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Full text of "The Bashford Dean memorial volume :"

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FOR THE PEOPLE 

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LIBRARY 

OF 

THE AMERICAN MUSEUM 

OF 

NATURAL HISTORY 




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THE 

BASHFORD DEAN MEMORIAL VOLUME 

ARCHAIC FISHES 



Edited By 
EUGENE WILLIS GUDGER 



s 



Part II 
TABLE OF CONTENTS 
ARTICLES VI, VII, VIII 

AND 

ANALYTICAL SUBJECT INDEX 



THE 

f AMERICAN 1 
MUSEUM 

NATURAL 
HISTORY 

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^SaENCE^ 
EDUOaiON 



NEW YORK 

PUBLISHED BY ORDER OF THE TRUSTEES 

1937-1942 



Ai-\S5^L']-(S4 . x£. 



PART II 
TABLE OF CONTENTS 

ARTICLE Bertram G. Smith page 

VI The Anatomy of the Frilled Shark, Chlamtdoselachvs AJiCumEUS 

Plate I-VII, text-figures 1-128, pages 331-520. 331 



E. W. GUDGER 

VII The Breeding Habits, Reproductive Organs and External Embryonic 
Development of Chlamtdoselachus Based on Notes and Drawings 

BY Bashford Dean 
Plates I-VI, text-figures 1-33, pages 521-646. 521 



Bertram G. Smith 
VIII The Heterodontid Sharks: Their Natural History and the 
External Development of Heterodohtus ]apoj<[icus Based on Notes 

AND Drawings by Bashford Dean 
Plates I-VII, text-figures 1-69, pages 647-784. 647 



Analytical Subject Index 785 



III 



Reprinted from The Amekican Naturalist, Vol. LXXX, No. 794, 
pages 579-583, September-October, 1946. 



OBITUARY 
BERTRAM GARNER SMITH, 1876-1945 

DE. E. W. GUDGEE 
American Museum of Natural History 

Dr. Smith was born October 7, 1876, at Painesville, 
Ohio, the son of Albert W. and Ella Garner Smitli. He 
died of a heart attack at his home in Albuquerque, N. M., 
July 30, 1945. He is survived by his wife and a daughter. 
He was of New England ancestry, through his grand- 
mother Smith, from the Mortons who settled New Salem, 
Mass., about 1660. 

When Smith was about two years old, his parents 
moved to Youngsville, Warren Co., northwestern Penn- 
sylvania. There he received his early education, gradu- 
ating from high school in 1893. In 1894, he entered the 
Pennsylvania State Normal School at Edinboro and 
graduated in 1896. For the next two years he taught 
in the public grade schools of his section of Pennsylvania. 
From 1899 to 1902, during the winters, he taught the 
sciences in the High Schools of AVarren, Dubois, and 
Corry, Pa., and between times attended the summer ses- 
sions of Cornell University. In 1903, he matriculated at 
the University of Michigan, where he was assistant in 
zoology to Professor J. E. Reighard 1904r-07, and from 
which he graduated A.B. in 1907. 

He was instructor in biology at Lake Forest College 
in the spring of 1907, in zoology at Syracuse University 
1907-09, and at Wisconsin in 1909-11. In 1911, he 
entered Columbia University as a graduate student in 
zoology under Dr. Bashford Dean, and because of much 
published research, he was able to take his Ph.D. in 1912. 
From this year's work stemmed a lifelong friendship 
with Dr. Dean. From 1912-16, he was assistant profes- 
sor of zoology at Michigan State Normal College and 
associate professor 1916-21. From 1921 to 1930 he was 
associate professor of anatomy in New York University 

579 



580 • THE AIMERICAX XATUKALIST [Vol. LX X X 




BEETEAM GAEXEE SinTH 



No. 794] BERTRAM GARNER SMITH 581 

j\Ieclical College and professor of anatomy from 1930 
until his retirement in September 1942. 

Over the years 1906-1929, Smith's scientific work was 
chiefly done on amphibians. Of his 49 published papers, 
22 were on members of this group, and 13 of these dealt 
with the giant salamander, CryptobrancJnts alleghenien- 
sis. His interest in this dates from boyhood, when, fish- 
ing in the stream near his home, he would frequently 
catch a Cryptobranchus instead of a fish. Thus, when 
he learned of the importance of this animal from a zoo- 
logical point of view, he knew where to find it. The 
breeding season and habits of this amiDhibian, sought for 
almost a generation, were a mystery until it was discov- 
ered that, unlike other amphibians, it breeds not in the 
spring but in the fall. Smith studied its habits and 
found how oviposition and fertilization are effected. His 
field observations ranged from 1905-1911, and his labora- 
tory work from 1906-1929. 

The difficulties of the field work of collecting and "fix- 
ing" the egg and life histoiy stages were great. But 
quite as great were those of the laboratory work of em- 
bedding and sectioning these yolk-laden amphibian eggs 
averaging 6.2 mm. in diameter and exceeded in size only 
by those of C. japonicus (c. 7 mm. in diameter). Smith 
was a good artist and his papers are illustrated by his 
own drawings and photographs. The work on his 
articles, from start to finish, was done with his own hands. 
Unlike many researchers, he never had the help of assis- 
tants. 

Smith's thirteen papers on the natural history and em- 
bryology of Cryptobranchus (published mainly in the 
Biological Bulletin and Journal of Morphology), range 
in date from 1906-1929. They comprise 484 pages and 
590 drawings and photographs. Even a general exami- 
nation of his papers on Cryptobranchus reveals what a 
prodigious amount of meticulous histological work he did 
on the development stages of these huge eggs and early 
embrvos. I do not recall anv vertebrate whose natural 



582 THE AMERICAN NATURALIST [Vol. LXXX 

history and embryology have been more thoroughly and 
successfully studied. These studies, together with those 
on Amblystoma and Neeturus, comprise the major inter- 
est of the first period of his scientific activities. 

The second period of Smith's productive scientific work 
began shortly after the death (December 6, 1928) of his 
teacher at Columbia, Dr. Bashford Dean. An organiza- 
tion of Dr. Dean's associates, students, friends and fam- 
ily was set up to establish memorials to him. Bronze 
plaques were cast and mounted in the American and 
Metropolitan Museums. Then came the question of what 
to do with four sets of splendid drawings (some in color) 
of certain archaic fishes — myxinoids and sharks — made 
for reproduction by lithography, and it was decided that 
these should be published as a Memorial Atlas under the 
direction of Dr. Smith and the writer (as editor). 

After much thought, I determined that, instead of a 
Memorial Atlas, we would publish a Memorial Volume 
if I could have Smith's heljo, since his training in embry- 
ology and anatomy would be invaluable. And when next 
he came to my office, I announced my proposed plan and 
without a moment's hesitation he held out his hand and 
said — "I came to tell you just that thing. I, too, owe it 
to Dr. Dean. ' ' Nothing more clearly illustrates the spirit 
of the man. Then began work that covered 13 years and 
in which we did five of the eight articles in the volume. 
This was especially hard for Smith, who was carrying a 
full teaching load in the department of anatomy of New 
York University Medical College. Furthermore, it was 
time-consuming for him to come to and return from the 
American Museum. But for all that — he came. 

In 1931 and 1933, we published two joint papers — one 
on the natural history of the frilled shark. Then came 
the long hard pull for more than three years in which 
Smith prepared his great "Anatomy of the Frilled Shark, 
Clilamydoselaclius anguineus," (published 1937) of 190 
quarto pages, 7 half-tone plates and 128 text-figures. In 
shark anatomy this book, on one shark only, measures up 



No. 794] BERTRAM GARNER SMITH 583 

to J. F. Daniel's " Elasmobranch Fishes" (3rd. eel., 1934, 
octavo, 322 pp., 270 figs.). 

But even this was equalled by the final article in the 
Memorial Volume, ' ' The Heterodontid Sharks : Their 
Natural History and the Development of Heteroclontiis 
japonicus, Based on Notes and Drawings by Bashford 
Dean." — 138 quarto pp., 7 lithographed plates (5 in 
natural color) and 69 text-figs. This I (as editor) had 
held for Smith and for the final article in the Memorial 
Volume, and when (October 1, 1942) I handed him the 
first copy from the binder, I said, ' ' This is the high note 
of the Volume, and also of your scientific writings. ' ' But 
little did I apprehend how true the latter statement was 
to be. 

Dr. Smith retired from his work in N. Y. University, 
September 1, 1942, settled up his affairs in the East and 
presently went to Albuquerque, N. M., where he bought 
a house and settled down to adapt it and the grounds 
(with Ms own hands) to make it a home. Things went 
well until in the Spring of 1945 he began to have heart 
attacks, to one of which he succumbed on July 30. Thus 
passed a fine man, who made elaborate studies of the 
natural history and embryology of one of the least known 
American amphibians. Later he made similar additions 
to our knowledge of the natural history, anatomy and 
embryology of two archaic sharks. These notable mono- 
graphs, the outcome of ability and persistent hard work, 
are the monuments in American Zoology to Dr. Bertram 
Garner Smith. 



THE 

BASHFORD DEAN MEMORIAL VOLUME 

ARCHAIC FISHES 



Edited By 
EUGENE WILLIS GUDGER 



Article VI 



THE ANATOMY OF THE FRILLED SHARK 
CHLAMYDOSELACHUS AhlGVll^EUS Garman 



By BERTRAM G. SMITH 

Professor of Anatomy 

New York University College of Medicine 

New York City 




NEW YORK 

PUBLISHED BY ORDER OF THE TRUSTEES 

Issued December 22, 1937 



ARTICLE VI 

THE ANATOMY OF THE FRILLED SHARK 
CHLAMTDOSELACHUS AJiGUIJiEUS Carman 

By Bertram C. Smith 



CONTENTS 

Introduction 335 

External Characters of Chlamydosdachus 336 

General Form of the Body 336 

Position of the Mouth , 338 

Gill-Covers and Spiracles 339 

Fins, Paired and Unpaired 340 

Abdominal or Tropeic Folds 342 

Scales and Teeth 342 

The Endoskeleton 350 

Skull of Chlamydoselachus 350 

The Cranium 351 

The Visceral Skeleton 356 

NoTOCHORD and Vertebral Column 364 

Appendicular Skeleton 370 

Pectoral Fins and Girdle 370 

Pelvic Fins and Pelvis 373 

The Dorsal Fin 377 

The Anal Fin 380 

The Caudal Fin 380 

The Muscular System 381 

The Metameric Muscles 381 

The Axial Muscles 382 

The Appendicular Muscles 394 

The Branchiomeric Muscles 396 

Digestive System and Associated Organs 401 

The Digestive Tube 401 

The Pharynx 402 

Esophagus and Cardiac Stomach 402 

The Pyloric Vestibule 404 

The Pylorus 405 

The Bursa Entl\na 406 

The Valvular Intestine 408 

Rectum and Rectal Gland 410 

The Digestive Tube as a Whole 411 

The Liver 412 

The Pancreas 413 

Organs Associated with the Digestive Tract 415 

The Thyroid Gland 415 

The Spleen 418 

The Respiratory Organs 419 

The Gills 420 

The Spiracles 423 

The Urogenital System 431 

Urogenital System of the Female 431 

Urogenital Sinus in the Female 431 

Organs of Excretion in the Female 434 

Genital Organs of the Female ■ 444 

Urogenital System of the Male 450 

Excretory and Internal Genital Organs 450 

Myxopterygia or Claspers 451 

The Abdominal Pores 453 

33J 



Pericardio'Peritoneal Canals 455 

Blood Vascular System 457 

The Heart 457 

The Blood Vessels 461 

The Arteries 461 

The Veins 471 

The Nervous System 472 

The Brain 473 

The Cranl-^l Nerves 475 

The Spinal Nerves 485 

The Sense Organs 487 

The Membranous Labyrinth 487 

The Sensory Canal System 489 

Discussion 492 

Bibliography 498 



334 



THE ANATOMY OF THE FRILLED SHARK 
CHLAMTDOSELACHUS AKGUIKEUS Garman 

By Bertram G. Smith 

Professor of Anatomy 

New York University College of Medicine 

INTRODUCTION 

Interest in Chlamydoselachus centers around the problem of its affinities. It has been 
said (Garman, 1884.1, .2) to have "a certain embryonic look." It has been called a living 
fossil. It has been designated (Garman, 1884.3, .4; Gill, 1884.1,. 2) the oldest living type 
of vertebrate. More conservatively, Woodward (1921, p. 37) regards Chlamydoselachus 
as one of the most primitive of the true Selachii. On the other hand, a study of the 
external characters alone (Gudger and Smith, 1933) is sufficient to indicate that Chlamy- 
doselachus possesses many structural adaptations of a very special nature. In the present 
article I have endeavored to distinguish those features that represent a high degree of 
differentiation, from others that link Chlamydoselachus with the most primitive fishes. 

Since the publication of Garman's (1885.2) description of a partly eviscerated speci' 
men with a slightly mutilated tail, there has been no comprehensive account of the 
anatomy of Chlamydoselachus; but there have been many investigations dealing with 
particular organs or parts of the body of this rare fish. Some of these contributions were 
published in such form as to be readily accessible, but much information concerning the 
structure of Chlamydoselachus lies buried under titles of a somewhat general nature. 
In bringing together a digest of all these records I have endeavored to supplement them, 
wherever it seemed desirable and practicable, by original observations on all the ma- 
terial available. 

This material includes three large female specimens (lengths 1350 mm., 1485 mm. 
and 1550 mm. respectively) brought from Japan by Dr. Bashford Dean, and now in the 
collections of the American Museum of Natural History; and a fourth large female 
specimen (1398 mm. long) kindly lent by Dr. E. Grace White. The first three specimens 
had been preserved in formalin and alcohol for about thirty years. The fourth shark 
had been preserved in formalin, then alcohol, for an unknown period. In all the specimens 
the viscera were in a more or less unsatisfactory condition for study, and from the fourth 
specimen the digestive organs had been entirely removed. Nevertheless, a careful exami' 



EDITOR'S NOTE: — The first study of the anatomy of Chlamydoselachus was made by Samuel Garman at the Museum of Com- 
parative Zoology, Cambridge, Mass., on the first specimen ever brought to America (1884). Carman's monograph was published in 
1885 and is referred to herein as 1885.2 The original drawings and the woodcuts made from these have fortunately been preserved 
in Cambridge. They have been most kindly sent to me by Dr. Thomas Barbour, Director of the Museum of Comparative Zoology. 
Many of the woodcuts have become warped and spUt by drying during the past half century, but it is a great satisfaction to be 
able to use three of them (Text-figures 94, and 101 a-b) in this paper, and to have new cuts made from certain of the original draw- 
ings — those representing the brain, which are reproduced here as Plate VI. 

335 



336 



Bashford Dean Memorial Volume 



nation of this material has enabled me to fill in some of the most important gaps in the 
hitherto available knowledge of the gross structure of Chlamydoselachus. Our knowledge 
of this interesting fish is still incomplete, and one purpose of the present article is to 
direct attention to the opportunities for investigation that still exist for one who is able 
to secure favorable material. 

Since the anatomy of the lower vertebrates is of interest chiefly from the comparative 
point of view, I have endeavored, within the limits imposed by practical considerations, 
to point out some of the resemblances and differences between Chlamydoselachus and 
other primitive sharks — particularly its nearest relatives, the Notidanidae. Fortunately 
for my purpose one of these, Heptanchus maculatus, forms the basis of Daniel's (1934) 
masterly treatise on the anatomy of the elasmobranch fishes — a volume which I have 
found very helpful. 

For those who view this and similar undertakings from afar, it may be permissible 
to state that only anatomists and embryologists realise how much the study of elasmo' 
branchs has contributed to our understanding of the present structure and past history 
of the human body. 

EXTERNAL CHARACTERS OF CHLAMYDOSELACHUS 

Since the external characters of the frilled shark have been described in detail by 
Gudger and Smith (1933), only a few of these features which are of particular significance 
for comparative anatomy need be considered here. 

GENERAL FORM OF THE BODY 

As compared with other sharks, Chlamydoselachus (Text'figure 1) is very slender. 
Therefore it is pertinent to inquire what an elongate form of body means in the evolution' 
ary history of a group of vertebrates. In general, the most primitive members of any 
large and divergent group are only moderately elongate, while a high degree of speciali- 




Text-figure 1. 

Chlamydoselachus anguineus Garman, adult female, 1473 mm. long. 

After Dean, 1895, Fig. 92; redrawn from Gunther, 1887, PI. LXIV. 



The Anatomy of Chlamydoselachus 



337 




zation may affect the body form in either of 
two ways : the body may become short and 
broad, as in skates, frogs and turtles; or it 
may become very slender, as in eels, coecil' 
ians and snakes. A consideration of the 
evidence upon which this generaliziation is 
based would take us too far afield, but it is 
a principle that appears to be accepted by 
most comparative anatomists. 

In the case of Chlaynydoselachus, the 
elongation of the body has proceeded far 
enough to remove it from the category of 
primitive characters. It serves, perhaps, as 
an adaptation to life on a rough sea bottom, 
where the animal is obliged, occasionally, to 
swim or crawl through crevices. In such 
situations, Chlamydoselachus may lie in hid' 
ing, or may even stalk its prey, then strike 
suddenly as does a snake. But there is another 
advantage to be gained from an elongate 
form of body. It may be observed that the 

ectoparasitic cyclostomes have bodies that are very slender, and that Echeyieis 
sucking fish, also is slender'bodied. These are creatures that fasten on to fishes larger than 
themselves and are towed along by the host. Owing to the slenderness of their bodies 
they are not readily shaken off. Because of the large mouth and the prehensile teeth 
(Text'figure 2), it has been surmised (Gudger and Smith, 1933) that Chlamydoselachus 
seizes and swallows Hving prey nearly as large as itself. The swallowing of a large fish 
struggHng to escape is presumably not an easy matter, and were Chlamydoselachus a form 
that offered much resistance to being dragged through the water, it might not be able to 
maintain its initial hold. 



Text'figure 2. 
Front view of the widely'distended mouth of 
a specimen of Chlamydoselachus collected in 
Japanese waters by Dr. Bashford Dean and 

presented to Columbia University. 

After Gudger and Smith, 1933, Fig. 3, pi. X. 



the 




Text'figure 3. 
Heptanchus (Heptahranchias) maculatus, adult female. 

!AJ!A[, nares; SP, spiracle. 
After Dean, 1895, Fig. 93. 



338 Bashford Dean Memorial Volume 

More than in most sharks, the head of Chlamydoselachus, though not its body, is 
decidedly flattened in a dorsoventral direction when the jaws are closed. This, together 
with the fact that the creature is usually taken at great depths, suggests that the frilled 
shark is, at least partly, a bottom-dwelling form. We need not, however, conclude that 
the flattening of the head tends to remove Chlamydoselachus from the category of archaic 
fishes. "For various reasons it seems likely that the primitive chordates were not swift' 
swimming, pelagic types but partly depressed, partly bottom-living forms" (Gregory, 
1933, p. 101). 

Among living sharks the notidanid Heptanchus maculatus (Text-figure 3), though 
stouter-bodied than Chlamydoselachus, presents the greatest similarity in general form, 
position and shape of the fins, and in the shape of the tail. Throughout the present 
article I have made many comparisons between Chlamydoselachus and Heptanchus. Dean 
(1895) stated that ^'Heptayichus, of all living sharks, inherits possibly to the greatest 
extent the features of its remote ancestors." This is doubtless still a fair generalization 
when one considers only the external characters, but in many, perhaps most, of the 
internal structures described in the present article, Chlamydoselachus is less specialised 
than Heptanchus. 

POSITION OF THE MOUTH 

In Chlamydoselachus the mouth is sub-terminal (Text-figure 4, after Garman), but 
it approaches a terminal position to a degree found in no other shark, so far as I know, 
save only Rhineodon, the whale-shark. Sharks are pre-eminently surface-feeding forms, 
but the mouth is usually ventral. In skates and rays, which are bottom-feeding fishes, the 
mouth is decidedly ventral. In teleosts, with the exception of a few bottom-feeding 
forms, the mouth is terminal or subterminal. Thus in fishes the position of the mouth is 
decidedly variable. In linking the great groups of fishes, to assign phylogenetic value to 
such a character is hazardous. One cannot fail to note the resemblance, in the position of 
the mouth, between Chlamydoselachus and the teleosts, but their real relationship must 
be decided on the basis of more stable characters. Nevertheless, it may be pertinent to 
inquire, what is the primitive position of the mouth in the vertebrates? 

Since in vertebrate embryos the mouth is ventrally situated, one might infer that 
this position is primitive for vertebrates. This inference is not supported by all the 
facts of development. The ventral position of the mouth of a vertebrate embryo is due, 
in part to a precocious enlargement of the anterior end of the brain, in part to the cephalic 
and cervical flexures which, in later development, tend to straighten out. If we consider 
only adult structures and accept the time-honored theory that the jaws represent a modi- 
fied gill-arch, then the mouth is formed on the morphologically anterior side of this gill- 
arch. In its primitive position the mouth would naturally open forward, though situated 
at a lower level than the cranium and to this extent not fully terminal. The vertebrate 
mouth is, primarily, anteroventral or subterminal. 



"the Anatomy of Chlamydoselachus 339 

From its primitive position, the mouth may be displaced either ventrally or terminal' 
ly. In elasmobranchs it is usually displaced ventrally by the thickening and forward 
elongation of the cranium to form a rostrum. In other words, when the cranium becomes 
extended anteriorly, the mouth of necessity becomes ventral. This may occur regardless 
of the si2;e of the mouth. In the basking shark, Cetorhinus, the mouth is very large but is 
nevertheless ventral because of the elongate snout. In the sawfishes the prolongation of 
the rostrum is carried to an extreme that makes the mouth decidedly ventral. In teleosts 
the mouth tends more often to become terminal, though in some forms, as in the fresh' 
water suckers, it is brought into a ventral position by an extensive development of the 
related soft parts. 

I conclude that, in connection with its enormous enlargement, the mouth of Chlamy^ 
doselachus has departed only slightly from the primitive orientation, and that this de- 
parture has been in the direction of a more nearly terminal position. The anatomical 
basis for this condition is described more fully in the section on the skull. The position 
of the mouth is decidedly more primitive in Chlamydoselachus than it is in most elasmo' 
branchs; it shows a closer parallel with the condition usually found in teleosts. But 
there is substantial evidence, which cannot be considered here, indicating that the line 
of cleavage between elasmobranchs and teleostomes extends back to forms more general' 
izied than any living fish. 

GILL-COVERS AND SPIRACLES 

The presence, in Chlamydoselachus, of a sixth pair of gill-slits has usually been 
accounted a primitive character of considerable phylogenetic importance, linking Chlamy- 
doselachus with the notidanids. But Pliotrema, a sawfish, has six pairs of gill'slits (Regan, 
1906.1), differing in this respect from other sawfishes. While there is abundant ground for 
the conviction that Chlamydoselachus is related to the notidanids, one must not lean too 
heavily on the evidence afforded by the number of gill-slits. "In the existing elasmo- 
branchs the normal number of gills is five and it may well be suspected that the six or 
seven gill-slits of the notidanids and the six of Pliotrema represent a secondary increase 
in number" (Gregory, 1933, p. 424). 

In Chlamydoselachus, the unusually well developed first pair of gill-covers (Text- 
figure 4), continuous as the gular fold across the mid'ventral line, simulates an operculum 
such as is found in bony fishes. Garman (1884.2) suggested that this operculum-like 
fold or collar of Chlamydoselachus is a character indicating that the frilled shark lies near 

Text-figure 4. 
A side view of the head of Chlamydoselachus to 
show the position of the mouth, the length of the 
lower jaw, the position of the nostril and of the 
eye, and the position and form of the gill-covers; 
about one-fourth natural si2;e. 
After Garman, 1885.2, pi. I. 




340 Bashford Dean Memorial Volume 

the primitive stock from which elasmobranchs and teleostomes diverged. On this point. 
Dr. W. K. Gregory, in a personal communication, commented as follows : '"''The idea that 
Chlamydoselachus stands nearer to the true fishes than do the sharks proper, is without 
a vestige of real evidence in its favor and with a mountain of evidence against it." 

In Chlamydoselachus the external openings of the spiracles (Text 'figures 70, p. 396; 
and 124, p. 489) are very small. In the notidanids the spiracles are said to be small. 
In some sharks that certainly bear no close resemblance to Chlamydoselachus, spiracles 
are absent altogether. In skates and rays, which are bottom'dwelling forms, the spiracles 
are proportionally large. It has been inferred that spiracles were developed in connection 
with a sea-bottom habitat; but this is true only of the valvular apparatus which, in skates 
and rays, enables the spiracle to function for the inta\e of water when the mouth is buried 
in sand or mud. In Squatina, a bottom-d welling shark, the spiracles sometimes admit 
water to the oropharyngeal cavity. But sharks are characteristically free-swimming 
forms in which the spiracles, if present, serve merely for the exit of water from the pharyn- 
geal cavity, thereby retaining their primitive function as gill-sHts. This is the function 
of the spiracles even in Chlamydoselachus, as will appear from the description of the 
spiracular canal (p. 423) in the section on the respiratory organs. 

The small si7;e of the external spiracular openings of Chlamydoselachus affords 
evidence that the spiracles are in a vestigial, not an incipient condition. Spiracles have 
not arisen de novo; they represent merely a modification, sometimes accompanied by 
a change in function, of a primitive pair of gill-slits situated between the mandibular and 
the hyoid arches. In the process of transformation of this primitive anterior pair of 
gill-slits into spiracles, the ventral portions of the openings close, while the dorsal portions 
persist — as is shown in Text-figure 62, p. 388. The internal aperture is much larger than 
the external. If one opens the mouth of any shark possessing spiracles, he will find a pair 
of large internal spiracular openings resembling gill-sHts, in exact serial relation with the 
dorsal portions of the gill-slits. In Chlamydoselachus, whose external spiracular opening 
is a slit only 2 or 3 mm. long (Text-figures 70, p. 396; and 124, p. 489), the internal spiracu- 
lar orifice is an elliptical aperture more than 20 mm. long and wide enough to admit easily 
the blunt end of a pencil. As in many other selachians, the spiracles of Chlamydoselachus 
possess vestigial gills, called pseudobranchs. 

FINS, PAIRED AND UNPAIRED 

The bunching of the pelvic, ventral and dorsal fins near the caudal (Text-figure 1) 
gives color to Carman's view (1884.1, .2) that these fins provide the creature with a ful- 
crum from which to strike. This arrangement of the fins is a very special feature. The 
pelvic fins, the anal fin and the ventral lobe of the caudal fin are sufficiently large to in- 
dicate that Chlamydoselachus is not closely confined to the sea bottom. The shape of the 
tail is much like that of Heptanchus (Text-figure 3). 

The weakness of the fins of Chlamydoselachus is due not only to the softness and 
fineness of the dermal fin rays, which are exoskeletal structures, but also to the rudimen- 



The Anatomy of Chlamydoselachus 



341 



tary character of the cartilaginous rods, particularly the radials, that stiffen the basal 
portions of the fins. These rods belong to the endoskeleton and will be further con' 
sidered in their proper place. In all the fins there is a wide expanse supported only by 
fine dermal fin rays. From the viewpoint of adaptation to environment, one may say 
that softness and flexibility of the fins is an advantage to a fish that must make its way 
through crevices in a rough sea bottom. In such a situation, stiff fins might be a decided 
impediment. Evidently Chlamydoselachus is not a rapid swimmer, since it must depend 
for locomotion partly upon serpentine movements of a slender body. 




Text-figure 5. 

Restoration of the Devonian shark, CladoseUche. Its iins were supported by simple 

parallel rods of cartilage extending nearly to the margin. 

After Dean, 1909, Fig. 41. 



In the earliest fossil remains of sharks that appear to have left modern descendants, 
the parallel rods of cartilage (radials) that support each fin extend almost to its margin, 
so that the entire fin must have been fairly rigid (e. g., as in Cladoselache, Text 'figure 5). 
In living sharks there has been a reduction and modification of the radials and a correspond' 
if^gly greater dependence on dermal rays for stiffening the fins. In Chlamydoselachus 
the reduction of the radials has proceeded to an unusual degree but without a compen' 
sating development of the dermal rays. 

The shortness and breadth of base of the fins of Chlamydoselachus bring to mind the 
fin'fold theory (Thacher, 1877; Balfour, 1878; Mivart, 1879) for the origin of the fins of 
fishes; but fins that are broad and short are found in some of the most highly specialized 
sharks and more notably in the skates and rays. So this form of fin is not necessarily 
primitive. In Chlamydoselachus, the shortness and breadth of the fins are in strict harmc 
ny with the marked elongation of the body which we consider a departure from the norm 
for primitive fishes. 

In discussing a series of elasmobranchs {Cladoselache, typically Devonian; Fleur acan- 
thus, typically Permo'Carboniferous; Hyhodus, typically Jurassic; and Chlamydosela- 



342 Bashford Dean Tvlemorial Volume 

chus, now existing but exemplifying the Cretaceous and Tertiary type) selected to 
illustrate the types prevailing in successive periods of time, Woodward (1921) says: 
"Very soon the remnants of lateral fin folds, which must have acted merely as two pairs 
of balancers in these fishes [the earliest known fossil elasmobranchs] concentrated into 
paddles, and these again passed into stout-based fins adapted for swimming." It is not 
explicitly stated, by the author quoted, that he regards this succession of types of paired 
fins as a phylogenetic series, but one may infer that he considers the breadth of base of 
the paired fins of Hyhodus and Chlamydoselachus as something secondarily acquired. 

It is known that Dean was an ardent advocate of the fin-fold theory for which he 
(1894 and 1895) obtained interesting evidence in the case of the fossil Cladoselache 
(Text-figure 5). The question of the origin of paired fins was one of the problems Dean 
had in mind while he was searching in Japanese waters for embryos of Chlamydoselachus, 
Cestracion (Heterodoiitus) and other primitive fishes. Subsequently, Dean's material 
was studied by Osburn (1906 and 1907) who defended the fin-fold theory against 
the attacks of those who favored the opposing gill-arch theory originally proposed by 
Gegenbaur (1865). 

ABDOMINAL OR TROPEIC FOLDS 

The abdominal or tropeic folds are a pair of slender longitudinal thickenings of the 
ventral abdominal wall, situated close to the median line and separated by an external 
groove. They are figured and comprehensively described by Gudger and Smith (1933, pp. 
283-284, Text-fig. 12), and are shown in transverse section in various figures inserted 
in my chapter on the muscular system (p. 381). 

No satisfactory explanation has ever been advanced to account for the presence of 
the tropeic folds, which are structures pecuHar to Chlamydoselachus. Concerning them 
Carman (1885.2, p. 3) wrote: "From their position, shape and extent, it is evident that 
the folds will furnish support to one of the theories regarding the origin of paired fins." 
I agree with Braus (1898) that "Der Kiel des Chlamydoselachus hat zur Cenese der 
paarigen Gliedmassen nicht die geringste Beziehung." In my section on the muscular 
system there is given a fairly satisfactory explanation (illustrated by Text-figure 58, p. 386) 
as to the manner of embryonic development, but this does not answer the question as to 
the fitness of these peculiar structures for the needs of Chlamydoselachus in its particular 
environment. One can infer from their form and position that they may have some sHght 
utility in locomotion similar to that afforded by the keel of a ship : but in some specimens 
they are too small to be of any appreciable use in this way. 

SCALES AND TEETH 

The variations in the form of the placoid scales or dermal denticles of Chlamy- 
doselachus on different parts of the body, the form of the teeth, and the arrangement of 
the teeth in rows have been described by Carman (1885.2), Rose (1895), and by Gudger 



The Anatomy of Chlamydoselachus 



343 



and Smith (1933). We are here concerned chiefly with the structural and developmental 
relations between scales and teeth. The latter are not ordinarily considered as external 
structures, but are discussed here because of their morphological relationship to scales. 

Some typical scales of Chlamydoselachus are shown in Text'figure 6. Each scale is, 
essentially, a hollow cone with ridges extending from the base to the apex. It is composed 
of dentine covered with a thin layer of enamel. In addition to the single prominent 
spine there are sometimes, as shown in Text-figure 6a, slight elevations near the margin 
of the base, formed by intersecting ridges. These elevations might easily develop into 





Text-figure 6. 
Three different views of a placoid scale or dermal denticle (x 130) from a 340-mm. embryo of Chlamy- 
doselachus: A, scale from the flank, viewed from above; B, lateral view of a scale from the region of 
the tail; C, scale from the region of the tail, seen from beneath. 
After Rose, 1895, Abb. 1, 2, 3. 



accessory spines. Of the atypical scales, those forming the "armature" on the anterior 
edge of the dorsal fin (Garman, 1885.2, p. 7; Gudger and Smith, 1933, p. 294) are interest- 
ing because, in form and arrangement, they resemble the "fulcral scales" of the Actin- 
opterygii. The latter are described by Goodrich (1909, p. 304), and are said to be quite 
peculiar to this group. 

A typical tooth, viewed from three aspects, is represented in Text-figure 7- It 
has three sharp, slender, curved cusps, and two rudimentary cusps or denticles. It is 
attached to the jaw in such fashion that the denticles project inward toward the mouth 
cavity. The broad base of the tooth is prolonged posteriorly (toward the interior of the 
mouth) and is forked so as to interlock with a paired excavation in the base of the suc- 
ceeding tooth. In the illustrations the prongs of the base might readily be mistaken for 
cusps, but in the actual specimens the appearance is very different since the base is com- 
posed entirely of dentine while the cusps are covered with shiny white enamel, 



344 



Bashford Dean Memorial Volume 





Text'figure 7- 

Three different views of a tooth of Chlamydoselachus, six times natural size: 

A, seen from above; B, from the side; C, from beneath. 

After Garman, 1885.2, Figs. 1, 3 and 4, pi. VI. 

The essential similarity of the internal structure in scales and teeth of sharks is 
evident from a comparison of Text-figure 8 with Text-figure 9. Each has the form of 
a hollow cone, slightly recurved at the apex. Each is composed of dentine (D., D.2) 
overlaid with enamel (e., S.). The dentine is traversed by canals (d. c.) radiating from the 
pulp cavity (p. c. and P.). 

Both scales and teeth are exoskeletal structures. Evidently teeth, which are the 
more complex, have developed from the same materials and in the same manner as scales. 
It would, perhaps, be a trifle crude to say that teeth are developed from scales, but it 
seems entirely proper to say that teeth are homologous with scales. This has long been 
admitted, but in Chlamydoselachus we have material exceptionally favorable for revealing 
the precise manner in which teeth correspond to scales. Superficially, the chief difference 




Text-figure 8. Text-figure 9. 

Sagittal sections showing similarity of structure between scales and teeth of sharks. 

Text-figure 8. Section showing finer structure of a placoid scale of Sc)'m?ius lichia. 

c.c. central canal; d.c, dentinal canal; e., enamel; p.c, pulp cavity. 

After Daniel, 1934, Fig. 35; redrawn from Hertwig, 1874, Fig. 2, Taf. XII. 

Text-figure 9. Section of a single-cusped tooth (x 75) from the lower jaw of a 
340-mm. embryo of Chlamydoselachus. 

D., dentine; D.2, strongly calcified dentine; P., pulp cavity; S., enamel; So., base. 
After Rose, 1895, Abb. 9. 



The Anatomy of Chlamydoselachus 345 

between a scale and a tooth in Chlamydoselachus is that the scale has but one projection 
large enough to be called a spine, while the tooth usually has three large spines or cusps, 
and two rudimentary cusps. The question arises: does a single scale correspond to an 
entire tooth, or does a tooth develop as an aggregate of several scale^like rudiments? 

Near the angles of the mouth of Chlamydoselachus, teeth sometimes grade into 
scales. In the four large specimens studied by Gudger and Smith (1933), the teeth of the 
last rows, as these approach the angles ot the jaws, become very small, irregular and 
rudimentary until finally it is with great difficulty, even with the aid of a strong lens, 
that rows of teeth can be distinguished from groups of undoubted scales like those shown 
in Text-figure 10. The teeth are not comparable to individual scales, but each cusp 



Text-figure 10. 
Placoid scales or dermal denticles 
(x 5) from the angle of the mouth of 
Chlamydoselachus. Each scale re- 
sembles a single cusp of the rudimen- 
tary three-cusped teeth occurring in 
this region. 
After Garman, 1885.2, Fig. 12, pi. VI. 



resembles a scale, and the scales are sometimes arranged in columns of threes in series 
with the rows of teeth. In two specimens the border line between teeth and scales 
could be distinguished with considerable certainty, but in the other two specimens there 
was room for doubt. On the other hand, Garman (1885.2, p. 5) says of his single adult 
specimen: "the change from teeth with broad base, three cusps, and two buttons [rudi- 
mentary cusps] is sudden and decided; i.e., they do not grade into each other. A strong 
lens, however, is necessary to distinguish them, since in the hinder row each cusp looks 
much like a single scale." The last statement, together with the observations of Gudger 
and Smith, suggests a multiple origin for each tooth. 

The development of a placoid scale has not been studied in Chlamydoselachus; but 
in the leopard shark, Tria}{is semifasciatus, a scale develops from a single primordium 
(Daniel, 1934, p. 26 and Fig. 29). It is of interest to inquire whether the multicusped 
teeth of Chlamydoselachus develop in the same manner. 

The teeth of a 340 mm. embryo of Chlamydoselachus have been studied by Rose 
(1895). In this embryo, none of the teeth (Text-figure 11) had attained its final form, but 
some in the middle of each row were like those of the adult except that they lacked the 
two very small cusps. The innermost teeth of each row were represented, individually, 
by three distinct cusps not yet united at their bases; apparently each cusp had developed 
from a separate primordium. The evidence certainly indicates that, at the inner end of 




346 



Bashford Dean Memorial Volume 



each row, teeth were being formed by the 
union of simple denticles homologous with 
placoid scales. At the outer ends of the 
rows, the teeth were small and rudimentary; 
each tooth had from one to three cusps. 
Those with a single cusp bore a strong resem' 
blance to placoid scales. In the teeth with 
two or three cusps, the cusps were so closely 
fused at their bases that the enamel was con- 
tinuous from one cusp to another. According 
to Rose, these teeth represent a stage transi' 
tional to the adult teeth of many teleosts. 
Possibly these teeth were anomalous, since in 
my four large specimens the outer teeth are 
only slightly different from those at the middle 
of each row: all have three cusps well devel' 
oped and well separated. Rose thinks that all 
the two' and three-cusped teeth of his embryo 
developed through the fusion of simple cusps. 
On one side of the upper jaw of his em- 
Teeth of the lower jaw (x 5) of a 340-mm. embryo ^ R5se found the first two teeth of the 

of Chlamydoselax:nus, in their natural positions. i . i • i i • i i i i- ■ i 

. , „ third row united at their bases, but delimited 

After Rose, 1895, Abb. 5. , , yr^ r r • x ^ 

by a deep groove (Text 'figure 12 herein). One 
of these teeth has but one cusp, the other has two cusps. Rose claims that this 
anomaly has a phylogenetic significance, since it indicates the manner in which a jawbone 
might arise through the fusion of teeth at their bases. Further, Rose asserts that the 
three- and especially the five-cusped teeth of an adult Chlamydoselachus furnish an 
excellent transition between a single-cusped shark tooth and the toothplates of an adult 
Siren, likewise of all urodele embryos. Also, he finds in his Chlamydoselachus embryo 
all possible forms intermediate between a simple placoid scale and a three-cusped tooth. 
The single-cusped tooth shown at the left in Text-figure 12 differs very little from a simple 
scale and is smaller than some of the scales found on the external surface of the body. 
Rose calls attention to the fact that in Chlamydoselachus the dentine (illustrated by his 
Fig. 10) develops in fundamentally the same way as in mammals. 




Text-figure 11. 



Text-figure 12. 

The first two teeth (x 45) of the third 

row of the upper jaw of a 340-mm. 

embryo of Chlamydoselachus. These 

teeth are united at their bases. 

After Rose, 1895, Abb. 6. 




The Anatomy of Chlamydoselachus 



347 






|#t| 




Text-figure 13. 
Placoid scales from two species of the Devonian shark Cladoselache. 

A — Scales (x 25) from various parts of the body of C. fyleri. From a specimen in 

the American Museum. 
B — Trifid scale (x 20) from near margin of mouth of C fyleri. From a specimen in 

the American Museum. 
C — Larger scales (x 10) of Cladoselache (probably clarl^). From a specimen in the 

British Museum. 
After Dean, 1909, Figs. 1, 2, 3. 



In Chlamydoselachus and in Heptanchus (Daniel, 1934, Fig. 27) the structure of the 
scales is simple and conforms to the same fundamental plan, though in both fishes the 
form of the scales varies considerably on different parts of the body. One should not 
attribute much phylogenetic importance to differences in the form of the scales of elas' 
mobranchs. Some of the most specialized elasmobranchs (e.g., Raja) have simple scales, 
while the fossil Cladoselache, one of the most primitive sharks, has scales of various 
forms ranging from those only slightly indented or subdivided (Text'figures 13a and b) 
to those indented to such a degree that their exposed surfaces bristle with cusp'like 
points or ridges (Text-figure 13c.) In Cladoselache as in modern sharks, the scales vary 
in size and shape in different regions of the body (Dean, 1909, p. 214). 

The teeth of Chlamydoselachus are 
barb-like, prehensile. In Heptanchus 
(Text-figure 14) the teeth are not alike on 
upper and lower jaws. The upper teeth 
seem adapted mainly for holding, the lower 
ones for cutting. The decided differences 
between the teeth of Chlamydoselachus 
and Heptanchus — forms which, in many 
important respects, seem closely related — 
serve to weaken one's faith in the validity 

Text-figure 14. 

Dentition of Heptanchus (AJotidanus) indicus. 

a, teeth in function; fa, teeth in reserve; u and I, upper and 

lower single teeth (natural size). 

From Goodrich, 1909, after Giinther, 




348 



Bashford Dean Memorial Volume 




Text-figure 15. Text-figure 16. 

Teeth of two fossil Chlamydoselachids from the Tertiary. 

Text-figure 15. Fossil teeth of Chhmydoselachus lawkyi from the Pliocene of Orciano, 
Tuscany, Italy. Note the lack of rudimentary cusps. 

1 and lb, teeth viewed from above; la, from below; Ic, from the side (lb, natmral size; all others x 2). 
After Lawley, 1876, Figs. 1 to Ic, pi I. 

Text-figure 16. A fossil tooth (A, natural size; B, x 2) of Chlamydosehchus tobleri from 

Trinidad, British West Indies. Note presence of rudimentary cusps. 

After Leriche, 1929. 

of phylogenetic deductions based on a comparison of present'day fishes with fossil forms 
that are known only by their teeth. 

In the fossil Chlamydoselachus lawleyi (Lawley, 1876), which is known only by 
its teeth (Text-figure 15), the resemblance to the teeth of C. angumeus is very close. 
Apart from their smaller si2;e, the teeth of C. lawleyi differ from those of C. anguineus 
only in that they lack the pair of very small cusps. In C. tohleri, which is known only 
from a single fossil tooth (Leriche, 1929), the small cusps are present, but in some other 
respects the tooth (Text-figure 16) is so different that one may regard the inclusion of 
this form in the genus Chlamydoselachus as merely tentative. 




Text-figure 17. Text-figure 18. Text-figure 19. Text-figure 20. 

Teeth somewhat resembHng those of Chhmydoselachus anguineus, from various fossil sharks. 

Text-figure 17. Tooth (x 5) of Cladoselache fyleri from the Devonian. 

After Dean, 1909, Fig. 5. 
Text-figure 18. Tooth of Cladodus acutus from the upper Devonian. 

After Agassiz, 1843. 

Text-figure 19. Tooth of Ctenacanthus clar}^ from the Carboniferous. 

After Dean, 1909, Fig. 42. 

Text-figure 20. Tooth of Hybodus reticuhtus from the lower Jurassic. 

After Zittel, 1923, Fig. 93. 



The Anatomy of Chlamydoselachus 349 

Among fossil forms assigned to other genera, teeth more or less resembling those 
of Chlamydoselachus anguineus are found in Cladoselache (Text'figure 17), in Cladodus 
(Text'figure 18), in Ctenacanthus (Text'figure 19), and in Hyhodus (Text'figure 20). In 
each of these fossil sharks the teeth vary in form, but those represented in the figures 
may be regarded as typical. In all these teeth the cusps are conical, and the central 
cusp is by far the most prominent. In Hyhodus the lateral cusps (3 or 4 on each side) 
become smaller in proportion to their distance from the central cusp. In Cladodus, 
Ctenacayithus and Cladoselache there are two cusps on each side of the central cusp, and 
the marginal cusps are larger than the intermediate cusps. In Cladoselache the inter' 
mediate cusps are very small, as in the frilled shark. In Hyhodus and in Cladodus most 
of the cusps are recurved at the tip. In Cteyiacanthus and in Cladoselache the cusps are 
more slender and appear practically straight, though Dean (1909) states that in Clado- 
selache clar}{i there is a slight sigmoid flexure of the cusps. Of the four forms considered, 
Cladoselache possesses the sharpest cusps. In this, as in many other respects, the teeth 
of Cladoselache most nearly resemble those of the frilled shark, but in this connection 
I quote the following from Dean, 1909, p. 253: 

When teeth of the type of Cladodus were discovered in different horizons from the 
Devonian well into the Mesozoic, it was naturally concluded that the sharks themselves would 
be found to correspond closely — to belong if not to the same genus at least to the same family. 
When, however, associated remains of the earlier forms were discovered, it became clear 
that these sharks were by no means closely allied. Instead of being proven to be cestracionts, 
one type of ^'Cladodus" {Cladoselache \epleri, C. fyleri; Upper Devonian), was found to be 
spineless, and quite different in essential structures from the modern cestraciont: another 
type of ''Cladodus" Symmorium Cope (Coal Measures), was then shown to be unlike both 
Cestracion and Cladoselache; and still another, ''Cladodus" neilsoni, was demonstrated by 
Traquair to be quite different in fin characters from all the rest. And now a fourth cladodont, 
Ctenacanthus, is found notably discrepant. It is, then, only the mesozoic group of "clado- 
donts" typified by Hyhodus which remains faithful to our preconceived notions as to what 
kind of a shark a cladodont tooth should predicate. The fact of the matter is that the clado- 
dont type of tooth is as ancient as it has been useful in the subclass Elasmobranchii, and that 
it has appeared in many different lines, either as an heirloom from primitive sharks, or, less 
probably, as an independent acquisition. Certain it is that it appears with little variation 
in as many as seven families of sharks, and in at least three distinct orders. 

When teeth are highly differentiated, resemblances amounting almost to identity 
(as between Chlamydoselachus anguineus and C. laivleyi) are probably significant. On 
the other hand, among living fishes we find instances where members of the same family 
have widely different teeth. On a priori grounds it seems likely that, where cusps are 
numerous and close together, development may proceed by the eHmination of some of the 
cusps in order that the others may be better nourished; or, putting the matter in another 
way, some cusps may develop at the expense of the others. It seems probable that, in 
the long lapse of time, teeth like those of Chlamydoselachus anguineus could have evolved 
out of rather irregular and rudimentary structures, like the teeth of Hyhodus reticulatus 



350 Bashford Dean Memorial Volume 

(Text'figure 20), quite as readily as from teeth like those of Ctenacanthus clar\i (Text' 
figure 19), Cladodus acutus Ag. (Text'figure 18) and Cladoselache fyleri (Text'figure 17), 
which they more nearly resemble. 

THE ENDOSKELETON 

The most comprehensive studies of the endoskeleton of Chlamydoselachus are those 
of Garman (1885.2), Deinega (1909 and 1923), and Goodey (1910.1). In addition, Giinther 
(1887) described the skeleton of the claspers; Braus (1902) that of the paired fins; Fiir' 
bringer (1903) and Garman (1913) the visceral skeleton; while Allis (1923), using material 
supplied by Dr. Bashford Dean, described the skull. Deinega's first (1909) paper is 
in Russian, but his original figures are reproduced in his later (1923) paper which 
is in German. 

As in selachians generally, the endoskeleton (excepting the notochord) of Chlamy- 
doselachus is composed entirely of cartilage. In most elasmobranchs the cartilage is in 
many places hardened by deposits of calcareous material without, however, assuming the 
histological character of true bone. In Chlamydoselachus, it appears that such calcifi' 
cation is very limited in extent. Thus Garman (1885.2) writes that the cartilage of the 
skull is soft except in the parachordal region where it is hard and granular. Allis (1923) 
says of the skull of Chlamydoselachus: ''The entire postero ventral region of the chon' 
drocranium is extensively calcified in all my specimens, my observations thus differing 
from Goodey's" (1910.1, p. 553). Goodey does mention (p. 543) a calcification of the 
floor of the cranium in the region of its junction with the vertebral column, and elsewhere 
in the same article he describes local calcifications forming the rudimentary centra of the 
vertebrae, but he emphasizjes (p. 553) ''the small amount of calcification appearing in the 
skeleton at all." 

In the softness of its cartilaginous endoskeleton, Chlamydoselachus agrees with 
Heptanchus which, according to Daniel (1934), has cartilage of the clear hyaline variety 
with very little in the nature of calcareous deposits. In both genera this is probably 
a primitive character. 

THE SKULL OF CHLAMYDOSELACHUS 

The vertebrate skull consists of the cranium and the visceral skeleton. The cranium 
serves to protect the brain and certain sense organs: the olfactory organs, the eyes and 
the membranous labyrinths. The visceral skeleton consists of a series of cartilaginous or 
bony arches which partly surround the mouth and the pharynx. These arches comprise 
the jaws or the mandibular arch, the hyoid arch, and the branchial arches or gill'arches. 
The term cranium is sometimes used as a synonym for skull. The cranium is then divisi' 
ble into two portions, the cerebral cranium or neurocranium, and the visceral cranium 
or branchiocranium. 



The Anatomy of Chlamydoselachus 351 

THE CRANIUM 

To illustrate various aspects of the cranium and some closely associated parts of the 
endoskeleton of Chlamydoselachus, I have selected the excellent figures of Allis (1923j 
for reproduction in my Plates I, II and III. In connection with his very detailed descrip' 
tion of the skull, Allis has critically reviewed the work of his predecessors, Garman 
(1885.2) and Goodey (1910.1). Of the work of Deinega (1909), Allis was probably un- 
aware since he makes no reference to it. 

Garman (1885.2, p. 8) writes thus of the "skull" (cranium) of his 1510'mm. specimen 
of Chlamydoselachus: 

The skull of the frilled shark is suggestive of immaturity; the thin walls, soft cartilage, 
and large pores and foramina with thin edges around them, seem to be those of a young, 
rather than an adult specimen. Compared with that of Heptabranchias [Heptanchus] 
it agrees better with an embryo than an adult. Looking at it from above, its shape may be 
likened to that of the body of a guitar, the vertebral column answering to the neck of the 
instrument, and the narrow section between the orbits to the middle of its box . . . The 
walls are very thin. In longitudinal section the thickness of floor and roof is comparatively 
uniform. There is a marked contrast in this respect if compared with the skulls of Hex' 
anchus and Heptahranchias, which in these portions are thick and irregular (see Gegenbaur, 
1872, Das Kopfskelett der Selachier, Figs. 1 and 2, pi. IV) . . . The chamber is large, and the 
brain small. 

Allis (1923), whose excellent figures showing dorsal, ventral and lateral aspects of 
the "neurocranium" of Chlamydoselachus are reproduced as my Plate I, says: "In dorsal 
view [my Figure 1] it greatly resembles the neurocranium of Hexanchus (Gegenbaur, 
1872), but its dorsal surface is even flatter." Also, in dorsal view the cranium of Chlamy 
doselachus is much like that of Heptanchus (Daniel, 1934, Figs. 45 and 46). According 
to Allis the cranium of Chlamydoselachus differs from those of Hexanchus and Hep- 
tanchus, and resembles those of Acanthias, Centrophorus and Scymnus (Gegenbaur, 
1872, p. 39) in that the ventral surfaces (Figure 2, plate I) of the occipital and labyrin- 
thine regions lie in the same level, and in that the eminence of the bulla acustica is found 
on this ventral surface and not on the lateral surface (Figure 3, plate I) of the neurocranium. 
This ventral position was considered by Gegenbaur to be secondary, due largely to 
a greater development of the hyomandibular articular facet than is found in Hexanchus 
and Heptanchus, or indeed in any other selachian skull figured by him. 

All who have studied the matter agree that the notochord of Chlamydoselachus is 
continued as a slender strand of tissue in the base of the cranium as far forward as the 
pituitary fossa. This is clearly shown in Garman's (1885.2) Fig. B, nc, pi. VII; also in 
my Text'figures 21 and 22 after Ayers, and in my Text-figure 30, p. 364, after Goodey. 
It is faintly indicated in Deinega's (1909 and 1924) Fig. 4, pi. II; in Goodey's (1910.1) 
Fig. 2, pi. XLII; and in my Figure 4, plate II (after Allis). This persistence of the anteri- 
or portion of the notochord in the region of the basis cranii is a very primitive character. 
To be sure, in all vertebrate embryos the notochord extends forward almost to the 



352 



Bashford Dean Memonal Volume 



infundibulum, bu: m rhe higher vertebrates it disappears from the basis cranii during 
later development. 

In connection Vv-ith his account of the persistence of the notochord of Chlamy- 
doselachus in the region of the basis cranii, Goodey (1910.1, p. 543) makes the following 
interesting statement: "The cartilage of the floor of the cranium in the region of its 
junction with the vertebral column is thick and somewhat hea\Tly calcified. It here 
shows some indications of its probable vertebral nature, by the sHght resemblance which 
the calcmcarion presents to the inverted V-formation found in the centra of the vertebral 
column." Avers ' lSS9j found more decided evidences (my Text-figures 21 and 22) of 





Test-figure 21. Test-figure 22. 

Sections through the skull of the frilled shark, Chlamydoselachus anguineus. 

Text-figure 21. A transection of the basis cranii near the vertebral articulation, to show the fig- 
ure made by the calcareous sheath (and its processes) of the notochord, resembling a vertebra of 

the trunk region. 

cent., ver te bral centnim (sheath rf notochord); di., chc^da dorsalis; cranxsv., cxanial cavity; ct., cartilage of the basis cranii; 

n.j>., neural {gorrs^; tj-.p., transverse process. 
After Ayers, 1889, Fig. 8. 

Text-figure 22. Left half of the hemisected cranium, to show the relations of the notochord and 
cranial aorta to the basis cranii and to the pituitary prominence and space. 

c, cranial aorta; du, chorda doialis (notochcxd); ir., iotemal carotid artery; \., cephalic aorta; p.pl., pituitary plexus; pt., 

pituitary space; tr.c, transverse canal; III, third pair of aortic arches. 

After Avers, 1889, Fig. 3. 



the persistence of the notochord (ch) and the rudimentary vertebral column in the basis 
cranii of his specimen; but in view of the doubts that have been expressed concerning 
the accuracy of many of Ayers' obser\7ations on Chlamydoselachus, one should accept 
this description and the accompanying figures with some reserve. In Hexa-iichus the 
notochord Text-figure 23, nc) persists in the posterior portion of the basis cranii, much 
as in ChJ.d-'nydoselachus. 

My Figure 4, plate II, shov.Tng a medial view of the cranium of Chlamydoselachus, 
should be compared with Text-figure 23, shouTing a similar view of the cranium of Hexan- 
chus. The t^-o figures are of interest chiefly because they show the foramina for the 
exit of the cranial and occipital nerve roots. 



The Anatomy of Chlamydoselachus 



353 



In Chlamydoselachus, any consideration of the cranium as a whole must take into 
account its relation to the upper jaw (palatoquadrate) and to the suspensory apparatus, 
on both of which it seems, to a considerable degree, to be molded. As one looks at the 
skull from the side (Figure 5, plate II) he is impressed by the extraordinary length of the 
jaws which begin posteriorly far behind the cranium and lie, when the mouth is closed, 
in a nearly horizontal position. The ectethmoidal process projects over the outer surface 
of the palatoquadrate, thus helping to hold it in place. The postorbital process of Chlamy- 
doselachus is exceptionally large, but even when the mouth is closed it fails to reach the 




c'a. 



c. 



octv. 



Text-figure 23. 
Inner view of the right half of the skull of Wexanchui to show the cranial portion of 

the notochord and the foramina for cranial nerves, 
ac., foramen for auditory nerve; a.p., antorbital process; c, carotid foramen; ca., interorbital canal; gp., 
glossopharyngeal nerve; m., membrane over fontanelle; -ac, notochord; o., optic nerve; ocn., spino-occipital 
nerve; om., oculomotor nerve; r., rostrum; tg., trigeminal nerve; Vr., trochlear nerve; Dg., vagus nerve; 

vs., occipitospinal nerve. 
From Goodrich, 1909, Fig. 93, after Gegenbaur, 1872. 



palatoquadrate. The nearly terminal position of the mouth is attained somewhat at 
the expense of the cranium, for the rostrum is short and thin, though broad, and the 
anterior third of the ventral surface of the cranium slants upward in such a way as 
to allow the anterior part of the upper jaw to lie on a level with the posterior part of 
the basis cranii. This is only one of several adjustments that make this creature, when 
viewed from in front with its enormous jaws spread apart (Text-figure 2), seem to be 
nearly all mouth. When this same specimen with the wide-open mouth is viewed from 
the side, it appears that, m the process of opening the mouth, the upper jaw (and of 
course, the cranium also) is elevated anteriorly, thus keeping the center of the mouth 
cavity in line with the body. The site of this flexure is not in the occipi to-vertebral 
articulation, but in the vertebral column a few centimeters posterior to it. How this 
flexion is accomplished I do not know, since the vertebral column has no articulations 



354 Bashford Dean Memorial Volume 

that seem to give any appreciable freedom of movement; but one should remember that 
even a solid rod of cartilage is flexible. 

In most selachians, when the mouth is closed the hyomandibular is directed down' 
ward, outward or even forward; but in Chlamydoselachus it is directed posteriorly. As the 
mouth opens, its angles spread apart so that the entire oropharyngeal cavity broadens; 
this is made possible by the length and mobility of the hyomandibular. When the mouth 
is closed, the hyomandibular is neatly folded between the palatoquadrate and the vertebral 
column, its anterior end lying somewhat apart from the cranium and a little above the 
level of the anterior end of the dorsal border of the hyomandibular facet (af in Figure 3, 
plate I). This facet is a broad groove extending longitudinally for a considerable distance 
on the posterior part of the lateral surface of the cranium. When the jaws are opened, the 
anterior end of the hyomandibular must slide posteriorly along the facet, while the 
posterior end swings laterad and somewhat ventrad through an angle of about 45° 
(Carman, 1885.2). Thus the articulation of the hyomandibular with the cranium is 
a sliding joint of unusually loose construction, aiding greatly in the range of movement 
of the hyomandibular. This peculiar hyostylism of the skull, together with the nearly 
terminal position of the mouth, the long jaws and indeed the entire complex of adjust- 
ments that gives Chlamydoselachus its enormous gape, are to be viewed as comparatively 
recent adaptations of a highly specialised character. Goodey (1910.1, p. 550) says of the 
jaws of Chlamydoselachus that "their disposition relative to the cranium is quite different 
from that found in any Selachian whose skull I have been able to examine or see a figure 
of. It resembles nothing among the Vertebrates so much, perhaps, as the general dispo- 
sition of the jaws in certain of the Ophidia." 

Allis has described a palatal process of the palatoquadrate which serves as a support 
for the soft parts of the horiziontal palatine shelf. ''The palatine process of Chlamy- 
doselachus ... is a curved flat plate of cartilage, of nearly even width, that projects antero- 
mesially beneath the anterior end of the neurocranium" (Allis, 1914, p. 354). The 
hori2,ontal palatine shelf, which is evidently a homologue of the maxillary breathing valve 
of certain teleosts, is fully described by Gudger and Smith (1933, p. 269). 

The cartilaginous lateral wall of the suprapalatine recess is perforated, on either 
side, by the nasal fontanelle {naf. Figure 2, plate I). In its position and relations the 
nasal fontanelle is, apparently, the strict topographical homologue of the fenestra choanalis 
of Amphibia (Allis, 1913 and 1914). In its natural state the nasal fontanelle of Chlamy 
doselachus is closed by a tough membrane (Allis, 1923, p. 132) which appears to be a part 
of the cranium. This membrane is distinct from the mucous membranes lining the nasal 
capsule and the mouth. The membrane evidently represents unchondrified portions of 
the subnasal plate and the nasal capsule. "The nasal cavity of Chlamydoselachus is 
thus separated from the suprapalatine recess by membranous and mucous tissues only, 
and if these tissues were to be secondarily [sic] perforated ... an internal nasal aper- 
ture would be formed which would lie directly above the horizontal palatine shelf" 
(Allis, 1914, p. 355). 



The Anatomy of Chlamydoselachus 355 

The postorbital process closely approaches the palatoquadrate but does not articulate 
with it. The orbital process of the palatoquadrate is unusually large and projects far 
into the deeper portion of the orbit, where it articulates with a large facet on the ventral 
edge of the anterior wall of the orbit. The orbital process forces the eyeball away from 
the medial wall of the orbit. These relations must change considerably when the pharynx 
is expanded, on account of the spreading of the jaws posteriorly and the shifting of the 
angles of the jaws ventrad (note the space between palatoquadrate and cranium in Text- 
figure 84, p. 429). The only articulation of the palatoquadrate with the cranium is by 
way of the orbital process, which is very loosely attached to the cranium. 

The eyestalk of Chlamydoselachus is a slender rod of cartilage which projects from 
the anterior edge of the trigemino-pituitary fossa and curves around the posterior surface 
of the capsular sheath of the orbital process of the palatoquadrate (Figure 2, plate I; 
Figures 5 and 6, plate II). Its distal end has a sliding articulation with the medial surface of 
the eyeball, without being attached to it. According to Gegenbaur (1872) the eyestalk 
of the plagiostomes does not belong genetically to the eye, neither does it, except in its 
basal portion, belong to the chondrocranium. In all the plagiostomes, the basal portion 
of the eyestalk is of firmer tissue than the remainder of the stalk, which is always of softer 
tissue than the chondrocranium. Gegenbaur suggested that the eyestalk (excepting 
its basal portion) might be a part of the visceral skeleton that had secondarily acquired 
relations with the eyeball. AUis (1923) cites Dohrn's suggestion that it might represent 
a part of a premandibular visceral arch, and recalls his own earlier suggestion (Allis, 
1914, p. 365) that ''the eyestalk is a modified branchial ray or rays, of a mandibular or 
premandibular arch, that has secondarily acquired relations to the eyeball." While such 
explanations are highly speculative, an origin from a branchial ray of the mandibular 
arch seems the most plausible. That the eyestalk originated from some pre-existing 
cartilaginous structure seems indicated by this statement from Allis (1914, p. 347): 

The eyestalk is certainly a retrograding and archaic structure, as its varying importance 
and wide distribution clearly indicate, and it seems certain that it could not have been de- 
veloped independently, merely as a support to the eyeball, a function it so inefficiently 
fulfils except in certain rays (Harman). And that it was developed as a point of attachment 
for the recti muscles seems improbable because it actually fulfils that function, so far as I can 
find, only in Chlamydoselachus (Hawkes, 1906) and possibly in Zygaena. 

At the bottom of the endolymphatic fossa (e/. Figure 1, plate I) are four apertures, 
two on each side, described by Goodey (1910.1) and by Allis (1923, p. 155). Each anterior 
aperture is a foramen ductus endolymphaticus, or aqueductus vestibuli, and affords 
passage for the ductus endolymphaticus. Each posterior aperture leads directly into the 
perilymphatic cavity of an ear, and is the so-called fenestra ovalis of Scarpa, or the fenestra 
vestibuli cartilaginei of Weber. In the natural state this aperture is closed by a membrane. 
In Chlamydoselachus and in Mustelus, the fenestra vestibuli lies immediately above the 
apex of the posterior membranous semicircular canal of the ear. 



356 Bashford Dean Memorial Volume 

A rear view of the skull (Figure 6, plate II) shows the foramen magnum (/m), and 
beneath it a small perforation, not labeled, for the extension of the notochord forward 
into the basis cranii. The figure shows also a posterior view of the hyomandibular 
articular facet (af), the postorbital process (pop), the ectethmoidal process (ecp), and the 
eyestalk (es). 

As in other elasmobranchs, the brain does not fill the cranial cavity, which is shown 
from the dorsal aspect in Figure 7, plate III. This figure shows also the olfactory capsules, 
partly dissected, lying on each side of the broad rostrum. 

THE VISCERAL SKELETON 

In most elasmobranchs there are seven visceral arches: the mandibular, the hyoid, 
and five branchial arches. In Chlamydoselachus and the notidanids there are additional 
branchial arches making a total of eight visceral arches in Chlamydoselachus and Hexaw 
chus, and nine in Heptanchus. 

Since the mandibular arch and the hyoid arch are usually regarded as derivatives 
of primitive branchial arches, some embryologists use the term branchial arch for each 
member of the entire series of visceral arches, and number them consecutively. In com' 
parative anatomy it is more common to designate the mandibular arch and the hyoid arch 
as such, and restrict the name branchial arch to the succeeding arches, which are numbered 
separately. Thus, the third visceral arch is the first branchial arch. 

In Chlamydoselachus, as in other elasmobranchs, the mandibular arch (Figure 5, 
plate II) is divided into an upper palatoquadrate or pterygoquadrate segment, and a lower 
mandibular segment (Meckel's cartilage). The articulation between these two elements 
is of a simple type, figured by AUis (1923) in his PI. XII. The ligaments connecting the 
palatoquadrate with the mandible, and the mandibular arch with the hyoid arch, are 
shown by AUis (1923) in his Pis. X and XI. AUis (1923, p. 149) states that the orbital 
process of the palatoquadrate has a capsular sheath, and (pp. 208 and 209) refers to 
a "somewhat ligamentous portion of the connective tissue that attaches the capsular 
sheath to the anterior wall of the orbit." Garman (1885.2, p. 10) writes: "Some of the 
most prominent differences between Chlamydoselachus and the notidanids are to be seen 
in the attachments and articulations of this cartilage [the palatoquadrate]." 

As compared with the same structures in other sharks, the jaws of Chlamydo- 
selachus (Te.xt'figure 24; Figure 5, plate II) are slender. This slenderness stands in marked 
contrast with the condition found in Heptayichus (Daniel, 1934, Fig. 48), and is correlated 
with a decided difference in the character of the teeth. In Chlamydoselachus, much 
more than in Heptanchus, the jaws resemble branchial arches. 

The anterior labial cartilage (Figure 5, plate II) gives insertion to a long and stout 
ligament attached to the cranium. From this ligament a series of ligamentous strings 
are sent off to the upper lip. The posterior upper labial has no direct supporting relations 
to the upper lip, but the posterior lower labial or mandibular labial gives attachment, at 
its posterior end, to the tendon of the protractor anguli oris, and from its point of artic 



The Anatomy of Chlamydoselachus 357 

ulation with the posterior upper labial it extends forward, along the ventral edge of 
the mouth, strongly attached to the inner surface of the dermis of the lower lip (AUis, 
1923). The presence of a mechanism for strengthening and mobili2;ing the soft tissues 
at the angles of the mouth supports my contention that Chlamydoselachus seizes and 
swallows large prey. 



Text-figure 24. 

Ventral view of the visceral skeleton (three-fourths natural size) of Carman's first specimen 

of Chlamydoselachus. The branchial rays are omitted from all arches except the hyoid. 

b-br, basibranchial; b-hy, basihyoid; br-r, branchial ray; c-br, ceratobranchial; c-hy, ceratohyoid; e-br, epibranchial; h-br, 

hypobranchial; m){, mandible or Meckel's cartilage; p-hr, pharyngobranchials. 

After Garman, 1885.2, PI. IX. 

The homologies of the labial cartilages of elasmobranchs are obscure. Pollard (1895) 
considered the labial cartilages to be the remains of the skeletal supports of a set of 
primitive oral cirrhi such as are found still in Amphioxus and in myxinoids. Others, 
like Sewertzoff (1916), believe the labial cartilages to represent vestiges of the visceral 
arches of two segments in front of the mandibular. Concerning this view Goodrich 
(1930, p. 448) writes as follows: ''Against the theory maintained by Sewertzoff it may 
be urged that there is no good evidence of the existence at any time of gill-pouches, 
arches, etc., anterior to the mandibular, that the labials are too superficial to be of visceral 
nature, and that the supposed vestiges of giU-pouches corresponding to them apparently 
occur anteriorly to the pharynx (endodermal gut). Possibly the labials are merely 
secondary in Gnathostomes and of no great morphological importance." The labials 
may be tentatively classified as extravisceral cartilages of the mandibular arch, in series 
with the extrahyoids and the extrabranchials. 



35 S Bashford Deari hiemorial Volume 

Neither Garman . 1SS5.2 nor Goodey 191l'M round anv ;r:racular cartilages in the 
specimens dissected by them, and Fiirbrmger 19'- 3. p. 3S9 :cu::_ cr.'.y a single spiracular 
cartilage in his specimen. Allis (1923, Fig. 22, pi. XIj found three small nodules of 
cartilage situated in a loose prespiracular band of connective tissue 'which does not have 
the same relations as a spiracular Kgament) on each side of one specimen. The cartilages 
are described by Allis (,1923, p. 169) as follows: 

These cartilage present stnkjngly the appearance of being rudiments c^ tlie basal 
portions of three adjoining branchial rays related to the mandibular arch, and, like the sir^le 
spiracular cartilage described by Fiirbringer in the oae specimen esamined by him, they lie 
lateral, and hence morphologically anterior, to the artery of die arch. They lie posterovoiGal 
to that part of the spiracular canal that bears the pseudobranchial filaments and in no sup- 
porting relations whatever to them, and hence, while possibly representing persistii^ 
rudiments of mandihnlar rays, they may not be true spiracular cartilages, for Gegenbsur 
(l872, p. 198) says that in aU the Plagiostomi in which it is found, die spir^orar csrrllige 
always Hes in the anterior wall of the spiracular canal, and that, where there is a pseu i : r r:. r ;h, 
the filaments of that organ lie direcdy upon die cartil^e. 

Evidently Daniel (1934, p. 63) considers that the dor^l s^ment of the second visceral 
arch of Chlamydoselachus is not a true hyomandibular, since he vsmtes of it that "the 
dorsal segment is on its way to become a hyomandibula or suspeosorium." According to 

Allis 1 1923 ,, there is no Hgament connecting the hyomandibular with the palatoquadrate; 
there are, however, ligaments connecting the hyomandibular with the ~ ar. iirle \ leckePs 
cartilage) in the region of the quadrato-mandibular articulation, and a broad capsular 
ligament binding the hyomandibular strongly to the cranium. The slidir.g ar::cc-?-tion 
of the hyomandibular with the cranium has already been described. The homolcgies of 
the hyomandibular of fishes are discussed by Allis 1915 ar.d by Gregory 1933, pp. 
80-82). Woodward (1921, p. 39) regards the hyoitybc s^ospension of the jaws, found in 
nearly all modem sharks and skates, as a condiricr. secondarily itc?.:r.ed. while the primi' 
tive mode of suspension oi the jaws is a]r.rh:;:vl:c. as ir. C'.s:.:S':.s:':i ir.z ir. the noti- 
danids). One may well be puzzled to decide '.vhe:her the recud^r ~ode c: s'jsper.sion of 
the jaw^s of Chlamydoselachus is azirhisrydc or hyostylic. It does not conform fully to 
either type, but comes nearer to being hyostylic. Goodey '1910.1, p. 544 states un- 
reservedly that "the suspension of the javrs is hyostylic."" 

The hyomandibular of Chlamydoselachus bears nine Garman, 1SS5.2 or more 
cartilaginous branchial rays. Goodey (1910.1'; shows, in his Fig. 1, pi. XLIII, ten rrinchial 
rays attached to the hyomandibular and one branchial ray sKghtly detached riom it. 
Allis (1923), in his figure renroduced as my Figure 5, plate 11, shows nine branchial ravs 
attached to the hyomandibular and live or sis others more or less detached bu: evidently 
related to it. 

The ceratohyoids (Test-figure 24, c-hy) parallel the mandibular or Meckelmn carti' 
lages {mX) and are intermediate in size between these and the ceratobranchials (c-br). 
Viewed from below, as in Garman"s figure, the -^-isceral skeleton or Chlamydoselachus 



The Anatomy of Chlamydoselachus 



359 



presents a striking picture of gradation between jaws and gill-arches. A more nearly 
perfect gradation is exhibited in Dean's reconstruction of Cladoselache fyleri, shown 
in my Text'figure 25. Since the ceratohyoids, as well as the hyomandibulars, of 
Chlamydoselachus bear branchial rays (my Figure 5, plate II), the hyoid arch can scarcely 
be derived from the velum of an amphioxid ancestor as alleged by Ayers (1931). In 
Heptanchus (Daniel, 1934) the hyoid segment possesses an extravisceral cartilage, not 
present in Chlamydoselachus. 

All the branchial arches of Chlamydoselachus, except' 
ing the sixth and the vestigial seventh, bear branchial rays 
(Text-figure 77; and Figure 8, plate III). These are very 
slender rods of cartilage, attached at one end to a branchial 
arch, and supporting the gill-septum. Goodey (1910.1) 
states that in his two specimens, male and female respective- 
ly, the greatest number of rays occurs on the hyoid arch, 
and as one proceeds posteriorly the number gradually de- 
creases. His tables showing the number of rays on the 
right and left sides of each arch, from the hyoid to the fifth 
branchial arch inclusive, support his statement. The same 
trend is shown in Collett's (1897) table showing the num- 
ber of rays for each branchial arch (one side only?), from 
the first to the sixth inclusive, in his large specimen; but 
it is probable that Collett's first arch, bearing nineteen 
rays, is really the hyoid arch, and his sixth branchial arch, 
bearing eight rays, is really the fifth. 

In each of the first five branchial arches of Chlamy- 
doselachus there is a dorsal extrabranchial cartilage, de- 
scribed by Fiirbringer (1903) and by Allis (1923, Fig. 49. 
pi. XVIII). In Furbrmger's Figs. 31, 32, 33, Taf. XVIII, the 
extrabranchial cartilages appear like detached or fragmented 
branchial rays, usually small. 

The basibranchials and hypobranchials constitute the most variable part of the 
visceral skeleton of Chlamydoselachus. Viewed as departures from an easily recognized 
type, these variations are interesting. In none of the specimens of Chlamydoselachus 
that have been described is there a distinct basibranchial associated with the first pair 
of ceratobranchials. To be sure, Garman (1885.2, p. 11) enumerates a first basibranchial 
in his series, but this would be a second if the series were complete. In order to make 
comparisons, one must revise his enumeration to correspond with that used by Goodey 
(1910.1) and others. With this change of labels, Garman describes and figures separate 
second and third basibranchials (my Text-figure 24). The fourth basibranchial is fused 
with the corresponding hypobranchials, is obHquely and indistinctly divided, and is closely 
joined with the fifth which is fused with the sixth and indistinguishable from it save by 




Text-figure 25. 
Reconstruction of the underside 
of the skull of a Devonian shark, 
Cladoselache fyleri, showing low- 
er jaw in series with gill-arches. 
After Dean, 1909, Fig. 6. 



360 Bashford Dean Memorial Volume 

its position and relations. The hypobranchials of the first pair are small and are situated 
dorsal to the medial ends of the ceratohyoids. The second and third pairs of hypo- 
branchials are distinct and well developed. The fifth and sixth pairs of hypobranchkls 
are mere rudiments fused uith the basibranchials. 

Fiirbringer's specimen (1903, Fig. 18, Taf. XVID presents several features that are 
different. A small median posteriorly directed prominence fused v.'ith the basfhyoid 
may represent the first basibranchial, and a pair of posterolateral processes of the basihyoid 
probably represents the first pair of hypobranchials. The second basibranchial appears 
to be entirely absent, but there is a pair of second hypobranchials. The third basibranch- 
ial is distinct from the fourth basibranchial, but is fused v.ith the fourth pair of hypo- 
branchials. The fourth basibranchial is distinct from the fifth, but the fifth and sixth 
basibranchials are fused together. The fifth and sixth pairs of hypobranchials are not 
identified v^ith certaint^^ There is a vestigial seventh branchial element. Some features 
of Fiirbringer's drawing are obscure, so that it is not suitable for reproduction here. 

Goodey (1910.1) described and figured (my Text-figure 26a) a small posteriorly 
projecting prominence (bhr. 1 ?) on the basihyoid which, as in Fiirbringer's specimen, 
probably represents a fused first basibranchial. Otherwise, Goodey"s drav-ing more 
closely resembles that of Garman (1SS5.2). There are, however, some differences. "The 
two lateral prominences [of the basihyoid], also at the posterior end, no doubt represent 
the hypobranchials of the first branchial arch" (Goodey, 1910.1, p. 545). In Garman's 
figure (my Text-figure 24) the hypobranchials of the first branchial arch appear to be 
separate elements over-lapped by the ceratohyoids. 

Garman (1913) described and figured (my Text-figure 26b) this region of the visceral 
skeleton in still another specimen. Here, there is no posterior projection of the middle 
part of the basihyoid to represent a vestigial first basibranchial, but the other basibran- 
chials are more numerous and regular than in any other specmien that has been figured. 
There are five elements represented in this series, of which the fourth probably represents 
the combined fifth and sixth basibranchials, while the slender posterior element may 
belong to the vestigial seventh branchial arch discovered by Fiirbringer ^1903). The 
first pair of hypobranchials Qihr. 1) is represented by posterolateral processes of the basi- 
hyoid, while one member of both the second and the fourth pairs of hypobranchials 
is fused with the corresponding basibranchial. The hypobranchials of the sixth pair 
are small and are displaced somewhat posteriorly. The most posterior pair of cartilages 
(r. hr. a. 7) presumably represent ceratohyoids of the seventh arch. 

AlHs (1923) agrees closely -w^th Garman (1885.2) in his description and portra^'al 
of the basibranchials, but in the fourth branchial arch of his specimen he finds one of the 
hypobranchials distinct and independent while the other is fused with the fourth basi- 
branchial to form a single median cartilage v.^th a lateral process on one side only. This 
fused hypobranchial is well shown in dorsal \^ew (^Figure 8, plate III), but is only partly 
shown in a ventral view (Figure 9, plate III). The former figure shows also a pair of 
rudimentary nodules representing the sixth hypobranchials, and both figures show a pair 
of rudimentary seventh hypobranchials. 



The Anatomy of Chlamydoselachus 



361 



Deinega's otherwise excellent figure (1909 and 1923, Fig. 5, pi. II) of the visceral 
skeleton of Chlamydoselachus does not show clearly the limits and the relations of all 
the basibranchials and hypobranchials, hence it cannot be used for comparison. 





bbr.5 



bbr.6? 



v.br.a.7-/-- 



.\cbr.6 



Text-figure 26. 

Ventral views of the median portions of the branchial skeletons of two specimens of 
Chlamydoselachus to show variations. 

A — Dissection by Goodey (1910.1) of a specimen in the University of Birmingham. 

bbr.](?)-6, basibranchials of the first (?) to the sixth arch; bh., basihyoid; cbr.1-6, ceratobranchials of the first to 
the sixth arch; /., foramen; hbr. (1) (?)-6, hypobranchials of the first to the sixth arches; th.c, thyroid con- 
cavity ; tifca7(?), vestigial seventh branchial arch. 
Redrawn, with some changes in labels, after Goodey, 1910.1, Fig. 6, pi. XLIII. 

B — Dissection by Garman (1913) of his second specimen in the Museum of Comparative 
Zoology. The original is without lettering. 

bbr.2, 5 and 6 (?), basibranchials; bh., basihyoid; cbr.4 and 6, ceratobranchials; chy., ceratohyoid; /., foramen in 

basihyoid cartilage; hbr.1,2 and 6, hypobranchials; v.br.a.7, vestigial seventh branchial arch. 

After Garman, 1913, Fig. 6, pi. 59. 



362 



Bashford Deo.': yriemorial Volume 




Text-figure 27- Text-figure 28. 

D;:£il and ventral views of the visceral skeleton of the notidanid shark, Heptanchus. 

Text-figure 27. Branchial skeleton o: Hioz^nchus sp., in dorsal view?. 



I-Vn, first to seventh tonchial arches; C, copula cr riiih'::i: _r. :ji.ei siyr.'z iri i- 
. to fifth hasitenchEls; fey, ceiatohyoid; 1, hypobrir.;:n!;: J. :eri::rri=:h:£=: j, e 

.After (^er-riur. IS":, Fig. 1. Taf. XVm 

Text-figure 2S. \":j:e-l skele::' :: H:p--:h:,s ■-.s.z-^. 

bfc.2, second basilKaDchial; ;-... rjii- .;:_. jr.. :eri:cirir.c:.iili. :-... :eri:;hy:;i: ^,; 

After Daniel, 1934= Kg. 50.A. 



ventral aspect. 
robranchials; mp., median piece. 



The vestigial seventh branchial arch in ChIa7n;ydoseI^u:hM^ was first described and 

figured by Fiirbringer 1903. p. 409 and Fig. IS, pi. X\''ir. In his specimen it consisted 
of a single small rod or cartilage on each side. In a young specimen described by Hawkes 
(1907) it consisted of four small pieces on one side and two on the other. In another 
specimen, an adult, examined by Hawkes there were only two pieces ""in a similar posi' 
tion," the larger one equal in length to the combined four pieces found in the smaller 
specimen. In a third specimen studied by Hawkes a seventh branchial arch v,^s entirely 
lacking. Oi two specimens examined by Goodey ' 1910.1\ in one this arch u-as lacking, 
in the other it u-as represented (Text-figure 26a. vha. IT} by ""a pair of small, segmental 
tapering pieces h"ing on the ventral side of the last basibranchial at the bases of the 
sixth ceratobranchials."" In a specimen described and figured by Garman ' 1913i the 
vestigial seventh arch >my Text-figure 26b > is represented by a pair of cartilages consider- 
ably larger than any described or figured in other specimens. The seventh branchial 
arch of a specimen studied by Allis is shown in my Figures 8 and 9, plate III, and is 
described by AlHs 1923, p. 179'i as rollows: 

Fr;— :he !ef: -:;:er; litaril c:~er :: :r.e ;:>::-. -.?:branchial, a chain of small thin nodules 
of ca":li;e exter.ij rcitencrly ini rerreser.:; :l-e . e;::gial seventh ceratobranchial . . . On 
the r:;r.: ;i ie of the head this chain of nodules is represented by a process of the basibranchial. 
Wedjed m between the base of this process and the distal end of the sixth ceratobranchial 



The Anatomy of Chlamydoselachus 363 

there is a small nodule of cartilage, a similar nodule being "found on the opposite side of the 
head wedged in between the basal one of the chain of three small nodules and the related 
ceratobranchial. These two Httle nodules are, in position and appearance, strict serial 
homologues of the two nodules that represent the proximal ends of the sixth hypobranchials, 
and they are accordingly quite probably the corresponding ends of the seventh hypobranchials, 
the posterior process of the large cardiobranchial then being the seventh basibranchial. 

A comparison of all the available figures of the seventh branchial arch in Chlamy- 
doselachus shows that this arch is extremely variable and is never fully developed. I am 
inclined to think that phylogenetically it is in process of disappearance rather than in 
process of development. A rudimentary ninth branchial arch is present in Heptanchus 
(Daniel, 1934, Fig. 50b). 

It is in the ventral portion of the branchial skeleton of selachians that the greatest 
amount of variation takes place. A complete series of basibranchials and hypobranchials, 
without fusion, is presumably the primitive condition, but so far as I know this condition 
is not fully realized in any living fish. Chlamydoselachus and the notidanids probably 
come the nearest. Gegenbaur's drawing (1872, Fig. 1, pi. XVIII) of the branchial skeleton 
of Heptayichus is here reproduced as Text'figure 27. The first basibranchial is lacking 
and the sixth and seventh are fused together. If one compares Fiirbringer's drawing of 
Heptanchus (1903, Fig. 29, Taf. XVIII), and DaniePs illustration (1934, Fig. 50a) re- 
produced as my Text'figure 28, one finds in the basibranchials of Heptanchus quite as 
much irregularity as I have noted for the same structures in Chlamydoselachus. On the 
other hand, in Heptanchus the hypobranchials form a more nearly perfect series, especially 
if one considers the vestigial first and seventh pairs figured by Daniel (my Text-figure 28). 
In Hexanchus (Gegenbaur, 1872, Fig. 2, Taf. XVIII; FGrbringer, 1903, Fig. 19, Taf. 
XVII), the basibranchials resemble those of Chlamydoselachus as figured by Goodey 
(my Text-figure 26a). In respect to both basibranchials and hypobranchials, Chlamy-- 
doselachus and the notidanids are primitive, yet so variable that they seem to possess the 
materials for a rapid evolutionary change. 




Text-figure 29. 

Longitudinal section of vertebral column and notochord in the cervical 

region of Chlamydoselachus. 

ch, notochord; in, interdorsal; is, interspinous process; tic, neural canal. 
After Garman, 1885.2, Fig. 3, pi. X. 



364 Bashford Dean Memorial Volume 

NOTOCHORD AND VERTEBRAL COLUMN 

In Chlamydoselachus, the notochord is persistent to a degree not found in the higher 
elasmobranchs. Perhaps in no other Hving shark does the notochord of the adult retain 
its primitive condition through so large a portion of its length. The notochord of Chlamy- 
doselachus extends from the pituitary fossa of the basis cranii to the extreme tip of the 
tail. In the basis cranii it is very slender, but elsewhere it is a fairly stout rod. 



ii. 



-fci, v.f. s.li. 3..f. s.<i.X. 



ci. '^^- i 4 





c.i.s 


rh<, 



Text'figure 30. 

Vertical longitudinal section of the anterior end of the vertebral column in a large female 

Chlamydoselachus, showing calcified cyclospondylous centra. 

bd., basidorsal; ca!., calcification; ex. 5, cyclospondylous centrum of the fifth cervical vertebra; ch., notochord; 
ch.s., chordal sheath; d./., dorsal root foramen; i.d., interdorsal cartilaginous element; s.bd., suprabasidorsal; 
s.d.L, supradorsal Hgament; soA, spino-occipital foramen; v.f., ventral root foramen; X, foramen for tenth 

cranial nerve. 
After Goodey, 1910.1, Fig. 10, pi. XLIII. 

In the cervical (cephaHc, according to Goodey's nomenclature) and main caudal 
regions the notochord of Chlamydoselachus shows pronounced metameric constrictions 
(Text-figures 29, 30 and 31) due to inward projecting thickenings of its sheath. In the 
trunk region and in the region of the dorsal and anal fins, the constrictions of the noto- 
chord are very slight (Text-figures 32 and 33); according to Garman (1885.2, Fig. 2, pi. X) 
they are limited to the ventral portion of the notochordal sheath and do not extend to 
the notochord proper. The metameric constrictions of the notochord are of interest 
because they occur in connection with the formation of rudimentary cyclospondylous 
centra. In Chlamydoselachus we find initial stages in the formation of these centra. 

Similar constrictions of the notochord occur in Heptanchus. For the cervical region 
and near the base of the anal fin, these are illustrated by Text-figures 34 and 35. In the 
trunk region of Heptanchu^ the constrictions of the notochord are sUght (Daniel, 1934, p. 
48). In Hexanchus (Regan, 1906.2, p. 740) the notochord is constricted by annular 
thickenings of the cartilaginous sheath, without calcification such as occurs in Hepta- 
branchias (Heptanchus) where the notochord is constricted vertebrally by a series of 
calcified rings. 

On page 351 I have described the continuity of the vertebral portion of the notochord 
with its more slender portion imbedded in the cranium. All observers agree in empha- 
sizing the firmness of the attachment of the vertebral column to the cranium. Goodey 



The Anatomy of Chlamydoselachus 



365 



t.ti. p.li. 



i. td. p. id 




Text'figure 31. 
Surface and sectional views of a portion of the vertebral column (x 1.25) from the main 

caudal region of Chlamydoselachus. 
A — Surface view showing ridged extensions of the arcualia around the notochord. 

bv., basiventral; ex., cyclospondylous centra; cfi.s., chordal sheath; h.s., haemal spine; i.bd., imperforate basi- 
dorsal; i.id., imperforate interdorsal; >u., interventral; p.bd., perforate basidorsal; p.id., perforate interdorsal. 

After Goodey, 1910.1, Fig. 15, pi. XLIV. 

B — Vertical longitudinal section (with anterior and posterior ends reversed) showing 
calcified cyclospondylous centra of two sizes. 

bi'., basiventral; h.c, haemal canal; h.s., haemal spine; I.c.c, larger cyclospondylous centrum; ne.c, neural canal; 

s.c.c, smaller cyclospondylous centrum. 
After Goodey, 1910.1, Fig. 16, pi. XLIV. 



V(i.3o 



S.fl.l. 



u/. U 




rb, a..ch.s. 

Text-figure 32. 
A portion of the vertebral column (x 1.5) from the trunk region of Chlamydoselachus. 

Note the rudimentary ribs. 

a.ch.s., annulation in the chordal sheath; bd., basidorsal; bu., basiventral; d.{., dorsal foramen; id., 

interdorsal; in., interventral; rb., rib; s.d.l., supradorsal hgament. 

After Goodey, 1910.1, Fig. 11, pi. XLIV. 



366 



Bashford Dean Memorial Volume 



(1910.1, p. 554) states: "The vertebral column is fused to the cranium quite firmly, so 
that but slight articulation is possible between the two.'' On this point AlUs (1923, 
p. 161) writes: 

In my specimens of Chlamydoselachus there is no continuity of the cartilage here, so far as 

I can determine from macroscopic examination. The opposing surfaces of the chondro- 
cranium and first vertebra are closely appHed to each other, and there is but Httle movement 
possible between them, but a certain amount of lateral movement is nevertheless possible, and 
the two articular surfaces can always be separated without breakage of the cartilage. 



S.d.L. llcL.69 




a.ctis. 



Text-figure 33. 

A portion of the vertebral column (s 1.4) of Chhmydosehchus, in the 

region of the dorsal and anal fins, showing the transition from mono- 

spondylous to diplospondylous vertebrae. 

a.ch.s., annulation in the chordal sheath; hd.69, basidorsal no. 69; hv., basiventrals; d./., 

dorsal foramen; h:, interventral; n.yO and n.72, neuromeres 70 and 72 respectively; s.bd., 

supra-basi dorsal; s.d.I., supradorsal Ugament; v.f., ventral foramen. 

After Goodey, 1910.1, Fig. 12, pi. XLIV. 



The vertebral column of Chlamydoselachus is of a very simple elasmobranch type. 
The best description is that of Goodey (1910.1), and I shall base my treatment mainly on 
his account. There is a long central cylinder, which comprises the notochord together 
with its enlarged sheath. Above the chordal sheath there is a series of cartilaginous 
vertebral elements arching over the spinal cord. These elements, comprising the neural 
arches or the dorsalia, are classified by Goodey, using Gadow's (I895j nomenclature, as 
follows: basidorsals, interdorsals and supra-basidorsals, the last-named being segmented 
oif from the apices of the basidorsals. Below the chordal sheath there is another series 
of vertebral elements, the ventralia, consisting of basiventrals, interventrals, ribs, and 
haemal spines in the caudal region. These various elements making up the vertebral 
column are illustrated in Text-figures 30-33 inclusive. There is an elastic supradorsal 
Ugament which extends from the cranium to a point just posterior to the dorsal fin. 
This must greatly strengthen the column. 

There is no detailed account of the histological structure of the chordal sheath in 
Chlamydoselachus, but in Heptanchus (Daniel, 1934, p. 48, and Fig. 52 reproduced as my 



The Anatomy of Chlamydoselachus 



367 



Text-figure 34) it is composed of three concentric layers as follows : "The outermost of 
these layers is relatively thin and consists of cartilage; within this cartilage is a second 
and lighter broad area which appears to be made up of transverse fibers. Within this 
second layer and bounding the notochord is a third layer of a white tissue. At regular 
intervals the third layer forms septa which produce the regular constrictions in the 
central part of the notochord. It will be observed that the septa are more pronounced 
ventrally than dorsally, and that they pass intra-centrally." The development of the 
sheath is discussed by Daniel (1934, p. 70). 

In a large female specimen of Chlamydoselachus described by Goodey (1910.1) the 
first eleven vertebrae possess ring-like thickenings of the chordal sheath, which project 
inward in such a manner as to constrict the notochord and make it appear somewhat 



Text-figure 34. 
Sagittal section through sixth to eighth 
segments of the vertebral column of 
Heptanchus maculatus, showing struc- 
ture of the chordal sheath. 

chd, notochord; iz, inner zone, mz, middle zone 

and oz, outer zone, of the notochordal sheath; 

nc, neural canal; s, septum constricting notochord. 

After Daniel, 1934, Fig. 52. 




like a string of beads (Text-figure 30). The soft notochordal tissue gradually becomes 
obliterated from the intervertebral spaces as it approaches the skull, so that in the space 
between the first centrum and the cranium soft tissue is not present at all (Goodey, 
1910.1, p. 555). This is apparently not true of Carman's large specimen (Text-figure 29) 
in which the notochord (ch) is nowhere completely interrupted by the constrictions of 
the chordal sheath. Continuing my account of the cervical region in Coodey's large 
specimen: Each constriction appears below a basidorsal, so that the constrictions are 
intra vertebral. Each thickening of the chordal sheath possesses a calcification, as shown 
by the deeply shaded areas in Text-figure 30, c. c, and in a median vertical longitudinal 
section of a single vertebra these calcified areas appear like two Vs placed point-to-point. 
Thus each centrum has the form of a short cylinder constricted round its middle. There 
are no articular surfaces, nor even septa, separating any two successive centra; the 
notochordal sheath is continuous and the intervertebral spaces are filled in by successive 
bead-like segments of the notochord. The relations of the notochordal sheath are 
shown somewhat better in a smaller and presumably younger specimen studied by 
Coodey (1910.1, Fig. 9, pi. XLIII), in which some of the constrictions are not so well 
developed and the calcifications are not complete. 

In the unusually long trunk region of Chlamydoselachus, the notochord (Text-figure 
32) is almost uniform in diameter; nevertheless, according to Coodey, it shows slight but 
unmistakable signs of segmentation. This segmentation is described by Goodey as follows : 



368 Bashford Dean Memorial Volume 

The segmentation is shown by a difference in the appearance of the chordal sheath 
along hnes corresponding in position to the ends of the basidorsals. At these points there 
appear to be narrow rings or annulations of the notochord as shown in Fig. 11 [my Text-figure 
32]. In a view of the cut surface of a vertical longitudinal section of a portion from this 
region, no apparent constrictions of the notochord are found to correspond with the external 
segmentation of the chordal sheath. The interior of the chord presents a fairly uniform 
appearance, as was noted by Garman. If, however, a horizontal longitudinal section be made 
of the notochord, a regular sequence of constrictions of the chordal sheath is at once apparent. 
Each of these occurs beneath a basidorsal, and extends between two consecutive segmen- 
tation marks on the exterior of the chordal sheath. Each takes the form of a bulging inward 
of the sheath, so that a slightly pinched-in cylinder is formed. 

There are no calcifications of the notochordal sheath in the trunk region of Chlamy 
doselachus. Rudimentary ribs are shown in Text'figure 32. 

The cervical and trunk regions are typically monospondylous, i. e., each ""neuromere" 
(Goodey's terminology) is made up of one of each kind of vertebral element: basidorsal, 
interdorsal, supra-basidorsal, basiventral and interventral. The foramina for the spinal 
nerves do not occur between the dorsalia but are actual perforations of the basidorsals 
and interdorsals. In the monospondylous regions each basidorsal transmits a foramen 
for a ventral root, and each interdorsal, one for a dorsal root. At the seventieth neuro' 
mere, Goodey found an interesting transition from the monospondylous to the diplo' 
spondylous condition (my Text-figure 33). There is a doubling of the number of basidor' 
sals, interdorsals and supra-basidorsals, but only the posterior interdorsals and basidorsals 
of each neuromere contain foramina for the exit of the roots of spinal nerves. In the 
seventy-second neuromere the monospondylous condition recurs dorsally, but the 
ventral elements are diplospondylous. The diplospondylous condition characteristic 
of the caudal portion of the vertebral column in sharks probably arises out of the monO' 
spondylous by a process of fragmentation of the primitive cartilaginous vertebral 
elements. 

Goodey does not tell us precisely where, with reference to external features, the 
transition from the monospondylous to the diplospondylous condition in Chlamydosela- 

ja 50 "it f.v.f.d. to 



Text-figure 35. 

Lateral view of the spinal column of Heptanchus maculatus in the region of transition from the 

monospondylous to the diplospondylous condition, near the base of the anal fin. 

chd., notochord; f.d., foramen for dorsal nerve root; /.«., foramen for ventral nerve root; h.a., haemal arch; r., rib; 

s., septum constricting notochord; 44-60, vertebrae. 

After Daniel, 1934, Fig. 53. 



The Anatomy of Chlamydoselachus 369 



»v'os n«9 



/■ — y — -, — y — y. — :^^ ^ TV 111 




ll\/.S 



Text-figure 36. 

Terminal caudal portion of the vertebral column of Chlamydoselachus, 

showing heterospondyly. 

ch, notochord; hs, haemal spine; n 108 — n 112, neuromeres. 
After Goodey, 1910.1, Fig. 17, pi. XLV 

chus occurs; but from a comparison of Text'figure 33, after Goodey, with Text-figure 48, 
p. 378, after Garman, it appears to be in the region of the dorsal and anal fins. Here, the 
condition of the notochord and of the chordal sheath (Text'figure 33) is similar to that 
in the trunk region (Text'figure 32). In Heptanchus (Daniel, 1934, p. 48) the transition 
occurs at about the fifty'sixth segment dorsally, and somewhat farther forward ventrally 
(my Text'figure 35); this region lies dorsal to the base of the anal fin. 

In the main caudal region of a large female specimen of Chlamydoselachus described 
by Goodey (1910.1), the diplospondylous condition is well established (my Text'figure 
31). The constrictions of the chordal sheath are of two sizes, the larger more calcified 
ones lying beneath the imperforate dorsals, and the smaller less calcified ones beneath 
the perforate dorsals. The segmented appearance of the notochord is due in part to 
constrictions by bands of cartilage. These bands are lateral extensions of the dorsal and 
ventral arcualia (basidorsals and basiventrals) round the chordal sheath, forming bridges 
that connect the dorsal and ventral cartilages from which they arise. These bridges 
alternate with spaces in which the chordal sheath is naked. In the trunk region, homolo' 
gous bands of cartilage occur but they are so thin that they are recognizable only in 
microscopical sections. 

Toward the tip of the tail the differences in the sizes of the cyclospondylous centra 
gradually become lost, the constrictions becoming equal in size along with the equali' 
zation in the size of the perforate and imperforate basidorsals. This stage marks a near 
approach to perfection in the expression of diplospondyly. 

In the extreme tip of the tail the vertebral column is a gradually tapering structure 
(Text'figure 36) which remains segmented up to the very end. The arrangement of the 
nerve foramina with relation to the number of dorsalia is such that Goodey characterizes 
this region as "heterospondylic." In Heptanchus (Daniel, 1934, p. 49) the segments of 
the tail are said to show ""an incomplete diplospondyly'' in the arches both above and 
below the central column. No exception is made in regard to the extreme tip of the tail. 



370 Bashford Dean Memorial Volume 

Concerning the occurrence of cyclospondylous centra, Goodey (1910.1) writes 
as follows: 

The points at which the calcified centra occur are perhaps deserving of some mention. 
It seems that they are found where there are the greatest demands made for strength. At 
the anterior end, combined with the fusion of the vertebral column to the cranium, they 
give a rigidity to the supporting elements which is of service no doubt in enabUng the fish to 
cleave the water. In the caudal region they meet the demand for increased strength caused 
by the purchase which the caudal fin obtains upon the water. 

It might be added that in the caudal region the cartilaginous bridges across the 
lateral surfaces of the chordal sheath give greater strength to the vertebral column. On 
the other hand, the diplospondylous condition gives greater flexibility (Ride wood, 1899). 
In general, the vertebrae are best developed in the region that is subjected to the most 
severe stresses. 

We have seen that the vertebral column of Chlamydoselachus is of interest in 
a number of ways. The notochord persists, in the adult, with so little modification 
that it is one of the most primitive known in living sharks. The cartilaginous elements 
of the vertebral column are of a very simple elasmobranch type and illustrate various 
stages in the formation of complete vertebrae. In the cervical and caudal regions one 
finds early stages in the formation of cyclospondylous centra; these arise as calcifications 
in the chordal sheath. In the main region of the tail the dorsal and ventral arcualia are 
connected by cartilaginous bridges, giving unity and completeness to the structure of 
each vertebra. In the region of transition from body to tail, monospondylous vertebrae 
gradually give way to diplospondylous vertebrae. Finally, at the extreme tip of the tail 
there is a condition of heterospondyly which is perhaps unique among selachians. 

APPENDICULAR SKELETON 

The appendicular skeleton of Chlamydoselachus includes the cartilaginous frame' 
work of the pectoral and pelvic fins, together with the pectoral and pelvic girdles; and 
the cartilaginous supports of the dorsal and anal fins. The endoskeletal supports of the 
tail fin belong mainly to the axial skeleton, but it is convenient to consider the framework 
of the caudal fin along with the skeletons of the other fins. 

PECTORAL FINS AND GIRDLE 

The skeleton of the pectoral fin of Chlamydoselachus has been described and figured 
by Carman (1885.2); Braus (1902); Deinega (1909 and 1923); and Goodey (1910.1). The 
pectoral girdle or coraco-scapular (Text-figures 37 and 38) bears a decided resemblance 
to that of Heptanchus (Daniel, 1934, Fig. 54) ; but in the fin proper the radials of Chlamy^ 
doselachus are relatively shorter, and are segmented to form typically three rows of 
cartilaginous elements while Heptanchus has about twice that number. 

Braus's figure of the pectoral fin skeleton of Chlamydoselachus portrays a ventral 
view. It differs from Carman's figure (aspect not stated) in a number of details, as may 



The Anatomy of Chlamydoselachus 



371 



Text-figure 37- 

Pectoral girdle and endoskeleton of pectoral fin of 

Chldmydoselachus, aspect not stated. 

cr, coraco-scapular; msp, mesopterygium; mtp, metapterygium; 

prp, propterygium. 

After Garman, 1885.2, Fig. 2, pi. XI. 




be seen upon comparing Text'figures 37 and 38. 
There are differences in the number, si7;es and shapes 
of the basal cartilages, particularly the mesopterygium. 
In Carman's figure this is triangular in outline, in 
Braus's figure it is more nearly quadrangular. The 
anterior radials are fused over a considerable area in 
Braus's figure, but exhibit a more limited amount 
of fusion in Carman's figure. In Braus's specimen, 
many of the radials posterior to the region of fusion 
have four or five segments; in Carman's specimen, 
there are nowhere more than three segments of a 
single radial. Deinega's Fig. 14, Taf. IV, portraying 
a pectoral fin (aspect not stated) of Chlamydoselachus 
closely resembles Carman's figure (my Text-figure 37) 
save that right and left are reversed. Deinega's Fig. 
15, Taf. IV, representing an inner (ventral) view of 
a pectoral fin of Chlamydoselachus, more nearly re- 
sembles Braus's figure (my Text-figure 38) which is 
also a ventral view. The chief differences in the fig- 
ures thus far considered are understandable on the 
assumption that Carman portrayed a dorsal view, 
and that Deinega's Fig. 14 is also a dorsal view. In 
Deinega's figures of the pectoral fin, some of the lines 
at the distal margin are so indistinct that one cannot 
determine the exact number of cartilaginous elements; 
but in his text he states that there are three rows of 
radial segments. Coodey's drawing (1910.1, Fig. 18, 
pi. XLV) of the left pectoral fin (aspect not stated) of 




Text-figure 38. 

Ventral (inner) view of a pectoral fin 

skeleton of Chlamydoselachus. 

Co, coracoid; F, foramen for blood vessel; G, 
shoulder joint; ms 1, primary mesopterygium; 
ms 2, secondary mesopterygium; mt, metapter- 
ygium; P, propterygium; S, scapula; Ss, supra- 
scapula; 1-4, cartilages in line with basals. 
After Braus, 1902, Fig. 1. 



372 



Bashford Dean hiemorial Voluyne 



Chlamydoselachus shows a large secondary mesopterygium, as in Braus's figure, and the 
primary mesopterygium also resembles that figured by Braus. The posterior radials are 
segmented to form no more than three rows of segments. At the extreme posterior ends 
of the fins shown in the various figures there are individual differences. 

In connection with his study of the development of paired fins, Sewertzoff (1926, 
p. 547) states: 

It is now generally accepted that the skeleton of the fins of the lowest cartilaginous 
fishes (Chondropterygii) has developed from metamerically disposed rays, and that the basal 
cartilage of the free parts of the fin, i.e., the pro-, meso-, and the metapterygium, as well as 
the girdles, were formed by the concrescence or fusion of the proximal segments of these rays. 
But this view may not be considered settled, and, looking over the Kterature of this question, 
we see that many writers, who accept the theory of the [metameric] origin of the paired 
fins, pass over in silence the question of the primitive structure of their skeletons or express 
themselves on that subject with considerable caution. 

In the pectoral fin skeletons of both Cladodus neilsoni Traquair (Text 'figure 39) 
and Symmorium reniforme Cope (Text-figure 40) there is only one basal that can be 




Text 'figure 39. Text-figure 40. 

Pectoral girdles and fin skeletons of two fossil sharks, Cladodus and Symmorium. 

Text-figure 39. Endoskeleton of the pectoral fin of Cladodus niehoni Traquair. 

B, basal piece; BL, fracture line; Mt, metapterygium; R, radial; S, furrow in outer proximal margin of 

the metapterygium. 
From Braus, 1902, Fig. 2; after Traquair, 1897, Fig. 1, pi. IV. 

Text-figure 40. Fragment of a pectoral fin skeleton of Symmorium reniforrne Cope. 

B, basal piece; Mt., metapter>'gium; R, some small radials at the distal end. 

From Braus, 1902, Fig. 3; after Cope, 1895. Fig. 1, pi. VIII. 



The Anatomy of Chlamydoselachus 



373 






Text-figure 41. 

Pectoral fins of the fossil sharks (A) Cladoselache, (B) Ctenacanthus, and (C) Cladodus neilsoni, 

indicating the mode of origin of the metapterygial axis. 

B, basalia; M, muscle of hindmost region of the fin; R, radials; SC, shoulder girdle. 
After Dean, 1909, Fig. 28. 

homologi7;ed with a basal in recent fishes, and it is considered to be a metapterygium. 
In front of this element there is, apparently, a series of radials in direct articulation with 
the pectoral girdle. In Symmorium the metapterygium itself shows a segmentation, 
probably metameric, along its distal margin. If the above interpretations are correct, 
they afford evidence that basals are developed by the concrescence of proximal segments 
of radials. For comparison I have inserted Dean's (1909) figures (my Text-figure 41) of 
the pectoral fins of Cladoselache, Ctenacanthus and Cladodus neilsoni. The origin of the 
girdles (discussed on p. 376) is obscure, but there seem to be sufficient data to warrant an 
acceptance of the theory of the metameric origin of the basals of the paired fins. 

PELVIC FINS AND PELVIS 

Since the pelvic fins of the male Chlamydoselachus are highly modified to form copu' 
latory organs (myxopterygia), it is necessary to describe the pelvic fins of the two sexes 
separately. 

Pelvic Fins and Pelvis of the Female. — The pelvis and the pelvic fin skeleton of 
the female Chlamydoselachus have been described and figured by Garman (1885.2), 
Deinega (1909 and 1923), and Goodey (1910.1). The figures by Garman and by Goodey 
are reproduced as my Text-figures 42, 43, and 89 (p. 434). 

The pelvis of Chlamydoselachus, as compared with that of Heptajichus, is very long 
(i.e., in the direction of the principal axis of the body). Commenting on this fact, Garman 



Text-figure 42. 

Dorsal view of the pelvis (one-half natural size) 

of an adult female Chlamydoselachus. 

hp, basipterygium; il, iliac ridge; pu, pubis. 
Redrawn after Garman, 1885.2, Fig. 1, pi. XI. 




374 



Bashford Dean lAemorial Volume 




Text-figure 43. 
Dorsal view of the right half of the peKas, and of the right pelvic fin, of a female 

Chlamydoselachus. 
htd., distal s^ment of the basipterygium; htp, proximal segment of the basipterygium; In/, longitud- 
inal row of foramina for nerves; pg, pelvic girdle; r, lateral radial s. 
Redrawn from Goodey, 1910.1, Fig. 19, pi. XLV. 

(1885.2) -^Tites: "'The peculiar shape of the pehas suggests an embryonic character of 
other sharks. In embr^'os the peMs is longer than in the adult, in comparison w^ith the 
transverse measurement. An embr^^o of Heptahranchias before me has it half as long 
as \^-ide. proportions which are intermediate between those of the adult and an adult 
Chlamydoselachus." From another point of view one may say that an elongate pelvis 
is in keeping Vv-ith the general body form of Chlamydoselachus. 

Carman's figure reproduced as my Text-figure 
89 (p. 434) is a ventral view, and shows a wedge- 
shaped piece inserted, at the anterior margin, between 
the two paired portions of the pelvis. Thus the median 
suture becomes Y-shaped. This wedge-shaped carti- 
laginous element is not shown in Carman's figure re- 
produced as my Text-figure 42, which is a dorsal view 
of the pehris, presumably of the same female ; nor is it 
shovvTi in any other published drawing of the pehns of 
Chlamydoselachus, male or female, dorsal or ventral. 
Apparently, it is an individual variation. Deinega's 
drawing (1909, 1923) shows a median groove or suture 
extending the entire length of the pehris. 

Along the lateral margins of Deinega's drawing 
of the pelvis, at regular intervals, there are faint trans- 
verse grooves pierced by foramina, marking off seg- 
ments in line x^nth the radials. These transverse 
grooves indicate a metameric origin of this portion of 
the pehds, presumably through the fusion of primitive 
radials to form basals which were later added to the 
pehds. The manner in which basals of the pehnc fins 
may be derived from radials is illustrated by Dean's 




Text-figure 44. 

Pelvic fin and girdle of the fossil shark, 

Cladosehche \epleri. 

b, basals; p, pelvic arch. 
After Dean, 1909, Fig. 18. 



The Anatomy of Chlaynydoselachus 



375 



figure of the fossil Cladoselache (my Text' 
figure 44). 

In the female Chlamydoselachus, the 
skeleton of the pelvic fin proper (Text- 
figures 43 and 89, the latter on p. 434) is 
much like that of Heptanchus as figured by 
Gegenbaur (1870, Fig. 3, Taf. XV); and as 
shown in my Text-figure 45a, after Daniel. 
In Chlamydoselachus the basipterygium is 
shorter and more of the radials are attached 
directly to the pelvis. There is very little 
fusion of radials in the pelvic fins of either 



liin 



ml 



II !■■ 




Text-figure 46. 

Pelvic fin skeleton of a male Chlamydoselachus: 

A, viewed obliquely from above; B, viewed from 

the inner (ventral) side. 

Be, medial radial belonging to the myxopterygium; Bm, abdom- 
inal musculature; mt, metapterygium; Mx, principal radial 
of the myxopterygium; P, pelvis; R, radials; T, pocket of the 
myxopterygium; TO, opening of the pocket. 
After Braus, 1902, Abb. 7 and 8. 




Text-figure 45. 

Skeleton of the pelvic fin and girdle of Heptanchus 

maculatus: A, female; B, male. 

Be, beta cartilage; b.l — 2, first and second connecting segments 
ha., basal or axial cartilage; ba.p., basipterygium; pi., pelvis; 
ra., radials. 
After Daniel, 1934, Fig. 55. 

Chlamydoselachus or Heptanchus, and this 
fusion is confined to the anterior end of the 
fin skeleton where some plates of cartilage 
may be regarded as rudimentary basals. In 
Deinega's drawing (1909 and 1923) of the 
pelvic fin of Chlamydoselachus, it is difBcult 
to determine the number of segments in the 
radials — the row of small distal segments is 
either not well shown or is absent. 

Pelvic Fins and Pelvis of the Male. — 
In the male Chlamydoselachus, the skeleton 
of the pelvic fins, together with the pelvis, 
has been fully described and figured by Braus 
(1902) and by Goodey (1910.1). Their figures 
are reproduced as my Text-figure 46 and my 
Figure 21, plate V. By comparison with 
Text-figures 42, 43, and 89 (p. 434) it will 



376 Bashford Dean Memorial Volume 

be seen that the pelvis is alike in the two sexes. In its basal, anterior and middle portions, 
the skeleton of the pelvic fin of the male is much like that of the female. In the specimen 
figured by Goodey there is a slight amount of fusion of radials at the extreme anterior 
end. This fusion of radials does not appear m Braus's figure. 

Osburn (1907) described and figured the pelvis and the pelvic fin skeleton of a 225' 
mm. embryo of Chlamydoselachus. The sex is not stated, but the condition of the most 
posterior radials is intermediate between that characteristic of the adult female and that 
shown in the male figured by Braus. Osburn noted that each pelvic girdle (lateral half 
of the pelvis) is pierced by eight foramina for nerves, and serves as a basal for about half 
of the radials of the fin. In the mesenchyme stage, the two girdles fuse at the mid-line, 
and in the stage figured "the separation at the anterior end is not yet complete.'' This 
"separation" presumably refers to the presence of a suture between the two cartilaginous 
elements in the adult stage. In the fossil Chladoselache (according to Dean, 1909) there 
are two quite separate pelvic girdles forming a pair, and in the fin skeleton the basals 
consist of small rod-like elements Hke the radials (Text-figure 44). 

After reviewing the Hterature on the embryological development of the paired fins 
of selachians, Regan (1906.2, p. 731) states: "The mode of development of the fin- 
girdles is in favor of the hypothesis that they are outgrowths of the basipterygia, and the 
latter may well have been formed from the coalescence of the originally separate basal 
segments of the supporting cartilages, since in the median fins also these are segmented 
off from continuous laminae." Osburn (1907, p. 188) also inclines to the view that the 
origin of the girdles may be traced to the supporting elements of the fin. He compares 
the pelvic girdle of Chlamydoselachus to the basals of unpaired fins. 

The Myxopterygia. — Posteriorly and medially, the skeleton of the pelvic fin in 
the male is decidedly different from that of the female since it is enlarged and modified 
to form the framework of the copulatory organ, the myxopterygium. The skeleton of the 
myxopterygium or "clasper" has been described and figured separately by Giinther 
(1887) and by Leigh-Sharpe (1926), whose figures are reproduced as my Text-figures 
47 and 115a (the latter on p. 472). It has also been described and figured as a part of the 
pelvic fin by Braus (1902) and by Goodey (1910.1) whose figures are reproduced as my 
Text-figure 46 and Figure 21, plate V. The endoskeletal elements involved in the for- 
mation of this organ are in Hne with the basals but are in serial relation with the radials. 
They appear to be radials that are enlarged, elongated and otherwise diiferentiated. 
In the several figures, there are minor differences in the radials associated with the one 
that is most highly developed, and m Braus's specimen the skeleton of the myxopterygium 
is not differentiated to the same degree as in the others. Possibly, Braus worked on 
a specimen that was not fully mature. Leigh-Sharpe's description (1926, p. 312) of the 
skeleton of the claspers, illustrated by his Fig. 5a (reproduced as my Text-figure 115a, 
p. 472), is as follows: 



The Anatomy of Chlamydoselachus 

The skeleton consists of a main stout bar of supporting cartilages, the myxapterygium 
[sic], with three additional minor cartilages, of which a pair on either side stiffens the apical 
expansile valves, the remaining one acting as a foundation for the supposed rhipidion. Two 
of the radial cartilages attached to the basipterygium, part of which is seen in the upper portion 
of the figure, come down to support the walls of the clasper cavity. 



377 




Text-figure 47- 

Skeleton of a clasper (myxopterygium) of Chlamydoselachus anguineus. 

a, principal cartilage; al, intermediate cartilage; b, basals of pelvic fin; !, lobe-like expansion of cartilage a; r, rl 

and r2, rays of pelvic fin; t, tl, movable calcified terminal pieces by which the canal can be opened or closed. 

After Giinther, 1887, Figs. D and Dl, pi. LXIV. 



Giinther (1887) states that, as compared with other elasmobranchs, the skeleton 
of the clasper of Chlamydoselachus (Text'figure 47) is extremely simple and is very similar 
to that of Acanthias as figured by Gegenbaur (1870, Fig. 15, Taf. XVI). Goodey (1910.1, 
p. 567) writes: 

When the mixipterygium [sic] of Chlamydoselachus is compared with that of Hexanchus 
griseus, described and figured by Huber, one is at once struck by the high degree of develop- 
ment presented by the organ in Chlamydoselachus. Whereas in Hexanchus the axial cartilage 
is represented by a comparatively short cartilage, scarcely distinguishable from a lateral 
radial, and bearing no accessory cartilages; the homologous part in Chlamydoselachus is 
a long, stout cartilage, furnished distally with three movable accessory cartilages. 

As described by Daniel (1934) and as shown in my Text-figure 45b, the skeleton of 
the myxopterygium of Heptanchus is somewhat simpler than that of Chlamydoselachus. 
The skeleton of the pelvic fin of a male Raja (sp.?) figured by Gegenbaur (1870, Fig. 21, 
Taf. XVI) is simpler than any that I have mentioned. Evidently, differences in the form 
of the skeleton of the claspers are of little phylogenetic significance. 

THE DORSAL FIN 

In the single dorsal fin of Chlamydoselachus, the cartilaginous elements (radials) 
forming the endoskeleton are very irregular, as shown in my Text-figure 48. The tapering 
anterior portion extends a considerable distance in front of the small membranous portion 
of the fin. Garman (1885.2, p. 15) interprets this condition as follows: 



378 - 



Bdshford Dean Memorial Volume 




Text 'figure 48. 
Endoskeleton of dorsal and anal fins of Chlamydoselachus anguineus. 

a, radial of dorsal fin; b, radial of anal fin; c, anterior radial of caudal fin. 
After Garman, 1885.2, pi. XIII. 

The great extent of the band compared with the size of the fin, and the manner in which 
it dwindles toward the front, taken in connection with the fact of the continuation of the 
peculiar scales of the fin-border some two inches in front of the cartilages, show that in 
ancestral forms of this animal the dorsal fin was much longer, and corresponded more nearly 
in proportions with the anal. 

The only additional figure of the adult dorsal fin skeleton that I have found is 
Deinega's (1909 and 1923), which is reproduced as my Text-figure 49. This figure is 
instructive in that it shows clearly a much greater number of cartilaginous elements 
than is shown in Carman's drawing (my Text-figure 48). Deinega distinguishes a series 
of thirty'two basal elements which he calls radials, whereas in Carman's figure there are 
scarcely half as many of these elements, which he also calls radials. 




Text'figure 49. 
Endoskeleton of the dorsal fin of Chhmydoselachus anguineus. 

m., fin membrane; 1-32, first row of radials (no. 1 not shown). 
After Deinega, 1909, Fig. 12, pi. Ill, 



The Anatomy of Chlamydoselachus 



379 



Osburn has published a drawing (1907, Fig. 19, pi. V) of the dorsal fin skeleton of 
a 225'mm. embryo of Chlamydoselachus. The total number of cartilaginous elements 
(thirty-'six) is smaller than in Carman's specimen (fortyfive), and much smaller than in 
Deinega's specimen (sixty'one). The larger number in the adult may possibly be due to 
fragmentation. Osburn notes the wide separation of the dorsal fin skeleton from the 
axial skeleton. 

In the absence of any further examples it appears that the entire endoskeleton of the 
dorsal fin of Chlamydoselachus is composed of radials. Some segments of these radials 
have undergone slight displacement, but there is Httle or no fusion. In Heptanchus 
cinereus (Text'figure 50) the radials (ra.) of the dorsal fin are much more regular and there 




Text-figure 50. Text-figure 51. 

Endoskeletons of the dorsal fins of Heptanchus and Mustdus. 

Text-figure 50. Cartilages of the dorsal fin of Heptanchus cinereus. 

be, basal; ra., radial cartilage. 
From Daniel, 1934, Fig. 56; after Mivart, 1879, Fig. 2, pi. LXXV. 

Text-figure 51. Cartilaginous elements of dorsal fin of Mustelus antarcticus. 

b.c, basal segments; h.c.l, median segments; b.c.2, distal segments. 
From Daniel, 1934, Fig. 89a, after Mivart. 



is a large but thin basal cartilage (be). In Mustelus (Text-figure 51) there is a distinct 
row of basal cartilages (b.c.) that appear to have been segmented off from the radials, 
but there is no fusion. 

There is no need of recourse to fossil forms to find evidence of the manner of origin 
of basal plates in the dorsal fin skeleton. Beginning with the condition exemplified by 
Mustelus, which I regard as primitive, there may be found in living forms all intermediate 
conditions leading to one in which fusion of basal segments of the radials has formed 
large basal plates. The literature pertaining to the fin skeletons of sharks abounds in 
figures which, upon comparison, illustrate the point, but it is sufficient to cite Mivart's 
(1879) well-known drawings. In Chlamydoselachus the endoskeleton of the dorsal fin, 
though primitive, seems to have suffered regression as evidenced by the irregular form 
and arrangement of many of the cartilaginous elements. 



380 



Bashford Dean Memorial Volume 



THE ANAL FIN 



In the endoskeleton of the anal fin of Chlamydoselachus (Text'figures 48 and 52 
after Garman and Deinega respectively) there is some fusion of proximal elements, and 
even a slight amount of fusion of distal elements. The elements of the basal series are 
usually oriented in a different direction from the distal elements. In the adult, this 
fin skeleton is very long and slender (in an anteroposterior direction). The same is true 
of the anal fin skeleton of a 225'mm. embryo figured by Osburn, 1907 (Fig. 6, pi. IV). 
In this embryonic specimen the fusion of basal elements is not so pronounced. The separa- 
tion of the fin skeleton from the vertebral column is very marked. In Heptanchus cinereus 
(Daniel, 1934, Fig. 57 after Mivart) there is a fairly large basal element in series with 
some smaller basal elements, all apparently formed by the fusion of radials. 




Text 'figure 52. 
Endoskeleton of the anal fin of Chlamydoselachus anguineus (showing basals 1-20). 

After Deinega, 1909, Fig. 13, pi. IV. 



THE CAUDAL FIN 



The general appearance of the cartilaginous supports for the dorsal and ventral 
lobes of the greater part of the tail fin is shown in Deinega's (1909 and 1923) Fig. 9, pi. Ill, 
which is too large for satisfactory reproduction here; also in Carman's (1885.2) PI. 14, 
which was drawn from a specimen in which the tip of the tail had been mutilated during 
life. Details are better shown in Goodey's (1910.1) drawings reproduced herein as 
Text-figures 31 and 36. 

The cartilaginous supports for the ventral lobe of the caudal fin of Chlamydosela' 
chus are suppHed almost entirely by the haemal spines, which belong to the axial skeleton. 
The occurrence of small radials distinct from the haemal spines is confined to the anterior 
portion (Text-figures 31 and 48) of the ventral lobe, and these radials are possibly seg- 
mented off from the haemal spines. 

The cartilaginous supports for the dorsal lobe of the caudal fin of Chlamydoselachus 
consist partly of neural spines, which belong to the axial skeleton; but there is an entire 
series of dorsal radial elements (Text-figures 31 and 36) distal to the neural spines. 
'Tor a short distance in front . . . the series is separated by a space from the neural 



The Anatomy of Chlamydoselachus 381 

intercalaria, as if the radials had originated, like those of the dorsal and anal [fins] in- 
dependently, and afterwards through downward growth had in the greater portion of the 
extent come in contact with the neural processes. These radials and interneurals are 
not fused like the radials and haemapophyses" (Garman, 1885.2, p. 16). With this 
interpretation Goodey (1910.1, p. 553) seems to agree, for he says: "The dorsal radial 
supports of the caudal fin I do not consider as dorso-spinalia, because at their commence- 
ment anteriorly they are not always continous with the neural arches, and, moreover, 
there is as much evidence to show that in general they originate independently of the 
vertebral column as there is in favor of their being portions segmented off from the dorsalia 
below them." 

In the section on external characters, attention has been called to the shortness of 
the cartilaginous fin rays of Chlamydoselachus, as compared with their condition in one 
of the most primitive of fossil sharks, Cladoselache. We are now in a position to ask, 
is there any evidence, in the patterns of the fin skeletons, to support the view that the 
somewhat rudimentary character of the appendicular skeleton in Chlamydoselachus is 
secondary, not primary? Along with the fusion of radials to form basals, radials are 
found breaking up into segments which do not always retain their original alignment. 
The shapes of these segments are sometimes irregular. As indicated by Woodward 
(1921), this fragmentation and displacement of typical parts seems to indicate retro- 
gression. The shortness of the radials is presumably due to arrested development. 



THE MUSCULAR SYSTEM 

Only the skeletal or voluntary striated muscles are considered here. Little is known 
concerning smooth muscle and cardiac muscle_ in Chlamydoselachus, and in any case 
these are best considered in connection with the organs of which they form a part. It is 
convenient to classify the skeletal muscles upon an embryological basis. In Chlamy- 
doselachus, as in other vertebrates, most of these muscles may be assigned to two great 
groups, the metameric muscles and the branchiomeric muscles. The great muscles of the 
body wall are metameric muscles. The branchiomeric muscles are of visceral-arch origin, 
but they do not include all the muscles attached to the visceral skeleton. 

THE METAMERIC MUSCLES 

The metameric muscles of fishes are divisible into two groups : the axial muscles, in 
which the metamerism is clearly expressed even in the adult; and the appendicular muscles 
or fin muscles. In the latter, the metameric condition is seldom recognizable in the adult; 
nevertheless, in primitive fishes the appendicular muscles arise from the metamerically 
arranged myotomes of the early embryo. 



382 



Bashford Dean lAemorial Volume 




THE AXIAL MUSCLES 

In fishes the axial muscles comprise (a) the great masses of muscle contributing to the 
formation of the body wall and tail; (b) a group of muscles in the hypobranchial region; 
and (c) the muscles that move the eyeballs. 

Muscles of the Trunk and Tail. — Metamerism is such a striking feature of the 
trunk muscles of fishes that it overshadows the longitudinal division into muscle bundles 
or layers and the incipient diiferentiation into indi'V'idual muscles — a development that, 
in the higher vertebrates, quite reverses the picture. 

In surface views of the six large embryos 
of Chlamydoselachus in the American Museum, 
ranging from 190 mm. to 374 mm. in length, the 
myomeres are more or less sharply defined. 
Along the lateral surfaces of the trunk and tail 
they are clearly outHned, and in some specimens 
they may be traced ventrally as far as the tropeic 
folds. Dorsally, they are usually obscure and in 
this situation better views were obtained by 
removing patches of skin from one of these em' 
bryonic specimens. In the adult specimens, only 
slight indications of the body musculature could 
be seen until after the skin had been reflected; 
then the myosepta stood out boldly. It is ap' 
parent, even from a cursory study of our mate- 
rial, that the myomeres of the trunk region of 
Chlaynydoselachus conform to the primitive 
elasmobranch type and bear a close resemblance 
to those of Heptarichus as described and figured 
by Maurer (1912) and Daniel (1934). From 
Daniel (1934, p. 89) I quote the following para- 
graph which is illustrated by my Text-figure 53 : 

In a side view, the muscles of the body oi Heptanchus maculatus axe divided at the lateral 
line (n.) into dorsal bundles (d.h.) which attach to the cranium, and ventrolateral bundles 
which attach to the pectoral girdle. Both the dorsal and the ventrolateral muscles extend 
to the tip of the tail. In these bundles the myosepta (ms.) are bent into rigsag shape. Above 
the lateral Hne one of the columns has the apices of its myosepta directed forward, the other 
backward. Below the Hne there appears to be a single column with apex pointed posteriorly. 
Some of the anterior fibers of the ventral bundle are specialized as the pectoral muscles of 
the pectoral fin. 

Howell (1933, p. 249) attaches considerable significance, from a developmental 
point of view, to the longitudinal division of the trunk musculature of fishes into dorsal 
and ventrolateral bundles. His account of the developmental processes leading to this 
condition follows: 




-'Y 



Text-figure 53. 

Lateral view of the body musculature in the 

pectoral region of Heptanchus maculatus. 

cl., gill-clcft; d.b., dorsal bundle; d.f., dermal fin rays; 

d.r.m., dorsal radial muscles of pectoral fin; I.b., lateral 

bundle; 11., lateral Une; ms., myoseptum; tr., trapezius 

muscle; v.h., ventral median muscle. 

After Daniel, 1934, Fig. 90. 



The Anatomy of Chlamydoselachus 383 

A frequent misconception regarding the development of the musculature is to the 
effect that the muscles ventral to the lateral Hne are formed by actual growth in that direction 
of the original, dorsally situated myotomes. Conditions vary in different parts of the body, 
but in the anterior trunk at least there appears to be a lateroventral muscle mass entirely 
distinct from the dorsal myotome. Between the two there is a connective tissue septum, 
and tending further to separate them at early stages of phylogeny are the pronephros and its 
duct, and the lateral line structures. The lateroventral musculature differentiates by con- 
densations of mesoderm progressively in a ventral direction, forming a lateral somatopleure, 
giving rise to the somatic musculature, and a medial splanchnopleure, from which is derived the 
smooth musculature of the intestinal tract. Whether or not all the striated branchial muscles 
are also derived from this element is not entirely certain. Between the two plates is a coelomic 
cavity. In other parts of the body, or in vertebrates that have long since discarded all vestige 
of a lateral line system, the distinctiveness in origin of the dorsal from the lateroventral 
musculature tends to become obscured in the embryonic picture. 



Text-figure 54. 

Model of myomere of a selachian 

(Squalus), showing divisions into 

longitudinal muscle bundles. 

DORS.MUSC.DIV., dorsal bundle; LAT. 
LIHE, lateral line; LAT.M.DIV., lateral 
bundle; VEHT.M.DIV., ventral bundle. 
After Howell, 1933, Fig. 3, modified from 
Langelaan and Daniel. 




VENT. M. DIV.— > 



A model of a single myomere of the trunk region of a selachian is illustrated by 
Text -figure 54. Regarding the basic segmental features of vertebrate trunk musculature, 
Howell (1933, pp. 255-256) writes: 

The original plan of vertebrate trunk musculature, well illustrated by cyclostomes, 
involves a series of segmental muscles each of which is separated from the muscles of adjoining 
segments by myocommata or myosepta. The axially directed muscle fibers of each segment 
are basically divided into a dorsal division, above the lateral line on either side of the mid-line, 
and a continuous lateroventral division below; this constitutes the primary muscular plan. 
It is a primitive scheme, suited to a low vertebrate that can bend with equal facility in any 
direction — the essentially vermiform type of control. 

In this plan the myosepta are virtually transverse and usually gently curved. Unlike 
the situation in mammals, most of whose muscles have one end solidly anchored on bone, in 
the primitive state the fibers at both ends are attached to yielding connective tissue. Accord- 
ingly there was originally a tendency for some of the groups of fibers to pull certain parts of 
the myosepta in a forward and others in a backward direction, as a result of specialized action 
of the groups concerned. This would have a contortional effect upon the myosepta, and in 
consequence some parts would have an anterior and others a posterior inclination, as suggested 
in the given diagram of a myomere of a shark (Fig. 3) [Text-figure 54 herein]. Presumably 
the swifter the fish (i.e., the stronger the muscle action) the more tortuous the pattern of 
the myosepta. 



384 



Bashford Dean MemoriaJ Volume 




Text-figure 55. 

Lateral view of the trunk musculature of ChlamydoseJachus in four different regions : A, anterior part of the 

trunk: B, middle part: C, posterior part; and D, anterior portion of the tail. 

a, b, c, d, the four longitudinal divisions of the ventral bundle (ventrolateral of other authors); al (alpha), he (beta), and ga (gamma), 
the three longitudinal regions into which the division h may be divided; I, lateral line; o. inf., muscuius obliquus inferior; o.s., musculus 
obliquus superior; R-p., rectvis profundus muscle — in A it is shown artificially spread out, as well as in its original pc^tion, inrolled. 
A line drawn from x to y, along each region, would separate, approximately, the inferior oblique from the superira: oblique musdes. 

After Maurer, 1912, Fig. 1, Taf. 1. 

Maurer (1912) has given us detailed infonnation concerning the trunk musculature 
of both Chlamydoselachus and Heptanchus. In Chlamydoselachus (Text-figure 55 1 the 
ventrolateral bundle has the same fundamental division into two columns (di\'ided 
otherwise by Maurer) as is found in the dorsal bundle. This is best exemplified in the 
region of the base of the tail (Text-figure 55d; where the ventrolateral bundle is the 



,-!*?-- 



Sr— 




'"'-,-«- J^^ ^S^ - ~ 



r-rl//.'.'^ ff/'. 



'^BU:^'^^ 



Text-figure 56. 

Lateral view of the trunk musculature of Yizptamims d-nereus. 

a., dorsal region of ventral bxmdle (ventrolateral of other authors); d., dorsal bundle; I., lateral line; o.inf., inferira: 

oblique; o.m. x o.s., portions of middle oblique and superior oblique overlapped by inferior oblique: o.s.. superior 

oblique; S, shoulder girdle. 
After Maurer, 1912, Fig. 4, Taf. 2. 



The Anatomy of Chlamydoselachus 



385 



mirrored image of the dorsal bundle; but it is expressed, with some modifications, in the 
trunk region also. These modifications have to do with (a) the incipient separation of 
a superior oblique muscle from an inferior oblique, and (b) the inroUmg of the ventral 
column of the ventrolateral bundle to form the muscles of the tropeic folds — structures 
peculiar to Chlamydoselachus. In Heptanchus (Text'figure 56) conditions are not so 
simple, for there is a small middle oblique muscle and there is considerable overlapping 
of the middle and superior oblique muscles by the inferior oblique. The figure for Chlamy- 
doselachus is drawn from a rather small specimen, 1330 mm. long. The figure for Heptan- 
chus is from a specimen 900 mm. long. 

Since the abdominal or tropeic folds are structures peculiar to Chlamydoselachus, 
their musculature is entitled to further consideration. The superficial appearance of the 
tropeic folds has been described, in three adult specimens and six large embryos, by 



Text-figure 57- 
Transverse section showing the tropeic 
folds (x 1) of an adult Chlamydo- 
selachus. This section was taken eight 
inches in front of the pelvis. 
After Garman, 1885.2, Fig. B, pi. XX. 




Gudger and Smith (1933). The internal structure of the abdominal folds in a single 
adult specimen has been figured by Garman (1885.2) in his Figs. A and B, pi. XX— the 
latter figure being reproduced as my Text'figure 57- Concerning these figures Garman 

(p. 21) says: 

One of the folds is seen to hang below each of the large abdominal vessels. The vessels 
are parallel or nearly so. Between them are two muscular bands, one to each fold. Each 
band is nearly an inch in width, very thin at its lower edge, and near one-fifth of an inch thick 
toward the rounded upper edge, between the veins. The fiber in these tropeic ... or keel 
muscles differs from that in the walls of the flank in being coarser in the bundles and plates, 
and more loosely put together. Apparently the keel muscle corresponds to the rectus 
abdominis of lower vertebrates. 

Carman's figures readily suggest that the keel muscle is derived during development 
by an infolding of the musculature of the ventral body wall. In order to test this hypoth- 
esis I have prepared transverse serial sections from a segment of the ventral abdominal 
wall excised from a 210-mm. male embryo. In this specimen the distance from pectoral 
fin to pelvic girdle is 55 mm. The segment comprised the region extending from 10 mm. 
to 20 mm. in front of the pelvic fins. A drawing (Text-figure 58) was made from a section 
taken approximately 15 mm. from the pelvic fins — corresponding very nearly to the region 
(200 mm. in front of the pelvic girdle) figured by Carman for his large adult specimen. 
In my sections I have found some further indications of the manner of origin of the muscle 



386 



Bashford Dean Memorial Volume 




Text-figure 58. 

Section through the tropeic folds (x 25) of a 210 mm. embryo of Chlamydoselachus, showing 

the keel muscle {\.m.). The section was taken about 15 mm. in front of the pelvis. 

Drawn from a specimen collected in Japan by Dr. Bashford Dean, and now in the American Museum. 

under consideration. It is clearly derived as a simple inpocketing of the ventral muscula' 
ture of the body wall, in the region where the ventral bundles of the two sides of the 
body meet. Furthermore, it is segmented after the fashion of the metameric muscles of 
the body wall — a feature that is entirely lacking in Carman's drawings and is not men' 
tioned in his text. Earlier stages would be required to show continuity of the muscula' 
ture in this region. 

Evidence regarding the manner of origin of the keel muscle was obtained by Braus 
(1898, Fig. 2, pi. XIII) in connection with his studies of the innervation. In this case 
the depth of the "keel" is remarkable. Braus appUes the term rectus to the thin muscle 
of the body wall in the region of the ventral mid'line — a muscle which is interrupted by 




MohL iM 




U.oU.uit. 



' Pentpn. ■ u 

K.mUrciM. "■ H.OOL.inl. 

Text-figure 59. 
Diagrams of sections (all inverted) showing the probable manner of origin of the keel muscle: 
A, absent in Squalus; B, hypothetical intermediate stage; C, as in adult Chlamydoselachus. 

ff. skin; M.obi.int., musculus obliquus internus; >(.i., intercostal nerve; Per., peritoneum;V.p., vena parietalis. 

After Braus, 1898, Text-fig. 3. 



The Anatomy of Chlamydoselachus 



387 



the tropeic groove. The deep muscle that Garman calls the rectus abdominis or keel 
muscle is called by Braus simply the keel muscle. Braus (1898, p. 337) states that the 
nerves that innervate the keel muscle lie on its lateral surface, and not on the medial 
surface as in the case of the musculus rectus abdominis and the obHque muscles of the 
body wall. He concludes, therefore, that an invagination, leading to inversion, of the 
ventral body wall has occurred at the mid-line; for it is well known that nerves ending in 
developing muscles tend to follow these muscles in their migrations. Braus has embodied 
these conclusions regarding the phylogenetic origin of this muscle in a diagram which 
I have reproduced as Text-figure 59. 



O.inf. 






Text-figure 60. Text-figure 61. 

Transverse sections of the ventral body wall of Chlamydoselachus showing the inrolling of the 

musculature in the region of the tropeic folds. 
Text-figure 60. Transverse section of the ventral abdominal wall immediately behind the 

pectoral girdle. 

la., linea alba; P., peritoneum; o.inf., musculus obliquus inferior; R.p., rectus profundus muscle, which is recogniable 

as an inroUed portion of the ordinary musculature of the body wall. 

After Maurer, 1912, Text-fig. 1. 

Text-figure 61. Diagrams showing the condition of the ventral musculature on one side of the 

body in four different regions: A, just behind the pectoral and likewise immediately in front 

of the pelvic girdle; B, in the second quarter, and C, in the third quarter of the trunk. 

R.fi., musculus rectus profundus; a, first; and h, second fold of the rectus profundus. 
After Maurer, 1912, Text-fig. 3. 

Maurer (1912) has given a somewhat different picture (Text-figures 60 and 61) of 
the manner of origin of the deeply situated ventral longitudinal muscle, which he calls 
the rectus profundus. These figures are based on sections taken from four different 
regions along the ventral body wall of his adult, or nearly adult, specimen. A connection 
between the rectus profundus and the ventrolateral bundle persists in the region im- 
mediately behind the pectoral girdle and immediately in front of the pelvic girdle, but 
is lost throughout the remaining extent of the tropeic folds. A curious feature of all 
Maurer's drawings of the ventral musculature of his specimens is that in none of them 
does he show any ventral protrusion of the body wall to form the keel which has been 
described by Garman (1885.2), Collett (1897), Braus (1898), and by Gudger and Smith 
(1933). But the most remarkable thing about Maurer's drawings of the musculature of 
the tropeic folds is that he represents the infolding process not as a simple invagination 
but as a parting of the musculature of the body wall along the mid-line, after which each 
edge becomes inroUed independently, like a scroll (Text-figures 55, 60 and 61). This 



388 



Bashford Dean Ivlemoria] Volume 



does not accord v^-ith the conditions portrayed by other authors in their drawings of 
transverse sections through the keel muscle. 

As to the function of the deep muscle \^riously called the keel muscle, the rectus 
abdominis, and the rectus profundus, it clearly aids in a rapid ventral flexion of the body; 
but why it should be so uniquely set apart from the remaining musculature of the ventral 
body wall is problematical. 




Text-figure 62. 
Diagram showing the relation between head somites and body somites, and the origin of the 
hypobranchial or hypoglossal musculature from trunk myotomes, in a larval Squalus acan- 
thias. The somites that degenerate in ontogeny are indicated by broken lines. The anlagen 
of the six eye muscles, which arise from the first three somites, are already differentiated. 

Id, dorsal moiety of the first myotome; Iv, ventral moiety of the first myotome; 2d, 2v, dorsal and ventral moieties 

of the second myotome; 3v, ventral moiety of the third myotome; 7, seventh myotome; a., anterior cavities; 

hyp.m., hypoglossal musculature; M., mouth; ot, otic capsule; sp., spiracle; thr., thyroid. 

After Neal, 1918, F^. 19. 



Goodey (1910.1) studied the relations of the myomeres to neuromeres in the tail 
and posterior part of the trunk of Chlamydoselachus. In the trunk, he found the limi ts 
of a myomere corresponding in extent with a monospondylous neuromere. In the main 
caudal region each myomere is equal in extent wath a diplospondylous neuromere. In 
the tip of the tail each irregularly divided or heterospondylous neuromere has its myomere. 
Thus the myomeres of the tail region are not particularly influenced by the secondary 
segmentation of the vertebral column in this region. 

The Hypobranchial Group. — In fishes, as in other vertebrates, the hypobranchial 
region has a group of muscles that appear to be a continuation of the longitudinal muscula- 
ture of the ventral body wall. The muscles of the hypobranchial group are attached 
posteriorly to the shoulder girdle and anteriorly to ventral portions of the visceral skeleton. 
This hypobranchial or hypoglossal musculature does in fact arise (Text-figure 62, hyp.m.) 
as a forward prolongation of some myotomes of the occipital and anterior trunk region 
which are in strict serial relationship with the myotomes that give rise to the segmental 



The Ayiatomy of Chlamydoselachus 



389 



muscles of the body and tail — as in Scyllium (Van Wijhe, 1883, p. 36 and Fig. 25, Taf. 
Ill); in Lacerta (Corning, 1895); in Fctromyzon and Squalus (Neal, 1897); and in Lepido- 
siren and Frotopterus (Agar, 1907). 

In Heptanchus (Davidson, 1918) the following 
muscles (Text-figure 63) are recognized as members 
of the hypobranchial group : the paired coracoarcu- 
ales communes (car.), the unpaired coracomandib- 
ularis (c.md.), the paired coracohyoidei (c.hy.), and 
seven pairs of coracobranchiales (c.br.1-7). In elas' 
mobranchs generally, according to Daniel (1934, p. 
108), all of these muscles excepting the coraco' 
branchiales arise from the first five trunk myotomes. 
Edgev^orth (1903) states that in Scyllium the coraco- 
branchiales develop from head myotomes. In the 
adult Heptanchus, the metameric nature of the cora' 
coarcuales is attested by the presence of a series of 
four transverse or sHghtly oblique myosepta (Text- 
figure 63). In the coracoarcuales of Scymnus, there 
are five such myosepta (Fiirbringer, 1897, Fig. 3, 
Taf. VI). In Heptanchus, Vetter (1874, Fig. 9, pi. 
XV) shows a myoseptum in the coracohyoideus 
muscle also. 

The hypobranchial group of muscles is often 
called the hypoglossal musculature because the mus- 
cles of this group are supplied, somewhat indirectly, 
by a nerve which, variously called the spino-occipi- 
tal, occipital or hypoglossal nerve in fishes and am- 
phibians, in the higher vertebrates is known as the 
hypoglossal (hypoglossus) or twelfth cranial nerve. 
This nerve is a composite structure, made up from 
a series of roots representing, perhaps, several 
neuromeres. 

AlHs (1917 and 1923) does not distinguish the 
hypobranchial muscles of Chlamydoselachus as a 
separate group. However, he describes the distribution of the branches of "a large 
nerve which was not traced upward to its origin, but which is either of spinal, or spinal 
and occipital origin" (AUis, 1923, p. 195). The muscles supplied by this nerve are 
identical with those included in Davidson's list of hypobranchial muscles in Heptan- 
chus, with the addition of a muscle which AlHs calls the "pharyngo-clavicularis." The 
hypobranchial muscles of Chlamydoselachus are shown, in color, by AlHs (1923) in his 
Figs. 35 and 37-40, pis. XIII-XV; but nowhere are these muscles of Chlamydoselachus 




Text-figure 63. 

Hypobranchial muscles of the notidanid, 

Heptanchus maculatus, ventral view. 

bh., basihyoid cartilage; car., musculus coracoar- 
cuales; ch.l, first ceratobranchial cartilage; c.br.1-7, 
first to seventh coracobranchial muscles; ch., 
ceratohyoid cartilage; c.hy., musculus coracohyoi- 
deus; CO., coracoid cartilage; c.md., musculus cora- 
comandibularis; ibu.HS, first to sixth ventral 
interbranchial muscles; md., mandibular cartilage. 
After Davidson, 1918, Fig. 4. 



390 



Bashford Dean hiemorial Volume 



figured as a complete and separate group. The coracoarcuales and coracobranchiales 
muscles of one side of the head are shown in Text-figure 64 after Gregory, and the 
first pair of coracobranchiales (cb.l) are shown in my Figure 8, plate III. Allis (1923, 
pp. 192-195) gives a detailed description of each of the muscles under consideration. 



idhy cjdd'id' ad.arc i''P^- /^i" 



ad-arc ^ 





leir.lab.sup. 



„ , cb^A / care 

pmang.or lab.cart ^^^^^^ ' J^ ^^^s 



Text-figure 64. 
Skull and visceral arches of Chlamydoselachus with the deep muscles of the branchiocranium. These 
muscles fall into two main groups: extensors of the oral and branchial arches, running anteroposte- 

riorly; and flexors, running vertically. 
ad.arc, musculi adductores arcuales 1-6. ad.d., musculi adductores dorsales 1-5; ad.mand., musculus adductor mandibulae; 
care, musculus coracoarcualis; cb., musculi coracobranchiales 1-6; co.sc, coracoscapular arch; hyom., hyomandibular; id., 
musculi interdorsales 1-5; id.hy., interarcualis between hyal and first branchial arch; lab.cart., labial cartilages; lev.lah.sup., 
musculus levator labii supcrioris; lev.mx.sup., musculus levator maxillae superioris; pal.qu., palatoquadrate; pro.ang.or., 
musculus protractor anguli oris; trpz., musculus trapezius. 
After Gregory, 1933, Fig. 4. 



As one would expect from the similarity of their cartilaginous branchial frame- 
works, there is a marked likeness between the hypobranchial musculatures of Chlamy^ 
doselachus and Heptanchus. Only a few points call for special consideration here. 

There are, to be sure, only six pairs of coracobranchiales in Chlamydoselachus, as 
compared with seven in Heptanchus, but this difference is correlated with the number 
of gill arches. Of these muscles in Chlamydoselachus, Allis (1923) says: "The more 
posterior coracobranchiales have no connection whatever with the musculi coraco- 
arcuales, Chlamydoselachus differing markedly in this respect from Heptanchus (Vetter, 
1874) and closely resembling Acanthias (Vetter, I.e.)." In Vetter's figure of Heptanchus 
(his Fig. 9, pi. XV), the coracobranchiales of the region under consideration appear to 
arise directly from the muscuH coracoarcuales, while one gets a somewhat different 
impression from Davidson's figure reproduced as my Text-figure 63. Davidson (1918, 
p. 162) describes the origin of the coracobranchiales muscles of Heptanchus as follows; 



The Anatomy of Chlamydoselachus 



391 



The first [coracobranchialis muscle] has its origin in the connective tissue directly over 
and attached to the coracohyoideus muscles. The origins of the second to the sixth coraco' 
branchiales are in the strong connective tissue just dorsal to the coracoarcuales. The anterior 
part of the origin of the seventh is continuous with the origin of the sixth while the posterior 
part has its origin on the pectoral girdle, just lateral to the origin of the coracoarcuales. 

Until we know more of the relations of the sheet of connective tissue that affords 
origin to the coracobranchiales of Heptanchus we cannot be sure that these muscles 
have any real connection with the coracoarcuales. Comparison should be made directly 
from dissections of the two forms. 

The muscle which AUis calls the pharyngo-clavicularis is described by him (1893, 
p. 195) as follows: 

Immediately dorsoposterior to the surface of insertion of the coracobranchialis VI on 
the sixth ceratobranchial, a broad muscle has its origin, and running ventromesially and 
contracting rapidly has its insertion on the clavicle dorsolateral to the coracoarcualis muscle 
of its side. This muscle would seem to be the homologue of the pharyngo-clavicularis of 
Amia (AUis, 1897), and it is not described by Vetter as a separate muscle in any of the 
selachians considered by him. 

The Eyeball Group. — In elasmobranchs and perhaps in vertebrates generally, 
the muscles that move the eyeballs arise (Marshall, 1881; Van Wijhe, 1883; Neal, 1918) 




Vcrbindung dcs 

Kiemenbogen- 

coeloms mit dem 

CavLim pericardii 




Text-figure 65. 

Diagrams showing the origin of eye muscles, and the extensions of the primitive coelomic 

cavity into the gill-arches, in selachian embryos. In A, the cavities of the pharyngeal 

arches are shown communicating with the pericardial portion of the coelomic cavity; in B, 

which is a later stage, the connections of these cavities have been lost. 

I> 2, 3, 4, gill-clefts; S.B.C.l — 5, pharyngeal arch extensions of the coelomic cavity; ch.dors., chorda dorsalis; 

oc.m., anlagen of the oculomotor muscles; M. obUq. sufj. and M.rect.lat., anlagen of the superior oblique and lateral 

rectus muscles respectively; nes. audit., otic vesicle. 

After Corning, 1925, Figs. 222 and 223; based on Froriep's (1902) Figs. 4 and 5 (Torpedo ocdlatus). 



392 



Bashford Dean Memorial Volume 



from mesodennal segments (head somites) which are serially homologous with those of 
the trunk (Text-figure 62). In primitive fishes, the head somites, Hke the trunk somites 
of vertebrates generally, are at first hollow and their cavities communicate with the 
primitive coelomic cavity. In other words, the coelomic cavity extends into the somites. 
In the head, this communication is by way of the mesoderm of the branchial arches, 
as shoum (for Torpedo) in Text-figure 65 after Corning. Van Wijhe (1883, Figs. 1 and 2, 
Taf. I) gives more exact drawings showing the same features in Scyllium canicula. These 
channels quickly close, and the somites later become solid structures. 



i^- ■ pi.t.ain:- praf. V 



, -* Ob'.iquus inf. 



> 1 '"■ 




R. maxiUomp.ndib. V. 

Text-figure 66. 
Dorsal view of the eye muscles of Chlamydoselachus on the right side. 

The Roman numerals distinguish the nerves supplying the eye: 11, second cranial or optic nerve; III, third 
cranial or oculomotor nen.'e; IV, fourth cranial or trochlear ner%-e. Other abbreviations are self-explanatory. 

After Nishi, 1923, Fig. 1. 



In Chlamydoselachus, the muscles of the eyeball and their innervation were described 
from two specimens by Hawkes U906), and later by Nishi (1922) who used four adult 
specimens. They were considered briefly by AlHs (1923), who merely supplemented the 
work of Hawkes by comparisons with his own specimens. 

The disposition of the various eye muscles of Chlamydoselachus is shown in Figures 
10, 11, and 12, Plate IV; also in Text-figures 66 and 67- It will be seen from Text-figure 67 
that the dorsal side of the eyeball has three muscles, while only two muscles supply the 



The Anatomy of Chlamydoselachus 



393 



ventral side. The combined strength of the dorsal group is obviously greater than that 
of the ventral group. As figured and described by Hawkes the inequality in the strength 
of these two groups is more striking. The dorsal group is strengthened to turn the eye 
upward, not only to a moderate degree for the purpose of looking upward, but to a much 
greater extent when the cornea is turned well under cover of the socket, for protecting 
this most delicate part of the surface of the eyeball. The part of the eyeball (sclera) 
then left exposed is covered with shagreen. These devices for protecting the eyes in 
the absence of lids have been described by Gudger and Smith (1933). 

Conditions are simpler in Heptanchus as described and figured by Davidson (1918, 
pp. 162-163 and Fig. 5). In this shark two groups of muscles (Text'figure 68) are present 
in the orbit. The first group is placed anteriorly and consists of the superior oblique 



Rectus sup. --- 
Rectus lat. ace. 

pectus lat. 



Fades artic. 



Rectus inf. 




Text-figure 67- Text-figure 68. 

Eye muscles of Chlamydoselachus and Heptanchus showing insertions on eyeballs. 

Text-figure 67- Semidiagrammatic figure of left bulbus oculi of Chlamydoselachus 

in medial aspect. 

The abbreviations are self-explanatory. 
After Nishi, 1923, Fig. 2. 

Text-figure 68. Eye muscles of Heptanchus maculatus in dorsal view, right side. 

a.r., anterior rectus; i.e., inferior oblique; i.r., inferior rectus; n.II, optic nerve; o.p., optic pedicel; 

p.r., posterior rectus; s.o., superior oblique; s.r., superior rectus. 

After Davidson, 1918, Fig. 5. 

(s.o.) and the inferior oblique (i.o.). These muscles extend from the anterior part of the 
orbit outward and caudad to be inserted on the eyeball. The second group consists of 
the four recti muscles, all of which arise from the posterior surface of the orbit around 
the base of the optic pedicel. The most dorsal member of this group is the superior rectus, 
the most ventral the inferior rectus, the most posterior the external or lateral rectus, and 
the most anterior the internal or medial rectus. They pass outward and forward to be 
inserted on the eyeball. 

The chief peculiarity of the musculature of the eyeball of Chlamydoselachus is 
the fact that all the muscuH recti, save only a portion of an accessory rectus lateralis 
(externus), take origin from the eyestalk. In Chlamydoselachus the function of the eye- 



394 Bashford Dean Memorial Volume 

stalk is twofold: it prevents the eye from sinking too far into the socket, and it supplies 
a more lateral basis for the origin of the recti muscles. The lateral rectus consists of two 

parts which have separate origins and insertions, although they are otherwise united by 
strong "strands of muscle nbers. One di\-ision or this muscle takes origin from the outer 
part of the optic stalk, while its insertion is on the posterior surface of the eyeball. This 
is the normal insertion for an undivided rectus lateralis. The other division is said by 
Hawkes to be twice as large, though in Nishi's figures (reproduced here as Text-figures 
66 and 67) it appears sHghtly smaller than it does in Hawkes" figures. Its origin is from 
the cranium as well as along the proximal portion of the optic stalk. The insertion is on 
the dorsal side or the eyeball, somewhat more external than that of the rectus superior 
which it partly overlaps. From the positions of its origin and insertion, this division 
must be considered as a secondary' or deri\-ative portion or the primitive rectus lateraUs. 
This secondary' muscle was probably spHt off from a rj-'pical rectus laterahs to aid the 
superior rectus and the superior obhque in tilting the eye upward. The recti superior, 
medialis (intemus) and inferior are all attached to the top of the optic stalk, just below its 
flattened head. 

THE APPESTDICXX.\R MUSCLES 

From embryological studies on certain elasmobranchs and primitive teleostomes it 
is clear that, in these fishes, buds from the myotomes grow into the embryonic fins and 
there break down into mesenchyme which is the source of the fin muscle : as in Spinax 
Braus, 1899 -^ ScvUfuvn (Goodrich, 19061; Cestracion (Osbum, 1907J; Acar.thias (E. 
Xliiller, 1911,i; in Amia and Lepidosteus (Schmalhausen, 1912). Thus the muscles that 
move the fins are metameric in origin: this appHes to both paired and unpaired fins. 
Some features of this developmental history have been interpreted in terms of the fin-fold 
theory of the origin of paired fins. Concerning this matter, Daniel (1934, p. 110) says: 

It is evident that the number of segments that take part in the formation of buds for the 
pectoral fin is fewer in the sharks than in the rays. This fact is clear when we consider two 
types like Miisteliis and Torpedo, in the former of which the fin is relatively narrow and in 
the latter is of great extent. According to Maurer (1912), in the embryo of Mustelus only 
10 s^ments contribute to the formation of the musculature of the pectoral fin; while in 
Torpedo there are 26 such s^ments. 

The further course of the development of these buds in two forms like the above has been 
studied in great detail because of the bearing which such development has on the lateral 
fin-fold theory. That, in a type like Mustelus, segments (myotomes) anterior to the pectoral 
fin and between the pectoral and the pelvic fins form buds which atrophy without entering the 
fin, is taken by those who accept the lateral fin-fold theory to mean that the fin previously 
had a much greater anteroposterior extent than at present; and it is hence in agreement with 
what would be expected from that theory. 

In common vi-ith the nbtidanids, Chlamydoselachus seems to afford tavorable material 
for the study of the origin and development of the fin muscles, but so far as I am aware, 
such studies have never been made on these forms. 

Of the fins of Chlamydoselachus, only the pehncs of the male have received attention 
■^ith respect to their musculature. The muscles oi these fins have been described in 



The Anatomy of Chlamydoselachus 



395 




Text-figure 69. 
Endoskeleton and musculature of male pelvic fins of 

Heptanchus maculatus. 
A — Skeleton of male left pelvic fin in dorsal view. 

h.l and b.2, connecting segments; ha., basal piece; ba.p., basipter- 

ygium; he., beta cartilage: pi., pelvic girdle; ra., radial cartilages. 

After Davidson, 1918, Fig. 8. 

B — Musculature of male right pelvic fin in dorsal view. 

ad., adductor muscle; cp., compressor muscle; d!., dilator muscle; 

f.e., flexor externus; f.i., flexor internus; p!., pelvic girdle; ra., radial 

muscles; s.m., muscle of sac or pocket. 

After Davidson, 1918, Fig. 9. 

detail by Goodey (1910. 1, pp. 564-565) whose 

Figs. 20 and 21, pi. XLVI, are reproduced as 

my Figures 22 and 23, plate V, alongside Fig' 

ure 21 which shows the endoskeleton. The 

radial muscles {Ra., Figure 23, plate V) ex' 

hibit a division into bundles paralleling the 

radial cartilages. Concerning the ventral radial 

muscles Goodey says: ''On the ventral side 

there are the radial muscles Ra., which originate on the pelvic girdle close to the 

median line and extend outward to the horny fibers. Toward the anterior end the separate 

bundles have fused together, thus corresponding with the fusion of the radials above." 

The muscles of the clasper have been described in Heptanchus by Davidson (1918, 
pp. 165-167 and Fig. 9). Davidson's figure of the musculature is here reproduced as 
Text'figure 69b alongside his figure of the endoskeleton (Text-figure 69a). In both 
Chlamydoselachus (Figures 22 and 23, plate V) and Heptanchus (Text-figure 69b), the 
musculature of the myxopterygium is simple as compared with that of most elasmobranchs. 
Few differences are found when Chlamydoselachus and Heptanchus are compared with 
each other. As pointed out by Daniel (1934, p. 110), the principal difference is in the ad' 
ductors. In Heptanchus the adductor (ad. in Text-figure 69b) is a long muscle; in Chlamy^ 
doselachus it (A in Figure 22, plate V) is relatively broad and fan-shaped. Also, in 
Heptanchus the external and internal flexors are united at their origins, while in Chlamy- 
doselachus the point of origin of the external flexor is far removed from that of the 
internal flexor. 

From a functional point of view, certain muscles of the myxopterygia or claspers 
of Chlamydoselachus are described by Leigh-Sharpe (1926, p. 312) as follows: ''The 
musculature is represented by the anteroflexor muscle, which anteroflexes the whole 
clasper for intromission, and the erector muscle which in this case causes expansion of 
the apical valves by pulling on a common tendon. The anteroflexor muscle is strongly 
developed in this genus." These muscles are shown (p. 472) in Text-figure 115b, after 
Leigh-Sharpe. 



396 



Bashford Dean Memorial Volume 



THE BRANCHIOMERIC MUSCLES 

The segmentation that gives rise to the branchial arches is of a different nature from 
that which carves out the somites. The term branchial arches is used by embryologists, 
in its voidest sense, to include the mandibular and hyoid arches which are considered 
to be modified gill-arches. By comparative anatomists, the entire series is usually designat- 
ed the visceral skeleton, and the arches are called visceral arches. It is common to speak 
of the branchiomeric muscles as the pharyngeal muscles, here also making no distinction 
between mouth and pharynx. 

superficiai co?7str/dor 
Tnuscles of^i/larches 



nerire 



eyemuscles 




lafeml 
cana/s 



adduclor muscles 
ofjaii/s 



MecMs 
cartilage 

Text-figure 70. 

A dissected head of C\i\am-^iosdac\iu& ang\xme.us in lateral view. 

From Gregory, 1933, Fig. 6; redrawn and slightly simplified after color figure in AlKs, 1923, pi. IV. 



'/■z.'in/r' 



While the metameric muscles are derived, at least in large part, from a dorsal zone 
of early mesoderm which has previously been cut up into somites, the muscles of the 
branchial (visceral) arches (excluding the hypobranchial group of muscles) do not arise 
from somites but from mesoderm that is commonly regarded as splanchnic. The nerves 
that supply these muscles are placed in a different category (visceral) from those (somatic) 
that supply metameric muscles. 

Fiirbringer (1903) described some of the muscles of gill-arch origin, particularly 
those of the mandibular arch, in C\Aam-^d.oselac}ms. Luther (1909) described the muscles 
innervated by the trigeminal nerve. Goodey (1910.1) described the muscles of the 
mandibular and hyoid arches. AUis (1923) has given a detailed, comprehensive and 
beautifully illustrated description of the pharyngeal muscles of Chlam^idoseldcfius, which 



The Anatomy of Chlamydoselachus 



397 



should be consulted by anyone wishing a more complete account than is given here. 
Most of the pharyngeal muscles are represented in Text-figures 64 and 70 after Gregory 
(1933). The interarcuales dorsales (lad.) and subspinales (S.sp.) are shown in Text-figure 
71, after AUis (1915), drawn from a specimen in which the interarcuales are somewhat 
atypical. In Text-figures 64 and 71 the methods of numbering the interarcuales differ, 
so that AUis's interarcualis IV corresponds to Gregory's interdorsaHs V. 



Text-figure 71- 
Ventral view of the roof of the pharyngeal 
cavity of Chlamydoselachus, after the lining mem- 
brane has been removed, showing the pharyngo- 
branchial cartilages, efferent arteries and inter- 
arcuales dorsales muscles in natural position. 

cc, common carotid artery; Coe, constrictor of the esophagus; 
eal, efferent branchial artery of the first branchial arch; 
eall, efferent branchial artery of the second branchial arch; 
EB II, epibranchial cartilage of the second branchial arch; 
EPB VI, epi-pharyngobranchial cartilage of sixth branchial 
arch; HMD, hyomandibular cartilage; lad IV, musculus 
interarcualis dorsalis between arches IV-V; ladhy, musculus 
interarcualis dorsalis between hyoid and first visceral arches; 
Ida, lateral dorsal aorta; !m!i, ligamentum mandibula' 
hyoideum; n., cut ends of nerves to tissues of roof of branchial 
chamber; PB I, pharyngobranchial cartilage of first branchial 
arch; PB IV, pharyngobranchial cartilage of the fourth 
branchial arch; Rabd, musculus retractor arcuum branchialium 
dorsalis; Ssp, subspinaUs muscle; tiad, ligamentous sheet 
formed by tendons of musculi interarcuales dorsales. 
After Alhs, 1915, Fig. 1. 




Davidson (1918) classified the pharyngeal (branchiomeric) muscles of Heptanchus 
as follows: (1) superficial circular [constrictor] muscles; (2) interarcuales; (3) subspinales; 
(4) adductors; and (5) the hypobranchials. For reasons concerned with the mode of 
development, the hypobranchials have already been considered under the category 
of metameric muscles, though it is more common to include them with the pharyngeal 
group, to which they functionally belong. 

All observers agree that the adductor mandibulae of Chlamydoselachus is "a thick 
massive muscle, filling up the concavities on the outer side of the palatoquadrate and the 
mandible" (Goodey, 1910.1, p. 547)- In all the illustrations (by various authors) of this 



398 Bashford Dean Memorial Volume 

muscle, it appears surprisingly large considering the slenderness and flexibility of the 
jaws. This is well shown in Gregory's drawing (Text-figure 64 herein) and is perhaps 
exaggerated in Fiirbringer's (1903) Fig. 1, pi. XVI. Consideration of the large size of 
this muscle strengthens the conviction that Chlamydoselachus is in the habit of seizing 
and swallowing fairly large prey. In this case the superficial constrictor muscles (Text' 
figure 70; also Allis, 1923, Fig. 46, pi. XVII, and Fig. 48, pi. XVIII) as well as practically 
every other muscle of the oral and branchial region, may be brought into play to assist 
in the act of swallowing which is finally completed by the constrictor of the esophagus. 
The superficial constrictor muscles that run in the gill'flaps are thin (Text-figure 78, p. 421) 
but they are broad and they overlap like the shingles on a roof, so that collectively they 
may exert considerable pressure. It has already been noted that the labial cartilages 
are held in place by strong ligaments and fascia; some of these cartilages serve for the 
attachment of special muscles. Thus an integumental muscle, the protractor anguli 
oris, has a tendon attached to the mandibular labial cartilage (Allis, 1923). The strong 
levator labii superioris (Allis, 1923, pp. 183-184 and Fig. 15, pi. X) may assist the creature 
in expanding the mouth opening while swallowing its prey. Of this muscle Allis says : 

The levator labii superioris, in all my specimens, is wholly independent of the adductor 
mandibulae, my specimens apparently differing in this respect from those examined by 
Fiirbringer (1903, p. 384) and Luther. The muscle arises by a relatively long tendon from 
the ventro'postero-lateral corner of the ectethmoidal process, and running almost directly 
posteriorly swells abruptly into a muscle body which is inserted on the anterior half of the 
posterior upper labial, some of the fibers apparently being inserted in the adjacent tissue 
of the upper Hp. The muscle is innervated, as both Fiirbringer and Luther have stated, 
by a branch of the mandibularis trigemini which arises from that nerve shortly after its 
separation from the maxillaris trigemini. 

In many selachians there is a fairly strong adductor muscle, related to the mandible, 
which is usually referred to as the muscle add. gamma of Vetter's (1874) description. 
In Chlamydoselachus, the long tendinous portion of this muscle is apparently represented 
by a strong ligament, which has its origin on a little process of the anterior edge of the 
hyomandibular and its insertion on the posterior edge of the postorbital process of the 
cranium (Allis, 1923, p. 187 and Fig. 23, pi. XI). I quote the following from Allis, 1923, 
pp. 187-188: 

Fiirbringer and Luther both say that this muscle is not found in Chlamydoselachus. 
Fiirbringer accordingly considers it to be a secondary arrangement, possibly the beginning 
of a differentiation of a superficial portion of the adductor mandibulae, such as is found in 
Amia and in many teleosts. Luther (1909, p. 54) thinks it is developed from the most posterior 
portion of the adductor, and he considers it to be an archaic feature (I.e., p. 64) notwith- 
standing that he did not find it in either Chlamydoselachus, Echinorhynchus or Odontaspis. 
In Squatina, it is to be noted, the muscle arises by a few fibers from the hyomandibula (Luther, 
1909, p. 60). 

One is especially impressed by the differences, with respect to this muscle add. 
gamma, between the closely related forms, Heptanchus and Chlamydoselachus. In 



The Anatomy of Chlamydoselachus 399 

Heptanchus (Vetter, 1874, Fig. 1, pi. XIV) the muscle is well developed; in Chlamy- 
iosdachus it is apparently represented by a ligament which is attached, not to the mandi' 
ble, but to the hyomandibular. It seems probable that the presence of this muscle, as 
in Heptanchus, is primitive for sharks while the related structure in Chlamydoselachus 
is a modification that has arisen in connection with the peculiar hyostylism of the jaws. 

In attempting to identify homologous muscles in different species of vertebrates, 
considerable dependence is placed on their innervation. The motor nerves, growing 
outward from the central nervous system, establish connections with the muscles or 
pre'muscle masses quite early in their development. Should the muscle subsequently 
migrate in order to reach its definitive position, its nerve follows it. Thus in the branchial 
region, it is generally considered that all the muscles innervated by the fifth (trigeminal) 
nerve are derivatives of the first visceral (the mandibular) arch, while all the muscles 
innervated by the seventh (facial) nerve are derivatives of the second visceral (the hyoid) 
arch. In most sharks, the musculus intermandibularis is supplied by the mandibular 
branch of the trigeminal nerve; but in Chlamydoselachus, Furbringer (1903, Fig. 1, Taf. 
XVI) figures the musculus intermandibularis as supplied only by branches of the seventh 
(the facial) nerve, and Hawkes (1906) states that "the mandibular ramus [of the trigeminal 
nerve] does not supply the large median muscles which lie in the angle made by the two 
sides of the lower jaw." Luther (1909) was unable to trace any branches of the trigeminal 
nerve to the intermandibular muscles of Chlamydoselachus, Hexanchus and Heptanchus. 
In the notidanids and in Chlamydoselachus, the superficial muscles spanning the halves 
of the mandible are supplied by branches of the seventh or facial nerve (Luther, 1909). 
For Chlamydoselachus and Heptanchus the distribution of these branches is shown in 
Luther's (1909) Fig. 1, Taf. I, and Text'figs. 9 and 10; for Chlamydoselachus they are 
better shown by AUis (1923) in his Fig. 6, pi. VI, which is in color. Luther (1909) 
concluded that when the intermandibular muscle is innervated wholly by the nervus 
facialis, a muscle of mandibular^arch origin has simply been crowded out by one of hyoid 
arch origin; but in his later work (1913, p. 46) Luther decided that the trigeminus muscle 
here persisted, but had secondarily acquired innervation by the nervus facialis. 

AUis (1917) gave particular attention to this matter of the innervation of the 
musculus intermandibularis in Chlamydoselachus and related forms. His conclusions 
appear to be embodied in the following statement (AUis, 1917, p. 389) : 

The interhyoideus and intermandibularis muscles of Chlamydoselachus could accordingly 
both be of facialis origin, so far as the relations of nerve and muscle are concerned, but in all 
probability only that portion of the intermandibularis that Hes anterior to the point where 
the nervus faciahs definitely disappears from its external surface could be of mandibular 
origin. And if this portion of the muscle be of mandibular origin, as several authors have 
maintained, I consider it certain that it is innervated by a branch of the nervus mandibularis 
trigemini, and that that branch has simply been missed in dissections, my own included. 

In the introduction to his 1923 memoir, AUis states: "The investigation of the 
nervous system had only just begun, and . . , this part of the cranial anatomy is only 



400 Bashford Dean M.emorial Volume 

briefly noticed in the present memoir." This leaves us in doubt whether Allis made any 
further dissections before writing (1923, pp. 188-189): 

The muscles innervated by the nervus faciaHs, all of which are here considered as belong- 
ing to the hyal arch, are represented by a single continuous muscle sheet, which is partially 
differentiated, by differences in the insertion of its fibers, into a constrictor superficialis, 
a levator hyomandibularis, an interhyoideus and an intermandibularis. . . . These several 
portions of the continuous muscle sheet are all apparently innervated exclusively by branches 
of the nervus facialis, and there is accordingly no musculus intermandibularis of mandibular 
origin in this fish. This has been fully discussed in an earHer work (AlHs, 1917), the course 
of the ramus hyoideus facialis and its relations to the several muscles there also being given. 

Whatever light future investigations may throw on the possible persistence of 
a vestigial musculus intermandibularis of mandibular arch origin, the fact remains that 
what appears to be the intermandibular muscle of Chlamydoselachus, Hexanchus and 
Heptanchus is innervated by a branch of the facial nerve, contrary to what has been 
found in all other sharks that have been investigated. This evidence, so far as it goes, 
tends to draw Chlamydoselachus and the notidanids closer together and at the same time 
to separate them further from other existing sharks. 

Considering the small size of the external opening of the spiracle and the absence of 
an authentic spiracular cartilage, it is not surprising that we have found no mention of 
a special spiracular muscle in Chlamydoselachus. Luther (1909, p. 12) mentions a spirac- 
ular muscle in Hexanchus, and in his Fig. 1, Taf. I, it is clearly shown as a prominent 
sphincter; but there appears to be no special differentiation of the muscles adjoining the 
spiracle of Heptanchus (Luther, 1909, Fig. 2, Taf. I). 

An interesting though probably anomalous condition of the musculi interarcuales 
dorsales was found by Allis (1915 and 1923) in one of three specimens of Chlamydoselachus 
studied by him. In the specimen under consideration, the musculi interarcuales dorsales 
form an almost continuous sheet of muscular and ligamentous tissue in the roof of the 
pharynx (Text-figure 71)- These muscles are better shown in AlHs's (1923) Fig. 56, pi. 
XXI, which is drawn from the same specimen but to a larger scale and in color. In the 
two other specimens of Chlamydoselachus studied by Allis, the individual muscles of 
the interarcuales dorsales group are better differentiated and there is no common sheet 
of muscular tissue mesial to the pharyngobranchials. Nevertheless, the related ligamen- 
tous sheet existed in the two specimens as in the other one, and "extended the full length 
of the branchial region" (Allis, 1915). From one of the two specimens thus described, 
Allis's (1923) Fig. 53, pi. XX, was drawn. The condition shown here is more like what 
is found in Heptanchus (Furbringer, 1897, Fig. 1, Taf. V; Davidson, 1918, Fig. 3), where 
the muscle is broken up into segments between the respective pharyngobranchial 
cartilages. Thus we find, in the musculi interarcuales dorsales of Chlamydoselachus, 
one more example of decided variability. 



The Anatomy of Chlamydoselachus 



401 



DIGESTIVE SYSTEM AND ASSOCIATED 
ORGANS 

There are few published descriptions of the di' 
gestive organs of Chldmydoselachus, and these accounts 
are very brief. This situation may be due, in part, to 
the circumstance that most of the specimens that have 
come into the hands of anatomists had been eviscer^ 
ated. The following account is based mainly on my 
studies and drawings of material in the collection of 
the American Museum of Natural History, but it in' 
eludes a review of the work of other investigators. 

My material includes the three large female speci' 
mens whose external characteristics have been fully 
described by Gudger and Smith (1933). In all these 
specimens, the body cavity had been opened by a 
ventral longitudinal incision and the digestive tube 
had been split open along its length. Thus it was not 
possible to view the digestive organs in an undisturbed 
condition. In two specimens, the liver was nearly all 
missing and the mesenteries had been much torn. The 
best'preserved specimen. No. I, had all the digestive 
organs, also the spleen, complete; but the mesenteries 
were considerably torn. Another large female speci- 
men, kindly lent by Dr. E. Grace White, was used 
here only for the study of the thyroid, since the di' 
gestive organs had been removed. I shall call this 
specimen No. IV. 

THE DIGESTIVE TUBE 

Before proceeding with a description of the vari' 
ous parts of the digestive system, it is advisable to 
call attention to Text'figure 72, drawn from specimen 
No. I, wherein each part of the digestive system, ex' 
cepting mouth and pharynx, is drawn to scale in its 
approximate relation to the whole. In order to dis' 
play certain organs to the best advantage, the natural 
position has in some instances been altered. Thus the 
lobes of the liver have been drawn aside, the cardiac 
stomach has been turned to the left in order to bring 




Text-figure 72. 
The digestive system of Chlamydo- 
selachus, ventral aspect, about one-fifth 
natural size. 

h.e., bursa entiana; c, colon; c.b.d., common bile 
duct; C.S., cardiac stomach; d.mes., dorsal 
mesentery; d.p., dorsal pancreas; es., esophagus; 
g.b., gall bladder; !.!., left lobe of liver; py., 
pylorus; py.ves., pyloric vestibule; r., rectum; 
r.g., rectal gland; r.!., right lobe of liver; sp.l, 
spleen; sp.2, accessory spleen; v.i., valvular 
intestine; v.mes., ventral mesentery; v. p., 

ventral pancreas. 

Drawn from specimen No. I in the collection of 

the American Museum of Natural History. 



402 Bashford Dean Memorial Volume 

the pyloric vestibule and the pylorus into view, and the rectal gland has been turned to 
the left. In this paper, the terms right and left mean the right and left sides of the fish 
itself, regardless of its position with respect to the observer. 

THE PHARYNX 

The mouth, including the teeth, has been adequately described by Gudger and Smith 
(1933). The pharynx is of importance for respiration, but since it affords passage for 
food it must be briefly considered from this point of view. 

The mouth and pharynx of Chlamydoselachus form one large cavity, the oro- 
pharyngeal cavity. For so slender a shark, the size of this cavity when fully distended 
is remarkable (Text-figure 2, p. 337)- Although a large mouth does not necessarily 
imply that large objects are taken as food, in the case of Chlamydoselachus there is col- 
lateral evidence, such as the character of the teeth, indicating that the animal seizes and 
swallows Hving prey of considerable size. It seems Hkely that the elaborate pharyngeal 
musculature, already considered, assists in the act of swallowing the prey, snake-fashion. 

Almost the entire oropharyngeal cavity is lined with close-set denticles. On the 
lining of the roof, the denticles are exceedingly small. On the floor, especially where 
this is upraised to form a structure superficially resembUng a rudimentary tongue, the 
denticles are appreciably larger. Some of these denticles, in a region overlying the thy- 
roid gland, are shown in Text-figures 75 and 76, p. 417- On the inner surfaces of the 
gill-arches, excepting only the hyoid arch and the dorsal portions of the most posterior 
branchial arch, they are particularly large, but are still smaller than those at the angles 
of the mouth (Text-figure 10, p. 345), described and figured by Gudger and Smith (1933). 
The larger denticles are of the same general character as those of the epidermis ; but the 
central cusp is longer and sharper, and curves backward. The denticles of the gill-arches 
and the floor of the pharynx offer little resistance to a finger tip passed over them in 
a cephalocaudad direction, but pierce the epidermis and cling tenaciously when the 
finger tip is pulled over them in the opposite direction. Presumably, the pharyngeal 
denticles assist the animal in retaining its hold on slippery prey, partly swallowed. 
Garman (1885.2) shows denticles on the inner surfaces of the gill-arches of his specimen 
(my Text-figure 77, p- 421), but they appear larger than those found in a corresponding 
situation in my specimens. 

ESOPHAGUS AND CARDIAC STOMACH 

As in most elasmobranchs, the wide, distensible esophagus passes without abrupt 
demarcation into the large, thin-walled cardiac portion of the stomach. In Chlamydo' 
selachus one cannot tell precisely where the esophagus leaves off and the stomach begins. 
The combined length of esophagus and cardiac stomach is remarkable (Text-figure 72; 
and Table I, p. 412), since together they form about half the total length of the digestive 
tube. In my best-preserved specimen, No. I, the collapsed and flattened esophagus is 



The Anatomy of Chlamydoselachus 



m 



about 55 mm. wide where it joins the pharynx, but it narrows rapidly to an almost uniform 
width of 30 mm. throughout most of its length. The diameter of the widest portion of 
the cardiac stomach is about 45 mm. 

In all the specimens in the American Museum, 
a previous dissection had shown the stomachs to be 
practically empty. Nevertheless in specimen No. Ill 
the cardiac stomach had evidently been hardened 
while in a distended condition, since its lumen is un' 
usually large and its walls are very thin. In this 
specimen, throughout a large portion of what is 
presumably cardiac stomach, the wall is only about 
1 mm. thick; I suspect, however, that most of the 
mucosa is missing. The inner surface is smooth. In 
my other specimens the cardiac stomach is less dis' 
tended and its wall is appreciably thicker; the inner 
surface is cast into slight longitudinal folds. In all 
three specimens the thickness of the wall of the car' 
diac stomach increases toward its caudal end, but 
it is nowhere more than 2 or 3 mm. thick. 

On the right side near the caudal end of the 
cardiac stomach of Chlamydoselachus, HdLwkts (1907) 
describes and figures (my Text'figure 73) a more dc' 
cided thickening (L.T.S.) which she suggests may 
be a "lymphatic gland." Hawkes does not tell how 
many specimens she studied, nor whether this thick' 
ening occurred in more than one specimen. I have 
found no such structure in any of my three speci' 
mens. From specimens I and III, I have excised 
some segments of the slightly thickened wall near 
the caudal end of the cardiac stomach, and upon 
microscopical examination have found only the layers 
characteristic of a stomach, including an inner 
glandular layer in a poor state of preservation. 
CoUett (1897) states that in his specimen of 
Chlamydoselachus measuring 1910 mm., the stom- 
ach proper is small and proportionally narrow; its length is 340 mm., its breadth is 
about 45 mm. 

In Heptanchus (Daniel, 1934) the stomach is U'shaped or V'shaped, the larger left 
limb being the cardiac portion, and the smaller right limb, the pyloric division. In two 
of my specimens of Chlamydoselachus a small division, the pyloric vestibule, is inter' 




Text-figure 73. 
Digestive tube of Chlamydoselachus, 
from the middle of the stomach to the 

middle of the valvular intestine. 
B.D., bile duct; B.D.B.E., dotted line showing the 
position of the enlarged end of the bile duct in 
the wall of the bursa entiana; B.E., bursa entiana; 
C, caecum at the hinder end of the larger arm 
of the stomach; L.T.S. , thickening of the stomach 
wall, probably due to a lymph node; Py.V., 
pyloric valve; S., stomach; S.l. short arm of 
stomach; S.V., spiral valve. 
After Hawkes, 1907, first text-figure. 



404 Bashford Dean Memorial Volume 

posed between the cardiac stomach and the pylorus. It seems probable that, when 
present, this di\asion in Chlamydoselachus is homologous with a part of the pyloric 
stomach of Heptanchus. 

THE PYLORIC VESTIBULE 

In my specimen No. I the cardiac stomach narrows considerably near its caudal end. 
It is marked off from the next division, which I shall call the pyloric vestibule, by a sharp 
constriction. The pyloric vestibule is cylindrical in form and is of smaller caHber than 
the cardiac stomach, though decidedly larger than the pylorus. The vestibule leads off 
from the dorsal surface of the cardiac stomach, beginning about 10 mm . from its caudal 
end, and extends somewhat cephalad, dorsal to the cardiac stomach, for a distance of 
about 25 mm., then makes an abrupt turn dorsad and caudad before joining the pylorus 
which extends obHquely to the right and caudad. Thus the pyloric vestibule, considered 
together v,ith the adjoining portion of the cardiac stomach, is somewhat S-shaped. In 
Text'figure 72 the pyloric vestibule (py.ves.) has been exposed by turning the cardiac 
stomach to the left. Therefore the vestibule has been rotated through an angle of nearly 
90° and appears almost as if viewed, in its natural position, from the right side. In the 
specimen under consideration, the pyloric vestibule is about 35 mm. long and (in a col- 
lapsed and flattened condition) about 22 mm. wide in its widest portion which is near its 
junction with the cardiac stomach. Its wall is about 1.5 mm. thick and is of the same 
general character as the wall of the cardiac stomach. The sharp constriction between 
the cardiac stomach and the pyloric vestibule is more marked internally since here the 
flattened lumen has a v,^dth of only 15 mm., which is 4 mm. less than the diameter of the 
lumen of the adjoining portion of the pyloric vestibule. At its pyloric end, the vestibule 
narrows abruptly to join the pylorus; here, the entrance has the same diameter as the 
lumen of the pylorus. 

In specimen No. Ill, the pyloric vestibule is much smaller. It is situated on the 
dorsal side of the caudal end of the cardiac stomach. In life it was probably spherical, 
but it is now much flattened by pressure between the cardiac stomach and the dorsal 
body wall; it has been hardened in that condition. Externally, on its anterior border 
it is marked off from the cardiac stomach by a deep groove. Internally, its lumen is 
partially separated from that of the cardiac stomach by a crescentic valve-like flap almost 
completely encircling the residual lumen but leaving a circular aperture about 15 mm. in 
diameter. On the anterior side, where it is best developed, the width of this flap is 
about 5 mm. I am of the opinion that the flap, as such, is an artifact due to pressure, 
since by stretching the wall of the stomach longitudinally the flap may be reduced to 
a low fold. There remains, however, a very decided constriction marking off the pyloric 
vestibule from the cardiac stomach. An aperture about 4 mm. in diameter leads off from 
the anterodorsal side of the pyloric vestibule into the pylorus which extends obliquely 
to the right and caudad. The proximal third of the pylorus adheres firmly to the wall 
of the pyloric vestibule. 



The Anatomy of Chlamydoselachus 405 

In specimen No. II there is nothing resembUng a pyloric vestibule; the pylorus 
comes off abruptly from the caudal end of the cardiac stomach and leads directly backward. 
The aperture leading from the cardiac stomach to the pylorus is very small, but admits 
a probe without difficulty. The muscular wall surrounding this aperture is unusually 
thick; evidently it serves as a sphincter. In the specimen figured by Hawkes (1907) 
and reproduced as my Text'figure 73, there is no division of the stomach corresponding 
to what I have called the pyloric vestibule. I cannot reconcile this difference further 
than to say that here, as in many other structures, Chlamydoselachus shows remarkable 
variability. 

THE PYLORUS 

In all my specimens, the pylorus is a slender portion of the digestive tube which, 
from superficial appearances, might more appropriately be designated a part of the small 
intestine. However, the region under consideration undoubtedly corresponds to what 
is called pylorus in other sharks, as in Galeus (Daniel, 1934, Fig. 135, p. 136). In Chlamy^ 
doselachus (Text'figure 72) the caudal extremity of the pylorus (py.) projects into the 
next division of the digestive tube, the bursa entiana (b.e.), as a large conical papilla, the 
pyloric valve. The muscular layers of the pylorus appear to be continuous with similar 
layers in the valve. At the summit of the papilla there is an aperture which, in the hard- 
ened condition of the material, is still large enough to admit a probe easily. This opening 
is the passageway from the pylorus to the bursa entiana. The cone-shaped valve is 
asymmetrically placed and adheres, more or less, to one side of the bursa. 

On account of the overlapping of the pylorus by the bursa, in recording their lengths 
for the purposes of Table I it was necessary to divide the region of overlapping equally 
between them. In specimen No. I (Text-figure 72) the overlapping occurs mainly on 
one side and is about 6 mm. in its greatest extent; the total length of the pylorus, including 
its valve, is 36 mm. The width of the pylorus, in its present collapsed and flattened 
condition, is about 8 mm. In specimen No. II the lumen of the bursa entiana overlaps 
the pyloric valve for a distance of 14 mm. on one side and 6 mm. on the other. The total 
length of the pylorus, including its valve, is 40 mm. In this specimen the pylorus is 
cylindrical and its diameter is only 6 mm. In specimen No. Ill the pylorus is unusually 
short. Its valve is overlapped, on one side only, by the lumen of the bursa entiana for 
a distance of 6 mm. and its total length is 28 mm. At its widest point, which is near 
its middle, the collapsed and flattened pylorus of this specimen measures 12 mm. across. 
In specimens I and III the wall of the pylorus is a scant millimeter in thickness; in No. II 
it is about 2 mm. thick. In all my specimens the inner surface of the pylorus is traversed 
by longitudinal folds. These are more prominent in No. II because of the contracted 
condition of the pylorus in this specimen. 

Hawkes (1907) describes the division which I have called the pylorus, as follows:' 
"The shorter arm of the stomach (S. 1) differs from the larger anatomically and functionally. 
It is a short, thick-walled tube incapable of distension, the lining mucosa of which is 



406 Bashford Dean Memorial Volume 

raised into parallel ridges. This arm opens into the intestine by a protruding pyloric 
aperture (Py. V.) which is furnished with distinct sphincter muscles." The pyloric 
valve (Py. V.) figured by Hawkes (my Text'figure 73) appears symmetrical, thin-wailed, 
slender and cylindrical — quite unlike any that I have observed, save that it protrudes into 
the bursa. Possibly the drawing is inaccurate, since the valve appears too thin to be 
provided with a sphincter muscle. In Heptanchus (Daniel, 1934, Fig. 123), as in Chlamy- 
doselachus, the pyloric valve projects as a well-defined circular band into the bursa. 

THE BURSA ENTIANA 

In Chlamydoselachus, as in sharks generally, the middle intestine or duodenum is 
short; as in certain other elasmobranchs, it is expanded to form a thin-walled sac, the 
bursa entiana (Text -figure 72, h. e.). In Chlamydoselachus the bursa entiana is shaped 
somewhat Hke the human stomach, but the orientation is difi^erent. Superficially, it 
would resemble the human stomach if the latter were reversed end-for-end and rotated 
so that the greater curvature would Ue to the right and dorsally. In my three specimens 
the amount of distention of the bursa varies greatly, so that the dimensions recorded 
here do not give any accurate information as to what the relative size would be if the 
structures were measured under identical conditions. 

In my specimen No. I the bursa entiana is moderately distended and has moderately 
thick walls; its condition is probably typical. Measured from the first coil of the spiral 
valve to the apex of the pyloric valve, its length is 33 mm.; but after including the total 
extent to which the bursa overlaps the pylorus, the length is 39 mm. Its greatest trans- 
verse diameter is about 14 mm. Its walls are very thin (less than 1 mm.) at the cephalic 
end, but toward the caudal end the thickness increases gradually to almost 2 nam. at the 
junction with the valvular intestine. 

In specimen No. II the bursa is greatly contracted. Measured from the villosities 
on the inner surface of the cephaHc end of the valvular intestine, to the apex of the 
pyloric valve, its length is 20 mm. Since the bursa overlaps the pyloric valve for a distance 
of 14 mm. on one side, its total length is 34 mm. Its greatest transverse diameter is 
about 10 mm. The thickness of its walls ranges from 1 mm. at the cephalic end to 3 mm. 
at the caudal end. 

In specimen No. Ill the bursa is greatly expanded. Its length, measured from the 
cephaHc end of the spiral valve to the apex of the pyloric valve, is 40 mm. After in- 
cluding the extent to which the bursa overlaps the pyloric valve, the total length is 
46 mm. The greatest transverse diameter, which is near the caudal end, is about 18 mm.; 
near the cephaUc end the transverse diameter is about 10 mm. The wall is everywhere 
less than 1 mm. thick. 

In the lining of the ventral side of the bursa entiana in specimen No. I there is 
a pocket (shown by a dotted outHne in Text-figure 72) about 10 mm. long, opening caudad 
into the lumen of the bursa. The opening is about 8 mm. v,ade and is situated about 



The Anatomy of Chlamydoselachus 407 

one-third of the distance from the apex of the pyloric valve to the beginning of the valvu- 
lar intestine. A probe inserted into the pocket readily entered the common bile duct 
(c.b.d.) which extends anteriorly. A similar but slightly larger pocket occurs in specimen 
No. Ill; it is situated a little further caudad, rather more than halfway toward the valvular 
intestine. A probe passed into this pocket did not find the opening of the bile duct. 
A bile duct could not be found in the vicinity, but this was probably because the region 
had been mutilated. In specimen No. II the pocket, as such, could not be found, but 
a channel or canal leads from the cephalic end of the valvular intestine into the rather 
thick, contracted wall of the bursa entiana. This channel was probed. After proceeding 
for a distance of about 15 mm. cephalad within the wall of the bursa, the probe entered 
the bile duct which extends anteriorly. The channel is, therefore, an extension of the 
bile duct caudad within the wall of the bursa entiana. 

In specimen No. I the inner surface of the bursa is fairly smooth save in a region 
extending caudad from the pocket which forms the opening of the bile duct. This area 
is traversed by longitudinal folds similar to those shown in Text-figure 73- In specimen 
No. I, these folds extend along the inner surface of the outer wall of the pocket and are 
visible through its thin inner wall. In specimen No. Ill, where the bursa is greatly 
expanded, its inner surface is smooth except that the area which in specimen No. I is 
cast into longitudinal folds, is here somewhat rough and flaccid. In specimen No. II, 
where the bursa is strongly contracted, its entire inner surface is cast into strong lon- 
gitudinal folds. The longitudinal canal within the wall of the bursa, which communi- 
cates with the bile duct anteriorly and opens into the valvular intestine posteriorly, was 
opened by a longitudinal incision after it had been probed. Its inner surface is very 
rough, with many small papillae like those found in the upper end of the valvular in- 
testine. Thus, in the character of its lining, this channel resembles the valvular intestine 
and differs from the bursa entiana. It constitutes a decided variation from the usual 
condition in which the bile duct enters the bursa entiana through a funnel-shaped pocket. 

Hawkes (1907) described and figured (my Text-figure 73) a pocket situated nearer 
the valvular intestine than the pockets described in my specimens No. I and III. The 
flap forming the inner wall of the pocket figured by Hawkes is not so well developed as 
in my specimens I and III, where its free edge extends in a straight line transversely 
or somewhat obliquely. The condition that I have described in specimen No. II, whereby 
the bile is conveyed through a special channel in the wall of the bursa directly into the 
valvular intestine, apparently has not been observed by any other investigator. 

In Heptanchus (Daniel, 1934, Figs. 120 and 123) the middle intestine or duodenum, 
corresponding to the bursa entiana of Chlamydoselachus, is not sharply marked off from 
the valvular intestine. Daniel (p. 124) states that "the valve of the spiral intestine extends 
forward throughout the length of the middle intestine and touches the pyloric valve.'' 
This contrasts strongly with the simpler condition in Chlamydoselachus, already 
described. 



40S Bdshford Dean Memorial Volume 

THE W^VTJLAR INTESTINE 

In my three specimens the vahnilar portion of the digestive rube is spindle'shaped, 
but tapers much more rapidly in its caudal half; the cephaUc end is almost truncate. 
Gunther"s (1887) figure (my Figure 15, plate IV) gives proportions similar to those found 
in my specimens save that in his dissection the \'aI\Tjlar intestine is laid widely open 
after being sHt longitudinally. In my specimens the external surface of the valvular 
intestine is either bluish-gray or brown, appearing much darker than the other portions 
of the digestive tube. The ^.-alls are ver}' thick, ranging from 5 or 6 mm. near the cephaHc 
end, to 1 or 2 mm . at the caudal end where it joins the colon. In two of these speci- 
mens the spiral valve extends to the extreme cephalic end of the thick-walled portion 
of the digestive tube, but in Xo. II the spiral valve stops at about 20 mm. from the ceph- 
alic end of the thick-v.-^Ued portion. For the remaining distance the inner surface 
shows \-Lllo5ities similar to, but larger than, those found in the region of the spiral valve. 
On this account, and also because of the thickness of its u-alls, this part is assigned to the 
\^h"ular intestine. For similar reasons I have included v.'ith the \^l\njlar intestine a short 
thick-walled portion, with a velvety lining, between the caudal end of the spiral valve 
and the thin-walled colon. In specimens I and III the length of this region is 15 mm. ; 
in Xo. II it is 20 mm. The posterior four-fifths of the vahnilar intestine lacks a mesentery. 

In my specimen Xo. I, the form of the \'ahnalar intestine seems perfectly preserved. 
The maximum diameter is only 26 mm., while the length is 190 mm. In Xo. II the val- 
\Tjlar intestine is much larger; its maximum diameter is about 33 mm., while its length 
is 240 mm. In Xo. Ill the organ is about the same size as in Xo. II, but is so irregularly 
molded that its diameter cannot be accurately measured. 

In Chlamydoselachus the spiral \'alve is a continuous ribbon-Hke structure attached 
by one edge to the inside of the wall of the intestine, while the other edge is either free, 
■^^-inding about a central ca\rity, or is attached to an axial strand. In specimen Xo. I 
the anterior third of the spiral valve has a central cavity large enough to admit a pencil; 
the posterior third has a much smaller central cavity, while the middle third has an axial 
strand. In specimen Xo. II a central cavity alternates with an axial strand at irregular 
intervals. In specimen Xo. Ill there is a central ca\'ity of moderate size extending the 
entire length of the spiral \^lve except in its middle portion, where there is a short axial 
strand. In the specimen portrayed by Giinther (my Figure 15, plate IV) it is clear that 
there is a central cavity in the caudal half and at the cephaHc end, while the interval 
between has possibly an axial strand. 

In its natural position, the spiral valve of Chlamydoselachus does not He vertical 
to the waU of the intestine; it slants either forward or backv.^rd. Thus each coil has the 
form of an asymmetrical cone, of which the apex may be missing. \\%en the intestine 
is contracted, the spiral \^lve makes an acute angle with the wa.]l of the intestine; when 
it is expanded, the spiral valve may be drav^-n into a nearly transverse position. 



The Anatomy of Chlamydoselachus 409 

In my best'preserved specimen, No. I, there are 44 coils of the spiral valve. In the 
nine anterior coils, the angle is very acute and the cones point cephalad; in the remaining 
coils the cones point acutely caudad. The transition between the two conditions is 
abrupt. In specimen No. II there are 45 coils; each of these makes an acute angle with 
the wall of the intestine, and points caudad. In specimen No. Ill there are 37 coils. In 
the anterior third, the coils or cones are obtuse but point definitely cephalad; those of 
the posterior third are acute and point caudad; while those in the middle third are 
apparently transverse, but this region is much distended and is poorly preserved. In 
this specimen the transitions between the regions described are gradual. 

Giinther's (1887) Fig. 5, pi. LXV (my Figure 15, plate IV) shows 35 coils in the 
spiral valve of Chlamydoselachus. Of these, the first 19 point forward, one is transverse, 
and the remaining 15 point backward. CoUett (1897, p- 13) states that in his specimen 
"the intestine (colon) is cylindrical, very muscular, and contains 47 spiral valves." In 
a specimen described by Hawkes (1907) there are 43 coils : the first 7 (my Text'figure 73) 
point forward, one is contorted, and the remaining 35 are directed backward. Hawkes 
points out that the inclination of the spiral valve has a physiological significance : where 
the valve is directed forward the passage of the food is undoubtedly slower than where 
it is directed backward. 

In Heptanchus maculatus (Daniel, 1934, Fig. 123 and pp. 124-125) the spiral valve 
makes 17 or 18 turns. The folds are far apart anteriorly and very much closer posteriorly. 
The valve is considerably broader than the diameter of the intestine and is thrown into 
a series of cones having their apices pointed anteriorly. The surface of the valve, viewed 
under the microscope, shows numerous finger^like villi. 

It has been noted in Chlamydoselachus that the anterior coils of the spiral valve 
usually point forward, and the posterior coils usually point backward. This condition 
of the spiral valve seems to be exceptional among elasmobranchs. A similar condition 
has been found (Parker, 1885) in a single specimen of Scyllium canicula, and something 
like it occurs in Zygaena (Parker, 1885, Fig. 8, pi. XI). In most sharks the apices of prac' 
tically all the coils point forward, as in Scyllium (Parker, 1885, Fig. 5, pi. XI); or backward, 
as in Heptrayichias perlo (Garman, 1913, Fig. 1, pi. 58). In some specimens of Raja (Parker, 
1885) the apices of all the coils point forward, while in other specimens all but the first 
coil are deflected backward. Moreover in some sharks, as in Cephaloscyllium umhratile 
(Garman, 1913, Fig. 2, pi. 58), and in some specimens of Raja (Parker, 1885), an axial 
cord extends the entire length of the valvular intestine. In other sharks, as in Isurus 
punctatus (Garman, 1913, Fig. 3, pi. 58), and in other specimens of Raja (Parker, 1885), 
there is instead an axial tube. Both axial cord and axial tube occur, in Chlamydoselachus, 
in each individual specimen, where they are restricted to different parts of the valvular 
intestine. Thus in the valvular intestine of Chlamydoselachus there are combinations of 
features that almost always occur separately in other elasmobranchs. This affords 
a striking example of the structural comprehensiveness usually considered characteristic 
of the more archaic members of a phylum or class. 



410 Bashford Dean Meynorial Volume 

RECTUM AND RECTAL GLAND 

In most elasmobranchs the portion of the digestive tube extending from the valvular 
intestine to the anal opening is differentiated into two parts, colon and rectum. In 
conformity v^ith the usual practice I have distinguished two regions, colon (c.) and 
rectum (r.), in Text-figure 72; but these parts are much aHke and there is no definite 
boundary' between them, therefore I shall here consider the two regions, combined, under 
the term rectum. 

The lengths, in my three specimens, are given in Table I, p. 412. It will be noticed 
that in specimen No. II the rectum is unusually long. In each specimen, the viridth of the 
rectum is about the same throughout its length, so that in ventral view it appears to be of 
uniform diameter; but when \-iewed from the side, the rectum appears somewhat funnel- 
shaped since it enlarges toward the anus. In specimen No. I the rectum is 9 mm. wide 
and has a dorsoventral diameter of 13 mm. at its cephaHc end, 16 mm. at its middle, and 
20 mm . at the anal end. Similar proportions are found in my other specimens. In speci- 
men No. II the rectum is 6 mm. v.dde; its dorsoventral diameter is 10 mm. at the cephalic 
end, and 16 mm. at the anal end. In specmien No. Ill the width is 8 mm.; the dorso- 
ventral diameter is 10 mm. at the cephaHc end, and 18 mm. at the anal end. From these 
dimensions it is evident that in each case the rectum is laterally compressed, and dorso- 
ventrally enlarged to\^-^rd the anus. The anal opening faces both ventrad and caudad, 
so that It leads directly to the exterior and also into the cloaca. The wall of the rectum 
is from 1 to 2 mm. thick. The Kning is cast into slight longitudinal folds which are more 
pronounced in specimen No. I. There is no mesorectum save the very small mesentery 
supporting the rectal gland, at the extreme caudal end of the rectum. 

The rectal gland is a laterally compressed, somewhat kidney-shaped body situated 
in the angle between the rectum and the cloaca. In Text-figure 72 the rectal gland 
(r.g.) is shown turned tou-ard the left. The dimensions in my three specimens are: No. 
I, 20 X 13 x 6 mm.; No. II, IS x 14 x 7 mm.; No. Ill, 17 x 12 x 9 mm. The duct leads 
anteriorly and ventraUy to open into the dorsal side of the rectum. In all three specimens 
the duct is 13 mm. long. The opening is distinctly \^sible on the inner surface of the 
rectum; it is guarded by a \^lve-Hke flap and readily admits a probe which passes easily 
into the rectal gland. In specimen No. I the opening is situated 20 mm. from the valvular 
intestine, just midway in the length of the rectum. In specimen No. II the opening is 
situated 40 mm. from the \^lvular intestine, also at the middle of the rectum. In speci- 
men No. Ill the opening is situated 15 mm. from the valvular intestine and 25 mm. 
from the anus. 

The proximity of the rectal gland to the cloaca has led to its being figured with the 
reproductive system. Thus Garman (1885.2) shows in his Fig. 2, pi. XIX (reproduced 
as my Text-figure 92, p. 440) an organ labeled "caecal pouch" which corresponds with 
what I have called the rectal gland. He does not describe its duct, but in his Fig. 3, pi. 
XIX a duct appears to open from this gland into the rectum. Giinther (1887) figures 
a gland (my Figure 19, plate V) in the position of a rectal gland, and asserts that it opens 



The Anatomy of Chlamydoselachus 411 

into the cloaca. Hawkes (1907) states that, in two specimens studied by her, the rectal 
gland opens into the rectum. It is so shown in her diagrammatic figure of the female 
cloacal region reproduced as Text-figure 90a, p. 435). The function of the rectal gland 
is unknown. 

In Heptanchus (Daniel, 1934) the portion of the digestive tube between the valvular 
intestine and the anus is divided into two parts, colon and rectum. The two parts are 
much alike, but the form of the colon is slightly bulbous. The duct of the rectal gland 
reaches the wall of the rectum at its cephalic end, but does not enter here; it courses 
cephalad in the wall of the colon to enter the lumen at the caudal end of the valvular 
intestine. 

THE DIGESTIVE TUBE AS A WHOLE 

We have seen that the digestive tube of Chlamydoselachus is but slightly longer 
than the body cavity, and that all its parts, save only the valvular intestine, are more or 
less flaccid when empty. This leaves some doubt as to the precise form of the tube in 
its natural position, both when empty and when distended with food. In all my speci' 
mens the digestive tube is empty. In specimen No. I, which has a well'developed pyloric 
vestibule, there is an abrupt S'shaped fold of the pyloric vestibule and related portion 
of the cardiac stomach, in what appears to be the natural position of these organs. In 
specimen No. II, which has a shorter pyloric vestibule, the smaller fold in the same region 
cannot be straightened out. There are no other folds that appear to be of a permanent 
nature, but in all my specimens there is considerable irregular folding in the walls of the 
cardiac stomach. The question arises whether the distention of this organ with food 
would be sufficient to take up whatever "slack" exists in this region. 

Table I gives the total length of the digestive tube, also the length of the body 
cavity excluding the small portions along the sides of the cloaca, in my three specimens. 
In specimen No. I the digestive tube is 100 mm. longer than the body cavity; in No. II 
it is 105 mm. longer; in No. Ill it is 203 mm. longer. In No. I and in No. Ill the recurrent 
course of the pyloric vestibule takes care of a small part of the excess length. It is probable 
that, in specimens I and II, when the cardiac stomach was fully distended with food the 
digestive tube became approximately straight; but the same statement could hardly 
apply to specimen No. III. 

Giinther (1887) writes of Chlamydoselachus: "The stomach is an extremely long 
cylindrical sack with thin walls ; the short and narrow intestine, after having made a short 
and incomplete convolution, passes into the dilated portion which contains the spiral 
valve." I have found no evidence of folding of the intestine in any of my specimens, and 
it seems possible that the "short and incomplete convolution" mentioned by Giinther 
really belonged to a pyloric vestibule. CoUett (1897) states that the intestinal canal of 
his specimen is almost straight throughout its length, only the short duodenum being 
turned aside between the pylorus and the dilated portion with the spiral valve. Deinega's 
half-tone reproduction (1925, Fig. 1) of a drawing of the viscera in situ is printed on 



412 



Bashford Dean IsAemoriai Volume. 



unsuitable paper and details are obscure. The digestive tube appears as a nearly straight 
tube in which three main regions are recognizable; there is possibly a small convolution 
in the region of transition from stomach to intestine. 

A continuous median dorsal mesentery, more fully described in the section on the 
urogenital system, supports the digestive tube of Chlamydoselachus throughout its 
its length excepting the posterior four-fifths of the valvular intestine and the entire 
rectum. The rectal gland has a special mesentery which is evidently an isolated division 
of the dorsal mesentery. The mesentery supporting the common bUe duct appears to be 
a ventral mesentery, but in my specimens it is considerably mutilated and some of its re- 
lations are obscure. 



TABLE I 



Length (in millimeters) of the digestive tube and its divisions in comparison with the total body length 
and the length of the body ca\aty anterior to the cloacal aperture, in three adult female specimens of 
CMamydoselachus. 



Specimen 
Number 


Total Body 
Length 


Esophagus 
and Cardia 


Pyloric 
Vestibule 


Pylorus 


Bursa | Valvular , Colon and 
Entiana ; Intestine Rectum 


'^°^ ' Body 

^^^'= . Cavity 
Tube 


I 

n 
m 


1350 
1485 
1550 


330 
365 
440 


35 

Absent 

25 


33 
33 
25 


36 190 40 
27 240 80 
43 ! 230 40 


664 
745 
803 


564 
640 
600 



THE LIVER 

In my specimens 11 and III the Hver is nearly all missing; but in Xo. I the Kver is 
intact and (macroscopically) in an excellent state of preservation. Therefore my descrip- 
tion is based entirely on a study of specimen No. I. 

The Hver of Chlamydoseladnus (Text-figure 72) is a very large organ. It consists 
mainly of two lobes (r.I. and 1. 1.), one on each side of the body, extending the entire 
length (about 600 mm.; of the body cavity including the portions lateral to the cloaca. 
At their anterior ends, these lobes are continuous with the short unpaired portion of the 
Hver w^hich is median in position. The lobes are of equal size and aHke in form save that 
there is a sHght excavation near the distal end of the left lobe. Thus the form of the 
Hver is decidedly symmetrical. Each lobe is flattened; the greatest wadth of a lobe is 
about 50 mm., but the thickness does not exceed 12 m m. In Text-figure 72 the lobes are 
shown in broad view, but in their natural position they would probably appear in an 
edge view. The unpaired portion of the Hver is about 60 mm. wnde, 55 mm. long, and 
8 mm. thick; it is wrapped about the ventral and lateral surfaces of the esophagus. The 
gall bladder (g.b.) is 42 mm. long and 16 mm. wide. It is attached to the ventral and 
median surface of the unpaired portion of the Hver, and projects sHghtly beyond its 
caudal margin. 



The Anatomy of Chlamydoselachus 413 

A large duct, the common bile duct (c.h.d.), leaves the right lobe of the liver about 
260 mm. from its anterior end to course within the ventral mesentery. Its course is 
shown in Text'figure 72; it empties into the pocket of the bursa entiana (b.e.). From the 
point where it leaves the right lobe of the liver, the duct was traced by palpation and 
dissection cephalad to the gall bladder. Its opening was found on the inside of the gall 
bladder, and a probe was passed through this opening into the duct. There is no duct 
visible at the surface, or leaving the surface, of the left lobe of the liver. 

Gunther (1887) states that the liver of Chlamydoselachus consists of two extremely 
long lobes which reach backward to the end of the abdominal cavity, and anteriorly 
receive the gall bladder between them. Hawkes (1907) writes that the liver consists of 
right, left and median lobes. The gall bladder is situated in the median lobe. The 
length of the lobes necessitates their being doubled upon themselves. Evidently these 
statements are based on more than one specimen, for she writes that in one specimen 
the end of the left lobe was found lying on the right side of the body. 

Of his 1910'mm. specimen of Chlamydoselachus, one of the largest ever taken, 
CoUett (1897) writes that the liver was enormous. Two and one^half months after the 
death of the fish, when it had presumably lost considerable oil, this liver weighed 4250 
grams. It consisted of two parallel and symmetrical lobes, the symphysis being 140 mm. 
long. Its total length was 950 mm. — nearly one'half the total length of the fish. The 
lobes were of equal thickness, and without side lobes except toward the end, where 
there was a small side flap. The height of each lobe was 100 mm., and the thickness 
55 mm.; their upper (dorsal) edges were somewhat flattened, almost lamellar, while 
their lower (ventral) edges were smooth and rounded. 

Deinega (1925, Fig. 1) shows, rather indistinctly, a liver of Chlamydoselachus similar 
to the one I have described, save that the gall bladder is larger. In Heptanchus (Daniel, 
1934, Fig. 119) the liver is constructed on the same general plan, but the lobes are shorter 
and relatively thicker than in Chlamydoselachus. 

THE PANCREAS 

In Chlamydoselachus, as in other sharks and in the embryos of higher vertebrates, 
there are two pancreases, dorsal and ventral respectively (Text'figure 72, d.p. and v. p.). 
The ventral pancreas is closely related to what appears to be a ventral mesentery, while 
the dorsal pancreas is supported by a special mesentery which seems to be a part of the 
dorsal mesentery. But in each of my specimens these mesenteries are considerably muti' 
lated and the digestive tube is free to rotate. The dorsal pancreas is present in all my 
three specimens. The ventral pancreas is present in only two; in the other specimen, 
the absence of the ventral pancreas is evidently the result of mutilation. In my two 
specimens possessing a ventral pancreas, it is combined with an accessory spleen. 

The dorsal pancreas is a flattened organ, irregular but somewhat triangular in shape, 
situated near the anterior part of the valvular intestine which it slightly overlaps, and 



414 Bashford Dean Memorial Volume 

very close to the bursa entiana. In its natural position the dorsal pancreas tends to curl 
around these organs, but in Text'figure 72 it (d.p.) is shown displaced to the left and spread 
out flat. In my best'preserved specimen (No. I) the dorsal pancreas measures 45 x 25 
X 2 mm. In my other specimens it is of approximately the same size, but is mutilated so 
that precise measurements are impossible. A piece of the dorsal pancreas from specimen 
No. I was removed for sectioning. Under the microscope the sections show, on one side, 
alveoli characteristic of a pancreas, but I was unable to identify the ducts. Considering 
that the material had been preserved for thirty years, the structure of the alveoli is 
surprisingly well preserved. On the other side of each section I found areolar tissue, 
blood vessels, cords of epithelioid cells and scattered epithelioid cells. This portion may 
possibly represent an organ of internal secretion. 

In my specimens, the ventral pancreas is easily distinguished from the accessory 
spleen, to which it is closely attached, by a difference in color: the ventral pancreas, 
like the dorsal pancreas, is pale yellow, while the accessory spleen, like the spleen proper, 
is very dark. Together, the ventral pancreas and the accessory spleen form a slender, 
somewhat crescentic, slightly-flattened body whose approximate position is shown in 
Text'figure 72 (v. p. and sp. 2). In specimen No. I this duplex organ is 40 mm. long 
by 8 mm. wide at its widest level; in specimen No. II it is 70 mm. long by 10 mm. wide. 
The ventral pancreas and the accessory spleen are of equal length and width, and are 
united side-by-side; thus they appear as a single organ divided into two longitudinal 
zones. From specimen No. I, segments were cut from the Hght zone and the dark zone 
separately, and sections were prepared for microscopical examination. The light zone 
was found to be in a very poor state of preservation, but is undoubtedly glandular. It 
contains cords of epithelial cells, groups of cells which may represent alveoli, and cells 
arranged so as to give the appearance of ducts; also scattered epitheHoid cells and many 
small blood vessels. A fairly large artery runs along one side of each section. The 
dark zone is in a much better state of preservation. It consists mainly of dense lymphoid 
tissue containing a multitude of leucocytes and many extravascular erythrocytes. These 
observations seem sufficient to identify the organ as a spleen. 

From specimen No. II a segment extending entirely across the duplex organ (ventral 
pancreas and accessory spleen) was cut into transverse serial sections. The material 
is in poor condition for histological study, but one side of each section is undoubtedly 
pancreas, the other, spleen. Each organ has a connective tissue capsule. In places the 
two organs are connected by their capsules, in other places the capsules are separated 
by a cleft. 

So far as I know, this combination of a ventral pancreas with an accessory spleen 
has not been observed in any other elasmo branch. In the teleost, Gamhusia patruelis, 
the mingling of spleen and pancreas is described by Potter and Medlen (1935) from whose 
paper I quote as follows: "The typical histological structure of this organ [the spleen] 
is modified by the presence of pancreatic tissue. The pancreas is located in the mesen- 



The Anatomy of Chlamydoselachus 415 

teries of the organs in this region, and it penetrates the substance of the spleen by fol' 
lowing the blood vessels which supply this organ." 

I was unable to find, by dissection, any undoubted pancreatic ducts. Such ducts 
are presumably present, unless they have disintegrated through long preservation of the 
material. Hawkes (1907) does not mention any pancreas in Chlamydoselachus, but 
describes a pancreatic duct which probably belongs to the dorsal pancreas since it opens 
into the valvular intestine where the spiral valve begins. 

Collett's (1897) description of the pancreas in his specimen of Chlamydoselachus is 
interesting in that he speaks of dark and light portions of the pancreas. His description 
is quoted in full: 

The pancreas consists of two large lobes, of which each is subdivided into an upper 
and lower portion, so that it really is in four divisions, of which the two hinder portions are 
lighter in color than the front ones. On the right side it forms, first, a short light-colored 
lobe, about 80 mm. long and 35 mm. broad. Anteriorly, it is almost entirely separated from 
a curved front portion, which is of darker hue than the hinder part. Posteriorly there also 
exists a lower portion, of a length of about 100 mm. ; above this hes a darker-colored portion 
whose length is about 48 mm., which adjoins the hinder hghter part, and is connected with it. 

Although CoUett does not mention a spleen, it seems likely that the dark organs 
described by him are accessory spleens. 

Deinega's (1925) drawing (his Fig. 1) of the digestive system of Chlamydoselachus 
does not show any organ labeled pancreas, but his Fig. 2 is a drawing of a section of some 
tissue said to have been taken near the pancreas. In it he distinguishes blood vessels, 
fibers and cells. He suggests that it may be splenic tissue. Evidently this material was 
in a very poor state of preservation for microscopical study. 

In Heptanchus (Daniel, 1934, Fig. 119) both dorsal and ventral pancreases are present 
and well developed. Their relations, as shown in this figure, appear to be much the same 
as in Chlamydoselachus. In another figure by Daniel (1934, Fig. 120) the names of the 
two divisions of the pancreas appear to have been interchanged. 

ORGANS ASSOCIATED WITH THE DIGESTIVE TRACT 

For convenience there are included in this section brief descriptions of two organs 
that are topographically related to the digestive system, but are not a part of it: the 
thyroid gland, which develops from the distal portion of a diverticulum from the floor 
of the pharynx; and the spleen, which has no developmental relation to any part of 
he digestive system. 

THE THYROID GLAND 

The position of the thyroid, attached to the ventral surface of the basihyoid cartilage, 
is shown in my Text'figure 26a, p. 361, after Goodey, 1910.1; also by Goodey (1910.2) 
in his Fig. 1 ; and by Allis (1923) in his Fig. 38, pi. XIV. 

The thyroid of Chlamydoselachus is especially interesting because, in the adult, 
it sometimes retains a primitive or embryonic feature. Phylogenetically, the thyroid is 



416 



Bashford Dean Memorial Volume 



regarded as a derivative of a median trough-like fold, the endostyle, such as is found in the 
floor of the pharynx in Amphioxus and the ascidians. In all vertebrates in v^hich the 
ontogenetic development of the thyroid has been studied, it arises in the embryo (tfir., 
Text-figure 62, p. 388) as an outpocketing from the floor of the pharynx. The distal 
portion of the outpocketing becomes the thyroid gland. The slender stalk persists for 
a time either as a hollow tube, the so-called thyroglossal duct, or as a soHd cord; but 
eventually it degenerates and disappears. Goodey (1910.2) made the remarkable dis- 
covery, in an adult Chlamydoselachus, of a persistent thyroid duct (my Text-figure 74, 
v.t.) opening into the pharynx through a perforation in the basihyoid cartilage, and ending 
bHndly where it comes into contact with the thyroid. This, of course, is not a functional 
duct; but it is comparable to the "thyroglossal duct" found in the embryos of many 
vertebrates. The so-called duct is Hned with pharyngeal mucous membrane in which 
are numerous incompletely developed pharyngeal denticles. 




Text-figure 74. 
Sagittal section (x 15) through the thyroid 
gland and persistent thyroglossal duct of 

an adult Chlamydoselachus. 
h.v., blood vessels; d., denticles; e., enamel organ; fo., 
follicles; I.t., lumen of tube; v.t., vestigial tube (thyro- 
glossal duct). 
After Goodey, 1910.2, Fig. 2. 



Since Goodey's account of the thyroglossal duct of Chlamydoselachus appears to be 
based on a single specimen, I have thought it worth while to investigate the possible 
occurrence of such a duct in the four large specimens at my disposal. From each specimen 
the thyroid was excised together with a large block of surrounding tissues including 
a portion of the basihyoid cartilage and the lining of the pharynx. The material was 
partially decalcified, then imbedded in celloidin and cut into serial sagittal sections. 
In each case the series extended completely through the large foramen in the basihyoid 
overlying the thyroid. In one case only (specimen No. I) there were two foramina; the 
anterior foramen is very small. This specimen. No. I, is the only one in which a thyro- 
glossal duct was found (Text-figure 75, d.), and this duct lies within the posterior and 
larger foramen. In specimens III and IV, a thyroglossal duct is demonstrably absent. 
In specimen No. II the material is in such poor condition that neither the presence nor 
the absence of a duct could be determined. 

In the series of sections from specimen No. I, the lumen of the thyroglossal duct is 
slightly tortuous, so that the continuity of the duct cannot be demonstrated in any 
single section. Text-figure 75, representing the thyroglossal duct, is a reconstruction 
from forty successive sections, each about 20 microns thick, and is slightly diagrammatic. 
The total thickness of the sections used in this reconstruction is about 800 microns 



The Anatomy of Chlamydyselachus 



417 




Text-figure 75. 
Median sagittal section (x 12) showing thyroid gland and thyroglossal 

duct of an adult Chlamydosdachus. 
a., artery; c, basihyoid cartilage; d., thyroglossal duct; p.i., pharyngeal denticle; thyr., 

thyroid gland. 
Drawn from Specimen No. I in the collection of the American Museum of Natural History. 




Text'figuer 76. 
Median sagittal section (x 10) showing thyroid gland of an adult OnUmydoselachus in which 

there was no thyroglossal duct. 

a., artery; c, basihyoid cartilage; p. d., pharyngeal denticle; thyr., thyroid; d., vein. 
Drawn from Specimen No. Ill in the collection of the American Museum of Natural History. 



418 Bashford Dean Ivlemorial Volume 

(less than a millimeter). The finer structure of this specimen is rather poorly preser^-ed, 
but permits of the foUo^^Tng obser\-ation5. The duct (d.) is lined u-ith stratified squamous 
epithelium continuous -^-ith the epithelial lining of the phar^^nx. The outer layer of the 
duct consists of a thick layer of dense connective tissue continuous v.'ith a similar layer 
comprising the deeper portion of the mucous membrane of the pharynx. Between the 
epithelium of the duct and its connective tissue layer, there are many calcifications ha\ing 
the form of rudimentan,'- denticles. These are smaller than the fully developed denticles 
(p.d.) that occur in the lining of the phar^^nx. The distal end of the duct ends blindly 
in close contact with the th^Toid (thyr.). 

Text-figure 76 is a drawing of the thyroid of one of my specimens (No. Ill) in which 
a th^TOglossal duct is absent. The histological condition of this material, also, is rather 
poor, but the topographical relations are well shouTi. Upon comparing Text 'figures 76 
and 75, it v,-ill be seen that in specimens I and III the position of the main mass of 
the thyroid (thyr.) with respect to the large foramen in the basihyoid cartilage (c.) is not 
quite the same. 

In specimen No. IV a large part of the th>Toid was cut av.^y in trimming the block 
preparatory to imbedding, but in the remaining portion the finer structure is well presen.-- 
ed. While the simple cuboidal epithelium of the follicles is in good condition, the lumens 
of the foUicles appear empty, as they do in the other specimens. In the sections of Xo. 
rV, the phar5.'ngeal denticles are beautifully sho-<;^-n. In all the sections, the epithelial 
Lining of the phar^^nx is very poorly preser\'ed. Fundamentally, it is stratified epithelium, 
but it contains many unusually large pale cells, singly or in groups, which are probably 
mucous cells. 

In Heptanchus (Daniel, 1934, p. 123) the thyroid gland is located "'at the symphysis 
of the lower jaws between the coracomandibularis and coracohyoideus muscles.'" FergU' 
son (1911), after studying many species of elasmobranchs, states that "The [th>Toid] 
gland rests upon the basihyal cartilage whose anterior margin forms an excellent guide 
to its location." His paper deals with the histological structure as weU as the form and 
gross anatomical relations of the thyroid in elasmobranchs, and includes a description of 
the blood vessels supplying the th\Toid. In Scylliu-m catulus and in S. camcula f^Goodey, 
1910.2), the th\Toid gland is situated close to a foramen in the basihyoid cartilage. In 
both species of Scyllium the connective tissue investment of the th\Toid extends into 
the foramen as a plug containing, in some instances, a small amount of th}Toid tissue, 
and in one instance, a problematical duct. So far as our present knowledge extends, 
Chlamydoselachus is the only vertebrate possessing, at least occasionally, a persistent 
th>Toglossal duct. 

THE SPLEEN' 

In ChlamydoseJachus the spleen proper fText-figure 72, sp.l) is a very elongate, 
somewhat comma-shaped, flattened organ lying in the dorsal mesenter)' at the level of 
the pylorus, pyloric vestibule, and caudal end of the cardiac stomach. In its natural 



The Anatomy of Chlamydoselachus 419 

position it is probably somewhat coiled about these portions of the digestive tube, but 
in Text-figure 72 it is shown displaced to the left. The color of the spleen, in my pre- 
served specimens, is a very dark bluish-gray. In my specimen No. I the spleen measures 
80 X 10 X 3 mm. ; in No. II, 60 x 10 x 4 mm. ; in No. Ill the spleen could not be found and 
had evidently been torn away. 

From specimen No. I, a transverse segment of the spleen was removed for sectioning. 
Under the microscope the sections were found to consist mainly of lymphoid tissue con- 
taining an abundance of leucocytes and many extra vascular erythrocytes; small arteries 
and veins were distinguishable. In its finer structure the spleen proper is very much 
Uke the accessory spleen already described in association with the ventral pancreas. 

Hawkes (1907) states that the spleen of Chlamydoselachus is divided into two parts 
which are separated by a space of 40 mm. The additional "lobe" (which is apparently 
comparable to what I have called the accessory spleen) is situated to the right of the 
stomach and somewhat dorsally. It is an ovoid body, 30 mm. long and nearly 20 mm. 
broad in its widest part, and is situated between the stomach and a fold of mesentery 
which supports the latter. The other part or spleen proper lies in the usual place at the 
angle of the stomach. The spleen proper, when examined by a low-power lens, presents 
the usual appearance; but the additional ''lobe" is much more compact. Hawkes does 
not mention a pancreas in association with the secondary spleen. 

In Chlamydoselachus, Deinega (1925, Fig. 1) shows, indistinctly, an organ labeled 
spleen, which appears to be on the right side of the body since it is crossed by the common 
bile duct on its way from the right lobe of the liver to the intestine. In Heptanchus, the 
spleen (Daniel, 1934, Figs. 119 and 120) is much more extensive, and is broken up into 
several different parts or "lobes." 

In concluding this section I note that the digestive system of Chlamydoselachus 
presents the following features of especial interest: (1) The great variability in the 
region of transition from stomach to intestine; (2) the differentiation of the coils of the 
spiral valve into two series, with apices facing in different directions; (3) the presence 
of an axial strand in the middle portion of the valvular intestine, along with an axial 
tube in both anterior and posterior portions; (4) the great length of the lobes of the 
liver, in adaptation to the form of the body; (5) variations in the position of the opening 
of the common bile duct into the intestine ; and (6) the presence of an accessory spleen 
associated with the ventral pancreas. In some specimens, there is (7) a persistent thyro- 
glossal duct which is lined with stratified squamous epithelium and which possesses 
rudimentary denticles. 

THE RESPIRATORY ORGANS 

In Chlamydoselachus, as in other fishes, the gill-filaments and their lamellae are the 
primary organs of respiration. Accessory structures such as the branchial skeleton and 
musculature, the oral breathing valve and the valvular gill-folds or gill-flaps, are concerned 



420 Bashford Dean Memorial Volume 

with regulating the passage of water, subservient to respiration, through the mouth into 
the pharynx and out through the gill-clefts. When the spiracular canal and external 
spiracular orifices of Chlamydoselachus are sufficiently large, doubtless a little water is 
expelled through the spiracles. The oral breathing valve, the external openings of the 
spiracles, and the gill-flaps have been described by Gudger and Smith (1933). In the 
present paper I have already described the skeleton and muscles of the oral and pharyn- 
geal region, and have noted the absence of a true spiracular cartilage. It remains to 
describe the gill-filaments in relation to their supporting structures — in other words, 
the gills — and to complete the description of the spiracles. The blood vessels of the 
gills are described in the section on the blood-vascular system. My own observations 
and drawings of the respiratory system of Chlamydoselachus are based on the three large 
specimens in the collection of the American Museum of Natural History, and a fourth 
large specimen kindly lent by Dr. E. Grace White. 

THE GILLS 

From the descriptions and illustrations in the article by Gudger and Smith (1933) 
it is apparent that the gill-clefts of Chlamydoselachus are unusually large in proportion 
to the si?e of the body. Some idea of the size of these clefts may be obtained from Text- 
figures 4 (p. 339) and 77- Of his specimen Garman (1885.2) writes: "The gill-openings 
are large; the first, when extended, will admit an object of four inches or more, and the 
last will take one of two inches in width." In my specimen No. I, which is 1350 mm. long 
(rather small for an adult), I find that the first gill-cleft (the one between the hyoid arch 
and the first branchial arch) will admit the fingers and thumb of an entire hand; the 
second, the four fingers as far as the palm; the third, the tips of four fingers; the fourth, 
three fingers; the fifth, two large fingers; and the sixth, a thumb. These crude measure- 
ments are sufficient to show the approximate size of the gill-clefts and the rapid decrease 
in their size posteriorly. 

Garman's (1885.2) drawing (my Text-figure 77) of a gill-cleft and related structures 
represents the fourth gill-opening on the right side. I have oriented the reproduction 
of Garman's figure with the dorsal side uppermost; this brings the anterior holo branch 
to the right. 

Each gill-arch of Chlamydoselachus affords attachment, distally, to one edge of 
a crescentic plate, the gill-septum. The framework of the gill-arches is supplied by the 
cartilaginous branchial arches, while the gill-septa are strengthened by very slender 
radially directed cartilaginous rods, the branchial rays. Each branchial ray begins in 
contact with the cartilaginous branchial arch and extends to the extreme edge of the 
gill-septum, where it may cause a slight projection of the overlying membrane. In places 
the margin of the gill-septum is strengthened by a delicate extrabranchial cartilage. 
On each side of a gill-septum there are long narrow primary folds, the gill-filaments, 
extending in a radial direction from the base of the gill-septum toward its margin (Text- 
figure 77; Text-figure 78, a.f. and p.f.). On each broad surface of a gill-filament there are 



The Anatomy of Chlamydoselachus 



421 



\ 




'•:s 



X 



■"^ 

y 







Text-figure 77- '~' 

The fourth gill-opening on the right side of a specimen of Chlamydoselachus anguineus, with the 
gills spread apart to display the gill-filaments and branchial rays. The uppermost side of the 

figure is dorsal, the right side anterior. 
After Carman, 1885.2, Plate V. 




Text-figure 78. 
Radial section (x4) of a gill of Chlamydoselachus, partly diagrammatic. The Hnes extending across 
each filament indicate the sites of attachment of the lamellae on one surface of the filament. The 
number of lamellae shown is approximately the actual number found in sections through the ventral 

portion of the gill of the first branchial arch on the right side of Specimen No. I. 
ad.m., adductor branchialis muscle; a.f., anterior filament; af.br.a., afferent branchial artery; c, cartilage of the gill-arch; 
cm., superficial constrictor muscle of the gill-flap, continuous with the thinner interbranchial muscle of the gill-septum; 
ef.br.a., efferent branchial arteriole; n., nerve; p.f., posterior filament; v., vein, presumably draining the small blood vessels 

of the gill-septum. 
Based on drawings of serial sections from two specimens in the American Museum of Natural History. 



422 



Bashford Dean Memorial Volume 



transverse secondary folds or lamellae (Text-figures 78, 79, 80 Im.) too small for ordinary- 
observation. Goodrich (1930) and some others apply the term lamella to the structure 
that I have called a filament, and designate as ''secondary lamellae" the small leaf-like 
folds that I have called simply lamellae. In my specimens, the distal end of a gill-filament 
is free for a distance of from 3 to 8 mm. ; the gill-filaments never reach the distal edge of 
the septum, but leave a smooth outer portion (from one-fourth to one-half of the entire 
surface of the septum) constituting the gill-flap or gill-fold. Successive gill-flaps overlap 
like the shingles on a roof. In addition to affording protection to the delicate gills, 
they function as respiratory valves. 




Text-figure 79. Text-figure 80. 



Sections showing filaments and lamellae of 
a gill of Chlamydoselachus. 

Text-figure 79. Portion of a section (x 12) 
through the ventral part of the gill of the 
fourth arch on the right side, cut trans- 
versely to the filaments. 

a.hr., afferent branchial arteriole; e.hr., efferent branchial 

arteriole. 

Drawn from a section of a giU from a specimen lent by 

Dr. E. Grace White. 

Text-figure 80. Outline of a portion of 
a section (x 36) taken lengthwise of a gill- 
filament, in the ventral part of the gill of 
the first arch on the right side. The upper 
end of the figure is distal. 
a., arteriole; \m., lamella. 
Drawn from a specimen in the American Museum of 
Natural History. 



All the gill-filaments between two successive gill-clefts, together with the structures 
supporting these gill-filaments, constitute a holobranch or entire gill. One of these is 
shown, in a radial section cutting lengthwise of the filaments, in Text-figure 78. The 
filaments on one side of a gill-septum constitute a demibranch or half-gill. There is 
a demibranch on both sides of each gill-cleft of Chlamydoselachus, excepting the posterior 
side of the sixth or last gill-sHt. In my specimens, as in Carman's figure, the filaments on 
the anterior side of a gill-cleft are always longer than those on the posterior side. In 
other words, the filaments of a posterior demibranch (posterior with reference to the 
septum, not to the gill-cleft) are always longer than those of the anterior demibranch of the 
same giU. Further, the filaments on both sides of the first gill-cleft are distinctly shorter 
than those in corresponding positions with reference to the other gill-clefts. Since the 
close-set filaments, all bearing numerous lamellae, of each demibranch are distributed 
along the entire length of each gill and extend, on the average, considerably more than 
halfway from the base of the septum to its free edge, it is apparent that the respiratory 



The Anatomy of Chlamydoselachus 



423 



surface is very large — perhaps larger, in proportion to body size, than in most elasmo- 
branchs. The blood vessels of the gills are described in the section on the blood- vascular 
system, but it may be noted here that, thin as they are, the lamellae nevertheless contain 
exceedingly rich capillary plexuses. 

The general plan of a gill of Chlamydoselachus is much like that of Heptanchus (Text' 
figure 81, which should be compared vv^ith Text'figure 78). Indeed, so far as the gills 
of elasmobranchs have been studied, there is a considerable degree of uniformity in their 
structure throughout the group. 

From my observations I conclude that the gills of Chlamydoselachus are of the usual 
elasmo branch type. In proportion to body size, the gill-clefts are unusually long (Text- 
figure 4); they are separated by very slender branchial arches. The widely-distensible 




Text-figure 81. 
Section, cutting parallel to branchial filaments, through second holobranch of Heptanchus maculatus. 

ad., adductor muscle; a/., third afferent artery; b.r., branchial ray cut short; csd., fourth dorsal constrictor muscle; eb., epi- 
branchial segment of cartilaginous branchial arch; efc.4-5, fourth and fifth efferent collector arteries; ex.b., extrabranchial 
cartilage; fi.a., anterior filament; fi.p., posterior filament; ib.d., dorsal interbranchial muscle; n., posterior division of the 

branchial nerve. 
After Daniel, 1934, Fig. 143. 



pharynx is adapted for the rapid expulsion of a large volume of water through the gill- 
clefts. This, in connection with the large respiratory surface afforded by the gill-filaments 
and particularly by their lamellae, makes an efficient mechanism for aerating the blood. 

A discussion of the question as to the phylogenetic significance of the unusually 
large number of gill-clefts and gill-arches in Chlamydoselachus and the notidanids would 
lead us too far afield. Considerable data regarding the number of gill-clefts, from Amphiox- 
us through the cyclostomes and fishes to the amphibian Cryptobranchus, is presented by 
Corrington (1930, pp. 246-251), together with a discussion of the subject from an evolu- 
tionary point of view. 

THE SPIRACLES 

The spiracles of elasmobranchs derive special interest from the fact that they arise 
through modifications of a primitive first pair of gill-slits (Text-figure 62, p. 388) which, in 
mammals, are represented by Eustachian tubes, tympanic cavities and external auditory 
meatuses. In elasmobranchs the modifications are almost entirely concerned with the 
regulation of the respiratory current, but the anatomical relations of certain parts presage 
their use in connection with organs of hearing. 



424 



Bashford Dean lAemorial Volume 



The following description of the spiracles of Chlamydoselachus is based on my four 
adult specimens, numbered I to IV respectively, of which the first three were dissected 
by me and the fourth was studied without dissection. 

The external spiracular apertures are ordinarily very small (Text-figures 70, p. 396; 
and 124, p. 489). With one exception to be described presently, they are mere sUts, 
from 1 to 3 mm . long. In my four specimens each aperture is situated in Hne with the 




Text-figure 82. 
Left internal spiracular aperture and cavity (x 1.5) of Chlamydoselachus. The boundaries 
of the cranium, hyomandibular, palatoquadrate, caecum and spiracular canal are indicated 

by broken Hnes. 

c.l, caecum; cr., cranium; hm., hyomandibular cartilage; i.s.c, internal spiracular aperture and cavity; l.p.i., 

Ugamentum postspiraculare inferior; ]5.q., palatoquadrate cartilage (upper jaw); s.c, spiracular canal. 

Drawn from specimen No. I in the collection of the American Museum of Natural History. 



spiracular division of the sensory canal system (Text -figure 124, p. 489), about 8 mm. 
from its anterodorsal end. In each case, the direction of the long axis of the sUt-Hke 
aperture coincides with that of the laterosensory canal. The lengths of the apertures in 
our four specimens are as follows: No. I, 3 mm. on each side; No. II, 2 mm . on the right 
side and 7 nun. on the left; No. Ill, 2 mm. on the right side and 1 mm. on the left; No. 
IV, 3 mm. on the right side and 2 mm. on the left. The exceptionally large aperture on 
the left side of No. II is not a slit, but an elHptical opening fully three milHmeters wide. 
The unusually small opening on the left side of No. Ill could not be found until a bristle 
had been inserted by way of the internal opening. It was overlooked entirely by Gudger 
and Smith (1933) w^ho also failed to identify as a spiracular opening the exceptionally 
large aperture on the left side of No. II, mistaking it for a perforation made by a hook. 

Each internal spiracular aperture or cavity (i.s.c.) is situated, in series with the gill- 
sHts, between the hyomandibular cartilage and the palatoquadrate (Text-figure 82, 



The Anatomy of Chlamydoselachus 425 

hm., pq.). In my four specimens these openings are very much aHke. They measure about 
20 to 25 mm. long and are about 12 mm. wide when the pharynx is fully expanded. Thus 
each internal spiracular aperture (i.s.c.) is large enough to admit a small finger. Its 
posteromedial and anterolateral margins are well defined; they converge toward the 
cranium and, when the pharynx is expanded, have the form of a furcula or "wishbone." 
The posteromedial margin is formed by a prominent ridge where a fold of the mucous 
membrane overlies a ligament (ligamentum postspiraculare inferior) extending along the 
ventral surface of the hyomandibular cartilage and connecting it with the cranium. The 
anterolateral margin is formed by a valvc'like fold or flap of the mucous membrane. 
There is no very definite ventrolateral margin, for here the inner surface of the pharynx 
slopes gradually into the spiracular cavity. This side lies toward the palatoquadrate. 
When the pharynx contracts, the posteromedial and anterolateral margins of the internal 
spiracular aperture approximate until the opening is reduced to a mere sht compressed 
between the hyomandibular and palatoquadrate cartilages. No doubt the opening may 
be completely closed by the contraction of the pharynx, but this can occur only after 
most of the water has been expelled from the pharynx. 

Each internal spiracular aperture leads into a broad cavity or sac, the internal 
spiracular cavity (Text'figure 82, i.s.c), which is no wider than its internal opening and 
is about 7 mm. deep in its deepest portion. The roof of this cavity lies in close proximity 
to the integument. By palpation I found that the overlying plate of tissues, covering 
not only the deeper portion of the cavity but also its sloping side toward the palatO' 
quadrate (Text'figure 82, p.q.), is decidedly thin. Evidently, it comprises Httle more than 
integument and mucous membrane which come almost into apposition. In its structure 
and in some of its relations this plate or membrane bears considerable resemblance to 
the tympanic membrane of an amphibian. However, this membrane is evidently not 
homologous with the structure described by Howes (1883) as the tympanic membrane 
in Raja. Forming the anteromedial end of the internal spiracular cavity, beneath a flap 
of mucous membrane, there is a pocket or caecum (c.l) which extends alongside the 
hyomandibular in an anteromedial direction for a distance of about 10 mm. Its distal 
end usually comes into contact with the auditory capsule of the cranium — a relation 
which is most interesting when we compare the internal spiracular cavity of Chlamy^ 
doselachus with the tympanic cavity of higher vertebrates. In three instances, I found 
in this caecum a large gelatinous mass, almost cartilaginous in consistency, which was 
easily removed. 

Before proceeding with the further description of the spiracle in my specimens 
I quote the following from Goodey (1910.1, p. 550), who appears to be the only author 
who has given any special attention to the spiracles of Chlamydoselachus: 

On removing the skin [of Chlamydoselachus] and carefully dissecting away the under' 
lying spongy cutis which covers the jaw muscles, it is seen that the lumen of the spiracle 
passes down into the oral cavity between the hyomandibular and the mandibular [sic] 
cartilages. Just inside the external opening, the cavity becomes enlarged and a short caecal 



426 Bashford Dean Memorial Volume 

diverticulum is given off anteriorly. This is overlaid by the levator maxillae muscle . . . 
The caecum extends as far forward as the anterior knob of the proximal end of the hyoman- 
dibular, which projects from the articular depression on the auditory capsule. It is not attached 
to the hyomandibular, but is separated from it by the hyoidean branch of the seventh nerve, 
which passes just internal and ventral to it. In all probabihty it is homologous with the 
more extensive caeca mentioned by Ridewood (1896) which have been described in other 
selachians by Miiller and Van Bemmelen. In Scyllium, for example, the caecum extends 
inwards over the hyomandibular and becomes firmly attached to the wall of the auditory 
capsule, being in some way concerned with the function of hearing. A similar caecum is 
found in Heptanchus, so that here we have another point in which Chlamydoselachus differs 
from this member of the Notidanidae. 

Text'figure 83. 
Anterolateral wall of the left pseu- 
dobranchial chamber and peripheral 
wall of the spiracular canal (x 3) 
of Chlamydoselachus, represented 
in one plane. 

p.f., pseudobranchial filament; s.c, spi- 
racular canal. 
Drawn from specimen No. I in the col- 
lection of the American Museum of 
Natural History. 



Along the posteromedial side of the deeper portion of the internal spiracular cavity, 
close to the hyomandibular, there is a narrow cleft with tumid Hps, about 13 mm. long 
and 5 mm. deep. This cleft (solidly black in Text-figure 82) is the pseudobranchial 
chamber. The anterolateral lip is decidedly serrate, the posteromedial Hp is slightly 
serrate. The pseudobranchial chamber will be further described presently. 

There is some variation in the manner in which the pseudobranchial chamber com 
municates with the external spiracular aperture. In specimen No. I, on the left side, 
a bristle inserted into the pseudobranchial chamber, anywhere along its length, passes 
posteromedially through a sHt-like aperture into the spiracular canal {s.c. in Text-figures 
82 and 83) which is compressed between the hyomandibular and the integument. The 
spiracular canal becomes narrower as it approaches the external spiracular aperture. On 
the right side, the pseudobranchial chamber communicates with the narrow spiracular 
canal only by way of a small round opening situated at the posterolateral end of the 
pseudobranchial chamber. In specimen No. II, on the left side, the external spiracular 
aperture is exceptionally large and leads directly into the pseudobranchial chamber. 
On the right side, the spiracular canal is hke that on the left side of No. I. In specimen 
No. Ill, which has unusually small external spiracular apertures, each pseudobranchial 
chamber opens into the slender spiracular canal by means of a very small aperture situated 
as it is on the right side of No. I. Thus I find, in my specimens, decided differences in 
the size of the spiracular canal in the region where it communicates with the pseudo- 




The Anatomy of Chlamydoselachus 427 

branchial chamber: and in one case, which I regard as anomalous since the external 
spiracular opening is very much larger than the others, the spiracular canal is absent. 

In specimen No. I a bristle inserted into either external spiracular opening passes 
anterolaterally, within the spiracular canal, to enter the pseudobranchial chamber. The 
distance from the external spiracular aperture to the pseudobranchial chamber is about 
10 mm., on each side. In specimen No. II, on the right side, a bristle inserted into the 
spiracular canal by way of the external spiracular aperture travels about the same distance 
and in a similar direction, before reaching the pseudobranchial chamber. In specimen 
No. Ill, on either side, only a very slender bristle could be inserted by way of the ex- 
ternal spiracular aperture, and this passed directly forward for a distance of about 5 mm. 
before entering the pseudobranchial cavity. By dissection I have opened the spiracular 
canals of specimens I, II, and III without finding anything of interest save a confirma- 
tion of my description based on exploration with a bristle. Their walls are smooth. 

The spiracular canal always lies just beneath the integument. Thus the external 
spiracular aperture is bordered, on the side toward the canal, by a somewhat flexible 
lip. In cases where the external opening is large enough to allow the passage of an 
appreciable amount of water, this lip may function as a valve preventing the intake of 
water through the spiracle while the pharynx is expanding. In my four preserved speci- 
mens the entire spiracular canal is very much flattened, since it is compressed between 
the hyomandibular cartilage and the integument. 

In the free-swimming sharks, the spiracles are not so highly speciali2;ed for purposes 
of respiration as in the skates and rays, which are bottom-dweUing forms. Concerning 
the function of the spiracles, Daniel (1934, p. 156) writes as follows: 

In the free-swimming sharks the current enters the mouth, from which it passes into 
the pharynx and into the gill-pockets, the external clefts, including the spiracle, at the same 
time remaining closed. The mouth then closes, the external clefts open, and the water is 
forced out. 

In the rays, which spend most of their time at the bottom and hence often in mud or 
sand, there is an interesting change in the direction of the current. In these the greater part 
of the current enters through the [large] spiracles and but little through the mouth. The 
valves of the spiracles then close and the water is forced out ventrally through the external 
branchial clefts. At the expulsion of the water the mouth does not entirely close, but only 
a little of the water is able to gain exit through it because of valves which are located on its 
roof and floor. 

In Squatina, a bottom-dwelling shark, the respiratory current is known to enter 
through the spiracles (Darbishire, 1907), though not exclusively (Daniel, 1934). From 
my observations on the structure of the spiracle in Chlamydoselachus it is obvious that 
this organ normally functions as in the free-swimming sharks and not as in Squatina. 
From the small si2;e of the external spiracular openings in Chlamydoselachus it is evident 
that very little water passes through them. 



428 Bashford Dean Memorial Volume 

In elasmobranchs the spiracle ordinarily differs from the gill'slits in never possessing 
gill'filaments, though it often has traces of these as a few small folds of the lining of its 
anterior wall, which constitute the pseudobranch or mandibular gill. AUis (1923, p. 
169) mentions pseudobranchial filaments in the "'spiracular canal" of Chlamydoselachus, 
but does not describe them. Goodey (1910.1, p. 550) writes of his specimens of Chlamy- 
doselachus: "'The pseudobranch in each spiracle consists of about ten short ridges, 
which lie on the anterior outer wall just inside the external aperture. In the Noti' 
danidae the pseudobranchs are said to be better developed than in any of the [other] 
selachians, so that in this respect we find Chlamydoselachus presenting a small difference 
from Heptanchus and Hexanchus.'" 

In my specimens I have distinguished a special chamber communicating with the 
internal spiracular cavity (i.s.c.) on the one hand and the spiracular canal (s.c.) on the 
other, which I call the pseudobranchial chamber (Text-figures 82 and 83). This chamber 
presents for examination two surfaces, anterolateral and posteromedial respectively. 
In specimen No. I each surface is about 13 mm. long (measured on the side toward the 
internal spiracular cavity) and 5 mm. wide (measured from the internal spiracular cavity 
to the beginning of the spiracular canal). Toward the internal spiracular cavity each 
of these surfaces is bounded by a distinct ridge or lip, decidedly serrate in the case of the 
anterolateral lip, only slightly so in the case of the posteromedial lip. The peripheral 
boundary is not so well defined, save in those cases where the two surfaces meet on the 
side toward the integument, leaving only a small round aperture leading from the postero- 
lateral end of the pseudobranchial chamber into the spiracular canal. In cases where 
the passage into the spiracular canal is large (as shown in Text-figures 82 and 83) the 
boundary between this chamber and the spiracular canal may be defined as the line where 
an abrupt change in direction occurs — for the pseudobranchial chamber lies along the 
anterolateral surface of the hyomandibular, the spiracular canal along its peripheral 
surface. 

On the anterolateral wall or surface of the pseudobranchial chamber, the pseudo- 
branchial filaments (Text-figure 83, p.f.) begin at regular intervals along the serrate lip 
and extend peripherally for a distance varying from 2 to 5 mm. The serrations corre- 
spond to the filaments — that is, the projections, which appear tooth-like when the lips of 
the pseudobranchial chamber are approximated, are seen to be the proximal ends of the 
folds or filaments when the chamber is opened to view. The pseudobranchial filaments 
are little more than mere ridges; the height of these filaments seldom exceeds 1 mm. 
and is never more than 1.5 mm. The longest filaments are usually those near the middle 
of the row. Some of the filaments — particularly those of the left pseudobranchial chamber 
of specimen No. II, which has the largest filaments — are free at their peripheral ends, 
where they project as finger-shaped structures as in the case of ordinary gill-filaments. 
The number of filaments composing each pseudobranch varies from eight to sixteen. 

So far as I know, a pseudobranch on the posteromedial surface of the pseudobranchial 
chamber has never been described in any elasmobranch. Nevertheless I find, on this 



The Anatomy of Chlamydoselachus 



429 



surface in some spiracles of my specimens, structures which may be vestiges of gill' 
filaments. These structures are low ridges, soft when palpated but not disappearing 
entirely when the mucous membrane is stretched at right angles to their long axes. They 
are spaced regularly, like gill'filaments. In number, position, length and direction they 
resemble the pseudobranchial filaments on the opposite side of the pseudobranchial 
chamber, but they are usually broader and are never so high. I suspect that if fresh 
specimens were available, the presence of vestigial gill'filaments on the posteromedial 
wall of the pseudobranchial chamber could be conclusively demonstrated. 

A pit or depression representing the ventral end of a primitive gill'cleft extending 
between the hyoid and mandibular arches has been described by Ridewood (1896) in 
Galeus, Carcharias, Zygaena, Triads and Chiloscyllium. It is faintly marked in Mus- 
telus, but is absent in Scyllium, ?{ptidanus and Acanthias. Concerning this pit or de' 
pression Ridewood writes as follows: 

If a line be drawn joining the lower ends of the pharyngeal apertures of the branchial 
clefts, it will pass through the lower or anterior extremity of the pit, just as a curved line 
joining the upper ends of the branchial clefts will, if produced, pass through the inner or supe- 
rior edge of the pharyngeal aperture of the spiracle. It is universally admitted that the 
spiracle of sharks represents only the upper part of the hyoid cleft, the middle and lower 
portions being obliterated. Hence, in this depression of the mucous membrane, is a structure 
which, in complete absence of evidence to the contrary, may be regarded as the internal or 
pharyngeal portion of the lower half of the hyoid cleft. 

In my four adult specimens of Chlamydoselachus I found, on each side of the floor 
of the pharynx, between the ceratohyoid and mandibular cartilages and directly ventral 
to the internal spiracular aperture, a large opening (Text-figure 84, v.g.c.) leading into 



Text-figure 84. 

Left internal spiracular aperture and vestigial 

gill-cleft (x 0.86) of Chlamydoselachus in their 

relation to each other and to the adjoining 

cartilages. 

hr.c.l, first gill-cleft, showing the demibranch attached to 
the hyomandibular and ceratohyoid cartilages; br.c.2-3, 
second and third gill-clefts; c.l, caecum of the internal 
spiracular cavity; c.2, caecum of the vestigial gill-cleft; 
ch, ceratohyoid cartilage; cr, cranium; i.s.c, internal 
spiracular aperture and cavity; hm, hyomandibular 
cartilage; l.p.i., ligamentum postspiraculare inferior; 
m, mandible or Meckel's cartilage; pq, palatoquadrate; 
s.c, spiracular canal; v.g.c, vestigial gill-cleft. 

Drawn from specimen No. I in the collection of the 
American Museum of Natural History. 




430 Bashford Dean Memorial Volume 

a pocket or caecum. This, like the pit or depression mentioned by Ridewood, is evidently 
a vestige of the ventral end of a primitive gill'cleft. Although Ridewood was careful to 
describe the relations of the pit or depression studied by him, he does not give any descrip' 
tion of the pit itself further than that implied in the terms used. I infer that the pit or 
depression examined by Ridewood is so simple that it does not need any further descrip' 
tion. In Chlamydoselachus the opening is in series with the ventral ends of the branchial 
clefts. In my four specimens it is from 8 to 15 mm. long and is bordered on the lateral 
side (toward the mandible) by a crescentic valve4ike flap or fold of the mucous membrane. 
The medial side has no definite boundary. The opening leads into a shallow cavity or 
caecum (Text-figure 84, c.2) extending beneath the flap posteriorly and laterally for 
a distance of from 3 to 5 mm., anteriorly for a distance of from 5 to 20 mm. Its average 
extension anteriorly is about 12 mm., as shown in the figure. The structure and relations 
of this cavity leave no doubt that it is a persistent ventral portion of a primitive gill' 
cleft originally continuous with the dorsal portion now represented by the spiracle. 
This primitive gill-cleft was bordered on the anterior side by the elements comprising 
the jaw-cartilages, on the posterior side by the hyoid arch represented by the ceratohyoid 
and the hyomandibular cartilages. 

Since writing the preceding paragraph and preparing the accompanying illustrations, 
(Text-figures 82 and 84), I have found in the midst of a description by AUis (1916, pp. 
110-111) of the mandibular artery of Chlamydoselachus, the following account of a some- 
what similar pocket in the lining of the oropharyngeal cavity of his specimen : 

This latter branch [of the arteria mandibularis], on both sides of the head of this speci- 
men, passes immediately anterior to a relatively deep tubular pocket, or recess, of the lining 
membrane of the mouth cavity which, beginning slightly posterior to the angle of the gape, 
extends dorsoposteriorly toward the quadrato-mandibular articulation. This pocket lies 
along the external surface of the hind end of the palatoquadrate, between that cartilage and 
those fibers of the musculus adductor mandibulae that pass uninterruptedly from the upper 
to the lower jaw. Posteriorly it ends blindly, its blind end being attached to ligamentous 
tissues which, continuing on in the line prolonged of the pocket, are attached to the hind 
(distal) end of the palatoquadrate. The pocket thus lies morphologically anterior to the 
palatoquadrate, in the relation to that cartilage that a persisting remnant either of the mandib- 
ular cleft or of a premandibular cleft would have, and its position, posterior to the musculus 
mandibulae, is not unfavorable to its being a remnant of either of those clefts, for the adductor 
muscle, if it be derived from the superficial constrictor of the mandibular arch, could readily, 
when it slipped from the external (actually posterior) edge of the arch on to its anterior 
(actually lateral) surface, have acquired a position superficial, and hence morphologically 
anterior, to the pocket. A branch of the artery is sent posteriorly, on either side of the 
pocket, to the adductor muscle. 

It is evident, upon comparing this description with Text-figure 84, that the pocket 
described by AUis does not have the same anatomical relations as the one described and 
figured by me. 



The Anatomy of Chlamydoselachus 431 

THE UROGENITAL SYSTEM 

In Chlamydoselachus, as in other vertebrates, the urogenital system comprises two 
functionally distinct parts, the excretory system and the reproductive system; but these 
are so closely related developmentally and anatomically, especially in the male, that it 
is often convenient to refer to them collectively. 

UROGENITAL SYSTEM OF THE FEMALE 

Since the literature on the urogenital system of Chlamydoselachus is very meager, 
the following account is based mainly on my own observations and drawings which were 
made from four large specimens: Nos. I, II and III collected in Japan by Dr. Bashford 
Dean and now in the American Museum of Natural History, and another specimen 
(No. IV) kindly lent by Dr. E. Grace White. All four specimens are females. References 
to the work of other investigators are made throughout the text. Brohmer's (1908) 
account of the excretory system of an embryo of Chlamydoselachus deals with an early 
stage and need not be considered here. 

UROGENITAL SINUS IN THE FEMALE 

In some elasmobranchs the expression"urogenital sinus" is hardly applicable to the 
female, but in the case of Chlamydoselachus I can see no reason for avoiding the use of this 
convenient term. In all my specimens the urogenital portion of the cloaca is quite plainly 
marked off from the rectal portion, though the distinction is most clear-cut in the decidedly 
immature specimen. 

In this specimen (No. IV) a small aperture (Text-figure 85, ug.s.), situated on the 
dorsal surface of the rectal portion of the cloaca, leads into the urogenital sinus which 
extends in an anterodorsal direction for a distance of about 13 mm. The urogenital sinus 
must be examined by dissection. It is about 10 mm. wide, but its opening into the rectal 
portion of the cloaca has a width of only 5 mm. On each side of the sinus, near its anterior 
end, there is an opening from the uterine portion of an oviduct. The urinary papilla is 
a longitudinal fluted ridge, free at its posterior end, situated on the dorsal surface of the 
sinus a little to the left of the median line. The urethral aperture, a narrow slit not more 
than 3 mm. long, is located near the center of the papilla. No urethral orifice could be 
found on the right side of this specimen. 

In specimen No. Ill, which is nearly mature, the urogenital sinus (shown without 
a label in Text-figure 86) is still sharply marked off from the rectal portion of the cloaca, 
though its opening is much larger than in specimen No. IV. The orifices of the uteri 
are not shown in the figure since they open into the anterior portion of the urogenital 
sinus, which lies dorsal to the rectal cloaca. The opening of the right uterus is large 
enough to admit a finger; the left is much smaller. The urinary papilla is a broad ridge, 
not well defined, on the dorsal surface of the urogenital sinus. The single urethral 
orifice is a round pore (ur.p.), readily admitting a probe. It is situated near the center 
of the dorsal surface of the urogenital sinus, but a trifle to the left. 



432 



Bashford Dean lAemorial Volume 



In specimen No. I, which is fully mature, the urogenital sinus (Text'figure 87) is 
still slightly constricted where it joins the rectal portion of the cloaca, but the openings 
of the uteri are readily visible and are indicated by line^shading in the figure. The right 
uterus has a much larger opening than the left. There are two urethral pores (ur.p.), 
right and left, and these are situated close together near the posterior end of the dorsal 




Text-figure 85. 



Text-figure 86. 



Urogenital system of the female ChlamydoseP 
achus, ventral views, one-fifth natural size. 

Text-figure 85. Urogenital organs of a specimen 

1398 mm. long. The excretory ducts are 

concealed by the oviducts. 

ah. p., abdominal pore; m., mesonephros; ovd., oviduct; 
ovy., ovary; r.cl., rectal portion of the cloaca; ug.s., open- 
ing from the urogenital sinus; v.l., ventral ligament of 

the oviduct. 

Drawn from specimen No. IV in the American Museum 

of Natural History. 



Text-figure 86. Urogenital organs of a specimen 
1550 mm. long. The shell glands and the 
adjacent portions of the oviducts are displaced 
laterally, and the excretory ducts are not shown. 

ab.p., abdominal pore; m., mesonephros; ovd., oviduct; 
ovy., ovary; r.cl., rectal portion of the cloaca; s.g., shell 
gland; ur.p., urethral pore; ut., uterus; v.]., ventral ligament 

of the oviduct. 

Drawn from specimen No. Ill in the American Museum 

of Natural History. 



surface of the urogenital sinus. The right urethral aperture is decidedly smaller than the 
left and is situated a little further posteriorly. There is no urinary papilla. 

In specimen No. II, which is fully mature, almost the entire urogenital sinus (Text- 
figure 88) seems built around the very large opening of the right uterus, indicated by line- 
shading in the figure. In the hardened condition of the material, this opening is still 
large enough to admit a thumb. The opening of the left uterus is much smaller. There 
are two urethral orifices, right and left, situated about 4 mm. apart near the center of the 
dorsal surface of the urogenital sinus. The right urethral aperture (ur.p.) is somewhat 



The Anatomy of Chlamydoselachus 433 

smaller than the left. There is no urinary papilla. The rectal portion of the cloaca is 
very short. 

A ventral view of the cloaca of Carman's (1885.2) adult female specimen of Chlamy 
doselachus is shown in his PI. XII, reproduced here as Text'figure 89. There is no line 
of demarcation between urogenital and rectal portions of the cloaca (cL). There is only 



Urogenital system of the female Chlamydo' 

selachus, ventral views, one-fifth natural size. 

The shell-glands and the adjoining portions of 

the oviducts are displaced laterally. 

Text-figure 87- Urogenital organs of a speci- 
men 1350 mm. long. The right uterus and 
ovary are incomplete. 

ah. p., right abdominal pore (the left is closed superfici- 
ally); c.t., collecting tubule; m., mesonephros; mes.i., 
mesonephric duct; mso., mesovarium; ond., oviduct; ovy., 
ovary; r.cl., rectal portion of the cloaca; s.g., shell gland; 
ur.p., urethral pores; ut., uterus; v.l., ventral Hgament 

of the oviduct. 

Drawn from specimen No. I in the American Museum 

of Natural History. 



Text-figure 88. Urogenital organs of a speci- 
men 1485 mm. long. A segment has been 
excised from the right uterus, and the right 
ovary is incomplete. The excretory ducts are 
not shown. 

ah. p., abdominal pore; m., mesonephros; ovd., oviduct; 
ovy., ovary; r., rectum; s.g., shell gland; ur.p., urethral 
pores; ut., uterus; v.l., ventral ligament of the oviduct. 
Drawn from specimen No. II in the American Museum 
of Natural History 




Text-figure 87- 




Text-figure 



one urethral aperture; this (u.a.) is rather large and its position is median. Carman 
states that "there is no appearance of a urethral papilla ; the anterior border of the opening 
is inflated into a flap or valve, which closes the opening against objects passing outward 
through the cloaca, or better, which is made to close it by the object themselves." 

Hawkes (1907) has represented the cloaca of her female specimen of Chlamydoselachus 
by a diagram which is reproduced as my Text'figure 90a. She notes that there are two 



434 Bashford Dean Ts/lemorial Volume 

small cloacal apertures (U.S.l) for the urinary sinuses {U.S.) of which only the one on 
the left side is shown. These apertures are situated close to the median line near the 
posterior border of the cloaca. She states further that in the female the rectal aperture 
(R.) is displaced to the right. The opening of the right oviduct (R.Ov.) is much larger 
than the left {L.Ov.), and appears to crowd the latter anteriorly. This, perhaps, explains 
the displacement of the rectal opening to the right. 




Text-figure 89. 
Ventral view of cloaca, pelvis and pelvic fin cartilages of a female Chlamydoselachus. 

ah. p., abdominal pores; bf)., basipterygium; c!., cloaca; u.a., urethral aperture. 
After Garman, 1885.2, PI. XII. 

ORGANS OF EXCRETION IN THE FEMALE 

The organs of excretion in the female Chlamydoselachus consist of a pair of meso' 
nephroi or functional kidneys, numerous collecting tubules, a pair of mesonephric ducts 
or Wolffian ducts, and a pair of urinary sinuses or functional bladders which are formed 
by the enlargement of the posterior portions of the mesonephric ducts. In each of my 
four specimens, the two urinary sinuses are entirely separate structures. 

The Mesonephroi. — In my four female specimens, the mesonephroi are a pair of 
slender flattened organs (m. in Text 'figures 85 to 88) extending through about 87 per cent 
of the total length of the body cavity (Tables II and III). Posteriorly, the mesonephroi 
begin dorsal to the posterior margin of the rectal portion of the cloaca, save in specimen 
No. IV where they begin as far back as the urethral orifice. Thus the mesonephroi do 
not begin at the extreme posterior limit of the body cavity, which extends farther caudad 
dorsally than it does ventrally. Dorsally, the body cavity extends as far back as the ex' 
ternal openings of the abdominal pores, which are situated ventrally. The members of 



The Anatomy of Chlamydoselachus 



435 



a pair of mesonephroi are usually of equal length, but in specimen No. II (Text'figure 88) 
the left mesonephros is shorter than the right. In most cases the mesonephroi thin 
out so gradually at the anterior end that the anterior limit can be made out only after a 
careful examination. 




F.I). 



LT.S. 




RA. 



A.P.- 



Text'figure 90. 
Diagrammatic figures of the cloaca in female (A) and male (B) .specimens 

of Chlamydoselachus. 
A.P., closed abdominal pore; Bl., so-called bladder (urogenital sinus); L.Ov., left oviducal open- 
ing; R., rectum; R.A.P., functional right abdominal pore; R.G., opening of rectal gland into 
the rectum; R.Ou., right oviducal opening; R.S., seminal vesicle; Ug., urogenital opening; 
Ur., opening of ureter into urogenital sinus; U.S., urinary sinus of female (one sinus is omitted 
from the drawing); V.S.I, openings of urinary sinuses into the cloaca; V.D., vas deferens 

(ductus deferens). 
After Hawkes, 1907, second text-figure, p. 476. 

In Table II are shown the lengths of the mesonephroi in my specimens, together 
with the ''over'all" length of the body and the total length of the body cavity. In Table 
III the ratios of length of mesonephros to body length and to length of the body cavity 
are expressed in percentages. From an inspection of Text'figures 85 to 88 it will be seen 
that specimen No. IV is sexually immature, No. Ill is nearly mature, while Nos. I and 
II are fully mature. The variations shown in Tables II and III are too small to be signif- 



TABLE II 



Length in millimeters of the mesonephros of the female Chlamydoselachus compared with the total 
length of its body and the entire length of its body cavity. The specimens are arranged in the order of 
sexual maturity. 



Specimen Number 


IV. 


III. 


I. 


II. 


Total Length of Body 
Length of Body Cavity 
Length of Mesonephros 


1398 
554 
486 


1550 
634 
554 


1350 
588 
518 


1485 
686 
605* 



*This applies to the right mesonephros only. In this specimen the left mesonephros is shorter; its 
length is 541 millimeters. 



436 



Bashford Dean Memorial Volume 



TABLE III. 



Length of the mesonephros in proportion to the total body length and to the entire length of the body- 
cavity, in four female specimens of Chlamydoselachus, shown in percentages. The specimens are arranged 
in the order of sexual maturity. 



Specimen Number 


IV. 


in. 


I. 


II. 


Length of Mesonephros 
Total Body Length 
Length of Mesonephros 
Length of Body Cavity 


34.7 
87.7 


35.7 
87.3 


38.3 
88.0 


40.7 
88.1* 



*Percentage computed from the right mesonephros only. 

icant of either developmental or retrogressive changes. Therefore I conclude that there 
is no appreciable change in the length of the mesonephros proportional to body length 
or to the length of the body cavity, within the age limits represented by my specimens. 
From dissections, one gets the impression that the mesonephroi originally extended 
a Httle further forward, since vestiges of these organs appear in front of the unequivocal 
portions represented in the figures. In any event, the length of the mesonephros in the 
female Chlamydoselachus is remarkable. In many of the more highly differentiated 
elasmobranchs (e.g., the skates) only the posterior portion of the female mesonephros 
persists in the adult. In Chlamydoselachus, the presence of the mesonephros through- 
out almost the entire length of the body cavity of the female must be accounted a 
primitive character. 

Throughout their entire extent, the mesonephroi lie against the dorsal body wall, 
close to the median Hne. At their posterior ends they are actually united, but they 
diverge a Httle anteriorly. Therefore, along the greater part of their course they He 
along the low ridge formed by the vertebral column, but at their anterior ends they 
depart sHghtly from this ridge. In specimens TV, III and I, the mesonephroi He almost 
flat against the dorsal body wall; therefore in Text 'figures 85, 86 and 87, which are drawn 
from these specimens, the mesonephroi are shown very nearly in broad view. Variations 
in the width of the mesonephroi are fairly well shown in these figures. In specimen No. 
Ill, which has the largest mesonephroi, each mesonephros has a maximum width of 13 mm. 
In specimen No. II (Text-figure 88), within the posterior half of the body cavity the 
mesonephroi are approximated to such a degree that the surfaces ordinarily dorsal are 
medial. Hence, in a ventral view, the mesonephroi are seen almost on edge, so that 
their actual width is not fully represented in the figure. In the anterior half of the body 
cavity of No. II, the mesonephroi gradually become flattened against the body wall as 
they diverge anteriorly. 

There is considerable variation in the extent of union of the mesonephroi at their 
posterior ends. In specimen No. IV the two mesonephroi are united across the median 
plane for a distance of about 80 mm. measured from their posterior ends; in No. Ill, 



The Anatomy of Chlamydoselachus 437 

for a distance of 70 mm.; in No. I, for about 100 mm.; while in No. II they are united 
for a distance of 296 mm. In this respect, as in some others already noted, the mesonephroi 
of specimen No. II are atypical. 

In general, the mesonephroi are thickest at their posterior ends, where each meso' 
nephros (considered as a separate entity) has a maximum thickness equal to about one- 
third its width. Anteriorly, the mesonephroi become thinner very gradually. No. IV 
is exceptional in that the caudal portion of each mesonephros, for a distance of 15 mm. 
measured from its posterior end, is abruptly thicker than the part immediately in front 
of it. This caudal portion has a thickness equal to about two-thirds its width. 

Since the mesonephroi are entirely retroperitoneal, they come into actual contact 
with the peritoneum only by their broad ventral or ventrolateral surfaces. Wherever 
the mesonephroi are approximated, they lie close to the base of the dorsal mesentery, 
which extends along the dorsal median Hne for the entire length of the body cavity. 
The dorsal mesentery gives rise, laterally, to special mesenteries supporting the oviducal 
organs and the ovaries; ventrally, to a continuous median mesentery supporting the 
digestive tube excepting the posterior four -fifths of the valvular intestine and the entire 
rectum. The mesenteries related to the mesonephroi and to the oviducal organs are 
particularly important, since these mesenteries contain the collecting tubules and the 
mesonephric ducts. 

In order to investigate the microscopic structure of the mesonephros and the relations 
of the right and left mesonephroi to each other, transverse serial sections were cut from 
segments taken at intervals along the length of these organs in all my specimens. In 
every case the material was found to be in very poor condition for histological study, but 
mesonephric tubules and glomeruli were readily identified. In the region of union, the 
two mesonephroi are sometimes connected by renal tissue, but more often by what 
appears to be lymphoid tissue. 

Since the mesonephroi are seldom, if ever, disturbed when newly-captured specimens 
are eviscerated by fishermen, it seems strange that there is so Httle recorded concerning 
them. CoUett (1897) describes the mesonephroi of his large female specimen as follows: 
"The kidneys were also very long, the right being the longer (length 780 mm.) and rather 
flat, the left being more cylindrical, and of a length of 770 mm. Posteriorly, both kidneys 
form a club-shaped, thickened, coalescent portion terminating somewhat abruptly toward 
the anus. The length of the coalescent portion is 120 mm." The only additional descrip- 
tion of the ""kidney" of Chlamydoselachus that I have found is that of Hawkes (1907, p. 
477), virhich reads as follows: 

The kidney in the female [Chlamydoselachus] is thin dorsoventrally and of irregular 
breadth. It extends from the region of the oviducal gland to the end of the body cavity, 
gradually widening as it passes backward in a sinuous line. The sinuosity is due to the 
arrangement of some of the dorsal muscles. Cephalad to the kidney and apparently uncon- 
nected with it, there is an irregular body (1.5 cm.) which extends somewhat beyond the end 
of the abdominal cavity. This is probably the head kidney (pronephros?) which in the adult 
has retained its position in the region to which the coelome extended in the embryo. 



438 Bashford Dean Memorial Volume 

In the absence of any statements to the contrary, it may be assumed that the "kidney'" 
of Hawkes' specimen was a paired structure, and that the two, more or less separate, 
members were of equal length. As already noted, in one of my specimens (and less 
significantly in CoUett's large specimen) the left mesonephros is shorter than the right. 
This does not necessarily mean a decrease in function of the left mesonephros, since 
a shortening of the thin anterior end might readily be compensated by a hardly noticeable 
increase in thickness posteriorly. A concentration of the adult female mesonephros into 
a compact organ situated in the posterior part of the body cavity is characteristic of the 
highly specialized elasmobranchs. 

Concerning the mesonephroi of the female Heptanchus, Daniel (1934, p. 287) writes 
as follows: ''Each kidney extends as a narrow ribbon of tissue from the pericardio- 
peritoneal septum posteriorly one-half the length of the body cavity; back of this it 
broadens out and becomes much thicker so that the main mass of the tissue lies posterior 
to the region of the superior mesenteric artery." From an inspection of Daniel's figures 
it appears that the broadening of the posterior part of the "kidney" is rather abrupt, not 
gradual as in the case of Chlaynydoselachus. The assertion that the kidney of the female 
Heptanchus extends from the pericardio-peritoneal septum is hardly understandable in 
view of DaniePs statement (p. 289) that the kidney of the male extends farther forward 
than that of the female. 

The Urinary Sinuses. — In specimen No. IV, which is immature, a probe inserted 
through the urethral orifice passes in one direction (anterodorsally) only, for a distance 
of about 10 mm. The slender cavity thus explored is the rudimentary left urinary sinus. 
Its posterior half is imbedded in the thick dorsal wall of the urogenital sinus, while its 
anterior half lies in a thick portion of the dorsal mesentery supporting the two uteri 
which are joined by their medial walls for a distance of 50 mm. anterior to the urogenital 
sinus. The left mesonephric duct, too small to be probed but clearly visible with a hand 
lens, extends anteriorly from the left urinary sinus along the base of the dorsal mesentery 
close to the left mesonephros. There is a right urinary sinus, of the same size as the left 
and in a corresponding position. Anteriorly, it is continuous with the right mesonephric 
duct which lies alongside the left; but I could not find any opening from the right urinary 
sinus into the urogenital sinus, either by way of the urethral orifice which serves as an 
outlet for the left mesonephric duct, or otherwise. The right urinary sinus was found 
by dissection, using the right mesonephric duct as a guide. I could not find any aperture 
connecting the two urinary sinuses, which are separated by a thick septum. 

In specimen No. Ill the two urinary sinuses (Text-figure 91a), right and left, lie 
close to the median plane. The left urinary sinus extends 75 mm. anterior to the urethral 
orifice. Near its posterior end this sinus is broad but shallow; its greatest width is 
9 mm. For a distance of 25 mm. from the urethral orifice, the expanded posterior portion 
of the left urinary sinus lies within the dorsal and left lateral wall of the urogenital sinus. 
Here, only the medial border of the left urinary sinus comes into relation with the dorsal 
mesentery which connects the urogenital sinus with the dorsal body wall and with the 



The Anatomy of Chlamydoselachus 



439 



mesonephroi. Anteriorly, the left urinary sinus gradually diminishes in caliber as it 
extends within the dorsal mesentery close to the uteri which are united by their medial 
walls for a distance of 40 mm. in front of the urogenital sinus. At 75 mm. from the 
urogenital orifice, the left urinary sinus tapers rather abruptly to become continuous with 
the left mesonephric duct which extends forward in the dorsal mesentery. The right 
urinary sinus is apparently cystic, and was found by dissection. It begins as far poste- 
riorly as the left urinary sinus, but is only 60 mm. long and 8 mm. wide in its widest 
portion. Its relations to the wall of the urogenital sinus and to the dorsal mesentery are 



Text'figure 91. 
Urinary sinuses (ventral views, three- 
fifths natural size) of three female 
specimens of Chlamydoselachus: A, 
specimen No. Ill; B, No. I; C, No. II. 
In order to show the correct propor- 
tions, the outlines are drawn as if the 
sinuses were spread in a horizontal 
plane. 

Drawn from specimens in the American 
Museum of Natural History. 




similar to those of the left urinary sinus. While the left urinary sinus readily admits 
a probe by way of the urethral pore, and the probe continues into the left mesonephric 
duct, no opening for the right urinary sinus could be found in any direction. 

Specimen No. I has a pair of well-developed urinary sinuses (Text-figure 91b) 
situated close to the median plane but lacking any direct communication with each other. 
In this specimen the two uteri are united by their medial walls for a distance of 50 mm. 
in front of the urinary sinuses, hence are supported, in this region, directly by the 
dorsal mesentery. The relations of the urinary sinuses to the wall of the urogenital 
sinus and to the dorsal mesentery are the same as in specimen No. Ill, save that here the 
urinary sinus of the right side is confined to the dorsal mesentery. Each urinary sinus 
connects posteriorly with its short urethral pore, through which it may be probed. The 
urinary sinus of the left side is larger than the corresponding sinus of No. Ill; it is about 
90 mm. long, and 10 mm. wide throughout more than half its length. The posterior end 
narrows abruptly, the anterior end so gradually that its Hmit must be determined some- 
what arbitrarily. The sinus is continuous anteriorly with the left mesonephric duct 
which was probed more easily than that of No. III. The right urinary sinus is sHghtly 
smaller than the left. It is 85 mm. long, and 8 mm. wide throughout its middle third; 



440 



Bashford Dean Memorial Volume 



it tapers gradually both anteriorly and posteriorly. Anteriorly, the right urinary sinus 
is continuous with the right mesonephric duct which was easily probed. 

In Specimen No. II the urinary sinuses (Text-figure 91c) are well developed and are 
situated close to the median plane. As in the other specimens, they are not united to 
form a single functional bladder. Each urinary sinus connects posteriorly with a short 
urethral pore, through which it may be probed. The two uteri are united by their medial 
walls for a distance of 50 mm. in front of the urogenital sinus, and so have a common 
dorsal mesentery. The relations of the urinary sinuses to the urogenital sinus and to the 




Text-figure 92. 

Longitudinal section through cloaca and right oviduct of Chlamydoselachus, 

three-fourths natural size. The dorsal side is uppermost. 

ab-p, abdominal pore; cl, cloaca; int, intestine; ov, oviduct; p, caecal pouch, or rectal gland; ua, 

urethral aperture. 
After Garman, 1885.2, Fig. 2, pi. XIX. 

dorsal mesentery are much the same as in specimen No. III. The left urinary sinus is 
only 50 mm. long, but it is comparatively broad, having a maximum width of 10 mm. 
The left mesonephric duct could not be probed. The right urinary sinus is about 100 
mm. long. It has a maximum width of 7 mm., but there is an abrupt constriction in its 
posterior third. In its anterior half it tapers very gradually to become continuous with 
the right mesonephric duct, which was probed for a distance of 20 mm. in front of the 
urinary sinus. 

In the well-developed urinary sinuses of specimens III, I, and II, the direction of 
greatest width is determined by the relations to the urogenital sinus and to the dorsal 
mesentery. In most cases by far the greater portion of the urinary sinus is imbedded in 
the dorsal mesentery, and the direction of greatest width of the sinus is therefore mainly 
dorsoventral. In Text-figure 91 some liberties have been taken with the anatomical 
relations in order to show the full width of the urinary sinuses. 



The Anatomy of Chlamydoselachus 441 

Garman (1885.2) states that in his (female) specimen of Chlamydoselachus the 
"ureters" unite before reaching the cloaca, into which they empty by means of a single 
aperture. From an inspection of his figure reproduced as my Text'figure 92, it appears 
probable that the so'called ureters are large mesonephric ducts which unite before reaching 
the single urethral opening. The fused portion may be considered a rudimentary urinary 
sinus. 

Concerning the urinary sinuses of Chlamydoselachus, Hawkes (1907, p. 477), whose 
observations were apparently made on a single specimen, writes : 

Each [urethral] aperture passes into an expanded chamber [U.S., my Text-figure 90a, 
after Hawkes] with laminated walls, the lumen of which has a diameter of 5 mm. in the 
cloacal region. The first portion of the sinus is imbedded in the thick cloacal walls. Each 
sinus extends forward for a distance of 6 cm. beyond the cloaca along the inner side of the 
kidney, but in front of this point it lies near the oviduct, at a distance from the kidney varying 
from 1 to 2 cm. 

A survey of the specimens described to date indicates that paired urinary sinuses, 
opening into the urogenital sinus by separate urethral apertures, are typical for the female 
Chlamydoselachus. Nevertheless, there is marked variability. The rudimentary median 
urinary sinus, or posterior fused portion of the mesonephric ducts, described by Garman, 
is anomalous. It illustrates one method by which a single median bladder, opening by 
a single urethral aperture, might be evolved. In my specimens, I find two instances 
(Text'figures 91a and b) where the right urinary sinus is smaller than the left, and one 
instance (Text'figure 91c) where the right urinary sinus is irregular in shape. In two 
instances (specimens IV and III) a right urethral aperture could not be found, while in 
two others (Nos. I and II) the right urethral aperture is smaller than the left. In No. Ill 
no connection of the right urinary sinus with a mesonephric duct could be found. To 
offset these deficiencies of the right urinary sinus and its openings there is but one instance 
of similar deficiency on the left side: in No. II a probe could not be passed from the left 
urinary sinus into the left mesonephric duct, though the latter is of normal si^e. It is 
evident that the urinary sinus and also the urethral pore of the right side are much more 
likely to be defective. That genetic factors are involved is probable from the condition 
in specimen No. IV, which is quite immature, and in No. Ill, which is not fully mature. 

In Heptanchus maculatus (Daniel, 1934) there is ordinarily a single median urinary 
sinus, but in one specimen two urinary sinuses, right and left respectively, were found. 
I have been unable to find any other instances, except in Chlamydoselachus, of a pair of 
urinary sinuses opening separately into the urogenital sinus of an elasmobranch. In the 
Myxinidae, the mesonephric ducts are said (Sedgwick, 1905) to open separately into the 
urogenital sinus, but in Petromyzon these ducts join to discharge their fluid through 
a single pore. In vertebrate embryos, the mesonephric ducts open separately. The 
condition found in Chlamydoselachus is probably primitive in a phylogenetic sense, 
but may be due to arrested development. 



442 Bashford Dean Memorial Volume 

Mesonephric Ducts and Collecting Tubules. — In specimen No. IV, which is 
immature, the mesonephric ducts are so slender that they are barely visible to the naked 
eye, but with the aid of a dissecting lens they were easily recognizjed. They were identi' 
fied also in transverse serial sections of the urogenital system taken at distances of ap' 
proximately 25 mm., 140 mm. and 400 mm. from the posterior ends of the mesonephroi. 
In all three regions the mesonephric ducts lie side by side — at 25 mm. and 140 mm., 
close together within the dorsal mesentery; and at 400 mm., some little distance apart, 
within the very narrow special mesenteries supporting the oviducts. The mesonephric 
ducts are of equal si2,e. Collecting tubules were not positively identified. 

In specimen No. Ill the left mesonephric duct was probed for a distance of 25 mm. 
from the left urinary sinus, and was bristled for an equal distance further. Throughout 
this posterior 50 mm. of its course, it runs in the narrow dorsal mesentery. Due, perhaps, 
to the poor preservation of the material, the duct could not be satisfactorily traced 
further. No duct connected with the right urinary sinus could be found by dissection. 
Collecting tubules could not be identified. A segment of the dorsal mesentery taken 
about 100 mm. in front of the urethral pore was sectioned transversely. The sections 
show two mesonephric ducts, side by side, but of unequal si2,e. The right duct is the 
smaller, and in places is almost obliterated. 

Of my four specimens. No. I (Text-figures 87 and 93) is most favorable for the study 
of the duct system. The left mesonephric duct (mes.d.) was easily probed, by way of the 
left urinary sinus, for a distance of about 80 mm. in front of the urinary sinus. Through- 
out this distance it runs in the dorsal mesentery; but just where the probe fails to 
penetrate, the duct leaves the dorsal mesentery to enter the special mesentery supporting 
the left uterus. In its further course the duct is quite conspicuous and it was easily 
traced almost to the anterior end of the mesonephros. In the anterior third of the body 
cavity, the duct again courses in the basal portion of the dorsal mesentery. The right 
mesonephric duct has a similar distribution. It was probed for 80 mm. from the right 
urinary sinus, but in general it is not quite so well developed as the left duct. Where 
the two ducts course together in the dorsal mesentery they do not lie side by side. Poste- 
riorly, the left duct is immediately dorsal to the right; anteriorly, the left duct is some 
little distance ventral to the right. Collecting tubules (c.t.) entering the right duct are 
about as numerous as those entering the left duct. All the tubules incline forward as 
they course ventrad from the mesonephroi to the ducts. In the dorsal mesentery the 
tubules leading to right and left ducts respectively are roughly alternate in position. 

Since the mesonephroi extend posteriorly much farther than the mesonephric ducts, 
the question arises whether any collecting tubules from the posterior end of a mesonephros 
enter the urinary sinus directly instead of by way of the mesonephric ducts. In the vicin- 
ity of the urinary sinus the dorsal mesentery is rather thick and quite opaque, so that 
it is difficult to determine whether collecting ducts are present. Nevertheless, two or 
three collecting tubules were found entering the anterior end of each urinary sinus, as 
shown for the right side in Text-figure 93. 



The Anatomy of Chlamydoselachus 443 

Transverse serial sections of the excretory system of specimen No. I were taken from 
a region near the center of the body cavity, where the mesonephric ducts course in the 
oviducal mesenteries; also from a region just posterior to the shell glands, where the ducts 
run in the dorsal mesentery. In each case the right duct is decidedly smaller than the 
left. In these sections of the mesenteries, the collecting tubules have much thicker walls 
than the arteries and veins; so it is unlikely that, in dissections, any blood vessels were 
mistaken for collecting tubules. 

In specimen No. II, due to poor preservation and excessive mutilation of the mesen' 
teries, only fragmentary portions of the mesonephric ducts and collecting tubules could 
be found. In their si2;e and distribution these portions conform to the general plan revealed 
in my other specimens, particularly in No. I. 

mes. (L. 

oud.mes. 



ct. r.m,. 

Text-figure 93. 

Excretory organs of the right side of a female C\i\avivjA.osdac\vxi in right lateral view, one-fourth 

natural size. The broken line, indicates the junction of the dorsal mesentery with the oviducal 

mesenteries. The ventral region is uppermost. 

ex., collecting tubule; mes.d., mesonephric duct; ovd.mes., line of attachment of the right oviducal mesentery to the 

right oviduct; r.m., right mesonephros; r.u.s., right urinary sinus. 

Drawn from specimen No. I in the American Museum of Natural History. 

The posterior portions of the mesonephric ducts of Carman's specimen (1885.2) 
are illustrated in my Text'figure 92. In this figure, as already noted in my account of the 
urinary sinuses, the mesonephric ducts are shown uniting to form a single large duct 
posteriorly. Hawkes (1907) states that in the female C\Aa'my&os,dac}\us: "The same 
mesentery which supports the oviduct also supports the urinary sinus and the mesone- 
phric ducts. The latter pass from the kidney at regular distances, there being approxi- 
mately one to each myotome." This description of the mesonephric ducts is doubtless 
intended for the collecting tubules. 

In the account of the urethral apertures and urinary sinuses of my four specimens, 
I have noted occasional deficiencies in these features on the right side. It remains to call 
attention to some observed instances of deficiency in the duct system on the right side. 
In specimen No. I the mesonephric ducts and collecting tubules, though well developed 
on both sides, are slightly smaller on the right. In specimen No. Ill the right mesonephric 
duct is of microscopic si2;e, though the left duct is well developed for at least 50 mm. 
in front of the urinary sinus. We might attribute these defects to pressure from the 
right uterus, which is enormously enlarged while the young are being carried, were it 
not for the fact that the most extensive defects occur in No. Ill, which is evidently not 
quite mature. It seems more likely that the tendency to shift the burden of excretion on 
to the left side is due to germinal variations which, however, are adaptive in view of the 
unbalanced development of the reproductive organs of the right side. 



444 Bashford Dean Memorial Volume 

Among related forms, the female Heptanchus (Daniel, 1934) presents a much more 
highly differentiated condition of the duct system. Only those collecting tubules from 
a little more than the anterior halves of the mesonephroi drain into the mesonephric 
ducts which, at the level of the ovaries, are coiled somewhat like the corresponding 
portions in the male. This coiling is correlated with the presence of a rudimentary testis. 
The remaining tubules, which lead from the broad and thick posterior portions of the 
mesonephroi, open into a pair of very large tubular "ureters" which, in this region, lie 
dorsal and lateral to the mesonephric ducts. Usually, each ureter joins a mesonephric 
duct, posteriorly, before the combined vessels enter the single urinary sinus. In an 
anomalous specimen with two urinary sinuses, right and left respectively, the meso' 
nephric duct and the ureter of each side open separately into the urinary sinus. 

The convergence and union of collecting tubules from the posterior portions of the 
mesonephroi, to form "ureters'" which enter the urinary sinus directly, are features 
more characteristic of the highly differentiated elasmobranchs, especially the skates and 
rays. Daniel (1934) states that the WolfBan duct (mesonephric duct) decreases in im^ 
portance as we approach the rays. In the female Squalus suc}{lii (Daniel, 1934, p. 295 
and Fig. 253a) the condition is essentially the same as in Chlamydoselachus : the mesone- 
phric duct receives the collecting tubules from practically the whole of the mesonephros. 
This is probably the primitive condition. It seems extraordinary that Heptanchus, in 
many respects one of the most primitive of living sharks, should have departed so far 
from this archaic type of duct system. 

GENITAL ORGANS OF THE FEMALE 

From an inspection of Text-figures 85 to 88, it will be seen that my four specimens 
display various degrees of development of the genital organs. Some of these differences 
are certainly associated with age, others may possibly be concerned with a sexual cycle. 
Though specimen No. IV is almost as large as the largest, its reproductive system retains 
strict bilateral symmetry, and is obviously immature. In all the other specimens the 
reproductive organs are better developed on the right side save that in No. Ill, which is 
probably not quite mature, the left ovary shows a slightly more advanced stage of de- 
velopment than the right. Specimens I and II are fully mature. Some structures seem 
better developed in No. II than in No. I, but since it is probable that there is a definite 
breeding season (Gudger and Smith, 1933, p. 302) these differences may be correlated 
with a sexual cycle. 

The largest known female, collected in Japan by Dr. Bashford Dean, had a total 
length of 1960 mm. The average length for 35 females, comprising all known post-natal 
female specimens for which the length has been recorded, is 1532 mm. (Gudger and Smith, 
1933, Table V, p. 263). We do not know how many of these were sexually mature, but 
only two of them had a length of less than 1220 mm. My two fully mature female 
specimens, Nos. I and II, measure 1350 mm. and 1485 mm. respectively. My largest 
specimen, No. Ill, has a total length of 1550 mm., yet it seems not quite mature. My 



The Anatomy of Chlamydoselachus 445 

quite immature specimen. No. IV, has a total length of 1398 mm. It is evident that, 
allowing for individual variations, the female Chlaynydoselachus reaches almost or quite 
full siz;e before attaining sexual maturity. 

The Ovaries. — In Chlamydoselachus, the ovaries (Text-figures 85 to 88) are a pair 
of elongate, more or less flattened organs situated in the anterior part of the body cavity 
and attached, rather indirectly, to the dorsal body wall by means of broad mesenteries. 
In specimens I and II, throughout their entire length the ovaries are attached by their 
special mesenteries (mesovaria) to the ventrolateral surfaces of the oviducts including the 
shell glands. In my immature specimen. No. IV, the ovarian mesenteries are attached 
to the median dorsal mesentery just ventral to the attachments of the oviducts. In 
No. Ill the ovarian mesenteries are attached as in No. IV, save that where these mesen- 
teries pass along the ventral surfaces of the shell glands they are fused to the latter 
organs. In Text-figures 85 to 88 the ovaries are displaced laterally as far as their attach' 
ments allow. 

In specimen No. IV the two ovaries (Text'figure 85) are much alike. The length of 
each ovary is about 180 mm., the maximum width (near the anterior end) is 20 mm., and 
the maximum thickness is 6 mm. The largest follicles, which are in a collapsed and 
flattened condition, measure only 10 mm. in their greater diameter. Since the mature egg 
may be 100 mm. long and 60 mm. wide — measurements based on Nishikawa's (1898) Fig. 
1, pi. IV — it is evident that, in the ovaries under consideration, the ovocytes are very 
incompletely developed. There are no ruptured foUicles indicating that ova have been 
liberated. Only the largest follicles are represented on the ventral surface. The dorsal 
surface shows, in addition to the large follicles, many smaller ones. 

In specimen No. Ill the ovaries (Text-figure 86) are of almost equal si2;e but the 
left is slightly better developed. In each ovary, the largest follicles are situated along the 
lateral margin. Since the largest folHcle has a diameter of only 17 mm., it is evident that 
the ovocytes are decidedly immature. 

In specimen No. I the posterior part of the right ovary (Text-figure 87) is missing, 
and has apparently been cut away. From the shape of the remaining portion, I infer that 
this ovary was originally much larger than the left one which is intact. No follicles are 
represented on the ventral surface of either ovary, but on the dorsal side of the left 
ovary some small follicles, none more than 2 or 3 mm. in diameter, were found. 

In specimen No. II the posterior part of the right ovary (Text-figure 88) is missing. 
The preservation of this organ is very poor, so that it is difficult to distinguish a cut edge 
from a mutilation produced by handHng. Doubtless the rupture of large foUicles has 
played a part in the disintegration or contraction of this ovary. No follicles are recog- 
nizable from the ventral surface. On the dorsal surface are protuberances due to the 
presence of many small follicles, none exceeding 4 mm. in diameter; there is also a con- 
cavity, 15 mm. in diameter, which represents the persisting half of a follicle. It is not 
likely that this folHcle has ruptured naturally. In the left ovary no follicles are recog- 



446 



Bashford Dean Memorial Volume 



ni2;able from the ventral surface, and the largest follicles represented on the dorsal 
surface measure only 6 mm. in diameter. 

Carman's (1885.2) figure, reproduced as my Text-figure 94, portrays the ovaries 
of his specimen. He states that the ovaries had been badly preserved and that they were 
much torn. Hawkes (1907) writes that the ovaries of Chlamydoselachus are diffuse 
bodies attached by broad mesenteries to the line of attachment of the "stomach" mesen- 
tery. The right ovary is placed somewhat more anteriorly than the left. 

In Heptay^chus (Daniel, 1934) and in Hexaiichus (Semper, 1875, Fig. 1, pi. XIV), 
a rudimentary testis is associated with each ovary. In Heptanchus maculatus this testis 
lies in the mesovarium, at the base of the ovary, and runs parallel with the ovary. The 




Text-figure 94. 
Ovaries and oviducts of Chlamydoselachus, drav;7n one-half natural size. 

ng, nidamental gland; o, ovary. 
Printed from the original wood-cut after the drawing by Paulus Roetter for Garman, 1885.2, Fig. 1, pi. XIX. 



rudimentary testis consists of an anterior larger portion, and a marked swelling or ridge 
which extends practically the entire length of the ovary. 

The Oviducts. — The oviducts of my four specimens are shown, in ventral view, in 
Text-figures 85 to 88 inclusive. In specimen No. IV there is but slight differentiation in the 
regions of the future uteri (ut.) and shell glands (s.g.)\ all parts of the oviducal system show 
strict bilateral symmetry save that the rudiment of the right shell gland is slightly larger 
than the rudiment of the left, and the right ventral ligament is quite noticeably larger than 
the left. In specimen No. Ill, all the oviducal organs of the right side are decidedly larger 
than those of the left. The discrepancy is even greater in my specimens I and II. To be 
sure, in specimen No. I a large part of the uterus has been cut away, but the form of the 
remaining portion gives evidence of the original size. I conclude that, so far as one can 
judge from the specimens at hand, only the right oviduct is ordinarily functional, but the 
degree of development attained by the left oviduct is such that it might possibly become 
functional. In any case, the oviduct proper must become greatly distended while an egg 
(60 X 100 mm.) is passing through it, and some idea of the siz,e of the uterus after it has 
contained developing embryos may be obtained from Text-figures 87 and 88. 



The Anatomy of Chlamydoselachus 447 

The common opening (ostium abdominale tubae uterinae) from the body cavity into 
the oviducts is situated in the region of junction of the oviducts at the extreme anterior 
end of the body cavity, ventral to the root of the liver. In specimen No. II (Text'figure 88) 
this opening is almost divided into two, one for each oviduct, which face somewhat medial- 
ly. It seems almost incredible that so large an egg as that of Chlamydoselachus can find 
its way into one of these openings, though the fluted, funnel'shaped ostium is evidently 
capable of distention. 

Throughout almost their entire lengths the oviducts are supported by special mesen- 
teries attached to the median dorsal mesentery. The only exceptions are found anteriorly, 
where in front of the shell glands the oviducts diverge to course along the dorsal, lateral 
and ventral walls of the body cavity, and then unite ventral to the root of the liver. In 
specimen No. IV each oviduct, where it traverses the lateral wall of the body cavity, is 
attached to this wall by a narrow mesentery. This mesentery, which we may call the 
dorsolateral mesentery of the oviduct, is not shown in Text-figure 85. It is not present 
in my older specimens where the corresponding part of the oviduct is closely applied to 
the body wall and is merely covered by the peritoneum. In all my specimens, special 
provision is made for the support of the ventral portions of the oviducts. In specimens 
IV and III this support is furnished by a pair of ventral ligaments (Text-figures 85 and 86), 
which are strong special mesenteries. Each has one end fastened to the ventrolateral 
portion of the oviduct and the other end attached to the ventral body wall near the mid-line. 
In my older specimens, Nos. I and II, these ligaments (Text-figures 87 and 88) are shorter 
and broader; they differ, too, in their histological structure, since they blend with the 
substance of the oviducts. 

In its enlarged state, on the right sides of my adult specimens, the so-called uterus has 
thin walls, a velvety inner surface and a fairly rich blood supply. The mucous membrane 
is not sufficiently well preserved to permit a study of the finer structure. 

The anterior portions of the oviducts ("some twelve inches in length") of Carman's 
specimen (1885.2) are represented in my Text-figure 94. It is interesting to note that there 
are two ostia, entirely separate from one another (compare my Text-figures 85 to 88 inclu- 
sive). Of his specimen Garman says: "Three inches from the anterior end of one of the 
oviducts it bore a nidamental gland; the gland of the other tube was an inch farther back. 
A piece left at the cloaca showed one of the ducts greatly distended, possibly with young 
that had hatched within it. Only one of the tubes had been in use." In Text-figure 92 
the opening of the oviduct that had not been expanded is shown on the left side, the 
other (right side) having been cut open to show the internal arrangement. Carman's 
intricate description, illustrated by his Fig. C, pi. XX, of the internal structure of the 
nidamental gland (shell gland) is too involved for consideration here. It should be com- 
pared with Borcea's account (1905, pp. 419-427, Text-figs. 93, 94 and 95) of the structure 
of the nidamental gland of Scyllium. 

Collett's (1897) pu2;2;ling description of the oviducts and "uteri" of his large female 



448 Bashford Dean Tvlemorial Volume 

specimen is quoted here with the comment that nowhere in his paper do I find any 
mention of the ovaries : 

The oviducts were extremely long, both being of about equal length. Towards their 
upper ends [sic] each expands to a uterus-hke sack, of which the right is somewhat larger 
than the left; both contained immature eggs. Below this expansion the oviducts are quite 
narrow, but subsequently expand slightly downwards towards the abdominal pores. The 
total length of each oviduct is about 900 mm. 

The right "uterus" was 240 mm. in length, and contained 10 large eggs, about the size 
of the yolk of a small hen's egg, but some varied in size. There were, besides, about 30 lesser 
yolks of the size of large and small peas, as well as a few bigger ones about the size of 
the yolk of a pigeon's egg. The length of the left uterus was 220 mm., and it contained 5 
large yolks, and about 20 small ones. 

Nishikawa (1898) states that the left oviduct of Chlamydoselachus is always rudi' 
mentary, and the nidamental gland of the right side is better developed than that of the 
opposite side. The right oviduct is much distended when it contains from 3 to 12 eggs, 
these numbers being the limits observed in 7 specimens. Each egg is 110 to 120 mm. long 
(transverse diameter not stated), while the oviduct is only 600 mm. long. As already 
stated, measurements based on Nishikawa's Fig. 1, pi. IV, representing an egg within its 
envelopes, give a length of 100 mm. and a transverse diameter of 60 mm. Doubtless 
changes in the form of the egg occur, since it must be compressed while passing through 
the oviduct proper. In a foot'note to Nishikawa's paper, S. Goto, who prepared the 
manuscript for publication, states that when no eggs are contained there is no perceptible 
difference in si2;e between the two oviducts. In another foot'note Goto writes: ''Mr. 
Nishikawa tells me . . . that the female genital organs of Chlamydoselachus are essentially 
like those of other sharks, and I can confirm his statement from a passing examination of 
a specimen brought some time ago to my laboratory. Collett's description of these organs 
appears to me irrelevant." 

Hawkes' (1907, pp. 475-476) description of the oviducts of the female Chlamydo- 
selachus is so instructive that it is quoted entire : 

The oviducts have large funnels which open ventrad to the stomach, instead of dorsad 
as is usually the case. The edges of the funnels are irregular and spreading, and are united 
in the median ventral line to one another, thus forming one large funnel. The anterior edges 
of the funnels become united to the anterior wall of the body cavity, whilst the posterior 
edges of the united fimbriae hang free. A triangular dorsal pouch is thus made between the 
wall of the abdominal cavity and the funnel. As this pouch is in the usual position of 
the coelomic openings of the oviduct, the eggs would tend to pass into it instead of into the 
latter, if this were not prevented by the unusual position of the ovaries which are ventral to 
the oviducts. For the first 6 cm. the oviduct is a straight tube, the walls of which are lined 
with numerous laminae. This region passes into the oviducal gland, the walls of which are 
much thickened, except along two longitudinal lines which are approximately dorsal and 
ventral. The length of the gland is 3 cm. Its interior is covered by fine laminae continuous 
with those in the preceding and succeeding portions of the oviduct. The laminae run spirally, 
and are very close together, instead of longitudinally and somewhat separated, as is the case 
throughout the remainder of the oviduct, The transverse deeper groove in the oviducal 



The Anatomy of Chlamydoselachus 449 

gland mentioned by Garman ] 1885.2] was found in the specimen examined. Passing from 
the oviducal glands, the oviducts regain their original diameter, but the walls are smoother, 
the laminae being reduced to slight striae. When the oviduct reaches the level of the anterior 
end of the colon, it enlarges. The enlargement is gradual and only increased in diameter about 
fourfold on the left side, but on the right the enlargement is sudden and very apparent, the 
diameter increasing 14 to 15 times. This region in addition to being enlarged has folded 
walls, in which occur one large and several small areas of dilated blood-vessels. The largest 
blood plexus occupies about one-third of the right side of the oviduct. In connection with 
each plexus, on its dorsal side, the oviducal wall is thickened over an area which equals the 
plexus in length and breadth. The enlarged vessels apparently supplied these thickened 
areas. The condition of the oviduct thus described suggests that this portion of the oviduct 
acts as a functional uterus, and that therefore Chlamydoselachus produces the young alive, as 
suggested by Garman. The final portion of the oviduct, which succeeds the uterine, has 
smooth walls and a large diameter, the latter gradually diminishing towards the cloaca. 
This region divides the functional uterus from the cloaca, thus functionally representing the 
the vagina of higher types. The opening of the right enlarged oviduct [Text'figure 90a, R.Ov. ] 
has acquired a median position, the left oviducal opening [L.Ov. ] lying cephalad to it. 

Deinega's (1925) small half-tone figure of the abdominal viscera of a female Chlamy- 
doselachus is printed on unsuitable paper, so that details are obscure. It is chiefly remark- 
able in that it shows a complete right uterus which is even larger than that of my specimen 
No. II. Its length, including the part bulging anteriorly, is equal to about five-sevenths 
of the length of the body cavity. It is somewhat kidney-shaped, with a maximum width 
of more than one-fourth its length. The left oviduct is not conspicuously enlarged in its 
uterine portion. 

Hawkes's observations on the presence of vascular plexuses in thickened portions 
of the uterine wall suggest a physiological relation between the maternal tissues and the 
young. I do not know whether the young are carried after the exhaustion of their store 
of yolk. It seems Hkely, however, that the young sharks are born as soon as, or even 
before, the yolk is entirely utili2,ed. The largest known intra-uterine specimen, taken by Dr. 
Bashford Dean, was a well-formed shark, 390 mm. (15.35 in.) long, yet its yolk sac meas- 
ured 100 X 70 mm. Additional data are given by Gudger and Smith (1933, pp. 298-301). 

It is unnecessary to review the evidence that the genital organs of the right side 
alone are functional in the female Chlamydoselachus. There is not a single known instance 
of complete development of the reproductive organs of the left side. Yet it must be borne 
in mind that the number of specimens that have been described is still very small. The 
organs of the left side are developed to such a degree that they can scarcely be called 
rudimentary. In view of the great variability found in many other organs of Chlamy 
doselachus, one should not be surprised if the examination of additional material should 
reveal cases in which the genital organs of the left side, or of both sides, are functional. 

In the adult female Heptanchus as described by Daniel (1934), the general plan of the 
oviducts is much the same as in the immature female Chlamydoselachus. According to 
Daniel "the oviduct ... is not so greatly enlarged in Heptanchus as in many other Elasmo- 
branchs in which it forms the conspicuous uterus." In the absence of any definite state- 



450 Bashford Dean Memorial Volume 

ment to the contrary, one might assume that the two oviducts of Heptanchus are of 
equal size; but if I interpret Daniel's fig. 251a correctly, the right oviduct is considerably 
larger than the left. 

UROGENITAL SYSTEM OF THE MALE 
I have no adult male specimens of Chlamydoselachus, and the literature on the male 
reproductive organs is very fragmentary. No description of the mesonephroi in the 
male has been found. It seems best to present the observations of each author in chrono' 
logical order, reserving for special treatment the myxopterygia or "claspers.'" 

EXCRETORY AND INTERNAL GENITAL ORGANS 

Giinther's (1887) material consisted of tv/o males, the larger 1473 mm. long. Both 
specimens seemed to be sexually mature. The testes are narrow elongate bodies of 
nearly equal size, about 127 mm. long and 13 mm. broad at the broadest part. They 
reach close to the anterior end of the abdominal cavity. In one of the males the arrange- 
ment of the urogenital organs and ducts, as well as of the external openings, is perfectly 
symmetrical (Figure 17, plate V), while in the other (Figures 18 and 19, plate V) the 
left side shows a much more highly developed condition than the right. In the former 
(bilaterally symmetrical) specimen, the urogenital organs are not further described. In 
the latter specimen the left ductus deferens is much wider than the right, and its interior 
contains low, circular, close-set septa (Figure 16, plate IV). Only faint traces of septa 
can be seen in the right duct. They are limited to the lower three or four inches of the 
duct. The left ductus deferens opens into ''the urinary bladder, if a bottle-shaped 
dilatation which terminates externally in a single small conical papilla may be so called." 
The right ductus deferens opens by a sHt at the side of the papilla directly into the cloaca. 

It is not clear how many male specimens Hawkes (1907) examined. In describing 
the urogenital system of the male, she refers to "my specimen," but in her description of 
the abdominal pores she unrites concerning "one of the males examined." She states 
that in the male there are two urogenital apertures (Text-figure 90b, after Hawkes), 
each being the outlet of an oval urogenital sinus (Bl.) which Giinther described as a urinary 
bladder. Anteriorly, the sinus coimnunicates by a very small aperture with a second and 
larger chamber (R.S.), which is continuous with the ductus deferens (V.D.) or meso- 
nephric duct, and possibly functions as a seminal vesicle. The ductus deferens has 
(presumably on its inner surface) one or more projecting spiral folds which run from one 
end of the duct to the other. In the posterior 100 mm. of the length of the duct, the 
folds are very obvious, but from this point forw^ard they become almost invisible to the 
naked eye. In the posterior part of the duct the folds are very close together (Giinther 
describes them as "circular" foldsj. Hawkes further states that the lumen of the left 
ductus deferens (which Giinther found, in one of his specimens, to be better developed 
than the right) is very irregular in diameter "in my specimen." At its widest, the duct 
measures about 5 mm., but where narrowest it allows only the passage of a bristle. 

Since the excretory and the internal genital organs of the male Chlamydoselachus 
are so imperfectly known, a comparison with other elasmobranchs would be unprofitable. 



The Anatomy of Chlamydoselachus 



451 



MYXOPTERYGIA OR CLASPERS 

The superficial appearance of the intromittent organs or so'called claspers of the male 
Chlamydoselachus is illustrated in Figure 20, plate V, after Giinther; Text-figures 95 to 
97, after Leigh'Sharpe. The skeletal anatomy has been discussed in the section on the 
endoskeleton, and is illustrated by Text-figure 46, p. 375, after Braus; Text-figure 47, P- 
377, after Giinther; Figure 21, plate V, after Goodey; and Text-figure 115a (p. 472), 
after Leigh-Sharpe. The muscles of the claspers have been considered in the section on 
the muscular system, and are illustrated by Figures 22 and 23, plate V, after Goodey, 
also by Text-figure 115b (p. 472), after Leigh-Sharpe. The peculiar blood vessels of the 
claspers are described in the section on the blood-vascular system. The present account 
deals with the general form and structure of the claspers, together with some inferences 
as to the manner in which they function. 

As an introduction to the study of the claspers I can do no better than to quote the 
following from Leigh-Sharpe (1920, pp. 245-246): 




Text-figure 95. 

Ventral view of the pelvic region of 

a male Chlamydoselachus, showing myx- 

opterygia or claspers. 

Cav., projection of cavity. 
After Leigh-Sharpe, 1926, Fig. 1, p. 308. 




CLGr. 



Text-figure 96. 

Ventral view of the pelvic region of a male 

Chlamydoselachus with claspers anteroflexed as 

in copula: A, with the clasper groove closed; 

B, with the clasper groove forced open. 

Ap., apopyle; Cav., cavity; Ci.Gr., clasper groove; H., 

hypopyle. 

After Leigh-Sharpe, 1926, Fig. 2, p. 309. 



452 



Bashford Dean Memorial Volume 



In the male elasmobranchs, where fertilization is internal, the basal element of each pelvic 
fin (basipterygium) is prolonged to form a stout backwardly directed skeletal rod supporting 
a portion of the fin which is demarcated from the remainder and especially modified to 
form a copulatory organ, the clasper. 

The clasper is rolled up in a manner resembling a scroll, so that instead of being a groove, 
as it is usually described, it is a sufficiently closed tube along the greater portion of its length, 
though the edges may not be and usually are not completely fused but overlapping. This 

tube is one along which spermatozoa pass, in- 
jected by an apparatus, the siphon, which has 
not hitherto been sufficiently well known and 
investigated. 

The anterior proximal opening into this 
scroU'Hke clasper groove or tube wiU be hereafter 
known as the apopyle, the posterior, distal exit 
from the same as the hypopyle. In the sharks 
and dogfish the apopyle is close to the cloacal 
aperture, while in the skates it is some consid- 
erable distance posterior to it, an inch or more 
in a moderately sized adult. 

Leading into the apopyle by a narrow ap- 
erture, so as to communicate with the clasper 
tube on either side, is a large cavity, the siphon, 
a sac with extremely muscular walls, situated 
immediately below the corium of the ventral sur- 
face of the abdomen, frequently several inches 
in length, close to the median Hne, and ending 
bHndly, ha\'ing no communication \^nth the 
coelom, and whose function and significance it 
will be my endeavor to elucidate. 

In the skates, on the other hand, no such 
hoUow sac is found, but its place is taken by the 
clasper gland, contained in a sac which it com- 
pletely fills. This gland has long been recognized, 
but its containing sac does not appear up to the 
present to have been demonstrated to be ho- 
mologous with the clasper siphon of the sharks 
and dogfish, which is but Httle known. 

Other accessory structures may be present 
on the claspers, such as the spurs and the Uke 
in Acanthias, but of these none attains such importance and is more frequently present 
than a fan-like expansion at the distal end of the clasper, the rhipidion, whose function is to 

spray the spermatozoa in aU directions in a radiating manner The rhipidion attains a greater 

development in the skates than in the sharks. 

The manner in which the various parts of a myxopterygium, particularly the siphon, 
function is described at length by Leigh-Sharpe (1920, pp. 247-251) in the case of 
Scyllium catulus. 




Text-figure 97- 
Pelvic fin region of a male Chla-mydosdachus: 
A, ventral aspect; B, left lateral aspect. 

Cav., cavity; Cl.Gr., clasper groove; I.V., iliac vein; CJ.P., 

urogenital papilla; V.F., ventral fin; V.S., venous sinus. 

After Leigh-Sharpe, 1926, Fig. 4, p. 311. 



The Anatomy of Chlamydoselachus 453 

Concerning the external anatomy of the myxopterygium of Chlamydoselachus, 
Goodey (1910.1, p. 564) states that: 

On the dorsal side of each appendage, bounded by muscles, is the channel, which, 
toward its posterior end, becomes somewhat lateral in position and is bounded here by the 
knife-edged, movable terminal cartilages T.d. and T.x;. [my Figure 22, plate V]. In a ventral 
aspect [my Figure 23, plate V] the most prominent feature of the appendage is the glandular 
sac [S] and compressor muscle, covered with loosely fitting, soft skin. The skin covering 
the sac and the termina Iparts of the appendages is very soft and is entirely free from 
dermal spines. 

For a more comprehensive description of the claspers of Chlamydoselachus, we are 
indebted to Leigh-Sharpe (1926) whose account is illustrated by my Text-figures 95 to 97, 
and 115 (p. 472). From Leigh-Sharpe (pp. 308-311) I quote as follows: 

This genus [Chlamydoselachus], though included from other characters in the Proto- 
selachii, does not show any affinities with J^otidanus in its copulatory organs. The claspers, 
far from being primitive, are long, tapering, and somewhat slender, though possessing strong 
skeletal supports, 13 cm. in length in this specimen, and devoid of dermal denticles (Fig. 1) 
[my Text'figure 95]. The clasper groove is long and closed for the greater part of its length 
(Fig. 2) [my Text-figure 96a], and the apopyle is small. The apex of the clasper is capable 
of expansion or erection, like a bivalve shell, the larger valve acting as a cover rhipidion. • 
The true rhipidion may be represented by a small protuberance, not far from the apex, which 
contains a separate cartilage, and is discernible in figure 5 [my Text-figure 115a, p. 472]. On 
this occasion the animal's left clasper has been dissected instead of the right as heretofore. 

There is no siphon present, but situate on the inner ventral aspect of the proximal end of 
the clasper is a large cavity which opens dorsally by the clasper groove of which it forms an 
expansion. In these two characters a startling similarity is shown to the Holocephali, more 
expecially to Rhinochimaera, and, as I was unable to dissect the latter, the details of the 
present type are portrayed more fully. 

The cavity, which occupies roughly three-quarters of the length of the clasper parallel 
with the clasper groove, is much distended, with powerful muscular walls, supported by 
two radial cartilages outspread in a fan-wise manner (Figs. 4 and 5a) [my Text-figures 97 
and 115a]. I have no doubt that it can be used for pumping spermatozoa, being, therefore, 
analogous with a siphon; and in this it agrees with the cavity of Callorhynchus and Rhino- 
chimaera, though not with that of Cestracion (which possesses a siphon) and some species of 
Chimaera. When the claspers are anteroflexed as in copula (Fig. 2) [my Text-figure 96], the 
cavity collapses and is compressed. By a comparison of measurements, it seems certain that 
the posterior part of the cavity must be included in that part of the clasper which is introduced 
into the oviduct of the female. 

The simplicity of the clasper has prompted a more detailed account of its anatomy. 

Regan (1906.2, p. 740) states that the myxopterygium of Chlamydoselachus and the 
notidanids is a more primitive structure than that of the galeoid sharks. 

THE ABDOMINAL PORES 

Although there is no immediate evidence that the abdominal pores have anything 
to do with the urogenital system, it is convenient to consider them here, since they are 
situated near the urogenital sinus and are often figured with it. 




454 Bashford Dean Memorial Volume 

The abdominal pores of my female specimens of Chlamydoselachus are a pair of 
short canals leading from the ventral portion of the body cavity, by the most direct 
route, to their external openings on each side of the ventral surface of the body just 
posterior to the cloaca. The body cavity extends along each side of the cloaca, but not 
so far caudad in its ventral as in its dorsal portion. The difference (about 15 mm.) is 
approximately equal to the length of the abdominal pores. The distal or superficial half 
of each canal lies just beneath the integument which is usually upraised to form a low 
ridge. The inner opening is somewhat funnel'shaped and is large enough to admit a pencil. 
The canals, when probed from the body cavity, are found to be quite uniform in caliber, 
well-rounded and about 5 mm. in diameter. The external openings (ah. p. in Text'figures 
85 to 88) vary considerably in si2;e. When well developed, as in specimens IV and III 
(Text-figures 85 and 86) they are elliptical, about 8 mm. long, and face obliquely ventrad, 
laterad and caudad. In specimens I and II (Text-figures 87 and 88) they are usually 

Text-figure 98. 

Pelvic fins, abdominal pores and 

cloaca! aperture of a 1220-mm. 

female Chlamydoselachus. 

After Garman, 1885.2. PI. I. 

round and comparatively small, but one is absent. On the right side of No. II the external 
opening is so small that it barely admits a probe. In the single case (specimen No. I) 
where an external opening is absent, the canal is fully developed internally but is closed 
externally by the integument. 

The external openings of the abdominal pores in Carman's (1885.2) specimen, a large 
female, are shown in his plates, reproduced as my Text-figures 98 and 89. Garman states 
that the mouth of each abdominal pore is inflated into a broad flap, by which the pores 
are hidden. Hawkes (1907), in a figure reproduced as my Text-figure 90a, shows the 
cloacal region of a female with two closed abdominal pores. 

The specimens thus far considered are all females. It remains to describe the condi- 
tion of the abdominal pores in the male. Giinther's (1887) illustrations include two 
figures (my Figures 17 and 18, plate V) showing the abdominal pores of his male speci- 
mens. One is normal, showing two open pores similar to those of the typical female; 
the other is anomalous, possessing only a single abdominal pore, which is unusually large. 
In his text, Giinther states that this single abdominal pore is situated immediately behind 
the cloaca and "in the median line (or very slightly to the left of it)" but his figure shows 
it definitely on the left side. Hawkes (1907) writes: "One of the males examined has 
two abdominal pores of which the right is the better developed." In the explanation of 
her diagrammatic text-figure (my Text-figure 90b) the left pore is said to be closed. 

From the meager evidence at hand it does not appear that there is any important 
difference between the abdominal pores of the male and the female, but it is clear that 



The Anatomy of Chlamydoselachus 



455 



both are decidedly variable. That they are not essential for the life of the fish is indicated 
by Hawkes' observation of an adult female with both abdominal pores closed. 

PERICARDIO'PERITONEAL CANALS 

In the embryonic development of higher vertebrates, the primitive coelomic cavity 
becomes divided into three cavities, pericardial, pleural and peritoneal respectively. In 
the adult elasmobranch there are only two coelomic cavities, pericardial and peritoneal, 
and their separation is not quite complete. A pair of slender thin-walled canals, joined 




Text'figure 99. 
Diagrams showing the pericardio'peritoneal canals (dorsal views) in: A, an 
adult Squalus; and B, an adult ScylUum. Dorsal parts removed by a hori- 
zontal cut. The canals below the esophagus are represented by dotted lines. 

dcv, ductus Cuvieri; dm, dorsal mesentery; !ig, lateral suspensory ligament of !, the liver; lo.ro, 
left and right openings of the pericardio-peritoneal canals; oe, esophagus; p, pericardial coelom; 
po, median opening of the pericardio-peritoneal canal into the pericardial coelom; rlig, right 
lateral suspensory fold; sm, sub-esophageal lesser mesentery (hepato-enteric mesentery). 
After Goodrich, 1918.1, Fig. 18. 

at their pericardial ends to form a single large canal opening into the pericardial cavity 
(Text 'fig. 99), course posteriorly along the ventral wall of the esophagus to open by wide 
apertures, thus placing the pericardial cavity in communication with the peritoneal 
cavity — as in Squalus and Scyllium (Goodrich, 1918.1, Fig. 18); and Raja (Monro, 1785). 

Pericardio-peritoneal canals of selachians were first described and figured by Monro 
in the skate. Balfour (1876-78) interpreted these canals as developmental arrests, but 
Hochstetter (1900) claimed that in Acanthias the early communication between the 
pericardial and peritoneal cavities became completely closed, and that the canal opening 
from one to the other in the adult is a new formation. Goodrich (1918.1) investigated 
the development of these canals not only in Squalus (Acanthias) but also in Scyllium, 
concluding that Hochstetter was mistaken in his interpretation and that Balfour's 
view is essentially correct. 

In each of my four large specimens of Chlamydoselachus, pericardio-peritoneal 
canals were found. Since there is considerable variation in the structure and relations 
of these canals, each specimen will be described separately. 



456 Bashford Dean Memorial Volume 

In specimen No. II the condition of the canals (Text-figure 100a) is most like that 
described for other elasmobranchs, though some differences are obvious. On the anterior 
surface of the posterior pericardium (p.p), close to its dorsal border, there is a large opening 
(c.) leading into a shallow cavity. The width of the cavity (and of its opening) is about 
12 mm.; its depth is only about 3 mm. This cavity, which I shall call the pericardio- 
peritoneal sac, represents the fused portion of the two canals (r.p.c. and l.p.c), which 
open into it by apertures about 4 mm. in diameter. The canals were probed. Each is 
about 4 mm. wide when collapsed, and is about 20 mm. long; the walls are very thin. 




Text-figure 100. 
Pericardio-peritoneal canals of Chlamydoselachus, leading from the pericardial 
cavity (above) to the peritoneal cavity (below); ventral views, natural sise. 

c, common opening of the canals into the peritoneal ca-inty; d.p., dorsal pericardium; l.p.c, left 
pericardio-peritoneal canal; es., esophagus; p.p., posterior pericardium; p.p.s., pericardio-peritoneal 
sac formed by the fusion of right and left canals; r.p.c, right pericardio-peritoneal canal. 
A is drawn from specimen No. II in the collection of the American Museum of Natural Historj'; 
B, from a specimen (No. IV) lent by Dr. E. Grace White. 



The canals pass dorsad along the posterior surface of the pericardial wall to reach the 
esophagus (es.), then caudad along the ventral surface of the esophagus, dorsal to the 
Kver, to open by wide crescentic apertures into the peritoneal cavity (Text-figure 100a). 

In my specimen No. I, conditions are practically the same as in No. II save that the 
pericardio-peritoneal sac is about 6 mm. wider than its opening into the pericardial 
cavity, and that the right pericardio-peritoneal canal is closed at its posterior end. 

In specimen No. Ill the common aperture and the pericardio-peritoneal sac are 
much the same as in specimen No. II, but their situation on the posterior wall of the 
pericardial cavity is a Httle further ventrad — not so close to the dorsal border as in the 
preceding specimens. Thus the paired canals must pass a Httle further dorsad in order to 
reach the esophagus. The canal on the right side is only 5 mm. long and does not reach 
the esophagus. The canal on the left side is 10 mm. long and turns posteriorly upon 
reaching the esophagus. Both canals are closed at their posterior ends. 



The Anatomy of Chlamydoselachus 457 

In specimen No. IV (Text'figure 100b) the common aperture (c.) of the pericardio' 
peritoneal canal is situated as in No. Ill, a few millimeters from the dorsal border of the 
posterior pericardial wall. This opening has about the same size (12 mm. wide) as the 
corresponding openings in the other specimens; but it is bordered laterally by thin lips 
due to an extension of the pericardio'peritoneal sac {p. p. s.) which is about 22 mm. wide 
though no deeper than in the other specimens. The openings into the paired canals 
are smaller, and the canals are more slender. Each canal is about 13 mm. long and ends 
in contact with the esophagus at the extreme anterior end of the peritoneal cavity. Both 
canals end blindly. 

In two respects the pericardio'peritoneal canals of Chlamydoselachus differ from the 
condition typical for elasmobranchs : the anterior unpaired portion is extremely short 
and broad, forming a shallow sac; and the paired canals often end blindly. Of the eight 
canals in my four specimens, five are closed at their posterior ends. It is noteworthy 
that the closed canals are usually smaller than the open ones. It is apparent that there 
is a tendency toward obliteration of the canals, and this may be interpreted as a depar' 
ture from primitive conditions. 

BLOOD' VASCULAR SYSTEM 

Studies of the blood'vascular system of Chlamydoselachus have been almost entirely 
limited to (1) the heart; (2) the arteries anterior to the heart; (3) the large venous trunks; 
and (4) the venous sinuses of the claspers. These comprise, however, the most interesting 
and complex portions of this system. In my own material, only a few portions of the 
blood'vascular system are in a condition favorable for investigation. I have therefore 
studied only the heart and the blood vessels of the gills. 

THE HEART 

Since there is much variation in the names that have been applied, by different 
authors, to the anterior division of the elasmobranch heart, it is desirable to justify my 
choice of the term conus arteriosus, which is used throughout this section. The present 
status of our knowledge of the homologies of this portion of the heart is set forth by 
Goodrich (1930, p. 538) in the following words: 

There has been considerable confusion in the nomenclature of the anterior region of the 
heart. Bulbus cordis is the name now generally applied by embryologists to the anterior 
chamber. But the name conus arteriosus, introduced by Gegenbaur to designate the anterior 
muscular region of the Selachian heart, is often given to it. Moreover, the Selachian conus 
does not [precisely?] correspond to that part of the heart so called in human anatomy. It 
is best, then, to apply the name bulbus cordis, introduced by A. Langer, to the embryonic 
structure throughout the Craniata, and keep the name conus arteriosus for the adult muscular 
contractile chamber derived from it in Pisces and Amphibia. 

Carman's figures of the heart of Chlamydoselachus are reproduced as my Text'figures 
101a and 101b. Of his specimen Carman (1885.2, pp. 18 and 19) writes : 



458 Bashford Dean tAemorial Volume 

Departing considerably from the conventional form of heart, this genus presents a shape 
that is somewhat pecuHar. Seen from below, it has a small subquadrangular ventricle, 
a large auricle, and a long bulbus arteriosus. The ventricle measures nearly three-quarters 
of an inch in either width or length. When fiUed, the auricle is subtriangular, and measures 
on each side an inch and a half. The bulbus is almost twice as long as the ventricle. Behind 
the auricle,and above and behind the ventricle, hes the sinus, w^hich has a capacity that nearly 




Text-figure 101. 

Heart of Chlamydoselachus : A, in ventral view; B, longitudinal section showing cavity 

in ventricle, also valves of the bulbus (conus) arteriosus. 
1, auricle (atrium); 2, ventricle; 3, bulbus (conus) arteriosus; 4, sinus venosus; J, dark tissue between cardiac 

and abdominal chambers; 6, cavity in ventricle; 7, valves in bulbus (conus). 
Printed from original wood-cuts after drawings by Paulus Roetter for Garman, 1885.2, Pis. XVII and XVUI. 



equals the bulk of the ventricle. From it the opening into the auricle is guarded by a pair of 
\'alves that are without chordae. The auriculo-ventricular opening is furnished w^ith a pair of 
valves provided with chordae tendineae. In the ventricle the cavity or chamber is small; its 
outhnes in longitudinal section resemble those of a pipe with a short stem, the stem being 
directed toward the left upper side and the bowl toward the bulbus. Along the inside of 
the passage (Fig. B, pi. XVIII) [my Text-figure 101b], the muscles he in bands (columnae) 



The Anatomy of Chlamydoselachus 



459 



loosely laid one upon another, those in the posterior section, or stem of the pipe, running 
transversely, and those of the anterior section being longitudinal. 

Behind the ventricle, in the partition, between the peritoneum and the pericardium, there 
is a spongy mass of dark tissue an eighth of an inch in thickness. 

Giinther (1887) had available for examination three well-preserved specimens of 
Chlamydoselachus. His drawings, illustrating the external form of the heart and the 
configuration of the valves of the conus, are reproduced as my Text-figures 102a and 102b. 
Giinther gives no general description of the heart, but it will be noticed that his figure 
confirms Carman's (1885.2) statement con- 
cerning its form. 

Ayers' (1889) Fig. 2 (reproduced as my 
Text-figure 105, p. 462) portrays the heart of 
Chlamydoselachus in sectional view, and the 
drawing appears to be semi-diagrammatic. 
Therefore this figure does not give us much /'^ 

information concerning the form of the heart 
in his specimen. His description (p. 194) of 
the conus arteriosus follows : •^' 



% 




The conus arteriosus forms a thick 
spindle-shaped trunk about an inch long and 
one-fourth of an inch in diameter. It is pro- 
vided with six rows of valves, all of which 
are quite small, except the anterior set of 
three, which are large, tridentate, and 
formed of a white tough tissue of a cartilag- 
inous consistency. 



Text-figure 102. 

Heart of Chlamydoselachus : A, in ventral view ; B, 

conus arteriosus opened longitudinally to show the 

arrangement of the valves. 

r, right atrium; !, left atrium. 
After Gunther, 1887, Figs. 7 and 8, pi. LXV. 



My observations do not entirely agree with those of Garman and Gunther regarding 
the proportions of certain parts of the heart. In my three specimens (from the fourth 
specimen the heart had been removed) the conus arteriosus is indeed long, as in Garman's, 
Giinther's, and Ayers' specimens; but the ventricle, even when empty, is larger than it 
appears in the figures by Garman and Giinther, and the si2,e of the atrium is variable. 
Text-figure 103a is drawn from my specimen No. Ill in which the ventricle (v.) is moder- 
ately distended with blood. The atrium (atr.) is empty, but in its flattened condition 
it retains a smoothly rounded outline, as shown in the figure. The size of the atrium is 
somewhat exaggerated due to its flattened condition; nevertheless, the atrium of this 

Text-figure 103. 
Hearts of two specimens of Chlamydosel- 
achus, in ventral view, one-half natural size: 
A, drawn from No. Ill; B, from No. II. 

atr., atrium; ecu., common cardinal vein; co., conus 

arteriosus; s.v., sinus venosus; v., ventricle. 

Drawn from specimens in the American Museum. 




460 Bashford Dean Memorial Volume 

specimen is certainly large. In specimen No. II (Text-figure 103b) the ventricle (v.) is 
partially distended with blood. Its si?e equals that of No. II but its form is quite different, 
more nearly resembling that of the human ventricles. The conus (co.) is so long that 
proximal and distal halves, when at rest, are bent almost at right angles to each other 
in order to find room within the pericardial cavity. In specimen No. I the proportions 
are much the same as in No. Ill, but the ventricle, which is empty, is kidneyshaped 
with its long axis extending transversely and its lesser curvature facing anteriorly. In 
the undisturbed condition, the left half of the ventricle was folded dorsal to the right 
half. In this condition, when viewed from the ventral aspect, the ventricle of No. I 
has much the same appearance as in Giinther's figure. Thus in my three specimens, even 
after allowing for differences due to expansion and contraction of its chambers, the form 
of the heart as viewed from the ventral aspect varies considerably, but the ventricles 
are uniformly larger than those shown in Carman's and Giinther's figures. 

In my three specimens, the sinus venosus {s.v. in Text'figure 103a) and the common 
cardinal veins or ducts of Cuvier (c.c.) are of the usual elasmobranch type, but seem rather 
large. Of the mass of spongy tissue in the posterior pericardial wall, mentioned by 
Garman, I can find no trace. 

Concerning the valves of the conus (bulbus) arteriosus in the specimen illus' 
trated by my Text'figure 101b, Carman (1885.2, p. 18) writes: "The bulbus contains 
six rows of valves, or seven if we count the single valve nearest the ventricle as a row. 
Two or three of the posterior series have chordae tendineae." Giinther's (1887, p. 4) 
description of the conus arteriosus in his specimen follows : 

The conus arteriosus (Figs. 7 and 8) [my Text-figure 102] is of considerable length, 
sHghtly bent towards the right, and of nearly the same diameter throughout. No special valve 
separates it from the ventricle. I find the valves much more regularly arranged than would 
appear from the figure given by Garman. They form three longitudinal and six transverse 
rows (Fig. 8). The largest are those of the distal transverse row, placed close to the end of the 
conus, and somewhat more distant from the next row than the five other rows are from each 
other. The next largest valves are those of the proximal row, those of the second and third 
being smaller, and those of the fourth still smaller, with only partially free anterior margins; 
the valves of the fifth row are quite rudimentary, and two of them merely indicated as raised 
papillae, which are confluent with those of the fourth row. Finally, a fourth intermediate 
longitudinal series is indicated by two minute valves, belonging to the first and second 
transverse rows. The larger valves are provided with tendinous chordae. 

The valves of the conus in my three specimens are regularly arranged in transverse 
rows, but the arrangement in longitudinal rows is not always perfect. In specimen No. 
Ill the valves are the largest, but this may be due to the fact that they are best preserved. 
In this specimen there are five transverse rows, with a space of double the usual extent 
between the fourth and fifth rows counting from the proximal end of the conus. The 
valves of the distal row are much the largest, as in Carman's specimen; the valves of the 
two proximal rows rank next in si2;e. The numbers of valves in each row, reckoning from 
the proximal end of the conus, are 3, 4, 4, 5, and 3 respectively. In specimen No. II there 



The Anatomy of Chlamydoselachus 



461 



br.af 



are four transverse rows with at least three valves in each row — the precise number is 
uncertain. The same may be said of No. I. 

As stated by Garman (1885.2), generally among sharks the conus is shorter and the 
transverse rows of valves less numerous, than in Chlamydoselachus. In Carman's Pis. 
56 and 57 (1913) we find illustrated (without text) the external form of the heart, and 
the form and arrangement of the valves of the conus arteriosus, in many different species 
of elasmobranchs. The heart of Heptanchus maculatus (Text-figure 104a) has a fairly 
long conus arteriosus — longer than that of Hep- hy af., 
tranchias {Heptanchus) perlo (Garman, 1913, Fig. 
1, pi. 56) but shorter than that of Chlamy- 
doselachus. In Heptanchus (Text'figure 104b) 
the valves of the conus arteriosus show partial 
suppression of the second row counting from the 
distal end of the conus, and complete suppression 
of the third row. 

THE BLOOD VESSELS 

For descriptions of the blood vessels of 
Chlamydoselachus, we must rely almost entirely 
on the work of Ayers (1889) and Allis (1908, 1911, 
1912 and 1923). In several respects, the condition 
of the arteries as described and portrayed by 
Ayers is not typical for Chlamydoselachus. His 
work has been severely criticised, but in view of 
the marked variability that has been found in 
other organs and parts of Chlamydoselachus, it 
seems possible that he worked on an anomalous 
specimen. I have included two of his figures 
(Text'figures 105 and 106), because of their his- 
torical importance and because they are more 
comprehensive than those of other authors. 




Text-figure 104. 

Ventral views of (A) heart and ventral aorta, 

(B) valves of the conus arteriosus, 

in Heptanchus maculatus. 

dp., aperture of last afferent artery; au., auricle (atrium); 
hr.af.l-6, first to sixth afferent branchial arteries; 
c.a., conus arteriosus; ct.I., left coronary artery; hy. aj., 
afferent hyoidean artery; p.c, pericardial artery; v.a., 
ventral aorta; v.c, valves of the conus; tin., ventricle. 
From Daniel, 1934, Fig. 150a and b; the latter redrawn 
after Garman, 1913, Fig. 1, pi. 59- 



THE ARTERIES 

In Chlamydoselachus, particular interest attaches to the study of the dorsal aorta 
(anterior portion), the branchial arteries, and the circulation within the gills. 

The Dorsal Aorta. — Ayers (1889) described a slender median artery, coursing 
in the basis cranii, which he called the cranial aorta (c in Text-figures 105, 106, and 22 
p. 352) since he regarded it as a direct continuation of the dorsal aorta. "Unlike all 
other gnathostomous vertebrates, Chlamydoselachus has a dorsal aorta (dorsal vessel) 
running the entire length of the notochord, to which it is intimately attached throughout 



462 



Bashford Dean Memorial Volume 




Text-figure 105. 
Semidiagrammatic figure of heart and anterior blood vessels (anomalous?) of a specimen of Chlamydosel' 

achus viewed from the left side. 

a., auricle (atrium); a.i., anterior innominate artery; an., anastomotic branch of first efferent branchial artery; h.a., bulbus arteriosus; 
br., brachial vein; c, cranial aorta; c. a., conus arteriosus; c.c, anterior carotid commissure; coe.mes., coeUaco-mesenteric artery; cor., 
coronary artery (plus hypobranchial trunk); c.s., cardinal sinus; c.v., cardinal vein; d.a., dorsal aorta (posterior to \.); e.c, external 
carotid artery; h.v., hepatic vein; hy., hypophysis; ic., internal carotid artery; i.c.f., internal carotid foramen; i.j.v., internal jugular 
vein; 1^., cephalic aorta; m.s., arteriae musculo-spinales; p.c.s., precaval sinus; fi.p!., pituitary plexus; scl, subclavian artery; s.j.v., 
superior jugular vein; sp., spiracle; s.r., sinus venosus; tT., tropeic (lateral abdominal) vein; v., ventricle; v.a., ventral aorta; I-III, 
first to third pairs of aortic roots (arches); 1-6, first to sixth pairs of efferent branchial arteries; 1 !-6 !, first to sixth pairs of afferent 

branchial arteries. 
After Ayers, 1889, Fig. 2. 




Text'figure 106. 
Efferent branchial vessels and dorsal aorta (anomalous?) of a specimen of Chlamydoselachus. 

an., anastomotic branch of first efferent branchial artery; c, cranial aorta; coe.mes., coehaco-mesenteric artery; d., dorsal aorta (posterior 

to \.); e.c, external carotid artery; h., hyoid arch; i.e., internal carotid artery; i.c.f., internal carotid foramen; \., cephaHc aorta; m.s., 

arteriae musculo-spinales; p.ph, pituitary plexus; sch, subclavian artery; sp., spiracle. I-IX, first to ninth pairs of aortic roots (arches); 

1-6, first to sixth pairs of efferent branchial arteries; lv-5v, first to fifth branchial arches. 

After Ayers, 1889, Fig. 1. 



The Anatomy of Chlamydoselachus 



463 



the greater part of its course" (Ayers, 1889, p. 195). Concerning the part of this vessel 
which Ayers calls the cranial aorta, AlHs (1908, pp. 111-112) comments as follows: 

Ayers shows and describes, in Chlamydoselachus, a small median vessel, which runs 
directly forward from the point where, according to his nomenclature, the dorsal aorta is 
joined by the third pair of aortic roots; that is, in the nomenclature employed by me, from 
the point where the lateral dorsal aortae unite to form a single median trunk. This vessel 




Text-figure 107. 

The dorsal aorta and its branches in Chlamydoselachus, ventral view. The myelonic 

(basilar) artery is displaced slightly to one side so as to be seen. 

ab, arteria basilaris; acp, a. cerebralis posterior; acr, a. centralis retinae; aom, a. ophthalmica magna; apsb, afferent 
pseudobranchial artery; da, dorsal aorta; ea 2-3, efferent arteries of second and third branchial arches; ec, external 
carotid artery; epsh, efferent pseudobranchial artery; ic, internal carotid artery; Ida, lateral dorsal aorta; fehy, 

posterior efferent hyal artery. 
After Allis, 1923, Fig. 60, pi. XXIII. 

is said by Ayers to extend forward to the pituitary body, and it is called by him the cranial 
aorta, that being the name given by Hyrtl to a similar vessel said to have been found by him 
in Scyllium. This median vessel, described in these two fishes, has been discussed by both 
Dohrn and Carazzi, and there seems some doubt as to its existence; or, if it exists, as to its 
being an artery. I have accordingly not given any consideration to it in my diagrams. 

Further, Allis (1911, p. 516) states concerning the ''cranial aorta" of Chlamy- 
doselachus: ''No trace whatever of such a vessel could be found in either of my two 
specimens, notwithstanding that it was most carefully and particularly looked for." 

Since the discredited concept of a cephalic or cranial aorta existing as a median 
unpaired structure is of some historical importance, I append a further consideration of 
it by quoting the following from Corrington (1930, pp. 227-228): 



464 Bashford Dean Memorial Volwne 

This imaginary artery has been one of the causes operating to delay recognition of the 
paired dorsal aortae. First described by Hyrtl (1872) in Catulus, its status and importance 
were established by the author's prestige. Later Ayers (1899) reported the same vessel in 
Chlamydoselachus, seemingly to place this artery on a firm basis. But many other workers 
have since been unable to find any trace of it whatever in any species, either in embryo or 
adult. Dohm attempted to explain Ayers's paper but only confused matters the more, and 




Text-figure 108. 

The dorsal aorta (anterior portion) and its branches, also the first efferent branchial artery 

and its branches, in Heptandms maculatus. 

ac., anterior cerebral; a.sp., arteria spinalis; hr.ef.l, first branchial efferent; d.a.I, paired dorsal aorta; d.a., dorsal 
aorta; hy.ef., hyoidean efferent; i.e., internal carotid; m.c, median cerebral; ns., nasal artery; o.m., ophthalmica 
magna; or., orbital artery; p.c, posterior cerebral; ps., pseudobranchial artery; r.a., ramus anastomoticus; rs., 

rostral artery; sg., segmental artery. 
After DanieL 1934, Fig. 152. 



it remained for Allis (1911.2) to re-examine the same species and to expose so many other 
glaring errors in the pre\dous work that Ayers's description has been entirely discredited. 

These paragraphs furnish the most striking case encountered in this investigation 
illustrating the danger of (l) erecting specific types from the dissection of a single specimen; 
(2) not making adequate allowance for a possible high degree of variability; and (3) attempting 
to establish adult homologies without thorough embryological preparation. 

The bifurcation of the dorsal aorta anteriorly, as portrayed in Text-figures 107, 108 
and 109, of Chlamydoselachus, Heptanchus and Squalus respectively, is a feature common 
to all elasmobranchs, so far as knov.Ti. From an embryological point of view this is 



The Anatomy of Chlamydoselachus 



465 






a primitive condition since, in the early embryo, the dorsal aorta is paired throughout 

its entire length. As students of embryology know, the members of this pair of vessels 

meet in the median line, throughout the greater part of their length, to form the single 

dorsal aorta of adult anatomy. In gnathostomous vertebrates generally, the common 

carotid and the internal carotid arteries are regarded as anterior portions of the primitive 

dorsal aortae, which persist in the paired 

condition throughout life. These consid' 

erations lend interest to the study of these 

arteries in CMia'myd.osdach.us. My Text' 

figures 107 and 110, after Allis, will en' 

able the reader to follow the description 

of these arteries which I quote from Allis 

(1911, pp. 516-518) as follows: 

Running forward and slightly later- 
ally, immediately beneath the broad and 
rounded base of the chondrocranium, the 
lateral aorta [ !da ] of each side is joined by 
the corresponding efferent hyoidean artery 
and then soon turns sharply laterally and, 
at the edge of the base of the chondro- 
cranium, receives the commissural vessel . . . 
from the efferent hyoidean artery; this com- 
missural vessel being considerably larger 
than the lateral aorta. The latter vessel, 
now becoming the common carotid, turns 
sharply forward, at an acute angle, in the 
direction prolonged of the commissural ves- 
sel, runs forward and slightly mesially along 
the lateral edge of the ventral surface of the 
chondrocranium, and soon gives off its ex- 
ternal branch. . . . 

The internal carotid, which is the an- 
terior prolongation of the lateral dorsal 
aorta beyond the point of origin of the ex- 
ternal carotid, runs forward and mesially 
along the base of the chondrocranium and, 
not far from the median line, traverses a 
foramen in the base of the skull and enters the cranial cavity 




Text-figure 109- 
The carotid system of arteries in SqaoXui acanthias, 

ventral aspect. 
ACA, anterior cerebral artery; APA, afferent pseudobranchial 
artery; BA, buccal artery; CA, cerebral artery; CC, carotid 
crossing; CCA, common carotid artery; CS, cephaUc sinus; DA, 
dorsal aorta; DBCA, dorsal branchial commissural artery; EBA, 
efferent branchial artery; £CA, external carotid artery; EHA, 
efferent hyal artery; EPA, efferent pseudobranchial artery; ICA, 
internal carotid artery; MCA, middle cerebral artery; OMA, 
ophthalmic artery; PC A, posterior cerebral artery; PDA, paired 
dorsal aorta; SA, segmental artery; SR, spiracular retia. 
From Corrington, 1930, Text-fig. 22; after Hyrtl, 1872. 



Having entered the cranial 
cavity, the internal carotid meets in the median line and anastomoses with, or is connected by 
a short commissure with its fellow of the opposite side, and then immediately turns directly 
laterally, and then forward and laterally in the cavity. There it is soon joined by the effer- 
ent pseudobranchial artery, which artery enters the cranial cavity by traversing a foramen 
in the orbital wall immediately anteroventral to the base of the eye-stalk. . . . Having 
been joined by the efferent pseudobranchial artery, the internal carotid soon gives off an optic 
branch and then separates into anterior and posterior cerebral branches, the latter of which 



466 Bashford Dean Memorial Volume 

fuses posteriorly, in the median line, with its fellow of the opposite side, to form a single 
median myelonic artery. The optic artery issues from the cranial cavity with the nervus 
opticus and penetrates the eyeball with or near that nerve. 

My Text'figure 107 of Chlamydoselachus (after Allis) should be compared with 
Text-figures 108 (after Daniel), and 109 (from Corrington, after Hyrtl), showing the 
corresponding arteries for Heptanchus and Squalus respectively. 

The Branchial Arteries. — Either Ayers' (1889) figures (reproduced as my Text' 
figures 105 and 106) are inaccurate, or his specimen of Chlamydoselachus was anomalous 




Text-figure 110. 
Branchial, pseudobranchial and carotid arteries of Chlamydoselachus. 

aal, 11, etc., afferent arteries in the 1st, 2nd etc. branchial arches; acer, anterior cerebral artery; 
ahy, afferent hyoidean artery; amd, afferent mandibular artery; apsh, afferent pseudobranchial 
artery; cc, common carotid; cor., coronary; da, dorsal aorta; eal, U etc., efferent arteries in 1st, 
2nd etc. branchial arteries; ec, external carotid; efiv, efferent hyoidean artery; epsb, efferent 
pseudobranchial artery; ic, internal carotid; Ida, lateral dorsal aorta; om, arteria ophthalmica 
magna; op, optic artery; peer, posterior cerebral artery; psh, pseudobranch; ta, truncus arteriosus. 

After AUis, 1911, Fig. 1. 

in this respect: only one efferent-collector artery is shown in each gill-arch, whereas in 
all other specimens of Chlamydoselachus that have been examined, my own specimens 
included, there are two such arteries. To be sure, Goodrich (1909, p. 137) wrote: "Ex- 
cept in Chlamydoselachus, the branchial arches of the Selachii, like those of the Dipnoi, 
have two efferent arteries;" but it is probable that Goodrich merely accepted Ayers' 
account without verifying it. In his later (1930) text, Goodrich figures Chlamydoselachus 
with two efferent arteries in each gill-arch. AUis (1908) at first accepted Ayers' de- 
scription of the efferent branchial arteries, but later (1911) he prepared a figure (my 
Text-figure 110) based on dissections of his own material, and commented (pp. 511-512) 
on the results as follows : 



The Anatomy of Chlamydoselachus 

In 1889 Ayers, in a work entitled "The Morphology of the Carotids," described the 
branchial and carotid arteries in Chlamydoselachus, and these arteries, as described by him, 
were in certain respects quite unusual. Ayers himself called especial attention to this fact, 
and on the conditions, as described by him, he based certain quite important conclusions. 
In 1908 I had occasion to consult this work by Ayers, and I then published (AUis, 1908) a 
diagrammatic representation of the carotid and related arteries in this fish, as described by 
Ayers but as interpreted by myself. The diagram was, however, most unsatisfactory, and 



467 



am p-cer e/: epsb 




amd 



Text-figure 111. 
Branchial, pseudobranchial and carotid arteries of Wtptandtw-s cmtrtxxs. 

aal, 11, etc., afferent arteries in the 1st, 2nd etc. branchial arches; acer., anterior cerebral artery; 
ahy, afferent hyoidean artery; amd, afferent mandibular artery; apsh, afferent pseudobranchial 
artery; cor, coronary artery; da, dorsal aorta; ea.I.II. etc., efferent arteries in the 1st, 2nd, etc. 
branchial arches; ec, external carotid; ehy, efferent hyoidean artery; epsh, efferent pseudo- 
branchial artery; ic, internal carotid; il/i, internal lateral hypobranchial artery; Ida, lateral dorsal 
aorta; om, ophthalmica magna artery; op, optic artery; peer, posterior cerebral artery; psb, 
pseudobranch; ta, truncus arteriosus. 
After AUis, 1912, Fig. 1. 

having since received several heads of this fish, most kindly sent me by Prof. Bashford Dean, 
I have had dissections made of the arteries concerned, in two of them, the dissections being 
prepared by my assistant, Mr. Jujiro Nomura. The arteries, as I find them, are shown in 
the accompanying Figure 1 [my Text-figure 110]. ... 

The arteries in Chlamydoselachus . . . differ in no important particular from those in the 
Scylhidae and in Mustelus (AUis, 1908), excepting in that the dorsal end of the efferent 
hyoidean artery has, in Chlamydoselachus, a double connection with the lateral dorsal aorta. 

In Chlamydoselachus, as in elasmobranchs generally, the efFerent'CoUector arteries 
(Text-figure 110) form complete loops around each gill'cleft excepting the last one. To be 



468 



Bashford Dean Memorial Volume 



J 



sure, Ayers notes the absence of such loops in his specimen, but they are shown in 
various figures by AUis (1911 and 1923). In Chlaynydoselachus a posterior efferent' 
collector may retain a dorsal connection ^-ith the anterior efFerent-coUector of the same 
gill (^Text-figure 110), an arrangement not usually found in adult elasmobranchs though 
commonly present in their early embryos. 

As portrayed in Text-figure 110, the afferent branchial arteries of Chlamydoselachus, 
excepting the hyoidean and the last branchial, bifurcate dorsally, one branch passing 
over the cleft anteriorly to join the afferent in front, the other passing posteriorly over 
the succeeding cleft to join the follov.'ing afferent. Thus the afferents, like the efferents, 
are connected into a series of loops around all the clefts. Complete afierent loops are not 
found in other sharks. Basing his opinion upon what is knouTi concerning the manner 
of development of the branchial arteries in other sharks (particularly in Squalus as de- 
scribed by Scammon, 1911), Corrington (1930) concluded that the anastomoses which 
complete the afferent loops around the gill-clefts in Chlamydoselachus could arise only 
late in embryonic development, after the arterial pattern had been nearly completed; 
therefore they are among the most recent acquisitions of the branchial arches. They 
represent a secondary' and speciaHzed condition — an interpolation — in Chlamydoselachus, 
and are probably incipient in Heptanchus (Text-figure 111). 

In elasmobranchs generally, each epibranchial arten,^ of the early embryo is situated 
dorsal to a gill-arch; but in later development these arteries become shifted to positions 
dorsal to the respective gill-slits (Goodrich, 1930, Figs. 531a-d and 532). In Chlamy- 
doselachus, the epibranchial arteries of the adult (Text-figure 110) are situated dorsal to 
the respective gill-arches — that is, they retain what is presumably their embryonic 
position. According to AUis (1912) they are ver>^ nearly in the same position in Heptan- 
chus (my Text-figure 111\ 

Corrington (^1930, p. 198) suggests that, since Daniel has given us the apt desig- 
nation of efferent-collector artery for the lower forks that gather up the oxygenated blood 
from the gills, we may restrict the name efferent branchial artery to the upper and single 
trunk, thus expressing its revehent correspondence to the afferent branchial artery in 
their relationships to the gills. Epibranchial thus becomes a synonym for efferent bran- 
chial. Concerning the efferent branchial (epibranchial) arteries in elasmobranchs, 
Corrington (pp. 198-199) writes as follows: 

The first of the series is the efferent hyal artery which courses forward and has been . . . 
long identified with the carotid system. . . . Then follow 4, 5 or 6 efferent branchials, de- 
pending on the species, and confonning to the number of giUs and of afferents, as previously 
noted. Usually these are all separate, but in j<lotorhynchus, Heptranchias [Heptanchus], 
Chlamydoselachus and doubtless in other notidanids, the last efferent joins the penultimate 
midway of its course so that the two have a common stem thence to the aorta. The condition 
indicates the approaching loss of the last giU in each case, and is a parallel circumstance to 
the fusion of the pharyngobranchials of the last tw,-o skeletal arches, so commonly seen in 
sharks. 



The Anatomy of Chlamydoselachus 



469 



Arterioles within the Gills. — In searching the literature on Chlamydoselachus, 
I have found nothing on the blood-vascular system within a gill proper. In order to study 
this I have been obliged to prepare serial sections of gill-arches and holobranchs excised 
from my specimens. 

The general plan of the blood- vascular system within a gill is indicated in my Text' 
figures 78, 79 and 80 (see pages 421 and 422), which do not, however, show any capil- 



n aef 




im 



Pl 



^^ P^f b Irk 




prnc 



Text-figure 112. Text-figure 113. 

Sections through gills of elasmobranchs, showing afferent and efferent vessels. 

Text-figure 112. Section across gill-bar of Scyllium canicula, late embryo 32 mm. 
long, showing blood supply to lamellae. 

aef, anterior efferent artery; af, afferent artery; al, anterior lamella (filament); b, branchial bar; em, 
external constrictor muscle; gr, gill-ray; gr% gill-raker; im, adductor branchialis muscle; n, nerve; 
pef, posterior efferent artery; pl, posterior lamella (filament) continued into external filament (not 

present in adult); s, gill-septum. 

After Goodrich, 1930, Fig. 516. 

Text-figure 113. Diagram illustrating the structure of a gill of a selachian. 

aef, anterior efferent artery of arch; af, afferent artery of lamella (filament); al, anterior lamella (fila- 
ment); gr, gill-ray; Im, capillary network; pef, posterior efferent artery; pl, posterior lamella (filament); 
prn, pretrematic nerve; prnd, branchial muscle; ptn, post-trematic nerve; s, outer region of septum; 
sc, superficial constrictor muscle; s\, skeletal arch. 
After Goodrich, 1930, Fig. 517d. 



laries. An afferent artery, (af. hr. a. in Text-figure 78), coursing along the outer side of 
the gill-arch, gives off a branch (afferent branchial arteriole) to each filament. Each 
afferent arteriole passes along the base of the corresponding filament (Text-figure 78), 
giving off numerous branches to it (Text-figures 79) and also to the septum. The precise 
manner of this branching has not been fully worked out, since the task requires an elabo- 
rate reconstruction, but it is evident that many of the arterioles are here somewhat 
lacunar in character. An efferent branchial arteriole (ef. hr. a. in Text-figure 78) courses 
along the outer edge of each filament, returning the blood from the capillaries of the 
filament to an efi^erent-collector artery of the gill-arch. A fairly large vein, (v. in Text' 



470 



Bashford Dean hiemorial Volume 



figure 78), presumably draining the blood from smaller vessels in the gill'septum, was 
found in the proximal portion of the septum. Just proximal to the main afferent artery 
of the gill-arch, in the location where an extension of the coelomic cavity presumably 
occurs in the early embryo, there is a fairly large space which probably represents a 
lymphatic vessel whose thin wall is incompletely preserved. 

The distribution of arteries within a gill of Chlamydoselachus is essentially the same 
as in other elasmobranchs, e. g., as in Heptanchus (Text-figure 81, p. 423); in Scyllium 
(Text-figure 112); and in selachians generally (Text-figures 113 and 114). Of these 
figures, Corrington's (my No. 114) is the only one showing an intermediate branchial 

<^^^ ^/^ny\ . OR 



^SC^ 



CT >^Qr 



ExbC 




/BCA 

Text-figure 114. 
Frontal section through a shark-gill, drawn semidiagrammatically. 

ABA, afferent branchial artery; ABAr, afferent branchial arteriole; AdA, adductor arcuus; AECA, anterior efferent' 
collector artery; AGF, anterior gill-filament; Cb, ceratobranchial; CS>\, constrictor superficiahs; CT, connective tissue; 
EBAr, efferent branchial arteriole; ExbA, extrabranchial artery; ^yhC, extrabranchial cartilage; GR, gill-ray, distal portion 
not shown; GR((, gill-raker; GS, gill-septum; lb, intrabranchialis; IBCA, intermediate branchial commissural artery; PECA, 
posterior efferent collector artery; PGF, posterior gill-filament; Pot, post-trematic ramus, branchial nerve; Prt, pretrematic 
ramus, branchial nerve; V7v{BV, ventral nutrient branchial vein. 
After Corrington, 1930, Fig. 10, p. 200. 

commissural artery {J.BCA) connecting the two efferent-collector arteries of a single gill. 
Such arteries exist in Chiaraydosdachus (Text-figure 110) as well as in many other elasmo- 
branchs. In some of my sections, I have observed a small artery in the appropriate 
location for an intermediate commissural artery but was unable to trace its connections 
due to the lack of a sufficient number of sections in the series. 

The gill-filaments of CHam-jdoseXadms contain few capillaries; they consist chiefly 
of connective tissue traversed by arterioles and bounded by a very thin integument. 
They serve, therefore, mainly as supports for the lamellae which are the essential organs of 
respiration. The lamellae are exceedingly rich in capillaries. In a section, such as that 
shown in outline in my Text-figure 80 (p. 422), most of the capillaries are cut trans- 
versely. Since the lamellae are only slightly thicker than the capillaries when the latter 
are distended with blood (as they usually are in my sections), each capillary comes in 
contact with the integument on two sides. So rich is the capillary plexus that there 
is scarcely any space between capillaries; in sections where the capillaries are cut trans- 
versely they look somewhat like a string of beads. 



The Anatomy of Chlaynydosdachus All- 

in studying the blood'vascular system of the gills of Chlamydosdachus, one is 
impressed by the enormous increase in the cross'sectional area of the blood stream as it 
leaves the gill'arch, as it enters the filaments, and again as it reaches the plexus of capil' 
laries in the lamellae. There is a corresponding decrease as the blood returns to the main 
efferent branchial arteries. The total arrangement functions to reduce the velocity of 
the blood as it passes through a multitude of tiny capillaries. 

In the section on the respiratory system I have pointed out that in proportion to 
body sizie the respiratory surface in Chlamydosdadius is very large — perhaps larger than 
in most sharks. It seems likely that in fishes that live in the deeper waters of the ocean, 
where it is always cold and where oxygen is not so plentiful as at the surface, there 
is need for more efficient organs of respiration; but adequate data for comparison are 
not available. 

In his well'organized treatise on the anterior arteries of sharks, Corrington (1930) 
gives a refreshingly clear presentation of the essential data, illuminated by discussions 
of its significance from a comparative point of view. His synonymy for these arteries 
will be found very useful. Some remarks by Corrington (p. 205) on the hypobranchial 
system of arteries will perhaps explain why I have not included a comparison of these 
vessels in ChlamyAosdachus with those of the same region in other sharks : 

These [hypobranchial arteries] are the last arteries of the head to be formed before 
assumption of the adult condition. This lateness of development and also absence in lower 
groups argue that this system was one of the last vascular acquisitions of the immediate 
shark ancestor. Increased bulk and muscular specialization of the subpharyngeal, inter- 
branchial area demanded an extra mechanism for nutritive supply, and this was hence derived 
from the nearest source. No homologies involving the alteration of any elements previously 
present are necessary or possible, and none have been suggested as far as I am aware. . . . 
There is no type arrangement for these arteries in either the Class or Order, or even in various 
species, so that description must be of a somewhat general nature. 

The most elaborate figures of the arteries of the head of Chlamydosdadius are those 
of Allis (1923). These (which are in color) should be consulted by any one wishing a more 
comprehensive account than is given here. 

THE VEINS 

Very little work has been done on the venous system of Chlainydosdadius. Ayers 
(1889) states that extensive venous sinuses, always simple in character, are developed 
in the course of the large venous trunks. Portions of the principal venous trunks are 
shown in Text'figure 105, copied from Ayers. These vessels are the internal jugular 
vein iS.j.v), the cardinal vein (c.v.), the hepatic vein {h.v), and the tropeic or lateral 
abdominal vein (tr.). The cardinal sinus (c.5.) seems unusually large, as in my own speci' 
mens. The marked development of the venous sinuses is regarded by Ayers as a primitive 
character. 



472 



Bashford Dean 'Meynorial Volume 



Hawkes (1906, p. 983) states that in Chlamydoselachus the anterior cardinal vein 
lies in the vicinity of the vanished seventh gill-cleft, though in most elasmobranchs it is 
in the position of the missing sixth gill-cleft. 

The claspers of Chlamydoselachus have been studied comprehensively by Leigh- 
Sharpe (1926). His Fig. 5a-c (my Text-figure 115a-c) shows the endoskeleton, certain 
muscles, and the venous sinuses of the claspers. His Figures 5a and b have been referred 
to in the sections on the endoskeleton (p. 376) and muscular system (p. 395) respectively. 
The venous sinuses of the claspers of Chlamydoselachus are described by Leigh-Sharpe 
(1926, pp. 312-313) as follows: 

The main blcxDd-vascular system is composed of 
two venous sinuses, parallel to, and on either side 
of, the myxapterygium (Fig. 5c) [Text-figure 115c], 
in connection with which no erectile tissue could 
be discovered. 

The inner [sinus], which is the longer and more 
superficial (Figs. 4a [my Text-figure 97a, p. 452] and 
5c [my Text-figure 115c]), arises posteriorly in the 
distal third of the clasper, and, surrounding the 
clasper muscles, ends blindly in the middle line 
anterior and ventral to the cloaca. Dorsal to the 
myxapterygial articulation it cotmnunicates with 
the other, more lateral, deep-seated sinus; the latter 
drains blood from the extra-cloacal region and from 
the edges of the clasper and, continuing forward, 
empties its contents into the iliac vein dorsal to the 
basipterygium. Five nerves, proceeding to the pel- 
vic fin and clasper, traverse this sinus, and also a 
space (apparently lymphatic) between it and the 
abdominal muscles. These structures are seen dis- 
played in Fig. 4b [my Text-figure 97b, p. 452], and 
the entire venous system in Fig. 5c [my Text-figure 
115c]. As stated above, the function of the blood- 
vascular system in Chlamydoselachus does not appear to be that of erection, nor would the 
metaboHsm of the muscles supplied by it warrant so extensive a system of vessels. Possibly 




Text-figure 115. 
Claspers of Chlamydoselachus in ventral as- 
pect: A, the cartilages; B, the musculature; 
and C, the venous system of the clasper. 

a.m., anteroflexor muscle; Ap., position of apopyle; 
C!., cloaca; Er.M., erector or expansor muscle; i.v., 

iliac vein; V.S., venous sinus. 

After Leigh-Sharpe, 1926, Fig. 5. 



the sinuses are required to provide easy play for the muscles in the position of antero-flexion. 



THE NERVOUS SYSTEM 

Although some careful work has been done on the nervous system of Chlamydo- 
selachus, much remains to be accomplished before a satisfactory account can be written. 
The brain has never been adequately described, even superficially, and the spinal cord 
has been ignored. The functional analysis of the cranial and spinal nerves is incomplete. 
Save for some references to the ciliary ganglion, the sympathetic system has been wholly 
neglected. Lack of time and suitable material prevents my attempting to remedy any of 
these deficiencies. 



The Anatomy of Chlamydoselachus 473 

THE BRAIN 

Garman's brief description (1885.2, pp. 16-17) of the brain of Chlamydoselachus, 
illustrated by his Pis. XV and XVI (my Plate VI) is the first, and remains the most 
comprehensive account of the form and structure of this organ. This comparative neglect 
may be partly explained by the fact that it appears to be very difficult to obtain specimens 
in which proper attention has been given to the preservation of the brain. Garman 
states that the brain of his specimen was very soft. When removed from the skull, it 
collapsed and spread out, so that the figures sketched are a trifle more broad and flattened 
than is natural. His entire description follows : 

The brain is very small. Comparatively the amount of forebrain is much smaller than 
in the higher sharks, Carcharias, Zygaena, and others. In outHnes and proportions there is 
great similarity between this brain and that of the Notidanidae. In both of the genera of 
that family the brain is equally elongate and the disposition of the nerves is not greatly 
different; the differences are mainly in details rather than in general build. . . . The olfactory 
lobe is shorter than that of Hexanchus (compare Maclay, Das Gehirn der Selachier, Plate 
II). The olfactory bulb is similar in shape in these genera; it is a club-shaped expansion 
with lobules at the end from which the nerve distribution takes place. Being broader in 
front, the hemispheres taper more toward the hypophysis than is the case in Hexanchus. As 
in the latter, the optic lobes are rounded above and in front, and are — when viewed from 
above — about half exposed. 

The cerebellum is of medium size, rather smooth on its upper surface, rounded in front, 
and presents an acute angle — with blunted apex — between the corpora restiformia. On the 
upper surface the longitudinal depressions are partly due to the uneven floor of the ventricle, 
on which the upper walls rest. There are three moderate transverse depressions. In the 
cerebellum the amount of pHcation is greater than that in Hexanchus as figured by Maclay. 
There is some likelihood that his figure is taken from a young specimen, and that a large one will 
be marked by greater complication. In Maclay's figure of Hexanchus the folds are represented 
by a simple upward line with a transverse bar on the top, like a letter T. To represent the 
same section in the new shark, we shall have to place another T on each end of the transverse 
bar. Maclay figures a longitudinal section of the cerebellum of a young Mustelus, which 
shows a pretty close agreement. An adult Mustelus, which is a great deal more complex, 
is also figured. 

The corpora restiformia are comparatively large; they approach each other behind the 
cerebellum till there is but a small space between them. 

The medulla is large, somewhat larger than the same portion in the Notidanidae. The 
waved appearance in the sinus rhomboidalis, fourth ventricle, is caused by the transverse 
bands of fibers in its membranous roof. . . . 

The close similarity existing between the brains of Chlamydoselachus and the Notidan' 
idae is a strong point in favor of genetic relationship. 

From the report on an address by Wilder (1905) before the American Philosophical 
Society, I quote the following: 

Here [in Chlamydoselachus] the walls of the forebrain are thinner and less differen- 
tiated [than in Scymnus], and in the lateral extensions toward the olfactory cups ('nostrils') the 
so-called cerebral portion expands nearly equally in every direction from the axis represented 
by the olfactory crus; in most other sharks and in rays or skates the special cerebral extension is 



474 Bashford Dean Memorial Volume 

toward the meson or middle line, so as to meet the corresponding part of the other side; in 
the lamprey the cerebral extensions are away from the meson; in the Dipnoi, as shown by the 
speaker in 1887, they are downward, while in the ordinary and higher air-breathing verte- 
brates, reptiles, birds and mammals, the cerebral hemispheres expand mostly upward. It 
is as if nature had experimented in the four directions at right angles with one another from 
the primitive condition, nearly as in Chlamydoselachus, where the extension is almost uni- 
formly in all directions from the olfactory axis. ... In this connection the speaker reiterated 
his previously expressed conviction that in evolution the olfactory portion of the brain had 
preceded the cerebral; that the ancestral vertebrates needed to smell rather than to think; 
that the organ of forethought had been, so to speak, an afterthought, and that the cerebral 
region, so preponderant in man, was rather an offshoot from the olfactory region, and had 
been interpolated between that and the hinder portions of the brain. 

Hawkes' (1906) figures (my Figures 13 and 14, Plate IV) representing dorsal and 
ventral views of the brain of Chlamydoselachus are not well adapted for showing the 
form of the brain, since each figure shows only a lateral half and some parts have been 
cut away. In general, the brain appears broader and shorter than in the other figures, 
and the breadth is particularly noticeable in the region of the medulla. Hawkes' descrip- 
tion (p. 987) of the brain follows : 

The external features of the brain [of Chlamydoselachus] having a typical arrangement, 
need not be described. . . . Two points only may be noticed: (1) there is a large rhinocoel 
extending to the end of the olfactory stalk; (2) the dorsal roof of both prosencephalon and 
rhinocoel is non-nervous. This second point is of considerable interest, as it recalls the 
condition of Ammocoetes and of the teleosts. The non-nervous roof may be regarded as prim- 
itive when compared with that of Ammocoetes, but as specialized when compared with 
that of the Teleosts. That a non-nervous roof should be found among the Elasmobranchs 
is a point of considerable interest, although its significance is as yet undetermined. 

It is not clear whether Hawkes made a microscopical examination of the roof 
described as non-nervous; she states merely that this observation was made on an 
immature specimen. 

AUis's (1923) artistic portrait of the brain of Chlamydoselachus is reproduced as 
my Figure 7, plate III. This figure gives the impression of being accurately drawn from 
a well-preserved specimen, and is evidently not in any sense a diagram. It should be 
explained that the membranes enclosing the brain had not been removed. AUis states 
that this dissection had not been completed nor controlled when work was stopped by 
the death of his assistant, Mr. Nomura. Comparison of this figure with Daniers (1934) 
figure representing a dorsal view of the brain of Heptanchus (reproduced as my Figure 
28, plate VII), gives point to Carman's remark that the brain of Chlamydoselachus 
closely resembles that of a notidanid. In Allis's figure, the optic lobes seem considerably 
smaller, and the cerebellum larger, than in Heptanchus. The olfactory lobes are longer 
than those of Heptanchus, though Carman says that they are shorter than those of Hexan- 
chus. These comparisons are of course based on the proportional size of each part in 
relation to the total size of the brain. The olfactory tracts diverge more strongly in 
Chlamydoselachus than they do in Heptanchus. 



The Anatomy of Chlamydoselachus 



475 



Concerning the source of his material for study 
of the cranial anatomy of Chlamydoselachus, Allis 
(1923, p. 123) wrote as follows: 

In 1902, Professor Bashford Dean, of Columbia 
University, New York City, most kindly sent me a 
single head of Chlamydoselachus, and it was given to 
my assistant, Mr. Jujiro Nomura, for dissection. It 
was, however, soon found that this one head would 
not suffice for the work contemplated, and, at my 
request. Professor Dean had several other heads sent 
me from Japan. 

In all the figures of the brain of Chlamydosela^ 
chus, the divisions are very incompletely labeled. 
To one familiar with the structures of the elasmo- 
branch brain, the parts are readily recognizable. In 
any event they may be identified by reference to 
my Figure 28, plate VII, and to Text'figure 116, 
after Daniel, representing dorsal and ventral views 
of the brain of Heptanchus, which is very similar 
to that of Chlamydoselachus. 

Today, there are available for comparison a 
wealth of figures of the elasmobranch brain that 
were not in existence when Garman wrote his 
description of the brain of Chlamydoselachus. 
Particular mention should be made of the many 
fine drawings of selachian brains published, much 
later, by Garman (1913) himself. These, buried 
in his great systematic monograph on "The Pla' 
giostomia," have probably never received the at' 
tention that they deserve. They do not, how 
ever, include figures of the brain of Chlamydoseh 
achus nor of any notidanid. 

THE CRANIAL NERVES 




md.v. 



Text-figure 116. 

The brain and cranial nerves of Heptanchus 

maculatus in ventral view. 

hu.VII, buccal branch of facial nerve; di., dien- 
cephalon; hmd., hyomandibular division of the facial 
nerve; il., inferior lobe; med., medulla; ms., mesen- 
cephalon; md.V, mandibular division of the fifth or 
trigeminal nerve; mx.V, maxillary division of the 
trigeminal; os.VII, ophthalmicus superficiahs division 
of the facial nerve; tl., telencephalon; v.s., vascular 
sac; w. to z., occipitospinal nerves; 11, III, IV, VI, 
IX and X, cranial nerves. 
After Daniel, 1934, Fig. 200b. 



Garman's (1885.2) account of the cranial nerves of Chlamydoselachus is limited to 
naming them and to describing, in a very general way, the superficial origin of their 
roots. Hawkes (1906) has given us the only comprehensive and detailed account of the 
entire series of cranial nerves; her illustrations of these nerves are reproduced herein. 



476 



Bashford Dean Memorial Volume 



Brohmer (1909) described briefly the cranial nerves of a 25'min. embryo. The account of 
the cranial nerves by AUis (1923) is, as the author states, incomplete. 

The general plan of the cranial nerves of vertebrates is best revealed in their em' 
bryos. For the embryo of Scyllium, this plan is set forth diagrammatically in Text'figure 
117. A somewhat comparable figure for Chlamydoselachus, based on a single embryo, 
is supplied by Text'figure 118, after Brohmer. 



TUC 




hXTh 

Text'figure 117. 

Diagram of the segmentation of the head in an embryo of Sc-yWium canicula. The myotomes are 

longitudinally striated, the nerves black, and the scleromeres dotted. The cartilaginous visceral 

arches, also the optic capsule and the nasal sac, are represented by dotted outlines. 

I' VI, gill-slits; I-ll, somites, prootic from 3 forwards, and metaotic from 4 backwards; a, auditory nerve; ah, abducens nerve; 
ac, auditory capsule ; ah, anterior head cavity ; c, coelom in lateral plate mesoblast ; cr, limit of cranial region ; /, facial nerve ; 
gl, glossopharyngeal nerve; ha, hyoid cartilaginous arch; hm, hypoglossal muscles from myotomes of somites 6, 7, 8; h)i, 
hypoglossal complex nerve; !a, lamina antotica; m, mouth; ml, second metaotic myotome; m6, sixth metaotic myotome; 
ma, mandibular cartilaginous arch; mb, muscle bud to pectoral fin; nc, nasal capsule, continuous with trabecula behind; 
aal and aa2, first and second occipital arches of segments 6 and 7; om, oculomotor nerve; prf, profundus nerve; scl, sclerotome 
of segmentlO; spl, vestigial dorsal root and ganglion of first spinal nerve; sp2, second spinal; t, trochlear nerve; tr, trigem- 
inal nerve; v, complex root of vagus nerve; vgl, vestigial dorsal root and ganglion of segment 7; vc, ventral coelom extending 
up each visceral bar; vr, ventral nerve root of segment 6, supplying second metaotic myotome and hypoglossal muscle; 

vs, Umit of visceral region. 
After Goodrich, 1918.2, Text-fig. 1. 



For the adult Chlamydoselachus, the chief cranial nerves are represented in my 
Figure 29, plate VII. The roots of the cranial nerves are shown in Figures 13 and 14, 
plate IV, and in Text'figure 119. For comparison, I have inserted a figure showing the 
cranial nerves of Squalus (Text'figure 120). My principal illustration of the cranial 
nerves of Chlamydoselachus (Figure 29, plate VII) is complicated by a diagram of the 
lateral line system of sensory canals. Hawkes, throughout her work on Chlamydoselachus, 



The Anatomy of Chlamydoselachus 477 

devoted much attention to the innervation of the lateral line system, renaming most of 
the divisions of that system in accordance with their nerve supply — a method first 
employed by Cole (1896) in his work on Chimaera, and which has since been generally 
adopted. 

The reader who is not familiar with the terms employed in the classification, on 
a functional basis, of the cranial nerve components of fishes should consult Herrick, 
1899, pp. 7-19; Johnston, 1905.1, pp. 176-184 and PI. IV; Norris and Hughes, 1920, 
Fig. 51, showing the cranial nerve components of Squalus in color; and Goodrich, 1930, 
pp. 725-755. 

A complete resume of the rather lengthy descriptions, by Hawkes (1906) and Allis 
(1923), of the cranial nerves of Chlamydoselachus seems unnecessary since, for the most 
part, these nerves are much like those of other elasmobranchs (e.g., Heptanchus, briefly 
described by Daniel, 1934; and Squalus, elaborately described by Norris and Hughes, 
1920). It seems sufficient to mention some respects in which the cranial nerves of Chlamy^ 
doselachus dxz more or less unique, or in which the descriptions of authors differ. The 
following account is based primarily on Hawkes' description. 

A nervus terminalis is not mentioned by Garman, nor is it shown in any of his 
figures of the brain. It is, however, described by Hawkes (who calls it Locy's nerve, 
L.?v[., Figure 13, plate IV) as large and welhdefined. Originating near the median Hne, 
somewhat to the ventral side of the forebrain, it passes outward, curving upward along 
the anterior and upper side of the olfactory stalk to be distributed between the end of the 
stalk and the beginning of the olfactory capsule. On reaching this point, the nerve 
becomes somewhat enlarged by flattening, then breaks up into a number of fine branches 
which pass toward the olfactory epithelium but could not be traced to their endings. 

Allis (1923) writes that in his specimen a small nervus terminalis runs outward 
along the anterior surface of each tractus olfactorius, and then turns upward onto its 
dorsal surface, as stated by Hawkes. The terminal portion of the nerve of the left side 
is shown (without a label) in Figure 7, plate III. 

The olfactory nerve of Chlamydoselachus is neither figured nor mentioned by any 
author. From this we may surmise that it is essentially the same as in other elasmobranchs, 
developing from neuroblasts in the epithelium of the olfactory capsule and extending as 
a double nerve backward to the olfactory bulb. In Heptanchus, as in some other forms, 
the nerve is so short as to be hardly recognisable without microscopical examination. 

The optic nerve (2, Figures 25, 26 and 27, plate VI, after Garman) does not take 
the most direct route to reach the eyeball. As described by Allis (1923) and as shown in 
his Figs. 52 and 59 (the latter reproduced as my Figure 7, plate III) this nerve runs antero- 
laterally. Having issued through its foramen, it turns ventro-latero-posteriorly around 
the anterior end of the capsular sheath that encloses the orbital process of the palato- 
quadrate, and reaches the eyeball, passing ventral to the somewhat Hgamentous portion 
of the connective tissue that attaches the capsular sheath to the anterior wall of the orbit. 



478 Bashford Dean hiemorial Volume 

The innervation of the muscles that move the eyeball is shown (with the exception 
of the abducens or sixth nerve, which innervates the external rectus) in my Figures 
10, 11 and 12, plate IV. The chief peculiarities of the muscles (p. 392, Text'figures 66 and 
67) are: (1) the external rectus is divided, as in some other elasmobranchs, into two 
parts; and (2) all the recti muscles are attached to the top of the eyestalk, near its flat' 
tened head. Allowing for these peculiarities of the muscles, the distribution of the third 
(oculomotor), fourth (trochlear), and sixth (abducens) nerves is the same as in vertebrates 
generally. The relations of these nerves are described by Allis (1923). 

Hawkes states that only one root of the trigeminal nerve (R.V. in Text'figure 
119a and b) is recognizable macroscopically, though presumably both sensory and motor 
components are present as in other forms. The single root is broad, but in a side view 
it is almost completely hidden by the ganglion buccaHs {VII in Text-figure 119a and b). 

The ophthalmicus profundus nerve (Pro.), together with the ophthalmicus super- 
ficialis V (S.Op.V.), originates from a small enlargement (presumably ganglionic) on the 
inner side of the Gasserian ganglion {V in Text-figure 119b). Thus, as in Chimaera 
(Cole, 1896) and in Petromyzon (Johnston, 1905.2), there is evidence that, at the present 
time, the profundus (prf.) is a branch of the trigeminal, although in origin it belongs to 
a more anterior segment (Johnston, 1905.1), as shown for Scyllium in Text-figure 117. 
In both Chimaera and Petromyzon, the profundus nerve has an undoubted ganglion. 
The distribution of this nerve is described by Hawkes (1906, p. 971) as follows: 

On entering the orbit the [profundus] nerve passes between the large rectus externus 
muscle and the cranial wall, sending dorsally a long ciliary nerve which ends around the 
upper part of the eyeball. The main nerve then passes outward, parallel with the oculomotor 
nerve, to which it sends or from which it receives an anastomosing branch. Five mm. beyond 
the origin of the ciliary branch the profundus passes somewhat ventrally between the eyeball 
and the external rectus muscle to disappear in the eyeball, near the point of insertion of the 
ventral part of the external rectus muscle. The profundus passes for about 1 cm. under the 
covering membrane of the eyeball, emerging near the point where the optic nerve originates 
from the eyeball. The nerve then passes anteriorly and out of the orbit immediately to the 
outer side of the attachment of the inferior oblique muscle. Almost at once the nerve divides 
into a number of branches, which spread over the olfactory capsules immediately below 
the skin. 

The course of the profundus nerve in the region of the eyeball is illustrated in 
Figures 10 and 12, plate IV, after Hawkes, who suggests that the anastomosis (A.B.) 
between the profundus and the oculomotor nerve may comprise the fibers that connect 
the ciliary ganglion and the oculomotor nerve, which here pass not directly to the ciliary 
ganglion, but by way of the profundus. The distribution and relations of the profundus 
nerve in the region of the eyeball are described in more detail by Allis (1923). 

Brohmer (1909) states that in his 25-mm. embryo of Chlamydoselachus the ciliary 
ganglion occurs in the course of the nervus ophthalmicus profundus, which sends a branch 
to the "nerve knot" on the wall of the premandibular cavity (Text-figure 118). From the 
nerve knot a branch, which Brohmer calls the oculomotorius {Oc), extends forward. 



The Anatomy of Chlamydoselachus 



479 



He was unable to trace this nerve to the brain. In his summary (p. 677) he writes: 
''Der Oculomotorius steht mit dem Trigeminus in Verbindung." 

Ziegler (1908) remarks that the 25'mm. embryo of Chlamydoselachus studied by 
his pupil, Brohmer, was cut in ''eine liickenlose Schnittserie." Ziegler 's account of the 
cranial nerves of Chlamydoselachus, which is based on Brohmer's studies and some 
observations of his own, is largely a confirmation of Brohmer's results. Ziegler evidently 
believes that, in elasmobranchs generally, the ciliary ganglion is closely associated with 
the profundus nerve, though many authors have emphasi7;ed its relation to the oculomotor. 

In various selachians, one or more 
small (ciliary) ganglia are related to the 
oculomotor nerve (Daniel, 1934). These 
ganglia give rise to nonmeduUated fibers 
which make up the short ciliary nerve. In 
Squalus (Norris and Hughes, 1920) the 
ciliary ganglion is connected by fibers 
with the oculomotorius, the ophthalmicus 
profundus V, and the palatinus VII nerves. 
A review of the literature on the relations 
of the ciliary ganglion in elasmobranchs is 
given by Norris and Hughes (1920). 

In Chlamydoselachus the superficial 
ophthalmic V, according to Hawkes, 
passes from the Gasserian ganglion side 
by side with the profundus nerve, which 
it equals in si?e. It at once passes dorsally 
and enters the same groove as the oph' 
thalmicus superficialis VII, with which, 
however, it does not unite. About as far 
forward as the external nares, but nearer 
the median line, it spreads out into many 
branches which lie immediately under the 
skin. This nerve apparently contains only 
cutaneous elements. A somewhat differ- 
ent account of the same nerve is given by 
Allis (1923, pp. 210-211) as follows: 

The ramus ophthalmicus superficialis 
trigemini, as I define this nerve, includes the 
similarly named nerve of Merritt Hawkes' 
descriptions and her ramus ophthalmicus 
superficialis facialis, and these two nerves 
were completely fused with each other in 
the two specimens examined, instead of 




Text'figure 118. 
Reconstruction of the cranial nerves in a 25'tnm. 

embryo of Chlamydoselachus. 
Ac, nervus acusticus; Cg., ciliary ganglion; D.e., ductus endolym- 
phaticus; F.Ac, n. facialis acusticus; Ggl.l, Gg!.2, remnants of 
the ganglionic crest; G!., n. glossopharyngeus; Gl.v., ventral root 
of the glossopharyngeal nerve; J^.l.v., n. lateralis vagi; Oc, n. 
oculomotorius; :„, nerve knot in the premandibular cavity; R.bucc, 
ramus buccalis; R.hy., ramus hyoideus; R.md., ramus mandibularis; 
R.mx., ramus maxillaris; R.o.s., ramus ophthalmicus profundus; 
Spr. (I)., spiracle (first gill-cleft); Tr., n. trigeminus; Vg., roots of 
the vagus nerve; Vg.5., the last branch of the vagus; J.Sp., first 
spinal gangHon; I.D., first ventral root (of the occipitospinal 
nerves); II, III, IV, V, second to fifth gill-clefts. 

After Brohmer, 1909. Text-fig. 10. 



480 



Bashford Dean Memorial Volume 



being wholly independent, as Merritt Hawkes describes and shows them. Further- 
more, it is to be noted that the origin of her ophthalmicus superficiaHs trigemini from that 
small s\^eUing on the inner side of the Gasserian gangHon from which the ophthalmicus 
profundus has its origin, would seem to indicate that it is a portio ophthakaici profundi 
and not a trigeminus ner\'e, and its origin in Squalus, as given by Landacre (1916), and its 
distribution in the same fish, as given by Norris and Hughes (1920), are not unfavourable 
to this interpretation of it. The nerve is, however, said by Norris and Hughes to arise 
from ganglionic cells in the Gasserian ganglion, while the fibers of the ophthalmicus profundus 
simply traverse that gangHon. The ner\-e, as I find and define it in Chlamydoselachus, is 
large, and running forward dorsal to all the ner\'es and muscles of the orbit, traverses the 



.ootA. 
•RootB. 



S.Op.VII-: 

s.op.v- 

Fro'. 







A- 




-S.Op.V 
{t-Fto. 

,vm jj \^\yys.op.vR 

B- Manyy ; ^^ucc 
JVfax.K 



Text-figure 119. 
Gangliated roots of fifth, seventh and eighth cranial ner\'es of Chlamy- 
doselachus: A, lateral view; B, medial (inner) view. 

Bucc., ramus buccalis VU; H., gangUon of the trvmcus hyomandibularis (i.e., the true 
ganglion of the facialis, combined with the acustico-hteraHs ganglion); Man. V and Max. V, 
mandibular and maxillary divisions of the facial ner%'e; P.I., pars intermedia; Fro., profundus 
branch of the facial; R-C, ramus communicans; R_ V., root of trigeminal nerve; S.Op.V 
and S.Op.VII, superficial ophthalmic divisions of the fifth and seventh cranial nerves. 
After Hawkes, 1906, Figs. 2 and 3, pL LXVm. 



preorbital foramen and reaches the dor^ surface of the nasal capsule, where it immediately 
breaks up into numerous branches which spread out, fan-shaped, and innen.'ate the sensory 
organs of the supraorbital laterosensory canal and the supraorbital ampullae, as shown in the 

figures. As the ner\'e traverses the orbit a number of branches are sent upward through the 
foramina supraorbitaHa to the related portion of the supraorbital canal. 

The maxiUar}' and the mandibular rami of the trigeminal nen.'e (Max. V. and 
Man. V. in Text-figure 119) come off separately from the Gasserian gangHon; there is 
no common maxillo-mandibular trunk. This condition is somewhat exceptional ainong 
elasmobranchs. Since, in Chlamydoselachus, the angle of the jaw is situated far posteriorly, 
the mandibular nerve leaves the maxillary early in its course and passes over the posterior 
wall of the orbit to reach the angle oi the mouth, as m Acanthias. The mandibular 
nerve does not supply the large median transverse muscle bridging the halves of the lower 
jaw in the gular region (Fiirbringer, 1903; Hawkes, 1906; Luther, 1909; AlHs, 1917 and 
1923). This unique feature has been fully discussed (p. 399) in the section on the 
muscular system. 



The Anatomy of Chlamydoselachus 481 

Hawkes finds many small branches of the maxillary nerve which terminate in the 
mucosa of the roof of the mouth and are therefore visceral, but she thinks it probable 
that these visceral components belong to the facial nerve and are only secondarily united 
with the trigeminal. 

Every student of comparative anatomy is familiar with the difficulty of separating 
the fifth and the seventh nerves where parts of different nerves are interwoven or run 
in the same sheath. Hawkes (1906, pp. 968 and 969) states that in Chlamydoselachus: 

No complete union between the [fifth and seventh] nerves has been found, except for 
a distance of about 1 cm. on the left side, where a branch of the ramus buccalis and of the ramus 
maxillaris are inseparable. The appearance of union occurs chiefly in the region just beyond 
the orbit, where there are plexiform connections between the buccalis VII, mandibularis V, 
maxillaris V, and their branches. Here, when two or more nerves come into close contact, 
they are loosely or tightly bound together by connective tissue, but, in all cases except the 
one mentioned above, in such a way that a separation can be effected by careful dissection. 
The smaller branches and these pseudo'unions vary considerably on the two sides of the 
same specimen and in different specimens. The variabihty, which is met with in every 
system of Chlamydoselachus, suggests that the species has considerable anatomical instability. 

There is considerable difference of opinion as to what parts, in the region of the 
gangliated roots, belong to the fifth and seventh nerves respectively. In most elasmo' 
branchs the ganglion of the buccal division of the seventh or facial nerve is intimately 
associated with the Gasserian ganglion, and the two are often inseparable. In Chlamy^ 
doselachus the two ganglia are distinct medially, as shown in Text'figure 119b, after 
Hawkes. Concerning some interrelations of the fifth and seventh nerves AUis (1923, pp. 
209 and 210) writes: 

The nervi profundus and trigeminus, as I interpret these nerves, arise by two main 
roots, the anteroventral one of which is formed by the combined roots of the profundus 
and that part of the trigeminus that is currently considered to form the entire nerve. The 
other root arises by two rootlets, in close connection with the root of the nervus facialis, the 
two rootlets being the facialis roots A and B of Merritt Hawkes' descriptions. This root 
joins the anteroventral root inside the cranial cavity, and, in the specimen used for the 
accompanying Fig. 58, the two roots traverse the membrane that forms the mesial wall of 
the acustico'trigemino-faciahs recess through a single foramen which lies anterior to the 
foramen for the root of the nervus facialis and wholly separate from it. In the acustico' 
trigemino'facialis recess these two roots enter a ganglionic complex, but this complex was 
not particularly examined. According to Merritt Hawkes a ganglion forms on each of the 
two roots, one of which she calls the Gasserian ganglion and the other the buccalis ganglion, 
the latter ganghon lying dorsal to the former and wholly [?] separate from it. On the "inner 
side" of the Gasserian ganglion there is said to be a small sweUing, from which the rami 
profundus and superficial ophthalmic V arise, side by side and of equal size. Comparison 
of these conditions, as thus described, with those in Squalus acanthias and Mustelus califor- 
nicus, as described by Norris and Hughes (1920), would seem to establish beyond question that 
the anterior root of Chlamydoselachus is composed entirely of motor and general sensory 
(spinal V) fibers, that the little swelling on the inner side of the so'called Gasserian ganglion 
is the ganglion of the nervus profundus, and that the posterior root of the complex derives 



482 Bashford Dean 'Memorial Volume 

its fibers both from the lateral line lobe and the acusticum. Whether these latter fibers are 
all strictly laterosensory ones, as Norris and Hughes conclude, or are in part to be compared 
to the communis fibers that enter into the trigeminus in the Teleostomi, seems to me still an 
open question. The three fine nerve strands said by Merritt Hawkes to be sent from the 
Gasserian ganglion to the facialis ganglion are evidently general sensory ones, as Merritt 
Hawkes suggests. 

In one respect, according to Hawkes (1906), the facial nerve is in an unusually 
priraitive condition, in that it has a remnant of the post'trematic ramus quite separate 
from the truncus hyomandibularis. Hawkes states that a chorda tympani, as defined by 
Cole (1896) and by Herrick (1899), is present; but Allis (1923) writes that the so-called 
chorda tympani described by Hawkes seems to be a ramus pretrematicus internus and 
hence, according to recent opinion, not the chorda. Further, the ramus mandibularis 
internus passes internal to the ligamentum mandibulo-hyoideum and then forward along 
the internal surface of the mandible, supplying the tissues of that region. This nerve, 
according to Allis, is a ramus post'trematicus internus facialis and is the one now generally 
considered to represent the chorda tympani. 

Hawkes describes, in Chlamydoselachus, a small branch of the glossopharyngeal 
nerve innervating neuromasts. A branch similar in function has been described in 
Squalus acanthias by Norris and Hughes (1920), but they state that in Raja radiata 
there are no lateral line elements in the ninth nerve. 

Brohmer (1909) finds, between the facialis acusticus and the glossopharyngeal 
nerves of his 25'mm. embryo, a small ventral root (Text-figure 118, Gl.v.) which he inter- 
prets as belonging to the glossopharyngeal. He thinks it likely that this ventral root 
disappears in later stages, and names it ''the rudimentary ventral root of the glosso- 
pharyngeal nerve." Goodrich (1918.2) represents (by a dotted Hne in front of gl.) this 
root in his schematic Text-fig. 1, reproduced as Text-figure 117 herein. 

Garman (1885.2) states that in his specimen ''The tenth pair (vagus) is somewhat 
asymmetrical, having eight roots on one side and twelve on the other. There are also 
four pairs of ventral roots near the median line." Hawkes (1906) states that the vagus 
arises by from nine to twelve roots from the hinder end of the medulla. The lateralis 
root, which is the most cephalad, is invariably large, the remainder are small. These 
small roots are not symmetrical in number and arrangement even in the same fish, much 
less do they agree in different fishes. The roots arise at the same level, being arranged in 
an arc which extends along the side of the medulla to the beginning of the spinal cord. 
The roots cannot be assigned to the separate rami, and the ganglia of the vagus cannot 
be separated completely by gross methods. The ramus lateralis vagi unites closely with 
the true vagus in the ganglionic region. There is a sixth ramus branchiaHs vagi which 
passes toward the remnants of the seventh branchial arch. Hawkes found no trace of 
any median ventral roots uniting with the vagal complex. Commenting on Carman's 
statement concerning the presence of ventral roots in his specimen, Hawkes writes: 
"If Garman were right, his specimen suggests the retention of the somatic motor compo- 



The Anatomy of Chlamydoselachus 483 

nent of the vagus, whereas, in all cases, so far as is known, the remains of that component 
have passed [as ventral occipitospinal roots] into the hypoglossal. . . . This would indeed 
be a primitive condition." Garman (1885.2) does not mention any occipitospinal nerves, 
but the ventral roots labeled "10" in his Fig. A, pi. XVI (my Figure 26, plate VI) are 
probably occipitospinales. 

Hawkes found, in Chlamydoselachus, four (pairs?) of spino-occipital (occipitospinal) 
nerves, which pass out of the cranium by four separate foramina. Three of these roots 
are shown in Figure 13, plate IV, after Hawkes. No ventral occipitospinal roots 
are shown in Hawkes' figure of the ventral surface of the brain. She records that two of 
the occipitospinal roots were placed completely under, the third partly under, the cover 
of the vagal roots. Immediately outside the cranium the occipitospinal nerves unite into 
a flattened strand, the hypoglossal nerve. Hawkes states that the third and fourth 
occipitospinales of Chlamydoselachus have each a dorsal branch, which, like the dorsal 
branches of the succeeding spinal nerves, passes upward and backward. No dorsal 
branches were found on the first two occipitospinal nerves. 

Johnston (1905.1, p. 231) interprets the occipitospinal nerves as follows: ''The 
dorsal and ventral 'hypoglossal' roots need not be considered as spinalartige nerves. 
They probably are not equivalent to spinal nerves at all, but are only the general cutaneous 
and somatic motor components of nerves of the vagus region, the visceral sensory and 
motor components of which have been collected into a single large vagus root." 

In his 25'mm. embryo, Brohmer (1909) describes and figures (my Text-figure 118) 
a series of ventral roots lying between the main branches of the vagus. The first of these 
(l.u.) is present on only one side, and is very small; the others are paired. Brohmer 
states that six of these ventral roots are occipitospinal nerves, but it seems possible 
that only four or five of the most anterior ones are really occipitospinales, the remaining 
posterior ones being ventral roots of spinal nerves. (Daniel, 1934, states that "as many 
as five" of the ventral occipitospinales have been located on each side in the young of 
Heptanchus and Chlamydoselachus). Dorsal to the third and fourth ventral roots, 
Brohmer found two ganglionic masses (Ggl.I., Ggl.2.), which he interprets as remains 
of the ganglionic crest. The more posterior of the two masses has two rootlets. 

In Heptanchus (Fiirbringer, 1897; Daniel, 1934) there are four pairs of ventral 
occipitospinal nerves or roots (Text'figure 116, w-z), but only two pairs of dorsal roots 
(Figure 28, plate VII). The members of the first dorsal pair join the corresponding 
members of the third ventral pair to form a pair of nerve trunks resembling spinal nerves 
in that they have both dorsal and ventral roots. The first roots to arise ventrally are 
near the median line and in origin are not unlike the sixth or abducens nerves. 

In a 26'mm. embryo of Spinax described by Braus (1899) there were four pairs of 
ventral roots representing occipitospinal nerves. Of these, one on the left and two on 
the right were joined by dorsal roots bearing ganglia, thus increasing the resemblance 
to spinal nerves. 



484 



Bashford Dean Memorial Volume 



The number of occipitospinal roots in Chlamydoselachus, Heptanchus and Spinax 
is unusually large. In Squalus (Text'figure 120) there are only two or three ventral 
and two dorsal occipitospinal roots. These nerves united with the first and second 
spinals are marked hh. in the figure. In Torpedo, a single (ventral) occipitospinal root 
is present (Daniel, 1934). 

According to Daniel (1934), the occipitospinal nerves of Heptanchus innervate the 
subspinaHs and dorsal interarcuales muscles; also, in elasmobranchs generally, the more 
posterior of these nerves unite with the first group of spinal nerves to form the cervical 




Text-figure 120. 
A projection, upon a sagittal plane, of the cranial, occipital and anterior spinal nerves of Squalus acanthias. 

hr.p., brachial plexus; hu.VII, buccalis of seventh nerve; d.X, ramus dorsalis of tenth; gn., first spinal gangUon; hh., hypobranchial 
bundle; hmd., hyomandibularis; !!.X, lateral line nerve; md.e.VII, mandibularis externus of seventh; md.i.VII, mandibularis internus 
of seventh; md.V, mandibularis of fifth; mx.V, maxillaris of fifth; op.V, ophthalmicus profundus; os.V, and os.VII, ophthalmicus 
superficiaUs of fifth and seventh; ph.IX, pharyngeal branch of ninth; pi. VII, palatinus of seventh; po.t., post-trematicus of ninth; 
pr.t., pretrematicus of ninth; sp., spiracle; st.IX, supratemporalis of ninth; st.X, supratemporalis of tenth; vi.X, visceral nerve; y and z, 
occipitospinal nerves; II, optic; III, oculomotor; IV, trochlearis; VI, abducens; VIII, auditory nerve. 

From Daniel, 1934, Fig. 220; after Norris and Hughes, 1920, fig. 51 (in colors). 



plexus which in turn joins the pectoral plexus. The nerves of the cervical plexus separate 
from the pectoral plexus and pass in front of the girdle to supply the hypobranchial 
muscles, as in Scyllium and in Squatina (Fiirbringer, 1897). 

In her summary for the cranial nerves, Hawkes (1906) notes that the lower jaw of 
Chlamydoselachus has been swung far back into a reptilian position, and suggests that 
this may explain: (a) the absence of a typical maxillo-mandibular trunk; (b) the union of 
branches of the vagus with one another and with the ramus lateralis vagi; and (c) the 
great development of a hypoglossal musculature and the presence of a hypoglossal nerve. 
She states that the number of roots by which the lateralis components arise confirms the 
suggestion that, in origin, the acustico-lateralis components belong to a series of segments. 
The connections between the acusticO'lateraHs elements of V, VII, and VIII show a ten' 



The Anatomy of Chlamydoselachus 



485 



dency toward unification of the system. The trigemino'facial complex is less primitive 
than that of Chimaera, but more so than that of most elasmobranchs. Hawkes' general 
conclusion is that the cranial nerves of Chlamydoselachus are not in so primitive a con' 
dition as would be expected from the low position of the species in the taxonomic series, 
especially as regards the vagus and the lateralis nerves. 

THE SPINAL NERVES 

Hawkes' description (1906, pp. 985-987) of the spinal nerves of Chlamydoselachus 
is concerned mainly with the spinal nerve roots. I quote her account almost entire: 

The ventral root of the first true or complete spinal nerve originates between the first 
and second vertebrae. Spinal nerves 1, 2, 3, 4, 5 (Fig. 1, pi. LXVIII) [my Figure 29, plate 
VII] unite with the spino'occipital nerves into a strand, which passes backwards, then out' 

Text-figure 121. 
Diagram of spinal nerves from anterior, middle 

and tail regions of Chlamydoselachus. 

C.S., connecting strands between dorsal and ventral roots; 

D.B., dorsal branch; D.R.G., dorsal root with its ganglion; 

'Ho., notochord; S.7^., spinal nerve; V.B., ventral branch; 

V. C, vertebral column; V. R., ventral root. 

After Hawkes, 1906, Text-fig. 141. 








wards towards the pectoral girdle. Spinal nerves 6 and 7 unite with one another before 
joining this plexus. Spinal nerve 8 runs by its side, but does not actually join. The spinal 
plexus gives off anteriorly two branches (S.h.l and S.h.2). Branch S.h.l, which is connected 
with vagus 6, passes forwards and downwards to join branch S.h.2. The resulting compound 
nerve passes forward near the median ventral line to supply a portion of the median man- 
dibular or hypoglossal musculature. It is probable that this nerve consists only of fibers from 
the spino-occipital nerves, and would therefore be the homologue of the hypoglossal nerve 
of higher forms. 

The brachial plexus consists of the remaining parts of the composite strand, i.e., the 
first eight complete spinal nerves of which the last remains distinct. The brachial plexus is 
here in a simple condition, for it consists of but few nerves, and those are not intimately 
united. . . . 

Each spinal nerve arises by two alternate roots, a dorsal and a ventral. The ventral root 
[V.R.] arises by three rootlets, then, after emerging from the vertebral column, gives off 
a large dorsal branch (Text-fig. 141, D.B.) [my Text-figure 121] before uniting with the dorsal, 
ganglionated root [D.R.G.]. In the anterior and middle regions of the vertebral column, 
this union takes place at a level with the top of the notochord, but in the tail region at a level 
with the base of the notochord, immediately to the inner side of the ramus lateralis vagi. 
The ventral branch (V.B.) is given off at varying points (Text-fig. 141) [my Text-figure 121]. 

The dorsal branch (D.B.) of the ventral root runs caudad and upwards, passing over 
the ganghon of the dorsal root (D.R.G.) to be distributed to the muscles of the middle region of 
the back. A similar root (ventral-dorsal) has been described by Ewart and Cole in Raia. No 
dorsal branch was found for the complete spinal nerve or for the dorsal root, as it is probable 
that the dorsal branch of the ventral root receives fibres from the dorsal root as it passes 
over the latter on its backward course. In one segment (Text-fig. 141) [my Text-figure 121] 



486 



Bashford Dean Memorial Volume 




Text'figure 122. 

Nen-Tis collector, consisting of longitudinal strands connecting the ventral rami of certain 

of the spinal nerves, in Chlamydoselachus. 

l.fl.ti., lateral abdominal vein; iiLfi-, pelvic plexus; sp.25,3S, twenty-fifth and thirty-eight spinal nerves. 
From Daniel, 1934, Fig. 224; after Braus, 1898, Fig. 1, Taf. XUl. 

the dorsal branch of the ventral root could be seen, by the naked eye, running over the 
dorsal root gangHon, from which it could not be separated; in the succeeding segment the 
dorsal and ventral roots were joined in the region of the sensory ganghon, and the dorsal 
branch appeared to arise from the ganglion itself. The spinal nerves here recall the condition 
of Laemargus, of Bdellostoma, and of Myxine, in that all three have (1) several rootlets for 
the ventral root, (2) a dorsal branch firom the ventral root which unites with the dorsal 
root ganglion or wth some portion of the dorsal root. 

The "nervus collector" studied by Braus (1898) in Chlamydoselachus and in a number 
of other elasmobranchs, consists of one or more longitudinal strands connecting the ventral 
rami of some of the spinal nerves situated posterior to the pectoral fin and in the region 
of the lateral abdominal vein. The principal collector nerve of Chlaynydoselachus (Text- 
figure 122) is plexiform, and consists of a multitude of anastomosing strands together with 
some branches that end freely. The nervus collector, though variable, appears to be 
best developed in primitive forms like Chlamydoselachus and Heptanchus (Text'figure 
123), in both of u^hich the tvv-entyfifth to the thirty-eight spinal nerves take part. The 




Text-figure 123. 
Nervus collector, connecting the ventral rami of certain of the spinal nerves, in Heptanchus cinereus. 
].a., lateral artery; l.a.v., lateral abdominal vein; pl.p-, pelvic pleius; sp. 25,3S, twentj'-fifth and thirty-eighth spinal nerves, 
From Daniel, 1934, Fig. 205; after Braus, 1898, Fig. 1, Taf. XI. 



The Anatomy of Chlamydoselachus 487 

collector is much more complex in Chlamydoselachus than it is in Heptanchus. In other 
forms few nerves take part (as in Spinax), or the collector may be absent (as in Squatina 
and in Raja). 

The nervus collector has been studied minutely by Braus and others (cited by 
Osburn, 1906 and 1907) because of its possible relation to the origin of the paired fins, 
with results that have been interpreted differently by exponents of the gill-arch and 
fin'fold theories respectively. 

From a functional point of view, the nervus collector is somewhat comparable to 
the caudal longitudinal collecting nerve trunks described by Speidel (1923) in Squalus 
acanthias and in Raja laevis. In both cases, the longitudinal trunks and accompanying 
nervous network provide a conducting system which may be effective in the coordi' 
nation of muscular action. 

The innervation of the tropeic folds, described by Braus (1898), has been considered 
in the section on the muscular system and is illustrated by my Text-figure 59, p. 386. 

THE SENSE ORGANS 

This account of the sense organs of Chlamydoselachus is necessarily very incomplete. 
None of these organs has been described histologically, and my material is unfit for 
study in serial sections. 

The external openings of the olfactory sacs have been described by Gudger and 
Smith (1933), whose account is based on the descriptions of various authors, supple- 
mented by their own observations ; but the internal structure of the olfactory organs of 
Chlamydoselachus has never been described. 

The external appearance of the eye and the peculiar mechanism by which the 
cornea may be protected in the absence of lids have been described by Gudger and Smith 
(1933). In the present paper I have described the muscles of the eye and their innervation, 
in the sections on the muscular system and the nervous system respectively. The internal 
structure of the eye has never been described. 

Of the various sense organs of Chlamydoselachus, the lateral line or sensory canal 
system and associated organs have received the most attention, but even here the various 
authors (Garman, 1888; Hawkes, 1906; and Allis, 1923) are concerned only with gross 
structure and distribution. The ear (membranous labyrinth) has been studied and describ- 
ed by Goodey (1910.1). 

THE MEMBRANOUS LABYRINTH 

Goodey's (1910.1) Figs. 7 and 8, pi. XLIII, illustrating medial and lateral views of 
the membranous labyrinth of Chlamydoselachus, are reproduced as my Figures 30 and 31, 
Plate VII. His description (pp. 551 and 552) of this organ is best given in his own words : 

On removing the skin from the dorsal surface of the cranium it is seen that the parietal 
fossa is rather deep and possesses four apertures, two on either side of the median longitudinal 
line. One of these apertures, the anterior, is small, and transmits the ductus endolymphaticus. 



488 Bashford Dean tAemorial Volume 

The posterior is larger and is closed with soft subcutaneous tissue. It is an opening into 
the perilymph cavity surrounding the posterior vertical canal, and seems to correspond to 
the tympanic aperture which Howes (1883) described in Raid. Before proceeding further, 
I may mention that in this account I am following the nomenclature used by Stewart (1906), 
which differs somewhat from that used by Retzius (1881) in his great monograph. 

The ductus endolymphaticus, on emerging from its cranial foramen, soon expands 
into the saccus endolymphaticus. The latter lies partly in the parietal fossa and is partly 
attached to the under surface of the skin covering this region. It is fairly regular in shape, 
somewhat rounded on its anterior surface, and extends posteriorly in a slightly outward 
direction, gradually becoming attenuated until it reaches its external aperture, which is 
quite small. Internally the ductus endolymphaticus leads into the sacculus. This is not 
rounded, but is laterally flattened, and gives off at its postero-inferior end the lagena in the 
form of a simple caecum. 

The utriculus in this species is like that in other Elasmobranchs, being divided into 
two portions, anterior and posterior, which do not communicate directly with each other, 
but indirectly through the sacculus. 

The anterior utricle is rather laterally compressed and gives off the anterior canal 
dorsally. The latter curves forward and slightly outward, and describes almost a semicircle 
in its course, expanding at its lower end into the anterior ampulla, which then opens by 
a wide portion into the lower end of the utricle again. 

The recessus utriculi is a somewhat spherical structure on the inferior and outer border 
of the anterior utricle. It communicates with the latter by means of a slit-like aperture just 
below that leading into the ampulla externus. The anterior utricle does not open directly 
into the sacculus, but communicates indirectly with it through the recessus utriculi, which 
opens into the sacculus by means of a rounded aperture on the posterodorsal side of the 
recessus. 

Arising from the dorsal end of the anterior utricle, and proceeding in a posterior and 
outward direction, is the external canal, which bends downward and comes to lie in an 
almost horizontal position. At its anterior end it is slightly elevated and expands into the 
ampulla externus, which communicates with the anterior utricle again by means of a short 
canal which rests on the upper side of the recessus utriculi, but does not open directly into it. 

The posterior utricle, which is situated more internally than the rest of the labyrinth, is 
somewhat cylindrical in shape and is slightly curved upon itself. It communicates directly 
with the sacculus by means of a short, almost vertical canal, the ductus utriculo-saccularis 
posterior. Arising from its dorsal end is the posterior canal, which curves outward and 
downward, and then expands into the posterior ampulla, which opens into the lower end of the 
utricle again. 

All three canals, anterior and posterior vertical, and external horizontal, are not rounded 
in section, but are markedly flattened, so that their height is equal to about twice their width. 
The external canal in its almost horizontal position lies with its compressed sides in the 
horizontal plane. 

Goodey then continues with an account of the nerve supply of the membranous 
labyrinth. In conclusion, he states that in structure and. in the distribution of the nerve 
supply the membranous labyrinth of Chlamydoselachus resembles rather closely that of 
J^otidanus (Hexanchus) griseus figured by Stewart, 1906. The membranous labyrinth 
of Heptanchus is described and figured by Daniel (1934). 



The Anatomy of Chlamydoselachus 



489 



THE SENSORY CANAL SYSTEM 

The distribution of the sensory canals of Chlamydoselachus has been described by 
Garman (1888), Hawkes (1906) and AUis (1923 and 1934). Their descriptions have been 
briefly reviewed by Gudger and Smith (1933), who added some observations on the 
specimens in the American Museum of 
Natural History. This account, which is 
fairly well illustrated, need not be repeated 
here. Some of the sensory canals of the 
head are shown in my Text'figure 70, 
page 396; and in Text'figure 124. The 
innervation of the sensory canals of the 
head has been worked out by Hawkes 
(1906), whose drawing is reproduced as 
my Figure 29, plate VII. For comparison, 
I have inserted a similar figure (Text-figure 
125) representing the sensory canals of 
the head in Squalus. It remains to con- 
sider the sensory canal system of Chlamy^ 
doselachus briefly from a comparative 
point of view. 

In all adult elasmobranchs, the sen- 
sory canals are fairly similar in their dis- 
tribution. A pair of these canals extend 
in or under the skin, from the tip of the 
tail to the vicinity of the ear, where they 
connect with other canals branching over 
the various regions of the head. At inter- 
vals, the canals open to the exterior by 
means of pores, so that their approximate 
distribution can usually be traced without 
dissection. 

Among living elasmobranchs it is 
very unusual for the sensory canals to be 
present as open grooves through so great 




_ i iamp 



Text-figure 124. 
Dorsal view of the head of Chlamydoselachus, show- 
ing the external openings of the ampullae of Lorenzini 
and of the laterosensory canals. 

amp, ampuUary pores; end, pore of the endolymphatic duct; iop, 

infraorbital laterosensory pores; lie, lateral line canal of body; 

sop, supraorbital laterosensory pores; sp, spiracular laterosensory 

canal; spr, spiracle. 

Redrawn after Allis, 1923, Pi. 11. 



a portion of their extent as is the case in 
Chlamydoselachus. The lateral line of Chlamydoselachus is an open groove from the tip of 
the tail almost as far forward as the spiracle (Garman, 1888). The anterior portion of the 
lateral line (lie.) is shown in Text-figure 124. Several of the longest sensory canals of the 
head are open — in particular, the spiracular (sp. in Text-figure 124), the gular and the oral. 
The latter are shown in Gudger and Smith's (1933) Figure 7, plate II, after AUis; they 
appear, without labels, in my Text-figure 70, page 396. In Figure 29, plate VII, after 



490 



Bashford Dean Memorial Volume 




Text-figure 125. 
Innervation of the senson,' canal system and certain of the pit organs in Squalus acanthias. 

hu.Vn, buccalis nerve; cc, supratemporal canal; dr.X, ramus dorsalis of tenth nerve; hmc., hyomandibular 

canal; ioc., infraorbital canal; 1!., lateral Kne canal; IIX, lateral line nerve; mc., mandibular canal; mde.VlI, 

external mandibular nerve; os. VII, ophthalmicus superficialis of seventh nerve; po., pit organs; soc., supraorbital 

canal; st.IX, supratemporaHs of ninth nerve; st.X, supratemporalis of tenth nerve. 

From Daniel, 1934, Fig. 245; after Nonis and Hughes, 1920, Fig. 50. 



Hawkes, the oral, gular and spiracular are labeled HLA, HLB and HLC respectively. 
The preceding statements concerning the open condition of the canals hold for my four 
large specimens, save that on the right side of No. I the groove is lacking for a distance 
of about 30 mm. from the tip of the tail. 

A more extensive occurrence of sensory canals as open grooves is found in the 
Holocephali, where most of the canals, including those of the head, are open; but in the 
Selachii, Chlamydoselachus appears to be unique in the extent to which its sensory canals 
are open. The nearest approach to its condition in this respect is found in the notidanids 
(Daniel, 1934j, where the lateral line is an open groove as far forvv^rd as the pectoral fin. 
In Heptanchus the canals of the head are all closed tubes, as far back as the fifth gill-cleft. 
Posterior to this, the lateral lines are represented by a pair of open grooves extending 
almost to the tip ot the tail. In Squalus (Text-figure 125) the canals are closed excepting 
in the region tov."ard the tip of the tail. In higher elasmobranchs, the canals are usually 
closed throughout their entire length. 

The open condition of the sensory canals found by Garman in Chlamydoselachus 
(Text-figure 126) is probably primitive, and in the light of all the evidence can scarcely 
be explained as due to arrested development in the embryonic sense. Lateral Hne canals 
as open grooves were found by Dean ( 1909, p. 252; m the Devonian fossil shark Ctenacaiv 
thus clar\^i (Text-figure 127,) as well as m many acanthodians. In all these forms the 
dermal denticles terminate abruptly at the margins of the groove, and the marginal 
denticles are, in most instances, unusually large, precisely as they are in Chlamydoselachus. 

Most of the terms used by Garman in describing the sensory canals of the head in 
his specimen have been abandoned, and in their places are names for the \^arious divisions 



The Anatomy of Chlamydoselachus 



491 



based on their innervation. Concerning 
certain sensory canals of Chlamydoselachus 
Carman (1888, pp. 82 and 83) writes : 

The aural [supratemporal] canal is closed. 
It has no tubules. Contrary to what obtains 
in other Galei, it lies in front of the so-called 
ear openings [endolymphatic ducts]. These 
openings, however, are at the ends of tubes the 
inner extremities of which are in front of the 
[supratemporal] canal. The canal is nearly 
straight, bending slightly forward in the middle 
and a little backward near each end. . . . At 
the end of the jugular, near the middle of the 
first branchial aperture, there are two branches 
not found in any other of the sharks examined : 
a spiracular [HLC in Figure 29, plate VII], 
turning upward and forward toward the spir- 
acle; and a gular [HLB in Figure 29, plate 
VII], turning down and forward near the 
median line, and finally uniting with the oral 
[HLA in Figure 29, plate VII] a short distance 
from the inner end. . . . Apparently the pre- 
nasal is reversed in direction, meeting the nasal 
in front and running backward to join the sub- 
rostral. . . . Like the corporals, the oral, gular 




Text-figure 128. 
Variations in lateral line canals of Chlamydo- 
selachus; A and B, supratemporal or commissural 
canal; C and D, ventral view of hyomandibular 
canal under the lower jaw; E, lateral Hne canal 

in the region of the dorsal fin. 
CCA. and C.C.B., anterior and posterior portions of com- 
missural canal; H.M., parts of the hyomandibular canal; 
L.L.R. and L.L.L., lateral canal on right and left sides. 
S., vestigial canals (?). 
After Hawkes, 1906, Text-fig. 140. 







tS^^^ 




Text-figure 126. 



Text-figure 127. 



Portions of open lateral line canals in a living and 

in an extinct shark. 

Text-figure 126. The open lateral line canal in 

the tail region of Chlamydoselachus. Note the 

elongate scales (x 5) which partially cover the 

open canal. 

After Garman, 1885.2, Fig. 10, pi. VI. 

Text-figure 127. Lateral line canal of the fossil 

shark Ctenacanthus dark}, showing the enlarged 

denticles at the margin of the groove. 

After Dean, 1909, Fig. 44. 

and spiracular [canals] are open grooves. 
In the spiraculars and gulars of this shark 
are found the nearest approach to the pleu- 
rals of the Batoidei. 

Hawlfes (1906) states that the lateral 
line system of the head of Chlamydosela- 
chus is much more complicated than is 
usual among elasmobranchs (excepting rays 
and skates). Evidently, she refers merely 
to the gross pattern or topographical 
relations of these canals. The supratem' 
poral or commissural canal in Chlaynydo- 
selachus is placed anterior to the openings 
of the ductus endolymphaticus, and is 
never the usual straight, transverse line 
connecting the right and left lateral canals. 
It varies greatly, as shown in her Text-fig. 
140 (my Text'figure 128a and b). There 
are indications of two instead of one com- 



492 Bashford Dean Memorial Volume 

missural canal, but it is impossible to state whether the present condition of these canals 
is vestigial or rudimentary. It is certain, however, that the condition of all the canals, 
but especially those in this region, is very unstable. Some variations in the hyomandibular 
region are shown in Text'figure 128c and d; other variations, in the pelvic and caudal 
portions of the lateral line, are represented in Text-figure 128e. Additional examples of 
variation in the posterior course of the lateral line are described by Gudger and Smith 
(1933, pp. 288-9) in three adult specimens. 

Hawkes concludes that the lateral line system of Chlamydoselachus is primitive as 
regards: (1) the open condition of a portion of the canals; (2) the cutaneous rather than 
subcutaneous position of the canals; and (3) the entire absence of tubules in many places. 
In the occipital and hyomandibular region, however, the system tends to a considerable 
topographical complexity. Again there are indications, in the occipital and lateral canals, 
of either a vestigial or a rudimentary complexity. 

In Heptanchus (Daniel, 1934), anterior to the spiracle and just posterior to the 
endolymphatic duct, a small transverse or supratemporal canal passes off from the lateral 
canal toward the median line. This, however, does not meet and fuse with the similar ca- 
nal from the opposite side. In Heptanchus maculatus there may be two supratemporal 
canals on a side, one posterior to the endolymphatic duct, the other anterior to it. Thus 
we find evidence, in this region, of a variability somewhat comparable to that described 
in Chlamydoselachus. In Heptanchus, Daniel describes a "gular line" of pit organs corre- 
sponding in position to Carman's gular division of the sensory canal system in Chlamy 
doselachus. Allis (1923; 1934), like Garman, describes and figures the gular line as a part 
of the canal system. ''The spiracular and gular canals [of Chlamydoselachus] form 
a continuous open groove" (Allis, 1923). This statement holds, without exception, for 
both right and left sides of my four large specimens. Norris (1929) writes: "The 
mandibular series of pit organs in Squalus (Norris and Hughes, 1920) and Mustelus 
(Johnson, 191?) evidently correspond to the gular canal organs in Chlamydoselachus 
(Hawkes, Allis)". 

Many other comparisons of the sensory canal, ampullary and pit organs of Chlamy- 
doselachus with those of other elasmobranchs are elaborated in the works of some of the 
authors cited, but these involve details that cannot be considered here. 

DISCUSSION 

The present section is concerned with the phylogenetic significance of the anatomical 
characters described on the preceding pages. In every section of this article, comparisons 
have been made between Chlamydoselachus and other vertebrates, so that it is not neces- 
sary to enter into details here. 

My own interest in Chlamydoselachus relates chiefly to the evolution of organs and 
organ systems as such. Nevertheless, while studying this shark I have been impressed 
by certain things that have a bearing on the question of its phylogenetic affinities : first, 



The Anatomy of Chlamydoselachus 493 

in some features it seems more primitive than any other living shark; second, in certain 
other respects it is highly specialised; third, it possesses some characters that are unique; 
fourth, it combines (as in the spiral intestine) some characters that are ordinarily segrc 
gated in different species; and fifth, it is highly variable. Within obvious limits, the 
frilled shark is a comprehensive type, and this constitutes one of the difficulties in the 
way of determining its affinities. 

It is recognised that we are here on treacherous ground. Opinions will differ con' 
cerning the evaluation of the anatomical characters of Chlamydoselachus, and concerning 
the status of the animal as a whole. Nevertheless, to give point to the discussion I have 
summarised the most important data (Tables IV and V, pp. 496-497) in two lists of 
characters: one palingenetic or primitive, the other cenogenetic or of relatively recent 
origin, with reference to comparable structures in other living sharks. Some very obvious 
features, such as the unusual number of gilPsHts and the dorsoventral flattening of the 
head, are excluded because of insufficient evidence as to their status. It is not expected 
that anyone will accept either list in its entirety. Each list might be greatly extended, 
affording endless opportunities for debate. 

The more striking peculiarities of Chlamydoselachus, such as the very elongate 
form of the body and the peculiar hyostylism of the skull, are obviously cenogenetic. 
The real difficulty lies in the disguises which may conceal other cenogenetic characters. 
Apparent primitiveness is frequently the result of degeneration or retrogession, in 
a phylogenetic sense; this, as applied to the individual, is usually a matter of arrested 
development. In Chlamydoselachus there are evidences of retrogression in the skeletons 
of the fins, in the mesonephric duct and urinary sinus of the right side, and in the vestigial 
seventh gill'arch. In each case there are decided irregularities. It seems to be a fairly 
general rule that, when the development of an organ is arrested, it does not merely fail 
to attain the ancestral condition, but exhibits a vestigial complexity. 

In Chlamydoselachus there are features, such as the thin walls and large foramina 
of the cranium, the incipient cyclospondylous vertebral centra, and the paired condition 
of the urinary sinuses in the adult, that appear more characteristic of an immature than of 
an adult shark. The position of the epibranchial arteries is that found in the embryos 
of other sharks. In all these cases there is no evidence that development has ever gone 
further. The alternative is to accept these features as primitive characters. The per' 
sistent thyroglossal duct may be anomalous, since it is not found in all specimens. Since 
the so'called duct differentiates like the wall of the pharynx, from which it is derived, 
it is obviously something more than an embryonic rudiment. 

I have said that, within obvious limits, Chlamydoselachus is a comprehensive type. 
This is true mainly with respect to features that may be found in other sharks, but some 
of the resemblances to higher vertebrates are striking. Of these, it is sufficient to mention 
the extreme length and mobility of the jaws, suggestive of the Ophidia; the gular fold, 
simulating a condition found in many of the Teleostomi; and the armature of scales on 



494 Bashford Dean Meinonal Volume 

the anterior border of the dorsal fin, resembling in torm and arrangement the "fulcral 
scales'' of the Actinopterygii. It is scarcely necessary to add that these resemblances to 
higher vertebrates have no phylogenetic significance. 

The expression "oldest Kving type of vertebrate'" used by Garman (1884.3 and 
1884.4) and by GiU (1884.1 and 1884.2) v.nth reference to Chlamydoselachus, quite ignores 
the cyclostomes. While the cyclostomes are in some respects degenerate, in others 
highly organized, they retain, to a greater degree than any other vertebrates, the funda- 
mental chordate structures. The view that skeletal degeneration has been a major trend 
in fish history has its Hmitations, particularly when one considers the endoskeleton rather 
than the external armor. Cartilaginous, calcified and bony vertebral centra develop 
largely at the expense of the notochord, and it seems unlikely that degeneration of the 
harder structures would result in the notochord being restored to its primitive condition 
as an effective organ in the adult. In Cyclostomata, as in Holocephali, the notochord is 
unimpaired. The ammocoetes larva of the lamprey Hnks this form v.'ith the lower chor- 
dates rather than with the fishes. If phylogeny be defined as the succession of adult 
forms in the line of evolution, this latter evidence is not admissible, but if organisms are 
genetically related in the adult stage, then they must be related at all stages of their 
development. The cyclostomes have long been regarded as the lowest group of Hving 
vertebrates (crania tes), and the e\'idence in support of this vie^w should not be lightly 
set aside. 

The very interesting question of the relationship ot Chlamydoselachus to fossil 
forms is one that I am quite willing to leave to paleontologists. Such studies must remain 
under the handicap that, m fossils, little knowledge is available concerning organs that 
are quite as important as the more enduring skeleton. Since the "hard parts" of Chlamy- 
doselachus, upon which we must depend for comparison w-nth fossils, have long been 
known, it can scarcely be expected that the present paper will add much that will be 
of value to paleontologists. W^hat has been added concerning the "soft parts" serves 
to confirm the generally accepted systematic relationship of Chlamydoselachus to the 
notidanids ■w.^ithout, however, bringing them any nearer together. WTiile Chlamydo- 
selachus and the notidanids must be assigned to different families, the relationship is 
closer than that between Chlamydoselachus and any other existing sharks. In this con- 
nection the following quotation from Woodward (1921) seems pertinent: 

The Hybodonts, which for the most part exhibit the primitive notochordal condition 
unto, the Lower Cretaceous Period, are especially interesting because, w-hUe their dentition 
and their general appearance resemble those of the existing Cestraciontidae, their skuU is 
very different and more closely agrees with that of the Notidanidae. They are indeed a 
generalized group from which several later families appear to have arisen, and they are the 
dominant sharks of the Jurassic and early Cretaceous periods. 

Pre\'ious discussions of the affinities of the frilled shark to fossil forms have been 
re\T.ewed at length by Gudger and Smith (1933j. Garman (1885.2) was particularly 
impressed by the resemblance of the teeth of Chlamydoselachus (Text-figure 7, P- 344) 



The Anatomy of Chlaynydoselachus 495 

to those of Cladodus, and went so far as to say that ''Chlamydoselachus is a cladodont." 
In the present paper (p. 349) I have compared the teeth of the frilled shark with those of 
two cladodonts, Cladoselache and Cladodus, and two hybodonts, Ctenacanthus and 
Hyhodus (Text'figures 17, 18, 19, 20, on p. 348). The resemblance between the teeth of 
Chlamydoselachus and the cladodonts is indeed striking, but the paleontological history 
of Chlamydoselachus goes back no further than the Tertiary, while the cladodonts are 
generally considered to be extinct since the Carboniferous. The teeth of hybodonts are 
more generalised and variable; nevertheless, out of such structures, teeth like those of 
Chlamydoselachus might readily have been evolved. The presence, in the hybodonts, 
of a large spine at the anterior border of each dorsal fin does not exclude this family from 
relationship with the Chlamydoselachidae. In the Spinacidae, some genera possess 
spines similarly located, while other genera lack them. 

Throughout this article I have recorded and emphasized the great variability of 
Chlamydoselachus in most of its structures. The significance of this variability is not 
self'evident. ''As a paleontologist knows . . . variability is a special characteristic of 
the struggling end of a disappearing race quite as frequently as it is a mark of the begin' 
ning of a new race" (Woodward, 1933). There are reasons why, in the case of Chlamy- 
doselachus, one may favor the former interpretation. The frilled shark has been taken 
only in Japanese waters and off the western coast of Europe. If it were a new species, 
one would not expect it to occur in waters so widely separated, particularly since it is 
not gifted with extraordinary powers of locomotion. Since it is quite rare even in these 
restricted localities, it seems to have a precarious hold on existence. It may be significant, 
in this connection, that Chlamydoselachus anguineus is somewhat isolated in its systematic 
position. The genus stands far enough from the Notidanidae to be placed in a separate 
family, the Chlamydoselachidae, containing no other genera. There are no other species 
save the fossil C. lawleyi and C. tohleri, both known only by their teeth (Text'figures 
15 and 16, p. 348), and one may question whether the latter really belongs to the genus 
Chlamydoselachus. The frilled shark appears to be a form that has long been differenti' 
ated in adaptation for a particular habitat and mode of life, in which it has not been 
altogether successful since it now seems to be facing extinction. 

My outstanding impression of the frilled shark is that it presents a strange assem' 
blage of characters ranging from very primitive to highly differentiated. In this, it is 
comparable to Chimaera, though the latter is specialized in a decidedly different way. 
Chlamydoselachus is a deep'sea adaptation of some rather ancient type of shark, and is 
now waging a losing battle in the struggle for existence.^ 

'Since writing these pages I have found in Deinega's (1925) English abstract of his Russian text the following statement: ""We 
may still consider Chlamydoselachus as one of the most ancient representatives of the vertebrates, having survived to our day and now 
undergoing extinaion" (italics mine). I do not know of any other author who has expressed the view that Chlamydoselachus is threaten' 
ed with extinction. In my opinion, Chlamydoselachus is not '"one of the most ancient representatives of the vertebrates." It is, 
however, one of the most primitive of existing sharks, 



496 Bashford Dean Memorial Volume 

TABLE IV. 
PALINGENETIC CHARACTERS OF CHLAMTDOSELACHUS 
Teeth, of "cladodont" type, are formed by the fusion of simple denticles. 
At the angles of the mouth, scales grade into teeth. 
The notochord persists with very little constriction. 
Calcification of the endoskeleton is very limited in amount. 
Cyclospondylous vertebral centra are incipient or rudimentary. 
The visceral skeleton shows a striking gradation between jaws and gill-arches. 
Nearly complete series of basibranchials and hypobranchials, with little fusion. 
In the trunk musculature, longitudinal divisions are few and simple. 
The digestive tube is relatively simple and is nearly straight. 
The bursa entiana is not invaded by the spiral intestine. 
In the valvular intestine, the apices of the anterior and posterior coils point in different directions. 

In the middle portion of the spiral intestine, there is an axial strand; in both anterior and posterior portions, 
there is an axial tube. 

The liver is bilaterally symmetrical. 

In some specimens, there is a persistent thyroglossal duct lined with pharyngeal mucosa. 

Pouch-like vestige of the ventral end of the spiracular gill cleft. 

In the female, the mesonephroi persist through almost the entire length of the body cavity. 

In females, there is a pair of urinary sinuses which open separately into the urogenital smus. 

In females, nearly all the collecting tubules enter the mesonephric duct. So-called ureters are absent. 

Epibranchial (efferent branchial) arteries are situated dorsal to the respective gill-arches, as in the embryos 
of other sharks. 

Posterior efferent collector arteries may retain a dorsal connection with the anterior efferent collector of the 
same gill. 

The brain is very small; the forebrain is small proportionally. 

The roof of the definitive forebrain is said to be non-nervous. 

In a 25-mm. embryo, the glossopharyngeal nerve has a ventral root. 

The "nervus collector" is unusually well developed. 

The lateral line sensory canal is an open groove from the tip of the tail as far forward as the spiracle. Several 
of the longer sensory canals of the head are open. 

Whether open or closed, the sensory canals of the lateral line system are cutaneous rather than subcutaneous. 

The gular division of the sensory canal system corresponds to the "gular line" of pit organs in Heptanchus, 
Squalus and Mustelus, 



The Anatomy of Chlamydoselachus 497 

TABLE V. 
CENOGENETIC CHARACTERS OF CHLAMYDOSELACHUS 
Unusually elongate form of the body. 
Weakness of the dermal fin rays. 

Bunching of the pelvic, dorsal and anal fins near the caudal. 
Unusually large mouth, and very distensible oropharyngeal cavity. 

First pair of gill-covers enlarged, loose-fitting and frilled. They are continuous with a gular fold, unique 
among sharks. 

Abdominal or tropeic folds, unique among vertebrates. 

Peculiar and imperfect hyostylism of the skull. The hyomandibular articular facet is very long, permitting 
a gliding action. 

Jaws are unusually long, and begin far posterior to the cranium. 

Heterospondyly of the extreme caudal end of the vertebral column. 

Shortness and irregularity (fragmentation, displacement, fusion) of cartilaginous fin rays (radials). 

Infolding of the musculature of the ventral body wall in connection with the tropeic folds. 

Alleged absence of an intermandibular muscle innervated by a branch of the trigeminal nerve. 

Dorsal group of eye muscles much stronger than the ventral group. 

Presence of an accessory musculus rectus lateralis. 

All the recti muscles, save only a portion of the accessory rectus laterahs, take origin from the eyestalk. 

Pyloric vestibule sometimes a sharply defined division of the digestive tube. 

The middle intestine is expanded to form a bursa entiana. 

Right and left lobes of the liver extend the entire length of the body cavity. 

The gill-clefts are unusually large, and the respiratory surface afforded by the gills is great. 

The external spiracular openings are very small. 

Mesonephric duct, urinary sinus and urethral pore of the right side are often defective. 

In adult females, the genital organs of the right side are much better developed than those of the left side ; 
the latter are probably not functional. 

The young are retained in the uterus until they reach an advanced stage of development. 

The anterior unpaired portion of the pericardio-peritoneal canal is very short and broad. The paired canals 
often end blindly. 

Afferent branchial arteries are connected by a series of loops over the gill-slits. 

The connections between the acustico-lateralis elements of the fifth, seventh and eighth cranial nerves 
show a tendency toward unification of the system. 

Peculiar mechanism by which the eyes may be protected in the absence of lids, 



498 Bashford Dean Memorial Volume 

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211-287, 16 pis., 65 text-figs. 

Deinega, W. a. 

1909 Contributions to the knowledge of the anatomy of Chlamydoselachus anguineus Garm. I. Skele- 
ton [Russian text]. Trudy Sravnit. Anat. Instit. Imp. Univ. Mos\va, no. 7, 66 pp., 4 pis. 

1923 Zur Kenntniss der Anatomie des Chlamydoselachus anguineus Garm. I. Skelett. Bull. Soc. 
Hat. Moscou (Sect. Biol.) for 1918-1922, n. s. 31, 1-58, 4 pis., text-fig. 

1925 On the abdominal viscera of Chlamydoselachus anguineus Garman [Russ. text, Eng. summary]. 
Bull. Soc. Hat. Moscou (Sect. Biol), n. s. 34, 194-206, 3 figs. 

Edgeworth, F. H. 

1903 The development of the head muscles in Scyllium canicula. Journ. Anat. Physiol, 37, 73- 
88, 7 pis. 



500 Bashford Dean Memorial Volume 

EwART, J. C, AND Cole, F. J. 

1895 On the dorsal branches of the cranial and spinal nerves of elasmobranchs. Proc. Roy. Soc. 
Edinburgh, 20, 475-480, 2 figs. 

Ferguson, Jeremiah S. 

1911 Anatomy of the thyroid gland of elasmobranchs, with remarks upon the hypobranchial circu- 
lation in these fishes. Amer. Journ. Anat., H, 151-210, 20 figs. 

Froriep, August 

1902 Zur Entwicklungsgeschichte des Wirbeltierkopfes. Anat. Anz. (Verh. Anat. Ges.), 21, 34- 
46, 5 figs. 

FURBRINGER, KaRL 

1903 Beitrage zur Kenntnis des Visceralskelets der Selachier. Morph. Jahrh., 31, 360-445, 3 pis. 

FURBRINGER, Max 

1896 Ueber die mit dem Visceralskelet verbundenen spinalen Muskeln der Selachier. Jena. Zeitschr. 
?iaturwiss., 30, 127-135. 

1897 Ueber die spino-occipitalen Nerven der Selachier und Holocephalen und ihre vergleichende 
Morphologic. (In Festschr. 70. Geburtstage C. Gegenbaur, Leip2;ig. Bd. Ill, 349-788, 8 pis., 
text'fig.). 

Gadow, Hans, and Abbott, E. C. 

1895 On the evolution of the vertebral column of fishes. Phil. Trans. Roy. Soc. London, 186 B, 
163-221, 13 figs. 

Garman, Samuel 

1884.1 An extraordinary shark [Chlamydoselachus anguineus]. Bull. Essex Instit., 16, 47-55, fig. 

1884.2 A peculiar selachian [Chiamydose/dchus anguineus]. Science, 3, 116-117, fig. 

1884.3 The oldest Hving type of vertebrata, Chlamydoselachus. Science, 3, 345. 

1884.4 The oldest Hving type of vertebrates [ Chlamydoselachus]. Science, 4, 484. 

1885.1 On the frilled shark [Chlamydoselachus anguineus Garman]. Proc. Amer. Assoc. Adv. Sci. 
for 1884, 33. meet., 537-538. 

1885.2 Chlamydoselachus ariguineus Garman — a living species of cladodont shark. Bull. Mus. Comp. 
Zool, 12, 1-35, 20 pis. 

1888 On the lateral canal system of the Selachia and Holocephala. Bull. Mus. Comp. Zool, 17, 

(Chlamydoselachus, pp. 82-83, pi. XV). 
1913 The Plagiostomia (sharks, skates, and rays). Mem. Mus. Comp. Zool, 36, (Chlamydoselachus, 

pp. 13-15, pi. 59, figs. 4-6; pi. 61, figs. 7-8). 

Gegenbaur, Carl 

1864-72 Untersuchungen zur vergleichenden Anatomic der Wirbelthierc. Leipzig. 

1870 Ueber das Skelctt der GHedmassen der Wirbelthiere in AUgemeinen und der HintergHedmassen 

der Selachier insbcsondere. Jena. Zeitschr. Med. Tvjaturuiss., 5, 397-458, 2 pis., 7 text-figs. 
1872 Untersuchungen zur vergleichenden Anatomic der Wirbelthiere. Heft 3. Das Kopfskelett der 
Selachier. Leipzig, x + 316 pp., 22 pis. 

QiLL, Theodore N. 

1884.1 The oldest Hving type of vertebrata [ChIa7n)'dose/achus]. Science, 3, 346. 

1884.2 The oldest h\'ing type of vertebrates [Chlamydoselachus]. Science, 4, 524. 



The Anatomy of Chlamydoselachus 501 

GOODEV, T. 

1910.1 A contribution to the skeletal anatomy of the frilled shark, Chlamydoselachus anguineus Gar. 
Proc. Zool. Soc. London, pt. 1, 540-571, 5 pis. 

1910.2 Vestiges of the thyroid in Chlamydoselachus anguineus, Scyllium catulus, and Scyllium canicula. 
Anat. Anz., 36, 104-108, 4 figs. 

Goodrich, E. S. 

1906 Notes on the development, structure and origin of the median and paired fins of fishes. Quart. 

Journ. Micr. Sci., 50, 333-376, 5 pis., 3 text-figs. 
1909 Cyclostomes and fishes. (In Lankester's Treatise on Zoology, pt. IX, pp. 1-518. London.). 

1918.1 Development of pericardio-peritoneal canals in selachians. Journ. Anat., Cambridge, 53, 
1-13, 18 figs. 

1918.2 On the development of the segments of the head in Scyllium. ^uart. Journ. Micr. Sci., 63 
1-30, fig. 

1930 Studies on the structure and development of vertebrates. London, 837 pp., 754 figs. 

Gregory, William K. 

1933 Fish skulls: a study of the evolution of natural mechanisms. Trans. Amer. Phil. Soc, 23 
75-481, 2 pis., 302 text-figs. 

GUDGER, E. W., AND SmITH, BerTRAM G. 

1933 The natural history of the frilled shark, Chlamydoselachus anguineus. Bashford Dean Mem. 
Vol., Archaic Fishes, Art. V, pp. 245-319, 5 pis., 31 text-figs. 

GuNTHER, Albert 

1887 Report on the deep-sea fishes collected by H. M. S. Challenger during the years 1873-76. 
(In Report on the Scientific Results of the Voyage of H. M. S. Challenger during the Years 
1873-76, London, Vol. XXII, pt. 57 [Chlamydoselachus, pp. 2-4, pis. 64hS5]). 

Harman, B. 

1899 The palpebral and oculomotor apparatus in fishes; observations on morphology and develop- 
ment. Journ. Anat. Physiol, 34, 1-40, 6 pis. 

Hawkes, Onera a. Merritt 

1906 The cranial and spinal nerves of Chlamydoselachus anguineus (Garm.). Proc. Zool. Soc. London, 
pt. 2, 959-991, 2 pis., 2 text-figs. 

1907 On the abdominal viscera and a vestigial seventh branchial arch in Chlamydoselachus. Proc. 
Zool. Soc. London, pt. 2, 471-478, 2 figs. , 

Herrick, C. J. 

1899 The cranial and first spinal nerves of Menidia: a contribution upon the nerve components of 
bony fishes. Journ. Camp. J<leurol., 9, 153-455, 7 pis., 4 text-figs. 

Hertwig, Oscar 

1874 Ueber Bau und Entwicklung der Placoidschuppen und der Ziihne der Selachier. Jena. Zeitschr. 
Haturwiss., 8, 331-404, 2 pis. 

HOCHSTETTER, F. 

1900 Ueber die Entstehung der Scheidewand zwischen Pericardial- und Peritonealhohle und iiber die 

Bildung des Canalis pericardiaco-peritonealis bei Embryonen von Acanthias vulgaris. Morph. 
Jahrb., 29, 141-168, pi., 12 text-figs. 



502 Bashford Dean Memorial Yolume 

Hou'ELL, A. Brazier 

1933 Morphogenesis of shoulder architecture. Part. I. General considerations, ^uart. Reu. Biol., 
8, 247-259, 4 figs. 

Howes, George Bond 

1883 On the presence of a tympanum in the genus Raia. Journ. Anat. Physiol, 17, 188-190, pi. 

Hyrtl, C. J. 

1872 Die Kopfarterien der Haifische. Den\schr. A\ad. Wiss. Wien, 32, 263-275, 3 pis. 

Johnson, S. E. 

1917 Structure and development of the sense organs of the lateral canal system of selachians (MusteJus 
canis and Squalus acanthias). Journ. Comp. J^euro]., 28, 1-74, 83 figs. 

Johnston, J. B. 

1905.1 The morphology'' of the vertebrate head from the \'iewpoint of the primitive functional divi- 
sions of the nervous system. Journ. Comp. TsJeuroL FsychoJ., 15, 176-275, 4 pis. 

1905.2 The cranial ner\'e components of Petromyzon. Morph. Jahrh., 34, 149-203, pi., 18 tert-figs. 

Landacre, E. L. 

1916 The cerebral ganglia and early nerves of Squalus acanthias. Journ. Comp. J^leurol., 27, 19- 
67, 13 figs. 

Lawley, Roberto 

1876 ' Nuovi studi sopra ai pesci ed altri vertebrati fossiK delle colline Toscane. Florence. {Chlamy' 
doselachus, p. 87; figs. 1-lc, pi. 1). 

LeigH'Sharpe, Willl^m H.^rold 

1920 The comparative morphology of the secondary sexual characters of elasmobranch fishes — the 
claspers, clasper siphons, and clasper glands. Mem. I. Journ. Morphol., 34, 245-266, 12 figs. 

1926 The comparative morphology of the secondary sexual characters of elasmobranch fishes. The 
claspers, clasper siphons, and clasper glands. Mem. VIII. Journ. Morphol. Physiol, 42, 
307-320, 15 figs. 

Leriche, Maurice 

1929 Sur une forme nouvelle du genre Chlamydoselachus (C. tohleri) rejetee par le volcan de boue de 
Chagonary (He de la Trinite, Petites- Antilles). Bull. Soc. Beige Geol Paleontol Hydrol, 38, 
55-58, 2 figs. 

Luther, Alexander Ferdinand 

1909 Untersuchungen (iber die vom Nervals trigeminus innervierte Muskulatur der Selachier (Haie 
und Rochen) unter Beriicksichtigung ihrer Beziehungen zu benachbarten Organen. Acta 
Soc. Sci. Perm., 36, no. 3, 176 pp., 5 double pis., 23 text-figs. 

Maclay (Miklucho-Maklai), Nikolai 

1870 Beitrage zur vergleichenden Neurologic der Wirbelthiere. I. Das Gehirn der Selachier. II. Das 
Mittelhim der Ganoiden und Teleostier. Leipzig, 74 pp., 7 pis. 

Marshall, A. M. 

1881 On the head cavities and associated nerves of elasmobranchs. ^uart. Journ. Micr, Sci., 21, 
72-98, 2 pis. 



The Anatomy of Chlamydoselachus 503 

Maurer, Friedrich 

1912 Die ventrale Rumpfmuskulatur der Fische (Selachier, Ganoiden, Teleostier, Crossopterygier, 
Dipnoer). Jena. Zeitschr. }{aturwiss., 49, 1-118, 8 pis., 18 text'figs. 

MivART, St. George 

1879 Notes on the fins of elasmobranchs, with considerations on the nature and homologies of verte- 
brate limbs. Trans. Zool. Soc. London, 10, 439-484, 6 pis., 6 text'figs. 

Monro, Alexander 2nd 

1785 The structure and physiology of fishes explained, and compared with those of man and other 
animals. Edinburgh. (Pp. 23 and 92, Tab. [pL] XVIII). 

MiJLLER, Erik 

1911 Untersuchungen iiber die Muskeln und Nerven der Brustflosse und der Korperwand bei 
Acanthias vulgaris. Anat. Hefte, 43, 1-147, 26 pis., 11 text-figs. 

Neal, H. V. 

1897 The development of the hypoglossus musculature in Petroynyzon and Squalus. Anat. Anz., 
13, 441-463, 2 figs. 

1918 The history of the eye muscles. Journ. Morphoh, 30, 433-453, 20 figs. 

NisHi, Seiho 

1922 Beitrage zur vergleichenden Anatomic der Augenmuskulatur. Arb. Anat. Instit. K. Japan. 
Univ. Sendai {Chlamydoselachus, Heft 7, 65-71, 2 figs.). 

NiSHIKAWA, T. 

1898 Notes on some embryos of Chlamydoselachus anguineus Garm. Annot. Zool. Japon., 2, 95-102, 
pi., 7 text-figs. 

Norris, H. W. 

1929 The distribution and innervation of the ampullae of Lorenzini of the dogfish, Squalus acanthias. 
Some comparisons with conditions in other plagiostomes and corrections of prevalent errors. 
Journ. Comp. AJeurol., 47, 449-465, 7 figs. 

Norris, H. W., and Hughes, Sally P. 

1920 The cranial, occipital, and anterior spinal nerves of the dogfish, Squalus acanthias. Journ. 
Comp. Tieurol, 31, 293-402, 53 figs. 

Osburn, Raymond C. 

1906 The origin of vertebrate limbs. Recent evidence upon this problem from studies on primitive 
sharks. Ann. J^ew Tor}{ Acad. Sci., 17, 415-436. 

1907 Observations on the origin of the paired fins of vertebrates. Amer. Journ. Anat., 7, 171- 
194, 5 pis. 

Parker, T. Jeffery 

1885 On the intestinal spiral valve in the genus Raja. Trans. Zool. Soc. London, 11, 49-61, 2 pis. 

Pollard, H. B. 

1895 Oral cirrhi of siluroids and the origin of the head in vertebrates. Zool. Jahrh. (Abth. Anat.), 8, 
379-424, 2 pis. 

Potter, George Edwin, and Medlen, Ammon Brown 

1935 Organography of Gambusia patruelis (Baird and Girard). Journ. Morphol., 57, 303-316 



504 Bashford Dean lAemoriaJ Volume 

Regan, C. Tate 

1906.1 Descriptions of new or little-known fishes from the coast of Natal. Ann. J<[atal Govt. Mus., 1, 
pt. 1, 1-6, 5 pis. 

1906.2 A classification of the selachian fishes. Proc. Zool Soc. London, pt. 2, 722-758, 10 figs. 

Retzius, G. 

ISSI. Das Gehororgan der Wirbelthiere. Morphologisch'histologisch Studien, Stockholm, Bd. I, 
Hft. 1, 1-217, [Elasmobranchs, Taf. 17-23]. 

RlDEi^-OOD, W. G. 

1896 On the spiracle and associated structures in elasmobranch fishes. Anat. Anz., 11, 425-433, 2 figs. 
1899 Some observations on the caudal diplospondyly of sharks. Journ. Linn. Soc. London, (Zool.), 27, 
46-59, 2 figs. 

Rose, C. 

1895 Ueber die Zahnentwicklung von Chlamydoselachus anguineus Garm. Morph. Arb., 4, 193- 
206, 12 figs. 

Semper, C. 

1875 Das Urogenitalsystem der Plagiostomen und seine Bedeutung fiir das der librigen Wirbeltiere. 

Arb. ZooL'Zoot. Instit. Wurzburg, 2, 195-509, 13 pis. 

SCHMALHAUSEN, J. J. 

1912 Morphologic der unpaaren Flossen. I. Die Entwicklung des Skelettes und der Muskulatur der 
unpaaren Flossen der Fische. Zeitschr. Wiss. Zool., 100, 509-587, 4 pis. 

Sewertzoff (Severtsov), A. N. 

1916 Etudes sur revolution des vertebres inferieurs. 1. Morphologic du squelette et de la muscula- 

ture de la tete des cyclostomes. Arch. Russes Anat. Histol. Embryo]., 1, 1-104, 6 pis. 
1926 Development of the pehac fins of Acipenser ruthenus. New data for the theory of paired fins 

of fishes. Journ. Morphol, 41, 547-579, 23 figs. 

Speidel, C-\rl Caskey 

1923 The caudal longitudinal collecting nerve trunks of elasmobranch fishes. Anat. Rec, 25, 23- 
29, pi. 

Stew.art, Charles 

1906 On the membranous labyrinth of certain sharks. Journ. Linn. Soc. London (Zool.), 29, 407- 
409, pi. 

Th.-^cher, J. K. 

1876 Median and paired fins. A contribution to the history of vertebrate limbs. Trans. Conn. 
. Acad. Sci. Arts, 3, 281-310, 11 pis., 4 text-figs. 

Van WijsE, J. W. 

1883 Ueber die Mesodermsegmente und die Entwicklung der Nerven des Selachierkopfes. Verh. 
K. A\dd. Wet., Amsterdam, Deel 22, 50 pp., 5 pis. 

Vetter, B. 

1874 Untersuchung zur vergleichenden Anatomie der Kiemen- und Kiefermuskulatur der Fische. 
Jena. Zeitschr. j^aturwiss., 8, 405-458, 2 pis. 

Wilder, Burt G. 

1905 On the brains of Scymnus, Mitsu\urina and Chlamydoselachus, with remarks upon selachian 
brains from standpoints morphic, ontogenetic, taxonomic, phylogenic and pedagogic. Science, 
n. s. 21, 812-814. 



The Anatomy of Chlamydoselachus 505 

Woodward, Arthur Smith 

1921 Observations on some extinct elasmobranch fishes. Proc. Linn. Soc. London for 1920-1921, 

133. sess., 29-39, 4 figs. 
1933 Early man and the associated faunas in the Old World. Science, n. s. 78, 89-92. 

WORTHINGTON, JuLIA 

1905 The brain and cranial nerves of Bdellostoma dombeyi. ^uart. Journ. Micr. Sci., n. s. 49, 137- 
181, 4 pis. 

ZlEGLER, H. E. 

1908 Ein Embryo von Chlamydoselachus anguineus Gar. Anat. Ariz., 33, 561-574, 7 figs. 

ZiTTEL, K. VON 

1923 Grund2;iige der Palaontologie. II Abtheilung: Vertebrata. Miinchen und Berlin. (Tooth of 
Hyhodus reticulatus, fig. 93). 



PLATE I 
THE ANATOMY OF CHLAMTDOSELACHUS AHGUmEUS 



PLATE I 

THE CRANIUM OF CHLAMTDOSELACHUS, WITH THE ANTERIOR END OF THE 
VERTEBRAL COLUMN ATTACHED 

Fig. 1. Dorsal view of the cranium, natural size. 

af, articular facet for hyomandibular; an, ala nasalis; cp, cavum precerebrale; ecp, ectethmoidal process; ef, endolym- 
phatic fossa; es, eyestalk; fp, foramen for nervus profundus; id, interdorsal; pc, preorbital canal or foramen; pop, 
postorbital process. 

After Allis, 1923, Fig. 9, pi. VIII. 



Fig. 2. Ventral view of the cranium, natural size. 

aop, antorbital process; ha, bulla acustica; fie, foramen for internal carotid artery; /so, foramina supraorbitalia; naf, nasal 
fontanelle; pb, palatobasal ridge. 

After Allis, 1923, Fig. 11, pi. IX. 

Fig. 3. Lateral view of the cranium, natural size. 

af, articular facet for hyomandibular; bd, basidorsals; fe, foramen for efferent pseudobranchial artery; ff, foramen for 
nervus facialis; fie, foramen for internal carotid artery; fo, foramen for nervus opticus; foe, foramina for occipital nerves; 
fom, foramen for nervus oculomotorius; fp, foramen for nervus profundus; ftr, foramen for nervus trochlearis; id, inter- 
dorsals; n, nodule of cartilage; naf, nasal fontanelle; one, orbitonasal canal; pb, palatobasal ridge; pe, preorbital canal, or 
foramen; r, rostrum; sbd, supra-basidorsals; tpf, trigemino-pituitary fossa. 

After Allis, 1923, Fig. 8, pi. VIII. 



Dean Memorial Volume 



Article VI, Plate I 




PLATE II 

THE ANATOMY OF CHLAMTDOSELACHUS AKGUIKEUS 



PLATE II 

THE CRANIUM AND PORTIONS OF THE VISCERAL SKELETON 
OF CHLAMTDOSELACHUS 

Fig. 4. Medial view of cranium and anterior end of the vertebral column, natural size. 

an, ala nasalis; bd, basidorsals; ef, endolymphatic fossa; fe, foramen for efferent pseudobranchial artery; /gl, foramen for 
nervus glossopharyngeus; fie, foramen for internal carotid artery; fo, foramen for nervus opticus; foe, foramina for 
occipital nerves; fol, foramen for nervus olfactorius; fom, foramen for nervus oculomotorius; ftr, foramen for nervus 
trochlearis; fv, foramen for nervus vagus; id, interdorsal; nc, notochord; pb, palatobasal ridge; pv, canal, or foramen, for 
pituitary vein; r, rostrum; tf, acustico-trigemino-facialis recess. 

After Allis, 1923, Fig. 12, pi. IX. 

Fig. 5. Lateral view of cranium, with jaw cartilages and hyoid cartilages attached, natural size. 

al, anterior upper labial cartilage; an, ala nasalis; aop, antorbital process; ch, ceratohyoid; ecp, ectethmoidal process; 
es, eyestalk; g( = gamma), the process corresponding to Addy of Vetter's (1874) description in other selachians; hmd, 
hyomandibular; Imh, hgamentum mandibulo-hyoideum; md, mandibular; ml mandibular labial cartilage; n, nodule of 
cartilage; naf, nasal fontanelle; orp, orbital process of palatoquadrate; pi, posterior upper labial cartilage; pop, postot' 
bital process; pq, palatoquadrate. 

After Allis, 1923, Fig. 7, pi. VII. 

Fig. 6. Posterior view of the cranium, natural size. 

af, articular facet for hyomandibular; ecp, ectethmoidal process; es, eyestalk; fm, foramen magnum; gvf, glossopharyngo- 
vagus fossa; pop, postorbital process. 

After AlUs, 1923, Fig. 10, pi. VIII. 



Dean Memorial Volume 



Artici.r VI, Plate II 



4 




tol 



fo ^r ^.. 


.- t . _ '- 


fv 

1 _ 

foe 
nc 


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PLATE III 
THE ANATOMY OF CHLAMTDOSELACHUS AKGUIKEUS 



PLATE III 

THE BRAIN AND PORTIONS OF THE VISCERAL SKELETON OF CHLAMTDOSELACHUS 
Fig. 7- Dorsal view of the brain and cranial cavity, natural size. 

a, artery; o, nervus opticus; ocm, n. oculomotorius; ol, tractus olfactorius; tr, n. trochlearis; v, vein. 
After AlUs, 1923, Fig. 59, pi. XXII. 

Fig. 8. Dorsal view of the branchial arches, natural size. The branchial rays related to the ceratobranchials 
have been removed. 

bbri, second basibranchial; hbr5-6, fused fifth and sixth basibranchials; bh, basihyoid; cbl, musculus coracobranchialis 
of the first arch; cbrl, ceratobranchial of the first arch; cbr6, ceratobranchial of the sixth arch; ch, ceratohyoid; ebrl, 
epibranchial of the first arch; ebrd, epibranchial of the sixth arch; hbr2, hypbbranchial of the second arch; phrS, pharyngo- 
branchial of the fifth arch. 

After Allis, 1923, Fig. 35, pi. XIII. 

Fig. 9. Ventral view of the median portion of the branchial skeleton, natural sizp. 

hbrS, basibranchial of the third arch; cbr6, ceratobranchial of the sixth arch; ch, ceratohyoid; hbr2, hypobranchial 
the second arch. 

After Allis, 1923, Fig. 36, pi. XIII. 



Dean Memorial Volume 



Article VI, Plate III 




'^'^■^'^^Itr^^i0^''~- 



I I 

I 



I 

I 



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-^rse:^ 




PLATE IV 
THE ANATOMY OF CHLAMTDOSELACHUS ATiGUmEUS 



PLATE IV 

EYE MUSCLES, BRAIN, VALVULAR INTESTINE AND DUCTUS DEFERENS 

OF CHLAMrDOSELACHUS 

Figs. 10, 11 and 12. The eye muscles and their nerves, excepting the nervus abducens which innervates 
the external rectus muscle. 

The explanation of the labels is combined with that for the next two figures. 
After Hawkes, 1906, Figs. 4-6, pi. LXIX. 

Figs. 13 and 14. Dorsal and ventral views of lateral halves of the brain, showing roots of cranial nerves. 

H, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V, VII, the united Gasserian and buccalis ganglia; VI, 
nervus abducens; VII b., ramus buccalis; VTI h., truncus hyomandibularis; VUI, the ganglion of the eighth nerve; IX, 
glossopharyngeal nerve; X, vagus nerve. 

A.B., anastomosing branch between the oculomotor and profundus nerves; C, ciliary branch of the profundus; Cer., 
cerebellum; Hy., hypophysis; 1.0., inferior obhque muscle; L.I., lobi inferiores; Lin.Lat., lineae laterales or restiform 
bodies; L.T"^., Locy's ner%'e (nervus terminalis); Oc.1,2,3, first three spino-occipital nerves; Op.S., optic stalk (cartilagO' 
sustentaculum ocuH); Op.L., optic lobes; O.S., olfactory' stalk; Pro., profundus branch of fifth or trigeminal nerve; 
Pros., prosencephalon; R.Ext., A and B, two parts of the rectus extemus muscle; R.In., rectus intemus muscle; R.In/., 
rectus inferior muscle; R.S., rectus superior muscle; S.Ob., superior obHque muscle; S. V., saccus vasculosus. 
After Hawkes, 1906, Figs. 7 and 8, pi. LXIX. 

Fig. 15. Valvular intestine sHt open to show the spiral valve and the thick muscular wall. 

After Gunther, 1887, Fig. 5, pi. LXV. 

Fig. 16. Lower part of left ductus deferens (vas deferens) opened longitudinally to show "annular" folds. 

After Giinther, 1887, Fig. 4, pi. LXV. 



Dean Memorial Volume 



Article VI, Plate IV 





/' 15 



^>^ 





Oc3 



16 

I', -^^' 



% 




I 



PLATE V 
THE ANATOMY OF CHLAMTDOSELACHUS A?iGUmEUS 



PLATE V 

THE UROGENITAL ORGANS OF CHLAMTDOSELACHUS 
Fig. 17- External (ventral) vie.w of the cloaca, and abdominal apertures in a normally developed male. 

d, cloaca; po, poms abdominalis; ug, urogenital openings; v, vent. 

After Giinther, 1S87, Fig. 1, pi. LXV. 

Fig. 18. External (ventral) view of the cloaca and abdominal apertures in an asymmetrically developed 
male. The ducts of the right side are not so well developed as those of the left. 

d. cloaca; po, poms abdominalis; ug, urogenital openings; v, vent. 

After Giinther, 1887, Fig. 2, pi. LXV. 

Fig. 19. Side view of the ductus deferentia (vasa deferentia) of a specimen with unequal development of 
the genital ducts. Compare preceding figure, drawn firom the same specimen. 

gi, gland; i, rectum opened; po, porus abdominalis; r, kidney; u, urinary bladder; ug, right, and ugl, left urogenital 
opening; vd, left, and udl, right ductus deferens. 

After Gunther, 1887, Fig. 3, pi. LXV. 

Fig. 20. Ventral view of pelvic fins, myxopterygia and cloacal aperture of a 1474'mm. male. 

Aft^ Giinther, 1887, Fig. C, pi. LXIV. 

Fig. 21 . Dorsal view of the right half of the pelvic girdle and endoskeleton of the right pelvic fin of a male. 

B., basipterygium; b., axial cartilage; bl, intercalary cartilage; Be. [beta], modified radial; I.n./., longitudinal nerve 
foramen; p.g., pehnc girdle; r., lateral radials; R-i., marginal ventral cartilage; T.d., terminal dorsal cartilage; T.d., 
terminal ventral cartilage. 

After Goodey, 1910.1, Fig. 22, pL XL VI. 

Fig. 22. Dorsal view of the pelvic fin and the right half of the pelvic girdle of a male, showing musculature. 
A., adductor muscle; B., basipterygium; Be.fbeta], modified radial; c.n., collector nerve; D., dilator muscle; Fl.e., 
musculus flexor extemus; Fi.i., musculus flexor intemus; I.r., last lateral radial; O., dorsal radial muscles; p.g., pel- 
vic girdle; R.V., marginal ventral cartilage; S., compressor muscle; T.d., terminal dorsal cartilage; T.v., terminal 
ventral cartilage. 

After Goodey, 1910.1, Fig. 20, plate XL VI. 

Fig. 23. Ventral view of the pelvic fin represented in Figs. 21 and 22, showing muscles. 

Fl.e., musculus flexor extemus; Ra., ventral radial muscles; S., compressor muscle; T.v., terminal ventral cartilage. 
Aft^r Goodey, 1910.1, Fig. 21, pL XL VI. 



Dean Memorial Volume 



Article VI, Plate V 



17 



"9 -^l... 



%,. 



~rlj 





18 




19 



gl ^J' 






Ra. 



ru 





PLATE VI 

THE ANATOMY OF CHLAMTDOSELACHUS AJiGlUKEUS 



PLATE VI 

THE BRAIN OF CHLAMDOSELACHUS 

Fig. 24. The brain in dorsal view and in transverse sections taken at various levels. 

Fig. 25. Ventral view of the brain of the frilled shark. 

Fig. 26. The brain of Chlamydoselachus in lateral view. 

Fig. 27. Vertical longitudinal section of the brain of Chlamydoselachus. 

1, olfactory lobe; 2, nervus opticus; 3, oculomotorius; 4, trochlearis; 5, trigeminus; 6, abducens; 7, facialis; S, acusticus; 
9, glossopharyngeus; 10, vagus. 

These figures are reproduced from the origiiial drawings by Paulus Roetter for Garman, 1885.2, Pis. XV and XVI. 



Dean Memorial Volume 



Article VI, Plate VI 




Z4 






» 



v/ 




i' 'W^i-^^ 




25 






Z6 




27 



PLATE VII 
THE ANATOMY OF CHLAMTDOSELACHUS ATiGUmEUS 



PLATE VII 

NERVOUS SYSTEM AND CERTAIN SENSE ORGANS OF HEPTAHCHUS 
AND CHLAMTDOSELACHUS 

Fig. 28. Brain, cranial nerves and associated sense organs of Heptanchus macuJatus, dorsal view. 

bu.VII, buccal branch of facial nerve; cb., cerebellum; cl., ciliary nerve; c.r., restiform body; hmd., hyomandibular 
division of the facial nerve; wid. V, mandibular division of the fifth nerve; m.n., median olfactory nucleus; med., medulla; 
mx.V, maxillary division of trigeminal nerve; ol.h., olfactory bulb; ol.I., olfactory lobe; oi.t., olfactory tract; op.l., 
optic lobe; op.V, ophthalmicus profundus division of the trigeminal nerve; os.V and VII, ophthalmicus superficialis 
of trigeminal and facial nerves; t!., telencephalon; tn., terminal nerve; y-z, occipitospinal nerves: I, olfactory nerve; U, 
optic; III, oculomotor; IV, trochlearis; VI, abducens; VIII, auditory; IX, glossopharyngeal; X, vagus. 

After Daniel, 1934, Fig. 200a. 

Fig. 29. Diagrammatic drawing of the cranial nerves and lateral line canals of ChJamyiioselachus. 

B.A., buccal ampullae; Bucc, ramus buccalis VII; C.F., general cutaneous fibres going to skin; Con. V5, nerve strand 
connecting the pre- and post-trematic rami of vagus 5; Con. V6, nerve strand connecting vagus 6 with a spinal nerve; 
D.G., dorsal branch of the glossopharyngeus, dividing into a cephalad branch which passes to the neuromasts, and 
a caudal branch whose distribution is undetermined; E.M. ( VII)(A,B,C,D,E), the five parts of the externus mandibularis 
VII; H., the ganglion of the truncus hyomandibularis, i.e., the true ganglion of the facialis, combined with one of the 
acustico-lateralis ganglia; H.A., hyoid ampullae; If.L.(A,B,C), the hyomandibular lateral line canal and its three main 
branches; H.M , the common trunk of the ramus hyoideus and ramus internus mandibularis VII; I.(A,B,C), the three 
principal rami intestinales; I.H., the cardiac branch of the ramus intestinalis; I.M.VII, ramus internus mandibularis 
VII; I.O.L., infraorbital lateral line canal; L.L., main lateral line canal; Mxb., branch of the maxillaris which becomes 
united with a branch of the buccalis; Mxb.b., two fine nerves which appear to originate from a branch of the buccalis, 
but which are composed of general cutaneous fibers which have come from Mxb.; P., palatine branches of the facialis; 
P.B.A., posterobuccal ampullae; Pr.F.(ch.), the chorda tympani; Pr. and Pt., the pre- and post-trematic rami of IX and 
of the vagus; Pro., profundus branch of V; Pt.F., post-trematic facialis; R.H., ramus hyoideus VII; R.Man. V, ramus 
mandibularis V; R.Max., ramus maxillaris V; R.O., ramus oticus with cutaneous branches R.O.C.; 5.(1,2,3,4,5,6,7,8), 
the first eight spinal nerves; s.h.(l,2), the two branches which make up the hypoglossal nerve; S.O., occipitospinal 
riband; S.O.A., supraorbital ampullae; S.O.L., supraorbital lateral line canal; S.Op.V, superficialis ophthalmicus V; 
S.Op.Wll, superficialis ophthalmicus VII; T.H., truncus hyomandibularis; V(l,2,3,4,5,6), the six branchial branches 
of the vagus; V.G., visceralis branch of IX; Vis., visceralis branches of the vagus; V, Vll, the united Gasserian and 
buccalis gangUa; IX, IXg., the glossopharyngeal nerve and its ganglion; X, Xg., the vagus nerve and its composite 
ganglion; X.A and X.B, dorsal branches of the vagus to neuromasts. The remaining abbreviations are not explained 
by the author. 

After Hawkes, 1906, Fig. 1, pi. LXVIII (in color). 

Fig. 30. Right membranous labyrinth (x 2) of Chlamydoselachus, medial aspect. 

The explanation of the labels is combined with that for the next figure. 
After Goodey, 1910.1, Fig. 7, pi. XLIII. 

Fig. 31. Right membranous labyrinth (x 2) of Chlamydoselachus, lateral aspect. 

a.a., ampulla anterior; a.d.e., apertura ductus endolymphaticus externus; a.e., ampulla externus; a.p., ampulla posterior; 
CO., canalis anterior; c.e., canalis externus; c.p., canalis posterior; d.e., ductus endolymphaticus; d.u.s.p., ductus 
utriculo-saccularis posterior; !., lagena; p.f-, parietal fossa; r.a.d., ramus of eighth nerve to ampulla of anterior canal; 
r.fl.e., ramus to ampulla externus; r.a.p., ramus to ampulla posterior; rec, recessus utricuU; r.l., ramus to lagena; r.n., 
ramus to macula neglecta; r.s., ramus to sacculus; r.u., ramus to utriculus; s., sacculus; s.e., saccus endolymphaticus; 
t., tympanic aperture; u.a., utriculus anterior; u. p., utriculus posterior; VIII, eighth cranial nerve. 

After Goodey, 1910.1, Fig. 8, pi. XLIII, 



Dean Memorial Volume 



Article VI, Plate VII 




THE 

BASHFORD DEAN MEMORIAL VOLUME 

ARCHAIC FISHES 

Edited By 
EUGENE WILLIS GUDGER 

Article VII 

THE BREEDING HABITS, REPRODUCTIVE ORGANS 

AND EXTERNAL EMBRYONIC DEVELOPMENT 

OF CHLAMYDOSELACHUS, BASED ON NOTES 

AND DRAWINGS BY BASHFORD DEAN 

By E. W. GUDGER 

Honorary Associate in Ichthyology 
American Museum of Natural History 



THE 

AMERICAN X§ 
MUSEUM 

NATURAL 
HISTORY 



^SOENCE^ 
EDIXOTON 



NEW YORK 
PUBLISHED BY ORDER OF THE TRUSTEES 

Issued October 15, 1940 



ARTICLE VII 

THE BREEDING HABITS, REPRODUCTIVE ORGANS, AND 

EXTERNAL EMBRYONIC DEVELOPMENT OF CHLAMTDOSELACHUS, 

BASED ON NOTES AND DRAWINGS LEFT 

BY BASHFORD DEAN 

By E. W. Gudger 



CONTENTS 

Introduction 525 

The Specimens and Their Source 527 

The Drawings and Their Authorship 529 

Viviparity (Ovoviviparity) in Chlamydoselachus 531 

Breeding Season of the Frilled Shark 534 

Evidence from the Ovaries 534 

Stages of Embryos in the Uteri 535 

Duration of Gestation 538 

The Reproductive Organs of the Male Chlamydoselachus 541 

Myxopterygia — External Organs of the Male 541 

The Reproductive Organs of the Female Chlamydoselachus 542 

The Ovaries 544 

Immature Ovarian Eggs 548 

A Mature Ovarian Egg 548 

The Oviducts 549 

The Abdominal Openings . 549 

The Shell Gland • • 550 

The Uterus 552 

Right Uterus Functional 552 

Left Uterus Sometimes Functional 55/ 

Do Embryos Receive Nutriment prom Uterine Wall? 559 

The Cloacae Openings 562 

Right Cloacae Opening Predominant 562 

Female Reproductive Organs of Certain Higher Sharks and Various Rays . . 564 

Ovaries and Oviducts of Some Florida Sharks 564 

Ovaries and Oviducts of Various Rays 565 

The Encapsuled Egg of Chlamydoselachus 566 

Ellipsoidal Eggs of the Frilled Shark 567 

Normal Ellipsoidal Encapsuled Eggs 567 

Unusual Ellipsoidal Eggs with Tendriliform Processes 569 

An Elliptical Egg 569 ■ 

Some Oblong Fertile Eggs 570 

An Elongate Infertile (Wind) Egg 571 

Round Eggs of the Frilled Shark 572 

Sizes of Eggs of Chlamydoselachus Compared with Those of Other Sharks 573 

Sees of Eggs and Embryos of the Frilled Shark 573 

Sizes of Eggs and Embryos of Isurid Sharks 574 

Sizes of Eggs of the Nurse Shark 57o 

Formation of the Egg Capsules of Chlamydoselachus and of Gingly mo stoma 578 

Formation of Tendriliform Processes ..... 579 

523 



External Embryonic Development of Chlaynydoselachus 581 

Early Development 582 

Blastulae 582 

GASTRin.AE 588 

Later Development 590 

Resume of Researches on the Internal Development 591 

Descriptions of Embryos Figured 592 

An Embryo of 11.5 Millimeters 593 

An Embryo 15.5 mm. in Length 594 

An Embryo Measuring 20 MaLiMETERS 595 

Two 25-MM. Embryos — Heads Only — Described by Ziegler and Brohmer 596 

Nishik.mi'a's 32'MM. Embryo — Head Only 598 

Dean's Embryo, 34 mm. in Length 603 

An Embryo of 39 Millimeters 601 

The 39-mm. Embryo and its Yolk Sac dj Color 602 

Nishikawa's 43'Mm. Embryo ok its Yolk S.^c 603 

Dean's Embryo of 46 millimeters 603 

Head of a 48'MM. Specimen in Ventral View 605 

Nishikawa's 50'MM. Embryo on its Yolk S.ac 605 

An Embryo of 54 Millimeters 607 

An Embryo Me.-\suring 55 Millimeters 608 

Carman's Embryo of 64 MaLiMETERs 609 

Dean's Embryo Measuring 66 MaLiMETERs 610 

An Embryo 103 mm. in Length 612 

An Embryo of 124 millimeters 612 

An Embryo of 175 mm. and its Yolk Sac 613 

An Embryo 185 mm. in Length 614 

A Young Frilled Shark 240 mm. Long '. 615 

A 390'MM. Chlamydoselachus IN N.atural Colors 615 

THE YOLK SAC CIRCULATION 61? 

Vitelline Circulation of the 39'MM. Embryo 618 

YoLK-S.*c Circulation of the 43-mm. Specimen 619 

Vitelline Circlt-ation of the 50'mm. Embryo 621 

Yolk-Sac Circl'lation of the 175'Mii. Fish 621 

Vitelline Circulation of the 390'MM. Shark 621 

The Adult Chlamydoselachus 622 

An Adult Female Frilled Shark 622 

An Adult Male ChlamydoseJachus 624 

He.AlD Only of the Adult Shark 625 

He.'^d — Dorsal View 625 

Head — Ventr.-\l Aspect 625 

External Gill'Filaments of Chlamydoselachus 626 

External Gill-filaments of the Embryo 626 

External Gill-filaments of the Adult Frilled Shark 629 

Bibliography 631 



'524 



THE BREEDING HABITS, REPRODUCTIVE ORGANS, AND 
EXTERNAL EMBRYONIC DEVELOPMENT OF CHLAMTDOSELACHUS, 
BASED ON NOTES AND DRAWINGS LEFT 
BY BASHFORD DEAN 

By E. W. GUDGER 

Honorary Associate in Ichthyology 
The American Museum of Natural History 

INTRODUCTION 

While on a leave of absence from Columbia University, Prof. Bashford Dean spent 
parts of 1900 and 1901 in Japan. There he collected and studied many rare and little- 
known marine animals — particularly certam archaic fishes and their eggs and embryos. 
That these collections were extensive, we know since there is a letter by him stating that 
when shipped to America by freight they filled seven cases. In this shipment were 
several adult frilled sharks, and others were sent to him later. Of the disposition of these 
and of Dean's generosity in sending specimens of this fish to various European investi- 
gators, Gudger and Smith have written (1933, pp. 250-252). 

Dean's embryological materials were collected to enable him to follow and to il- 
lustrate the early life histories of two primitive elasmobranchs — the frilled shark, Chlamy- 
doselachus anguineus, and the Port Jackson shark, Heterodontus (Cestracion) phiUppi. 
Back in America, Dean found gaps in his materials and figures, so he returned to Japan and 
did further work on these fishes during the months from May to October, 1906. Further- 
more, other frilled-shark material was still later collected in Japan and sent to him in 
America. I have records of specimens received by Dean on February 10, 1911, and on 
January 13, 1912. I have been unable to trace these specimens, but other lots came to him 
and were deposited in the Dean collection in the 2;ooIogical museum of Columbia Univer- 
sity. Among the specimens loaned from Columbia are four lots of young embryos without 
yolk sacs labelled "Bought in Tokyo Market, February 4, 1913; April 4, 1913; January 22, 
1914; April 23, 1917"- His Japanese collectors evidently found the fresh-caught adult 
sharks in the Tokyo market, opened the fish, cut the embryos from the uterine eggs, 
and sent these embryos to Dean. 

Since the above was written, I have learned that in 1917 Dr. Dean paid a flying visit 
to Japan to collect armor and objects of art for the Metropolitan Museum of Art, in 
which he was at that time curator of arms and armor. He reached Japan on March 28 and 
embarked for the U. S. on May 19. This I have from a member of the party and from 
his letters to Mrs. Dean. Hence he was in Japan when five embryos (to be referred to 
later) were collected on April 23. These and the ones referred to above, were obtained 
by his friends (whom he names in these letters), and preserved for him. The specimens 
collected in 1917 (and possibly the others listed with them) were brought back by him in 
May- June of that year. 

525 



526 Bashford Dean Memorial Voume 

Among the embryological records accumulated by Dr. Dean during these two trips 
and left unpublished at his death, are numerous drawings showing various stages in the 
development of the primitive shark, Chlamydoselachus. In keeping with the plan and 
purpose of this volume, as briefly set forth by Gudger and Smith on page 49 of Article II, 
the present contribution has been prepared in order to preserve for science these excel- 
lent drawings. 

This article (No. VII) forms the third and last of a series dealing with this rare 
shark. In the first, Gudger and Smith (1933) brought together from widespread sources 
everything then known concerning the natural history of the fish, to form a background 
for work on the anatomy and the embryology. Next came Dr. B. G. Smith's monograph on 
the anatomy. This includes a review of the results of many investigators, but to these 
studies. Dr. Smith added the results of his own investigations on certain organ systems 
either wholly or partly omitted by other writers. Smith's dissections, it is interesting to 
note, were done on specimens obtained in Japan by Dean. 

And now there are set before me two tasks. The first is to make a study of Dean's 
notes on the breeding habits and seasons and on the structure and functioning of the re- 
productive organs of the frilled shark. These notes are few, fragmentary and scat' 
tered throughout a notebook marked Chlamtdoselachus and in various loose notes, 
sketches and photographs. However, I have been able to piece together from Dean's 
notes, from the specimens loaned from Columbia University, and from the scanty litera- 
ture, sufficient data to extend considerably our knowledge of these subjects. I am fortu- 
nately able to bring forward for comparison data from my observations on the breeding 
habits and genital organs of various sharks and rays, and particularly of the nurse shark, 
Ginglymostoma cirratum, whose reproductive habits and large shelled eggs are remarkably 
like those of Chlamydoselachus. 

My second task is to prepare descriptions and explanations of the admirably drawn 
figures of the eggs and embryos of this shark left unpublished by Dr. Dean at his untimely 
death. For reasons to be given later, it will be clear why these figures do not portray 
a completely graded series of embryos but only such stages as were procurable with great 
difficulty. But before beginning the consideration of these drawings, other and intrc 
ductory studies of the fish must be made. 

Almost nothing has been published about the breeding seasons and breeding habits 
of the frilled shark and equally Httle concerning the functioning of the reproductive organs. 
Even less is known about the development of Chlamydoselachus. But when the breeding 
habits and seasons and the reproductive organs have been studied and the figures of the 
embryos described, the reader will have a fair idea of the life history of the frilled shark. 

Some years before his death in 1928, Dr. Dean asked me to collaborate with him in 
preparing an article such as this. But having much work planned for years ahead, I pre- 
sented my case, and, Dean, generous as always, withdrew his request and urged me to 
proceed with my own studies. And now that he is gone, I am trying to do what could 
have been done long ago so much better in collaboration with him, since his memory 



The Embryology of Chlamydoselachus 



527 



would have supplied details not recorded among the very few notes available. 

In this difficult task, I have been fortunate in having the active help and cooperation 
of Dr. B. G. Smith. It is a pleasure to acknowledge my large obligation to him. 

THE SPECIMENS AND THEIR SOURCE 

That the collecting of eggs and embryos of Chlamydoselachus was not the main 
object of Dean's first visit to Japan, and that the finding of these eggs was somewhat un- 
expected, it attested by this statement (Dean, 1901.1) — ''My first object in visiting Japan 
[in 1900] was to secure the eggs and embryos of the Port Jackson shark [Heterodontus = 
Cestracion].''' The eggs oi Heterodontus were found among rocks and seaweed in shallow 
water, and were easily collected by divers and maintained without difficulty in aquaria of 
running water or in floats in the sea. Hence it is not surprising that Dean procured 
a fairly complete series of early stages of the embryos of this shark and that he devoted 
most of his time to their study. The drawings of the eggs and embryos of Heterodontus, 
which are more numerous than those of Chlamydoselachus, will form the basis of the final 
article in this Memorial Volume. 




Text-figure 1 
A map of the Sagami Sea, the Miura Peninsula, and part of the Gulf of Tokyo, showing the position of 
the Misaki Laboratory in which Doctor Dean worked, and the waters from which his specimens of 

Chlamydoselachus were obtained. 
From an old chart compiled by Prof. I. Ijama. 



528 Bashford Dean Memorial Volume 

Dean knew of Carman's monograph on the anatomy of Chlamydoselachus (1885) and 
of Nishikawa's pioneer work (1898) on the breeding habits and embryology. But in 1901 
he wrote: "I hardly had hopes ... of obtaining [at Misaki] a series of embryos 
[of Chlamydoselachus] ... on account of its great rarity; for one could easily count on 
his fingers all of even the adult specimens which had hitherto been brought from 
Japan. . . I found, however, that ... if one could secure many adult specimens there was 
a fair chance of obtaining embryos, since this shark was known to be viviparous." 

During his twelve months in Japan (1900-1901), an intensive search for Chlamy- 
doselachus was carried on. During his temporary absence from Misaki, this search was 
prosecuted by his assistants, and, even after his departure for the United States, the hunt 
was kept up — certainly as late as 1917- But so rare was the fish that in 1904, Dean wrote 
that '\ . . in the course of a year, the neighborhood [the Sagami Sea] yields about a dozen 
specimens [of both sexes]". And in his notebook under the heading "Abundance" is 
this statement "1904. About 6 — 1 gravid". In another place is this notation — "1905. 
Kuma fished for about 5 weeks in the best ground off Odowara — special tackle — squid 
bait, depth from 300-600 fathoms, took 3 fish" — one male and two females. The scarcity 
of specimens and the difficulty of procuring them, it may be noted, is due to the fact that 
they have to be fished for with trawl hooks at depths averaging from 1200 to 3600 feet. 

Although 10 adult specimens of Chlamydoselachus have been taken in the seas of 
western Europe, the only region where embryos have been obtained is still the Sagami 
Sea, more particularly the waters around the Miura Peninsula on which the Misaki 
Biological Station is situated. Dean states that he had females with young from Sagami 
Bay (and particularly from the Odowara Maye); while other materials came from the 
Gulf of Tokyo — another arm of the Sagami Sea. For these localities see Text-figure 1 . 

The chief collector at the Misaki Station in Dean's day and for long afterwards was 
Kuma Aoki, an ex-fisherman, who had a remarkable knowledge of all the specific localities 
where Chlamydoselachus might be found. In addition to fishing directly for Dean, Kuma 
made arrangements with other fishermen in. Sagami Bay that all frilled sharks taken by 
them should be brought to the laboratory. Also Prof. Mitsukuri of the Imperial Uni- 
versity of Tokyo arranged with the market people in Tokyo that all specimens brought 
there from any source whatever should at once be sent to the station at Misaki. From all 
these sources, material slowly came to Dean at the laboratory on the Miura Peninsula. 

In the fragmentary entries in various handwritings in Dean's notebook, a total of 42 
adults are listed — 16 males and 26 females. These cover the years 1900-1906 inclusive. 
In Dean's own handwriting, there are listed with measurements 21 adult fishes — 7 males 
and 14 females. I surmise that these were the results of Dean's collecting for the 12 months 
of 1900-1901. It is probable that the grand total of 42 adults, from all records in various 
handwritings in his notebook, contains a number of duplications. Of the 26 females 
listed, 10 are credited with producing 56 eggs. For 24 of these eggs it is stated that two 
were in the blastula stage, two in the gastrula, while 20 had on them embryos varying 
from 11.5 to 390 mm. in length. 



The Embryology of Chlamydoselachus 529 

The difficulty of arriving at a total for these eggs and embryos is due to the fact that 
these notes were made by at least two other persons besides Dean. The table in Dean's 
handwriting recording 21 adults must have been compiled from various other entries 
in the notebook labelled Chlamtdoselachus. Finally, the matter is complicated by 
the fact that the entries cover the catches of the years 1901-1906 inclusive. Here it 
must be noted that between Dean's departure from Japan in 1901 and his return in 1905, 
specimens of adults and embryos were collected and sent to him in America. Some of 
these are listed separately in the notebook referred to. 

There was another small but valuable lot of material made available to Dean. A 
young Japanese student, T. Nishikawa by name, had in May, 1896, collected eggs and 
embryos of Chlamydoselachus. By June, 1897, he had finished a brief but interesting 
paper ("Notes on some embryos of Chlamydoselachus anguineus Garman"). This was 
published in 1898. In 1900, Dean at Misaki began to get eggs and embryos of the same 
shark. Nishikawa, having finished with his materials and having published his article, 
turned over to Dean all his specimens and slides to further Dean's researches. Evidence 
of this will be adduced in various sections of this article to follow. 

Of the embryological material brought back by Dean in 1901 and 1905, or sent from 
Japan to him at various times, I have had access to certain embryos of Chlamydoselachus 
as follows. In the American Museum are six specimens ranging from 190 to 370 mm. in 
length. In the zoological collection of Columbia University, and loaned to me by Prof. 
J. H. McGregor, are 13 embryos of various sizes (but none so large as ours), some with 
and some without yolk sacs ; and five eggs without embryos ; then in addition there are 
four lots of embryos (mainly very young) collected in 1913, 1914 and 1917- Lastly from 
the Museum of Comparative Zoology, Cambridge, Massachusetts, there have come 
through the courtesy of Dr. Thomas Barbour, one small embryo brought from Japan in 
1907; and an egg with a larger embryo presented by Dr. Dean in 1912. 

THE DRAWINGS AND THEIR AUTHORSHIP 

Found among Dean's records are 55 finished drawings reproduced herein as plates 
I to VI. These drawings range from a representation of what is evidently an ovarian egg 
to figures of specimens, male and female, in which the yolk sacs are no longer present. Of 
the 55 drawings, three are in color and the others are in grey (pencil), but all were pre- 
pared for reproduction by lithography. These figures were assembled on eleven unnum- 
bered sheets of heavy cardboard, each plate comprising from one to nine figures. I could 
not make out any graded arrangement of these drawings as affixed to the sheets which 
have come to me. With the help of Dr. B. G. Smith, I have endeavored to consolidate the 
drawings of eggs and embryos and arrange them in sequence so far as is practicable — except 
that the colored figures have been grouped on one plate. All the drawings of adults have 
been grouped on the final plate. 

The matter of the execution of the drawings, which form the basis for this article, 
was at first a puzzle. It seemed probable that some of them were made by Dean, but 



530 Bashford Dean Memorial Volume 

there was reason to believe that most of them were done by Japanese artists under his 
direction. No one, who is familiar with Dean's skill as an artist, will doubt that he was 
capable of making drawings like those reproduced in this article. But his time at Misaki 
must have been fully occupied with pushing the collection and preparation not only of the 
embryological material of his archaic fishes (particularly the more abundant eggs and em' 
bryos of Heterodontus) but of the other rare zoological materials which he brought back to 
Columbia University. 

As will be shown later, Chlamydoselachus is an ovoviviparous shark. The embryos 
with their huge yolk sacs, enclosed in egg capsules, were obtained from the uteri of the 
female fish newly caught in Sagami Bay. Brought up from depths of from 300-600 fathoms, 
these embryos presumably could not be kept alive in aquaria. They would be subjected to 
two greatly changed conditions — a lower pressure and a higher temperature. Further, 
there is probably a difference in the chemical composition of the surrounding medium 
when eggs and embryos are transferred from the uterine fluid to sea water. However, 
in the light of some personal observations, I cannot be sure of this. While a guest-in- 
vestigator at the Tortugas (Florida) Station of the Carnegie Institution of Washington 
(1912-15), I found that when the similar thick-shelled intra-oviducal eggs of the nurse 
shark, Ginglymostoma cirratum (a shallow- water form), were removed from the uterus, 
opened, and the perivitelline fluid tasted, this was found to be salt. It may be noted here 
that the cloaca of the nurse shark has a wide external opening and that the common 
opening into it of the two gravid uteri will often admit three or four fingers. A similar 
testing of the perivitelline fluid of the uterine egg of a just-caught Chlamydoselachus 
would be very instructive. 

Even if the factor of chemical composition of the surrounding medium is ruled out, 
still, because of the great alterations of pressure and temperature, the embryos of Chlamy- 
doselachus would die quickly. Hence if they were to be drawn alive, the assistance of 
several skilled artists would be required. In this connection and in corroboration of the 
idea expressed above, Mrs. Dean states that she clearly remembers that Dr. Dean, while at 
Misaki in 1900-1901, had the assistance of six artists and that on the second visit (1905) 
he had four artists making drawings. Mrs. Dean is fortunately able from her diary to 
give the names of the six artists — one of them being a man named Kuwabara. 

Furthermore, Dean was, at the time of the collection of embryos of Chlamydoselachus, 
also studying the much more abundant eggs and embryos of Heterodontus which were 
comparatively easy to procure from shallow water with the aid of divers. 

Since there are many drawings of the young stages of this shark, it is probable that 
the artists devoted more time to these than to the embryos of Chlamydoselachus. Because 
of the abundance of valuable Heterodontus material and because the less viable embry- 
os of Chlamydoselachus must be preserved immediately, it seems probable that figures 
of the embryos of the frilled shark were drawn at a later date from preserved specimens. 
I surmise that the colored figures and probably some of the uncolored ones were made at 
once from fresh specimens at Misaki, or that rough color sketches were made there, and 



The Embryology of Chlamydoselachus 531 

that later the finished sketches were made from these and from preserved specimens. 

Finally, I have received from Dr. Naohide Yatsu, of Tokyo Imperial University, 
information which confirms the conjectures above and adds further to our knowledge of 
the authorship of these excellent drawings. Dr. Yatsu was associated with Dr. Dean 
on the first visit to Japan, and afterwards at Columbia University, where he was a student 
of Dean's and later an assistant in the Department of Zoology. 

On the matter in question, Yatsu writes that at Misaki, Dean made sketches in 
pencil and in color from living embryos of Chlamydoselachus. Indeed among Dean's 
relicta is such a color sketch of the internal organs of a female Chlamydoselachus. As to 
the finished drawings, Yatsu is sure that the color figures were made from Dean's color 
sketches and the pencil drawings from Dean's sketches and also from preserved material. 
These were done in Tokyo in 1905 under Dean's supervision at the Zoological Institute of 
the University by Isaburo Kuwabara, the Institute draftsman. This is also the testimony 
of Yatsu's colleague. Dr. Tanaka. 

VIVIPARITY (OVOVIVIPARITY) IN CHLAMYDOSELACHUS 

All elasmobranchs (sharks and rays), whether oviparous or viviparous, have internal 
impregnation and fertilization. To effectuate this, the male is provided with intromittent 
organs, the claspers. These are modified portions of the hinder and inner part of each 
pelvic fin, which are inserted into the cloaca of the female and served to hold her fast and 
to transmit the seminal fluid. 

The preponderant evidence is that oviparity was the original method of reproduction 
in elasmobranchs. It persists today in certain sharks and skates, which extrude eggs en' 
closed in horny envelopes provided with tendrils by means of which they become at' 
tached to marine objects. In Chlamydoselachus the large egg is enclosed in a keratinoid 
capsule provided at each end with a process which varies greatly in form and structure. 
It is sometimes blunt but in many instances it is long, curved, and frayed at the apex into 
tendrils (Figures 2, 7 and 13, plate I). If these encapsuled eggs were found outside the 
body of the fish, one would surmise that these curved processes serve as organs of attach' 
ment. But egg and capsule are retained within the uterus even after the developing 
embryo has burst the shell, as will be shown later. 

Thus in this shark, the presence of the egg shell with curved horns or frayed pro' 
cesses plainly indicates that the ancestors of Chlamydoselachus practiced oviparity. Yet in 
the frilled shark, possessing so many primitive characters, there prevails the most highly 
specialized form of reproduction — viviparity, or more properly ovoviviparity as will be 
explained later. This is another instance of the strange admixture of primitive and 
specialized characters found in Chlamydoselachus as pointed out by Smith in his study of 
the anatomy (1937). 

That the fish is viviparous must have been known to Ludwig Doderlein, who, in the 
years 1879-1881, made an extensive collection of Japanese fishes. These were brought in 
1881 to Vienna, and among them were two specimens of Chlamydoselachus taken in 



532 Bashford Dean Memorial Volume 

Tokyo Bay in 1881. At least one of these was a female. For the scanty history of these 
two sharks see Gudger and Smith (1933, p. 248). As may be read therein, Doderlein 
described the two specimens of Chlamydoselachus but his paper was lost. It is plain, 
however, that he recognized that this shark is viviparous. For this see Rose's statement 
in a later paragraph in this section. 

In 1884, the Museum of Comparative Zoology, Cambridge, Massachusetts, pur^ 
chased a slender snake4ike shark from Prof. H. A. Ward, who had obtained it from Japan. 
Samuel Carman, curator of fishes, seeing that it was a new form, at once published 
preliminary descriptions of it and named it Chlamydoselachus anguineus (the snake'like 
cloak'gilled shark). In 1885 Carman described the anatomy of this partially eviscerated 
female specimen. He found the badly preserved ovaries and oviducts much torn, but of 




Text-figure 2 

A female Chlamydoselachus with the eggs which have been cut out of her body. 

This figure has been carefully retouched to make the outlines clearer. 

After Nishikawa, 1898, Fig., p. 95. 

one of the oviducal tubes he says that "A piece left at the cloaca showed one of the [ovi] 
ducts greatly distended, possible with young that had hatched within it". 

That this was a sound deduction is shown by Rose's statement (1895, p. 194) that 
"One of the animals [a female Chlamydoselachus brought from Japan by Doderlein] had 
'im Leibe' an embryo about 340 mm. [13.4 in.] long, which Professor Doderlein had the 
kindness to turn over to me for study". With this statement of Rose's, it became almost 
certainly established that Chlamydoselachus brings forth its young alive. 

However, the man who personally first definitely demonstrated that the frilled 
shark is viviparous was the Japanese student, Nishikawa. In 1898, he wrote ''Chlamy^ 
doselachus anguineus is viviparous, and the breeding season is spring, extending from 
about the end of March to the beginning of June". Furthermore, he figured a female 
shark and a number of eggs (Text'figure 2) taken from her body. This photograph was 
poorly reproduced on soft paper and is without any explanatory legend. It is plain, 
however, that these eggs are enormous in proportion to the siz,e of the body of the fish. 



The Embryology of Chlamydoselachus 533 

It is impossible to determine with certainty how many eggs are represented in this 
figure. There seem to be about a dozen and in addition there are various objects not 
clearly recognizable. There is no date given for the capture of this fish, but from a female 
taken May 26, 1896, Nishikawa obtained six embryos ranging from 32-60 mm. in length. 
"Each embryo was attached to its large yolk-sac by means of an umbilical cord, which 
allowed considerable movement to the embryo". 

Thus Nishikawa in 1898 was the first to demonstrate by dissection and publication 
that Chlamydoselachus is viviparous. He had dissected seven specimens in 1896. Since 
Dean kept closely in touch with the literature on the archaic fishes, it is likely that he 
knew of Nishikawa's article (1898) as is evidenced by his statement (Dean, 1901.1): 
"I found . . . that if one could secure [at Misaki] many adult [female] specimens [of 
Chlamydoselachus] there was a fair chance of obtaining embryos, since this shark was 
known to be viviparous". 

Dean's extensive experience in collecting eggs and embryos at Misaki abundantly 
confirmed the conclusion that Chlamydoselachus is viviparous. His stages ranged from 
blastulae to embryos varying in length from 11.5 mm. to 390 mm. (15.35 in.) — all attached 
to yolk sacs. 

The spawning habits of the frilled shark are unknown to this day. It seems to me 
that this fish must properly be called not viviparous but ovoviviparous, because it carries 
in its uterus not eggs in very thin'walled capsules as do some viviparous sharks and rays, 
but eggs with rather heavy keratinoid shells fit to be expelled into the water (Figures 2 
to 10, plate I). 

I have found that the tropical littoral nurse shark, Ginglymostoma cirratum, carries 
in its uteri very large eggs enclosed in very heavy keratinoid shells. Evidence (to be 
adduced later) leads to the belief that, when the embryo has attained some size the shell is 
burst and is expelled through the cloaca into the sea, while the egg and embryo are re' 
tained in the uterus for a considerable time For these reasons, it seems to me that such 
a shark ought to be designated as ovoviviparous rather than viviparous. I have studied 
the nurse shark extensively and since its reproductive organs and breeding habits are very 
similar to those of the frilled shark, comparisons will frequently be made in order to clear 
up many puzzling questions about the reproduction of Chlamydoselachus. 

The young frilled shark certainly breaks its egg shell long before it is old enough to 
be extruded from the uterus into the water (Figure 11, plate I). But we do not know at 
what stage in the development of the embryo the insoluble keratinoid egg capsule is cast 
off into the uterus nor when it is extruded into the sea. Nor is it known whether the 
embryo is expelled into the water before all the yolk is absorbed as occurs in the dogfish, 
but is seems improbable. If the young Chlamydoselachus or Ginglymostoma were extrud' 
ed early, it would swim poorly because of its great yolk mass (Figure 49, plate V) and 
would be an easy prey for any marauding fish. One must conjecture that the young of 
both sharks are retained in the uterus until, when passed out into the sea, they are able 



534 



Bashford Dean Memorial Volume 



to fend for themselves. In support of this I have found (Gudger, 1918) that the 20'mm. 
eggs of the marine gaff-topsail catfish (Felichthys felis), which are orally incubated, are 
retained in the mouth of the male not only until the egg shell is thrown off but until all 
the large yolk mass is taken into the body of the young fish. Thus the little three- or 
four-inch fish when set free in the ocean is better equipped to escape its enemies and 
capture its food. 

BREEDING SEASON OF THE FRILLED SHARK 

Because of its deep-sea habitat, no direct observations on the breeding behavior and 
season of this shark have ever been made. Consequently we are confined to a study of the 
records indicating the stages of development of ovarian eggs and of uterine embryos on 
the dates of capture of the females. The evidence from the ovaries, since it does not 
include accounts of eggs ready to be discharged, is not of great value. Of prime im- 
portance, however, are the data as to stages of development of embryos in the oviducts. 
The all too scanty evidence from both sources will now be presented. 

EVIDENCE FROM THE OVARIES 

With one exception, the only available evidence from this source as to the breeding 
season of Chlamydoselachus is contained in the entries in Dean's notebook concerning eggs 
found in these organs. These fragmentary statements, being dated, do throw some light 
on the matter. 




Text-figure 3 
The partially opened abdomen of a 1510-mm. female frilled shark taken November 28, 1938, 
in the Sagami Sea. Five eggs, each measuring 80 — 83 mm., were contained in each ovary. 

Photograph by courtesy of Fumio Momose. 



The Embryology of Chlamydoselachus 535 

In the handwriting of Dean's unnamed Japanese collector — possibly Kuma — are two 
records. In the ovary of a 1500'mm. Chlamydoselachus taken February 8, 1905, six 
"immature" eggs were found. And on April 30, 1903, he found in a female, 1670 mm. in 
length, three ''immature" eggs in one ovary and nine in the other. Unfortunately the 
si2;es of these eggs were not noted. However, under date of April 27 (1902?), Dean 
diagrammatically figured and also photographed the ovaries with eleven large eggs in 
a female measuring I960 mm. — the largest Chlamydoselachus on record. In the left ovary 
were five eggs, size 70 x 30 mm., and in the right nine of the same size and two measuring 
60 X 30 mm. As will be seen later, these eggs, though large, were not mature, but one 
may conjecture that they would have reached maturity later in the calendar year. Thus 
Dean recorded on October 1, 1905, ''female, no eggs [in oviducts ?], large ovar." 

Since the above was written, Momose (1938) has described the visceral anatomy of 
a nearly ripe female taken in Sagami Bay, November 28, 1938. Each ovary contained five 
eggs measuring from 80 to 83 mm. in diameter. Momose has kindly sent me two photo- 
graphs showing this fish opened along the mid'ventral line to reveal the ovaries. The 
better of these photographs is reproduced herein asText'figure 3. Since ripe ovarian eggs 
and newly fertilized eggs (Figures 1, and 4, plate I) average about 95 mm. in diameter, it 
is clear that these 80-83'mm. eggs were almost mature. 

The evidence from the ovaries is scanty but nevertheless significant. To recapitulate, 
ovarian eggs taken February 8 and April 30 were noted as "immature" but no sizes were 
recorded. However, on April 27 some eggs were measured and found to be 70 x 30 mm. 
On October 1 a "large ovar." was noted, and on November 28, several eggs measuring 
about 83 X 80 mm. were photographed (Text'figure 3) — eggs almost "ripe". These data 
indicate strongly that eggs in the ovaries of Chlamydoselachus ripen at any season through- 
out the year. But better evidence of a long breeding season will now be introduced. 

STAGES OF EMBRYOS IN THE UTERI 

The evidence as to the surprising range of the breeding season of the frilled shark, 
based on the ages of embryos obtained from the uteri, at various times in the year, will 
now be set out in chronological order. 

Nishikawa (1898) gives the first intimation of a definite breeding season for the frilled 
shark. He states that "... the breeding season is spring, extending from about the end of 
March to the beginning of June". He had eggs in early and late blastula stages but he 
does not give the dates when these were obtained. Of his seven gravid female fish, 
he gives date of collection for but one. His youngest batch of embryos (from a 1700-mm. 
female) came to him on May 26, 1896. These embryos were six in number and measured 
32, 35, 43, 48, 50 and 60 mm. long respectively. 

Dean's notes give a far greater range of dates when uterine eggs and embryos were 
collected, and ordinarily he gives measurements for one or both. Thus he notes "1905, 
Early Jan. [not JuneY^ eggs with embryos 11.5, 15.5, and 20 mm." Furthermore, in the 
jar of material from Columbia University referred to above there are two embryos of 



i 



536 Bashford Dean Memorial Volume 

about 20 and 45 mm. in length, without yolk sacs, bought in the Tokyo market January 22, 
1914. These and other embryos from this jar are badly crumpled, hence the "about" for 
this and the three other lots. In this same jar are four embryos about 15, 1 8, 20 and 25 mm. 
"over all", "from Tokyo market February 4, 1913". In the same receptacle are seven 
embryos ranging from about 60-130 mm. in length "Bought Tokyo Market April 4, 
1913". In his notebook Dean states that he got three blastulae on April 10 (year not 
noted). Next and last of the four Columbia University lots are five embryos measuring 
about 23, 25, 30, 43 and 47 mm. bought on April 23, 1917- 

The remainder of the available data is also from Dean's notebook. On April 25 he 
records seven eggs with embryos — 165, 175, 185, 195, 205, 210 and 250 mm. in length. 
Then in the writing of his unkno'^Ti note-taker and correspondent, judged to be a Japanese, 
are recorded eggs from the oviducts of three females each measuring 1770 mm. The 
first taken April 25 had seven eggs with, embryos (not measured), the second (of the same 
date) had five "broken eggs" in the oviduct: the third, taken April 27, had in the oviduct 
three "mature" eggs (two broken). Next in Dean's writing is this record "4 embs. large, 
taken about May 1, 1905". These measured in millimeters 317, 331 (yolk sac 111 x 100), 
352, 390 (yolk 100 x 70). Then I find in Dean's writing a record,"? May 23, 1906," of five 
embryos (no measurements) firom a 1390'mm. female. The next records come from late in 
the calendar year and are so important that they must be given in a separate paragraph. 

Four eggs were taken from the uteri of a female captured in the Odowara Bank on or 
about October 1, 1905. This record is based on three separate notes in Dean's writing on 
three separate pages of his notebook. No one of these, no two would establish this fact; 
but when aU three are studied together, date, place, and number of eggs all tie up into 
this definite record. Three of these eggs are noted as "oblong eggs, 2 drawn, in r. oviduct, 
small vs.ind egg (drawnl in opposite [1.] oviduct, stage early [small pencil sketch] probably 
gastrula". For the two "oblong eggs", see Figures 2 and 3, plate I. Apparently the 
oblong egg with the probable gastrula, shown in the pencil sketch (Text'figure 26), was 
not drav^Ti. For the "small wind egg" see Figure 51, plate V. 

Among Dean's loose papers, I have found a rough sketch in water color of an egg and 
embryo labelled fin a hand other than Dean's) ^'Chlamydoselachus angmneus. Egg taken 
at out of Okinose, Sagami Sea. (Depth 360 fms.) December "06". The egg and embryo 
were presumably drauTi natural size. The ellipsoidal yolk measured 122 x 69 mm., and the 
embryo 55 mm. — when taken in December! 

Here let us recapitulate the dates throughout the whole calendar year on which 
embryos of the sizes noted have been taken: "Early Jan.", six specimens measuring 11.5 
to 20 mm.: April 4, seven — 60 to 130 mm.; April 10, three blastulae; April 23, five 
embryos — 23 to 47 mm.; April 25, seven, 165 to 250 mm.: April 25 and April 27, fifteen 
eggs and embryos in three uteri; May 1, four embryos — 317 to 390 mm. ; May 23, five — no 
measurements; October 1, three eggs — probably blastulae; December '06, one embryo 
55 mm. — m length. 



The Embryology of Chlamydoselachus 537 

The evidence from the ovaries is fairly strong, that from the uteri cumulative and 
overwhelming, that Chlamydoselachus ripens eggs in batches in its ovaries, and broods 
and hatches embryos in its uteri throughout the whole calendar year and probably in 
every month of the year. 

When one thinks the matter out, this does not seem so extraordinary as at first blush. 
Chlamydoselachus lives at the bottom of the Sagami Sea under uniform conditions of 
darkness, great pressure, low temperature, with a restricted oxygen supply, and on food 
with presumably little change in kind and quality. The maximum depth of the habitat of 
the frilled shark is about 3600 feet, the average 1500 to 1800. At 1800 feet the pressure is 
814 lbs. to the square inch, the temperature about 43° F. and the human eye would find 
total darkness. Under the prevailing and unvarying conditions at these depths, the 
frilled shark would presumably have no special breeding season such as is found in surface^ 
dwelling sharks in the Sagami Sea. In these, in contrast, breeding might be expected 
to take place in late spring or early summer due to the lengthening daylight period, the 
rising temperature, and the more abundant food consequent upon the return of the sun. 
In Chlamydoselachus, on the contrary, it is to be expected that eggs would ripen in the 
ovaries at any time during the year as indicated above and that breeding would take place 
during any month. Thus the findings of eggs with blastulae in October and of embryos 
10-20 mm. long in January, and others measuring 317-390 mm. in May — as recorded by 
Dean — are understandable. 

Before leaving this subject, it is pertinent to call attention to the notes above, which 
show that not all the eggs in a single uterus are in precisely the same stage of development. 
Even as the eggs break out of the ovary one at time as they ripen, so they make their way 
into the oviduct one at a time. Hence there must be a continuous process of fertili2;ation, 
shell formation, and early development going on within a single female during a limited 
period of time. This I have found to take place in the shallow-water nurse shark of Florida- 
Likewise, there will be much later, in the uterus of each individual female Chlamydo- 
selachus, a serial process of breaking and throwing off of egg capsules by the growing 
embryos, and finally a succession of young sharks being extruded into the sea. 

It should be noted that ovarian eggs are matured in batches or clutches (a small 
number of approximately the same large siz,e) and that, when nearly mature eggs are 
present in the ovary, there are no other eggs in the ovaries of the same individual at all 
comparable in si?e. Also, there are limits to the range of variation in sizes of embryos 
obtained from a single female at the same time. One does not find very early and very 
late embryos developing in a single individual at the same time. These observations indi- 
cate that in each individual Chlamydoselachus there is a definite cycle of reproductive 
activity, but one quite independent of seasonal influences, hence any single phase of re- 
production and development may occur in different individuals at different seasons of the 
year. In this, Chlamydoselachus is unlike most vertebrates, but a comparable condition 
is found in civilized man. 



538 



Bashford Dean 'Memorial Volume 



DURATION OF GESTATION 

The duration ot the period of gestation in the frilled shark is not known, and, because 
of the habitat of the breeding fish and of the absence of any definite breeding season, it 
cannot be ascertained by direct observation. However, it will be of interest to set forth 
some facts that indicate that the period is protracted. The same factors of constant low 
temperature, great pressure, and restricted oxygen supply, that lead to an extension of the 
breeding season to cover the calendar year, would also be conducive to slow development 
of the embryos and a lengthened period of gestation. 




Text-figure 4 
Egg shell (measuring 128 mm.), egg (100 x 65 mm.), and embryo (43 mm.) of Chlamydo- 

selachus, reproduced in natural siz;e. 
After Nishikawa, 1898, Fig. 1, pi. IV. 

An idea of the duration of this period may be gained by studying a series of growing 
embryos and noting the relative diminution of their yolk sacs. But first one must endeavor 
to establish the normal si2;e of the yolk mass at, or shortly following fertilization. The 
matter of the varying sizes of the eggs of Chlamydoselachus will be taken up later. Here 
^ve are interested in the size of the eggs in blastula or gastrula stages or in early stages 
of embryonic development. Only two investigators have studied such eggs. The first of 
these, Nishikawa (1898), states that the eggs (in early stages of development, probably 
segmentation), range from 65 to 75 mm. in short and from 102 to 124 mm. in long diameter. 
He writes of other eggs ranging from 110 to 120 mm. in long diameter. These measure- 
ments are probably made over the egg shell. Thus Text-figure 4 (his Fig. 1, tab. IV) 
is 128 mm. long in a straight line over the horns of the shell, whereas the egg itself 
measures 100 x 65 mm., and the embryo 43 mm. in length. The egg shown in Text-figure 4 
is in natural size. 



The Embryology of Chlamydoselachus 539 

Dean portrays three eggs in blastula or gastrula stages in Figures 4, 5, and 6, plate I. 
The yolks measure : A, 97 x 88 mm. ; B, 96 x 87; C, 90 x 87- Of eggs and early embryos in 
stages of development comparable to Nishikawa's 43'mm. embryo, Dean had three drawn. 
Figure 7, plate I shows a yolk 100 x 65 mm. with an embryo of 43 mm.; (as will be seen 
later, this is a copy of Nishikawa's Fig. 1, plate IV); in Figure 9, plate I, the yolk measures 
108 X 68, the embryo 50 mm.; and lastly there is the drawing in color, Figure 50, plate V, 
with a yolk 95 x 69 and an embryo of 39 mm. In these early stages there is practically no 
diminution of yolk si2;e. 

To illustrate the slow rate of absorption of yolk, we may consider three large embryos 
listed by Dean. Thus in Figure 11, plate I, an embryo of 175 mm. (magnified to 205 mm.) 
sits on a yolk measuring 92 x 89 mm. This was collected April 25. Then "taken about 
May 1, 1905" were two still larger embryos. The smaller measured 331 mm. in length 
and had a huge yolk sac measuring 110 x 100 mm. The other is the largest embryo of 
which there is record. This fish, shown in color in Figure 49, plate V, was 390 mm. 
(15.35 in.) long and its yolk sac was 100 x 70 mm. in its transverse diameters. 

To recapitulate, Dean's notes will be quoted. The specimens of Oct. 1, 1905, 
"stage early, probably gastrula", might possibly have grown by "early January" into 
embryos measuring 11.5, 15.5, and 20 mm. on yolk sacs undiminished in size. But it 
does not seem Hkely that by "Apr. 25" one of these could have attained the sizie of the 
l75'mm. embryo of Figure 11, plate I. Nor could the I75'mm. fishlet by "May 1" have 
grown to an embryo of 390 mm. (yolk 100 x 70), which is represented in Figure 49, plate V. 
From the above data it is clear that the fish grows much faster than the yolk decreases. 

It is evident that all the yolk must be resorbed before the little shark is thrown out. 
into the sea to fend for itself. The 15.35'in. fish portrayed in Figure 49, plate V, would be 
so encumbered in swimming, and the large yolk covered with blood vessels would be so 
conspicuous and attractive to marauders, that the free life span of the fish would probably 
be but a few hours at most. But how large would the young shark be when it has used up 
all the food yolk? Surely it would be much larger — perhaps 20-24 in. (508-610 mm.) 
long. The latter si2,e is that of a free-swimming Chlamydoselachus taken by the Prince 
of Monaco at Madeira (CoUett, 1910). But would the uterus of the average-sized female 
contain such a large "baby" without its being folded or curled up? And could it contain 
several embryos of this si2,e? 

All the evidence points to a very long period of gestation in Chlaynydoselachus. But 
how long? Because of its habitat and its breeding throughout the year, it is of course 
impossible to find the answer in the body or in the habits of the frilled shark. It is 
practically impossible to ascertain the length of time for the hatching of any shark's egg 
save in the oviparous forms — and only in those species small enough to be kept in aquaria, 
where the date of egg-extrusion and of egg-hatching can be recorded. This has been done 
in terms of "about so many days" for two species of dogfish. One must say "about" for 
one cannot know how far in development an internally-fertiliz;ed oviparous egg has gone 
when it is "laid". Here are all the facts, so far as known to me. 



540 Bashford Dean Memoria] Volume 

As early as 1867, Coste described how a pair of spotted dogfish, Squalus (ScylJium ?) 
catulus were introduced into the vivarium at Concarneau (a rock-encircled arm of the sea 
shut off by gratings ). The female extruded 18 eggs during the month of April, and the 
young were hatched out during the month of December. Thus the period between 
laying and hatching -^^as about 8 months — not ""about 9" as stated by Coste. 

Bolau f 1881 1 is more exact. On April 12, 1877, the Hamburg Aquarium received 
from the Brighton Aquarium a number of eggs of the European dogfish, Scyllium canicula, 
(how long after extrusion is not stated). Four of these hatched as follows — December 3, 
1877, and January 1, 4, 17, 1878. Their periods were 235. 264, 267, 280 days— from 7 
months and 21 days to 9 months and 10 days. Seven eggs ot the catshark, Sc\'lliu7n 
catulus (also from Brighton), hatched from August 19 to October 16 — a time space of 
129-187 days or 4 months and 9 days to 6 months 7 days. That same season an egg laid 
in the aquarium hatched in 180 days. During 1878 a number of catshark eggs were de- 
posited in the same aquarium and 10 of them hatched in periods varying from 157 to 178 
days or from 5 months and 7 days to 5 months and 28 days. 

These are the known lacts, but more data are needed. In comparison there is reason 
to beHeve that, while incubation is going on, the temale frilled shark is living in ^x-ater ot 
probably not over 43°F. (at a depth of 1800 feet.). But what were the ranges of tempera- 
ture to which the dogfish eggs were exposed at Concarneau and at Hamburg? We have 
already noted the great size of the egg of Chlamydoselachus. Bolau tells us that the barrow- 
or stretcher-shaped eggs of Sc>'IIiu7n camcula were 110 mm. long (over the hornsj by 
41 mm. broad (over the case). The corresponding measurements of the similar eggs of 
S. catulus are 60-55 mm. long by 24-22 wide. The sizes of the yolk masses in these eggs 
are not given, but they are undoubtedly far smaller than those ot Chlamydoselachus — 
probably not more than one-third to one-fourth as large. 

If it takes these relatively small eggs of the European dogfishes from 5.5 to 9.5 
months to hatch at the spring, summer and autumn temperatures of the English Channel 
and the North Sea, how much longer must it take for the huge eggs of the frilled shark to 
hatch at the uniformly low temperatures of 1800 to 3600 feet do\^Ti in the Sagami Sea? 
At first I u^s incHned to think that the incubation period lasted at least one year. But 
since Kyle (Biolog}^ of Fishes, p. 66) says that the embryo oi Acanthias takes about a year 
to develop, it seems probable that it wiU take at least two years tor the embryo of Chlamy 
doselachus to attain its fuU development. 

It is unfortunate that Dean did not get large frilled-shark embryos later than Klay 1. 
and larger than the longest of that date (390 mm., yolk 100 x 70 mm.;, with yolks either 
gone or nearing resorption. Such data would be of great value not only for the question 
under consideration, but for giving an idea of the amount of distention ot the uterus ""at 
term", and as indicating the size of the young shark at the time of birth. It is also unfortu- 
nate that no young free-swimming sharks were taken in the intensive deep-sea hook- 
trawl fishing carried on in the Sagami Sea by Kuma and the market fishermen. The 
smallest free-swimming specimen (a female) recorded by Dean measured 1240 mm. (48.8 



The Emhryology of Chlamydoselachus 



541 



in.), and the smallest ever put on record was taken by the Prince of Monaco at Funchal, 
Madeira, in 1889. Gollett (1890) found this to be a female only 610 mm. (24 in.) long. 
He notes that it differed from typical adults from Japan only in insignificant details. He 
gives no figure. 

THE REPRODUCTIVE ORGANS OF THE MALE 
CHLAMTDOSELACHL/S 

In general, the internal reproductive organs of the male frilled shark are like those of 
the other elasmobranchs. They have been figured and described by Smith in the preced- 
ing article of this volume. Here it is necessary to present only a brief account of the 
external organs of reproduction in the male. 

MYXOPTERYGIA— EXTERNAL ORGANS OF THE MALE 

The male shark has the curious intromittent organs, peculiar to the elasmobranchs, 
called the myxopterygia or claspers. They are modifications of the hinder inner parts of 
the pelvic fins of the male shark or ray. These secondary sex organs, as Text'figure 5 




Text-figure 5. 
A 1500'mm. (?) male frilled shark from the Odowara Bank, 
Sea of Sagami, Japan. Note the large myxopterygia or claspers. 
These are developed from the inner parts of the pelvic fins. 
The claspers help the male shark to hold the female during 
copulation. 
After Doflein, 1906, p. 257. 



Text-figure 6 
Ventral view of the pelvic region of a male Chlamydoselachus, 
showing myxopterygia or claspers. Through the tubular 
claspers, the seminal fluid is introduced into the cloaca of the 
female. This is necessary since in all sharks impregnation of 
the eggs is internal. The cloacal aperture may be seen be- 
tween the bases of the myxopterygia. 

Cat)., projection of cavity. 
After Leigh-Sharpe, 1926, Fig. 1, p. 308. 








cw 






542 Bashford Dean Ts/Iemorial Volume 

shows, enable one at a glance to distinguish the male. The claspers are necessary because 
impregnation in all sharks is internal. These myxopterygia are the only reproductive 
structures of the male that we need consider here. For elasmobranchs in general, they 
have been admirably described by Leigh^Sharpe, (1920, p. 245) from whose article I quote 
the following: 

. . . the basal element of each pelvic fin (basipterygium) is prolonged to form a stout 
backwardly directed skeletal rod supporting a portion of the fin which is demarcated from 
the remainder and specially modified to form a copulatory organ, the clasper or myxoptet' 
ygium . . . The clasper is rolled up in a manner resembling a scroll [Text-figure 6] so that in- 
stead of being a groove, as it is usually described, it is a sufficiently closed tube along the 
greater portion of its length, though the edges may not be and usually are not completely 
fused but overlapping. This tube is one along which spermatozoa pass. 

Not only do the claspers serve as intromittent organs, but inserted into the cloaca 
of a female they help hold her fast during copulation. Their appearance in lateral view of 
a male Chlamydoselachus is shown in Text-figure 5 and of another in Figure 53, plate VI. 
In Text-figure 6, we see these roUed-up organs in ventral aspect with the cloaca between 
their bases. No further description is necessary here. 




Text-figure 7 
A 1510-mm. female Chlamydoselachus, whose enlarged abdomen is due to the presence in her ovaries 
of 10 eggs measuring 80 — 83 mm. in diameter, as seen in Text-figures 3 and 9. Note the absence of 

any external secondary sex characters. 
Photograph by courtesy of Fumio Momose. 

REPRODUCTIVE ORGANS OF THE FEMALE 
CHLAMTDOSELACHUS 

The female frilled shark (Text-figure 7) has no external secondary sex characters, but 
when the ovarian eggs approach ripeness or particularly when the uteri are filled with 
huge eggs undergoing development, the distended abdomen indicates pretty clearly the 
sex of the fish even though the pelvic fins are not distinctly visible. Thus all the repro- 
ductive organs of the female, the ovaries and the oviducts(with their various subdivisions), 
are internal. They have been thoroughly described by Smith (1937) in the article dealing 
with the anatomy of Chlamydoselachus, but it will be necessary to consider here certain 
features having to do with viviparous reproduction in this fish. These are: first, the 
enormous size attained by the eggs while still in the ovary; second, the great distention 



The Emhryology of Chlamydoselachus 



543 



of the uterine portion of the right, and rarely the left oviduct, which is necessary to ac- 
commodate the huge eggs and later the yolk sacs and the developing embryos in this 
viviparous shark. 

In going through Dr. Dean's few scattered notes — literally with a magnifying glass 
because they are at times written in a minute hand — I have been able to correlate certain 
widely separated records and to find certain data either overlooked or not clearly evaluated 
before. These have to do mainly with the reproductive organs of the female and with the 
question as to whether those of both sides are functional or whether those of only one 
side are used in reproduction. These data are so interesting and so valuable that they 
deserve careful study. However, we will first take up the literature dealing with each 
set of organs — ovaries and oviducts — and then consider Dean's notes which will throw 
much hght on both structure and function. 




Text-figure 8 
Ovaries and oviducts of Chlamydoselachus, drawn one-half natural size. 
n. g., nidamental glands. 

Printed from the original woodcut after the drawing by Paulus Roetter for Garman, 1885, Fig. 1, pi. XIX. 

The ovaries and the anterior portions of the oviducts of Chlamydoselachus were 
first figured by Garman (1885). Because of its historic interest, his drawing is reproduced 
from the original woodcut (Text-figure 8 herein). Garman merely says of these organs 
''A section some 12 inches in length of the ovaries and oviducts is represented in the 
sketch". It is a long jump from Garman's figure (1885) to Deinega's representation (1925) 
of the genital organs of our fish. His small figure printed on poor paper is not easy to 
understand. However, Smith's admirable drawings, made from his dissections of four 
specimens from Japan in the Museum collection, give a clear picture of the form and the 
relative sizes of the female reproductive organs in various stages of development. They 
will be referred to later for positions and structures of both ovaries and oviducts. 

And last of all Momose (1938) has figured the abdominal viscera of a 1510-mm. 
female Chlamydoselachus with the huge ovaries removed. This figure is reproduced in 
his article in small size on soft paper and is not suitable for reproduction. However, 
Momose has been good enough to send me the original drawing with the huge ovaries 



544 



Bashford Dean Meynorial Volume 



(with their 10 eggs, each measuring 80-83 mm. in diameter) sketched in. This is re- 
produced herein as Text'figure 9. Being labelled, it needs no explanation here beyond the 
remark that the non^gravid uteri are of approximately the same si2,e. 




Text-figure 9 
Semi-diagrammatic sketch to show the repro- 
ductive organs of a 1510-mm. female Chlamydosel- 
achus. Note the five huge eggs (80 — 83 mm.) in 
each ovary, and the paired oviducts with their 
subdivisions. One shell gland is opened to show 
its structure, and both uteri are somewhat 
dilated. 
Sketch by courtesy of F. Momose. 



THE OVARIES 

In Chlamydoselachus, the ovaries are paired, 
elongate, and in the non-breeding female, 
more or less flattened organs situated in the 
anterior part of the body cavity and attached, 
rather indirectly, to the dorsal body wall by 
means of broad mesenteries. These organs 
like others in this fish are subject to some 
interesting variations which will be pointed 
out further on. 

Before Smith's studies (1937), but three in- 
vestigators had published observations on the 
ovaries of Chlamydoselachus. Garman (1885) 
merely remarks — ''The ovaries [Text-figure 8] 
had been badly preserved and were much 
torn". CoUett (1897) describes the oviducts 
and then continues as follows: "The right 
uterus [ovary?] was 240 mm. in length, and 
contained 10 large eggs about the size of the 
yolk of a small hen's egg, but some varied in 
size. There were, besides, about 30 lesser 
yolks of the size of large and small peas, as 
well as a few bigger ones about the size of the 
yolk of a pigeon's egg. The length of the left 
uterus [ovary] was 220 mm., and it contained 
five large yolks, and about 20 small ones." 

This is understandable only on the sup- 
position that Collett used the word "uterus" 
but meant ovary. In the paragraph preceding 
the one quoted, he crudely described the 
oviducts — stating that they were 900 mm. 
long and that each expanded into "a uterus- 
like sack". His description of the "uterus" in 
the above quotation, if "uterus" is replaced 
by ovary, absolutely fits the structure of the 
immature elasmobranch ovary having in it 



The Emhryology of Chlamydoselachus 



545 



eggs of various si2,es and of various degrees of ''ripeness" such as I have found in the 
ovaries in scores of dissected sharks and rays. Furthermore, although, as I have found, all 
the eggs in the uterus of a viviparous shark or ray may vary somewhat in si2;e, the limits 
are fairly close. They do not vary from "the size of the yolk of a small hen's egg" to that 
"of large and small peas". Then too when a wind egg is found, it, though smaller in size. 



Urogenital system of the female Chlamydosel- 
achus, ventral views, one-fifth natural sizie. 

Text-figure 10. Urogenital organs of a specimen 

1398 mm. long. The excretory ducts are 

concealed by the oviducts. 

ah.p., abdominal pore; m, mesonephros; ovd., oviduct; ovy., 
ovary; r.cl., rectal portion of the cloaca; ug.s., opening from 
the urogenital sinus; v.l, ventral ligament of the oviduct. 
Drawn from specimen No. IV in the American Museum 
of Natural History. 
After Smith, 1937, p. 432. 



Text-figure 11. Urogenital organs of a specimen 
1550 mm. long. The shell glands and the 
adjacent portions of the oviducts are displaced 
laterally, and the excretory ducts are not shown. 
ab.p., abdominal pore; m., mesonephros; ovd., oviduct; 
OFy., ovary; r.cl., rectal portion of the cloaca; s.g., shell 
gland; ur.p., urethral pore; ut., uterus; f.I., ventral ligament 

of the oviduct. 

Drawn from specimen No. Ill in the American Museum 

of Natural History. 

After Smith, 1937, p. 432. 







Text-figure 10. 



Text-figure 11. 



is plainly recognisable as being a shell without embryo and yolk. To settle the matter 
effectively, attention is called to the fact that Collett does not speak of egg shells. He 
wrote uterus but he surely meant ovary. 

It seems that this misidentification of the genital organs may be due to the possibility 
that Collett wrote in Norwegian and that his thesis was translated into English by another 
hand and that it was published without his seeing the proofs. 

Hawkes (1907) had several specimens, but, of the organs under consideration, she 
briefly states that "The ovaries are diffuse bodies attached by broad mesenteries to the 



546 Bashford Dean Memorial Volume 

line of attachment of the stomach mesentery". From this, one may judge that her speC' 
imens were either immature or with ovaries spent. Deinega's specimen (1925) had had 
the ovaries removed. Smith (1937), however, gives definite data, particularly in that he 
records the sizes of eggs found in the ovaries of two of his fish. Unfortunatley, there are 
no dates of capture of any of his specimens. 

In a sexually immature female specimen, 1398 mm. long (Text 'figure 10), Smith found 
that the ovaries were small and exhibited perfect bilateral symmetry. The largest fol- 
licles measured only 10 mm. in their greatest diameter. In a larger and nearly mature fish, 
1550 mm. long, he found that both ovaries were well developed and contained follicles 
ranging in size up to 17 mm. in diameter as shown in Text-figure 11. Of the follicles large 
enough to be easily distinguished macroscopically, there were 13 on the left and 15 on the 
right. Some of those in the left ovary were larger than any in the right organ. In sexually 
mature specimens, 1350 and 1485 mm. long respectively, he found the ovaries of the right 
sides were spent and that those of the left sides were intact but small and contained only 
very small ovocytes, none more than 6 mm. in diameter (Text-figures 14 and 15). 

In Dean's notebook on a pasted-in sheet (from its phraseology evidently from one of 
his Japanese collectors) are two records concerning the ovaries. The first is dated 
February 8, 1905, and reads ''Six immature eggs in left ovary" of a 1500-mm. female. 
Under date of April 30, 1903, this entry occurs: "Three immature eggs were in the left 
ovary and nine immature eggs were in the right ovary" of a female 1670 mm. long. How 
large these eggs were cannot be stated, but at least they were of considerable size. Never- 
theless, for another fish, we do have measurements of the eggs. 

There is in this same notebook a rough pencil sketch and some notes in Dean's own 
writing, showing that on April 27th he dissected a 1960-mm. female (the largest Chlamy 
doselachus on record). This fish had in the right ovary 11 eggs in two rows (nine measur- 
ing 70 x 30 mm. and two 60 x 30 mm.), and 5 (70 x 30 mm.) in the left ovary. These large 
eggs are found on the margin of the genital fold precisely as they are shown in Text-figure 
11 (Smith's 1550-mm. specimen), and as I have found them in mature ovaries in sharks of 
southern Florida. These eggs were surely approaching maturity. 

Among Dean's Chlamydoselachus records is a faded photograph of the viscera of this 
same female. This shows the 5 large eggs on the left side, but on the right only 6 or 7 
can be counted — the precise number is uncertain because some are covered by the other 
viscera. Lastly there is an incomplete water-color sketch of this same dissected fish. The 
photograph and the color sketch were evidently intended to furnish the basis for a finished 
figure in color. This, unfortunately, was either never made or has been lost. Dean's 
photograph is faded and the ovaries with their eggs are too much obscured by other 
viscera to permit its use. The wash drawing and pencil sketch are plainly unfinished. 
But fortunately other photographs are at hand to show these organs. 

Momose in 1938 procured from Sagami Bay a 1510-mm. female having 10 nearly 
ripe eggs (size 80-83 mm.) in the ovaries — 5 on each side. His figure is poorly printed on 
soft paper and is not suitable for reproduction. But, in answer to a request conveyed 



The Embryology of Chlamydoselachus 547 

through Dr. N. Yatsu, he has sent me two photographs showing the body cavity open- 
ed along the mid-ventral line. The better of the photographs, and the one which he re- 
produced, is shown herein as Text-figure 3. Momose also kindly sent me his drawing of 
the abdominal viscera of his Chlamydoselachus with the two huge ovaries sketched in, as 
seen in Text-figure 9. Each ovary contains five great eggs, measuring 80-83 mm. in di- 
ameter. It is interesting to find in Momose's photograph (Text-figure 3) and sketch 
(Text-figure 9) absolute corroboration of what is seen in Dean's 35-year-old photograph, in 
his rough colored wash drawing, and in his rougher pencil sketch. 

So far as all this evidence goes, it strongly indicates that more eggs ripen in the right 
than in the left ovary — a total of 25 in the right and 19 in the left ovary in the four cases 
cited above. In Dean's specimen, having 5 eggs in the left and 11 (in two rows) in the 
right, and in Momose's fish having 5 eggs in each ovary are found the only cases on record 
in which the left ovary contained eggs approaching maturity. Smith's 1550-mm. specimen 
contained young eggs in both ovaries, but the larger ovocytes (up to 17 mm. in diameter) 
were found in the left ovary. Even with these bilateral ovaries considered, the weight of 
evidence is that the right ovary is the predominant egg-producer. 

It is interesting to note the relative positions of the ovaries with regard to each other. 
Carman's drawing (1885) shows the two ovaries on the same level (Text-figure 8 herein). 
Hawkes (1907) says of her specimens (number not noted) that "The right ovary is placed 
somewhat more anteriorly than the left". Dean's rough sketch shows the two organs on 
the same level. Smith's young and sexually immature fish (1398 mm. long) had the two 
ovaries on the same level (Text-figure 10 herein). Another, measuring 1550 mm. with 
eggs up to 17 mm. in the left ovary, had this ovary somewhat further forward than the 
right (Text-figure 11). In each of his two other mature specimens (1350 and 1585 mm. 
long) the right ovary was placed markedly forward of the left (Text-figures 14 and 15). 
Momose's sketch shows the relative positions of the ovaries in his specimen. The right 
ovary is placed forward of the left by about two-thirds the diameter of one of the huge 
eggs (Text-figure 9). 

Of the eight females for which we have data, three had the ovaries on the same level 
(one being sexually immature), one had the left anterior to the right, and four had the 
right placed further forward. This difference in position brings the right ovary nearer to 
the entrance funnel to the oviducts. 

The matter of the one-sidedness of elasmobranchs in their reproductive organs — 
particularly that in Chlamydoselachus the right ovary only tends to be functional — is of 
very great interest and deserves some study. Fortunately I have made some firsthand 
observations as to unilaterality of the functioning of both ovaries and oviducts in various 
sharks and rays. It seems best to postpone the consideration of these data for ovaries 
until the oviducts of Chlamydoselachus have been studied, since in them also a tendency to 
unilateraHty will be found, and since the functioning of the two are interdependent. But 
before going into the matter of oviducts, it seems well to consider here the question of the 
si2;e attained by the egg before it is discharged from the ovary. 



J 



548 



Bashjord Dean Memorial Volume 



IMMATURE OVARIAN EGGS 

Among the frilled-shark material loaned by the Department of Zoology of Columbia 
University are five ovarian eggs of different sizes. No. 1 (42 x 34 x 34 mm.) is greatly 
flattened on one side and is devoid of follicular membranes. No. 2 (45 x 38 x 38 mm.) 
is shaped like a hen's egg and is surrounded with fragments of the follicular membranes. 
No. 3 (46 X 46 X 35 mm.) is without follicular membranes. No. 4 (58 x 50 x 44 mm.) is 

enclosed in follicular mem- 
branes. No. 5 — also enclosed 
in follicular membranes — 
measures 60 x 49 x 49 mm. 
These are all immature eggs, 
probably about half-grown. 

Other sizable (and in this 
case larger) ovarian eggs are 
those noted and sketched by 
Dean and taken from his huge" 
1960-mm.sharkcaptured April 
27. Of the 16 eggs in question 
in the two ovaries, 14 measur- 
ed 70 x 30 mm. and 2 were 
60 X 30 mm. They approached 
maturity much more than the 
smaller eggs just listed above. 
Last of all are the huge ovarian 
eggs reported by Momose 
(1938) fromhisl510-mm. speci- 
men taken November 28. 
These, measuring 80-83 mm. 
in diameter (Text-figures 3 
and 9), were almost mature as 
will be seen from the data in 
the following paragraphs. 




Text-figure 12 
A ripe ovarian egg in its ovarian and follicular membranes. The 
circular area on top is probably a thin place in the membranes where 
the follicle will rupture to set the egg free into the coelom. This is 
probably the same egg as that shown in Figure 1, plate I. It is 
presumably figured in natural sizie. 

Photograph by Bashford Dean. 



A MATURE OVARIAN EGG 

Such an egg is shown in Figure 1, plate I. In the original drawing, it measures 
90 X 96 mm., and it was presumably drawn in natural size. It is of approximately the 
same size as the eggs in round capsules shown in plate I. Its measurements are close to 
those of eggs with gastrulae or very young embryos described by Nishikawa and by Dean 
as found in the uteri. 

This egg (Figure 1, plate I) is enclosed in the egg follicle and is covered by the thin 
peripheral membranes of the ovary. These membranes are folded into ridges shown as 



The Emhryology of Chlamydoselachus 549 

light streaks in the figure. Follicular blood vessels are shown as a dark network. This 
rich vascular network is concerned with the nutrition, development and growth of the 
huge egg. The circular area in the upper part of the figure is presumably a thin region of 
the ovarian membranes where the follicle will rupture to allow the egg to escape into the 
body cavity. It would seem that this egg is practically mature. 

Among Dean's records I find a photograph (Text-figure 12) of an ovarian egg. Study 
of the detailed markings in drawing and photograph shows both to have been made from 
the same egg. The drawing was probably made first, the photograph possibly after the 
egg had been hardened and when a portion of the yolk had been torn away as shown in 
the photograph. The text'figure is reproduced in the sizie of the original drawing so that 
an accurate idea may be had of the natural size of this mature ovarian egg. 

In this photograph the limits of the circular area shown in the upper part of Figure 1, 
plate I, are more sharply defined. Similar areas are visible in five of the large but immature 
eggs in the ovary shown in situ in Dean's photograph referred to above. On ovarian eggs 
Nos. 4 and 5, recorded in the Hst from Columbia University and mentioned in a preceding 
paragraph, are found similar areas. Upon dissecting off the follicular membranes from the 
circular area in one of these ovarian eggs, there was found a whitish region of correspond' 
ing shape and size, which presumably represents the germinal area. This area is surround- 
ed by a shallow depression — a circular groove. The remainder of the egg is a dark yellow 
and appears to be composed entirely of yolk. I therefore conclude that the circular area, 
represented in Figure 1, plate I, and in Text-figure 12, overlies the germinal area and is of 
about the same size. It would be very desirable to study this egg but it cannot be found 
among the specimens from Columbia University at my command. 

When the ovarian follicles break, the ripe eggs in some way, as yet not clearly 
understood, find their way into the funnel of an oviduct, and begin their descent into 
this tubular organ in which fertilization, shell formation and gestation take place. 

THE OVIDUCTS 
As in other sharks, the oviducts are elongate paired organs joined at their anterior 
ends where they communicate with the abdominal cavity through wide funnel-shaped 
openings or sometimes through a single median aperture. Posteriorly each opens separate- 
ly into the cloaca. When an egg gains entrance into an oviduct through the funnel, it is 
fertilized by a spermatozoon, passes into and remains in the shell gland while the keratinoid 
shell is being formed around it and then it descends into the uterine enlargement where 
segmentation, gastrulation, and the formation and growth of the embryo take place. 
There will now be considered some interesting features relating to these divisions of 
the oviduct. 

THE ABDOMINAL OPENINGS. 

In Chlaynydoselachus the abdominal openings of the oviducts are of particular interest 
because of their variability. These variations will now be pointed out. 

In Carman's specimen (1885), each oviduct (Text-figure 8) has its own opening 
widely separated from the other. Hawkes (1907, p- 475) does not state how many female 



J 



550 Bashford Dean Memorial Volume 

specimens she examined, but she describes the funnels as follows: "The oviducts have 
large funnels, which open ventrad to the stomach. . . . The edges of the funnels are ir' 
regular and spreading, and are united in the median ventral line to one another, thus 
forming one large funnel. The anterior edges of the funnels become united to the anterior 
wall of the body cavity, whilst the posterior edges of the united fimbriae hang free." 

Deinega's one specimen had a single unpaired opening. So also in three of Smith's 
specimens (including one that is sexually immature), the oviducts communicate with the 
body cavity through a single opening (Text figures 10, 11 and 14). In a fourth fish (which 
is mature), the abdominal opening has become transversely elongated until it functions as 
two separate openings — one for each oviduct (Text-figure 15). Momose's specimen 
(1938) had a single oviducal funnel. 

In Dean's notebook is a good outline drawing, in pencil, evidently intended to form 
the basis of a complete drawing. This shows a single large common abdominal opening of 
both oviducts. In this respect, his specimen resembled those described by Hawkes (1907) 
and by Smith (1937). 

THE SHELL GLAND 

The Uterine egg of ChlamydoseJachus is enclosed in a keratinoid shell. This is 
secreted by a gland, the shell or nidamental gland, which is an enlargement of an anterior 
portion of the oviduct. The glands of the two oviducts may be at the same level, as in 
Smith's immature specimen seen in Text'figure 10 and in Dean's rough sketch showing the 
oviducts and the two ovaries with large eggs. 

In contrast, m Carman's specimen (Text-figure 8), the left gland was anterior to the 
right. So also was it in Smith's three sexually mature fish as portrayed in Text-figures 11, 
14 and 15. Deinega (1925) merely states that the shell gland of the right oviduct of his 
specimen was placed somewhat further back than the left. This asymmetric position of 
the shell glands (the left further forward) appears to be an adaptation to the slender form 
of the body of Chlaynydoselachus, and is probably correlated with the fact that the right 
uterus is always functional and occupies much of the hinder abdominal cavity. 

In Carman's fish (1885) the shell glands were of about equal siz,e (Text-figure 8), as 
they are in Dean's sketch showing them and the ovaries with large eggs. Concerning 
this matter, Nishikaw^a says. ''. . . the nidamental gland of the right side is better developed 
than that of the opposite side", but he does not say how many specimens he examined. 
Smith graphically shows (Text-figures 11, 14 and 15) that in three sexually mature females 
the right gland was noticeably better developed, and Deinega (1925) states this for his one 
fish. Why the right gland is the better developed will be understood when the uterus has 
been considered. 

Carman (1885) figured and first described the internal structure of the nidamental 
gland (Text-figure 13 herein). Here is his description. 

The gland consists, in appearance, of two thick plates of laminated structure. The 
plates are longer and thicker in the middle, and shorter and thinner at each side. The short 
sides have been applied and united; this leaves an acute point descending from the thicker 



The Embryology of Chlamydoselachus 

portion on the inside of the tube. The insides of the walls are crossed by minute striae, be- 
tween the laminae, which appear transverse, but in reality are spiral and ultimately — 
following the outlines of the anterior or posterior borders — terminate, forward and back- 
ward, in the longitudinal folds of the tube itself. The inner edges of the laminae are set with 
minute pores. Near the middle of its length there is a deeper transverse groove. This is 
crossed by the laminae without change in their directions on its account. The plates are not 
distinct from each other through the whole of their length ; branches frequently cross obliquely 
from one to the other. The bottoms of the grooves between them have closely-set transverse 
partitions. The walls of the gland are thicker anteriorly; they begin abruptly or even extend 
a little in front of their points of attachment to the tube. The appearance is such as would 
result from twisting the inside walls of the duct very closely for a short distance. In this we 
have a hint as to the origin of the gland. 



551 




Text-figure 13 
Interior of the shell gland of the frilled shark, Chlamydoselachus anguineus. Note the laminated structure. 

Printed from the original woodcut after the drawing by Paulus Roetter for Garman, 1885, Fig. C, pi. XX. 



This is not very clear nor does Carman's figure (Text-figure 13 herein), devoid as it is 
of explanatory lettering, help matters much. However, both must be reproduced here; 
the text because it is the only full description ever published, and the figure because it 
is the only one on record. 

This gland has also been studied and described by Hawkes (1905) and it seems well to 
quote her brief description. She gives no figure. 

For the first 6 cm. the oviduct is a straight tube, the walls of which are Uned with 
numerous laminae. This region passes into the oviducal gland, the walls of which are much 
thickened, except along two longitudinal lines which are approximately dorsal and ventral. 
The length of the gland is 3 cm. Its interior is covered by fine laminae continuous with those 
in the preceding and succeeding portions of the oviduct. The laminae run spirally, and are 
very close together, instead of longitudinally and somewhat separated, as is the case throughout 
the remainder of the oviduct. The transverse deeper groove in the oviducal gland mentioned 
by Garman was found in the specimen examined. Passing from the oviducal glands, the 
oviducts regain their original diameter, but the walls are smoother, the laminae being reduced 
to slight striae. 



J 



552 Bashford Dean Memorial Volume 

Unfortunately, after more than 30 years in preservative, the condition of the speci' 
mens in the American Museum is such that the internal structure of the shell glands can- 
not be studied advantageously. 

THE UTERUS 

In all viviparous sharks, the hinder part of the oviduct is enlarged into a more or less 
capacious sac in which are received the fertilised ova when they pass downward from the 
shell gland. Here the embryos undergo their development and here they are retained 
until the shells are cast off and until the young are so far developed that they may be 
passed out into the sea to fend for themselves. To fit the uteri for these purposes, they 
are much modified in various sharks and rays, and marked differences arise in the function- 
ing of the right and left organs. This asymmetrical functioning we shall now study in 
Chlamydoselachus. 

Right Uterus Functional 

Since the oviducal apparatus of a shark is bilateral, one might expect to find the two 
oviducts equally developed in Chlamydoselachus. And so they are in sexually immature 
females such as Smith's 1398-mm. fish (Text-figure 10). In a footnote to Nishikawa's 
article (1898), Goto says, ''When no eggs are contained there is no perceptible difference 
in size between the two oviducts." Such also is the condition shown in Momose's 
figure (1938) and much more clearly in the sketch sent me (Text-figure 9). This condition 
is rather unexpected in this fish when one views the 80-mm. eggs contained in both 
ovaries (Text-figure 9). That this condition is not always and necessarily true when eggs 
are absent from the oviducts is seen in Smith's drawing (my Text-figure 11) of the oviducts 
of his 1550-mm. specimen. This fish was almost sexually mature but like Goto's specimen 
was nonbreeding. The right oviduct (Text-figure 11) was noticeably larger than the left, 
and the ovaries contained growing eggs up to 17 mm. in diameter. Presumably the right 
uterus only in this fish was destined to be functional. 

Our earliest information concerning the inequality of development of right and left 
oviducts in the frilled shark comes from Samuel Garman (1885), the man who first dissected 
Chlamydoselachus. In his specimen, which had been partially eviscerated, the anterior 
portions of the oviducts (about 12 in. long) remained as shown in his drawing (Text-figure 
8 herein). But of the hinder end he was fortunately able to say — ''A piece left at the 
cloaca showed one of the ducts greatly distended, possibly with young that had hatched 
within it [or which had been removed before the specimen came to him]. Only one of 
these tubes had been in use". 

Next comes Collett (1897) who states that in his 1910-mm. fish each oviduct was 
900 mm. long, and that "Towards their upper [lower ?] ends each expands to a uterus-like 
sack of which the right is somewhat larger than the left; both contained immature eggs". 
As noted above in the section on the ovaries, Collett or his translator got his identification 
of organs mixed, and here as there I have supplied the correction in brackets. His state- 
ment that both oviducts (the right being better developed) contained eggs, even if im- 
mature, is significant. It will be referred to later. 



The Embryology of Chlamydoselachus 553 

In 1898, Nishikawa gave us our first definite data on the inequality in structure and 
function of the oviducts. He states that the left one is always rudimentary but that 
"The right oviduct is very much distended and contains from 3 to 12 eggs, these numbers 
being the limits observed in 7 specimens". 

Hawkes (1907) notes that the right oviduct in her specimens was much larger than 
the left. So Smith found and graphically shows for three fish in Text'figures 11, 14 and 15 
herein. The uteri of Hawkes's specimens contained no embryos; nor did Smith's. Since 
Smith's specimens were brought from Japan by Dean, it is probable that, when the two 
gravid fish were caught, the uteri (Text'figures 14 and 15) were opened to get the eggs and 
embryos for him. 

Deinega (1925) was evidently under the impression that Chlamydoselachus, like 
most other sharks, should carry eggs and embryos in both uteri. He states that in his 
specimen "the left oviduct, in its exterior form, produces the impression of being under' 
developed or of being in a temporarily non 'functioning condition". However, the right 
oviduct, a short distance behind its large shell gland, "suddenly expands into a rather 
capacious sac". It contained no eggs. 

Dean's notes afford both negative and positive evidence of the differential function' 
ing of the oviducts. Thus of a 1565'mm. fish he says, "left ovid. greatly reduced, eggs 
fr. r."; of a 1575'mm. female he notes "left ovid. greatly reduced, no dilat. uterus"; 
another 1565'mm. fish had "1. ovid. small, small uterus". On the other hand Dean 
records the taking of various eggs and embryos from the right oviducts of specimens of 
Chlamydoselachus captured in the Sagami Sea. From one fish he got two eggs and from 
another three. Then he notes "8 in female" — oviduct not recorded but presumably the 
right. As seen above, and as will be noted later, had it been the left he would pretty 
surely have so stated. In the records of his Japanese collector are listed three eggs from 
right oviduct of one fish, five from another, and seven from the right oviduct of each of 
two other females. These last eggs were all in early stages and had egg shells. 

Distention of Gravid Right Uterus. — Unfortunately there are little data available 
as to the size attained by the right uterus as gestation goes forward to birth. However, 
there are two ways of studying the problem : one by bringing together the few scattered 
measurements of the organ, the second by setting forth the number of eggs and embryos 
(with their measurements) found in the uterus. These compilations will now be made. 

Measurements of Gravid Right Uterus. — Hawkes (1907) states that the oviducts 
begin to enlarge when they reach the level of the anterior end of the colon. On the left 
the diameter is increased gradually and only about four'fold, but "on the right, the en' 
largement is sudden and very apparent, the diameter increasing 14 to 15 times". She 
nowhere speaks of finding embryos in the uterus. 

Deinega's description (1925) of the reproductive system is very brief. But the two 
things that the reader gets from it are that the left oviduct "produces the impression of an 
underdeveloped oviduct or a temporarily non'functioning one". While the right one in its 
posterior part "suddenly expands in the form of a rather capacious sac about 130 mm. in 



J 



554 



Bashford Dean Memorial Volume 



diameter". This very great expansion is clear in his figure which, however, is so poorly 
printed on soft paper that it cannot be reproduced here. 

Smith dissected and figured the reproductive organs of two sexually mature frilled 
sharks measuring 1350 and 1485 mm. respectively. He does not give measurements of the 
oviducts but Text'figures 14 and 15 give the relative si2,es of the oviducts and other organs. 



Urogenital system of the female Chlamydo' 

selachus, ventral views, one-fifth natural si2;e. 

The shell glands and the adjoining portions of 

the oviducts are displaced laterally. 

Text-figure 14. Urogenital organs of a speci- 
men 1350 mm. long. The right uterus and 
ovary are incomplete. 

ah. p., right abdominal pore (the left is closed superfici- 
ally); c.t., collecting tubule; m., mesonephros; mes.d., 
mesonephric duct; mso., mesovarium; ovd., oviduct; ovy. 
ovary; r. cl., rectal portion of the cloaca; s.g., shell gland; 
ur.p., urethral pores; ut., uterus; v. I., ventral ligament 

of the oviduct. 

Drawn from specimen No. I in the American Museum 

of Natural History. 

After Smith, 1937, p. 433. 




Text-figure 14. 




Text-figure 15. Urogenital organs of a speci- 
men 1485 mm. long. A segment has been 
excised from the right uterus, and the right 
ovary is incomplete. The excretory ducts are 
not shown. 

ah. p., abdominal pore; m., mesonephros; ovd., oviduct; 
oily., ovary; r., rectum; s.g., shell gland; ur.p., urethral 
pores; ut., uterus; v.l., ventral ligament of the oviduct. 
Drawn from specimen No. II in the American Museum 
of Natural History. 
After Smith, 1937, p. 433. 



These fish had evidently been gravid and the enlarged right uterus of each had been opened 
and the eggs removed. These adults (and probably the eggs also) came to Dean — presum' 
ably at Misaki, or were later sent to him in America. 

In Dean's notebook is a rough sketch of the reproductive apparatus of his huge I960' 
mm. female. This shows the two ovaries with many eggs (elsewhere referred to) and two 
empty uteri — the right twice as large as left. (Here recall Smith's drawing, my Text- 



The Embryology of Chlamydoselachus 555 

figure 11, showing similar organs). On this page, above Dean's sketch, is the statement 
"Ovid, [uterus?] of r. [side] dilated [through a length of] 340 mm.". Two pages away is 
another and more elaborate sketch of a non^gravid right oviduct (previously referred to) 
in which the uterus is labelled 25 mm. wide and 280 mm. long. 

None of these specimens (except Nishikawa's) had ova in their uteri, and none of 
these uteri save those figured by Deinega and by Smith give us any clear idea of the size 
and the degree of distention attained before the young are born. However, some under' 
standing of the degree of this dilation may be had by considering the number of eggs and 
embryos (with their measurements) that have been found in some gravid uteri. Earlier in 
this article some of these data have been used for other purposes but for completeness they 
will have to be repeated here. 

Number of Eggs and Embryos in Gravid Right Uterus. — From two men only do we 
get firsthand data as to uterine embryos and their yolk sacs. Nishikawa introduces us 
to the subject briefly. But from Dean's notebook and from specimens brought back from 
Japan or sent thence to him, we get a good idea of the great size of eggs and embryos and 
of the uterine distention to which they give rise. 

Nishikawa (1898) says "The right oviduct [600 mm. in total length] is very much 
distended . . when as many as 12 eggs [his upper limit] each 110-120 mm. long are con^ 
tained in it". Some of his eggs had embryos — the largest only 60 mm. long. He also 
speaks of having other eggs 65 to 75 mm. in shortest diameter and from 102 to 124 mm. in 
longest measurement. He figures in natural size an egg (Text'figure 4 herein) 67 x 100 mm. 
in an egg shell measuring 137 mm. including the processes. 

Of large uterine embryos, Dean lists 14 specimens ranging from 165 to 390 mm. 
(6.6 to 15.35 in.). Of these only two have measurements of the yolk sacs set down. 
However, Dean brought from Japan and deposited in the zoological museum of Colum' 
bia University three embryos with yolk sacs, and in the American Museum six embryos 
with yolk sacs. From the Museum of Comparative Zoology, there has been loaned a large 
embryo on its yolk sac. This was presented by Dr. Dean in 1912. The measurements of 
these embryos with yolk sacs give one a full conception of the distention they would 
produce. They will be considered later, but it may be well first merely to list the embryos 
without yolks. 

Dean's notebook records 12 such fishlets. To these I have added a specimen (190 
mm.), in the collection here, from which the yolk has been removed. The measurements 
of these little fishes are from snout to tail'tip. These 13 range from 165 to 352 mm. 
(6.5 to 13.8 in.) as follows— 165, 175 (2 specimens), 185 (2), 190, 195, 205, 210, 240, 250, 
317, 352 mm. 

To get a better idea of the distention of the gravid right uterus one must consult 
table I wherein are listed embryos ranging from 170 to 390 mm. (6.7 to 15.35 in.). These 
sit on yolk sacs whose diameters (measured in the lines of length and depth of the fish) 
vary from 67 x 55 mm. (fish, 327 mm.), to 111 x 100 (fish, 331 mm.), to 73 x 51 (fish, 374 
mm.). With from 8 to 12 of these contained in the slender body of this snake-like {anguine 
eus) shark, one can judge the enormous enlargement of uterus and abdomen. 



556 



Bashford Dean Memorial Volume 



TABLE I 
SIZES IN MILLIMETERS OF UTERINE EMBRYOS AND EGGS 



Ho. 


Embryo 


ro\\Sac 


Where 


1 


170 


72x68 


Columbia University 


2 


175 


92x90 


Figure 11, plate I 


3 


180 


77x75 


Columbia University 


4 


210 


75x57 


Am. Mus. of Nat. Hist. 


5 


210 


85x66 


Mus. of Comp. Zool. 


6 


245 


74x60 


Am. Mus. of Nat. Hist. 


7 


305 


83x57 


" '' 


8 . 


320 


76x64 


" " 


9 


327 


67x55 


Columbia University 


10 


331 


111x100 


Dean's Notebook 


11 


374 


73x51 


Am. Mus. of Nat. Hist. 


12 


390 


100x70 


Figure 49, plate V. 



Just here it should be recorded that in Dean's notebook on the page of his list of 
specimens to be drawn is this entry. ''Bt. in Tokyo June 20: 317; 331, yolk sac HI x 100; 
352; 390, yolk sac 100 x 70; 4 embs. large taken about May 1, 1905. 8 in fecaale". I judge 
that the ''4 embs. large" refer to the four for which he gives sizes, that they were taken 
from the female captured May 1, that they were preserved, and that he purchased them 
June 20 in Tokyo. This seems pretty certain. Possibly they were 4 of the "8 in female" 
as noted. Judging by their close gradation in sizie, I conjecture that they came from one 
uterus. If so, one can judge the tremendous distention of this. But what if one uterus 
contained "8" such embryos and eggs! It seems almost unthinkable, yet Nishikawa 
(1898) says ''The right oviduct is very much distended and contains from 8-12 eggs. . . . 
The limits observed in seven specimens." 

Two of the specimens recorded in the table were drawn for Dean and are reproduced 
in the plates. In Figure 11, plate I, the embryo measured 175 mm. and the yolk 92 x 90 mm. 
Still more striking is the colored Figure 49, plate V of a fish 390 mm. (15.35 in.) long on 
a yolk sac which measured 100 x 70 mm. Let the reader imagine (if he can) 8 to 12 embryos 
and yolk sacs of this size in the uterus of even a 1960'mm. female (the largest Chlamydo- 
selachus on record). The egg and embryo of the colored figure are in our collection here, 
and the fish in its jar of alcohol looks even larger than it does when portrayed in its 
natural colors. 

As one studies this table, three things attract attention. The first is that there are 
several discrepancies in the sizes of the yolk sacs in proportion to the sizes of the little 
fish found thereon. Surely some of the discrepancies date back to the varying sizes of 
eggs in the ovary. There must be more variability in the size of mature eggs in the 
oviduct than has heretofore been thought. The next idea is that the period of gestation 
must be very long to give time for the resorption of these great yolks, and then that the 
young fish when ready for extrusion must be from 20 to 25 in. long. The matter of 
the long period of gestation (surely at least 2 years) has been treated earlier. 



The Emhryology of Chlamydoselachus 557 

The third matter is also based on the great disparity between the slight diminution of 
the yolk sac and the considerable growth of the embryo. It comes to me in this form — 
Does the embryo of this viviparous or ovoviviparous shark receive any nutriment from 
the uterine wall of the mother? The shallow water Httoral tropical nurse shark, Gingly- 
mostoma cirratum, is also ovoviviparous. It carries in its uteri huge (c. 145 mm. long) 
blunt'cnded, thick -shelled eggs (Text-figure 16) entirely comparable to those of Chlamydo^ 
selachus. I have had the good fortune to make extensive studies on Ginglymostoma, the 
nurse shark, and from these I hope further on to throw light on this question. 

All these data (save those from Deinega's article) were known to Smith when his mo- 
nograph on the anatomy of Chlamydoselachus was pubhshed in 1937- But in the matter of 
the reputed unilaterality of the functioning of the oviducal apparatus of Chlamydoselachus, 
he showed sound judgment in his concluding remarks on the reproductive organs of 
the female of this shark. Here is his matured statement published before I had made 
my minute study of Dean's notes presently to be referred to. Smith (1937, p. 449) 
wrote as follows: 

There is not a single known instance of complete development of the reproductive organs 
on the left side. Yet it must be borne in mind that the number of specimens that have been de- 
scribed is still very small. The organs on the left side are developed to such a degree that 
they can scarcely be called rudimentary. In view of the great variability found in many 
other organs of Chlamydoselachus, one should not be surprised if the exammation of ad- 
ditional material should reveal cases in which the genital organs of the left side, or of both 
sides, are functional. 

In the light of the data given above as to the functioning of the right oviduct only in 
Chlamydoselachus, there are now to be presented certain data showing that the left ovi- 
duct also is sometimes functional in this shark. In these data will be found the verifi- 
cation of Smith's prognosis. 

The Left Uterus Sometimes Functional 

It has already been seen that in the adult, while the right ovary is the predominant 
one, the left ovary does sometimes contain large eggs; i.e., is functional. Evidence that 
the left uterus is occasionally functional will now be presented. This is a matter of ex- 
ceptional interest. 

The earliest intimation, that the left oviduct may contain eggs, comes from CoUett 
(1897)- In his short and not always clear description of the oviducts of a 1910-mm. 
specimen, he says that "each expands to a uterus-like sack, of which the right is somewhat 
larger than the left; both contained immature eggs". There is no doubt that he was 
referring to the oviducts, but what he meant by "immature eggs" is very obscure. I can 
only conjecture them to have been wind eggs like that figured by Dean (Figure 51, plate 
V). In many years' dissections of viviparous sharks and rays, I do not recall ever having 
found in a uterus an "immature" egg, meaning an undeveloped or unripe or shell-less egg, 
but I have in the nurse shark found what my notes record as "infertile eggs". I do not 
recall that I opened one to get at its contents. I did not then know of the term "wind 



/ 558 Bashford Dean Memorial Volume 

eggs", but that is what these eggs were. I measured a number of these capsules from 
Ginglymostoma and found them always smaller than normal (fertile) eggs such as that 
shown in Text'figure 16. 

The only other evidence of bilateral functioning of the oviducts- in Chlamydo- 
selachus is found in Dean's notebook. In one place he says of a l620'mm. specimen "both 
ovid. same size", but he does not say that both were functioning. They may have been 
found in a sexually immature fish such as Smith had (Text'figure 10). However, from a 
1392'mm. female taken about October 1, 1905, Dean records "3 oblong eggs, 135 mm. and 
larger in r. ovd." and a "small wind egg in 1.". He states that two oblong eggs and the 
wind egg were drawn. The two oblong eggs I identify with the drawings shown in 
Figures 2 and 3, plate I; and the wind egg as that portrayed in color in Figure 51, plate V. 
From another female taken May 25, 1906, Dean records eggs "1. ovd. 3, 2 in r." but 
unfortunately he gives no description of these eggs. 

It is very interesting and possibly significant that, so far as we have data, when eggs 
are found in both oviducts of Chlamydoselachus, there is something wrong with them. 
According to Collett both sets of eggs from his fish were "immature" — whatever that 
may mean. In Dean's first case, the egg from the left uterus was abnormal — an empty 
dwarf shell — while the eggs from the right side were at least unusual if not abnormal. All 
three were "oblong" — two of them in varying degrees, (Figure 2 and 3, plate I). One 
(Figure 2) is oblong but symmetrical, the other (Figure 3) is not only oblong but unsym' 
metrical, and is possessed of a most unusual process. Of the eggs from the two oviducts 
of his specimen taken May 25, 1906, Dean unfortunately gives neither figures nor 
descriptions. 

As bearing on this matter, it may be noted here that the nurse shark has the right 
ovary only fertile but both uteri functional. Infertile wind eggs, always smaller than 
fertile ones (size about 105 mm. long by 120 in circumference) are found in both uteri of 
this shark, but are apparently more abundant in the left. 

One wishes much for definite data here about Chlamydoselachus. What were 
Collett's "immature eggs?" What kind of eggs were those noted by Dean in the "1. ovid. 
3"? Were they defective? The predominance of the right oviduct is of course correlated 
with the narrow abdomen of this "snakclike" shark — there is not room in the crowded 
abdominal cavity for two gravid uteri. Yet Dean states that he found such in two speci- 
mens. Here is a problem for someone in Japan to solve. 

These data from Collett and from Dean show us that the commonly accepted dictum, 
that the right oviduct only in Chlamydoselachus is functional, is not always true, even 
though all other investigators have so found or thought. Since Dean's notes show that 
the "1. ovid." is sometimes functional, they have been quoted carefully and in full. Into 
Dean's hands there undoubtedly came more female specimens (26 in number) than have 
been had by all other students of Chlamydoselachus taken together. This of course made 
possible his discovery of the functioning of the left oviduct in his two specimens. Un- 
doubtedly this functioning is very unusual and apparently it is not wholly normal. 



The Embryology of Chlamydoselachus 559 

But in any case, we are sure that, in some few instances, Chlamydoselachus does have 
both oviducts functional. 

Here then is confirmation of Smith's statement (1937) — "In view of the great varia' 
biHty found in many other organs of Chlamydoselachus, one should not be surprised if 
examination of additional material [Dean's 26 female specimens] should reveal cases in 
which the genital organs of the left side, or both sides, are functional''. And all through 
his work. Smith points out generalised or primitive structures in Chlamydoselachus in 
consonance with the lowly position assigned it in the scale of shark life. Then again he 
finds highly specialized structures. 

Chlamydoselachus is in process of becoming viviparous by getting rid of its primitive 
keratinoid egg shell — it has almost gotten rid of the hold'fast processes. Then further to 
make possible this viviparity in a small and narrow body cavity, it has almost achieved 
unilaterality in the functioning of its reproductive organs. 

For comparison, evidence will later be presented to demonstrate that in certain 
higher viviparous sharks and in certain rays (highly specialized elasmobranchs) the 
unilaterality found imperfectly expressed in Chlamydoselachus has come to full fruition. 

There is now to be considered certain indefinite evidence referred to above — the 
question whether the embryos of Chlamydoselachus are nourished by secretions from 
the wall of the maternal uterus. 

Do Embryos Receive Nutriment From the Uterine Wall? 

On this point Hawkes (1907) writes of the enlarged (uterine) portion of the right 
oviduct as follows : 

This region in addition to being enlarged has folded walls, in which occur one large 
and several small areas of dilated blood vessels. The largest blood plexus occupies about 
one-third of the right side of the oviduct. In connection with each plexus, on its dorsal side 
the oviducal wall is thickened over an area which equals the plexus in length and breadth. 
The enlarged vessels apparently supplied these thickened areas. The condition of the 
oviduct thus described suggests that this portion of the oviduct acts as a functional uterus. 

Smith had hoped by study of our specimens to throw more light upon the internal 
structure of the uterus as described by Hawkes. But he had little success. He notes, 
however, (1937, p. 447) that — ''In its enlarged state, on the right sides of my adult 
specimens, the so'called uterus has thin walls, a velvety inner surface and a fairly rich 
blood supply. The mucous membrane is not sufficiently well preserved to permit a study 
of the finer structure". 

To anyone with a firsthand knowledge of the structure and functioning of the uterine 
wall of viviparous sharks and rays, these findings are very significant. From a mere 
glance at Figure 49, plate V, it is apparent that there will never be a yolk-sac placenta 
connection between embryo and mother in Chlaynydoselachus. It the uterus nourishes 
the embryo, this must be accomplished in some other way. In the hope of getting some 



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560 



Bashford Dean Memorial Volume 



light on this obscure problem, let us now examine the uterus of that ovoviviparous shark 
whose reproduction most nearly parallels that of Chlamydoselachus. 

The tropical shallow-water nurse shark, Ginglymostoma cirratum, carries in each 
greatly dilated uterus as many as 21 huge thick-shelled eggs like that shown in natural 
size in Text-figure 16. The inner wall of each uterus is made up of circumferential bands 
of hems or plaits overlapping like the shingles on a roof. The plaits are 5 or 6 mm. wide 
and are highly vascularized — "as red as a piece of fresh-cut beefsteak" my notes read. 




Text-figure 16 
The egg case (140 mm. long), egg, and embryo of the ovoviviparous nurse shark, Ginglymostoma 
cirratum — in natural size. Note the left, older, more finished looking end of the capsule and the 
larger, blunter, younger right end. The yolk blastopore is seen just to the right of the tail of 

the embryo. 

Photograph by Alfred Goldsborough Mayor. 



We have no statement of the collectors that embryos and their yolks are found in the 
uteri of Chlamydoselachus free of their shells, but it is evident that an embryo even as 
relatively young as that shown in Figure 11, plate I, or as old a one as that shown in 
color in Figure 49, plate V, has thrown off its heavy egg capsule. These large broken 
capsules could not be carried in the uterus without hurt to the delicate embryos. They 
must be thrown out into the sea. Similar reasoning must be applied to similar conditions 
in the nurse shark and its embryos enclosed in a larger and thicker egg shell. 

The boatmen at the laboratory of the Carnegie Institution of Washington at Tortu- 
gas, Florida, where my studies were made, were all Florida and Bahama men, well ac- 
quainted with the nurse shark. They all told me that when the young are pretty well 
developed, they break out of the shells, and these latter are cast out while the embryos are 



The Embryology of Chlamydoselachus 561 

retained in the uteri during further development. I was told by the director, Dr. A. G. 
Mayor, that this was his understanding, but after these years I cannot recall if this was 
his personal observation. I was never fortunate in procuring large embryos nor small 
free-swimming young. Development is slow and the advent of the hurricane season led 
to the closing of the laboratory late in July of each year before the slowdeveloping eggs 
had gone far enough for the embryos to break out of their shells. 

The young and growing fishes in the uteri of these two viviparous sharks must have 
oxygen. If sea water could penetrate the cloaca and into the uteri, it might provide this 
need. The nurse shark has a wide cloaca and the oviducal opening into it will sometimes 
admit "three or four fingers bunched into one mass", as my notes read in one case, and in 
them it is also recorded that a female Ginglymostoma hung up by the tail had the common 
oviducal opening measuring 1.5 in. in diameter. The opening must be this large to admit 
the outward passage of the large empty egg shells even if crumpled. Furthermore, I have 
opened a uterine egg of the nurse shark and on tasting the perivitelline fluid have found 
this salty. The embryo was very young. 

I unwittingly performed another experiment which demonstrated that the egg 
capsule of Ginglymostoma is permeable to sea water. I took an egg capsule with its 
lively embryo out of the uterus of a just-killed female, cut a window in the capsule over 
the embryo, cleared out all the perivitelline fluid that I could and replaced it with mo- 
lecular magnesium sulfate in order to anesthetize the embryo. The egg was then unthink- 
ingly placed in a dish of sea water which did not cover the window. Twenty-two hours 
later the little shark was about as lively as ever. The sea water had penetrated the egg 
shell by osmosis and had so diluted the anesthetic solution that the embryo still lived. 

There seems to be little doubt that the embryos of Ginglymostoma may get oxygen 
from the sea water which may come into the uterus through the dilated cloaca and the 
large oviducal openings. No experiments such as those above have been performed on 
Chlamydoselachus, but Dr. Smith tells me that the cloaca is open in his preserved speci- 
mens and that the right oviducal opening even when hardened in formalin will sometimes 
admit a man's thumb. So one may conjecture that sea water invades the uterine cavity of 
Chlamydoselachus and bathes the eggs. Thus the embryo could get oxygen from this 
water. 

On the whole it seems quite probable that the young of both sharks may receive some 
oxygen by difi^usion from the uterine wall into the fluids surrounding the embryo. Fur- 
thermore, from my knowledge of uterine gestation in other sharks and in various rays, I 
am strongly of the opinion that the uterine wall in both Chlamydoselachus and Ginglymos' 
toma secretes Hquid food materials to nourish the young after they are freed from the egg 
capsules. As shown in Figure 34, plate III, and Figure 43, plate IV, the embryos of 
Chlamydoselachus have short external gills, gills far shorter than I have found in the 
young of some viviparous sharks and particularly of various rays. Presumably the young 
of Ginglymostoyna also have such gills. The long external gills of embryos of rays and of 
other sharks, when bathed in the uterine fluid, may take in not only oxygen but mineral 



562 



Bashford Dean Meinorial Volume 



salts and possibly other food substances as well. The rich plexus oi vitelline capillaries 
will also be bathed in the fluid of the uterine cavity and they may absorb some food and 
oxygen from it. If this takes place in Chlamydoselachus, it must go on tor a long time, 
until and even after the yolk, shown m the colored Figure 49, plate V, is resorbed, and 
this yolk must be used up before the fish is born, else the free oceanic life ot this little 
shark would be very brief. 

THE CLOAC.\L OPENINGS 

As has been shovv'n, the oviducts at their anterior ends have openings into the ab- 
domen to receive the eggs set free from the ovaries. So, posteriorly the oviducts have 
openings into the cloaca through which the embryos, having used up their yolk masses m 
development, pass out to take up their free life in the sea. The lower end ot the uterus 
progressively diminishes in size until, as a tube considerably reduced in cross-section, it 
opens out on the dorsal side of the cloaca. But even here, as everywhere else in this 
primitive shark, are found some surprising and interesting variations. 

Right Cloac.^l ChTDuc^L Opekixg PREi>Oi!rs-.A>.T 

Since the right oviduct is predominant, since its uterine portion carries the develop- 
ing young, and since these must pass out through its opening into the cloaca, one would 
expect to find that the right opening is larger and is possibly somewhat centrally placed. 

Hawkes (1907j first and very briefly refers to the relative sizes of the oviducal 
openings into the cloaca thus: "The opening of the right enlarged oviduct ... has 
acquired a median position, the left oviducal opening . . . lymg cephalad to it"". Only 
this, but she gives a diagrammatic figure to make these relative positions clear — Text- 
figure 17 herein. Demega (1925; confirms Hawkes and writes at length. Thus he says 
"The right oviduct opens out by a large orifice in the middle of the cloaca" — as is shown 
in Hawkes's figure. Of the opening of the left oviduct he ^^nrites more fully "The left 
oviduct opens in the dorsal wall of the cloaca, rather far in front, so that it makes an im- 
pression as though it opens into the posterior section ot the right oviduct; this orifice 
appears in the form of a cross fissure". 




Text-figure 17 
Diagrammatic figure of the cloaca of 

a female Chlamydoselachus. 
A. P. closed abdominal pore; L.Ov., lert 
oviducal opening; R., rectum; R.G., opening 
of rectal gland into rectum; R.Ov'., right 
oviducal opening; VS., urinary sinus (the 
other sinus is omitted); U.S. 1, openings of 
urinary sinuses into cloaca. 
After Hawkes, 1907, p. 476. 



The Embryology of Chlamydoselachus 



56i 




Text-figure 18 
Longitudinal section through cloaca and right oviduct of Chlamydoselachus, 
three-fourths natural size. The dorsal side is uppermost. 

ab'p, abdominal pore; cl, cloaca; int, intestine; ov, oviduct; p, caecal pouch or rectal gland; ua, 

urethral aperture. 
After Garman, 1885, Fig. 2, pi. XIX. 



The relative positions of the two openings as stated by Deinega make somewhat 
clearer these openings as portrayed in Carman's drawing (Text-figure 18) of the cloaca of 
his specimen. If one holds the page in the vertical plane in the line of vision with the 
dorsal side of the figure uppermost and the cloacal end toward the observer, the relations 
will become clearer. The right lateral wall of the right oviduct (ov in the light area) has 
been cut away near the pomt of junction of the left oviduct {ov in center in dark area). 
The figure shows a common tube leading into the cloaca. From this, it is seen that the 
left oviducal opening is situated in the wall of the right aperture. 

Smith found the two openings in all his specimens, but, excepting in the youngest, 
the right opening was predominant. This was markedly true in his two sexually mature 
females as shown in Text-figures 14 and 15. In the cloaca in each figure the large shaded 
area on the (fish's) right side is the opening of the right oviduct, the smaller shaded area 
on the left the opening of the left tube. Note how very predominant the right opening 
is in Text-figure 15. Here is Smith's statement on this condition in the fully mature 
specimen referred to: '\ . . almost the entire urogenital sinus seems built around the very 
large opening of the right uterus indicated by line-shading in the figure [No. 15 herein]. 
In the hardened condition of the material, this opening is still large enough to admit 
a thumb. The opening of the left uterus is much smaller". 

Here again is further proof of the unilaterality of functioning of the right oviduct of 
the frilled shark. Shell gland, uterine enlargement, posterior opening into cloaca, each 
overshadows its fellow on the left. 



564 Bashford Dean Memorial Volume 

FEMALE REPRODUCTIVE ORGANS OF CERTAIN HIGHER SHARKS 

AND VARIOUS RAYS 

For the trilled shark, Chlamydoselachus, it has been shown that unilateral functioning 
of the rpproductive organs is the general rule, that the right ovary and oviduct are uni' 
formly fertile, but that rarely are both organs on the left side also functional. I have made 
some studies on this subject of unilateral functioning of reproductive organs based on 
dissections of sharks and rays at the U.S. Fisheries Laboratory at Beaufort, N. C, and in 
the reports on these (Gudger, 1912, 1913) I have given references to a number of articles 
bearing on this subject. To all these the interested reader is referred. 

The records of my studies on the reproductive organs of sharks and rays dissected at 
Key West and at Dry Tortugas, Florida, while a guest-investigator at the marine labor- 
atory of the Carnegie Institution of Washington, have never been published. Since some 
of these notes bear directly on the subject in hand, and particularly since one of the sharks 
(Ginglymostoma cirratum) in its eggs and reproductive apparatus shows certain marked 
likenesses to these structures in Chlamydoselachus, it seems well to quote from these 
notes here. 

OVARIES AND OVIDUCTS OF SOME FLORIDA SHARKS 

Since the sharks examined in southern Florida show the least departure from their 
early ancestors in the bilaterality ot their reproductive organs, they will be studied first. 
The first departure from bilaterality like that noted in Chlamydoselachus has to do with 
the ovary. 

The Nurse Shark, Ginglymostoma cirratum. — In eight dissected female specimens of 
this large, flat-bodied, sluggish, shallow-water shark with a large abdomen, both oviducts 
were always functional, but in each fish the right ovary only was functional. The fish were 
adults about 8 ft. in length, "over all". One had in the right ovary "30 eggs the size of 
small oranges (equatorial diameter=60-65 rmn.)". Another had 33 ripe eggs in the right 
ovary. Still another had ''right ovary enormously enlarged with 40 eggs size of billiard 
balls, some about 6 in. ui circumference. These would have filled a peck measure or an 
ordinary water bucket". Three had "right ovary full of gaping pits from which ripe eggs 
had been erupted". Nearly all these enlarged right organs were median in position, while 
of the left ovary my notes say "insignificant in size", "hardly recognizable", "had to be 
hunted for". Not one left ovary had any eggs. It is to be regretted that none of these 
huge right ovaries was measured. 

Various Other Florida Sharks. — The large, active, voracious tiger shark, Galeocerdo 
tigrinus, has the oviducts bilateral and functional. In four fish the left ovary was generally 
small and always non-functional, the right large, and functional with eggs in the anterior 
part. I have notes for three species of the requin shark, Carcharhinus. In four specimens 
of C. ohscurus with bilateral functional oviducts, the left ovary was "small", "very small", 
"reduced"; while the right was always large and functional. In one 8-ft. fish, it w^as 2 ft. 
10 in. long with 12 eggs, .5 to 1 in. in diameter. In one specimen of C. falciformis, my 



The Embryology of Chlamydoselachus 565 

notes read "I. ovar. very small, r. nearly twice as large". A solitary C. platyodon had 
the left ovary small and the right large with eggs in the anterior part. Both these sharks 
had both oviducts well developed and functional. 

Of the genus Hypoprion, I dissected two species — H. hrevirostris and H. signatus. 
In each, the oviducts were bilateral and functional, but the left ovary was small and with' 
out eggs; the right ovary was large and functional with eggs in the anterior end. The 
same condition of oviducts and ovaries was also found in ScoUodon terranovae. 

From these data on some of the tropical sharks of the eastern Gulf of Mexico, it is 
plain that they are on the way toward unilateral functioning of the reproductive organs. 
They have not gone so far in this matter as has Chlamydoselachus, since both oviducts 
are functional while only one ovary (the right) produces eggs. No reason for this can 
now be given, since they are sizable sharks with large abdominal cavities. This is especial' 
ly true of the flat-bodied Ginglymostoma, in whose roomy abdomen are contained large 
uteri which when gravid much resemble in si2;e and shape a pair of old'fashioned saddle' 
bags. This size and form make it possible for each to contain, or are conditioned upon its 
containing, 20-21 eggs c. 140 mm. long x 185 in circumference. From these sharks with 
partial unilaterality of genital organs, we now pass to the rays in some of which complete 
unilaterality has been attained. 

OVARIES AND OVIDUCTS OF VARIOUS RAYS 
The rays are elasmobranchs flattened in the dorsoventral or vertical plane to fit them 
for bottom'living. They comprise the most specialized group of the Elasmobranchii. 
They are referred to here because there are found in these viviparous fishes the same vari' 
ations in the reproductive organs that are found in Chlamydoselachus, the reputedly 
lowest form of the strap-gilled fishes. There is an extensive literature on this subject 
but I shall confine myself to my own researches. 

Pteroplatea maclura. — The butterfly ray is abundant at Beaufort, N. C In 1912 
(Gudger, 1913) I dissected four female specimens. The reproductive organs of both sides 
were functional, but in every fish the left ovary was better developed than the right 
(in fish No. II, 25 per cent larger). Furthermore, in each case the left uterus was better 
developed and contained more eggs. Fish No. I had three eggs in the left uterus and an 
empty shell (wind egg) in the right; No. II had one egg (but with two yolks) in 1. and 
an imperfect egg in r.; No. Ill had two eggs in 1. (one with a malformed shell) and one in 
r.; No. IV had both uteri gravid but left twice as large as right. Unfortunately these 
two uteri were not dissected. 

It is significant that in this ray the reproductive organs of the left side are better 
developed and more functional than those of the right. This is just the reverse of con- 
ditions in Chlamydoselachus. Another notable point is that imperfect eggs are found in 
both uteri of the ray. Parenthetically it may be noted that this same condition seems to 
prevail in the nurse shark. From all these data, I draw the conclusion that Pteroplatea 
maclura is in an intermediate stage between those rays having perfect bilaterality of the 



J 



566 Bashford Dean hiemorial Volume 

reproductive organs and those having only one side functional as in Dasyatis say now to be 
briefly considered. 

Dasyatis say. — The common stingray or "stingaree" also abounds at Beaufort, and in 
1912 I reported the results of my dissections over a number of years. Sixteen non-breeding 
females (uteri showing no signs of having eggs in them) ranging from 13 to 35 in. in width 
had the left ovary from two to three times the size of the right. Thirteen breeding females 
(13 to 35 in. wide) had the left ovary functional (with eggs 12-18 mm. in diameter) and 
the left uterus greatly dilated — some with embryos, and some awaiting the coming of eggs. 
In the course of several summers' work, no right ovary was found with any eggs in it 
and no right uterus was ever functional. These facts were paralleled by my studies of 
another species of the same genus. 

Dasyatis hastata. — This is the common stingray of southern Florida. At Key West 
and at Tortugas, I dissected 10 specimens. Five were adults ranging from 3 to 4.5 ft. 
wide. In these, the left uterus only was enlarged and functional (some with embryos). 
In all, the right ovary was "insignificant" but the left was large and in many cases had 
large eggs in it. I also dissected five half 'grown to adult specimens from 13 to 26 in. wide. 
Even in these, the left uterus was large and seemingly ready to receive eggs, the right 
reduced and indistinct. In all five the right ovary was small and non-functional. The 
left was always larger (in the 26-in. ray ten times larger) and filled with growing eggs. 

Here is described a progressive gradation from partial to complete unilateraHty in the 
functioning of the reproductive organs of elasmobranchs. In the butterfly ray, Pteroplatea 
maclura, both ovaries and both uteri are functional, but in all dissections the left organs 
were invariably better developed — i.e., the right ones are beginnmg to degenerate. The 
sharks described (Chlamydoselachus excepted) all have bilaterally functioning oviducts, 
but unilateraHty in the ovaries in that the right ones only are functional. Finally in the 
stingrays, Dasyatis say and hastata, complete unilateraHty is found — left ovaries and left 
oviducts only are functional. Here then are those specializations in the functioning of the 
reproductive organs which are adumbrated in Chlamydoselachus, the lowest ranking 
shark and lowest elasmobranch. In the rays as in the frilled shark, there is found the 
same correlation of unilateral genital organs with a restricted body cavity. In Chlamydo- 
selachus, the body cavity is narrow but is somewhat long to contain the closely-packed 
embryos; in the rays the cavity is both short and narrow and in the single uterus the 
few embryos are rolled up scroll-fashion. 

From other notes made from my dissections and from a rather extensive but widely 
scattered literature, other similar unilateral functionings of ovaries and oviducts in other 
elasmobranchs might be given if it seemed necessary to go into the matter further. 

THE ENCAPSULED EGG OF CHLAMTDOSELACHUS 

The encapsuled egg of Chlamydoselachus, as it emerges from the shell gland and 
passes into the uterus, consists of a large yolk mass with a protoplasmic germinal area. 



The Embryology of Chlamydoselachus 567 

Shortly after the egg enters the oviduct, fertilization, encapsulation, and segmentation 
take place, followed later by gastrulation and the formation of the embryo. It is not 
known at what stage in the development of the growing embryo the capsule is burst, 
thrown off the yolk sac, and expelled from the uterus into the sea. But it must be long 
before the embryo attains the stage shown in Figure 11, plate I. However, we are here 
concerned with the early stages in which the egg is still encapsuled. These eggs occur in 
two distinct forms — as ellipsoidal and as round eggs. 

ELLIPSOIDAL EGGS OF THE FRILLED SHARK 

This form and shape of the encapsuled egg of Chlamydoselachus seems to be the 
typical one. At least, save for four round eggs portrayed by Dean, all eggs figured by all 
authors are ellipsoidal. This is true even of eggs freed from their capsules. Thus Brohmer 
(1909) figured without capsule an ellipsoidal egg 110 mm. long with an embryo of 75 mm. 
As drawn the yolk mass is 108 x 60 mm. And Garman (1913) portrayed a shelMess egg 
98 X 56 mm. with a 59'mm. embryo on it. Neither figure will be reproduced here since, 
lacking details, they are of no particular value in this study. 

Dean figured in color (Figure 50, plate V) a shell-less ellipsoidal egg 95 x 56 mm. 
with an embryo 39 mm. long. Then, among his miscellaneous Chlamydoselachus records, 
I have found a water-color sketch of a 55'mm. embryo on a yolk sac measuring 122 x 69 
mm. This sketch, which is rather crude, was not made by Dean and was not intended for 
reproduction. The egg, from which the capsule had been removed, was taken off Okinose 
(Sagami Sea) in December, 1906. The references to these eggs without capsules are 
merely to show that the ellipsoidal form is the predominant one. Attention will now be 
directed to the capsules of these great eggs. 

As portrayed by Dean, ellipsoidal encapsuled eggs seem to be of two kinds — normal 
and abnormal or at least unusual. These, as figured by him and by other investigators, 
will now be studied. 

NORMAL ELLIPSOIDAL ENCAPSULED EGGS 

The first encapsuled egg of Chlamydoselachus ever figured may be taken as an ex' 
ample of the normal egg of this type. The description and figure are from Nishikawa 
(1898). His material came from seven female specimens from the Sagami Sea. These 
fish contained from 3 to 12 eggs each — all ellipsoidal in form. His statement follows and 
evidently has to do with eggs in very early stages since he speaks of their having blastO' 
derms on them. He also had eggs of the same type with early embryos as will be now 
shown. Here is Nishikawa's description: 

The egg is ellipsoidal, and varies between 65-75 mm. in its shorter diameter and 102-124 
mm. in its longer diameter, the measurements being made in physiological solution of salt (Figs. 
1 & 2) [Fig. 1 = Text-figure 4 herein]. It bears a stumpy excrescence at one end and a sHghtly 
recurved flattened process, about 35 mm. long, at the other. The capsule is light brown and 
transparent. The space between the capsule and the yolk sac is, in earlier stages, very in- 
significant, being confined mostly to the two poles of the eggs, and is filled with the white, 
which is very fluid. The yolk is of a pinkish color, and the yolk-sac is very delicate. 



^ 



568 Bashford Dean lAemorial Volume 

This description is of a live egg just taken from the body of the mother. I have found 
a very similar condition in the encapsuled intra-uterine egg of the nurse shark, Ginglymo- 
stoma cirratum (Text-figure 16). Here is a thick heavy capsule enclosing the huge round 
yolk w^th its embryo surrounded by a clear glairy fluid — evidently the counterpart of 
Nishikawa's "white'\ Lining the interior of the shell and particularly noticeable at the 
ends is a thicker jelly-like material which cushions the yolk as the egg rolls about in 
the saddle-bag-shaped uterus of the female Ginglymostoma as she twists and turns 
in avoiding enemies. 

Nishakawa's drawing (Text-figure 4) shows an elHpsoidal egg in a capsule (natural 
size) 135 mm. over the processes (following the curve of the long one). The egg proper is 
100 mm. long by 65 deep, with an embryo 43 mm. long on it. Attention is called to the 
blunt nipple-shaped process on the left, while on the right, the capsule terminates in 
a finger-like curved process about 40 mm. long over its outer curve. The capsule is trans- 
parent and here dravvTi to show the embryo and its circulatory system, but on the lower 
side just inside the heavy line representing the capsule is a light line portraying the 
raphe of the capsule. This extends from the end of the short blunt process along the shell 
and out on the long curved process. This raphe is bilateral — the other half being found 
on the side of the egg away from the observer. 

Dean's drawings of encapsuled eggs number eight, including the wind egg previously 
referred to. These figures portray elhpsoidal eggs of two kinds: normal eggs with a blunt 
nipple-shaped process at one end and a long curved finger-Hke process at the other; and 
abnormal or at least unusually long eggs having at one end a long process with tendrils. 
There are also four drawings of round eggs. The normal ellipsoidal eggs will be studied 
first, the unusual types will later be considered in series. 

Dean has figured two elHpsoidal eggs of the normal type. The first is shown in both 
dorsal and ventral aspects in Figures 7 and 8, plate I. Careful comparison of Figure 7, 
plate I, with Text-figure 4, a reproduction of Nishikawa's Fig. 1. pi. IV, shows that 
Dean"s figure is a copy of Nishikawa's. The embryo measures 43 mm. in both; the yolk 
in Dean's figure is 65 x 100, in Nishikawa's the same. Likewise the eggs in ventral aspect 
(Figure 8, plate I, and Nishikawa's Fig. 2, pi. IV) are identical. Nishikawa also had an 
egg with a 50-mm. embryo on it, but he had no drawing made of it. This however, Dean 
had drawn in both dorsal and ventral aspects as may be seen in Figures 9 and 10, plate I. 

Having cleared up these points, let us now return to a study of the ellipsoidal 
capsules, which have been designated as normal. But first let it be said that no one else 
has ever obtained or at any rate portrayed capsules such as these. Each of the capsules, 
shown in Figures 7 and 9, plate I, has at the left end a rounded, blunt, nipple-shaped 
process or eminence. On the right, each capsule terminates in a curved, finger-like 
stumpy process, about 30 mm. long, and each curved m the same direction. In the drawing, 
each egg has on its lower side a distinct raphe, whose relation to the blunt process is 
obscure but which extends out onto the long curved process. The capsule of the younger 
egg measures 128 mm. in a straight line, that of the older egg 143 mm. 



The Embryology of Chlamydoselachus 



569 



J 



UNUSUAL ELLIPSOIDAL EGGS WITH TENDRILIFORM PROCESSES 

There are now to be considered certain eggs whose capsules may generally be desig' 
nated as ellipsoidal but which depart rather widely from the forms studied. All bear 
tendriliform processes. One is unusual in form but is by no means abnormal. However, 
it does bear tendrils. Of all the unusual eggs, it departs so little from the normal that it 
will be considered first in this category. 

An Elliptical Egg 

This egg is elliptical rather than ellipsoidal in outline and bears tendrils at one end 
(Text'figure 19). It is the only encapsuled egg, other than Nishikawa's (Text'figure 4) 




Text-figure 19 
An elliptical encapsuled egg (in natural size — 112 mm.) in the Museum of Com- 
parative Zoology, Cambridge, Mass. Note the striae on the capsule and the 
tendril-bearing process on the left. The stump on the right looks as if a similar 

process had been cut off. 
After Garman, 1913, Fig. 4, pi. .59. 

that has ever before been portrayed as a published figure. In 1906, this egg was brought 
from Japan by Dr. Thomas Barbour and deposited in the Museum of Comparative 
Zoology at Cambridge, Mass. In 1913 it was figured but not described by Samuel 
Garman. As my Text-figure 19 shows, the outline of this capsule is an almost perfect 
ellipse. The egg measures about 90 x 70 mm. The total length of the capsule is 112 mm. 
and of this the long process accounts for about 18 mm. At the left, the long seemingly 
round process breaks up into three short unequal-si?ed stumps and each of these into 
a number of smaller processes, of which the finer outer parts (see Figure 13, plate I) have 
broken away. At the right end is the stump of a process, apparently the product of an 
amputation by means of a dull knife of such a process as is still present on the left. The 
shell is covered with parallel striations. The egg is so drawn that the raphe forms both 
upper and lower edges or limits of the figure. Garman also figures the egg yolk with its 
59'mm. embryo removed from the capsule as has been noted. 



j 



570 Bashford Dean Memorial Volume 

Next for study are three ellipsoidal tendril'bearing eggs found portrayed in Dean's 
portfolio of drawings of Chlamydoselachus . These eggs are not merely ellipsoidal but are 
decidedly oblong. Two of them were fertile, while the third, the wind egg previously 
referred to, was infertile. 

SoifE Oblong FERTriE Eggs 

In Dean's notes, as already referred to herein, the small wind egg is recorded as 
coming from the left oviduct of a female Chlamydoselachus taken off Misaki in 1905. From 
the right oviduct of this same fish were obtained "3 oblong eggs" of which two were 
"drawn". The one of the oblong eggs, not drawn, was roughly sketched in pencil in the 
notebook with the caption "stage early, probably gastrula". This sketch is reproduced as 
number C in my Text-figure 26. Note that the capsule has a tendril-bearing process at 
one end. This is very like the process in one of the "drawn" eggs now to be studied. 

Symmetrical Oblong Eggs. — With the notes just quoted is the cryptic statement 
"135 mm. x 70 and longer". I identify the two oblong eggs "drawn" with Figures 
2 and 3, plate I. The smaller egg (Figure 3) is symmetrical and measures (in the original 
drawing) 116 mm. excluding the processes and 140 mm. over them; it is 78 mm. deep. At 
the right end is a very short process, apparently the remains of a longer one. At the left 
end is a slightly curved stumpy process, 20 mm. long. Apparently the tip of this has been 
broken off leaving some splinter-like fragments. Along one side is a raphe which extends 
out on the long process. Its relation to the fragment of the process at the right is not 
clear. The capsule is everywhere covered with close-set parallel striations. At the left 
many of these striations are gathered together and extend out on the long process. 

Among the Chlaynydoselachus material deposited in the zoological collection of 
Columbia University and loaned by Prof. McGregor for this study, is an oblong encapsul- 
ed egg. This measures 108 x 71 mm.: is not only oblong but slightly asymmetrical, and 
has a large raphe similar to that on the egg figured. The raphe extends from a rudimentary 
blunt process at one pole of the egg over the yolk mass and out onto a short process ending 
in tendriliform fragments. This tendrilitorm process is somewhat shorter than that in 
Figure 3, plate I, and the egg is somew^hat smaller. I believe, however, that this egg is the 
one figured, and that the slight differences are due to shrinking after 33 years in alcohol. 

In the 108-mm. oblong egg, and in two others of about the same size from Columbia 
University (both having embryos), the raphes are complete. They entirely encircle 
the eggs, but are better developed on one side than on the other. Their function is 
not known. The color of the capsules of these preserved eggs is a Hght brown. A 
crumpled capsule, from w^hich egg and embryo have been removed, appears decidedly 
browner than those capsules enclosing yolk masses. Possibly this difference in color 
between these capsules and that of the wind egg (Figure 51, plate V) is due to their long 
immersion in alcohol. 

Asymmetrical Oblong Eggs. — The larger of the two oblong eggs, referred to in 
Dean's notes, is decidedly asymmetrical (Figure 2, plate I). Its length (excluding its one 
process — the other, if present, is hidden) is 135 mm. and its width 87 mm. It is pre- 



The Embryology of Chlamydoselachus 571 

sumably the "larger" of the two oblong eggs recorded in Dean's notebook. Its asym' 
metry is probably not the result of handling, as might be surmised, but was impressed 
upon the egg while the capsule was being formed. The long curved process measures 
about 30 mm. to the fork of the tendrils and these extend out about 15 mm. further. The 
capsule is everywhere traversed by line longitudinal striations which converge at the left 
end and run out onto the long tendril'bearing process. The raphe, seen on the side of 
the egg next the observer, is very large and heavy. It runs out on the process which is 
plainly twisted to the left. 

In the Dean collection of frilled'shark material in the Department of Zoology at 
Columbia University is a large somewhat asymmetrical ellipsoidal egg which deserves 
description. It measure 90 mm. long x 57 deep and has on it an embryo 71 mm. long. 
The large yolk mass has become split open by the action of the preservative and the result- 
ing expansion has split the capsule along that raphe near to and somewhat parallel with 
the body of the embryo. At the end of the egg near the tail of the little fish I can find no 
evidence of a process. At the other end near the head of the fish is a process (broken off 
from the capsule) which, as hardened by the preservative, is quite flattened. 

This process is shown in Figure 13, plate I. In nature, the basal part is about 17 mm. 
long and about 8 mm. wide. Each of its outer edges is constituted of the end of a raphe. 
Between these raphe-formed edges, in the flat body of the process, about seven horny 
strands can be made out with the aid of a magnifying glass. This process is very like that 
on the egg shown in Figure 2, plate I. The outer end of the process is split in two and 
each half breaks up into a twisted mass of fine tendrils. Here as in Figure 2, plate I, the 
raphes form a part of the tendril mass, exactly as they do in the egg cases of certain skates 
and European small sharks ("dogfishes'"). 

In the first plate of Dean's figures is a separate drawing (Figure 14, plate I) which 
shows such a very much frayed-out process. This process seems also to be flat and to have 
the raphes forming its outer edges. It breaks up into one large and three small tendril 
masses. The larger at the base seems to be constituted of about 10 string-like bodies. 
The other three tendrils are separate and grade in size from outside in, the innermost 
being the smallest. The larger tendril mass seems to have had a filament cut off at the 
second bend, one tendril only remaining. Of the three others the median one seems to be 
broken up into two. The outer and inner tendrils are of about the same length. All are 
much crumpled. It seems not improbable that this drawing was made from such a process 
as that described in the preceding paragraph. Since the striae run onto the processes, one 
wonders what part they play in the formation of the strands in the process and of the 
tendrils. One wishes for fresh material here. 

An Elongate Infertile (Wind) Egg 

Last of all of Dean's drawings of elongate eggs is the wind egg portrayed in color in 
Figure 51, plate V. It is hardly ellipsoidal but it is elongate and it has a long tendril- 
bearing process as may be seen in the figure. It was presumably drawn in natural size. 



4 572 Bashford Dean lAemorial Volume 

Its width is 23 mm. and its length over the processes (but excluding the tendrils) is 102 
mm. At the larger end is a conical process. The long pointed end of the capsule breaks 
up into a group of tendrils measuring about 10 mm. The surface of the capsule exhibits 
very fine striations. Very clear is the longitudinal ridge or raphe extending from the 
tendrils along the small end of the egg capsule to and across the base of the conical process. 
Not visible is the corresponding one on the other side. At the lower side of the larger 
end ot the capsule is a clearly delimited pale area. What it is I do not know. This egg 
apparently contained no yolk whatever and hence it is called "wind egg". The color as 
shown in the figure is presumably that common to all egg capsules. 

ROUND EGGS OF THE FRILLED SHARK 

Last among Dean's materials for the study of encapsuled eggs are three drawings of 
round eggs reproduced as Figures 4, 5, and 6 of plate I. These are labelled C, B, and A 
on the drawings, and are listed in this order in Dean's notebook in his writing, as indi' 
eating their progressive stages of development. Each egg capsule is round and has short 
curved processes. These eggs will be considered here in the order of size. 

Egg A (Figure 6, plate I) in the original drawing measures 129 mm. over the processes, 
and the diameters of its yolk mass are c. 88 mm. in the line of the processes x 87 wide. 
Of the three eggs, its processes are the longest and slenderest, are of about the same size 
and length, and are curved in the same direction. Egg B (Figure 5) is 115 mm. over the 
processes, and its diameters are c. 87 x 96. Its processes are short and stumpy, are of 
about equal size, but are twisted in opposite directions. Egg C (Figure 4) is 116 mm. over 
the processes, and its diameters are c. 90 x 89. Its stumpy processes are short, of unequal 
size — one more than double the size of the other — but are curved in the same direction. 
All these processes appear to be "stumpy"', but it may be that they were sharply curved 
away from the artist's line of sight and were longer than they appear in the drawings. 
Those of Egg A (Figure 6) certainly recall the longer process portrayed by Nishikawa in 
my Text-figure 4, and by Dean in his Figures 7 and 9, plate I. In this respect this capsule 
approaches what has been taken as the normal type. 

In the capsule of each egg the raphe extends across the germinal region, where it is 
drawn much wider. It runs out onto and helps form each process. The striae are not 
visible over the egg but show faintly at the poles, where they converge and extend out 
on the processes. The formation of these processes is not easy to understand and so far 
as I know has never been explained. The anterior process of the capsule must be formed 
in the lower outlet of the shell gland while the egg in the shell gland is having its capsule 
laid down. As I shall show later the posterior process is formed as and when the en- 
capsuled egg passes out of the gland on its way to the uterus. The exit orifice of the shell 
gland is small and its sphincter muscle evidently constricts the ends of the shell while 
they are still soft and gelatinous. While the processes are being formed, the striae on 
them are laid down in a way not as yet understood. 



The Embryology of Chlamydoselachus 573 

These encapsuled round eggs have been designated '"unusual" since no one save 
Dean seems ever to have seen such, but they cannot be termed abnormal. Each seems to 
have a late blastula on it (these will be considered later) and there is undisputable proof 
that these round eggs go on to full development. This is admirably shown in Figure 11, 
plate I. The young fish was 175 mm. long and it is fast to a round yolk sac which in the 
original drawing measures 92 x 90 mm. and which is now freed of its capsule. Thus this 
yolk, bearing this advanced embryo, has still the almost perfectly round form of the three 
eggs shown in Figures 4, 5 and 6, plate I, and, judging by the si2,es of these three other 
round eggs, it has decreased but little in bulk. 

SIZES OF EGGS OF CHLAMYDOSELACHUS 
COMPARED WITH THOSE OF OTHER SHARKS 

From his studies of all these extraordinarily large encapsuled eggs of Chlamydo- 
selachus, Dean drew certain general conclusions as to their size and phylogenetic origin. 
These conclusions are contained in the only description (a single paragraph) of the eggs of 
the frilled shark which he ever published (1903). From this, I excerpt the following: 
''Chlamydoselachus has specialized in the line of producing large eggs, the largest indeed 
among recent animals, ostrich hardly excepted [egg 150 mm., 5.9 in., in long diameter]; 
that it was, however, until recently an egg-depositing shark is apparent from the character 
of the horn'like capsule (with rudimentary tendrilform processes) which the egg still 
retains". 

At the time that Dean wrote, the egg of Chlamydoselachus was the largest egg 
known to him save only that of the ostrich, but since his day larger shark eggs have been 
discovered. Larger eggs are now known to be carried by various sharks of the family 
Isuridae, and by the ovoviviparous nurse shark, Ginglymostoma cirratmn, often referred 
to earlier in this article. The eggs of these sharks will now be described that the reader 
by comparisons may see how large the eggs of Chlamydoselachus really are. 

SIZES OF EGGS AND EMBRYOS OF THE FRILLED SHARK 

As a basis for comparing the size of the egg of the frilled shark with that of other 
sharks, it will be necessary to establish the size of this egg. Our earliest information 
comes from Nishikawa (1898) who had eggs ranging from 102 to 124 mm. in long and 
from 65 to 75 mm. in short diameter. He also speaks of eggs ''110-120 mm. long". These 
measurements were presumably made over the egg capsule and its processes. His one 
figured egg (Text-figure 4) thus measured is 128 x 65 mm., but the yolk mass is only 100 x 
65 mm. natural size. 

Let us now turn to Dean's materials. The three round eggs (yolks only) measure 
90 X 87 mm., 96 x 87, and 97 x 88 in the original drawings. His two oblong eggs (yolks 
only) measure 119 x 80, and 138 x 90. Of his other material, Figure 9, plate I, portrays 
a 50-mm. embryo on a yolk measuring 108 x 68 mm. Then his Figure 11, plate I shows a 
large embryo on a yolk sac 92 x 90 mm. Also Dean records an embryo of 331 mm. on 
a yolk 111 X 100 mm. And finally there is the huge embryo of 390 mm. (15.35 in.) 



574 Bashford Dean Memorial Volume 

on a yolk measuring 100 x 70 mm. This is portrayed in color in Figure 49, plate V. 
All these measurements are of the original drawings. 

When one considers these measurements of such huge eggs as had never before been 
recorded of any animal marine or terrestrial (save only the ostrich), it is no wonder that 
Dean wrote (1903, p. 487) that "'Chlamydoselachus has specialised in the line of producing 
large eggs, the largest indeed among recent animals, ostrich hardly excepted". But we 
will consider some eggs that exceed even the very large ones of Chlamydoselachus. 

SIZES OF EGGS AND EMBRYOS OF ISURID SHARKS 

Interestingly enough at about the very time that Dean was collecting adult speci' 
mens of Chlamydoselachus and studying their eggs in the Sagami Sea, Fran? Doflein 
was also making very extensive collections of marine fauna from the same waters. He 
either collected or at any rate saw specimens of the frilled shark, for in his book (1906, p. 
257) he figures a male specimen — the best portrayal (Text-figure 5 herein) yet published 
of the male fish. He also obtained a huge shark egg and later described it in the follow 
ing terms: 

The eggs of a giant shark were to me one of my most surprising discoveries. I had often 
gotten these eggs from the fishermen but I never obtained the mother fish. They were, 
however, taken from the mother fish, which evidently belongs to the viviparous sharks. 
With their enormous yolks, they seem to be the largest eggs yet known from the animals of 
that region. They were considerably larger than ostrich eggs [150 mm. long]. One could 
tell them from the eggs of other sharks by the fact that the embryo was not connected with 
the yolk sac by a long, ribbon-like umbilical cord, but grew directly from it. 

When I had read thus far, I strongly conjectured that these were eggs of Chlamydo' 
selachus, particularly since they came from a viviparous shark and since Doflein knew and 
figured Chlamydoselachus in his book. But fortunately, on the page following the para- 
graph quoted, Doflein figured one of these eggs and embryos. It is plainly a young Isurid 
shark, and the statement is added that the yolk sac has a (long?) diameter of 220 mm. No 
size is recorded for the little shark, but it is still comparatively young, probably not more 
than one-quarter grown. 

Doflein brought back to Germany two of these huge Isurid uterine eggs along with 
his other Japanese fish collections. These eggs and embryos were turned over to Johannes 
Lohberger who made a thorough study of their external morphology and internal anatomy 
(1910). He found that the larger and older embryo (Text-figure 20 herein), after being in 
preservative for four years, was 553 mm. long (21.8 in.) and 63 mm. wide where it rested 
on the yolk mass. The length of the yolk mass was 211 mm. (8.3 in.) and its transverse 
diameter 123 mm. (4.85 in.). The weight of embryo and yolk was 2.68 kg. =5.9 lbs. 
The size of the female Lamna from which embryo and eggs were taken is not given and 
probably was not obtained. 

In the same year that Lohberger published on his Lamnid embryos from Japan, 
Shann (1910) described embryos of Lamna cornuhica from Scottish waters. He 
quotes H. C. Williamson that the largest porbeagle embryo he had ever seen was "19 
inches in total length ... the yolk measuring 9.25 inches in length". Shann's description 



The Embryology of Chlamydoselachus 



575 



and table of measurements of his own four embryos are so involved that I can make out 
little about them. He had four embryos measuring 10.25, 18, 18.5 and 24 inches respec 
tively and all in about the same stage of development. His detailed yolk'sac measurements 
are unintelligible to me — one wishes for diameters such as those given above. Shann 
states that one of the largest embryos he examined "was a female measuring 21.75 inches 
and the yolk sac was still of enormous bulk". This is confirmed by his roughly^drawn 




Text-figure 20 

Egg and embryo of an Isurid shark (Laynna sp.) obtained in the Sagami Bay by Franz; Doflein 

C.1905. The embryo was 553 mm. (21.8 in.) long. The yolk sac measured 211 mm. (8.3 in.) x 123 mm. 

(4.8 in). The whole weighed 2.68 kg. =5.9 lbs. 

After Lohberger, 1910, Fig. 1, pi. I. 



figure which shows that the word ''enormous" is correctly used. The yolk reaches almost 
from the angle of the jaw to the base of the caudal fin. He judges that at birth the young 
fish would be approximately 30 inches from tip to tip. 

Other Isurids have large embryos on huge yolk sacs. Two cases will be indicated. 
Sanzo (1912) figures and describes from the Mediterranean the intra-uterine embryo of 
Carcharodon rondeletii, the great white shark or ''man-eater". The embryo was 361 mm. 



576 Bashford Dean Memorial Volume 

(14.2 in.) long but no dimensions of the elongate yolk sac are given. The specimen weigh- 
ed 800 g. (28.2 oz.) of which the yolk alone weighed 500 g. (17-9 oz.) In his figure the long 
yolk mass extends from the pectorals to beyond the cloaca. 

Since the above was v^^ritten, I find that, unknown to Dean, Lohberger, Shann, 
Sanzo and myself, a far larger egg and embryo of another Isurid shark had been recorded by 
VaiUant in 1889. He described but unfortunately did not figure an embryo of Oxyrhina 
spallanzanii whose total length was "50 cmt." (500 mm., 19.65 in.) on a yolk sac measuring 
235 X 140 mm. (9.25 x 5.5 in,). Fish and yolk had been more than 50 years in alcohol. 
Yet, "Le poids total de cette piece, qui represente en somme un oeuf gigantesque de 
Selacien, est, dans etat actuel de conservation, de 3 kil. 250 gr.'" This weight (3250 g., 
114.6 oz., 7.2 lbs.) seems incredible hence I have quoted VaiUant verbatim. So far as 
I know this is the largest egg and embryo of any shark ever described. 

I can not find that the egg capsule of an Isurid shark has ever been figured. Not 
only does one wish to see an embryo and yolk sac of one of these sharks tor comparison 
with a like stage oi Chlaynydoselachus, but also for comparison one wishes to see and 
examine the capsules which enclose the largest eggs in the animal kingdom — eggs much 
larger than those of the ostrich. 

There is in the Museum collection an egg and embryo of Chlamydoselachus mounted 
for display on a sheet of glass in a rectangular jar of alcohol. The embryo measures 370 
mm. (14.55 in.) and the yolk sac 78 x 60 mm. Dismounted, and w^ith the excess of alcohol 
drained olF, egg and embryo weigh 213 g. (7-5 oz.) Another yolk sac of about the same 
size (.74 X 60) detached from its embryo w^eighed 142 g. (5 oz.) The little fish, drawn when 
fresh (Figure 49, plate V), measured 390 mm. and the unhardened yolk 100 x 70 mm., but 
after being in alcohol for at least 33 years it has shrunk to the dimensions noted above. 
The weight has also decreased somew^hat. There is much yellow oil in the yolk. This 
soaks out into the alcohol, which has periodically to be replaced by fresh alcohol. 
This automatically reduces the weight of the yolk. 

The young frilled shark is a little longer (370 vs. 361 mm.) but much more slightly 
built, especially in the forward parts, than Sanzo's Carcharodon. The total weights are 
very different — 213 vs. 800 g.; but after all the greatest difference is in the weight of the 
yolk sac— 142 vs. 500 g. Here contrast Dean's Chlamydoselachus (Figure 49, plate V) 
with Lohberger's Lamna (Text'figure 20). 

SIZES OF EGGS OF THE NURSE SHARK 

I have unfortunately never seen the eggs and embryos of Lamna nor Carcharodo7^ 
but I have studied the encapsuled eggs and early embryos of the nurse shark, Gingly- 

mostoma. ^^nd since these heavy-shelled intra-oviducal eggs are in many ways similar 
to those of Chlaynydoselachus, some data concerning them m the encapsuled stage will be 
valuable here for comparison. My figures give lengths and unfortunately girths instead of 
uridths of the capsules. Furthermore since it was not easy to measure the horizontal 
diameter of the yolk mass through the thick and oftentimes scarcely transparent capsule, 



The Embryology of Chlamydoselachus 577 

I mistakenly did not record the measurements of the yolks. Since the capsules are not 
round but flattened dorsoventrally, it would have been difficult to get measurements in 
this dimension. 

In my notes I have measurements of 5 wind eggs recorded as "infertile". These are 
105 mm. long x 120 in circumference; 105 x 145, 116 x 110, 122 x 145; and 130 x 146 mm. 
I noted the measurements of 6 average'sized fertile eggs as follows: 133 mm. long x 185 
in circumference; 134 x 192; 141 x 185 (2 capsules); 142 x 193; 150 x 190 — average 140 
long X 187 in girth. From this it is seen that there is considerable variation in size — less 
in girth than in length. The girth of the capsule is pretty constant because the size of the 
contained yolk mass is fairly uniform. The variation in length is mainly due to variations 
in form and shape in the posterior or last-formed end of the capsule. This is sometimes 
pointed and sometimes blunt but always seemingly "pinched together". The anterior or 
first-formed end looks "finished", the posterior end, the last to emerge from the shell 
gland, looks unfinished. For these points see Text-figure 16. This matter of the posterior 
or unfinished end of the capsule will be referred to later. 

It was difficult to get the weight of the yolk. This is surrounded by a clear glairy 
fluid which slowly flows like thick syrup. Next to the shell this becomes a thick jelly 
which adheres to the shell. At the ends of the shell this jelly forms the "plugs" already 
noted — see Text-figure 16. These substances — glairy fluid and jelly — probably corre- 
spond to the "white" of Nishikawa. To get at the weight of the yolk, shell and contents 
were weighed. Then a window was cut in the upper part of the shell, and the yolk and 
some of the surrounding glairy matter were poured out. The shell, the jelly and the re- 
maining glairy material were then weighed. The data for my two largest eggs are as 
follows. Egg 1, 180 mm. long x 220 mm. in girth, weighed 318 g. The shell and jelly 
weighed 64 g. and the yolk 254 g. Egg. no. 2 was about the same size (no figures recorded) 
and weighed 311 g. The shell and jelly weighed 56 g. and the yolk 255 g. 

From the data set out above, and from the eggs and capsules shown in Text-figures 
16 and 21 it is manifest that, while the encapsuled egg of Ginglymostoma is very large, it 
is not so large as that of Lamna or Carcharodon. The average for the 6 normal-sized eggs of 
Ginglymostoma is 140 mm. (5.5 in.) long x 187 (7-4 in.) in girth. These eggs are somewhat 
flattened and have thick heavy raphes on each side. These help increase the girth measure- 
ments. Text-figure 16 was made from a large and entirely normal encapsuled egg. Its life 
size was unfortunately not noted, but as shown in the text-figure, it has been reproduced 
140 mm. in length — the average as worked out above. This is just sHghtly more than the 
natural size of the encapsuled egg of Ginglymostoma figured by Garman (1913, Fig. 3, pi. 
59). From these data it is seen that in size of their eggs these sharks rank thus; Chlamy- 
doselachus has the smallest, Ginglymostoma the intermediate-sized, and the Isurids the 
largest eggs. 

Again must comparison be drawn between the body size of Chlamydoselachus and 
that of these other sharks. The frilled shark has an elongate slender body averaging c. 



^ 578 Bashford Dean Memorial Volume 

5.1 ft. (largest 6.4 ft.) — with a correspondingly small abdomen (Text-figures 5 and 7)- 
Yet in its right uterus it may carry as many as 7^12 large eggs and embryos. On the other 
hand, the nurse shark is large (average adult about 8 ft. long), broad and somewhat flat, 
and has a large abdominal cavity. Both of its uteri are functional and at breeding season 
become enlarged into a pair of saddlebag-like organs each of which may contain as many 
as 21 of the large eggs portrayed m Text-figure 16. The porbeagle is a fairly large shark. 
Shann notes females from 5-9 ft. long — more of the smaller size being recorded. I have 
no data for the size of the body cavity, but it must be large to accommodate the eggs and 
embryos noted above. Both uteri of Laynna are functional. Three and occasionally four 
young are produced, but one on each side, or one on one side and two on the other are 
more common. The young at birth are probably 28-31 in. long, and, since these young 
sharks are very large forward, they must fill the uteri and the abdominal cavity quite full. 
But to sum up, it can be said with assurance that the evidence points to the belief that 
in proportion to the size of its hody cavity, the frilled shark ripens and incubates the largest 
eggs known at this writing. 

With the making of these historical notes a part of the record dealing with the size of 
the encapsuled eggs ot Chlamydoselachus, we will now turn to the study of the formation 
of the capsule. 

FORMATION OF THE EGG CAPSULES 
OF CHLAMTDOSELACHUS AHD OF GIHCLTMOSTOMA 

The presence of the thick keratinoid shell about the egg of an ovoviviparous shark is 
surely an archaic feature. As Dean long ago (1903) pointed out, this is a heritage from its 
egg-laying ancestors. Now all egg-laying elasmobranchs known to me have on their 
shells tendrils or holdfasts which catch on seaweed, stones, and other objects. Thus 
anchored, shell and egg escape being rolled about and injured or covered with sand or 
silt, and are assured of fresh water and oxygen. 

As in other sharks, so in Chlaynydoselachus these capsules are secreted by the shell 
gland, the interior of which is shown in Text-figure 13. For a description of this gland 
see page 550. As I have pointed out earlier, the egg shell exhibits minute striae, which 
sometimes have a faint spiral arrangement, and which in all cases are gathered up and 
extend out on the processes. For these see Figures 2 and 3, plate I. These striae are 
undoubtedly impressed on the capsule during its formation. The peculiar internal 
structure of the shell gland seen in Text-figure 13 must be responsible for these. The shell 
gland is somewhat flattened in torm and I judge that the raphes are formed at the sides 
where the dorsal and ventral inner surfaces of the gland are united. The structure of the 
shell gland in Chlamydoselachus has yet to be thoroughly described and the details of its 
function explained. 

Excepting only the round eggs portrayed by Dean, all egg capsules of the frilled 
shark figured have a long functional process at one end of the capsule. In most of the 
other eggs portrayed, the other end of the capsule has a low conical blunt nipple-like 



The Embryology of Chlamydoselachus 579 

process — as figured by Nishikawa (my Text'figure 4); and by Dean, Figures 7 and 9, 
plate I. Or this is very blunt and looks cut off as shown by Garman inText'figure 19. Or, 
at this end of the capsule, the process is almost or entirely lacking as seen in Figures 2 
and 3, plate I, and as found in eggs deposited by Dean in the zoological museum of Colum' 
bia University. Thus one end of the capsule looks "finished" and the other — especially 
when the process breaks up into tendrils — looks decidedly unfinished. However, the 
practical disappearance of the process at one end of the capsule, taken in connection with 
the fact of uterine gestation of the egg, is surely indicative of an evolutionary movement to 
get rid of the capsule around the egg of Chlamydoselachus. 

Nothing is known as to the method of formation of the capsule and its processes in 
Chlamydoselachus. This could only be had by dissection of females immediately after 
capture in the hope of finding capsules still in the glands. How improbable is such an 
opportunity, the reader will readily realize from considering the habitat of the fish and the 
difficulty of its capture. However, I have fortunately been able to make such dissections 
and observations on the nurse shark, Ginglymostoma cirratum, which, as noted, carries 
in each uterus eggs with large thick'walled blunt-ended capsules. In this capsule, one 
end is likely to be smaller and seemingly pinched together, more "finished", like that of 
Chlamydoselachus, while the other is larger, somewhat drawn out and blunter, unfinished 
looking — this end being presumably that last formed. In Text'figure 16 one cannot make 
this distinction very readily, because the ends are very much alike. But since I have 
examined scores of these eggs, I am satisfied that the longer and broader end of the capsule 
is the younger. Furthermore, the blunter end is plainly the younger in the eggs shown in 
Text-figure 21. Then there is another criterion on which to base judgment. The egg 
(yolk mass) is placed excentrically in the shell (Text-figures 16 and 21). This results from 
the fact that the jelly-like substance lining the shell forms a larger plug in one end of the 
capsule. In these unequal-ended capsules of the nurse shark, this larger amount of jelly 
is in the "unfinished" or younger end as may be seen in the figures referred to. 

Now it is clear that Ginglymostoma is the last of a line of oviparous sharks, and that 
like Chlamydoselachus, it is an ovoviviparous selachian well on the way toward a vivipa- 
rous mode of reproduction. As such, Giyiglymostoma like Chlamydoselachus might be 
expected occasionally to retain tendrils at the larger, blunter, younger, or "unfinished" 
end of its capsule. That it does this is shown in Text-figure 21. Furthermore, while at 
Tortugas in 1912, I fortunately by dissection learned how and when these tendrils are 
formed. The facts as ascertained will now be given from my notes. 

FORMATION OF TENDRILIFORM PROCESSES 

On June 16, 1913, I dissected several female specimens of Ginglymostoma and found 
that "No. I fish had in the section of the left oviduct just behind the shell gland an egg 
whose backward [really its anterior] end was covered with a hard tough shell (like any of 
the eggs in the uterus) with the short blunted base of the absent horns drawn toward each 
other, as may be seen in Carman's drawing (1913, Fig. 5, pi. 59). The posterior end of the 



580 



Bashford Dean hiemorial Volume 



shell, however, still projected into the hinder part of the shell gland, and when drawn out 
this was found to be soft and gelatinous with prolongations which were evidently tendrils 
in the process of making. These were broken off in removing the egg, but they were 
placed in their normal position as shown in the photograph reproduced as Text'figure 21. 
This egg was '"non-fertile". 

From another female dissected on this day, I got an egg capsule with a pair of pro- 
cesses 55 mm. long, and on another capsule one process 120 mm. long. These eggs were 
undersi2;ed and probably infertile — though this unfortunately was not specifically noted 
as it was for other eggs below standard limits of size. My notes record five other cases 
from specimens dissected June 19. Some shells had processes on the posterior (i.e. last 

formed) end, a few had them on the anterior (first-formed) end, 
though here the capsule was generally ' 'blunt" or rounded. The 
posterior end of the capsule still in the shell gland or just out of it 
was always soft, light in color and often translucent. That end 
first formed and first out of the gland, the anterior end, was 
always hard, dark in color, and noted as ""finished". These in- 
fertile eggs were plainly wind eggs comparable to that of Chlamy 
doselachus shown in Figure 51, plate V. 

From these facts the only conclusion 
that can be drawn is that in Gingly 
mostoma the formation of these rudiment- 
ary and very variable processes indicates 
that they are vestigial structures inherited 
from oviparous ancestors whose egg shells 
had tendrils for holdfasts. Everything 
points to the face that the ovoviviparous 
shark Ginglymostoma is on its way toward 
becoming a truly viviparous one. 

No dissections and no direct obser- 
vations of the formation of the egg capsule 
of Chlamydoselachus have ever been made. 
But several scientific men on being asked 
which end of the egg capsule of the frilled 
shark was finished first (was the older) 
have unhesitatingly answered "the blunt 
end", and when asked why have answered 
that "It looks finished" — and so it does, 
while the end having the process looks 
"unfinished". For these points contrast 
the two ends of the capsule in Nishikawa's 
egg (my Text-figure 4) and in Deans' 





Text-figure 21 
Two typical egg capsules of the nurse shark 
Ginglymostoma cirratum. The first, a wind egg, 
has the rudiments of tendrils at the hinder end. 
The second, a fertile egg, has the normal, blunt, 
unfinished hinder end to its capsule. 
Photograph by E. W. Gudger. 



The Embryology of Chlamydoselachus 581 

drawings (Figures 7 and 9, plate I). More markedly does this contrast appear in Gar^ 
man's drawing (Text'figure 19 herein) and in Dean's two oblong eggs (Figures 2 and 
3, plate I). 

Not being able to decide by observation which is the anterior or older end of the 
egg capsule in Chlamydoselachus, let us turn for comparison and explanation to the very 
similar egg shell of the nurse shark, Ginglymostoma, in which I have settled the matter 
by dissection and direct study. My observations on the formation of the process of the 
egg shell of Ginglymostoma make clear when and how the long processes seen on the cap' 
sule of Chlamydoselachus are formed. Here let the reader note the twisted processes in 
the figures just referred to, and the tendriliform holdfast organs seen on Carman's egg 
and on Dean's oblong specimens. The bluntly conical, the "finished" end, is the anterior, 
the older, the first formed; the twisted and the tendrilform ends are the younger, posterior, 
or later formed. So also one can understand the formation of the very much frayed-out 
tendril'bearing tips shown in Figures 13 and 14, plate I. The finished ends of the capsules 
plainly came through the shell gland first and quickly, while the tendriliform ends came 
last of all, lingered and were then formed. 

It is difficult to explain the formation of the three round egg cases and their short 
blunt processes at each end as portrayed in Plate I. However, the smaller process of the 
egg in Figure 6 was probably formed last. It seems likely that, in some way not clearly 
understood, each end of a round capsule, as it passed through the sphincter at the hinder 
part of the shell gland, remained in the orifice the same length of time and received the 
same treatment. And as a result the two processes of each capsule are practically identi' 
cal. It would seem that had these eggs at the close of shell formation lingered in passing 
through the sphincter the posterior process would have become long'drawn-out as seen 
in the oblong capsules and as observed by me in process of formation in the nurse shark. 

Thus the structure of the posterior or last'formed end of the egg capsule of Gingly^ 
mostoma with its abortive tendril'like processes, affords a clue to and explanation of the 
formation not only of the curved finger-like process on the normal egg capsules of Chlamy- 
doselachus but also of the aberrant tendriliform ones of the atypical egg shells. 

EXTERNAL EMBRYONIC DEVELOPMENT 
OF CHLAMTDOSELACHL/S 

In earlier parts of this paper I have discussed the breeding habits and have described 
the reproductive organs of the frilled shark. These sections are based on Dean's scattered 
but invaluable notes and upon the scanty literature. These studies have considerably 
extended our knowledge of the reproductive activities of this shark and have laid a founda- 
tion for a study of its external embryonic development. For this there is at hand practical' 
ly nothing but the excellent drawings reproduced in the plates. In the almost complete 
absence of notes, all that can be done is to arrange the drawings in the order of develop- 
ment of the embryos and to describe these as accurately as possible, always comparing 



582 Bashford Dean Memorial Volume 

each stage with the one just preceding it and noting the progress in development of 
various organs. Here I must acknowledge my indebtedness to Scammon's excellent work 
published in 1911. 

EARLY DEVELOPMENT 

Since the total number of gravid females (26) obtained by Dean was not large, it is 
not surprising that he secured very few fertilized eggs in early stages of development. 
None of these has been preserved intact, nor do I find among Dean's materials any blasto- 
derms excised from the eggs and preserved in toto — either mounted or unmounted. My 
only information concerning this material has been derived from a few scattered notes, 
a small number of serial sections, and a few drawings — some in a more or less finished 
condition, others mere sketches. 

BLASTULAE 

Nishikawa (1898) is the only student of the frilled shark who has published any 
observations on eggs with early blastoderms. He states that "The blastoderm has a yel- 
lowish red color, as in other sharks. The earliest stage that I have been able to obtain 
was nearly circular in form and had a diameter of 1.3 mm". This is confirmed by my 
observations on the eggs of Ginglymostoma. The blastoderms were noted in 1912 as 
"yellow spots", always placed "asymmetrically on the egg, generally in the corners so to 
speak". In 1914 my notes read — "Blastoderms very small, even minute [unfortunately 
they were not measured], placed excentrically; in one lot of eggs from one female, 7 at 
one end, and one on one side of egg". These blastoderms in Gmglymostoma were so 
small that I found them only by their color. But when removed and placed under the 
microscope I could make out the cells. 

This colored spot seems to be a characteristic feature of the eggs of the Elasmo- 
branchii. Leydig (1852) was, so far as I know, the first to figure and describe the "orange- 
yellow spot" on an elasmobranch egg. On the egg of Pristiurus melanostomum, he found 
it at the end of the egg next to the rounded end of the capsule — i.e., that with short horns, 
the finished or older end of the egg shell of this oviparous fish. It measured c. 3.2 mm. in 
diameter. Balfour (1885, p. 222) also found this spot on the eggs of Pristiurus, on the ova 
of two species of Scyllium, and on the eggs of Raja sp. He states that these blastoderms 
were asymmetrically placed on the eggs of Pristiurus and Scyllium. Haswell (1897, p- 97) 
found the yellow spot at the broader (older) end of the egg shell of Heterodontus philippi 
of Australia. Dean shows this spot in his plates of the development of Heterodontus 
japonicus, which will illustrate Article VIII of this Volume Haswell, in his preliminary 
report on the development of Heterodoiitus philippi (1897), says "The blastoderm in its 
earUer stages, appears to the naked eye, as in other Elasmobranchs, as a circular reddish 
orange spot around which is a narrow light yellow band. When this orange spot has 
attained a diameter of about 2 mm. it assumes an oval shape". Then Haswell generaHzed 
about this spot thus — "There can be little doubt . . . that the 'orange spot', which forms 
such a striking feature of the egg of an Elasmobranch in its early stages, has been handed 



The Embryology of Chlamydoselachus 



583 



down with little change from Palaeozoic times". It is interesting to note the occurrence 
of this spot on the egg of that shark (Chlamydoselachus) to which systematists have as- 
signed the lowest rank among recent elasmobranchs. 

Nishikawa (1898) also had older blastoderms of Chlamydoselachus. He says ''The 
next stage was a blastula, with a distinct segmentation cavity, whose floor was bounded 
by what has been termed 'periblast' with fine granular yolk, and merocytes with vacuo- 
lated protoplasm, due perhaps to the dissolution of the contained oil drops, and many 
nuclei. One end of the blastula was thicker than the other, and is evidently the 'em- 
bryonic end' of Balfour, and the 'anterior end' of Riickert". Unfortunately Nishikawa 
does not figure the blastoderm on the yolk, nor the entire blastoderm either in surface or 
sectional view, nor does he give the size to which it has grown. It is greatly to be re- 
gretted that Nishikawa did so little with this precious early material. 



CU,t.o i ijij} (, 



Text-figure 22 
Diagrammatic sketches representing the 
cleavage pattern in four different types of 
vertebrate eggs: A, probably a hypo- 
thetical type ancestral to elasmobranchs; 
B, Chlamydoselachus; C, sharks; and D, 
a type reverting from the meroblastic to 
the holoblastic condition. 
Sketches by Bashford Dean. 




In Dean's notebook labelled Chlamtdoselachus there are in various places 
notes on eggs and embryos obtained during his two visits to Japan, or collected after 
each visit and sent to him in America. One paragraph is labelled "Material and 
List of Figures". Here I find "? Blastula", and on another page "Apr 10, 3 blastulae". 
He makes no specific mention of early blastulae — i.e., of early segmentation stages. 
Whether the alleged "blastulae" were in early or late stages is not known since Dean had 
no surface drawings made and since no preserved specimens can be found among his 
materials. If he had live eggs of Chlamydoselachus, perhaps he had the same trouble in 
finding early blastoderms that I had with live eggs of Ginglymostoma — i.e., that they 
were so small that he overlooked them, since these yellow spots would be obscured by the 
brownish-yellow capsules, as they were in Ginglymostoma by its thicker and darker 
capsules. This difficulty would be increased in preserved eggs since the "white" (a thin 
layer of glairy fluid) would be coagulated and some of the color of the germinal area would 
be destroyed by the preservative. 



584 Bashford Dean Memorial Volume 

However, on still another page of his notebook, Dean lists and briefly describes two 
■'Blastulae"' one of which he states measured "44 mm."" in diameter. These were "drawn'" 
(Figures 4, and 6, plate I), but, since in the original drawings they measure 44 and 48 mm. 
in diameter, it seems to me that they were surely not blastulae but gastrulae. As such 
they will be discussed later. 

As has been noted above. Dean went to Japan in 1900 particularly to get material 
for the embryology of the bull-head shark, Heterodontus. He obtained a large number of 
its eggs and embryos in various stages of development ^including segmentation). On the 
egg of this shark. Dean published a short paper (1901.2) entitled "Reminiscences of 
Holoblastic Cleavage in the Egg of . . . Heterodontus jap07iicus^\ When he unexpectedly 
began to get embryological material of Chlamydoselachus, the shark assigned by sys' 
tematists to the lowest position among the Elasmobranchii, Dean not unnaturally looked 
for similar reminiscences in its eggs. But, neither among his notes nor iinished drawings 
is there any indication that he obtained eggs in early cleavage stages. 

However, there is some slight evidence that Dean found something that made him 
suspect the possibility oi holoblastic cleavage in the eggs of Chlamydoselachus. Among 
his rough pencil sketches I iind a series of four diagrams comparing, in equatorial view, the 
cleavage patterns in eggs of four different types (Text-figure 22). The first (A) is moder- 
ately telolecithal but clearly holoblastic. This probably represents a hypothetical 
ancestral type. The second drawing (B) is labelled '^Chlaynydoselachus'\ It represents 
an egg vfith a large blastoderm (here defined as a mass of completely formed blastomeres) 
from which meridional furrows extend without interruption to an imaginary line drawn 
parallel to the equator and about 35'^ above it. If this line represents the margin of the 
crerminal area, as it appears to do, then the size of this area is considerably exaggerated. 
Some of the meridional lines continue further, but are more or less broken. A few reach 
nearly to the vegetal pole. The third drawing (C) is labelled "Sharks" — evidently 
meaning typical sharks. It represents an egg with a very small blastoderm and no radial 
cleavage furrows extending beyond the margin of the mass ot completely formed blasto- 
meres. The fourth drawing (D), Hke the first, is not labelled. It portrays an egg with 
a small blastoderm from which many meridional furrows extend to the equator and some 
beyond it. Those that extend into the lower hemisphere are represented by broken lines. 
A few of these broken lines reach nearly to the vegetal pole. This drawing evidently 
represents a type of cleavage reverting from the meroblastic to the holoblastic condition. 
The cleavage pattern of Chlamydoselachus, as portrayed in the second drawing, bears 
some resemblance to that of Cestracion as figured by Dean (1901.2). 

But are the lines crossing the margin of the germinal area really cleavage furrows? 
Among Dean"s records I find three pencil drawings representing in greater detail the 
circular grooves shov.-n in eggs C. B, and A (Figures 4, 5, and 6, plate I). These pencil 
drawings show very numerous fine lines crossing the groove in a radial direction. Because 
of the delicacy of these lines, these drawings are not suitable for- reproduction. I have 
found similar lines at the margins of the germinal area in the nearly mature ovarian eggs. 



The Embryology of Chlamydoselachus 



585 



Here, they are merely wrinkles in the very delicate vitelline membrane, probably due to 
shrinkage of the yolk mass during preservation in the mixture of formalin and alcohol. 
Unless examined with a lens, they might readily be mistaken for radial cleavage furrows. 
Some of the lines extend halfway to the equator of the egg. I find that Scammon (1911, 
Figs. 6 and 7, pi- I) shows similar radial wrinkles outside the blastoderm in early gastrula 
stages of Squalus acanthias. These I take to be identical with the very fine lines in 
Dean's sketches. 

The germinal area of the egg of Chlamydoselachus (as outlined by the circles in 
Figures 4, 5, and 6, plate I) is unusually large. The question arises, how much of this area 
is occupied by the mass of completely formed blastomeres in the late blastula or early 
gastrula stages. In his description of egg C, a "blastula". Dean states that it (the germinal 
area?) shows segmentation over its entire extent. This segmentation might include 
radial furrows extending beyond the limits of the blastoderm proper. The only drawing 
which gives a comprehensive picture of the cleavage pattern is the one in the phylogenetic 
series (Text'figure 22), an equatorial view. In this, the blastoderm proper is not sharply 
defined. It is evidently larger than that of most elasmobranchs, but decidedly smaller 
than the germinal area in which it lies. Nishikawa (1898) states that the earliest stage 
(a blastoderm) that he was able to obtain was nearly circular in form and had a diameter of 
1.3 mm. He mentions a later blastula, but does not give its size. 

It is therefore clear that the blastoderm, in the narrow sense, occupies only a small 
central portion of the germinal area. If, during cleavage, the radial furrows extend to, or 
beyond, the margin of the germinal area, they must be extraordiarily long. I have 
mentioned the presence, in late ovarian eggs, of fine parallel wrinkles in the vitelline mem^ 
brane, extending in a meridional direction and simulating cleavage furrows. My ob' 
servations were made on eggs in preservative for more than thirty years and I have had 
no opportunity to examine eggs in the blastula stage. I do not know of any other shark, 
save only Cestracion (Dean, 1901.2), in which the radial cleavage furrows extend so far 
from the region of completed blastomeres. 



Text-figure 23 
Section through the margin of the 
blastoderm of an egg of Chlamydo- 
selachus in a late blastula stage. 
This drawing probably represents 
the thicker end of the blastoderm in 
the same series used by Dean for the 
drawing reproduced in my Text' 
figure 24. 
After Nishikawa, 1898, p. 97. 




586 Bashford Dean Memorial Volume 

Nishikawa (I898j states that the yolk has a pinkish color. Presumably his obser- 
vations were made on fresh material. In our specimens, in various stages of development 
but not including blastula and gastrula stages, the yolk is usually pale yellov;? but occasion' 
ally some portions are very pale pink. That Dean had Hve eggs with pink yolk is evi- 
denced by his two drawings in color — Figures 49 and 50, plate V. 

Among Dean's few Chlaynydoselachus slides there are none of either whole mounts or 
sections of the blastula stage. However, there is evidence that, along with the other 
materials turned over to him by Nishikawa, there were sections of segmenting blasto- 
derms . In one paragraph of his notebook are a number of rough outline sketches of sections 
of blastulae labelled "Nishikawa's Slides Early''. Nishikawa (1898, p. 97) portrayed 
{Text-figure 23) without caption one edge of a segmenting blastoderm but never carried 
his studies further. Dean had these slides and drew a number of the sections. 

Among Dean's finished drawings are two, labelled Chlaynydoselachus, which show 
sections through an early cleavage stage and a late blastula stage respectively. These are 
reproduced as Text-figures 24 and 25. The magnifications are not given, and the slides 
from which the drawings were made have been lost. There is nothing very striking 
about the mode of development portrayed, since it is typically elasmobranch; but Dean 
in his only pubhcation f 1903 ) dealing with the development of Chlamydoselachus — a brief 
note — calls attention to "the great depth of the zone of yolk nuclei". This is well shown 









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Text-figure 24 
A section through the germinal area of a segmenting egg of ChlamvcJoseldchus in an early blastula 

stage, showing the blastoderm (at left, above) and the broad and deep zone of periblast. At the 
left, about four-fifths of the lateral extent of the periblast has been trimmed off from the original 

drawing; at the right, one-fourth. 
Drawing by Bashford Dean. 



The Emhryology of Chlamydoselachus 587 





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Text-figure 25 
Median sagittal section (?) through the blastoderm, subgerminal cavity, and periblast of an egg 
of Chlamydoselachus in a late blastula stage. The zone of periblast is evidently not shown 

in its entirety. 
Drawing by Bashford Dean. 

in the early cleavage stage represented by Text'figure 24. Judging from Text-figure 25, 
the late blastula also is remarkable for the depth and breadth of the zone of yolk nuclei, 
which is evidently shown incompletely. Two other drawings of a late blastula, not 
reproduced, are very similar to the one shown in Text'figure 25, and were probably 
made from the same set of sections. These drawings all studied together indicate that 
in these early stages the extent of the germinal area is greater than the portion of it which 
is cut up into blastomeres. 

It is my belief that all these drawings were made by Dean. On the boards on which 
they are mounted are notes in Dean's handwriting. The minute details in which the 
drawings abound are executed in Dean's characteristic style — according to his former 
students to whose attention they have been called. 

The internal structure of the late blastula described by Nishikawa (1898, pp. 96-97) 
is evidently similar to the one studied by Dean and portrayed in my Text'figure 25. 
Indeed Dean's drawing was probably made from Nishikawa's blastoderm and from 
a section near the one shown in Text'figure 23. Nishikawa's description is as follows: 

The next stage was a blastula, with a distinct segmentation cavity, whose floor was 
bounded by what has been termed "periblast" with finely granular yolk, and merocytes, with 
vacuolated cytoplasm, due perhaps to the dissolution of the contained oil drops, and many 
nuclei. One end of the blastula was thicker than the other, and is evidently the "embryonic 
end" of Balfour, and the "anterior end" of Riickert. On the surface of the blastoderm the cells 
are arranged epithelially. Most cells of the blastoderm are rich in yolk granules, but at the 
bottom of the blastoderm they have only a coarsely granular cytoplasm. The blastodermic 
cells are added from the periphery by the merocytes with fine yolk granules, as may be seen 
from cut 1 [Text-figure 23 herein] which has been composed from two consecutive sections. 
I have also found a cell simply resting on the floor of the segmentation cavity; but I axnnot 
say for certain whether it originated from the periblast or from the blastoderm. 




588 Bashford Dean Memorial Volume 

Dean's drawing (Text-figure 25) is raade from a section cut parallel to the long axis 
of the future embryo. I wish to call attention particularly to the slight difference in the 
portrayal of the thicker margin by Dean and by Nishikawa. Dean represents the limit of 
the thickened end by a smoothly curved unbroken nearly vertical line separating the 
blastomeres from the region of pericytes. Nishikawa, whose drawing was made with 
a higher magnification, shows one of the embryonic cells incompletely cut off from the 
yolk mass (Text-figure 23). If this cell had gone on to complete separation, then 
the margins of the two figures would have been almost identical. 

GASTRULAE 

Earliest of all, Nishikawa collected but failed to figure and describe a gastrula of the 
frilled shark. Of his one egg he states — "I have also obtained a gastrula, which was oval 
in form and 3 mm. in length. I have nothing special to add about it as it was like the 
gastrula of any other shark". But was it? There is so much variability about Chlamydo- 

Text-figure 26 
Sketches from Dean's notebook. A and B — /^"!;^=^ ,^— ^^ 

"Gastrulae 2 stages;" C one of "3 oblong eggs." f C ^J\ /Q[j^ 
For "2 drawn" — no gastrulae shown — see Fig- V y' 'v^ / 

ures 2 and 3, plate I. C was never "drawn," b 

though labelled "probably gastrula." 
Sketches by Bashford Dean. 

selachus that one wishes for surface views and sections. To me this seemed very small for 
a gastrula and at first I was inclined to think that Nishikawa was in error, that no shark 
gastrula could be so small as 3 mm. in greatest diameter. But on looking up the literature 
I found that Ziegler (1902, p. 117) figures a gastrula of Torpedo 2 mm. long. And Scammon 
(1911) portrays gastrulae of Squalus acanthias 4.2 and 4.4 mm. long. Thus both Ziegler 
and Scammon give presumptive evidence that Nishikawa was correct. 

On the page of Dean's notebook headed "Material and List of Figures", one finds this 
notation, "Gastrulae 2 stages", followed by two pencil sketches showing eggs with 
relatively large circles on them like those in Figures 4, 5, and 6, plate I. I have thought it 
well to reproduce these pencil sketches as Text-figure 26. Then on the page of the note- 
book on which Dean described the "3 oblong eggs", referred to later, there is a pencil 
sketch of an oblong egg with an incomplete ring placed asymmetrically (Text-figure 26), 
and having at the opposite end a tendril-bearing process. This egg is labelled "stage 
early, probably gastrula". Two of these "oblong eggs" were drawn and are identified 
and reproduced as Figures 2 and 3, plate I. Of the oblong egg with the gastrula, un- 
fortunately no finished drawing was ever made. 

On still another page of the notebook referred to is the heading, "Earlier stages, 3 
eggs C B. & A." Then follows brief descriptions of two which he thought were blastulae 
and of a third which he believed to be a gastrula. Here follow his descriptions: 



The Embryology of Chlaynydoselachus 589 

[Egg] C [Figure 4, plate I]. Blastula shown in drawing (44. mm.) round. Shows segtn. 
over entire surface [of germinal area ?] — margin not good but at several places good transition 
from marginal blastomeres into central bl'ms. Not possible to trace furrows far down side of 

egg- 

[Egg] B [Figure 5, plate I]. 81. somewhat later than C, [germinal area 38 x 39 mm.]. 
Margl. blast, fine — surface blast, smaller and less conspicuous. At several points of marg. 
there are certain irregular folds of which none are (surely) gastrulation erscheinungen [mani- 
festations]. 

[Egg] A [Figure 6, plate I]. Gastrula 44 x 48 mm. — drawn. No surface markings — 
except at margins as shn. in fig. [a pencil sketch in outline sectional view accompanies this 
note] — these continued sometimes over the marg. of yolk. 

This is what Dean wrote and what is portrayed (half the original size) in Figures 4, 
5, and 6, plate I. Egg A (the circle measuring 44 x 48 mm.). Dean thought to be a gastrula. 
Eggs B (circle 38 x 39 mm.) and C (circle, 44 x 44 mm.), he calls blastulae. If A, having the 
largest circle, is a gastrula, then, for all that I can see from the evidence at hand, B and C 
are not blastulae but gastrulae. Just here note that in C the germinal area (delimited by 
a shallow circular groove) is asymmetrically placed on the yolk. This asymmetry is 
like that noted for the third egg shown in Text'figure 26. Furthermore, it may be well 
to recall here that this is what I have found to be the general rule in the large eggs of 
G inglymostoma. 

Each egg, as represented in Figures 4, 5, and 6, plate I, has the germinal area marked 
off by a faint ring apparently representing a shallow circular groove. A similar groove 
bounds the margin of the germinal area in the preserved, half mature ovarian eggs examined 
and described earlier in this article. It is quite likely that this groove, if present in the 
living egg, would persist through cleavage and gastrula stages; or, if it is a fixation artifact, 
the same conditions would produce it in these stages. Balfour (1885, p. 222) found such 
grooves in living and sectioned elasmobranch eggs studied by him. 

In these drawings (Figures 4, 5, and 6, plate I), the presence of the germinal area is 
indicated by faint circles only slightly darker than the remainder of the upper surfaces of 
the eggs. Indeed in eggs B and C, on one side the circle, as drawn, is so faint that it 
disappears into the general upper surface of each egg (especially B). Take away the 
circles and there would be nothing to indicate any germinal area. For another reason it 
must be noted here that one side of the ring is drawn more heavily shaded than the other. 
Balfour (1885, p. 225) noted this on his preserved material — "In sections of the germinal 
disc [of Pristiurus], the groove which separates it from the yolk is well marked on one 
side, but hardly visible at the other extremity of the section". What then did Dean's 
artist draw and how did he see anything to draw? If he drew preserved eggs, as is most 
likely, he drew the thickened edges of the blastoderms in early gastrula stages, more 
thickened on one edge than the other. This Balfour found as cited above and shows in 
a cross section of the blastoderm. These dark parts of the circles (Figures 4, 5, 6, plate I), 
I take to be the edges of the blastoderms wherein the embryos will be found later. In 
fixed eggs the thickened edges of the late blastoderms would show up more opaque than 
the inner and thinner regions. 



590 Bashford Dean Memorial Volume 

But suppose that the artist had before him living eggs, would not the whole germinal 
area have the same color? The answer to this question is I believe to be found in my 
observations of living gastrula stages in the large thick-shelled intra-oviducal eggs of the 
nurse shark, Ginglymo stoma cirratum. On some eggs examined on July 21, 1912, I found 
an orange'colored ring enclosing an area which covered one-fourth to one-third of the 
upper (or visible) side of the egg. This object was more plainly seen by cutting a window 
in the capsule over this colored ring and removing some of the glairy liquid surrounding 
the egg. Then, when a little sublimate-acetic was dropped on it, the whole blastoderm 
became visible with the beginning embryo in it. This was again seen on July 22, on an 
egg from another female. From another egg I got a "Blastoderm about the size of a silver 
dollar", and on another egg "Large blastoderm partly on top and partly on side of yolk". 
Another had "Blastoderm covering a little more than half the upper side of yolk, with one 
edge dipping over the side". On an egg examined on July 23, the "edge of the blastoderm 
was a rusty orange; embryo transparent and colorless, only visible when in motion". In 
the plates of the next article of this volume — that on the embryology of Heterodontus — 
will be seen the same orange-colored ring of a blastodisc embracing an area covering one- 
fourth to the whole of the upper visible surface of the 55-mm. egg with an embryo so 
small and transparent as to be almost invisible. 

Thus the early gastrula stages of eggs of Chlamydoselachus, eggs alive or dead, were 
presumably seen as drawn in Figures 4, 5, and 6, plate I. It drawn alive at Misaki then the 
artist saw and drew the colored edges of the late blastodiscs. If the eggs had been "fixed", 
then it must be concluded that they were in early gastrula stages before embryos had been 
formed, but that as Balfour puts it "The embryonic rim is represented by a darker shading 
at the edge". Lastly it should be noted that these blastoderms in the gastrula (?) stages 
shown in the figure cited cover a substantial part of the upper surface of the eggs. 

Finally, it must be said that if the eggs shown in Text-figure 26 are in the gastrula 
stage as Dean expressly states, then the three eggs portrayed in greater size and detail in 
Figures 4, 5, and 6, plate I, are also presumably in the gastrula stage. To me the sketches 
all show eggs in the same stage. Nothing in drawings or text diiferentiates them. 

As noted at the beginning of this section, Nishikawa (1898) states that he obtained 
an early gastrula. This was sectioned and the sections were in 1901 or 1902 turned over 
to Dean. Among Dean's sHdes in my possession are five of serial sections of an early 
gastrula of Chlamydoselachus. I presume that these were sections prepared by Nishikawa 
and presented to Dean. In Dean's notebook are outline sketches made from these sections. 
The plane of the sections is oblique to the axis of the forming embryo and consequently 
these sections are not very favorable for study. In general the mode of development is 
like that found in other elasmobranchs. 

LATER DEVELOPMENT 

In this study of the frilled shark, my readers and I have now come to that part which 
perhaps holds the most interest since it is the most concrete — the study of the embry- 



The Embryology of Chlamydoselachus 591 

ology as portrayed in Dean's drawings. This perforce must be a study of the external 
development of the embryos from the smallest figured (11.5 mm. — Figure 15, plate II) to 
the largest (390 mm.) — shown in its life colors in Figure 49, plate V. 

It does not lie within the scope of this article, as indicated by its title, to attempt any 
consideration of the internal development. To be sure, in my account of the blastula and 
gastrula stages I have included the meager information available concerning their internal 
structure. But Dean left neither notes nor drawings dealing with the early formation 
of the embryo and the development of organs. I have found a few serial sections of 
advanced embryos, but these are in poor condition. Therefore any consideration of the 
internal development would necessarily be limited to a review of previous contributions. 
In his article on the anatomy of Chlamydoselachus, Smith (1937) has included references to 
the scanty literature concerned with the development of organs, and has reviewed certain 
topics. It will suffice here to indicate briefly, for the convenience of future investigators, 
the contents of the few publications dealing with the organogeny of Chlamydoselachus. 

RESUME OF RESEARCHES ON THE INTERNAL DEVELOPMENT 

Rose (1895) studied the teeth of a 340'mm. embryo. These teeth were not all in 
the same stage of development; therefore they afforded a graded series. Rose's obser^ 
vations indicate that the three large cusps of a typical tooth develop from separate an' 
lagen; teeth are formed by the union of simple denticles homologous with placoid scales. 
None of the teeth studied by Rose had attained its final form. 

Nishikawa (1898) figured four transverse sections through the head of a 32'mm. 
embryo in the region of Rathke's and Seessel's pouches; also a section through the ''grow 
ing point" of a lateral line of the same embryo. He states that throughout the greater 
part of the lateral line there is a lumen, which is slit-shaped in transverse sections, but 
at the posterior extremity it is absent. In the anterior part, where the lateral nerve is in 
close contact with the anlage of the lateral line, the lumen opens to the exterior at several 
points. In this connection it should be stated that, as noted by various authors (Smith, 
1937), in the adult the lateral line is open throughout almost its entire length. 

Dean (1903) published a preliminary report on the embryology of Chlamydoselachus. 
The date of this paper comes after Dean's first visit to Japan, but before his second visit. 
Since this article is very brief, and constitutes Dean's only publication on the embryology 
of Chlamydoselachus, it is here quoted in full: 

In view of the archaic features in the adult, he (Dean] noted as significant in the de- 
velopment of this form the great depth of the zone of yolk nuclei, the absence of external gills, 
the more nearly terminal position of the anus, the relatively smaller size of the head, the 
enormous spiracular cleft and the almost typically fin-fold type of limb. Chlamydoselachus 
has specialized in the line of producing large eggs, the largest indeed among recent animals, 
ostrich hardly excepted; that it was, however, until recently an egg-depositing shark is ap- 
parent from the character of the horn-like capsule (with rudimentary tendriliform processes) 
which the egg still retains. 

One may query Dean's statement concerning the absence of external gills. In Dean's 
own drawings, gill-filaments are shown projecting beyond the gill-flaps throughout the 



592 Bashford Dean Memorial Volume 

advanced stages of embryonic development. It is probable that what Dean meant is that 
these external gill-filaments are merely temporary modifications of the gill-filaments 
that persist in the adult; also that they are not so long as they are in other embryonic 
sharks. This matter of external gills in both embryos and adults of Chlamydoselachus will 
be taken up fully in a later section of this paper. Hence it need not detain us here. 

In his earlier article on the origin of vertebrate limbs, Osburn (1906) briefly mentions 
some features in the development of the skeleton of Chlamydoselachus. His later article 
(1907) on the same subject includes a more detailed consideration of the fin skeletons and 
pelvis, accompanied by some figures of these structures in a 225-mm. embryo. 

Brohmer ( 190S ) studied the excretory system ot a 25-mm. young embryo ot Chlamydo- 
selachus. In the stage described, the pronephros is vestigial and the mesonephros is in an 
early stage of development. 

Ziegler (1908i studied two embryos in the same stage, each 25-mm. long. His 
paper deals wnth the organogeny, particularly in the head region, with special attention to 
the "head cavities."" These are cavities which, in elasmobranch embryos, occur in con- 
nection with mesodermal structures called "head somites," and are regarded as detached 
portions of the primitive coelomic cavity. For a further discussion see Smith, 1937, pp. 
391-392. Ziegler w^s unable to find the anterior head cavity discovered by Piatt in 1891 
in certain other selachians, although he did find an anomalous cavity which he beHeved to 
be constricted off from the mandibular head cavity. Ziegler described also the infundib- 
ulum, Rathke's pouch, and the cranial nerves (reconstructed by his pupil, Brohmer). 

Brohmer (1909 • described in more detail the head somites in a 25-mm. embryo of 
Chlamydoselachus. Like Ziegler, he w^as unable to find the anterior head cavity described 
by Piatt. Brohmer and Ziegler agree that there is but a single premandibular head 
cavity in Chlamydoselachus. Brohmer"s contribution, Hke Ziegler's, includes a description 
of the cranial nerves ot a 25-mm. embryo. 

DESCRIPTIONS OF EMBRYOS FIGURED 

On that page of Dean's notebook labelled "Material & List of Figures" is a Hst of 
embryos to be drawn. This list has been a partial guide tor this section of the present 
article — partial only, because not all the embryos there listed were drawn, or if drawn 
some of the figures have in the long years since been lost. Then again the Hst is only 
partial because I find in the plates a number of figures not included in the list. Almost 
every draunng has noted on it the length of the embryo drawn, but some do not. These 
latter figures are rather ditficult to locate in the series. Again other drawings with. 
lengths indicated are not on the Hst. In addition to Dean's dra wrings of eggs and embryos, 
there have been introduced in their proper places, but as text-figures, a few illustrations of 
embryos described in external aspect by other authors. These fill in gaps in Dean's 
series and enable me better to show the progressive development of the external form 
of the embr\'os. 

Owdng to the complete absence of descriptive notes and the almost entire absence of 
material, the stages of development must be described as they are shown in the individual 



The Embryology of Chlamydoselachus 593 

drawings. Each figure will be compared point by point with the next younger in order to 
show the relative progress in development. Then so far as possible, comparisons will be 
made with embryos of Squalus acanthias of about similar si2;e as portrayed so well in 
Scammon's "Normal Plates" (1911). 

An Embryo of 11.5 Millimeters 

This is the smallest embryo listed and figured. It and two other small embryos 
(15.5 and 20 mm.) were taken "1905 Early January." Presumably all came from the same 
mother. If so, this shows that the embryos and eggs in a given uterus may be of different 
but closely related ages. This is to be expected since the eggs presumably ripen one at 
a time and are discharged from the ovary singly; certainly they pass one at a time into the 
oviducal funnel, are fertilized and encapsuled as they pass down into the uterus. FertiH' 
nation of these shelled eggs must take place before the capsule is formed. In Ginglymostoma 
I have taken segmenting eggs from the oviduct above the shell gland. 

This embryo, seen in right lateral aspect, is labelled in the original drawing "Emb. 
C 11. 5 mm.", and is shown in Figures 15 and 16, plate II. Figure 15 bears the notation 
'■'■X10+", and in the original drawing it measures 121 mm. Figure 16 is drawn to larger 
scale. In length this embryo corresponds to Scammon's (1911) Fig. 24 of an 11.5'mm. 
Squalus acanthias shown in his pi. II. In development the two embryos are in about the 
same stage. As my Figure 15, plate II, shows, the frilled-shark embryo is attached to 
the large yolk sac by a short yolk stalk. In the original drawing this has an antero- 
posterior diameter of 10 mm. but in life of about 1 mm., which is the measurement for the 
cord of the 11.5-mm. Squalus. This is the "umbilical cord" of Nishikawa (1898). How- 
ever, this is not an umbilical cord but merely a yolk stalk. 

On the dorsum of this frilled-shark embryo (Figure 15, plate II), there is a convexity 
over the gill-arch region, a concavity over and behind the vertical of the yolk stalk, 
a sHght convexity behind this, and a marked downward bend of the tail. The forebrain 
and midbrain make an angle of approximately 90° with the main axis of the body. The 
forebrain looks downward. The midbrain is delimited from the forebrain by a groove and 
superficially is sharply marked off from the hindbrain. The nasal groove, having its 
greatest invagination in front, is placed just below the eye. The optic cup is circular and 
without trace of optic fissure. The lens is prominent and circular in outline. The mouth 
is widely distended. The gill-plate is prominent, showing seven branchial grooves — the 
first indistinctly. Not all the grooves appearing in this region are branchial grooves. The 
second branchial groove appears to be forked, but the anterior limb is not a branchial 
groove as may be seen by comparing this drawing with Figure 16 where the gill-clefts 
are shown in larger scale. 

The pectoral-fin rudiment is well-outlined for this early stage, and extends backward 
and downward, reaching some distance back of the hinder edge of the yolk cord. The 
cloacal elevation is quite prominent and in front of it is a sHght swelling which I take to be 
the anlage of the pelvic fin. The tail ends in a point bent sharply downward. The 
V-shaped myomeres show faintly in the upper half of the trunk. 



594 Bashford Dean Ivlemorial Volume 

This same specimen was stained, cleared and drawn somewhat enlarged (to l6l 
mm. — X 14), apparently in order that the neuromeres and myomeres might be studied and 
counted. In this Figure 16, plate II, there is plainly seen between fore-and midbrain 
a small rounded body which I take to be the rudiment of the epiphysis. The neuromeres 
are divided into two sets of three each by a very short neuromere (?) which I do not under- 
stand. The auditory vesicle is prominent, standing over the bar between the second and 
third gill-clefts. From this vesicle to the end of the tail are 102 myomeres. This was 
noted in pencil on the original drawing. Plainly visible are six gill-clefts, the seventh 
being very faint. The heart is prominent — as is a large blood vessel, the vitelline artery, 
branching off from the dorsal aorta. The cloacal eminence is very prominent, and in 
front of it is a thickening which is presumably the rudiment of the pelvic fin. The fine 
line bounding the entire figure represents the superficial ectoderm. 

An Embryo 15.5 mm. in Length 

The next drawing called for in Dean's ''Material & List of Figures" portrays an 
embryo of this size in lateral aspect (Figure 17, plate II). This drawing is labelled "Emb. 
B 15.5 mm." on the drawing. This embryo agrees in length and in development very 
closely with Scammon's stage No. 26 (his pi. II), a 15-mm. Squalus. Dean's figure is 
marked "X10+" but in the original drawing it measures 177 rnm. From the head, the 
back line slopes down to a point about over the yolk-stalk junction. Thence it runs back- 
ward almost straight to a point over the cloaca, from which region the tail bends down 
sharply. The forebrain together with the olfactory rudiment is prominent and is slightly 
upturned. The midbrain is large and bulges forward strongly. Thus the profile of the 
head of this embryo has a striking resemblance to that of a bulldog — though the parts do 
not correspond. The epiphysis is indicated by a slight swelling above the forebrain and 
in front of the eye. The optic cup and lens show some enlargement. The mouth still 
gapes widely. 

The prominent bulge in front of the yolk is due to the presence of the heart. The 
pectoral fin is larger than that of the 11.5-mm. embryo. On the ventral surface of the 
body is a ridge, probably an evidence of the beginning of the gut. The cloacal swelling 
is very marked. In front of this is a thickening, presumably the anlage of the pelvic fin. 
Above the cloacal eminence, the straight dorsum slants downward as the tail. This ends 
in a curious upward hook Hke that found on the caudal extremity of a Boston terrier 
whose tail has been bobbed and the point bent upward. 

In this 15.5-mm. Chlamydoselachus (Figure 17, plate II) the gill-arch region is very 
prominent. Some of the gill-arches appear crumpled. This crumpling is, I judge, an 
artifact due to shrinkage. In the dorsal portion of the branchial region, there appear 
three ridges that resemble incomplete gill-arches. Of these, the two anterior ones are 
probably not gill-arches but parts of the cranium, while the third is a portion of the first 
visceral arch. One notable difference between the 15.5-mm. embryonic Chlamydoseh 
achus (Figure 15, plate II) and the 15-mm. embryonic Squalus, shown in Scammon's 
Fig. 26, pi. II, is that the little Squalus has at least one gill-filament projecting from each 
first, second and third sUt, whereas these are entirely lacking in our embryo. 



The Embryology of Chlamydoselachus 595 

An Embryo Measuring 20 Millimeters 

The next drawing called for on the "List" is of this size. It bears the notation ''Emb. 
A 20 mm." The original drawing is marked xlO+ but it measures 222 mm. The 
drawing represents the embryo (in lateral view) as pulling forward on the yolk sac 
(Figure 18, plate II). There is fair correspondence between this embryonic Chlamydo' 
selachus and Scammon's 20.6'mm. Squalus (his Fig. 28, pi. III). Compared with the 15.5' 
mm. embryonic frilled shark, the forebrain of the 20'mm. specimen is more prominent, the 
midbrain has become swollen laterally and is separated from the hindbrain by a con' 
striction of its lateral and (morphologically) ventral surface. The dorsal line of this 
embryo, in contrast with the younger ones, runs almost straight to what is evidently the 
anlage of the dorsal fin — located just behind the vertical through the cloaca. The tail 
bends down sharply without, however, any upturned point as in the preceding stage. 
It is more like that in the 11.5'mm. specimen (Figure 15, plate II). 

Returning to the head region, attention is called to the changed olfactory anlage and 
to the much enlarged eye. The mouth is somewhat less widely open than in the preceding 
stage. The gill-arch region is more prominent than ever. As in the preceding stage, some 
of the arches are in their lower halves sharply angled forward. There are eight distinct 
gill-arches with seven gill-clefts. The first visceral (the mandibular) arch forms the upper 
and lower jaws (palatoquadrate and Meckel's cartilage respectively). In the stage shown, 
with wide-open mouth, the jaws are open at an angle of about 90°. The ridge immediately 
behind the eye is probably not a branchial arch but a part of the cranium; likewise the 
two short ridges dorsal to the one just mentioned are presumably also eminences of 
the cranium. 

The arch immediately behind the mandibular arch is the second visceral or the hyoid 
arch. Its dorsal half, lying immediately behind the protuberance of the skull previously 
mentioned, will give rise to the hyomandibular cartilage. This, in the adult, articulates 
with Meckel's cartilage at the angle of the jaw, thus helping to support the jaw. The 
first branchial cleft appears to be closed ventrally. Its dorsal portion, lying immediately in 
front of the dorsal segment of the hyoid arch, will become the spiracle. For the position 
and relations of the spiracular canal in the adult, see Smith (1937, Text-figs. 82 and 84). 
The other visceral arches (the gill-arches of the adult) are quite regular in form save for 
the crumpling already mentioned. 

The bulge on the ventral surface of the embryo, immediately in front of the yolk 
stalk, is caused by the heart. The pectoral fin has become much broader and looks to be 
almost functional in a rudimentary fashion. The pelvic fin now shows clearly. The 
wart-like cloacal eminence is but little larger than that shown in the 15.5-mm. embryo. 
In front of it, the pelvic fin is clearly outlined. Back of it is the rudiment of the anal fin. 
The tail ends in a point sharply hooked downward. The somites are far advanced and now 
have the perfected zig zag shape faintly foreshadowed in the preceding stage — 15.5 mm. 
(Figure 17, plate II). 

Scammon's Fig. 28, pi. II, of his 20.6-mm. Squalus is further developed than Dean's 
20-mm. Chlamydoselachus. The dogfish has all the fins, the pectoral being better de- 



596 Bashford Dean Memorial Volume 

veloped. But most noticeable in the dogfish is a profusion of long gill'filaments coming 
out of slits 1-2-3, while shorter ones are to be seen in the spiracular cleft and the fifth 
slit. There is no indication of such filaments in the 20'mm. Chlamydoselachus, although 
the slits have apparently broken through. 

Two 25'MM. Specimens — Heads Only — Described by Ziegler and Brohmer 

In 1908, Paul von Rautenfeld brought to Germany from Japan a collection of 2;oologi' 
cal material, among which were three embryos of the frilled shark — two of 25 mm. 
without yolk sacs and one of 70 mm. with a yolk sac. These presently came to H. E. 
Ziegler for study. He figured and described (1908) one 25'mm. head in both lateral and 
ventral aspect. Then he cut sections of this and studied them as noted above. The 
other 25--mm. embryo and the 70'mm. specimen on its yolk sac, briefly referred to else' 
where, were turned over to his student, Brohmer. The latter deposited the larger embryo 
in the museum at Jena, but figured and described the head of the 25'mm specimen in 
dorsal aspect (1909). Then he sectioned it and studied it in comparison with Hke em- 
bryonic material from other sharks.. 

Dean's embryos above were all portrayed in lateral aspect only. The head of 
Ziegler's embryo was figured in lateral and ventral views and Brohmer 's of the same size 
was portrayed in dorsal view. Since nearly all Dean's embryos figured are shown in all 
three aspects dorsal, lateral and ventral — these figures will be studied in that order. For 
this reason it has seemed well to begin consideration of the 25'mm. specimens by properly 
combining and studying the figures of Brohmer and Ziegler. 

Head in Dorsal Aspect. — First let us consider Brohmer's figure (1909) of the head of 
the 25-mm. embryo seen from above reproduced herein as Text'figure 27a. Here the 
head seems to be pointed. The eyes are prominent, as are the spiracles. The gill-arches 
stand out widely — the first at about right angles to the body, the other five being directed 
obliquely backward. All have very short external gill-filaments. The pectoral fins show 
the beginnings of the basal cartilages. The most striking thing shown in this embryo 
is the transparent roof of the hindbrain — through which can be seen the floor with 
its median groove. 

Ziegler (1908) figured the head of one of the 25-mm. embryos in both lateral and 
ventral aspects (my Text-figure 27). I will first give Ziegler 's descriptions of his figures, 
and will then call attention to particular points. Ziegler wrote as follows : 

Der weit geofFnete Mund ist jederseits von dem Kieferbogen begren2;t. Die Ober- 
kieferwiilste sind gross und lassen vorn median zwischen sich noch eine Liicke, an welche sich 
eine kleine mediane Rinne an der Unterseite des Vorderkopfes anschliesst. Auffallend ist die 
Grosse des Spritzloches und die ausserordentliche Weite der ersten echten Kiemenspalte. 
Die folgenden Kiemenspalten sind schmal und unter einander nicht viel verschieden. Bekannt- 
lich gleicht Chlamydoselachus insofern dem Hexanchus, als 6 Kiemenspalten auf das Spritz- 
loch folgen. 

Hinter der letzten Kiemenspalte liegt noch ein kleiner Wulst, welcher die Kiemenregion 
abschliesst; an Fig. 1 wird er durch die letzte Kiemenplatte verdeckt. Dann folgt die vorder 
Extremitat, sowie ventral der Nabelstrang. 



The Embryology of Chlamydoselachus 



597 




Text-figure 27 

Heads in three aspects (dorsal, lateral, and ventral) of two 25'mm. 

embryos of Chlamydoselachus. 

A after Brohmer, 1909, Text-fig. 2; B and C after Ziegler, 1908, Text-figs. 1 and 2. 



Head in Lateral View. — In addition to Ziegler's brief general description of the head 
of his 25-mm. embryo, comparison of it in this aspect (Text-figure 27b) should be made 
with the head of the 20-mm. specimen in lateral view (Figure 18, plate II). The head of 
the 25-mm. embryo is filled out and rounded with the forebrain pointing downward. 
The mouth still gapes widely. Brohmer (1909, Text-fig. 3) had a drawing made of his 
25-mm. embryo in lateral aspect. This in its portrayal of the anterior visceral arches 
differs somewhat from Ziegler's figure of his specimen of the same size. It is difficult to 
understand the mode of development of the anterior visceral arches as portrayed in lateral 
view by these two investigators. Possibly their embryos were abnormal. However, in 
some ways they are related to what we shall find in Nishikawa's 32-mm. specimen. 

In Ventral Aspect. — There is no like view of the head of the 20-mm. embryo 
available for comparison. This is our first description of the head of an embryonic 
Chlamydoselachus seen from below (Text-figure 27c). The snout-like forebrain stands 
out against the background of the larger rounded midbrain. The eyes and nasal capsules 
show faintly. The opening of the expanded mouth is about as broad as long. The halves 
of both upper and lower jaws are separated by fossae — the upper fossa is the wider. 
The gill-arches are distended, and short filaments are seen on their hinder sides. The 
pectoral-fin fundament shows traces of the basal cartilages. The yolk cord is large in 
comparison with the size, of the body. 



598 Bashford Dean Memorial Volume 

Scammon's drawing of his 24.7'nim. Squalus is in full-length lateral aspect only. 
When Ziegler's drawing of the lateral head of his 25'mm. specimen is compared with the 
head only of Scammon's Squalus, it is at once seen that the latter is more developed. Its 
gill'arches are more finished and are filled with a profusion of long external filaments. The 
spiracle is closed off and is also filled with filaments. Its pectoral fin, however, is in about 
the same stage of development as that of Chlamydoselachus. 

Nishikawa's 32-mm. Embryo — Head Only 

The next stage called for in Dean's "List of Figures" for the development of Chlamy- 
doselachus, is noted thus "Emb. of mm. 32 — general view 2 figs.; head 3 pos'ns." No 
"general view 2 figs." can be found, but there are views of the head only, in dorsal, 
lateral, and ventral positions. These are reproduced as Figures 19, 20 and 21, plate II. 
But before describing them, I wish to set forth here a very interesting matter. Earlier in 
this article, I have expressed the belief that all Nishikawa's materials were turned over to 
Dean while he was working at Misaki and Tokyo. Nishikawa's brief article had been 
published in 1898 and in it he had figured the head of a 32'mm. embryo (his smallest 
specimen) in dorsal, lateral and ventral aspects. Dean had no specimens of his own be- 
tween 20 and 34 mm. To lessen this gap in Dean's series of drawings showing the pro- 
gressive development of the frilled shark, the figures of the head of Nishikawa's 32-mm. 
embryo were redrawn at the University (by Kuwabara ?) for reproduction by lithog- 
raphy. I have compared the two sets of three figures minutely and can affirm that they 
are identical. 

But the reader may be wondering why Dean had Nishikawa's figures copied instead 
of having drawings made de novo, and why no full-length drawings are available as called 
for. The answer is to be found in Nishikawa's article (1898, pp. 98-99) wherein he 
figures diagrammatically and describes sections of the head of this embryo — it had been 
cut into sections in 1896. 

Head in Dorsal Aspect. — The head of the 32-mm. embryo is seen from above in 
Figure 19, plate II. This head must be contrasted with that of the 25-mm. embryo por- 
trayed in Text-figure 27a. The head in each figure is pointed. The curious outline on 
the head in Figure 19, plate II, is probably caused by the shrinking of the skin on the 
embryonic skull. In the 25-nmi. head as drawn, the tissues are transparent and allow one 
to see the floor of the brain cavity. The 32-mm. head has the openings of the endolym- 
phatic ducts which are lacking in the 25-mm. head. The former has the large spiracles 
seemingly placed higher on the head than those of the younger embryo. There are short 
filaments on both sides of the widely spread gill-arches of each head. The rudimentary 
pectoral fins are about in like stages of development in each embryo. On the whole the 
head of the 32-mm. specimen looks older and more perfected. 

Head in Lateral View. — It is to be regretted that no full-length drawing of the 32- 
mm. embryo in lateral aspect is available for comparison with that of the 20-mm. specimen 
(Figure 18, plate II). One wishes to see what differentiation has taken place in body and 
tail as well as in the head. However, Figure 20, plate II, shows some interesting struc- 



The Emhryology of Chlamydoselachus 599 

tures absent in the head of the 20'mm. specimen but found in the beginning stage in the 
25'mm. embryo as seen in Text-figure 27b. 

As Figure 20, plate II, shows, this 32'mm. specimen differs markedly in the head 
region from the 20'mm. embryo portrayed in Figure 18. The smoothly rounded fore- and 
midbrain vesicles are separated from each other by a cleft. The olfactory organ is well 
established, as is the eye which on the ventral side shows a trace of the optic cleft. The 
mouth is still widely open but far less so than in the 20'mm. embryo (Figure 18, plate II). 
The seven pairs of visceral clefts are open to the exterior and to the pharyngeal cavity, 
the second being the largest and the seventh (the sixth branchial cleft) the smallest. The 
first, the spiracular cleft, is almost closed off ventrally. 

Further comparison of the 20' and 32'mm. specimens shows that the crumpled gill' 
slits of the 20'mm. embryo are in the 32'mm. head replaced by the more normal straight 
ones. All the clefts (including the spiracular) have external filaments in the 32'mm. head. 
It is interesting to note that the ridge immediately posterior to the eye in the 20'mm. 
specimen together with the hinder region of the upper jaw have here developed into a very 
prominent cheek'like process. The growth of this process apparently assists in the for' 
mation of the hinder part of the upper jaw and of the cheek region while at the same time 
superficially closing off the spiracle on its ventral side. It also assists in bringing the 
posterior end of the upper jaw in closer proximity to the hyomandibular element of 
the hyoid arch. 

Let us now contrast the lateral view of the 25'mm. head shown in Text'figure 27b 
with that of the 32'mm. specimen portrayed in Figure 20, plate II. The 25'mm. head is 
more smoothly rounded. The eye has a fissure at its hinder edge whereas the other head 
has it in a ventral position. The mouth of the younger fish is more widely open. But 
most unusual of all are the curious structures around the spiracular opening. These I do 
not understand — possibly this specimen was abnormal. In any case these objects seem to 
be forerunners of the cheek pieces of the 32'mm. specimen shown so prominently in 
Figure 20, plate II. There is nothing unusual about the gill-arches and clefts of the 
25'mm. fish save that the first is more widely open than that of the older specimen. 
Behind the seventh cleft on each head and almost over the yolk'Stalk are the stubby pecto' 
ral fins. Faint traces of the lateral line are seen on each specimen. 

Head in Ventral Aspect. — The drawing of the ventral aspect (Figure 21, plate II) 
gives one a clearer idea of the morphology of the organs on the sides and lower surface of 
the head. Note the head, blunt'pointed in this aspect, the prominent eyes, and also the 
kidney'shaped outlines of the nasal pits. The cartilages of the lower jaw have united, but 
between those of the upper there is still a gap. In the mouth behind this gap is a structure 
which Nishikawa, by sectioning this head, identified as Rathke's pouch extending back 
toward the infundibulum. In contrasting the 32'mm. head with that of the 25'mm. 
specimen in ventral aspect, it is seen at once that the former is much older and more 
"finished". Contrast the widely gaping round mouth of the younger fish, with its two 
median fossae, with the far more normal mouth of the older specimen. No further comment 



600 Bashford Dean Memorial Volume 

is necessary. Note that in both heads, the isthmus grows progressively narrower from 
back to front. Short external filaments are found on each side of each arch. 

Scammon's stage of Squalus nearest to this 32'mm. Chlamydoselachus is one of 
28'mm. portrayed in fulMength lateral, dorsal and ventral aspects (his Fig. 30a, b and c, 
pi. III). Since there is no fulMength drawing of the 32'mm. Chlamydoselachus, com' 
parisons are difficult. But comparisons of heads only show that this 28'mm. Squalus is 
much farther developed than the 32'nmi. Chlamydoselachus. This is particularly true in 
the gill'tegion. The spiracular cleft of the dogfish is finished, and from it and the other 
clefts a profusion of long external gill'filaments protrude. 

Dean's Embryo 34 mm. in Length 

The "List of Figures" calls for "Embr. of 34 mm. Entire: head 2 other positions". 
And fortunately there are of this embryo a fulMength drawing in lateral aspect (223 mm. 
long in the original) shown in Figure 23, plate II, and also dorsal and ventral figures of the 
head. Comparisons will be made of the head of this specimen in three aspects with 
the drawings of the head of the 32'mm. embryo. In addition comparison of the figure 
of the 34'mm. specimen in full lateral view will be made with the similar figure of the 
20'mm. embryo. 

Head in Dorsal View. — As may be seen in Figure 22, plate II, the head of this 
embryo contrasts strongly with that of the 32'mm. specimen. It is bluntly rounded and 
the eyes are less prominent. Let the reader contrast the markings on the head over the 
brain in the two figures. I do not understand them unless they are due to shrinkage of 
the soft tissues on the embryonic skull. Let the observer particularly note that the open' 
ings of the endolymphatic ducts are no longer visible. The spiracular openings are 
smaller. The gill'covers are less widely spread and in this aspect no filaments are seen in 
them. The pectorals are about as they were in the 32'mm. embryo. 

Lateral Aspect, Head Only. — The head in this view (Figure 23, plate II) should be 
compared with the lateral view of the head of the 32'mm embryo (Figure 20, plate II). 
The head of the 34'mm. embryo is more rounded. The eye still shows the choroid 
fissure. The greatest progress however is to be noted in the mouth and spiracle. The 
mouth begins to look somewhat like that of a shark. Most noticeable is the fact that the 
cheek'piece so conspicuous in the 32'mm. embryo (Figure 20, plate II) has here grown 
fast to the hyoid arch. The external opening of the spiracle is much smaller and is in line 
with the medial borders of the gill'slits. The first gill-sHt is very large, and its arch and 
all the other arches show backward folds where they join the body above and the 
isthmus below. 

Head in Ventral View. — In this aspect (Figure 24, plate II) it is noticeable that the 
nasal pits are smaller. The fossa between the cartilages of the upper jaw is much reduced, 
the mouth itself is less widely open than in the 32'mm. specimen (Figure 21, plate II), 
and is more adult in appearance. The reduction in width of the isthmus from the region 
of the sixth flap forward to the first is very noticeable. The distended first gill'Covers 



The Embryology of Chlamydoselachus 601 

nearly meet across the isthmus, presaging the condition that suggested the name of our 
fish — the cloak'gilled shark. 

Lateral Aspect, Full Length. — Comparison from this viewpoint of the 34'mm. 
embryo (Figure 23, plate II) with that of the 20'mm. specimen (Figure 18, plate II) shows 
clearly that both differentiation and growth have taken place. The head has rounded out 
and is almost protuberant, the mouth is almost closed and looks like a mouth. The gill' 
slits have lost the embryonic look even though short filaments are present. The paired 
fins show progress. The pectoral'fin base has some of the radial cartilages faintly shown. 
The pelvic fin is well differentiated. Even more differentiation is seen in the tail parts. 
Noticeable is the development of the dorsal and anal fins and of the dorsal and ventral 
lobes of the caudal (the latter lobe being better developed). This caudal, however, has 
an even more marked downward swing than that of the 20'mm. embryo. The original 
drawing of this figure measured 223 mm. 

Comparison of this 34'mm. frilled shark in lateral aspect (Figure 23, plate II) with 
Scammon's 34'mm. dogfish in like aspect (his Fig. 31, pi. IV) shows that the dogfish is 
further advanced in development than the frilled shark. The fins (both median and paired) 
of Squalus are much better developed, and from its spiracles and gill'arches extend a great 
profusion of long external gills. Its lateral'line system is more prominent. The mouth of 
Chlamydoselachus, however, is far better developed than that of Squalus. 

An Embryo of 39 Millimeters 

Of this specimen. Dean's "List" calls for drawings, ''Entire in three positions". 
This is the first embryo of which there are three full'length portraits. There are four 
other embryos each drawn full'length in three aspects — dorsal, lateral, and ventral. For 
all five embryos, these full'length drawings will be studied in the order just noted, and the 
embryo in each aspect will be compared with the next younger embryo in the like aspect. 
Studied in such order one will get the most comprehensive view possible of each stage. 

Dorsal Aspect. — The original drawing of this embryo measures 258 mm. and the 
magnification is 6.6. As seen in Figure 26, plate III, this is a trim'built embryo. The 
head is much rounder in front than that of the 34'mm. embryo shown in Figure 22, plate 
II, but it is still wide between the eyes. Forward of the first gill'flaps, are found the large 
spiracular clefts. The gill'folds are all well developed — the first markedly so. The 
pectoral fins are still in about the same stage of development as was found in the 34-mm. 
specimen. The pelvics, however, show up plainly alongside the slender body. The 
dorsal fin and the upper lobe of the caudal are faintly outlined . 

Lateral Aspect. — In making this drawing of the 39"mm. embryo (Figure 25, plate 
II), the artist availed himself of artistic license to the amount of 10 mm. over the preceding 
figure — the original drawing measuring 268 mm. This specimen will now be compared 
with the 34'mm. fish in similar aspect (Figure 23, plate II). In the drawing it is seen that 
the head in front of the eyes has elongated somewhat. The olfactory organ has moved 
forward with reference to the eye- -which no longer shows the choroid fissure. The 



602 Bashford Dean Memorial Volume 

upper jaw has elongated beyond the vertical of the eye. The spiracle also has moved 
forward and slightly upward, and is now in the vertical of the angle of the jaw. The 
gill'Straps are still angulate backward at their dorsal and ventral extremities. The first 
has the free edge irregular, as though it had been bitten. External filaments are found 
in gill'openings 1-4, but are still lacking in the spiracle. The pectoral and pelvic fins 
show little progress. The dorsal and anal fins, however, have grown larger. Contrary to 
what was found in the 34'mm. embryo (Figure 23, plate II) the caudal fin is bent upward 
but the soft parts of the fin seem little larger than they were in the 34'mm. fishlet. 

Ventral View. — The original drawing of the 39'mm. embryo in this aspect is also 
268 mm. long. This portrayal (Figure 27, plate III) is very instructive when compared 
with that of the head only of the 34'mm. fish in like aspect (Figure 24, plate II). The fore' 
head is decidedly round. The edges of the olfactory pits are thickened, as if the valves 
are beginning to form. The eyes in this aspect are still prominent. The mouth is stretch' 
ing forward toward the snout. The lower jaw has taken on something of the form found 
in the adult, and the upper jaw no longer has a fossa in the symphyseal region. The an' 
terior part of the isthmus is broader in this embryo than in the 34'mm. embryo. The gill- 
arches all bear external filaments, those of the first slit being especially long — longer than 
they are shown in the lateral view (Figure 25), and longer than they are in the stages im- 
mediately following. The hindmost right gill'Strap is curiously twisted. The stumpy 
pectoral fins show no progress, but the pelvics are well developed and the cloacal eminence 
appears between their hinder ends. Faintly outlined in the drawing is the ventral lobe 
of the caudal fin.. 

Brief comparison of the 39'mm. Chlamydoselachus may be made with Scammon's 
37'mm. Squalus. In the latter, the fins are better developed. On the head the nasal pits 
are much more developed, and the latero-sensory canal system shows plainly. If present 
on Chlamydoselachus is it not shown in the drawings. The mouth of the frilled shark, 
however, is better developed. The embryonic gill'filaments of Squalus are profuse and 
long, some still coming from the spiracles. In Chlamydoselachus they are present in the 
gill'slits only, but are short and inconspicuous. 

The figures of the 37'mm. Squalus are the last of Scammon's drawings made of 
specimens in the flesh. His other figures (text'figures) are reconstructions of serial 
sections of these embryos (portrayed in his plates I-IV). Comparisons with the drawings 
in his plates have been very instructive and helpful, and it is regretted that his series of 
plate drawings does not extend to older and larger embryos. 

The 39'mm. Embryo and its Yolk Sac in Color 

Colored drawings were made of but three of Dean's Chlamydoselachus specimens — all 
shown on Plate V. Fortunately one of these is of the identical egg of which detailed 
figures have just been studied. This embryo and its yolk sac are beautifully portrayed 
in Figure 50, plate V. The embryo measures 39 mm. in length and the yolk sac 95 x 65 
mm. The yolk stalk averages about 2.5 mm. in width and is about 7 mm. long. This long 



The Embryology of Chlamydoselachus 603 

and slender yolk stalk allows the embryo considerable freedom of motion. Embryo and 
egg are undoubtedly drawn in natural si2,e. No mention of this figure is to be found in 
Dean's notebook. 

Proceding out from under the head of the embryo is the single vitelline artery, which, 
after traversing about 90° of the circumference of the yolk sac, divides into two. Coming 
in under the tail of the embryo is the vitelline vein which receives at right angles many 
tributaries. These are abundant in the proximal portion of the vein even to the point 
where it enters the yolk stalk. The complete circulatory pattern will be considered 
later when older stages are described. Note should be made of the pale pink color of the 
surface of the yolk mass. This drawing confirms Nishikawa's statement that "The yolk is 
of a pinkish color". 

Nishikawa's 43'mm. Embryo on its Yolk-sac. 

There is no specimen of this size called for in Dean's list, but such an embryo is shown 
in his Figure 7, plate I. Here is the history of this egg as I have reconstructed it. 

The egg with the 43'mm. embryo on it which Nishikawa figured in an outline pen 
and ink drawing (my Text'figure 4) was redrawn for Dean in pencil for lithographic 
reproduction, as may be seen by comparing the outline text'figure with Figure 7, plate I. 
This, I conjecture, was done not so much to fill in a gap in the series (there are no large 
drawings showing details of the morphology of this embryo) as to show the egg capsule 
and the yolk'sac circulation. Here it may merely be noted that the large unbranched 
vessel on the yolk is an artery, the much'branched one a vein. This specimen has already 
been studied for the structure of the capsule in the section on "The En capsuled Egg". 
The yolk-sac circulation will be described later. Both original figures- -text and plate — 
show egg and embryo in natural size. Even in figure 4 (reproduced natural size), the little 
fish is too small to show any details. 

Dean's Embryo of 46 Millimeters 

The "List" does not call for a specimen or figures of an embryo of this size, but I find 
carefully executed drawings in dorsal, ventral and lateral views. Moreover, two of 
these drawings are labelled in Dean's writing. Grouped with the three drawings, of the 
46'mm. embryo are three each for embryos of 54, 66, and 103 mm. These drawings, all 
done in one technique by the same hand and mounted on a different kind of board, look to 
me to have been made more recently than any drawings thus far studied and more recently 
than single drawings of larger and older specimens to be studied later. All the older 
drawings of embryos both smaller and larger than these four are mounted on a poor 
quality of yellow cardboard, old, dog-eared, soft and crumbling. The drawings themselves 
are yellow with age and often spotted and dirty. These drawings are years older than the 
four sets referred to. The most tangible evidence of the technique of the newer drawings 
is found in the "window" in the eyes of the figures of these four sets of embryos. There is 
no evidence as to where and when they were made. 

Dorsal Aspect. — The original drawing of this 46'mm. embryo seen from above 
measures 257 mm. (i.e, x 5.6). It is reproduced in Figure 28, plate III. When this drawing 



604 Bashford Dean Memonal Volume 

of this embryo is compared with that of the 39'mm. specimen m the same view, it is 
seen that the larger embryo has a rounder and shorter snout with eyes somewhat 
less prominent and more normal. There are faint traces of the sensory canal system on 
the head. The spiracles are smaller, and are more dorsally situated — higher on the 
head. The gill-flaps are more widely distended than those of the smaller specimen. The 
external gill-filaments, lacking in this view in the 39-mm. embryo, are very noticeable 
especially in the first, second and third slits, and a few short ones are even tound projecting 
from the spiracles. Both paired and median fins are better differentiated than in the 39- 
mm. embryo, and the artist has been able to portray m outline the dorsal fin and the soft 
dorsal part of the tail fin. 

Lateral View. — Comparison and contrast will now be made ot the 46- and 39-mm. 
embryos as seen m side view in Figure 29, plate III. and Figure 25, plate II. Where the 
39-mm. fish is almost straight from head to dorsal fin, the 46-mm. fish has a depression in 
the vertical of the spiracle and angle of the mouth. Back of this the little fish is very 
sway-backed clear to the dorsal fin. The head ot the 46-mm. specimen is shorter and more 
flatly rounded. The depth of the head is noticeably less than that of the 39-mm. fish. 
The nasal aperture is greatly reduced. Eye and mouth are both closer to the end of the 
snout, and the eye is very large. The spiracle is now a narrow sHt seemingly not placed so 
high as it is shown in the dorsal view of this 46-mm. embryo. The first gill-cover seems 
either distorted or anomalous, unduly exposing the filaments of the first demibranch. The 
39-mm. embryo has only short gill-filaments but m the 46-mm. specimen all the slits, but 
especially the first, have a profusion of slender external filaments — there are two projecting 
even from the spiracle. The paired fins are better developed than those of the younger 
specimen. Likewise dorsal and anal fins show much growth. Note that they look cut 
off squarely behind. The caudal fin is sharply bent down but the soft parts are devel- 
oping Vi'ell. 

Ventral Aspect. — Seen from below (Figure 30, plate III), the 46-mm. embryo is very 
much like the 39-mm. one (Figure 27, plate IIIj. The head is narrower and more rounded. 
This brings the nasal capsules and eyes closer to each other. The mouth has elongated 
somewhat. There is a remnant of a fossa in the median part ot the upper jaw. This jaw is 
more heavily built and more sharply outlined than that ot the younger fish. The mouth 
is still widely open and the lower jaw noticeably approaches the form of that ot the 
adult. The gill-arches are widely distended and bear a profusion ot external filaments. 
The isthmus is very narrow and the first pair of gill-covers is confluent over it. Thus 
first of all this embryo of 46-mm. justifies the name assigned this shark — Chlamydoselachus, 
the cloak-gilled shark. Lastly, the paired fins are much more developed than those of the 
39-mm. specimen, and the cloaca shov^-s conspicuously between the tips of the pelvics. 
The artist has also been able to show the anal fin and the lower lobe of the caudal. 

The head of this 46-mm. embryo in both dorsal (Tigure 28, plate III) and ventral 
(Figure 30, plate III) aspects seems entirely normal. But portrayal from the side shows 
a head which seems abnormal in every respect (Figure 29, plate IIIj. One almost doubts 
'if the three drawings were made from the same embryo. 



The Embryology of Chlamydoselachus 605 

Head of a 48-mm. Specimen in Ventral View 

We now return to Dean's ''List'\ which calls for "Embr. of 48 mm. ventral (head)" 
and on the opposite page is "48? Another, head only stained". Among the older draw- 
ings I find one without the figures "48" but with the significant label "head only stained". 
Moreover the drawing (Figure 31, plate III) shows this head in ventral view. From these 
data, and despite the fact that this "head . . . stained" in ventral view looks somewhat 
younger than the head of the 46'mm. embryo in ventral aspect and decidedly younger 
than that of the 54'mm. specimen (Figure 34, plate III), I believe that this head shown in 
ventral view is that of the 48'mm. embryo. Nishikawa had a 49'mm. specimen, and I 
believe that the "head only, stained" shown in Figure 31, plate III, is Nishikawa's speci' 
men stained in toto (as was the practice in those days) but never sectioned. 

Compared with the 46'mm. embryo (Figure 30, plate III), the head looks wider and 
more rounded, the eyes less prominent and the nasal organs better developed. The mouth 
is less advanced than that of the 46'mm. specimen. The upper jaw still has a definite 
median gap between the two halves, but the lower seems to be about normal for this 
stage. The gill'flaps are widely spread, especially the first pair — which are not continu- 
ous across the isthmus. Filaments seem to be absent, save in the first and second gill'slits 
on the right side. The pectoral fins are hardly so well developed as those in the 46'mm. 
embryo. The gular fold is lacking. That the 48'mm. embryo seems younger than the 
46'mm. specimen is probably an individual variation. 

Nishikawa's 50-mm. Embryo on its Yolk Sac 

Nishikawa (1898) had a 50'mm. embryo of Chlamydoselachus on its yolk sac. He 
did not have either yolk sac or embryo drawn, but he does portray the head only in both 
dorsal and ventral aspects (Text'figure 28a and b). Whether Dean got a specimen of 
this siz;e, through the help of Kuma or the commercial fishermen, cannot be said. But 
I suspect that Dean's drawings of egg and embryo (Figures 9 and 10, plate I) were made 
from Nishikawa's specimen. I have shown that Dean's Figures 7 and 8, plate I, are 
duplicates of Nishikawa's Figs. 1 and 2 of his pi. I. Here compare my Text'figure 4 with 
Figure 7, plate I. Now the capsules of the egg seen in Figures 7 and 9 plate I, are of the 
same type. Dean may have had eggs with capsules such as these, but, since no others of 
this kind are figured by him, I doubt it. In my judgment, the egg with the 50'mm embryo 
is the one listed by Nishikawa, and, since it had not been drawn for Nishikawa's article 
(1898), it was turned over with other specimens for Dean's studies. 

On its Yolk Sac. — This 50'mm. embryo (shown in half size in Figure 9, plate I) is 
of course too small (even in Dean's drawing in natural size) to show any morphological 
details. It was probably drawn to show the capsule and the circulation over the yolk sac. 
The capsule has already been studied. It is a counterpart of that around the 43'mm. 
embryo and its yolk sac. The yolk circulation is somewhat more advanced than that on 
the yolk of the younger specimen. It will be discussed shortly. Fortunately the details 
lacking in Figure 9, plate I, may be found in Nishikawa's line drawings of the head (his 
Figs. 7 and 8, plate IV) which will now be considered. 



606 



Bashford Dean tAemorial Volume 




Text-figure 28 

Head of a 50'mm. Chlainydoselachus anguineus in two aspects; A in left -oblique 

dorsal view, B as seen from below. 

After Nishikawa, 1898, Figs. 7 and 8, pi. IV. 

Head Only, Dorsal View. — Nishikawa's drawing (my Text-figure 28a) was made in 
oblique-dorsal view. In it the front head is bluntly rounded. Being drawn in large 
scale, it shows the sensory-canal system on the head with the lateral line extending 
backward onto the body. The small spiracular cleft is devoid of filaments. The gill-covers 
are distended (the first very widely) and abound in external gill-filaments — some of which 
appear to be longer than any thus far noted. It is difficult to compare this head with 
that shown in Figure 28, plate III. 

Head Only, Ventral Aspect. — The 50-mm. head (Text-figure 28b) must be com- 
pared with that of the 48-mm. in the same view. The heads seem (as might be expected) 
to be in practically the same stage of development. The 50-mm. head is slightly more 
pointed. Eyes and nostrils show no perceptible divergence in the two specimens. 
Mouths are alike save that the upper jaw of this specimen has no fossa in the symphyseal 
region. The gill-arches are shown widely distended and, unlike those of the 48-mm. 
head, are filled with protruding filaments — those on the left side being the more abundant 
and certainly the longer. They are found on both sides of the five hinder arches. The 
gular fold is barely continuous across the isthmus. 



The Embryology of Chlamydoselachus 607 

■■■■'■. An Embryo OF 54 Millimeters 

In Dean's "List", the next call is for "Embryo of mm. 55. Entire — draw dorsal and 
ventral views [of head]". These drawings I find. But, in the plates of newer drawings of 
later origin (as noted above), I find three full-length drawings — in dorsal, lateral and 
ventral aspects — of an embryo labelled "54 mm." in Dean's writing. The full-length 
figures of the 54-mm. specimen will now be contrasted with those of the 46-mm. embryo. 
The figures of the 55-mm. fish (belonging to the older set of drawings) will be studied 
next. Each of the original drawings of the 54-mm. embryo measures 257 rnm. — i. e. 
is multiplied by 4.7- 

Dorsal Aspect. — When comparison of this drawing (Figure 32, plate III) is made 
with a similar one (Figure 28, plate III) of the 46-mm. specimen, the head and trunk are 
found to be notably larger. The fish is decidedly like an elongate tadpole. The latero- 
sensory canal system on the head is clearly seen. The first gill-covers are not so widely 
spread. From all the gill-slits profuse elongate filaments contrast with the shorter 
ones of the younger embryo. Then, too, from the spiracle protrude more and longer 
filaments. The pectoral and pelvic fins show decided growth, but in this aspect one 
cannot say about the dorsal fin and the upper lobe of the caudal. The body between 
pectorals and pelvics is relatively shorter than in the 46-mm. embryo. 

Lateral View. — Marked contrasts may be drawn between the 54- and the 46-mm. 
embryos seen in lateral aspect (Figure 33, plate III, and Figure 29 on the same plate III). 
The 46-mm. fish is very sway-backed, the 54-mm specimen has a marked concavity in 
the neck region but behind this it is moderately hump-backed and has something of the 
look of the adult fish. The head is rounder and better developed than in any previous 
stage. The pits of the latero-sensory canal system are well developed over head and 
first gill-cover. The lower jaw has become greatly elongated and faintly recalls that 
of the adult. The almost vertical hinder edge of the first gill-cover contrasts marked- 
ly with the open U-shaped structure of the 46-mm. specimen — which is probably 
anomalous. The external gill-filaments are well developed. Some are found in the 
spiracle, which is much higher up on the side of the head than that of the 46-mm. fish. 
Both paired and unpaired fins of the 54-mm. fish are somewhat better developed than 
those in the younger one. The tail of the present fishlet is as much bent up as that of the 
46-mm. specimen is bent down. Other than this, the tail regions are much alike. 

Ventral Aspect. — Considerable contrast is to be noted when the two fish are com- 
pared in ventral view (the 54-mm. in Figure 34, plate III, and the 46-mm. fish in Figure 
30 of the same plate. The head of the 54'mm. specimen is much broader as was noted in 
dorsal aspect. The eyes are larger, the openings of the olfactory slits smaller. The pits 
of the latero-sensory canal system show clearly. The mouth shows marked develop- 
ment — it resembles that of the adult but is still ventral in position. The first gill-covers 
form a wide cloak covering the isthmus. The gill-arches — standing out fairly at right 
angles in the younger specimen — are here bent somewhat backward. Every gill-slit is 
crowded with external filaments which reach their maximum development here. Trunk 



608 Bashford Dean Memorial Volume 

and paired fans show some development, and anal £n and lower lobe ot caudal are shown 
in wavy outline. As one would expect by referring to Figure 33, plate III (the lateral 
view), the dorsal and anal fins and lobes of the caudal are practically continuous. Along 
the mid-ventral line is a ridge which I take to be the beginning of the tropeic folds. Note 
how much like a tadpole the little fash appears. 

An EiiBRYO PLEASURING 55 Millimeters 

As noted above, Dean's "List" calls for drawings of the entire embryo and dorsal and 
ventral views (presumably of the head) of an embryo of this size. These three drawings 
I find, but, since they look old and are mounted on discolored cardboard, I conjecture that 
they were made in Japan in 1901-02. They will be compared with the later-made draw- 
ings of the 54-mm. specimen. The tull-length drawing ot the 55-mm. embryo in lateral 
aspect measures 238 mm. ( = X 4.3+). 

Head Only. Dorsal View. — It is now m order to contrast the head (Figure 35, 
plate III) of the 55-mm. embryo with the head of the 54-mm. specimen shovvTi in full 
view in Figure 32, plate III. The 55-mm. head seems narrower but is rounded like the 
other, the eyes are a little further forward, and the sensory-canal system shows very 
indistinctly. The spiracles seem larger but show no gill-filaments. Nor are any filaments 
visible in the widely separated gill-arches. One queries why the 54-mm. embryo has and 
the 55-mm. one lacks these external filaments. Note that the pectoral fins of the 54-mm. 
fish have little hook-like spaces between fin and body, while these are lacking in the older 
embryo. In general it can be said that, contrasting the heads of two specimens, one gets 
the impression that the 55-mm. head looks more finished — i.e., older. 

Full-length, Lateral Aspect. — The full-length lateral-view drawing of the 55-mm. 
specimen (Figure 36, plate III) will be contrasted with the like drawing (Figure 33, plate 
III) of the embryo of 54-mm. Naturally the differences between them are individual 
rather than of stages of development. The original dravdng of the 55-mm. fish measures 
238 mm . (i.e., X4.3— ), that of the 54-mm. one measures 257 mm. (i.e., x4.7-r)- In the 
55-mm. embryo, head and trunk are straight above and the head rounds off forwardly to 
a rather distinct snout. The nasal apertures are situated well forward almost in their 
definitive position. The lower jaw is not so long as that of the 54-mm. embryo. The 
lateral-line system show^s plainly on the trunk but on the head is hardly so well-developed. 
The gill-covers (especially the first) are also hardly so w^ell developed and the external 
filaments are not nearly so long as those in the 54-mm. fish. The spiracle of the 55-mm. 
specimen is higher on the head and contains several short gill-filaments. Ot the fins, 
pectorals, pelvics and dorsal are about equally developed in both embryos. The anal fin is 
better developed and more sharply marked off from the lower lobe of the caudal in the 
55-mm. embryo. The caudal fin droops, whereas that of the 54-mm. fish swings upward. 
Unfortunately the artist has used dark lines to indicate some grooves between somites, 
which thus appear like branches of the lateral-line canal. 

Head Only, Ventral View. — Perhaps most instructive will be a comparison of the 
under surfaces of the two heads — the 55-mm. specimen in Figure 37, plate III, and 



The Embryology of Chlamydoselachus 



609 



the 54'mm. in Figure 34, plate III. The head of the former looks decidedly older than 
that of the latter. The head in front of the mouth is shorter, and across the mouth 
region it is narrower. The nasal cavities are located well forward. The mouth of the 
55'mm. fish looks less embryonic, older and better developed. The gill-arches are not so 
dilated and the filaments are, as noted above, entirely lacking. In both, the first gill'flap 
is continuous across the isthmus. The sensory-canal system on the under side of the 
head is well developed. 

Here are two embryos differing in length by but one millimeter, but varying widely 
from each other. The morphological differences are principally in the head and mostly in 
the ventral head. In degree of development the mouth structures so differ that, on the 
basis of this one character with no others visible, one would separate these embryos as of 
two widely different stages. Whether this represents an actual difference in embryos 
of a shark whose variableness is greater than in any other known to me, or is due to a 
difference in artists cannot be said. Were the two embryos at hand, the matter might 
possibly be settled. 

Carman's Embryo of 64 Millimeters 

When Dr. Thomas Barbour, now Director of the Museum of Comparative Zoology, 
Cambridge, Mass., returned in 1906 from a visit to Japan, he brought with him this 
embryo. It was figured but not described by Samuel Carman in 1913 (Figs. 7 and 8, 
pi. 61). For its historical interest and for the sake of completeness, Carman's figures 
(lateral and ventral aspects) are reproduced herein as text'figures and are described. 

Lateral Aspect. — Comparison must be made of the 64'mm. embryo (Text'figure 
29a) with that of 55 mm. (Figure 36, plate III). Excepting in the head region, the two 




Text-figure 29 
Two views (lateral and ventral) of a 64-mni. embryo of Chlamydoselachus. 
After Carman, 1913, Figs. 7 and 8, pi. 61. 



610 Bashford Dean Memorial Volume 

drawings show embryos much alike. The head of Garman's fish is thinner and is smoothly 
rounded down to the upper jaw. Dean's specimen is thick in head and gill-region and the 
head rounds steeply to the upper jaw. The mouth of the 64'mm. embryo is in about 
the same stage of development as that of the 55'mm. fish. The spiracle of Carman's 
fishlet is not so high on the head as that of the other embryo but is elongate vertically 
and has more gill-filaments protruding. There is some slight diiference in the shape of the 
gill-openings, but both little fish are well supplied with external filaments. Remarkably 
alike are the fins, paired and unpaired. Both tails have about the same droop. 

In Ventral View. — Carman's full-length figure of his 64-mm. embryo in this aspect 
is shown in Text-figure 29b. For adequate comparison we must turn to Figure 37, 
plate III, Dean's 55-mm. specimen in ventral head aspect. Carman's embryo has the 
mouth not quite so well developed, and the nostrils are not placed so far forward. The 
first gill-cover in each fish is continuous across the isthmus. Carman's specimen (Text' 
figure 29b) has a great number of short filaments protruding trom each slit. Dean's fish 
has none showing in the figure in ventral aspect (Figure 37, plate III) although they are 
portrayed in the lateral view (Figure 36 on the same plate). As Text-figure 29b shows, 
the 64-mm. embryo has the pelvic fins well developed. Note the cloaca between their 
hinder ends. Anal and caudal show in the drawing. The pectoral fins and the yolk 
stalks look much alike. 

These drawings (Text-figures 29a and b), made on a much smaller scale than Dean's, 
show few details. The specimen, loaned by Dr. Barbour, is before me as I write, and I can 
testify that the little fish is accurately drawn. The inclusion oi Carman's figures herein 
help make the transition between the 54-rmn. embryo and that now to be described. 

Dean's Embryo Measuring 66 Millimeters 

Third in the series of drawings of embryos noted above as being done by a diiferent 
hand and at a later time, is the embryo under consideration. In the original drawings 
this 66-mm. sharklet is enlarged to 256 mm. (i.e., is x c 3.9). Seeking a younger embryo 
with which to compare it, I have made only secondary comparisons with Carman's 
64-mm. specimen as being too close and because his figures show too tew details. I have 
also passed over Dean's 55-ram. embryo which has but one full-length figure. Direct com- 
parison will be made with the close neighbor of the 55-mm. embryo, the more typical 
54-mm. fishlet, which like the present specimen, is portrayed in all three aspects. 

Dorsal View. — Comparison of this 66-mm. embryo with the 54-mm. specimen — the 
former in Figure 38, plate IV; the latter in Figure 32,pla te III — shows that the 66-mm. fish 
is plainly older. The front curve of the head is flatter, the eyes are prominent, the con- 
striction back of the eyes is greater, but the sensory-pore system is hardly so clear. The 
gill-covers are widely distended, and there is still a profusion of external gill-filaments — 
but these are shorter and those in the spiracle are fewer. The differentiation in the trunk 
region, faintly foreshadowed in the dorsum of the 54-mm. fish, is here far more clearly 



The Embryology of Chlamydoselachus 611 

marked. This is to be seen all the way from head to the dorsal fin. Pectoral and (especial- 
ly) pelvic fins show development. The dorsal fin is now clearly seen in the drawing and 
the upper lobe of the caudal stands out on the thicker vertebral part of the tail. 

Seen from the Side. — More marked are the differences in the lateral views of the two 
embryos — the older (66 mm.) shown in Figure 39, plate IV, and the younger (54 mm.) in 
Figure 33 on plate III. The head of the older specimen is smaller and is curiously round' 
ed. The eye is larger, the nasal groove has moved forward. The mouth is closed and the 
lower jaw is plainly longer. The spiracle is placed in about the mid'lateral line whereas it 
is above it in the 54'mm. fish. The first gill-cover has a ragged or frilled edge and seems 
retracted — as it is in the 54-mm. fish and (particularly) in the 46-mm. specimen (Figure 
29, plate III). The gill-filaments in general are smaller, fewer and not so far protruded. 
The "back-of-the-neck" hollow seen in Fig. 33 has here become a great ''sway-back" de- 
pression, giving the idea of a definite necl{ between head and body. The body is more 
humped than that of the 54-mm. embryo. The paired fins show growth. Dorsal and 
anal are larger and better differentiated. The tail bends gracefully downward. The 
ventral lobe is here sharply separated from the well-developed anal fin, unlike the close 
approximation seen in the 54-mm. fish. This is the earliest embryo showing the tail fin 
in approximately the adult condition. 

Dean's 66-mm. embryo contrasts strongly with Carman's 64-mm. specimen. It has 
the top of head high and rounded. In the neck region it has a long "sway-back", the body 
is decidedly arched, and the tail behind the dorsal-anal vertical bends down strongly. 
The dorsal region of Carman's fish (Text-figure 29a) is nearly straight, having at most 
very flat curves. Even more difference is to be found in the shape of the gill-flaps. Those 
of Dean's fish are convex posteriorly, save the first which has a frilled edge standing nearly 
vertical. For the rest — mouths, spiracles, fins, and tail-tips are very like each other. 

In Ventral Aspect. — Seen from below (Figure 40, plate IV), the 66-mm. fish 
shows considerable development compared with the 54-mm. specimen (Figure 34, plate 
III). The head in front of the mouth is greatly shortened and more blunt. This has 
brought nares and eyes closer to the front of the head. The long mouth begins plainly to 
foreshadow that of the adult. The inner surface of the upper jaw is serrate, probably due 
to the presence of rudimentary teeth which have not yet erupted. Both upper and lower 
jaws are narrower in the transverse and longer in the sagittal plane — more like the adult. 
The head, back of the angle of the jaws, shows a marked constriction. The sensory- 
canal system is clearly portrayed. The gill-covers are still pretty widely distended, but 
with their outer edges bent toward the rear. The gill-filaments still protrude but less than 
in the preceding stage. The confluent first gill-covers form a convex U over the isthmus. 
Pectoral fins show little difference from those of the 54-mm. fish, but the pelvics are much 
further developed. The cloaca has become a longitudinal slit and on either side of its 
hinder end the abdominal pores make their first appearance. As in the 54-mm. embryo, so 
here, in the mid-ventral line is the rudiment of the tropeic folds. The anal fin and the 
ventral lobe of the caudal are fairly distinct. 



612 Bashford Dean Memorial Volume 

When Figure 40, plate IV (the 66'mm. embryo) is compared with Text-figure 29b 
(Carman's 64'mm. specimen), it is plainly seen that the two embryos are very much like 
each other. The heads are alike broad and blunt. The distance from the center of the 
upper jaw to the tip of the snout in the 66'mm. specimen is shorter than in the other. 
The first gill-covers in each are confluent across the isthmus — with a blunt backward 
central point in Figure 40, plate IV, and a straight line across in Text-figure 29b. Both 
heads in this aspect show a profusion of external gill-filaments in each gill-opening. In 
the 66-mm. embryo, there is seen the beginning of the tropeic folds reaching from yolk 
stalk to cloaca. Nothing of the sort is to be seen in the 64-mm. fish. 

An Embryo 103 mm. in Length 

This embryo, the last of the new lot of four drawn in three aspects, is about one and 
one-half times the length of the 66-mm. fishlet, but in the original drawing it measures 
approximately the same — 257 mm. (i.e., x 3.9). 

Seen from Above. — The merest glance shows that this 103-mm. fishlet (Figure 41, 
plate IV) has advanced much over the preceding stage (Figure 38, plate IV). The head is 
smaller, more compact, more finished looking. The latero-sensory canals are well develop- 
ed. The spiracles are so reduced in size that the external openings are barely visible. The 
gill-covers are far less distended than in the 66-mm. fish, and the filaments are somewhat 
fewer but generally longer. The paired fins show marked growth and the dorsal is some- 
what in evidence. 

In Lateral Aspect. — Seen in side view (Figure 42, plate IV) and in contrast with the 
like aspect of the 66-mm. specimen, it is apparent that the larger embryo has gone forward 
markedly in development. It now begins to look like the adult. Note the pointed snout 
and the long mouth with the fold above, marking off the jaw cartilage. Eye and nasal 
opening are in their normal positions. All the gill-covers are for the first time distinctly 
frilled. The external gill-filaments are still persistent. The lateral-line and head-canal 
systems are continuous. The fins, paired and unpaired, are well developed. The tail is 
straight and the lower lobe of the caudal has a faint notch near the tip. The little shark 
begins to look snake-like — anguineus. 

Seen from Below. — In this aspect the 103-mm. fish (Figure 43, plate IV) looks more 
developed than does the 66-mm. embryo (Figure 40, plate IV). The head is narrower and 
more pointed. The mouth is slightly narrower and the lower jaw considerably longer — it 
distinctly recalls that of the adult. The gill-covers (especially the first pair) are seen to 
be frilled. They are less distended than those on the heads previously studied. The 
external gill-filaments persist and protrude. Both the paired fins, the pectorals especially, 
show much development. The cloacal opening looks as though it might be functional, 
and the abdominal pores are prominent. On the mid-line of the ventral trunk is the 
tropeic ridge and on either side the somites show distinctly. 

An Embryo of 124 Millimeters 

Having finished the study of the later-portrayed series of embryos shown each in 
three full-length drawings, we will now proceed to a consideration of some figures of 



The Embryology of Chlamydoselachus 613 

older embryos drawn at an earlier date and recorded in Dean's notebook. Here the 
''List" reads for the next stage — "Embr. of mm. 123 entire. Ventral (head) dorsal head". 
I do not find such figures, but I do find a full-length lateral drawing and another of a dorsal 
head, both marked "124". These drawings I take to have been made from the specimen 
referred to — the difference of one mm. being insignificant. Whether or not the "ventral 
head" was drawn cannot be said. But on the plates as made up by Dean, I find occasional 
scars on the board where drawings have been removed. It is of course possible that the 
drawing of the "ventral head" of this stage has been removed and lost. The drawings of 
the 124'mm. embryo will now be studied in comparison with those of the 103'mm. 
specimen — the preceeding stage. 

Head in Dorsal Aspect. — When comparison is made of the drawing (Figure 44, 
plate IV) of the "dorsal head" of the 124'mm. embryo, with that of the head of the 103- 
mm. fish (Figure 41, plate IV), it looks older, more finished. The head of the 124'mm. 
fish looks longer and narrower, and the eyes are less conspicuous. The spiracle is not 
visible, being probably too small to show in this low magnification (x 2 + , the same 
magnification as Figure 45, plate IV, the fish in lateral view). The gilhcovers are some- 
what distended but reveal no trace of gilbfilaments. The lateraMine system shows on the 
trunk but is indistinct on the head. The pectorals are smaller. One wishes for the draw 
ing of the "ventral head" to show the form of the mouth and the ventral parts of the gill' 
covers, especially the first. 

Full-length Lateral View. — It was noted that the 103'mm. fish, portrayed in lateral 
view in Figure 42, plate IV, showed some decided resemblance to the adult form. How 
much more is this true of the 124'mm. specimen seen in Figure 45, plate IV. Here the 
whole fish is plainly a young Chlamydoselachus. Note the pointed snout, the forwardly 
placed nasal aperture, the eye in about the vertical of the middle of the mouth, the long 
lower jaw reaching close to the end of the snout. The gill-covers (the first much the 
larger) decrease in length normally from 1st to 6th, and have their dorsal edges backwardly 
bent as in the adult. No gill-filaments can be seen. The spiracle is not shown in this 
drawing, even though the original measures 257 mm. in length — i.e., x 2 + • The pectoral 
fin is much larger than that of the 103-mm. specimen, but the pelvic is of about the same 
siz;e. The dorsal and anal are somewhat smaller than these fins are in the younger fish. 
The back is nearly straight from head to dorsal fin. The body has elongated, not in the 
tail region but in the body proper, i.e., between pectoral and pelvic fins. The tail ends in 
a fine-pointed caudal fin which droops slightly downward. The soft parts of the caudal 
fin are smaller than those of the 103-mm. fish. The lateral line is well developed and 
shows an interesting curvature behind the vertical through the tips of caudal and anal. 

An Embryo of 175 mm. and its Yolk Sac 

The "List" next calls for "Embr. of mm. 175, entire, dorsal aspect with yolk". This 
I find as portrayed in Figure 11, plate I. In the original drawing, the fish, measured 
carefully over the curves, is 205-mm. long and the yolk sac measures 92 x 90 mm. On the 
page of Dean's notebook opposite the "List" is a record of seven specimens taken "April 



614 Bashford Dean Memorial V^olume 

25". Among them is a specimen of 205 mm. This I judged to be the specimen drawn 
and I concluded that it was dra\^m in natural size since the embryo of Figure 11, plate I 
measures 205 mm. around the curves. Furthermore, it seemed that a yolk sac 92 x 90 mm. 
would not be too large for an embryo of this size. But the figure bears in Dean's writing 
the notation "175" and the last embryo of the seven taken "April 25" is Hsted as "175" 
mm. So it seems clear that, in the original drawing, the 175'mm. embryo and yolk sac 
are enlarged 1.2 times. There is no drawing of the 205 -mm. embryo. 

Seen from Above. — The only embryo with which to compare this I75'mm. specimen 
(Figure II, plate I) is that of 124'mm. and of it the drav.nng of the head only (Figure 44, 
plate IV). The head of the 175'mm. fish looks distinctly older even though the remnants 
of external gill-filaments show in the arches. In contrast, the snout of the Httle I75'mm. 
fish is blunter than that of the 124'mm. embryo, the eyes far less prominent, and the gill- 
covers far less spread out. The presence of gill-filaments even though small, is not un' 
usual since they are found in far older specimens as will be seen later. The pectoral and 
pelvic fins have a decidedly '"growTi up" appearance. Dorsal and anal fins are well de- 
veloped and the lower lobe of the caudal looks very much Hke that of an adult. The tip 
of the caudal is bent downward and is devoid of a notch. The lateral-line system is 
clearly marked, and the latero-sensory canals and ampullae on the head are well delineated. 
On the trunk region, the lateral-line grooves appear to be connected across the dorsum 
by transverse broken lines drawTi in white. These are like those shown in the tail-region 
of the 55-mm. embryo (Figure 36, plate III). They are surely inter-somitic grooves, not 
portions of the lateral-line system. This portrayal (Figure 11, plate I) shows the vitelline 
circulation in an advanced stage of development. It will be considered shortly. Alto- 
gether this is the most artistic drawing thus far found. 

i\s" Embryo 185 mm. k Length 

Dean's "List" calls next for an embryo of 185 mm. to be drawn full-length in lateral 
aspect without yolk. This drawing is reproduced herein as Figure 46, plate IV. The 
original drav.Tng measures 185 mm., hence is natural size — the first of the embryos so 
draum. This little fish looks very like an adult even though it was attached to the yolk 
sac by a yolk cord measuring 11 mm. in diameter. To see how tar this embryo has 
progressed, it must be compared with the 124-mm. specimen (Figure 45, plate IV), 
seen in the same aspect. (The 175'mm. embryo cannot be used in comparison, since it 
is portrayed in dorsal aspect, and is moreover not drawn straight). The snout ot the 
185'mm. fishlet is more pointed ( dorsO'ventrally compressed); nasal capsule and eye are in 
their normal positions. The long lower jaw brings the mouth almost to the terminal 
position. The gill-flaps are nearly as normal as those of the fine 124'mm. embryo, which 
lacks the remnants of gill-filaments present in the 185-mm. fish. The body is humped 
and on it is a well-developed lateral line with latero'sensory branches on the side ot the 
head, and v.^th marked bends under the dorsal fin. Above the lateral line, the artist has 
inserted broken lines as if they were branches of the lateral Hne. They are spaced to 
correspond with the grooves between the myotomes immediately ventral to the lateral 



The Emhryohgy of Chlamydoselachus 615 

line. The paired fins have well'deve loped bases. The dorsal and anal fins look much like 
those in the adult fish and even more is the caudal like the tail fin of an adult Chlamydo- 
selachus. The tropeic folds, noticeable in the 103'mm. fish, are here plainly visible. 

Head in Ventral Aspect. — The list calls only for "Embr. 185 mm. lateral aspect". 
It does not call for ventral view of the head, but such a drawing I find. This is reproduced 
as Figure 47, plate IV. The next youngest head in like aspect with which it can be 
compared is that of the 103'mm. embryo (Figure 43, plate IV). Here one sees that the 
profuse external gill'filaments of the 103'mm. head are reduced to mere remnants in 
the gill'slits of the 185'mm. fish. Furthermore, the mouth of the older fish looks more 
finished, more nearly adult. The first gill'flaps are continuous across the isthmus. These 
flaps show some evidence of being ''frilled". In the 103'mm. embryo, the yolk stalk has 
been cut off close to the body. In the 185'mm. fish the basal part is shown attached to 
the body. This is very large and I judge that here it is really part of the sac that is seen, 
that we have here the attachment of body to yolk directly comparable to that seen in the 
390'mm. shark portrayed in color (Figure 49, plate V). 

A Young Frilled Shark 240 mm. Long 

The next embryo on the "List" is one of this size to be drawn in full length, lateral 
aspect, without yolk. This little fish was drawn slightly smaller (3 mm.) than natu- 
ral size. As Figure 48, plate IV. shows, it is even more like the adult than is the 185' 
mm. specimen (Figure 46, plate IV). The long mouth has nearly attained the terminal 
position, nostril and eye call for no remarks, the gill'flaps are frilled and show short 
filaments in the openings. There is a small spiracular opening precisely in its adult location. 
All the fins are better developed and even more closely resemble the adult organs than 
those of the preceding stage. The lateral line runs the full length of the body and shows 
only very slight variations under the dorsal fin in contrast with both the 185- and the 
124'mm. young. The little fish is still attached to its yolk sac by a cord 7 mm. in diameter. 
The caudal, like that of the I85'mm. fish, is slightly bent upward. 

A J90'MM. Chlamydoselachus in Natural Colors 

Next and last. Dean's "List" calls for four embryos to be drawn. These were "taken 
about May 1, 1905", and were "Bt. in Tokyo, June 20". They measured in millimeters 
317, 331 (yolk sac. 111 x 100), 352 and 390 (yolk sac, 100 x 90), and probably all came from 
one mother. However, since they were presumably twins and since the youngest differed 
from the largest embryo by only 38, and the others by 59 and 73 mm. respectively, it was 
clearly unnecessary to go to the expense of having all four drawn. So Dean seems to 
have compromised by having the largest specimen drawn in color. This exquisite drawing 
is accurately reproduced in the original colors as Figure 49, plate V. 

It may be of interest to attempt to reconstruct the history of the specimen and of the 
drawing. Since the four embryos were "taken about May 1, 1905" and "Bt. in Tokyo, 
June 20", they must have been in preservative about seven weeks before they came into 
Dean's possession. Now Dean states (1901) that he had the active cooperation and 



6l6 Bashford Dean Memorial Volume 

effective help of Prof. Mitsukuri ot the Imperial University of Tokyo to the end that all 
specimens of Chlamydoselachus taken in the Gulf of Tokyo should be reserved for him 
(Dean). Hence one may judge that the fish had been taken by the fishermen to the Depart- 
ment of Zoology in the University, there opened and the embryos secured for Dean. 

The original drawing (Figure 49, plate V) measures 382 mm. between perpendiculars, 
and the yolk sac is 92 x 70 mm. If the fish was drawn alive or just dead, the discrepancy 
of 8 mm. between its length and that of the largest of the four embryos Usted above 
(390 mm.) may be disregarded, as it may for the discrepancy in yolk measurements (92 x 70 
in the figure vs. 100 x 70 mm. in the notes"). These may be errors of the artist. But I have 
shov.Ti earlier in this paper that embryos brought up within the mother from a depth of 
300 to 500 fathoms, from a region of great pressure and low temperature, to the University 
of Tokyo in May, could only have survived a few minutes. Here then is what I judge to 
have been done when this specimen came in. A quick sketch in color ■w.'as made while 
embryo and yolk were fresh. Then to preserve it, the fish u^s put in formalin (which 
bleaches out color less than alcohol). Later, and as soon as possible, the completed draw- 
incr was made — the size from the specimen in preservative, the color from the hasty color 
sketch. The embryo in preservative for a month would easily have shrunk 8 mm. The 
shrinkage of 8 mm. in the length of the long axis of the yolk is entirely within the limits 
as I have observed it in the large yolks of other fishes. To strengthen this case it may be 
noted that among Dean's frilled-shark materials there is a water-color sketch of the 
reproductive organs of a just-opened female Chlamydoselachus evidently intended as 
the basis of a figure in natural color. Unfortunately this drawing was never made or has 
been lost. But we do have here this beautiful drawing showing this late embryo, the 
yolk sac, and on the side of the egg the yolk-sac circulation, all in their natural colors. 

There is in the Museum collection — it stands before me as I wTite — what I believe 
to be the very specimen from which the drawing (Tigure 49, plate V) was made. The 
shape of the head and mouth, the fold across the snout above the upper jaw, the form and 
position of the gill-sUts, the upturned pectoral fin, the form and position of the other fins 
and the tail, the irregularities in the lateral line, the shape and position of the yolk sac — all 
are practically identical. This is surely the fish from which the drawing was made. The 
fish, after at least 33 years in formalin and alcohol, measures 370 mm. in total length and 
the yolk mass 78 x 60 mm. But those who have had to do with specimens in preservative 
know that this decrease in the size of the fish is not beyond limits. However, the yolk has 
undergone even greater shrinkage than the fish. The ordinary fish -egg yolk shrinks con- 
siderably in presen-'ative, but there is in the egg yolk of Chlarnydoselachus an additional 
factor in its shrinking. There is in these yolks an unusual amount of oil which is dissolved 
out by the alcohol. This alcohol, even to this day, has to be changed frequently. This 
dissoh-ing of the oil aids materially in the diminution of the volume of yolk as it hardens. 

The likeness of this 15.35-inch embryo to an adult is close both m the general mor- 
phology and in the details. The mouth, reaching far back of the eye, is almost terminal 
and evidently has a great gape. There is the groove marking off the cartilage of the upper 



y 



The Embryology of Chlamydoselachus 6l7 

jaw. The nasal aperture of the embryo is not yet completely divided into two. The 
gill'covers have pocket'like folds where they join the body. The first plainly extends 
across the throat — i.e., the isthmus and throat are "cloaked". Note that there are visible 
very short gill'fiilaments. The body is humped above and on the ventral edge is seen one 
side of the tropeic folds. ^ Plainly visible is the latercsensory canal on the first gill'cover 
and the lower jaw, and the lateral line extending along the body and the tail to its very 
tip — with the previously noted irregularities under the dorsal fin. 

In this drawing, the artist has again inserted short dotted lines (in white) extending 
dorsally from the lateral line. These are more widely spaced than the zigzag intersegment- 
al grooves seen along the sides of the body. Examination of the original specimen and of 
one but slightly smaller discloses that the intersegmental grooves above the lateral line are 
occasionally visible. Nothing in this region in this fish could easily be mistaken for branch- 
es of the lateral line. 

The fins are very like those of the adult, including the well-formed caudal fin with 
the notch at the tip of the lower lobe — faintly presaged in the 103-mm. fish, but here seen 
plainly for the first time in this drawing of a large frilled shark embryo. What more can 
be said in description of this striking figure? The reader must study it for himself. 

THE YOLK-SAC CIRCULATION 

The vitelline blood vessels from small beginnings come finally to spread over all 
the large yolk sac of Chlamydoselachus. Their function is to bring food stuff to the de- 
veloping embryo. These vessels have been briefly referred to earHer in this paper in 
describing certain embryos figured on their yolk sacs — the 39-mm. embryo (in color), the 
43- and 50-mm. embryos and the l75-mm. fishlet (in gray), and lastly the 390-mm. shark 
(in color). . The early stages of the development of this circulation are lacking in these 
drawings but the intermediate and later stages are shown. These portrayals are so in- 
formative as to call for special study. 

Opportunities to study the yolk-sac circulation on the eggs of sharks occur very 
infrequently. In my investigations on live eggs and embryos of the sharks and rays else- 
where referred to, I was so occupied with other observations that those on the yolk-sac 
circulation were very incomplete. Dean's figures unfortunately do not show the early 
stages, so to make things clear, I refer the reader to Balfour's classical work (1885, pp. 
465-466, pi. 9). In this he figures (diagrammatically) and describes the early circulation 
on the egg of Pristiurus essentially as it will presently be portrayed for Chlamydoselachus. 
Here is a synopsis of what he wrote. 

As may be seen in Text-figure 30a, the blastoderm in this early stage covers about 
three-fifths of the yolk. The embryo is found in the bay of the blastoderm and from under 
its head extends forward the vitelline artery (a). This presently divides into two forks 
right and left and these are the beginnings of the arterial ring. In Text-figure 30b, it is 



'For data concerning this extraordinary structure, found in no other shark, the reader must turn to Gudger and Smith (1933, 
Article V of this Memorial Volume, pp. 283-284, Text-figure 1 2) by whom it is figured and comprehensively described. ; 



618 



Bashford Dean Memorial Volume 




Text-figure 30 

Three diagrammatic figures showing the development of the vitelline circulation on the 

egg of Pristiurus. A is a beginning, C an intermediate, and D an advanced stage. 

a, vitelline artery; v, vitelline vein, y\, yolk blastopore, y, (in C) marks the spot where the venous ring and yolk 

blastopore were closed by the growth of the blastoderm. 

After Balfour, 1885, Figs. 1, 2, and 3, pi. 9. 

seen that the blastoderm has grown over all the yolk save a central area (the so-called yolk 
blastopore, y}(), forward of which the embryo is found. The two arms of the vitelline 
artery (a) are in the act of joining behind to form the arterial ring. These arms give off 
many small arteries on the inside of the hinder half of the ring. Surrounding the yolk 
blastopore, a venous ring has arisen in the edge of the blastoderm. From its anterior part, 
there has developed a main venous trunk which reaches to the yolk stalk. The venous 
ring receives many veinlets on its outer side. 

In Text-figure 30c, the vitelline circulation has made much progress. The arterial 
ring is complete, has increased in size, and even in the anterior region gives off many small 
arteries. The yolk blastopore has disappeared, due to the complete enclosure of the yolk 
by the growing blastoderm. The letter y marks the point of closure of the blastopore. 
The venous ring has been replaced by the main venous trunk (v) which has grown not 
only longer but larger as it approaches the yolk stalk. With its many lateral branches, 
the vitelline venous system much resembles a tree. These veinlets receive blood from the 
arterioles, and the great venous trunk brings to the growing embryo much blood laden 
with food stuff. 

With this brief explanation, let us now turn to Dean's drawing showing the earliest 
circulation on an egg of Chlamydoselachus found by him. 

Vitelline Circulation in the 39-mm. Embryo 

One of Dean's three drawings in color for the embryology of Chlamydoselachus 
portravs this embryo and yolk (Figure 50, plate V). In this the artist has shown the 



The Embryology of Chlamydoselachus 619 

proximal portions of both vitelline artery and vein. The artery extends out from under 
the head of the embryo as a single vessel until it forks narrowly into two branches before 
passing over the equator of the egg. The dendritic system of vessels under the tail of the 
embryo is venous and laden with food absorbed from the yolk mass. This circulation on 
the upper side of the egg carrying the 39'mm. embryo is essentially like that portrayed 
on a flat surface by Balfour (Text'figure 30). Unfortunately there is no drawing showing 
the relation of arterial and venous vessels on the opposite side of the egg of this 39'mm. 
Chlamydoselachus. For this we shall have presently to go to the drawings of the 43' 
mm. embryo and its yolk sac. 

Arterial and Venous Trunks in the Yolk Cord. — Inspection of the yolk cord of the 
39'mm. embryo (Figure 51, plate V) shows that the artist has not differentiated 
the trunks of artery and vein in the cord. They are not portrayed in the 43'mm. 
specimen (Figure 7, plate I). In the 50'mm. embryo the arterial and venous vessels are 
plainly shown in the yolk stalk (Figure 9, plate I), but (as in the 39'mm. specimen) they 
are not distinguished from each other. Probably they run side by side and are too small to 
be shown separately in these drawings made in this small but natural si2;e. In the 175' 
mm. fishlet (Figure 11, plate I) the yolk cord cannot be seen due to the position of the 
wide head. Probably it is too short for the yolk'cord trunks to be seen, as is the case in 
the 390'mm. shark (Figure 49, plate V). 

Yolk-Sac Circulation of the 43'mm. Specimen 

This is the only embryo and egg of Chlamydoselachus whose vitelline circulation has 
previously been described. This was done by Nishikawa (1898, p. 97) who had at least 
six eggs with young embryos (32-60 mm. long) but he seems not to have been aware of the 
studies of his predecessors — not even of Balfour's well'known work. Had he consulted 
this author, he surely would not have made such errors as fill his page and give point to 
Balfour's remark (1885, p. 465) "The observations recorded on the subject [the circulation 
of the yolk'sac in sharks] are, so far as I am acquainted with them, very imperfect, and in 
most cases the arteries and veins appear to have been transposed". What our Japanese 
author wrote illustrates this point. 

The circulation in the yolk'sac could be clearly traced and is reproduced in Figs. 1 and 2 
[my Text-figure 4, and Figures 7 and 8, plate I]. On leaving the umbilical cord [yolk cord] 
the artery and vein run in opposite directions. The former receives on its course a number of 
smaller veins from the two poles of the yolk-sac, and divides finally into three main branches. 
The artery runs for some distance without giving off any branch, and then divides into two 
main vessels, which, after running for a short distance parallel to each other, form at last, on 
the opposite side of the yolk-sac, an elongated, irregularly shaped arterial ring, from which 
numerous small vessels radiate toward the periphery. The arterial ring just mentioned is still 
wide apart in the embryo of 32 mm., but in one of 43 mm. its two halves almost touch each 
other [Figure 8, plate I j, but in other respects there is no change in the circulation. 

Nishikawa's description contains many errors. An attempt was made by the 
present writer to correct these by insertions in brackets, but when done the resulting 
paragraph was so conglomerate and confusing that it was discarded. It has seemed best 
to quote just what Nishikawa wrote, and then to describe in my own words the cir' 



620 



Bashford Dean Tviemorml Volume 



culation as shown in Dean's drawings Pigures 7 and 8, plate I . The reader can then 
compare the two statements and detect the errors. 

Circulation on Dorsal Surface of Yolk Sac. — As explained above, Dean had Nishi- 
ka-w,-a"s figures redra^^^ii for reproduction by lithography. It may be seen in the Kne 
cut TText 'figure 4 1 and in the copy fTigure 7- plate I that the 43'mm. fish has considerable 
freedom of movement on its yolk sac, as is shov^-n in the position of the artery under the 
tail of the reversed embryo. This arter>^ is unlike that of the 39'mm. embryo Figure 50, 
plate V) in that it gives off on the left side one small quickly bifurcating branch, but is 
Hke the former in that the main arter>^ divides into two just where it passes over the 
equator of the yolk mass. The venous system on the embryonic side of this egg shows 
much grovvth and differentiation over that of the 39'mm. embryo portrayed in Figure 50, 
plate \'". In the hinder and lower segment of this half of the yolk, the dendritic arrange- 
ment of the venous system shows about as in the 39'mm. embr>'o. But in the region just 
posterior to the yolk stalk, large veins on each side empty into the main trunk. 




Test-ngure 31 
The egg oi Acanthias vulgaris in its horr.y ci55. This is the earliest figure found 
portrajong the embryo and its viteUine circulatory system. For explanation see 

caption to Text-figure 30. 
After Lev%, 1852, Fig. 6, pL m. 

The oldest figure known to me portraying the circulatory system of a shark • Acan- 
thias vulgar\s=Squalus acanthias^ is that by Leydig '1852, Fig. 67, pi. Ill shown in my 
Text-figure 31. Here the viteUine artery branches at the edge oi the blastoderm and 
forms the arterial ring -his "sinus terminaHs"'), which gives off many branches behind. 
These communicate with the developing venous system whose main trunk enters the 
yolk stalk from the rear. This figure portrays a circulation intermediate between that of 
Dean's 39' and 43'mm. embryos. 

Circulation on Ventral Surface of Yolk. — The blood-vascular system on the ventral 
(lower) side of the egg carrying the 43'mm. embryo will now be considered. It is un- 
fortunate that there is not at hand at least one figure 5ho\<.-ing in an earlier stage the 
development in Chlamydoselachus of the yolk'\-ascular system on this side of the egg. As 
shown in Figure 8, plate I, the bifurcating viteUine artery, just below the equator of the 
egg, has formed the arterial ring, which shows a number of striking irregularities. The 



The Embryology of Chlamydoselachus 621 

ring has contracted until now only about one-fifth the area of the yolk mass is not covered 
by the arterial system. The ring gives off a multitude of branches or small arteries on its 
outer side. These communicate by capillaries with the forming venous system as 
Figure 8 shows. As may be seen on the lower side in Figure 8, all the veins on this side 
of the ring are gathered to form the great vein entering the yolk stalk under the tail of the 
fishlet — if it were drawn in its normal position. The small veins formed on the upper 
side of the arterial ring (Figure 7) empty from both sides into the main vein just before it 
enters the yolk stalk. 

Vitelline Circulation of the 50-mm. Embryo 

Since this little fish is but 7 mm. longer than the 43'mm. specimen, its yolk-vascular 
system might be expected to be in about the same stage of development. However, on 
the dorsal surface (Figure 9, plate I), the artery, which is under the tail of the rotated 
embryo, shows six small branches before its main trunk passes over the equator of the egg 
to form the normal bifurcation. The venous system on the upper side of this yolk is far 
better developed than that of the younger embryo (Figure 7, plate I), the whole hinder 
surface of the egg being thickly covered with small veins. 

In ventral aspect (Figure 10, plate I), it is seen that the arterial ring is in about the 
same stage of development as is that of the 43-mm. specimen (Figure 8, plate I). Notable 
IS the fact that the irregularities of the two rings are almost identical. Here there is the 
same profusion of small arteries radiating outward from the ring, but not a single one 
on the inside. 

So far as I can find, the earliest portrayal of the closing arterial ring on the ventral 
surface of an elasmobranch egg was made by Wyman (1867, Fig. 3, plate 1). On the yolk 
of a rapidly developing embryo of Raia hatis in the selachian stage, the ring has nearly 
closed, and the yolk-sac circulatory system is in about the stage of that shown in Dean's 
Figures 9 and 10, plate I, for the 50-mm. Chlamydoselachus. 

Yolk-sac Circulation of the 175-mm. Fish 

Little can be seen of this on the dorsal side of the egg (Figure 11, plate 1). Venous 
blood vessels seem to cover this side of the yolk pretty thoroughly. On the fish's right is 
a large vein which may be the principal one going into the yolk stalk. On the ventral 
surface (Figure 12, plate I), it is shown that the arterial ring is breaking up. Only parts of 
the original artery are seen and these for the first time give off branches on the insxde of the 
ring as well as on the outside. The yolk-sac circulatory system of the 175-mm. embryo has 
plainly reached a high stage of development, and the growth of the little fish must 
go forward much more rapidly than ever with the incoming of larger amounts of 
food materials. 

Vitelline Circulation of the 390-mm. Shark 

Compared with the circulatory system of the 175-mm. shark, this stage is noteworthy 
for the complete absence of the arterial ring. We see extending out under the head of the 
fish one long arterial trunk which breaks up into a multitude of branches. Hence it is 



622 Bashford Dean Memorial Volume 

a reasonable conclusion that the disintegration of the ring, seen in process of going to 
pieces in Figure 10, plate I, has gone on to completion. Not enough of the venous system 
is shown to justify description. 

Although, as stated above, I have never been so fortunate as to study the progressive 
development of the yolk-vascular system on an elasmobranch egg, I have done so on 
the large-yolked 20-mm. egg of the gaff-topsail catfish, Felichthys feUs. Here was found the 
same artery coming out from under the head of the embryo, bifurcating to form the arterial 
ring. Then a venous system developed as in the sharks, with a main trunk coming in under 
the tail of the embryo. The closing of the arterial ring was very like that in elasmobranchs. 

THE ADULT CHLAMTDOSELACHUS AKGUITiEUS 

At the head of Dean's ''List of Figures" is this notation, "Adult — natural color" 
and on the line below "Adult — photo of head, lat. & ventral". The photographs 
— old, dark, and faded — I find. But, instead of a drawing of an adult in "natural color", 
I find drawings of two adults — a male and female shown in lateral aspect — and two draw- 
ings of the head, in dorsal and ventral aspects. The drawing of the head in lateral aspect 
was not needed since both adults were portrayed in this position. Presumably these 
specimens are shown in "natural color". 

These figures are all reproduced on plate VI, which has been reserved for the adult 
stage. With the reproduction and description of these drawings, the life history of 
Chlamydoselachus anguineus as portrayed in Dean's drawings and recorded in his frag- 
mentary notes will have been adequately figured and followed, and we will then have seen 
how correctly Samuel Garman named it the cloak-gilled snake-like shark. 

AN ADULT FEMALE FRILLED SHARK 

Such a Chlamydoselachus is portrayed in what is presumably natural color in Figure 
52, plate VL There is no record of its length and no indication as to the scale on which 
this figure is drawn. The original drawing measures 603 mm. to the broken-off tip, and 
with the tip completed — 614 mm. (24.2 in.). A glance at the plate shows that the 
drawing of the female (614 mm.) is longer than that of the male (538 mm.) by 76 mm. 
(about 3 in.). This is to be expected. The female (shark or bony) fish is generally larger 
than the male. Gudger and Smith (1933, pp. 262-263, Tables IV and V) were able to 
record the lengths of 35 female specimens of Chlamydoselachus ranging from 610 to I960 
mm. (24 to 77-2 inches) — and averaging 1532 mm. (60.3 inches). They could find measure- 
ments for only 15 males. These ranged from 920 to 1650 mm. (36.25 to 65 inches) and 
averaged 1293 mm. (50.9 inches). However, one has to see the tables (Article V. of this 
volume, pp. 262-263) to have it made clear that the females uniformly run larger than the 
males. The largest male measured 1650, the next one but 1474 mm. There are 16 females 
ranging between these limits of the males, and there are 10 females ranging between 
1670 and 1960 mm. The females average considerably larger than the males. This is 



The Emhryohgy of Chlamydoselachus 623 

because the females must have body and blood to manufacture the huge ovarian eggs, 
and must have a larger body-space to carry during the long gestation period the 8 to 12 
eggs and embryos such are as portrayed in Figure 49, plate V. 

A mere glance at Figure 52, plate VI, shows a long and slender shark whose head 
and body from snout to pelvic fin are of approximately the same diameter throughout. 
This uniform size of body surely enables Chlamydoselachus to creep through the inter- 
stices of debris at the bottom of the sea that would stop any other shark and almost any 
large teleost other than an eel. Possibly this very slender body is connected with the 
feeding habits of the shark. However, this slender appearance must be considerably 
changed when the fish is gravid or when the ovaries contain nearly ripe eggs (Text-figure 
7). This slenderness of the body will be emphasized by giving some ratios of total length 
to depth. Thus a male 1473 mm. long was in length 16.4 times the depth of the body. 
A non-gravid female 1910 mm. long gave a ratio of 11.5 to 1. A 920-mm. female gave 
a ratio of 12.3 to 1 — a fair average between the other two. A female measuring 1860 mm. 
was judged from the figure to be gravid. Her ratio was 7-7 to 1. Lastly a figure of a full- 
bellied female, also presumably gravid, from measurements of the figure gave a ratio of 
6.67 to 1. 

Let us now go more into the details of the external form of our fish as seen in Figure 
52, plate VL The eye is round but the socket is somewhat distorted by the mouth being 
drawn gaping. The mouth is nearly terminal and the gape is very large in both vertical 
and horizontal measurements. The briar-like teeth are faintly indicated, but even plainer 
are the denticles on the lips and the plications in the skin at the angles of the jaws. The 
gill-covers are frilled, the frills being due to the points of the branchial rays which aid the 
covers in respiration. The gill-covers of the first pair are continuous across the isthmus. 
Where the covers are attached to the body are the curious curved surfaces noted in the 
embryos. Visible are the ends of the gill-filaments. Surely Chlamydoselachus is 
the ''fringe-gilled'" shark. 

The back of this fish is nearly straight from the top of the head to the insertion of 
the dorsal fin. On head and cheek are some of the sensory canals and on the side of the 
body runs the lateral line, normal throughout — including the customary irregularity 
under the dorsal. The abdomen looks full and leads to the suspicion that this female is 
possibly gravid. Along the ventral surface of the abdomen are the curious tropeic folds 
probably functioning as bilge keels. These keels end between the pelvic fins and immedi- 
ately in front of the cloacal aperture. 

At the junction of trunk and tail and just in front of the caudal fin are the dorsal 
and anal fins set in a vertical line. Concerning this interesting concentration of the fins of 
Chlamydoselachus, Gudger and Smith (1933, p. 296) have this to say: ''The close as- 
sociation of dorsal, anal and pelvic fins with the caudal gives the creature a fulcrum on 
which to straighten its body in striking forward to seize its prey. This was first suggested 
by Garman. In ordinary swimming, right and left strokes of the caudal will send the body 
forward with the sinuous motion common to all slender fishes." 



624 Bashford Dean Memorial Volume 

AN ADULT MALE CHLAMTDOSELACHUS 

An adult male frilled shark is accurately portrayed in Figure 53, plate VI. In the 
original drawing, this figure is 538 mm. (21.2 in.) in total length. From the fact that this 
drawing shows the mouth closed, one gets a clear idea of the great length of the jaws 
which reach to a point well behind the rear of the skull. For measurements of the jaws of 
four adult specimens of Chlamydoselachus, see Gudger and Smith (1933, p. 268). The 
extraordinary structure and functioning of the jaws of this shark have been admirably 
characterised by Goodey (1910, p. 550) as follows: 

Perhaps the most important point in regard to the specialization of the skull of Chlamydo- 
selachus is to be seen in the extreme length and mobility of the jaws. These are exceptionally 
long, extending from the anterior, almost terminal mouth to a point well behind the posterior 
limit of the cranium. This extension is remarkable; in fact, one quarter of the total length of 
the jaws is found in this region, and it is this feature, connected with the exceptional length 
of the hyomandibular, which gives the jaws their great mobility. Indeed, their disposition 
relative to the cranium is quite different from that found in any other Selachian whose skull I 
have been able to examine or to see a figure of It resembles nothing among the Vertebrates 
so much, perhaps, as the general disposition of the jaws in certain of the Ophidia. 

As seen in Figure 53, plate VI, in the front of the mouth are a few teeth, and above 
and sHghtly lateral is the vertical nostril with two divisions — the upper for ingress and the 
lower for egress of water. The gill'covers are normal, and it can be seen that the first pair 
flare widely and are continuous across the throat. Short external gill'filaments are seen 
in every slit as in the female on this plate. The lateral line runs straight back to the re' 
gion of the dorsal fin where the usual (normal?) irregular bendings are found. The body 
cavity of the male is plainly not nearly so large as that of the female, nor is the tro- 
peic'fold region so well marked. On the other hand, the myomeres in the body of the 
male are distinct whereas none are shown on the trunk of the female. 

The above are, however, but minor differences. The one particular thing, that at 
a glance differentiates this and all other male individuals from the females, is the presence 
of the myxopterygia or claspers. As shown in Figure 53, plate VI, these are grooved 
finger'like modifications of the hinder and inner parts of the pelvic fins. When the male 
inserts these into the cloaca of the female during copulation, he holds her fast for the 
passage of the spermato2;oa. It is not necessary here to go further into the structure and 
function of these organs. These matters have been treated earlier in this article. This 
drawing is the best representation of the male Chlamydoselachus ever published. 

There is another structure in which these particular drawings of the two sexes 
differ — i.e., in the end of the caudal fin. In the female the tail and tail fin — as properly 
restored — end in a fine point. And so do the caudal fins of most of the embryos studied. 
On the other hand the drawing of the tail fin of the adult male ends in a rounded point 
and there is a notch near the tip of the ventral lobe. Thus from these figures one might 
jump to the conclusion that the female fish have pointed caudals and the males notched 
ones. But this is not true. Gudger and Smith (1933, pp. 293-297) have gone rather fully 
into the question of the form of the tip of the tail in the frilled shark, reproducing every 



The Embryology of Chlamydoselachus 625 

published figure of an adult Chlamydoselachus, and recording its form in their own four 
specimens. But, unfortunately, they did not record the sex of each fish noted. This 
I have done for all the specimens figured by them. Of these, 2 males and 4 females have 
pointed tails, and one female has a tail that appears to be notched. Of the 6 adult speci' 
mens in the Museum collection (4 used in previous researches, and 2 found since), all — 2 
males and 4 females — have pointed tails, 3 straight and 3 drooping. 

THE HEAD OF THE ADULT SHARK 
The lateral aspect of the head of Chlamydoselachus in both sexes, and with mouth 
open and shut, is admirably portrayed in Figures 52 and 53, plate VI. What are needed to 
make the portrayals complete are drawings of the dorsal and ventral aspects. Dean's 
''List" for "Adult" calls for "photo of head lateral and ventral". These I find, but I also 
find two excellent drawings of the adult head seen from above and below. They will 
now be described. There are no notes for these as there are none for the photographs. 

HEAD— DORSAL ASPECT 

The head in dorsal view is shown in Figure 54, plate VI. From the angle of the 
jaws, the head narrows gradually to the rounded blunt snout — a marked contrast to 
the broad blunt snouts of the tiger and whale sharks and to the keen'pointed ones of the 
Isurid sharks. The eyes are set in shallow cavities. From the angle of the jaws, the head 
widens to its maximum over the hinder edge of the first gill-cover. In all the gill'slits, 
except the last, short external filaments are visible — as they are in the specimens repre- 
sented in the fulHength drawings. Whether or not this head is that of the male fish, 
portrayed in lateral view in Figure 53, plate VI, cannot be said, but it certainly is not that 
of the female fish of Figure 52 on the same plate. Her first gill-cover looks as if it had the 
edge bitten off. Also the space between the first and second arches is much wider than 
that between the second and third, etc. In Figure 54, the widths of the openings are very 
uniform save for the last ones at the bases of the pectoral fins. These fins are entirely 
normal. Running along the back on either side is the lateral line. Of the latero-sensory 
head canals, nothing can be seen save one curving gracefully in front of each first gill- 
cover. No spiracle is shown. The opening was probably so small that the artist did not 
find it. That this head seen in dorsal aspect is that of an adult Chlamydoselachus may 
be judged by comparing it with the head of the l75-mm. specimen portrayed in dorsal 
view (Figure 11, plate I). 

HEAD— VENTRAL ASPECT 

The ventral aspect of this same head (the figures have the same measurements) may 
be seen in Figure 55, plate VI. Above and on either side of the mouth, the nostrils show 
faintly. The almost terminal mouth, with some of the upper teeth showing, is very 
prominent. So great is the front-to-back gape, that the angle of the mouth is a little 
further than halfway back of the median point between tip of snout and hinder edge of the 
first gill-cover. The throat has the skin plicate to allow for expansion when large objects 
are swallowed. The gill-covers of the first arch are confluent across the isthmus or throat 



626 Bashford Dean hiemona] Volume 

— i.e. the shark is cloak-gilled (Greek, Chlainys. a cloak). Paired latero-sensory canals are 
found on each first gill-cover and extend far on the throat region toward the symphysis of 
lower jaw. The hindmost ot these canals are continuations or the ones seen on the first 
pair of gill-covers in the dorsal aspect. The short gill-filaments are visible. 

The stout pectoral fins with, their strong bases look ""finished"". Beginning between 
them and extending backward are the tropeic tolds or bilge keels with therr deep median 
groove. One wishes that this excellent drav^Tng portrayed the ventral surface clear 
back to the tip of the caudal fin. 

As noted, Dean's '"List"" calls ror ""Adult, photo oi head lat. it ventral"". These 
I have found, old and faded. The specimen, firom which these photographs were made, had 
been mutilated in both gill-regions — the parts of particular interest just here — and ap- 
parently had suffered partial maceration. Furthermore, the shrunken gill-flaps and the 
distorted gill-filaments indicate that they had undergone considerable drying. These 
photographs portray gill-region conditions unlike what are tound m the eleven figures of 
heads and of whole fish reproduced by Gudger and Smith ' 1933 '. Such conditions were 
not found m a single one of the srs specimens m the ^American \Iuseum studied by Smith 
(1937j. nor are they portrayed in any of Dean's four figures reproduced herein as plate VI. 
It is e\'ident that the photographs do not portray a normal specimen as it appeared in life 
and that they possess no scientific \^lue whatever. There are no notes to teU us by whom 
they were taken, why they were made, nor why they were included in Dean's records. 
They will not be reproduced in this article. 

EXTERX.\L GILL-FILAMEXTS IX CHLAMTDOSELACHUS 

Before concluding this study of the breeding habits and external embryonic develop- 
ment of Chla-mydoselachns, the matter of its external gills must be taken up. These, as 
indicated above, are commonly round in the embryos but very rarely in adults. In the 
embr\'os they are in origin totally unlike the external gills tound present m Crossopterygii, 
Dipnoi, and in .Amphibia, and are considerably different m length and profusion from the 
external gills figured and described in the embryos of many species ot elasmobranchs. 
Chlamydoselachus is the only shark known to me to possess in the adult stage, even occa- 
sionally, short external gill-filaments. This matter of external gill-filaments is so important 
that it must be considered carefully. 

EXTERX.^L GILL-FIL.'WIENTS OF THE EMBRYOS 

The embryos of all non-placental viviparous sharks and rays known to me have long 
external gills. The eggs of these elasmobranchs have thin diaphanous shells, through 
which uterine fluids readily penetrate. These fluids are milk-like secretions ot the uterine 
mucosa and ser\'e as food ror the growing embryos, which absorb this tood through their 
long filamentous gills. It has been indicated above that the relatively thick shells of 
Chlamydoselachus are burst by the growmg embryo, are cast off into the uterus (Figure 11, 



The Embryology of Chlamydoselachus 627 

plate I), and are then or later thrown out into the sea. Two investigators (Hawkes, 1907; 
and Smith, 1937), have found highly vascularized areas in the wall of the right uterus. 
These observations suggest that these areas might have served to secrete food stuffs into 
the uterus. Then the long gestation period and the enormous size of the relatively late 
embryos still attached to large yolk sacs seem to indicate that these embryos grow not 
at the expense of the yolk alone. All these things lead to the inevitable question — ''Do 
the external gills of the embryos of Chlamydoselachus serve to absorb food from a uterine 
secretion?" The facts and inferences as to such a possible source of food in Chlamydo^ 
selachus have been set forth above. It seems quite sure that in any case, these external 
gills of the non^extruded juvenile sharks serve as respiratory organs. 

Chlamydoselachus has been ranked by the systematists as the lowest, most primitive 
living shark. Yet in its reproductive organs, as this paper shows, and in many other 
organs, as Smith has pointed out in his monograph on the anatomy (1937), it is very 
highly specialized. Its embryos have external gill-filaments, which never grow very long 
and which eventually shorten until they are almost or quite concealed from view by the 
gill'flaps. Now external gills, as they are ordinarily understood, are embryonic or an- 
cestral organs which tend to become eliminated in the process of evolution. External 
gill-filaments are either evanescent structures of external origin, developed as outgrowths 
on the outermost edge of a visceral arch before the clefts have broken through, or they 
are precocious growths of normal gills which tend to shorten in the course of later de- 
velopment. Let us now study these filaments as they are shown in the drawings of the 
embryos of this archaic shark and see to which category they belong. 

The first evidence of the presence of gill-filaments in the embryos of Chlaynydo- 
selachus is found in the 25-mm. stage as portrayed by Ziegler (1908, Fig. 2). Ziegler's 
figure (my Text-figure 27c) is poorly reproduced on soft paper, and the budding filaments 
show up indistinctly. However, in the figure these buds appear not on the outer edges of 
the gill-arches but on the hinder inner sides of arches 1-5, and on both sides of No. 6. 
Furthermore, it is clear that the gill-clefts have become perforated, and that the outside 
liquid penetrates into the pharynx through the slits. 

Brohmer's drawing (1909, Fig. 3) of his 25-mm. specimen (also poorly reproduced) 
shows the gill-filament buds on both sides of arch No. 2 (my Text-figure 27a). Probably 
they are present in a beginning stage on both sides of each arch. They are next seen (as 
far as data are at hand) in Nishikawa's 32-mm. embryo (Figures 19-21, plate II) where 
they appear on both sides of every arch — excepting of course the first. Passing over the 
34-mm. specimen, we go to the 39-mm. embryo in which stage the filaments first begin to 
show externally, particularly in the first sHt (Figure 25, plate II). These filaments are in 
about the same stage of development as those in Scammon's 18-mm. Squalus (1911, Fig. 
27, pi. III). But in size and abundance they are far behind the filaments protruding from 
the gill-sHts of Scammon's 20.6-mm. embryo of the dogfish. 

External filaments are seen to be pretty well developed in Dean's ''new series" of 
drawings of embryos 46, 54, 66, and 103 mm. in length. These can be best studied in the 



628 



Bashford Dean Memorial Volume 



ventral views reproduced in Plates III and IV. where they seem to be growing on both 
sides of each slit. That this is a fact, I have proved by microscopic examination of the 
head of an embryo about 45'mm. long found in the Dean material in the Museum. This 
specimen had been fixed in bichromate of potash and under the binocular microscope 
showed filaments on both the anterior and posterior sides of every arch save the hyoid — 
and some protruded even from the spiracle. These external filaments are somewhat better 
developed in the 103'mm. fish (Figures 41-43, plate IV) than in any younger embryos. 
But even here they are hardly so well-grown as those in Scammon's 20.6'mm. Squalus 
(his Fig. 28, tab. III). 

Among the embryos loaned from Columbia University for this research, I could for 
a long time find no specimen with gill-filaments longer than those of the 46-mm. young 
(Figures 28-30, plate III) and of the 103-mm. fish (Figures 41-43, plate IV). However, 
one day in examining the egg with the split yolk (referred to previously) as having a cap- 
sule with the curious tendriliform process seen in Figure 13, plate I, I removed the crum- 
pled shell, and to my great surprise and pleasure found the little fish with long filaments 
now to be studied. 

This specimen (71-mm. long), as seen in Text-figure 32, has longer and more profuse 
external gill-filaments than any young Chlamydoselachus figured by Dean. This will be 
noted at once when Text-figure 32 is contrasted with Figure 41, plate IV (the 103-mm. 
specimen). It is impossible to measure these filaments since they are more or less sinuous, 
and sometimes spirally coiled. Due to their being tangled, they sometimes appear to be 
branched, but under the binocular microscope this is seen to be an optical illusion due to 
their overlying each other. For comparison's sake, there is introduced here, as Text-figure 
33, Scammon's figure of his 28-mm. Squalus in about the same stage of gill-filament 
development as the 7l'mm. Chlamydoselachus. Possibly if the filaments of the little 




Text-figure 32 
A 7l'mm. frilled shark with a profusion of external gill-filaments. These are the longest found in any 
specimen or drawing of this shark in this research. 
Photograph by Charles H. Coles, A. M. N. H. 



The Embryology of Chlamydoselachus 



629 




Text-figure 33 
A drawing of a 28-mm. Squalus acanthias in about the same stage of external gill-filament develop- 
ment as is the young Chlamydoselachus shown in Text-figure 32. 
After Scammon, 1911, Fig. 30a, PI. III. 

frilled shark could be straightened out they might be as long as those of the dogfish. The 
two little sharks are shown in the same size, though in life Chlamydoselachus is 2.5 times 
longer than Squalus. This shows how much faster and farther the dogfish had gone in 
development. For a frilled shark of approximately the same size as this Squalus, see 
Figure 23, plate II of a 34'mm. Chlamydoselachus. 

In Dean's figures of older embryos measuring 124, 175, 185, 240, and 390 mm., and 
all drawn at an earlier date then those of 46, 54, 66, and 103 mm., the external filaments are 
very much reduced. They are hardly visible underneath the flaps. From all the data 
carefully marshalled above, I draw the conclusion that these so-called external gills of the 
larval frilled shark are nothing but precociously overgrown permanent gills, which later on 
shorten until but a bare remnant shows beyond the gill-opening, as may be seen in the 
largest (390-mm.) embryo portrayed by Dean (Figure 49, plate V). 

From these facts, found in the drawings cited, it is clear that these protruding gill- 
filaments in the embryos of Chlamydoselachus are not true external filaments like those 
of the Crossopterygii, Dipnoi, and Amphibia. In the larvae of the dogfish and of the 
various rays dissected and studied by me, the external filaments are many, long, and plu- 
mose. By the time of hatching these have disappeared. Whatever may be the part of 
these external gills in the nutrition and respiration of the embryo, they are almost always 
absent in the adult. 

EXTERNAL GILL-FILAMENTS IN THE ADULTS 

No other adult shark or ray known to me has even the semblance of external gills, 
but some specimens of the adult Chlamydoselachus do have such a semblance. Allis 
(1923) has a drawing (reproduced by Gudger and Smith, 1933, in their Fig. 7, pi- II — 
Article V of this Memorial Volume) made from an adult head supplied to him by Dean, 
which shows such remnants of protruding filaments as are seen in Dean's figures on 



630 Bashford Dean Memorial Volume 

Plate VI. Allis's figure in his article (1923) appears to be in natural size, and Dean's 
figure of a female fish in the original drawing measures 614 mm. (24.2 in.). This, it should 
be noted, is just about the size of a young specimen taken by the Prince of Monaco at Ma' 
deira, and pronounced by Collett (1890) to differ from adults only in the matter of size. 

Elsewhere it has been stated that there are in the Museum collection six adult 
frilled sharks. What is the evidence from them as to protruding gill-filaments ? Three of 
these sharks have been dissected by Smith (1937) who found that the gill-filaments did 
not show externally. Similar conditions were found in the three undissected specimens. 
None showed protruding filaments. We also have a head only, straight and well-preserv- 
ed, but it shows no external filaments. As to the function of these slightly protruding 
gill-filaments, one can infer that they make the gills of such adults as possess them, some- 
what more efficient in respiration. 

From the data given, it is probable that some embryos of Chlamydoselachus (Fig- 
ure 49, plate V) carry over into the adult stage remnants of their embryonic external gills. 
But it is evident that most adults lack such protruding gill-filaments. For figures in which 
they are absent, see Gudger and Smith's (1933) article on the natural history of Chlamydo- 
selachus, wherein all known figures ot the whole fish and ot its head are reproduced. That 
external gills sometimes occur in the adult Chlaynydoselachus is additional evidence of the 
unpredictable characteristics of this primitive shark. Perhaps I cannot do better than to 
quote Smith's summation (1937, p. 495) — "My outstanding impression of the frilled 
shark is that it presents a strange assemblage of characters ranging from very primitive to 
highly differentiated". 



The Emhryology of Chlamydoselachus 631 

BIBLIOGRAPHY 

Allis, Edward Phelps, Jr. 

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II, pp. 1-17, 2 pis.). 

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COSTE, J. J. 

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1934. The elasmobranch fishes. 3rd. ed. revised. Berkeley, California. 332 pp., 270 figs. 

Dean, Bashford 

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japonicus Macleay. Annot. Zoo/. Japon., 4, 1-7, pi. 

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Deinega, W. a. 

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DoFLEiN, Franz 

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Ceylon. Leipzig. (Data on Ch/amydose/achus, pp. 257, 267-268, fig.) 



632 Bashford Dean Memorial Volume 

Garman, Samuel 

1885. Chlamydoselachus anguineus Gar. — a living species of cladodont shark. Bull. Mus. Comp. 
Zoo/., 12, 1-35, 20 pis. 

Garman, Samuel 

1913. The Plagiostomia (sharks, skates and rays). Bull. Mus. Comp. Zool., 36, (Eggs and embryos of 
Chlamydoselachus anguineus: pi. 59, figs. 4 and 5; pi. 61, figs. 7 and 8. 

GOODEY, T. 

1910. A contribution to the skeletal anatomy of the frilled shark, Chlamydoselachus anguineus Gar. 
Proc. Zool. Soc. London, pt. 1, 540-571, 5 pis. 

GUDGER, E. W. 

1912. Natural history notes on some Beaufort, N. C. fishes, 1910-11. No. I. Elasmobranchii — with 
special reference to utero-gestation. Proc. Biol. Soc. Washington, 25, 141-156. 

1913. Natural history notes on some Beaufort, N. C. fishes — 1912. Proc. Biol. Soc. Washington, 26, 
97-110. 

1918. Oral gestation in the gafF-topsail catfish, Felichthys felis. Papers Dept. Marine Biol, Carnegie 
Instit. Washington (Pub. no. 252), 12, 25-52, 4 pis. 

GuDGER, E. W. AND SmITH, B. G. 

1933. The natural history of the frilled shark, Chlamydoselachus anguineus. Bashford Dean Mem. 
Vol. : Archaic Fishes, Art. V, pp. 243-330, 5 pis. and 31 text-figs. 
Haswell, W. a. 

1897- On the development of Heterodontus {Cestracion) phillipi. Proc. Linn. Soc. T^ew South Wales, 
22, 96-103, 2 pis. 
Hawkes, O. a. Merritt 

1907- On the abdominal viscera and a vestigial seventh branchial arch in Chlamydoselachus. Proc. 
Zool. Soc. London, 471-478, 3 figs. 
Leigh-Sharpe, William Harold 

1922. The comparative morphology of the secondary sexual characters of elasmobranch fishes — the 
claspers, clasper siphons, and clasper glands. Mem. I. Journ. Morphol., 34, 245-266, 12 figs. 
Leydig, Franz 

1852. Beitrage zur mikroskopischen Anatomie und Entwickelungsgeschichte der Rochen und Haie. 
Leipzig. (Embryologischer Teil, pp. 90-120, pis. Ill and IV). 
LoHBERGER, Johannes 

1910. Ueber zwei riesige Embryonen von Lamna. Abh. Bayer. A\ad. Wiss., Suppl. Bd. 4, (Beitrage 
zur Naturgeschichte Ostasiens, Abt. 2, 45 pp., 5 pis). 

MOMOSE, F. 

1938. A newly arrived specimen of the "Frilled Shark" [text in Japanese]. T^atural Science and 
Museum, Tokyo, 9, (no. 8), 2-5, 7 figs. 
Nishikawa, T. 

1898. Notes on some embryos of Chlamydoselachus anguineus Garman. Annot. Zool. Japon., 2, 
95-102, pi., 3 text-figs. 
Osburn, Raymond C. 

1906. The origin of vertebrate limbs. Recent evidence upon this problem from studies on primitive 

sharks. Ann. J^ew Tor}{ Acad. Sci., 17, 415-436. 
1907- Observations on the origin of the paired fins of vertebrates. Amer. Journ. Andt., 7, 171-194, 
5 pis. 



The Embryology of Chlamydosdachus 633 

Rose, C. 

1895. Ueber die Zahnentwicklung von Chlamydoselachus anguinens Gaiin. Mor/ili. Arb., 4, (A 340- 
mm. embryo ivi Leibe of a female Chlamydoselachus, p. 194). 

Sanzo, Luigi. 

1910. Embrione di Carcharodon rondeletii M. Henle, con particolare disposiziione del sacco vitellino. 
MeiTi. R. Comit. Talassog. Ital., no. 11, 1-10, 2 pis. 

ScAMMON, Richard E. 

1911. Normal plates of the development of Squalus acanthias. In Keibel. F. Normentafeln zur 
Enwicklungsgeschichte der Wirbeltiere. Jena. Heft 12, 140 p., 4 pis., 26 text-figs. 

Shann, Edward W. 

1910. A description of the advanced embryonic stage of Lamna cornubica. 28. Ann. Rept. Fishery 
Board Scotland, pt. Ill, Sci. Invests., 73-79, pi. 

Smith, Bertram G. 

1937- The anatomy of the frilled shark, Chlamydoselachus anguineus Garman. Bashford Dean Mem. 
Vol.; Archaic Fishes, Art. VI, 331-520, 7 pis., 128 text-figs. 

Vaillant, Leon 

1889. Note sur un foetus gigantesque d'Oxyrhina spallanzanii Bonap. Bull. Soc. Philomath. Paris, 8. 
ser. 1, 38-39. . 

Wyman, Jeffries 

1867. Observation on the development of Raia batis. Mem. Amer. Acad. Arts and Sciences, n. s. 9, 
31-44, pi. 

ZlEGLER, H. E. 

1902. Lehrbuch der vergleichenden Entwickelungsgeschichte der niederen Wirbeltiere. Jena. (Sela- 
chier. pp. 101-152, 55 figs.). 

ZlEGLER, H. E. 

1908. Ein Embryo von Chlamydoselachus anguineus Garm. Anat. Anz., 33, 561-574, 7 figs. 



PLATE I 
EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE I 
EGGS AND EGG CAPSULES OF CHLAMTDOSELACHUS 

Fig. 1. A ripe ovarian egg of the frilled shark. The original drawing measures 90 x 96 mm., and is pre- 
sumably in natural size. See also Text-figure 12. 

Fig. 2. An asymmetrical oblong egg of the frilled shark. The asymmetry of this egg probably originated 
during the process of shell formation. 

Fig. 3. A symmetrical oblong egg of Chlamydoselachus surrounded by its transparent keratinoid capsule. 

Fig. 4. A round egg of the frilled shark — C of Dean's list. 

Fig. 5. Another encapsuled round egg — numbered B by Dean. 

Fig. 6. A third round egg — numbered A by Dean. 

Fig. 7. An ellipsoidal encapsuled egg having a 43-mm. embryo attached by a yolk stalk. 
This figure is a copy of Nishikawa's drawing portrayed in natural sik in Text-figure 4. 

Fig. 8. The vitelline blood vessels on the under side of the egg portrayed in Figure 7- 

After Nishikawa, 1896, Fig. 2, pi. IV. 

Fig. 9. An ellipsoidal encapsuled egg with an older embryo (50 mm.) and a slightly more advanced vitelline 
circulation than that seen in Figure 7- 

Fig. 10. Underside of the egg shown in Figure 9. The yolk-sac circulation is slightly more advanced than 
that portrayed in Figure 8. 

Fig. 11. A 175-mm. embryo of Chlamydoselachus attached to its yolk sac and without its capsule. 

Fig. 12. Under side of egg portrayed in Figure 11. This shows a late stage of the vitelline blood vessels. 

Fig. 13. A tendriUform process from the capsule of an asymmetrical oblong egg in the collections of Co- 
lumbia University. This process is similar to that seen in Figure 2. 

Fig. 14. A much-branched tendriliform process. Note its close similarity to those shown in Figures 13 
and 2. 

Each figure on this plate save number 13 is half the size of the original, and hence is presumably one halt natural size. 

Figure 13 is the only figure on these six plates not drawn by or for Dr. Bashford Dean. 



Dean Memorial Volume 



Article VII, Plate I. 






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EMBRYOLOGY OF CHLAMYDOSELACHUS 



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PLATE II 
EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE II 

THE EARLIEST EMBRYOS OF CHLAMTDOSELACHUS OBTAINED 
BY BASHFORD DEAN 

Fig. 15. The earliest embryo (11.5 mm.) of Chlamydoselachus figured by Dean. Original drawing = 121 mm. 

Note the attachment of the embryo to the yolk sac by a short yolk cord. 

Fig. 16. The 11.5-mm. embryo stained, cleared, and drawn considerably enlarged — to 161 mm. 

Fig. 17- A larger embryo (15.5 mm.) shown in lateral aspect. The original drawing measures 177 mm. 

Fig. 18. The largest (20 mm.) of Dean's very small embryos of the frilled shark. The original drawing 

measures 222 mm. 

Fig. 19. Dorsal view, head only, of Nishikawa's 32'mm. embryo, considerably enlarged. 

Fig. 20. Lateral aspect, the head only, of Nishikawa's 32-mm. embryo. 

Fig. 21. Head only of Nishikawa's 32'mm. embryo seen from below. 

Fig. 22. Dorsal aspect of head only of Dean's 34-mm. Chlamydoselachus. 

Fig. 23. Lateral view — full-length — of the 34-mm. embryo. 

Fig. 24. Ventral aspect of the head only of Dean's 34-inm. specimen. 

Fig. 25. Dean's 39-mm. embryo portrayed in full-length lateral aspect. 

All the figures on this pkte are reduced by one-third — i.e., are reproduced 
two-thirds the sizes of the original drawings. 



Dean Memorial Volume 



Article VII, Plate II. 




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EMBRYOLOGY OF CHLAMYDOSELACHUS 



PLATE III 
EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE III 

FRILLED SH.-\RK EMBRYOS OF IXTERAIEDIATE 5IZE: 
39, 46, 48, 54, 55 \L\L 

Fig. 26. An embryo of ^Q- mm portrayed in full-length dorsal aspect. 

Fig. 27. Ventral view — ^full-lengtii — of the 39-mm. specimen. 

Fig. 28. Full-length portrayal in dorsal aspect of a 46-inm. embryo. 

Fig. 29. Lateral full-length \'iew of the 46-mm. embryo. 

Fig. 30. The 46-mm. embryo seen firom belo^w. 

Fig. 31- "Head only stained" of a 48-mm. embryo — ^\'entral aspect. 

Fig. 32- A 54-mm. embr>'o shown in full-length dorsal view. 

Fig. 33. A full-length lateral \-iew of the 54-mm. fishlet. 

Fig. 34. The tadpole-shaped 54-mm. embryo portrayed from below. 

Fig. 35. Dorsal aspect — ^head only — of a 55-mm. embryo. 

Fig. 36. Lateral full-length \-iew of a 55-mm. specimen. 

Fig. 37. Head only of a 55-mm. embryo seen from below. 

All figures on this plate have been reduced by ooe-third their original length. 



Dean Memorial Volume 



Article VII, Plate III. 



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EMBRYOLOGY OF CHLAMYDOSELACHUS 



PLATE IV 
EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE IV 

LARGER EMBRYOS OF CHLAMTDOSELACHUS: 
66, 103, 124, 185, 240 MM. 

Fig. 38. Dorsal view — full-length — of a 66-mm. embryonic Chlamydosehchus. 

Fig. 39. A 66-mm. embryo of the frilled shark seen from the left side. 

Fig. 40. Ventral aspect of the 66-mm. specimen. 

Fig. 41. A specimen 103 mm. long viewed from above. 

Fig. 42. A 103-mm. embryonic frilled shark seen from the side. 

Fig. 43. A young 103-mm. Chlamydoselachus in ventral aspect. 

Fig. 44. Head of a 124-mm. embryo seen from above. 

Fig. 45. A 124-mm. Chlamydosehchus portrayed in lateral aspect. 

Fig. 46. Lateral view of an embryo 185 mm. long. 

Fig. 47. Head only of the l85-mm. embryo — ventral aspect. 

Fig. 48. An embryo measuring 240 mm. seen in lateral view. 

All the figures on plate IV. are reproduced two-thirds the size of the original drawings. 



Dean Mejiorial Volume 



Article VII, Plate IV. 






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PLATE V 
EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE V 

A 390-MM. FRILLED SHARK, A 39'MM. EMBRYO, AND A WIND EGG: 
ALL PORTRAYED IN NATURAL COLORS 

Fig. 49. Dean's largest (390-mm.) embryo of Chlamydoselachus portrayed in lateral view 

in its natural colors. 
Fig. 50. A 39'mm. embryo, its yolk mass, and its yolk'vascular system shown in natural colors. 
Fig. 51. A wind egg of Chlamydoselachus shown in its natural colors. 

Figure 49 on this plate is reduced from 15.35 in. to 11 in. Figures 50 and 51 are reproduced in the si?e 

of the original drawings. 



Dean Memorial Volume 



Article VII, Plate V. 





51 






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50 




Bashford Dean del. 



A. HOEN & Co. LlTH. 



EMBRYOLOGY OF CHLAMYDOSELACHUS 



^ 



PLATE VI 

EXTERNAL DEVELOPMENT OF CHLAMTDOSELACHUS 



PLATE VI 

MALE AND FEMALE SPECIMENS OF CHLAMTDOSELACHUS 

AND TWO HEADS FROM ADULT FISH, ALL SHOWN IN 

THEIR NATURAL COLORS 

Fig. 52. Lateral view of a female Chlamydoselachus. 

Fig. 53. Lateral view of a male frilled shark. 

Fig. 54. Dorsal view of the head of an adult frilled shark. 

Fig. 55. Ventral view of the head of an adult Chlamydoselachus. 

Figures 52 and 53, in the original drawings, measure 614 mm. (28.4 in.) and 538 mm. (21.2 in.) 
respectively. As reproduced on this plate, the fishes measure 505 mm. (19-9 in.) and 443 mm. 
(17.4 in.) each. Figures 54 and 55 are reproduced in the si?e of the original drawings. 




DuKrulID DUS DEI. 



EMBRYOLOGY OF CHLAMYDOSELACHUS 



THE 

BASHFORD DEAN MEMORIAL VOLUME 

ARCHAIC FISHES 



:r?,7;^V 



Gj«X 



Edited By 
EUGENE WILLIS GUDGER 



Article VIII 

THE HETERODONTID SHARKS: 

THEIR NATURAL HISTORY, AND THE EXTERNAL 

DEVELOPMENT OF HETERODOKTVS JAFOKICUS 

BASED ON NOTES AND DRAWINGS 

BY BASHFORD DEAN 

By BERTRAKl G. SMITH 

Professor of Anatomy 

New York University Ck)llege of Medicine 

New York City 




NEW YORK 

PUBLISHED BY ORDER OF THE TRUSTEES 

Issued Oaoher 1, 1942 



ARTICLE VIII 

THE HETERODONTID SHARKS: THEIR NATURAL HISTORY, 

AND THE EXTERNAL DEVELOPMENT OF HETERODOHTUS 

(CESTRACIOTi) JAPOHICUS BASED ON NOTES 

AND DRAWINGS BY BASHFORD DEAN 

By Bertram G. Smith 



CONTENTS 

Introduction 651 

Material and Records 652 

The Specimens and Their Source 653 

Authorship of the Drawings 655 

Written Records Left by Bashford Dean ; 656 

Classification and Synonymy 657 

Heterodontus and Heterodontidae 657 

Synonymy 658 

Common Names — Bullhead Sharks 660 

Family and Generic Characters 661 

The Species of Heterodontus 663 

Heterodontus pMlipi Blainville 664 

Heterodontus zebra Gray , . . . 675 

Heterodontus quo)ii Freminville 676 

Heterodontus francisci Girard 6ol 

Comparison of H. quoyi and H. francisci 684 

Hetaodontus galeatus Gunther 686 

Heterodontus japonicus Macleay 688 

Affinities to Fossil Forms 694 

Sexual Dimorphism and the Reproductive Organs 702 

The Egg Capsule: Its Structure and Functions 705 

Habits of Heterodontus 709 

Habitat and General Habits 709 

Food and Feeding Habits 710 

Breeding Season 711 

Egg-Laying Habits; The Nests 712 

Methods of Collecting Eggs and Embryos 7i6 

Embryonic Development of Heterodontus japonicus 7i7 

Rate of Embryonic Development 717 

General Mode of Development 722 

The Egg and Its Membranes 723 

Reminiscence of Total Cleavage 724 

Discoidal Cleavage and the Blastula 728 

Gastrulation and Early Embryogeny 732 

The Yolk Blastopore 738 

Later Embryonic Development 740 

The Vitelline Circulation 748 

Hatching and the Newly Hatched Young 752 

A 280'MM. Young Heterodontus japonicus 757 

External and Internal Gill Filaments 758 

Development of the Teeth 760 

Bibliography 764 

649 



THE HETERODONTID SHARKS: THEIR NATURAL HISTORY, 

AND THE EXTERNAL DEVELOPMENT OF HETERODOJiTUS 

(CESTRACIOK) JAPOHICUS BASED ON NOTES 

AND DRAWINGS BY BASHFORD DEAN 

By Bertram G. Smith 

Professor of Anatomy 

New York University College of Medicine 

New York City 

INTRODUCTION 

Sharks of the family Heterodontidae (Cestraciontidae) have an especially well' 
defined pedigree. The genus Heterodontus (Cestracion), which includes the only species 
living at the present time, dates at least from the Upper Jurassic; the family Cestracion ti' 
dae, as defined by Zittel (1932), from the Lower Jurassic. The closely related family 
Hybodontidae, represented only by fossils, dates from the Devonian or Lower Carbonifer' 
ous to the Cretaceous. Therefore the geologic histories of the two families overlap; but 
the Hybodonts were approaching extinction when the Heterodonts came into being. 
Since there appears to be genetic continuity between the two families, one might readily 
conclude that the recorded lineage of sharks of the genus Heterodontus is more ancient 
than that of any other living vertebrate. In this circumstance we find the key to Dean's 
interest in the embryology of Heterodontus. 

At the time when Dean began collecting the eggs and embryos of the Japanese 
Bullhead Shark, Heterodontus japonicus, all that was known concerning the embryonic 
development of any species of Heterodontus was contained in HaswelPs brief account 
(1898) of the blastula and gastrula of H. phiUipi. This deficiency was the more notable in 
view of the fact that the family Heterodontidae has no other genus, besides Heterodontus, 
represented by living species. But Heterodontus was not, from Dean's point of view, 
merely another kind of shark to be studied in order to fill a gap in our knowledge of 
comparative embryology. It is well known that Dean, like many other biologists of his 
generation, was interested in the study of animals chiefly from the viewpoint of organic 
evolution. Thus it is not surprising to find in his notebook the following carefully 
worded statement : 

The embryology of the Cestracionts [Heterodonts] is expected to prove of value not 
merely in comparison with other sharks, but in estimating the general significance of develop- 
ment in "recapitulating" ancestral characters. For granting that these sharks represent 
a peculiarly primitive branch of the descent-tree of Selachians, we would reasonably expect 
to find in their embryonic stages certain simpler, more archaic characters than in the cor- 
responding stages of the commoner groups of sharks. Furthermore, and this is the importance 
of such a study, if we do find that Cestracion [Heterodontus] presents definitely more primi- 
tive embryonic characters than sharks of a more modern type, we can certainly maintain 

651 



652 Bashford Dean Memorial Volume 

that recapitulation is not to be given the scant courtesy with which it has come to be treated 
by a modern school of embryologists. In a word, the present theme may be found to provide 
a new (and critical) means of testing the value of the biogenetic law. 

These hopes and expectations led to the publication, in 1901, of Dean's article 
entitled "Reminiscence of Holoblastic Cleavage in the Egg of the Shark, Heterodontus 
(Cestracion) japonicus Macleay." This contribution is reviewed, in considerable detail, 
later in the present paper. Our knowledge of the embryology of Heterodontus is still 
incomplete, so that the possibilities suggested by Dean have never been fully explored. 

To Dr. E. W. Gudger, editor of the Dean Memorial Volume, I am indebted for many 
helpful suggestions throughout the preparation of this article, and especially for taking 
the major part in the difHcult task of making up the plates. 

MATERIAL AND RECORDS 

For the proper evaluation of any scientific record, it is necessary that the reader 
should be informed concerning the identity, amount and source of the material, also the 




Text'figure 1. 

The Marine Zoological Station at Misaki, Japan. 

From a photograph by Bashford Dean, 1904, p. 198. 



The Embryology of Heterodontus japonicus 



653 




Text-figure 2. 
A map of the Sagami Sea, the Miura Peninsula, and part of the Gulf of Tokio, showing the position 
of the Misaki Laboratory in which Dr. Dean worked, and the waters from which his specimens 

of Heterodontus were taken. 

From an old chart compiled by Professor I. Ijama. 

After Gudger and Smith, 19J3, Text-figure 3, page 251. 



conditions under which the observations were made. In the present instance, this 
information is not so adequate as it would be if Dr. Dean had lived to finish his projected 
article on the embryology of Heterodontus japonicus; for his written records have come 
down to us in fragmentary and incomplete form. 

THE SPECIMENS AND THEIR SOURCE 

From Dean's notes, also from Mrs. Dean, we learn that eggs and embryos of Hetero- 
dontus were obtained in Japan in 1900, 1901 and 1905, while Dean was a guest of the 
Imperial University of Tokyo; also, collecting was carried on for him during his absences 
from Japan, in 1903, 1904 and 1906. The material was collected at the Marine Zoological 
Laboratory of the University (Text-figure 1) situated at Misaki on the Miura Peninsula 
which projects into the Sagami Sea between Sagami Bay and the Gulf of Tokyo (Text- 
figure 2). Collecting was done at various times throughout the year. The specimens 
represented numerous stages from early cleavage to young at the time of hatching, in all 
about 200 embryos. Of these, the majority were examined living, and notes and draw- 
ings were sometimes made before the embryos were preserved. 



654 Bashford Dean Memorial Volume 

It is known that Dean, while in Japan, made extensive collections of biological 
material other than Heterodontus, and that he was also engaged in the collection of 
Japanese armor; but his keen interest in the embryology of Heterodontus is attested by the 
following statements included in a letter (Dean, 1901.2, p. 85) to the Columbia University 
Quarterly : 

My first object in visiting Japan was to secure the eggs and embryos of the Port Jackson 
[sic] shark, a form which there is some reason to believe traces a direct descent from known 
sharks of Carboniferous times. Its embryos, therefore, might reasonably be looked upon to 
furnish evidence as to the relationships of the oldest sharks, and, therefore, as to the oldest 
backboned animals. At Misaki I soon found that this form was moderately common, and the 
native divers and fishermen finally brought me in a valuable series of its eggs. 

In his article on the embryology of Chlamydoselachus, Gudger (1940) has noted that 
Dean collected embryos of Heterodontus and Chlamydoselachus in the same general locality 
(though in different habitats) and simultaneously. When we consider the results of the 
two undertakings, certain differences are very obvious: whereas for Chlamydoselachus 
there was a scarcity of early stages and a fairly complete series of older embryos, for 
Heterodontus nearly all stages are represented. To illustrate this, one need only compare 
the plates illustrating the present article with those of Gudger's article on the Embryology 
of Chlamydoselachus, No. VII in this Volume. 

Of the approximately 200 embryos of Heterodontus japonicus collected by Dean, 
there are now, after more than 35 years, available for study only the following: (a) Six 
embryos in a crumpled condition, preserved in alcohol. Roughly measured, these range 
from 38 mm. to 90 mm. in length. In general, the condition of this material is as good as 
could be expected since it has been preserved for thirty^iive or forty years, (b) A single 
embryo about 3.5 mm. long, stained, cleared and mounted in toto on a slide, (c) Twelve 
slides containing serial sections of seven different embryos in stages ranging from an 
early blastula to an embryo about 10 mm. long. Several series are imperfect or very 
incomplete, but the orientation is good and the stain (apparently borax carmine) has not 
faded appreciably. Nevertheless, the paucity of material is such that for the embryology 
ical portion of this article we must depend almost entirely on Dean's notes and drawings. 
Fortunately the drawings represent not only surface views, but quite a number of embryos 
that had been stained, cleared, and mounted whole. 

It was at Misaki that Dean made the only photograph of a fresh'caught Japanese 
Bullhead Shark on record (my Text-figure 3, further described on page 693). This photo- 
graph is particularly valuable since there is but one juvenile and no adult specimen of 
Heterodontus japonicus in the American Museum at the present time. Fortunately, there 
are available two specimens of H. quoyi, one young and the other adult or nearly so; and 
two specimens of H. francisci, one nearly full-grown and the other undoubtedly adult. 
The external anatomy of all these specimens is briefly described in the section on "The 
Species of Heterodontus''\ 



The Embryology of Heterodontus japonicus 



655 




Text-figure 3. 

Photograph of a fresh'caught Bullhead Shark (Heterodontus, prohshly japonicus) taken at Misaki, Japan. 

The specimen is an adult female about 1043 mm. (41 inches) long. 

After Dean, 1904, p. 203. 



AUTHORSHIP OF THE DRAWINGS 

Owing to the lapse of many years since the drawings of Heterodontus and Chlamy- 
doselachus were made, the precise circumstances have become involved in some obscurity. 
When, where and by whom were the finished drawings made? It is known that Dean was 
an artist of no mean ability, and that he was skilled in the various techniques employed in 
illustrating his published works. He made pencil sketches with surprising speed and 
fidelity; he had an artist's ready perception of form and quick appraisal of Hght and shadow. 
His more finished drawings reveal an accuracy of outline and delicacy of shading that 
invariably arouse the admiration of the beholders. During his sojourn in Japan, he 
had learned to use the brush in making fine lines, often in color. It is known that he had 
made drawings similar to those of Heterodontus, and so it was natural that the idea should 
develop among some of his friends and associates that all the drawings of Heterodontus 
were the work of his own hands. But, considering the variety and the scope of Dean's 
activities, it seems physically impossible for him to have made all the drawings that 
illustrate his published works, and also the drawings that were left unpublished after his 
untimely death. It seems more likely that Dean often made sketches to illustrate the 
character of the drawings desired, and then left the execution of the finished drawings to 
artists whom he employed. 

So far as Chlamydoselachus is concerned, the matter of the authorship of the draw' 
ings has been fully considered by Gudger (1940) who came to the conclusion that they 
were made by Japanese artists under Dean's direction. The same considerations hold for 
Heterodontus, with the following additional circumstances: The present writer remem' 



656 Bashford Dean Memorial Volume 

bers that in 1911 Prof. Dean showed him the plate figures of the projected article on the 
embryology of Heterodontus and remarked that they were made by the best artist (or 
artists?) available. I do not recall whether he stated that the artists were Japanese, but it 
seems that some of the drawings bear intrinsic evidence of Japanese handiwork. A foot- 
note to Dean's article (1901.1) on the "cleavage" of the egg of Heterodontus states that 
these drawings were made by Messrs. N. Yatsu and I. Kuwabara. hi one of Dean's 
notebooks there is a table listing embryos of Heterodontus japonicus collected at Misaki, 
and recording occasional brief data concerning them. In this table there are many 
entries, in Dean's almost microscopic handwriting, reading ^'Tatsu drawn.'' Whether 
these drawings were pre limin ary sketches or figures intended for publication is not 
evident from these records; but on the original of Figure 40, plate VI, there was found, 
apparently in Dean's handwriting, the word ''Tatsu\ 

After diligent inquiry it appears certain that some, at least, of the plate figures used 
to illustrate the present article were made by Yatsu, and that part of his work was done in 
this country. One can readily appreciate the advantages of having the drawings of pre- 
served material made by one who had seen, and possibly sketched in color, the material in 
the Hving condition. That all the drawings were not made by the same person seems 
obvious. Whatever their origin, all who have seen them agree that most of them are 
remarkably well done. 

WRITTEN RECORDS LEFT BY BASHFORD DEAN 

Dean's notes concerning Heterodontus comprise three documents : First, a notebook 
containing a list of embryos collected (see also page 654), a very few miscellaneous notes, 
and a large number of rough sketches of embryos. Some of these sketches are in color, and 
are presumably made from Hving embryos as a preliminary to more finished portraits of 
preserved material. Most of these drawings are on pieces of stiff cardboard adhering to 
the pages of the notebook. Second, there is a notebook from which a considerable number 
of pages have been cut out and are missing. Of the remaining pages, all are blank except 
six, and these contain notes relating to the literature of paleontology and comparative 
anatomy, with special reference to the phylogenetic relationships of Heterodontus. 
Finally, there is a brief and very incomplete typed manuscript entitled: ''Cestraciont 
Sharks and their Development." The "Table of Contents" attached to this manuscript 
reveals that a very comprehensive article, paleontologic, phylogenetic, embryologic and 
ecologic, was planned. Of this we find, in Dean's manuscript, only an introduction, 
brief sections dealing with the habits of the fish, methods of collecting its eggs, rate of 
embryonic development, the egg and its capsule; and a final longer section on "Segmen- 
tation" or cleavage. Of the 32 pages of this manuscript, 9 are devoted to cleavage. The 
text here is almost identical with portions of Dean's article entitled "Reminiscence of 
Holoblastic Cleavage in the Egg of the Shark, Heterodontus (Cestracion) japonicus Mac- 
leay," pubHshed in 1901. There is intrinsic evidence that the manuscript under con- 
sideration was v.T:itten at a considerably later date, for in it reference is made to Goodrich's 



The Embryology of Heterodontus japonicus 657 

volume on "Cyclostomes and Fishes" published in 1909. Therefore it appears that the 
portion of Dean's manuscript dealing with the phylogenetic aspects of cleavage is in- 
tended as a repetition, with revision, of the contents of his article published in 1901. 

Considering these written records in their totality, none of the miscellaneous notes 
and only certain portions of the manuscript are in a condition suitable for publication 
without revision. These portions will be quoted verbatim. The manuscript was 
originally typed, but much of it is so complicated by changes and additions (in script) 
that both its style and its organisation are impaired. It seems best to treat these 
portions as notes, to be rewritten and incorporated in the present article. Notwith- 
standing its limitations. Dean's manuscript does give us much interesting information 
not recorded elsewhere. 

In concluding the introductory portion of his manuscript. Dean made the following 
acknowledgments : 

Before beginning his descriptive paper, the writer wishes to acknowledge numerous 
courtesies which were extended him during various stages of his work. Especially to his 
colleagues in Japan, Dean Mitsukuri and Professor Ijima his sincere thanks are due for ar- 
rangements made at Misaki which resulted in the success of his collecting. He acknowledges 
also his indebtedness to the assistant at the station, Mr. T. Tsuchida, whose never-faihng 
patience and diplomacy stood in good stead with the fisherpeople. Finally, he is indebted 
to Dr. Naohide Yatsu, whose help, at all seasons and in all ways both in Misaki and in New 
York, greatly lightened the burden of the work. 

CLASSIFICATION AND SYNONYMY 

Regan (1908) grouped the species of living Cestraciontidae (Heterodontidae) into 
two genera, Gyropleurodus and Cestracion. Nearly all later authors recognise only one 
genus (variously designated Heterodontus, Cestracion or Centracion) of the living Hetero- 
dontidae. The species included in this genus are collectively equivalent to those of 
Regan's two genera. The common name Bullhead Sharks has been used by Jordan and 
Evermann (1896), by Bridge (1904), and by many later authors, for the members of the 
family Heterodontidae. 

HETERODOKTUS AND HETERODONTIDAE 

In the present article I have adopted the generic name Heterodontus for the six 
species of Bullhead Sharks represented by specimens living at the present time. Of these, 
the best-known is the Port Jackson Shark, H. pMlipi (Text-figure 4). For the genus 
a synonym, Cestracion, is so firmly imbedded in the literature that it cannot be ignored. 
Nevertheless, there are fairly convincing reasons why the name Heterodontus should 
prevail. For my information regarding this matter I am indebted chiefly to Dumeril 
(1865, pp. 423-426); Maclay and Macleay, (1879, pp. 303 and 309) and Carman (1913, 
pp. 4, 155, and 180). 



658 



Bashford Dean Memorial Volume 




Text-figure 4. 
A full-grown female Port Jackson Shark, Heterodontus phillipi, photographed from life. The four posterior 
gill-slits, which were indistinct in the original, have been strengthened. 
After Saville-Kent, 1897, p. 194. 



SYNONYMY 

The term Heterodontus has priority over Cestracion, having been used by Blainville 
in 1816. The word means literally "different teeth", thus describing one of the most 
striking characteristics of the genus (Text-figure 10, page 670). The word Cestracion was 
first used by Klein, in 1742 and again in 1776, as a name for the Hammerhead Sharks, and 
has since been used by Dumeril to designate the group of sharks termed, by Cuvier, 
Zygaena. In 1817 Cuvier, without assigning any reason, gave the generic name Cestracion 
to the Port Jackson Shark, the only living species of Bullhead Shark known at that time. 
Presumably he did not know that Blainville, a year previously, had already given to that 
species the generic name Heterodontus. Concerning the precise meaning of the name 
Cestracion (from the Greek) there seems to be room for doubt. The matter is discussed 
by Maclay and Macleay (1879) and by Carman (1913). 

The generic name Centracion was given to one of the Bullhead Sharks by Gray (1831) 
in the first number of his "Zoological Miscellany" (p. 5). There he described a new species 
named by him Centracion zebra. Gray did not explain his choice of the word Centracion, 
and possibly the spelling was a mistake, for he wrote Cestracion instead of his own 
term Centracion when, in 1851, he adopted the name Heterodontus for the genus. 

Garman (1913) followed Klein and also Dumeril in adopting Cestracion as the generic 
name for the Hammerhead Sharks. In his choice of the name Centracion for the Bullhead 
Sharks, Garman was not so fortunate. He objected to the name Heterodontus for the 
reason that the word Heterodon, identical in derivation, had been applied by Latreille 
(1802) to a group of reptiles. To the present writer this objection does not seem so 
serious as the possibility that Centracion might be mistaken for Cestracion when these 



The Embryology of Heterodontus japonicus 659 

names are used for different genera of sharks. I have not found the name Centracion used 
by any writers other than Gray and Garman. 

For the reasons stated, I prefer the generic name Heterodontus Blainville for those 
species of Bullhead Sharks that are represented by specimens living at the present time. 
Since many authors, mainly paleontologists, have used the name Cestracion for the same 
genus, it is necessary to recognize this term in reviewing their publications. For con' 
venient reference, I have compiled the following synonymy : 

HETERODOHTUS (Blainville) 

Port Jackson Shark (in genus Squalus). Phillip, 1789, Voyage to Botany Bay, pp. 283-284, pi. 
Heterodontus. Blainville, 1816, Bull. Soc. Philom. Paris, 3. ser. 3, p. 121 (not Heterodon 

Latreille, 1802). 
Les Cestracions. Cuvier, 1817, Regne Animal, II, p. 129 (not Cestracion Klein, 1742 and 

1776; nor Walbaum, 1792). 
Centracion. Gray, 1831, Zool. Misc., I, p. 5. 
Heterodontus, Tropidodus, and Gyropleurodus. Gill, 1863, Proc. Acad. Nat. Sci. Philadelphia, 

14, p. 489. 
Heterodontus. Dumeril, 1865, Histoire Naturelle des Poissons, I, p. 424. 
Heterodontus Bl. Maclay and Macleay, 1879, Plagiostomata of the Pacific. Proc. Linn. Soc. 

New South Wales, 3, p. 309. 
Heterodontus Bl. Ogilby, 1890, Australian Palaeichthyes. Proc. Linn. Soc. New South Wales, 

2. ser. 4, p. 184. 
Cestracion Cuvier. Woodward, 1889, Catalogue Fossil Fishes British Museum. Part I, 

p. 331. Woodward, 1891, Hybodont and Cestraciont Sharks of the Cretaceous Period. 

Proc. Yorkshire Geol. and Polytech. Soc, 12, part 1, p. 67. 
Heterodontus Bl. Jordan and Fowler, 1903, Proc. U. S. Nat. Mus., 26, p. 599. 
Centracion. Garman, 1913, Plagiostomia. Mem. Mus. Comp. Zool., 36, p. 180. 

Having adopted the name Heterodontus for the genus that includes the only living 
representatives of the Bullhead Sharks, I think it appropriate that the family name for 
these sharks should be Heterodontidae. This name or its equivalent in a different language 
has already been used, in the sense indicated, by several authors: e.g., Striiver, 1864; 
Dumeril, 1865, p. 623; Maclay and Macleay, 1879, p. 307; McCoy, 1890; Ogilby, 1890, 
p. 184; Bridge, 1904 ("Cambridge Natural History", vol. VII, p. 444); Jordan and Clark, 
1930, p. 10. Since Klein (1742), Dumeril (1865), and Garman (1913) have assigned the 
generic name Cestracion to the Hammerhead Sharks, it seems advisable to reserve 
the name Cestraciontidae for the family that includes these sharks, as done by Garman 
(1913, p. 155). Nevertheless, it should be borne in mind that the name Cestraciontidae 
has been widely used, particularly by paleontologists, for the family that includes the 
genus Heterodontus (Cestracion). It is so used by Woodward, 1889 ("Catalogue Fossil 
Fishes British Museum," Part I); Regan (1906 and 1908); and Zittel (1911, 1923 and 1932). 
These are authors who retain the name Cestracion for the genus of Bullhead Sharks under 
consideration. Goodrich (1909) uses the name Cestraciontidae for the family though he 
seems to prefer Heterodontus for the genus. 



660 Bashford Dean Memorial Volume 

COMMON N.^MES— BULLHEAD SHABJCS 

In view of the existing confusion in the use of scientific names for the genus and 
family under consideration, the need for an undisputed common name is obvious. A few- 
authors (Waite, 1896; Dean, 1901.2 and 1904; and Whitley, 1938 and 1940) have used the 
term Port Jackson Shark in a generic sense: but to the present wnriter this practice seems 
very objectionable. For more than a century, the name Port Jackson Shark had been used 
for one species only — the one first found at Port Jackson — save in a few instances where 
the identification of species was incorrect. 

Waite (1898 and 1899) has referred to Heterodontus galeatus, in which the supraor' 
bital ridges are very tall, as the "'Crested Shark'', and WTiitley (1938 and 1940) has called 
it the ""Crested Port Jackson Shark''. The name Crested Shark would be appropriate for 
the entire genus, but it has not been so used. Whether it would apply to the entire 
family Heterodontidae (Cestraciontidae) as at present constituted (following the most 
recent classification, that of Zittel, 1932) is problematical. 

BuLLHE-\D Sh.\rks. — There is no satisfactory common name that has been 
used exclusively to designate all species of the genus Heterodontus, but the term Bullhead 
Sharks (from the form of the head and snout) has been used by Jordan and Evermann 
(1896) and by Bridge (1904) for the family Heterodontidae. Since all the surviving species 
of this family belong to one genus, Heterodontus, the name Bullhead Sharks will serve the 
needs of those who are mainly interested in recent forms. The same consideration applies 
even though many genera (e.g., Hyhodus) included by Bridge in the family Heterodontidae, 
are now assigned to a separate family, the Hybodontidae. The fact that the common name 
Bullhead Shark seemingly appHes to two (closely related) families of sharks, one entirely 
extinct, need trouble no one — least of all the paleontologists, who are not much interested 
in common names. 

The neime Bullhead Shark is appropriate for all six species of Heterodontus. Fremin' 
\T.lle"s drav,-ing (1840) of H. quoyi, which shows a small head, is inaccurate. A better 
drav,Tng of the same specimen, by Valenciennes (1846), is reproduced as my Text 'figure 
16, page 676. For related fossil forms, the evidence is naturally incomplete; but an 
example with nearly perfect skeleton may be found in Hyhodus haujfianus E. Fraas (Text- 
figures 27 and 28, page 695). The profile of the head and anterior part of the body 
bears a marked resemblance to Heterodontus as represented by my specimens of H. quoyi 
and H. francisci, described in a later section of this article. These specimens (two of each 
species) are not only "bullheaded" but more or less humpbacked, like the fossil Hyhodus, 
in the region dorsal to the bases of the pectoral fins. This feature is not represented in 
some drau-ings of Heterodontus; but it is showm in Carman's outHne drawing of an adult 
H. phiUipi (1888, Fig. 1, pi. 18); in Maclay and Macleay's drawings of a very young 
specimen of H. phillipi (my Text-figure 8, page 668) and of a young female H. japonicus 
(my Text-figure 23, page 691); in Jordan's portrayal (1905, Fig. 315) of an adult H. 
francisci; also in Kumada and Hiyama's figure (1937) of an adult Gyropleurodus peruanus 
(Heterodontus quoyi). Dean's photograph of a fresh-caught Japanese Bullhead Shark (my 



The Embryology of Heterodontus japonicus 661 

Text-figure 3) shows no more than a faint suggestion of this humpbacked appearance. The 
hump is only slightly developed in the adult Heterodontus phillipi photographed (from 
life) by Saville-Kent (my Text-figure 4). In one of my specimens of H. francisci, the hump 
is so low as to be scarcely noticeable. On the basis of all the available data, one can scarce' 
ly say that the hump is typical for the genus Heterodontus. It occurs in at least four 
species, but is decidedly variable. In those individuals in which the hump is well de- 
veloped, the head and "shoulders" have a profile mildly suggestive of a buffalo bull. This 
resemblance may be partly responsible for the name "Bullhead Shark." 

FAMILY AND GENERIC CHARACTERS 

In this section we are concerned with the distinctive characters common to those 
representatives of the family Heterodontidae that have survived to the present time. 
Since all recent species belong to one genus, Heterodontus, the distinction between family 
and generic characters is, for our purpose, of little importance. In the family Hetero- 
dontidae, Bridge (1904) includes at least five other genera that are known only as fossils; 
nevertheless, his brief description constitutes an excellent introduction to the study of 
living Heterodontids. Some points in the following quotation (from Bridge, 1904, p. 444) 
are illustrated by references, in square brackets, to figures in the present article. 

Family Heterodontidae (Bullhead Sharks) 
Head large and high, with a blunt snout projecting but little in front of the small and 
almost terminal mouth, and with prominent supraorbital crests [Text-figures 3, 4 and 5] . Trunk 
thickset and almost trihedral, covered with fine shagreen. Nostrils ventral but nearly termi- 
nal, with oronasal grooves [Text-figures 25 and 40, pages 692 and 711]- Spiracles small, beneath 
the eyes [Text-figures 3 and 4] . Two dorsal fins, each with a spine in front, the first opposite 
the interval between the pectorals and the pelvics, the second in front of the anal. Vertebral 
centra asterospondylic when fully developed. Palatoquadrate cartilages with an extensive 
articulation with the sides of the preorbital regions of the cranium [Text-figure 33, page 700], 
the normal suspensoria of a hyostylic skull (hyomandibular cartilages) taking little share in 
their support. Dentition similar in both jaws [Text-figures 11 and 14c, pages 671 and 673]. 
Teeth at the symphysis numerous, small and conical, furnished with three to five cusps in the 
young; those behind broad and padlike, arranged in oblique rows, the teeth forming the two 
middle rows being much larger than those in the front or behind. Living species, oviparous. 
Egg cases large with an external spiral lamina [Text-figure 37, page 706; and Figures 76 to 
78, plate VII]. 

Continuing, Bridge notes that all the living representatives of this family are in- 
habitants of the Pacific Ocean, and that they feed principally on molluscs, the shells of 
which are crushed by their massive grinding teeth. According to Bridge, the different 
species vary in size (length) from two to five feet. 

Some additional characters of the family Heterodontidae (Cestraciontidae) are listed 
by Goodrich (1909) as follows: The base of the pectoral fin grows forward below the 
last three branchial slits (my Text-figure 6, page 666). The pectoral girdle is very powerful 
(see also Daniel, 1915, Fig. 6, pi. III). According to Goodrich the suspension of the 



662 Bashford Dean Memorial Volume 

jaws of Heterodontus is hyostylic, but with a very extensive articulation of the palatO' 
quadrate with the cranium, so that the hyomandibular scarcely acts as a real support 
(my Text'figure 33, page 700). The suspension of the jaws is further discussed on pages 
699 to 701 of the present article. 

Carman's definition (1913) of the family Heterodontidae (his Centraciontidae) 
attempts to separate family characters from generic ones; but since he excludes fossils, the 
description really applies to only one genus, Heterodontus. Carman vvorites: 

The Hving species of this family are small sharks which have short bodies and heads, 
blunt snouts, small spiracles below the hinder part of the eye, a narrow mouth near the end of 
the snout, with about four lobes in each half of the upper Hp, both cuspidate teeth and grind' 
ers, five gill-openings of which several are above the pectorals, eyes without nictitating 
membranes or folds, nostrils connected with the mouth by naso-oral grooves, without cirri, two 
dorsals each preceded by a strong rigid spine, an anal behind the second dorsal, a short deep 
caudal, small carinate scales, a preorbital articulation between upper jaw and skull, and 
asterospondylous vertebrae. 

In the phrase "eyes without nictitating membranes or folds", it is not quite clear 
what Carman means by the word "folds". If he means a fold of ordinary skin, then my 
adult specimen of H. quoyi is an exception, for it possesses a fold of skin capable of over- 
lapping the eye somewhat like an upper eyelid. 

The genus Heterodontus, which Carman calls Centracion, is characteri2;ed by him 
(1913) as follows: 

Head short, snout blunt, crown narrowed, between strong orbital ridges. Eyes small, 
lateral. Nostrils with two thick valves reaching the mouth and curving toward the grooves. 
No narial cirri. Mouth narrow, with thick labial folds on both jaws. Teeth alike in upper 
and lower jaws, cuspidate in the anterior series, elongate longitudinally ridged grinders 
posteriorly. Pectorals large, dorsals moderate, anal small, caudal short. 

The present writer has not been able to examine specimens of all species of Hetero' 
dontus, but the evidence at hand indicates that unusual breadth of the head and anterior 
part of the body, and decided flatness of the ventral surfaces of both head and body, are 
typical for adult specimens of this genus. A slightly humpbacked appearance, observed in 
my specimens of H. quoyi and H. jrancisci, is possibly a generic or even a family character. 
The supraorbital ridge leans outward, overhanging the eye. The anterior teeth are 
quincuspid in the very young; and acutely tricuspid in older specimens, with the median 
cusp increasingly predominant. In the adult they are often simple, becoming blunt 
when old. The lips, nasal apertures and naso-oral grooves of a single specimen of Hetero' 
dontus, probably jrancisci, have been described in detail by Allis (1919, pp. 158-164 and 
Figs. 6 and 7, pi- I- 

A vestigial sixth branchial arch was found by Hawkes (1905) in two species of 
Heterodontus — phillipi and jrancisci. The other species were not available for exami- 
nation. Hawkes states that the presence of a rudimentary sixth branchial arch in Hetero^ 
dontus is in harmony with the view that the Heterodontidae are in some respects inter- 



The Embryology of Heterodontus japonicus 663 

mediate between the Notidanidae and Chlamydoselachidae on the one hand, and the 
remaining Selachii on the other. In Heterodontus francisci as figured by Daniel (1915) 
the vertebral column is better developed, and the notochord is more constricted than 
in Heptanchus and Chlamydoselachus. Presumably these structures are much alike in 
all species of Heterodontus. 

THE SPECIES OF HETERODONTUS 

In Volume VIII of his "Catalogue of the Fishes in the British Museum", under the 
heading Cestraciontidae, Giinther (1870) lists and briefly describes four species of Ces- 
tracion (Heterodontus): phillipi, quoyi, francisci, and galeatus. Another species known at 
that time, Heterodontus (Cestracion) zebra Gray, was lumped (by Giinther) with phillipi. 
Thus it appears that, of the species now recognized, all but one (Japonicus) were known at 
this early date (1870), though zebra was not uniformly recognizied as a distinct species. 
As we shall see later, even japonicus was then represented in museum collections, and 
drawings of this species had been published before it was identified as a species distinct 
from phillipi. 

Garman (1913, pp. 180-181) gives a key to the species of Heterodontus, which he 
calls Centracion, based mainly on the position and shape of the anal fin, the position of 
the first dorsal with respect to the pectorals, and the color pattern of the entire body. 
This is followed by a synonymy and a comprehensive list of the distinctive external 
characters for each species. Carman's classification agrees, in the main, with that of 
Maclay and Macleay (1879, 1884 and 1886) but differs from that of Regan (1908). 

CARMAN'S KEY TO THE SPECIES OF CEJiTRACIOK (HETERODONTUS) 

Base of anal about two' thirds of its length distant from the caudal. 

Origin of first dorsal above the hind portion of the pectoral base, hind margin concave. 

Bands transverse and broad to absent galeatus [page 686] 

Base of anal nearly one length distant from the caudal. 

Origin of the first dorsal above the forward part of pectoral base, hind margin concave. 

Spots black, small, scattered francisci [page 681] 

Base of anal two-thirds of its length distant from the caudal. 

Origin of first dorsal behind the end of the pectoral base, hind margin convex. 

Spots black, moderate, more or less grouped in twos and fours quoyi [page 676] 

Base of anal fin two or more times its length from that of the caudal. 

Origin of first dorsal above the middle of the base of the pectoral, hind margin deeply 
concave. 

Bands transverse, narrow zebra [page 675] 

Base of anal little less than twice its length from that of the caudal. 

Origin of first dorsal above mid'pectoral base; fin somewhat concave on hind margin. 

Bands both transverse and longitudinal phillipi [page 664] 

Base of anal about one and one-fourth times its length from that of the caudal. 

Origin of first dorsal above the end of the pectoral base, hind margin concave ([some- 
times] convex in second dorsal). 

Bands transverse, broad japonicus [page 688] 



664 Bashford Dean Memorial Volume 

According to Garman there are six species of Heterodontus (Centracion) living at the 
present time, and these are found only in the Pacific Ocean. But it is not certain that 
sharks of the genus Heterodontus originated in the Pacific, since fossil Heterodonts have 
been found in Bavaria and in England (see p. 698). 

Two species are confined to the eastern Pacific Ocean : Heterodontus francisci off the 
coast of California and the western coast of Mexico; and H. quoyi around the Galapagos 
Islands (it has also been taken at the Lobos de Fuero Island, nearer the coast of Peru). In 
the western Pacific, H. phillipi, the Port Jackson shark, is found off the coasts of eastern 
and southern Australia, and off New Zealand; and H. galeatus occurs off New South 
Wales and Queensland. The two other species are H. zebra, ranging from China (rarely 
from Japan) to the East Indies; and H. japonicus from the coasts of the Japanese islands 
south of Hokkaido. Thus two species occur in Japanese waters: H. zebra has been 
taken in the Sagami Sea, but the species usually found there is H. japonicus, the Japanese 
Bullhead Shark. 

It is not necessary here to go into details concerning the surface anatomy of the 
adults of these species, but a brief account of their distinctive characters will be helpful. 
The species are here discussed in the order of their recorded discovery — meaning not 
merely the capture and description of a specimen but its correct identification. In the 
section devoted to each species, jaws and teeth are described last. 

HETERODOHTUS PHILLIPI BLAINVILLE 

This, the Port Jackson Shark, is the best-known species, and for half a century it was 
the only species recogni2;ed. According to Whitley (1940) it occurs in the following 
Australian waters: South Queensland, New South Wales, Victoria, South Australia, 
Great Australian Bight to Southwestern Australia; commonest in the south. Found in 
littoral waters to depth of 94 fathoms. 

The specific name, phillipi, has been spelled in different ways, but the species was 
named for Governor Phillip. His name is thus spelled on the title page of the book 
describing his voyage to New South Wales, with observations on the fauna and flora of 
that region. This book (Phillip, 1789) contains the first authentic description and draw 
ings of the Port Jackson Shark — so named by Phillip because his specimen was captured at 
Port Jackson (Sydney Harbor), Australia. It was called Le Squale Phillip by Lacepede 
(1798); Heterodontus phillipi by Blainville (1816); and Cestracion phillipi by Cuvier (1817). 
An extensive synonymy is given by Garman (1913) under the title Centracion phillipi. 

According to Maclay and Macleay (1879) this shark was called Tabbigaw by the 
Sydney aborigines. McCoy (1890) wrote that because of the form of the head and muziTjle 
it was called the Bulldog Shark by Victorians. Saville-Kent (1897) states that Oyster- 
crusher, Pigfish, and Bulldog Shark are names by which the Port Jackson Shark was known 
locally to Australian fishermen. 

Mainly because of its historical importance, the somewhat conventionalized (but 
otherwise correct) drawing of the Port Jackson shark in the volume describing Phillip's 



The Embryology of Heterodontus japonicus 



665 




Text-figure 5. 
A Port Jackson Shark, Heterodontus phillipi Blainville. This female specimen, 610 mm. (24 inches) long, 
was captured at Port Jackson (Sydney Harbor), Australia. 
After Phillip, 1789, pi. facing p. 283. 

voyage is reproduced here (in Text-figure 5). For nearly a century this drawing remained 
the best portrait of Heterodontus pMlipi. Under the heading "Port Jackson Shark", 
Phillip described the ''new species" (in one sentence!) as follows: 

The length of the specimen from which the drawing was taken is two feet; and it is 
about five inches and an half over at the broadest part, from thence tapering to the tail: the 
skin is rough, and the colour, in general, brown, palest on the under parts: over the eyes on 
each side is a prominence, or long ridge, of about three inches, under the middle of which the 
eyes are placed: the teeth are very numerous, there being at least ten or eleven rows; the 
forward teeth are small and sharp, but as they are placed more backward, they become more 
blunt and larger, and several rows are quite flat at top, forming a kind of bony palate, some- 
what like that of the Wolf-fish; differing, however, in shape, being more inclined to square 
than round, which they are in that fish : the under jaw is furnished much in the same manner as 
the upper: the breathing holes are five in number, as is usual in the genus: on the back are two 
fins, and before each stands a strong spine, much as in the Prickly Hound, or Dog Fish : it has 
also two pectoral, and two ventral [pelvic] fins: but besides these, there is likewise an anal 
fin, placed at a middle distance between the last and the tail : the tail itself, is as it were divided, 
the upper part much longer than the under. 

One may add that, in the words of Garman (1913), the spiracle is small, below the 
orbit and immediately behind a vertical from its posterior edge. The distribution of 
the lateral-line system of Heterodontus phillipi was earlier (1888) figured and described by 
Garman. For characters diagnostic of the species, see Garman's key. The photograph 
by Saville-Kent (my Text-figure 4) probably gives a better conception of the general 
appearance of this shark than any drawings reproduced herein. 

Lesson's colored figure (1826) of a male Heterodojitus (Cestracion) phillipi has been 



666 



Bashford Dean Memorial Volume 



criticised by Maclay and Macleay (1879;, who alleged that it is so unlike the fish it is 
intended to represent as to suggest a doubt of its being the same species. In 1884 Maclay 
and Macleay stated definitely that this figure, which they call "a very bad one", does not 
represent the Port Jackson Shark. In Lesson's figure the color pattern of the body is 
unHke that of any other drawing of Heterodontus ph-illipi known to me, and the shape of the 
ventral lobe of the caudal fin is unHke that shov.Ti in all other drawings of specimens 
belonging to the genus Heterodontus. It is not necessary to reproduce this figure, since it 
■w.^s e\'idently drav.Ti from a dried and distorted specimen. 

Miiller and Henle's full'length colored portrait (1841, pi. 31) labelled Cestracion 
philUpi is reproduced, under its proper name, as my Text-figure 21, page 690. In 1879 
Macleay expressed a doubt as to the identity of the species represented by this figure, and 
in particular stated that the form of the six-cusped tooth pictured by Miiller and Henle 
(but omitted from my Text-figure 21) had never, they beHeved, been seen in any adult 
specimen of the Port Jackson Shark. Further, in 1884, Maclay and Macleay stated that 
Miiller and Henle's figure is most likely of the Japanese species, the number of vertical 
bands being identical, and that the tooth portrayed in the same plate is certainly not of 
either species. x'\t the present time one can scarcely doubt that Miiller and Henle's 
figure of the entire fish is a fairly accurate representation of the Japanese Bullhead 
Shark, Heterodontus japonicus. The same may be said of Brevoort's drawing (1856) of 
a specimen collected by the Perry Expedition to Japan. This specimen was labelled 
Cestracion phillippi; it is reproduced, under its proper name, as Te.xt-figure 22, page 690. 

Striiver (1864) has contributed what appears to be an accurate drawing of a badly 
posed specimen of Heterodontus philUpi. Perhaps this fish had been hardened in a laterally 




Text-figure 6. 
A full-grown male specimen of the Port Jackson Shark, Heterodontus philUpi, 795 mm. (31.4 inches) 
long. The external opening of the spiracle (retouched to make it more clearly visible) is shown behind, 

and a little below, the eye. 

After Maclay and Macleay, 1879, F^. 8, pL 23. Right and left are here reversed. 



The Embryology of Heterodontus japonicus 667 




Text-figure 7- 

Dorsal view of the 795'mm. male specimen of Heterodontus phillipi shown, in lateral view, in Text-figure 6. 

The external openings of the spiracles are shown in the dark band crossing the head. 

After Maclay and Macleay, 1879, Fig. 3, pi. 22. 

flexed condition. The color pattern is not shown. The external spiracular opening is 
unusually large. It does not seem necessary to reproduce this figure. 

In the order of historical sequence, the next authentic drawings of Heterodontus 
phillipi that have come to my attention are those of Maclay and Macleay (1879). Text- 
figure 6 is a copy of their drawing of an adult male specimen in lateral view. This is 
probably the best drawing of an adult male Port Jackson shark ever published. One 
should notice particularly the large head and the color pattern of the head and body. 
The authors state that the skin is roughly shagreened, and that the color in the fresh 
specimen is reddish'brown above and yellow with a pinkish tinge beneath. The color 
pattern (made up of brownish'black stripes) becomes indistinct within a few hours after 
death and in this drawing of a preserved specimen the color pattern is represented as seen 
in perfectly fresh specimens. In addition, the authors portray a dorsal view of the same 
adult specimen (my Text-figure 7). One is impressed by the breadth of the head including 
the branchial region. The color pattern of the dorsal surface is decidedly more complex 
than that of the lateral surface. The authors state that the average si2,e of adult specimens 
of the Port Jackson Shark of both sexes is a little over three feet and that they seldom, if 
ever, attain a length of four feet. The external reproductive organs of an adult male are 
represented by Maclay and Macleay (1879) in their Figs. 24 and 25, pi. 24. Each 
myoxpterygium is armed with a sharp spine. 

Of particular interest are Maclay and Macleay's figures (1879) showing lateral and 
dorsal views (my Text-figures 8 and 9) of a very young specimen only 225 mm. (8.8 inches) 
long. The authors state that this specimen was probably hatched only a day or two previ- 



668 Bashford Dean 'Memorial Volume 




Text-figure 8. 

Lateral view of a very young (recently hatched) female specimen of the Port Jackson Shark, 

Heterodontus phillipi, about 225 mm. (8.8 inches) long, drawn while fresh. 

After Maclay and Macleay, 1879, Fig. 5, pi. 23. Right and left are here reversed. 

ously; but to me it seems likely that it was about two weeks old. The entire color 
pattern is more distinct and somewhat more complex in this young specimen than in the 
adults. Concerning this specimen Maclay and Macleay wrote: "The very remarkable 
marking, the rounded form of the head and the proportionally large tail are peculiar to 
this stage". From the dorsal view of this specimen, we see that the head is not so broad, 
proportionally, as in the adult. 

McCoy (1890) contributed two figures, in color, representing side views of male and 
female specimens of Heterodontus phillipi. The delicacy of the outlines of these drawings 
makes them unsuitable for reproduction here. In these figures the color pattern is not 
well shown, but McCoy's detailed description of the distribution of the dark-brown 
stripes corresponds closely with the pattern shown in Maclay 's drawings (lateral and 
dorsal views). According to McCoy the dark'brown bands are most distinct in the 
young, nearly obsolete in the old, and invisible in stuffed, dried, or spirit specimens. 

The photograph of the Port Jackson Shark by Saville-Kent (1897) is reproduced as 
my Text'figure 4, page 658. The specimen was alive when photographed. The original 
figure measures six and onchalf inches long and is said to be one-tenth natural size. This 
would make the shark over five feet long. If the reduction is accurately stated, this is the 
largest Port Jackson Shark on record; but experience shows that one cannot always depend 
on records of this kind. 

Waite (1898) collected specimens of the Port Jackson Shark, Heterodontus phillipi, 
from 14 difi^erent stations, and records that none of the specimens was longer than two 
feet. The majority were but little over 18 inches. He states that this shark is not known 
to grow longer than four and one-half feet, and that it is harmless. 



The Embryology of Heterodontus japonicus 



669 



Whitley's excellent representation (1940, Fig. 52) of a female Heterodontus phillipi, 
said to be after Waite, bears a remarkable resemblance to Saville-Kent's photograph 
reproduced as my Text-figure 4. The four posterior gill-slits and the color pattern of the 
sides of the body are more distinct in Whitley's figure. In addition, Whitley (1940, Fig. 
53) has published an excellent original drawing of a female Heterodontus phillipi. Concern- 
ing the coloration, he writes: "Color grayish to light brownish. A dark blotch on snout. 
A blackish interorbital bar as broad as eye, continued and expanded below eye. A series 
of blackish stripes on body rather like harness." 

Glands associated with the dorsal fin spines of certain sharks have been studied by 
Evans (1924). In Squalus, this author found a large groove along the base of each dorsal 
spine, on the side facing the fin. The groove is filled with a follicular gland, which was 
studied microscopically. Evans cites evidence that the secretion discharged by this gland 
has venomous properties. He states further that the dorsal fin spines of Cestracion 
(Heterodontus) phillipi are similar to those of Squalus, but with a shallower groove. This 
groove likewise contains a follicular gland, but the nature of the secretion was not studied 
in Heterodontus. The author makes comparisons of the dorsal fin spines of Squalus and 
Cestracion (Heterodontus) with those of some fossil Cestracionts, and of Hyhodus. The 
presence of a large groove along the bases of the dorsal fin spines of these fossil forms 
suggests that, in life, glands were present at the bases of these spines also. 




\ 



Text-figure 9. 

Dorsal view of the very young female Port Jackson Shark, Heterodontus phillipi, about 225 mm. (8.8 inches) 

long, shown in lateral view in Text-figure 8. The drawing was made while the specimen was fresh. 

After Maclay and Macleay, 1879, Fig. 1, pi. 22. 



670 



Bashford Dean Memorial Volume 



Jaws and Teeth. — Goodrich (1909) contributes an outline drawing of an in- 
complete skull of Heterodontus pMlipi, here reproduced as Text-figure 33, page 700. 
This drawing is introduced primarily to show the mode of suspension of the jaws; but 
when we compare this figure, showing these jaws in lateral aspect, with other figures 
(Text-figures 10, 11 and 14) showing them in dorsal and ventral aspects, we are impressed 
by their massive pincer-like character — somewhat like the jaws of Heptanchus outlined by 




Text-figure 10. 

Teeth of the Port Jackson Shark, Heterodontus pMlipi. Whether the figure 

represents an upper or lower jaw is not stated, but apparently it is a lower jaw. 

After PhiUip, 1789, pi. feeing p. 283. 

Goodrich, 1909, Fig. 59a. One can readily imagine how powerful these jaws are 
when equipped with, the grinding teeth — set well back toward the angle of the jaws — and 
with the musculature necessary for crushing the shells of molluscs that form the principal 
food of this species of Heterodontus. Garman also (1913, Atlas, Fig. 4, pi. 47) has figured 
the jaws of Heterodontus pMUpi in lateral view, but in form so different from Goodrich's 
portrayal that one might think the two drawings were made from different species. 

Phillip's drawing (1789) of the teeth of the Port Jackson Shark is reproduced here as 
Text-figure 10. The author does not state whether this is an upper or a lower jaw, but 
upon comparison with, the figures of Striiver (1864), Maclay and Macleay (my Text-figure 
11) and McCoy (my Text-figure 14) it appears to be a lower jaw. In this specimen 



The Embryology of Heterodontus japonicus 



671 



(Text'figure 10) there are 33 rows of teeth. The anterior teeth (13 series or transverse 
rows) are distinctly tuberculate, but, due to the overlapping of the teeth in each row, 
their form is not completely shown except in the most anterior members of each series . 
Each anterior tooth possesses one large central cusp, and there may occasionally be seen 
in the drawing a rudimentary lateral cusp on one or both sides of the central cusp. The 
posterior teeth (ten rows on each side) are 
large, smoothly rounded, and in their natural 
arrangement combine to form an exposed 
surface resembling that of a stone'block pave' 
ment. Thus the anterior teeth are adapted for 
holding the prey, the posterior ones for crush' 
ing and grinding it. 

Striiver (1864) made drawings of the teeth 
of both upper and lower jaws of Heterodontus 
phillipi. With respect to the dentition, upper 
and lower jaws are much alike, save that the 
lower is slightly shorter and more obtuse in 
front, which makes some difference in the 
arrangement of the teeth. In this respect the 
lower jaw resembles the jaw figured by Phillip 
(1789) ; but in Striiver's figures both jaws show 
a more gradual transition between anterior 
(cusped) teeth and posterior (grinding) teeth, 
so that the line of demarcation between the 
two kinds of teeth is not sharply defined. 
However, one might assign 15 transverse rows 
to the anterior region in the upper jaw, and 13 
rows to this region in the lower jaw. The total 
number of teeth in the upper jaw is 33, in the 
lower jaw 31. In Striiver 's figures the anterior 
teeth are pointed but without obvious second' 
ary cusps; each posterior tooth has an indistinct 
longitudinal ridge. 

Miklouho'Maclay (in Maclay and Macleay, 

1879) figured the teeth of upper and lower jaws 

in both adult and young specimens of H. 

phillipi. The dentition of an adult, as shown in 

his figures (my Text'figure 11) resembles that ^ r ,, 

J c, 1 N A Text-figure 11. 

represented m Struver s drawmgs (1864). As ^^^^^ „f ^^ ^d^lt Heterodontus pMUpi: 

in Striiver 's figure, the lower jaw is shorter A, upper jaw; B, lower jaw. 

than the upper, and is more obtuse in front. After Maclay and Macleay, 1879, Figs. 16 and 17, pi. 24. 




672 



Bashford Dean Memorial Volume 



The transition between anterior (cusped) teeth and posterior (grinding) teeth is so 
gradual that any division into two types must be somewhat arbitrary. However, of 
the 33 rows of teeth on the upper jaw one might assign 19 rows to the anterior region, 
leaving 14 (seven on each side) in the posterior region. In the lower jaw there are 32 
rows of teeth of which 14 rows may be 
assigned to the anterior region, leaving 
18 (nine on each side) for the posterior 
region. Thus there seem to be more rows 




Text-figure 12. 

Anterior teeth of a young Hetero- 

dontus phiUipi about 761 mm. (22.1 

inches) long: A, from the upper; 

B, from the lower jaw. 

After Maclay and Macleay, 1879, Figs. 18a 
and 18b, p. 24. 

of anterior (cusped) teeth on the upper 
jaw than on the lower (as in Striiver's 
figure). In another specimen Maclay 
counted 34 rows of teeth on the upper 
jaw and 31 on the lower. The largest 
number of rows of teeth noted by Maclay 
on a lower jaw is not stated, but we infer 
In Maclay's figures, as in Striiver's, the 
each; but in Maclay's figure these are more 



^j^^j^M 



f7< 



^^^p/y 


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^f %^^^ '^hHb 






¥^ ^ 


"^Wm 


^^^ ' / 










•vj, 






f\ 




\ 




B 




-sl?^ 




i 


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m 






W 


." 




w 



Text-figure 13. 
Dentition of a very young (recently hatched) 
female fieterodontus phillipi about 225 mm. 
(8.8 inches) long: A, upper jaw; B, lower jaw. 
After Maclay and Macleay, 1879, Figs. 14 and 15, pi. 24. 

was 36 on an upper jaw; the largest number 
that it was less. 

anterior teeth of the adult have only one cusp 
blunt as if worn by use. Maclay states that 



The Embryology of Heterodontus japonicus 



673 



the anterior teeth (my Text'figure 12) of a not fully developed Heterodontus phillipi 
761 mm. (22.1 inches) long are distinctly tricuspidate, the central cusp predominating, 
while those of the adult become almost pavement-like, with an inconspicuous cusp. He 
further states that on the posterior teeth of a young specimen 418 mm. (16.4 inches) long, 
a longitudinal ridge is much more pronounced than in older specimens. 

Maclay (Maclay and Macleay, 1879) portrayed also the dentition of both upper and 
lower jaws in their very young specimen of Heterodontus phiUipi only 225 mm. (8.8 inches) 
long. Comparatively few teeth are exposed (my Text-figure 13) and these are nearly all 
cuspidate. About 40 teeth are visible on the upper jaw and about 32 on the lower jaw, 
roughly arranged in transverse rows of two or three teeth each, giving about 17 rows on 
the upper jaw and 13 on the lower jaw. Most of these teeth have three to five cusps, and 
seldom a predominating central cusp. The cusps are best developed in the most anterior 
teeth and are less conspicuous posteriorly. They are absent in one or two teeth of 
the last row on each side. Maclay states that some other teeth came into view after the 
mucous membrane had been dissected off. He calls attention to "the very great similarity" 
between the dental armature of the young Heterodontus and that of (adult?) Notidanids. 











'ky 



r 




Text-figure 14. 
Head and teeth of the Port Jackson Shark, Heterodontus phillipi, in three aspects: A, 
anterior view of the head, mouth closed, showing exposure of teeth above and below. 
B, teeth of lower jaw in natural si2;e. C, mouth widely opened, to show the similarity 

of dentition above and below. 
After McCoy, 1890, pi. 113. 



674 Bashford Dean Memorial Volume 

McCoy's descriptions and drawings (1890) of the teeth of H. phillipi (my Text-figure 
14) are excellent. "Teeth alike in both jaws, the median tront rows very small, acutely 
tricuspid when young, simple and ■w.'ith obtusely triangular cusp in middle age, blunt and 
hexagonal when old: more posterior teeth large, oblong, longer than broad, flattened, 
arranged in oblique, spiral row-s on each side ot the jaw, the anterior and posterior ones 
smaller than those in the middle."" His figure of the lower jaw (my Text-figure 14bj 
reveals a distinct longitudinal ridge on each of the posterior grinding teeth — a feature 
mentioned but not figured by Maclay (1879). The lower jaw shows a distinct line of 
demarcation between anterior cusped teeth and posterior grinding teeth — as in the 
figure by Phillip (Text-figure 10) but not to the same degree. In this jaw there are only 
eleven transverse rows of anterior cusped teeth. These, w^th eight rows, on each side, of 
posterior grinding teeth, make a total of 27 rows in this lower jaw. Text-figures 14a 
and 14c show, respectively, the appearance of the mouth when it is closed and when it is 
open. The lower jaw^ in Text-figure 14c is identical with that in Text-figure 14b. The 
upper jaw, shown in Text-figure 14c, likewise has 27 row^s of teeth. Of these, 12 or 13 
rows are anterior or cuspidate teeth. The transition between cuspidate and grinding 
teeth is not so abrupt as it is in the lower jaw. 

Carman (1913, Figs. 4 to 6, pi. 47) portrays the teeth of a male Heterodontus phillipi 
about 864 mm. (34 inches) long. The transition between anterior (cuspidate) and posterior 
(^grinding; teeth is not so abrupt, in this specimen, as in some others. The dividing lines 
here chosen are somewhat arbitrary. The upper jaw has 13 transverse rows of anterior 
(cuspidate) teeth and 10 rows (5 on each side 1 of posterior (grinding) teeth, making a total 
of 23 rows. The lower jaw has 11 rows of anterior (cuspidate) teeth and 8 rows (4 on 
each side) of posterior (grinding) teeth, making a total of only 19 rows. Carman"s figures 
of the posterior grinding teeth or "molars"" show on each tooth a distinct longitudinal 
ridge or ""keel"", and on each side of this, many fine transverse ridges. Carman states that 
the ridges on the molars of younger specimens become less conspicuous w^th age and use, 
and that the harder the food in a particular locality the fainter the ridges appear. 

To summarize the recorded data on the dentition of the adult or nearly adult Hetero- 
dontus philUpi, one may sute that all the descriptions and drawings emphasi2;e the decided 
differences between anterior and posterior teeth — differences that suggested the generic 
name, Heterodontus. When we compare the dentition of upper and lower jaws, we find 
that Bridge's statement "dentition similar on both jaw^s'' is true of all specimens that have 
been described. One may be more definite and explain that the dentition (meaning the 
kind, number and arrangement of the teeth ) is aHke on upper and lower jaws, with certain 
slight reservations. First, as McCoy states, there are usually "a few more rows in upper 
than [in] lower jaw"". Using the meager data available we find that the average number of 
transverse rows on the upper jaw (6 cases, average 31.0 rows) is slightly greater than 
on the lower jaw (6 cases, average 28.8 rows). In only one instance (McCoy's drawing) is 
the number of rows of teeth the same on both jaws. The largest number of teeth recorded 



The Embryology of Heterodontus japonicus 



675 



for an upper jaw is 36; for a lower jaw, 33. Second, I have noted that, in the figures of 
various authors, there is a slight difference in the shape of the opposed surfaces of upper 
and lower jaws : in the lower jaw this surface is a trifle shorter. This may account for the 
diiference in the number of rows of teeth. Third, in every case recorded the upper jaw 
has more rows of anterior (cuspidate) teeth than the lower jaw. 

HErERODOHTUS ZEBRA GRAY 

This species ranges from the coasts of China and (rarely) Japan, to the East Indies. 
It was first described in 1831 by Gray, who named it Centracion zebra. In 1851 he adopted 
the name Heterodontus for the genus. 

The earliest drawings of this species that I have been able to find are those of 
Maclay and Macleay (1886). These were made from a preserved specimen, a young 
female about 518 mm. (20.4 inches) long, captured at Swatow in the South China Sea. 




^»irrw**^Mr 






Text-figure 15. 
A male specimen of Heterodontus zebra Gray, about 1220 mm. (48 inches) long. 

From a drawing in color by Ito, 1931, Fig. 6, pi. V. 

The color pattern is more adequately shown in my Text-figure 15, from a folio volume 
entitled "Illustrations of Japanese Aquatic Plants and Animals", published by the 
Japanese Fisheries Society in 1931. This represents an adult male about 1220 mm. (48 
inches) long. The Japanese common name is said to be ''Simanekozame". 

The most conspicuous peculiarity of this species is the presence of numerous narrow 
transverse dark-brown stripes (Text-figure 15) which suggested the specific name, zebra. 
Except in a few places, these dark-brown stripes alternate with lighter-brown narrower 
ones. Garman (1913) states that in a 19'inch female specimen studied by him, the body 
and head are more slender, the head more pointed and the fins longer, than in other species 
of the genus. Maclay and Macleay 's drawing of a dorsal view of their specimen shows 
head and body very narrow as compared with other species. In this drawing the head is 
rotated slightly, so the width cannot be measured for comparison with the total length. 
Maclay and Macleay 's figures show prominent supraorbital ridges in both lateral and 



676 Bashford Dean Meinorial Volume 

anterior views but these are lacking in the Japanese dravi-ing reproduced as my Text-figure 
15. Klaclay and Macleay state that the dorsal fins are ver>'- falcate. This feature is per- 
haps exaggerated in their drawing, which wzs made from a preser\'^ed specimen; it is 
more moderate and more Hfe-Hke in the Japanese drawing. In the latter figure the 
anterior margin of the pectoral fin is opposite the fourth gill-sHt, while in Maclay and 
Macleay's figure it is opposite the second. 

Tke Teeth. — ^According to Maclay and Xlacleay (1886), the anterior teeth of 
their young female specimen of H. zebra (518 mm. long) were five-cusped. Garman (1913) 
states that the anterior teeth are quincuspid in the young, tricuspid in the adult. 

HETERODO?mJS §UOri FREMTNTVILLE 

Examples of this species (Text-figure 16) have been taken off the western coast of 
South America, specifically at the Galapagos and Lobos de Afiiera Islands — the latter 




Text-figure 16. 

Heterodontus quoyi Freminville: a male specimen about 475 mm. (18.7 inches) long, taken at the Galapagos 

Islands. The original figure, in color, is labelled Ccstracion paniherinus. 

After Valendennes, 1S46, Atks (Poissons), Fig. 2, pL 10. 

close to the coast of Peru. In addition, a Heterodontid shark taken at the Lobos de 
Tierra Island, Peru, belongs to this species. This specimen ■^'as described and figured by 
Evermann and Radcliffe (19l7j who named it Gyropleurodus peruanus. Of this fish they 
UT~ite: "The species appears to be most closely related to the poorly described G. quoyi, 
but differs in coloration, in insertion of anal, and relative si?e of pectoral' ". ^After a careful 
study of the matter, Beebe and Tee- Van (1941) conclude that all the Heterodontid sharks 
thus far taken off the western coast of South ^America belong to the species peruanus 
(quoyi) as redescribed by Valenciennes and later authors. They state that the alleged 
differences between quoyi and peruanus do not exist, although there is some individual 
\'ariation in the color patterns. With this conclusion the present writer is thoroughly in 
accord. The native name of H. quoyi is "Gato" (Nichols and Murphy, 1922). 



The Embryology of Heterodontus japonicus 677 

There remains some doubt concerning the identity of a Heterodontid shark taken off 
the western coast of Mexico, or perhaps of Central America, which was described and 
figured by Kumada and Hiyama (1937)- They named it Gyropleurodus perua7%us. Their 
drawing portrays a shark in most respects like H. quoyi, but the color pattern is inter- 
mediate between H. quoyi and H. francisci. Since the color pattern of the former is 
somewhat variable, the drawing was probably made from a specimen of H. quoyi; but 
there is no other record of the occurrence of this species so far north. 

Heterodontus quoyi was first figured and described by Freminville (1840); and later 
by Valenciennes (1846 and 1855). Their figures are based on the same specimen, a male 
taken at the Galapagos Islands; but these differ so much that they might be considered 
as representing two different species. Valenciennes called this specimen Cestracion 
pantherinus, though it had been previously named Cestracion quoyi by Freminville. The 
brief accounts by Dumeril (1865), Gvinther (1870), Maclay and Macleay (1879) are based 
on either Freminville's or Valenciennes' description and figure; they contain nothing 
new. Maclay and Macleay's figure (1879) is a copy of Freminville's. Until Carman 
(1913) described at least one new specimen (a female taken at the Calapagos Islands), 
Freminville's male specimen of H. quoyi remained the only example of the species. In 
his very inadequate description, some comparisons with Heterodontus phillipi are 
irrelevant since they involve the acceptance of erroneous features in Lesson's (1826) 
drawing of the Port Jackson Shark. Freminville's figure of H. quoyi does not inspire 
confidence, and I have therefore reproduced Valenciennes' life-like portrait of the same 
specimen (my Text-figure 16) as the basis of this account. 

The length of Freminville's specimen is variously recorded as a little more than 
a foot and a half, by Freminville; 475 mm. (18.7 inches) by Valenciennes; 460 mm. (18.1 
inches) by Dumeril; and two feet (evidently a blunder) by Maclay and Macleay. Car- 
man's female specimen measured 18 inches long. Carman states that its body is rather 
stout as compared with a specimen of H. zebra of equal length. Some passages in Carman's 
characterization imply that he had more than one specimen, but he does not give the 
lengths of any others. 

The most noteworthy feature of Freminville's drawing of H. quoyi is the small size 
of the head. The author states that the head is smaller and a little more elongate than 
that of Cestracion phillipi. As portrayed by Freminville, the head is very small and 
pointed. In Valenciennes' drawing (my Text-figure 16) the head is proportionally much 
larger. Carman does not say that the head of his specimen (or specimens?) is small. He 
does write that the snout is blunt, the cheeks swollen, the eye and spiracle small. Fremin- 
ville states that the supraorbital ridge is comparatively weak ("moins forte") but Carman 
records that it is strong, somewhat overhanging the orbit, not ending abruptly as in H. 
francisci. In Valenciennes' figure (my Text-figure 16) the posterior extremity of the 
supraorbital ridge ends rather abruptly, as in Kumada and Hiyama's figure of H. francisci 
(my Text-figure 18, page 682). Some specimens of H. quoyi examined by me show vari- 
ations in the form of the supraorbital ridge, as described later. 



678 Bashford Dean Meynorial Volume 

Authors agree that in H. quoyn the origin of the first dorsal is well behind the root of 
the pectoral. Garman states that the dorsal fins are of moderate size, with convex hind 
margins; the base of the anal fin is two-thirds its length distant from the caudal; and the 
anterior gilhopening is more than twice as "vvade" as the hindmost. Freminville states 
that the skin is entirely shagreened, is colored a ruddy-brown and is everywhere strewn 
with dark'brov^m spots, generally round. Concerning the coloration of H. quoyi Garman 
(1913) writes: 

Back rusty-brown, yellow below, -^^th scattered spots of black, from mere specks to 
spots as large as the orbit or larger, over the entire body and fins. Ckimmonly the spots show 
a tendency toward grouping in twos and fours ; in [some] cases they are more confluent. On 
some [specimens] there are five or six rather indefinite transverse bands of darker separated by 
spaces of equal width; a band crosses the nape, another hes in front and a third behind the 
first dorsal, one in front and one behind the second dorsal and one in front of the caudal. 
A darker area extends from each orbit across the cheek. 

It remains to record some observations on two specimens of H. quoyi, from the col- 
lections of the American Museum of Natural History, which I have been permitted to 
examine. The larger specimen is a female about 527 mm. (20.75 inches) long, measured 
after 20 years' immersion in alcohol. It is probably adult or nearly adult. This specimen 
u^s collected on January 5, 1920, by Dr. R. C. Murphy, on the Lobos de Afuera Island 
(ofi^ the coast of Peru) where it v,"as u-ashed ashore in a dying condition. The other 
specimen is a male only 372 mm. (14.6 inches; long, and evidently very young. It was 
taken on June 9, 1925, by Dr. R. C. Murphy at Albemarle Island of the Galapagos group, 
from the stomach of a Tiger Shark (Galeocerdo). It seems in good condition after 15 
years" preservation in alcohol. Concerning these specimens it is necessary to consider 
here only a few external characters, particularly those relating to the form of the body. 
Certain details, including additional measurements, are left for a later section of the present 
article entitled "Comparisons of H. quoyi and H. francisci''\ 

In the absence of pubHshed drauTngs of either dorsal or ventral views of H. quoyi 
one is immediately impressed, upon examining these specimens, by the breadth of the 
head and by the flatness of the ventral surfaces of both head and body. The outline of 
the entire body, viewed from above, is quite tadpole-like. In the adult female the head 
is much broader, proportionally, than in the young male. The head height of the young 
male is greater, proportionally, than the head height of the adult female. In both speci- 
mens the body height is greatest immediately in front of the first dorsal fin, where it 
exceeds the height of the head sufiiciently to give the fish a humpbacked appearance. In 
its middle third, the supraorbital ridge is low and broad. In both specimens, this portion 
is merely a told of the skm not supported by the endoskeleton. In both specimens, the 
external spiracular openings are small, measuring from 2 to 3 mm. in their larger diameters. 
The first gill-sht is about twice, the length of the fifth. The origin oi the first dorsal is well 
behind the posterior end of the pectoral base. The base of the anal fin is about three-fourths 
its length from the caudal. 



The Embryology of Heterodontus japonicus 679 

In my 527'mm. female specimen of H. quoyi, the entire supraorbital ridge is low, but 
it is lowest in its middle third where it is a mere fold of skin, not supported by the endo' 
skeleton. This fold overlaps the eyeball like an upper eyelid. Its function is doubtless 
protection of the eye while the fish is forcing its way under rocks or into crevices. When 
pressed upon, this fold of the skin reduces the palpebral fissure to a narrow slit. Though 
in all species of Heterodontus the supraorbital ridge leans outward, thereby overhanging 
the eye, H. quoyi is probably the only species in which any part of it actually overlaps the 
eyeball. In my adult female specimen of H. quoyi the supraorbital ridge does not end 
abruptly, as it does in H. francisci. 

In the same adult female specimen of H. quoyi, the "cheeks" appear swollen, and the 
gill'covers, especially the first, bulge outward as if inflated by pressure from within. It 
seems hardly likely that this condition could be produced by unequal shrinkage, since 
it does not occur in other specimens preserved in the same way. As viewed from above, 
the head is broad behind and somewhat pointed in front, like the head of a venomous 
snake. The ventral surface of the head is decidedly flat, and lies in the same plane as the 
ventral surface of the body. The nasal apertures open ventrad. As viewed from the side, 
the dorsal surface of the head slopes forward to a fairly sharp rostrum directly in front 
of the nostrils. The dorsal fins are small. The hind margin of the first dorsal is slightly 
convex, that of the second dorsal is almost straight. The dorsal spines are decidedly small 
but are much worn ; they project less than a centimeter beyond the skin. The pectoral fins 
are broad and when extended (as far as possible in their rigid condition) the distance from 
tip to tip is about 250 mm., equal to nearly half the body length. The scales on the 
ventral surface of the body are smooth ; those on the dorsal surface are tuberculate and 
are much larger than the scales on the ventral surface. 

The form of my young specimen of H. quoyi (a male 372 mm. long) differs considerably 
from that of the adult specimen (a female). Both head and body are more slender, especial' 
ly in width. The ventral surface of the head is not so flat as in the adult. The supra' 
orbital ridges are taller proportionally; they are especially well developed at their posterior 
ends, where they terminate abruptly. Though the middle portion of each supraorbital 
ridge is depressed, it overhangs the eye much less than in the adult. The dorsal fins are 
proportionally larger, and the spines longer and sharper, than in the adult. The posterior 
edges of both dorsals are so frayed that the original shapes of their margins cannot be 
determined. It seems unHkely that any of the differences noted are due to sex. Some 
characters, like the abrupt termination of the supraorbital ridges, may be individual vari' 
ations, but most of the differences are probably correlated with differences in age. 

In my two specimens of H. quoyi, the entire body, including the fins, is ornamented 
with many dark'brown (nearly black) spots of various sizes. Of these, few are larger 
than the orbit. These spots are occasionally grouped in twos, threes and fours. On the 
dorsal surface there is a fairly regular bilateral arrangement of spots or groups of spots, 
though in the large female the spots on that surface are more or less obscured by a dark' 
brown ground color. On the ventral and ventrolateral surfaces the distribution is 



680 



Bashford Dean Memorial Volume 



random, and the spots are distinct because the ground color is a light-brown. In the small 
male specimen of H. quoyi the ground color is paler than in the adult female, so that the 
spots are everywhere clearly visible. I do not find in either specimen the ""five or six 
rather indefinite transverse bands" mentioned by Garman (1913). The spots on the 
dorsal surface are distributed at fairly regular intervals in such fashion that when in- 
distinct they might suggest broad transverse stripes; but such stripes would be more 
numerous than those described by Garman. 




Text-figure 17. 
Jaws and teeth of Heterodontus quoyi, in lateral view. The original 
is labelled Centracion quoyi. 
After Garman, 1913, Atlas, Fig. 1, pi. 47. 

Jaws axd Teeth. — In Carman's figure (1913j showing the jaws of H. quoyi in 
lateral view (my Text-figure 17) the upper jaw projects anteriorly beyond the lower jaw, 
as in his figure of the jaws of H. phillipi drawn from the same aspect. Both jaws appear 
very strong. 

Some samples of both anterior and posterior teeth of H. quoyi are described and 
sketched by Freminville; but Garman (1913, Atlas, Figs. 1 to 3, pi. 47) portrays the entire 
dentition of both jaws. Authors agree that the anterior teeth are sharp and tricuspid, 
with the middle cusp prominent. Garman records that the ''molar" teeth are elongate, 
narrow, each with a longitudinal ridge or keel. In Carman's drawings the upper jaw has 
11 transverse rows of anterior (cuspidate) teeth and 8 rows (4 on each sidej of posterior 
(grinding) teeth, making 19 rows in all. The lower jaw has 9 rows of anterior (cuspidate) 
teeth and 6 rows (3 on each side) of posterior (grinding) teeth, making 15 rows in all. In 



The Embryology of Heterodontus japonicus 681 

general, the dentition resembles that of a half'grown specimen of H. phillipi. The anterior 
teeth of my adult female H. quoyi are tricuspid with the middle cusp prominent; but the 
anterior teeth of my young male specimen are quincuspid. 

HETERODOHTUS FRAHCISCI GIRARD 

This species has been taken off the coast of California and the western coast of 
Mexico — especially in the Gulf of California. It was first described by Girard (1856). 
The external form of the body has been figured by Maclay and Macleay (1879); Jordan 
and Evermann (1900, Fig. 9, pi. HI); Jordan (1905, vol. 1, Fig. 315); Daniel (1934, Fig. 17); 
Kumada and Hiyama (1937, pis. 44 and 45). The best figures are probably those 
of Kumada. His figures of a 540'mm. female are reproduced as Text'figures 18 and 19. 

Girard's description of Heterodontus francisci (which he calls Cestracion francisci) is 
limited to a single paragraph, which I quote in full: 

The largest of these specimens now before us, and measuring nearly two feet, bears a very 
strong resemblance to C. phillipi, though of a somewhat more bulky appearance. The bony 
ridge, above the eye, is much more developed, and the fins are larger also. The posterior 
margin of the caudal is bilobed instead of being rounded : an emargination corresponding to the 
top [sic] of the vertebral column. The anal is placed farther back; its tip projecting beyond 
the anterior margin of the inferior lobe of the caudal. The posterior extremity of the ventrals 
[pelvics] extends beyond the anterior margin of the second dorsal. Color, above yellowish' 
gray, darker in the young; beneath light yellow. Small roundish-black spots are spread all 
over the body and fins. 

Girard's comparison of the caudal fin of H. frayicisci with that of H. phillipi is based 
on Lesson's erroneous figure. The emargination corresponds to the tip, not the "top", of 
the vertebral column. 

Some other points in which this species differs from H. phillipi are mentioned by 
Maclay and Macleay (1879) whose account differs in some respects from Girard's. 
Their drawings were made from an adult male H. francisci, 708 mm. (27.9 inches) 
long, from the Bay of Monterey, California. Dorsal and lateral views of the entire fish 
are shown, but without spots — perhaps the specimen had been long in alcohol. In the 
lateral view the pectoral and pelvic fins are not well displayed. As compared with H. 
phillipi, the head is proportionally broader and less high; its profile is less steep and more 
convex; the supraorbital ridges are less prominent, continuing almost to the snout and 
terminating abruptly behind the eyes. The spiracle is larger and farther from the eye. 
The first gill'Opening is scarcely twice the length of the fifth. The dorsal spines are very 
strong and are more than half the length of the dorsal fins. The dorsal fins themselves are 
more broadly rounded at the apex and slightly emarginate behind. 

Garman (1913) states that the color of H. francisci is grayish or olivaceous'brown 
with small scattered spots of black over body and fins. On large specimens the spots are 
sometimes absent or nearly so. The body is yellowish beneath. In the figures by Jordan 
(1905) and by Daniel (1934) a few small roundish'black spots of fairly uniform si2,e are 
scattered over the entire body including the fins, and the supraorbital ridges differ from 



682 



Bashford Dean TAemorial Volume 




Text-figure 18. 
Lateral view of a 540'mm. (21'mch) female specimen of Heterodontus francisci Girard. 

After Kumada and Hyama, 1937, pi. 44. 

those described by Maclay and Macleay (1879) and by Garman (1913) in not ending so 
abruptly behind the eyes. 

The principal external characters of an adult or nearly adult female H. francisci are 
well illustrated in my Text-tigures 18 and 19, after Kumada and Hiyama (1937j. These 
authors state that this shark, which is abundant in their collection, scarcely exceeds two 
feet in length. The body is brown, the belly much fainter. Small round black spots are 




Text-figure 19. 
Dorsal view of the 540-mm. (21-inch) female specimen oi Heterodontus francisci Girard, shown in 

lateral view in Text-figure 18. 

After Kumada and Hyama, 1937, pi. 44. 



The Embryology of Heterodontus jal^onicus 683 

scattered all over the body and fins. The authors list this species under the generic name 
Gyropleurodus. 

To Kumada and Hiyama (1937) we are also indebted for figures representing dorsal 
and lateral views of a young female H. francisci about 240 mm. (9.84 inches) long. In this 
specimen, the supraorbital ridges are low in the middle third, as in the two specimens, 
respectively young and adult, of H. quoyi examined by me. The color pattern of the 
young specimen of H. francisci figured by Kumada differs from that of adults of this 
species. The spots are larger and more complex; on the dorsal surface they are arranged 
according to a definite pattern. The spots are more numerous on the dorsal surface than 
on the lateral and ventral surfaces; on the fins, excepting the caudal, they are either in' 
distinct or absent. Each spot consists of a very dark central portion surrounded by 
a moderately dark zone. On the dorsal surface of head and body, the very dark spots 
are grouped in about ten transverse rows, each imbedded in a moderately dark 
stripe. On the body these stripes, each with its enclosed darker spots, are crescentic in 
outline, the concave margin facing forward; but on the head there are, anteriorly, two 
straight transverse stripes and, posteriorly, one crescentic stripe with its concave margin 
facing caudad. Collectively, these transverse stripes form a pattern which is bilaterally 
symmetrical with respect to the dorsal mid-line of the body. 

The skeleton of H. francisci has been described by Daniel (1914 and 1915). From 
his figures it appears that the vertebral column is better developed and the notochord is 
more constricted in Heterodontus than in Heptanchus (Daniel, 1934) and Chlamydoselachus 
(Goodey, 1910, reviewed by Smith, 1937). 

My material for the study of H. francisci consists of two female specimens (one is 
an adult) collected by Dr. 0. H. Townsend of the Albatross Expedition of the American 
Museum of Natural History on April 10, 1911, at Angel de la Guardia Island, Gulf of 
California. The larger specimen is about 705 mm. (27.75 inches) long, and the smaller 
one 565 mm. (22.25 inches). Some additional measurements, for comparison with H. 
quoyi, are given on page 684. 

The two specimens of H. francisci are much alike. In both, the head including the 
gill'region is broad, but in the larger fish it is broader in proportion to the total length. 
In the smaller and presumably younger specimen, the height of the head, in proportion to 
its width, is greater. The larger shark has a decided hump between the head and the 
first dorsal fin, but a similar hump on the smaller fish is less conspicuous. In both speci- 
mens, the supraorbital ridges are rather tall. They are supported throughout their 
length by the endoskeleton, and they terminate rather abruptly at their posterior ends. 
The length of the first gill-sHt is about double that of the fifth, as in H. quoyi. The 
spiracular openings are comparatively large: in the larger specimen their longer diameter 
is from 4 mm. to 5 mm., in the smaller fish 3 mm. to 4 mm. Dorsal fins and dorsal spines 
are larger than in H. quoyi. In both specimens, the origin of the first dorsal is directly 
above the posterior margin of the pectoral base (as in Carman's H. japonicus). The hind 
margins of both dorsals are concave. The base of the anal fin is slightly more than its 



684 Bashford Dean Memorial Volume 

lencrth distant from the caudal. The scales on the dorsal surface of the body are not 
particularly large. A few dark spots are visible: these are small, widely scattered, and 
most of them were found only after a careful scrutiny. 

Taws .\icd Teeth. — In his "Atlas" (1913) Garman figures teeth and jaws of very 
young, medium-sised and adult specimens of H. fraiicisci. In his figure showing the 
jaws in lateral view, they bear a close resemblance to those of H. quoyi (my Test-figure 17j. 
In Daniel's figure of the skull of H. jraTicisci (1915, Fig. 6, pi. IIIj the form of the jaws as 
seen in lateral view is somewhat intermediate between the two quite different forms 
portrayed by Goodrich (my Text'figure 33) and Garman (1913: Fig. 4, pi. 47) for H. 
phiUipi. One infers that these differences are individual and not specific. 

Maclay and J^Iaclea^- ( l879j state that the front teeth of H. jraiicisci are strongly 
tricuspid, those at the sides are longitudinally ridged. Garman (1913) writes that the 
anterior teeth have five cusps, the middle one the longest: with age the outer cusps 
become less apparent and the middle cusps much stronger. His drawings show the 
posterior teeth longitudinally ridged in all stages. In my two large remale specimens 
the anterior teeth are tricuspid. 

OOXIPARISON OF HETHlODO.\nJS ^VOXI A?qp FBJOiCISCI 

In my descriptions of the specimens of H. quoyi and H. fra7icisci belonging to the 
American Museum of Natural History, some statements were made concerning the form 
of the body. It seems desirable to bring together the data upon which these statements 
were based, in order that certain features in the two species may be accurately compared. 
Incidentally, a few comparisons will be made with other species. 

The measurements upon which the present discussion is based are given in Table I. 
In this connection one should bear in mind that the female specimen of H. quoyi is presum- 

T.-VBLE I 
SOME XlEASUREXffiNTS IS" MUlDvIETERS OF KXJR SPECIMENS OF HETERODOXTL'S 



Speoei H. quoyi H. francisci 



Ses csf SpscEoai Fanale i Male i Female I Female 



Tcftsl lengili (fiiEn tip rf sDoiit to lip csf lail fin) 527 372 705 j 565 

Greatest width df bead (at first gil-covers) I 118 ;| 60 , 13S ,1 97 

Greatest Leig^it of liead lat postsiar end supiaorhital dd^) , 64 41 86 ; 67 

Gr^tEst height of body (in tiansv^ise p^ari? p:>«mg throng fiftli giH-covers) 80 | 4S ■ 110 ' 75 

Lei^gtbi of first gifi-slit ■ 30 ! 15 | 34 ! 28 

LeEgtiiaffiiti[giS-sKt 14 s 17 14 

Lon^tDdiiHl distaiiiabetweaj bases of iKctaralaEdfcadcKsa! fins. 25 12 

Length of base of anal fin 2S IS ' 42 ! 32 

Distance bers-een base of anal fin and ventral lobe csf caudal 34 23 43 



JO 



ably advdt or nearly adult, while the male of the same species is decidedly young. The 
larger specimen of ff. fraricisci is known to be adult. 

I may say at once that the two species are readily separable. In certain features of 



The Emhryology of Heterodontus japonicus 685 

their external anatomy they differ so much that they are distinguishable at a glance; but 
I suspect that even a gifted artist could not portray all their subtle and almost intangible 
differences of contour. 

In both species the head is broader than the body (excluding the paired fins). The 
region of greatest breadth lies between the first gill'covers. In the large female specimen 
of fi. quoyi, the greatest breadth equals 22.3 per cent of the total length; in the decidedly 
small and immature male specimen of the same species, only 16. 1 per cent. In the larger 
female specimen of H. fra7^cisci, the greatest breadth equals 19.5 per cent of the total 
length; in the smaller female of the same species, only 17.1 per cent. It is apparent that in 
both species the breadth of the head, in proportion to total length, is greater in the older 
specimen ; but when allowance is made for age (ignoring sex as a possible factor) H. quoyi 
is definitely broader than H. francisci. For further information we must have recourse to 
published drawings, which are not so satisfactory as specimens since we have no assurance 
that they were made from accurate measurements. There are no drawings of either 
dorsal or ventral views of H. quoyi. In Maclay and Macleay's dorsal view (1879) of 
their 708'mm. specimen of H. francisci, the greatest breadth (which is in the region of the 
first gill'Covers) equals 17-5 per cent of the total length — a proportion somewhat smaller 
than that obtained for my larger specimen of H. francisci, which has almost exactly 
the same length. 

It may be of interest to extend this comparison to other species, but there we must 
depend entirely on drawings which may not be made to scale. Maclay and Macleay's 
dorsal view of a fuU'grown specimen of H. phillipi (my Text'figure 7, page 667) has 
a head that appears broad as compared with most sharks, but is decidedly narrower than 
the heads of my adult specimens of H. quoyi and H. francisci. Maclay and Macleay's very 
young specimen of H. phillipi (my Text-figure 9, page 669) has a head that is much 
narrower than that of their adult of the same species. In a young female specimen of H. 
zehra described and figured by Maclay and Macleay (1886) the width of the head cannot 
be measured because in the dorsal view the head is turned slightly to one side; but it 
appears very narrow, and the entire body is narrow as compared with other species of 
Heterodontus. In a drawing by Maclay and Macleay representing a dorsal view of a young 
female specimen of H. japonicus about 406 mm. long (my Text-figure 24, page 691), the 
width of the head equals 15.7 per cent of the total length. This is slightly narrower 
than the head of my young male specimen of H. quoyi, and of course much narrower than 
the heads of adult specimens of H. quoyi and H. francisci. 

In my adult female specimen of H. quoyi, the height of the head (including the 
supraorbital ridge) equals 54.2 per cent of its breadth, while in my young male of the same 
species the proportion is 68.3 per cent. In my larger female specimen of H. francisci 
the height of the head equals 62.3 per cent of its breadth; in the slightly smaller female 
of the same species the corresponding percentage is 69.0. We do not know if sex is 
a factor in determining the si2,e or bodily proportions in these species, so this possibility 
must be ignored. With this reservation, the data indicate that in the adults of both 



686 Bashford Dean Memorial Volume 

species the head is dorsoventrally depressed, but more so in H. quoyi than in H. francisci. 
In both species, during growth the head becomes broader and less tall proportionally, but 
only the ventral surface becomes actually flat. Because of differences in the shape of the 
head, its bulk in the two species cannot be compared by ordinary measurements. 

From the total evidence it appears that most species of Heterodontus, in adaptation to 
a bottom'dwelling mode of Hfe, have differentiated moderately in the direction of a broad' 
ening of the head and anterior part of the body, accompanied by a lessening of the head 
height and a flattening of the ventral surface of both head and body. These features 
emerge in the course of development after hatching, and are not found in the very young — 
a circumstance which leads us to infer that the more or less remote ancestors of this group 
were not bottom-dwelling forms. From the meager information available, it is possible 
that H. zebra has evolved in a different direction, tending to become eel'Hke in form. 
This, also, is an adaptation to life on the ocean bottom. 

Another feature common to my specimens of both H. quoyi and H. francisci is the 
slightly humpbacked appearance. This has already been mentioned as a possible generic 
or family character. The hump is not due to an arched condition of the body. In each of 
my specimens the greatest height of the dorsal surface, excluding the dorsal fins, occurs in 
the region above the fifth gill'slit, which is also above the base of the pectoral fin. In the 
pectoral region the ventral body wall is firm and the height of the body may be measured 
accurately. The height of the hump may be computed by subtracting the head height 
from the body height. Comparison of the height of the hump, in proportion to body 
height in different specimens, may be made on a percentage basis. In my large female 
specimen of H. quoyi the height of the hump equals 20 per cent of the body height; in the 
small male specimen of the same species, 14.5 per cent. In the larger female specimen of 
H. francisci the excess of body height over head height equals 21.8 per cent of the body 
height; in the slightly smaller female, 10.6 per cent. It is noteworthy that in H. francisci 
the smaller of two large female specimens has a hump only half the height of the other. 
Judging from the drawings that have been published, this variability occurs also in H. 
phillipi and H. japonicus. 

HETERODOKTUS GALEATUS GUNTHER 

The range of H. galeatus, so far as known, is limited to the waters of Queensland 
and New South Wales. Whitley (1940) writes that in the northern part of New South 
Wales this species (which he calls Molochophrys galeatus) tends to replace H. phillipi. 

H. galeatus was first described, from a single specimen, by Giinther (1870). The 
first drawings of the entire fish are those of Maclay and Macleay (1879); they comprise 
lateral, dorsal and frontal views. These drawings were made from a stuffed female 
specimen (length not given) in the Australian Museum. A much better portrayal of 
a lateral view, published by Whitley (1940), is here reproduced as Text'figure 20. Whitley 
records that the length of sharks of this species is about five feet. Presumably this refers 
to adult specimens. 



The Embryology of Heterodontus japonicus 



687 



<.. 




y^ s,^ 



Text-figure 20. 
A female specimen of Heterodontus galeatus Giinther captured off Sandon Bluff, New South Wales, Australia. 
The inset figure shows the mouth opening, the nares, oro-nasal grooves, labial folds and some of the front teeth. 

After Whitley, 1940, Fig. 56, p. 73. 

The most outstanding peculiarity of this species is the unusual height of the supra' 
orbital ridges. These ridges approach each other anteriorly, and diverge posteriorly; 
they end abruptly a short distance behind the eye. Garman (1913) says that they end ab' 
ruptly in young specimens, less so in old. As shown in a frontal view by Maclay and 
Macleay (1879) the ridges lean outward (laterad) at an angle of about 45 degrees from the 
median plane. Waite (1898 and 1899) and Whitley (1940) refer to this shark as 
the "crested species". The name Crested Shark seems appropriate, though it might with 
some justice be applied to any species of Heterodontus. The name "Crested Port Jackson 
Shark", used by Whitley, seems inadmissable. 

Garman (1913) states that the form of H. galeatus is similar to that of H. francisci, but 
the head is short and angular. The anterior gill-opening is more than twice as "wide" 
(presumably meaning high or long) as the hindmost. The origin of the first dorsal fin is 
above the hinder part of the pectoral base; the hind margin of the first dorsal is concave. 
The base of the anal fin is about two-thirds of its length distant from the lower lobe 
of the caudal. 

The color pattern is not well shown in Maclay and Macleay's lateral view (1879), 
but is quite distinct in their dorsal view of the same specimen. Six broad transverse dark 
stripes are said to be visible, but in the drawing the most posterior stripe is very faint. 
Garman (1913) states that the general color is brown, with a transverse stripe of darker 
across the orbits, widening upon the cheek; another band in front and one behind the 
ventrals (pelvics); one through the second dorsal and one in front of the anal, less definite 
than the anterior — making five instead of six as enumerated by Maclay and Macleay. The 



688 Bashford Dean Memorial Volume 

color pattern is not very distinct in Whitley's figure (1940) reproduced as my Text-figure 
20. Whitley states that the color is light-brownish, with the interorbital region and the 
back in front of (the first?) dorsal fin blackish; a broad blackish bar below the eye; back 
with some dark transverse bars, one at base of each dorsal fin most prominent, but not 
joining to depict a "harness". This shark sometimes becomes stained a reddish color on 
teeth or skin apparently through eating the purple sea urchins of Australian harbors. 

At the time when Maclay and Macleay's description was written (1879), only two 
specimens of H. galeatus were known : the stuffed specimen in the Australian Museum, 
and Dr. Giinther's specimen in the British Museum. Maclay and Macleay wrote that it 
was not at all improbable that the fish might not, after all, be of such very rare occurrence. 
"The general resemblance to H. pMlipi is considerable, and fishermen are generally far 
from being acute observers of fish which are not of a marketable character." Ogilby 
(1890) wrote that, at Port Jackson, the species was almost as common as H. phillipi. He 
stated that he had also received specimens from Port Stephens, New South Wales. 
Waite (1898) made extensive collections of marine fishes in the waters adjoining New 
South Wales, including specimens of H. phillipi from 14 different stations. Concerning H. 
galeatus he wrote: "Although a careful lookout was kept for the crested species, 
Heterodontus galeatus, it was never taken and notwithstanding this fact, all the egg cases 
I saw southward in the shop windows of WoUongong and Kiama were of the latter species 
[galeatus], those of our commoner form (phillipi) being either rare or quite unknown". 

Teeth. — Waite (1899) pubHshed a photograph of the teeth of both upper and lower 
jaws of H. galeatus (which he called Gyropleurodus galeatus) and stated that the teeth 
portrayed by Maclay and Macleay (1879, Figs. 30 and 31, pi. 25) and attributed to H. 
galeatus, were not of that species. The differences in the figures of the posterior teeth 
are very marked. In Waiters figure the posterior or grinding teeth are much smaller, 
more nearly uniform in size and more numerous. In Maclay and Macleay's figure they do 
not differ materially from those portrayed, by various authors, for other species, except 
that they are more elongate. In one respect the figures of the posterior teeth by Waite 
and by Maclay agree: the longitudinal ridge is distinct, perhaps stronger than in any 
other species. My general impression is that the teeth of H. galeatus figured by Waite 
are more primitive (in that the posterior or grinding teeth do not differ so much from the 
anterior or cuspidate teeth) than the teeth of any other species of Heterodontus. 

HETERODOJiTUS JAPOHICUS MACLEAY 

For many years, specimens of Heterodontus collected in Japanese waters were classi- 
fied as Cestracioyi (Heterodontus) phillipi, the Port Jackson Shark. Thus the specimens 
figured and described under this name by Miiller and Henle (1841) and by Brevoort (1856) 
were collected in Japan. Also Siebold (1850, in his "Fauna Japonica") stated that a shark, 
which he called Cestracion phillipi, was very common during spring and summer along the 
southwestern coast of Japan, especially in the Bay of Nagasaki. He wrote that it attains 
a length of three feet and that it was much sought after for food by the Japanese. There 



The Embryology of Heterodontus japonicus 689 

is now no doubt that the species of Heterodontus ordinarily taken in Japanese waters is 
not H. phillipi but a different species, named by Macleay (in Maclay and Macleay, 1879) 
Heterodontus japonicus. A related species, H. zehra, has been taken but rarely in Japanese 
waters, and there is no authentic record of H. phillipi ever having been taken off Japan. 
Thus the English common name, Japanese Bullhead Shark, seems appropriate for Hetero- 
dontus japonicus. 

As stated early in this article, Dean collected eggs and embryos of H. japonicus in 
the Sagami Sea, at the entrance to the Gulf of Tokyo. In his notes Dean states that this 
shark is not uncommon along the coasts of the Japanese islands south of Hokkaido. In 
certain regions it is known to be abundant, as along the shores of the Inland Sea and in the 
Sagami Sea. 

The Japanese Bullhead Shark has received several local names. Siebold (1850) 
stated that the local name was Sasiwari. Brevoort (1856) explains that this name is 
doubtless derived from Sas-ir, to stick in, and war, to cleave — in allusion to the spines in 
front of the dorsal fins. Jordan, Tanaka and Snyder (1913, p. 8) record the following 
colloquial names: J^ekpzam'e (Tokyo market; Misaki; Sagami); Sazaewari (Prov. Shima; 
Osaka; Prov. Tosa); Sazaiwari (Nagasaki). It is called "Neko2;ame" in the volume entitled 
''Illustrations of Japanese Aquatic. . . Animals" (1913) elsewhere referred to. Dr. Dean 
calls it Neko2;ame. A synonymy of scientific names follows : 

HETERODONTUS JAPOJilCUS Macleay 

Cestracion phillipi. Miiller and Henle, 1841, Plagiostomen, p. 76, pi. 31. 

Cestracion phillipi. Siebold, 1850, Fauna Japonica: Pisces, p. 304. 

Heterodontus zehra (not Gray). Bleeker, 1854, Verh. Bat. Gen., 26, 127- 

Cestracion phillipi. Brevoort, 1856, Perry Expedition, vol. II, Fig. 2, pi. 12. 

Cestracion phillipi var. japonicus. Dumeril, 1865, Elasm., p. 426. 

Cestracion phillipi. Giinther, 1870, Cat. Fishes Brit. Mus., vol. VIII, p. 415. 

Heterodontus japonicus Mel. Maclay and Macleay, 1884, Proc. Linn. Soc. New South Wales, 

8, p. 428, pi. XX. 
Heterodontus japonicus Mel. Steindachner, 1896, Ann. K.K. Naturhist. Hofmus., Wien, 11, 

p. 224. 
Heterodontus japonicus. Jordan and Fowler, 1903, Proc. U.S. Nat. Mus., 26, p. 599. 
Cestracion japonicus (Dumeril). Regan, 1908, Ann. Mag. Nat. Hist., 8. ser. 1, p. 496. 
Centracion japonicus. Garman, 1913, Plagiostomia. Mem. Mus. Comp. Zool., 36, p. 184. 
Heterodontus japonicus Dumeril. Jordan, Tanaka and Snyder, 1913, Journ. Coll. Sci., Imp. 

Univ. Tokyo, 33, Art. 1, p. 8. 

The Japanese Bullhead Shark, Heterodontus japonicus, was first figured and described 
by Miiller and Henle (1841). Their specimen and figure were labelled ''Cestracion 
phillipV\ At the time when their monograph was published, only three species of 
Heterodontus (Cestracion) were known: H. phillipi, H. zehra and H. quoyi. No evidence 
other than the figure itself (my Text'figure 21) is necessary to prove that the specimen 
drawn was not one of these. Miiller and Henle listed nine specimens of H. phillipi 
stored in various museums, and stated that they were collected in "Neuholland" (now 



690 



Bashford Dean Memorial Volume 




Text-figure 21. 
A male Japanese Bullhead Shark, Heterodontus japcmicus Macleay, length not recorded. The original figure 

is in color and is labelled Cestracion phillipi. 
After Muller and Henle, 1841, pL 31. Right and left are here reversed. 

Australia) and in Japan. But Heterodontus phillipi does not occur in Japanese waters. 
Moreover, Siebold (1850, p. 304) noted that the Muller and Henle figure was drawn by 
Biirger from a fresh specimen collected in Japan. 

A specimen of H. japonicus described and figured by Brevoort (1856) was labelled 
""Cestracion phillipi'' . This specimen (my Text-figure 22) was collected at Simoda 




Text-figure 22. 
A very young (recently hatched) male Japanese Bullhead Shark, Heterodontus japonicus, collected by the 
Perry Expedition to Japan. The original figure, from a recently procured specimen only 216 mm. (8.5 inches) 

long, is in color and is labelled Cestracion philUpi. 
After Brevoort, 1856, pi. XU. 



The Embryology of Heterodontus japonicus 



691 




Text-figure 23. 

A young female Japanese Bullhead Shark, Heterodontus japonicus. This specimen, collected in Japanese 

waters, was about 406 mm. (16 inches) long, and was drawn after preservation in alcohol. 

After Maclay and Macleay, 1884, Fig. 1, pi. 20. Right and left are here reversed. 

(Shimoda, at the entrance to the Sagami Sea?) by the Perry Expedition to Japan. Brevoort 
states that all the drawings of fishes were made from recently procured specimens; but 
that no professional zoologists accompanied the expedition, hence in making the drawings 
no close attention was paid to specific characters. From the small si?e of Brevoort's 




Text-figure 24. 

Dorsal view of the 406-mm. (l6-inch) preserved female specimen of Heterodontus japonicus shown in lateral 

view in Text-figure 23. The inset figure is an outline of a front tooth. 

After Maclay and Macleay, 1884, Figs. 2 and 5, pi. 20. 



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Bashford Dean Memorial Volume 



specimen (only 216 mm. or 8.5 inches long) one infers that it must have been recently 
hatched. Brevoort's description of the color and color pattern follows : 

Its general color is of a pale sepia'like brown, darker on back and fins, with a pinkish 
tinge on lower parts of the body. Irregular bands and large blotches of several shades of the 
same brown are distributed from the pectorals to the caudal, grouped in five principal bands, 
with smaller ones near the back between the first three large ones. The first of these last is 
just back of the pectorals, the second back of the first dorsal and in front of the ventrals, 
spreading laterally near the abdomen. The snout and cheeks are shaded also with darker-brown 
cloudings. Small pale-brown dots, besides the above, cover the back of the head and body 
and about one-half of the pectorals, dorsals and caudal. Ventrals, anal, and lower lobe of 
dorsal of a more uniform brown. 

The first specimen to be described, figured and labelled Heterodontus japonicus is 
that of Maclay and Macleay (1884). This specimen is a 406'mm. (16-inch) female obtained 
from Japan; it is evidently not full-grown. The authors state that the "coloration and 
markings'" of their specimen are not by any means distinct, the fish having been long in 
spirits; but the remains of numerous dark-brown bands across the back present a very 
different style of marking from those of the other known species of the genus. Maclay 
and Macleay 's drawing of the entire fish in lateral view (my Text-figure 23) shows the 
transverse dark bands with essentially the same distribution as in Miiller and Henle's 
figure, save that the band immediately in front of the first gill-slit is lacking. In their 
drawing of the same specimen in dorsal view (my Text-figure 24) the transverse bands 
are more prominent. 

Maclay and Macleay's further description of their 406-mm. (16-inch) female specimen 
of Heterodontus japonicus is here given very nearly in the words of the authors, but with 
some rearrangement and clarification. They state that the snout is very bluntly rounded 
(my Text-figures 23 and 24). The mouth (Text-figure 25) differs from that of H. phillipi 
in having the inner nasal fold less long, the fold of the upper lip rounder and shorter, and 
the inferior margin of the fold of the lower lip covered with soft skin having only a very 
few scutellae (placoid scales). The spiracle (Text-figures 23 and 24) is distinct, and larger 
than in H. phillipi. It is placed a little below and behind the eye. The lateral line is 
straight and continuous from the supraorbital ridges. The first dorsal fin is high and 



Text-figure 25. 
Anterior part of the head of Heterodontus japonicus 
seen from the ventral side, showing the mouth open- 
ing, nares and oro-nasal grooves, the labial folds and 
some exposed anterior teeth. From the young female 
specimen about 406 mm. (16 inches) long, shown in 
Text-figure 23 and 24. 

After Maclay and Macleay, 18S4, Fig. 3, pi. 20. 




The Embryology of Heterodontus japonicus 693 

falciform; the height is exactly twice the length of the portion of the base attached to the 
back. The spine is small and acute (as compared with that of H. pMlipi), being only half 
the length of the fin. The second dorsal is shaped like the first, but is less in height, and 
its base of attachment to the back is about the same. The distance between the two 
dorsals is equal to that between the second dorsal and the commencement of the caudal 
fin, and to that between the first dorsal and the eye. The pectorals are large and tri- 
angular, and about equal in length to the caudal. The ventrals (pelvics) are situated in 
a line intermediate between the two dorsals. The anal commences distinctly behind the 
second dorsal, and does not nearly reach the caudal. The lower lobe of the caudal is very 
deeply and less than rectangularly notched. The authors do not mention the hump on the 
anterior part of the body, which is quite prominent in their figure representing a lateral 
view (my Text'figure 23). 

To Bashford Dean we are indebted for the only photograph of a fresh-caught adult 
Japanese Bullhead Shark on record. This was published (Dean, 1904) in the Popular 
Science Monthly in an article entitled "A Visit to the Japanese Zoological Station at 
Misaki" and is reproduced herein as Text-figure 3, page 655. The original legend reads 
"A Freshly Caught Port Jackson Shark", but since Dean states in the accompanying text 
that a Port Jackson Shark is abundant at Misaki, it is evident that he was using the name 
in a generic, not a specific sense — for Heterodontus phillipi does not occur at Misaki. 
Thus the species is almost certainly H. japonicus, though H. zebra, a more slender form, 
does occur somewhat rarely in the vicinity of Misaki. The photograph does not show the 
color pattern, which would make identification easy. In Dean's photograph, one must 
make some allowance for the trick of the camera in enlarging objects in the foreground : 
the pectoral fin is probably a little too large. Since the mouth is partly open, the lower 
jaw has sagged and the cranium is slightly upraised. 

Among Dean's records there is a faded photograph showing a dorsal view of an 
adult or nearly adult Heterodontus, presumably japonicus. The supraorbital ridges are 
well shown. They are strongly upraised, though narrow, and approach each other at 
their anterior ends, diverging posteriorly. At their posterior ends they terminate 
rather abruptly, though not so abruptly as in H. galeatus (Text-figure 20 and in Maclay 
and Macleay's lateral view). The breadth of the head, measured between the first pair of 
gill-covers, equals 19 per cent of the total length. The pectoral fins are extended, and the 
distance from tip to tip equals 56 per cent of the total length. 

A young female specimen of Heterodontus japonicus in the collections of the American 
Museum of Natural History measures about 280 mm. (eleven inches) in length "over all". 
It is described on page 757 and portrayed in Text-figure 65, of the present article. 

There remains to be considered a figure of the Japanese Bullhead Shark contained in 
a folio volume entitled "Illustrations of Japanese Aquatic Plants and Animals", published 
by the Japanese Fisheries Society in 1931. An adult specimen of Heterodontus japonicus 
is there portrayed in color. Upon comparing this figure with those of other authors 
(including the photograph by Bashford Dean reproduced in my Text-figure 3) one gets 



694 



Bashford Dean Memorial Volume 




Test-ngure 26. 

Dentition of Heterodontus japonicus: A, upper 

jaw; B, lower jaw. Dra^sTi from the young female 

spedmen, 406 mm. (16 indies) long, shown in 

Text-figures 23 to 25. 

After Maday and Madeay, 1SS4, 

Figs. 4a aad 43, pL 20. 



an impression that it is inaccurate in several 
respects. The eye is too large and too near 
the top of the head: the supraorbital ridge is 
omitted or represented as part of a circular 
ridge extending entirely around the eye. The 
notch in the ventral lobe of the caudal fin is 
curved instead of angular. The dark brown 
transverse stripes are more regular and less 
numerous than in any other drav-nng of this 
species. For these reasons this figure is not 
reproduced here. The legend states that the 
species is not good for food — contrar^T- to the 
statement in Siebold's "Fauna Japonica"'. "De 
gustihus non est disputandum" . 

Teeth. — In Maclay and \Iacleay"s young 
(16'inch) female specimen of the Japanese Bull- 
head Shark, there are 23 transverse rows of 
teeth in both upper and lower jaws (my Text- 
figure 26). The anterior (cuspidate) teeth are 
r\^pically five-cusped. In the upper jaw, the 
number of teeth in the central row is eight (one 
is not visible in Text-figure 26). In the lower 
jaw, the transition betw^een anterior (cuspidate) 
and posterior (grinding) teeth is very abrupt; 
in the upper jaw^ it is more gradual. In making 
comparisons unth the teeth of other Hetero- 
dontid sharks, it should be borne in mind that 
\Iaclay and Macleay's description is based on 
a single specimen, and that this specimen was a 
decidedly young one. 

The development of the teeth of Hetero- 
dontus japonicus is further described in the final 
section of this article, ■w.-hich contains also a 
concise summary of the main course of develop- 
ment of the teeth of the entire genus. 

.'YFFINITIES TO FOSSIL FORMS 

In the introduction to this article I have 
pointed out that the genus Heterodontus in- 
cludes some fossil forms, so that the paradoxi- 
cal term "living fossils" might pardonably be 



The Embryology of Heterodontus japonicus 



695 




Text-figure 27- 

Hyhodus hauffianus E. Fraas : skeleton, with skin (shagreen) outlining the entire body which is about 

2240 mm. (88 inches) long. Upper Lias; Holzmaden, Wiirttemberg. 

After Koken, 1907, Taf. I. 

applied to present-day representatives of the group. Of greater importance is the close 
relationship between the Heterodontidae and the Hybodontidae, which will now be 
discussed. Since paleontologists almost uniformly use the term Cestracion instead of 
Heterodontus, and Cestraciontidae in place of Heterodontidae, it is advisable, in review- 
ing their work, to adopt their language without a tiresome repetition of synonyms. . 

In his "Catalogue of the Fossil Fishes in the British Museum", Woodward (1889) 
defined the Cestraciontidae very broadly as follows : ''Dorsal fins each armed with a spine, 
the first opposite to the space between the pectoral and pelvic fins. Teeth mostly obtuse, 
never fused into continuous plates; several series simultaneously in function". He 
further states that "No distinctive characteristics of value having yet been discovered, 
the so-called Orodontidae and Hybodontidae are included in this family". 

This classification, or something like it, seems to have been adopted by Goodrich 
(1909) since he includes Orodus and Hybodus (the latter portrayed in my Text-figures 27 
and 28) in the family Cestraciontidae. Regan (1906) had already separated the Ces- 
traciontidae from the Hybodontidae. Most of the characters that Regan lists for the 
two families are identical, but he states that in the Cestraciontidae the pterygoquadrate 



3C»pf- Soptnetv 



CUxqtwfiot'xU 








'////f(i<§^; 



■""■■--\'Cn~ ^^P' \ 

J -iKX- J3„e.,,,(li„, 

Text-figure 28. 

Reconstruction of the skeleton and outline of the body of Hyhodus hau^anus E. Fraas, based on a 

specimen about 1220 mm. (48 inches) long. Upper Lias of Hohmaden, Wiirttemberg. 

After Jaekel, 1906, Fig. 2. 



696 



Bashford Dean Memorial Volume 



(palatoquadrate) has a preorbital articulation with the cranium, while in the Hybodontidae 
the attachment is postorbital. Nine genera, including Paleospinax and Synechodus, were 
assigned to the Hybodontidae, leaving one genus, Cestracion, for the Cestraciontidae. 

In the second German edition of his "Grund^iige der Palaeontologie", Zittel (1911) 
listed in his family Cestraciontidae seven genera including Cestracion. Eight other genera, 
including Hyhodus and Orodus, made up his family Hybodontidae. The most recent 
(fourth) German edition of Zittel (1923) departs only slightly from this classification. In 
the separation of the two families, Woodward appears to have taken part. In the second 
English edition of Zittel, revised by Woodward in 1932, the family Cestraciontidae 
includes only three genera {Cestracion, Paleospinax, and Synechodus) while the family 
Hybodontidae comprises thirteen genera including Hyhodus and Orodus. Woodward's 
definitions of the two families deserve careful attention : 



DISTINCTIVE CHARACTERS OF THE HYBODONTIDAE AND THE CESTRACIONTIDAE 

According to Woodward in Zittel (1932). 



HYBODONTIDAE 

Teeth numerous, mostly obtuse, never 
fused into continuous plates; several series 
simultaneously in function. Notochord 
persistent. Some ribs long and slender; 
neural arches also long and slender. Each 
of the two dorsal fins armed with a spine, 
which is as deep as the fin; the spine orna' 
mented on the sides and bearing one or two 
rows of posterior denticles. Anal fin with- 
out spine. Tail heterocercal. Paired 
hooked head spines often present. Devonian 
or Lower Carboniferous to Cretaceous. 



CESTRACIONTIDAE 

Teeth as in Hybodontidae. Vertebral 
centra cyclospondyHc or asterospondylic. 
Ribs and neural arches very short and broad. 
Each of the two dorsal fins armed with 
a spine which is less deep than the fin; the 
spine is almost or completely unornamented, 
and without posterior denticles. Anal fin 
without spine. Tail heterocercal. No head 
spines. Lower Jurassic to Recent. 



Several of the characters Hsted above are much alike in the two families. The degree 
of this likeness, and its significance, need some evaluation; but first let us note some pos' 
sible additions to the list of resemblances. Certain peculiarities in the form of the head 
and anterior part of the body of some Cestracion ts, leading to the common name "Bull- 
head Sharks", find a counterpart in fossil forms like Hyhodus (Text-figures 27 and 28). 
This matter has been discussed on pages 660 and 686. A considerable degree of flatness of 
the ventral surfaces of both head and body may also be common to the two families. 
Woodward (1921) states that in their general appearance the Hybodonts resemble the 
Cestracionts. The pectoral girdles of both Heterodojitus (Daniel, 1915, Fig. 8, pi. IV) 
and Hyhodus (my Text-figures 27 and 28) are very strong. 

Some of the characters common to the two families are included in the definitions 
presumably for comparison with other families in the same suborder, or to show inclusion 



The Embryology of Heterodontus japonicus 



697 




Text-figure 29. 
Teeth of Hybodus, outer aspect, natu- 
ral size: A, three associated teeth of 
Hybodus delahechei Charlesworth ; B, 
three associated anterior teeth of 
Hybodus reticulatus Agassiz. 
After Woodward, 1889, Part 1, pi. X. 



in some larger group; but we are here concerned mainly with the interrelations of the 
two families. From this point of view, the descriptions of the teeth by Woodward are 
inadequate when isolated from the special accounts of the teeth of the various genera. 
There is considerable variation in the teeth of different genera in both families, and the 
differences are of the same kind. 

In Hybodus the teeth (Text-figures 29 and 30) are all cuspidate. In the anterior teeth 
the cusps are more or less acute, with the central cusp predominant and the other cusps 
somewhat irregular in sizie and number. In the posterior teeth there is a tendency toward 
differentiation into grinders; for these teeth are larger than the anterior teeth and their 
cusps are almost or quite obtuse. But in some other genera of the family Hybodontidae, 
low rounded crushing teeth, slightly ridged and with only a few vestigial cusps, occur 
(e.g., as in Orodus, figured by Eastman, 1903; and Acrodus, beautifully illustrated by 
Woodward, 1889). 

Similar differences occur in the three genera of the Cestraciontidae. The teeth of 
Synechodus (Text-figure 31) are much like those of Hybodus (Text-figures 29 and 30) 




Text-figure 30. 

Posterior teeth of Hybodus, in natural sizes. A, Hybodus delabechei Charlesworth: four 

posterior series of teeth, coronal aspect; one tooth of each of three series is shown also 

in side view. B, Hybodus raricostatus Agassiz: two posterior series of teeth and portions 

of a third, coronal aspect; two teeth are shown also in side view. 

After Woodward, 1889, part 1, pi. X. 



698 



Bashford Dean Memorial Volume 




Text-figure 31. 
Dentition of Synechodus dubrisiensis Mackie, a member of the family Heterodontidae (Cestraciontidae) 
represented only by fossils. These teeth are twice natural size, with six separate teeth enlarged four times. 

Upper Cretaceous, Sussex. 
After Woodward, 1889, Part 1, Text-fig. 12, p. 326. 



except that the anterior teeth of Synechodus are larger than the posterior ones. The teeth 
of Paleospinax show progress in the direction taken by Heterodontus: the few anterior 
teeth are high'crowned and prehensile with only a single pair of lateral denticles, while 
the posterior teeth are low-crowned with two or three pairs of lateral denticles reduced to 
minute beads (Zittel, 1932). Finally in Heterodontus, the only genus represented by 
living specimens, the anterior teeth of the adult are typically tricuspid, the central cusp 
predominating; while the posterior teeth are large, and set in oblique rows, without 
cusps but with the grinding surface of each tooth traversed by a slender longitudinal 
ridge — unless this is worn away by use. Nearly complete skeletons of Heterodontus 
(Cestracion) have been found in the Lithographic Limestone (Upper Jurassic) of Bavaria 
and the Chalk of England. The teeth of these fossils, which include several extinct 
species, are said to differ little from those of recent examples of the genus save that the 
crowns of the grinding teeth are rugose in addition to having a longitudinal keel. 

The spines of the dorsal fins are not limited to sharks of the families under consider' 
ation, but one of the most obvious differences between the two families is the ornamenta' 
tion of the dorsal spines in the Hybodontidae and the almost entire lack of it in the 
Heterodontidae. The "ornamentation" consists of longitudinal ridges along the sides and 
sometimes the front of the spine, and the presence of tubercles on its rear surface. In two 
genera of fossil Heterodontidae, Paleospinax and Synechodus, the dorsal fin spines are 
almost uniformly smooth, and in Heterodontus they are entirely smooth. 



The Embryology of Heterodontus japonicus 699 

On the basis of the mode of suspension of the jaws, it appears impossible to make 
a clear-cut distinction between the families Hybodontidae and Cestraciontidae as consti- 
tuted by Woodward (in Zittel, 1932). Some genera of the Hybodontidae (e.g., Orodus) 
are known only by their teeth, or by their teeth and dorsal spines. Where genera are 
represented by fairly complete skeletons (e.g., as in Hyhodus), there is apparently some 
lack of uniformity in the method of jaw suspension. Nevertheless Woodward (1921) 
generalized as follows: ''The Hybodonts. . . are especially interesting because, while 
their dentition and their general appearance resemble those of the existing Cestraciont- 
idae, their skull is very different and more closely agrees with that of the Notidanidae". 
It is possible that the word skull, as used here, means cranium, as it seems to do in 
several places in Woodward's writings. 

The terms autostylic, hyostylic and amphistylic were introduced by Huxley (1876) 
to designate three types of skull and of suspension of the first visceral arch — the mandibu- 
lar arch, or the jaws. We are here concerned only with the second and third types as 
they occur in sharks. In both, the palatoquadrate cartilage (constituting the framework of 
the upper jaw) is quite distinct from the chondrocranium. The palatoquadrate is, at 
most, in contact with the cranium only by articular surfaces, and connected with it by 
ligaments. In front, the palatoquadrate is often loosely connected with the lateral 
ethmoid (preorbital) region of the skull by way of a palatobasal or ethmoid process (of the 
palatoquadrate), but this type of connection apparently has little or nothing to do with 
the classification under consideration. In most sharks, the dorsal element of the hyoid 
arch, called the hyomandibular cartilage, attains a large size, gains an attachment to the 
auditory capsule, and becomes the chief apparatus for suspending the palatoquadrate from 
the cranium. This type of suspension is called hyostylic, and is exemplified by the skull of 
Scyllium (Text-figure 32). In the hyostylic skull the upper jaw is held somewhat away 
from the cranium, and retains a considerable degree of mobility. In the amphistylic 
skull, according to Huxley, the palatoquadrate cartilage is wholly, or almost wholly, 
suspended by its own ligaments; the hyomandibular is small and contributes but little to 
its support. Some authors (e.g., Goodrich, 1909, p. 95) have interpreted, or modified, 
this definition to require that, in the typical amphistylic skull, the quadrate region of the 
upper jaw must have a postorbital articulation with the auditory capsule in addition to 
being connected with it by the hyomandibular: as in Heptanchus (Goodrich, 1909, Fig. 
59a) ; a typical Acanthodian (Goodrich, 1909, Fig. 159); and in Hyhodus hauffia^ius accord- 
ing to Jaekel (my Text-figure 28) . 

It will suffice here to attempt a comparison between the skulls of Heterodontus and 
Hyhodus, with special reference to the manner in which the jaws are attached to the 
cranium. The skull of Heterodontus (Text-figure 33) is usually classed as hyostylic, 
though it does not conform closely to this type. One should examine also the more 
elaborate figures of the skull of Heterodontus philUpi by Huxley (1876, Fig. 8) and that of 
H. francisci by Daniel (1915, Fig. 6, pi. IV). In both figures the cranium is more closely 
molded on the palatoquadrate cartilages (upper jaws) than is represented in Goodrich's 



700 



Bashford Dean Memorial Volume 



figure (my Text-figure 33). According to Huxley, the hyomandibular is of moderate 
sizie; it articulates with a process on the underside of the auditory capsule and supports 
the posterior end of the palatoquadrate, with which it is connected by a strong ligament- 
ous capsule. The huge palatoquadrate is connected with the cranium in the preorbital 
region by a broad joint (ethmoidal articulation) and in the orbital region by fibrous tissue. 
The postorbital region of the cranium of Heterodontus appears short, and the preorbital 
region long, as compared with most sharks. The cranium as a whole is much longer than 
the jaws, which appear as if thrust forward. Anteriorly the upper jaw extends almost or 
quite as far as the snout, but posteriorly it does not reach the auditory capsule. Thus the 
lower end of the hyomandibular cartilage is pulled forward. 

In sharks of the genus Hyhodus, according to Woodward (1916), the pterygoquadrate 
(palatoquadrate) is not articulated with the preorbital region of the cranium (as it is in 
Heterodontus). In Hyhodus haujfianus, according to Jaekel (1906), the suspension of the 
jaws is amphistylic (my Text-figure 28, page 695). The skull of Hyhodus duhrisiensis, as 
described by Woodward (1886) is even more typically amphistylic, resembling that of 
Heptanchus. Woodward's figure shows the palatoquadrate with a small but definite 
facet in position for a postorbital articulation with the cranium; the hyomandibular is 
slender, but evidently gives some support to the jaws. But in Hyhodus hasanus, as 
described by Woodvv^rd (1916), there is no articulation between the palatoquadrate 




mfc 



Text-figure 32. Text-figure 33. 

Incomplete skulls of Scyllium and Heterodontus, illustrating methods of suspension of the jaws. 
Text-figure 32. The skuU of Scyllium, illustrating the hyostyHc method of suspension of the jaws. 

a., auditory capsule; ch., ceratohyal cartilage; or., cranium; ep., ethmoid process; h., hyomandibular branch of facial nerve; hm., hyoman- 
dibular cartilage; 1., labial cartilage; m\., Meckel's cartilage; rm., nasal capsule; q., quadrate region of the palatoquadrate cartilage; 

r., rostral process; sp., spiracle. 

After Goodrich, 1909, Fig. 59c. 

Text-figure 33. Cranium, jaws and hyoid arch of the Port Jackson shark, Heteroaontus phillipi. 

a., auditory capsule; ch., ceratohyoid; ea., ethmoid articulation; hm., hyomandibular; 1., labial cartilage; m\., Meckel's cartilage; 
na.. nasal capsule; nc., nasal cartilage; q., quadrate region of the palatoquadrate; pc., prespiracular cartilage. A dotted ring behind 
the prespiracular cartilage indicates the position of the spiracle. 
After Goodrich, 1909, Fig. 5S.-i. 



The Eynhryology of Heterodoyitus japonicus 



701 




and the cranium. In the skull of Hyhodus hasanus (my Text-figure 34), the cranium is 
rather short, with a relatively large orbit and with short postorbital and rostral regions. 
The jaws, which are relatively large and massive, are longer than the cranium, so that the 
hyomandibular suspensorium extends backward, while the upper jaw extends forward as 
far as the end of the snout. The rami of the mandible, though deep and massive behind, 
rapidly taper forward and meet in a com- 
paratively feeble symphysis which does not 
extend so far forward as the front of the 

Text'figure 34. 

Restoration of the skull of Hyhodus hasanus 

Egerton, a little less than one-half natural size. 

The deeply shaded portion is the orbit. 

cr., cranium; hy., hyomandibular; I., one of the labial cartilages; 

m., lower jaw or mandible; q., quadrate region of the pal- 

atoquadrate. The lettering does not appear on the original. 

After Woodward, 1916, Fig. 3b. 

upper jaw. The palatoquadrate is weak and 
depressed at its anterior end, but deepens 
rapidly backward. According to Woodward, 
it can scarcely have articulated with the postorbital prominence of the cranium. 

According to Huxley (1876) the skull of Heterodontus is the link that connects the 
primitive amphistylic skull with the ordinary selachian skull, which is hyostylic. Like- 
wise, Goodrich (1909) wrote: ". . . it is well established that Hyhodus and Synechodus had 
typical amphistylic skulls, with the palatoquadrate and hyomandibular as in the Notidani- 
dae and other primitive Elasmobranchs." This view accords with Woodward's observa- 
tion (1886) that the skull of Hyhodus duhrisiensis is typically amphistylic, and with 
JaekePs interpretation of the skull of Hyhodus haujfianus (my Text-figure 28); but it 
does not harmonize with Woodward's later statement (1916) that the pterygoquadrate 
(palatoquadrate) of Hyhodus hasanus "can scarcely have articulated with the postorbital 
prominence of the cranium". It seems remarkable that species of the same genus should 
differ in a manner so important; but if the skull of Hyhodus hasanus really does lack a post- 
orbital articulation with the cranium, then it is hyostylic and therefore more like the skull 
of Heterodontus. By the same token, if such divergences can exist within a single genus of 
Hybodonts, how trivial become the differences between the skulls of any species of the 
Mesozoic Hyhodus and the present-day Heterodontus! In view of the well-known diiE- 
culties attending the restoration of the fossil vertebrate remains to life-like attitudes, one 
suspects that there is a flaw in the data somewhere; but, considering the long lapse of 
time, the evolution of the skull of Heterodontus from that of any Hybodont does not seem 
impossible. 



702 Bashford Dean Memorial Volume 

It is apparent that paleontologists have experienced considerable difficulty in 
disentangling the Cestraciontidae frora the Hybodontidae. The two families have, at 
least once, been lumped together, and authors have seldom agreed on the criteria by means 
of which they should be divided. Wherever the line has been drawn, the distinction 
seems more or less arbitrary : the differences between the families seem no more impressive 
than the differences between genera w^ithin at least one of the families. These facts 
cannot be wholly explained on the ground of difficulty in reading the paleontological 
record; for nearly complete skeletons belonging to several different genera have been 
obtained. The only adequate explanation is that there exists a close genetic relationship 
between the famiHes. With respect to famiHes other than the Hybodontidae, the Het' 
erodontidae occupy a relatively isolated position. Woodward (1921) states that the 
Hybodonts are a generalised group from which several later famiHes appear to have 
risen. They were the dominant sharks of the Jurassic and Early Cretaceous Periods. To 
the present writer it seems not only possible but highly probable that the Mesozoic 
Hyhodus, or some Hybodont closely related to it, is the direct ancestor of Heterodontus. 
After this glimpse into the past, we return to the study of Hving Heterodonid sharks. 

SEXU.^ DIMORPHISM AND THE REPRODUCTIVE ORGANS 

Concerning the Port Jackson Shark, Heterodontus phillipi, Maclay and Macleay 
(1879) state that the two sexes scarcely differ in size and marking. With the aid of special 
drawings, they describe the intromittent organs (myxopterygia or "claspers") of the male 
H. phillipi. More recently, the claspers of three species of Heterodontus (philUpi, japonicus 
and galeatus) have been described and figured by Leigh-Sharpe (1922 and 1926). Some 
marked specific differences in this organ are noted. 

According to Dean's notes, Heterodontus japonicus show^s marked sexual dimorphism. 
The female is larger than the male, heavier in body and somewhat different in proportions. 
Dean states that the female, when full-growm, measures about 1200 mm. (47 inches) in 
total length: the male, about 1000 mm. (39 inches). There is little difference in color, 
though Dean at one time befieved that the males could invariably be distinguished, in the 
w^ell of a fishing boat, by a darker and richer tone. 

Since I have no adult female specimen of H. japonicus available for dissection, it is 
a satisfaction to be able to record the results of my examination of the reproductive organs 
of the larger female specimen of H. francisci belonging to the American Museum of 
Natural History. This shark is 705 mm. (27-7 inches) long, and is fully adult. The oviducts 
of both sides of the body are well developed, with especially large, thick-walled shell 
glands. Evidently both oviducts are functional. As in the adults of most sharks, the 
two oviducts have a common abdominal aperture. In decided contrast to the oviducts, 
the ovaries of the two sides of the body are very unequally developed. 

On the right side, the large ovary contains eggs in various stages of development. Of 
these, the two largest measure about 35 rmn. in diameter, the next largest one about 



v/ 



The Embryology of Heterodontus japonicus 703 

30 mm. The smaller ovocytes remaining in the ovary are all 12 mm. or less in diameter. 
It is not known whether H. francisci, like H. japonicus, matures and deposits its eggs in 
pairs; but it is possible that this may be the case, for the ovary under consideration had 
been injured in making a large incision in the body wall to admit the preserving fluid. 
From this opening, part of the ovary protruded, and one large mutilated follicle contained 
only a few fragments of an egg. The mesentery supporting the ovary extends posteriorly 
almost to the rectal gland. Throughout much of its extent it is thickened by what 
appears to be a posterior sterile portion of the ovary. This is probably the "epigonal 
organ" of certain sharks, which extends from the ovary along the dorsal body wall 
posteriorly to where it joins the mesentery of the rectal gland (Daniel, 1922, p. 316). On 
the left side of the body the ovary is rudimentary — so slender and smooth that it could 
scarcely be recognised as an ovary except by position and relations. The epigonal organ 
is much larger — quite as large as the one on the right side. The right and left epigonal 
organs differ in shape: the one on the right is broader and thicker anteriorly, tapering 
posteriorly; the reverse is true of the one on the left. Ovary and epigonal organ of the 
left side (like those on the right) are continuous structures, supported by a single con' 
tinuous mesentery. 

Among Dean's records I find a drawing of a dissection showing the reproductive 
organs of an adult female Heterodontus japonicus. This drawing (my Text'figure 35) is 
not labelled, nor is it described in Dean's notes, and in the absence of the dissection some 
features are obscure. In the mid'line near the top of the figure, one readily notes the 
common abdominal opening of the oviducts. On the extreme right side of the figure 
(left side of the fish) the oviduct with its three divisions — oviduct proper, shell gland and 
uterine portion— are easily identified. Halfway between the oviduct and the middine of 
the body there is an elongated object of which the anterior portion is a rudimentary 
ovary, the posterior larger portion the epigonal organ. This rudimentary ovary is not so 
slender as the corresponding ovary of H. francisci described in the preceding paragraph. 
The rectal gland is visible in the middine near the lower end of the abdominal cavity. On 
the left side of the figure (right side of the fish) the oviduct, excepting the posterior end 
of its uterine portion, is obscured by other organs. Apparently the intestine, which 
together with the stomach occupies a large part of the left side of the figure, has been 
transected at its posterior end to aid in turning it aside. The relations of the mesenteries 
on this side of the fish are obscure. It is probable that the epigonal organ of the right side 
of the fish is concealed by the stomach and intestines. It is unfortunate that these organs 
were not removed. The right ovary is conspicuous in the upper left part of the figure, and 
this organ deserves special consideration. 

The right ovary shown in Text-figure 35 contains a number of large eggs, of which 
two are larger than the others. In one fish, Dean observed two ovarian eggs which were 
almost ripe, showing large "stigmata" (orange spots or germinal discs?). The other eggs 
of the same ovary were smaller. Nothing is written concerning the condition of the 
eggs, if any, in the other ovary. It is not known whether the fish whose ovarian eggs are 



704 



Bashford Dean Memorial Volume 




Text-figure 35. 

Dissection showing the reproductive organs of an adult female Heterodontus ja^ionicus. 

Note that the right ovary contains two eggs much larger than the others. 

From a drawing left by Bashford Dean. The paper on which this drawing was made is much darkened 
by age, hence the drawing is not so clear as it must have been originally. 



The Embryology of Heterodontus japonicus 



705 



thus described is the one represented in Text'figure 35. Dean states that though several 
gravid sharks yielded each but a single encapsuled egg, in each case the condition of the 
"opposite" ovary indicated that another egg had already been laid. These observations 
support the data recorded in the section on ''Egg-laying Habits", and indicate that two 
eggs are laid at about the same time. We also infer that occasionally both ovaries are 
functional at the same time. From Text-figure 35 it appears that the "uteri" of both 
sides are well developed. 



THE EGG CAPSULE: ITS STRUCTURE AND FUNCTIONS 

The earliest published drawings of the egg capsule of Heterodontus pMlipi are 
those of Dumeril (1865), reproduced as my Text-figures 36a and 36b. These drawings 
have been extensively copied, but Waite (1896) states that they are not very good, being 
doubtless drawn from dry and distorted specimens. The frayed condition at the apices of 
the two spiral appendages is an artifact. McCoy (1890) contributed a drawing that 
differs from DumeriPs in that the apices of the two spiral appendages are blunt and are 
not frayed. McCoy states that these 
"eggs" (capsules) are conical in shape, 
about six inches long, and surrounded with 
two broad keels extending spirally and 
obliquely round the egg from one end to 
the other, like six turns of a broad screw; 
the substance is of a tough, dark-brown, 
horny appearance. 

A suggestion as to the advantage of 
the peculiar form of the Heterodontid egg 
is offered by Allen (1892) as follows: 

That well-known frequenter of Aus- 
tralian harbours, the Port Jackson Shark, 
lays a pear-shaped egg, with a sort of spiral 
staircase of leathery ridges winding around 
it outside, Chinese pagoda-wise, so that 
even if you bite it (I speak in the person of 
a predaceous fish) it eludes your teeth, and 
goes dodging off screw-fashion into the 
water beyond. There's no getting at this 
evasive body anywhere; when you think 
you have it, it wriggles away sideways and 
refuses to give any hold for jaws or palate. 
In fact, a more slippery or guileful egg was 
never yet devised by nature's unconscious 
ingenuity. 




Text-figure 36. 

Egg case of the Port Jackson shark, Heterodontus 

phillipi: A, entire specimen; B, egg case with interior 

exposed. According to Dumeril the egg case is about 

130 mm. (5.1 inches) long. 

After Dumeril, 1865, Atlas, Figs. 2 and 3, pi. 8. 



■A 



706 



Bashford Dean hiemorial Volurne 





Text-figure 37. 
Egg capsules of Heterodontus phillipi and H. gakatus: A, egg case of H. phiUipi; B, egg case of 
H. phillipi with interior exposed; C, egg capsule of H. gakatus. The author states that the egg case 
of H. phillipi is about sis inches (152 nun.) long; that of H. gakatus 4.5 inches (114 mm.) long — 

presumably without the tendrils. 
After Waite, 1896, f\. 12 

The only adequate account of the egg capsules of Heterodontus phillipi is that of 
W^aite (1896), who also described the egg capsules of H. galeatus. His drawings of the 
egg capsules of both species are reproduced as my Text -figure 37- Because of their 
unique value, Waiters descriptions are here quoted in full. 

The egg cases of both species [phillipi and gakatus] have the foUowing points in com- 
mon: All parts are composed of a flexible hom-Hke substance of brown color. The body 
consists of a chamber, shaped Hke a pear; the coronal portion is compressed into a cervix 
through which the young shark eventually escapes. From each side of the cervix, and integral- 
ly connected with it, arises a ribbon exactly resembling a strip of kelp. These ribbons are 
attached basaUy, their free edges turned towards the cervix and deflected considerably from 
the body. They pass round alternately and obliquely, and form the thread of a righthanded 
double screw, together making five or sis turns to the base [smaller end of the capsule] . These 
ribbons originate [with] about half the width they quickly attain, and continue their course 
of even breadth, again narrowing on approaching the base. The interior, as shown by 
a section [Text-figure 37b] is wide and capacious; the fissure does not proceed to the base as 
generally portrayed, but terminates some distance short of it; the inside is marked with 
obKque striae corresponding to the direction of the spirals, and resembHng the lines inside 
a vessel turned upon a potter's wheel. 

The principal differences between the egg cases of the two species may be recounted 
thus: Cestracion [Heterodontus] phillipi [Text-figures 37-a. and 37b]: Of larger size; about 



The Embryology of Heterodontus japonicus 



707 



six inches in length. The spirals are very broad and, in part, hide the body when viewed 
laterally; at the base they narrow quickly and terminate bluntly, and are not produced into 
tendrils. Beach-worn examples generally have the terminations more or less frayed. 

Cestracion [Heterodontus] gakatus [Text-figure 37c] ■• Of smaller size; about four inches 
and a half in length. The spirals are not very broad, and in no part hide the body completely; 
basally they become narrow and are produced into long flattened tendrils. In the most 
perfect specimen examined, each tendril is 90 inches in length, and tapers to the slenderest 
thread, becoming tangled and knotted like a skein of silk. They are, however, very tough, 
and may be unravelled without fear of breaking. One of the tendrils terminates in a thick- 
ened tag (shown in the figure) which, although doubtless an individual pecuHarity, indicates 
that the tendrils are entire. 

Further, Waite calls attention to the fact that the appendages, with which the egg 
capsules of sharks are furnished, serve to moor them in some suitable situation, otherwise 
they would be likely to be knocked about to the detriment of the contained embryo, or 
might even be washed ashore where their destruction would be certain. The spiral 
appendages of Heterodontus philUpi are no exception to the rule; the elastic flanges permit 
the egg to be forced further into a fissure, whence extraction is resisted by the free edges 
of the ribbon catching against the rocks. Although, in a lesser degree, the egg case of 
H. galeatus possesses these spirals, they do not appear to have the same use; for attach- 
ment is here effected by the entanglement of the tendrils among seaweed. 

The egg capsule of H. francisci is figured by Daniel (1934, also in earlier editions). 
His figure is reproduced here as my Text-figure 38. This 
capsule lacks tendrils and bears a general resemblance 
to the egg capsule of H. phillipi; but it is more slender. 



Text-figure 38. 
Egg capsule of Heterodontus 

francisci. 
After Daniel, 1922, Fig. 254, p. 318. 




Text-figure 39. 
An egg case of Heterodontus 
japonicus with an opening 
cut to show the young em- 
bryo within. The cleft in 
the upper left-hand portion 
of the figure follows the line 
of the respiratory groove. 
After Doflein, 1906, p. 209. 




yoS Bashford Dean Memorial Volume 

The spiral flanges are narrow at the broader end of the capsule, and widen as they 
approach the narrower end. 

Barnhart (1932) states that the egg case of H. francisci is about 120 mm. (4.7 inches) 
long, and 50 mm. (2 inches) wide at its largest diameter, with two wide flaps running 
spirally from end to end (as in his Fig.l). The si2;e varies, depending probably on the 
age of the parent. I have no definite information concerning the egg cases of H. zehra 
and H. quoyi. 

Before entering upon a somewhat detailed account of the structure and functions of 
the egg capsule of Heterodontus japonicus, it seems desirable to examine some general 
features of this capsule as a basis for comparisons with the other species already con' 
sidered. Egg capsules of H. japonicus are illustrated in Text-figures 39 and 59 (page 752), 
also in Figures 76 to 78, plate VII. These capsules appear to be stout-bodied, like those of 
H. phillipi and H. galeatus— not slender like those of H. francisci. The width of the spiral 
flanges is less than in H. phillipi, greater than in H. galeatus, and approximately the same 
as in H. francisci. In the capsules of H. japonicus the two spiral flanges make comparative- 
ly few turns about the body of the capsule : each flange encircles it from one and one-half 
to two times. In the capsules of the other species considered, there are nearly twice as 
many turns of the spiral flanges. In other words, in the capsule of H. japonicus the 
spirals formed by the flanges are unusually loose. Since in this species the flanges are 
only moderately wide, it follows that an unusually large amount of the surface of the 
body of the capsule is exposed. 

The primary function of an egg capsule is of course protective, but provision must 
be made for the aeration of the embryo and for its eventual hatching. The gross structure 
of the egg capsule of Heterodoixtus japonicus, and its role in respiration and hatching, are 
described in Dean's notes on which the following account is based. 

The capsule of H. japonicus (Figures 76 to 78, pi. VII,) varies considerably in sizie: 
in length from 120 to 180 mm. (4.7 to 7 inches), and in weight from 145 to 238 grams, 
including yolk and embryo. It is somewhat conical in shape, drawn to a point at one end 
(''lower", distal or "vegetal") but to a "chisel-like" edge at the other ("upper", proximal 
or "animal"). It is provided with two marginal bands which encircle the capsule spirally 
somewhat as the "thread" surrounds a screw. These bands arise at the sides of the upper 
or broad end of the capsule, and are homologous with the marginal bands which occur in 
the egg capsules of many sharks and chimaeroids. But instead of passing straight down- 
ward, they wind about the capsule two and a half times (according to Dean's notes) 
until they terminate with short processes at the lower end. Here the spiral bands are 
wider and are more nearly transverse. The freshly deposited capsule is dark bottle-green 
in color, as shown for the first time in Dean's drawings (Figures 76 to 78, pi. VII). Later 
the capsules become paler, brownish or sometimes ochreous. Altogether they resemble 
certain large cysted brown sea-weeds, but whether this resemblance is a protective one 
is not known. 



The Embryology of Heterodontus japonicus 709 

While the embryo of H. japonicus is developing, the capsule undergoes steady 
deterioration, as in Chimaera (Dean, 1906) and in other elasmobranchs. The substance of 
the capsule becomes thinner, more ''tense" and fragile. An arrangement is also developed 
which enables the young fish to carry on respiration. At either side of the upper or 
larger end of the capsule, near the line of junction of each marginal band, there is a deep 
infolding in the wall (as indicated by the arrow in Figure 76, plate VII) . Later, by a process 
of weathering, this respiratory groove opens and widens as a slit (Text'figure 59, page 752). 
(A respiratory slit of this kind in the eggs of elasmobranchs appears first to have been 
mentioned, though hardly described, by Home, 1810, page 213). In addition, similar 
respiratory slits appear at the "lower" or more pointed end of the capsule. 

The upper slits in the egg capsule of H. japonicus play an active role in the process 
of hatching, which is described by Dean as follows : 

By a continuation of the process of weathering, the upper slit comes to open not only in 
its lower portion (i.e., in the direction of the contained egg) but in an extended line along 
the upper and median margin [of capsule] . By this process the entire chisel-like rim of the 
capsule finally weathers open, and its sides separate, leaving a slit between. This follows 
the absorption of the hard wedge of albumen which has from the beginning blocked up the 
large end of the capsule. Old capsules, it was observed, are "tense", and hatching occurs, 
with a rapidity which reminds one of the dehiscence of certain seed pods. The sides of the 
terminal aperture open and shut in a twinkling, and one is given the impression that the 
young fish is shot out of the capsule. There is a writhing on the part of the imprisoned fish, 
and it emerges with a rapidity which quite disconcerts the observer if, as in my own experience, 
he happens to be holding the egg capsule in his hand. [For further details, see page 753] . 

Among the capsules which passed through Dean's hands, there were several which 
were newly deposited and perfect except that none contained an egg. Such empty 
capsules are called "wind eggs". Externally, these capsules were quite indistinguishable 
from the others, except by their lighter weight. Dean assumed that they resulted from 
unilateral ovulation, during which the oviduct of the side opposite to the gravid one was 
stimulated to produce a capsule. 

HABITS OF HETERODOKTUS 

In this section, and in those that follow, we are concerned primarily with the 
Japanese species, Heterodontus japonicus; but reference will be made to other species 
wherever information is available. 

HABITAT AND GENERAL HABITS 

There is a curious lack of information concerning the depths at which adults of some 
species of Heterodontus have been taken, though depths at which the eggs of one of 
these species have been found are recorded in a later section of this article. Osburn and 
Nichols (1916) record the capture of a specimen of Gyropleurodus (Heterodontus) francisci 
8 inches long, dredged from 13 fathoms of water, in Magdalena Bay, Lower California. 



710 Bashford Dean Memorial Volume 

Regarding the same species, Barnhart (1932) writes that, while many of these sharks have 
been taken in shallow water, there are several instances of large numbers being taken at 
depths of over 500 feet by rock-cod fishermen. He further states that this species migrates 
from shallow to deep water and from deep to shallow water at certain times of the year. 
Whitley (1940) states that Heterodontus pMlipi is found in littoral waters to a depth 
of 94 fathoms. 

According to Dean's notes, Heterodontus japonicus (called Nekosame by the natives 
at Misaki) occurs in moderately shallow water, roughly between 3 and 20 fathoms. It 
frequents places where the sea bottom is covered with rock fragments or sea-weeds. 

Concerning the habits of Heterodontus, other than feeding and spawning habits, our 
information is very meager. Of H. phillipi, the Port Jackson Shark, Maclay and Macleay 
(1879) write that the adults are very tenacious of life, but no data are given to support 
this statement. For H. japonicus it is possible to quote directly from Dean's manuscript 
as follows : 

Cestracion [Heterodontus japonicus] is deliberate in its movements: it swims slowly, 
and changes its direction readily. Its great pectoral iins are inactive; in fact for a form so well 
provided with large fins it seems to make surprisingly little use of them. Nor is it alert. 
Indeed, the divers took by hand the greater number of specimens which were brought to me, 
although it may well be that the fish, being about to deposit eggs, were less attentive to 
externals than under usual conditions. The divers report that "Nekosame" stays close to the 
bottom and spends its time "nosing" among rock fragments and seaweeds. When disturbed it 
swims off near the bottom, and not over the heads of the divers as many fishes do. 

FOOD AND FEEDING HABITS 

Concerning the Port Jackson Shark, Heterodontus phillipi, Maclay and Macleay 
(1879) wrote that its stomach is generally well-filled with fragments of shells, but these are 
not so well comminuted as might be expected from the character of the teeth; and that 
the "bowels" are often well charged with cestode worms. McCoy (1890) states that 
this shark is common in Hobson Bay (Victoria), and that the stomach is filled with 
fragments of shells. Some interesting information regarding the feeding habits of the 
Port Jackson shark is furnished by Saville-Kent (1897, pp. 192-193), as follows : 

Oysters are the favorite food of this shark [Heterodontus phillipi], and in consequence 
of its predilection for this bivalve, it has proved a formidable enemy to oyster growers in 
both Tasmania and on the mainland seaboard. At Spring Bay, in the former island colony, 
the writer found it even necessary to fence round certain of the Government Oyster Re- 
serves with closely matted brushwood in order to protect the oyster stock laid down, from 
this shark's depredations. In some localities, Cestracion [Heterodontus] feeds almost ex- 
clusively upon Sea Urchins or Echini, the sharp spines of which have apparently no other 
effect than the pleasant titillation of its palate. The proof of the extent to which this piquant 
food is favored by this shark is afforded by the fact that the entire pavement of teeth of 
captured specimens are not infrequently permanently stained a deep purple, through constant 
indulgence in a dietary of the commoner purple urchin. 



The Embryology of Heterodontus japonicus 



711 



Maclay and Macleay (1879) state that Echini (Sea Urchins) form the chief food of 
Heterodontus galeatus and probably of all the genus. The strong dorsal spines and the 
prominent supraorbital ridges of these sharks enable them to force their way under rocks 
and stones in pursuit of their prey. A fine specimen of H. galeatus in the Macleay 
Museum had the dorsal spines worn down to half their proper length, evidently as a result 
of scraping against rocks, and its "viscera" were full of finely triturated Echinus tests. 

My only information regarding the food and feeding habits of the Japanese Bullhead 
Shark is derived from Dean's manuscript, from which I quote the following : 

It [Heterodontus japonicus] is a 
bottom feeder, and is known to have 
a varied diet: crustaceans, mollusks, fish 
and sea urchins. With its formidable 
dentition it crushes mollusks of consid- 
erable size, and its well-worn grinding 
teeth show that the crushing of shells 
is a frequent habit. At first sight the 
mouth appears extremely small, and one 
gets the impression from the narrow 
ends of the jaws which are exposed that 
the fish is a "nibbler", and cannot open 
its mouth widely. The photograph, 
however (Text-figure 40) shows how 
completely the shark may open its 
mouth; and the captive fish is apt to 
offer many demonstrations of this habit. 
The jaws in such cases will sometimes 
be snapped together noisily, indicating 
great muscular leverage. In the case 
figured, the fish was an old one and its 
mouth was by no means in good order. 
On either side of the large teeth were 
tufts of sertularian hydroids; also there 
were half a do2;en leeches in the neighbor- 
hood, some specimens measuring about 
2K inches in length. 




Text-figure 40. 
View of the wide-open mouth of a new-caught Hetero- 
dontus, presumably japonicus. Note the large grinding 
teeth in the posterior part of the roof of the mouth. 
From a photograph taken by Bashford Dean at Misaki, Japan. 



BREEDING SEASON 
Concerning the Port Jackson Shark, Heterodontus phillipi, Maclay and Macleay 
(1879) state that, if the accounts of the fishermen are to be believed, it is very slow of 
reproduction — the females never having more than two eggs at a time and only one 
brood a year. McCoy (1890) states that Cestracion (Heterodoiitus) phillipi never lays 
more than two eggs at a time, and only once a year. He does not say how or where he 
obtained his information. In view of the results obtained by Dean through examination of 



/ 712 Bashford Dean Memorial Volume 



the ovaries of H. japonicus, the statement that the Port Jackson Shark spawns but 
once a year cannot be accepted without further evidence. 

Waite (1896) writes that living eggs of Port Jackson Sharks (meaning both H. 
phillipi and H. galeatus) are most abundant in spring (August and September) but are 
found also throughout the summer. The empty egg cases may be found washed up on 
beaches at any time of the year, especially after stormy weather. At Jervis Bay, New 
South Wales, Haswell (1898) collected eggs of H. phillipi in blastula and gastrula stages 
during September (a spring month in the southern hemisphere). It appears that he found 
eggs in these stages in considerable numbers. He does not mention any later stages 
collected during September. Whitley (1940) states that he has observed developing 
embryos of H. phillipi in December, and young hatching in May. 

Regarding the eggs of H. francisci, Barnhart (1932) states that material collected 
tends to show that several eggs are spawned during the year. 

In the region of Misaki, according to Dean's notes, spawning of Heterodontus 
japonicus takes place throughout the entire year but the especial spawning season is 
evidently the month of March. The divers brought in the maximum number of eggs 
during April and May, and most of these were in stages which Dean estimated to be 
a month or six weeks old. Throughout June, eggs in early stages of development were 
brought in occasionally; throughout July, early stages were still more uncommon, perhaps 
one in twenty; and later in the season, early embryos were found but rarely. Supple' 
mentary evidence in regard to the breeding season was obtained by examining the ovaries. 
Judging from the condition of the ovarian eggs. Dean concluded that H. japonicus spawns 
a number of times during the "season", probably from six to twelve times, and that two 
eggs are matured at about the same time. During the spring months the eggs are evidently 
deposited at short intervals. This is deduced from the presence of almost ripe ovarian 
eggs in Japanese Bullhead Sharks from which encapsuled eggs were obtained. Further 
data bearing on the breeding season are given in the section on ''Rate of Embryonic 
Development". 

EGG-LAYING HABITS; THE NESTS 

Waite (1896) wrote that the eggs of Cestracion (Heterodontus) phillipi were found in 
moderately shallow water, wedged in among rocks. Whether they were actually dropped 
into the crevices he did not know, but he thought it more probable that they were 
deposited on the sand at the bases of the rocks, into the fissures of which they were after' 
ward swept by the tide. They were so jammed, larger end outward, that they could 
only be removed either by turning them around and withdrawing the small end first, or by 
actually unscrewing them; both forces being most unlikely to occur under natural con- 
ditions. When empty they are somewhat more pliable, which may account for the empty 
capsules being loosened and cast ashore. In a later publication (1899) Waite wrote that 
H. phillipi was common in Jervis Bay (New South Wales) which was for these fishes 
a favorite breeding resort. Here, empty egg cases could be found in large numbers washed 



The Emhryology of Heterodontus japonicus 713 

ashore or wedged in among rocks ; here also, in 20 fathoms of water and under, living eggs 
might be freely obtained. 

Haswell (1898) likewise collected capsules containing living eggs of H. phillipi in 
Jervis Bay, New South Wales. He states that he found many of these at low tide, 
sticking in the crevices of the rocks, firmly wedged in by means of the spiral flange which 
forms such a remarkable feature of the egg shell. 

So little is known about the spawning habits of H. galeatus that the following account 
of their spawning grounds, quoted from Waite (1896), may be of interest: 

Although most rare upon the beaches, the eggs of C. [Heterodontus] galeatus prove to be 
not uncommon when searched for in their native habitat. Through the kindness of Messrs 
Darley and Grimshaw, I recently had the pleasure of searching for them 50 feet below the 
surface. Although not successful in obtaining specimens, I got an excellent idea of the 
general situation. In places, immense masses of brown seaweed grow to the height of two 
or three feet so densely that scores of eggs may be securely concealed among them, protected 
by their likeness to seaweed in color and texture. Mr. Cameron, the diver who kindly took 
me in charge, told me that he always finds the eggs in the weed, so attached by their long 
tendrils [Text-figure 37c] that it is scarcely possible to secure them whole, without cutting 
the seaweed. In deep water they are freer from the violent disturbances, tending to detach 
them, to which the eggs of the more common species (H. pihillipi) are subject 

Barnhart (1932) writes that eggs of H. francisci are frequently found wedged between 
or under rocks in the extreme low-tide zone. 

In his notes Dean states that one can usually determine when a Heterodontid shark 
is gravid by noting the greater abdominal girth. Also, a digital examination can readily 
be made. In order to understand the process of egg laying in the Japanese Bullhead 
Shark, one should be familiar with the external form of the egg capsule which is described 
in a previous section of this article. 

Heterodontus japonicus deposits two eggs at about the same time. In numerous 
instances encapsuled eggs were brought to the station (at Misaki) in pairs, and in the 
same stage of development. It was therefore assumed that they had been deposited in 
pairs. This assumption was verified on two occasions, when pairs of encapsuled eggs 
were taken directly from the fish. Evidence that two eggs mature at about the same 
time has been given in the section on the reproductive organs. 

Data as to the mode of depositing the egg are scanty. The fish is apt to fold its 
pelvic fins around the cloacal region, and one must bend the fins aside in order to see if 
a capsule is protruding. In one instance, a shark brought to the station deposited an egg 
within a few hours (Text'figures 41a to 41d). When the fish was first examined (Text- 
figure 41a) no trace of a capsule could be seen between the pelvic fins. An hour or two 
later, the smaller end of the capsule protruded slightly (Text-figure 41b). Within an 
hour, a second turn of the capsule's lateral frill or spiral lamina could be seen (Text-figure 
41c) and in less than an hour later there appeared Text-figure 41d) the third turn of the 
frill. At this time the egg slipped out, and Dean noted that in the final rapid phase of 



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714 



Bashford Dean Memorial Volume 




Text-figure 41. 
Ventral view of the pelvic region of a female Heterodontus japonicus showing a series of stages (A to D) in the 
process of extrusion of the encapsuled egg. In A, the cloacal region is shown between the pelvic fins, but the 
extrusion of the egg has not commenced. In D, the dotted lines represent portions of the egg case still within 

the body of the mother. 

From drawing left by Bashford Dean. 

extrusion the capsule rotated about its long axis as though it had been unscrewed. 
Evidently this was not the only occasion when Dean saw an egg protruding from the 
cloacal aperture of one of these sharks, for on the margin of his drawing reproduced as 
my Text'figure 41d there was found a penciled note in Dean's handwriting: "Sometimes 
4 ridges show". 

Dean thought that, in the case just described, the final extrusion of the capsule was 
hastened by unskillful handling of the fish. But he notes that there are several considera' 
tions indicating that the sudden extrusion of the capsule, which he observed, may have 
been like the normal process of deposition. The capsule at this stage is very slimy. The 
shark exercises a voluntary control over the sphincters of the oviducal apertures. It can 
tighten or loosen its hold on the capsule, and it may even envelop the entire cloacal region 
with the bases of the pelvic fins. The very suddenness of the process may have a distinct 
advantage to the fish, for by it the capsule, on account of its peculiar form, is caused to 
rotate — a motion which would obviously project it downward and backward in a straight 
line, making it less subject to deflection by water currents. 

Eggs Found in Nests. — Of special interest is Dean's account of the occurrence 
of the eggs of Heterodontus japonicus in "nests'" on the sea bottom: 

It is well known by the fishermen that the eggs of "Nekosame" are found among rock 
fragments. On sandy bottom and in weedy reaches they rarely occur. The professional divers 
(with suits) whom I employed to search for these eggs in the neighborhood of Misaki examined 
carefully various kinds of bottom in water from three to eight fathoms, but without success, 
for at that time we had not discovered where the eggs are usually located. For this discovery 
I was indebted to the fishermen who dive for Haliotis, and from them I learned that the eggs 
of Cestracion {Heterodontus) occur in "nests". An instance of their mode of occurrence may 
be cited. 



The Embryology of Heterodontus japonicus JlS 

A "nest" was discovered October 4, 1905, in the channel off the fishing town of Miura- 
Misaki behind the island Jogashima, at a depth of 28 feet. It contained 15 eggs in various 
stages of development. The bottom of the nest was of seaweed, its sides were formed by 
irregular rock masses, some of large size, and the nest was largely concealed by several flat 
stones which the divers removed only with difficulty. (It appeared fortunately that this 
particular spot was rich in Haliotis and was being inspected with great care). The eggs were 
shown to be arranged in a space about six feet long, the greater number of them lying together 
closely embedded in the seaweed, "four out of five" of them being wedged in, with the Httle 
end of the capsule downward. I visited the spot and it may be worth while to picture 
a restoration of this nest (Text-figure 42) as near as I could make it out without diving, relying 
upon the fisherman's reconstruction. 

From the preceding account, it appears that there is similarity in the egg capsules 
and in the spawning habits of Heterodontus phillipi and H. japonicus. In both species, 
the capsules are surrounded by a pair of broad spiral valvC'like appendages which end 




Text-figure 42. 

Reconstruction of a typical "nest" oi Heterodontus japonicus found at the bottom of the Sagami Sea at a depth 

of 28 feet. The nest was surrounded by large rock fragments. Some encapsuled eggs may be seen entangled 

among sea weeds at the bottom of the nest, and other eggs are wedged into crevices in the rocks. 

From a drawing by Bashford Dean, whose initials appear in the lower right-hand corner. 



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716 Bashford Dean Memorial Volume 

bluntly, without tendrils. These eggs are deposited on the sea bottom among large rock 
fragments, or surrounded by rocks. In such situations, some become entangled in sea- 
weeds, others wedged into crevices between rocks. The egg capsules of Heterodontus 
galeatus are different, in that the spiral appendages are narrower and end in very long and 
slender tendrils which become thoroughly entangled among seaweeds. The only records 
available indicate that living eggs of these species have been taken at the following depths : 
Heterodontus japoi^icus at 28 feet; H. phillipi at 120 feet or less: and H. galeatus at a depth 
of 50 feet . There is no record of any direct observations of the process of e gg laying by any 
species of Heterodont shark in its natural habitat. 

METHOD OF COLLECTING EGGS AND EMBRYOS 

The earliest developmental stages of the egg of Heterodontus phillipi figured by 
Haswell (1898) were already in late cleavage. These were eggs that had been deposited — 
as stated more explicitly in a later article by the same author (Haswell, 1916). In this 
later paper, Haswell described some eggs taken from oviducts ("uteri"). Of these, the 
two earliest stages were portrayed in a figure which is reproduced as my Text'figure 49a 
and 49b (page 731). The other eggs, taken from uteri some weeks later, showed more 
advanced stages of cleavage. 

As previously stated, the eggs of Heterodontus japonicus were collected at all seasons 
of the year. According to Dean's notes, the greatest numbers of encapsuled eggs were 
taken during the month of May. They were gathered in small numbers daily, the 
maximum catch being 21, a number as large as 8 or 10 being uncommon. The greatest 
number of eggs came from the fishing village of Nagai, between Misaki and Hayama. 

The precise method used in collecting the eggs is not only interesting but is of 
technical importance. It is well described in Dean's own words: 

In collecting eggs of Cestracion [Heterodontus] divers are indispensable. But these are 
fortunately numerous in the neighborhood of Misaki, where they are constantly scrutinizing 
the shore rocks for edible moUusks, especially Haliotis. They have thus an excellent training, 
for if they can detect these protectively colored Hmpets, they can observe closely enough to 
collect shark eggs; moreover they are in the habit of examining fissures between the rocks, 
and they firequently displace stones of considerable size. In general their operations are 
usually carried on in water of from 12 to 30 feet, though they sometimes exploit a depth of 
40 feet — all this without the use of special suits, the divers usually swimming to the bottom, 
remaining under several minutes (2 to 6). They operate usually in pairs, going about in 
sampans, each boat provided with a screen, and an hibachi (fire-pot) over which the fishers 
crouch during intervals of rest. A familiar sound near the zoological station at Misaki is the 
pecuhar whistle of the diver as he expands his lungs before going down. 

Dean states that the eggs are hardy, and are readily kept alive in floating cages. Thus 
the various embryonic stages may be selected from time to time. The stage of development 
may be determined with fair precision without the necessity of opening capsules at 
random, for the character of the capsule gives a clue to the period of incubation. The 



The Embryology of Heterodontus japonicus 7l7 

capsules with a slimy coating are those recently deposited, and the degree of sliminess 
lessens perceptibly during the first days and weeks. The capsule then acquires a smooth 
but elastic surface; the spiral band is thick and rubber-like. In later stages the capsule be' 
comes rougher in texture, thinner and more brittle; its upper and lower edges become 
frayed, and its lateral band is apt to be imperfect. On its surface various foreign growths 
appear: bryozoa and barnacles especially. 

When capsules were opened and kept in aquaria, the young (still within the capsules) 
lived for some time. Early stages were kept alive for several days, especially if well- 
covered with albumen; later stages lived for weeks. Death in such cases results ultimately 
from invasion of bacteria and infusoria: these attack the yolk, causing it to soften in spots 
and finally to break down. 

Several times. Dean obtained gravid females; but he never found eggs whose capsules 
were in an early stage of formation. The adult Heterodontus japonicus is not often taken. 
It rarely is caught in seines, probably because it occurs in regions where rocks are abundant 
and where a seine is not likely to be drawn. Even when netted, it is rarely retained, for 
it is not marketable (see also pages 688 and 694). Since it was found impracticable to 
secure a large supply of spawning fish, the stages of fertiliziation and beginning cleavage 
were not obtained. These stages doubtless occur during the descent of the egg and its 
enclosure in the capsule. The earliest embryonic stages studied by Dean were fairly 
early (but not the earliest) cleavage stages (Figures 7 and 8, plate I). These were eggs 
already in capsules which were practically completed, and were soon to be deposited. 
Dean states that the egg is in a blastula stage at the time of deposition. 

Heterodontus japonicus, like H. pMlipi, is oviparous and not ovoviviparous. In both 
species, the earliest stages of cleavage occur while the egg is still in the oviduct. 

EMBRYONIC DEVELOPMENT OF HETERODONTUS JAPONICUS 

As the title of this article indicates, we are here concerned primarily with the em- 
bryology of the Japanese Bullhead Shark, as set forth in Dean's notes and drawings; but 
the observations of other authors, working mainly with H. phillipi or with H. japonicus, 
will be noted for comparison. It will be evident that descriptions of the development of 
H. pMlipi are confined to the early stages; while practically all that is known concerning 
the embryology of Heterodontus japonicus has been either discovered by Dean or made 
possible by his labors. 

RATE OF EMBRYONIC DEVELOPMENT 

Under "Breeding Seasons", I have already recorded observations to the effect that 
eggs of H. phillipi in blastula and gastrula stages are abundant in August and September 
(spring months in the southern hemisphere) and that hatching has been observed in 
May. In the absence of more adequate data, this indicates a probable duration of nine 
months for embryonic development. Whitley (1940) states that the period of incubation 
for H. galeatus is "at least five months". 



718 Bashford Dean Memorial Volume 

Barnhart (1932) notes that it takes eight to ten weeks for the young of H. francisci 
to hatch from the egg case, at which time the yolk is completely absorbed and the young 
shark is 14.5 inches long. Eggs have been hatched in the aquarium of the Scripps Insti- 
tution at La Jolla, California, in June, September and December. Nothing is said about 
the temperature of the aquarium water in comparison with that of the ocean water at the 
depths where eggs are found. 

In his brief manuscript containing a summary of his observations on the embryology 
of Heterodontus japonicus. Dean states that the term of development (before hatching) is 
reckoned at about one year, with the possibility that i