspis as doubtful. But even if we grant that all
Ptyctodonts are Chimaeroid, we have still the testimony that the sharks were
in earlier periods overwhelmingly more numerous and more diversified. And we
have equally to admit that, even at that early period, many sharks, from horizon
to horizon, modify the character of their cuspid teeth in the direction of tritoral
plates. In short, admitting the evidence of dentition, one may state conservatively,
that even in their epoch Ptyctodontids stood to the sharks, both in number and
in variety, only as one to one hundred. And from this testimony alone we can
almost reject the thesis that Chimseroids were ancestral sharks. Unfavorable to
the latter view, moreover, is the fact that the culmination of the Chimaeroid line,
i. e., in genera and species, did not occur before the Cretaceous, while that of
sharks antedated the Permian.

152 CHIMyEROID FISHES AND THEIR DEVELOPMENT.

(<$) Shark-like morphological characters of early Chimceroids:

The earliest definitely known Chimseroids were clearly shark-like. In this
regard attention need only be called to the facts: (i) That they had shark-like
dermal denticles scattered over the body; (2) a male clasping organ in the form
of a selachian fin-spine; (3) rudiments of vertebral centra in the postoccipital
region; and (4), in one form at least, tritors in the anterior dental plates which
in arrangement resemble strikingly the teeth of a Cestraciont shark.

Furthermore, the earliest Chimseroids present no characters which can be
fairly interpreted as more primitive than those of sharks. They were, on the con-
trary, more modified. Thus in their males they had already evolved the three sets
of clasping organs.

EMBRYOLOGICAL EVIDENCE IN FAVOR OF THE VIEW THAT CHIM/ERO1DS ARE DERIVED

FROM SELACHIAN ANCESTORS.

The riddle of Chimseroid development can, I am convinced, be read in only
one way; for the evidence yielded by the various phases of embryology points to
the modified nature of Chimseroid descent: That is, if we grant the value of tran-
sitional stages in demonstrating the descent of the more complicated from the less
complicated type, we may in the present case obtain a mass of evidence which
must, it seems to me, be regarded as conclusive. The scope of this evidence is
seen in the following summary:

I. Chimseroids are more complicated than sharks in sexual characters.
Males differ from females to a greater degree in point of size and proportions, and
in the development of clasping organs. Of the latter, sharks have only mixip-
terygia, while Chimaeroids add to these the antero-ventral claspers (which are
modified anterior radials of the ventral fin) and the frontal organ (which is inter-
preted as a transposed fin-spine).

II. The egg-capsule of the Chimseroid is the more complicated. It is larger
in proportion to the size of the fish, and is adapted more especially to the needs of
the young fish. In this regard we recall its remarkable regional differentiation
(i. e.t for head, trunk, and tail of the young fish), breathing pores, opercular valve,
and organ of attachment — characters more complicated than in the egg-capsules of
sharks.

III. The early egg membranes are more complex than in sharks. Here we
refer to the changes in the tunic and the behavior of its nuclei.

IV. The phenomena of fertilization. As one instance of complexity in
Chimsera we recall that following polyspermy, the sperm merocytes divide at once
amitotically; while in shark amitosis is attained only after a decadent series of
mitotic divisions. Witness also, in the Chimseroid, the peculiar features of the sperm
track and the character of the asters.

V. Early cleavage lines, as in the case of the (highly modified) rays, are
suppressed, and the synchrony of segmentation is soon lost. Further complication
in Chimsera appears in the germinal wall — in which are confused yolk-masses,

SPECIALIZED CHARACTERS. 153

small blastomeres, merocytes and undivided yolk — and in the periphery of the
blastoderm. We find further that amitosis occurs plentifully within the blastoderm.

VI. The fragmentation of the egg, which begins at gastrulation, doubtless
arose as a primitive character, i. e., holoblastism. Its function, however, in the
modern Chimseroid has become a distinctly complicated one. By this process a
large part of the yolk is diverted from its primitive use and is appropriated by the
embryo secondarily, via gills and gut. The yolk-sac, accordingly, is reduced to
miniature size. '

VII. The embryo develops precociously. While still minute in size, i. e.,
in terms of the blastoderm, it presents complicated structures; when 2.5 mm. in
length it has already 25 somites, and suggests the adult. Compared to the young
shark it is also more specialized in its relation to the germinal yolk and in the
development of the vascular system. In this connection note also the differen-
tiation of many types of merocytes, and the evidence that megaspheres are not
primitive ova.

VIII. The head region of the embryo indicates precocious specialization.
We thus note the early appearance and great size of the eyes, the appearance of
the cephalic "hood," the greatly shifted position and the reduced size of the
spiracle, the condition of the head mesoblast, the fewer and larger gill lamellae, the
moniliform character of the external gills, due to the presence of special blood-
producing organs, the reduction of the fifth gill, and the early differentiation of the
branchiostegal flap.

IX. The trunk region bears similar testimony in the matter of precocious
specialization. We thus observe the early period at which the greatly elongated
tail is produced, the anterior position of the anal region even in early embryos, the
speedy obliteration of the lumen communicating between myo- and splanchnoccele,
the early appearance of the dorsal fin-spine and of mixipterygia, the last a feature
worthy of especial comment, since it indicates the appearance of secondary sexual
characters in even small embryos. Also to be noted is the great size early assumed
by the paired fins.

X. Larval characters are also developed prominently. To be mentioned in
this regard are: Larval coloration; larval proportions of head, trunk, and fins;
appearance of greatly enlarged dorsal scales; larval dentition, in which the outer
rims of the dental plates become specially developed.

The foregoing are but the most conspicuous characters to be selected from the
present embryological materials. Nevertheless there can be, I believe, no valid
question as to their significance; for in no essential regard can they be interpreted
as representing conditions so unmodified as to have given rise to the present condi-
tions in the development of sharks. *

*One might, it is true, regard the modern sharks as arrested " larvae" of Chimasroids, and thus maintain that shark
embryos exhibit less complicated conditions than their ancestral forms. But if the diversity of specialized characters,
as shown in the foregoing summary, is duly considered, this extreme view, it seems to me, can only fall of its own
weight. For in view of the many lines of specialization of Chimaeroids, it seems about as improbable that these
forms could have represented the ancestral sharks as that a bird could have represented the ancestral reptile, or that a
recent horse could have been the progenitor of Protohippus.

154 CHIM^EROID FISHES AND THEIR DEVELOPMENT.

If this general position be granted, we have still to consider the question
whether Chimaeroids actually possess any primitive characters. Reviewing the
materials at hand I think we may here refer to the following:

I. Holoblastism. — The egg cleaves totally. Of this there can be no doubt,
although, as we have seen, this condition is complicated in many ways (pp. 58-63),
and its retention is with strong probability due to the highly modified physiological
needs which it now subserves. In other words, the holoblastism of Chimaera is
less primitive than adaptive, and thus may not represent the ancestral condition in
cleavage of such a form as the shark Cestracion (Heterodontus).

II. Gastrulation. — The appearance of the blastopore in front of rather than
at the rim of the blastoderm is, I take it, of no little significance as a primitive
character. Its retention is probably correlated with the survival of a holoblastic
type of cleavage.

III. Primitive conditions in the mouth region. — No one, I assume, will deny
that a pharyngobranchial element in the hyoid arch is a primitive feature. And of
kindred significance are: The presence (i) of copular segments in the branchial
arches, (2) of a mandibular copula, (3) of a pharyngobranchial process in the mouth
arch, and (4) of more distinct "preoral arches" than in sharks. On the basis of
these characters, then — and they are clearly of no little weight — may we conclude
that Chimaera pictures more accurately than shark the ancestral gnathostome? To
this conclusion there are clearly two lines of objections. First, that in many other
features Chimaera is singularly modified, and, second, that the mouth region of
Chimaeroids is the less easily compared with that of recent sharks on account of the
autostylism which has prevailed in the former groups since (at least) Jurassic times.
In other words, in view of the first objection, it would be judicious, I conclude, to
interpret the foregoing remarkable characters in the mouth parts of recent Chim-
aeroids in the following way : That autostylism, although in itself a modified
condition, tended less to alter the neighboring branchial structures than did the
adaptation of a more flexible support for the jaw-hinge (c. g., as in the modern
sharks). And that thus, under the partially conservative influence of autostylism,
Chimaeroids, in spite of other structural modifications, have nevertheless retained a
few of the characters of primitive sharks.

The foregoing conditions (I, II, and III) are, as far as I am aware, the most
important findings of embryology as to the primitive position of Chimaeroids. Less
important in this question are the earlier data of morphology (v. pp. 4-5). Thus:

IV. Absence of ribs. — This character becomes of minor importance, in the
light of developmental documents. The early shortening of the visceral cavity
would obviously be unfavorable to the development of ribs, even if these elements
had been present in the ancestral form. As to the latter condition, it may be
mentioned that at the present time there is good reason for the belief that in the
earliest sharks (Acanthodians and Cladoselachids) ribs were not present.

V. Stomach, Kidney, Mazza' s Glands. — In these structures also the question
of primitive conditions is by no means clear. For the early shortening of the
visceral cavity may readily have been accompanied by secondary modifications in
the viscera.

CHIM^ROIDS IN VERTEBRATE DESCENT. 155

VI. Musculatiire. — The muscles of the branchial arches, like the arches
themselves, retain primitive features; thus the adductor of the jaw retains its inter-
branchial character. On the other hand, there is no ground for the belief that the
muscles of the shoulder girdle are unaltered; Gegenbaur (1901), for example,
frankly admits that they are more modified than those of sharks, and he calls
attention to the general blending of the segmental muscles of the trunk. There
appear also in Chimera special muscles developed in connection with the erectile
spine and clasping organs which can best be interpreted as derived from the simpler
elements in sharks.

VII. Nervous System. — In this connection it may be remarked that some of
the primitive characters of Chimaera — open lateral line, separate nerve roots,
simple auditory organ — are clearly paralleled in sharks, e.g., Notidanids.

SUMMARY.

Chimaeroids, accordingly, are widely modified rather than primitive forms.
The evidence contributed by anatomy, embryology, and paleontology is unmistak-
ably in favor of this interpretation. And there can be no doubt that the recent
forms retain less perfectly the general characters of the ancestral gnathostome than
do living sharks. On the other hand, it must be admitted that Chimaeroids have
retained several characters of their Palaeozoic selachian ancestors which modern
sharks have lost. According to many converging lines of evidence we may indeed
go so far as to conclude that the ancestral Holocephali diverged from the selachian
stem near or even within the group of the Palaeozoic Cestracionts. * Indeed, the
recent Chimaeroids and Cestracionts retain many features of kinship. Among
these need only be mentioned at the present time approximations in dentition,
labial cartilages, articulation of mandibles, structures of fins, and urogenital system.
Even the complicated egg-capsule of Chimaeroids finds its nearest parallel in
the recent Cestraciont, a comparison often lost sight of on account of the spiral
arrangement of the lateral webs in the capsule of the latter form.

From the standpoint of taxonomy, on the other hand, it must be clearly recog-
nized that the Chimaeroids have been separate from the early sharks for so long a
time and have acquired such different characters that they are to be given a high
rank among the divisions of the subclass Elasmobranchii, the equivalent, let us
say, of such groups as pleuracanths or pleuropterygians.f

*This conclusion recalls the remarks of W. K. Parker, in his paper on the skull of cyclostomes (Phil. Trans. 1883,
p. 451) : "Even the Chimaeroids come so near the ordinary Elasmobranchs as to suggest that their embryology would
not be so helpful (in the matter of the descent of the Cyclostomes) as one might imagine, especially if their solid upper
face has been acquired as a secondary modification and not a -primary condition, such as we see in the Tadpole, which
is especially solid and largely continuous with the basis cranii, in the larval Aglossal types, Dactylethra and Pipa.
(The interposition of those remarkable sharks, Cestracion and Notidanus, between the ordinary kinds and the Chimae-
roids, makes the likelihood of the solidity of the upper jaw being primary a very doubtful thing ; I once thought
otherwise, but found Mr. Balfour strongly set against me in this suggestion,. ) "

t One recalls at this point an early remark of Huxley : "For, considering, in addition to the cranial characters,
the structure of the vertebral column, and of the branchiae, the presence of an opercular covering to the gills, the
peculiar dentition, the almost undeveloped gastric division of the alimentary canal, the opening of the rectum quite
separately from and in front of the urogenital apertures, the relatively small and simple heart, the Chimaeroids are
far more definitely marked off from the Plagiostomes than the Teleostei are from the Ganoids."

156 CHIM^ROID FISHES AND THEIR DEVELOPMENT.

Of the interrelationships of the various modern Chimaeroids enough has been
said in the foregoing pages; on many grounds it is evident that Callorhynchids
have retained more nearly the characters of the ancestral Holocephali than have
Chimserids.

If, finally, the data of Chimseroid development be carefully scrutinized,
there will, I am sure, be found material for interesting reflection. For such a
study brings with it considerations of greater significance than the pedigree of a
group of little-studied vertebrates. It touches, first of all, the larger problem as to
the degree to which embryology may be used in determining the kinship of animals.
Moreover it furnishes somewhat definite illustrations of the processes — usually so
obscure — of "shortening up" or "concentrating" developmental stages, and of
embryonic "specializations." It also contributes, but in a minor degree, to the
problem of germinal layers and, in even a more difficult field, to the interpretation
of amitotic cell-division.

LITERATURE LIST.

LITERATURE LIST.

(Omitting references to a number of text-books and early zuorks.)

CHIM^ROIDS.
General and Systematic.

1833-44. AGASSIZ, L. Poissons fossiles. Texte III, pp.

3-4, Tab. C. (C. monstrosa.)
1871. Reference to separation of Chimaeroids

from sharks, v. Wilder, Proc. Bost. Soc. Nat.

Hist, Vol. XIV, p. 214.
1892. ALCOCK, A. Reference to "C. monstrosa, Linn.?"

occurring off Coromandel coast. Indian Marine

Survey.
1613. ALDROVANDUS. De Piscibus. Liber IV, pp. 402,

403.

1772. ASCANIUS, T. Icones rerum nat. PL xv.
1886. BEDDARD, F. E. Reference to Howe's view as to

descent of elasmobranchs and dipnoans from

Chimaeroids. Proc. Zool. Soc. Lond., p. 524.
1870. BENEDEN, P. J. VAN. Reference to food of Chi-

rmera. Mem. Acad. Roy. Belg., Vol. XXXVIII,

in Les Poissons des Cotes de Belgique.
1839. BENNETT, J. Zoology of Capt. Beechey's Voyage,

p. 71, PL xxiii. (C. colliei.)
1862-78. BLEEKER, P. Ichthyol., IV part, p. 69, PL

cxxiv. (C. monstrosa.)
1852. Ichth., Fauna van Amboyna en Ceram,

1859.

p. 81.

Elfde Bijdrage Vischfauna Amboyna.

1832-42 and 1846. BONAPARTE, C. L. Iconographia

Fauna Ital. and Catal. Pesci Europei, No. 82,

p. 20.
1823. BORY DE SAINT-VINCENT. Diet. Class. Hist. Nat.,

Vol. Ill, p. 62, PL v. (Cal. milii.)
1891. BRUHL, C. B. Dipnoi- u. Holocephalikopf. 4to.

Pis. vii. Wien.

1898. BYRNE, L. W. On the general anatomy of Chi-
maera. Preliminary notice. Proc. Zool. Soc.

Lond., Jan. 18.
1898. Chimaera monstrosa in the North Sea.

Naturalist, p. 206.
1872. CANESTRINI, G. Reference in Fauna Italiana.

Parte 3A, pp. 61 et seq.

1868. CAPEIXO, F. DE BRITO. Jour. Sc. Math., Phys. e

Nat. Lisboa, Vol. LV, p. 314, PL in. (C. affinis.)

1819. CLOQUET, H. Diet. Sci. Nat., Vol. VIII, p. 581,

PL xiv.
1605. CLUSIUS, C. Exoticorum libri decem, p. 137.

(C. monstrosa.)

1878. COLENSO, W. Trans. N. Z. Inst., Vol. XI, pp.
298-300, PL xvn. (Cal. dasycaudatus.)

1904.
1905.

1873.

1852.
1798
1895.
1904.
1904.
1900.

1902.
1803.

1856.

1865.
1829.

CoLLETT,-R. Chr. Videnskabs-Selskabs Forh., No.
4> PP- 5-6. [C. (Bathyalopex) mirabilis.]

Rep. on Norwegian Fishery and Marine

Investigations. Vol. II, No. 3, p. 35, PL i.
[Complete account of C. (Bathyalopex) mi-
rabilis.]

COPE, E. D. A contribution to the ichthyology of
Alaska. Proc. Amer. Philos. Soc., Vol. XIII,
No. 90, pp. 24-32. (C. colliei.) V. also Chi-
maeroids, Skeleton, and Chimaeroids, Fossil.

COSTA, O. G. Chimaera (anat.), Fauna di regno
Napoli. Pis. i-vii. (C. monstrosa.)

and 1817. CUVIER. Tableau filementaire and in
Regne Animal, Vol. II, pp. 382, PL cxin.

DEAN, BASHFORD. Fishes, Living and Fossil (Mac-
millan), cf. pp. 287-288.

Jour. Sci. Coll., Tokyo, Vol. XIX, Art.

3, pp. 10, PL i. (C. phantasma and C. mitsukurii.)

Jour. Sci. Coll., Tokyo, Vol. XIX, Art.

1901.

1904.

4. pp. 23, PL ii. (Rhinochimaera pacifica.)

DELFIN, F. T. In Catalogo de los Peces de Chile.
Rev. Chil. Hist. Nat, Vol. Ill (1899), i, IV,
1900. (Cal. callorhynchus and Cal. argenteus.)

Concordancia de Nombres Vulgares i

Cientificos de los Peces de Chile. Abstract in
Riv. Chil. Hist. Nat., Vol. VI, pp. 71-76.

DONOVAN, E. Nat. Hist. Brit. Fishes. Rivington,
London. PL cxi, and accompanying descrip-
tion. Reference to a "C. monstrosa" which had
conspicuously spotted fins.

DUMERIL, A. Ichthyologie analytique. Indicates
Chimaera near Spatularia — a hypostomate chon-
drostean (gives name Chismopnes to Chimasra,
Lophius, Batistes, etc.).

Hist. Nat. des Poissons. I. filasmobranches,

pp. 663-697, Pis. (Atlas) xin-xiv. (Standard
reference to Chimaeroids.)

FABER, F. Naturgeschichte der Fische Islands,
p. 45. Frankfurt. (C. monstrosa, its habits,
food, etc.)

GAIMARD, J. P. Voyage en Islande et au Green-
land. Zool. PL xx. Figures Chimaera mon-
strosa (<,> ).

CARMAN, S. Proc. N. Eng. Zool. Club, Vol. II,
pp. 75-77. (Rhinochimaera and taxonomical con-
siderations.)

. The Chimaeroids (Chismopnea Raf. 1815,

Holocephala, MiilL, 1824), especially Rhinochi-
maera and its allies. Bull. Mus. Comp. Zool.,
Vol. XLI, pp. 243-272, Pis. i-xv.

i6o

LITERATURE LIST.

1901. GEGENBAUR, C. Many ref. in Vergl. Anat. der
Wirbeltiere. 2 vols. Engelman. Vertebral col-
umn "even in many points in a less differentiated
condition" than sharks ; the chorda is of uni-
form thickness through the centra ; palato-quad-
rate fused with cranium ; median union of three
rostral cartilages in Chimaera more shark-like
than in Callorhynchus ; male median clasper
a new structure ; ventral labial cartilage a
"second under jaw" (J. Miiller) ; agrees with
Solger that the position of spiracle was be-
hind the articulation of the mandible; no
mesopterygium (fused with propterygium, as
in Cestracion) ; antero-lateral clasper de-
rived from a radial cartilage; muscles of
shoulder girdle more modified than in sharks ;
loss of myocommata; flattened cord, like cyclo-
stomes ; lateral line primitive, with open canal ;
simplest acoustic macula ; grooved nostril, like
dipnoan ; teeth reduced, i. e., dental plates, equiv-
alent to oblique rows of separate teeth, and
produced by "concrescence of numerous simpler
teeth ;" appears to regard the few turns of intes-
tinal valve as ancestral to condition of Lepi-
dosteus and Ceratodus ; comments on hinder
position of pori abdominales.
1620. GESNER, C. De Aquatilibus, pp. 877 et seq.
1896. GILBERT, C. H. Ichthyological collection of "Al-
batross," 1891-92. (C. colliei.) Rep. U. S.
Comm. of Fisheries. Vol. for 1893. Washing-
ton, 1896, p. 398.

Fishes obtained by steamer "Albatross "

in St. Catalina Island, Monterey Bay, and vicin-
ity. (C. colliei.) Rep. U. S. Comm. of Fish-
eries for 1898. Washington, 1899, p. 25.

GILL, TH. Smithsonian Misc. Collections, p. 63.

— • Cat. of Fishes of the E. Coast of N. Am.

Proc. Acad. Nat. Sci. Phila., pp. 1-63.

— Proc. Acad. Nat. Sci. Phila., p. 331. [Hy-

1899.

1860.
1861.

1862.
1872.
1877.
1882.
1883.
1894.

1859.
1894.
1894.
1896.

drolagus (=Chimaera) colliei.]

Arrangement of the Families of Fishes.

Smithsonian Misc. Collections, pp. i-xlvi : 1-49.
Tr. Phil. Soc. Washington, Dec. 22, p. I.

(C. plumbea.)
Bull. U. S. Nat. Mus., Bibliogr. Fishes Pac.

Coast. (C. colliei.)
Proc. U. S. Nat. Mus., Vol. VI, p. 254-

(C. abbreviata.)

Mem. Nat. Acad. Sc., Vol. VI, p. 130.

(Chimaeridae divided into Chimserinae and Har-

riottinae.)
GIRARD, C. Rep. U. S. Pacific R. R., Fish, p. 360.

(C. colliei.)
GOODE and BEAN. Oceanic Ichthyology, pp. 243-

272, PI. xv.
— Proc. U. S. Nat. Mus., Vol. XVII, pp.

471-473, PI- xix. (Harriotta raleighana.)
GRIEG, J. A. Ichthyologiske Notiser. Bergens

Mus. Aarbog for 1894-95. Bergen, 1896.

1756. GRONOVIUS, L. T. Museum Ichthyologicum and in
Systema Naturae. (C. monstrosa.)

1763. Zoophylacium, Pt. I, p. 32. (Callo-
rhynchus.)

1854. GRONOVIUS. Gray's Edition of Catalogue Fishes,
pp. 15-16. (Callorhynchus centrinus and C. at-
lanticus.)

1763. GUNNER. Der Trondhiemske Selskabs Skrifter,
Vol. II, p. 270, Pis. v and vi.

1870. GUNTHER, A. Cat. Fishes in British Museum,
Vol. VIII, p. 350.

1880. Introduction to the Study of Fishes, pp.

348-350.

1887. Reference to very young specimens of C.

monstrosa. Challenger Report, Vol. XXII, pp.
12-13.

1840. HOBSON. Tasmanian Jour. Sci., Vol. I. (Cal.
australis.)

1872. HUTTON, F. W. Fishes of New Zealand. Co-
lonial Museum and Geological Survey. Hughes,
Wellington, p. 74. (Cal. antarcticus.)

1895. HOLT, E. W. L., and CALDERWOOO, W. L. Report

on the rarer fishes. Survey of Fishing Grounds,
West Coast of Ireland, 1890-91. Scientific
Trans. Roy. Dublin Soc., Vol. V, Ser. II, Pt. IX,
pp. 361-524-

1902. JAEKEL, O. Reference to Chimaera as the most
primitive Plagiostome in Ueber verschiedene
Wege phylog. Entwicklung. Fischer, Jena.
Pp. 58. (Ex. V. Internal. Zool. Cong. Berlin,
1901.)

— . JARDINE. Naturalist's Library. Fishes, Vol. Ill,
pp. 295-296. (C. monstrosa.)

1896. JORDAN, D. S., and EVERMANN, B. W. The

Fishes of North and Middle America, Vol. I,

PP. 93-97-
1883. JORDAN, D. S., and GILBERT, C. H. Synopsis.

P. 54-

1900. JORDAN, D. S., and SNYDER, J. O. Proc. U. S.

Nat. Mus., Vol. XXIII, pp. 338-339- (C. phan-
tasma.)

1901. - A preliminary check-list of the fishes of

Japan. Annot. Zool. Jap., Vol. TH, Pts. II and
III, pp. 3I-I59- Tokyo.

1904. On the species of White Chimoera from

Japan. Proc. U. S. Nat. Mus., Vol. XXVII,
pp. 223-226, 2 figs. (C. mitsukurii Dean MS.)

1838-53. KROYER, H. Danmarks Fiske, Vol. Ill, p. 783.

1798-1803. LACEPEDE. Hist. Nat. d. Poissons, Vol. I,
p. 392, PI. xix.

1825. LATREILLE. Uses Acantherina for Chimrera, a
family of Chondropterygiens with fixed gills.
Families naturelles du regne animal.

1839. LAY and BENNETT, v. BENNETT.

1851. LEYDIG, F. Zur Anat. u. Histol. d. Chimera mon-
strosa. Mill. Arch. f. Anat. u. Phys., Vol.
XVIII, pp. 241-271.

1881-90. LILLJEBORC, W. Sveriges fiskar, Vols. I-III.

LITERATURE LIST.

161

1754, 1755. LiNNfe, C. Systema Naturae: various edi-
tions, cf. esp. Gmelin's. (C. monstrosa.)
1883. MACLEAY. Fishes of Australia. (Callorhynchus.)
1877. MALM, A. W. Goteborgs och Bohuslans fauna.

Ryggradsdjuren. Goteborg. (C. monstrosa.)
1896. MAZZA, FELICE. Note anatomo-istologiche sulla
Chimaera monstrosa Linn. Atti Soc. Ligust.
Sc. Nat. e Geogr. Ann. 6, Fasc. 4, 15 pp., PI. I.
1889. MONTICELLI, F. S. Reference to food of Chi-
maera. Atti d. reale Ace. Lincei, Vol. (4) V,
Sem. i.

1833. MULLER, J. V. Chimaeroids Skeleton.
1776. MULLER, O. Prodr. Zool. dan., No. 320, p. 38.

(C. monstrosa.)

1832 and 1855. NILSSON, S. Prodr. ichth. scand., p. 112,
and Skand. faun. Fisk, p. 705. (C. mon-
strosa.)

1896. OLSSON, PETER. Sur Chimaera monstrosa et ses
parasites. Mem. Soc. Zool. France, Vol. IX,
No. s, pp. 499-512.
1812. PENNANT, T. British Zoology; Fishes, Vol. Ill,

P. 159-

18G8. POEY, F. Synopsis Piscium Cubensium, p. 445.
— . PONTOPPIDAN. Norges, etc. (Translation of
History of Norway, Vol. II, p. 114, PI. xxi.
(Reference to C. monstrosa.)

1815. RAFINESQUE, C. S. Analyse de la Nature, p. 92.
(Adopts Chismopnea for Chimaeroids and other
groups.)
1713. RAY, J. Reference in Synopsis Piscium, p. 23.

(C. monstrosa.)

1877. REGIUS, J. F. M. Essai sur 1'histoire naturelle
de la Provence et des departements circon-
voisins. I. Partie, Poissons, p. 78. Paris, Bail-
Here. (C. monstrosa.)
1835. RICHARDSON, J. Fauna boreali-Americ., Vol. Ill,

p. 286. (C. colliei.)
1810. Risso, A. Ichthyol. Nice, p. 53.
1826. _ — Hist. nat. Eur. merid., Vol. Ill, p. 168.

(C. mediterranea.)
1804. SHAW, G. General Zoology, Vol. V, Pt. 2, p. 365,

PI. CLVII. (C. monstrosa.)

1898. SMITT, F. A. Poissons de 1'Expedition Scien-
tifique a la Terre de Feu, etc. Bihang till K.
Svenska Vet. Akad. Handlingar, Vol. XXIV,
Afd. IV, No. 3, pp. 1-30.

1847. TEMMINCK, C. J., and SCHLEGEL, H. H. Fauna
Japonica, p. 300, PI. cxxxn. ("C. monstrosa.")
1877. THACHER, J. K. Reference to Chimaera as a di-
vergent form of shark, whose nearest relative is
Cestracion. Trans. Conn. Acad., p. 284.
1762. VULPECULA, STROM. Phys. og oeconom. beskriv.

overfogder. Sondmor, p. 289.

1898. WAITE, E. R. Report upon trawling operations
off the coast of New South Wales, between the
Manning River and Jervis Bay, carried on by
H. M. C. S. "Thetis." N. S. Wales Sea Fish-
eries, pp. 56-58. (C. ogilbyi.)

1904. WAITE, E. R. Mem. N. S. W. Naturalists' Club,
No. 2, p. ii. (C. ogilbyi.)

1899. WAITE, E. R. Scientific results of the trawling ex-
peditions of H. M. C. S. "Thetis." Introduction,
and Fishes. Mem. Austr. Mus., Vol. IV, Pt. I,
pp. 48-51. (C. ogilbyi.)

1904. Mem. N. S. W. Naturalists' club, No. 2,

p. 11. (C. ogilbyi.)

1685. WILLOUGHBY. Historia piscium, p. 57; also fig.,
copied from Clusius. (C. monstrosa.)

1829. YARRELL. Reference in British Fishes, Vol. II,
_pp. 464-467. (C. monstrosa).

1891. WOODWARD, A. SMITH. V. Chimaeroids Fossil.

1887. ZITTEL, K. V. V. Chimaeroids Fossil.

SKELETON. EXTREMITIES.

1833-44. AGASSIZ, L. Reference to clasping organs,
cf. Chimaeroids General; also, 1871, in Proc.
Boston Soc. Nat. Hist., Vol. XIV, p. 339.

1897. ALLIS, E. P. The morphology of the petrosal
bone and of the sphenoidal region of the skull
of Amia calva. Zool. Bull., Vol. I, pp. 1-26.

1899. BRAUS, H. Beitrage zur Entwicklung der Mus-
kulatur und des peripheren Nervensystems der
Selachier. 2 Theile. Morph. JB., Vol. XXVII,
3 u. 4, Leipzig, pp. 415-629.

1901. Die Muskeln und Nerven der Ceratodus-

Flosse. Ein Beitrag zur vergleichenden Mor-
phologic der freien Gliedmasse bei niederen
Fischen und zur Archiptergiumtheorie. Semon's
Zool. Forschungsreisen Austr. Malay. Archip.,
Vol. I, Lief. 3, pp. 137-300. (Deutsch. med.
nat. Gesell. Jena, Vol. IV.)

1870. COPE, E. D. Contribution to the Ichthyology of
the Lesser Antilles. Amer. Philos. Soc., Vol.
XIV, pp. 445-463.

1879. DAVIDOFF, M. Beitr. zur vergl. Anat. der hint.

Gliedmassen der Fische. Morph. JB., Part I,
pp. 450-520, Pis. xxvm-xxxi.

1883. - — Part III. Ceratodus. Morph. JB., Vol.
IX, pp. 117-162, PI. vni. (Chimxra pelvic girdle
and fin, pp. 142-143.)

1880. DAVIS, J. W. On the teleostean affinities of the

genus Pleuracanthus. Ann. Mag. Nat. Hist.,
Ser. 5, Vol. V, pp. 349-357-

1856. DUMERIL, A. Cf. Chimaroids General.

1903. FURBRINGER, KARL. Beitrage zur Kenntniss des
Visceralskelets der Selachier. Morph. JB., Vol.
XXXI, Heft 2 u. 3, pp. 360-445 (and Nachtrag,
ibid., H. 4, pp. 620-622).

1904. Beitrage zur Morphologic des Skelets der

Dipnoer. Semon's Zool. Forschungsreise, p. 502.
(Chimaeroids stand further from Prodipnoans
than Pleuracanthus.)

1897. FURBRINGER, M. Ueber die spino-occipitalen
Nerven der Selachier u. Holocephalen u. ihre
vergleichende Morphologic. Festschr. f. Gegen-
baur, Vol. Ill, pp. 347-788. Reference to Ex-
tremitatentheorie. Pp. 728 et seq. Reference
to lip cartilages (fusion of ventral labial carti-
lage of Callorhynchus secondary), p. 434.

l62

LITERATURE LIST.

1888. GADOW, HANS. Modifications of the first and sec-
ond visceral arches, with especial reference to
the homologies of the auditory ossicles. Phil.
Trans., Vol. CLXXIX, pp. 451-485, Pis. LXXI-
LXXIV.

1877. CARMAN, S. On the pelvis and external sexual

organs of selachians. Proc. Boston Soc. Nat.

Hist., Vol. XIX. Reference to Chimaeroids,

pp. 198-201.
1865. GEGENBAUR, C. Ueber den Brustgurtel und die

Brustflosse der Fische. Jen. Zeitschr., Vol. II,

pp. 121-125.

1869. U. d. Skelet d. Gliedmassen d. Wirbeltiere

im Allgemeinen u. d. Hintergliedmassen d.
Selachier insbesondere. Ibid., Vol. V, pp. 397-

1870.

1872.

447-

— t). d. Modificationen des Skelets der Hin-
tergliedmassen d. Mannchen d. Selachier u. Chi-
maeren. Ibid., pp. 448-458, fig. (Derives antero-
ventral clasper from fin skeleton.)
Reference in Das Kopfskelet der Sela-

chier.

1904. GOODRICH, E. S. On the dermal fin rays of fishes,

living and extinct. Quart. Jour. Micr. Sci., N.

S., Vol. XLVII, pp. 465-522, Pis. vii, 6 figs.

(Reference to Chimaeroids.)
1904. GREGORY, W. K. Reference to the relations of the

anterior visceral arches in Chimaera. Biol. Bull.,

Vol. VII, pp. 54-69, figs.
1879-82. HASSE, C. Das natiirl. System d. Elasmo-

branchier. Jena, p. 37.
1887. HowES, G. B. On the skeleton and affinities of

the paired fins of Ceratodus, with observations

upon those of Elasmobranchii. Proc. Zool. Soc.

Lond., pp. 3-26.

1890. - — Observations on the pectoral fin skeleton

of the living batoid fishes, and of the extinct
genus Squaloraja, with especial reference to the
affinities of the same. Proc. Zool. Soc. Lond.,
pp. 675-688.

1891. On the affinities, interrelationships, and

systematic position of the Marsipobranchii.
Proc. and Trans. Liverpool Biol. Soc., Vol. VI,
pp. 122-147. (Figures labial cartilages of Chi-
maeroids (Callorhynchus) and compares them
to those of Myxinoids.)

1902. In address before the Brit. Assn. refers

to chordal type of skel. in Chirmera. Nature,

Sept. 25, p. 526-
1901. HUBER, O. Die Kopulationsglieder der Selachier.

Zeitschr. f. Wiss. Zool., Vol. LXX, p. 87.
1876. HUBRECHT, A. A. W. Die Ordnungen d. Fische.

Bronn's Klassen u. Ordnungen. Liefg. I-IV,

Leipzig.
1876-78. Fins of Chimaera. Bronn's Klassen u.

Ordnungen, Vol. VI, I. Abth., p. 22, Taf. xxvin,

Reference to horn fibers not confirmed by P.

Mayer.

1877. HUBRECHT, A. A. W. Beitrage zur Kenntniss
des Kopfskelets der Holocephalen. Niederl.
Arch. f. Zool., Vol. Ill, pp. 255-276.

1877. Notiz iiber einige Untersuchungen am

Kopfskelet der Holocephalen. Morph. JB., Vol.
Ill, pp. 280-282.

1876. HUXLEY, T. H. Reference to Chimseroid fin.
Proc. Zool. Soc. Lond., pp. 52-53- Cf. also his
Comparative Anatomy of the Vertebrate Animals.

1899. JAEKEL, O. Organisation d. Petalodonten. Zeit-
schr. deutsch. geolog. Gesell., Vol. LI, Heft 2,
pp. 256-298.

1897-99. JAQUET, MAURICE. Contribution a 1'anatomie
comparee des systemes squelettaire et muscu-
laire de Chimaera colliei, Callorhynchus antarc-
ticus, Spinax niger, Protopterus annectans, Cera-
todus forsteri et Axolotl. Arch. Sci. Med. Bu-
carest, Vol. II, pp. 174-206; Vol. Ill, pp. 300-
340; Vol. IV, pp. 189-225, 241-273.

1898. JUNGERSEN, H. F. G. Reference to Chimaeroid

claspers. Anat. Anz., Vol. XIV, pp. 498-5*3-

1899. . On the appendices genitales in the Green-
land shark, Somniosus microcephalus (Bl.
Schn.) and other selachians. Danish Ingulf.
Expedition, Vol. II, pp. 88, Pis. v. Reference
to Chimaera, pp. 18, 20, 21, 76, 77, 83.

1893. KLAATSCH, H. Beitr. zur vergl. Anat. der Wirbel-
saule. I. Morph. JB., Vol. XIX, pp. 649-680.
General reference to Chimaera, pp. 666-670.

1859. KOLUKER, A. On the structure of the chorda dor-
salis of the Plagiostomes and some other fishes,
and on the relation of the proper sheath to the
development of the vertebrae. Proc. Roy. Soc.
Lond., Vol. X, pp. 214-222.

1887. LwoFF, B. Vergleichend-anatomische Studien
iiber die Chorda und die Chordascheide. Bull.
Soc. Imp. Naturalistes de Moscou, No. 2, Pis.
iv, pp. 442-482.

1879. METSCHNIKOFF, OLGA. Reference to girdles of
Chimsera monstrosa in Zeit. f. wiss. Zool., Vol.
XXXIII, pp. 425, 428-430, 436, PI. xxiv.

1886. MEYER, P. Reference to vertebral characters of
Chimaera. MT. Stat. Neap., Vol. VI, pp. 265-270.

1879. MIVART, S. G. Notes on the fins of elasmo-
branchs, with considerations on the nature and
homologies of vertebrate limbs. Trans. Zool.
Soc. Lond., Vol. X, pp. 439-484, and abstr., 1878,
Trans. Zool. Soc., pp. 116-120.

1834. MULLER, J. Summarizes characters of Chimxroid.
Abh. Akad. Berl., p. 74; note also pp. 131, 141, 149,
structure of cartilage, vertebral arches, anterior
condylar facets. Also 1838, p. 238, labial carti-
lages ; pp. 197-202 (variable) ; quadrate fusion,
pp. 200-202, 221; dental plates, p. 200; skull and
suspensorium, pp. 217-223; gills, pp. 217, 220;
snout cartilages, pp. 229, 230, 233; nasal cap-
sules, pp. 235, 236.

1886. PARKER, T. J. On the claspers of Callorhynchus.
Nature, Vol. XXXIX, p. 635.

LITERATURE LIST.

i63

1897. PARKER and HASWELL. Reference in Textbook of
Zoology (Macmillan), Vol. II, pp. 173-183, to
pharyngohyal of second arch ("represents hyo-
mandibular of shark") ; halves of pelvic arch
separate (joined by ligament only) ; calcified
ring-vertebrae in Chimaera ; fused pterygiophores
in dorsal.

1883. PARKER, W. K. On the skeleton of the marsipo-
branch fishes. Phil. Trans. Roy. Soc. Refer-
ence to Chimaera, pp. 450-451.

1902. PRINCE, E. E. Reference to fin of Chimaera in

paper on Lamna in Supp. to 32d Annual Rep. of
Dept. of Marine Fisheries. Ottawa, 1901.

1897. RABL, C. Theorie des Mesoderms. Engelmann,
Leipzig, p. 299. (Accepts Chimaeroids and No-
tidanus as phylogenetically older sharks.)

1901. — • Reference to fins of Chimaera as indicating

little or no tendency for fusion of radials
around metapterygium. Zeit. f. wiss. Zool., Vol.
LXX, pp. 479, 482-483, 524, 525, S3L Reference
to vertebral column in Chimaeroids, p. 454.

1892. REIS, O. M. Reference to skel. characters, "cen-
tra," claspers, in O. d. Kopfstacheln b. Menas-
pis armata Ewald. Miinchen, Kutzner.

1.1!)5. On the structure of the frontal spine and

the rostro-labial cartilages of Squaloraja and
Chimaera. Geol. Mag., Decade IV, Vol. II, pp.
385-391, PI. xn.

1897. REYNOLDS, S. H. The vertebrate skeleton. Cam-

bridge.

1887. RIESS, J. Reference to histol. structure of clasp-
ers of Chimaera. Palaeontographica, Vol.
XXXIV, p. 17, PL H, fig. 12.

1904. SABATIER, A. Sur les mains scapulaires et pel-
viennes des Poissons holocephales et chez les
dipneustes. C. R. Acad. Sci. Paris, Vol.
CXXXVIII, pp. 249-252.

1901. SCHAFFER, JOSEF. Ueber den feineren Bau und
die Entwicklung des Knorpelgewebes und iiber
verwandte Formen der Stutzsubstanz. Zeit. f.
wiss. Zool., Vol. LXX, pp. 109-170.

1903. SCHAUINSLAND, H. Beitragc zur Entwicklungs-

geschichte und Anatomie der Wirbelthiere.
Zoologica, Vol. XVI, Heft 39, pp. 1-98.

1904. Reference to vertebral column of Chi-
maera in O. Hertwig"s Handbuch d. Entwick-
lungsgeschichte d. Wirbeltiere.

1817. SCHULTZE. Nonnulla de primordiis systematis
ossium et de evolutione spinae dorsi in animali-
bus. Merkel's Archiv, Vol. IV, p. 329. Refers
to vertebrae of Chimaera as a higher " Bildung-
stufe " than chordal. 500 rings present.

187G. SOLGER, B. (Chimaera monstrosa. On two hith-
erto undescribed cartilages in the visceral skele-
ton.) Morph. JB., Vol. I, Heft I, pp. 219-221.

MUSCLES, INTEGUMENT, AND TEETH.

1898. ALLIS, E. P., jr. Muscles et Nerfs chez 1'Amia

calva. Arch, de Zool. Exp. et Gen., 3e serie,
Vol. VI, pp. 63-00.

1900. CORNING, H. K. Ueber die vergleichende Anato-
mie der Augenmuskulatur. Morph. JB., Vol.
XXIX, i, pp. 94-140. Refers to origin of rectus
internus, and to course of oculomotor. Former
resembles condition in Petromyzon, and, accord-
ing to Allis and Gegenbaur, is primitive — their
view not accepted by Corning.

1852. COSTA, O. G. V. Chimaeroids General.

1894. DEAN, BASHFORD. V. Chimaeroids General.
1904. — — — Notes on the anatomy of Rhinochimaera

in Jour. Sci. Col. Tokyo, Art. 4, pp. 23, Pis. II.

1903. FURBRINGER, K. Reference to musculi levatores

anguli oris in Chimaera as constrictors, thus con-
firming Vetter as to their primitive nature.
Morph. JB., Vol. XXXI, H. 2 u. 3, p. 387.
1897. FURBRINGER, M. Ueber spino-occipitalen Nerven
der Selachier u. Holocephalen u. ihre verglei-
chende Morphologic. Leipzig, Gegenbaur Fest-
schrift, Vol. Ill, pp. 347-788.

1904. GARMAN, S. V. Chimaeroids General.

1870. GUNTHER, A. Catalogue of Fishes in the British
Museum, Vol. VIII. Reference to dorsal row
of scales in Chimaera and in .Scyllium, p. 403.

1873. HEINCKE, FR. Untersuchungen iiber die Zahne
niederer Wirbelthiere. Zeit. f. wiss. Zool., Vol.
XXIII, pp. 495-591-

1897-99. JAQUET, M. V. Chimaeroids, Skeleton.

1886. MEYER, P. Reference to dermal denticle ridges in
sharks, which appear closely akin to those of
Chimaera. MT. Stat. Neap., Vol. VI.

1840. OWEN, R. Odontography, Vol. I. Reference to
Chimaeroid, pp. 64-68. Regards dental plates
as "an extreme but still more anomalous modi-
fication of the chondropterygious type," "like
Cestracion."

1891. POLLARD, H. P. Anat. Anz., Vol. VI, pp. 338-344.
Reference to the reduction of dermal defenses
in Chimaeroids.

1895. REIS, O. M. Illustrationen zur Kenntniss des

Skelets von Acanthodes Bronni, Agassiz. AH.
Senckenberg. naturforsch. Gesell., pp. 49-64, PI.
Reference to median tooth of "Prognathodon-
ten Holocephalen," p. 51.

189G. Ueber Acanthodes Bronni, Agassiz.

Schwalbe's Morph. Arb., Vol. VI, pp. 143-220.
Reference to levator anguli oris as also closing
mouth (adductor in Chimaera) — similar condi-
tion to Acanthodes, spines also correspond struc-
turally, and granular calcification of cartilage
(Ischyodus).

1878. VETTER, B. Z. vergl. Anat. d. Kiemen- u. Kiefer-
musculatur d. Fische. II. Jen. Zeitschr., Vol.
XII, pp. 431-450. Accepts fusion of palate with
skull. Muscles like Heptanchus, but " less spe-
cialized and differentiated than in any one of
the sharks investigated, a state indeed which in
its ground plan enables us to reconstruct hypo-
thetically the comparative estimate of the latter."

164

LITERATURE LIST.

1886. WORTMAN, J. S. Teeth of the Vertebrata. Ref-
erence in vol. from Amer. System of Dentistry,
PP- 364-379.

VISCERA, CIRCULATORY.

1886. BEMMELEN, J. F. VAN. Reference to the entire
degeneration of the hindmost (sth) gill slit in
Chimaera. MT. Stat. Neapel, p. 171.

1898. BLES, E. J. On openings in wall of body-cavity
of Vertebrates. Proc. Roy. Soc. Lond., Jan. 13,
Vol. LXII, pp. 232-247.

— The correlated distribution of abdominal

1898.

189T.
1837.

1839.
1865.

1884.
1886.
1890.

1890.

1891.
1853.
1879.
1894.

1895.
1836.

pores and nephrostomes in Fishes. Jour. Anat.

and Phys., Vol. XXXII, pp. 483-512.
COLLINGE, W. E. The supra-renal bodies of

Fishes. Nat. Sci., Vol. X, No. 63, pp. 318-322.
DUVERNOY, M. Sur deux bulbes arteriels faisant

les fonctions de cceurs accessoires, qui se voient

dans les arteres innominees de la Chimere arc-

tique. Annales des sciences naturelles, Vol.

VIII, pp. 35-41, PI. in, fig. 2.

Du mecanisme de la respiration dans les

Poissons. Paris. Ibid., Vol. XII, p. 27, Pis.

V-VI.

GEGENBAUR, C. Zur vergleichenden Anat. des
Herzens. I. Ueber den Bulbus arteriosus der
Fische. Jen. Zeitschr., Vol. II, pp. 365-385.

Ueber d. Abdominalporen der Fische.

Morph. JB., Vol. X, pp. 462-464.

Ueber d. Conus arteriosus d. Fische.

Morph. JB., Vol. XIII, pp. 405.

HOWES, G. B. Reference to rudiment of vesicula
seminalis in female Chimaera (re cloacal caecum).
Linn. Soc. Jour., Vol. XXIII, p. 405.

Reference to Chimaeroids in visceral anat-
omy of Australian Torpedo (Hypnos subni-
grum). Proc. Zool. Soc. Lond., No. XLV,
pp. 669-674.

Reference to Holocephala having (with

sharks) nephrochidic characters. Cardiff Meet-
ing of British Ass'n.

HYRTL, J. Reference to viscera, especially repro-
ductive organs, of Chimaera. SB. Akad. Wien,
Vol. XI, p. 1085 et seq.

LANKESTER, E. R. On the hearts of Ceratoclus,
Protopterus u. Chimaera. Proc. Zool. Soc. Lond.,
Vol. X, pp. 493-506, Pis. n.

MAZZA, F., and PERUGIA, A. Sulla glandula digiti-
forme (Leydig) nclla Chimaera monstrosa Linn.
Atti Soc. Lig. di Sc. Nat., Anno V, fasc. II.
Genoa.

MAZZA, F. Note anatomo-istologiche sulla Chi-
maera monstrosa. Atti Soc. Lig. di Sc. Nat.,
Vol. VI, pp. 15, PI. xn. Reference to spermato-
genesis.

MULLER, J. Vergl. Anat. d. Myxinoiden. AH.
Akad. Berlin. Reference to bulbus, p. 193; circ.
cephal., pp. 196-289; gill ves., p. 196; pseudo-
branch absent, p. 253.

1S96. OPPEL, A. Reference to stomach, in Lehrb. d.

vergl. mikr. Anat. d. Wirbelth., Vol. II. Jena,

Fischer.
1898. Verdauungs-Apparat ; Mundhohle mit

Zunge ; Speicheldriisen ; Schlund ; Magen ;

Darm ; Brunnersche Driisen ; Bauchspeichel-

driise ; Leber. III. Ergebnisse der Anat. u.

Entwickelungsgeschichte, Vol. VIII, pp. 124-100.
1867. PANCERI, P. Circa particolaria appendici delle

branche della Cephaloptera giorna. R. Accad. d.

Sci. d. Napoli, pp. 3-7.
1898. PARKER and HASWELL. Reference in Textbook of

Zoology (Macmillan), Vol. II, pp. 173-183, to gills,

testes, spermatophores, vestigial Miillerian duct.

1898. REDEKE, H. C. Onderzoekingen betreffende het

Urogenitaalsysteem der Selachicrs en Holoce-
phalen. Helder, C. de Boer Tt., pp. 85, Pis. n.

1899. Kleine Beitrage zur Anatomic der Pla-

giostomen. Tijds. Ned. Dierk. Ver. (2), Vol.
VI, pp. II9-I35-

1894. SPENCER, B. Contributions to our knowledge of
Ceratodus. PI. I. The blood vessels. Macleay
Memorial Volume, pp. 1-34, Pis. v. Reference
to opercular gill of Chimaeroids, cartoids, intra-
intestinal vein.

1898. D. Bau der Lungen v. Ceratodus u.

Protopterus. DS. Med. Naturw. Gesell., 4, 8 pp.

1903. STEPHAN, P. L'evolution des corpuscles centraux
dans la spermatogenese de Chimaera monstrosa.
C. R. Soc. Biol. Paris, Vol. LV, pp. 265-267.

1876-77. STOHR. Ueber d. Conus arteriosus d. Selach.,
Chim. u. Ganoiden. Morph. JB., Vol. II, pp.
197-228.

1902. STUDNICKA, F. K. Ueber das Epithel der Mund-
hohle von Chimaera monstrosa mit besondcrer
Berikksichtigung der Lymphbahnen derselben.
Bibliogr. Anat. Nancy, Vol. XI, pp. 217-233, 5 figs.

1874. VETTER, B. Unt. z. vergleich. Anat. d. Kiemen-
u. Kiefermusculatur d. Fische (Elasmobranchii).
Jen. Zeit. Nat., Vol. IX, pp. 405-456.

NERVOUS SYSTEM AND END ORGANS.

1897. ALLIS, E. P. The morphology of the petrosal

bone and of the sphenoidal region of the skull
of Amia calva. Zool. Bull., Vol. I, pp. 1-26.

1898. BRAUS, H. Cf. Chimaeroids, Skeleton.

1838. BRESCHET, M. G. Recherches anatomiques et phy-
siologiques sur 1'organe de 1'oui'e des Poissons.
Mem. Acad. Sci. Inst. France, Vol. V, pp. 7°-73-

1894. BURCKHARDT, R. Bauplan d. Wirbelthiergehirns.
Schwalbe's Morph. Arb., Vol. IV, pp. 131-150;
V, p. 137, PI- vin.

1893. Vergl. Anat. d. Vorderhirns bei Fische.

Anat. Anz., Vol. IX, pp. 375-382.

1901. BURNE, R. H. Note on the innervation of the
supraorbital canal in the catfish (Chimaera mon-
strosa). Proc. Zool. Soc. Lond., Vol. I, pp.
184-187.

1849. BUSCH, W. De Selachiorum et Ganoideorum En-
cephalo. Inaug. Dissert. Berlin.

LITERATURE LIST.

189G. COLE, F. J. The cranial nerves of Chimaera mon-
strosa. Proc. Roy. Soc. Edinb., Vol. XXI,
March, pp. 49-50.

1896. — — On the sensory and ampullary canals of
Chimaera. Anat. Anz., Vol. XII, No. 7, pp.
172-182.

1890. On the cranial nerves of Chimaera mon-

strosa Linn., with a discussion of the lateral
line system and of the morphology of the mem-
brana tympani. Trans. Roy. Soc. Edinb., Vol.
XXXVIII, part 3, No. 19, pp. 631-680.

ISDN. — — Structure and morphology of the cra-
nial nerves and lateral sense organs of fishes,
with special reference to the genus Gadus.
Trans. Linn. Soc. Lend., (2) Zool., Vol. VII,
pp. 115-221, Pis. in. Reference to Chimaera.

1898. — - Reflexions on the cranial nerves and sense
organs of fishes. Trans. Liverp. Biol. Soc., Vol.
XII, pp. 228-247. Reference to Chimaera: Cra-
nial nerves have, except in one case, independent
roots, archaic, perhaps primitive ; Chimaeroids
less divergent skeletally from palaeozoic ances-
tors than teleosts from theirs. P. 244.

1899. On the cranial nerves and sense organs

of fishes. Anat. Anz., Vol. XVI, No. 2, pp. 40-48.

1896. COLLINGE, W. E. On the sensory and ampullary
canals of Chimaera. (Abstr.) Zool. Anz., Vol.
XIX, No. 493, p. 31. Same title: Proc. Zool.
Soc. Lond., Vol. IV, pp. 878, 888, 800.

1892. EWART, J. C. The lateral sense organs of elasmo-
branch. I : The sensory canals of Laemargus.
Edinb. Roy. Soc., July, 1891, Vol. XVII, pp. 59-
105. Zool. Anz., No. 387, 1892, pp. 1-3.

1896. FURBRINGER, M. Ueber die spino-occipitalen Ner-
ven der Selachier und Holocephalen und ihre
vergl. Morphologic. Festschr. f. C. Gegenbaur,
Vol. Ill, pp. 351-788.

1888-89. CARMAN, S. Lat. line of selach. and holoce-
phali. Bull. Mus. Comp. Zool., Harv. Coll., Vol.

XVII, p. 57.

1877. HUBRECHT, A. A. W. Beitrag zur Kenntniss des
Kopfskelets der Holocephalen. Niederl. Archiv
f. Zool., Vol. Ill, pp. 255-276.

1903. JAEKEL, O. Reference to the presence of an epi-

physeal opening in the cranium of Chimaera
monstrosa. SB. Gesell. Naturf. Freunde Ber-
lin, pp. 35-36.

1851. LEYDIG, F. Zur Anat. u. Histol. d. Chimaera mon-
strosa. Mill. Arch. f. Anat. u. Physiol., Vol.

XVIII, pp. 241-271.

1864. MAYER, F. J. C. Reference to Chim. in Ueber den
Bau des Gehirns Fische in Beziehung auf eine
darauf gegriindete Eintheilung dieser Thier-
klasse. Nova Acta Acad. Cass. Leop. Nat. Cu-
rios., Vol. XXX, AH. VI.

1904. MERRITT, O. A. The theory of nerve components.

J. Anat. and Phys., Vol. XXXIX. Reference to
Chimaera, p. 207.

1870. MIKLUCHO-MACLAY (and GEGENBAUR, C.). Note

on brain of Chimaera. Jen. Zeitschr., Vol. V,

p. 132.
1851. MULLER, H. Ueber d. nervosen Follikel-Apparat

d. Zittcrrochcn u. d. sogen. Schleimkanale der

Knorpel-Fische. Erl. Verh. Phys.-Med. Gesell.

Wiirzburg, Vol. II, No. 10, pp. 134-150.
1842. MULLER, J. Remarks upon Valentin's paper on

the nerves and heart of Chimaera. Bericht iiber
— die Fortschritte der vergleichenden Anat. der

Wirbelthiere im Jahre (1842). Archiv f. Anat.,

1843, p. 253.
1846. Reference to Chimaera in Ueber den

Bau und die Grenzen der Ganoiden und iiber das

natiirliche System der Fische. Abhandl. Akad.

Wiss. Berlin, pp. 117-216.

1898. PARKER and HASWELL. Reference in Textbook of

Zoology (Macmillan), Vol. II, pp. 173-183, to
brain of Callorhynchus as unlike Scyllium, but
having fairly close resemblance to Scymnus.

1901. RABL, C. Reference to Fiirbringer's work on cra-
nial nerves of Chimaeroids. Zeit. wiss. Zool.,
Vol. LXX, p. 529.

1881-84. RETZIUS, G. Das Gehororgan d. Wirbelthiere.
Morph.-histol. Studien. 2 Theile. Stockholm,
pp. 101-104.

1897. RUGE, G. Reference to distribution of facial
nerve in Chimaeroids. Festschr. f. Gegenbaur,
Vol. Ill, pp. 207, 213, 250-254.

1879. SCHWALBE. Reference to nerves of Chimaera in

Das Ganglion Oculomotorii. Jen. Zeitschr., Vol.
XIII, p. 173-

1880. SOLGER, B. Reference to histology of sensory

canals in Chimaera in Neue Untersuchungen zur

Anatomic der Seitenorgane der Fische. Archiv

mikr. Anat., Vol. XVII, p. 95-
1889. Mauthner'sche Fasern bei Chimaera. Morph.

JB., Vol. XV, pp. 322-324, PI. xxvn.
1849. STANNIUS, H. Reference to Chimaera in Das

periph. Nervensystem. Rostock.
1854. Handbuch der Anatomic der Wirbelthiere.

Berlin.

1895. STUDNICKA, F. K. Beitrage zur Anatomie und

Entwickelungsgeschichte des Vorderhirns der
Cranioten. SB. bohm. Gesell. Wiss., pp. 1-42.

1896. - — Same title, pp. 1-32.

1899. Ueber das Ependym des Centralnerven-

systems der Wirbelthiere. SB. bohm. Gesell.
Wiss., pp. 1-7.

1900. Zur Kenntniss der Parietalorgane und

der sog. Paraphyse der niederen Wirbelthiere.
VH. d. Anat. Gesell., pp. 101-110.

Ueber das Ependym des Centralnerven-

1900.

systems der Wirbelthiere. SB. bohm. Gesell.
Wiss., No. 45, pp. 7.

1900. Der "Reissnersche Faden" aus dem Cen-

tralkanal des Riickenmarkes und sein Verhalten
in dem Ventriculus (Sinus) terminalis. Ibid.,
No. 36, 10 pp.

1 66

LITERATURE LIST.

1842. VALENTIN. Ueber das centrale Nervensystem

und die Nebenherzen der Chimaera monstrosa.

Miiller's Archiv f. Anat, pp. 25-45.
1877. WILDER, B. G. Brain of Chimaera monstrosa.

Proc. Phil. Acad. Sci., May, pp. 219-250.
1898. Reference to olfactory portion of brain of

Chimsera. Science, N. S., Vol. VII, pp. 150-152.

EMBRYOLOGY.
(Mainly references to egg capsules.)

1890. ALCOCK, A. Cf. Wood-Mason and Alcock.
1892. Reference to egg capsule of Chimaera

monstrosa dredged at 410 fathoms off the Coro-

mandel coast. Indian Marine Survey.
1869. BESSELS, E. Reference to egg of Ischyodus

from Jurassic of Wiirtemberg in Jahreshefte d.

Ver. f. vaterl. Naturkunde in Wiirtt., Vol. XXV,

p. 152, PL in.
1875. COLLETT, R. Norges Fiske. Tillaegshefte til Vi-

denskabs Selsk. Forhandl. for 1874. Christ., 1875.

Figures egg of Chimaera.
1871. CUNNINGHAM, R. O. Notes on Callorhynchus :

egg figured. Nat. Hist, of Strait of Magellan

(of the "Nassau"), p. 340.
1897. DEAN, B., CALKINS, G. N., HARRINGTON, N. R.,

and GRIFFIN, B. B. The Columbia University

Zoological Expedition of 1896. With a brief

account of the work of collecting in Puget

Sound and on the Pacific Coast. Trans. N. Y.

Acad. Sci., Vol. XVI, pp. 33-42.
DEAN, BASHFORD. On the embryology and phy-

logeny of Chimaera. Abstr. of paper before

Amer. Morph. Soc. Science, N. S., Vol. XI,

pp. 169-170.
— The early development of sharks from a

comparative standpoint. Science, N. S., Vol.

XV, No. 381, p. 626.

The development of Chimsera colliei.

1900.

1902.

1903.
1904.

1904.
1904.
1904.

1904.
1904.

1865.

Biol. Bui., Vol. IV, pp. 270-286, figs.

Reference to capsule of Chimaera mitsu-

kurii. Jour. Sci. Coll. Tokyo, Vol. XIX, Art. 3,
pp. 6-7, PI. i, fig. 2.

Reference to capsule of Chimasra phan-

tasma. Jour. Sci. Coll. Tokyo, Vol. XIX, Art. 3,
pp. 5-6, PI. i, fig. 4.

Reference to capsule of Rhinochimasra

pacifica. Jour. Sci. Coll. Tokyo, Vol. XIX, Art.
4, pp. 18-19, PI. II.

Evolution in a determinate line as illus-

trated by the egg cases of Chimaeroid fishes.
Biol. Bull., Vol. VII, pp. 105-112.

The egg cases of Chimasroid fishes. Am.

Nat., Vol. XXXVIII, pp. 486-487.

L'osuf de Chimaera colliei et 1'adaptation

de sa capsule. C. R. de la Soc. de Biologic
(Seance du 2 Juillet), Vol. LVII, p. 14-
DUMERIL, A. Reference to capsule of Callo-
rhynchus in Elasmobranches, Vol. I, p. 683, and
Atlas, PI. vin, figs. 6, 7, and 8.

1899.

1905.
189C.

1899.
1880.

18S7.

1889.

GARMAN, S. Report on an expedition off the
west coast of Mexico. Mem. Mus. Comp. Zool.,
Vol. XXIV, p. 20, and PI. LXIV, fig. 2. Refer-
ence to capsule of "Callorhynchus antarcticus.''

GILL, THEO. An interesting Cretaceous Chimae-
roid egg-case. Science, N. S., Vol. XXII, pp.
601-602.

GRIEG, J. A. Ichthyologiske Notiser. Bergens Mu-
seums Aarbog for 1894-95. Figures imperfect
capsule of C. monstrosa.

Similar note. Ibid, for 1898.

GUNTHER, A. Figure of capsule of Callorhynchus

in Study of Fishes, p. 169.

In Challenger Reports, Vol. XXII, pp. 12-

13, reference to very young individuals taken by
"Triton" and "Knight Errant," and comments
on the precocious appearance of claspers. "No
well-authenticated egg (of Chimaera) in any
collection."

Deep-sea trawling cruise off the S. W.

coast of Ireland. Chimaera "monstrosa" egg cap-
sule 6f/2 inches long dredged at 315 fathoms. 'No
filaments for adhesion ; they would probably be
useless at a depth where the water is probably
quiet. The eggs lie on the ground or are im-
planted in the ooze by their styliform end.' Ann.
N. H. (6), Vol. IV, pp. 415-417, ng. Refer-
ence to capsule of C. phantasma, but without
description or figure.

1897. HOWES, G. B. Remarks on eggs of Bdellostoma
and Chimaera. Linnaean Soc. (Exhibition of
above), Feb. 4.

1901. JAEKEL, O. Notes on capsules of Chimaera, Callo-
rhynchus and Ischyodus (=Aletodus) in
Neues JB. f. Mineral., Geol. u. Palaeont., Vol.
XIV, pp. 552-554. P's. xxn-xxiv, and figs. 3.

1858. LUTKEN, C. F. Reference to capsule of Chimasra
in Nogle Bemasrkninger om de nordiske
Aegaarter. Vid. Meddel. fra d. naturh. For.,
Nos. 5-7.

1877. MALM, A. W. Similar reference in Goteborgs
och Bohuslans fauna. Ryggradsdjuren. Gote-
borg.

1895. MAZZA, F. Reference to development of frontal

organ in Chimaera in Atti Soc. ligus. Sci. nat.,
Vol. VI, p. IS, PL xii.

1842. MULLER, J. Fig. of egg capsule of Callorhynchus
in "Ueber den glatten Hai." SB. Akad. Berlin,
PL vi, fig. 3. (Still the best figure of this cap-
sule!)

1855. NILSSON, S. Skandinavisk fauna, Vol. IV, Fis-
karne. Lund.

1896. OLSSON, P. Sur Chimaera monstrosa et ses Para-

sites. Mem. Soc. Zool. France, Vol. IX, No. 5,
pp. 449-501. (Figures an imperfect egg capsule.)

1897. PARKER and HASWELL. Textbook of Zoology.

Figures capsule of Callorhynchus, Vol. II, p. 182.

LITERATURE LIST.

167

1886. RENAULT, B., and ZELLER, R. Reference to Fayo-
lia and Palxoxyris (Spirangium) in Comptes
rendus de 1'Academie des Sciences, Vol. CVII,
p. 1022.

1903. SAUVAGE, H. E. Reference to Jurassic Spiran-
gium in Mem. Real. Acad. Cienc. Art. de Barce-
lona, Vol. IV, pp. 6-7, PL i, fig. i.

1903. SCHAUINSLAND, H. Beitrage zur Entwicklungs-
geschichte und Anatomie der Wirbelthiere. I.
Callorhynchus. Zoologica, Vol. XVI, Heft 39,
pp. 1-98, Pis. xn-xxiv. (Also preliminary notice
in VH. V., internat. Zool. Congr. Berlin, pp.
658-659.)

1903. STEPHAN, P. L'evolution des Corpuscles Cen-
traux dans la Spermatogenese de Chimaera mon-
strosa. Comptes rendus des seances de la Re-
union Biologique de Marseille, Feb. 17, pp. 1-3.
Also in C. R. Soc. Biol. Paris, Vol. LV, pp.
265-267.

1882. VAILLANT, L. "Travaillgur" finds young Chi-
maera (130 mm.) with fragments of egg case in
Gulf of Gascony.

1901. VAVRA. Comments upon and figures egg capsule
of Callorhynchus in Vesmir, pp. 184-185.

1891. WOOD-MASON, J., and ALCOCK, A. Reference to
capsule of " PCallorhynchus " ( = ?Harriotta
indica) in Ann. Mag. Nat. Hist., 6 ser., Vol.
VIII, pp. 21-22, fig. Specific name by (1899)
Garman, S., in Mem. Mus. Comp. Zool., Vol.
XXIV, p. 21.

FOSSIL CHIM/EROIDS.

[In preparing the present summary the author acknowledges
his indebtedness to Smith Woodward's Catalogue of Fossil
Fishes in the British Museum, Vol. II.]

AGASSIZ, L.

1833-44. Recherches sur les poissons fossiles.

Reference to Spinacorhinus (=Squaloraja).
Feuill., 1837, p. 94, and Vol. Ill, Pis. XLII, XLIII,
and 1834, Vol. Ill, p. 381.

Reference to Chimxra (Ischyodon) johnsonii, p.
344, PI. XL c, fig. 22; also Chimxra (Ischyo-
don) egertoni, Vol. Ill, p. 340, PI. XL c, figs.

I-IO.

Reference to Myriacanthus. Ibid., p. 38, PI. vi, and

p. 39, PI. vni a, figs. 14, 15.
Reference to Myriacanthus granulatus. Ibid., p.

40, PI. vni a, fig. 16, 1837.
Reference to Lcptacanthus tenuispinus. Ibid., p.

27, PI. i, figs. 12, 13.
Reference to Spinacorhinus polyspondylus. Ibid.,

Pis. XLII, XLIII, and Feuil., p. 94, 1836.
Reference to Lcptacanthus (Ganodus), Vol. Ill,

p. 27, (in part), 1837.
Reference to Psittacodon (Ganodus). Ibid., 1843,

p. 340; Psittacodon (Edaphodon). Ibid., 340

(in part).
Reference to Chimaera (Ganodus) owenii. Ibid.,

p. 347, PI. XL, figs. 6.

AGASSIZ, L. — (Continued.)

Reference to Chimxra (Ganodus) colei. Ibid.

(ex Buckland MS.), p. 346, PI. XL, figs. 8-10.
Reference to Chimaera (Ischyodon) tessoni. Ibid.,

p. 342, PI. XL, fig. 19.
Reference to Chimaera (Ischyodon) beaumontii.

Ibid., p. 346.

Reference to Chimaera (Ischyodon) townsendii.
Ibid., p. 343, PI. XL, figs. 20-22 ; PL XL c, figs. 17,
_i8._
Reference to Chimaera (Ischyodon) brevirostris.

Ibid., p. 344 (name only).
Reference to Chimaera ( Ischyodon )agassizii. Ibid.,

PL XL c, figs. 14, 15.
Reference to Chimxra (Ischyodon) centertrii.

Ibid., p. 345.
Reference to Chimaera (Psittacodon) sedgwickii.

Ibid., p. 349, PI. XL, figs. 17, 18.
Reference to Chimasra (Psittacodon) mantelli.
Ibid., p. 348, PL XL a, figs, i, 2, Vol. Ill, 1843.
Reference to Chimaera(Ischyodon)agassizii. Ibid.,
p. 341, PL XL a, figs. 3, 4 ( ?s), PL XL c, figs. 16
(non figs. 14, 15).
Reference to Edaphodon bucklandi. Ibid., p. 351,

PL XL d, figs. 1-4, 9-12, 19-24.
Reference to Edaphodon eurygnathus. Ibid., p. 352.
Reference to Edaphodon leptognathus. Ibid., p.

352, PL XL a, figs. 5-8, 13-18.
Reference to Ischyodus [=Chimaera (Ischyodon)]

helvetica. Ibid., p. 345, PI. XL c, figs. 20, 21.
AMMON, LUDWIG VON.

1896. Ueber neue Stiicke von Ischyodus. Berichte
Naturwiss. Ver. Regensburg, Heft 5 (Fest-
schrift), 1894-95, pp. 253-263, 2 Taf., i fig. (I.
schtipleri, avitus).
1899. Ein schemes Exemplar von Ischyodus avitus.

Geogn. Jahresh., Vol. XI, pp. 158-160, I Taf.
BASSANI, F.

1901. Reference to Chimaera bucklandi in "Sue alcuni
avanzi di pesci del pliocene toscano." Monitore
Zoologico Italiano, Vol. XII, N. 7, p. 189.
BENSTED, W. H.
1862. Reference to Ischyodus agassizii. Geologist, Vol.

V, p. 378 (errore).
BESSELS, E.

1869. Reference to egg-case of Plschyodus (Jurassic of
Wiirttemberg). Jahreshefte d. Ver. f. vaterl.
Naturkunde in Wiirtt., Vol. XXV, p. 152, PL in.
BUCKLAND, W.

1835. Chimaera egertonii, townsendii, and mantellii ; also
Chimxra agassizii. Proc. Geol. Soc. Lond., Vol.
II, p. 206; v. also in Phil. Mag. (3), Vol. VIII,
p. 5, 1836.

1838. Reference to Passalodon (Syn. Edaphodon).
Proc. Geol. Soc. Lond., Vol. II, p. 687.

COOMARASWAMY, A. K.

1903. List of Fish Teeth of Bagshot Lands (London
Basin), etc. Proc. Geol. Assoc. Lond., Vol. IX,
pp. 83-84.

1 68

LITERATURE LIST.

COPE, E. D.

1869. Reference to Edaphodon (=Ischyodus) monolo-
phus. Proc. Bost. Soc. Nat. Hist., p. 314.

Reference to Edaphodon (=Ischyodus) smocki.
Ibid., p. 316.

Reference to Ischyodus (mirificus, smocki, mono-
lophus, divaricatus). Ibid., p. 314.

Reference to Sphagepcea aciculata. Proc. Amer.
Philos. Soc., Vol. XI, p. 241.

Reference to Edaphodon (Ischyodus) divari-
catus. Proc. Bost. Soc. Nat. Hist., p. 315, and
Vert. Cret. Form. West., Vol. II, pp. 185-292,

1875.

Reference to Leptomylus densus. Proc. Bost.
Soc. Nat. Hist, Vol. XII, p. 313.

1871. Reference to Leptomylus cooki. Proc. Amer.

Philos. Soc., Vol. XI, p. 384.
Reference to Edaphodon (Ischyodus) lateri-

gerus. Ibid., p. 243.
1875. Reference to Edaphodon (Ischyodus) steno-

bryus. Vert. Cret. Form. West., Rep. U. S.

Geol. Surv. Territ., Vol. II, pp. 284-285.
Reference to Edaphodon (=Ischyodus) triparti-

tus. Ibid., pp. 284, 286.
Reference to Diphrissa. Ibid., p. 283.
Reference to Edaphodon (Ischyodus) eoccenus.

Ibid., pp. 285-288.
Reference to Edaphodon (Ischyodus) fecundus.

Ibid., pp. 285, 290.
Reference to Edaphodon (Ischyodus) gaskilli.

Ibid., pp. 285, 290.

Reference to Leptomylus forfex. Ibid., p. 281.
Reference to Edaphodon (Ischyodus) incrassa-

tus. Ibid., pp. 285, 289.
Reference to Edaphodon (Ischyodus) laterigerus.

Ibid., pp. 284, 288.
Reference to Edaphodon (Ischyodus) longiros-

tris. Ibid., pp. 284-287.

Reference to Ischyodus miersii. Ibid., pp. 285, 292.
Reference to Ischyodus mirificus. Ibid., pp. 285,

291.
1878. Reference to Chimaeroids in classification as lower

in the scale than sharks. Proc. Amer. Assoc.

Adv. Sci., Vol. XXVI, p. 292.
1884. Reference to holocephali as giving rise to selachii,

ichthyotomi (from which hyopomata are de-
rived), dipnoi. Amer. Naturalist, p. 255.
1891. General notes on Chimasroids in Syllabus of Lec-
tures on Geology and Palaeontology. Ginn and

Co., pp. 135.
DAVIES, W.

1872. On the rostral prolongations of Squaloraja poly-

spondyla. Geol. Mag., Vol. IX, p. 145, PI. iv.
DAVIS, J. W. '
1880. Reference to similarity of species of Pleuracan-

thus and Ischyodus, and general resemblance

of base of spines of Ischyodus and Siluroid.

Ann. and Mag. Nat. Hist., May, p. 355.
1883. Detailed reference to Jurassic Petalodonts, etc.,

in Trans. Roy. Dub. Soc., pp. 327-350.

DAVIS, J. W. — (Continued.)

1888. Reference to Callorhynchus hectori. Trans. Roy.
Dub. Soc. (2), Vol. IV, p. 41, PI. vn, figs. 14-15'.
Reference to Ischyodus brevirostris. Ibid., p. 42,
PI. vii, figs. 10-13.

1890. Reference to Ischyodus brevirostris. Ibid., pp.
414-415. (Cretaceous of Scandinavia.)

DEAN, BASHFORD.

1904. Reference to position of Menaspis armata. Sci-
ence, Vol. XIX, p. 253, and Am. Geologist, Vol.
XXIV, pp. 49-53, PL ii.

DIXON, F.

1850. Reference to Edaphodon sedgwicki. Foss. Sus-
sex, p. 203.
Reference to Edaphodon mantelli. Ibid., p. 203,

PI. xxxiv.
Reference to Edaphodon eurygnathus. Ibid., p.

in, PI. x, figs. 18, 19, 22; PI. xii, fig. 5.
Reference to Edaphodon leptognathus. Ibid., p.
in, PI. x, figs. 20, 21.

EASTMAN, C. R.

1898. On the dentition of Devonian Ptyctodontidae.
Amer. Nat., Vol. XXXII, pp. 473-488, 546-
560, 50 figs. Reference to Ptyctodus obliquus,
major, molaris, calceolus, ferox, compressus,
panderi ; Rynchodus secans, occidentalis, exca-
vatus, rostratus, major; Palseomylus predator,
frangens, crassus, greenei ; Ichthyodorulites.

1898. Reference to Ptyctodus and to Synthetodus (re-
garded by Eastman as dipnoan) ( PChimaeroid)
in Ann. Rep. Iowa Geol. Surv., Vol. VII, pp.
108-116, PI. i.

1900. Reference to Rhynchodus major in Am. Geol.,
Vol. XXV, pp. 391-392.

1900. Einige neue Notizen iiber devonische Fischreste
aus der Eifel. Centralb. Min. Geol. Pal., pp.
177-178. (Rhynchodus emigratus.)

1903. A peculiar modification amongst Permian Dip-

noans. Am. Nat., Vol. XXXVII, pp. 493-495,
2 figs. ( ?Chimseroid affinities.)

1904. On the dentition of Rhynchodus and other fossil

fishes. Am. Nat., Vol. XXXVIII, pp. 295-299,

2 figs. Rhynchodus major, rostratus, pcrtenuis,

emigratus (=Ramphodus tetrodon) ; Ptyctodus

calceolus.
EGERTON, Sir P.
1843. Reference to Ischyodus colei. Proc. Geol. Soc.

Lond., Vol. IV, p. 156.
Reference to Chimaera (Ischyodus) beaumonti.

Ibid., pp. 155, 156.
Reference to Chimaera (Ischyodus) emarginata.

Ibid., pp. 154, 156.

Reference to Chimaera dufrenoyi. Ibid., p. 155.
Reference to Ischyodus duvernoyi. Ibid., p. 156.
Reference to Elasmodus. Ibid., p. 156.
Reference to Ischyodus townsendii. Ibid., p. 156.
Reference to Ischyodus brevirostris. Ibid., p. 156

(name only).
Reference to Ischyodus dutertrei. Ibid., p. 156

(dutertrii) ; Ischyodus agassizi, p. 156.

LITERATURE LIST.

169

EGERTON, Sir P. — (Continued.)

Reference to Chimaera dutertrei. Am. Mag. Nat.

Hist., Vol. XII, p. 469, and Proc. Geol. Soc.,

Vol. IV, p. 154.
Reference to Ischyodus sedgwicki. Ibid., p. 156.

1847. Reference to Elasmodus hunteri. Proc. Geol.

Soc. Lond., Vol. Ill, p. 351, and Ganodus den-

tatus, p. 353.
Reference to Ganodus colei. Quart. Journ. Geol.

Soc., Vol. Ill, p. 352.
Reference to Ischyodus. Ibid., p. 351, PI. xm,

fig. i.
Reference to Edaphodon sedgwicki and Edapho-

don mantellii. Ibid., p. 352.
Reference to Edaphodon. Ibid., p. 351, PI. xm,

figs. 2, 3.
1852. Reference to Elasmodus hunteri. British Fossils,

Dec., Vol. VI, No. i, PI. I.

1869. List of type fossils in Egerton Collection. Refer-
ence to "Chiniaera." Geol. Mag., Vol. VI, p. 4.

1871. Ischyodus orthorhinus. Quart. Journ. Geol. Soc.,

Vol. XXVII, p. 275, PI. xm.

1872. Reference to Prognathodus (=Myriacanthus)

giintheri. Quart. Journ. Geol. Soc.,Vol. XXVIII,
pp. 233-236, PI. vm.

ElCHWALD, E. VON.

1846. Reference to Aulacosteus (=Ptyctodus) in
Geognosy of Russia (in Russian). According
to Leth. Rossica, Vol. I, pp. 15-48, 1860.

EWALD.

1848. Describes Menaspis in Monatsber. Ber. Akad.

Wiss., p. 33. Cf. Neues JB. fur Mineral., 1849,
p. 1 20.

FiJRBRINGER, K.

1903. Reference to Janassa (lip cartilages). Morph.
JB., Vol. XXXI, H. 2 u. 3, pp. 364, 382.

GEINITZ, H. B.

1875. Reference to Chimaera mantelli. Palseontogr., Vol.

XX, PI. n, p. 206, PI. xxxix, figs. 11, 12.
Reference to Chimaera agassizii. Ibid., p. 206, PI.
xxxix, figs. 8-10.

GERVAIS, P.

1869. Reference to Dipristis ( = ? Chimxra). Zool. et
Pal. Gen., p. 240.

GIEBEL, C.

1856. Reference to Menapis. Zeitschr. f. d. gesamm-

ten Naturwiss. Berlin, Bd. VII, p. 367, Taf. in

and iv.

GILL, THEO.

1905. Reference to a Rhinochimaera-like egg-capsule

from the Laramie (Cretaceous) sandstone.

Science, N. S., Vol. XXII, pp. 601-602.

HAMY, E. T.

1866. Reference to Ischyodus beaumontii. Bull. Soc.

Geol. France (2), Vol. XXIII, p. 656, fig. I.
Reference to Ischyodus sauvagei. Ibid., p. 655,

fig. 2.

HASSE, C.

1885. Reference to Squaloraja polyspondyla. Palaeon-
togr., Vol. XXXI, p. 4, PI. i, figs. 2, 3.

HOWES, G. B.

1890. Reference to Squaloraja (Chimaeroid) exterm.

Proc. Zool. Soc. Lond., Dec. 2, p. 687.

1891. Reference to Chimaeroid-like column of Palaso-

spondylus. Trans. Biol. Soc. Liverp., Vol. VI,
PJ44-

HUENE, F. VON.

1900. Devonische Fischreste aus der Eifel. Nat. JB. f.

Min., Geol. u. Palaeontol., Vol. I, pp. 64-66.
Reference to Rhynchodus emigratus v. Huene.
Centralb. f. Mineralogie, I p.

JAEKEL, O.

1890. Ueber fossile Ichthyodorulithen. SB. Gesell. na-

turforsch. Freunde, Berl., No. 7, pp. 117-131.
Oracanthus bochumensis, n. sp. Refers this to
his (order) Trachyacanthidae.

1891. Ueber Menaspis, nebst allgemeinen Bemerkungen

u. d. Systematische Stellung d. Elasmobranchier.
SB. Gesell. naturforsch. Freunde, Berl., No. 7,
pp. 115-131, PL I-

1892. Reference to Chalcodus permianus as equivalent

to Menaspis armata : not a Chimreroid, as Wood-
ward believed, but a "Trachyacanthid." SB.
Gesell. naturforsch. Freunde, Berl., No. 9, Nov.
IS, PP. IS7-I58.

Reference to Chalcodus (=Menaspis) and to
Reis's referring it possibly to Chimaeroid. SB.
Gesell. naturforsch. Freunde, Berl., No. 9, pp.
156-158.

Ueber Dichelodus Gieb. und einige Ichthyodoru-
lithen. Eine Entgegnung an Herrn A. Smith
Woodward. Neue JB. fiir Mineralog., Vol. I,
pp. 6.

1896. Chimaeriden-Eier aus dem unteren Dogger von
Heininge in Wiirttemberg. Zeitschr. deutsch.
geol. Ges., Bd. XLVIII, p. 691.

1899. Ueber d. Organization d. Petalodonten. Zeitschr.
d. deutschen geol. Gesellsch., Vol. LI. Heft 2,
pp. 257-298, PI. ii.

1901. Ueber jurassische Zahne und Eier von Chima-

riden. Neues JB. Min. Geol. Pal. Berl., Vol.
XIV, pp. 540-564, PI- 4, 3 figs.
Reference to Ischyodus aalensis, ferrugineus
(=Aletodus ferrugineus), Callorhynchus antarc-
ticus.

LEIDY, J.

1873. Reference to Eumylodus. Extinct Vert. Fauna

W. Territ. (Rep. U. S. Geol. Surv. Territ.),

Vol. I, p. 309, PI. xix, figs. 21, 22; PI. xxxvii,

figs. 13, 14.
Reference to Edaphodon mirificus. Ibid, p. 306,

and Proc. Acad. Nat. Sci. Phila. (1856), p. 221.

iyo

LITERATURE LIST.

LERICHE, M.

1901. Reference to Ischyodus thurmani and to Edapho-

don sedgwicki — of the latter figuring mandible

and a (?) spine. Ann. Soc. Geol. du Nord,

Vol. XXXI, p. 125-129. Cf. also 1903, ibid., pp.

239-252. (Chimaeroids in Landenien.)
1903. Further reference to these genera. Ibid., Vol.

XXXII, pp. 239-252.
MANTELL, G. A.
1844. Reference to Chimsera. Medals of Creation, p.

621.

MARSH, O. C.
1869. Reference to Dipristis. Proc. Amer. Assoc. Adv.

Sci., p. 230.
Reference to Edaphodon miersi; Dipristis miersii.

Ibid., p. 230.
MEYER, H. VON.
1855. Reference to Rhynchodus, sp. ind. : ( Physichthys

hoeninghausii.) Palaeontogr., Vol. IV, PI. xv,

fig. 9 (errore).

1859. Reference to Ischyodus acutus. Palaeontogr.,

Vol. VII, p. 17, PI. II, figs. 9-12.
Reference to Ischyodus (Chimaera) rostratus.
Ibid., p. 14, PI. ii, figs. 3-8.

1860, Chimsera (Ganodus) prisca. Neues JB., p. 212.

(Name subsequently withdrawn.)

1862. Chimaera (Ganodus) avita. Palaeontogr., Vol. X,
p. 87, PI. xn.

MONSTER, G. VON.

1840. Reference to Myriacanthus franconicus. Beitr.

Petrefakt., Vol. Ill, p. 127, PI. in, fig. 8.
1842. Myriacanthus vesiculosus. Ibid., p. in, PI. vi,

fig- 3-

NEWBERRY, J. S.
1871. Reference to Rhynchodus.
1873. Palaeomylus frangens : Rhynchodus frangens.

Rep. Geol. Surv. Ohio, Vol. I, Ft. II, p. 311, PI.

xxvin, figs. 2, 3.

Reference to Rhynchodus. Ibid., p. 307.
Reference to Rhynchodus secans. Ibid., p. 310,

PI. xxvui, figs. 1-3.
Reference to Palaeomylus crassus (=Rhynchodus

crassus). Ibid., p. 312, PI. xxix, fig. 3.
1875. Reference to Ptyctodus calceolus. Rep. Geol.

Surv. Ohio, Vol. II, Pt. II, p. 59, PI. LIX, fig. 13.

1877. Reference to Rhynchodus excavatus. Rep. Geol.

Surv. Wise., Vol. II, p. 397.

1878. Reference to Rhynchodus occidentalis and exca-

vatus. Am. N. Y. Acad. Sci., Vol. I, p. 192.
1889. Reference to Palaeomylus greenei (Rhynchodus

greenei). Rep. Geol. Surv. Ohio, Vol. I, Pt. II,

P. Si-
Reference to Rhynchodus. Mon. XVI, U. S. Geol.

Surv., pp. 29, 45-51.
Reference to Rhynchodus crassus. Ibid., pp. 49, 50,

286, ?H9, PI. xxvin, fig. 4.
Reference to Rhynchodus excavatus. Ibid., pp. 50,

51, 288, PI. xxix, fig. i.

NEWBERRY, J. S. — (Continued.)

1889. Reference to Rhynchodus frangens. Ibid., pp. 29,

46, 48, 49, 288, PI. xxix, figs. 2, 3.

Reference to Rhynchodus greenei. Ibid., pp. 51, 62.
Reference to Rhynchodus occidentalis. Ibid., p. 62.
Reference to Rhynchodus secans. Ibid., pp. 29-46,

47, 48, 286.

Reference to Ptyctodus. Ibid., pp. 62, 63, 68, 69.
Reference to Ptyctodus calceolus. Ibid., p. 62.
Reference to Chimaera. Ibid., p. 46. Townsendii

of Buckland, perhaps generically identical with

Rhynchodus frangens.
NEWBERRY and WORTHEN.

1866. Reference to Rhinodus (=Ptyctodus). Palaeon-
tology of Illinois, Vol. II, p. 106, PI. x, fig. 10.
NEWTON, E. T.

1876. On two Chimaeroid Jaws from the Lower Green-
sand of New Zealand. Q. Jour. Geol. Soc., Vol.

XXXII, pp. 326-331, PI. xxi.
Reference to Callorhynchus hectori. Quart. Jour.

Geol. Soc., Vol. XXXII, p. 329, PL xxi, figs. 6-9.
Reference to Ischyodus brevirostris. Ibid., p. 326,

PI. xxi, fig. 5.
1878. Chimaeroid Fishes, Brit. Cret. Rocks. Mem. Geol.

Surv., Monogr. IV, p. 41, PI. xn, figs. 1 1, 12.

Reference to Callorhynchus hectori.
Reference to Elasmodectes. Ibid., p. 43.
Reference to Ischyodus planus. Ibid., p. 37, PI.

XII, figs. I, 2.
Reference to Ischyodus brevirostris. Ibid., p. 27,

PI. ix.

Reference to Ischyodus latus. Ibid., p. 32.
Reference to Ischyodus incisus. Ibid., p. 38, PI.

xii, figs. 3-10.
Reference to Edaphodon sedgwickii. Ibid., p. 7,

Pis. i, ii.
Reference to Edaphodon mantellii. Ibid., PI. iv,

figs. 1-9.
Reference to Edaphodon agassizii. Ibid., p. 12,

PI. ill.
Reference to Edaphodon crassus. Ibid., p. 21,

PI. vn.

Reference to Edaphodon reedii. Ibid., p. 19, PI. vi.
Reference to Edaphodon laminosus. Ibid., p. 24,

PI. vni.
Reference to Edaphodon mirificus. Ibid., p. 24.

1881. Reference to Ischyodus townsendii. Proc. Geol.

Assoc., p. 116, fig.
NIKITIN, S.

1882. Reference to Edaphodon, from Cretaceous of Cen-

tral Russia. Mem. Comite Geol., Vol. V, No. 2,

p. 42, PI. iv, fig. 16.
NOETLING, F.
1885. Reference to Edaphodon bucklandi. AH. geol.

Specialk. Preussen u. Thiiring. Staaten, Vol.

VI, Pt. Ill, p. 3, PI. i, fig. i.
OWEN, R.
1840. Reference to Elasmodus hunteri, extinct Chimaera.

Odontography, Vol. I, p. 66.

LITERATURE LIST.

171

PANDER.

1858. Ueber die Ctenodipterinen des devonischen Sys-
tems St. Petersburg. Ref. p. 50 to structure of
dental plates of Ptyctodus as combining Gym-
nodont and Chimaeroid characters.

PARENT, H.

1903. Reference to Chimaeroids in Wealdon of Bas-
Boulonnais, in Ann. Soc. Geol. Nord, Vol.
XXXII, pp. 17-48.

PHILIPPI, E.

1897. Ueber Ischyodus suevicus nov. spec. Palaeontogr.,
Vol. XLIV, pp. i-io, PI. n.

PHILLIPS, J.

1871. Reference to Ischyodus egertoni. Geol. Oxford,
p. 306, PI. xii, fig. 24.

PICTET, F. J.

1854. Reference to Edaphodon. Palaeontologie, ed. 2,
Vol. II, p. 233.

PICTET and CAMPICHE.

1858. Reference to Ischyodon thurmanni. Foss. Terr.
Cretace St.-Croix (Pal. Suisse), p. 76, PI. ix,
fig. 8.

PRIEM, F.

1901. Reference to Edaphodon bucklandi. Bull. Soc.
Geol. France, 49 sen, Vol. I, p. 485.

PROBST, J.

1882. Reference to (fig.) Chimaera deleta in Jahreshefte

d. Ver. f. vaterl. Naturw. in Wurtt, pp. 120-131.

QUENSTED, F. A.

1852. Reference to Chimaera aalensis. Handb. Petrefakt,
p. 185, PI. xiv, figs. 14-16, and Der Jura (1858),
PP. 339, 347, PI- XLVII, figs. 21-28.
Reference to Ischyodus personal! : Chimaera per-
sonati. Ibid., ed. I, p. 185, PI. xiv, fig. 17, and
Der Jura, p. 339, PI. XLVI, figs. 8, 9.

1858. Reference to Chimaeracanthus (=Ischyodus).

Der Jura, p. 347.

Reference to Chimaera schuebleri. Ibid., p. 782,
PI. xcvi, fig. 39.

1883. Reference to Ischyodus bifurcati : Chimaera bifur-

cati. Handb. d. Palreont., ed. 3, p. 293, PI. xxm,

fig. 25.
REIS, O. M.
1890. Zur Kenntnis des Skelets der Acanthodinen.

Geognost. JB., p. 30.

1894. Ueber Phosphoritisirung d. Cutis, d. Testikel u.

d. Riickenmarks. (Reference to Ischyodus.)
Arch. mikr. Anat., Vol. XLIV, pp. 87-119, PI. vi.
?1892. Ueber d. Kopfstacheln b. Menaspis armata
Ewald. Mtinchen, M. Kutzner, pp. 13.

1895. On the structure of the frontal spine and the ros-

tral-labial cartilages of Squaloraja and Chimasra.

Geol. Mag. Lend., Decade IV, Vol. II, pp.

38S-39I, PI- xn.
RENAULT, B., and ZEILLER, R.
1886. Reference to Fayolia and Palaooxyris (Spiran-

gium) in C. R. Acad. Sci. Paris, Vol. CVII, p.

1022.

RlESS, J.

1887. Reference to Ischyodus schuebleri. Palaeontogr.,

Vol. XXXIV, p. 17, PI. i. fig. 8.
Reference to Edaphodon kilheimensis. Ibid., p.

20, PI. i, fig. ii.

Reference to Chimaeropsis paradoxa. Palaeontogr.,
Vol. XXXIV, p. 21, PI. n, figs. 9-11; PI. m,figs.

I-IO.

Reference to Ischyodon quenstedti. Ibid., p. 6,

PI. T, figs. l-S ; PI. n, figs. 1-7.
Reference to Ischyodus avita. Ibid., p. 14, PI. I,

figs. 6, 7; PI. n, fig. 8.
Reference to Ischyodus aalensis. Ibid., p. 19, PI. i,

fig. 9-

Reference to Ischyodus bifurcati : Chimaera bifur-
cati. Ibid., p. 19.
Reference to Ischyodus ferrugineus. Ibid., p. 20,

PI. i, fig. 10; PI. in, fig. ii.
RILEY, H.
1833. Reference to squaloraja dolichognathos. Proc.

Geol. Soc. Lond., Vol. I, p. 484, and (2) Vol. V,

p. 83, PI. iv.
ROHON, J. V.
1892. Beitrag zur Kenntnis der Gattung Ptycotodus.

VH. russ. Kais. mineralog. Gesellsch. St. Pe-
tersburg (2), Vol. XXXIII, pp. 1-16, PI. i, P.

obliquus, ancinnatus, major.
ROMANSKY, H.
1864. Reference to spine of Myriacanthus semigranu-

latus. Bull. Soc. Imp. Nat. Moscou, p. 167, Pt.

II, PI. iv, fig. 34.
RUTOT, A.
1904. Reference to fossil. Chimaeroids found in the

neighborhood of Brussels in Bull. Soc. beige,

Geol. Pal. Hydrol., Vol. XVII, pp. 383-499.
SAUVAGE, H. E.
1843. Reference to Ischyodus dutertrei. Proc. Geol. Soc.

Lond., Vol. IV, p. 89, PI. in, figs. 17-19.
1867. Reference to Auluxacanthus (^Ischyodus). Catal.

Poiss. Form. Second Boulonnais (Mem. Soc.

Acad. Boulogne, Vol. II), p. 63.
Reference to Ischyodus dufrenoyi. Ibid., p. 73,

PI. iv, fig. 12.
Reference to Ischyodus beaumontii. Ibid., p. 83,

PI. iv, figs. 4, 5.
Reference to Ischyodus rigauxi. Ibid., p. 766, PI.

IV, figs. 14, 15.
Reference to Ischyodus bouchardi. Ibid., p. 81,

PI. iv, fig. 6.
Reference to Ischyodus beaugrandi. Ibid., Vol. 1 1,

p. 79, PI. iv, figs. 7, 8; I. sauvagei, p. 86, PI. iv,

figs. 2, 3.
1896. Les Ischyodus des terrains jurassiques superieurs

du Boulonnais. Bull. Soc. Geol. France, (3),

Vol. XXIV, pp. 456-465, PI. ii.
1902. Les Poissons et les Reptiles du Jurassique Supe-

rieur du Boulonnais au Musee du Havre. Bull.

de la Soc. Geol. de Normandie, Vol. XXI

(1001), pp. 3-4. Reference to Ischyodus.

172

LITERATURE LIST.

SAUVAGE, H. E. — (Continued.)

1903. Noticia sobre las peces de la Caliza litografica de
la provincia de Leride (Cataluna). Memorias
de la real Academia de Ciencias y Artes de Bar-
celona, Vol. IV, No. 35, pp. 6-7. Reference to
Spirangium as doubtfully a capsule of a Chimas-
roid. PI. i, fig. i.

SEELEY, H. G.

1864. Reference to Edaphodon huxleyi. Ann. and Mag.
Nat. Hist. (3), Vol. XIV, p. 276 (name only).

TRAQUAIR, R. H.

1003. Reference to Gemiindina (L. Devonian) "as pos-
sibly being a Chimaeroid." Trans. Roy. Soc.
Edinburgh, Vol. XL, Pt. IV, p. 736.

WAGNER, A.

1857. Reference to Chimaera (Ischyodon) quenstedti.

Gelehr. Anz. k. bay. Akad., Vol. XLIV, p. 288.
1862. Reference to Chimaera (Ischyodon) quenstedti.

Abh. math.-phys. Cl. k. bay. Akad. Wiss., Vol.

IX, p. 286, PI. i, fig. i.

WALCOTT, C. D.

1892. Preliminary notes on the Discovery of Vertebrate

Fauna in Silurian (Ordovician) Strata. Bull.

Geol. Soc. America, Vol. Ill, pp. 153-172, Pis.

m-v. Reference to "Chimaeroid" on pp. 163-166.

WEYL, T.

1884. Squaloraja polyspondyla (foss.). Hasse. Palae-

ontogr. (3), Vol. VII, p. 4, PI. i, figs. 2 and 3.

Oligocene of Palmnicken.
WOODWARD, A. S.
1886. Reference to Squaloraja polyspondyla. Proc. Zool.

Soc. Lond., p. 527, PI. LV, figs. 1-5, 7, 8, and 1887,

p. 481.
Reference to Squaloraja tenuispina. Ibid., p. 530,

PI. LV, fig. 6.
Note on the lateral line of Squaloraja. Ibid.,

p. 481.
Anatomy and systematic position of Squaloraja

polyspondyla. Ibid., pp. 527-528. PI. LV, and

1887, p. 481.
1888. Reference to English Cretaceous Chimaeroids,

Ischyodus, Edaphodon, and Elasmodectes in

Proc. Geologists' Ass., Vol. X, No. 5, pp. 209-

301, 333-

Reference to absence of Chimaeroids in the Mount
Lebanon Cretaceous in Rep. British Ass., Sec. C.

WOODWARD, A. S. — (Continued.)

1889. On the Myriacanthidas, an extinct family of Chi-
maeroid fishes. Ann. N. H. (6), Vol. IV, pp.
275-280. A new family to include Myriacanthus,
Ag. and Chimaeropsis, Zittel.

1889. Reference to Myriacanthus paradoxus. Ann.

Mag. Nat. Hist. (6), Vol. IV, p. 279.
Reference to Ischyodus egertoni. Palaeont. in
Maiden Mus. Geol. Mag., Dec. Ill, Vol. VI,
p. 363.

1890. Reference to Ganodus oweni. Proc. Geol. Ass'n,

Vol XI, p. 303, PI. in, fig. 4.

1891. Detailed reference to fossil Chimaeroids. Cata-

logue of Fossil Fishes of British Museum, Vol.
II, pp. xvi, 37.

Critique of Jacket's Menaspis and Trachyacanthid
papers. Geol. Mag., Sept.

Reference to Elasmodus greenoughi (Belgian Neo-
zoic). Ibid., Dec. Ill, Vol. VIII, No. 321, pp.
112-113.

1892. Reference to supplementary observations on some

fossil fishes of the English Lower Oolites. Proc.

Geologists' Ass'n, Vol. XII, pp. 238, 239.
On the skeleton of a Chimaeroid fish (Ischyodus

egertoni?) from the Oxford Clay of Christian

Malford, Wiltshire. Ann. Mag. Nat. Hist. (6),

Vol. IX, pp. 94-96.
On some teeth of new Chimaeroid fishes from the

Oxford and Kimmeridge clays of England.

Ann. and Mag. Nat. Hist., July, pp. 13-16, PI. in.

Reference to Pachymylus leedsii, Brachymylus

altidens and minor, Elasmodectes secans.
1898. Review of fossil Chimaeroids. Vertebrate Palae-
ontology, pp. 54-61.
WOODWARD and SHERBORN.
1890. Reference to fossil Chimaeroids. Cat. Brit. Foss.

Vertebrata.
ZITTEL, K. A. VON.
1887-90. Reference to Chimaeropsis paradoxa. Handb.

d. Palaeont., Vol. Ill, p. 114, fig. 126.
Reference to Chalcodus permianus. Ibid., p. 72,

fig. 66.
Reference to Metopacanthus (=Myriacanthus).

Ibid., p. no.
Reference to Metopacanthus orthorhinus. Ibid.,

p. in.

EXPLANATION OF PLATES.

PLATE I.
THE DEPOSITING OP THE EGG OF CHIMERA COLUEI.

(All figures about natural size. )

a. Anus. l.g. Lime gland.

c. Crease in tumid eminence in median ventral line, m. Cord representing rudiment of dorsal mesentery,

just posterior to opening of oviducts. Fig. 2. and containing the posterior mesenteric

c. Crease in oviduct in which marginal web of vessels.

capsule was laid down. Fig. 4. o. Ovary.

c. a. Tumid eminences formed by prolapsed ends of op. Opening of oviducal sinus into cardinal sinus.

oviducts. ovd. Oviduct.

c. f. Capsular filament. ovd. a. Oviducal artery.

c.o. Capsular organ of attachment. ovd. s. Oviducal sinus.

c. s. Cardinal sinus. (Margin of. ) p. Urinary papilla.

/. Funnel of oviduct. r. Folds at lower end of rectum.

h. Heart. r.s. Receptaculum seminis.
/. Liver.

Fig. i. — Preparation of gravid female, showing eggs in oviduct. The egg-capsules are well formed,
the egg-containing portion situated in the hinder portion of the oviduct. The external
openings of the oviduct protrude from the body. The receptaculum seminis is shown at
r. s. The oviducts extend far forward ; their single opening appears at /., immediately
behind the position of the heart, h. The mesovarium is greatly restricted; it can, how-
ever, be distinguished on the left side of the figure where the capsular gland has been
drawn out. The oviducal artery is extremely conspicuous at this stage.

Fig. 2. — Region of ventral fins of a specimen which has recently deposited eggs, showing the pro-
lapsed ends of the oviducts.

Fig. 3. — Filamentous end of egg-capsule showing bulb-shaped organ of attachment. After sketch
by Professor Wilbur.

Fig. 3 a. — Filamentous end of similar capsule.

Fig. 4. — Preparation showing oviducts of a specimen about to deposit egg-capsules. The oviducts,
as shown in fig. i, pass back on either side from the median funnel, f. The one at the
right in the figure is shown lying in a capacious blood-filled sac of the peritoneum, ovd. s.
This sinus is slung from the dorsal wall of the body cavity : its sides (right and left)
draw closer together as they leave the oviduct and approach the (dorsal) wall of the
body cavity. And here appears finally a series of openings, op., through which blood of
the oviducal sinus obtains free communication with the cardinal sinus, c. s. It is evident, of
course, that the oviduct, ovd., is bathed in the blood contained in the sinus; and that it can
well be seen only where it lies against the wall of the sinus, the blood then forming the dark-
red masses at either side of the oviduct. The preparation has been made so that the
external opening of one oviduct is retained. From it one sees protruding the narrow
end of the egg-capsule. The opposite oviduct is shown opened. The details of the lime
gland appear at /. g. Immediately below it from a transverse fold in the oviduct arises
the viscid secretion, c. o., which draws together posteriorly and becomes the capsular
filament, c. f. One observes many creases in the wall of the oviduct. In the deepest,
c., the lateral web of the egg-capsule is laid down. The creases are especially note-
worthy near the hinder opening of the oviduct. Here its muscular walls serve to hold the
capsule as it hangs in the water while the remainder of the capsular filament is being devel-
oped.

CHIMAERA

PLAT

f>vd,a-

ilVil II

•

Litl: AnstvWerner&Wuner, Frankfu

PLATE II.
OVIDUCT OF CHIMERA COLUEI AND MODE OF FORMATION OF THE EGG-CAPSULE.

(All figures natural size, excepting the last, fig. n.)

b.
c.

c.p.
d. k
l.w.

Fig.

Line in which the lip of the operculum separates m-

from the side of the capsule.
Blastoderm.
Aperture (cervix) through which the anterior end of m. o.

the capsule is beginning to protrude. o.

Capsular gland. In this region a series of trans- oi'd.

verse zones can be made out extending as far ovd. a.

posteriorward as t. o. o^>d. s.

Foldings in the margin of the capsule in which r.

later appear the perforations in the caudal

sheath. *•

Groove in which dorsal keel of egg-capsule is laid /. o.

down. At either side of this are thickened

areas which form the dorsal wall of capsule.
Folds in oviduct, in which the lateral web of the t. s.

capsule is laid down.

Rudiment of mesentery of gut containing ves-
sels. This lies behind oviduct (cf. plate I,
figs, i and 4).

Mesovarium.

Ovum about to break from the ovary.

Oviduct.

Oviducal artery.

Oviducal sinus.

Folds in groove of lateral web by which the
rugae of the capsule are established.

Stigma.

Folds under the edge of the lime gland in which
the terminal organ of the filamentous capsule
is laid down.

Thickened area in which is molded one side of
the tail-sheath.

Fig,
Fig.

Fig,

Fig.
Fig.

Fig,

5. — Ovary and oviduct of left side, showing egg about to be taken into the oviduct. The ovary
is closely enveloped in the mesovarium, m. o., the fold of which is continued back, encloses
the oviduct and shows at ovd. s. the beginnings of the oviducal sinus. It will be observed
that the egg, o., about to escape from the ovary, is of great size. This is due to its fluid
consistency at this stage, its contents having spread out when the preparation was made.
A conspicuous stigma is present, to which nutrient blood-vessels converge. At this stage
the oviduct is situated close to the dorsal wall of the cavity of abdomen. In later stages,
during growth of the capsule, the oviduct hangs down freely into the abdomen and is
bathed by the blood in the enlarged sinus, ovd. s.

6. — Preparation of oviduct from which a developing capsule was removed, showing the fold-
ings of the lining membrane which serve in modeling the capsule.

7. — Preparation of anterior end of oviduct, showing a portion of the egg-capsule in situ. This
figure illustrates the "segmental" character of the capsular gland, for each segment of which
vessels are provided by the oviducal artery. The narrow end of the egg-capsule is shown
within the oviduct ; at t. p. foldings are shown in its marginal walls, which later produce
the perforations of the caudal sheath. At either side of the deep groove, d. k., in which
the dorsal keel of the capsule is molded, appears a mass of glandular tissue. This is out-
rolled on either side into the marginal creases in which the lateral web of the capsule is
being laid down.

8. — Immature capsule containing egg. The tail end of this capsule was incomplete, but by
means of a ligature it was so preserved that the egg was incubated. By the tension of the
ligature, however, the shape of the capsule was somewhat altered and the egg became more
spherical in form. The lateral web of this capsule is delicate and extremely wide.

9. — Egg-capsule opened, showing shape into which the egg is elongated during incubation.
io, — Egg-capsule at about the time of deposition, defective only in its terminal filament. This
was, in fact, deposited while the fish was in captivity. From this figure one obtains an
idea of the translucency of the freshly deposited capsule.

ii and Fig. n a-c. — Details in structure of egg-capsule. Fig. n shows a detail in the struc-
ture of the opening valve. The fold in the wall near apex of capsule, a. /., passes
upward and inward into a ridge, the walls of which are folded into thickened and thinner
areas alternately. At a. a transverse section shows height of this ridge. At b. appears a
lateral view of the same ridge, indicating how it is made up of alternating elements. By
a process of weathering in the thin intervening areas fenestrae are formed which insure
respiration and which later, by a continued process of weathering, break open the valve of
the capsule. In fig. n c. is shown the continuation of this folding process, occurring at
sides of tail region of capsule. By the weathering of the thin spaces between the folds res-
piratory openings are gradually formed.

176

CHIMAERA

PLATE n.

tn.o. ovd.a.

/

il

ashford Dean del. •

Lith.Anstv Werner iWinter, Frankfurt'-M

oT c."

• ; '.
• c

PLATE III.
THE EGG-CAPSULE OF CHIMERA COLLIEI SHOWN AT DIFFERENT STAGES OF DEVELOPMENT.

( All figures about natural size.)

Fig. 12. — Capsule at the stage of the fertilization of the egg. The lowermost, i. e., valve-bearing,
end of the capsule is fairly complete, but its substance is delicate. The present capsule
collapsed during the process of removing it from the oviduct ; the egg it contained rup-
tured and flowed out through the unfinished end.

Fig. 13. — Capsule slightly older than the preceding. The opening end is of firmer consistency ;
the lateral web is well formed and somewhat pigmented.

Fig. 14. — Capsule slightly older than the preceding. The lateral dorsal webs are more perfectly
formed.

Fig. 15. — Capsule in which the tail-sheath is beginning to be formed.

Fig. 16. — Egg-capsule in which the egg-inclosing portion is nearly completed. The tail-sheath is
still a shapeless mass. The lateral webs are widest at this stage ; they later become
molded more closely and their delicate margins wear away soon after the egg is deposited.
Rugae are appearing near the posterior end of the capsule. An egg at this stage can be
incubated if a ligature is placed near the base of the caudal sheath. (In figs. 12 to 16
capsules are shown in dorsal aspect.)

Fig. 17. — Egg-capsule from which embryo has been naturally hatched. This is the most perfect of
the specimens which the writer dredged in Puget Sound. Its lateral webs are still
largely uninjured, the filamentous tip alone being defective — lacking the bulbous organ of
attachment. The ventral aspect is here shown, and we note at d. h. the enlargement of the
wall of the capsule in which the mandibular region of the young fish comes to lie. The
figure shows also the close laminae in which the substance of the capsule is laid down.

Fig. 17 a. — Capsule of foregoing figure shown in lateral aspect. The valve of the capsule is repre-
sented as opened, a position assumed naturally only at the time of the escape of the young
fish, the valve and its springy mechanism reminding one of the "mouth" of the corolla of a
labiate plant. This figure shows the ridges, r. and /., which overlap (r. overlapping /.)
up to time the young fish escapes. It shows also how the neighboring tip of capsule
weathers, leaving only three eminences protruding, of which the one belonging to the lid of
the valve is the longest. The dorsal keel of the capsule is here well shown, d- k. It
varies little in height and passes nearly the whole length of capsule.

Fig. 17 b. — Capsule of foregoing specimen shown in dorsal aspect. This specimen shows adequately
the extent and character of the rugae of the lateral web. At its anterior end, at r. , appears
the rim of the valvular opening. In a capsule from which the fish has naturally escaped
this ridge no longer returns to its former position under the ridge /.

Fig. 17 c. — Capsule of foregoing specimen shown from in front. This figure was prepared to illus-
trate the character of the overfolded margins of opercular opening, and the peculiar curving
of the sides of valve. It shows also the prominence of the dorsal keel.

(The capsule of fig. 17 is somewhat light colored for one which has been long deposited. Old capsules are usually
greenish black in color.)

CHIMAERA

PLATE in.

13

14

17 »

ka del.

LithAns'v.Wen'.erJ. Winter, Frdnkfurla/M.

PLATE IV.
STAGES OF FERTILIZATION, SEGMENTATION, AND BLASTULA.

(Preparations magnified about 15 diameters. All drawings from fresh material. Figs. 22 to 28 from camera drawings
of embryos which had been removed from the egg and viewed as transparent objects.)

Fig. 1 8. — Late stage of fertilization. The oblong shape of the germinal area is due to artifact. The

preparation illustrates the number and size of the entrance pits of spermatozoa and the

extent of the marginal groove.
Fig. 19. — Later stage of fertilization. This indicates the extent of the marginal groove and the

difference in size of the entrance pits of the spermatozoa.
Fig. 20. — Stage showing in surface view a single furrow. As already noted, however, this stage is

not one of first segmentation, since it contains several segmentation nuclei. Surrounding

the germinal area is a narrow groove margined outwardly by eminences containing sperm

nuclei.

Fig. 21. — Stage similar to foregoing, but showing at the surface four '' blastomeres."
Fig. 22. — Stage of early segmentation. Here the marginal areas containing sperm nuclei are far

less conspicuous.

Fig. 23. — Stage similar to the preceding.
Fig. 24. — Stage of segmentation.

Fig. 25. — Stage of late segmentation. Blastomeres in resting stage.
Fig. 26. — Stage of late segmentation.
Fig. 27. — Stage of late segmentation. The darker color of the central blastomeres indicates a

greater depth in this region of the germ.
Fig. 28. — Blastula. In this stage inter-blastomeral lines were traced over the light-colored circum-

germinal ring.
Fig. 29. — Blastula. Viewed as an opaque object, and showing a sharply marked boundary between

the blastoderm and the circumgerminal ring.

180

18

ft

PLATE V.
BLASTULA, GASTRUI,^, AND EARLY EMBRYOS.

(Preparations magnified about 15 diameters. In Figs. 30-34 the circumgerminal zone has been inaccurately litho-
graphed ; it should appear less conspicuous, its outer margin merging insensibly into the surrounding yolk.)

Fig. 30. — Late blastula, showing especially the extent of the circumgerminal ring and its irregular

margin.
Fig. 31. — Early gastrula. The transverse shadow at the lower end of the germinal area represents

the beginnings of the archenteric cavity.

Fig. 32. — Early gastrula, showing the extent of the archenteric space-
Fig- 33- — Gastrula, showing the appearance of the head region of the embryo. In this preparation

merocytes could be distinguished in the outer part of the circumgerminal ring.
Fig. 34- — Gastrula, showing the early embryo and the extent of the segmentation cavity.
Fig- 35- — Gastrula, slightly older, showing the early vascularization of the blastoderm.
Fig. 36. — Gastrula, showing early embryo at a stage corresponding with Balfour's stage c in the

shark.

Fig. 37. — Blastoderm, showing embryo at a stage corresponding with Balfour's stage F in the shark.
Fig. 38. — Blastoderm and embryo at a stage corresponding with Balfour's stage G in the shark.

182

CHIMAERA

30

31

A B

PLATE v

°^ A

A B

33

34

37

38

PLATE VI.
DETAILS OF EARLY EMBRYOS.

a. Archenteron. »• Neurenteric opening.

ec. Ectoderm. of. Optic vesicle.

fill. Entoderm. /«• Pronephric region.

ffi. g-n. First and second gill-clefts. v. i. Vitello-intestinal vein.

A. Heart.

Fig. 39. — Detail of embryo shown in plate i, fig. 35, viewed as an opaque object.

Fig. 39 a-e. — Same embryo viewed in various positions as transparent object.

Fig. 40. — Embryo shown in plate vi, fig. 36, viewed as a transparent object.

Fig. 41. — Embryo shown in plate vi, fig. 37, viewed as a transparent object.

Fig. 41 a. — Embryo shown in plate vi, fig. 38, viewed as an opaque object.

Fig. 41 b. — Embryo shown in plate vi, fig. 38, viewed as a transparent object.

184

CHIMAERA

PLATE vi.

39

,

40

39 u

41'

(

' fl\

.. r

.. B

TiWinter, Frjr

PLATE VII.
LATBR EMBRYOS.

(Preparations magnified about 25 diameters.)

a. Anus. ot. Otic vesicle.

at. Atrium. ot. o. External opening of otic vesicle.

b. Epiphysis. p. Pineal outgrowth.

c. Conus arteriosus. -p. a. g. Postanal gut.
c. e. Caudal eminence. £n. Pronephros.

c. v. Caudal vein. fn, d. Pronephric duct.

gj, g". Gill slits. f. f. Pectoral fin.

k. Cephalic knob. s. Spiracle.

of. Optic vesicle. s. v. Sinus venosus.

v. Ventricle.

Fig. 42. — Embryo, age about 25 days, corresponding to Balfour's stage G (+) of shark. This
embryo bent during the process of fixation. It shows especially well the knob-like out-
growth, k. in the region of the forebrain.

Fig. 42 a and b. — Anterior region of preceding embryo. Shown in nearly lateral and in dorsal
aspect.

Fig. 43. — Embryo, age about 29 days, corresponding approximately to Balfour's stage i in shark.

Fig. 43 b. — Anterior region of specimen similar to preceding.

Fig. 44. — Embryo, age about 31 days, corresponding approximately to Balfour's stage j in shark.
It shows a bulbous caudal thickening.

Fig. 45. — Embryo, age about 40 days, corresponding approximately to Balfour's stage K in shark.
The circular area under the letters g.' g." was found to be artifact.

Fig. 46. — Embryo, age about 45 days, somewhat more advanced than Balfour's stage L in shark.
At the time of fixation the embryo probably twisted, so that its axis came to lie nearly
parallel to the neighboring margin of the blastoderm. (Length of embryo 20 mm.)

186

CHIMAERA

PLATE vn

46

iJthAnstyWerneri Winter, Fr.:.>

. ••• . •

PLATE VIII.
EMBRYOS OF CHIMERA COLLIEI.

ch. Notochord. sp. Spiracle.

n. Neural tube. x. Irregularity in line of postanal gut. Possibly artifact.

n. c. Neurenteric canal. y. Yolk.

/. a. g. Postanal gut. y. s. Stalk of yolk-sac.

Fig. 42 c. — Ventral aspect of the head region of specimen shown on plate vn, fig. 42. This indi-
cates especially the extent of the stomadeal invagination.

Fig. 46 a. — Detail of tip of tail of specimen shown in plate vn, fig. 46. It illustrates especially the
character of the caudal knob and the extent of the postanal gut.

Fig. 47. — Embryo and blastoderm shown attached to irregular mass of yolk. The embryo is of the
stage shown in plate vn, fig. 44. It will be seen that a deep crease marks the line of sepa-
ration of blastoderm and yolk, y.

Fig. 47 a, b. — Figures showing the foregoing specimen in natural size. These give an idea of the
extent of the yolk mass around which the blastoderm is growing.

Fig. 47 c. — Margin of blastoderm in the region which, in fig. 47, is concealed by the tail. It is
here slightly nicked, and a line of fusion can be traced in the direction of axis of embryo.

Fig. 48. — Embryo of stage shown in plate vn, fig. 45. The blastoderm has by this stage almost
entirely inclosed the yolk mass noted in fig. 47. A small portion of the yolk is, however,
seen in lower part of figure. The figure also shows, although indistinctly, a line of fusion
passing from the embryo in the direction of the rim of the blastoderm.

Fig. 48 a. — Preceding specimen shown in posterior aspect. This indicates the extent to which the
rim of the blastoderm has inclosed the yolk. The irregularity in its margin is due
probably to artifact. In the yolk itself masses can be distinguished, even under a low
power, which suggest separate blastomeres. The exposed surface of the yolk is somewhat
irregular, suggesting that a portion of the yolk material has recently become detached. The
blastomeres themselves are loosely associated, so that some of them could be removed with
dissecting needles. Their peripheries are not quite as distinct as the present figure indicates.

Fig. 49. — Late embryo. Age unknown (probably five or six months), corresponding approximately
to Balfour's stage N in shark. Although this specimen was examined living, and was
apparently uninjured, its body cavity was filled with blood cells. Observe also the
enlarged blood-knots in the external gills and the position of the spiracle denoted in this
figure by the small red spot immediately above the rim of the upper jaw. (Embryo's
length 35 mm.)

Fig. 49 a. — Dorsal aspect of preceding specimen. This pictures more clearly the blood-knots of
the external gills.

Fig. 49 b. — Ventral aspect of preceding specimen. This shows especially the masses of yolk, y,
attached to the external gills; also the point of attachment of the stalk of the yolk sac, y. s.

Fig. 49 c. — Detail of facial region of preceding specimen, indicating the extent to which the gill
arches protrude at the side of the head. The gill filaments are cut away, but from their
bases one observes that they occur only on the anterior rim of each gill slit.

Fig. 49 d. — Lateral aspect of preceding specimen. This pictures again the gill region from which
the external filaments have been removed. The spiracle, sp., is seen immediately under
the eye.

188

CHIMAERA

PLATE vni.

1-7'1

1-7 '

D

49b

^

4-7'

49C

1-8' l

T

48

nn del.

er, Frankfurt^H

PLATE IX.
LATE EMBRYO OF CHIMERA COLUEI.

a. cl. Antero-pelvic clasper. mix. Mixipterygium.

a. d. p. Anterior dental plate. p. d. f. Palatine dental plate.

f. o. Frontal organ.

Fig. 50. — Late embryo, age about six months, corresponding approximately to Balfour's stage P

in shark. Lateral view. The attachment of small masses of yolk to the side of the

embryo is probably artifact. The opercular fold has here been partly cut away, so as to

expose the gills. X about 3.

Fig. 50 a. — Ventral aspect. External gills removed from the left side.
Fig. 50 b. — Dorsal aspect.
Fig. 50 c. — Anterior aspect. External gills removed from the left side. Observe particularly the

large size of the frontal clasping organ.
Fig. 50 d. — Ventral region, showing extent to which the opercular fold has overgrown the gill

lamellae. A detail is given as to the origin of the external filaments.
Fig. 50 e. — Region of the mouth. This shows especially the appearance of the sensory canals and

the early condition of the dental eminences and of the labial cartilages.
Fig. 50 f. — Ventral fin, showing the early condition of the mixipterygium and of the antero-ventral

clasping organ.
Fig- 5° g- — External gill filaments, giving detail of vein and artery.

190

CHIMAL-RA

PLATI-: ix.

Liih.Anst v Werner iWimer. Frankfurta/M.

PLATE X.
" OP CHIMERA COLLIEI.

These specimens were dredged off the Californian coast by the U. S. Fish Commission
steamer Albatross, in water of about 300 fathoms. Figures are of nearly natural size.

Fig. 51. — Newly hatched young. Length about 10 cm. This shows especially the great width of
the pectoral fin, the relatively large eye, and the lack of lateral coloration.

Fig. 51 a. — Dorsal aspect of foregoing specimen. Observe particularly the large size of the open-
ings of the auditory organ, au.

Fig. 51 b. — The ventral aspect of foregoing specimen. At y. s. is shown the scar, marking the
point of entrance of the yolk-sac.

Fig. 52. — Young of about 12.5 cm. This specimen shows a marked differentiation of the dorsal
fin, also noteworthy changes in coloration.

Fig. 52 a. — Dorsal aspect of foregoing specimen.

Fig. 53. — Young, 18.5 cm. in length. This exhibits an extreme degree of pigmentation.

Fig. 53 a. — Dorsal aspect of foregoing specimen.

Fig. 53 b. — Ventral aspect of foregoing specimen.

192

CHI MAE RA

PLAIT: x.

51

51E

53a

Lith Anstv.Werneri'Winler, Frankfurt a/M

PLATE XI
IMMATURE SPECIMEN OF CHIMERA COLLIEI.

This was drawn from a freshly taken specimen and is intended to represent the fish in its
natural colors ; it does not, however, give an adequate idea of the brilliantly metallic shades of
the living fish, or of the translucency of the snout region. At this stage the fins are deeply pig-
mented. Natural size.

194

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