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NATURAL HISTORY pe! i ; Ve sony £ HbA aT ihek y W A | Pte 7 ; J Weds BASHFORD DEAN MEMORIAL VOLUME ENRCIGUEME lelislales Edited By IQ. 4 EUGENE WILLIS GUDGER Part Il TABLE OF CONTENTS ARTICLES VI, VII, VIII AND ANALYTICAL SUBJECT INDEX NATURAL STO N / K aN AG Ww Al y NIX y) SCIENCE y < 01 Y NEW YORK PUBLISHED BY ORDER OF THE TRUSTEES 1937-1942 43-15 5469- Oa . 26 ARTICLE VI VII VIII PART II WABEEVOEVEONMENTS Bertram G. SmitTH THe ANATOMY OF THE FRILLED SHARK, CHLAMYDOSELACHUS ANGUINEUS Plate I-VI, text-figures 1-128, pages 331-520. E. W. GupGER THE Breepine Hasirs, REPRODUCTIVE ORGANS AND ExTERNAL EMBRYONIC DEVELOPMENT OF CHLAMYDOSELACHUS BaAsED ON Notes AND DRAWINGS BY BAsHFORD DEAN Plates LVI, text-figures 1-33, pages 521-646. BERTRAM G. SMITH THE HETERODONTID SHARKS: THEIR NatTurAL History AND THE ExtERNAL DEVELOPMENT OF HETERODONTUS JAPONICUS BaAsED ON NOTES AND Drawinecs By BAsHFORD DEAN Plates I-VII, text-figures 1-69, pages 647-784. ANALYTICAL SuBJECT INDEX Ill PAGE 331 521 647 785 Reprinted from THe AMERICAN NATURALIST, Vol. LXXX, No. 794, pages 579-583, September—October, 1946. OBITUARY BERTRAM GARNER SMITH, 1876-1945 DR. E. W. GUDGER AMERICAN MusbUM or NATURAL HISTORY Dr. SmirH was born October 7, 1876, at Painesville, Ohio, the son of Albert W. and Hlla Garner Smith. 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 Warren, 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. EK. Reighard 1904-07, 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 AMERICAN NATURALIST [Vol. LXXX BERTRAM GARNER SMITH No. 794] BERTRAM GARNER SMITH 581 Medical 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, Cryptobranchus alleghenien- sis. His interest in this dates from boyhood, when, fish- ing in the stream near his home, he would frequently eateh 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 amphibian, sought for almost a generation, were a mystery until it was discoy- 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 history stages were great. But quite as great were those of the laboratory work of em- bedding and sectioning these yolk-laden amphibian ege's 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. Hven 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 embryos. I do not recall any vertebrate whose natural 582 THE AMERICAN NATURALIST [Vol. LXXxX history and embryology have been more thoroughly and successfully studied. These studies, together with those on Amblystoma and Necturus, 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 help, 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 theman. 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, Chlamydoselachus 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 ‘‘ Hlasmobranch Fishes’’ (3rd. ed., 1984, 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 Heterodontus 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 Hast and presently went to Albuquerque, N. M., where he bought a house and settled down to adapt it and the grounds (with his 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. RELE BASHFORD DEAN MEMORIAL VOLUME EN NOUS, JellSisles Edited By EUGENE WILLIS GUDGER ArtTIcLe VI fae ANA OMY OF Mrik PRIELED SkAIK CHLAMYDOSELACHUS ANGUINEUS 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 EAN AO MYSOE SHES ERICEE DE SEU AK CHLAMYDOSELACHUS ANGUINEUS Garman By Bertram G. SmitH CONTENTS INR ODO CLIO Ni teeee eer er BPR mon ma An 2 asd) aprsits ata Ree oem Oe 335 EXKERINAT @HARACTERSIORNC@ lami dosclachtspmrime i ae eiaiel aie ae eee 336 GENERATHR OR MIOFATHED BODYS Eee Rae eLRE CaE Ri Pi eee 336 JPkars eal onsy (Ova Unsdss INA MO\OAMEKS putts odo laia'o o okra plarho Miajows uaa ale alte dia ola caida kn ole Grobe aeow a 338 Gin GOVERSEAND 1 OPERA CLES Hi seecter tay temnel on War aucn wi Mayan. cata iatentseretaweelray ne Weiac aR eee reactor ny ee 339 RINSWRATREDVANDIWINPATRED A © cue can ciaccuelient, ca lsseen cle cycseie Moin tedisiey ates selfs canes eat pe yee rene cee 340 PAE DOMINATAO RMER OPEC UE OLDS ieee cui este Ine SIP MoH CET tae ene sree 342 SGIATE SWAIN DIMER TET aaa tip Sv aay pene oe stat ser tame tye ty HET AAR haps aii 8 VeVNE Go NU isin Seg SAO 342 FIBER END OSKE IEE: © NRE ict ii erain ee er RONG Deh cyanea ies acy ciate Edis fete ee ea Ege 350 SRUETROES ORIG MYGOSELAGHU SH rita a enero rated eras aaron eineataleyer ota suse aenete equ ane co Seaeueu rel 350 TUNETEN RIA NEUE aU MT OE OSSe OTT Te Raat ant antes TES UG EAE Se enter 351 ST TEN ASCERUATS SRELETON rte eeee eer ee aE Ceara ener oee eee: 356 INGROGEORD Ania WiranarUNG (COMET, 5 soca dooknunaesboumoocosouooHadboe bas Or00se 364 FAPPENDICULARTO KELE TON See Oruean tricone eR Meco cele ear iv eae EASED acu eT 370 PECTORIATNEINS AND) GIRDLE Spare creator reo oP eer ISO: Ri eee 370 PEL VIGREINS VAN DISPEL VIS MEY Sar ECT Ry ere eRe ST RL AAT AST TTS ohs Conse le Tore rater pees 373 SHE) DOR SATEEN AC sy ere rece Nee Eden Sioe EES LEU HE PRN OORT Sve PIS orsloke Ace eee 377 SIS WAIN A TAR IN Rete ore Re Serre Ce ANIA AHR no ciety a Stout, i ee REN Rit aoa re 380 SISTERS CAUDAL VEINE Aaya ee oO ea En OE SOE ences ree 380 BIWET EIN AWTS UIE AIRMO VST Eien Otte gr rm netgear eh aie ey a pM les th ue Ae ale ae 381 BSH RENAE TAQMERIC UNL USCLES oie Vert yee cc) SESE SERN canna SFL peeing os eRe 381 aE MAKTATC NLU SCLES ME GAIT ae eer ETRE A Sehr aR ROAR ISAC ES toe 382 Thine APPEN DICULARSNAUSCLES 1 0-02 Fest r RCN eee edna betel TRAE nd Aare leur eae eer 394 Waly RANGEMOMTARIG IMIURCHEB, oop coc od boos secon boo oo OOD OOO GOS OOO UUDODOOOODSSE 396 DIGESTIVE SYSTEM AND ASSOCIATED ORGANS. ........-0- 0000 eevee ee eee eee ee 401 MISE ODI GES TIVE SRW BERS are oe Se See et es CoC ones oi Siiatarcas aie aes cee eee 401 SSE PILAR Y NX han tetera eee ICT aCe ETT ee I or roe EE ee 402 IESOPHAGUSVANDS @ARDIAG STOMACH AAR nee Ca eEe Cece eo eee errr 402 SHIP YE ORICAWESTIBULE Nee tthe ooh cE Oo Er OETA er: REC er 404 STSETEUPVLOR UB RON Ree ape Re pete Eg esi EME eee Oe oT aE EE RE Cro ere 405 Sng BURSAGENTIAN AS ace ETAT Ecos EEE EEC OL On CER ER One nee 406 SHE AVAL VULARMINTESTINE Series accra TT RP TESS ere eee arr rete rere 408 IREGTUMPANDIRECTAL GLAND A sys ore A TT ESC LEVC RS See A eet ar Peete Se eee 410 BISHES DIGESTIVE WUBEPASTAM WHOLE Matec etcetera eee Lrernctersreeariieterayrercrmets 411 AIDE ENLGI WERE Pie ttt Fam eke on 2a ly OPER na cinta hac eat Lane ls Ses tebe ee Neaach, center anes 412 “a Dy ech 1 BAGS TSH NGA ora carne eee cine lee oes Herat eh te aapits ner See ase ane a atian cst ecifemereucn Eran acy ete 413 OrcGaAns AssOCIATED WITH THE DIGESTIVE TRACT.........2 200 cc eee eee eee eee eee renee 415 “Ndr IER aXolie) Cle Wine dink Roden Aue Hp UTERO eH SOM Hobe ance COOL DeM iE renames ae oo ey nado 415 GIR a GACT ACTA STI Ae UN tec ACW Aye aT RP Meee ta Me see east an Ror ee chet ce 418 PEE VRGESPIRCATORYA ORGANS] He toe tires eM ag cin ee ope ya aioe tee ours mask 419 MIRETE YG IETS Rees Are ape DUG e > RE lu cent. SUM tiet PRA Stes mechucrey ncn cuisvRe cane epicien tacks toma vietoteioh seistate ope 420 SINETE NS PIRVA CLES aes cle raya chem ooo EUs Dar eaten Stas ata caspenhe a tenets den ce scurpee ge Reeae cere 423 BISFIE WIR O GENIAL HOY STE NTE te teyrie os aerate ey Siesta averu a iy Faces uO ctl rrr ge peat Eg 431 WROGENELATIOYSTENUOELEHE PEE NCATE nine neta rene te etter neon etre tric Rea Ren tore 431 WROGENTTAT] SIN USHINETHEIREM ATE Ane nn Een eran ernin eerie tiene ceeieeeeieiires 431 ORGANS OFIEXCRETIONINITHRI FEMALE SEER een inte merce eee eccioniiracecn tanec 434 Grnrrari OrGANs|OR THE ;REMATE BREE Eee erecta eerie ieee eeeiacreiister 444 URGE STEN Shenae Ge Gis IMMUNO, coco ooo noobs ooo DUD oOo DOD CON CU UNDDOO DAHL ODOOUEE 450 EXCRETORYSANDI INTERNAL GENITAL) ORGANS EE eiciicisteisicinicinicie ciate ee ciiaieteeiietiiicicrinieieieieieielsiseiste 450 INATROPTERY GIAVOR CUASPBRS 35 c5:c1s cre pT TSE NOS PY TN Ten eT a creyststsictensiee esevanersierapelcror 451 ARHERAIBDOMINATY E ORES tic 5cieun Seer. cee SO TU OLIILIE CIs Ci AIMS Scene nine) sqstsudityans 453 HES SENSER ORGANS See eee BSTEINIEMBRIAN@ USHIGABYRINTHt liu. bcerrresctrek Meret Mate (ay) Rol m eae PVCS eit Se URE AIRTIER SENSOR VA CANAT OVSTE Mie ira tt, © hee teal ae ehs oe Retin coarse Ue ene ae [DISC USSTO Neeser eee eh tts ee Bs on ane DUNS OA) he 8 Sette ks Bee em See eee ae : | BUTSHETLO GRATE Ge aie Sea rc te te tm PA See aR ROGER mM NTR Oat RA a cael Al i 334 THE ANATOMY OF THE FRILLED SHARK CHLAMYDOSELACHUS ANGUINEUS 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). Garman’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 split 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 101a-s) 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 realize 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, Pl. 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 generalization 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 Chlamydoselachus, the elongation of the body has proceeded far enough to remove it from the category of Sa primitive characters. It serves, perhaps, as XY ih SN an adaptation to life on a rough sea bottom, Af ¥ YW _ where the animal is obliged, occasionally, to ; swim or crawl through crevices. In such Text-figure 2. situations, Chlamydoselachus may lie in hid’ Front view of the widely-distended mouth of ing, or may even stalk its prey, then strike specimen of Chlamydoselachus collected in : Japanese waters by Dr. Bashford Dean and suddenly as doesa snake. But there is another aiosaaicel (9 Caltmibn Unniarster, advantage to be gained from an elongate After Gudger and Smith, 1933, Fig. 3, pl. X. form of body. It may be observed that the ectoparasitic cyclostomes have bodies that are very slender, and that Echeneis, the 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 living prey nearly as large as itself. The swallowing of a large fish struggling 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 3. Heptanchus (Heptabranchias) maculatus, adult female. NWN, 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 “Heptanchus, 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 specialized 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 preeminently 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 forma rostrum. In other words, when the cranium becomes extended anteriorly, the mouth of necessity becomes ventral. This may occur regardless of the size 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- ized 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 size. After Garman, 1885.2, pl. 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 intake of water when the mouth is buried in sand or mud. In Squatina, a bottom-dwelling 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-slits. 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 size 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-slits, 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 Garman’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. WKH Een RAAqauogs Text-figure 5. Restoration of the Devonian shark, Cladoselache. Its fins 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- ingly 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 harmo- 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; Pleuracan- thus, typically Permo-Carboniferous; Hybodus, typically Jurassic; and Chlamydosela- 342 Bashford Dean Memorial 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 Hybodus 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 (Heterodontus) 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 peculiar to Chlamydoselachus. Concerning them Garman (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 Genese 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 slight 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 Garman (1885.2), Rdse (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. 204) are interest- ing because, in form and arrangement, they resemble the “‘fulcral scales” of the Actin- opterygit. 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, pl. VI. The essential similarity of the internal structure in scales and teeth of sharks is evident from a comparison of Textfigure 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 Scymnus 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. Textfigure 9. Section of a single-cusped tooth (x 75) from the lower jaw of a 340mm. 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 of 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, pl. 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, Triakis 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. Textfigure 11. On one side of the upper jaw of his em- Teeth of the lower jaw (x 5) of a 340-mm. embryo bryo, Rose found the first two teeth of the of Chlamydoselachus, in their natural positions. 5 5 Re, eat SRO. IS third row united at their bases, but delimited 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. Rése 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 12. The first two teeth (x 45) of the third row of the upper jaw of a 340mm. embryo of Chlamydoselachus. These teeth are united at their bases. After Rése, 1895, Abb. 6. The Anatomy of Chlamydoselachus 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 clarki). From a specimen in the British Museum. After Dean, 1909, Figs. 1, 2, 3. 347 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 s) 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 (Notidanus) indicus. a, teeth in function; b, teeth in reserve; u and I, upper and lower single teeth (natural size). From Goodrich, 1909, after Gunther, 348 Bashford Dean Memorial Volume Textfigure 15. Text-figure 16. Teeth of two fossil Chlamydoselachids from the Tertiary. Text-figure 15. Fossil teeth of Chlamydoselachus lawleyi from the Pliocene of Orciano, Tuscany, Italy. Note the lack of rudimentary cusps. 1 and 1b, teeth viewed from above; 1a, from below; Ic, from the side (1b, natural size; all others x 2). After Lawley, 1876, Figs. 1 to Ic, pl. I. Text-figure 16. A fossil tooth (A, natural size; B, x 2) of Chlamydoselachus 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. anguineus is very close. Apart from their smaller size, the teeth of C. lawleyi differ from those of C. anguineus only in that they lack the pair of very small cusps. In C. tobleri, 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 resembling those of Chlamydoselachus anguineus, from various fossil sharks. Textfigure 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. Textfigure 19. Tooth of Ctenacanthus clarki from the Carboniferous. After Dean, 1909, Fig. 42. Textfigure 20. Tooth of Hybodus reticulatus 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 Hybodus (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 Hybodus the lateral cusps (3 or 4 on each side) become smaller in proportion to their distance from the central cusp. In Cladodus, Ctenacanthus 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 Hybodus and in Cladodus most of the cusps are recurved at the tip. In Ctenacanthus and in Cladoselache the cusps are more slender and appear practically straight, though Dean (1909) states that in Clado- selache clarki 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 kepleri, 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 Hybodus 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. lawleyi) 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 elimination 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 Hybodus reticulatus 350 Bashford Dean Memorial Volume (Text-figure 20), quite as readily as from teeth like those of Ctenacanthus clarki (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, Gunther (1887) described the skeleton of the claspers; Braus (1902) that of the paired fins; Fur- 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 posteroventral 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 emphasizes (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 (1923) for reproduction in my Plates I, and HI. 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 isa marked contrast in this respect if compared with the skulls of Hex- anchus and Heptabranchias, which in these portions are thick and irregular (see Gegenbaur, 1872, Das Kopfskelett der Selachier, Figs. 1 and 2, pl. 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 i 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, pl. 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, pl. II; in Goodey’s (1910.1) Fig. 2, pl. 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 Memorial Volume infundibulum, but in the higher vertebrates it disappears from the basis cranii during later development. In connection with 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 heavily calcified. It here shows some indications of its probable vertebral nature, by the slight resemblance which the calcification presents to the inverted V-formation found in the centra of the vertebral column.” Ayers (1889) found more decided evidences (my Text-figures 21 and 22) of Text-figure 21. Text-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., vertebral centrum (sheath of notochord); ch., chorda dorsalis; cran.cav., cranial cavity; ct., cartilage of the basis cranii; n.p., neural process; tr_p., transverse process. After Ayers, 1889, Fig. 8. Textfigure 22. ft 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., ctanial aorta; ch., chorda dorsalis (notochord); i.c., internal carotid artery; k., cephalic aorta; p.pl., pituitary plexus; pt., pituitary space; tr.c., transverse canal; III, third pair of aortic arches. After Ayers, 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’ observations on Chlamydoselachus, one should accept this description and the accompanying figures with some reserve. In Hexanchus the notochord (Text-figure 23, nc) persists in the posterior portion of the basis cranii, much as in Chlamydoselachus. My Figure 4, plate II, showing a medial view of the cranium of Chlamydoselachus, should be compared with Text-figure 23, showing a similar view of the cranium of Hexan- chus. The two 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 tg. Ole J ac. i GP. V9. t m. Cia. % ocn. Text-figure 23. Inner view of the right half of the skull of Hexanchus 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; nc., notochord; o., optic nerve; ocn., spino-occipital nerve; om., oculomotor nerve; 7., rostrum; tg., trigeminal nerve; tr., trochlear nerve; vg., 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, in 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 occipito-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° (Garman, 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 specialized 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 horizontal palatine shelf. “The palatine process of Chlamy- doselachus .. . isa 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 horizontal 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 1). 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 I). Its distal end hasa 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. Allis (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 (ef, 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 (fm), 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 Hexan- 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 Allis (1923) in his Pl. XII. The ligaments connecting the palatoquadrate with the mandible, and the mandibular arch with the hyoid arch, are shown by Allis (1923) in his Pls. X and XI. Allis (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 (Text-figure 24; Figure 5, plate II) are slender. This slenderness stands in marked contrast with the condition found in Heptanchus (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 IJ) 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 (Allis, 1923). The presence of a mechanism for strengthening and mobilizing 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 Garman’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; mk, mandible or Meckel’s cartilage; p-br, pharyngobranchials. After Garman, 1885.2, Pl. 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 gill-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. 358 Bashford Dean Memorial Volume Neither Garman (1885.2) nor Goodey (1910.1) found any spiracular cartilages in the specimens dissected by them, and Furbringer (1903, p. 389) found only a single spiracular cartilage in his specimen. Allis (1923, Fig. 22, pl. XI) 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 ligament) on each side of one specimen. The cartilages are described by Allis (1923, p. 169) as follows: These cartilages present strikingly the appearance of being rudiments of the basal portions of three adjoining branchial reys related to the mandibular arch, and, like the single spiracular cartilage described by Furbringer in the one specimen examined by him, they lie lateral, and hence morphologically anterior, to the artery of the arch. They lie posteroventral 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 persisting rudiments of mandibular reys, they may not be true spiracular cartilages, for Gegenbaur (1872, p. 198) says that in all the Plasiostomi in which it is found, the spiracular cartilage always lies in the anterior wall of the spiracular canal, and that, where there is a pseudobranch, the filaments of that organ lie directly upon the cartilage. Evidently Daniel (1934, p. 63) considers that the dorsal segment of the second visceral arch of Chlamydoselachus is not a true hyomandibular, since he writes of it that “the dorsal segment is on its way to become a hyomandibula or suspensorium.” According to Allis (1923) there is no ligament connecting the hyomandibular with the palatoquadrate; there are, however, ligaments connecting the hyomandibular with the mandible (Meckel’s cartilage) in the region of the quadrato-mandibular articulation, and a broad capsular ligament binding the hyomandibular strongly to the cranium. The sliding articulation of the hyomandibular with the cranium has already been described. The homologies of the hyomandibular of fishes are discussed by Allis (1915) and by Gregory (1933, pp. 80-82). Woodward (1921, p. 39) regards the hyostylic suspension of the jaws, found in nearly all modern sharks and skates, as a condition secondarily attained, while the primi- tive mode of suspension of the jaws is amphistylic, as in Cladoselache (and in the noti- danids). One may well be puzzled to decide whether the peculiar mode of suspension of the jaws of Chlamydoselachus is amphistylic 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 jaws is hyostylic.~ The hyomandibular of Chlamydoselachus bears nine (Garman, 1885.2) or more cartilaginous branchial rays. Goodey (1910.1) shows, in his Fig. 1, pl. XLII, ten branchial rays attached to the hyomandibular and one branchial ray slightly detached from it. Allis (1923), in his figure reproduced as my Figure 5, plate II, shows nine branchial rays attached to the hyomandibular and five or six others more or less detached but evidently related to it. The ceratohyoids (Text-figure 24, chy) parallel the mandibular or Meckelian carti- lages (mk) and are intermediate in size between these and the ceratobranchials (cbr). Viewed from below, as in Garman’s figure, the visceral skeleton of Chlamydoselachus The Anatomy of Chlamydoselachus 359 presents a striking picture of gradation between jaws and gillarches. 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 gillseptum. 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- Text-figure 25. doselachus there is a dorsal extrabranchial cartilage, de- Reconstruction of the underside scribed by Furbringer (1903) and by Allis (1923, Fig. 49. ofthe skull of 2 Devontanishavk; S ; fara Cladoselache fyleri, showing low- pl. XVIII). In Furbringer’s Figs. 31, 32, 33, Taf. XVIII, the Sr rawmuintecrion ait neilbancten extrabranchial cartilages appear like detached or fragmented NgeoDexn, 1099) Fig. 6 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 obliquely and indistinctly divided, and is closely joined with the fifth which is fused with the sixth and indistinguishable from it save by 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 hypobranchials are mere rudiments fused with the basibranchials. Furbringer’s specimen (1903, Fig. 18, Taf. XVII) presents several features that are different. A small median posteriorly directed prominence fused with the basihyoid 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 with 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 with certainty. There is a vestigial seventh branchial element. Some features of Furbringer’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 (bbr. 1?) on the basihyoid which, as in Furbringer’s specimen, probably represents a fused first basibranchial. Otherwise, Goodey’s drawing more closely resembles that of Garman (1885.2). 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 26s) 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 specimen 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 Furbringer (1903). The first pair of hypobranchials (hbr. 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 (v. br. a. 7) presumably represent ceratohyoids of the seventh arch. Allis (1923) agrees closely with Garman (1885.2) in his description and portrayal 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 with a lateral process on one side only. This fused hypobranchial is well shown in dorsal view (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, pl. 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. [Se nee \-hbr.1(?) bbr2X% - ---- cbr 2. - Vo ae BINS 4K -hbré bree + FERRE 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.1(?)-6, basibranchials of the first (?) to the sixth arch; bh., basihyoid; cbr.1-6, ceratobranchials of the first to the sixth arch; f., foramen; hbr. (1) (?)-6, hypobranchials of the first to the sixth arches; th.c., thyroid con- cavity; vba7(?), vestigial seventh branchial arch. Redrawn, with some changes in labels, after Goodey, 1910.1, Fig. 6, pl. 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; f., foramen in basihyoid cartilage; hbr.1,2 and 6, hypobranchials; v.br.a.7, vestigial seventh branchial arch. After Garman, 1913, Fig. 6, pl. 59. 362 Bashford Dean Memorial Volume Text-figure 27. Text-figure 28. Dorsal and ventral views of the visceral skeleton of the notidanid shark, Heptanchus. Text-figure 27. Branchial skeleton of Heptanchus sp., in dorsal view. EVIL, first to seventh branchial arches; C, copula or basihyaid; CI, fused sixth and seventh basibranchials; c I—c V, second _ to fifth bastbranchals; ky, ceratohyoid; 1, hypobranchials; 2, ceratobram ; 3, epibranchials; After Gegenbaur, 1872, Fis. 1, Taf. XVI Text-figure 28. Visceral skeleton of Heptanchus maculatus, ventral aspect. 4, pharyngobranchials. bb.2, second basibranchial; bh., basihyoid; cb., ceratobranchiels; ch., ceratohyoid; hb., hypobranchials; mp., median piece. After Daniel, 1934, Fig. 50. The vestigial seventh branchial arch in Chlamydoselachus was first described and figured by Furbringer (1903, p. 409 and Fig. 18, pl. XVII). In his specimen it consisted of a single small rod of 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. Ina third specimen studied by Hawkes a seventh branchial arch was entirely lacking. Of two specimens examined by Goodey (1910.1), in one this arch was lacking, in the other it was represented (Text-figure 26a, vba. 7?) by “a pair of small, segmental tapering pieces lying on the ventral side of the last basibranchial at the bases of the sixth ceratobranchials.” In a specimen described and figured by Garman (1913) the vestigial seventh arch (my Text-figure 26s) 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 Allis (1923, p. 179) as follows: From the left posterolateral comer of the sixth basibranchial, a chain of small thin nodules of cartilage extends posteriorly and represents the vestigial seventh ceratobranchial... On the right side of the head this chain of nodules is represented by a process of the basibranchial. Wedged in 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 little 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. Iam 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. 50s). 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, pl. XVIII) of the branchial skeleton of Heptanchus is here reproduced as Text-figure 27. The first basibranchial is lacking and the sixth and seventh are fused together. If one compares Furbringer’s drawing of Heptanchus (1903, Fig. 29, Taf. XVIII), and Daniel’s 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; Furbringer, 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; nc, neural canal. After Garman, 1885.2, Fig. 3, pl. 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 living 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 cranti it is very slender, but elsewhere it is a fairly stout rod. 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; cal., calcification; c.c.5, cyclospondylous centrum of the fifth cervical vertebra; ch., notochord; ch.s., chordal sheath; d.f., dorsal root foramen; i.d., interdorsal cartilaginous element; s.bd., suprabasidorsal; s.d.l., supradorsal ligament; so.4, spino-occipital foramen; v.f., ventral root foramen; X, foramen for tenth cranial nerve. After Goodey, 1910.1, Fig. 10, pl. XLII. In the cervical (cephalic, 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, pl. 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 Heptanchus the constrictions of the notochord are slight (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 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. bu., basiventral; c.c., cyclospondylous centra; ch.s., chordal sheath; h.s., haemal spine; i.bd., imperforate basi- dorsal; i.id., imperforate interdorsal; iv., interventral; p.bd., perforate basidorsal; p.id., perforate interdorsal. After Goodey, 1910.1, Fig. 15, pl. XLIV. B—Vertical longitudinal section (with anterior and posterior ends reversed) showing calcified cyclospondylous centra of two sizes. bv., basiventral; h.c., haemal canal; h.s., haemal spine; l.c.c., larger cyclospondylous centrum; ne.c., neural canal; s.c.c., smaller cyclospondylous centrum. After Goodey, 1910.1, Fig. 16, pl. XLIV. td,30 s..l. us. def. 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; bv., basiventral; d.f., dorsal foramen; id., interdorsal; iv., interventral; rb., rib; s.d.]., supradorsal ligament. After Goodey, 1910.1, Fig. 11, pl. XLIV. 365 366 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 Allis (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 applied to each other, and there is but little 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. bd.cs way osibd an UH ag. PAI Text-figure 33. A portion of the vertebral column (x 1.4) of Chlamydoselachus, 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; bd.69, basidorsal no. 69; bv., basiventrals; d.f., dorsal foramen; iv., interventral; n.70 and n.72, neuromeres 70 and 72 respectively; s.bd.. supra-basidorsal; s.d.]., supradorsal ligament; v-f., ventral foramen. After Goodey, 1910.1, Fig. 12, pl. 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 (1895) nomenclature, as follows: basidorsals, interdorsals and supra-basidorsals, the last-named being segmented off 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 ligament 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 Garman’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 Goodey’s large specimen: Each constriction appears below a basidorsal, so that the constrictions are intravertebral. 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 Goodey (1910.1, Fig. 9, pl. 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 Goodey, 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 lines 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- 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; f.v., 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 W108 109 nito TM LADLE DTS: we ee Wii eee Sees Sr 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, pl. 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 enabling 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 (Ridewood, 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 Garman (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 Garman’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 Chlamydoselachus, aspect not stated. cr, coraco-scapular; msp, mesopterygium; mtp, metapterygium; prp, propterygium. After Garman, 1885.2, Fig. 2, pl. XI. be seen upon comparing Text-figures 37 and 38. There are differences in the number, sizes and shapes of the basal cartilages, particularly the mesopterygium. In Garman’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 Garman’s figure. In Braus’s specimen, many of the radials posterior to the region of fusion have four or five segments; in Garman’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 Garman’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 Garman portrayed a dorsal view, and that Deinega’s Fig. 14 is also a dorsal view. In Text-figure 38. Deinega’s figures of the pectoral fin, some of the lines Ventral (inner) view of a pectoral fin at the distal margin are so indistinct that one cannot skeleton ef Chemposelactus: ; 5 : Co, coracoid; F, foramen for blood vessel; G, determine the exact number of cartilaginous elements; shoulder joint; ms 1, primary mesopterygium, but in his text he states that there are three rows of ms 2, secondary mesopterygium; mt, metapter radial segments. Goodey’s drawing (1910.1, Fig. 18, 780m: * Propteryeium; S, scapula; ‘Ss, supra scapula; 1-4, cartilages in line with basals. pl. XLV) of the left pectoral fin (aspect not stated) of After Braus, 1902, Fig. 1. Siz Bashford Dean Memorial Volume 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 literature 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 nielsoni 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, pl. IV. Text-figure 40. Fragment of a pectoral fin skeleton of Symmorium reniforme Cope. B, basal piece; Mt., metapterygium; R, some small radials at the distal end. From Braus, 1902, Fig. 3; after Cope, 1895, Fig. 1, pl. 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; SG, shoulder girdle. After Dean, 1909, Fig. 28. homologized 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. Petvic Fins AnD Petvis 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 Heptanchus, 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. bp, basipterygium; il, iliac ridge; pu, pubis. Redrawn after Garman, 1885.2, Fig. 1, pl. XI. 374 Bashford Dean Memorial Volume LIFT L SOT S 0 ° oo 68 ‘ln f Pg Text-figure 43. Dorsal view of the right half of the pelvis, and of the right pelvic fin, of a female Chlamydoselachus. btd., distal segment of the basipterygium; btp, proximal segment of the basipterygium; Inf, longitud- inal row of foramina for nerves; pg, pelvic girdle; r, lateral radials. Redrawn from Goodey, 1910.1, Fig. 19, pl. XLV. (1885.2) writes: ~The peculiar shape of the pelvis suggests an embryonic character of other sharks. In embryos the pelvis is longer than in the adult, in comparison with the transverse measurement. An embryo of Heptabranchias before me has it half as long as wide, 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 with the general body form of Chlamydoselachus. Textfigure 44. Pelvic fin and girdle of the fossil shark, Cladoselache kepleri. b, basals; p, pelvic arch. After Dean, 1909, Fig. 18. Garman’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 Garman’s figure re- produced as my Text-figure 42, which is a dorsal view of the pelvis, presumably of the same female; nor is it shown in any other published drawing of the pelvis 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 pelvis. 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 with the radials. These transverse grooves indicate a metameric origin of this portion of the pelvis, presumably through the fusion of primitive radials to form basals which were later added to the pelvis: The manner in which basals of the pelvic fins may be derived from radials is illustrated by Dean’s The Anatomy of Chlamydoselachus 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); andas 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 mn eS i We 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. 375 1a. Text-figure 45. Skeleton of the pelvic fin and girdle of Heptanchus maculatus: A, female; B, male. Be, beta cartilage; b.1—2, first and second connecting segments ba., basal or axial cartilage; ba.p., basipterygium; pl., 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 dificult to determine the number of segments in the radials—the row of small distal segments is either not well shown or is absent. Petvic Frys 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 in 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 like the radials (Text-figure 44). After reviewing the literature 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. Tue Myxoprerycta.—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 Gunther (1887) and by LeighSharpe (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 line with the basals but are in serial relation with the radials. They appear to be radials that are enlarged, elongated and otherwise differentiated. In the several figures, there are minor differences in the radials associated with the one that is most highly developed, and in 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. LeighSharpe’s description (1926, p. 312) of the skeleton of the claspers, illustrated by his Fig. 54 (reproduced as my Text-figure 115a, p- 472), is as follows: The Anatomy of Chlamydoselachus By) 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. Text-figure 47. Skeleton of a clasper (myxopterygium) of Chlamydoselachus anguineus. a, principal cartilage; a1, intermediate cartilage; b, basals of pelvic fin; 1, lobe-like expansion of cartilage a; r, 71 and r 2, rays of pelvic fin; t, tl, movable calcified terminal pieces by which the canal can be opened or closed. : After Gunther, 1887, Figs. D and D1, pl. LXIV. Gunther (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 45z, 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. XV]I) 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 Bashford 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, pl. 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 Garman’s drawing (my Text-figure 48). Deinega distinguishes a series of thirty-two basal elements which he calls radials, whereas in Garman’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 Chlamydoselachus anguineus. m., fin membrane; 1-32, first row of radials (no. 1 not shown). After Deinega, 1909, Fig. 12, pl. III, The Anatomy of Chlamydoselachus 379 Osburn has published a drawing (1907, Fig. 19, pl. 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 Garman’s specimen (forty-five), 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 little or no fusion. In Heptanchus cinereus (Text-figure 50) the radials (ra.) of the dorsal fin are much more regular and there (Z/ es Text-figure 50. Text-figure 51. Endoskeletons of the dorsal fins of Heptanchus and Mustelus. 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, pl. LXXV. Text-figure 51. Cartilaginous elements of dorsal fin of Mustelus antarcticus. b.c., basal segments; b.c.1, median segments; b.c.2, distal segments. From Daniel, 1934, Fig. 89a, after Mivart. is a large but thin basal cartilage (bc.). 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, pl. 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. fon Yas: Sy o> aa OLIIDINL SDSS Text-figure 52. Endoskeleton of the anal fin of Chlamydoselachus anguineus (showing basals 1-20). After Deinega, 1909, Fig. 13, pl. 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, pl. III, which is too large for satisfactory reproduction here; also in Garman’s (1885.2) Pl. 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 supplied 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. ‘For 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 forma 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 Memorial 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. Muscies OF THE TRUNK AND Tat.—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 differentiation into individual muscles—a development that, in the higher vertebrates, quite reverses the picture. Text-figure 53. Lateral view of the body musculature in the pectoral region of Heptanchus maculatus. cl., gill-cleft; d.b., dorsal bundle; d.f., dermal fin rays; d.r.m., dorsal radial muscles of pectoral fin; I.b., lateral bundle; I]., lateral line; ms., myoseptum; tr., trapezius muscle; v.b., ventral median muscle. After Daniel, 1934, Fig. 90. In surface views of the six large embryos ot 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 outlined, 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 Chlamydoselachus conform to the primitive elasmobranch type and bear a close resemblance to those of Heptanchus 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: Ina side view, the muscles of the body of Heptanchus maculatus are divided at the lateral line (J].) into dorsal bundles (d.b.) 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 zigzag shape. Above the lateral line one of the columns has the apices of its myosepta directed forward, the other backward. Below the line 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: 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 line 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. DORS. a ——_ ee Text-figure 54. MUSS PN Model of myomere of a selachian A (Squalus), showing divisions into LAT. LINE. -- longitudinal muscle bundles. DORS.MUSC.DIV., dorsal bundle; LAT. LINE, lateral line; LAT.M.DIV., lateral bundle; VENT.M.DIV., ventral bundle. After Howell, 1933, Fig. 3, modified from Langelaan and Daniel. --- LAT. M. DIV. VENT. M. DIV----> EE 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 Memorial Volume sS== \\ AK SS} Text-figure 55. Lateral view of the trunk musculature of Chlamydoselachus 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), be (beta), and ga (gamma), the three longitudinal regions into which the division b may be divided; I, lateral line; o. inf., musculus obliquus inferior; o.s., musculus obliquus superior; R.p., rectus profundus muscle—in A it is shown artificially spread out, as well as in its original position, inrolled. A line drawn from ~x to y, along each region, would separate, approximately, the inferior oblique from the superior oblique muscles. After Maurer, 1912, Fig. 1, Taf. 1. Maurer (1912) has given us detailed information concerning the trunk musculature of both Chlamydoselachus and Heptanchus. In Chlamydoselachus (Text-figure 55) the ventrolateral bundle has the same fundamental division into two columns (divided 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 55p) where the ventrolateral bundle is the SS ===> SS = — A ae 0. ing Text-figure 56. Lateral view of the trunk musculature of Heptanchus cinereus. a., dorsal region of ventral bundle (ventrolateral of other authors); d., dorsal bundle; I., lateral line; o.inf., inferior oblique; 0.m. x0.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 inrolling 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, pl. 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, pl. 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. Garman’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 210mm. 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 Garman 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 (k.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 Garman’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, pl. XIII) in connection with his studies of the innervation. In this case the depth of the “keel” is remarkable. Braus applies 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 Ke i Lil --Per H i ONG Ain ahr ute. B NG ie perio Mobl int x A N. intercost. 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. H. skin; M.obl.int., musculus obliquus internus; N.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 oblique 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. 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 recognizable as an inrolled 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.p., musculus rectus profundus; a, first; and b, 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 inrolled independently, like a scroll (Text-figures 55, 60 and 61). This 388 Bashford Dean Memorial Volume does not accord with the conditions portrayed by other authors in their drawings of transverse sections through the keel muscle. As to the function of the deep muscle variously 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. 1d, 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, Fig. 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 limits of a myomere corresponding in extent with a monospondylous neuromere. In the main caudal region each myomere is equal in extent with 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. Tue HypopraANcHIAL Group.—lIn 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-fgure 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 Anatomy of Chlamydoselachus 389 muscles of the body and tail—as in Scyllium (Van Wijhe, 1883, p. 36 and Fig. 25, Taf. III); in Lacerta (Corning, 1895); in Petromyzon and Squalus (Neal, 1897); and in Lepido- siren and Protopterus (Agar, 1907). Text-figure 63. Hypobranchial muscles of the notidanid, Heptanchus maculatus, ventral view. bh., basihyoid cartilage; c.ar., musculus coracoar- cuales; cb.1, 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; ibv.1-6, first to sixth ventral interbranchial muscles; md., mandibular cartilage. After Davidson, 1918, Fig. 4. In Heptanchus (Davidson, 1918) the following muscles (Text-figure 63) are recognized as members of the hypobranchial group: the paired coracoarcu- ales communes (c.ar.), 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. Edgeworth (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 slightly oblique myosepta (Text- figure 63). In the coracoarcuales of Scymnus, there are five such myosepta (Furbringer, 1897, Fig. 3, Taf. VI). In Heptanchus, Vetter (1874, Fig. 9, pl. 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. Allis (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’ (Allis, 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 Allis calls the “‘pharyngo-clavicularis.” The hypobranchial muscles of Chlamydoselachus are shown, in color, by Allis (1923) in his Figs. 35 and 37-40, pls. XIII-XV; but nowhere are these muscles of Chlamydoselachus 390 Bashford Dean Memorial 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.1) are shown in my Figure 8, plate HI. Allis (1923, pp. 192-195) gives a detailed description of each of the muscles under consideration. idhy add’id’ ad. arc’ ti Yeo oS (TURES lev: lab. Sup. / y proangor lab.cart. 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., musculiadductores dorsales 1-5; ad.mand., musculus adductor mandibulae; carc., 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.lab.sup., musculus levator labii superioris; 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, l.c.)." In Vetter’s figure of Heptanchus (his Fig. 9, pl. XV), the coracobranchiales of the region under consideration appear to arise directly from the musculi 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 Allis 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 (Allis, 1897), and it is not described by Vetter as a separate muscle in any of the selachians considered by him. Tue Eyzsatt Grour.—In elasmobranchs and perhaps in vertebrates generally, the muscles that move the eyeballs arise (Marshall, 1881; Van Wijhe, 1883; Neal, 1918) M. oblig. sup. ™. rect lat. Verbindung des Kiemenbogen- coeloms mit dem Cavum 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. 1, 2, 3, 4, gill-clefts; S.B.C.1—5, pharyngeal arch extensions of the coelomic cavity; ch.dors., chorda dorsalis; oc.m., anlagen of the oculomotor muscles; M. oblig. sup. and M.rect.lat., anlagen of the superior oblique and lateral rectus muscles respectively; ves.audit., otic vesicle. After Corning, 1925, Figs. 222 and 223; based on Froriep’s (1902) Figs. 4 and 5 (Torpedo ocellatus). 392 Bashford Dean Memorial Volume from mesodermal segments (head somites) which are serially homologous with those of the trunk (Text-figure 62). In primitive fishes, the head somites, like 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 shown (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. Text-figure 66. Dorsal view of the eye muscles of Chlamydoselachus on the right side. The Roman numerals distinguish the nerves supplying the eye: II, second cranial or optic nerve; III, third cranial or oculomotor nerve; IV, fourth cranial or trochlear nerve. 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 (1906), and later by Nishi (1922) who used four adult specimens. They were considered briefly by Allis (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 Rect b PSs ectus sup. snd ie Obliquus sup. Rectus lat. acc. ~-...../ _- Rectus med. Rectus lat. ate ot bceeS N. ophthalm. prof. “ss. N. opticus. Rectus inf. ol AN kf SSS Obliquus 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.o., inferior oblique; i.7., inferior rectus; n.II, optic nerve; o.p., optic pedicel; p.r., posterior rectus; S.0., superior oblique; S:T5 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 1s the fact that all the musculi 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 fibers. One division of 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 slightly 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 of 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 derivative portion of the primitive rectus lateralis. This secondary muscle was probably split off from a typical rectus lateralis to aid the superior rectus and the superior oblique in tilting the eye upward. The recti superior, medialis (internus) and inferior are all attached to the top of the optic stalk, just below its flattened head. THE APPENDICULAR 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); Scyllium (Goodrich, 1906); Cestracion (Osburn, 1907); Acanthias (E. Muller, 1911); in Amia and Lepidosteus (Schmalhausen, 1912). Thus the muscles that move the fins are metameric in origin; this applies 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 Mustelus 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 segments contribute to the formation of the musculature of the pectoral fin; while in Torpedo there are 26 such segments. 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 with the notidanids, Chlamydoselachus seems to afford favorable material for the study of the origin and development of the fin muscles, but so far as ] am aware, such studies have never been made on these forms. Of the fins of Chlamydoselachus, only the pelvics of the male have received attention with respect to their musculature. The muscles of 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. b.1 and b.2, connecting segments; ba., basal piece; ba.p., basipter- ygium; be., beta cartilage: pl., pelvic girdle; ra., radial cartilages. After Davidson, 1918, Fig. 8. B—Musculature of male right pelvic fin in dorsal view. ad., adductor muscle; cb., compressor muscle; dl., dilator muscle; f.e., flexor externus; f.i., flexor internus; pl., 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, pl. 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 69s), 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 69s) 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 LeighSharpe (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 115s, after LeighSharpe. 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 widest 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. supemicial constrictor iby muscles of Gillarthes Mm RheTVe Spiracte W\\S RQ \ SX \\ QO SEERA S = eM ey ZA lalla el CUMS pity adductor muscles cartilage OF ja WS Text-figure 70. A dissected head of Chlamydoselachus anguineus in lateral view. From Gregory, 1933, Fig. 6; redrawn and slightly simplified after color figure in Allis, 1923, pl. IV. 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. Furbringer (1903) described some of the muscles of gillarch origin, particularly those of the mandibular arch, in Chlamydoselachus. Luther (1909) described the muscles innervated by the trigeminal nerve. Goodey (1910.1) described the muscles of the mandibular and hyoid arches. Allis (1923) has given a detailed, comprehensive and beautifully illustrated description of the pharyngeal muscles of Chlamydoselachus, 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 (Iad.) and subspinales (S.sp.) are shown in Text-figure 71, after Allis (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 Allis’s interarcualis IV corresponds to Gregory’s interdorsalis 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; EBII, epibranchial cartilage of the second branchial arch; EPB VI, epi-pharyngobranchial cartilage of sixth branchial arch; HMD, hyomandibular cartilage; Iad IV, musculus interarcualis dorsalis between arches [V—V; I adhy, musculus interarcualis dorsalis between hyoid and first visceral arches; Ida, lateral dorsal aorta; Imh, ligamentum mandibula- hyoideum; n., cut ends of nerves to tissues of roof of branchial chamber; PBI, pharyngobranchial cartilage of first branchial arch; PBIV, pharyngobranchial cartilage of the fourth branchial arch; Rabd, musculus retractor arcuum branchialium dorsalis; Ssp, subspinalis muscle; tiad, ligamentous sheet formed by tendons of musculi interarcuales dorsales. After Allis, 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 Furbringer’s (1903) Fig. 1, pl. 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, pl. XVII, and Fig. 48, pl. 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, pl. 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 lip. The muscle is innervated, as both Furbringer 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, pl. XI). I quote the following from Allis, 1923, pp. 187-188: Firbringer and Luther both say that this muscle is not found in Chlamydoselachus. Furbringer 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.c., 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, pl. XIV) the muscle is well developed; in Chlamy- doselachus 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 Allis (1923) in his Fig. 6, pl. WI, 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. Allis (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 (Allis, 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 lies anterior to the point where the nervus facialis 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, Allis states: “The investigation of the nervous system had only just begun, and . . . this part of the cranial anatomy is only 400 Bashford Dean Memorial Volume 5 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 facialis, 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 supertficialis, 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 earlier work (Allis, 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 Allis’s (1923) Fig. 56, pl. 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, pl. 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 DIGESTIVE SYSTEM AND ASSOCIATED ORGANS There are few published descriptions of the di- gestive organs of Chlamydoselachus, 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- cludes 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 401 Text-figure 72. The digestive system of Chlamydo- selachus, ventral aspect, about one-fifth natural size. b.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; 1.1., left lobe of liver; py., pylorus; py.ves., pyloric vestibule; r., rectum; 7.g., rectal gland; 7.1., right lobe of liver; sp.1, valvular v.p., spleen; sp.2, accessory spleen; v.i., intestine; v.mes., ventral mesentery; 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 living prey of considerable size. It seems likely 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 resembling 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 403 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. II 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, Hawkes (1907) describes and figures (my Text-figure 73) a more de- 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- Text-figure 73. Digestive tube of Chlamydoselachus, from the middle of the stomach to the mens. From specimens I and III, I have excised middle of the valvular intestine. some segments of the slightly thickened wall near B.D., bile duct; B.D.B.E., dotted line showing the the caudal end of the cardiac stomach, and upon °°" Gf dn Gallas) Gane) Git Cina [Bil Gnesi H the wall of the bursa entiana; B.E., bursa entiana; microscopical examination have found only the layers — C.,, caecum at the hinder end of the larger arm characteristic of a stomach, including an inner eee Fee rane Sees glandular layer in a poor state of preservation. pyloric valve; S., stomach; S.1. short arm of Collett (1897) states that in his specimen of ee ae nh 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- 404 Bashford Dean Memorial Volume posed between the cardiac stomach and the pylorus. It seems probable that, when present, this division 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 caliber 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 obliquely to the right and caudad. Thus the pyloric vestibule, considered together with 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 width 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. III, 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 5mm. 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 resembling 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. III 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-walled, 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, b. e.). In Chlamydoselachus the bursa entiana is shaped somewhat. like the human stomach, but the orientation is different. Superficially, it would resemble the human stomach if the latter were reversed end-for-end and rotated so that the greater curvature would lie 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 mm. 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 cephalic end of the valvular intestine, to the apex of the pyloric valve, its length is 20mm. 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. III the bursa is greatly expanded. Its length, measured from the cephalic 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 46mm. The greatest transverse diameter, which is near the caudal end, is about 18 mm.; near the cephalic 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 outline in Text-figure 72) about 10 mm. long, opening caudad into the lumen of the bursa. The opening is about 8 mm. wide 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. III; 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. III, 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. Iand 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. IJ, 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. 408 Bashford Dean Memorial Volume THE VALVULAR INTESTINE In my three specimens the valvular portion of the digestive tube is spindle-shaped, but tapers much more rapidly in its caudal half; the cephalic 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 valvular intestine is laid widely open after being slit 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 walls are very thick, ranging from 5 or 6 mm. near the cephalic 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 No. II the spiral valve stops at about 20 mm. from the ceph- alic end of the thick-walled portion. For the remaining distance the inner surface shows villosities 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 walls, this part is assigned to the valvular intestine. For similar reasons I have included with the valvular 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 No. Ilitis 20mm. The posterior four-fifths of the valvular intestine lacks a mesentery. In my specimen No. I, the form of the valvular intestine seems perfectly preserved. The maximum diameter is only 26 mm., while the length is 190 mm. In No. II the val- vular intestine is much larger; its maximum diameter is about 33 mm., while its length is 240 mm. In No. III the organ is about the same size as in No. II, but is so irregularly molded that its diameter cannot be accurately measured. In Chlamydoselachus the spiral valve is a continuous ribbon-like structure attached by one edge to the inside of the wall of the intestine, while the other edge is either free, winding about a central cavity, or is attached to an axial strand. In specimen No. | 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 No. IJ a central cavity alternates with an axial strand at irregular intervals. In specimen No. III there is a central cavity of moderate size extending the entire length of the spiral valve except in its middle portion, where there is a short axial strand. In the specimen portrayed by Gunther (my Figure 15, plate IV) it is clear that there is a central cavity in the caudal half and at the cephalic end, while the interval between has possibly an axial strand. In its natural position, the spiral valve of Chlamydoselachus does not lie vertical to the wall of the intestine: it slants either forward or backward. Thus each coil has the form of an asymmetrical cone, of which the apex may be missing. When the intestine is contracted, the spiral valve makes an acute angle with the wall of the intestine; when it is expanded, the spiral valve may be drawn 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. III 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. Gunther’s (1887) Fig. 5, pl. 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. Collett (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 Scylliwm canicula, and something like it occurs in Zygaena (Parker, 1885, Fig. 8, pl. XI). In most sharks the apices of prac- tically all the coils point forward, as in Scyllium (Parker, 1885, Fig. 5, pl. XI); or backward, as in Heptranchias perlo (Garman, 1913, Fig. 1, pl. 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 Cephaloscyllivm umbratile (Garman, 1913, Fig. 2, pl. 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, pl. 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 Memorial 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 with the usual practice I have distinguished two regions, colon (c.) and rectum (r.), in Text-figure 72; but these parts are much alike 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 width of the rectum is about the same throughout its length, so that in ventral view it appears to be of uniform diameter; but when viewed from the side, the rectum appears somewhat funnel- shaped since it enlarges toward the anus. In specimen No. | the rectum is 9 mm. wide and has a dorsoventral diameter of 13 mm. at its cephalic 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. wide; its dorsoventral diameter is 10 mm. at the cephalic end, and 16 mm. at the anal end. In specimen No. III the width is 8 mm.; the dorso- ventral diameter is 10 mm. at the cephalic 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 toward 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 lining 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 toward the left. The dimensions in my three specimens are: No. I, 20x 13 x 6 mm:; No. II, 18 x 14x 7 mm:; No. IJ], 17 x 12 x9 mm. The duct leads anteriorly and ventrally to open into the dorsal side of the rectum. In all three specimens the duct is 13 mm. long. The opening is distinctly visible on the inner surface of the rectum; it is guarded by a valve-like 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 valvular intestine, also at the middle of the rectum. In speci- men No. III 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, pl. 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, pl. XIX a duct appears to open from this gland into the rectum. Gunther (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 isempty. 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. IJ, 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. I it is 105 mm. longer; in No. I] it is 203 mm. longer. In No. Iand in No. HI 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. Gunther (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 Gunther really belonged to a pyloric vestibule. Collett (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 Memorial 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 bile 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 cavity anterior to the cloacal aperture, in three adult female specimens of Chlamydoselachus. | Specimen | Total Body Esophagus | Pyloric Bursa Valvular | Colon and Total Sern Body | Number | Length | and Cardia| Vestibule | PY!IOS | Entiona | Intestine | Rectum meee Cay | u I 1350 330 35 33 6 190 40 664 =O) C564 Ul 1485 365 Absent 33 2 240 80 745 640 Il 1550 440 | 25 25 3 230 40 803 | 600 THE LIVER In my specimens II and III the liver is nearly all missing; but in No. I the liver 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 liver of Chlamydoselachus (Text-figure 72) is a very large organ. It consists mainly of two lobes (r.l. and I.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 liver which is median in position. The lobes are of equal size and alike in form save that there is a slight excavation near the distal end of the left lobe. Thus the form of the liver is decidedly symmetrical. Each lobe is flattened; the greatest width of a lobe is about 50 mm., but the thickness does not exceed 12 mm. In Text-figure 72 the lobes are shown in broad view, but in their naturai position they would probably appear in an edge view. The unpaired portion of the liver is about 60 mm. wide, 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 liver, and projects slightly beyond its caudal margin. The Anatomy of Chlamydoselachus 413 A large duct, the common bile duct (c.b.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 salem Collett (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. 1) the dorsal pancreas measures 45 x 25 x 2mm. 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. | this duplex organ is 40 mm. long by 8 mm. wide at its widest level; in specimen No. IJ 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 light 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 epithelioid 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. I 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 elasmobranch. In the teleost, Gambusia 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 lies a darker-colored portion whose length is about 48 mm., which adjoins the hinder lighter part, and is connected with it. Although Collett 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, pl. 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 which the ontogenetic development of the thyroid has been studied, it arises in the embryo (thr., 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 solid 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 blindly 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 lined 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. b.v., blood vessels; d., denticles; e., enamel organ; fo., follicles; |.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 417 The Anatomy of Chlamydyselachus WMZZA! 2 Text Median sagittal section (x 12) figure 75. showing thyroid gland and thyroglossal duct of an adult Chlamydoselachus. thyroglossal duct; p.d., pharyngeal denticle; thyr., thyroid gland. Drawn from Specimen No. I in the collection of the American Museum of Natural History. c., basihyoid cartilage; d., a., artery; h showing thyroid gland of an adult Chlamydoselachus in whic Median sagittal section (x 10) there was no thyroglossal duct. ; p. d., pharyngeal denticle; thyr., thyroid; v., vein. Drawn from Specimen No, III in the collection of the American Museum of Natural History. a., artery; c., basihyoid cartilage 418 Bashford Dean Memorial Volume (less than a millimeter). The finer structure of this specimen is rather poorly preserved, but permits of the following observations. The duct (d.) is lined with stratified squamous epithelium continuous with the epithelial lining of the pharynx. The outer layer of the duct consists of a thick layer of dense connective tissue continuous with 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 having the form of rudimentary denticles. These are smaller than the fully developed denticles (p.d.) that occur in the lining of the pharynx. The distal end of the duct ends blindly in close contact with the thyroid (thyr.). Text-figure 76 is a drawing of the thyroid of one of my specimens (No. III) in which a thyroglossal duct is absent. The histological condition of this material, also, is rather poor, but the topographical relations are well shown. Upon comparing Text-figures 76 and 75, it will 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 thyroid was cut away in trimming the block preparatory to imbedding, but in the remaining portion the finer structure is well preserv- ed. While the simple cuboidal epithelium of the follicles is in good condition, the lumens of the follicles appear empty, as they do in the other specimens. In the sections of No. IV, the pharyngeal denticles are beautifully shown. In all the sections, the epithelial lining of the pharynx is very poorly preserved. 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 [thyroid] gland rests upon the basihyal cartilage whose anterior margin forms an excellent guide to its location.” His paper deals with the histological structure as well as the form and gross anatomical relations of the thyroid in elasmobranchs, and includes a description of the blood vessels supplying the thyroid. In Scyllium catulus and in S. canicula (Goodey, 1910.2), the thyroid gland is situated close to a foramen in the basihyoid cartilage. In both species of Scyllium the connective tissue investment of the thyroid extends into the foramen as a plug containing, in some instances, a small amount of thyroid 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 thyroglossal duct. THE SPLEEN In Chlamydoselachus the spleen proper (Text-figure 72, sp.1) is a very elongate, somewhat comma-shaped, flattened organ lying in the dorsal mesentery 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. III 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 extravascular erythrocytes; small arteries and veins were distinguishable. In its finer structure the spleen proper is very much like 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 gillflaps 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 size 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 holobranch to the right. Each gill-arch of Chlamydoselachus affords attachment, distally, to one edge of a crescentic plate, the gillsseptum. 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 gillseptum there are long narrow primary folds, the gill-filaments, extending in a radial direction from the base of the gill-sseptum toward its margin (Text- figure 77; Text-figure 78, a.f. and p.f.). On each broad surface of a gill-fllament there are The Anatomy of Chlamydoselachus 421 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 Garman, 1885.2, Plate V. Text-figure 78. Radial section (x 4) of a gill of Chlamydoselachus, partly diagrammatic. The lines 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; c.m., 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 gillflap 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. 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.br., afferent branchial arteriole; e.br., efferent branchial arteriole. Drawn from a section of a gill from a specimen lent by Dr. E. Grace White. Textfigure 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 a., arteriole; Im., lamella. “BS, de Drawn from a specimen in the American Museum of figure 79. Text-figure 80. Natural History. All the gill-flaments 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 gillsseptum 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-slit. In my specimens, as in Garman’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 gill. 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 with 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 elasmobranch 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 ibd. Text-figure 81. Section, cutting parallel to branchial filaments, through second holobranch of Heptanchus maculatus. ad., adductor muscle; af., 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; fl.a., anterior filament; fl.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 flaments 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 Memorial 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 slits, from 1 to3 mm. long. In my four specimens each aperture is situated in line with the - = a = = SS yy, = ———— eee = ——— (14 Ws = > LUlilt ————_—_—_ nS 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 lines. c.1, caecum; cr., cranium; hm., hyomandibular cartilage; i.s.c., internal spiracular aperture and cavity; I.p.i., ligamentum postspiraculare inferior; p.g., 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 slit-like 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 mm. on the left; No. III, 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. Il is not a slit, but an elliptical opening fully three millimeters wide. The unusually small opening on the left side of No. III 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) who 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 slits, between the hyomandibular cartilage and the palatoquadrate (Text-figure 82, The Anatomy of Chlamydoselachus 425 hm., pg.). In my four specimens these openings are very much alike. 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 valve-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 slit 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 little 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.1) 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 probability it is homologous with the more extensive caeca mentioned by Ridewood (1896) which have been described in other selachians by Muller 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 lips, 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 lip 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 slit-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. I], 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 like that on the left side of No. I. In specimen No. IJ, 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. III, 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 specialized for purposes of respiration as in the skates and rays, which are bottom-dwelling 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 size 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. Allis (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 1.5mm. 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 gillfilaments. 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, Triacis and Chiloscyllium. It is faintly marked in Mus- telus, but is absent in Scyllium, Notidanus 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. br.c.1, first gill-cleft, showing the demibranch attached to the hyomandibular and ceratohyoid cartilages; br.c.2-3, second and third gill-clefts; c.1, 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; |.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. | 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 valve-like 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 Allis (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 Allis 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 5mm. 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. III, 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 Memorial 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 Urogenital system of the female Chlamydosel- 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. ab.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. III in the American Museum of Natural History. rch.’ 26.p---YOs Text-figure 85. Text-figure 86. 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 Garman’s (1885.2) adult female specimen of Chlamy- doselachus is shown in his Pl. 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. TE eee rr ab.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. 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. ab.p., abdominal pore; m., mesonephros; ovd., oviduct; ovy., Ovary; 7., rectum; s.g., shell gland; ur.p., urethral pores; ut., uterus; v.l., ventral ligament of the oviduct. 7 Drawn from specimen No. II in the American Museum Ar of Natural History unp. el \ 26 p, Text-figure 87. Text-figure 88. one urethral aperture; this (u.a.) is rather large and its position is median. Garman 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 Memorial Volume small cloacal apertures (U.S.1) 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. ab.p., abdominal pores; bp., basipterygium; cl., cloaca; u.a., urethral aperture. After Garman, 1885.2, Pl. 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. Tue MesonepuHroi.—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 Il and III). Posteriorly, the mesonephrot 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. Text-figure 90. Diagrammatic figures of the cloaca in female (A) and male (B) specimens of Chlamydoselachus. A.P., closed abdominal pore; BI., 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.Ov., 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); U.S.1, 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. II is nearly mature, while Nos. I and I 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. ashes Specimen Number | IV. | Ill. | I Il. | | | | | fin TTT eh aa | li ee = al Total Length of Body | 1398 | 1550 | 1350 | 1485 Length of Body Cavity 554 634 588 686 Length of Mesonephros__ | 486 554 | 518 605* | | *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 II. 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. I. | L UL. Length of Mesonephros A 35. 38.3 40. Tage Peeyy Waa ool Doll 7 Length of Mesonephros ||. eetooerie ene Seer are 87.7 87.3 88.0 88.1* | Length of Body Cavity | | | *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 little 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 line. At their posterior ends they are actually united, but they diverge a little anteriorly. Therefore, along the greater part of their course they lie along the low ridge formed by the vertebral column, but at their anterior ends they depart slightly from this ridge. In specimens IV, III and I, the mesonephroi lie 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. III, 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. IU, 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 296mm. 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 line 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 little recorded concerning them. Collett (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), which 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 Collett’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 Chlamydoselachus. The assertion that the kidney of the female Heptanchus extends from the pericardio-peritoneal septum is hardly understandable in view of Daniel’s statement (p. 289) that the kidney of the male extends farther forward than that of the female. Tue Urinary Stnuses.—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 asa guide. I could not find any aperture connecting the two urinary sinuses, which are separated by a thick septum. In specimen No. III the two urinary sinuses (Text-figure 914), 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 9mm. Fora 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. III; 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 91s) 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. III, 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. II; 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 limit 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 slightly 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, pl. XIX. 2 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. III 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. Il a probe could not be passed from the left urinary sinus into the left mesonephric duct, though the latter is of normal size. 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. II, 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 MaesonePuRic Ducts AND CoLLecTING TusBuLes.—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 recognized. 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 size. Collecting tubules were not positively identified. In specimen No. III 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 size. 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 size and distribution these portions conform to the general plan revealed in my other specimens, particularly in No. I. mes. d. Text-figure 93. Excretory organs of the right side of a female Chlamydoselachus 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. c.t., collecting tubule; mes.d., mesonephric duct; ovd.mes., line of attachment of the right oviducal mesentery to the right oviduct; 7.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 Garman’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 Chlamydoselachus: “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 approxt 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. III the right mesonephric duct is of microscopic size, 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. III, 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 Wolffian duct (mesonephric duct) decreases in im- portance as we approach the rays. In the female Squalus sucklii (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. III, 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. III, 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 Chlamydoselachus reaches almost or quite full size before attaining sexual maturity. Tue 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 IJ, 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. III 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, pl. I[V—it is evident that, in the ovaries under consideration, the ovocytes are very incompletely developed. There are no ruptured follicles 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. III the ovaries (Text-figure 86) are of almost equal size but the left is slightly better developed. In each ovary, the largest follicles are situated along the lateral margin. Since the largest follicle 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, | 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 handling. Doubtless the rupture of large follicles 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 follicle has ruptured naturally. In the left ovary no follicles are recog- 446 Bashford Dean Memorial Volume nizable from the ventral surface, and the largest follicles represented on the dorsal surface measure only 6 mm. in diameter. Garman’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 Heptanchus (Daniel, 1934) and in Hexanchus (Semper, 1875, Fig. 1, pl. 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, drawn one-half natural size. ng, nidamental gland; 0, ovary. Printed from the original wood-cut after the drawing by Paulus Roetter for Garman, 1885.2, Fig. 1, pl. XIX. rudimentary testis consists of an anterior larger portion, and a marked swelling or ridge which extends practically the entire length of the ovary. Tue Ovipucts.—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. IH, all the oviducal organs of the right side are decidedly larger than those of the left. The discrepancy is even greater in my specimens Iand 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 size 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 midline. 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 Garman’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. Garman’s intricate description, illustrated by his Fig. C, pl. XX, of the internal structure of the nidamental gland (shell gland) is too involved for consideration here. It should be com- pared with Borcéa’s account (1905, pp. 419-427, Text-figs. 93, 94 and 95) of the structure of the nidamental gland of Scyllium. Collett’s (1897) puzzling description of the oviducts and “uteri” of his large female 448 Bashford Dean Memorial 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-like 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, pl. 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 footnote 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 size 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. IJ. 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 likely, however, that the young sharks are born as soon as, or even before, the yolk is entirely utilized. 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 x70 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 Giunther’s (1887) material consisted of two 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 slit 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 writes concerning “one of the males examined.” She states that in the male there are two urogenital apertures (Text-figure 90s, after Hawkes), each being the outlet of an oval urogenital sinus (BI.) which Gunther described as a urinary bladder. Anteriorly, the sinus communicates 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 forward they become almost invisible to the naked eye. In the posterior part of the duct the folds are very close together (Gunther describes them as “circular” folds). Hawkes further states that the lumen of the left ductus deferens (which Gunther 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 Gunther; Text-figures 95 to 97, after LeighSharpe. 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 1154 (p. 472), after LeighSharpe. 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 1158 (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 LeighSharpe (1920, pp. 245-246): 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. Text-figure 95. Ventral view of the pelvic region of a male Chlamydoselachus, showing myx- opterygia or claspers. Cav., projection of cavity. A le C ae Nive \ustinsirrass, WGH4, TD ih, wy AOS p., apopyle; Cav., cavity; Cl.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 scroll-like clasper groove or tube will 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 line, and ending blindly, having no communication with the coelom, and whose function and significance it will be my endeavor to elucidate. In the skates, on the other hand, no such hollow 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- Cav., cavity; Cl.Gr., clasper groove; I.V., iliac vein; U-P., mologous with eas CRE SipROR GI Une alban urogenital papilla; V.F., ventral fin; V.S., venous sinus. and dogfish, which is but little known. After Leigh-Sharpe, 1926, Fig. 4, p. 311. Other accessory structures may be present on the claspers, such as the spurs and the like 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 all directions ina radiating manner. . .. The rhipidion attains a greater development in the skates than in the sharks. Zé, Text-figure 97. Pelvic fin region of a male Chlamydoselachus: A, ventral aspect; B, left lateral aspect. The manner in which the various parts of a myxopterygium, particularly the siphon, function is described at length by LeighSharpe (1920, pp. 247-251) in the case of Scyllium catulus. 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.v. [my Figure 22, plate V]. Ina 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 LeighSharpe (pp. 308-311) I quote as follows: This genus [Chlamydoselachus], though included from other characters in the Proto- selachii, does not show any afhnities with Notidanus 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 (ab.p. in Text-figures 85 to 88) vary considerably in size. 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 cloacal aperture of a 1220-mm. female Chlamydoselachus. After Garman, 1885.2, Pl. 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. J) 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 Garman’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. Gunther’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 90s) 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 Scyllium. Dorsal parts removed by a hort zontal cut. The canals below the esophagus are represented by dotted lines. dcv, ductus Cuvieri; dm, dorsal mesentery; lig, lateral suspensory ligament of I, 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 Scylliwm (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 (7.p.c. and I. 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 size. c., common opening of the canals into the peritoneal cavity; d.p., dorsal pericardium; I.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 History; 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 liver, 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. III the common aperture and the pericardio-peritoneal sac are much the same as in specimen No. IJ, but their situation on the posterior wall of the pericardial cavity is a little further ventrad—not so close to the dorsal border as in the preceding specimens. Thus the paired canals must pass a little 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 100s) the common aperture (c.) of the pericardio- peritoneal canal is situated as in No. III, 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-V ASCULAR 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. Garman’s figures of the heart of Chlamydoselachus are reproduced as my Text-figures 1014 and 101s. Of his specimen Garman (1885.2, pp. 18 and 19) writes: 458 Bashford Dean Memorial Volume Departing considerably from the conventional form of heart, this genus presents a shape that is somewhat peculiar. 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 filled, 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, lies the sinus, which 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; 5, 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, Pls. XVII and XVIII. equals the bulk of the ventricle. From it the opening into the auricle is guarded by a pair of valves that are without chordae. The auriculo-ventricular opening is furnished with a pair of valves provided with chordae tendineae. In the ventricle the cavity or chamber is small; its outlines 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, pl. XVIII) [my Text-figure 1018], the muscles lie 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. Gunther (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 102 and 102s. Gunther gives no general description of the heart, but it will be noticed that his figure confirms Garman’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. 7, right atrium; I, left atrium. After Giinther, 1887, Figs. 7 and 8, pl. 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, Gunther’s, and Ayers’ specimens; but the ventricle, even when empty, is larger than it appears in the figures by Garman and Gunther, and the size of the atrium is variable. Text-figure 103 is drawn from my specimen No. III 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. III; B, from No. II. atr., atrium; c.c.v., common cardinal vein; co., conus arteriosus; s.v., sinus venosus; v., ventricle. Drawn from specimens in the American Museum. < De 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 size 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. | the proportions are much the same as in No. III, but the ventricle, which is empty, is kidney-shaped 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 Gunther’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 Garman’s and Gunther’s figures. In my three specimens, the sinus venosus (s.v. in Text-figure 1034) 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 101s, Garman (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.” Gunther’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, slightly 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. III 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 Garman’s specimen; the valves of the two proximal rows rank next in size. 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 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 Garman’s Pls. 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 1044) has a fairly long conus arteriosus—longer than that of Hep- tranchias (Heptanchus) perlo (Garman, 1913, Fig. 1, pl. 56) but shorter than that of Chlamy- doselachus. In Heptanchus (Text-figure 1048) 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 ee Baie Text-figure 104. work has been severely criticised, but in view of Ventral views of (A) heart and ventral aorta, the marked variability that has been found in (B) valves of the conus arteriosus, other organs and parts of Chlamydoselachus, it in Heptanchus maculatus. seems possible that he worked on an anomalous 4b: aperture of last afferent artery; au., auricle (atrium); 5 ete . | al d t f iA fi br.af.1-6, first to sixth afferent branchial arteries; specimen. ave include wo O 1s Hgures c.a., conus arteriosus; cr.I., left coronary artery; hy.af., (Text-figures 105 and 106), because of their his- afferent hyoidean artery; p.c., pericardial artery; v.a., $ ventral aorta; v.c., valves of the conus; vn., ventricle. torical ump CuuaroIee and because they ENS jatose From Daniel, 1934, Fig. 150a and s; the latter redrawn comprehensive than those of other authors. Atee Cagney 16M, 18, 1, ab SO. 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 Dorsat 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 S f Nic-Z wc (* ieee cc. EP == ke $i iL z GS s an erry, / 2 Z us y ‘2 mas v: é cor. va. 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; b.a., bulbus arteriosus; br., brachial vein; c., cranial aorta; c. a., conus arteriosus; c.c., anterior carotid commissure; coe.mes., coeliaco-mesenteric artery; cor., coronary artery (plus hypobranchial trunk); c.s., cardinal sinus; c.v., cardinal vein; d.a., dorsal aorta (posterior to k.); 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; k., cephalic aorta; m.s., arteriae musculo-spinales; p.c.s., precaval sinus; p.pl., pituitary plexus; scl, subclavian artery; s.j.v., superior jugular vein; sp., spiracle; s.v., sinus venosus; tr., 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., coeliaco-mesenteric artery; d., dorsal aorta (posterior to k.); e.c., external carotid artery; h., hyoid arch; i.c., internal carotid artery; i.c.f., internal carotid foramen; k., cephalic aorta; m.s., arteriae musculo-spinales; p.pl., pituitary plexus; scl., subclavian artery; sp., spiracle. I-IX, first to ninth pairs of aortic roots (arches); 1-6, first to sixth pairs of efferent branchial arteries; 1v—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, Allis (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 Gy K o = SSeesonde A Scesccocoast K\ ; Z { acr epsb apsb pehy 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; epsb, efferent pseudobranchial artery; ic, internal carotid artery; Ida, lateral dorsal aorta; pehy, posterior efferent hyal artery. After Allis, 1923, Fig. 60, pl. 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 Volume 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. Dohrn 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 Heptanchus maculatus. ac., anterior cerebral; a.sp., arteria spinalis; br.ef.1, first branchial efferent; d.a.1, paired dorsal aorta; d.a., dorsal aorta; hy.ef., hyoidean efferent; i.c., internal carotid; m.c., median cerebral; ns., nasal artery; o.m., ophthalmica magna; or., orbital artery; p.c., posterior cerebral; ps., pseudobranchial artery; 7.a., ramus anastomoticus; 7s., 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 previous work that Ayers’s description has been entirely discredited. These paragraphs furnish the most striking case encountered in this investigation illustrating the danger of (1) 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 known. 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 Chlamydoselachus. 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 [Ida] 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; thiscom- 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 PA Text-figure 109. The carotid system of arteries in Squalus 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, cephalic sinus; DA, dorsal aorta; DBCA, dorsal branchial commissural artery; EBA, efferent branchial artery; ECA, external carotid artery; EHA, efferent hyal artery; EPA, efferent pseudobranchial artery; ICA, internal carotid artery; MCA, middle cerebral artery; OMA, ophthalmic artery; PCA, posterior cerebral artery; PDA, paired dorsal aorta; SA, segmental artery; SR, spiracular retia. From Corrington, 1930, Text-fig. 22; after Hyrtl, 1872. foramen in the base of the skull and enters the cranial cavity. ... 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. Tue BRANCHIAL ArTERIES.—Either Ayers’ (1889) figures (reproduced as my Text- figures 105 and 106) are inaccurate, or his specimen of Chlamydoselachus was anomalous om te °P acer : a Text-figure 110. Branchial, pseudobranchial and carotid arteries of Chlamydoselachus. aal, II, etc., afferent arteries in the Ist, 2nd etc. branchial arches; acer, anterior cerebral artery; ahy, afferent hyoidean artery; amd, afferent mandibular artery; apsb, afferent pseudobranchial artery; cc, common carotid; cor., coronary; da, dorsal aorta; eal, II etc., efferent arteries in Ist, 2nd etc. branchial arteries; ec, external carotid; ehy, efferent hyoidean artery; epsb, efferent pseudobranchial artery; ic, internal carotid; Ida, lateral dorsal aorta; om, arteria ophthalmica magna; op, optic artery; pcer, posterior cerebral artery; psb, pseudobranch; ta, truncus arteriosus. After Allis, 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 gillarch. Allis (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 467 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 (Allis, 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 0) om pcer ec epsb acere : A, Hay daar PSO apsb ely eall call da C3 Ida : Brae Bae ae : Text-figure 111. Branchial, pseudobranchial and carotid arteries of Heptanchus cinereus. aal, II, etc., afferent arteries in the lst, 2nd etc. branchial arches; acer., anterior cerebral artery; ahy, afferent hyoidean artery; amd, afferent mandibular artery; apsb, 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; epsb, efferent pseudo- branchial artery; ic, internal carotid; ilh, internal lateral hypobranchial artery; Ida, lateral dorsal aorta; om, ophthalmica magna artery; op, optic artery; pcer, posterior cerebral artery; psb, pseudobranch; ta, truncus arteriosus. After Allis, 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 Scylliidae and in Mustelus (Allis, 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-collector arteries (Text-figure 110) form complete loops around each gill-cleft excepting the last one. To be 468 Bashford Dean Memorial Volume sure, Ayers notes the absence of such loops in his specimen, but they are shown in various figures by Allis (1911 and 1923). In Chlamydoselachus a posterior efferent- collector may retain a dorsal connection with the anterior efferent-collector 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 following afferent. Thus the afferents, like the efferents, are connected into a series of loops around all the clefts. Complete afferent loops are not found in other sharks. Basing his opinion upon what is known 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 specialized condition—an interpolation—in Chlamydoselachus, and are probably incipient in Heptanchus (Text-figure 111). In elasmobranchs generally, each epibranchial artery of the early embryo is situated dorsal to a gillarch; but in later development these arteries become shifted to positions dorsal to the respective gill-slits (Goodrich, 1930, Figs. 531a—p and 532). In Chlamy- doselachus, the epibranchial arteries of the adult (Text-figure 110) are situated dorsal to the respective gillarches—that is, they retain what is presumably their embryonic position. According to Allis (1912) they are very 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 conforming to the number of gills and of afferents, as previously noted. Usually these are all separate, but in Notorhynchus, 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 gill in each case, and is a parallel circumstance to the fusion of the pharyngobranchials of the last two skeletal arches, so commonly seen in sharks. The Anatomy of Chlamydoselachus 469 ARTERIOLES WITHIN THE Gitts.—In searching the literature on Chlamydoselachus, Ihave 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 gillarches 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 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; grk, gill-raker; im, adductor branchialis muscle; n, nerve; pef, posterior efferent artery; pl, posterior lamella (filament) continued intc 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; lm, 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; sk, skeletal arch. After Goodrich, 1930, Fig. 517p. laries. An afferent artery, (af. br.a. in Text-figure 78), coursing along the outer side of the gillarch, 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. br. a. in Text-figure 78) courses along the outer edge of each filament, returning the blood from the capillaries of the filament to an efferent-collector artery of the gillarch. A fairly large vein, (v. in Text- 470 Bashford Dean Memorial 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 CAA GR AN Pot ABA STC! FECA /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-flament; Cb, ceratobranchial; CSf, constrictor superficialis; CT, connective tissue; EBAr, efferent branchial arteriole; ExbA, extrabranchial artery; ExbC, extrabranchial cartilage; GR, gill-ray, distal portion not shown; GRR, gill raker; GS, gill-septum; Ib, intrabranchialis; IBCA, intermediate branchial commissural artery; PECA, posterior efferent collector artery; PGF, posterior gill-flament; Pot, post-trematic ramus, branchial nerve; Prt, pretrematic ramus, branchial nerve; VNBV, ventral nutrient branchial vein. After Corrington, 1930, Fig. 10, p. 200. commissural artery (IBCA) connecting the two efferent-collector arteries of a single gill. Such arteries exist in Chlamydoselachus (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 Chlamydoselachus 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 Chlamydoselachus 471 In studying the blood-vascular system of the gills of Chlamydoselachus, 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 size the respiratory surface in Chlamydoselachus 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 Chlamydoselachus 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 Chlamydoselachus 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 Chlamydoselachus. 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 (i.j.v.), the cardinal vein (c.v.), the hepatic vein (h.v.), and the tropeic or lateral abdominal vein (tr.). The cardinal sinus (c.s.) 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 Memorial 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 LeighSharpe (1926, pp. 312-313) as follows: The main blood-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 communicates 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, Text-figure 115. empties its contents into the iliac vein dorsal to the Claspers of Chlamydoselachus in ventral as‘ basipterygium. Five nerves, proceeding to the pel- pect: A, the cartilages; B, the musculature; vic fin and clasper, traverse this sinus, and also a and C, the venous system of the clasper. space (apparently lymphatic) between it and the a.m., anteroflexor muscle; Ap., position of apopyle; abdominal muscles. These structures are seen dis- oe ey See aS. aaa ee “*= played in Fig. 48 [my Text-figure 97s, p. 452], and After Leigh-Sharpe, 1926, Fig. 5. 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 metabolism of the muscles supplied by it warrant so extensive a system of vessels. Possibly 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 Pls. 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 outlines 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 plication is greater than that in Hexanchus as figured by Maclay. There is some likelihood that his figure is taken froma 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 thinocoel is non-nervous. This second point is of considerable interest, as it recalls the condition of Ammoccetes 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. Allis’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. Allis 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 Daniel’s (1934) figure representing a dorsal view of the brain of Heptanchus (reproduced as my Figure 28, plate VII), gives point to Garman’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 Garman 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. Inall 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 Chlamydosel- achus nor of any notidanid. THE CRANIAL NERVES Text-figure 116. The brain and cranial nerves of Heptanchus maculatus in ventral view. bu. 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 superficialis division of the facial nerve; tl., telencephalon; v.s., vascular sac; w. to z., occipitospinal nerves; II, III, IV, VI, IX and X, cranial nerves. After Daniel, 1934, Fig. 200s. 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-mm. embryo. The account of the cranial nerves by Allis (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 Scylliwm, 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. Text-figure 117. Diagram of the segmentation of the head in an embryo of Scyllium 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. LVI, gill-slits; 1-11, somites, prootic from 3 forwards, and metaotic from 4 backwards; a, auditory nerve; ab, abducens nerve; ac, auditory capsule; ah, anterior head cavity; c, coelom in lateral plate mesoblast; cr, limit of cranial region; f, facial nerve; gl, glossopharyngeal nerve; ha, hyoid cartilaginous arch; hm, hypoglossal muscles from myotomes of somites 6, 7, 8; hy, hypoglossal complex nerve; la, lamina antotica; m, mouth; m2, 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 segmentl10; sp1, vestigial dorsal root and ganglion of first spinal nerve; sp2, second spinal; t, trochlear nerve; te, 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, limit 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 Pl. IV; Norris and Hughes, 1920, Fig. 51, showing the cranial nerve components of Squalus in color; and Goodrich, 1930, pp. 725-755. A complete résume 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 are 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.N., Figure 13, plate IV) as large and well-defined. Originating near the median line, 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 recognizable 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 ligamentous portion of the connective tissue that attaches the capsular sheath to the anterior wall of the orbit. 478 Bashford Dean Memorial 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 buccalis (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 119s). 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 25mm. 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 He was unable to trace this nerve to the brain. 479 In his summary (p. 677) he writes: “Der Oculomotorius steht mit dem Trigeminus in Verbindung.” Ziegler (1908) remarks that the 25mm. embryo of Chlamydoselachus studied by his pupil, Brohmer, was cut in “eine luickenlose 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 emphasized 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 nonmedullated 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 VI/ 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 size. 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-mm. embryo of Chlamydoselachus. Ac., nervus acusticus; Cg., ciliary ganglion; D.e., ductus endolym- phaticus; F.Ac., n. facialis acusticus; Ggl.1, Ggl.2, remnants of the ganglionic crest; Gl., n. glossopharyngeus; Gl.v., ventral root of the glossopharyngeal nerve; N.l.v., n. lateralis vagi; Oc., n. oculomotorius; 4, 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); I7., n. trigeminus; Vg., roots of the vagus nerve; Vg.5., the last branch of the vagus; 1.Sp., first spinal ganglion; 1.v., first ventral root (of the occipitospinal nerves); II, II, IV, V, second to fifth gill-clefts. After Brohmer, 1909. Text-fig. 10. 480 1923). 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 superficialis trigemini from that small swelling on the inner side of the Gasserian ganglion from which the ophthalmicus profundus has its origin, would seem to indicate that it is a portio ophthalmici profundi and not a trigeminus nerve, 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 ganglion. The nerve, as I find and define it in Chlamydoselachus, is large, and running forward dorsal to all the nerves and muscles of the orbit, traverses the Text-figure 119. Gangliated roots of fifth, seventh and eighth cranial nerves of Chlamy- doselachus: A, lateral view; B, medial (inner) view. Bucc., ramus buccalis VII; H., ganglion of the truncus hyomandibularis (ie., the true ganglion of the facialis, combined with the acustico-lateralis ganglion); Man.V and Max.V, mandibular and maxillary divisions of the facial nerve; P.L., pars intermedia; Pro., 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. LX VIII. preorbital foramen and reaches the dorsal surface of the nasal capsule, where it immediately breaks up into numerous branches which spread out, fan-shaped, and innervate the sensory organs of the supraorbital laterosensory canal and the supraorbital ampullae, as shown in the figures. As the nerve traverses the orbit a number of branches are sent upward through the foramina supraorbitalia to the related portion of the supraorbital canal. The- maxillary and the mandibular rami of the trigeminal nerve (Max. V. and Man. V. in Text-figure 119) come off separately from the Gasserian ganglion; there is no common maxillomandibular trunk. This condition is somewhat exceptional among 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 of the mouth, as in Acanthias. The mandibular nerve does not supply the large median transverse muscle bridging the halves of the lower jaw in the gular region (Furbringer, 1903; Hawkes, 1906; Luther, 1909; Allis, 1917 and This unique feature has been fully discussed (p. 399) in the section on the muscular system. a a il le 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 variability, 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 119s, after Hawkes. Concerning some interrelations of the fifth and seventh nerves Allis (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-facialis 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 ganglion 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 swelling, 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 primitive 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, isa 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 line 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 branchialis 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 Garman’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, pl. 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 (1.v.) 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.1., Ggl.2.), which he interprets as remains of the ganglionic crest. The more posterior of the two masses has two rootlets. In Heptanchus (Furbringer, 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 26mm. 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 hb. 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 subspinalis 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. br.p., brachial plexus; bu. VII, buccalis of seventh nerve; d.X, ramus dorsalis of tenth; gn., first spinal ganglion; hb., hypobranchial bundle; hmd., hyomandibularis; I].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 superficialis of fifth and seventh; ph.IX, pharyngeal branch of ninth; pl. VII, palatinus of seventh; po.t., post-trematicus of ninth; pr.t., pretrematicus of ninth; sp., spiracle; st.1X, 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 (Furbringer, 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-lateralis 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, pl. 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; No., notochord; S.N., 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.1 and S.h.2). Branch S.h.1, 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 anda 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 ganglion 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. Nervus collector, consisting of longitudinal strands connecting the ventral rami of certain of the spinal nerves, in Chlamydoselachus. I.a.v., lateral abdominal vein; pl.p., pelvic plexus; sp.25,38, twenty-fifth and thirty-eight spinal nerves. From Daniel, 1934, Fig. 224; after Braus, 1898, Fig. 1, Taf. XIII. the dorsal branch of the ventral root could be seen, by the naked eye, running over the dorsal root ganglion, from which it could not be separated; in the succeeding segment the dorsal and ventral roots were joined in the region of the sensory ganglion, 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 from the ventral root which unites with the dorsal root ganglion or with 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 Chlamydoselachus (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 which the twenty-fifth to the thirty-eight spinal nerves take part. The sp.25 Text-figure 123. Nervus collector, connecting the ventral rami of certain of the spinal nerves, in Heptanchus cinereus. 1.a., lateral artery; |.a.v., lateral abdominal vein; pl.p., pelvic plexus; sp. 25,38, twenty-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 gillarch 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, pl. 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 Memorial 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 Raia. 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 Notidanus (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 Allis (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 a portion of their extent as is the case in 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, ampullary pores; end, pore of the endolymphatic duct; iop, infraorbital laterosensory pores; llc, lateral line canal of body; sop, supraorbital laterosensory pores; sp, spiracular laterosensory canal; spr, spiracle. Redrawn after Allis, 1923, Pl. II. 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 (IIc.) 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 Allis; 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 sensory canal system and certain of the pit organs in Squalus acanthias. bu. VII, buccalis nerve; cc., supratemporal canal; dr.X, ramus dorsalis of tenth nerve; hmc., hyomandibular canal; ioc., infraorbital canal; JI., lateral line canal; JI.X, lateral line nerve; me., mandibular canal: mde. VII, external mandibular nerve; os. VII, ophthalmicus superficialis of seventh nerve; po., pit organs; soc., supraorbital canal; st.IX, supratemporalis of ninth nerve; st.X, supratemporalis of tenth nerve. From Daniel, 1934, Fig. 245; after Norris 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, 1934), where the lateral line is an open groove as far forward 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 of the tail. In Squalus (Text-figure 125) the canals are closed excepting in the region toward 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 line canals as Open grooves were found by Dean (1909, p. 252) in the Devonian fossil shark Ctenacan- thus clarkii (Text-figure 127) as well as in 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 various divisions The Anatomy of Chlamydoselachus based on their innervation. Concerning certain sensory canals of Chlamydoselachus Garman (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 line canal in the region of the dorsal fin. C.C.A. 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. Text-figure 126. Portions of open lateral line canals in a living and in an extinct shark. Text-figure 127. Textfigure 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, pl. VI. ; Text-figure 127. Lateral line canal of the fossil shark Ctenacanthus clarki, 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. Hawkes (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 Chlamydo- 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 ands). 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 p; other variations, in the pelvic and caudal portions of the lateral line, are represented in Text-figure 128z. 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 Garman’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, 1917) 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 specialized; third, it possesses some characters that are unique; fourth, it combines (as in the spiral intestine) some characters that are ordinarily segre- 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 afhinities. It is recognized 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 summarized 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 gill-slits 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 gillarch. 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 Memorial Volume the anterior border of the dorsal fin, resembling in form 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 living type of vertebrate” used by Garman (1884.3 and 1884.4) and by Gill (1884.1 and 1884.2) with 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 limitations, 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 links this form with 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 living vertebrates (craniates), and the evidence in support of this view should not be lightly set aside. The very interesting question of the relationship of Chlamydoselachus to fossil forms is one that Iam quite willing to leave to paleontologists. Such studies must remain under the handicap that, in 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 with fossils, have long been known, it can scarcely be expected that the present paper will add much that will be of value to paleontologists. What has been added concerning the “soft parts” serves to confirm the generally accepted systematic relationship of Chlamydoselachus to the notidanids without, however, bringing them any nearer together. While 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 until the Lower Cretaceous Period, are especially interesting because, while their dentition and their general appearance resemble those of the existing Cestraciontidae, their skull 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. Previous discussions of the affinities of the frilled shark to fossil forms have been reviewed at length by Gudger and Smith (1933). Garman (1885.2) was particularly impressed by the resemblance of the teeth of Chlamydoselachus (Text-figure 7, p. 344) The Anatomy of Chlamydoselachus 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 Hybodus (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 generalized 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. tobleri, 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 extinction” (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 CHLAMYDOSELACHUS 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 sinus. 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. Ina 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 Mustelys, 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 lateralis, 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. 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Anz., 33, 561-574, 7 figs. ZiTTEL, K. von 1923 Grundztige der Paldontologie. II Abtheilung: Vertebrata. Munchen und Berlin. (Tooth of Hybodus reticulatus, fig. 93). PLANT e II THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS ALN IO Il THE CRANIUM OF CHLAMYDOSELACHUS, 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; cb, cavum precerebrale; ecb, 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, pl. VIII. Fig. 2. Ventral view of the cranium, natural size. dop, antorbital process; ba, bulla acustica; fic, foramen for internal carotid artery; fso, foramina supraorbitalia; naf, nasal fontanelle; pb, palatobasal ridge. After Allis, 1923, Fig. 11, pl. 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; fic, foramen for internal carotid artery; fo, foramen for nervus opticus; foc, 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; onc, orbitonasal canal; pb, palatobasal ridge; pc, preorbital canal, or foramen; 7, rostrum; sbd, supra-basidorsals; tpf; trigemino-pituitary fossa. After Allis, 1923, Fig. 8, pl. VIII. Dean MemortaLt VoLuME Articte VI, Prate I PAVE aul THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS LAL NIN, II THE CRANIUM AND PORTIONS OF THE VISCERAL SKELETON OF CHLAMYDOSELACHUS 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; fgl, foramen for nervus glossopharyngeus; fic, foramen for internal carotid artery; fo, foramen for nervus opticus; foc, 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; 7, rostrum; tf, acustico-trigemino-facialis recess. After Allis, 1923, Fig. 12, pl. IX. Fig. 5. Lateral view of cranium, with jaw cartilages and hyoid cartilages attached, natural size. i=) 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, ligamentum mandibulo-hyoideum; md, mandibular; ml mandibular labial cartilage; n, nodule of cartilage; naf, nasal fontanelle; orp, orbital process of palatoquadrate; pl, posterior upper labial cartilage; pop, postor- bital process; pq, palatoquadrate. After Allis, 1923, Fig. 7, pl. VII. Fig. 6. Posterior view of the cranium, natural size. af, articular facet for hyomandibular; ecp, ectethmoidal process; es, eyestalk; fm, foramen magnum; guf, glossopharyngo- vagus fossa; pop, postorbital process. After Allis, 1923, Fig. 10, pl. VIII. Dean Memorial VOLUME Articte VI, Prate II i i | t ' LAs JUUL THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS ALANIS JOU THE BRAIN AND PORTIONS OF THE VISCERAL SKELETON OF CHLAMYDOSELACHUS Fig. 7. Dorsal view of the brain and cranial cavity, natural size. a, artery; 0, nervus opticus; ocm, n. oculomotorius; ol, tractus olfactorius; tr, n. trochlearis; v, vein. After Allis, 1923, Fig. 59, pl. XXII. Fig. 8. Dorsal view of the branchial arches, natural size. The branchial rays related to the ceratobranchials have been removed. bbr2, second basibranchial; bbr5—6, fused fifth and sixth basibranchials; bh, basihyoid; cb1, musculus coracobranchialis of the first arch; cbr1, ceratobranchial of the first arch; cbr6, ceratobranchial of the sixth arch; ch, ceratohyoid; ebr1, epibranchial of the first arch; ebr6, epibranchial of the sixth arch; hbr2, hypobranchial of the second arch; pbr5, pharyngo- branchial of the fifth arch. After Allis, 1923, Fig. 35, pl. XIII. Fig. 9. | Ventral view of the median portion of the branchial skeleton, natural size. bbr3, basibranchial of the third arch; cbr6, ceratobranchial of the sixth arch; ch, ceratohyoid; hbr2, hypobranchial the second arch. After Allis, 1923, Fig. 36, pl. XIII. Dean Memoria VOLUME Articte VI, Pirate III LANE, IY THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS PEATE ANY EYE MUSCLES, BRAIN, VALVULAR INTESTINE AND DUCTUS DEFERENS OF CHLAMYDOSELACHUS Figs. 10, 1l 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, pl. LXIX. Figs.13 and 14. Dorsal and ventral views of lateral halves of the brain, showing roots of cranial nerves. II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V, VII, the united Gasserian and buccalis ganglia; VI, nervus abducens; VII b., ramus buccalis; VIIh., truncus hyomandibularis; VIII, the ganglion of the eighth nerve; LX, 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; I.O., inferior oblique muscle; L.I., lobi inferiores; Lin.Lat., lineae laterales or restiform bodies; L.N., Locy’s nerve (nervus terminalis); Oc.1,2,3, first three spino-occipital nerves; Op.S., optic stalk (cartilago- sustentaculum oculi); 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 externus muscle; R-In., rectus internus muscle; R.Inf., rectus inferior muscle; R.S., rectus superior muscle; S.Ob., superior oblique muscle; S.V., saccus vasculosus. After Hawkes, 1906, Figs. 7 and 8, pl. LXIX. Fig. 15. Valvular intestine slit open to show the spiral valve and the thick muscular wall. After Ginther, 1887, Fig. 5, pl. LXV. Fig. 16. Lower part of left ductus deferens (vas deferens) opened longitudinally to show “annular” folds. After Ginther, 1887, Fig. 4, pl. LXV. Articte VI, Prate IV Dean MemoriaL VOLUME PEAMERY THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS Fig. Fig. Fig. 17. 18. = 19) ig. 21. 22. PEER) THE UROGENITAL ORGANS OF CHLAMYDOSELACHUS External (ventral) view of the cloaca and abdominal apertures in a normally developed male. cl, cloaca; po, porus abdominalis; ug, urogenital openings; v, vent. After Ginther, 1887, Fig. 1, pl. LXV. 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. cl. cloaca; po, porus abdominalis; ug, urogenital openings; v, vent. After Ginther, 1887, Fig. 2, pl. LXV. Side view of the ductus deferentia (vasa deferentia) of a specimen with unequal development of the genital ducts. Compare preceding figure, drawn from the same specimen. gl, gland; i, rectum opened; po, porus abdominalis; r, kidney; u, urinary bladder; ug, right, and ugl, left urogenital opening; vd, left, and vd1, right ductus deferens. After Ginther, 1887, Fig. 3, pl. LXV. Ventral view of pelvic fins, myxopterygia and cloacal aperture of a 1474-mm. male. After Ginther, 1887, Fig. C, pl. LXIV. 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-f., longitudinal nerve foramen; p.g., pelvic girdle; 7 lateral radials; Rv. marginal ventral cartilage; T.d., terminal dorsal cartilage; T.v., terminal ventral cartilage. After Goodey, 1910.1, Fig. 22, pl. XLVI. ote view of the pelvic fin and the right half of the pelvic girdle of a male, showing musculature. A., adductor muscle; B., basipterygium; Be.[beta], modified radial; c.n., collector nerve; D., dilator muscle; Fl.e., musculus flexor externus; Fl.i., musculus — internus; I.r., last lateral radial; O., dorsal radial muscles; p.g., pel- vic Bice, Rv., marginal ventral cartilage; S., compressor muscle; Teds terminal dorsal cartilage; T.v., terminal ven cartilage. After Goodey, 1910.1, Fig. 20, plate XLVI. Ventral view of the pelvic fin represented in Figs. 21 and 22, showing muscles. Fl.e., musculus flexor externus; Ra., ventral radial muscles; S., compressor muscle; T.v., terminal ventral cartilage. After Goodey, 1910.1, Fig. 21, pl. XLVI. Articte VI, Prate V Dean MeEmorIAL VOLUME p= ag OS, 7 Si / & Les, WAI THE ANATOMY OF CHLAMYDOSELACHUS ANGIUNEUS Fig. 24. Fig. 25. Fig. 26. Fig. 27. RIP AW EDA THE BRAIN OF CHLAMDOSELACHUS The brain in dorsal view and in transverse sections taken at various levels. Ventral view of the brain of the frilled shark. The brain of Chlamydoselachus in lateral view. Vertical longitudinal section of the brain of Chlamydoselachus. 1, olfactory lobe; 2, nervus opticus; 3, oculomotorius; 4, trochlearis; 5, trigeminus; 6, abducens; 7, facialis; 8, acusticus; 9, glossopharyngeus; 10, vagus. These figures are reproduced from the original drawings by Paulus Roetter for Garman, 1885.2, Pls. XV and XVI. Dean MemortaL VOLUME Articte VI, Prate VI leben, \AUL THE ANATOMY OF CHLAMYDOSELACHUS ANGUINEUS ALAIN YU NERVOUS SYSTEM AND CERTAIN SENSE ORGANS OF HEPTANCHUS AND CHLAMYDOSELACHUS Fig. 28. Brain, cranial nerves and associated sense organs of Heptanchus maculatus, 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; md. V, mandibular division of the fifth nerve; m.n., median olfactory nucleus; med., medulla; mx.V, maxillary division of trigeminal nerve; ol.b., olfactory bulb; ol.l., olfactory lobe; ol.t., olfactory tract; op.l., optic lobe; op.V, ophthaimicus profundus division of the trigeminal nerve; os.V and VII, ophthalmicus superficialis of trigeminal and facial nerves; tl., telencephalon; tn., terminal nerve; y-z, occipitospinal nerves: I, olfactory nerve; II, optic; II, 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 Chlamydoselachus. 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; H.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; L.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.; S.(1,2,3,4,5,6,7,8), the first eight spinal nerves; s.h.(1,2), 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. VU, superficialis ophthalmicus VII; T.H., truncus hyomandibularis; V(1,2,3,4,5,6), the six branchial branches of the vagus; V.G., visceralis branch of IX; Vis., visceralis branches of the vagus; V, VII, the united Gasserian and buccalis ganglia; IX, IXg., the glossopharyngeal nerve and its ganglion; X, Xg., the vagus nerve and its composite ganglion, ae and X.B, dorsal branches of the vagus to neuromasts. The remaining abbreviations are not explained by the author. After Hawkes, 1906, Fig. 1, pl. LX VIII (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, pl. 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; c.a., 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.a., ramus of eighth nerve to ampulla of anterior canal; 7.a.e., famus to ampulla externus; r.a.p., ramus to ampulla posterior; rec., recessus utriculi; 7.1., ramus to lagena; r.n., ramus to macula neglecta; 7.s., ramus to sacculus; 7.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, pl. XLIII, Dean MemortiAL VoLuME Articte VI, Prate VII aoe. — Za AA ast AN Se agen, in PERE : Fre oe COOL 2 ee ee SS 7 (WWD ee a a ie Se ae rear Se Closed iS Ley 1 iy ah act y Fai Ay Hine Alls Pont ORD DEAN MEMORIAL VOLUME ENNCoIAC Jelisleles Edited By EUGENE WILLIS GUDGER Articie VII THE BREEDING HABITS, REPRODUCTIVE ORGANS AND EXTERNAL EMBRYONIC DEVELOPMENT OF CHEAMiDOSERACEHOS, BASED ON NOTES AND DRAWINGS BY BASHFORD DEAN By E. W. GUDGER Honorary Associate in Ichthyology American Museum of Natural History NEW YORK > PUBLISHED BY ORDER OF THE TRUSTEES Issued October 15, 1940 ARTICLE VII THE BREEDING HABITS, REPRODUCTIVE ORGANS, AND EXTERNAL EMBRYONIC DEVELOPMENT OF CHLAMYDOSELACHUS, BASED ON NOTES AND DRAWINGS LEFT BY BASHFORD DEAN By E. W. Gudger CONTENTS ING R'OD UW CTIO NA ee eee te eae arco cree! cs sacl etoe an its ee 525 SIRES SPECIMENS PANDA DHEIRT SOURCE NNN Aa nce ian Ale een ener oS 27) Date IDRARAIES AIio) Ii ANUABSONGSNID, . 5 ono once ened ono uooseunssuaddonuce 529 Viviparity (Ovoviviparity) IN Chlamydoselachus................-.0...00-. 531 BREEDING SEASON OE LEHE LP RIEEEDLO HAR Kanes Slr nr ee aia on) a ee 534 EWAIDENGESER OMETEE| OVARIES pan eae toate ee ere eee ye era acer 534 STAGESKO ESE NIB RSYOSBINEISETEN O55 Rae ea emer Pn en 535 DuRATION OF GESTATION aS OST EOS Ee OO OMA SCROLL AIT GSES EO OL Oa Ga oh fOCOREn Crt ce Sat Eeorc sree eee sie 538 Tue REPRODUCTIVE ORGANS OF THE Mate Chlamydoselachus.................. 541 MyxorTeRYGIA—EXTERNAL ORGANS OF THE MALE..................- 000000 e eee sees 541 Tue REPRODUCTIVE ORGANS OF THE FEMALE Chlamydoselachus................ 542 BIRFTES @) W/AVRITES ROPe eh oy ee ety Tete A HOUR ir ic er PRO ER DPOReae th Oem tH cn le re AG UR ae aa 544 TMMCATUR ETO VARTANAEGGSAN AA eae alee var erieg era Ee eeatate RGR Meson ALI BRE LS ecole 548 VARNAATRURE | OWARTANGE GG Ay eco freee eo CR eT SE NST SEY IDR oe Poe ou Cae se 548 BIRETRS QV TDW CSE toes eee ae ee eae arr aly ECS Pea MSC Re Tee Ure clin aR ar Ste 549 THE WABDOMIN AD © PENINGS i batccra lacie Sct err OIE CHES eps e are ee tinicen ees gee noe Tey Perea 549 SIME SHELTS GUA NDS oe heen c= cnisieceraiecper tage een SRT al ME SAP Salt gah et aah deers oe Bi ee Sa Ney Me 550 FISHES TER USS sete ester eee ee Gee nor oon Te tar Te ch ee Ne ate Ge pene encr ois et eet see 552 RicHTAWTERUSHRUNCTIONAL MEE eee enicee rine Pee SAR a ae Sate ah ue TARE 552 Lerr Urerus SOMETIMES FUNCTIONAL...............-0--+05- ERT ae ALTE eae Te 557 Do Emsryos Receive NuTRIMENT FROM Uterine WALL?.............--- 0-2-2 eee eee 559 Tue Croacar Openincs. PAO ae tek Vegettidt oo cot a eee ROG ge ROR UR 5 IMRT NPN bE 562 Ree a Gene cae meee: Sey eee Artes ees 562 FEMALE REPRODUCTIVE ORGANS OF ene nee anaes AND Wanton: Rae . 564 @VARIES AND) ©viDUCTS OF SOME) FLORIDAU SHARKS) »....05--425 000 0se so snes sss ee eee: 564 OWARIES AND O\nmiiens Ox WANROURIRNB. coo cncnucoeuoucccuccn ceo oanunbnveec ee 565 arESENCAPSUDEDIEGGIOER Chlamydosclachusm =e) ae eee ee 566 ERE TOMDVAL, ESS Oi INsny JOT NAD) EVN, 525664 0ncudonogocuscacodndvendcueuvene sed 567 Normat Etiipsoipat Encapsutep Eccs..............-.-.-..-- FE COT ae Tae ee eee 567 Unusuat Exzipsorpar Eccs with TENDRILIFORM Processes.......... SF ay my ee Preten te seat 569 JANSECLIPDICATIE GG REESE EE eee: NS ised cd Ae EN ned eae eer ChE ee 569 Some Ostone Ferrite Eccs...........-...-- ne: ag ar a ARE MEU ey 6 570 An Etoncate Inrertive (Wind) Ecc..............-..-- EEE Ae ee etre ME OPIS Bee ae 571 IROUNDIECCSIOE CHE MRIDUEDIOHAR Kei saree ene rie Sci cie iets reece 572 Sizes or Eccs or Chlamydoselachus CoMPARED WITH THOsE OF OTHER SHARKS..........-- 573 Sizes or Eccs AND EMBRYOS OF THE FRILLED SHARK.......... Pe et en on Oy ee 573 SizeslOPEGGS/ANDIE MBRYOs|OF)ISURIDI SHARKS eee incieeinieit tei ines isiee 574 SIzEstORIEGGS|OELTHERNIURSE: SETA R Kept St este ne eam et a Ora wa 576 ForMATION OF THE Eco Capsutes oF Chlamydoselachus AND OF Ginelymoscomna | ee ree 578 FORMATION OF TENDRILIFORM PROCESSES... .....0 0: -¢ eee nec deeeee ces Beg a nied Hae sede 579 ExTERNAL EmpBryonic DEVELOPMENT OF Chlamydoselachus.................... Earty DEVELOPMENT Résumé or RESEARCHES ON THE INTERNAL DEVELOPMENT.........-.-2-+-2-02--0 eee e eee eeeeee IDESCRIETIONS OF EMBRYOSIRIGURED eae ene rate es ee eee Tue Avutt Chlamydoselachus An Aputt FEMALE FRILLED SHARK Aw Aputt Mate Chlamydoselachus Heap On ty of THE ADULT SHARK ExTERNAL GILL-FILAMENTS OF Chlamydoselachus ExTERNAL GILL-FILAMENTS OF THE EMBRYO (ANIEMBRYO\OFS IES ONIDEIMETERS 4 ce, says ae ois acts =) = eaten eo eee An Emsryo 15.5 wot. iN LENGTH................ IANJEMBRYOPMIEASURING)2O) NAILETMETERS pee eter tora ete coer Two 25-m™. Empryos—Heaps Onty—Descrisep sy ZIEGLER AND BROHMER INISHIKAW.ANS}3 22MM EMBRYO—— HEAD) ONLYase eee oan eee eee DEAN SIEMBRYO:/ 34 MMINIEENGTH Ac cian ck ieieic sae aie © OC OR OEE Erne eon Aw Empryo oF 39 MILLIMETERS... .... SRE OMA MBRYOZANDILTS YOLKS OAC INI COLOR=E PE eee et en een nny eee NisHIKAWA’s 43-mMM. EmMBryO ON ITs YOLK SAC ............... DEAN'S EMBRYO (OF146 QAILLIMETERS & <=, c= Spo 5 2 cv SS apes oe ees ee ee eee I ee IFIED ORFAC4 52 NEM) SPEC IMENGSIN (A VENSER A Tn VTE Wy oar INISHIK-AW/AGS 5 OzMMep EE MBRY OLONILTS PY OLESOA Cee ee /ANVEMBRYO) OF S45 MILLIMETERS op ooyge enc Py sen tetas en ee ds de era CT a /ANJEMBRYOMMEASURING O59) MILLIMETERS Se ay ee 2 ee eee ar ince eee ee GARMANS! EMBRYOIOF{64) MIDLIMETERS psy Gey ee eee oe DEAN|S EMBRYO) MEASURING 66) MIELIMETERS Sei eee eee eee eee ee (ANS EMBRYO}103 UMMEINS EENGTHi is oes er eee en Oe eee JANI EMBRYOIOBRHL24 MOCETMETERS feo oh5/ f= cus /5).s0c) ccky 3cooees ci Sehr Oe ee tenons ZANTE MABRY O{OEs1// DIMM VANDILES HY OLRIO AC Hen ey errno eT nee Sie va AN TEMBRYO1 85) MM) INVCENGDH Se Wa e an eae eae pe oP eee Reena eee ence ree eee ee ee ACY OUNG ERTELED SHARK! 240) MOM LONG otc Pi worl aa eee oS Sapa ZAV390-aasts) Chlamydoselachusiines NATURAL COLORSERE EE Soe eee reesei eee THE YOLK SAG CIRCULATION: Ae ee See oe ee ee ae eee ae ee WITELEINE | @iR CULATION OF-EHE SG O2MMa EMBRYO meee aaerr te eee eae ean eee SYOLK- SAC) CIRCULATION) OF-THE(43200Ma, OFECIMEN See ee et MiITEELINE/ CIRCULATION] OFTHE 07MMa EMBRYO Pee ee nee WOEK—SAC] CIRCULATIONIOR THEM / 54 Meie) RISE pee ee ee WiIITELLINE: CIRCULATION OBETHE O00 zsN04, LAR Kae ee ee THE BREEDING HABITS, REPRODUCTIVE ORGANS, AND EXTERNAL EMBRYONIC DEVELOPMENT OF CHLAMYDOSELACHUS, BASED ON NOTES AND DRAWINGS LEFT BY BASHFORD DEAN By E. W. Gupcer 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 certain 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) philippi. 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. Ihave been unable to trace these specimens, but other lots came to him and were deposited in the Dean collection in the zoological 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. 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 I, 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 CHLAMYDOSELACHUs 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 intro- 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 little 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, | 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 Si] 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 isa 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 of 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. 139 5 lo 15° 20 25) 30 35° 40) 45 7 aes Lr T T T =F ot T Ua T T 26} GULFo TOKYO ‘ipa XH > VY oa Va z CASS Some oe PENINSULA Odawara Maye b 2 > see oe W280 MMe YOUNG Eleterodontius) ya pomicuss asa se aye ee eee cee FE XERINAT AN DEINDERNAT | Gili) hIPAMENDS.) 6c es ier tent eicr ee e IDENARUOMMIsINAe Oi Weis Issarets Loo a dena be oarococupesogobnsongnc coco scudans BIBEIOG RABE Ure Hemet me iene ties eevee tal ene s WM ncaly So ale ish centres teamerccs eatyraiellsyceinteh THE HETERODONTID SHARKS: THEIR NATURAL HISTORY, AND THE EXTERNAL DEVELOPMENT OF HETERODONTUS (CESTRACION) JAPONICUS 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 Cestracionti- 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 Haswell’s brief account (1898) of the blastula and gastrula of H. phillipi. 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 difficult 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 653 139° 5 10" 1s° 20° 25 30 35° 40° 45° 50° 1 1 . y . —— — . GULF o TOKYO 20 Odawara Maye SAGAMI BAY Atami Maye CENTRAL BASIN a : 5 ae 5 OF THE Bo. SAGAMI SEA Sig ey [oyna € : tings. ema pray 3 35° 5 On tA ° sve SCALE IM KILOMETERS. erapnase67869 551 ss” 1 oe ——— 4 —————— Ee he 4 4 139 5 10 15 20 25 30° ELF 4O 4S 50 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, 1933, 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 TeemHES 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 frst 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-five 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 embryolog- 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. Tt 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, probably 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 light 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. In 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 ““Yatsu drawn.” Whether these drawings were preliminary 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 “Yatsu’”’. 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 living 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 living 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,” published in 1901. There is intrinsic evidence that the manuscript under con- sideration was written 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 organization 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-failing 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 recognize 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. HETERODONTUS 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. phillipi (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 Dumeéril (1865, pp. 423-426); Maclay and Macleay, (1879, pp. 303 and 309) and Garman (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 Duméril 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 Garman (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 Duméril 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: HETERODONTUS (Blainville) Port Jackson Shark (in genus Squalus). Phillip, 1789, Voyage to Botany Bay, pp. 283-284, pl. Heterodontus. Blainville, 1816, Bull. Soc. Philom. Paris, 3. ser. 3, p. 121 (not Heterodon Latreille, 1802). Les Cestracions. Cuvier, 1817, Régné 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. Duméril, 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; Dumeéril, 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), Duméril (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 NAMES—BULLHEAD SHARKS 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 writer 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 Whitley (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. BULLHEAD SHaRKs.—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., Hybodus) included by Bridge in the family Heterodontidae, are now assigned toa separate family, the Hybodontidae. The fact that the common name Bullhead Shark seemingly applies 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 name Bullhead Shark is appropriate for all six species of Heterodontus. Fremin- ville’s drawing (1840) of H. quoyi, which shows a small head, is inaccurate. A better drawing 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 Hybodus hauffianus 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 Hybodus, in the region dorsal to the bases of the pectoral fins. This feature is not represented in some drawings of Heterodontus; but it is shown in Garman’s outline drawing of an adult H. phillipi (1888, Fig. 1, pl. 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 25and 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, pl. 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. Garman’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. Garman writes: The living 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 lip, both cuspidate teeth and grind- ers, five gillopenings 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 Garman 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 Garman calls Centracion, is characterized 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. francisci, 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 francisci, have been described in detail by Allis (1919, pp. 158-164 and Figs. 6 and 7, pl. I. A vestigial sixth branchial arch was found by Hawkes (1905) in two species of Heterodontus—phillipi and francisci. 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 Gunther) 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 recognized 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. Garman’s classification agrees, in the main, with that of Maclay and Macleay (1879, 1884 and 1886) but differs from that of Regan (1908). GARMAN’S KEY TO THE SPECIES OF CENTRACION (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. SpotsmblackssmallRiccattered enn een nina a eae aee 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. Band sitransversessia ci Ow. ree elaine reaee 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). Bandsitransyerse broad pape eer tee ie ae eee eran: 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. HETERODONTUS PHILLIPI BLAINVILLE This, the Port Jackson Shark, is the best-known species, and for half a century it was the only species recognized. 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 Lacépede (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 muzzle it was called the Bulldog Shark by Victorians. SavilleKent (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, pl. facing p. 283. voyage is reproduced here (in Text-figure 5). For nearly a century this drawing remained the best portrait of Heterodontus phillipi. 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 SavilleKent (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 Heterodontus (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 unlike that ofany other drawing of Heterodontus phillip: known to me, and the shape of the ventral lobe of the caudal fin is unlike that shown in all other drawings of specimens belonging to the genus Heterodontus. It is not necessary to reproduce this figure, since it was evidently drawn from a dried and distorted specimen. Miller and Henle’s full-length colored portrait (1841, pl. 31) labelled Cestracion phillipi 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 Muller and Henle (but omitted from my Text-figure 21) had never, they believed, been seen in any adult specimen of the Port Jackson Shark. Further, in 1884, Maclay and Macleay stated that Miller 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. At the present time one can scarcely doubt that Muller 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 Text-figure 22, page 690. Striiver (1864) has contributed what appears to be an accurate drawing of a badly posed specimen of Heterodontus phillipi. Perhaps this fish had been hardened in a laterally Text-figure 6. A full-grown male specimen of the Port Jackson Shark, Heterodontus phillipi, 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, Fig. 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, pl. 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 size 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, pl. 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, pl. 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 one-half 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 different 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 Hybodus. 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, pl. 22. 670 Bashford Dean Memorial Volume Jaws anp TeetH.—Goodrich (1909) contributes an outline drawing of an in complete skull of Heterodontus phillipi, 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 phillipi. Whether the figure represents an upper or lower jaw is not stated, but apparently it is a lower jaw. After Phillip, 1789, pl. facing 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, pl. 47) has figured the jaws of Heterodontus phillipi 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 represented in Striiver’s drawings (1864). As in Struver’s figure, the lower jaw is shorter than the upper, and is more obtuse in front. Text-figure 11. Teeth of an adult Heterodontus phillipi: A, upper jaw; B, lower jaw. After Maclay and Macleay, 1879, Figs. 16 and 17, pl. 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 phillipi about 761 mm. (22.1 inches) long: A, from the upper; B, from the lower jaw. After Maclay and Macleay, 1879, Figs. 18a and 18s, p. 24. Text-figure 13. of anterior (cusped) teeth om the upper Dentition of a very young (recently hatched) jaw than on the lower (as in Struver’s female Heterodontus phillipi about 225 mm. figure). In another specimen Maclay (8.8 inches) long: A, upper jaw; B, lower jaw. counted 34 rows of teeth on the upper After Maclay and Macleay, 1879, Figs. 14 and 15, pl. 24. jaw and 31 on the lower. The largest number of rows of teeth noted by Maclay was 36 on an upper jaw; the largest number on a lower jaw is not stated, but we infer that it was less. In Maclay’s figures, as in Struver’s, the anterior teeth of the adult have only one cusp each; but in Maclay’s figure these are more 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 phillipi 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. 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 size. C, mouth widely opened, to show the similarity of dentition above and below. After McCoy, 1890, pl. 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 front rows very small, acutely tricuspid when young, simple and with obtusely triangular cusp in middle age, blunt and hexagonal when old; more posterior teeth large, oblong, longer than broad, flattened, arranged in oblique, spiral rows on each side of the jaw, the anterior and posterior ones smaller than those in the middle.” His figure of the lower jaw (my Text-figure 14s) 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, with eight rows, on each side, of posterior grinding teeth, make a total of 27 rows in this lower jaw. Textfigures 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 148. The upper jaw, shown in Text-figure 14c, likewise has 27 rows 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. Garman (1913, Figs. 4 to 6, pl. 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) 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. Garman’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. Garman states that the ridges on the molars of younger specimens become less conspicuous with 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 phillipi, one may state that all the descriptions and drawings emphasize 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 jaws” 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 alike 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 difference 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. HETERODONTUS 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. 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, pl. 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 Memorial Volume anterior views but these are lacking in the Japanese drawing reproduced as my Text-figure 15. Maclay and Macleay state that the dorsal fins are very falcate. This feature is per- haps exaggerated in their drawing, which was made from a preserved specimen; it is more moderate and more life-like in the Japanese drawing. In the latter figure the anterior margin of the pectoral fin is opposite the fourth gill-slit, while in Maclay and Macleay’s figure it is opposite the second. Tue TretH—According to Maclay and Macleay (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. HETERODONTUS QUOYI FREMINVILLE Examples of this species (Text-figure 16) have been taken off the western coast of South America, specifically at the Galapagos and Lobos de Afuera 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 Cestracion pantherinus. After Valenciennes, 1846, Atlas (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 was described and figured by Evermann and Radcliffe (1917) who named it Gyropleurodus peruanus. Of this fish they write: “The species appears to be most closely related to the poorly described G. quoyi, but differs in coloration, in insertion of anal, and relative size 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 variation 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 peruanus. 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 Duméeril (1865), Gunther (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 Garman (1913) described at least one new specimen (a female taken at the Galapagos 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. Gar- man’s female specimen measured 18 inches long. Garman states that its body is rather stout as compared with a specimen of H. zebra of equal length. Some passages in Garman’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. Garman 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 Garman 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 Memorial Volume Authors agree that in H. quoyi 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 gill opening is more than twice as “wide” as the hindmost. Freminville states ‘that the skin is entirely shagreened, is colored a ruddy-brown and is everywhere strewn with dark-brown spots, generally round. Concerning the coloration of H. quoyi Garman (1913) writes: Back rusty-brown, yellow below, with scattered spots of black, from mere specks to spots as large as the orbit or larger, over the entire body and fins. Commonly 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 lies 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 was collected on January 5, 1920, by Dr. R. C. Murphy, on the Lobos de Afuera Island (off the coast of Peru) where it was washed 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 published drawings 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 sufficiently 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 fold of the skin 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-slit is about twice the length of the fifth. The origin of 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 toa 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 unlikely 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 “‘fve 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, pl. 47. JAws AnD TeeEtH.—In Garman’s figure (1913) 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, pl. 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 Garman’s drawings the upper jaw has 11 transverse rows of anterior (cuspidate) teeth and 8 rows (4 on each side) 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. HETERODONTUS FRANCISCI 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, pl. III); Jordan (1905, vol. 1, Fig. 315); Daniel (1934, Fig. 17); Kumada and Hiyama (1937, pls. 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. francisci 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 size are scattered over the entire body including the fins, and the supraorbital ridges differ from 682 Bashford Dean Memorial Volume Textfigure 18. Lateral view of a 540-mm. (21-inch) female specimen of Heterodontus francisci Girard. After Kumada and Hyama, 1937, pl. 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-figures 18 and 19, after Kumada and Hiyama (1937). 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 of Heterodontus francisci Girard, shown in lateral view in Text-figure 18. After Kumada and Hyama, 1937, pl. 44. The Embryology of Heterodontus japonicus 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. C. 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 gillregion 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-slit 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 4mm. 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 Garman’s H. japonicus). The hind margins of both dorsals are concave. The base of the anal fin is slightly more than its 68+ Bashjord Dean Memorial Volume length 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. Jaws anp TreTH—In his “Atlas” (1913) Garman figures teeth and jaws of very young, medium-sized and adult specimens of H. francisci. In his figure showing the jaws in lateral view, they bear a close resemblance to those of H. quoyi (my Text-figure 17). In Daniel’s figure of the skull of H. francisci (1915, Fig. 6, pl. III) 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, pl. 47) for H. phillipi. One infers that these differences are individual and not specific. Maclay and Macleay (1879) state that the front teeth of H. francisci are strongly tricuspid, those at the sides are longitudinally ridged. Garman (1913) wnites 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 female specimens the anterior teeth are tricuspid. COMPARISON OF HETERODONTUS QUOYI AND FRANCISCI In my descriptions of the specimens of H. quoyi and H. francisci belonging to the American Museum of Natural History, some statements were made concerning the form oi 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 In this connection one should bear in mind that the female specimen of H. quoyi is presum- TABLE I SOME MEASUREMENTS IN MILLIMETERS OF FOUR SPECIMENS OF HETERODONIUS | Species H. quoyi H. jrancsa Female | Male Female | Female 527 372 705 365 118 6 | 138 S7 & 41 86 67 80 48 110 75a 30 is 34 | 4 S 17 14 eal | 25 12 ) o. | 28 is 42 32 of anal $n and veniral Jobe of caudal... ...-....-...---.-- 34 23 43 33 | j ably adult or nearly adult, while the male of the same species is decidedly young. The larger specimen of H. francisci is known to be adult. I may say at once that the two species are readily separable. In certain features of The Embryology 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 H. 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. francisci, 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 full-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. zebra 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. Ina 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 size 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 life, 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-like 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 frm 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. HETERODONTUS 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 Text-figure 20. A female specimen of Heterodontus galeatus Gunther 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. i 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 ina 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 gillopening 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 finis 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. phillipi 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 Wollongong and Kiama were of the latter species [galeatus|, those of our commoner form (phillipi) being either rare or quite unknown”. TrEeTH.— Waite (1899) published 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, pl. 25) and attributed to H. galeatus, were not of that species. The differences in the figures of the posterior teeth are very marked. In Waite’s 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. HETERODONTUS JAPONICUS MACLEAY For many years, specimens of Heterodontus collected in Japanese waters were classi- fied as Cestracion (Heterodontus) phillipi, the Port Jackson Shark. Thus the specimens figured and described under this name by Muller 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. zebra, 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: Nekozame (Tokyo market; Misaki; Sagami); Sazaewari (Prov. Shima; Osaka; Prov. Tosa); Sazaiwari (Nagasaki). It is called ““Nekozame” in the volume entitled ““TIlustrations of Japanese Aquatic. .. Animals” (1913) elsewhere referred to. Dr. Dean calls it Nekozamé. A synonymy of scientific names follows: HETERODONTUS JAPONICUS Macleay Cestracion phillipi. Miller and Henle, 1841, Plagiostomen, p. 76, pl. 31. Cestracion phillipi. Siebold, 1850, Fauna Japonica: Pisces, p. 304. Heterodontus zebra (not Gray). Bleeker, 1854, Verh. Bat. Gen., 26, 127. Cestracion phillipi. Brevoort, 1856, Perry Expedition, vol. II, Fig. 2, pl. 12. Cestracion phillipi var. japonicus. Duméril, 1865, Elasm., p. 426. Cestracion phillipi. Ginther, 1870, Cat. Fishes Brit. Mus., vol. VIII, p. 415. Heterodontus japonicus Mcl. Maclay and Macleay, 1884, Proc. Linn. Soc. New South Wales, 8, p. 428, pl. XX. Heterodontus japonicus Mcl. 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 (Duméril). 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 Duméril. Jordan, Tanaka and Snyder, 1913, Journ. Coll. Sci., Imp. Univ. Tokyo, 38, Art. 1, p. 8. The Japanese Bullhead Shark, Heterodontus japonicus, was first figured and described by Miller and Henle (1841). Their specimen and figure were labelled ““Cestracion phillip’. At the time when their monograph was published, only three species of Heterodontus (Cestracion) were known: H. phillipi, H. zebra 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. Miller 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 japonicus Macleay, length not recorded. The original figure is in color and is labelled Cestracion phillipi. After Miller 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 Burger 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 Textfigure 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 phillipi. After Brevoort, 1856, pl. XII. 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, pl. 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 size of Brevoort’s Text-figure 24. Dorsal view of the 406-mm. (16-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, pl. 20. 692 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 fullgrown. 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 Muller 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-fhigure 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, 1884, Fig. 3, pl. 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. phillipi), 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. Ameng 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 Text-figure 26. Dentition of Heterodontus japonicus: A, upper jaw; B, lower jaw. Drawn from the young female specimen, 406 mm. (16 inches) long, shown in Text-figures 23 to 25. After Maclay and Macleay, 1884, Figs. 4a and 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 drawing of this species. For these reasons this figure is not reproduced here. The legend states that the species is not good for food—contrary to the statement in Siebold’s “Fauna Japonica”. “De gustibus non est disputandum’. TeetH.—In Maclay and Macleay’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 K typically fve-cusped. In the upper jaw, the number of teeth in the central row is eight (one is not visible in Text-fgure 26). In the lower jaw, the transition between anterior (cuspidate) and posterior (grinding) teeth is very abrupt; in the upper jaw it is more gradual. In making comparisons with the teeth of other Hetero- dontid sharks, it should be borne in mind that Maclay 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, which contains also a concise summary of the main course of develop- ment of the teeth of the entire genus. AFFINITIES 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. Hybodus hauffianus E. Fraas: skeleton, with skin (shagreen) outlining the entire body which is about 2240 mm. (88 inches) long. Upper Lias; Holzmaden, Wurttemberg. 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 1 Dorveahs Xonf: Gace agen ohle “if Lp Mp Wh CZ ULM, fhe Ny Hi \ NAVAN Mii Ze sss dadesdastusnsssbissglTTes W Wr VANVAN Vv vane NAY WS W Anaff'loss0 Caudatf tore ANN WwW ee uN Seton Lessa D3 ccRerftoss € Text-figure 28. Reconstruction of the skeleton and outline of the body of Hybodus hauffianus E. Fraas, based on a specimen about 1220 mm. (48 inches) long. Upper Lias of Holzmaden, Wurttemberg. 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 ““Grundztige der Palaeontologie”’, Zittel (1911) listed in his family Cestraciontidae seven genera including Cestracion. Eight other genera, including Hybodus 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 Hybodus 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 CESTRACIONTIDAE Teeth as in Hybodontidae. Vertebral centra cyclospondylic 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 rows of posterior denticles. Anal fin with- out spine. Tail heterocercal. Paired hooked head spines often present. Devonian or Lower Carboniferous to Cretaceous. spines. Lower Jurassic to Recent. Several of the characters listed 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 Cestracionts, leading to the common name “Bull head Sharks”, find a counterpart in fossil forms like Hybodus (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 Heterodontus (Daniel, 1915, Fig. 8, pl. IV) and Hybodus (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 delabechei Charlesworth; B, three associated anterior teeth of Hybodus reticulatus Agassiz. After Woodward, 1889, Part 1, pl. 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 size 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, pl. 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, Paleosbinax 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 Hybodus), 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 Hybodus hauffianus accord- ing to Jaekel (my Text-figure 28). It will suffice here to attempt a comparison between the skulls of Heterodontus and Hybodus, 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 phillipi by Huxley (1876, Fig. 8) and that of H. francisci by Daniel (1915, Fig. 6, pl. 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 size; 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 Hybodus, according to Woodward (1916), the pterygoquadrate (palatoquadrate) is not articulated with the preorbital region of the cranium (as it is in Heterodontus). In Hybodus hauffianus, according to Jaekel (1906), the suspension of the jaws is amphistylic (my Text-figure 28, page 695). The skull of Hybodus dubrisiensis, 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 Hybodus basanus, as described by Woodward (1916), there is no articulation between the palatoquadrate Text-figure 32. Text-figure 33. Incomplete skulls of Scyllium and Heterodontus, illustrating methods of suspension of the jaws. Textfigure 32. The skull of Scyllium, illustrating the hyostylic method of suspension of the jaws. a., auditory capsule; ch., ceratohyal cartilage; cr., cranium; ep., ethmoid process; h., hyomandibular branch of facial nerve; hm., hyoman- dibular cartilage; 1., labial cartilage; mk., Meckel’s cartilage; na., nasal capsule; g., quadrate region of the palatoquadrate cartilage; r., Tostral process; sp., spiracle. After Goodrich, 1909, Fig. 59c. Text-figure 33. Cranium, jaws and hyoid arch of the Port Jackson shark, Heterodontus phillipi. a., auditory capsule; ch., ceratohyoid; ea., ethmoid articulation; hm., hyomandibular; 1., labial cartilage; mk., Meckel’s cartilage; na., nasal capsule; nc., nasal cartilage; g., 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. 58a. The Embryology of Heterodontus japonicus 701 and the cranium. In the skull of Hybodus basanus (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 Hybodus basanus Egerton, a little less than one-half natural size. The deeply shaded portion is the orbit. cr., cranium; hy., hyomandibular; 1., 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. 3s. 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 Hybodus 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 Hybodus dubrisiensis is typically amphistylic, and with Jaekel’s interpretation of the skull of Hybodus hauffianus (my Text-figure 28); but it does not harmonize with Woodward’s later statement (1916) that the pterygoquadrate (palatoquadrate) of Hybodus basanus “can scarcely have articulated with the postorbital prominence of the cranium”. It seems remarkable that species of the same genus should differ ina manner so important; but if the skull of Hybodus basanus 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 Hybodus and the present-day Heterodontus! In view of the well-known difh- 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 from 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 within 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 families. With respect to families other than the Hybodontidae, the Het- erodontidae occupy a relatively isolated position. Woodward (1921) states that the Hybodonts are a generalized group from which several later families 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 Hybodus, 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 living Heterodonid sharks. SEXUAL 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 (phillipi, japonicus and galeatus) have been described and figured by LeighSharpe (1922 and 1926). Some marked specific differences in this organ are noted. According to Dean’s notes, Heterodontus japonicus shows 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-grown, 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 believed that the males could invariably be distinguished, in the well 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 mm. in diameter, the next largest one about The Embryology of Heterodontus japonicus 703 30mm. 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 recognized as an ovary except by position and relations. The epigonal organ is much larger—dquite 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 mid-line 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 mid-line 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 japonicus. 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 phillipi are those of Duméril (1865), reproduced as my Text-figures 36a and 368. 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 Dumeril’s 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 Text-figure 36. you have it, it wriggles away sideways and Egg case of the Port Jackson shark, Heterodontus refuses to give any hold for jaws or palate. _phillipi: A, entire specimen; B, egg case with interior In fact, a more slippery or guilefulegg was exposed. According to Duméril the egg case is about never yet devised by nature’s unconscious 130 mm. (5.1 inches) long. ingenuity. After Duméril, 1865, Atlas, Figs. 2 and 3, pl. 8. 706 Bashford Dean Memorial Volume Text figure 37. ules of Heterodontus phillipi and H. galeatus: A, egg case of H. phillipi; B, egg case of Fgg cap nm of H. phillipi is about six inches (152 mm.) long; that of H. galeatus 4.5 inches (114 mm.) long— presumably without the tendrils. After Waite, 1896, pl. 12. The only adequate account of the egg capsules of Heterodontus phillipi is that of Waite (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, Waite’s descriptions are here quoted in full. The egg cases of both species [phillipi and galeatus] have the following points in com- mon: All parts are composed of a flexible horn-like substance of brown color. The body consists of a chamber, shaped like 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 basally, 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 six 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 37s] 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 oblique striae corresponding to the direction of the spirals, and resembling 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 374 and 37s]: 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] galeatus [Text-figure 37c]: Of smaller size; about four inches anda halfin 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 peculiarity, 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 phillipi 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. 708 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.1). The size varies, depending probably on the age of the parent. I haveno definite information concerning the egg cases of H. zebra 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 Heterodontus 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, pl. VII,) varies considerably in size: 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 toa 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, pl. 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 asa 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 HETERODONTUS 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 phillipi is found in littoral waters to a depth of 94 fathoms. According to Dean’s notes, Heterodontus japonicus (called Nekosamé 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 fins 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 ““Nekosamé”’ 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 Tse ame 20, tufts of sertularian hydroids; also there View of the wide-open mouth of a new-caught Hetero- were half a dozen leechesintheneighbor- dontus, presumably japonicus. Note the large grinding hood, some specimens measuring about teeth in the posterior part of the roof of the mouth. 2!5 inches in length. 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 (Heterodontus) 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 2 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 Goane 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. Ina 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 Embryology 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. phillipi) 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 414 to 41D). When the fish was first examined (Text- figure 414) 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 418). 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 41p) the third turn of the frill. At this time the egg slipped out, and Dean noted that in the final rapid phase of 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 41p 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. Ecces Founp 1n 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 “Nekosamé” 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 715 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 little 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, \ Sup Mh... I A \\ NK \, NNR Text-figure 42. Reconstruction of a typical “nest” of 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. Ny \Y From a drawing by Bashford Dean, whose initials appear in the lower right-hand corner. 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 japonicus 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 egg 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 498 (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 mollusks, especially Haliotis. They have thus an excellent training, for if they can detect these protectively colored limpets, they can observe closely enough to collect shark eggs; moreover they are in the habit of examining fissures between the rocks, and they frequently 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 peculiar 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 ale) 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 fertilization 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 ina blastula stage at the time of deposition. Heterodontus japonicus, like H. phillipi, 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. phillipi 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 it may extend over a period of two years, at an average water temperature of about 65° F. He writes that, in his estimate of the rate of development, he was aided by the fact that eggs found in any one season are usually in about the same stage. This latter statement may need further qualification. Some generalities bearing on this subject are recorded under “Breeding Season” on page 712 of the present article. It is there stated that in the vicinity of Misaki spawning occurs throughout the year, though the special spawning season is evidently the month of March. From the original data contained in Dean’s notebook, it appears more likely that spawning reaches its height during the month of April and continues at a rapidly reduced rate during the months of May and June, after which it is almost negligible. As might be expected, there is an increasing range of variation in the stages collected during each month after the first month of spring. Hatching has been observed in April, at which time the young shark is presumably at least a year old. In Dean’s manuscript there is an outline for a time scale in which it was intended to give the stage of development that predominates in each month, by reference to Balfour’s stages in Pristiurus and other sharks. Unfortunately, the spaces left for the letters indi- cating the stages have not been filled in. There is also a series of diagrams or outline drawings representing developmental stages from the time of spawning to the time of hatching. All excepting the last two (which are outlines copied from Figures 82 and 84, plate VII) are reproduced as my Text-figures 43 to 45. Two of the original drawings are annotated with the names of months. Fortunately these are drawings representing stages for which data would otherwise be lacking. In the legends for Text-figures 43 to 45, I have specified the month or months in which each stage seems to predominate according to the information at hand, but we can be fairly certain only for the months of April, May and June. Dean records that a total of approximately 200 embryos of Heterodontus japonicus were collected for him at Misaki. In his notebook there is a table giving individual records for 135 living embryos collected during April, May, June and July (up to July 6 only). This table is dated at the top, in Dean’s handwriting, “Dec. 15, 1904”. It is probable that it does not contain any entries subsequent to this date, for all the entries are in chronological order and there are no gaps in the series affording space for further entries. We know that Dean was in Japan (though not continuously at Misaki) from July to October in the year 1900; March to July in 1901; and June to October in 1905. The Embryology of Heterodontus japonicus 719 During the season of 1900, the work was of a preliminary nature; considerable time was spent in exploring the sea bottom in search of favorable localities for collecting. Since the table in Dean’s notebook contains no entries later than July 6, none of the entries could apply to specimens taken during the summer of 1900. Therefore it seems likely that all the entries in the table apply to one season only; the spring and summer of 1901. How- ever this may be, we have no individual records for embryos collected earlier than April nor later than July 6 in any year, despite Dean’s statement that collecting was carried out for him “at various intervals throughout the year”. It is known to Dean’s colleagues that collecting for him was carried on at various times during his absences from Japan. That some records are missing is obvious. I have found no records for individual embryos aside from those in Dean’s table. The missing records include all stages over 35 mm. total length, excepting a few newly hatched. Text-figure 43. Diagrams representing stages in the early development of Heterodontus japonicus. A, blastula stage shortly after deposition of the egg, which occurs chiefly in March and April. The egg is drawn as seen from above, with the upper pole, which Dean calls the animal pole, in the center. The germinal disc appears near the equator in the upper part of the figure. Band C, stages in gastrulation and early embryo-formation found most frequently in May. From drawings left by Bashford Dean Of the 135 embryos listed by Dean, 14 were taken in April, 59 in May, 20 in June, and 42 in July (first week only). This distribution does not quite accord with Dean’s statement, recorded in his manuscript, that ““The divers brought in the maximum number of eggs during April and May”, unless some records for April are missing. From the original records it appears that most of the 14 eggs collected during April were in late cleavage, or blastula, stages (Text-figure 43a). This, according to Dean, implies that the eggs were newly spawned. A very few had reached an early gastrula stage, and (significantly) one was in the hatching stage. During May, a great majority of the 59 eggs collected were in gastrula stages (Text-figures 438 and 43c), but there was a sprinkling of eggs in both younger and older stages. A few yolk sacs bore embryos old enough to perform wriggling movements. In June, with only 20 embryos, the range of 720 Bashford Dean Memorial Volume Text-figure 44. Outlines representing stages in the early development of Heterodontus japonicus. The stages shown in A and B are most abundant in collections made in June; the stage shown in C is probably representative of the month of July. In A, the extent of the area vasculosa is indicated by dotted lines; in B and C, the principal blood vessels are represented by solid lines. From drawings left by Bashford Dean. variation was greater: there were embryos of all stages from late cleavage to one of 31 mm. total length. The average condition was somewhere between the stages shown in Text- figures 444 and 44n. It should be noted that by this time the average condition no longer represents accurately the rate of development of eggs spawned in April, on account of the lag occasioned by continued spawning. Of the 42 eggs taken in July, the majority were collected on July 3 and opened the same day; the others were taken on July 4 and opened on July 6. Here, there are surprising numbers of gastrulae and of slightly later stages, which can hardly be considered as representative of this month; but there are twelve embryos ranging from 15 to 35 mm. long. For July as a whole we have no adequate data indicating the average stage of development, but in view of what follows we assign Text-figure 44c to this month. The original drawing reproduced as Text-figure 45 bears the annotation ““Aug‘Sept’. The next later stage, represented by Text-figure 453, we assign to October because the following one, portrayed in Figure 82, plate VII, is marked, on the original, ““Nov-Dec”’. The newly hatched young, in dorsal view, is represented by Figure 83, plate VII. A slightly older specimen, in lateral view, is portrayed in Figure 84, plate VII. In his manuscript Dean states: “In capsules that have long been incubated, I have found in April the only stages where the young is about to escape from the capsule”. He records also that “in a single instance the act of hatching was observed”. This event took place early in April, and is described on pages 709 and 753 of the present article. It is important to note that this specimen had been collected only a few days previously. The young shark at hatching is said by Dean to measure about 7 inches (180 mm.) long. As indicated by the original notes, this measurement refers to the single specimen of H. japonicus observed in the act of hatching. The Embryology of Heterodontus japonicus 721 Dean states that at first sight his list of embryos of various sizes seems to yield reason- ably complete evidence that the entire term is twelve months or thereabouts. On the other hand, he realizes that a weak spot in the evidence lies in the fact that the series of later stages is not complete. He is not sure that stages such as those assigned to August- September, October and November-December are the dominant ones for the months that have been suggested. Specimens in these stages are not at all common, and the range of size has become so varied that one cannot tell whether a stage such as the one represented in Text-figure 45. is really the sequent of the one portrayed in Text-figure 45a, or is much older (i.e., from an egg which was deposited, say, in September of the previous year). Development is probably much slower during the winter months. The age of the embryo represented in Figure 82, plate VII, which is hardly less than seven or eight months, might be 14 to 20 months. And at hatching the embryo, which can hardly be less than 12 months old, is possibly aged 20 to 24 months. The only direct observations on the growth rate are not in favor of the view that the incubation period greatly exceeds one year. A late embryo in its opened capsule was placed in an aquarium on August 10. It measured 45 mm. in total length. On October 5, that is, within a little less than two months, it had attained a length of 110 millimeters. This growth is so extraordinarily rapid (for a shark) that if the same rate were continued, estimating roughly an increase in length of 30 mm. each month, the young fish would have hatched by December or January (the young at hatching measure about 180 mm.). This would make the entire period of incubation, assuming that the egg was spawned in April, from nine to ten months. But the experiment was probably not conducted under strictly natural conditions. The temperature of the aquarium must have been considerably higher than that of the sea bottom; and if the egg, after opening of the capsule, was left uncovered the embryo may have been better aerated than it would have been if the capsule Text-figure 45. Outlines representing stages in the development of Heterodontus japonicus. A, stage collected mainly during August and September; B, stage presumably most abundant during the month of October. From drawings left by Bashford Dean. 22 Bashford Dean Memorial Volume had not been opened. Under these conditions development must have been almost abnormally rapid. As a somewhat parallel case, I note that embryos and larvae of the amphibian Cryptobranchus allegheniensis, kept during winter at moderate temperatures in a basement, developed much more rapidly than embryos and larvae of the same species left in their natural environment—in cavities under rocks in a stream often frozen over. Much of the evidence here presented is complicated by the fact that egg laying may occur at any time of the year, though most often in spring. Moreover, it is obvious that much variation in the rate of development is to be expected because of differences in temperature, seasonal and otherwise. We have Dean’s statement that eggs were col- lected, in one instance, at a depth of 28 feet, and that Heterodontus japonicus is known to inhabit depths varying from 3 to 20 fathoms (18 to 120 feet). At the maximum depth the water is presumably much colder than it is near the surface, or in a laboratory aquarium. Aeration of the eggs is another factor to be considered. An egg exposed to water cur- rents, particularly an offshore current, is presumably better aerated than one shut off from such currents. Lacking adequate data, it would be rash to attempt to estimate the amount of variation in the rate of development due to environmental causes, but it must be considerable. GENERAL MODE OF DEVELOPMENT This subtitle is inserted mainly to afford an opportunity to introduce at this point Dean’s evaluation of his results from the study of the embryology of Heterodontus japoni- cus, and his hopes for future accomplishments, in his own words taken from his brief and very incomplete manuscript: Heterodontus, although separated from its nearest genera during long ages (at least since the earliest Mesozoic), exhibits a plan of development not differing greatly from that de- scribed among sharks of the present time. The egg is about the same relative size, its en- velopes are similar, its early development follows the same course, its embryos have essentially the same forms as Scyllium, Pristiurus or Squalus. It must not, however, be concluded that its embryology is lacking in interest, for, as will be seen in the following pages, the differences which occur in Cestraciont development are in clear accord with its more ancient lineage, and we will find that these differences will give us an interesting light on the puzzling question of to what degree development may in time come to be modified. It will be seen, for example, that a Cestraciont still retains traces of an holoblastic cleavage, and that its blastoderm still grows around the egg before the embryo is of large size, features which stand clearly in the gap which has separated the plan of development of recent sharks from that which occurs in ganoids and lungfshes, a plan which, on many grounds, must also have existed in primitive sharks. But these considerations may best be examined in later pages of our work. In a somewhat similar vein, Haswell (1898) had previously written concerning Heterodontus phillipi: “. . . the hope is not an unreasonably sanguine one that the em- bryonic development of a type so ancient might exhibit some important primitive features. With regard to the stages now described, however, any expectation of the kind cannot be said to have been fulfilled; and what impresses one most is the extraordinary persistence The Embryology of Heterodontus japonicus 723 of certain characters which are not known to have any vital significance.”” As an example, he cites the “orange spot” which forms such a striking feature of the egg of an elasmo- branch in its early stages. This, in Haswell’s opinion, has been handed down with little change from Paleozoic times. The evidence for this view is not given, but it probably rests on the fact that the “orange spot” appears in the eggs of genera that have been segre- gated in different families from a very early period. It is not from surface features alone, nor from early stages alone, that one should look for developmental characters linking Heterodontus to the most primitive elasmo- branchs. In studying the phylogenetic relationships of the various groups of vertebrates, the later stages of embryonic development often yield evidence more satisfactory than anything the early stages afford. In Heterodontus, the field of organogeny is largely unexplored. There are, to be sure, a few contributions that deal wholly or incidentally with the development of organ systems in Heterodontus: such as those of Osburn (1907) on the origin of paired limbs; Luther (1909) on the musculature innervated by the trigem- inal nerve; and de Beer (1924.1,.2 and.3) on the development of the head. Since it does not lie within the province of the present article to review the literature on organogeny, no attempt has been made to make this list complete. THE EGG AND ITS MEMBRANES The orientation of the early blastoderm of Heterodontus phillipi within the egg capsule has been described by Haswell (1898). He states that the blastoderm, which appears as a circular reddish-orange spot about 2 mm. in diameter, occupies a constant position in the egg: it is always situated much nearer the broader end of the egg shell. The extremity of the blastoderm destined to become posterior is always directed away from the broader end of the egg shell. This indicates that the egg is anchored by the albumen in such fashion that it is free to rotate only about an axis that corresponds to the long axis of the capsule. In the egg of Pristiurus, the germinal disc is always situated at the pole of the egg which is near the rounded end of the egg capsule (Leydig, 1852). In Dean’s article entitled “Reminiscence of Holoblastic Cleavage in Heterodontus (Cestracion) japonicus’, published in 1901, there is some ambiguity in his use of the term ‘animal pole”. This difficulty arises in part from our preconceptions, for certain features of the egg during early development are apparently unique. In his later manuscript Dean seldom uses the term “animal pole’’, thereby attaining greater clarity in his descrip- tion of the egg, which follows: The egg [of Heterodontus japonicus] measures from 40 to 50 mm. in diameter. It is pale greenish-yellow in color, but bright red in the germinal spot [Figure 79, plate VII]. It is of semifluid consistency, as in sharks generally, and can be removed unbroken from the capsule only with the greatest difficulty. It is enclosed in a glistening, somewhat firm vitelline membrane, and supported by viscid albumen, which in turn is attached to the stout capsule. The orientation of the egg is conditioned by gravity, the germinal area [equivalent to the “orange-yellow spot” of other Elasmobranchs] remaining near the upper pole. It probably does not take its position [precisely] at the upper pole although this was not decided, since as 724 Bashford Dean Memorial Volume soon as the capsule is opened, the tension maintained by the albumen is destroyed and the germinal area probably loses its normal position. In nearly every case it remained near the equator of the egg. The albumen is thick and glairy, transparent save at the extreme upper and lower regions [of the capsule?]. Here it becomes opaque and is attached firmly to the capsule. The albumen shows clearly its origin in tunics: one envelope is especially clear near the egg, forming a whitish membrane, reminding one of the inner layer of the albumen of an amphibian egg (e.g., Necturus). When this is ruptured the contour of the egg is disturbed. When the albumen is in part removed, as when the upper portion of the capsule is cut away with the attached albumen, so that the egg is better exposed, there is a relaxed pressure which results in a flattening of the exposed surface of the egg and, in cases, gives rise to the rupture of the vitelline membrane. In such cases the egg appears with a hernia-like expansion. Under usual conditions an egg may be shifted about within the capsule so that the germinal area can be seen. As one sees from an inspection of Figures 1 to 6, plate I, there are furrows, travers- ing the region of the upper pole, which are apparently cleavage furrows. Their pattern suggests that this region may be a primary center of development; but it will soon be superseded by the germinal disc, which is already undergoing segmentation and will presently assume complete control. These subjects are fully discussed in the two following sections. REMINISCENCE OF TOTAL CLEAVAGE The portion of Dean’s manuscript dealing with this topic is in a finished condition as compared with most other parts. It is evidently a revision of his article published in 1901. In the figures illustrating that article, the outline of the germinal disc, which is small and very faint in the original drawings, does not appear with sufficient clearness to attract the attention of the observer, expecially since it is not labelled. In most of the drawings, as reproduced in 1901, the outline of the germinal disc cannot be seen at all, even with the aid of a strong reading glass. Therefore I have had some of these drawings reproduced by lithography (Figures 1 to 6, plate I), and have inserted here the correspond- ing portions of Dean’s manuscript without change save for the rearrangement of some tabulated matter, the substitution of reference numerals to meet a revised arrangement and enumeration of the figures, and the insertion of some additional references to figures. The peculiar interest in the development of Heterodontus is that it still bears witness to an earlier condition of holoblastic cleavage. There can be no doubt that the great size of the egg of recent selachians is a secondary embryological character, and that the early ancestors of sharks produced eggs which, like those of ganoids and lungfishes, were small, poor in yolk and fertilized externally. Indeed we already know that the Palaeozoic Cladoselachians and Acanthodians were not provided with intromittent appendages, and that therefore small eggs and a more or less holoblastic cleavage probably then prevailed within the group of sharks. We have found furthermore [Dean, 1906] that a recent Chimaeroid, Chimaera colliei, undergoes in its early stages a curious process of fragmentation of the egg which can best be explained on the ground that it represents a form of holoblastic cleavage, specialized and retained for a new physiological function. On such evidence, accordingly, there was The Embryology of Heterodontus japonicus strong reason, a priori, for prophesying that in so conservative a shark as Cestracion [Hetero dontus] there might still—in spite of the great size of the egg— persist traces of the ancestral holoblastism. It was of peculiar interest, therefore, to find such a condition present. The earlier stages [Figures 1 to 6, plate I; and Figure 79, plate VII] invariably showed a series of lines (furrows) traversing the surface of the eggs in a fashion which corresponds closely with the early superficial furrows appearing in the eggs of Amia [Dean, 1906] or, better still, Lepidosteus [Eycleshymer, 1899]—and in these [latter?] instances there is no question that the furrows represent cleavage. Before, however, considering the question of the homology of these “cleavage” lines in the egg of Cestracion [Heterodontus] we may describe their conditions in various stages. In the ripe ovarian egg no traces of these lines occur. In an egg taken from the oviduct—the earliest stage in my material—the furrows in the yolk region are already present, almost as numerous as in later stages. But there is this very noteworthy difference, that in the neighbor- hood of the (red) germinal area there appear a number of unpigmented lines and circles [Figures 40 to 43, plate IV] occupying a wide zone between the red germinal area and the yellow yolk region—the most conspicious of these being a white circle immediately sur- rounding the germ [Figures 7 and 8, plate I]. As development proceeds, this entire intermediate zone becomes less and less con- spicuous: it is later noted in the early stages of gastrulation. I believe that this zone represents a region in which the interblastomeral spaces of the segmented germ pass over into the furrow spaces on the surface of the yolk region. For this was clearly seen in the earliest stage which I was able to collect (capsule taken from the oviduct); especially clear were the lines when one carefully removes the living germ (e.g. in a spoon-shaped spatula) and examines it (in salt solution) by transmitted light. Such a preparation will be seen in [Figure 7, plate I] from a camera drawing. It shows a stage of late cleavage (? 7-10 cleavage) [more likely sixth to seventh cleavage] with the blastomeres containing the red pigment situated in an irregular central area, and with the surrounding unpigmented band traversed radially by shallow furrows. The latter spread out peripherally and could not be traced further since the soft yolk around the margins had escaped in the preparation. In another and older specimen, from a capsule which was partly protruding from the oviduct, the condition of the marginal zone could be seen more satisfactorily [Figure 8, plate I]. In this, the preparation was partly hardened (sublimate-acetic) before it was examined by transmitted light. There could then be seen not only the central pigmented blastomeres but in the circle surrounding them a series of blastomeres, somewhat larger in outline and separated from one another by wider spaces. Beyond these, and in the region of the yolk, were a number of faintly outlined biastomeres, whose intervening spaces suddenly dilated into the beginnings of the great furrows which traverse widely on the surface of the egg. It may be remarked that stages of or near this period give but the faintest indication of blastomeres in the “transitional zone” if examined as opaque objects, whether in living or in hardened material [Figure 9, plate I]; and it is clear that the indication of these blastomeres is marked out not by actual separation of the cells, but by shallow superficial grooves and by a thinning away of the cytoplasm in planes in which (perhaps in earlier stages of ontogeny) cell boundaries probably existed. By this process the yolk had become drawn into the central portion of each potential blastomere, leaving the intervening parts transparent—conspicuous when examined by transmitted light. Examining now a series of early stages (all drawn from living specimens) we may convince ourselves as to the character and disposition of these larger furrows. In Figures [1 and 2, plate I] are shown two blastulae as they appeared in the open capsule, viewed from above. The germinal area [indicated by a tiny circle] lies nearly or quite at the margin of the 725 726 Bashford Dean Memorial Volume drawing. I note that when the albumen is removed close to the egg (so that the surface may be better examined) the germinal area passes out of sight below the equator of the egg. Indeed it is quite probable that the germinal area has its normal position nearer the upper pole before the tension of the albumen is relaxed by the rupture of the wall of the capsule. In these stages the earliest [Figure 1, plate I] has the fewest furrows. All show the furrows clustered in the upper part of the egg, and extending thence more or less radially toward the periphery. In side view [Figures 3 to 5, plate I] (the egg having been rotated into this position by means of hooked needles thrust into the albumen) the furrows are seen to pass down the sides of the egg in nearly parallel series precisely as they do in Lepidosteus, Amia or Necturus: some of the furrows extend lower than their fellows, and all round out, flattening at the ends. [Figure 6, plate I, shows a somewhat oblique view of the lower hemisphere, with the furrows converging toward the vegetal pole]. The similarity of such a stage to the blastula of a ganoid is made the more striking by the range of color in the Cestraciont egg. The animal pole is of a pale-straw tone, the lower hemisphere is greenish-yellow and the intermediate (equatorial) zone has usually an orange or brownish cast. [In his notebook Dean states that the equatorial zone has a green- ish color. For the upper hemisphere, the colors are shown in Figure 79, plate VIJ]. Another regard in which the furrows indicate their homology with cleavage lines is their behavior with respect to the downgrowing blastoderm [a product of the germinal disc]. This begins at the side of the segmented “animal pole” of the egg, extends across it and en- closes the egg in such a way that the [yolk] blastopore closes at nearly the opposite point on the equator of the egg to the one where the germ was situated, in this regard suggesting the conditions of Lepidosteus or Amia. In this connection it is to be noted that when the [yolk] blastopore in Cestracion [Heterodontus] is closing one may see through it a few long furrows which belong to that portion of the egg (near the equator) where the lines become nearly parallel (Figures 52 to 56, plate V). It is none the less an extraordinary thing to maintain that a shark’s egg, especially one as large as [that of] Heterodontus, possesses a form of holoblastic cleavage. Accordingly it would not be amiss to consider the objections which might be urged against such a thesis. Let us tabulate the objections as follows, and set against them the facts favorable to the view that a rudimentary holoblastism is present. Concerning the Homology of the Furrows of the Egg of Heterodontus to Cleavage Furrows of a Holoblastic Egg: They may be surface wrinkles only.—In this event we might expect them to occur in the mature egg, to be more or less inconstant, and to be subject to change by artificial means. They are, however, absent in the egg about the time of fertilization. They are constant in all eatly stages examined (about a hundred specimens). They are not altered in shape and position by artificial means, such as pressure or tension; nor do they become obliterated (according to observations on an opened egg which was kept alive for thirty hours). They can be distinguished after the egg has broken, and it can then be seen that the furrows are not superficial merely, but that they pass deep into the yolk, by actual measurement at least 1.5 mm. in the upper part of the egg. Moreover the furrows do not occur at hazard. One always finds a central series of segments in the upper part of the egg, and in the lower part a peripheral series, with furrows nearly parallel; occasionally, moreover, as in the egg of Lepidosteus or Amia, several of the marginal furrows may be traced into the region of the vegetal pole and may even traverse it [Figure 6, plate I]. These numerous, close and constant correspondences can hardly, therefore, be without homological significance. The Embryology of Heterodontus japonicus Teall These furrows are known to occur in no other Selachian.—Compare, however, the segmen- tation stages of Chimaera [Dean, 1906], and take into account the paleontological history of Heterodont sharks. In a word it is precisely since they do occur in Heterodontus that these furrows may well be homologous with cleavage lines. The furrows have not been traced back into the earliest segmentation stages. —A gap in the evidence, truly, but by no means a fatal one. In earliest stages examined a continuity has been shown between the inter-blastomeral spaces in the germ and the circum-germinal furrows. The furrows may have no relation to the nuclei.—We note however, that the furrows do not occur in the egg about the time of fertilization: i.e. prior to segmentation. It has been demonstrated that nuclei are abundant in the region beyond the germinal area, to a distance of about 10 degrees on all sides. We have some reason to infer that they extend further peri- pherally since the neighboring circum-germinal yolk is similar in character to that in the region where they occur. Unhappily, however, owing to technical difficulties, the outer re- gion of the yolk has not been sectioned. But it does not follow that, because nuclei in this region have not been demonstrated, the furrows in question cannot be concerned with cleavage. For such an objection would apply equally well to the case of such eggs as those of Necturus where nuclei have not been demonstrated in the vegetal region, yet where one does not question the homology of the furrows with cleavage lines. The furrows may be due to the action of merocytes, which are known in Pristiurus and Torpedo to form blastomere-like structures.—Even in this event the furrows must be classified | broadly, I think, as within the category of cleavage lines, and hence as an expression of a holo- blastic condition. For if an egg subdivides, when deprived of its nucleus and later provided with a sperm nucleus, does not this division come under the general head of cleavage? There is, however, no evidence that furrows of so distinct a type have ever been produced in a meroblastic egg by merocytes. There is on the contrary evidence for assuming that mero- cytic division in Cestracion [Heterodontus] would be less evident than in more modern types of sharks. For all will agree that polyspermy, in vertebrates at least, isa secondary character and less apt, therefore, to have been prominent in the oldest sharks, like Cestracion. Indeed, we already know, thanks to Riickert’s studies (1899) that the migration of merocytes into the yolk is less marked in Pristiurus (an older form) than in Torpedo (a later and derived form). We conclude, accordingly, that the weight of the evidence is unquestionably in favor of regarding the furrows in the early Cestraciont egg as the homologues of cleavage lines. Among Dean’s records I find several photographs of eggs exhibiting the alleged “holoblastic” cleavage furrows. These photographs are in part identical with those published in Dean’s article (1901) on cleavage. Some of the photographs show the furrows quite as clearly as they are portrayed in Dean’s drawings. But it is not likely that these drawings were made from photographs. Inserted in Dean’s notebook there are many carefully executed drawings of these “cleavage” stages, annotated in Dean’s handwriting. Some correspond to the drawings already published; but few, if any, correspond to the photographs. In some of the drawings found in Dean’s notebook the region of the upper pole of the egg, which Dean sometimes calls the animal pole, has the appearance of a well-defined large blastoderm or region of micromeres, from which nearly parallel furrows radiate like meridians down over the equatorial region (as in Figures 1 to 6, plate I). Thus the egg has 728 Bashford Dean Memorial Volume the appearance of an egg of Lepidosteus (Eycleshymer, 1899), or of the amphibian Crypto- branchus (Smith, 1912), in an advanced stage of cleavage. In nearly every drawing of the egg of Heterodontus japonicus in the stages under consideration there is indicated, in addition to the “cleavage” pattern just described, a very small circular germinal disc similar to that of other Elasmobranchs. The germinal disc is usually situated a few degrees above the equator. From Dean’s note and manuscript it appears that this con- ventional germinal disc (described as reddish in H. japonicus, reddish-yellow, orange- yellow or simply orange in other Elasmobranchs) is already cut up into blastomeres (Figures 7 and 8, plate I). Ina preliminary sketch, found in Dean’s notebook, of the egg represented in Figure 5, plate I, the small circular area is labelled “b’d’m” (blastoderm). The most puzzling thing about the cleavage of the egg of Heterodontus as described by Dean is that there are apparently two distinct centers of blastomere formation. If there are really two, the relationship between them is not clear. On this topic Dean (1901.1, p. 4) comments as follows: ‘There is evidence that the present position of the germ disc is a secondary one, for in eggs just deposited, (1) it is nearer the animal pole than in later stages; (2) there is a kind of track, whitish in color, extending from the direction of the upper pole of the egg, suggesting therefore that the disc has shifted its position, leaving a wake behind”. Dean (1901.1, p. 7) writes further: “Cestracion (Heterodontus) also indicates that the change in the position of the germ disc occurred before holoblastic cleavage was given up, and we have with it a suggestion that it was from some new or modified physiological cause that a distinction came to arise between the germ disc and the region of the upper pole.” Certain it is that the tiny germinal disc soon takes the lead in the formation of the embryo. DISCOIDAL CLEAVAGE AND THE BLASTULA Figure 79, plate VI, in color, shows the general appearance of the egg at the begin- ning of the stages about to be described. In this egg, the furrows traversing the general surface assume a pattern that is not the most fortunate to illustrate Dean’s thesis that they are cleavage furrows, but the drawing is the best one available to portray the colors as described in Dean’s notes. In his notebook Dean has written, concerning this early stage, that the uppermost portion of the egg is “light” (yellow) and the equatorial region is “greenish” (yellow). The region below the equatorial zone is designated simply~ yolk”. In the drawing, the germinal disc appears pink (Dean calls it “‘reddish”’), and it is surround- ed by a white zone—repeatedly mentioned by Dean in his notes. Attention must now be focussed on the progress of segmentation within the germi- nal disc. The very early stages of cleavage in the germinal disc of Heterodontus japonicus have not been described. These stages must occur while the egg is still in the oviduct, before or during the formation of the capsule. The earliest stages obtained by Dean are those illustrated in Figures 7 and 8, plate I. These eggs were taken from the body of the fish; they were enclosed in capsules that were practically complete, and were soon to be deposited. A later stage is portrayed in Figure 9, plate I. In this drawing the blasto- The Embryology of Heterodontus japonicus 729 Text-figure 46. Some stages of mitosis in the blastomeres of Heterodontus japonicus: A, metaphase or middle phase of mitosis; B, anaphase; C, early telophase. In C, the chromosomes have begun their transfor- mation within chromosomal vesicles. From drawings left by Bashford Dean. derm is surrounded by a very shallow circular groove. The type of cleavage is, of course, discoidal. It is sufficient to add that the cleavage patterns of these blastoderms are not essentially unlike those of other Elasmobranchs: e. g., Scyllivm as portrayed by Ruckert, 1899, Figs. 10 and 11, pl. LII. There is a noticeable gap between the figures thus far discussed and the one il- lustrating the earliest gastrula stage. This gap is partly bridged by Dean’s drawing show- ing the segmentation cavity of a blastoderm dissected off the yolk mass and viewed by transmitted light. Upon focussing with the low power of the microscope through the thin roof of the blastocoele, an optical section is obtained which shows that the cavity is crescent-shaped (Figure 10, plate I). There are no other figures, suitable for reproduction, showing the cellular structure of the blastoderm in a later stage of cleavage; but the colored drawing reproduced as my Figure 80, plate VII, shows the general appearance of what is presumably a late blastula (compare Figure 44, plate IV). In Figure 80, plate VII, the blastoderm is probably con- fined to the elliptical reddish area; but when the corresponding figure on plate IV is Text-figure 47. Late stages of mitosis in the blas- toderm of Heterodontusjaponicus. . In A, late telophase, the forma- = tion of chromosomal vesicles is nearly complete; in B, the chro- mosomal vesicles of a single daughter nucleus are represented. From drawings left by Bashford Dean. 730 Bashford Dean Memorial Volume B Cc Text-figure 48. Late stages in the reconstruction of a “resting” nucleus in the blastoderm of Heterodontus japonicus. In A, the daughter nucleus is composed of chromosomal vesicles—some fused into larger vesicles. In B, the process of fusion is almost complete, but maternal and paternal components are segregated in two distinct groups. In C, the duplex character of the nucleus is indicated only by a notch on one side. From drawings left by Bashford Dean. compared with those that immediately precede and follow it, one gets the impression that the pale-yellow zone also is a part of the blastoderm. On this view, it becomes easier to explain the round dark spot at the posterior (lower) end of Figure 80, plate VII: it may be derived from the crescentic area (dark when viewed by reflected light) which is the optical expression of the segmentation cavity. But one notes, in this figure, that the posterior and lateral margins of the reddish area are slightly upraised, which is fairly convincing evidence that this area alone constitutes the blastoderm. If we consider the blastoderm to be confined to the reddish area, then the dark spot may be simply an oil globule. Probably, the figure under consideration was drawn, under low magnification, as seen through a thick layer of albumen. It does not lie within the scope of this article, as indicated by its title, to consider the internal development. Nevertheless, it seems desirable to bring together the scanty available data concerning the early stages. The few drawings made from microscopic sections, found among Dean’s records, seem of sufficient historical interest to justify their inclusion here. These drawings (Text-figures 46 to 48) are concerned with mitosis during cleavage. The originals, probably drawn by Dean himself, lack explanations or labels save the words “‘Cestracion blastomeres” written below Text-figures 46a, 478 and 48B; also the words “Cestracion—budding of blastomeres” under Text-figure 474. These explanations are in Dean’s handwriting. The drawings are not dated, but the paper is yellow with age. In the light of our present knowledge, the transformation of chromosomes within chromosomal vesicles is clearly portrayed in Text-figures 46c and 47a. Chromo- somal vesicles of a single daughter nucleus are shown in Text-figure 478. Fusion, in varying degrees, of chromosomal vesicles derived from the same parent is shown in Text- The Embryology of Heterodontus japonicus P| figure 48a and 488. In the latter figures the nucleus appears double, and in Text-figure 48c it is notched. These are indications of the duplex character of the nucleus, which consists of both maternal and paternal components. Had the preceding stages of mitosis been favorably oriented, doubtless the duplex organization of the nucleus would have been revealed there also. At the time when Dean’s drawings were presumably made, obser- vations of this kind on the segmenting eggs of vertebrates were rare. Fora fairly adequate bibliography of the literature on the individuality of the germ nuclei and the history of the chromosomal vesicles during cleavage, the reader is referred to the contributions of Rich- ards (1917) and Smith (1929). In an early section of this article, mention has been made of a few slides bearing serial sections of embryos of Heterodontus (presumably japonicus). These include sagittal sections of three blastoderms in early, advanced, and late blastula stages respectively. In the sections, which were cut in parafhn, the early blastula measures about 1.1 mm. long, the advanced blastula 1.3 mm., and the late blastula about 3 mm. In life these blastulae must have been appreciably larger, since such material shrinks during the process of preparing it for sectioning. In all essential respects the two earlier blastulae, as represent- ed in sections, are like those of other Selachians: e.g., Torpedo and Pristiurus as portrayed by Rickert (1899, Figs. 51 and 53, pl. LVI). They closely resemble the corresponding stages of Heterodontus phillipi, discussed in the final paragraphs of this section. The late blastula is imperfect, so that comparisons are unprofitable. In a brief contribution, Haswell (1916) describes surface views of two very early stages of cleavage in the germinal discs of eggs taken from oviducts of H. phillipi (my Text-figure 49 and 49). He states that in both eggs the cleavage lines are entirely confined to the area of the orange spot, and do not show any trace of a tendency to become extended beyond its limits. Two other eggs, taken from “uteri” some weeks later, showed more advanced stages of cleavage. Neither in these eggs, nor in those studied in 1898 (described in the next paragraph), did Haswell find any indications of furrows such as those of H. japonicus interpreted by Dean as a reminiscence of holoblastic cleavage. Haswell (1898) studied the later stages of cleavage in H. phillipi from eggs that had been deposited in the sea. He states that during cleavage the blastoderm appears 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, its longer axis corresponding with the future long axis of the body. At its posterior end appears A B Text-figure 49. Surface views of early cleavage in two blasto- derms, A and B, of Heterodontus phillipi. The eggs were taken from the oviducts. After Haswell, 1916, Fig. 1. 732 Bashford Dean Memorial Volume a a crescentic dark area which has very much the appearance of a cleft passing through the blastoderm. The study of sections reveals that this dark area is really a cavity, the segmentation cavity, covered by a thin transparent roof. As the blastoderm extends, this dark area becomes less strongly marked and gradually disappears. (It has previously been noted that a similar crescentic “dark” area occurs also in H. japonicus at a corresponding stage, as evidenced by a sketch, without explanation, found among Dean’s drawings. In this sketch, dark and light areas are reversed, since the object was drawn, under low magnification, by transmitted light). In the egg of H. phillipi the light-yellow border, previously mentioned, extends more rapidly than the blastoderm, and soon forms a broad zone around the latter. It is quite evident that Haswell does not consider the light- yellow zone to be a part of the blastoderm; it is apparently the superficial expression of the “parablast”’ (periblast). The internal structure of some early stages in the development of H. phillipi is the chief topic of Haswell’s article published in 1898. Beginning with a fairly early stage of cleavage, the development of the germinal disc through the blastula and gastrula stages is described and illustrated by figures drawn from sections. Two of these figures, represent- ing early and late blastula stages, are reproduced here as my Text-figures 50 and 51. Their resemblance to Dean’s sections of corresponding stages of H. japonicus has already been pointed out. GASTRULATION AND EARLY EMBRYOGENY In Elasmobranchs the changes that occur during gastrulation and early embryo formation are complex, and cannot be adequately described without recourse to serial sections. My only information concerning these stages in Heterodontus japonicus is obtained from Dean’s drawings of both opaque and cleared total embryos, and from one gy SRS 2 AM poet Rea Sng sages dee oR Be SPIO ROSE Soe? 30,00 NOs EE Sonata! ee Ses, 3 93,29 989, A ne POAT OSS CSS FRG os) E Text-figure 50. Sagittal section of a blastoderm of Heterodontus phillipi in a stage showing the begin- ning of the segmentation cavity (at the posterior end, to the right of and below the segmented area in the figure). ant, anterior; ect, ectoderm. After Haswell, 1898, Fig. 1, pl. IV. The Embryology of Heterodontus japonicus 733 Text-figure 51. Sagittal section of a blastoderm of Heterodontus phillipi in a stage in which the segmentation cavity is well established. ant, anterior; para, parablast or periblast. After Haswell, 1898, Fig. 4, pl. IV. series of sagittal sections of a gastrula stage. It has therefore been necessary to interpret Dean’s drawings in the light of what is known concerning the development of other species of Elasmobranchs. The most helpful contributions are those of the Zieglers (1892 and 1902); Haswell (1898); Ruckert (1885 and 1899); and Scammon (1911). Among Dean’s drawings, the one reproduced as Figure 11, plate I, represents the earliest blastoderm that shows indications of gastrulation. This blastoderm is decidedly elongate—a transient phase in its development. Its margins, constituting the embryonic rim or germinal ring, are slightly upraised, particularly at the posterior (lower) end. At this end a small and rather indistinct pit indicates the site of beginning invagination; but the pit may be an artifact. The central portion of the blastoderm retains some of the reddish color characteristic of the germinal disc of an earlier stage. The pale-yellowish zone surrounding the blastoderm is broadest at its anterior (upper) end. It represents the marginal portion of the periblast. The original figure bears the notation “5 mm.” in Dean’s handwriting. This probably refers to the length of the blastoderm. Figures 45 and 46, plate IV, show the rapid disappearance of color within the blastoderm except for a narrow line along its border. They show also the change from an elliptical outline to one that is approximately circular. Figure 12, plate I, represents a blastoderm a little older than that shown in Figure 11, plate I. It is only moderately ellip- tical, and the presence of an upraised portion at the posterior end constituting the so- called embryonic shield indicates that it isa gastrula. The median groove traversing the ectoderm of the embryonic shield is the neural groove. Figure 13, plate I, is slightly later and corresponds to Figure 47, plate 1V, which shows the entire egg in color. Here, and in the following stage (Figure 48, plate IV), one notes the extension of the blast- oderm over the surface of the yolk. That this extension is relatively rapid may be de- duced from the slight increase in the size of the embryo proper between the stages repre- sented by Figures 46 to 48, plate IV. Figure 14, plate I, represents the first of a series of embryos of H. japonicus detached from the yolk mass, stained, cleared and mounted in toto. These embryos may have been 734 Bashford Dean Memorial Volume drawn directly, under low magnification, by transmitted light; but in the table in Dean’s notebook many embryos are listed as photographed and also drawn. Most of the draw- ings must be interpreted as optical sections, so it is possible that they were drawn from photomicrographs. Such drawings show only what can be seen by focussing at a single level, and are sometimes difficult to interpret. It is unfortunate that, with very few exceptions, the embryos from which Dean’s drawings were made cannot be found. As an aid to the study of the drawings, I have examined, under both monocular and binocular microscopes, a close series of Elasmobranch embryos, chiefly Squalus acanthias, stained and mounted by me nearly thirty years ago. Figure 14, plate I, represents a stage intermediate between Figures 12 and 13. It lacks the high lights characteristic of a surface view. Posteriorly, it represents that portion of the thickened margin of the blastoderm adjoining the embryonic shield. Here, by a process of inturning accompanied by a limited amount of concrescence and a very considerable amount of overgrowth, the thin rim of the early blastoderm has formed a deeper layer, the entoderm, not shown in the drawing. In the angle between the super- ficial layer (ectoderm) and the entoderm a middle layer, the mesoderm, is being proliferated. The thickened margin of the blastoderm contains all three germ layers, hence it is some- times called the germinal ring. At the posterior end of the figure a pair of dark zones, one on each side of the mid-line, probably contain axial mesoderm. Anteriorly, a dark zone having the form of an arch represents an optical section through upraised ectoderm at the edge of the germinal shield. The neural groove is out of focus and is not shown. Figure 15, plate I, represents a stage slightly later than Figure 13. It shows a well- defined notochord, with its characteristic irregular transverse striations, extending along the mid-line of the lower two-thirds of the figure. On each side of the notochord we see the axial mesoderm, very thin and not ready to be cut into somites. Lateral to this, on each side, a broad dark zone represents the inner limb of the neural folds. The outer limb of the neural folds forms the margin of all the anterior two-thirds of the figure. The beginning of the foregut may be present in this stage, but if so, it is not clearly shown. The figure is possibly a ventral view. Figure 16, plate I, is the earliest drawing showing mesoblastic somites. Of these, four pairs are complete. In the head region the neural folds appear asymmetric. On the left side, both outer and inner limbs of the neural folds are well shown, but on the right side the inner limb is incomplete. Evidently the drawing represents an optical section, and the apparent asymmetry of the neural folds is due toa slight rotation of the embryo on its long axis. The continuation of this rotation will soon bring the embryo to lie on its left side. Parenthetically, it may be remarked that the embryo of Torpedo, as figured by Ziegler (1892 and 1902), tends to lie on its right side; but in my whole mounts of Squalus, the embryo lies on its left side as in Heterodontus japonicus. In the stage under con- sideration the beginning of the fore-gut, extending forward beneath the brain as a pocket- like portion of the entoderm, is presumably present; but it occurs at a lower level than the structures shown in the drawing. The Embryology of Heterodontus japonicus 735 In Figure 16, plate I, there are some incomplete intersegmental grooves marking off three or four (probably four) pairs of incomplete somites in front of those that are com- plete. The anterior portion of the notochord is slightly obscured by the inner limb of the left neural fold; but it appears to extend forward farther than the first intersegmental groove, which is quite distinct. It is dificult to identify accurately all the limits of the primary brain vesicles in this drawing; but it seems fairly obvious that the first inter- segmental groove marks the posterior end of the midbrain. In none of the following drawings do we find the somites extending so far forward, though the series often ends anteriorly with one or two incomplete somites. The region of incomplete somites in Text-figure. 52. Diagram showing the relation between head somites and body somites in a larval Squalus acanthias. The somites that degenerate in ontogeny are indicated by broken lines. 1d, dorsal moiety of the first myotome; 1v,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, Fig. 10. Figure 16, plate 1, probably coincides with the four somites that, in Squalus, degenerate during ontogeny. These have been figured by Neal (1918) in a diagram reproduced herein as Text-figure 52. The occurrence, in sharks, of four anterior somites that subsequently disappear is doubtless of evolutionary significance, indicating a metameric origin of the posterior part of the cranium. These somites serve also to connect the anterior head somites with the body somites and thereby establish their serial relationship. Before proceeding further with the account of the external development of the Japanese Bullhead Shark, it seems advisable to consider what is known concerning the internal changes during gastrulation in Heterodontus. The internal structure of some embryos of H. phillipi in early gastrula stages has been studied in serial sections by Haswell (1898). Three of his figures are reproduced as my Text-figures 53 to 55. Before considering these stages directly, it is necessary to describe some preparations for gastrulation made by the advanced blastula. 736 Bashford Dean Memorial Volume Text-figure 53. Sagittal section of a blastoderm of Heterodontus phillipi in a stage in which gastrulation has just begun. ant, anterior; ect, ectoderm; end’, parablast or periblast entoderm. After Haswell, 1898, Fig. 6, pl. V. The blastula represented in my Text-figure 51 (after Haswell) is not ready for gastru- lation. Before gastrulation begins, the blastoderm increases somewhat in diameter, and the segmentation cavity (or blastocoele) extends throughout almost its entire length. The floor of this cavity consists of a layer of yolk with unusually fine granules, unsegmented but containing nuclei. Haswell (1898) refers to this layer as the “parablast”’, but it is evidently the “periblast” or “yolk syncytium” of other authors (e.g., Ziegler, 1902). As shown in Haswell’s figure of a very late blastula, the roof of the blastocoele becomes very thin except in its anterior third. At the posterior end of the segmentation cavity there is a collection of cells of irregular shape. Most of these cells have evidently come from the roof of the blastula; but Haswell states that some of them are evidently being formed from the parablast of the floor of the cavity, and that this accumulation of cells constitutes the starting point in the formation of the parablast entoderm (end’) in Text-figures 53 and 54). In the embryo represented in Text-figure 53, the formation of parablast entoderm is particularly active at the posterior end. Text-figure 54. Sagittal section of a blastoderm of Heterodontus phillipi in an early gastrula stage. ant, anterior; ect, ectoderm; end, entoderm; end’, parablast (periblast) entoderm; ent, archenteric cavity. After Haswell, 1898, Fig. 7, pl. V. The Embryology of Heterodontus japonicus Wey Text-figure 55. Transverse section through the posterior portion of a blastoderm of Heterodontus phillipi in a stage somewhat later than the preceding, but before the differentiation of the notochord. ect, ectoderm; end, entoderm; ent, archenteric cavity. After Haswell, 1898, Fig. 8, pl. V. In Heterodontus phillipi, as in other Elasmobranchs, gastrulation takes place mainly by a process of involution. According to Haswell (1898) the first phase of gastrulation consists of an arching upward of the posterior portion of the blastoderm, so that where it passes into the parablast it becomes, for a short distance, vertical. It soon inclines forward (as illustrated in my Text-figure 53), forming the embryonic rim which extends along the entire posterior margin of the blastoderm. At the same time the accumulation of cells at the posterior end increases at the expense of the segmentation cavity. In the stage represented by Text-figure 53 the segmentation cavity has become extremely shallow, and its roof has acquired a compact epithelial character. The stage represented by Text-figure 54 possesses a definite entoderm, hence it is a well-established gastrula. To the present writer it seems that the cleft, separating the poorly-defined layer of cells marked end’ from the irregular layer above, is mainly an artifact. Text-figure 55 is a transverse section through the archenteric cavity of a stage a little farther advanced than the one shown in Text-figure 54. It shows no new features, but is helpful in affording a different point of view. At first the floor of the archenteric cavity consists only of yolk; but soon the anterior portion of the archenteron will form an entodermal pocket, the fore-gut. Text-figure 56. Sagittal section, approximately median, of Heterodontus (presumably japonicus) in an advanced gastrula stage. ant, anterior; ect, ectoderm; end, endoderm; per, periblast; per’, periblast endoderm; vac, vacuole. Drawn from a slide simply labelled Cestracion, in the collection left by Bashford Dean. 738 Bashford Dean Memorial Volume The gastrula of Heterodontus (presumably japonicus), represented by serial sagittal sections found among Dean’s embryological preparations, is in a stage considerably later than Haswell’s embryo shown in median sagittal section in my Text-figure 54. A median sagittal section of Dean’s gastrula is represented in Text-figure 56. The section cuts through the entire length of the blastoderm, which measures 8 mm. (on the slide); but the embryo proper, shown in the figure, is only about one millimeter long. Both ectoderm and the definitive entoderm, as shown in the drawing, are decidedly thick; but at the anterior end of the embryo the ectoderm gradually decreases in thickness until in the extra- embryonic portion of the blastoderm it is a simple squamous epithelium. The periblast is represented by a pale zone of predominantly fine yolk granules interspersed with cytoplasm, underlying the archenteric cavity and extending a short distance anterior to it. Beneath the archenteric cavity it is much thicker (deeper) than it is anteriorly. This thick portion lacks nuclei, but contains a number of fairly large vacuoles. Underlying the anterior end of the definitive entoderm, and extending forward beneath the ectoderm, isa thin layer of irregularly shaped cells that constitute the periblast entoderm. They seem to grade into the definitive entoderm, and perhaps contribute to it; anteriorly, the layer becomes even thinner and in the extra-embryonic portion of the blastoderm it is represented (in sections) by a single row of sparsely distributed cells lying between the ectoderm and the yolk mass. Underlying the thick portion of the periblast entoderm, a little distance anterior to the archenteric cavity, there are a few periblast cells (not merely nuclei) imbedded in the yolk. The advanced gastrula of Torpedo figured in median sagittal section by Ziegler (1892) is in about the same stage as the embryo of Heterodontus japonicus represented in my Textfigure 56. Ziegler’s figure shows the section continuing throughout the entire length of the blastoderm. A striking difference is the much greater thickness (2 to 5 cells deep) and compactness of the periblast entoderm in the extra-embryonic portion of the blastoderm, as compared with Dean’s gastrula in which this layer is only one cell thick and the cells are separated by fairly wide intercellular spaces. THE YOLK BLASTOPORE Before going further with a description of strictly embryonic development it seems advisable to give brief attention to the formation and closure of the yolk blastopore, which may be regarded as a delayed phase of gastrulation. The yolk blastopore is simply that portion of the surface of the yolk mass which, subsequent to the beginning of gastrulation, is not yet covered by the blastoderm (Figures 46 to 59, plates IV and V). It is bounded by the rim of the blastoderm and is continuous with the floor of the archenteric cavity. The name blastopore seems more appropriate after the blastoderm has covered more than half the yolk mass, but the morphological re- lations are the same in earlier stages. One reason for regarding the yolk blastopore as related to gastrulation is that, in heavily yolk-laden eggs, circumcrescence (overgrowth of the yolk by the blastoderm) is an important factor in gastrulation—it assists in laying The Embryology of Heterodontus japonicus 739 down the definitive entoderm. In later stages, circumcrescence provides a protective and vascular covering for the yolk mass. These extra-embryonic structures will be eventually resorbed. The yolk blastopore of Heterodontus japonicus is probably unique in that the surface of the yolk is traversed by furrows that appear to be cleavage furrows. These are clearly shown in Figures 46 to 56, plates [V and V. They are distinct in some of Dean’s photo- graphs, both published and unpublished (cf. page 727). In Figures 52 to 56, plate V, the appearance of the yolk blastopore is strikingly like that of the yolk plug of some amphibian eggs (e.g., Cryptobranchus as described by Smith, 1912, Figs. 115 and 138 to 140). In both cases the yolk is traversed by furrows, and the pattern is much the same. It is obvious that in nearly all the drawings of developing eggs of H. japonicus, in stages from the beginning of gastrulation until after the closure of the yolk blastopore (Figures 46 to 61, plates IV and V), some of the problematical cleavage furrows are visible even after they have been covered by the translucent blastoderm. The closing phases of the yolk blastopore (Figures 57 to 61, plate V) are marked by variability in its outlines and by the presence of the vitelline vessels (considered in a later section). Figure 61, plate V, represents the final stage in the closure of the blastopore. The site of closure is not far behind the yolk stalk. ; In a portion of his manuscript already quoted in my section on “General Mode of Development”, Dean states that the blastoderm of Heterodontus japonicus “still grows around the egg before the embryo is of large size” and seems to regard this as a character of considerable phylogenetic importance. This view implies that in more modern sharks closure of the yolk blastopore is delayed. Some measurements of the size of the early embryo in relation to the size of the entire blastoderm have a bearing on the problem. The advanced gastrula of Heterodontus japonicus represented in surface view in Figure 13, plate I, has a blastoderm about ten times as long as the embryo proper, which ts about one millimeter long; while a gastrula of Torpedo ocellatus in about the same stage, drawn by Ziegler (1892, Text-fig. 3) in surface view, has a blastoderm only five times its length. A similar comparison may be made in median sagittal sections. Dean’s gastrula represented in my Text-figure 56 has a blastoderm (extra-embryonic portion not shown in the drawing) about eight times as long as the embryo proper; while Ziegler’s figure (1892, Fig. 15, Taf. III) of a gastrula of Torpedo ocellatus in approximately the same stage has a blastoderm (drawn entire) about three and one-half times the length of the embryo proper. These measurements indicate that the blastoderm of Heterodontus japonicus grows faster, or at least spreads out more rapidly, in proportion to the size of the embryo, than does the blastoderm of Torpedo ocellatus. There remains the question concerning the comparative sizes or stages of develop- ment of embryos at the time when overgrowth of the yolk by the blastoderm is completed. ’ The egg (yolk mass) of H. japonicus in the early stages of embryonic development measures from 40 to 50 mm. in diameter. The egg depicted in Figure 61, plate V, is in the stage in which the yolk blastopore has just closed. As compared with the other eggs in approxt- 740 Bashford Dean Memorial Volume mately the same stage, it has an unusually large yolk mass, probably about 50 mm. in diameter. The length of the embryo (when straightened) equals about one-fourth of the diameter of the yolk mass. One wishes for similar data concerning modern sharks, but a cursory search of the literature reveals nothing that is helpful in this connection. LATER EMBRYONIC DEVELOPMENT The account of the embryonic development of Heterodontus japonicus has been interrupted quite arbitrarily, following the stage with four pairs of mesoblastic somites, in order to consider the yolk blastopore before reaching a stage too far removed from its origin. The remaining stages of embryonic development, as represented in Dean’s drawings, will now be considered in serial order. Figure 17, plate I, represents a cleared embryo with 12 pairs of complete and one pair of posterior incomplete somites. The course of the right neural fold in this figure is not easy to follow, but it seems quite certain that the neural folds have almost met anteriorly as well as posteriorly. What appears to bea neural fold on the right side of the figure is the floor of the neural plate seen in optical section. According to this interpreta- tion, the head region has rotated anticlockwise through almost 90 degrees. In the absence of rotation, it would be impossible to obtain a side view of the beginning cephalic flexure and the structures underlying the brain. The pocket situated ventrad and caudad to the brain is the foregut. The arch-like anterior intestinal portal, leading from the broad subgerminal cavity into the narrower fore-gut, is plainly visible. An embryo of Squalus acanthias possessing the same number of somites has the neural tube almost closed throughout its length. Figure 18, plate I, represents a cleared embryo with 12 pairs of complete somites, one posterior and two anterior incomplete somites. The latter appear to be undergoing degeneration. The neural folds appear to be united in their middle thirds. Anteriorly, the folds appear less close together than in Figure 17, and the cephalic flexure is less pronounced; the amount of rotation in the head region is less. Evidently the brain is not quite so far along in its development, despite the fact that some other structures are slightly more advanced. The fore-gut and the anterior intestinal portal are well shown. A sheet of mesoderm is found dorsal, anterior and ventral to the fore-gut; its ventral portion is evidently mesenchymatous. The deep dent at the anterior end of the right neural fold is an artifact. Figure 19, plate I, represents a cleared embryo with 14 pairs of complete somites and one pair of anterior incomplete somites. The neural tube is closed except for a short distance at each end. There is a pronounced cephalic flexure and a beginning cervical flexure. The fore-gut is enlarged dorso-ventrally. This drawing shows a decided under- cutting and uplifting of both head and tail-bud. Figure 20, plate II, represents a cleared embryo with 18 complete somites and one anterior incomplete somite. The right side only is shown, but presumably the left side has the same number. The cephalic and cervical flexures are slightly more pronounced The Embryology of Heterodontus japonicus 741 than in the preceding drawing. The brain shows differentiation into the primary vesicles (forebrain, midbrain, hindbrain) and there are indications of a secondary division of the hindbrain into myencephalon and metencephalon. The bulge at the side of the forebrain represents an early stage in the formation of the optic vesicle. I have found in Dean’s collection of microscopic slides a total mount of an 18-somite embryo labelled ‘‘Cestracion.” This appears to be the specimen from which Figure 20, plate II, was drawn. The embryo is slightly overstained, but corresponds to the drawing in every respect save that the small round black spot in the region of the neurenteric canal is lacking, and the triangular dark area (mesodermal?) at the anterior end of the fore-gut is not so sharply defined. In view of the scarcity of information concerning sizes of the embryos represented in the plates, it is interesting to note that this 18-somite embryo, measured on the slide, is 3.5 mm. (about one-eighth inch) long. Figure 21, plate I, portrays in surface view an embryo of about 24 somites (one side only). This figure, and the one immediately following, appear to be drawn at a magnifi- cation lower than that employed for the cleared specimens that precede them. The body of this embryo leans to the left, while the head is turned slightly to the right. The tail bud projects for some distance beyond the posterior rim of the blastoderm, and the head is entirely free from the underlying structures. In this embryo both cephalic and cervical flexures have almost reached their maximum. The right optic vesicle and lens are faintly indicated. The pronounced bulging in the hyoid region and that dorsal to the midbrain are probably abnormal. In Figure 22, plate II, a surface view, only 20 somites are readily visible; but in the caudal region four or five more are faintly indicated, making a total of about 25. In addition, there is an incomplete somite, probably degenerating, at the anterior end of the series. This embryo appears normal save for the presence of a large bulge of the ectoderm over the midbrain and a lesser bulge of the same kind dorsal to the anterior (incomplete) somite. For the first time in this series, we see something like a yolk stalk—in this stage very short and thick. The rudimentary eye is decidedly larger than in the preceding drawing, and there is more differentiation in the branchial region. Of the visceral arches the mandibular, hyoid and first branchial are recognizable; of the branchial grooves, the spiracular (Y-shaped) and first branchial. The forebrain bulges a little dorsally. Figure 23, plate II, represents a cleared embryo with at least 26 somites. It seems to be drawn at a slightly higher magnification than the two preceding figures which are surface views. It can scarcely be said to possess a yolk stalk since it is attached to the yolk mass along almost the entire length of the body proper. Vitelline arteries and veins are faintly indicated on the extra-embryonic blastoderm near the embryo. The optic vesicle shows a distinct chorioid fissure. Dorsally, in the region of the hindbrain, there is a somewhat indistinct otic vesicle. The blister-like elevation of the ectoderm, dorsal to the midbrain and to the anterior part of the hindbrain, is probably abnormal. Some neuromeres occur in the myelencephalon, immediately behind the otic vesicle. Between the foregut and the diencephalon there is a straight bar of tissue which may represent the 742 Bashford Dean Memorial Volume het anlage of the epithelial hypophysis. It extends from the oral ectoderm to a slight de- pression in the floor of the diencephalon—an evagination which may be the rudiment of the infundibulum. Figure 24, plate II, represents in surface view an embryo with at least 28 somites. Unlike the preceding embryos, this one was drawn from the left side and has been re- produced with right and left sides reversed to facilitate comparisons with other figures on the same plate. It is evidently drawn to the same scale as Figures 21 and 22 (same plate). There is some increase in length but little advance in external differentiation. However, spiracular and first branchial grooves begin to look like gill-clefts. This is the first drawing to show distinctly the region of the heart—just in front of the broad yolk stalk. There isa slight caudal flexure. The angular projection of the forebrain is probably abnormal. Figure 25, plate Il, a surface view, portrays an embryo with about 35 complete somites. Like the preceding figure, this one was drawn from the left side and has been reproduced with right and left reversed. Here, for the first time in this series, we find the sites of the spiracular cleft and the first and second gill-clefts sharply defined. It is not certain that the closing plates between branchial grooves and pharyngeal pouches are already perforated, but this seems a good place to begin referring to these fissures as clefts instead of grooves. The cervical flexure is pretty well straightened out, but in the cephalic flexure there is not much change. The dark spot dorsal to the first gill-cleft (not the spiracular cleft) indicates the site of the otic vesicle. The region of the heart is clearly indicated. Figure 26, plate II, pictures a cleared embryo with about 37 complete somites and one or two incomplete somites at the anterior end of the series. This drawing appears to have been made at a higher magnification than the preceding fgure. The principal divis- ions of the brain are fairly well shown, though not so clearly as in Figure 20 of the same plate. One notes, in the branchial region, the entoderm-lined spiracular cleft and gill-clefts alternating with mesodermal visceral arches. The greater size of the spiracular cleft is noteworthy, considering its small size in the adult. In its early stages it looks like a gillcleft, and indeed it is homologous with the gill-clefts. The notochord is clearly visible throughout most of its length; it ends anteriorly just above the spiracular cleft. Almost at the tip of the tail bud, the neurenteric canal is sharply outlined. Though the hind-gut is rather vaguely defined, there is a distinct posterior intestinal portal. Auricular and ventricular divisions of the heart can be distinguished. The optic cup shows a very thin outer and a thick inner layer: these layers are united along the borders of the chorioid fissure. The otic vesicle, dorsal to the first gill-slit, is quite prominent. In front of the dorsal part of the spiracular cleft and close to the brain (Figure 26, plate II) there is a thick-walled roughly circular sac which may be a “head cavity” or head somite. In Elasmobranchs and perhaps in vertebrates generally, the muscles that move the eyeball arise (Marshall, 1881; Van Wijhe, 1882; Scammon, 1911; Neal, 1918) from mesodermal segments (head somites) which are serially homologous with the somites The Embryology of Heterodontus japonicus 743 of the trunk (Text-figure 52, page 735). In Elasmobranchs the head somites, like the trunk somites of vertebrates generally, are at first hollow and their cavities communicate with the primitive coelomic cavity. In the head, this communication is by way of the pharyngeal or visceral arches (mandibular, hyoid and branchial arches), as shown for Torpedo in Text-figure 57a. These channels quickly close (Text-figure 57s) and the somites become solid structures. M. oblig. sup. M. oblig. sup. ™. rect lat. ) exe /ahy Ovex 1 Verbindung des Kiemenbogen- coeloms mit dem Cavum pericardii Text-figure 57. 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. 1, 2, 3, 4, gill-clefts; S.B.C.1—5, pharyngeal arch extensions of the coelomic cavity; ch.dors., chorda dorsalis; oc.m., anlagen of the oculomotor muscles; M. oblig. sup. and M. rect.lat., anlagen of the superior oblique and lateral rectus muscles respectively; ves.audit., otic vesicle. After Corning, 1925, Figs. 222 and 223; based on Froriep’s (1902) Figs. 4 and 5 (Torpedo ocellatus). Figure 27, plate II, portrays a cleared embryo of about 41 complete somites. Like the preceding figure, it appears to have been drawn under unusually high magnification. This embryo exhibits a moderate caudal and a pronounced cervical flexure—the latter presumably unusual for this stage since it does not appear in the stages immediately following. The optic cup shows, more distinctly than heretofore, the outer as well as the inner layer. The otic vesicle is larger, and nearer the branchial region; it is dorsal to the first gill-cleft. The bulbus cordis and the ventral aorta are distinctly outlined and the latter has given rise to the first three aortic arches. The hind-gut is outlined faintly along its ventral border and at both anterior and posterior ends of its dorsal border. The neurenteric canal is well shown. 744 Bashford Dean Memorial Volume Figure 28, plate II, represents a surface view of an embryo with at least 50 complete somites. It is drawn at a magnification corresponding to Figures 24 and 25 on the same plate. In this embryo the caudal flexure attains an unusual degree of curvature—the posterior half of the embryo is hook-shaped. A cervical flexure is lacking, but the cephalic flexure is slightly greater than in any previous stage. There is a yolk stalk, not shown in the drawings that immediately precede this one, and just above the yolk stalk there ap- pears to be a tubular midgut. Of interest are the thin roof of the medulla (not seen in any previous stage) represented by the heavily shaded portion of the hindbrain; the closure of the ventral portion of the spiracular cleft; and the large size of the first gill-cleft. The second gill-cleft is of moderate size, and the sites of the future third and fourth gill- clefts are occupied by pharyngeal grooves. If the circular pale spot on the forebrain indicates the position of the eye, then it is nearer the dorsal end of the mandibular arch than it has been in any preceding stage. In this surface view, one cannot be sure of the position of the otic vesicle, but it appears to be dorsal to the first gill-cleft. Figure 29, plate II, portrays a surface view of an embryo with about 55 complete somites. The mid-gut is not so far advanced in its development as it is in the preceding figure. The lower two-thirds of the spiracular cleft is closed, and there is a distinct third gill-cleft. The mandibular arch is more prominent than it has been in previous stages. The myelencephalon (medulla oblongata) shows prominent neuromeres. The otic vesicle appears to be dorsal to the first branchial arch. In the last three stages studied, there has been a steady growth of the forebrain. Figure 30, plate II, pictures the head and anterior part of the body of a cleared embryo drawn at a higher magnification than that employed for the surface views just considered. The number of somites is unknown, and it is not certain that this specimen is older than the one represented in the preceding figure. Evidently the artist had trouble in getting a clear view of some parts of this large embryo, for the drawing does not show as much detail as one would expect ina figure of this size. There isa slight cervical flexure and the usual pronounced cephalic flexure. The form of the brain has undergone some changes; in particular the telencephalon or secondary forebrain has increased in size. The spiracular cleft is not shown. The otic vesicle is still situated dorsal to the first gill-cleft, though in adult sharks its derivative, the membranous labyrinth, is more closely associated with the spiracular canal; e.g., as in Chlamydoselachus (Smith, 1937, pp. 423 to 430 and Text-figure 82.) Figure 31, plate II, portrays a surface view of an embryo with about 74 somites—now represented by myomeres. This embryo is the first to show a fin bud—the pectoral. Rudiments of the first and second dorsal fins, and of a pelvic fin, are recognizable only by comparison with the figures that follow. The tail is bordered by a continuous fin fold out of which will emerge the anal and caudal fins. There seems to be a low fold con- necting the rudiments of all the unpaired fins; but one cannot be sure, from the figure, whether pectoral and pelvic fin rudiments are connected by a fin fold. The yolk stalk is now attached to the pectoral region only, just behind the heart. The spiracu- The Embryology of Heterodontus japonicus 745 lar cleft is closed except for a small dorsal portion. For the first time, in this series, we see rudimentary gill- filaments projecting from gill-clefts— the first, second and third, in this embryo. Due to differential growth of associated parts, the eye is now situated very close to the dorsal end of the mandibular arch where a swelling indicates the anlage of the future maxillary process. The position of the otic vesicle is no longer indicated in surface views. There isa shallow olfactory pit. The hind-gut is fairly well defined. Figure 32, plate I, portrays in surface view an embryo with about 85 myomeres. One notes that the yolk stalk is more slender, and that there are five gill-clefts. Gill filaments project from all five gill-clefts, but there are none from the spiracular cleft. The rudiment of the maxillary process is more prominent than in the preceding stage. Figure 33, plate II, represents a surface view of an embryo with at least 88 myomeres (those near the tip of the tail are indistinct). This embryo shows a decided advance over the preceding one. To be sure, no new structures have emerged save a single gill filament protruding from the spiracular cleft; but all the embryonic structures mentioned in the preceding drawings are present in a more advanced stage of development. The myomeres show a higher degree of differentiation. The rudiments of the fins—pectoral, pelvic, first and second dorsals, anal, and caudal—are recognizable at a glance, though all the median fin rudiments appear to be connected by a fin fold. Both pectoral and pelvic fin rudiments are very broad at the base, but they are evidently not connected by a fin fold. One sees, more clearly than in the two preceding figures, the contour of the brain. The yolk stalk is more slender, as one would expect in this stage. There seems to be some injury to the cardiac region. Figure 34, plate III, pictures in surface view an embryo somewhat older than the one shown in the preceding figure, but evidently drawn at a lower magnification. The myomeres are not visible. All the fin rudiments are now discrete: i.e., not connected by a fin fold. Gill-filaments are more numerous, and some are decidedly larger. The spiracu- lar gill-cleft reveals four or five short gill-filaments; this cleft is now somewhat farther from the first and nearer the eye. As compared with the preceding figure, there is a remarkable enlargement of a region of the brain comprising the mesencephalon (mid- brain) and metencephalon (anterior division of the hindbrain, containing the cerebellum). The olfactory pit is larger and deeper. The maxillary process of the mandibular arch is no longer clearly defined in surface views. It extends beneath the posterior rim of the optic cup. An embryo in Dean’s collection, slightly older than the one represented in Figure 34, plate III, is about 38 mm. (1.5 inches) long. Its external gill-filaments are slightly longer than those represented in this figure. Figure 35, plate III, shows almost maximal development of the external gill filaments. The spiracular cleft is closer to the eye and directly posterior to it. The mouth opening, bordered by rudimentary labial folds, is now recognizable. The pectoral fin is quite large, and the caudal fin is very long. The dorsal fins are taller, and narrower at their 746 Bashford Dean Memorial Volume bases, than in the preceding stages. Cartilaginous fin rays are indicated in both dorsal fins, also in the pelvic fin. An embryo in the same stage of development as the one represented in Figure 35, plate III, was found in Dean’s collection. It measures about 50 mm. (2 inches) in length. Its external gill filaments are abundant and resemble those shown in the figure. The embryo portrayed in Figure 36, plate III, is obviously older. This is shown by the marked development of the cartilaginous fin rays and by the increased size of the cranium. Due to the persistence of the cephalic flexure, the mouth opening still faces caudad as well as ventrad. The spiracular cleft, situated just behind the eye, is shown more distinctly than in the preceding figure. Indistinct myomeres, extending to the extreme tip of the tail fin, are indicated in the posterior half of the figure. This embryo is remarkable for the entire absence of external gillfilaments—a deficiency that is more striking when we observe that both the preceding and the following stages show a luxu- riant development of these filaments. There is an indistinct lateral line. Figure 81, plate VII, represents (in color) an embryo only slightly older than the one just described. This beautiful figure is noteworthy in several respects. First, it shows the extreme development of the external gill-filaments; second, a tuft of these comprising about 9 or 10 filaments protrudes from the spiracular cleft; third, the figure represents the oldest embryo in which the eye is known to possess a chorioid fissure; fourth, it shows a rudimentary supraorbital ridge; fifth, the pelvic fin appears to possess a rudimentary myxopterygium; and sixth, the figure shows the entire yolk sac. Figure 37, plate III, is noteworthy for the size of the external gills, which are as long, and almost as abundant, as those in the embryo just considered. In some features, the embryo portrayed in this drawing is decidedly more advanced in its development. This is particularly true of the mouth region. The cephalic flexure has unbent toa degree that brings the mouth into nearly its adult position. This change is accompanied by increased depth of the branchial and pectoral regions, so that the profile of the ventral surface is straightened (cf. Figure 36, plate III). Only five gill flaments protrude from the spiracular cleft. Structures in the branchial and pectoral regions are obscured by the gillfilaments. There is a supraorbital ridge, best developed at its posterior end. Some of the fins are larger than in the preceding stages. The lateral line is indistinct. An embryo in Dean’s collection appears to be identical with the one represented in Figure 37, plate III. It is about 70 mm. (2.75 inches) long. Another embryo, in Dean’s collection, which appears slightly more advanced in its development, measures only about 60 mm. (2.36 inches) in length. Its external gillfilaments have reached their maximal development. The embryo portrayed in Figure 38, plate III, shows important changes. The head, including the branchial region, has increased in depth so that in side view the embryo is shaped more like a tadpole. Through a sort of telescoping of the branchial and pectoral regions, the three posterior gill-clefts have come to lie dorsal to the base of the pectoral fin, as in the adult. The distance between the spiracular cleft and the first gill-cleft has The Embryology of Heterodontus japonicus 747 greatly increased. The fins, excepting the caudal, are larger than in the preceding figure, and all the fins show an advance in differentiation. The tips of the spines of the dorsal fins are now exposed, and the ventral lobe of the caudal fin exhibits the notch that is characteristic of adults of the genus Heterodontus. The lateral line, extending along the side of the body, is fairly distinct, and portions of the sensory canal system of the head are indicated by white lines in the drawing. The external gill-filaments are shorter, more delicate, and perhaps less numerous, than in the preceding stage. Seven or eight filaments project from the spiracular cleft. The demibranch on the anterior side of the first branchial cleft shows some of the shortened gill-fllaments that persist in the adult. In this drawing, the supraorbital fold would scarcely be noticed if one were not familiar with its form in the adult fish. One of Dean’s embryos is about 72 mm. (2.8 inches) long. It is slightly less advanced in its general development than the one represented in Figure 38, plate III, but has external gills that resemble those shown in this figure. Another embryo in Dean’s collection, apparently identical with the one depicted in Figure 38, plate III, is about 78 mm. (3 inches) long. Figure 39, plate III, represents an embryo definitely older than the preceding. This is shown by the emergence of several new features. The body proper, and the bases of certain fins, are covered with dermal denticles. The color pattern of the embryo at the time of hatching is vaguely foreshadowed. The dorsal fins have acquired somewhat their form in the adult, though in adults of this species the posterior margin of the second dorsal is sometimes partly or wholly convex. The tips of the spines of the dorsal fins are barely visible. If one looks sharply he may see, just behind the gill-clefts and continuing caudad for some distance, a series of grooves parallel to the gill-clefts and spaced like them, but not so distinct. These grooves are better shown in Figure 84, plate VII, considered later. The supraorbital ridges are hardly noticeable and are perhaps not well develop- ed in this embryo. The general form of the body, now approximately the same as in the adult, differs little from that represented in the preceding figure. The spiracular opening is not shown. An embryo in Dean’s collection, apparently identical with the one represented in Figure 39, plate III, is broken in two in the middle and is somewhat mutilated in this region. It cannot be accurately measured but is about 90 mm. (3.5 inches) long. The embryo depicted (in color) in Figure 82, plate VII, is a little older than the one represented in Figure 39, plate III. The presence of a sizable yolk sac shows that it was taken long before hatching. In some respects, this embryo is unique and is probably either distorted, abnormal or inaccurately drawn. In particular, the nasal opening ap- pears high up on the front of the head and not connected with the mouth by a nasolabial groove. Upon comparing this figure with later stages (Figures 83 and 84, plate VII), the size of the dermal denticles arranged in a V-shaped pattern posterior to the eye appears exaggerated. The dorsal portion of the pelvic fin forms a finger-shaped projection pointing dorsad. This may possibly be an upturned rudimentary myxopterygium. Aside from 748 Bashford Dean Memorial Volume these problematical features, the figure shows a moderate advance in pigmentation and a slight increase in the size of the pectoral and first dorsal fins. It is of interest principally because it is the most advanced embryo figured with a yolk sac. The stage at hatching, portrayed in Figure 83, plate VII, is discussed in a later section of this article. The embryo represented in Figure 84, same plate, is two weeks older and therefore the consideration of this figure is likewise deferred. THE VITELLINE CIRCULATION Since the vitelline circulation in Heterodontus japonicus is essentially like that of other sharks, the diagrammatic figures by Balfour (1885) representing stages in the de- Text-figure 58. Diagrammatic figures showing the development of the vitelline circulation on the egg of Pristiurus: A, early; B, intermediate; and C, advanced stages. a, vitelline artery; v, vitelline vein; yk, yolk blastopore. The letter y (in C) marks the spot where the venous ring and the yolk blastopore were closed bythe growth of the blastoderm. After Balfour, 1885, Figs. 1, 2, and 3, pl. 9. velopment of the vitelline vessels of Pristiurus will serve as an introduction to the study of Dean’s drawings. Three of Balfour’s figures are reproduced as my Text-figure 58. A single unpaired vitelline artery emerges from the yolk stalk and proceeds cephalad along the blastoderm under cover of the head of the embryo (Text-figure 58a). This arterial trunk divides to form two arcuate branches that turn toward the posterior margin of the blastoderm. In the stage represented in Text-figure 58, the blastoderm has over- grown the entire surface of the yolk mass excepting a small nearly circular area (yk, the yolk blastopore) posterior to the yolk stalk. The two main arterial branches have almost surrounded the yolk blastopore, but are situated at some distance from it. Numerous small secondary branches grow toward the yolk blastopore, and some of these connect The Embryology of Heterodontus japonicus 749 with small veins emptying into a venous ring close to the margin of the blastoderm. The main trunk of the vitelline vein drains the venous ring and courses straight to the yolk stalk. In the stage shown in Text-figure 58c, the yolk blastopore has been entirely over- grown by the blastoderm. The venous ring has disappeared, and the area formerly occupied by the yolk blastopore is now traversed by a continuation of the main trunk of the vitelline vein. This trunk now receives numerous small veins, usually joining it at right angles. The arterial ring, formed by the two main branches of the vitelline artery, gives off numerous secondary branches which subdivide repeatedly as they grow toward the venules. The arterioles interdigitate with the venules or connect with them presum- ably by means of capillaries. There are no branches extending in a centrifugal direction from the arterial ring. The main arterial trunk does not give off side branches. The later stages in the development of the vitelline vessels of Pristiurus need not be considered. Dean’s series of figures depicting stages in the development of the vitelline vessels of Heterodontus japonicus is the most extensive and detailed portrayal of these vessels in any Elasmobranch known to the writer. Even the smallest vessels appear to be drawn with great fidelity and accuracy, but owing to their profusion many of them, even in the cajginal drawings, can be distinguished only by using a reading glass. In Dean’s series of drawings, the first to show vitelline vessels is Figure 56, plate V. In this figure two delicate arteries on each side, branches of a median unpaired vitelline artery, proceed laterad and then caudad. These arteries give off a few short secondary branches barely distinguishable in the drawing. The posterior artery on the right is in process of disappearance, having lost its connection with the main trunk. The thick red ring surrounding the yolk blastopore in this and in earlier stages is not a blood vessel; it is the remains of the pigment of the “orange spot’’, now confined to the extreme margins of the blastoderm. In Figure 57, plate V, there are two branches of the vitelline arterial trunk on the left, but only one on the right; there are only faint indications of secondary branches. A great many very small venules (best seen with a reading glass) drain into the red zone surrounding the yolk blastopore. Presumably the red zone now contains a venous ring or at least a venous network. The simple pattern of the arteries pictured in Text-figure 58a is attained, in Het- erodontus japonicus, only after the early developmental irregularities have been smooth- ed out. In Figure 58, plate V, we see such an arterial pattern, but the veins have attained the stage shown in Text-figure 588. In H. japonicus the venules that drain into the venous ring are very numerous, but they are so slender and set so closely together that individual venules can be made out only with the aid of a reading glass. In the stage represented in Figure 58, plate V, there is an irregular venous ring. This figure, and some of those that follow, are complicated by the presence of the problematical “holoblastic cleavage” pattern, described by Dean and illustrated by Figures 1 to 6, plate I, of this article. These “cleavage” furrows have been overgrown by the blastoderm, but in the living egg they 750 Bashford Dean Memorial Volume show through it. In the original, a spot in front of the embryo probably represents the optical effect of an oil globule in the yolk mass. It has been removed. In Figure 59, plate V, the pattern of both arteries and veins is essentially the same as in the preceding figure, but the yolk blastopore is smaller and some of the venules seem to drain into an incomplete inner venous circle. This, perhaps, is an individual variation. The venules are longer than those delineated in the preceding figure. The vitelline vein, crossed by the tail of the embryo, may be seen leading forward to the yolk stalk which is attached to the pectoral region of the embryo. Figure 60, plate V, shows right and left branches of the vitelline artery diverging more widely than in the preceding stages; their extremities extend to the margin of the figure. The yolk blastopore is reduced to a tiny circular area just behind the pelvic region of the curved embryo. A venous circle is lacking, and the venules converge toward irregular masses, colored red, closely surrounding the yolk blastopore. These masses may, in part, represent pigment, but it seems likely that they consist mainly of extrav- asated blood. Some of the venules begin at the extreme lower edge of the figure. The embryo lies partly on its right side, so that a blood vessel, presumably the vitelline vein, appears to the left of its ventral surface. In Figure 61, plate V, the trunk and the two main branches of the vitelline artery are more prominent than in any of the preceding figures; but the branches extend to the opposite side of the egg, which is not represented by a drawing. The yolk blastopore has completely disappeared. The vitelline vein receives two parallel main branches close to the yolk stalk. The veins and venules have assumed a dendritic pattern. The round spot underneath the middle of the embryo is probably the optical effect of an oil globule in the yolk mass. The egg represented in Figure 62, plate V, is anomalous. It bears two embryos (twins) each with its own vitelline artery and vein; but the two veins drain the same nexus, into which all the venules empty. The unpaired vitelline arterial trunk leading toward the top of the figure is longer than any shown in earlier stages. This artery ends in the usual two branches, but the other artery passes to the margin of the figure and cannot be traced further. In Figure 63, plate V, the vitelline artery passes to the opposite side of the egg before branching. This figure, taken in connection with those that follow, indicates that the arterial circle forms entirely on the hemisphere of the egg farther away from the yolk stalk. The vitelline vein is still short and its manner of branching dendritic. Figure 64, plate VI, represents a stage slightly later than the preceding, though the vitelline artery divides before reaching the upper part of the figure. Leading to the yolk stalk, there are two main vitelline veins; the more anterior branches of these veins are the strongest. This is an example of a tendency, by no means universal, for the vitelline veins to occur in two groups, right and left respectively. Figure 65, plate VI, is perhaps intended to represent the reverse side of the same egg, since the drawings of this plate retain their original paired arrangement; but a careful study shows that the two figures The Embryology of Heterodontus japonicus Tal are not entirely compatible, though they represent different aspects of two eggs in nearly the same stage. This is the first drawing to show the arterial circle, though it may occur in an earlier stage. The arterial circle gives off many branches that reach the margin of the figure, but none of these appear in Figure 64, plate VI, except possibly a few connecting with the vitelline vein. Figure 65 shows the vitelline artery giving off two side branches, but these are not present in Figure 64. Likewise the venules of the two figures do not correspond. The embryo, as shown by its orientation, is now free to rotate at least 90 degrees on the axis of the yolk stalk. Figure 66 and 67, plate VI, are companion drawings. The arterial ring shown in Figure 67 is very narrow, and its branches are numerous. Some of the arterioles reach the surface shown in Figure 66; and conversely, some of the venules shown in profusion on this surface interdigitate and probably connect with the arterioles on the opposite side of the egg. There are two vitelline veins, coursing nearly parallel to each other, each with its own system of branches. An extreme example of the tendency for the vitelline veins to occur in two groups, right and left, is found in the egg represented in Figure 78, plate VII. The arrangement here reminds one of the condition found in the corresponding stage of Chlamydoselachus (Gudger, 1940, pages 603 and 619; Figure 7, plate I; and Text-figure 4). All the smaller vitelline veins, in Chlamydoselachus, drain into a single median vein; but two groups of veins, right and left, are prominent. Figures 68 and 69, plate VI, are companion figures representing different aspects of the same egg— ina stage slightly later than the preceding. There is no essential difference in the pattern of the vitelline vessels save that the arterial circle is nearly closed by the coalescence of segments that have become approximated. The two main branches, right and left, of the vitelline veins unite before reaching the yolk stalk. Figures 70 and 71 (companion figures on plate VI) are similar to the preceding with the exception that Figure 71 shows complete absence of the arterial circle. This has been replaced by an extension of the main trunk of the vitelline artery. The portion of the arterial trunk derived from the arterial circle branches profusely, while the stem portion, shown in Figure 70, lacks branches. This figure represents the latest stage in which the patterns of both arteries and veins retain a high degree of bilateral symmetry. Figure 72, plate VI, shows little change from the preceding stage save that the veins and venules are more profuse. Its companion, Figure 73, plate VI, exhibits a decided lack of symmetry in both arteries and veins. Its most striking feature is that, on one side, a large number of venules reach almost to the main branches of the vitelline artery. The dark area around the head of the embryo in Figure 72 is probably the optical effect of an oil drop in the yolk mass. Figure 74, plate VI, shows around its margin a profuse interdigitation and intercon- nection of arteries and veins. The same situation prevails in the upper portion of Figure 75, which shows the reverse side of the same egg. Here, as in the preceding stage, the vitelline artery has two main, though unequal, branches. The large circular dark area 752 Bashford Dean Memorial Volume around the base of the yolk stalk in Figure 74 probably represents the optical effect of an oil globule in the yolk mass. The only remaining figure showing the vitelline vessels of Heterodontus japonicus is Figure 81, plate VII. This represents a much later stage. The large vessel on the right side of the figure is the vitelline artery; therefore the embryo must have reversed its original orientation on the yolk sac. A profuse system of vitelline veins is distributed to the left side of the figure (original right side of the yolk sac). Evidently there is a similar group on the opposite side, as in Figure 78, plate VII. =, ——s Yh / ff if f/ y yj Ys ff IIL [i M 4G | Text-figure 59. An embryo of Heterodontus japonicus shortly before hatching, showing its coiled condition and its orientation within the capsule. t T. a., respiratory aperture. From a drawing left by Bashford Dean, but evidently not his handiwork. It has been necessary to correct the positions of the gill-clefts, eye, mouth, and nasal aperture. HATCHING AND THE NEWLY HATCHED YOUNG The part played by the egg capsule in the mechanics of hatching is described, for Heterodontus japonicus, on page 709. It has already been mentioned that, in his notebook, Dean records the length of a newly hatched Japanese Bullhead Shark as about 7 inches (180 mm.). This was the length of the fish observed in the act of escaping from the egg capsule. A newly hatched fish, in dorsal view, is portrayed in Figure 83, plate VII. The Embryology of Heterodontus japonicus Woe Since the young fish pictured in Figure 84, plate VII, is only two weeks older, it is best considered in this section. Dean’s observations are here quoted from his typed manuscript. A stage shortly before hatching is shown [Text-figure 59]. The young fish is coiled compactly, the fins wrapping around the body, the head being below |i.e., toward the small end of the capsule], the trunk bent into a loop and the tail continued so that it approaches the larger end of the capsule. The snout lies close to the breathing apertures of the smaller end of the capsule, and the gill-openings are not [very] distant from the right and left aper- tures of the capsule’s larger end. These apertures at such a stage are large, the weathering of their margins having progressed to such a degree that a considerable current of water may be circulated through the capsule from the smaller to the larger end. The circulation is effected by the young fish, for in the partly opened capsule one may see with what strong muscular effort the fish is compressing and expanding its gill-pouches, drawing the water in through its mouth at the smaller end of the capsule and ejecting it in the opposite direction. Text-figure 60. Outline drawing showing the attitude of a newly hatched Heterodontus japonicus, with its head upraised and partly out of water as if seeking to escape from the aquarium in which it was confined. From a drawing left by Bashford Dean. In a single instance the act of hatching was observed. An egg was brought in which was curiously light in weight, its walls papery and studded with barnacles: at first sight it seemed empty, but an examination showed that the larger end of the capsule had not opened. On April 4, it was placed ina laboratory aquarium: four days later, happening to take it in my hand, I felt it suddenly vibrate, as though it enclosed a young fish which had been alarmed by my touching it. This movement lasted a few seconds, then the fish suddenly appeared. The hatching took place so quickly and unexpectedly that its details were not followed. The valve opened and closed, and there was a young fish swimming about in the aquarium. It had emerged tail foremost, that was about all that was definitely noticed.1 A student of animal behavior would have been interested in this newly hatched fish. For it showed the most finished instincts. It swam around the aquarium actively for about half a minute, breathing quickly and expanding its gills. It had from the beginning the move- ‘In Dean’s original notes it is stated, in his own handwriting, that the young fish had emerged head foremost. Considering that in this stage the yolk mass had almost entirely disappeared, it appears probable that the fish would be able to reverse its orientation within the capsule, and thus either end might escape first from the capsule—presumably from its broad end. 754 Bashford Dean. Memorial Volume Text-figure 61. Attitude of a newly hatched Heterodontus japonicus, with its back arched upward, exploring the corners of the aquarium. From a drawing left by Bashford Dean. This drawing has been slightly modified to secure correct positions for the gill-clefts and the pectoral fin. ments of the grown fish, it swam easily and quickly, it readily changed direction, and I soon found that it could swim around obstacles; and, if touched, it could draw itself backward, using its pectorals as supports. Att first it was inclined to thrust its head out of water [Text-figure 60] as if anxious to escape,'and in doing this it showed considerable flexibility in its neck, and it would even arch the back upward: at times it would explore the corners of the aquarium [Text-figure 61], the head and anterior part of the body flexing downward: occasionally it would bend the head, showing again the suppleness of the neck [Text-figure 62]. A period of rest was next observed, then a period of activity, these alternating with more or less regu- larity. A position of rest is shown [Text-figure 63] when the young fish raises its head, spreads out its pectorals and depresses its unpaired fins, the tail flattened against the bottom, the tip of the dorsals falling over on the (left) side. The latter habit may be explained in one of two ways: either as a survival of its flatten- ing of the fins during the period of incubation, or asa larval adaptation by which it becomes in- conspicuous or less easily seized by a predatory neighbor. The young fish impressed one with the finished character of its movements: it Text-figure 62. Diagram showing two attitudes of the head of a newly hatched Heterodontus japonicus, illustrating the flexibility of the neck. From a drawing left by Bashford Dean. The gill- clefts have been redrawn in a more nearly correct position. The Embryology of Heterodontus japonicus 755 Text-figure 63. A position sometimes assumed by a newly hatched Heterodontus japonicus when resting on the bottom of the aquarium. From a drawing left by Bashford Dean. The gill-clefts have been redrawn in a more nearly correct position. swam easily and well, it showed varied movements of its pectorals: it bit, retreated and ad- vanced, it stood on the defensive, and it opened its mouth widely [Text-figures 648 and 64c] as though to inspire fear. During [ordinary] breathing [Text-figures 644] it showed normally only the most anterior teeth. The color of the fish at hatching is dark [Figure 83, plate VII] with a series of light bands: it is covered with a dense “bloom” of mucus. Two weeks later [Figure 84, plate VII] it has grown 25 mm.; it has changed color, shows a kind of opisthure', holds its fins more rigidly. The present figure indicates that down the sides of the body, in this as in [some] earlier stages, there is a row of (16-17) deep vertical creases immediately behind the gillslits. They suggest a continuation of the line of the gills, with which obviously they have nothing to do. One reflects that it would be easy for an enthusiast to construct a phylogeny in which these deep creases fused with gut pouches and became of respiratory value. The spiracle is still of considerable size, and the dermal denticles are prominent. The latter condition is doubtless protective, guarding against injury from rubbing, and correlated with a long period of incubation in a capsule. WD Text-figure 64. Drawings showing the mouth of a newly hatched Heterodontus japonicus in three different poses: A, during ordinary breathing; B, moderately and C, widely open. From drawings left by Bashford Dean. 'Opisthure: The posterior end of the caudal axis of certain fishes and embryos of fishes, which degenerates into a rudimentary organ, or becomes absorbed in the permanent caudal fin developed in front of it (Century Dictionary). 756 Bashford Dean Memorial Volume In his manuscript Dean states that, at the time of hatching, the yolk sac has been completely resorbed. A small scar (about 8 x 5 mm.) shows where it last appeared. In a footnote to this manuscript Dean quotes Goodrich’s statement (1909, p. 132) that the yolk sac protrudes from the ventral surface of the embryo often after birth [hatching?]. Dean gravely doubts that this occurs in sharks under normal conditions. “I have witnes- sed birth [hatching] in the cases of Cestracion (Heterodontus), Spinax, Raja, Pristiurus, Text-figure 65. A young female specimen, 280 mm. (11 inches) long, of Heterodontus japonicus in the collection of the Ameri- can Museum of Natural History. Probably it was obtained at Misaki by Bashford Dean. The color pattern has faded considerably, and is not well shown in the photograph. The mouth cavity has been opened by a lateral incision, here shown closed by several stitches. Photograph, American Museum of Natural History. and in no instance was there still an external yolk sac. Viviparous sharks will, however, under the stress of capture frequently give birth to young more or less immature”. Very likely, in oviparous sharks, hatching may be slightly hastened by handling the egg cap- sules. In his original notes on Heterodontus japonicus, Dean writes concerning the fish observed in the act of hatching: “Yolk sac, so large [size indicated by a circle 3 mm. in diameter], yellow, apparent between pectorals”. But Dean does not definitely state that this diminutive yolk sac protruded from the body of the fish. Perhaps it had been drawn into the body, and the yellow color was subsequently visible through the skin. Dean’s figure of a young H. japonicus aged two weeks after hatching (Figure 84, plate VII) should be compared with Brevoort’s figure representing another specimen in approximately the same stage (Text-figure 22, page 690). Dean’s specimen was 205 mm. (8.2 inches) long, while Brevoort’s measured 216 mm. (8.5 inches). Dean’s fish wasa fe- male, Brevoort’s a male. In the drawing Brevoort’s specimen appears to be more slender, and the fins longer. The transverse furrows of the ventrolateral body wall are not so numerous and well-defined in Brevoort’s figure as they are in Dean’s. The color pattern in Brevoort’s figure approaches more nearly that of the adult as portrayed in my Text- The Embryology of Heterodontus japonicus Woy figure 21. Some portions of the color pattern of Brevoort’s specimen appear to be unique. It is possible that an adequate collection of this species would reveal considerable varia- tion in the color pattern in all stages of its development. A 280M. YOUNG HETERODONTUS JAPONICUS This young female (Text-figure 65) belongs to the collections of the American Museum of Natural History and was probably procured in Japanese waters by Bashford Dean. It is one of the specimens used by Dean for the study of the developing teeth. An incision leading from the mouth nearly to the first gill-slit was made in order to expose the mouth cavity. This incision was closed by large stitches with fine white thread, but still shows as an irregular line in the photograph (Text-figure 65). Two lines, both nearly vertical but meeting at an acute angle, at the extreme anterior end of the snout, are mere artifacts—creases in the skin—and have nothing to do with the olfactory organ. The fifth gill-slit is smaller and less conspicuous than the others, both in the specimen itself and in the photograph. The spiracular opening is still large enough to be sharply defined. The parallel vertical grooves along the side of the body posterior to the gill-slits are less numerous, less regular and less conspicuous than they are in the specimen represented in Figure 84, plate VII, which is considerably younger. Some careful measurements of the specimen under consideration are given in Table II. TABLE II SOME MEASUREMENTS IN MILLIMETERS OF A 280-mm. FEMALE HETERODONTUS JAPONICUS Inoeall eng. concadocnsnsopsvevooooUgONOO SOUS ONOOUoOAODODOUDKOOODOD ODDO ACOUDHOODOODAOGGODE 280 (Greatestrwidthvofhead|(athrstipill-covers) Meee eect cient ert trier tt 44 Greatest height of head (at posterior end supraorbital ridge)... 2... 2.2220 35 Greatest height of body (in a transverse plane passing through fifth gillcovers)..............- 000s see ee ee eee 42 [Laan GH ieee. Jo posoocanncopdocodda adodson boDboboccaconoDooDDonADOboRgdQUGeOaCCODNN 17 Lard aGriniangillans.. > ccoapnanodoanodopoogdacHHoboNdoocOODSgDOUON SOO DAD OOD OODOO COORD ENODUNS 8 Baselownhrstdorsaltoverlaps|basciompectoral enn ernie e eerie retire tic ieichnercereticreth Rackets tck isle rett reer -T- 8 engthiofibaseovanallin pee ee nene eer eee etter innit kere iat taper 16 Distance between base of anal fin and ventral lobe of caudal... 0.1... eee eee eee 2 Distancefromitipitoitiplokextendedipectoraltfinsmmereeeren ieee eritiielrnerekitelteicieterrer kee tenet ices 160 Vertical distance from ventral surface to tip of extended first dorsal fin. .... 0.0.2... ccc 100 Most important for the identification of the species is the fact that the color pattern of this 280-mm. fish is fairly well preserved (though it does not show well in the photo- graph). The color pattern agrees in most respects with the color pattern of the younger specimens portrayed in Figures 83 and 84, plate VII. If one ignored the color pattern and depended entirely on Garman’s key (page 663 of the present article) one would be very likely to classify this specimen as Heterodontus phillipi instead of H. japonicus. But the differences in the color patterns of the two species are very great, especially in young 758 Bashford Dean Memorial Volume specimens (compare Text-figures 8 and 9, page 668, with Figures 83 and 84, plate VII). Garman’s key, which depends mainly on the positions of certain of the fins, was perhaps not intended to apply to such young specimens. Changes in the spacing of the fins may be brought about by differential growth. EXTERNAL AND INTERNAL GILL-FILAMENTS To the list of embryos of Heterodontus japonicus, already described, that bear ex- ternal gill-filaments, one must add those embryos represented by Figures 66, 68, 70, 72 and 74, plate VI. In the last-named figure the external gill-filaments are very profuse. So far as one may judge from the series of embryos portrayed in Dean’s drawings, marked individual variations in the degree of development of the external gill-flaments of Heterodontus japonicus are rare. To be sure, the embryo pictured in Figure 36, plate III, is entirely lacking in external filaments; whereas in another embryo of approximately the same general stage (Figure 81, plate VII) the external filaments attain their maximum development. But it is probable that the condition shown in Figure 36, plate III, is exceptional. If this embryo were left out, the remaining series (including those embryos, already noted, which are not represented by drawings) would show a fairly regular gradation in the development and regression of the external gill-filaments. The latest member of this series of embryos showing external gills is the one repre- sented in Figure 38, plate III. Therefore the external gill-flaments of Heterodontus japoni- cus are not known to persist to such an advanced stage of general development as they do in Chlamydoselachus (Gudger, 1940, pages 629-630 and plate VI). Of Chlamydosela- chus, a female specimen 614 mm. long and a male specimen 538 mm. longare portrayed with short external gills. These specimens had attained the adult form, but were not full-grown and were probably not sexually mature. The reproductive organs of a 1398-mm. female Chlamydoselachus dissected by me (Smith, 1937, Text-figure 85) were decidedly imma- ture, and in a female Chlamydoselachus 1550 mm. long (ibid., Text-figure 86) they were just approaching maturity. In these specimens, as well as in the two sexually mature females dissected by me, the gill-flaments did not show externally with the gill-flaps closed. The question arises, what is the relation of the external gill-filaments of the embryo to the permanent gill-filaments of the adult? Of Chlamydoselachus, Gudger (1940, p. 639) writes: “these so-called external gills of the frilled shark are nothing but precociously overgrown permanent gills, which later on shorten until but a bare remnant shows beyond the gillopening.” I have been able to examine gills of Heterodontus in critical stages of their development and to observe that the external gill-filaments are not fundamentally different from the rudiments of the permanent filaments, but are essentially the same structures lengthened distally. It is better to begin with the adult stage and to trace the history of the gill-flaments backward. Thave had no adult specimen of H. japonicus, but I have examined the gill-filaments in an adult H. quoyi. Here, the filaments are short and deep-set, so that the gill flaps must be pried well apart before one can observe the filaments with a lens. The fundamental The Embryology of Heterodontus japonicus 759 plan of these gill-flaments is not unlike that described for Chlamydoselachus (Smith 1937). Each filament of Heterodontus is a narrow band attached by one edge to the gill-septum which it traverses in a radial direction. Thus the filaments lie approximately parallel to one another; they are very numerous and are set close together. The extreme distal end of each filament stands slightly away from the gill-septum; in other words, the distal ends are free from direct attachment to the septum. Each filament bears on both surfaces a series of close-set parallel ridges, the lamellae, which extend transversely to the long axis of the filament. In Heterodontus the close-set lamellae project slightly beyond the free edge of the filament, giving it a serrated appearance. In the 280-mm. (11-inch) young female Heterodontus japonicus the gill-filaments are much the same as in the adult specimen of H. quoyi; but the filaments are longer and their distal extremities project farther from the gillseptum. Except for their serrated appear- ance, these finger-shaped extremities of the gill-filaments suggest the rudimentary filaments of the early embryo. The filaments of this specimen are easily exposed, since they cover a considerable extent of the gillseptum. They are not, however, visible when the gill flap is closed. In the 78mm. (three-inch) embryo of H. japonicus already mentioned, I found the rudiments of the internal gill-flaments (those that persist in the adult) in connection with external filaments (shown in Figure 38, plate III). The two kinds of gill-filaments are continuous structures. The rudimentary internal filaments are attached, throughout all but a small distal portion, to the gillseptum and are distinguished by the presence of rudimentary lamellae. The distal ends of these internal filaments are continuous with the rod-like external gillflaments, which lack lamellae. Bearing in mind this relationship between the external gill filaments of the embryo and the internal gill-filaments of the adult, the occurrence of gill-filaments protruding from the spiracular cleft is conclusive evidence (if such evidence were needed) that the spiracu- lar cleft in sharks was primitively a gill-cleft functioning in the usual manner. During early development the spiracular cleft is as large as the gill-clefts, with which it is serially homologous; but dur- ing later development its external orifice becomes very small, and the spiracular canal takes on special functions concerned with respiration. In some specimens of Heter- odontus the spiracle is so small that it seems vestigial. Text-figure 66 Roof of the mouth cavity of a 78mm. (3-inch) embryo of Heter- odontus japonicus. The dental ridge, formed by the upper jaw, is situated between the olfactory region anteriorly and the breath- ing valve posteriorly. The small pit, shown in the center of the figure, leads into Rathke’s pouch. From a drawing left by Bashford Dean. 760 Bashford Dean Memorial Volume DEVELOPMENT OF THE TEETH Among Dean’s drawings of Heterodontus japonicus are four figures, which were found mounted in serial order, illustrating the development of the teeth. These are reproduced as my Text-figures 66 to 69. There are no records concerning the original drawings, neither accompanying the drawings nor in Dean’s notebooks. 2%; 23 Wea Gu GULLS € Text-figure 67. Text-figure 68 Interior of the mouth and pharynx of a young (probably recently hatched) Japanese Bullhead Shark, Heterodontus japonicus. Text-figure 67. Roof of the oro-pharyngeal cavity, revealing the teeth of the upper jaw, the breathing valve, and the pharyngeal denticles. Text-figure 68. Floor of the oro-pharyngeal cavity, showing the teeth of the lower jaw, also both oral and pharyngeal denticles. After drawings left by Bashford Dean. The earliest stage, represented by Text-figure 66, represents the roof of the mouth cavity viewed from below. This drawing was made from the 78mm. embryo, in Dean’s collection, described and figured (Figure 38, plate III) in the present article. The lower jaw of this embryo has been cut away in order to expose the roof of the mouth. I have compared this dissection with Dean’s drawing (Text-figure 66) and can state that the drawing corresponds, in every detail, with the structures revealed by the dissection. Teeth are not yet visible; but the arch-like dental ridge (formed by the lower surface of The Embryology of Heterodontus japonicus 761 the palatoquadrate cartilages covered with mucous membrane) is readily seen between the olfactory region anteriorly, and what appears to be a breathing valve! posteriorly. The small pit represented in the center of the figure presumably leads into Rathke’s pouch. Text-figure 67, like the preceding, represents an upper jaw. It is the first drawing, of this series, portraying teeth. Presumably, this drawing was made from a recently hatched specimen. (For similar teeth of a recently hatched H. phillipi, observe Text-figure 13, page 672). The anterior teeth represented in Text-figure 67 are larger than the posterior teeth (contrary to the condition in the adult) and each anterior tooth possesses five cusps. Posteriorly, the number of cusps grades from five tonone. More distinctly than in Text- figure 66, the breathing valve appears divided into two main portions, anterior and pos- terior respectively. The central third of the anterior portion is subdivided into a large number of short lobules. The filamentous portions of the breathing valve bear an irregular fringe of lobules. Text-figure 68 portrays what is apparently the same stage in a lower jaw. This drawing should be compared with Text-figure 13, showing the teeth of a recently hatched specimen of H. phillipi. There is no sharp division between anterior (cuspidate) and posterior (grinding) teeth, and the total number of transverse rows is less than in the adult. The anterior two-thirds of the teeth are typically five-cusped. The extreme posterior teeth are almost or quite lacking in cusps. In the intermediate region, the num- ber of cusps is usually four. As in the upper jaw, the extreme posterior teeth, which lack cusps, are smaller than the largest anterior teeth. In the absence of any drawing showing the teeth in an earlier stage, it seems probable that most of the anterior teeth possess five cusps from the beginning—for it is known that Dean had a fairly close series of stages from which to select specimens for drawings. In the figure under consideration there is a row of unusually large oral denticles situated close to the inner margin of the jaw. Between these denticles and the teeth drawn in broad view, one may see the serrated edges of an inconspicuous inner row of teeth. Text-figure 69 represents the roof of the mouth cavity of the 280-mm. female Hetero dontus japonicus portrayed in Text-figure 65, page 756. Text-figure 69 depicts faithfully not only the form but the precise number and arrangement of the teeth in this specimen. There are three longitudinal rows, with an extra tooth at the extreme posterior end making a transverse row of four. The anterior teeth are still typically five-cusped. Two transverse rows of the most posterior teeth lack cusps, but each of these teeth bears a prominent longitudinal ridge. The posterior ridged teeth are much larger (especially longer) than the anterior teeth. The transition between anterior (cuspidate) and posterior (grinding) teeth is more abrupt than it is in earlier stages. The middle portion of the anterior division of the breathing valve consists of a compact group of long finger-like lobules—which may be seen more clearly in the specimen than in the drawing. 1T have found this problematical breathing valve not only in the 78-mm. embryo of Heterodontus japonicus, but also in the 280-mm. specimen of the same species and in a young 368-mm. H. quoyi. I have had no opportunity to observe it in the living fish, hence cannot state positively what is its function; but its position and structure suggest strongly that it is a breathing valve. 762 Bashford Dean Memorial Volume In the present article, the structure of the adult teeth of Heterodontus has been described for every species except japonicus. Teeth of young specimens (after hatching) have been described for every species except galeatus. Teeth of an embryo of Hetero- dontus have not been described for any species. Upon comparing the accounts, by various authors, of the teeth of the six species of Heterodontus, it seems to the writer that the specific differences are not very great and Text-figure 69 Roof of the mouth of a 280-mm. (11-inch) young Heterodontus japonicus, showing teeth of the upper jaw. From a drawing left by Bashford Dean. The Embryology of Heterodontus japonicus 763 that most of the observed differences are correlated with age and use. The most important points may be summarized as follows: The most anterior of the cuspidate teeth begin, as a rule, with five cusps, but some of the more posterior cuspidate teeth begin with only three or four cusps. The typically five-cusped condition of the anterior teeth persists until long after hatching. Before the adult (sexually mature) stage is reached, the number of cusps in these teeth is reduced to three, with the central cusp most prominent. Gradu- ally the lateral cusps become inconspicuous or even absent. With age and use (the food consisting mainly of molluscs, crustaceans, and sea urchins) the central cusp may become worn down until the anterior teeth, collectively, appear almost pavement-like. (The word pavement, as used here, refers to the old-fashioned much-worn stone-block pave- ment). The posterior or grinding teeth never have prominent cusps, and some are entirely without cusps. The few rudimentary cusps that appear in the early stages soon give place to a longitudinal ridge, useful in grinding the food. In older specimens, this ridge may be entirely worn away, leaving the tooth with a smooth rounded surface. Thus the posterior teeth become more pavement-like than the anterior teeth; in the adult they are much larger and stronger. In their prime, the anterior teeth are well-fitted for prehension, the posterior teeth for crushing and grinding. All the descriptions and illustrations of both young and adult teeth emphasize the differences between anterior and posterior teeth—differences that suggested the generic name, HETERODONTUs. Another view (see also Text-figure 1) of the Marine Zoological Station at Misaki where Dr. Dean studied the Japanese Bullhead Shark. BIBLIOGRAPHY ALLEN, GRANT. 1892 Science in Arcady, London. (Egg cases of the Port Jackson shark, p. 169). Attis, EDwArD PHELPs, JR. 1919 The lips and the nasal apertures in the gnathostome fishes. Journ. Morph., 32. (Heterodontus, 158-164, pl. II, figs. 6 and 7). Batrour, Francis M. 1885 The Works of Francis Maitland Balfour; memorial edition, edited by M. Foster and Adam Sedgwick. London. (The development of elasmobranch fishes, text, vol. I, pp. 60-520; pls., vol. IV, 3-23). BARNHART, PERRY SPENCER. 1932 Notes on the habits, eggs and young of some fishes of Southern California. Bull. Scripps Instit. Oceanog. Tech. Series, 3. 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Fenn., 36, 1-176, 5 pls. 768 Bashford Dean Memorial Volume Marsuart, A. M. 1881 On the head cavities and associated nerves of elasmobranchs. Quart. Journ. Micr. Sci., 21, 79-98, 2 pls. McCoy, FREDERICK. 1890 Natural history of Victoria. Melbourne and London. (Heterodontus phillipi, I, pp. 53-57, pl. 113, text-fig.). Mixrouno-Mactay, N., AnD Macreay, WHLLIAM. 1879 Plagiostomata of the Pacific. PartsT-II]. Proc. Linn. Soc. New South Wales, 3. (Heterodontus phillipi, galeatus, francisci and quoyi, 306-334, 5 pls.). 1884 Idem. Proc. Linn. Soc. New South Wales, 8. (Heterodontus japonicus, 426-431, pl. ). 1886 Idem. Proc. Linn. Soc. New South Wales, 10. (Heterodontus zebra, 673-678, 2 pls.). Muzier, J., unp Henze, J. 1841 Systematische Beschreibung der Plagiostomen. Berlin. (Heterodontus japonicus, p. 76, pl. 31). Neat, H. V. 1918 The history of the eye muscles. Journ. Morph., 30, 433-453, 20 figs. Nicxots, J. T., anD Murpuy, R. C. 1922 Ona collection of marine fishes from Peru. Bull. Amer. Mus. Nat. Hist., 46. (Gyropleurodus peruanus, p. 504). Ocisy, J. Douezas. 1890 List of the Australian Palaeichthyes, with notes on the synonymy and distribution. Proc. Linn. Soc. New South Wales, 2. ser. 4. (Heterodontidae, p. 184). Ospurn, Raywonp C. 1907. Observations on the origin of the paired limbs of vertebrates. Amer. Journ. Anat., 7, 171-194, 5 pls. Ospurn, R. C., anp Nicxots, J. T- 1916 Shore fishes collected by the “Albatross” expedition in Lower California with descriptions of new species. Bull. Amer. Mus. Nat. Hist., 35. (Gyropleurodus francisci, p. 141). Pair, ARTHUR. 1789 The voyage of Governor Phillip to Botany Bay (Australia). London. (Heterodontus phillipi, pp. 283-284, pl. facing p. 283). Reean, C. Tate. 1906 ~- Aclassification of the selachian fishes. Proc. Zool. Soc. London. Pt. 2, 722-758, text-figs. 1908 A synopsis of the sharkso f the family Cestraciontidae. Ann. Mag. Nat. Hist., 8. Ser. 1, 493-497. Ricuarps, A. 1917. The history of the chromosomal vesicles in Fundulus, and the theory of the genetic continuity of the chromosomes. Biol. Bull., 32, 249-291, 4 pls. RUcxert, JOHANN. 1885 Zur Keimblattbildung bei Selachiern. Ein Beitrag zur Lehre vom Periblast. $.B. Ges. Morphol. Physiol., 1, 48-104, figs. 1899 Die erste Entwickelung des Eies der Elasmobranchier. (In Festschrift zum siebenzigsten Geburtstag Carl von Kupffer, Jena, pp. 581-704, 8 pls., 7 text-figs.). The Embryology of Heterodontus japonicus 769 SAVILLE-KEentT, W. 1897 The naturalist in Australia. London. (Cestracion, pp. 192-194, fig.). ScamMMon, RICHARD E. 1911 Normal plates of the development of Squalus acanthias. (In Keibel’s Normentafeln zur Entwickelungsgeschichte der Wirbeltiere, Jena. 12. Heft, 140 pp., 4 pls., 26 text-figs.). SreBOLpD, Poitier FRANZ. 1850 Fauna japonica: Lugduni Batavorum. Pisces (Cestracion phillipi, p. 304). SmitH, BertTRAM G. 1912 The embryology of Cryptobranchus allegheniensis. Part II. General embryonic and larval development, with special reference to external features. Journ. Morph., 23, 455-579, 8 pls., 148 text-figs. 1929 The history of the chromosomal vesicles in the segmenting egg of Cryptobranchus allegheniensis. Journ. Morphol. Physiol., 47, 89-133, 6 pls. 1937. The anatomy of the frilled shark, Chlamydoselachus anguineus Garman. Bashford Dean Me- morial Volume: Archaic Fishes. WII, 331-520, 7 plates, 128 text-figs. STEINDACHNER, FRANZ. 1896 Bericht ueber die wahrend der Reise Sr. Maj. Schiff “Aurora” von Dr. C. Ritter v. Mieros- zewski in den Jahren 1895 und 1896 gesammelten Fische. Ann. K. K. Naturhist. Hofmus. Wien, 11. (Heterodontus japonicus, p. 224). : STRUVER, JOHANNES. 1864 Beschreibung des Heterodontus phillipi Bl. (Cestracion phillipi Bl.) mit Riicksicht auf seine fossilen Verwandten. Nova Acta Akad. Leopold-Carol., 23, 412-416, 2 pls. VALENCIENNES, A. 1855 Ichthyologie. (In Du Petit-Thouars, A. Voyage autour du monde sur... la Venus, pendant... 1836-39). Paris. (Cestracion pantherinus, XV, Zoologie (1855), pp. 350-351; Poissons, Atlas (1846), fig. 10, pl. 10). Van Wye), J. W. 1882 Ueber die Mesodermsegmente und die Entwicklung der Nerven des Selachierkopfes. Verh. K. Akad. Wet., Amsterdam, 22, 1-50, 5 pls. Watrte, Epcar R. 1896 On the egg cases of some Port Jackson sharks. Journ. Linn. Soc. London, 26, 325-329, pl. 12. 1898 Scientific report on the fishes. (In Report upon trawling operations off the coast of New South Wales, . . . carried on by H.M.C.S. Thetis”). Sydney. (H. phillipi and H. galeatus, p. 53). 1899 Scientific results of the trawling expedition of H.M.C.S. “Thetis”. Fishes. Mem. Australian Mus., 4. (Heterodontidae, 30-31, pl.). Wauittey, Grsert P. 1938 The eggs of Australian sharks and rays. Australian Mus. Mag., 6. (Heterodontus p. 373). 1940 The fishes of Australia, Part 1: The sharks, rays, devil-fish and other primitive fishes of Aus- tralia and New Zealand. Sydney. Roy. Zool. Soc. New South Wales. 280 pp., 303 figs. Woopwarp, A. SMITH. 1886 On the relations of the mandibular and hyoid arches in a Cretaceous shark (Hybodus dubrisien- sis). Proc. Zool. Soc. London, 218-224, pl. 770 1889 1891 1916 1921 Bashford Dean Memorial Volume Catalogue of the fossil fishes in the British Museum. London. Part 1, Elasmobranchii, 474 pp., 16 pls., 13 text-figs. Hybodont and cestraciont sharks of the Cretaceous period. Proc. Yorkshire Geol. and Polytech. Soc., 12, 62-68, 2 pls. Fossil fishes of the English Wealden and Purbeck formation. Part 1. Monog. Paleontog. Soc., 69. (Skull of Hybodus basanus Egerton, pp. 6 and 7, fig. 3). Observations on some extinct elasmobranch fishes. Proc. Linn. Soc. London, 133. sess., 29-39, 4 figs. ZIEGLER, HEINRICH ERNST. 1902 Lehrbuch der vergleichenden Entwickelungsgeschichte der niederen Wirbeltiere. Jena. (Selachians, pp. 101-152, 55 figs.). ZigEGuLER, H. E., uND ZIEGLER, F. 1892 Beitrage zur Entwickelungsgeschichte von Torpedo. Arch. Mikr. Anat., 39, 56-102, 2 Taf. ZITTEL, KARL A. VON. 1911 1923 1932 Grundztige der Palaeontologie. Munchen und Berlin. II, Vertebrata—Pisces. (Hybodontidae and Cestraciontidae, pp. 53-57, 11 text-figs.). Idem. (Hybodontidae und Cestraciontidae, pp. 58-63, 11 text-figs.). Text-book of palaeontology. Translated and edited by Charles R. Eastman. Second English Edition revised, with additions, by Arthur Smith Woodward. London. II. Vertebrata- Pisces. (Hybodontidae and Cestraciontidae, pp. 65—71, 12 text-figs.). Rei EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. IU 12. 13% 14. 15. 16. 17. 18. 19. READE Ss! EARLY DEVELOPMENT OF THE EGG OF HETERODONTUS JAPONICUS Egg taken at time of deposition. Polar view of upper hemisphere. The germinal disc (“orange spot’’) is indicated by a tiny circle close to top of figure. Upper hemisphere of an egg ina slightly later stage. The germinal disc is situated on the side of the egg away from the observer. It is indicated, as if seen through the egg, by a tiny dotted circle near the right hand margin of the figure. Lateral view of an egg ina stage between Figures 1 and 2. The position of the germinal disc is not indicated. Lateral view of an egg similar to the one shown in Figure 3. The germinal disc is indicated by a small dark spot on the right of the figure. An egg shown in lateral, slightly oblique, view. The germinal disc is indicated, as if seen through the egg, by a dotted circle in the upper right quadrant of the figure. An egg in a slightly later stage, oriented with ordinarily lower pole nearly uppermost. The germinal disc is situated on the side of the egg away from the observer. It is indicated by a tiny dotted circle in the upper left quadrant of the figure. . Figs. 1 to 6 have been published by Dean in the Annotationes Zoologicae Japonensis, 1901, vol. 4. They show furrows interpreted by Dean as a reminiscence of holoblastic cleavage. Eggs in these stages vary from 40 to 50 millimeters in diameter. The earliest observed stage of cleavage in the germinal disc. This region, constituting the early blastoderm, was removed from the yolk mass. Viewed by transmitted light, it was drawn, under magnification, in natural colors. A later stage in the segmentation of the germinal disc. The blastoderm, removed from the egg and viewed by transmitted light, was drawn under magnification in natural colors. Slightly later stage of cleavage in a germinal disc viewed as an opaque object. Blastoderm in an advanced cleavage stage, removed from the yolk and viewed by transmitted light. The crescentic light area in lower part of figure is the blastocoele seen by focussing down- ward through its roof. Elongate blastoderm, perhaps ready for gastrulation, viewed as an opaque object and drawn in natural colors. This blastoderm is 5 mm. long. The pale area surrounding it is the marginal zone of the periblast. Surface view of a blastoderm in an early stage of gastrulation. Note, at the posterior (lower) end, the neural groove bordered by upraised neural folds. Surface view of a blastoderm, with rudimentary embryo, slightly later than the preceding. Optical section through embryonic region in a stage intermediate between Figures 12 and 13. This figure, like the remaining ones of this plate, was drawn from a cleared preparation. Optical section of an embryo slightly later than the one shown in Figure 13. Optical section of an embryo with 4 pairs of complete mesoblastic somites. Optical section of an embryo with 12 pairs of complete somites. Optical section of an embryo with 14 or 15 pairs of somites. Optical section of an embryo with 15 or 16 pairs of somites. ArticLe VIII, Prarte I. A. Hoen & Co., Lrrn. EMBRYOLOGY OF HETERODONTUS JAPONICUS ’ BEANE I EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. REAR E SI LATER EMBRYOS OF HETERODONTUS JAPONICUS A cleared embryo with 18 complete somites. Measured on the slide, it is 3.5 mm. (about one-eighth inch) long. Surface view of an embryo with about 24 somites. Like some of the embryos represented in the surface views that follow, this one appears to have been drawn at a lower magnification than that used for cleared preparations. Surface view of an embryo with about 25 somites. A cleared embryo with at least 26 somites. Surface view of an embryo with at least 28 somites. This figure was drawn from the left side, but it has been reversed to facilitate comparison with other figures on this plate. Surface view of an embryo with about 35 somites. This figure, like the preceding, was drawn from the left side but has been reversed. A cleared embryo with about 37 complete somites. An embryo with about 41 complete somites, drawn after being cleared. Surface view of an embryo with at least 50 complete somites. An embryo with about 55 complete somites, drawn in surface view. Head and anterior part of the body of a cleared embryo. The number of somites is unknown. Surface view of an embryo with about 74 somites, now represented by myomeres. An embryo with about 85 myomeres, drawn in surface view. Since all the figures of this plate are lateral views, the number of somites (in later stages represented by myomeres) is recorded for one side only. 2 Dean Memoriat VoLUME a ArmicLe VIII, Prate II. BasHrorp Dean, Dir. A. Hoen & Co., Litn. EMBRYOLOGY OF HETERODONTUS JAPONICUS > fultt-< ee eh Wieser! Waipak fue i ae i Wy Les 100 EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. 33. . 34. ig. 35. S Bish ig. 39. PLATE III LATE EMBRYOS OF HETERODONTUS JAPONICUS An embryo with at least 88 myomeres (those near the tip of the tail are indistinct). An embryo somewhat later than the preceding. The myomeres are not visible externally. Another embryo, in Dean’s collection, slightly older than the one portrayed here, but younger than the one represented in the following figure, measures 38 mm. (about one and one-half inches) long. An embryo later than the one shown in the preceding figure. Except at the tip of the tail, the myomeres are not visible externally. Another embryo in the same stage of development, found in Dean’s collection, measures about 50 mm. (two inches) long. An embryo, with myomeres visible only in the posterior half of the figure. The absence of ex- ternal gill filaments in this stage is unusual. An embryo with profuse external gills. It measures about 70 mm. (two and three-fourths inches) long. This embryo is approximately 78 mm. (three inches) long. It has shorter and more delicate external gills. Note the lack of external gills in this embryo, which is about 90 mm. (three and one-half inches) long. moe ey aie FS Li ae a ArticLte VIII, Prare III. Basurorp Dean, Dir. A. Hoen & Co., Litn. EMBRYOLOGY OF HETERODONTUS JAPONICUS AEE SY) EMBRYOLOGY OF HETERODONTUS JAPONICUS PEASE RIV, ENTIRE EGGS OF HETERODONTUS JAPONICUS SHOWING THE RELATIONS OF THE EMBRYO AND THE OVERGROWTH OF THE YOLK MASS BY THE BLASTODERM Figs. 40 to 42. Upper hemisphere of eggs taken shortly after deposition. The germinal disc or “orange spot” is presumably undergoing cleavage. In Figures 40 and 41, the disc is surrounded by concentric white zones; in Figure 42, by a single white zone (periblast?). Fig. 43. A slightly older egg in which the germinal disc is in a late blastula stage. Fig. 44. The germinal disc or blastoderm is now almost ready for gastrulation. For larger and more accurate drawings of blastoderms in approximately the same stage, see Figure 11, plate I, and Figure 80, plate VII. Fig. 45. Anegg slightly later than the preceding. The blastoderm is larger, and is circular in outline. Fig. 46. This blastoderm is much larger than the preceding one. Its posterior (lower) margin is upraised and is in a very early stage of gastrulation. See also Figure 12, plate I. Fig. 47. A still larger blastoderm showing at its posterior edge the upraised embryonic area. For details see Figures 13 and 14, plate I. Fig. 48. There is shown here a marked increase in the size of the blastoderm. The embryo shows a definite head region. An embryo in approximately the same stage is shown in detail in Figure 16, plate I. Figs. 49 to 51. These figures show the blastoderm spreading over a hemisphere of the egg while the embryo, situated at the slight notch in the posterior margin of the blastoderm, is still very small and cannot be accurately delineated on this scale. The three stages are probably equivalent to Figures 22, 24, and 25, plate II. The drawings of this plate are in natural colors, save that the embryos represented in Figures 49 to 51, which in life are colorless and translucent, are portrayed in opaque white. All the drawings are reproduced about natural size. In all the figures, the yolk mass shows the furrows interpreted, by Dean, as a reminiscence of holoblastic cleavage. DEAN Memoriat Votume ARTICLE VIII, Prare IV. 40 41 42 43 44 45 46 47 48 49 50 51 Basurorp Dean, Dir. A. Hoey & Co., Lrtn. EMBRYOLOGY OF HETERODONTUS JAPONICUS PLATTS, \y/ EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. Fig. Fig. Fig. 5 5 eek . 34. 5 DBs 5 SLO: > Sp ig. 58. . 59. 60. 61. 62. 63. AL /ANIN 8) \W/ ENTIRE EGGS OF HETERODONTUS JAPONICUS SHOWING CLOSURE OF YOLK BLASTOPORE AND ORIGIN OF VITELLINE VESSELS The blastoderm covers more than a hemisphere of the yolk mass. The stage of embryonic devel- opment is perhaps equivalent to that shown in Figure 26, plate II. In this figure the yolk blastopore is appreciably smaller, though the embryo is no larger than the one represented in the preceding figure. Here the embryo appears to be in a stage slightly younger than the one shown in Figure 53, though the yolk blastopore is smaller. In this figure the embryo is in a stage approximately the same as the preceding. This is the first stage showing vitelline vessels, here entirely arterial. The main arterial trunk is not visible. There are two pairs of secondary vitelline arteries, right and left. The embryo is larger than the one shown in the preceding figure. This figure shows a decided increase in the size of the embryo and in the degree of closure of the blastopore. There are two vitelline arteries on the left, but only one on the right. A venous ring, surrounding the yolk blastopore, is in process of formation. The main trunk of the vitelline artery is shown proceeding forward from the yolk stalk, and branching to form only one pair of arcuate arteries. A multitude of radially-directed vitelline venules drain into the venous ring. The yolk blastopore is nearly closed. There is no change in the arterial pattern, but the venules are further developed. The embryo is in approximately the same stage as the one represented in Figure 29, plate II. The venous ring has contracted almost to the point of disappearance. The arterial pattern is unchanged. The embryo is decidedly larger than the one shown in the preceding figure. In this figure the vitelline vessels are especially well shown. Right and left vitelline veins extend to the margin of the figure. There are two main branches of the vitelline vein, extending from the plexiform group of venules to the yolk stalk. An egg with two embryos (identical twins), perhaps with a single tail. Each embryo has its own vitelline artery and vein, but the veins drain the same nexus of venules. The arterial vitelline trunk passes unbranched to the other side of the egg. There is a single vitelline vein draining a dendritic group of venules. The embryo still heads in the direction of the vitelline artery. Figures 52 to 59 show stages in the closure of the yolk blastopore. In Figures 52 to 56 the problematical “cleavage” furrows of the yolk are conspicuous in the yolk blastopore. In Figures 53 and 54 some of these furrows show faintly, and in Figures 58 and 59 many of them show conspicuously through the translucent blastoderm. Figures 56 to 63 show early stages in the development of the vitelline vessels. In some of these drawings, the pattern a ie vessels is more or less obscured by the presence of “cleavage” furrows in the yolk, which show through the astoderm. All these drawings are in natural colors save that the embryos, which in life are colorless and translucent, are portrayed in Greque white. With the possible exception of Figures 58, 59 and 60, all the drawings are here reproduced about natural size. Dean Memorrat Votume 55 61 Basnrorp Dean, Dir. 53 56 59 EMBRYOLOGY OF HETERODONTUS JAPONICUS 54 60 63 ArTICLE VIII, Prate V. A. Hoen & Co., Litn. bellies, \V/IL EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. 64. Fig. 65. Fig. 66. Fig. 67. Fig. 68. Fig. 69. Fig. 70. Fig. 71. Fig. 72. Fig. 73. Fig. 74. Fig. 75. PLAIN W/L FURTHER DEVELOPMENT OF THE VITELLINE VESSELS IN HETERODONTUS JAPONICUS In this figure the embryo, for the first time in this series, lies at right angles to the direction of the vitelline artery, showing that the embryo is able to rotate by twisting the yolk stalk. The vitelline artery branches before reaching the margin of the figure. There are two vitelline veins leading to the yolk stalk. An egg in nearly the same stage as the preceding, showing the hemisphere opposite the one to which the embryo is attached. The two main branches of the vitelline artery have joined an- teriorly to form the arterial circle. A later stage in which the arterial pattern resembles that shown in Figure 64, while the branching of the vitelline veins is much more profuse and extensive. Opposite hemisphere of the egg represented in the preceding figure, showing the convergence of right and left sides of the arterial circle, which is profusely branched. Here the embryo has been tilted to expose the yolk stalk, which shows the main trunk of the vitelline veins. The vitelline artery does not branch before passing to the other hemisphere of the egg. The opposite hemisphere of the egg portrayed in the preceding figure. The arterial circle is nearly obliterated by the coalescence of right and left sides. The arterial and venous vitelline trunks are here seen pursuing parallel courses as they enter the yolk stalk. The larger branches of the vitelline vein occur in two groups, right and left. The opposite hemisphere of the egg represented in the preceding figure. The right and left sides of the arterial circle have coalesced to form an extension of the main arterial trunk. Both arterial and venous patterns are similar to those shown in Figure 70, but the branching of the veins is more profuse. The opposite hemisphere of the egg depicted in the preceding figure, showing a symmetrical branching of the vitelline artery. In this figure there is a fairly long vitelline vein having side branches. The embryo is in a stage slightly older than the one represented in Figure 35, plate III. Opposite hemisphere of the egg portrayed in the preceding figure. The pattern of the arterial branching is nearly symmetrical, though quite unlike that shown in Figure 71. All the figures on this plate are in natural colors. The drawings are reproduced about natural size. Dean Memorrat VotumE ArticLe VIII, Prate VI. BasHForp Dean, Dir. A. Hoen & Co., Lrru. EMBRYOLOGY OF HETERODONTUS JAPONICUS eat y Iie He LAIe, SVU EMBRYOLOGY OF HETERODONTUS JAPONICUS Fig. 84. PEARESVAl EGG CAPSULES, EGGS, EMBRYOS AND NEWLY HATCHED YOUNG OF HETERODONTUS JAPONICUS An egg capsule in side view. The arrow points towards the respiratory groove, just beginning to deepen and lengthen into the respiratory cleft. The length of the capsule varies from 120 to 180 mm. (four to seven inches). Oral, upper or proximal view (showing the larger end) of the capsule. An egg case opened to show the yolk sac and embryo within. Upper hemisphere of an egg at the time of deposition. This figure shows the tiny germinal disc (reddish, surrounded by a white zone) and some problematical furrows distributed over the greater part of the surface of the yolk. Reproduced about four-fifths natural size. A late blastula drawn as an opaque object seen through a layer of albumen. The blastoderm is limited to the reddish area, which is surrounded by a pale yellowish zone, the periblast. Advanced embryo with yolk stalk and yolk sac. The figure is slightly larger than natural size. The external gill-flaments have reached their maximal development. Later embryo with yolk stalk and yolk sac. In some respects (e.g., the position of the nasal apertures) this embryo is either distorted, abnormal or incorrectly drawn. Dorsal view of a newly hatched Heterodontus japonicus. Its length isabout 180 mm. (seven inches). Lateral view of a young female Heterodontus japonicus, about two weeks after hatching. Its length is about 205 mm. (eight inches). All the figures of this plate are in natural colors. DEAN Memoria VoLuME ArTICLE VIII, Prare VII. Basurorp Dean, Dir. A. Hoen & Co., Lrtn. EMBRYOLOGY OF HETERODONTUS JAPONICUS ANALYTICAL SUBJECT INDEX The Dean Memorial Volume is so large and heavy that it seems advisable that it be bound as Part I containing Articles I, II, II, IV and V; and Part II containing Articles VI, VII and VIII together with the Index. The pagination is continuous and Part II begins with page 331. Abel, O., on Dinichthys, 176, 180 Heterostius, 180 Acanthaspida, 157, 169, 177, 199, 200, 208 carapace, 179, 210 fin, dorsal, 198 Acanthaspis, fin, 198 scales, 210 spinal (plate), 176, 177 Acanthias, canals, 455 cranium, 351 muscles, 390, 394 vitelline circulation, 620 A. vulgaris, see Squalus acanthias Acanthodians, myxopterygia, 724 Acrodus, dentition, 697 Adams, L. A., on Arthrodira, 184, 187, 198 Dinichthys, 121, 152, 185, 188, 189, 190 Adams-Jaekel theory, 185, 187 Agar, W. E., on Protopterus, 389 Agassiz, L., on Coccosteus, 145, 202, 208 Agnathostomata, 67, 100 Allen, G., on Heterodontidae, 707 Allis, E. P., on Chlamydoselachus, 268, 269, 278, 279, 290, 350, 351, 355, 356, 357, 359, 360, 362, 391, 396, 397, 398, 399, 400, 415, 416, 428, 463, 465, 474, 475, 477, 479, 480, 481, 492, 629 Heterodontus, 662 Squalus, 492 Amia, egg, cleavage lines, 725, 726 Amphibia, gills, 629 Amphioxus, 70, 357, 416 cartilage, labial, 357 thyroid, 416 : Angarichthys, spinal (plate), 177 Angulare (plate), 175, 185 Antiarchi, 177, 180, 187, 208-209 Aorta, Chlamydoselachus, 461-466 embryonic, 465 Heptanchus, 464 Squalus acanthias, 464, 465 Apertures, Chlamydoselachus, abdominal, VI-v* urethral, 443 Arches, basibranchial, Chlamydoselachus, 359, 361, 362, 363 Heptanchus, 363 Hexanchus, 363 basihyoid, Chlamydoselachus, 360 branchial, Chlamydoselachus, 358-363, 396, 420, 468, 661,662,742, 743, 744 ,746; VI Heptanchus, 363 Heterodontus, 662, 744, 745 H. japonicus, 742, 743, 744 H. phillipi, 662 gill, Arthrodira, 199-202, 207, 391 Chlamydoselachus, 358, 363, 420-423, 593, 595, 597, 598, 599, 600, 601, 604— 617, 623, 626 Coccosteus, 199 Dinichthys, 199, 200-202 Selachii, 391, 743 Squalus, 594, 596, 600, 601 hyoid, Arthrodira, 207 Chlamydoselachus, 359 Dinichthys, 201 sharks, 699 hyomandibular, Chlamydoselachus, 358 Heptanchus, 700 Heterodontidae, 662 Hybodus basanus, 701 sharks, 699, 700 mandibular, Chlamydoselachus, 356, 396 Dinichthys, 202 Heterodontus japonicus, 662, 744, '745 neural, Cestraciontidae, 696 Hybodontidae, 696 pharyngeal in Selachii, 743 phylogeny of, 363 visceral, Chlamydoselachus, 356, 363, 390, 396 Heptanchus, 356 Hexanchus, 356 nerves, origin of, 399 Scyllium canicula, 476 Torpedo, 743 Armor, Antiarchi, ventral, 209 Arthrodira, head, 122-126, 208 ventral, 198, 201 Chondrostei, head, 204 Dinichthys, dorsal, 117, 119, 120, 125, 160-170 head, 117, 125, 127-152, 153-159, 185- 188, 189-192, 205; IV-1—IV-n1 ventral, 119, 120, 125, 170-174, 175, 180, 188, 189, 191, 192, 200 Macropetalichthys, 204, 206 Rhynchodontus, 203 Armor plates, see Arthrodira, Coccosteus, Dinichthys Arterial ring, Chlamydoselachus, 617-622, 749 Heterodontus japonicus, 749 Pristiurus, 618, 748-749 Arteries, Bdellostoma, 90 Chlamydoselachus, 461-471, 603, 617-621 Elasmobranchii, 471 Heptanchus, 467-468 Heterodontus japonicus, 749, '750, 751, 752; VIIL-v, Villbvi Notorhynchus, 468 vitelline, see Heterodontus and Pristiurus below Atterioles, Chlamydoselachus, 749, 751 Arthrodira, arch, gill, 199-202, 207 hyoid, 207 armor, head, 122-126, 208 ventral, 198, 201 armor plates, antero-ventro-lateral, 172 post-marginal, 134, 135 post-sub-orbital 202 spinal, 176, 179 canal, sensory, 122, 126, 135-137, 139 dentition, 146, 206, 207 fins, 195, 197-198, 200 pectoral, 197, 198, 200 gill, 210 girdle, pelvic, 197, 198 head, 180, 200, 204, 205, 218 jaw, 145, 184-185, 187, 207 mouth, 187-192 muscles, 194 neurocranium, 192-194 phylogeny, 202-211 reconstruction, 122, 123, 142 Asterolepida, 132, 179, 180, 208 Ayers, H., on Bdellostoma, 77, 92 Chlamydoselachus, 352, 459, 461, 463, 467, 471 *Since the plates of each article are numbered consecutively they are herein referred to by designations indicating both articles and plates. Thus, V-11, means Article five, Plate two. 785 786 Balfour, F. M., on Elasmobranchs, 582 fin-fold theory, 341 Pristiurus, 589, 617, 619, 748-749 Selachii, 455 Barnhart, P.S., on Heterodontus francisci, 708, 710, 712, 713, 718 Bdellostoma, 43-62, Il1, In; 63-110, WI-1—Il1v artery, 90 bibliography, 101-102 distribution, 80-83, 97-98 hermaphroditism, 67, 69 longevity, 92 reproductive system, 69, 83-88, 90, 95; I4—illiv sex, 70, 77-78 testis, '70, 83-85, 87, II4 Bdellostoma burgeri, distribution, 80 eggs, 86, 87, 89, 95, 97, Ilan embryos, 68, 97 hermaphroditism, 67, 77, 82, 85, 86, 89, 95, 96, 98 ovaries, 86, 88, 89, 91, 92; II1-4 reproductive system, 76, 83-88, 90, 95; IWa—tll-iv size, 82, 98 testis, II]-1 Bdellostoma forsteri, distribution, 77 hermaphroditism, 76-78 Bdellostoma stouti, brain, 99 breeding season, 94, 95 corpora lutea, 89, 92, 95 distribution, 79, 83 egg, 47-62, 84, 85, 86, 87, 88; Il, In blastoderm (disc), 54, 55 blastomeres, 52, 53, 54, 55, 56 blastopore, 56 capsule (shell), 49, 50, 51 anchor filaments, 50, 51 micropylar canal, 51, 52 operculum, 49, 50, 51, 62 cleavage, 47-57; I+, In furrow, 52, 53, 55 pattern, 53, 54, 55 fertilization, 51, 85 gastrulation, 56, 302 germinal area, 47 disc, 47, 50, 52, 56, 57; I, lar hillock, 50, 52, 54, 56, 57; I1 granulosa, 51 growth, 88-92 meroblastic, 47 micromeres, 55, 56 reconstruction, 47 segmentation, 47-57; Ia, In embryos, 51, 57, 97, 98, 99 Bashford Dean Memorial Volume eye, 99 hermaphroditism, 77-78, 83 mesonephros, 90, 98 mesorchia, 70, 78, 83, 84 myxopterygia, 92 ovarian follicle, 49, 51 reproductive system, 83-88, 90, 95; Wa— Ilav size, 79, 83, 85 spawning, 92-97 Beebe, W. and Tee-Van, J., on H. quoyi, 676 Bertrand, L., on Chlamydoselachus, 255, 265, 266, 273, 294 Bibliographies, Bdellostoma, 101-102 Chlamydoselachus, 631-633 Dean, 23-34 Dinichthys, 213-224 Heterodontus, 764-770. Blainville, H. M., on Heterodontus, 658, 659, 664 Blastoderm (blastodisc), Bdellostoma, 54, 55 Chlamydoselachus, 582, 583, 584, 585, 617, 618, 620 Elasmobranchii, 582 Ginglymostoma, 582, 585, 590 Heterodontus japonicus, 582, '722, 729, 730, 731, 732, 733, 734, 738, 739, 741, 748, 749; VIIa, Villy, VII-v H. phillipi, 582, 723, 731, 732, 733, 737, 738 Pristiurus, 582, 589, 748, 749 Scyllium, 729 Squalus, 585, 733 Torpedo, 733, 739 Blastodisc, see Blastoderm above Blastomeres, Bdellostoma, 52, 53, 54, 55, 56, 725 Heterodontus, 725, 278, 729, 730, 731, 732 Blastopore, Bdellostoma, 56 Chlamydoselachus, 618 Cryptobranchus, 739 316-319; 498-505; Ginglymostoma, 560 a Heterodontus japonicus, 726, 738-740, 748, 749; VIIL-v Pristiurus, 748, 749 yolk, Chlamydoselachus, 618 Heterodontus japonicus, 739, 740, 749, 750; VIL-v Pristiurus, 618, 748 Blastula, Chlamydoselachus, 539, 573, 582-588 Elasmobranchii, 582 Heterodontus, 79, 712, 717, 719, 729, 731, 732, 733, 735, 736, 737, 738 Pristiurus, '731 Torpedo, 731 Bolau, H., on Chlamydoselachus, 540 Bolivar, I., on Chlamydoselachus, 255, 265, 291, 294 Borcea, J., on Scyllium, 447 Bothriolepis, 199 Brain, Bdellostoma, 99 Chlamydoselachus, 473-475, 593-595, 597- 600; VI-—VIL-v Heptanchus, 474-475 Heterodontus, 735, 740, 741, 742, 744, 745 Necturus, 99 Branson, E. B., on Dinichthys, 119, 120, 135, 142, 143 Braus, H., on Chlamydoselachus, 283, 342, 350, 370, 376, 386, 483, 486 Breathing valve, Chlamydoselachus, 269-270, 420; V-1v, Vv Heterodontus, 735 Breeding habits, Bdellostoma, 92-97 Chlamydoselachus, 301-302, 535 Ginglymostoma, 533-534 Heterodontus galeatus, 713 H. japonicus, '712—715, 716, 718 H. phillipi, 712-713, 715 Breeding season, Bdellostoma, 94, 95 Chlamydoselachus, 298-302, 534 Heterodontus, 711-712, 713, 717 Brevoort, J. C., on Heterodontus japonicus, 666, 688, 689, 690, 691, 692, 756 Bridge, T. W., on Heterodontus, 202, 659, 660, 661 Brohmer, P., on Chlamydoselachus, 476, 478- 479, 482, 483, 592, 596, 627 Broili, F., on Acanthaspida, 177, 198, 199, 200 Gemundia, 188 Bryant, H., on Coccosteus, 198, 199, 200 Dinichthys, 121, 135, 151, 159, 168, 169 Bulldog Shark, 664, see Heterodontus phillipi Bullhead Sharks, 660-661, see Herodontidae Canal, haversian, 146, 157 head in Chlamydoselachus, 287-290 hypobranchial, 359-362, 364 micropylar in Chlamydoselachus, 51, 52 nasal in elasmobranchs, 195 neurenteric in Heterodontus japonicus, 745 olfactory in Dinichthys, 195 pericardio-peritoneal, Acanthias, 455 Chlamydoselachus, 455-457 Raja, 455 Canal—pericardio-peritoneal—(continued) Scyllium, 455 Selachii, 455 Squalus, 455 sensory, Arthrodira, 122, 126, 133-137, 139 Chlamydoselachus, 204, 205, 208, 209, 210, 266, 287-290, 294, 489-492, 606, 607, 608, 609, 611, 612, 613, 614, 615, 617, 623, 624, 625, 626, 717; Vivir Ctenacanthus clarkii, 490 Dinichthys, 126, 133, 134, 135, 136, 142 Heptanchus, 490, 492 Heterodontus japonicus, 743, 747 Macropetalichthys, 206 Mustelus, 492 Notidanidae, 490 Placodermata, 209, 210, 211 Raja, 455 Squalus, 489-490, 492 spiracular, Chlamydoselachus, 426-427, 744 Heterodontus japonicus, 759 Capsule, auditory, 699, 700 see also Egg, capsule Carapace, body, Acanthaspida, 179, 210 Antiarchi, 208-210 Arthrodira, 198, 201 Asterolepida, 132, 208-209 Coccosteus, 175, 198, 210, 211 Dinichthys, 119, 120, 125, 160-174, 175, 180, 188, 189, 191, 192, 200 Macropetalichthys, 206 Pholidosteus, 176 central, Dinichthys, 123, 129, 130, 132, 133, 135, 136, 141, 205 dorsal, Dinichthys, 117, 119, 120, 125, 160-170 head, Asterolepis, 132 Coccosteus, 134, 141, 211 Dinichthys, 127-152, 153-159, 185-188, 189-192, 205; [V-1—IV-m ventral, Dinichthys, 119, 120, 125, 170-174, 175, 180, 188, 189, 191, 192, 200 Carcharhinus obscurus, ovaries and oviducts, 564, 565 Carcharhinus platyodon, 565 Carcharodon rondeletii, egg and embryo, 575, 576, 577 Cartilage, in Chlamydoselachus, q.v. Centracion, 658-659, see Heterodontus Centraciontidae, 662, see Heterodontidae Centrophorus, 351 Cephalaspidae, 176 Cephaloscyllium umbratile, 409 Analytical Subject Index Cestracion, 658-659, see Heterodontus C. francisci, see Heterodontus francisci C. pantherinus, see Heterodontus quoyi C. phillipi, see Heterodontus phillipi C. quoyi, see Heterodontus quoyi Cestraciontidae, 651, 699, '702, see Hetero- dontidae affinities, 694-702 arches, neural, 696 dentition, 695, 696 embryology, 651 fins, 695-696 jaw, 699 palatoquadrate, 695-696 spine, dorsal, 696 tail, 696 Cetorhinus, mouth, 277, 304, 339 Chimaera, egg, 709, 724 Chlamydoselachidae, 247-314, 663 Chlamydoselachus anguineus, 243-330; V1— V-v; 331-520; VI1—VI-vu; 521- 646; VII1—VII-vi aorta, dorsal, 461-466 arches, basibranchial, 359, 361, 362 basihyoid, 360 branchial, 358-363, 396, 420, 468, 661, 662, 742, 743, 744, 746; Vian gills, 358-363, 396, 420-423, 466-467, 593, 597, 598, 599, 600, 601, 602, 604-617, 623, 626 hyoid, 359 hyomandibular, 358 labial, 398 mandibular, 356 visceral, 356, 363, 390, 396 arteries, 461-471 embryonic, 603, 617-621 bibliography, 316-319; 498-505; 631-633 blood-vessels, 457-472 body cavity, 434, 435, 447 body form, 281-290, 336-338, 625 brain, 473-475; VIau, VIav, VI-vi embryonic, 593-595, 597-600 breathing valve, 269-270, 275, 420; V-1v, Vv breeding, 298, 301 breeding season, 299, 302, 534 bursa entiana, 406-407, 412 canals, head, 287-290 hypobranchial, 359, 360, 361, 362, 364 micropylar, 52 pericardio-peritoneal, 455-457 sensory, 204, 205, 208, 209, 210, 266, 287-290, 294, 489-492, 606, 607, 608, 609, 611, 612, 614, 615, 617, 623, 624, 625, 626, 717; Vivir spiracular, 426-427, 744 787 cartilage, dorsal, 369 hyomandibular, 424, 426 labial, 269, 357; VI-n mandibular, 429 Meckel’s, 356, 358 ventral, 369 ceratohyoids, 358-359 cenogenetic characters, 497 chorda tympani, 482 cloaca and cloacal openings, 282, 285-286, 290, 293, 300, 301, 410, 411, 431, 432, 433, 434, 435, 440, 441, 450-454, 531, 532, 542, 562-563, 593-595, 610-612, 623, 624; V-v; Vi-v colon, 410, 411, 412 color, 265-266 cranium, 309, 310, 350-356, 390, 493; Via, Vin denticles, dermal, 285, 286, 287, 342-350, 623 pharyngeal, 402 dentition, 248, 249, 253, 260, 267, 271- 277, 305-311, 312, 313-314, 342-350, 591, 623, 624, 760-763; V-11—V-v cusps, 346-349 embryonic, 274, 591 digestive system, 401-419 discovery, 248 distribution, 249-258, 264, 265, 291, 294, 303, 304, 495 ducts, deferens, 450; VI-1v, Vi-v mesonephric, 434, 437, 438, 439, 440, 441, 442-444, 450 duodenum, 406 ear, 355, 487-488 egg, 250, 252, 264, 299, 300, 301, 302, 303, 445, 446, 448, 531, 532, 533, 541, 542, 545, 548-549, 555, 557, 558, 567-580, 626-627; VI4 blastoderm (disc), 582, 583, 584, 585, 589, 590, 617, 618, 620 blastopore, 618 blastula, 539, 573, 582-588 capsule, 531, 560, 566-573, 578-579, 603; VII-4 tendrilliform processes, 581 case, 301, 560, 620 cleavage, 584, 585, 587 ovarian, 548-549, 623 shell, 300, 523, 538, 545 size of, 302, 303, 445, 446, 448, 544, 548, 567-574 wind, 545, 557, 568, 570, 571, 572; VIL-v yolk, attached, 300, 530, 627; VII-m cord, 301; VII mass, 300, 301, 303, 449, 533, 555-557, 559, 571, 572, 575; Vln 788 Chlamydoselachus anguineus—yolk—(contd.) sac, 300, 301, 303, 449, 533, 555-557, 559, 571, 575, 576, 595, 596, 602, 603, 610, 612-621, 627; VIL-n stalk, 593, 595, 597, 602, 603, 605, 610, 612, 614, 615, 618-621; VIIa vascular (vitelline) system, 614, 617— 622, 751; VILv embryos (embryology), 48, 250, 252, 257, 275, 277, 288, 291, 296, 298-300, 302, 303, 382, 383, 463, 468, 478-479, 483, 528, 529, 530, 555-557, 561, 573-574, 576, 581-621; VIIm—VII-v brain, 593-595, 597-600 circulatory system, 465, 603, 606, 614, 617-622, 751; VILv dentition, 274, 591 digestive system, 411-412, 415, 419 eye, see below fins, see below folds, 608, 611, 623-625 food, 561, 626-627 gastrulation, 539, 570, 585, 588-590 gills, see below mouth, 593-597, 599-602, 604, 605, 607-616; VII-n, VII-m myomeres, 382, 383, 388, 593, 624 nasal opening, 293, 599, 600-602, 604, 607-617; VILu, VIlm nerves, 478-479, 483 on egg; VIL-v size, 302, 393, 555, 556, 559-562, 573- 574, 578 somites, 388 spiracles, 279-281, 340, 423-430, 506, 598, 599, 600, 601, 602, 604, 607, 608, 610-613, 615; V-m esophagus, 402-403 evolution, anatomical, 492-495 eye, 277-278; V-11 embryonic, 277, 355, 593, 594, 597, 599, 600-602, 604-608, 610, 611, 612, 613, 614, 623, 625 muscles, 391-394, 478; VI-1v lid, 278, 314 fins, 260, 291-297, 314, 340-342 anal, 280, 291, 303, 304, 364, 380 embryonic, 602, 604,608,610-615,623 caudal, 280, 281, 288, 290, 293-297, 340, 380-381 embryonic, 601, 602, 608, 610-615, 617, 623-625 dorsal, 209, 281-283, 285, 288, 292-293, 340, 364, 377-379 embryonic, 595, 601, 602, 604, 608, 611-615, 617, 623 pectoral, 281, 288, 307-373 embryonic, 291, 295, 593-595, 598, 600-602, 604-605, 607-608, 611-615, 626 Bashford Dean Memorial Volume pelvic, 291, 292, 340, 373-377, 394, 395, 434, 450, 541; V-v; Viv embryonic, 573, 594, 595, 601, 602, 604, 607, 608, 610-612, 614-615 see also myxopterygia below fold, maxillary, 269, 281 opercular, 281 tropeic, 281-285, 342, 385-388 embryonic, 608, 611, 623-625 follicles, ovarian, 445, 546, 549 food, 297 foramen magnum, 356 ganglion, ciliary, 478-479 Gasserian, 479, 480, 481 gestation, 302-303, 538-540, 556 gills, 306-308, 420-423; V-m arches, 359, 463, 467, 468 blood vessels of, 420, 469-471 clefts, 422, 429-430, 468 covers, 267, 281, 304, 339-340 embryonic, 593-595, 597-602, 604-617, 623, 626-629, 758; VIla—VIL1v external in adults, 629-630 filaments, 420-423, 429, 470, 626-630, 758, 759 slits, 266, 314, 371-373; VI-v girdle, pectoral, 370-373 pelvic, 373-377; VL-v glands, nidamental, 432, 433, 434, 445, 446, 448, 550-552, 578 pancreatic. 413-415 rectal, 410-411 thyroid, 415-418 glomeruli, 437 head, 266-280, 396, 606, 625-626; V-u, Van heart, 457-461 intestine, valvular, 408-409; VI1v jaw, 268, 269, 272, 281, 353, 354, 356, 358, 484 liver, 412-413 mating, 301 5 membranous labyrinth, 487-488; Vv mesentery, 437, 438, 439, 440, 442, 443, 445, 447 mesonephros, 432, 433, 434-438 tubules of, 437 mouth, 267-269, 295, 338-339, 623, 625; VA embryonic, 593-597, 599-602, 604, 605, 607-616, 623-625 muscle bundle, 484, 485 muscles, 381-400; VL-1v appendicular, 381, 394, 395 axial, 382-394 branchiomeric, 396-400 embryonic, 382, 394 eye, 355, 391-394, 478; VIiv hypobranchial, 388-391 intermandibular, 399-400 innervation of, 399 keel, 387-389 metameric, 391-395 m. rectus abdominalis, 387-389 m. rectus profundis, 387-389 myxopterygial, 395 pharyngeal, 397 tail and trunk, 382-391 ventrolateral, 384-385 myxopterygia, 291-292, 295, 298, 373, 376-377, 395, 451, 452, 453, 454, 472, 541-542, 624; V-v; VL-v nasal organs, 207, 279, 503, 593, 599, 600- 602, 604, 607-617 nerves, 472-487; VI-vi chorda tympani, 482 nervus collector, 486-487 cranial, 475-485; VI-vu facial, 482 fifth, 481 glossopharyngeal, 482 occipital, 483-485 oculomotor, 479-480 optic, 477 seventh, 481 spinal, 368, 485-487 trigeminal, 478, 480-481 vagus, 482-484 embryonic, 483 neurocranium, 350 nomenclature, 303-305 colloquial, 304-305 notochord, 351, 352, 363-370, 492 ovaries, 299, 432, 433, 445-446, 447, 535, 543, 544-547 oviduct, 299, 302, 431, 432, 433, 434, 435, 437, 445, 446-450, 543, 544, 549-550, 558, 559, 562, 563 oviparity, 300, 301, 531-533, 578, 579, 580 ovoviparity, 580 palatoquadrate 353-354, 355, 356, 358, 424-425 papilla, urethral and urinary, 431, 432, 433 parasites, 298 pelvis, 373-376; VI-v pharynx, 397, 402 phylogeny, 305-311, 314-315, 492-495 pit organs, 288-290 placenta, 301 pores, abdominal 285-286, 432, 434, 435, 440, 450, 453, 454 455; V-v head, 289-290 urethral, 432. 433, 439, 440, 441, 442 pylorus, 405-406 vestibule of, 404-405, 412 radials, 376, 377, 378, 379, 380, 381 Chlamydoselachus anguineus—(continued) raphe, 571, 572 rectum, 410-412 reproductive system, 412, 431-455, 541- 564; VI-v respiratory system, 267, 279-281, 339- 340, 359, 419-430, 466-471, 593- 595, 596, 597-602, 604-617, 625-630, 758, 759; VIla1—VIL-i1v scales, 286, 287, 288, 294, 342-350 sense organs, 487-492 sinus, urinary, 438-441, 442, 443 urogenital, 431-434, 438, 439, 440, 450 size, 248, 252, 254, 255, 260-265, 273, 274, 279, 281, 282, 283, 290, 295, 444, 546, 577, 578, 662, 663 skeleton, 350-380, 494 visceral, 355, 356-364, 390; VI-u, Vian spawning habits, 301, 302, 535 spleen, 418-419 stomach (cardiac), 403-404, 412 tail, 248, 249, 250, 288, 289, 290-291, 293, 364, 369-370, 624-625 embryonic, 296, 593, 594, 598, 601, 604, 607, 611-614, 617, 620-621 fin, 450 testes, 450 tongue, 270; V-u1 tubules, collecting, 437, 442-444 urethral aperture, 432, 441, 442, 448 uterus, 432, 433, 439, 443, 446, 447, 449, 535, 536, 548, 552-562 venous system, 471-472 embryonic, 603, 618-622 vitelline, 614, 617-622, 751 vertebral column, 363, 366, 367, 368-370, 436; Via, Via viviparity, 298-301, 528, 531-534, 542, 559 yolk, attached, 300, 530, 627; VIL cord, 301; VII- mass, 300, 301, 303, 449, 533, 555-557, 559, 571, 572, 575; Vila sac, 300, 301, 303, 449, 533, 555-557, 559, 571, 575, 576, 595, 596, 602, 603, 610, 612-621, 627; VIL stalk, 593, 595, 597, 602, 603, 605, 610, 612, 614, 615, 618-621; VII 1 vascular (vitelline) system, 614, 617- 622, 751; VIL-v young, 300 Chlamydoselachus lawleyi, 311-313, 348, 349, 495 C. tobleri, 313-314, 348 Chondrostei, 204 Circulatory system, Acanthias, vitelline, 620 Chlamydoselachus, 461-472, 603, 614, Analytical Subject Index 617-622, 751 Elasmobranchii, 621 Felichthys, 622 Heterodontus japonicus, 739, 742, 743, 744, 748, 749, 750, 751, 752, 753, 755, 756; VIIL-vir Pristiurus, vitelline, 618, 748-749 Squalus, vitelline, 620 Cladodus, 306, 311, 372, 373, 495 dentition, 308-309 C. acutus, 308, 348, 349, 350 dentition, 348, 349, 350 C. mirabilis, 308 C. neilsoni, fin, 372, 373 Cladoselache, 9-10, 341, 375, 376 dentition, 348, 349, 350 dermal denticles, 347 fin, 375 myxopterygia, 724 Clark, J. M., on Dinichthys, 119 Clavicular (plate), 117, 119-120, 160, 166, 175, 177, 179, 185 Claypole, E. W., on Arthrodira, 126, 127 Dinichthys, 117, 118, 135, 142, 145, 152, 160, 166, 176, 195 Cleavage, see Egg, cleavage Cloaca, Chlamydoselachus, 282, 285-286, 290, 293, 300, 301, 410, 411, 431, 432, 433, 434, 435, 440, 441, 450-454, 531, 532, 542, 562-563, 593-595, 610-612, 623, 624; V-v; Viv Elasmobranchii, 549 Ginglymostoma, 530 Heterodontus, 713 Coccosteus, 144, 158, 168, 175, 180, 184, 188, 202, 211 armor, 134, 141, 175, 198, 210, 211 armor plates, antero-dorso-lateral, 199 antero-lateral, 199 post-marginal, 134 post-sub-orbital, 143, 199 postero-dorso-lateral, 199 postero-lateral, 199 spinal, 176, 177, 210 dentition, 145 gill arches, 199 head, 211 jaw, 185, 187 muscles, 190 vertebral column, 196, 197 C. angustus, 198, 200 C. birkensis, 176 C. decipiens, 127, 134, 136, 143, 144, 168, 176, 177 Collections, Bdellostoma, 48 Chlamydoselachus, 789 American Museum, 254, 255, 258-259, 266, 291, 335, 403, 420, 489, 529, 625, 626, 630 Columbia University, 529, 548, 570, 571, 579, 638 Museum of Comparative Zoology, 569, 609, 610 von Rautenfeld, 596 White, 335 Dinichthys, American Museum, 116, 141, 143, 146, 151, 169, 174, 177, 197 Buffalo, 134, 135, 151, 169, 170, 174, 177, 190, 197 Bungart, 169 Cleveland, 115-116 Jaekel, 175 Museum of Comparative Zoology, 174 Heterodontidae, American Museum, 654, 678, 684, 693, 702, 756 Collett, R., on Chlamydoselachus, 254, 255, 267, 268, 273, 277, 279, 291, 294, 359, 403, 411, 413, 415, 437, 447-448, 541, 544, 545, 557, 558, 630 Color pattern, Chlamydoselachus, 265, 266 Gyropleurodus, 677 Heterodontus, 663, 669 H. francisci, 677, 681, 683, 684 H. galeatus, 687-688 H. japonicus, 692, 693, 694, 702, 747, 748, 755, 756, 757 H. phillipi, 666, 667, 668, 669 H. quoyi, 676, 677, 678, 679, 680 H. zebra, 675 Conel, A., 63-110 on Bdellostoma, 78 Myxine, 75 Cope, E. D., on Chlamydoselachus, 306-309 Corning, H. K., on Lacerta, 389 Corrington, J. D., on Chlamydoselachus, 464 elasmobranchs, 471 gills, 423 Cranium, Acanthias, 351 Centrophorus, 351 Chlamydoselachus, 309, 310, 350-356, 390, 493; VI4, VIat Elasmobranchii, 701 Heptanchus, 351, 699-700 Heterodontus, 662, 684, 699, 700, 701 Hybodus, 699, 700, 701 Scyllium, 699, 700 Scymnus, 351 shark, 699 Synechodus, 701 Crested Shark, 687, see Heterodontus galeatus Crossopterygii, 629 790 Cryptobranchus, 722, 728, 739 Ctenacanthus clarkii, 348, 349, 350, 373, 490 dentition, 348, 349, 350. fins, 373 Cunningham, J. J., on Myxine, 70, 71, 72, 73, 75, 76, 77, 91, 92, 93 Cuvier, G. C. L., 568, 659, 664 Cyclostomes, 97, 99, 209 Daniel, J. F., on Chlamydoselachus, 382, 395, 485 Elasmobranchii, 336, 345, 347, 351, 358, 363, 366, 370, 374, 389 Galeus, 405 Heptanchus, 403, 407, 409, 411, 415, 418, 441, 444, 446, 449, 474-475, 483, 484, 492 Heterodontus, 661, 663, 681, 684, 696, 699-700, 703, 707, muscles, 394 Notidanus, 490 spiracles, 427 Squalus, 444 Torpedo, 484 Darbyshire, A. D., on Squatina, 427 Dasyatis, ovaries and oviduct, 566 Davidson, P., on Heptanchus, 389, 391, 393, 395, 396 Davis, J. W., on Cladodus (teeth), 309, 310 Dean, B., bibliography, 23-34 biography, 1-22; 35-42; 7 portraits Bdellostoma, original drawings, 83, 86, 87, 89; Il4, IL-n; W14—II1v original notes, 48, 68, 80, 81, 82, 83, 85, 94, 95, 96, 97, 98 Chlamydoselachus, original drawings, 247, 526, 529, 531, 539, 554, 568, 571, 572, 573, 576, 578, 583, 587, 588-589, 590, 592-616, 618, 626; VII1—VIIv1 original notes, 247, 250-252, 257, 258, 262, 265, 280, 297, 300-301, 302, 303, 525, 535, 536, 543,-546, 548, 549, 555, 556, 558, 570, 583, 584, 588-589, 590, 592 Heterodontus japonicus, original drawings, 655-656, 704, 714, 715, 719, 720, 721, 729, 730, '732, 733-734, 737, 738, 739, 740, 745, 746, 747, 748, 749-752, 753-755, 756, 760, 762 original notes, 651-652, 653, 654, 656, 657, 689, 702, 703-705, 708, 710-712, 713, 717, 718, 719, 721, 722, 724-728, 752, 753-755, 756 on Amia, 725 Arthrodira, 125, 145, 180 Bdellostoma, 11, 12, 47, 51, 55, 56, 78, Bashford Dean Memorial Volume 79, 86, 87, 88, 89, 90, 91, 92, 99 Chlamydoselachus, 250, 475, 526, 527, 528, 533, 546, 574, 585 Chimaera, 709, 724 Cladoselache, 9-10, 349, 375, 376 Triakis semifasciatus, 345 tubercles, 210 Didymodus, 306-309 Dinichthys, arches, Coccosteus, 175 Ctenacanthus, 490 Cyclostomes, 97, 98 Dinichthys, 117, 118, 119, 120-121, 145, 160, 166, 169, 1°70, 173, 174, 184, 196 embryology, 10 fin-fold theory, 342 fins, origin of paired, 9-10 Heptanchus, 338 Myxinoidea, 67-69, 97-100 Ostracoderms, 99 Palaeospondylus, 11 Placoderms, 9 Deinega, W. A., on Chlamydoselachus, 350, 351, 360, 370, 371, 373, 380, 413, 415, 419, 449, 553, 562, 563 Denticles, dermal, Chlamydoselachus, 285, 286, 287, 342— 350, 623 Cladoselache, 347 Heterodontus, 747, 755, 760 pharyngeal, 402 Dentition, Acrodus, 697 analogy to scales, 344-347 Arthrodira, 146, 206, 207 Cestraciontidae, 695, 696 Chlamydoselachus, 248, 249, 253, 260, 267, 269, 271-277, 305-311, 313-314, 343-350, 591, 623, 624, 760-763; Viu—V-v Cladodus, 308-310, 348, 349, 350 Chladoselache, 348, 349, 350 Coccosteus, 145 Ctenacanthus, 348, 349, 350 Didymodus, 306 Dinichthys, 145-146, 184, 186, 187, 188, 190, 211 Heptanchus, 270, 311, 347 Heterodontus, 662, 698 H. francisci, 684 H. galeatus, 687, 688 H. japonicus, 691, 694, 711, 759, 760-763 H. phillipi, 666, 670-675, 681 H. quoyi, 680-681 H. zebra, 676 Hybodontidae, 348, 349, 696, 697 Jagorina, 206 Mylostoma, 186 Notidanidae, 673 Paleospinax, 698 phylogenetic significance, 347-348 Pleuracanthus laevissimus, 310 Synechodus, 697-698 gill, 199 hyoid, 201 armor, connecting, 179-192 dorsal, 117, 119, 120, 125, 160-170 head, 117, 125, 127-152, 153-159, 185- 192, 205; IV1—IV-11 ventral, 119, 120, 125, 170-174, 175, 180, 188, 189, 191, 192, 200 armor plates, antero-dorso-lateral, 117, 118, 119, 124, 162, 163-165, 168, 180, 182, 183, 184, 204, 211 antero-lateral, 124, 125, 165, 166-169, 170, 171, 174, 177, 178, 179, 182, 190, 191, 192, 200, 201 antero-median-ventral, 123, 125, 126, 172, 173-174, 191, 192, 201 antero-supra-gnathal, 123, 125, 145, 146-147, 149, 153, 160, 190, 207 antero-ventro-lateral, 125, 126, 171, 172, 173, 175, 177, 178, 185, 211 central, 123, 125, 128, 132, 135-136, 160, 161 clavicular, see antero-lateral above externo-basal, 123, 128, 129, 133-135, 160, 161, 181, 184, infero-gnathal, 123, 125, 148-150, 153, 160, 186; [V-vir interno-lateral, 124, 125, 126, 169, 175—- 179; [V-vint marginal, 120, 123, 125, 128, 132, 133- 134, 135, 160, 161; [V-m median-basal, 123, 125, 128, 132, 133, 160, 161 median-dorsal, 118, 124, 125, 160-163, 170, 178, 179, 184, 188, 191, 200, 201 median-ventral, 125, 126, 172, 173, 192 pineal, 123, 128, 132, 137, 160, 196 post-marginal, 123, 125, 128, 132, 134- 135, 160, 161, 192 post-maxillary, 117, 118, 119 post-nasal, 123, 125, 139, 141-143, 153, 158, 160, 192; IV-11 post-orbital, 123, 125, 132, 136, 141, 143-146, 160, 161, post-sub-orbital, 123, 125, 143-146, 150, 153, 158, 159, 160, 187, 190, 191, 192, 200, 207, 211; [V-iv post-supra-gnathal, 153 postero-dorso-lateral, 119, 124, 125, 159, 165-166, 169, 170, 177, 204 postero-infero-gnathal, 123, 125, 150- 152, 153, 184, 192, 208; IV-vir postero-lateral, 120, 124, 125, 169-170, Dinichthys—armor—postero-lateral—(contd.) 177, 192, 199; IV-vir postero-supra-gnathal, 123, 125, 145, 147-148, 153, 160, 186 postero-ventro-lateral, 125, 126, 172, 173, 204 pre-nasal, 158 pre-orbital, 123, 125, 128, 132, 139, 141, 142, 157, 158, 160, 161, 205 rostral, 123, 125, 132, 137, 141, 157, 158, 160, 161 spinal, 124, 125, 126, 159-179, 197, 198; TV-1x sub-orbital, 118, 119, 123, 125, 138-141, 142, 143, 153, 157, 158, 160, 191, 200, 205, 211 bibliography, 213-224 branchial shield, 199 canals, olfactory, 195 sensory, 126, 133, 134, 135, 136, 142 condyle, 163, 164, 180, 181, 182, 188, 192, 196 dentition, 145, 146° 184, 186, 187, 188, 190, 211 fins and fin rays, 197-199, 202 fontanelle, 117 food, 202 fossa glenoidalis, 180, 181, 182 gills, 199, 200-202 arches, 199 gnathal elements, 122, 183-187, 192, 207, 209, 210, 211; IV-v—IV-v1 head, 127-159, 189, 193, 194, 195, 211; IVi—IV-m history, 115 jaws, 118, 121, 138-155, 184, 185, 187, 188, 189, 190, 191, mandible, 121, 148, 184, 185; [V-vir maxilla, 121, 122, 144, 152 movements, 158, 189, 192 muscles, 187-192 premaxilla, 122 mouth, 187 muscles, 188, 189-191 jaw, 187-192 m. adductor mandibuli, 190 m. depressores capitis, 190-191 m. depressores gnathalis, 191 m. levatores capitis, 189-190 m. levatores gnathalis, 191 neurocranium, 192-196 orbit, 118, 128, 157, 161 phylogeny, 192, 194, 202-213 pineal organ, 141, 196 plastron, 170-174 quadrate, see armor plates, post-sub- orbital above reconstructions, 117-122, 142, 143,145, 152, 160, 161, 166, 168, 169, 174, 202, 203 Analytical Subject Index body, 180, 188, 189, 192 head, 153-159, 191, 192 sclerotic ring, 158-159 skeleton, 192, 199 spine, pectoral, 198 vertebral column, 196-199 Dinichthys curtus, 197; [V-vut D. intermedius, 133, 150, 154, 159, 169, 175; 1V-3—1V-10, [V-vu, [V-1x D. lincolni, 207 D. magnificus, 121, 159, 168 D. mirabilis, 121 D. terrelli, 119, 120, 122, 135, 136, 141, 142, 143, 144, 160, 173; [V-1v, 1V-vir Dinognathus ferox, 152 Dinomylostoma, 126, 151 Diplodus, 306, see Didymodus Dipnoi, 184, 629 Distribution, Bdellostoma, 77, 79, 80-82, 83, 97-98 Chlamydoselachus, 249-258, 264, 265, 291, 294, 303, 304, 495 Heterodontidae, 661 Heterodontus francisci, 664, 681, 683, 709- 710 H. galeatus, 664, 686, 687 H. japonicus, 653, 654, 688-689, 709-710 H. phillipi, 664, 686, 689, 710, 712, 713 H. quoyi, 664, 676, 677 H. zebra, 664, 675, 689, 693 Myzxine, 72, 73, 75 Déderlein, L., on Chlamydoselachus, 248, 249, 278, 298 Doflein, F., on Chlamydoselachus, 253, 277, 291, 295, 296, 574 Dumeril, A., on Cestracion, 658, 659 Heterodontus quoyi, 677, 705 Duodenum, Chlamydoselachus, 406 Heptanchus, 407 Eastman, C. R., on Arthrodira, 180, 187, 202 Dinichthys, 118, 119, 135, 160, 166, 169, 170, 173, 175 Macropetalichthys, 204 Orodus, 697 Echeneis, 357 Edgeworth, F. H., on Scyllium, 389 Egg, Amia, 725, 726 Bdellostoma, 47-61, 86, 87, 88-91, 95, 97; Ia—tIlan B. burgeri, 86, 87, 89, 95, 97; UW1- B. stouti, 47-62, 84, 85, 86, 87 blastoderm (blastodisc), Bdellostoma, 54, 55 Chlamydoselachus, 582, 583, 584, 585, 617, 618, 620 791 Elasmobranchii, 582 Ginglymostoma, 582, 585, 590 Heterodontus japonicus, 582, 722, 729, 730, 731, 732, 733, 734, 738, 739, 741, 748, 749; VIlI4, VIllav, VIIL-v H. phillipi, 582, 723, 731, 732, 733, 737, 738 Pristiurus, 582, 589, 748, 749 Scyllium, 729 Squalus, 585, 733 Torpedo, 733, 739 blastomeres, Bdellostoma, 52, 53, 54, 55, 56, 725, Heterodontus, 725, 728, 729, 730, 731, 732 blastopore, Bdellostoma, 56 Chlamydoselachus, 618 Cryptobranchus, 739 Ginglymostoma, 560 Heterodontus japonicus, 726, 738-740, 748, 749; VIL-v Pristiurus, 748, 749 yolk, Chlamydoselachus, 618 Heterodontus japonicus, 739, 740, 749, 750; VIII-v Pristiurus, 618, 748 blastula, Chlamydoselachus, 539, 573, 582-588 Elasmobranchii, 582 Heterodontus, 712, 719, 729, 731, 732, 733, 735, 736, 737, 738 Pristiurus, 731 Torpedo, 731 capsule, Bdellostoma, 49, 50, 51 Carcharodon, 575, 576, 577 Chimaera, 709 Chlamydoselachus, 531, 560, 561, 566- 573, 578, 579, 603; VIL1 Ginglymostoma, 530, 558, 560, 561, 568, 576-577, 579, 580-581 Heterodontus francisci, 707-708 H. galeatus, 706-707, 715 H. japonicus, 705, 707-709, 712, 713- 714, 715, 717, 720, 727, 752, 753; Vill-vu H. phillipi, 705-707, 712, 713, 723 see also case, shell and tendrilliform processes below Carcharhinus, 564 Carcharodon, 207, 575, 576, 577 case, Cestracion, 584, 585 Chimaera, 709, 724 Chlamydoselachus, 300, 301, 560, 620 Ginglymostoma, 560 Chlamydoselachus, 250, 252, 264, 299, 300, 301, 302, 303, 445, 446, 448, 531, 532, 792 Egg—Chlamydoselachus—(continued) 533, 541, 542, 545, 548, 555, 557, 558, 566-680; VII4, VILv cleavage, Amia, 725, 726 Bdellostoma, 47, 51-57; Il1, In Cestracion, 584, 585 Chimaera, 724 Chlamydoselachus, 584, 585, 587 Cryptobranchus, 728, 729 discoidal, 51, 728-732 furrows, 52, 53, 55, 739; VIIl4 Heterodontus, 584, 653, 656, 716, 722, 724-732, 739, 749; VIll4, VIlL-vn holoblastic, 724-725, 727, 748 Lepidosteus, 726, 728 lines, 47, 584, 585, 725-728, 731, 732 Necturus, 726 pattern, 53, 54, 55 Pristiurus, 589 Scyllium, 729 Cryptobranchus, 728 Elasmobranchii, 545, 578, 582, 709 Galeocerdo, 564 gastrulation, | Bdellostoma, 56, 302 Chlamydoselachus, 539, 570, 585, 588- 590 Heterodontus japonicus, 719, 720, 725 729, 732-738, 739 H. phillipi, 717, 733, 735, 736, 737, 738 Torpedo, 738 germinal disc, Bdellostoma, 47, 50, 52, 56, 57; IL1, In Chlamydoselachus, 589, 590 Heterodontus japonicus, 723, 725, 726, | 728, 733, 749; VIll4, VIIL1, Villvn H. phillipi, 723 Pristiurus, 589, 723, 727 Ginglymostoma, 301, 530, 533, 557, 558, 559, 560, 561, 564, 568, 573, 576-577, 579-581 Heterodontus francisci, 702-703, 707-708, 712 H. galeatus, '706-707, 712, 713, 715, 716 H. japonicus, 527, 584, 641, 689, 703-705, | 708-709, 712, 713-715, 716, 717, 719, 720, 722, 724-727, 728, 729, 730, 731, 732, 733, 749, 752-753; VIII, Villa, VIILv, Vill-vn H. phillipi, 705-707, 711, 712, 713, 723, | 731, 732 | Homea burgeri, 48 Lamna, 574 Lepidosteus, 726, 728 Myzxine, 74, 88-91, 90 Necturus, 726 Oxyrhina, 576 Bashford Dean Memorial Volume polarity, Bdellostoma, 49-52 Heterodontus japonicus, 726-728 Pristiurus, 589, 723, 727 Pteroplatea maclura, 565 Scyllium, 729 segmentation, see cleavage above shells, Bdellostoma, 49 Chlamydoselachus, 300, 533, 538, 545 Elasmobranchii, 578 Ginglymostoma, 533, 576, 581 see also capsule and case above and tendrilliform processes below size, Bdellostoma, 89, 95 Carcharodon, 575, 576 Chlamydoselachus, 302, 303, 445, 446, 448, 544, 548, 567-574 Ginglymostoma, 573 Heterodontus, 725 Lamna, 574, 575 Oxyrhina, 576 Squalus, 585 tendrilliform processes of capsule Chlamydoselachus, 581 Ginglymostoma, 579, 581 Heterodontus galeatus, 706 Torpedo, 739 wind, Chlamydoselachus, 545, 557, 568, 570, 571-572, 577; VILv Ginglymostoma, 558 Pteroplatea maclura 565 yolk, blastopore, Cryptobranchus, 739 Heterodontus japonicus, 739, 740, 748, 749, 750; VIll1v, VIILv cord, 301; VII-n mass, Chlamydoselachus, 572; VILv Ginglymostoma, 577, 579 Heterodontus japonicus, 733, 739, 741; Vilav, VIILv Pristiurus, 748 sac, Chlamydoselachus, 300, 301, 303, 449, 533, 555-557, 559, 571, 573 576, 595, 596, 602, 603, 610, 612-621; Villon Heterodontus japonicus, 719, 746, 747, 748, 752, 756 Pristiurus, 756 Raja, 756 Spinax, 756 stalk, Chlamydoselachus, 593, 595, 597, 602, 603, 605, 610, 612, 614, 615, 618- 621; VI-u—VII-vn Heterodontus japonicus, 741, 744, 745, 750, 751; VULv1 Pristiurus, 748 syncytium, see Heterodontus japonicus, periblast vascular system, Chlamydoselachus, 620-622; VIL-v Felichthys, 622 Eichwald, G. E. von, on Arthrodira, 202, 208 Elasmobranchii, 201, 204, 206, 208 anatomy, 336 canal, pericardio-peritoneal, 455 capsule, nasal, 195 cartilage, labial, 357 circulatory system, 465, 471, 621 cloaca, 549 cranium, 701 eggs, 544, 545, 578, 582, 709 blastoderm (disc), 582 blastula, 582 embryos, 10, 301, 578, 582, 709 myomeres, 382 somites, 742, 743 spiracle, 342, 428 fins, 341-342 jaw, 745 muscles, 391, 394, 742, 743 appendicular, 394 embryonic, 742, 743 eye, 391, 742, 743 myxopterygia, 531 ovaries and oviducts, 301, 549, 565-566 reproductive system, 547 skeleton, 366 thyroid gland, 418 uterine mucosa, 301 vertebral column, 366 viviparity, 301 Embryos and Embryology, Bdellostoma, 51-57, 68, 97, 98, 99 canal, sensory, see Canal above Carcharodon rondeletii, 575-576 Cestracion, 651 Chlamydoselachus, 48, 250, 252, 257, 275, 277, 288, 291, 296, 298-300, 302, 303, 382, 383, 393, 463, 468, 478-479, 483, 528, 529, 530, 535-537, 555-562, 573- 574, 576, 581-621, 758; VIlm—VIL-v For details see Chlamydoselachus, embryos circulatory system, Chlamydoselachus, 465, 603, 614, 617- 622, 751 Felichthys felis, 622 H. japonicus, 739, 742, 743, 744, 748, 749, 750, 751, 752, 753, 755, 756; Vill-vm dentition, Chlamydoselachus, 274, 591 Heterodontus japonicus, 759, 760-763 Embryos—dentition—(continued) H. phillipi, 761, 762 ectoderm and entoderm, Heterodontus japonicus, 734, 738, 739, 741, 742 H. phillipi, 737 elasmobranchs, 10, 301, 552, 582, 621, 742 eye, Chlamydoselachus, 277, 355, 593-594, 597, 599, 600-602, 604, 608, 611, 612, 613, 614, 623, 625 Heterodontus japonicus, 741, 742, 743, 745, 746, 747 Felichthys felis, 622 fins, Chlamydoselachus, 291, 295, 575, 593- 595, 598-602, 604, 605, 607, 608, 610-625, 626 Heterodontus japonicus, 740, 741, 742, 743, 744, 745, 746, 747, 748, 755 Squalus, 595, 601, 755 folds, Chlamydoselachus, 608, 611, 623-625 Heterodontus, 734, 740, 745, 746, 747 food of embryos, Chlamydoselachus, 561, 626-627 Ginglymostoma, 561 Ganoids, 722 gastrulation, Bdellostoma, 56 Chlamydoselachus, 539, 570, 585, 588- 590 Heterodontus japonicus, 719, 720, 725, 729, 732-738, 739 H. phillipi, 717, 733, 735, 736, 737, 738 Torpedo, 738 gills, Chlamydoselachus, 468, 593-595, 597- 602, 604-617, 623, 625-629, 630, 758; VII u—VIL-v Heterodontus japonicus, 742-747, 752, 753, 758, 759, 760; VIIL1—VIIL- H. quoyi, 758-759 Selachii, 743 Squalus, 594, 596, 600, 627, 628, 629 Ginglymostoma, 301, 560-562 Heterodontus francisci, '718~721 H. japonicus, 527, 651, 653, 654, 662-663, 689, 693, 694, 709, 717-751, 753, 754, 758, 760-763; VUL1—VU vr For details see H. japonicus, embryo H. phillipi, 582, 672, 712, 716, 717, 722- 725, 731, 732, 734, 735, 736, 737, 738, 761 For details see, H. phillipi, embryo H. quoyi, 574-575 Lamna, 574-575 mouth, Chlamydoselachus, 593-597, 599-602, 604, 605, 607-616; VIL-n, VIL Analytical Subject Index Heterodontus japonicus, 745, 746, 747, 759, 760; VU, VILL myomeres, Chlamydoselachus, 382, 383, 388, 593, 624 Heterodontus japonicus, 744, 745, 746, VUl-n, VIL Squalus, 383 Myzxine, 68 nasal openings, Chlamydoselachus, 293, 599, 600-602, 604, 607-617; VIL, VIL-u Heterodontus japonicus, 747 nerves, Chlamydoselachus, 478-479, 483 Spinax, 483 oxygen used by, 560, 561 Oxyrhina, 576 Pristiurus, 722, '748, 750 Scyllium, 476, 722 Selachii, 742, 743 size, Chlamydoselachus, 302, 303, 573-576, 592-617 Heterodontus francisci, 718, 744-747 H. japonicus, 654, 720, 721, 739, 740- 742, 745-747, 759, 760, 761, 762 Lamna, 574 spiracle, : Chlamydoselachus, 279-281, 340, 423- 430, 596, 598-602, 604, 607-608, 610-613, 615; VIL, VIlm Elasmobranchii, 340, 428 Heterodontus francisci, 681, 683 H. japonicus, 692, 741, 742, 744, 745, 746, 747, 755, 757, 759 H. phillipi, 665, 666, 667 H. quoyi, 677, 678 Hexanchus, 428 Squalus, 487, 600 Squatina, 340, 427 Spinax, 600 Squalus, 593-595, 596, 600, 601, 627, 628, 629, 722, 734, 735, 742 tail, Chlamydoselachus, 275 Heterodontus japonicus, 741, 742, 744, 746 Torpedo, 734 vitelline circulation, Acanthias, 620 Chlamydoselachus, 603, 614, 617-622 Felichthys felis, 622 Heterodontus japonicus, 748, 749, 750, 752, 753, 755, 756; VUl-v, VUI-vi Pristiurus melanostomum, 618, 748-749 Squalus, 620 Evans, H. M., on Heterodontus, 669 Evermann, B. W. and Radcliffe, L., on Heterodontus, 660, 676, 681 793 H. francisci, 681 H. quoyi, 676 Excretory system, see, Mesonephroi Eycleshymer, A. C., on Lepidosteus, 728 Eye, Bdellostoma stouti, 99 Chlamydoselachus, 277-278, 280; V-v Heptanchus, 393 Heterodontus francisci, 677 H, japonicus, 662, 694, 741, 742, 743, 745, 746, 747 H. quoyi, 677, 679 Felichthys felis, 622 Ferguson, A. S., on Elasmobranchs, 418 Fins, anal, Cestraciontidae, 696 Chlamydoselachus, 281, 290, 291, 303, 304, 364, 380 embryonic, 602, 604, 608, 610-623 Heptanchus, 380 Heterodontus francisci, 681, 683 H. galeatus, 687- H. japonicus, 663, 693 embryonic, 744, 745 H. quoyi, 676, 678 Hybodus, 696 caudal, Chlamydoselachus, 280, 281, 288, 290, 293-297, 340, 380-381 embryonic, 601, 602, 608, 610-615, 617, 623-625 Coccosteus, 210 Heterodontus francisci, 681 H. japonicus, 693, 694, 744, 745, 746, 755 embryonic, 744, 745, 746, 755 H. phillipi, 666 H. quoyi, 678 dorsal, Acanthaspis, 198 Cestraciontidae, 695, 696 Chlamydoselachus, 209, 281-283, 285, 288, 292-293, 340, 364, 377-379 embryonic, 595, 601-602, 604, 608, 611-615, 617, 623 Dinichthys, 917 glands in, 669 Heptanchus, 379 Heterodontus francisci, 663, 681, 683 H. galeatus, 687 H. japonicus, 663, 692-693 embryonic, 744, 745, 747, 748 H. phillipi, 669 H. quoyi, 678, 679 H. zebra, 676 Hybodus, 669, 696 Mustelus, 379 794 Fins—dorsal—(continued) Squalus, 669 Elasmobranchii, 341-342 Heterodontidae, 342, 660, 663 origin of, 379 paired, 9-10, 341-342 pectoral, Arthrodira, 197-198 Cestraciontidae, 696 Chlamydoselachus, 281, 288, 370-373 embryonic, 291, 295, 593-595, 598, 600-602, 604-605, 607-608, 611-615, 626 Cladodus neilsoni, 372, 373 Ctenacanthus, 373 Dinichthys, 196-199 Heterodontus francisci, 663, 681 H. galeatus, 663, 687 H. japonicus, 663, 693 embryonic, 744, 745, 746, 748 H. phillipi, 663, 665 H. quoyi, 676, 678, 679 Hybodus, 341-342 Notidanidae, 490 Symmorium reniforme, 372, 373 Squalus, 595, 601 pelvic, Arthrodira, 198 Cestraciontidae, 695 Chlamydoselachus, 291-292, 340, 373- 377, 394-395, 434, 450, 541; VI-v embryonic, 573, 594, 595, 601, 602, 604, 607, 610-612, 614-615 Cladoselache, 375 Dinichthys, 196-199 Heterodontus francisci, 681 H. japonicus, 663, 693, 713 embryonic, 744, 745, 747 H. phillipi, 665 Pleuracanthus, 341-342 radials in Chlamydoselachus, 376, 377, 378, 379, 380, 381 rays, Chlamydoselachus, 294, 295, 340 Dinichthys, 197 Heterodontus japonicus, 746 Fin-fold theory, 341-342, 744, 745 Follicles, ovarian, Bdellostoma, 49, 91, 95 Chlamydoselachus, 445, 546, 549 Heterodontus francisci, '703 Food, Chlamydoselachus, 297 Dinichthys, 202 Heterodontus galeatus, 711 H. japonicus, 711 H. phillipi, 710 Fowler, H. W., see Jordan, D. 8. Freminville, M., on Heterodontus quoyi, 660, 677, 678, 680 Bashford Dean Memorial Volume Fraas, E., on Hybodus hauffmani, 660, 695 Firbringer, K., on Chlamydoselachus, 350, 358, 359, 362, 396, 398, 399 Heptanchus, 483 Galeocerdo tigrinus, 277, 678 ovaries and oviducts, 564 Galeus, pylorus, 405 Gambusia patruelis, 414-415 Ganoids, 722 Garman, 5., on Cephaloscyllium umbratile, 409 Cestracion, 658, 659, 663 Chlamydoselachus, 247, 249, 265, 272, 273, 277, 278, 279, 281, 283, 285, 286, 287, 288, 289, 290, 291, 293, 294, 296, 298, 299, 303, 305-206, 308, 309, 315, 335, 339, 340, 342, 343, 345, 350, 356, 358, 359, 360, 370, 373, 377, 380, 381, 385, 402, 410, 420, 433, 443, 446, 447, 458, 473, 475, 482, 490-491, 494, 532, 543, 550, 551, 569, 577, 579, 609 Heterodontus francisci, 681, 682, 684 H. galeatus, 687 H. phillipi, 660, 664, 665, 670, 674 H. quoyi, 677, 678, 680 H. zebra, 675 Heptanchus perlo, 409 Tsurus punctatus, 409 Gastrulation, Bdellostoma, 56, 302 Chlamydoselachus, 539, 570, 484, 488-490 Heterodontus japonicus, 719, 720, 725, 729, 732-738, 739 H. phillipi, 717, 733, 735, 736, 737, 738 Torpedo, 738 Gegenbauer, C., on fin origin, 342 Heptanchus, 355, 363 Hexanchus, 351 Gemundia, 188 Gestation, Chlamydoselachus, 302-303, 538-540, 556 Ginglymostoma, 533, 580 Gill, T. N., on Chlamydoselachus, 306-308, 335, 494 Heterodontus, 659 Gills, Amphibia, 629 Arthrodira, 210 Cetorhinus, 277, 304 Chlamydoselachus, 260, 281, 339-340, 358-363, 371-373, 420-423, 429-430, 466-471, 593-595, 597-602,604-617, 626-629, 758; VI-v; VII41—VIliv For details, see Chlamydoselachus, gills clefts, Chlamydoselachus, 422, 429-430, 467, 468 Heterodontus japonicus, '742, 743, 744, 745,747, 752, 753, 760 covers, Cetorhinus, 277, 302, 304 Chlamydoselachus, 281, 304, 339-340 Heterodontus, 679, 685, 693 Crossopterygii, 629 Dinichthys, 199-202 Dipnoi, 629 evolution of, 423 external in adult Chlamydoselachus, 629- 630 filaments, Chlamydoselachus, 420-423, 429, 470, 623-630, 758, 759 Crossopterygii, 629 Dipnoi, 629 Heterodontus japonicus, 745-747, 758, 759 H. quoyi, 757, 758-759 Heptanchus, 423 Heterodontus francisci, 681, 683, 685 H. galeatus, 687 H. japonicus, 685, 693,755 embryonic, 742, 743, 744, 745, 746, 747, 752, 753, 755, 758, 759, 760; VU 1-1 H. quoyi, 678, 679, 685, 757 embryonic, 758-759 H. zebra, 676 openings (slits), Arthrodira, 210 Chlamydoselachus, 260, 266, 314, 371- 373; Viv Heterodontus francisci, 681, 683 H. galeatus, 687 H. phillipi, 669, 678 H. quoyi, 678 H. zebra, 676 phylogeny of, 423 Pliotrema, 339 Squalus, 594, 596, 600, 627, 628, 629 see also clefts above Ginglymostoma cirratum, 564, 565, 576-581 cloaca, 561 egg, 301, 530, 561, 564, 573 blastoderm (disc), 582, 583, 590 blastula, 560 capsule (case), 530, 558, 560, 561, 568, 576-577, 579, 580-581, tendrilliform processes, 579-581 gastrulation, 589 germinal disc, 589, 590 ovarian, 557, 564 plugs, 577, 579 size, 557, 563, 573, 576-577 wind, 558, 577, 580 yolk blastopore, 560 yolk mass, 533, 568, 577, 579 embryos, 301, 533, 560-562 perivitelline fluid, 530, 561, 577 Ginglymostoma cirratum—(continued) gestation, 533, 565 gland, nidamental, 580, 581 ovaries and oviduct, 561, 564 ovoviviparity, 557, 573, 579 viviparity, 533, 580 Girard, C. F., on Heterodontus francisci, 681, 682 Girdles, origin, 373, 376 pectoral, Chlamydoselachus, 371-373 Cladodus, 372 Heptanchus, 370 Heterodontus, 661, 696 Hybodus, 372 Symmorium, 372 pelvic, Arthrodira, 197, 198 Chlamydoselachus, 373-376; VI-v shoulder, Cladoselache, 373 Glands, in fins, 669 follicular, 669 nidamental, Chlamydoselachus, 432, 433, 434, 445, 446, 448, 450-452, 543-544, 550-552, 554, 578-581 Ginglymostoma, 579-580 Heterodontus, '703 Scyllium, 447 pancreatic, Chlamydoselachus, 413-415 Gambusia patruelis, 414-415 Heptanchus maculatus, 415 rectal, Chlamydoselachus, 410-411 Heptanchus, 411 Heterodontus, 703 thyroid, Amphioxus, 416 Chlamydoselachus, 415-418 Heptanchus, 418 Scyllium, 418 Gnathostomes, 67, 100, 357 Goodey, T., on Chlamydoselachus, 268, 350, 351, 355, 358, 359, 360, 362, 363, 366, 367, 368, 373, 376, 377, 380, 381, 388, 395, 396, 397, 415, 416, 425-426, 428, 453,487- 488, 624 Scyllium, 418 Goodrich, E. S., on Cestraciontidae, 569, 661, 670, 695 Chlamydoselachus, 291, 292, 343, 357, 422, 457, 482 Dinichthys, 145 Heterodontus, 684, 700 Scyllium, 455, 700 skull types, 699, 701 Analytical Subject Index Squalus, 455 yolk sac, 756 Goto, on Chlamydoselachus, 448, 552 Gray, J. E., on Centracion, 658, 659, 665 Gregory, W.K., on body form, 338 Chlamydoselachus, 282, 283, 311, 340, 397, 398 Cladodus, 311 Pliotrema, 339 Grieg, J. A., on Chlamydoselachus, 255 Gudger, E. W., 43-62; 243-330; 521-646 on Chlamydoselachus, 336, 337, 342, 343, 345, 385, 401, 402, 420, 444, 449, 487, 498, 623, 624, 626, 629, 654, 751, 758 Elasmobranchii, 301 Ginglymostoma (original notes), 533, 534, 558, 560, 561, 564, 568, 576-577, 579, 580-581, 582, 590 Gunther, H., on Chlamydoselachus, 249, 250, 265, 267, 285, 291, 292, 293, 294, 350, 376, 377, 408, 409, 410, 411, 413, 450, 459 Heterodontus, 663 H. galeatus, 686, 687 H. quoyi, 677 Gyropleurodus, 657, 659, 676, 677, 686 G. galeatus, see Heterodontus galeatus G. peruanus, see Heterodontus quoyi Haswell, W. A., on Elasmobranchii, 582 Heterodontus phillipi, 712, 713, 716, 723, 731, 732, 733, 735, 736, 737, 738 Hawkes, O. A. M., on Chalamydoselachus, 273, 278, 288, 362, 392, 393, 394, 399, 403, 405, 406, 411, 413, 415, 419, 433, 434, 443, 446, 448, 449, 472, 474, 475, 477, 478, 484, 485, 486, 491, 492, 545, 546, 547, 549, 550, 551, 559, 562, 627 Heterodontus, 662 Head, Arthrodira, 180, 200, 204, 205, 218 Asterolepidae, 132 Chlamydoselachus, 266-280, 396, 606, 625— 626; V-m Coccosteus, 211 Dinichthys, 127-159, 189, 193, 194, 195, 211; [Vi—IV-m Heterodontus, 678, 679, 685, 686, 699-700, 701 Lunaspis, 200 Macropetalichthys, 206 Scyllium, 476 Heart, Chlamydoselachus, 457-461 Heterodontus, 742, 743, 744 Heptanchus, 461 Heintz, A., 115-224 on Acanthaspida, 157, 198 795 Arthrodira, 154 Dinichthys, 115-212 Heterostius, 134 Homostius, 169 spinal (plate), 177 Hermaphroditism, Bdellostoma, 67-69, 76-78, 82, 83, 85, 86, 89, 95, 96, 98 Myxinoidea, 69-83, 88 Myxine, 70-76, 87, 88 Henle, J., see, Miiller, J. Heptanchus maculatus, 336, 337, 338, 339 arches, basibranchial, 363 branchial, 363 hyomandibular, 700 brain, 474-475 canal, sensory, 490, 492 circulatory system, 461, 464, 465, 467-468 aorta, 464 cranium, 351, 699, 700 dentition, 270, 311, 347 digestive system, 403, 407, 409 eye, 393 fins, 379-380 gill, 423 girdle, pectoral, 370 gland, pancreatic, 415 rectal, 411 intestine, valvular, 409 jaw, 670 mesonephroi, 438 mesonephric ducts, 444 mouth, 270 muscles, branchiomeric, 396 eye, 393 hypobranchial, 389 intermandibular, 399-400 trunk, 384, 385 myxopterygia, 395 nerves, 474-475, 483, 484, 485; VI-vi notochord, 364, 366-367, 369, 683 ovaries and oviducts, 446, 449-450 palatoquadrate, 700 pelvis, 373, 375 pyloric vestibule, 403 reproductive system, 411, 441, 446, 449- 450 skeleton, 350 spiracles, 428 tail, 340 testes, 446 urinary sinus, 441 Heptranchias perlo, 409, 461 Heterodontidae, 651-784 afhnities to Hybodontidae ,694~702 arch, hyomandibular, 662 bibliography, 764-770 796 Heterodontidae—{continued) classification, 657-664 collections of, see Collections above color pattern, 663 cranium, 701 distribution, 661 embryology. 651 eye, 662 fins, 660, 663, 669 fossil, 664 girdle, pectoral, 661 gills, 662 hump, 660, 661, 662 jaw, 661, 699-700 nomenclature, 657-664 palatoquadrate, 662 sexual dimorphism, 702-705 spine, dorsal, 698 see also Cestraciontidae Heterodontus (as 2 genus), classification, 657-664 color pattern, 663 dentition, 662, 698, 761, 762, 763 eggs, 527 capsules, spiral flanges, 705-708 eye, 662 fins, 342, 663 head, 662, 686, 699-700, 701 hump, 660, 661, 662 phylogeny, 651 spiracles, 662 Heterodontus francisci, 654, 661 arch, branchial, 662 breeding season, 718 color pattern, 677, 681, 683. 684 cranium, 684, 699-700 dentition, 684 distribution, 664, 681, 683, 709-710 egg. 712 capsule, 707-708 ovarian, 702-703 embryo, 718-721 size, 718 spiracle, 681, 683 epigonal organ, 703 eye, 677 fins, 660, 663. 681, 683 gills, 681, 683 girdle, pectoral, 661, 696 gland, rectal, 703 head, 683, 685-686 hump, 683 jaw, 684, 699-700 mesentery, 703 nest, 713 notochord, 683 ovarian follicle, 703 ovanies and oviducts, 702-704 ridge, supraorbital, 679, 681, 683 scales, 684 Bashford Dean Memorial Volume size, 679, 681, 682, 683, 684, 702 skeleton, 683 spine, dorsal, 681, 683 urogenital system, 702-705 Heterodontus galeatus, 660 breeding season, 712, 713. 717 color pattern, 687-688 dentition, 687, 688 distribution, 664, 686, 687 egg, 712, 713 capsule, 706-707, 715 tendrilliform processes, 706 fins, 663, 687 food, 711 gills, 687 head, 687 myxopterygia, 702 nasal openings, 687 nests, 713, 716 ridge, supraorbital, 687 size, 686 spawning, 713 spine, dorsal, 711 Heterodontus japonicus, 651-764 arch, mandibular, 662, 744, 745 bibliography, 764-770 brain, 735 embryonic, 740, 741, 742, 744. 745 breathing valve, 759 canal, : neurenteric, 743 sensory, 746, 747 spiracular, 759 cloaca, 713 color pattern, 692, 693, 694, 702. 755. 756, 737 embryonic, 747, 748 dental ridge, 759 denticles, dermal, 747, 755 oral, 760, 761 dentition, 691, 694, 711 anterior (cuspidate), 694, 763 development, 760-763 embryonic, 759 posterior (grinding), 694 rows, 694 distribution, 653, 664, 688-689, 709-710 eggs, 584, 689, 712, 723 discoidal, 728-732 furrows, 739; VII-va holoblastic, 722, 724~725, 726-727, 749 lines, 724-728, 731, 732 total, 724-728 collecting, 631, 716 development, 703, 716, 717, 718, 739 disc, germinal, 719, 723, 725, 726, 728, 731, 733, 749; V4, VU, Viva embryos on, 752, 753; VilL-vn extrusion of, 713-714 gastrulation, 719, 720, 725, 729, 732- 738. 739; VIll1 mitosis, 729, 730, 731 nucleus, 729, 730, 731 ovarian, 703-705, 712, 728 polarity, 726-728 segmentation of, 728-732 size, 723-724 vitelline circulation, 748, 749, 750, 752, 753, 755, 756; VIll-v, Vivi yolk, blastopore, 739, 740, 748, 749, 750; VIILv mass, 733, 739, 741; VIL, VIIl-v sac, 719, 746, 747, 748. 752, 756 stalk, 741, 744, 745. 750, 751; VII-v1 embryos, 527, 654, 689, 709, 717-751; VIll-n, Vim blood vessels, 720 brain, 740, 741, 742. 744. 745 branchial region, 746, 747 circulatory system, 720, 748, 749, 752, 753, 755, 756 color pattern, 747, 748 dentition, 759, 760-763 development, 651, 717-722, 740-748 ectoderm and entoderm, 734, 738, 739, 741, 742 eye, 741, 742. 743, 745, 746, 747. fins, see below flexures, caudal, 743, 744 cephalic, 740, 741, 742. 744. 745. 746 cervical, 740, 741, 742, 743, 744 fold, labial, 745, 746, 747 neural, 734, 740 blastoderm (disc), 582, 722, 729, 730, 731, 732, 733, 734, 738, 739. 741, 748, 749; VIll4, VIL, VIL-v blastomeres, 725, 728. 729, 730, 731, 732 blastopore, 726, 738-740, 748, 749; VIlL-v blastula, 719, 729, 732. 733, 737, 738 capsule, 705, 707-709, 713-714, 715, 717, 720, 728, 752, 753; Vill-va cleavage, 584, 653, 656, 724-732; VIIl1 gills, 742, 743, 744, 745. 746. 747. 752. 753, 758, 759, 760; VIll-m grooves, 747 branchial, 742, 743, 744 pharyngeal, 744 gut, fore, 734, 737 hind, 742, 743, 745 mid, 744 hatching of, 753, 720, 753 heart, 742, 743, 744 Heterodontus japonicus—embryos—(contd.) jaw, 745, 761 mesoderm, 734, 740, 741, 742 myomeres, 744, 745, 746; VIILu, Villain neuromeres, 741 on egg, 752, 753; VII-vu periblast, 733, 736, 738 phylogenetic significance, 722 pouch, Rathke’s, 759, 761 ridges, supraorbital, 746, 747 serial sections, 731 size, 720, 721, 739, 740, 741, 742, 745, 746, 747, 759, 760, 761, 762 somites, 734, 735, 740, 741, 742, 743, 744; VIII spiracle, 742, 744, 745, 746, 747, 755, 757, 759 tail, 741, 742, 744, 746, 754 epigonal organ, 703 eye, 662, 694 embryonic, 741, 742, 743, 745, 746, 747 muscles, 742, 743 fins, 663, 752, 754; VUl-vu anal, 663, 693 embryonic, 744, 745 caudal, 663, 693, 694 embryonic, 744, 745, 746, 755 dorsal, 663, 692-693 embryonic, 744, 745, 747, 748 pectoral, 663, 693 embryonic, 744, 745, 746, 748 pelvic, 663, 693, 713 embryonic, 744, 745, 747 fin folds, 744, 745 fin rays, 744, 745, 746 food, 711 gills, 755 cleft (embryonic) 742, 743, 744, 745, 747, 752, 753, 760 covers, 685, 693 filaments (embryonic), 745, 746, 747, 758, 759; VIL glands, nidamental, 703 rectal, 703 habits, 709, 710, 715 head, 683, 693 hump, 693 jaw, 711, 745, 761 mesentery, 703 mouth, 692, 711, 735 embryonic, 745, 746, 747, 759, 760 myxopterygia, 702 embryonic, 746, 747 nasal openings, 692 embryonic, 747 nest, 714-715, 716 nomenclature, 657-662, 688-693 Analytical Subject Index colloquial, 689 notochord, 734, 735, 742 opisthure, 755 ovaries, 542-549, 703, 711-712 oviducts, 549-562, 703, 704, 714 palatoquadrate, 761 reproductive system, 542-563, 703-705 ridge, supraorbital, 692, 693, 694, 746, 747 embryonic, 746, 747 sexual dimorphism, 702 size, 685, 688, 690, 691, 692, 693, 694, 702, 756, 757 spawning, 712, 713-715, 716, 718 spines, dorsal, 689, 693, 747 spiracle, 692, 755, 757, 759 embryonic, 741, 742, 744, 745, 746, 747 tail, 754 embryonic, 741, 742, 744, 746, 754 venous system, 749, 750, 751; VIILv, Vivi venules, 749, 750, 751 young, 753-755, 756, 757, 758; VUll-vir Heterodontus phillipi, 657, 658, 660, 661, 664-675, 677, 681, 688, 693 arch, branchial, 662 breeding season, 711-712 capsule, auditory, 700 color pattern, 666, 667, 668, 669 cranium, 699-700 dentition, 666, 670-675, 681 anterior (cuspidate), 671, 672, 674 embryonic, 672, 761 lower, 673, 674 number, 673 posterior (grinding), 671, 672, 674 rows, 672, 673, 674 upper, 673, 674 distribution, 664, 686, 689, 712, 713 egg, 731, 732 blastocoele, 736 blastoderm (disc), 582, 723, 731, 732, 733, 737, 738 blastula, 712, 717, 731, 732, 735, 736 capsule, 705-707, 712, 713, 725 cleavage, 716 lines, 731, 732 disc, germinal, 723, 731, 732 gastrulation, 717, 733, 735, 736, 737, 738 embryos and embryology, 712, 722-725, 731 dentition, 672, 761 ectoderm and entoderm, 737 periblast, 736 fin, 663 caudal, 666 dorsal, gland and spine, 669 pectoral, 663, 665 pelvic, 665 food, 710 797 gill slits, 669 head, 685 jaw, 670-675, 700 myxopterygia, 667, 702 nests, 712~713, 715, 716 nomenclature, 657-662, 664-674 notochord, 737 palatoquadrate, 760 reproductive system, 667 sexual dimorphism, 702 size, 665, 666, 667, 668, 669 Heterodontus quoyi, 654, 657-662, 686 color pattern, 676, 677, 678, 679, 680 dentition, 680-681 anterior, 680 rows, 681 distribution, 664, 676, 677 eye, 677, 679 fins, 663 anal, 676, 678 dorsal, 676, 678, 679 pectoral, 676, 678, 679 gills, covers, 685 filaments (embryonic), 758-759 openings (slits), 678, 679 head, 678, 679 jaw, 680-681, 684 nasal openings, 679 ridge, supraorbital, 677, 678, 679, 683, 685 scales, 679 size, 676, 677, 678, 679, 684 skeleton, 678, 679 spines, dorsal, 679, 747 spiracle, 677, 678 Heterodontus zebra, 657-662, 663, 664 color pattern, 675 dentition, 676 distribution, 664, 675, 689, 693 fins, 663, 676 head, 685 ridge, supraorbital, 675 size, 675, 677 Heterostius, 134, 154, 180, 200 Hexanchus, 351 arch, basibranchial, 363 muscles, 399-400 neurocranium, 351 notochord, 352, 364 ovary, 446 see also Notidanus griseus Hiyama, Y., see Kumada, T. Hochstetter, F., on Acanthias, 455 Home, E., on elasmobranch eggs, 709 Homea burgeri, 48 Homostius, 132, 140, 141, 154, 169, 180, 192, 205 Howell, A. B., on Chlamydoselachus, 382, 383 798 Hussakof, L., on Arthrodira, 125, 180, 190, 191 Dinichthys, 116, 119, 121, 145, 149, 151, 160, 168, 169, 170, 173, 175, 184, 187 202, 208, Huxley, T. H., on Heterodontus phillipi, 699-700 skull types, 699-700, 701 Hybodontidae, affinities, 694-702 arch, neural, 696 dentition, 696, 697 fin, 696 jaw, 699 notochord, 696 spine (dorsal), 669 Hybodus, 660, 696, 699 cranium, 700, 701 dentition, 697 fins, 341-342 girdle (pectoral), 696 notochord, 494, 696 palatoquadrate, 700 spine (dorsal), 669 H. basanus, arch, hyomandibular, 701 cranium, 701 jaws, 701 palatoquadrate, 700-701 H. delabechei, 697 H. dubrisiensis, 700, 701 H. hauffianus, 660, 695, 699, 700, 701 cranium, 699, 701 H. raricostatus, 697 H. reticulatus, 348, 349, 697 dentition, 348, 349 Hypoprion brevirostris, 565 H. signatus, 565 Ijima, I., 251, 657 Intestine, valvular Cephaloscyllium umbratile, 409 Chlamydoselachus, 408-409, 412; VI-1v Heptanchus maculatus, 409 Heptranchias perlo, 409 Isurus punctatus, 409 Raja, 409 Scyllium canicula, 409 Zygaena, 409 Tsurus punctatus, 409 Ito, K. (artist), 253, 268, 295, 675, 993 Jaekel, O., on Arthrodira, 125, 142, 153, 185, 187, 197, 200, 201 Coccosteus, 143, 144, 175, 177, 199 Dinichthys, 152, 175, 180, 181, 184, 190 Hybodus hauffianus, 699, 700, 701 Pholidosteus, 134, 151, 175 Synosteus, 205 Bashford Dean Memorial Volume Jaekel-Adams theory, 185, 187 Jagorina, dentition, 206 Jansen, J., on Myxine glutinosa, 99 Japanese Bullhead Shark, 664, see Hetero- dontus japonicus Jaw, Antiarchi, 187 Arthrodira, 145, 184-185, 187, 207 Cestraciontidae, 699 Chlamydoselachus, 268, 269, 272, 353, 354, 356, 358, 484 Coccosteus, 185, 187 Dinichthys, 118, 121, 138-155, 184, 185, 187, 188, 189, 190; [V-vir Heptanchus, 670 Heterodontidae, 661, 699-700 Heterodontus francisci, 684, 699-700 H. japonicus, 711, 745, 761 H. phillipi, 670-675, 700 H. quoyi, 680-681, 684 Hybodontidae, 699 Hybodus basanus, 701 Scyllium, 700 Johnson, S. E., on Mustelus, 492 Johnston, J. B., on occipitospinal nerve, 483 Jordan, D. S., on Chlamydoselachus, 265, 273 Heterodontidae, 659, 660 Heterodontus francisci, 681 H. japonicus, 679 Kemna, A., on gills, 199 Kidneys, see Mesonephroi Klein, J. T., on Cestracion, 658, 659 Koenen, A. von, on Arthrodira, 180, 197 Coccosteus, 176 Dinichthys, 197, 198 Kumada, T., and Hiyama, Y., on Heterodontus francisci, 681, 682, 683 H. quoyi, 677 Kupfer, C. von, on Bdellostoma, 98, 99 Kuwabara, I. (artist), 530, 656 Lacépede, B., on Heterodontus, 654 Lacerta, 389 Lamna cornubica, 574-575 eggs, 574; size, 575 embryo, 574, 575 reproductive system, 578 Lawley, R., on Chlamydoselachus, 311-312, 348 Leigh-Sharpe, W. H., on Chlamydoselachus, 348 Heterodontus, 702 myxopterygia, 376, 395, 451, 452, 453, 472, 542, 702 Lepidosiren, 389 Lepidosteus, 394, 726, 728 Leriche, M., on Chlamydoselachus tobleri, 348 Lesson, R. F., on Heterodontus phillipi, 665, 666, 677, 681 Leydig, F., on blastoderms, 582 Squalus acanthias, 620 Lohberger, J., on egg of Lamna, 575 Loppe, E., see, Pellegrin, J. Lozano Rey, L., on Chlamydoselachus, 256, 266, 273 Lunaspis heroldi, 199, 200 Lungfish, 722 Luther, A. F., on Chlamydoselachus, 399 Heptanchus, 399 M Coy. F.., on Dinichthys, 145 Heterodontus phillipi, 659, 664, 667. 670, 673, 674, 705, 710, 711 Placodermata, 202, 209 Maclay, N. and Macleay, W., on Heterodontidae, 657, 658, 659, 660, 663, 670 Heterodontus francisci, 681, 682, 685 H. galeatus, 686, 687, 688, 711 H. japonicus, 689, 690, 691 H. phillipi, 664, 666, 667, 668, 671, 673, 674, 702 H. quoyi, 677 H. zebra, 675, 676 Macleay, W., see above Macropetalichthys, 193, 194 armor, 204 canal, sensory, 206 carapace, 206 phylogeny, 204, 206 Marshall, A. M., on Elasmobranchs, 391, 742 Maurer, F., on Chlamydoselachus, 382, 384 Medlen, A. B., see Potter, G. E. Mertens, R., on Chlamydoselachus, 253, 265, 282, 295 Mesentery, Chlamydoselachus, 437, 438, 439, 440, 442, 443, 445, 447 Heterodontus, 703 Mesonephroi, Bdellostoma, 90, 98 Chlamydoselachus, 432, 433, 434-438 Heptanchus, 438 Myxinidae, 441 Mesopterygium, see Girdle, pectoral Mesovaria, Chlamydoselachus, 432 Myzxine, 70, 90, 91 see also Mesentery Miller, H., on Arthrodira, 197, 199, 208 Coccosteus, 145 Dinichthys, 184, 187 Mivart, St.G., on fin folds, 341 Momose, F., on Chlamydoselachus, 535, 543, 546, 547 Moodie, R. L., on Dinichthys, 145, 146 Mouth, Arthrodira, 187-192 Cetorhinus, 339 Chlamydoselachus, 267-269, 295, 338- 339, 593-597, 599-602, 604, 605, 607-616, 623-625; V-11 Dinichthys, 187, 189-190 Heptanchus, 270 Heterodontus japonicus, 292, 711, 745, 746, 747, 755, 759, 760 Teleostomi, 338, 339 Miller, J., and Henle, J., on Heterodontus, 666, 688, 689 Myzxine, 69, 70, 71 Munro, A., on Raja, 455 Murphy, R. C., see Nichols, J. T. Muscles, Acanthias, 390, 394 Amia, 394 Arthrodira, 194 Cestracion, 394 Chlamydoselachus, 381-400, 484, 485;V Liv For details see, Chlamydoselachus, muscles Coccosteus, 190 Dinichthys, 188, 189-191, For details see, Dinichthys, muscles Elasmobranchii, 391, 394, 742, 743 Heptanchus, 384, 385, 389, 390, 391, 393, 395, 396, 399-400 Hexanchus, 399-400 Lacerta, 389 Lepidosiren, 389 Lepidosteus, 394 Scyllium, 389, 392, 394 Scymnus, 389 Selachii, 391 Squalus, 389 Teleostomi, 394 Mustelus, canal, sensory, 492 ear, 355 fin, dorsal, 379 Mylostoma, dentition, 186 Myomeres, Chlamydoselachus, 382, 383, 388, 593, 624 Heterodontus japonicus, 744, 745, 746; Villian Squalus, 383 Myotomes, Chlamydoselachus, 388-389 Lacerta, 389 Lepidosiren, 389 Petromyzon, 389 Protopterus, 389 Scyllium, 389, 476 Squalus, 389 Analytical Subject Index source of hypobranchial muscles, 388 Myxine, corpora lutea, 90, 97 distribution, 72, 73, 75 ducts, 441 eggs, 74, 75, 90 hermaphroditism, 70, 75, 76, 77, 78 mesorchia, 70, 78, 83, 84 mesovarium, 70, 90, 91 ovary, 90 phylogeny, 99 reproductive system, 70, 75,77 sex, 72, 73, 74 spawning, 93, 94, 96 spermatogenesis, 73, 85 spermatozoa, 72. 74, 76 testis, 70, 75, 77 Myxine glutinosa, 69, 79, 89, 91, 99 hermaphroditism, 70-76 mesorchium, 70 mesovarium, 70 ovary, 70, 72, 74, 90 Myxinidae, mesonephric ducts, 441 Myxinoidea, 47-62, 67-69, 97-100 age, 92 cartilage, labial, 357 classification, 69 egg, 88-91 embryo, 68 feeding habits, 69 parasitic, 69 phylogeny, 97-100 reproductive system, 67-75, 78-87; II]4, Ilav spawning, 67, 93, 94, 96 Myxopterygia, Arthrodira, 724 Bdellostoma, 92 Chlamydoselachus, 291, 292, 295, 298, 373, 376-377, 395, 451-454, 472, 541, 542, 624; V-v; VI-v Cladoselache, 724 Elasmobranchii, 531 Heptanchus, 395 Heterodontus, 702 H. galeatus, 702 H. japonicus, 702, 746, 747 H. phillipi, 667, 702 Nansen, F., on hermaphroditism, 78 Myxine, 72, 73, 74, 75,76, 93 Nasal organs, Chlamydoselachus, 207, 279, 503, 593, 599. 600-602, 604 607-617 Heterodontus galeatus, 627 H. japonicus, 602, 747 H. quoyi, 679 Neal, H. V., on muscles, 389, 391 799 somites, 735 Necturus, brain, 99 egg, 726 Nerves, Chlamydoselachus, 368, 472-487; VI-vu For details see, Chlamydoselachus, nerves Heptanchus, 474, 475, 483, 484; VIl-vu Raja, 487 Spinax, 483 Squalus, 484, 487 Torpedo, 484 Nests, Heterodontus japonicus, 712-715, 716 H. phillipi, 712-713, 715, 716 Neurocranium, Arthrodira, 192-194 Chlamydoselachus, 350, 351 Dinichthys, 192-196 Hexanchus, 351 primordial, 192-196 Newberry, J. 5., on Acanthaspis, 176 Arthrodira, 180, 187, 202, 208 Cephalaspidae, 176 Dinichthys, 115, 117, 118, 119, 127, 135, 160, 166, 169, 170, 175, 179, 184, 190, 195, 197, 198 Nichols, J. T., and Murphy, R. C., on Heterodontus quoyi, 678 Nishi, $., on Chlamydoselachus, 392 Nishikawa, T., on Chlamydoselachus, 250, 257, 265, 299, 300, 302, 445, 448, 528, 529, 555, 567, 573, 582, 583, 585, 586, 587, 588, 591, 593, 598, 619 Norris, H. W., on Squalus, 492 Notidanidae, canal, sensory, 490 dentition, 673 ear, membranous labyrinth, 487-488 fin, pectoral, 490 Notidanus (Hexanchus) griseus, 488 Notochord, Chlamydoselachus, 351, 352, 363-370, 494 Heptanchus, 364, 366, 367, 369, 683 Heterodontus francisci, 683 H. japonicus, 734, 735, 742 H. phillipi, 737 Hexanchus, 52, 364 Hybodontidae, 494, 696 Notorhynchus, 468 Obrutschew, D. W., on Angarichthys, (spinal plate), 177 Dinichthys, 145 Ogilby, J. D., on Heterodontus, 659 H. galeatus, 688 800 Opisthure, 755 Orodontidae, 695 Orodus, 696, 697, 699 Osburn, R. C., on Chlamydoselachus, 342, 376, 592 Heterodontus francisci, 709 Osorio, B., on Chlamydoselachus, 256 Ostracoderms, 99 Ovarian follicles, see Follicles, ovarian Ovary, Bdellostoma, 86, 88, 89, 91, 92; IlI1 Carcharhinus, 564, 565 : Chlamydoselachus, 299, 432, 433, 445, 446, | 447, 535, 543, 544-547 Galeocerdo, 564 Ginglymostoma, 564 Heptanchus, 446 Heterodontus francisci, 702-703 H. japonicus, 542-549, 703, 711, 712 Hexanchus, 446 Myxine glutinosa, 70, 72, 74, 90 Pteroplatea maclura, 565-566 Oviducts, Carcharhinus obscurus, 564, 565 C. platyodon, 564, 565 Chlamydoselachus, 293, 299, 302, 431, 432, 433, 434, 435, 437, 445, 446-450, 543, 544, 549-550, 558, 559, 562, 563 Elasmobranchii, 301, 549, 565-566 Galeocerdo, 564 Ginglymostoma, 564 Heptanchus, 449-450 | Heterodontus francisci, 702 | H. japonicus, 549-562, 703, 704, 714 Pteroplatea maclura, 565-566 Oviparity, 300, 301, 531-533, 578, 579, 580 Ovoviviparity, 301, 531-533, 578, 579, 580 see also Viviparity Oxyrhina, egg and embryo, 576 Oyster-crusher, 664, see Heterodontus phillipi Palaeospondylus, 11, 67 Palatoquadrate, Cestraciontidae, 695-696 Chlamydoselachus, 353, 354, 356, 358, 424, 425 Heptanchus, 700 Heterodontidae, 662 Heterodontus japonicus, 761 H. phillipi, 760 Hybodus basanus, 700-701 sharks, 699 Paleospinax, 696-698 dentition, 698 denticles, 698 spine, dorsal, 698 Palmen, J. A., on Chlamydoselachus, 255 Pancreas, see Glands, pancreatic Pander, C. A., on Arthrodira, 163, 180, 192, 208 ( Bashford Dean Memorial Volume Coccosteus, 175 Dinichthys, 184 Placoderms, 145 Parker, T. J., on Raja, 409 Scyllium canicula, 409 Zygaena, 409 Patten, W., on Dinichthys, 184, 187, 199, 208 Pellegrin, J., and Loppé, E., on Chlamy- doselachus, 255 Pelvis, Chlamydoselachus, 373-376 Heptanchus, 373, 375 Perivitelline fluid, 561 Petromyzon, mesonephric ducts, 441 muscles, 389 Phillip, A., on Heterodontus phillipi, 664, 670 Phlyctaenaspis, 127, 134, 141, 142, 148, 175, 177, 205 P. acadica, 134 Pholidosteus, 134, 144, 151, 175,177 spinal (plate), 177 Pigfish, 664, see Heterodontus phillipi Placodermata, 9, 145, 202, 209-211 canals, sensory, 209, 210, 211 Plagiostomes, eye-stalks, 355 Pleuracanthus, 341-342 dentition, 310 fins, 342 P. laevissimus, 310 Pliotrema, gills, 339 Pollard, H. B., on labial cartilage, 357 Potter, G. E., on Gambusia patruelis, pan- creas, 414 Pouch, Rathke’s, 759, 761 Price, G. E., on Bdellostoma, 93, 94, 98 Myzxinoidea, 98 Pristiurus melanostomum, 582 egg, blastoderm (disc), 582, 589, 748, 749 blastopore, 748, 749 blastula, 731 cleavage, 589 germinal area, 589 germinal disc, 723, 727 vitelline circulation, 748-749 yolk: mass, 748; sac, 756; stalk, 748 embryo, 722, 748, 750 arterial ring, 749 arterioles, 749, 751 Protoplasm, 52, 53, 56, 57 Protopterus, 389 Pteroplatea maclura, 565—566 Pterygoquadrate, see Palatoquadrate above Putnam, F. W., on Myxine, 93 Pylorus, Chlamydoselachus, 405-406, 412; vestibule of, 404-405, 412 Galeus, 405 Heptanchus, vestibule of, 403 Radcliffe, L., see Evermann, B. W. Raia batis, 621 Raja, canals, pericardio-peritoneal, 455 sensory, 455 intestine, valvular, 409 nerve, spinal, 487 yolk sac, 756 R. laevis, 487 Reconstruction, Arthrodira, 122, 123, 142 Bdellostoma, egg, 47 Dinichthys, 117-122, 142, 143, 145, 151, 152, 153, 159, 160, 161, 168, 169, 174, 180, 188-189, 191, 192, 202, 203 Regan, C. T., on Cestraciontidae, 695 Heterodontidae, 657, 659, 663 Pliotrema, 339 Reproductive system, Bdellostoma, 83-88, 90, 95; I1]1—IIL1v Chlamydoselachus, 412, 431-455, 541-564; Viv Elasmobranchii, 547 Heptanchus, 411, 441, 449-450 Heterodontus francisci, 702-705 H. japonicus, 542-563, 703-705 H. phillipi, 667 Lamna, 578 Myxine, 67-75, 78-87; I111—Il1v see also Ovary, Oviduct, Testes, Uterus Respiratory system, Arthrodira, 199-202, 207 Chlamydoselachus, 267, 279-281, 339-340, 359, 419-431, 467-472, 593-595, 596, 597-602, 604-617, 625-630, 758;V-n, Vav; Vilu, Vila, Viliv Heterodontus japonicus, 692, 741, 742, 743, 745, 746, 747, 752, 753. 755, 757, 758, 759; Vila H. phillipi, 665, 666, 667, 668, 669 H. quoyi, 677, 678, 685, 758-759 Selachii, 743 Squalus, 594, 596, 600, 601, 627, 628, 629 Rhineodon typus, 277 Richards, A., on egg chromosomes, 731 Ridge, supraorbital, Heterodontus francisci, 679, 681, 683 H. galeatus, 687 H. japonicus, 692, 693, 694, 746, 747 H. quoyi, 677, 678, 679, 683, 685 H. zebra, 675 Rose, C., on Chlamydoselachus, 248, 286, 298, 342, 346, 591 Roule, L., on Chlamydoselachus, 254, 255 Riickert, J., on blastula, Pristiurus, Torpedo, 731 Sanzo, L., on Carcharodon rondeletii, 575, 5'76 SavilleKent, W., on Heterodontus phillipi, 661, 664, 665, 668, 669, 710 Scales, Acanthaspida, 210 Chlamydoselachus, 286, 287, 288, 294, 342-350 Heterodontus francisci, 684 H. quoyi, 679 placoid, see Denticles, dermal Scammon, R. E., on Squalus, 468, 585, 593, 733, 742 Schreiner, A., and K. E., on Myxine, 73, 75, 76, 88, 91, 94 Sclerotic ring, Arthrodira, 206 Coccosteus, 211 Dinichthys, 158-159 Placodermata, 209 Macropetalichthys, 206 Scoliodon terraenovae, 565 Scyllium, canal, pericardio-peritoneal, 455 cranium, 699, 700 egg, blastoderm, 729 cleavage, 729 embryo, 476, 722 gland, nidamental, 447 jaw, 700 muscles, appendicular, 394 hypobranchial, 389 myotomes, 389 Scyllium canicula, arches, visceral, 476 embryo, 476 hatching of egg, 540 intestine, 409 muscles, 389, 392 eye, 392 myotomes, 476 thyroid gland, 418 Scyllium catulus, 540, see Squalus catulus Scymnus, cranium, 351 muscles, hypobranchial, 389 Seabra, A. F. de, on Chlamydoselachus ang- uineus, 256 Selachii, arches, gill and pharyngeal, 743 canal, pericardio-peritoneal, 455 embryo, 742 muscle, eyeball, 391 respiratory system, 743 Selenosteus, 158 Semper, C., on Hexanchus, 446 Analytical Subject Index Sewertzoff, A. N., on labial cartilage, 357 paired fins, 372 Sex, Bdellostoma, 70, 77-78, 82, 83, 85, 86, 89, 95, 96 Ginglymostoma, 560 Heterodontus francisci, 681, 682, 683, 684, 702 H. japonicus, 690, 691, 692, 693, 694, '702 H. phillipi, 669, 681, 702 H. zebra, 675, 676 Myxine, 72, 73, 74 Shagreen, 278, 286, 695 Shann, E. W., on Lamna cornubica, 574 Shark, Bulldog, 664, see Heterodontus phillipi Bullhead, 660-661, see Heterodontidae chrondocranium, 699 Hammerhead, 658, 659, see Zygaena Japanese Bullhead, 664, see Heterodontus japonicus Nurse, see Ginglymostoma palatoquadrate, 669 Port Jackson, 664, see Heterodontus phillipi Tiger, see Galeocerdo Siebold, P. F., on Heterodontus japonicus, 688, 689, 690 Size, Bdellostoma, 82, 98 Chlamydoselachus, 248, 252, 254, 255, 256, 260-265, 273, 274, 279, 281, 282, 283, 290, 295, 444, 546, 578, 662, 663 Heterodontus francisci, 679, 681, 682, 683, 684, 702 H. japonicus, 685, 688, 690, 691, 692, 693, 702 H. phillipi, 665, 666, 667, 668 H. quoyi, 676, 677, 678, 679, 684 H. zebra, 675, 677 Skeleton, calcification, 350 Chlamydoselachus, 350-380, 390, 494; Via, Vian visceral, 200, 355, 356-364; VI-n, VI-m Dinichthys, 192, 196, 199 Heptanchus, 350 Heterodontus francisci, 683 H. quoyi, 678, 679 Smith, B. G., 43-62: 243-330; 331-520; 647- 784 on Chlamydoselachus, 335, 336, 337, 342, 343, 345, 385, 401, 402, 420, 444, 449, 487, 492, 542, 544, 546, 557, 559, 561, 591, 595, 623, 624, 626, 627, 630, 744, 758, 759 Cryptobranchus, 728, 739 Squalus, 627, 628, 629 Somites, Chlamydoselachus, 388 801 Elasmobranchii, 742, 743 Heterodontus japonicus, 734, 735, 740, 741, 742, 743, 744; VU Heterodontus japonicus, 734, 735, 740, 741, 742, 743, 744; VIL Squalus, 735, '740 Snyder, J. O., see Jordan, D. S., Speidel, C. C., on Squalus acanthias, 487 Spermatogenesis, 73-74, 76, 85 Spinal (plate), Acanthaspis, 176, 177 Angarichthys, 177 Arthrodira, 176, 179 Coccosteus, 176, 177, 210 Dinichthys, 159, 172, 174, 176-179, 198; 1V-x Pholidosteus, 177 Spine, dorsal, Cestraciontidae, 696 Heterodontidae, 698 Heterodontus francisci, 681, 683 H. galeatus, 711 H. japonicus, 689, 693, 747 H. quoyi, 679, 747 Hybodontidae, 669, 696, 698 Paleospinax, 698 Squalus, 669 Synechodus, 698 pectoral, Dinichthys, 198-199 Spinax, nerves, occipital, 483 yolk sac, 756 Spiracle, Chlamydoselachus, 279-281, 340, 423-430; Va embryonic, 423-430, 596, 598, 599-602, 604, 607-608, 610-613, 615 Elasmobranchii, 340, 428 Heptanchus, 428 Heterodontus francisci, 681, 683 H. japonicus, 692, 755, 757 embryonic, 741, 742, 744, 745, 746, 747 H. phillipi, 665, 666, 667 H. quoyi, 677, 678 Hexanchus, 428 Squalus, 487, 600 Squatina, 340, 427 Spleniale (plate), 185 Squalus acanthias, canal, pericardio-peritoneal, 455 sensory, 489-490, 492 circulatory system, 620: aorta, 464, 465 arteries, 468 ducts, 441 egg, 585 blastoderm, 585, 733 802 Squalus acanthias—(continued) embryo, 593, 594, 595, 601, 627. 628, 629, 22, 734, 742 myomeres, 383 somites, 735, 740 spiracle, 487, 600 fins, dorsal with spine. 669 pectoral (embryonic), 595, 601 gills (embryonic), 594, 596, 600, 627, 628, 629 glands, follicular, 669 of dorsal spine, 669 muscles, 389 nerves, occipitospinal, 484 spinal. 487 Squalus catulus, hatching of eggs, 540 S. sucklit, mesonephric ducts, 444 Squatina, spiracle, 340, 427 Stead, D. G., on Chlamydoselachus, 257 Steindachner, F., on Chlamydoselachus, 248 Stensio, E. A., on Arthrodira, 126, 146, 184, 187, 206, 208 Dinichthys, 148, 176, 178, 187, 188 Macropetalichthys, 193, 204, 205 Ostracoderms, 99 Phlyctaenaspis, 141, 142, 148 Stetson, H., on Arthrodira, 208 Dimichthys, 122, 145, 148, 154, 159, 191. 194, 195, 199 Stewart, C., on Notidanus (Hexanchus) griseus, 488 Stockard, C. R., on Bdellostoma, 99 Stomach, Chlamydoselachus, 403-404 Heptanchus, 403 Striver, J., on Heterodontus phillipi, 659, 666, 671, 672 Symmorium renijorme, 372-373 girdle, pectoral, 372 Syncytium, 733, 736, 738 Synechodus, 696 cranium, 701 dentition, 697-698 spine, dorsal, 698 Synosteus, 205 Tabbigaw, 664, see Heterodontus phillipi Tail, Cestraciontidae, 696 Chlamydoselachus, 248, 249, 250, 288, 289, 290, 293, 364. 369-370, 624-625 embryonic, 296, 593, 594, 598, 601, 604, 607. 611-614, 617, 620-621 Heptanchus, 340 Heterodontus japonicus, 754 embryonic, 741, 742, 744, 746, 754 Tee-Van, J., see, Beebe, W. Teleostomi, 201, 339 mouth, 338, 339 muscle, appendicular, 394 Testis, Bdellostoma, 70, 83-85, 89; II Cestraciontidae, 696 Chlamydoselachus, 450 Heptanchus maculatus, 446 Myxine, 70-75, 7 Thacher, J. K., on fin-fold theory, 341 Thyroid, see Gland, thyroid, above Titanichthys, 140, 166 Torpedo ocellatus, blastoderm (disc). '733, 739 blastula, 731 gastrula, 734 nerve, occipitospinal, 484 Townsend, C. H., on Heterodontus, 683 Traquair, R. H., on Arthrodira, 125, 180, 187, 195, 197, 199, 200 Coccosteus, 143. 168, 169, 176 Dinichthys, 144, 184 Phlyctaenaspis, 134 Trautschold, H. von, on Arthrodira, 197 Triakis semifasciatus, dentition, 345 Vaillant, L., on Oxyrhina, 576 Valenciennes, A., on Heterodontus quoyi, 660, 676, 677 Van Wijhe, J. W.. on Scyllium, 382, 392 Selachii, 391. 742 Vertebral column, Chlamydoselachus, 363, 364-366, 367. 368-370. 436 Coccosteus, 196, 197 Dinichthys, 196-199 Vetter, B., on Heptanchus, 390, 399 Viviparity, Chlamydoselachus, 298-301, 528, 331-534, 542, 559 development from ovoviviparity, 580 Elasmobranchii, 301 Ginglymostoma, 533, 580 Vitelline circulation, see under Embryo above Waite, E. R.. on Heterodontus galeatus, 660, 687, 688, 706, 707, 712, 713 H. phillipi, 668, 669, 705, 706, 712 Weber, M., on Myxine, 71, 93 White, E. G.. on Chlamydoselachus, 253, 274 Whitley, G. P., on Heterodontus galeatus,686,687 688.717 H. phillipi, 660, 669. 710, 712 Wilder, B. G., on Chlamydoselachus, brain, 473. 474 Woodward, A. 5., Bashford Dean Memorial Volume on Acanthaspis, 177 Acrodus, 697 Arthrodira. 125, 163, 180, 187, 197. 199, 202 Cestraciontidae, 695, 696, 699 Chlamydoselachus, 335, 342 Coccosteus. 143, 199 Dinichthys, 122, 170, 173, 184, 192 Heptanchus, 700 Heterodontus, 659 Hybodontidae, 494, 696, 697, 699, 700, 701, 702 Wright, A. A., on Dinichthys, 119, 170, 173 Wyman, J., on Raia batis, 621 Yatsu, N. (artist), 656, 657 Yolk, blastopore, Cryptobranchus, 739 Heterodontus japonicus, 739, 740, 748, 749, 750; Villav, VIIL-v cord, 301; VIL-n mass, Chlamydoselachus, 572; VIL-v Ginglymostoma, 577, 579 Heterodontus japonicus, 733, 739, 741; Villa, VIIL-v Pristiurus, 748 sac, Chlamydoselachus, 300. 301, 303, 449 533, 555-557, 559, 571, 573, 576, 595, 596. 602, 603, 610, 612-621, 627; Vila Elasmobranchii, 301 Heterodontus japonicus, 719, 746, 747. 752, 756 Pristiurus, 756 Raja, 756 Spinax, 756 stalk, Chlamydoselachus, 593, 595, 597, 602, 603, 605, 610, 612, 614, 615, 618-621 Heterodontus japonicus, 741,°744, 745, 750, 751; Vivi Pristiurus, 748 syncytium, 733, 736, 738 vascular system, Chlamydoselachus, 620-622; VIL-v Felichthys, 622 Ziegler, H. E., on Chlamydoselachus, 303, 592, 596, 627 Torpedo ocellatus, 733, 734. 739 Zittel, K. A. von, on Arthrodira, 202, 208 Cestraciontidae, 651, 696 Heterodontus, 659, 660 Hybodontidae, 696 Zygaena, 409, 658 intestine. 409 eRe he BASHFORD DEAN MEMORIAL VOLUME ARCHAIC FISHES Edited By _ EUGENE WILLIS GUDGER Articte VI THE ANATOMY OF THE FRILLED SHARK CHLAMYDOSELACHUS ANGUINEUS Garman By BERTRAM G. SMITH Professor of Anatomy New York University College of Medicine New York City AOI Ot Ce, <1 NEW YORK PUBLISHED BY ORDER OF THE TRUSTEES Issued December 22, 1937 5 Zz *~ =A Meare NENA at THE BASHFORD DEAN MEMORIAL VOLUME ARCHAIC FISHES | EDITED BY EUGENE WILLIS GUDGER Published by The American Museum of Natural History New York City * Article No. I. Mezmortat or Basrorp Dean, sy W.K, Grecory. 1930, pp. 1-42, 8 half—tone plates (7 portraits), 2 text-figures. Price $1.25. Article No. Il. Tue SEGMENTATION OF THE Ecc Or THE Myxinorp, Bdellostoma stouti, BASED ON THE DRAWINGS OF THE LATE BASHEORD DEAN, By EUGENE Wittis GupGER AND BERTRAM G. SMITH. 1931, pp. 43-62, 2 lithographed plates, 3 text-figures. Price 60 cents. Article No. II. Tu Genrrat System or THE Myxtnomwea: A Stupy Basep on Notes anp Drawincs OF THESE ORGANS IN Bdellostoma Maver py BasHrorD Dean, sy J. Leroy Congr. 1932, pp. 63-110, 4 lithographed plates, 1 text-figure. Price $1.75. Article No. IV. Tue Srructrur® oF Dinichthys: A ConrripuTion TO ouR KNOWLEDGE OF THE ArtTuropira, By ANATOL Heintz. 1932, pp. 111-242, 9 half-tone plates, 91 text-figures. Price $2.50 Article No. V.. THe Narurat History or THE Frittep SHarK, Chlamydoselachus anguineus, BY Eucens W. Gupcer AND BertRAM G. SmirH. 1933, pp. 243-330, 5 half-tone plates, 31 text figures. Price $1.00. Article No. VI.. THe ANaToMy oF THE FRILLED SHARK, * Guibasiacliches anguineus, By BERTRAM G, Smita. 1937, pp. 331-520, 7 halftone plates, 128 text-figures.. Price $3.50. The Dean Memorial Volume will probably be completed with two more articles. Title page with table of contents and an introduction will be supplied when the volume is finished. THE ~BASHFORD DEAN MEMORIAL VOLUME ARCHAIC FISHES Edited By EUGENE WILLIS GUDGER Articie VIL 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. oP SO NEW YORK PUBLISHED BY ORDER OF THE TRUSTEES Issued October 15, 1940 A} ee ai Mare i ee Le ro S THE BASHFORD DEAN MEMORIAL VOLUME ARCHAIC FISHES EDITED BY EUGENE WILLIS GUDGER Published by The American Museum of Natural History New York City Article No. I. Memoria or Basurorp Dzan, By W. K. Grecory. 1930, pp. 1-42, 8 half-tone plates (7 portraits), 2 text-figures. Price $1.25. a Article No. I]. Tue Sz¢MenraTION OF THE Ecc or THE Myxtnom, Bdellostoma stouti, BAssD ON THE _ DRAWINGS OF THE LATE BASHFORD DEAN, BY EUGENE WILLIs GuUDGER AND BERTRAM G. SMITH. 1931, pp. 43-62, 2 lithographed plates, 3 text-figures. Price 60 cents. Article No. II]. Tue Genrrat System or THE Myxinomwea: A Srupy BAsep on Notes AND Drawincs OF THESE OrGans IN Bdellostoma Mave sy BasHrorp Dean, By J. Leroy Congr. 1931, pp. 63-110, 4 lithographed plates, 1 text-figure. Price $1.75. Article No. IV. Tue Srructure or Dinichthys: .A ContrisuTION TO OUR KNOWLEDGE OF THE Arturopira, By Anatot Heintz. 1932, pp. 111-242, 9 half-tone plates, 91 text—figures. Price $2.50 i Article No. V. Tse Natura Hisrory or THE Fritep SHARK, Chlamydoselachus anguineus, BY Eucens W. Gupcer AND BertraM G. Smit. 1933, pp. 243-330, 5 half-tone plates, 31 text- figures. Price $1.00. Article No. VI. THe Anatomy OF THE FRItLED SHARK, Chlamydoselachus anguineus, BY BERTRAM G. Smirx. 1937, pp. 331-520, 7 half—tone plates, 128 text—figures. Price $3.50. Article No. VII. Tue Breepinc Hasits, RepropuctivE ORGANS AND ExTERNAL EMBRYONIC DEVEL- OPMENT OF Chlamydoselachus, BAseD oN Notes AND Drawines Lert By BAsHrorD DEan, by E. W. Gupcer. 1940, pp. 521-646, 6 lithographed plates, 33 text-figures. Price $2.50. a> The Dean Memorial Volume will be combed with one more Article, No. VIII, on the Bee ology of the Japanese bullhead shark by Dr. B. G. Smiru. A title page, introduction, table of contents and an index will be furnished when the Volume is completed. "papraoid aq []}46 83U23U09 Jo sajqr3 om pur sased 21913 omg ‘]] pu | sqieg se punog aq 0} any [jim auMjoA 343 aouTC ‘uoljonpoI3Uy ue pue ‘BUINJOA [EHOUaY Ueaq] ay} 0} xepuy ue papremM.to} aq [[IM e149 ‘paredaid aq Ue Lay} sv UOOS sy ‘00'S$ S91Ig + *saiInsy-7x23 69 ‘(aqjoo ur ¢) sazed paydeisoysy / 4g/-/49 dd