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Egg-cases of the swell shark, Cephaloscyllium ventriosum : formation, function, and population differences Grover, Charles Allan 1970

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THE EGG-CASES OF.THE SWELL SHARK, CEPHAL0SCYLLIUM VENTRIOSUM: •FORMATION,- FUNCTION, AND POPULATION DIFFERENCES. by CHARLES A. GROVER B.Sc. C a l i f o r n i a State College at, Long Beach 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s t h e s i s as conforming to the req u i r e d standard The U n i v e r s i t y o f B r i t i s h Columbia August, 1970. In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a i i ABSTRACT • , The s w e l l shark, CephaloscyIlium ventriosum Garman ( S c y l i o r h i n i d a e ) , i s an i n s h o r e , r e e f - d w e l l i n g , n o c t u r n a l s p e c i e s of the Eastern P a c i f i c rim. Reproduction i s oviparous. One ovary i s developed. Ova are t r a n s p o r t e d through the coelom by c i l i a , to a s i n g l e ostium, which serves both o v i d u c t s . Egg formation i s u s u a l l y synchronous i n both o v i d u c t s , and proceeds g e n e r a l l y as i n other elasmobranchs, but p u b l i s h e d and new data are combined i n a new d e s c r i p t i o n of the egg-forming sequence. Photomicrographs show sperm s t o r e d i n the s h e l l - s e c r e t i n g tubules of the s h e l l gland. T h i s storage allows the production of f e r t i l e eggs i n the absence of males f o r some months a f t e r mating. A membrane surrounds the embryo and yolk during the e a r l y stages of development, c o n t r a r y to p r i o r d e s c r i p t i o n s of r e l a t e d s p e c i e s . A c h a l a z a - l i k e s t r u c t u r e i s attached to t h i s membrane. The young of t h i s and s e v e r a l other oviparous s p e c i e s of sharks posess two d o r s o - l a t e r a l rows of enlarged d e n t i c l e s . In the s w e l l shark, these appear to f u n c t i o n i n the emergence of the shark from the egg-case. Eggs are preyed upon i n nature, p o s s i b l y by a S t e n o g l o s s i d gastropod. The sharks form at l e a s t two d i f f e r e n t p o p u l a t i o n s , separated by as l i t t l e as 30 km. The egg-cases of one p o p u l a t i o n have no t e n d r i l s over 2cm.; the other p o p u l a t i o n has long t e n d r i l s , to 2 m. D i f f e r e n c e s are a l s o found i n egg s i z e and i n the morpho-metries of the a d u l t sharks. TABLE OF CONTENTS PAGE ABSTRACT i i LIST OF TABLES i i i LIST OF FIGURES i v ACKNOWLEDGEMENTS v INTRODUCTION 1 MATERIALS AND METHODS 4 RESULTS 8 1. D e s c r i p t i v e Anatomy of the Female Reproductive System. 8 a. Ovary, ova, and p e r i t o n e a l c i l i a t i o n f u n c t i o n i n g i n ovum tr a n s p o r t . b. Ostium and oviducts. 9 c. C i r c u l a t o r y system. 11 d. S h e l l gland s t r u c t u r e , s e c r e t i o n s , and sperm storage. 1 2 2. Egg-case S t r u c t u r e . 16 3. Mechanics and Sequence of Egg-case Formation. 2 6 4. Development of the Embryo and Egg-case Changes. 35 5. Emergence of the Shark from the Egg-case. 40 6 . Predation on Egg-case. 43 7. Population D i f f e r e n c e s . 45 DISCUSSION 52 SUMMARY 61 REFERENCES 6 4 LIST OP TABLES Page Comparisons by two-tailed t-test of measurements of egg-case samples from sharks captured at Isthmus Cove, Santa CataJLina Island, and the mainland near Los Angeles. 49 Comparisons by two-tailed t-test of morphometric ratios of samples of sharks from Isthmus Cove, Santa Catalina Island, and Point Dume, C a l i f o r n i a . 51 i v LIST OP FIGURES 1. Diagramatic s e c t i o n drawings of a s h e l l gland. Page 15 2. Oblique s e c t i o n of a k e r a t i n s e c r e t o r y tubule. 1 7 3. S e c t i o n at base of laamellae of a s h e l l gland. 1 8 4. Egg-case showing t e n d r i l s . 20 5 . T y p i c a l p a i r of egg-cases. 21 6. T y p i c a l quartet of egg-cases. 22 7 . Egg-case c o n t a i n i n g an embryo. 23 8. Diagramatic s e c t i o n s of egg-cases. 24 9 . Two incomplete eggs l a i d by a s w e l l shark. 31 10. A c t i v e and i n a c t i v e s h e l l glands. 32 11 . B a c k l i t photograph of an embryo i n i t s case. , 38 12. A newly-hatched s w e l l shark. 41 13. Source l o c a t i o n s of egg-cases. 48 V ACKNOWLEDGEMENTS I wish to dedicate t h i s work to the memory of the l a t e Arthur S.Lockley, formerly of the Biology Department, C a l i f -o r n i a State College at Long Beach. He was a dedicated teacher and a good f r i e n d . I wish to thank Dr. R. Fay, of P a c i f i c Bio-Marine Supply, Messrs. F.Brocato, F.Calendrino, and B. Falcone, c o l l e c t o r s at Marineland of the P a c i f i c , andJ. P r e s c o t t , Curator? without t h e i r a s s i s t a n c e , t h i s work would not have begun. Dr. S. Applegate, Los Angeles County Museum of Natu r a l H i s t o r y , Mr. S. Springer, U.S. Bureau of Commercial F i s h e r i e s , Dr. C. Hubbs and Dr. R. Rosenblatt, Scripps I n s t i t u t i o n of Oceanography, and Mr. J . F i t c h , C a l i f o r n i a Department of F i s h and Game, have a l l contributed assistance and valuable d i s c u s -s i o n of the work i n progress. Drs. J . McPhail, N. VJilimovsky, and R. L i l e y , Depart-ment of Zoology, U.B.C, have provided h e l p f u l c r i t i c i s m of the manuscript. Mr. L. Sharman ably handled the preparation of the h i s t o l o g i c a l m a t e r i a l . F i n a l l y , my thanks to Mr. and Mrs. I . Neish, f o r t h e i r assistance i n preparation of f i g u r e s , and typing the manuscipt. INTRODUCTION The s w e l l shark, Cephaloscyllium ventriosum Garman (= C_. uter) . of the f a m i l y S c y l i o r h i n i d a e , i s common i n the waters of C a l i f o r n i a from Monterey Bay south. I t i s occasion-a l l y found as f a r south as Acapulco, Mexico, and i s found i n Chilean waters (Kato, Springer, and Wagner, 1967). I t a l s o i n h a b i t s the waters of at l e a s t some of the offshore i s l a n d s . The n a t u r a l h i s t o r y of t h i s shark has not been described, so I have included some of my own observations. Around Santa C a t a l i n a I s l a n d , C a l i f o r n i a , t rapping data and d i r e c t observation using SCUBA d i v i n g gear i n d i c a t e that the sharks are normally found i n depths of twenty to f o r t y meters, both day and nig h t , and are l e s s abundant i n greater and shallower depths. Two specimens have been taken i n deep trap s e t s ; one from about 160 meters (pers. comm., Brocato), and one from about .560 meters (pers. comm., 3 . Applegate). These sharks are predominantly n o c t u r n a l , and are found during the day i n the c r e v i c e s of rocky r e e f s . The members of t h i s genus have the pe c u l i a r a b i l i t y to i n f l a t e t h e i r stomachs with water, g r e a t l y i n c r e a s i n g t h e i r body s i z e . The anatomy of t h i s mechanism has been described (Clark, 1947). When d i s t u r b -ed, they use t h i s a b i l i t y to wedge themselves i n t o the r e e f c r e v i c e s generating an i n t e r n a l pressure s u f f i c i e n t to make i t quite d i f f i c u l t f o r a d i v e r (and, presumably, any other p o t e n t i a l predator) to remove them from the rocks, once they - 2 -are f u l l y i n f l a t e d . V/hen removed from the water, the sharks w i l l o f t e n i n f l a t e themselves with a i r , and, i f returned to the water i n t h i s c o n d i t i o n , they w i l l f l o a t , upside down and h e l p l e s s , f o r some time. However, t h i s l a t t e r behavior plays no part i n the n a t u r a l ecology of the animal, as they are bottom dwellers (see Herald, 1962). The femaJ.es reach a maximum l e n g t h of about 1.1 meters; the l a r g e s t males found with them are s l i g h t l y s maller. Their feeding behavior has not been studied i n d e t a i l , but f i s h are e v i d e n t l y an important part of t h e i r d i e t . P i s h are among the best b a i t s f o r trapping. Laboratory observa-t i o n s of feedings of whole f i s h show that even a quite s m a l l , f r e s h l y caught she.rk w i l l q u i c k l y manipulate a f i s h i n i t s mouth so that i t may be swallowed head f i r s t , no matter where the f i s h i s i n i t i a l l y grasped. The small teeth are not used to chew or b i t e pieces from the prey; i f i t i s too l a r g e to swallow whole, i t i s r e j e c t e d . However, the l a r g e mouth and g u l l e t and the h i g h l y d i s t e n s i b l e stomach can accomodate f i s h which are quite large i n p r o p o r t i o n to the shark. A shark of about 40 cm. can eventually swallow a Pacit^ic mackerel some 30 cm. long. V i s i o n plays l i t t l e or no part i n feeding. P i s h j u i c e s introduced i n t o l a b tanks induce a c t i v e swimming and snapping i n quiescent sharks during the day ( r e c a l l that they are noc-t u r n a l J. When food i s introduced, i t s d e t e c t i o n seems h i t -- 3 -or-miss; dependant upon the shark a c t u a l l y running i n t o the food, r a t h e r than o r i e n t i n g to i t v i s u a l l y . This study i s concerned with the egg-case of the s w e l l shark. While the various sections of the t h e s i s are a l l r e l -ated • i n t h i s respect, they are a l s o r e l a t i v e l y independent of one another. Consequently, the p e r t i n e n t h i s t o r i c a l background and the r e s u l t s of my own work have been grouped together w i t h i n each s e c t i o n . The work f a l l s i n t o the f o l l o w i n g sec-t i o n s . 1. D e s c r i p t i v e Anatomy of the female Reproductive System. a. Ovary, ova, and p e r i t o n e a l c i l i a t i o n f u n c t i o n i n g i n ovum transport. b. Ostium and oviducts. c. C i r c u l a t o r y system. d. S h e l l gland s t r u c t u r e , s e c r e t i o n s , and sperm storage. 2. Egg-case s t r u c t u r e . 3. Mechanics and Sequence of Egg-case Eormation. 4. Development of the Embryo and Egg-case Changes. 5 . Emergence of the Shark from the Egg-case. 6. Predation on Egg-cases. 7. Population D i f f e r e n c e s . MATERIALS AND METHODS Sharks were captured by cage trap and while SCUBA d i v i n g at various l o c a t i o n s off the C a l i f o r n i a coast i n the v i c i n i t y of Los Angeles, and at Santa C a t a l i n a I s l a n d , C a l i f o r n i a . Some of the sharks and eggs examined are i n the Scripps I n s t i t u t i o n of Oceanography Museum, and are so designated. With the exception of four l i v e eggs taken while d i v i n g at Santa C a t a l i n a I s l a n d , and one from the mainland which was brought to the l a b o r a t o r y , a l l l i v e eggs were obtained from sharks held i n running sea water tanks at the Marineland of the P a c i f i c l a b o r a t o r y . The eggs were removed to smaller tanks. No continuous temperature records were a v a i l a b l e . Because of f l u c t u a t i o n s i n water supply and room temperature, p e r i o d i c temperature readings could not provide an accurate p i c t u r e of the temperature f l u c t u a t i o n s i n the tanks, but I would estimate the absolute l i m i t s of seasonal and short-term f l u c t u a t i o n s to be between 13° and 22° C. Dead and empty cases obtained by d i v i n g and those brought to the l a b o r a t o r y by beachwalkers were also examined. The f i r s t three s e c t i o n s of the t h e s i s - reproductive anatomy, egg-case s t r u c t u r e , and egg-case formation - are based on gross d i s s e c t i o n s of f r e s h and preserved m a t e r i a l , and on microscopic examination of f r e s h m a t e r i a l and of stained h i s t o l o g i c a l s e c t i o n s . - 5 -P o r t i o n s of the oviducts were f i x e d i n Bouin's, then changed to 70>£> isopropanol at 3-5 days. Sections were stained with Van G-ieson's to show co l l a g e n and muscle. Shell, glands were f i x e d i n the same manner. Sections were stained i ^ i t h Heidenhain's i r o n hematoxylin, a chromatin s t a i n , to demonstrate the presence of sperm. Section fo u r , concerned with the embryo i n the egg-case, i s based p r i m a r i l y upon observations made by s h i n i n g a strong l i g h t through i n t a c t egg-cases, which are g e n e r a l l y more t r a n s -parent than those of other elasxnobranchs. In a d d i t i o n , s e v e r a l embryos were removed from t h e i r egg-cases and examined under a d i s s e c t i n g scope f o r comparison with published d e s c r i p t i o n s of the course of development of other species. Section f i v e describes the e x i t of the shark from the egg-case, and i s based upon the experimental s i m u l a t i o n of n a t u r a l c o n d i t i o n s . I t was not p r a c t i c a l to observe and f i l m the n a t u r a l emergence of a shark f o r s e v e r a l reasons; the time of hatching couldii't be predicted with any accuracy, hatching could not be induced at w i l l , and a l l n a t u r a l hatchings, at l e a s t of eggs held i n aquaria, occurred at nig h t . To circumvent these problems, a shark that had hatched the night before was r e - i n s e r t e d i n t o the egg-case through an i n c i s i o n i n the curve of the p o s t e r i o r end of the case, next to the ridge which forms the edge of the case (see f i g u r e 4). The s t r u c t u r e and consistency of the egg-case i s such that, - 6 -i f the experimental case was l a t e r a l l y compressed, the i n c i s i o n woxild open, but would s p r i n g closed when the pressure was r e l -eased . A f t e r the shark was replaced i n the egg-case, i t was returned to the aquarium, and a l l a i r e x p e l l e d ; The " r e -hatching" was recorded on 35 nun. c o l o r motion p i c t u r e f i l m , which was l a t e r examined both i n normal p r o j e c t i o n and frame-by- frame. Section s i x , on predation, r e s u l t e d from the examination of a sample of egg-cases c o l l e c t e d on one dive at Ship Rock, Santa C a t a l i n a I s l a n d , C a l i f o r n i a . S ection seven, on population d i f f e r e n c e s , s t a r t e d with the discovery of a consistent d i f f e r e n c e i n the morphology of egg-cases i n samples from various l o c a t i o n s , described i n the t e x t , and l e d me to make morphometric comparisons of samples of the sharks themselves. Sharks measured f o r morphometric comparison came from the mainland side of Santa C a t a l i n a I s l a n d , and from the region of Point Dume, approximately 10 km. north of Los Angeles (see f i g u r e 13). Both samples were measured on the same day. Both had been f r e s h - f r o z e n f o r storage, and were measured immediately a f t e r thawing. The dimensions u l t i m a t e l y chosen f o r comparison are given i n appendix 1. Because of a very f l e x i b l e body, such dimensions as jaw width, body depth, g i l l s l i t width, g i l l - 7 -s l i t i n terspace, e t c . , were not reproducible with any accuracy. The d o r s a l f i n height measurements were found to be c o n s i s t e n t -l y reproducible i f the f i n was spread f l a t on the ta b l e surface, one point of the c a l i p e r placed i n the notch at the p o s t e r i o r f i n base, and the other p o i n t swung i n an arc at the f i n t i p . fa 9 The caudal width was taken i n a s i m i l a r manner, swing 1'the c a l i p e r i n an arc from a point on the edge of the lower caudal lobe at the widest point of the t a i l , to the d o r s a l edge of the t a i l . In a d d i t i o n , preserved specimens i n the Scripps I n s t i t u -t i o n Museum C o l l e c t i o n , from I s l e Guadaloupe, Santa C a t a l i n a I s l a n d , and various points on the mainland, were compared f o r c o l o r p a t t e r n and gross morphological d i f f e r e n c e s . Measure-ments of some of these specimens were taken a l s o , but small d i f f e r e n c e s between shark specimens measured when f r e s h and those measured when preserved are not to be r e l i e d upon, because of dimensional changes i n the c a r t i l a g i n o u s skeleton caused by f o r m a l i n and a l c o h o l p r e s e r v a t i o n (pers. comm., S. Sprin g e r ) . The v e r t e b r a l counts given i n appendix 2 were obtained from whole-body X-ray p l a t e s which I made of preserved specimens at the Scripps Museum. Caudal vertebrae are ex-cluded from these counts; they vary g r e a t l y (pers. comm., S. Springer) and are i n any case d i f f i c u l t to count accurat-e l y , toward the t a i l t i p . A p i n was i n s e r t e d i n t o the s p i n a l column through the center of the curve at the r i s e of the t a i l , - 8 -and the vertebrae counted between i t and the chondrocranium. Because of v a r i a b i l i t y i n the i n s e r t i o n of t h i s p i n , I would estimate an e r r o r i n these counts of - 1. RESULTS 1. D e s c r i p t i v e Anatomy of the Female Reproductive System. a. Ovary, Ova, and P e r i t o n e a l C i l i a t i o n Functioning i n Ovum Transport. In many elasmobranchs, only one ovary develops as such and becomes f u n c t i o n a l (Daniel, 1934, G h i e f f i , 1962). A f t e r o v u l a t i o n , the la r g e ova are transported i n the coelom by c i l i a r y a c t i o n . Metten (1939) has described t h i s process i n great d e t a i l , as i t occurs i n another s c y l i o r h i n i d , S c y l i o r h i n u e  canicuius ( = S c y l l i o r h i n u s caniculumj. He found that almost a l l the surfaces i n the coelom - p e r i t o n e a l w a l l , mesentaries, and organ surfaces - between the ovary and the ostium are evenly c i l i a . t e d . In C.ventriosum , only one ovary i s f u n c t i o n a l . I t i s attached to the coelom w a l l by a mesovarium i n the usual manner. In a la r g e female, i t has a volume of 600-700 cc. A d e t a i l e d survey of ovarian development through the year ws.s not done, but a l l mature females dis s e c t e d were found to have ova of a l l s i z e s . This i s consistent with the year-round production of eggs, which w i l l be discussed la. t e r . C_. ventriosum i s l i k e 2>. canicuius i n that n e a r l y a l l surfaces i n the coelom are c i l i a t e d , but d i f f e r s i n the pat-t e r n of c i l i a t i o n . The c i l i a occur i n d i s c r e t e patches, ra t h e r than being d i s t r i b u t e d evenly. b. Ostium and Oviducts. The o v i d u c a l o s t i a of elasmobranchs are l o c a t e d at the a n t e r i o r end of the coelom, and are supported by or incorpor-ated i n t o the f a l c i f o r m ligament. They may be separate (Hobson, 1930), or combined, with a s i n g l e common opening. Metten (1939) ha.s described t h i s l a t t e r c o n d i t i o n as i t occurs i n £>. cani cuius. In t h i s species, the s i n g l e opening l i e s between the two f i m b r i a l septa of the f a l c i f o r m ligament. These septa are asymmetrical. The opening of the r i g h t o v i -duct forms the a c t u a l funnel which receives ova from the coelom, while the l e f t oviduct opens i n t o the w a l l of the r i g h t , j u s t i n s i d e the ostium. Both oviducts are f u n c t i o n a l i n almost a l l elasmo-branchs (Daniel, 193if) . From t h e i r opening(s), they curve l a t e r a l l y and caudally along the sides of the coelom to the cloaca, i n t o which they empty. A s h e l l ( o v i d u c a l , n i d i m e n t a l , nidamentary, of other authors) gland forms a part of each oviduct, and i s l o c a t e d a n t e r i o r to the middle of the oviduct. I t i s i n t h i s . g l a n d that the ovum receives i t s coatings of albumen and s h e l l m a t e r i a l . This process i s the subject of - 10 -a l a t e r s e c t i o n of t h i s t h e s i s . That p o r t i o n of the oviduct a n t e r i o r to the s h e l l gland i s described as c r a n i a l , and the p o s t e r i o r p o r t i o n as caudal. In C. ventriosum, I found the s t r u c t u r e of the f a l c i -form ligament and s i n g l e ostium to be quite d i f f e r e n t from that described by Metten f o r £5. c a n i c u l u s . The ostium l i e s between two septa of the f a l c i f o r m ligament, as i n S. c a n i c u l u s . but there the s i m i l a r i t y ends; there i s no asymmetry. The f i m b r i a l septa are equal i n s i z e and i n t h e i r l a t e r a l d i s -placement from the body midl i n e . The s i n g l e ostium, of a s i z e to j u s t admit a s i n g l e ovum when stretched, opens i n t o a s l i g h t l y l a r g e r sac. Prom t h i s sac, two openings of equal s i z e are symmetrically l o c a t e d on e i t h e r s i d e , and lead to the r i g h t and l e f t oviducts. This e n t i r e s t r u c t u r e , and the c r a n i a l oviducts, are t h i n , membranous, and c i l i a t e d on t h e i r inner surfaces. L i t t l e i f any smooth muscle can be seen i n the h i s t o l o g i c a l s e c t i o n s . The caudal oviducts are quite d i f f e r e n t i n s t r u c t u r e , though only s l i g h t l y greater i n diameter (about 1.5 cm.) when empty. Instead of t h i n - w a l l e d tubes, down which the contents are moved by c i l i a r y a c t i o n , the caudal oviducts are t h i c k - w a l l e d and muscular. The i n t e r i o r w a l l s are h i g h l y convoluted, and are l i n e d with a smooth, u n c i l i a t e d , columnar epithelium. The w a l l i s composed of an inner, annu-l a r l a y e r of smooth muscle, and an outer, l o n g i t u d i n a l l a y e r - 1 1 -of smooth muscle. Both l a y e r s contain and are separated by f i b r o u s connective t i s s u e . D i s s e c t i o n s of females with eggs i n the caudal oviducts showed that the w a l l s were t i g h t l y stretched around the egg-cases. This, the i n t e s t i n e - l i k e s t r u c t u r e , and the absence of c i l i a , leave l i t t l e doubt that the transport of completed eggs down the caudal oviducts to the cloaca i s accomplished by p e r i s t a l t i c c o n t r a c t i o n s , c. C i r c u l a t o r y S.vstan Daniel (l9j54) » i n h i s d e f i n i t i v e work on elasmobranch anatomy, describes the a r t e r i a l system supplying the oviducts and s h e l l glands of S c y l i o r h i n u s (= Scyllium) and other sharks, but makes no mention of "che ve s s e l s d r a i n i n g these organs. Nor have I found more than passing reference to t h i s venous system by any of the authors who have i n v e s t i g a t e d the reproduct-ive anatomy of sharks, who are c i t e d l a t e r i n t h i s work. For example; "In preparing an ov i d u c a l gland f o r s e c t i o n i n g pur-poses, the c i l i a t e d p e r i t o n e a l epithelium on the outside r e a d i l y detatches i t s e l f , and i t does not f i g u r e i n the accounts of any of the authors mentioned". So wrote Metten (±939). I found a s i m i l a r " c i l i a t e d p e r i t o n e a l epithelium" i n C. ventriosum; i t i s part of a l a r g e blood sinus surrounding the oviduct and s h e l l gland. Blood i s supplied to these organs v i a segmental a r t e r i e s a r i s i n g from the d o r s a l a o r t a , as described by Da n i e l . I t drains to a tubular sinus which encloses the e n t i r e oviduct - 12 -( i n c l u d i n g the s h e l l gland), and i s l o o s e l y attached to i t by t h i n trabeculae. This sinus i s enlarged i n the area of the s h e l l gland, and extends m e d i a l l y , where i t empties i n t o the p o s t c a r d i n a l v e i n , v i a many anastomoses. The r i g h t and l e f t p o s t c a r d i n a l s are confluent i n t h i s area, so the oviduct sinuses of both sides and the p o s t c a r d i n a l s form what i s , i n e f f e c t , one l a r g e blood sinus. In an egg-producing female, this sinus complex and the enclosed organs are engorged with blood; as much as 100 cc. Since only some 400 cc. can be drained from a h e a v i l y heparinized shark of near maximum* s i z e , i t i s ap-parent that t h i s l a r g e sinus complex contains a high propor-t i o n of the t o t a l blood volume i n an egg-producing female. d. S h e l l G-land Structure. Secretions, and Sperm Storage The s h e l l gland s t r u c t u r e of S. caniculus and C h i l o -s c v l l i u m griseum have been described, r e s p e c t i v e l y , by Metten (1939), and N a l i n i (1940), both of whom have reviewed the p e r t -inent previous work i n d e t a i l . Both of these authors described four separate secretory p o r t i o n s of the gland. In a n t e r i o r -p o s t e r i o r order, these are: albumen, a n t e r i o r mucus, k e r a t i n , and p o s t e r i o r mucus. Threadgold (l957) h i s t o c h e m i c a l l y demonstrated f i v e separate secretory zones i n the s h e l l gland of S.caniculus i n a d d i t i o n to the p o s t e r i o r mucus zone, with which he d i d not d e a l . Hiz zone A corresponds to what i s known as the albumen s e c r e t i n g p o r t i o n . However, the "albumen" i s non-protein; Please i n s e r t the f o l l o w i n g paragraph at the a s t e r i s k on p. 13. Metten (1939) was the f i r s t to l o c a t e . t h e sperm storage s i t e i n the k e r a t i n s e c r e t o r y tubules of the s h e l l gland. He p u b l i s h e d photomicrographs showing bundles of tubules' i n the t u b u l e s . He found no sperm i n e i t h e r the albumen s e c r e t o r y por-t i o n of the gland ( l o c a t e d a n t e r i o r to the s h e l l s e c r e t o r y por-t i o n ) , or i n the c r a n i a l o v i d u c t . I m a l a t e r paper (Metten, 1 944), he showed that some sperm are a l s o found embedded i n the w a l l s of the caudal o v i d u c t . - 13 -Threadgold suggested that i t i s probably a mucopolysaccharide. Collenot (1966) confirmed t h i s . Threadgold*s zone B equals the area described e a r l i e r as the a n t e r i o r mucus tubules, and a l s o secretes a carbohydrate. Zones C-E are d i f f e r e n t areas of the k e r a t i n or s h e l l s e c r e t i n g p o r t i o n . As t h i s study i s not concerned with the chemistry but with the mechanics of egg-case formation, I w i l l continue to use the term albumen, with the understanding that i t s use i s r e s t r i c t e d to the t r a d i t i o n a l "egg-white" sense. In a d d i t i o n , I w i l l consider the s h e l l s e c r e t i n g p o r t i o n as a homogeneous f u n c t i o n a l u n i t . Clark (1922) suggested the occurrence of sperm storage i n elasmobranchs. He described s e v e r a l instances of rays l a y i n g numerous f e r t i l e eggs a f t e r s e v e r a l weeks of i s o l a t i o n i n aquaria. Libby (1959) described one instance of an i s o l a t -ed ray which l a i d i n f e r t i l e eggs u n t i l a male was introduced i n t o the aquarium f o r a short period, and then removed. The female then l a i d two f e r t i l e eggs about every four days f o r nearly nine months, with no fux-ther matings. Clark placed the s i t e o f sperm storage " i n the upper reaches of the oviduct". N a l i n i (1940), upon reading Metten's e a r l i e r paper, r e -examined her m a t e r i a l from C. griseum. and found what might have been bundles of sperm i n the s h e l l tubules, but reserved judgement. Prasad (1945) described sperm i n the s h e l l secretory - 1 4 -tubules of a spe cimen of G-alQocerdo c u v i e r i (— G. t i g r i n u s ) , a l i v e - b e a r i n g shark. I t had ova i n both the c r a n i a l oviducts and the u t e r i . I found the s h e l l gland s t r u c t u r e of C. ventriosum to conform c l o s e l y to the d e s c r i p t i o n s given by Metten and by N a l i n i , c i t e d above. The f o l l o w i n g d e s c r i p t i o n may thus be taken as t y p i c a l of a number"of oviparous sharks, as w e l l as s p e c i f i c to the s w e l l shark. Figure 1 (a & b) shows diagramatic s a g g i t a l (with r e s -pect to the gland) and cross sections of the s h e l l gland, with the plane of each s e c t i o n i n d i c a t e d on the other. Notice that there are two separate secretory masses, which form the two faces of the lumen. The s h e l l gland i s oriented i n the animal so that these two masses l i e d o r s a l and v e n t r a l to the lumen. Three of the four secretory areas are e a s i l y d i f f e r e n t -i a t e d i n gross d i s s e c t i o n s ; the albumen, k e r a t i n , and p o s t e r i o r mucus (see f i g . 1 ) . Notice that, though the area of k e r a t i n s e c r e t i o n i n t o the lumen of the gland i s but a small p o r t i o n of the lumen's area, the k e r a t i n secretory tubules themselves form the major p o r t i o n of the mass of the gland. The proximal ends of these k e r a t i n tubules empty i n t o the lumen i n rows, between successive rows of deeply-folded lamellae, which l i e i n a plane normal to the l o n g i t u d i n a l a x i s of the gland. This may be seen i n f i g u r e 1c , a diagramatic d o r s a l view of the v e n t r a l secretory mass, which forms the v e n t r a l w a l l of the lumen. - 1 5 -Figure 1. Diagramatic s e c t i o n drawings of a s h e l l gland. A. S a g g i t a l . B. Cross. C. F r o n t a l . Dashed l i n e s a-a, b-b, c-c; planes of sections A,B, and C. a l ; albumen s e c r e t i n g areas. l a ; lamellae of the k e r a t i n s e c r e t i n g areas. k; k e r a t i n s e c r e t i n g tubules. mu; mucus se c r e t i n g areas. l . g . ; grooves at the edge of the s h e l l gland lumen (the lumen i s shown i n f i n e l i n e s i n s e c t i o n A.). - 16 -The s h e l l gland of oviparous elasmobranchs coats the ovum su c c e s s i v e l y with albumen, a keratinous capsule, and f i n a l l y , a mucus l a y e r which f a c i l i t a t e s the egg's passage down the caudal oviduct. There i s good evidence, i n the s w e l l shark and at l e a s t two other species, that the s h e l l gland also serves as a s i t e of sperm storage. Figure 2 i s a s l i g h t l y oblique s e c t i o n of a s h e l l gland secretory tubule. Sperm (arrow) may be seen i n the lumen of the tubule. Figure 3 i s a p o r t i o n of the area where the kera-t i n tubules empty between the lamellae i n t o the s h e l l gland. The sperm are i n d i c a t e d hy the arrow . The sperm of elasmobranchs c h a r a c t e r i s t i c a l l y have s p i r a l heads (Metten, 1939, M e l l i n g e r , 1965). Metten was able to detect the s p i r a l of the heads only i n l i v e m a t e r i a l , but the sections f i g u r e d here, from a d i f f e r e n t species and stained d i f f e r e n t l y , c l e a r l y show the s p i r a l at 325 X m a g n i f i c a t i o n under the microscope. Metten found that sperm were more numerous i n those po r t i o n s of the tubules proximal to the s h e l l gland lumen; I found the same. The sections f i g u r e d here came from a shark which had complete, f e r t i l e eggs i n the caudal oviducts. 2. Egg-case Structure Before considering the remaining s e c t i o n s , we must develop a c l e a r p i c t u r e of the s t r u c t u r a l d e t a i l s of the egg-case. - 1 7 -Figure 2. Oblique s e c t i o n of a k e r a t i n secretory tubule. Sperm are i n d i c a t e d by the arrow. M a g n i f i c a t i o n , about 2000X. -18-Figure 3. Section at base of lamellae of k e r a t i n secretory area of a s h e l l gland. Sperm (arrow) shown between two lam-e l l a e . M a g n i f i c a t i o n , about 2000X. - 19 -Edwards ( 1 9 2 0 ) , Daniel (1934 and e a r l i e r e d i t i o n s ) , and Cox ( 1 9 6 3 ) have a l l f i g u r e d s i n g l e egg-cases of Cenhalosc.yllium  ventriosum (= _C. u t e r ; = Catulus u t e r ) . Edwards gave the dimensions of her s i n g l e specimen as 116 by 4 9 mm. Cox gave the range of lengths as 90 to 125 mm., and the widths as 28 to 55 mm., but included no sample data. Appendix 3 contains the measurements of some of the eggs l a i d by sharks from two d i f f e r e n t l o c a t i o n s i n two d i f f e r e n t years. The c o n f i g u r a t i o n of the eggs i s such that l e n g t h measurements cannot be taken with any consistent accuracy. However, the widths and weights can be reproduced a c c u r a t e l y . Figures 4-7 show various egg-cases; each w i l l be used to i l l u s t r a t e s p e c i f i c p o i n t s . The upper ends of the eggs f i g u r e d are p o s t e r i o r i n the oviduct; the lower ends are a n t e r i o r . These designations wi 11 be retai n e d i n subsequent d i s c u s s i o n . The egg-cases vary considerably i h c o n f i g u r a t i o n and c o l o r , as w e l l as s i z e . The c i r c l e enclosed by the horns at the post-e r i o r end i s u s u a l l y s l i g h t l y l e e s than a cm. ( f i g . 5 )» but can vary from completely closed ( f i g . A), to nearly 2 cm. The shape of the a n t e r i o r end v a r i e s from a deeply lunate curve to an almost s t r a i g h t edge between the horne. The s i z e and sharpness of the l a t e r a l bulges j u s t p o s t e r i o r to the a n t e r i o r end v a r i e s , a l s o . I could detect no apparent p a t t e r n i n these v a r i a t i o n s . -20-Figure 4. Swell shark egg-case, showing t e n d r i l s . The arrows i n d i c a t e the area where the i n c i s i o n was made on another egg-case f o r the i n s e r t i o n of a newly-hatched shark, to simulate hatching. - 2 1 -Figure 5. A t y p i c a l p a i r of egg-cases. Both, show a b^nd of s h e l l m a t e r i a l of a d i f f e r e n t shade across t h e i r width. - 2 2 -Figure 6. A t y p i c a l quartet of egg-cases. -23-Figure 7. Egg-case containing an embryo. The arrows i n d i c a t e the p o s i t i o n s of the four r e s p i r a t o r y s l i t s . -24-Figure 8. Diagramatic sections of egg-cases. A. L o n g i t u d i n a l . B. Cross. The dashed l i n e s a-a and b-b i n d i c a t e the planes of sections A and B. The dotted l i n e i n d i c a t e s the approximate plane of the a n t e r i o r end of the egg-case (removed from s e c t i o n B), when viewed from the a n t e r i o r end. - 25 -Notice that the eggs i n f i g u r e s 4 and 7 have long, c o i l e d t e n d r i l s at the four corners of the cases, while those i n f i g u r e s 5 and 6 do not. The t e n d r i l s of these l a t t e r eggs have n e i t h e r been d e l i b e r a t e l y or a c c i d e n t a l l y removed, nor are the eggs malformed. This i s a consistent population d i f -ference, and w i l l be expanded upon i n s e c t i o n 7. The c o l o r and opacity of the egg-cases .vary both during the course of aging of the eggs, and from one egg to another. S h e l l m a t e r i a l which has j u s t been secreted i s a milky white, becoming yellow and t r a n s l u c e n t i n the p o s t e r i o r p o r t i o n of the s h e l l gland. Eggs i n the caudal oviduct are s l i g h t l y darker i n c o l o r , and more transparent. Newly l a i d eggs are a l i g h t olive-brown and u s u a l l y quite transparent. As eggs age, they darken and become l e s s transparent. However, i n d i v i d u a l v a r i a t i o n i s such that some eggs are as transparent when se v e r a l months o l d as others are when newly l a i d . A v a r i a b l e s t r e a k i n g of opaque yellow i s seen on some eggs. The darken-i n g of the s h e l l i s accompanied by a change i n consistency; i t becomes tougher and more r e s i l i e n t . E a r l i e r w r i t e r s sug-gested or assumed that t h i s was the r e s u l t of the egg-case ex-posure to sea water. This may w e l l be so, but Threadgold (1957) has presented histochemical evidence which suggests that some type of quinone tanning i s the operative process, at l e a s t i n the s h e l l gland i t s e l f . Figure 8 shows l o n g i t u d i n a l and cross sections of the egg-case. Kotice the thickened p o r t i o n s at e i t h e r edge of - 26 -the case i n the cross s e c t i o n . These are continuous w i t h the filaments extending from the corners of the case. These t h i c k -ened edges are di s p l a c e d toward opposite sides of the egg-case at both ends of the egg-case (see next paragraph, f i g u r e 7 ) . The egg-cases a l s o show a s l i g h t t o r s i o n at t h e i r a n t e r i o r ends. I f the cross s e c t i o n i s taken as being viewed from the a n t e r i o r end, the dotted l i n e i n d i c a t e s the approximate plane of the a n t e r i o r end. Close examination of the a n t e r i o r ends of the egg-cases i n f i g u r e 6 w i l l show the same t h i n g ; the l e f t corner of each was s l i g h t l y c l o s e r to the camera. The arrows i n f i g u r e 7 i n d i c a t e the p o s i t i o n of four openings which are formed i n t o the egg-case, known as r e s i j i r -atory s l i t s . The p o s i t i o n s of these s l i t s conform to the d i s -placement of the edges of the case, which was mentioned above. Only the two on the r i g h t are v i s i b l e because of t h i s ; those on the l e f t are on the other side of the case. This d i s p l a c e -ment i s i n the same d i r e c t i o n i n a l l eggs, whether they come from the r i g h t or l e f t oviduct. These s l i t s are plugged with a dense albumen when the egg i s l a i d . Their opening,and f u n c t i o n i s discussed i n s e c t i o n 4 . 3. Mechanics and Sequence of Egg-case Formation. The process and timing of egg-case formation i n elasmo-branchs have been subjects of s p e c u l a t i o n f o r numerous authors - 27 -f o r about the l a s t hundred years. Hobson (1930), Metten (1939), N a l i n i (194C-), Setna and Sarangadhar (1948) , and Prasad ( l 9 5 l ) have reviewed t h i s e a r l i e r l i t e r a t u r e , and a l l but the l a s t author c i t e d have added the r e s u l t s of d i r e c t observations. I t was v a r i o u s l y held by e a r l i e r authors t h a t : 1 . The egg-case was formed i n the caudal oviduct from :the secretions of the s h e l l gland. 2. The albumen and s h e l l were simultaneously l a i d down around the ovum i n the s h e l l gland as the ovum passed through. 3. Secretion s t a r t e d i n the s h e l l gland before the ovum reached i t , but the whole of the egg-case i s formed around the ovum i n the s h e l l gland. 4. The caudal p o r t i o n of the egg-case i s formed before the ovum reaches the gland, and the a n t e r i o r end of the case i s closed a f t e r the ovum has entered the case. Hobson supported t h i s l a s t view. A f t e r examining some 150 egg-carrying females of the ray, Raja r a d i a t a . he found one i n which the s h e l l glands contained p a r t i a l l y formed egg-cases. I quote h i s d e s c r i p t i o n : "The half-formed egg case i s q u ite empty [ ^ i t a l i c s mine] . I t s d o r s a l end v e n t r a l w a l l s are w e l l separated from one-another so that at the a n t e r i o r end there i s an opening which w i l l admit the egg [ i t a l i c s mine] when i t i s ready to pass i n t o the case ... At l e a s t h a l f , and p o s s i b l y considerably more, of the egg case i s already formed before the egg comes i n contact with the nidamental organ at - 28 -a l l . " R e f e r r i n g to Hobson's work, Metten d e s c r i b e d a number of incomplete egg-cases i n the s h e l l glands of £>. c a n i c u l u s . He found that none which were l e s s than t h r e e - f o u r t h s completed contained ova, but gave no f u r t h e r d e s c r i p t i o n of t h e i r con-d i t i o n . N a l i n i discounted Hobson's hypothesis that p a r t of the egg—case i s formed f i r s t , then r e c e i v e s the egg i n t o i t . To her, t h i s i m p l i e d a discontinuous process which might be ex-pected to r e s u l t i n a suture i n the egg-case, which i s not seen. Prom what she d e s c r i b e d as "... the egg case i n f u l l y formed c o n d i t i o n i n s i d e the nidamental organ of ' [jthe sharlTj C h i l o s -c y l l i u m griseum.", she adhered to the premise that "... the s e c r e t i o n s are poured over the egg a f t e r i t reaches the nidament-a l . " But, Setna and Sarangadhar found egg-cases about two-t h i r d s complete i n C. griseum, and d e s c r i b e d them thus: "The f e r t i l i z e d eggs, surrounded by dense masses of albumen, had alr e a d y entered [ i t a l i c s mine] the egg-cases, and more albumen was seen to be s t i l l e n t e r i n g through the open ends." Prasad suggested that "... when the egg reaches the n i d a -mental gland there w i l l be a p a r t l y formed egg-case to r e c e i v e Q l t a l i c s mine] the egg.", but that subsequent s e c r e t i o n s are continuous with those which have formed the f i r s t p o r t i o n , thus e x p l a i n i n g the l a c k of a suture. - 29 -Despite the apparent c o n f l i c t between the accounts quoted and described above, I b e l i e v e that they are a l l p a r t i a l l y cor-r e c t . F i r s t , consider those portions of the quotations which I have i t a l i c i z e d . Hobson described h i s skate egg-cases as "quite empty", yet the w a l l s were separated. I can but assume that he meant only that the ovum was not present, f o r i f the open egg-case end contained no albumen, i t would not only be contrary to the other author's and my own f i n d i n g s , but would mean that the case, to be open, must contain some gas which would have to be d i s p l a c e d by subsequent albumen s e c r e t i o n s ; t h i s seems to me to be a s t r u c t u r a l i m p o s s i b i l i t y . The other i t a l i c i z e d p ortions point out that the various authors s t a t e or imply that the ovum and/or albumen move i n t o the p r e v i o u s l y formed p o s t e r i o r p o r t i o n of the egg-case. In contrast, remember that N a l i n i held that the s e c r e t i o n s took place as the ovum passed through the gland. On three occasions I examined p a r t i a l l y formed egg-cases of C_. ventriosum. In the f i r s t instance, d i s s e c t i o n of a shark revealed p a r t i a l l y formed t e n d r i l s extending p o s t e r i o r l y from the s h e l l gland i n t o the caudal oviducts. The p o s t e r i o r end of the egg cases had not yet formed, so that the two t e n d r i l s i n each oviduct were not connected to one another. The second instance was the l a y i n g of two incomplete eggs. These are shown'. i n f i g u r e 9 with a normal egg f o r - 30 -comparison. The eggs are s l i g h t l y more than h a l f completed. They both contained albumen, which a l s o protruded from the i n -complete ends. Both contained fragments of broken ova. Notice the t h i n edges of the incomplete ends. The t h i r d involved the d i s s e c t i o n of a female k i l l e d while i n the process of forming eggs. Figure 10 shows one of the distended s h e l l glands containing a p a r t i a l l y formed egg, the incomplete egg from the other s i d e , and an i n a c t i v e s h e l l gland from another shark f o r comparison. Both of these eggs contained complete ova, with albumen both p o s t e r i ^ a n d a n t e r i o r to the ova. From the d e s c r i p t i o n s of the authors quoted, examination of a v a r i e t y of other elasmobranch eggs, and my own observa-t i o n s j u s t described, I have deduced a somewhat d i f f e r e n t sequence of egg-case formation. I w i l l describe i t here f o r C. ventriosum. but I suspect i t t o be g e n e r a l l y v a l i d f o r a wide v a r i e t y of elasmobranchs. The i n i t i a l k e r a t i n s e c r e t i o n s move p o s t e r i o r l y i n the grooves at e i t h e r side of the lumen of the s h e l l gland, which form them i n t o the p o s t e r i o r egg-case t e n d r i l s . As these near completion, the albumen p o r t i o n of the gland begins s e c r e t i n g . As t h i s i n i t i a l albumen moves p o s t e r i o r l y , i t i s covered with successive l a y e r s of k e r a t i n produced from between the rows of lamellae of the k e r a t i n s e c r e t i n g area (see f i g . X). In the d i s s e c t i o n s mentioned e a r l i e r , of the s h e l l glands which -31-Figure 9. Two incomplete eggs l a i d by a s w e l l shark. The com-ple t e d egg i s included f o r comparison. -32-Pigure 1 0 . A c t i v e and i n a c t i v e s h e l l glands. The gland to the l e f t contains a p a r t i a l l y completed egg. The egg r e -moved from the opposite gland of the same shark i s at lower r i g h t . An i n a c t i v e gland from another shark i s at upper r i g h t . The a n t e r i o r ends of the glands and the p o s t e r i o r end of the egg are uppermost. - 33 -contained p a r t i a l l y formed eggs, I found that the f i r s t t h i n l a y e r of milky white s h e l l m a t e r i a l was i s s u i n g from between the f i r s t two lamellae. This i n i t i a l mass of keratin-covered albumen i s formed i n t o the p o s t e r i o r end of the s h e l l gland lumen, \i?hich functions as a female mold, e x a c t l y matching the shape of the f i n i s h e d egg, with i t s r e s p i r a t o r y s l i t s and t h e i r albumen plugs. As t h i s molding takes place, k e r a t i n and albumen continue to flow. The s h e l l gland extends l o n g i t u d i n -a l l y somewhat, a l l o w i n g the p o s t e r i o r p o r t i o n of the egg to " s e f ' i n the "mold", despite the continuing s e c r e t i o n of ma t e r i a l and i n c r e a s i n g egg s i z e . Thus, there would be no h a l -t i n g of the s e c r e t i o n s , and r e s u l t i n g suture i n the egg-case. The ovum a r r i v e s , i s coated with the continuing s e c r e t i o n s of albumen and k e r a t i n as i t moves along, and i s added onto -does not "enter"-the enlarging egg. Albumen s e c r e t i o n slows and ceases. The sheets of k e r a t i n come together as the l a s t of the albumen passes the lamellae. These k e r a t i n sheets s e a l together to form the a n t e r i o r end of the egg-case, and the formation of the sheets ceases. The k e r a t i n which forms the a n t e r i o r t e n d r i l s continues to flow i n t o the l a t e r a l grooves of the lumen, then ceases as the egg continues down the oviduct, and the t e n d r i l s are f i n i s h e d . The egg i s complete. - 34 -I see the s h e l l gland as f u n c t i o n i n g both as a mold and as an ex t e n s i b l e e x t r u s i o n d i e f o r i t s own s e c r e t i o n s . The p o s t e r i o r end f i r s t f unctions as a mold, shaping t h e / f i r s t s e c r e t i o n s reaching i t i n t o the c h a r a c t e r i s t i c shape of the p o s t e r i o r end of the egg. This portion:does not move i n the gland u n t i l the shape i s "se t " . The cross s e c t i o n a l shape of the lumen, with i t s l a t e r a l grooves, acts as e x t r u s i o n d i e , forming the continuing s e c r e t i o n s i n t o the c h a r a c t e r i s t i c cross s e c t i o n of the egg. The c h a r a c t e r i s t i c l o n g i t u d i n a l shape of the egg, tapering from the ends to a maximum t h i c k -ness i n the middle, may w e l l be c o n t r o l l e d simply by the amount of albumen and ovum a r r i v i n g at the s h e l l s e c r e t i n g lamellae to be coated. This i s suggested by the f a c t that "wind eggs" - eggs normal i n shape, but containing only albumen and no ova - are smaller than normal eggs. These have been described f o r other species by s e v e r a l of the authors c i t e d , and are al s o formed by the s w e l l shark. Another phenomenon described by those authors mentioned who have studied egg-case formation i s the synchrony of devel-opment of the eggs i n both oviducts. I observed the same t h i n g . In the three instances described e a r l i e r , i n which I examined p a r t i a l l y completed egg-' cases, both sides of the system were i n the same stage of devel-opment. The same t h i n g i s seen i n that they are u s u a l l y l a i d i n pairs, or quartets. Figure 6 shows a t y p i c a l quartet - 35 -of eggs. The two eggs at the top form a p a i r , those at the bottom another. Notice that the members of a p a i r are nearly-i d e n t i c a l i n s i z e and c o n f i g u r a t i o n , but d i f f e r n o t i c e a b l y from the other p a i r . Notice a l s o that the p a t t e r n of l o n g i t u d i n a l c o l o r s t r i a t i o n s i s from the top to the bottom eggs on'each side of the f i g u r e , showing that the eggs on the l e f t came from, one "extrusion d i e " - s h e l l gland - and those on the r i g h t from the other. Figure 5 shows another p a i r of eggs. The transverse, l i g h t - c o l o r e d l i n e i s i n the same place on both eggs, i n d i c a t -i n g that some p h y s i o l o g i c a l event, changing the character of the k e r a t i n s e c r e t i o n s momentarily, afi"ected both eggs at the same place. 4. Development of the Embryo and Egg-case Changes. The embryology of s e v e r a l elasmobranchs has been described i n great d e t a i l , as i n B a l f o u r (1878) and Smith (1940, 1942). H a r r i s (1952), d e s c r i b i n g the development of another s c y l i o -r h i n i d , has stated that i t s development to the g i l l f i l a m ent stage i s i d e n t i c a l to that of Squalus acanthias. a l i v e - b e a r i n g shark of a d i f f e r e n t taxonomic order. From these published accounts i t appears that the course of development of a wide v a r i e t y of selachians i s much the same, p a r t i c u l a r l y i n the e a r l y stages. C_. ventriosum seems to f i t t h i s p i c t u r e . I t s embryology 36 -i s not the subject of t h i s t h e s i s , and only a b r i e f sketch w i l l be given. While the development of the embryo i t s e l f seems to correspond to the p a t t e r n seen i n other sharks, there are other s t r u c t u r e s present to which I have been able to f i n d no reference i n the l i t e r a t u r e . I didn't r e a l i z e t h e i r pos-s i b l e s i g n i f i c a n c e at the time the work was being c a r r i e d on, and paid them no s p e c i a l a t t e n t i o n . Nelsen (1953, P. 165), drawing from the work of Bal f o u r , describes the egg membranes of S c y l i o r h i n u s caniculus (= S c y l l i u m c a n i c u l a ) . He s t a t e s that an outer "homogenous v i t e l l i n e membrane", and an inner zona r a d i a t a , combine i n the mature egg to form a t h i n , composite v i t e l l i n e membrane. He state s t h a t , at about the time of f e r t i l i z a t i o n , t h i s membrane separates from the egg's surface, enclosing the p e r i v i t e l l i n e space thus formed. However, Ba l f o u r (1881, p. 35)» s t a t e s that the elasmo-branch ovum i s without a v i t e l l i n e membrane at the time of im-pregnation. I t has, by h i s account, disappeared by the time the egg enters the oviduct ( B a l f o u r , 1880, p.50). Smith (1957) st a t e s that during the e a r l y cleavages, when the embryo i s a r e l a t i v e l y s m a ll mass of d i v i d i n g c e l l s , the ovum i s covered by a t h i n , n o n - c e l l u l a r membrane, which i s replaced by organized embryonic t i s s u e a f t e r g a s t r u l a t i o n . - 37 -Read (1968) i n h i e study o f osmoregulation i n Ra.ia  h i & o c u l a t a . mentions an "extremely d e l i c a t e membrane" func-t i o n i n g i n urea r e t e n t i o n i n undeveloped eggs. F i g u r e 11 i s a b a c k - l i t photograph of an embryo i n the case. The embryo i s dead, and not t y p i c a l i n form. But the membrane extending up from the y o l k and surrounding the embryo i s t y p i c a l of embryos o f t h i s age, with the exce p t i o n of the d i s t o r t i o n o f the embryo's t a i l touching i t . I saw t h i s membrane on numerous oc c a s i o n s . I t was read-i l y v i s i b l e when the more transparent egg-cases of younger embryos were "candled". I t i n c r e a s e d i n s i z e as the embryos grew. I d i d not n o t i c e at what stage i t disappeared, but i t was c e r t a i n l y gone by the time the r e s p i r a t o r y s l i t s i n the egg-case opened. The other u n d i s c r i b e d s t r u c t u r e cannot be seen d i r -e c t l y , but can only be i n f e r r e d from i t s e f f e c t on the mem-brane j u s t d e s c r i b e d . I f an egg i s viewed as i n f i g u r e 1 1 , and t i l t e d back and f o r t h , the embryo and y o l k r o t a t e s l i g h t l y , as i f the embryo were more buoyant than the y o l k mass. But, the movement i s l i m i t e d . T h i s might be a t t r i b u t -ed s o l e l y to the confined space, were i t not f o r a d i s t o r t i o n which appears i n the apex of the membrane over the embryo. Imagine an i n v i s i b l y t h i n thread attached to the sur-face of a p a r t i a l l y i n f l a t e d b a l l o o n , and p u l l e d j u s t t a u t . I f the b a l l o o n i s then r o t a t e d s l i g h t l y , the d i s t o r t i o n of i t s surface by the p u l l of the thread can be seen, even though the -38-Figure 11. B a c k l i t photograph of an embryo i n i t s case, showing the membrane enclosing i t and the yolk sac. - 39 -thread cannot. The d i s t o r t i o n of the membrane i n the egg f o l -lows t h i s analogy, and changes i t s o r i e n t a t i o n a p p r o p r i a t e l y as the egg i s t i l t e d from one side to the other. From t h i s , I deduce the presence of a s t r u c t u r e i n the albumen of the eggs of t h i s shark which i s analogous to the chalaza of a hen' egg, and which i s l i k e l y homologous with i t . Clark (1922) noticed that the embryos of rays i n newly-l a i d eggs were i n d i f f e r e n t stages of development. The same th i n g occurs i n the s w e l l shark; the embryos may be i n any stage from b l a s t o d i s c to an embryo up to 4mm., on a y o l k s t a l k and showing muscular c o n t r a c t i o n s . These e a r l y c ontractions are myogenic (Harris,1962). Development of the shark i n the aquarium to hatching takes 7T-10 months; I assume that the ra t e of development i s , as has been found i n other sharks ( H a r r i s , 1962), temperature-dependant. The egg-case i s closed f o r only about a t h i r d of t h i s time, u n t i l the r e s p i r a t o r y s l i t s begin to open. I t may take as long as a month f o r the albumen plugs to disappear from a l l four s l i t s . The dense albumen forming the plugs i s apparently metabolized by the shark; l i t t l e i f any erosi o n of the surfaces exposed to the surrounding water occurs. The time of disappearance of the e x t e r n a l g i l l f i l a ments roughly corresponds to the complete opening of the s l i t s . At t h i s p o i n t , the embryos can be removed from the egg-case and - 40 -s u r v i v e , i f placed i n a smooth-walled container through which the aquarium water may c i r c u l a t e . At hatching, the sharks are about 15 cm. t o t a l length. The e x t e r n a l y o l k sac may have been completely absorbed, or there may remain a s t a l k of up to a cm. long, attached to a sac of 3 or 4 m m . diameter. In a d d i t i o n to an even covering of sma l l , pointed dent-i c l e s over the e n t i r e body, the young have two l o n g i t u d i n a l , d o r s o - l a t e r a l rows of l a r g e r d e n t i c l e s of d i f f e r e n t form. Ford ( l 9 2 l ) described these d e n t i c l e s as primary, and l i s t e d eight oviparous species of sharks - seven s c y l i o r h i n i d s and an or e c t o l o b i d - the young of which have such d e n t i c l e s . The young of some chimaeroids a l s o have two s i m i l a r rows of d e n t i c l e s , though the adult s have naked s k i n (Norman and Greenwood, 1963). A newly-hatched s w e l l shark, showing the primary d e n t i c l e s , i s shown i n f i g u r e 12. 5. The Emergence of the Shark from the Egg-case. The d e t a i l s of egg-case s t r u c t u r e have been described. Remember that the a n t e r i o r end of the case, through which the shark emerges, i s d i f f e r e n t i n s t r u c t u r e from the p o s t e r i o r end. Look at the l o n g i t u d i n a l s e c t i o n i n f i g u r e 8. Imagine the two sides of the case, where they j o i n at the a n t e r i o r end, - 4 1 -Figure 1 2 . A newly-hatched s w e l l shark, showing the l a r g e r primary d e n t i c l e s on i t s back. L i f e s i z e . - 42 -as two pages of a book which have been l i g h t l y glued together at t h e i r edges. A f i n g e r i n s e r t e d between these pages and moved outward w i l l separate them. The f i r s t step i n t h i s sequence i s the opening of the case by the shark. The shark's snout i s the " f i n g e r t i p " between the "pages". The shark's body i s longer than the i n t e r i o r of the egg-case, and the necessary force i s supplied by the bent t a i l t h r u s t i n g against the p o s t e r i o r end of the case. When t h i s f i r s t step i s completed, the head and g i l l r e gion of the shark - the widest p o r t i o n of i t s body - are protruding from the opened a n t e r i o r end of the egg-case, which i s j u s t l a r g e enough to allow passage. The t a i l i s now straightened out, and can no longer t h r u s t against the closed p o s t e r i o r end. In the second step, the shark completes i t s e x i t from the case by a s e r i e s of exaggerated l a t e r a l f l e x i o n s . R e c a l l the two d o r s o - l a t e r a l rows of primary d e n t i c l e s described e a r l i e r . I t appears that these l a r g e r d e n t i c l e s i n t e r a c t with the edge of the egg-case opening i n the manner of a r a t c h e t with a pawl, p r o v i d i n g a purchase which renders the l a t e r a l movements of the shark e f f e c t i v e i n moving i t out through the opening, a f t e r the t a i l pan no longer t h r u s t against the other end. Each successive l a t e r a l movement brings more p o s t e r i o r l y placed d e n t i c l e s i n contact with the edge of the opening, which i s close against the shark's body. This - 43 -"anchoring" allows the l a t e r a l movement of the forward p o r t i o n of the body to be t r a n s l a t e d i n t o forward t h r u s t against the edge of the opening, which moves the shark out through i t . The d i s t r i b u t i o n of these primary d e n t i c l e s on the shark's body i s optimum f o r t h i s f u n c t i o n . The rows are l a t e r a l to the m i d l i n e , e f f e c t i n g the maximum forward movement f o r a given l a t e r a l movement. They begin p o s t e r i o r to that p o r t i o n of the body which i s th r u s t through the opening by the i n i t i a l t h r u s t of the t a i l , and are continued p o s t e r i o r l y to the area where the body cross s e c t i o n i s s u f f i c i e n t l y smaller to allow easy passage of the r e s t of the body through the opening. The reduction i n comparative s i z e and disap-pearance of these d e n t i c l e s i n the ensuing months of growth suggests t h a t , whatever t h e i r f u n c t i o n , i t has been served. 6. Predation on Egg-cases. I have found no mention i n the l i t e r a t u r e of predation on elasmobranch eggs, l e t alone i n the manner to be described. In 1969, a "nesting area" of the s w e l l shark was d i s -covered at Ship Hock, which i s about a mile offshore from Santa C a t a l i n a I s l a n d . In the c r e v i c e s of the submarine t a l u s slopes at the base of t h i s rock, i n 25-35 m. depths, l i t e r a l l y hundreds of egg-cases are to be seen. This i s i n contrast to nearby B i r d Rock, where the sharks can a l s o be found, but 4 44 -where I have found only two eggs, despite having spent much more time d i v i n g i n the l a t t e r area. Forty-two eggs were c o l l e c t e d i n one dive at Ship Rock. Of these, only two contained embryos. Of the remainder, 29 had one or more holes i n them - 11 had one hole, 11 had two holes, 6 had 3 holes, and one had 5. The holes were c i r c u l a r , with an i r r e g u l a r l y serrated edge which tapered inward toward the center of the hole through the thickness of the egg-case. Most were 2-5 mm. across, but one was 15 nim. Several egg-cases showed p a r t i a l l y completed holes. The only candidate I consider l i k e l y to p e r f o r a t e the eggs i n t h i s manner would be a gastropod of the suborder Steno-glossa; "Marine s n a i l s with...radula narrow, o f t e n adapted f o r a-carnivorous d i e t . " ( L i g h t , et a l . , 1957)• I e l i m i n a t -ed Octopus bimaculatus. a common carnivore i n the area, a f t e r comparison of i t s beak shape with the holes i n the egg cases, and t h e i r p o s i t i o n s . While the octopus a l s o posesses a radula, i t seems l i k e l y that the egg-cases would show some beak, marks, at l e a s t along the edges, i f the octopus were the predator. I have seen one other type of p r e d a t i o n upon shark eggs. In the 2,000,000 l i t e r marine community tank at Marineland of the P a c i f i c , the l a r g e l a b r i d t e l e o s t , Pimelometopon pulerum, w i l l , b i t e and puncture the eggs of C.ventriosum and Hetero-dontus f r a n c i s c i which are l a i d i n the tank. This has not - 45 -been reported from nature, but would be a p o s s i b i l i t y , consider-ing the o p p o r t u n i s t i c feeding h a b i t s of t h i s f i s h , which i s sympatric with the sharks mentioned. 7. Population D i f f e r e n c e s . As mentioned e a r l i e r , s w e l l sharks from some l o c a l i t i e s produce eggs with long t e n d r i l s at the four corners; eggs from other places have short t e n d r i l s . A i y a r and N a l i n i (1938) have described a s i m i l a r d i f f e r e n c e i n t e n d r i l s on the eggs of G h i l o s c y l l i u m griseum at Madras, I n d i a , and those of Malabar. Figure 13 shows sample source areas, s i z e s of egg samples, and the known d i s t r i b u t i o n of the presence or absence of t e n d r i l s . My f i r s t samples came from mainland sharks, and had t e n d r i l s from 80-200 cm. long. The next sample came -from the inshore s i d e of Santa C a t a l i n a I s l a n d ; the eggs had no t e n d r i l s over two cm. long. Numerous d e s c r i p t i o n s of various t e n d r i l - b e a r i n g e l a s -mobranch egg-cases stat e or assume that the t e n d r i l s are f o r attachment, to prevent the egg's being tossed about by wave a c t i o n or currents. Indeed, those eggs with t e n d r i l s are often found entangled i n marine algae strands and d e t r i t u s . The mainland coast where t e n d r i l - b e a r i n g s w e l l shark eggs are found receives almost continuous moderate to heavy s u r f . The inshore side of Santa C a t a l i n a I s l a n d , from whence came my second sample, which produced t e n d r i l - l e s s eggs, r a r e l y has any s u r f . To check t h i s c o r r e l a t i o n between s u r f and t e n d r i l s , I obtained sharks from the offshore side of the i s l a n d , which i s , l i k e the mainland, surfswept. Their eggs had no t e n d r i l s . (With the exception of one p a i r which had 15 cm. t e n d r i l s at one end.) So, the c o r r e l a t i o n was between the presence of t e n d r i l s and being found on the mainland, not between t e n d r i l s and su r f . As shown i n f i g u r e 13, two egg-cases ( i n the S.I.O. Museum c o l l e c t i o n ) from I s l e G-uadaloupe, Mexico, which i s some 260 km. from the mainland, and 420 km. from Santa C a t a l i n a I s . a l s o l a c k t e n d r i l s . The d i f f e r e n c e between the eggs from sharks from Santa C a t a l i n a I s . and those from the mainland i s c o n s i s t e n t , whether the eggs are found i n nature, or are l a i d i n the aquarium. This suggests genetic r a t h e r than environmental c o n t r o l . The absence of exceptions to or intergrades between the two t e n d r i l types i n the two l o c a t i o n s studied (with the exception of the one instance mentioned) f u r t h e r suggests reproductive i s o -l a t i o n . Santa C a t a l i n a Island i s only some 30 km. from the main-land, but the i n t e r v e n i n g basin i e 3000 m. deep. When i t i s r e c a l l e d that t h i s i s a r e e f - d w e l l i n g shark not given to swimming i n midwater, i t i s conceivable that t h i s basin i s an - 47 -e f f e c t i v e geographical b a r r i e r which prevents, or at l e a s t severely r e s t r i c t s , migration between these two populations. This reasoning l e d me to look f o r other d i f f e r e n c e s . Table 1 shows the r e s u l t s of t w o - t a i l e d t - t e s t comparisons of the lengths, widths, and weights of the two samples of eggs i n appendix 3; one sample l a i d i n one year by sharks captur-ed on the mainland, the other l a i d the next year by sharks captured at C a t a l i n a . The comparisons of a l l three parameters show that there i s a : s i g n i f i c a n t d i f f e r e n c e between the s i z e s of the eggs i n the two samples. I t i s conceivable that there was a treatment d i f f e r e n c e - feeding, handling, temperature, etc. - between the two samples of sharks i n the two d i f f e r e n t years, which might p o s s i b l y have caused the egg s i z e d i f f e r e n c e s . Nevertheless, I consider the data to be supportive, when considered together with the other d i f f e r e n c e s . In search of other d i f f e r e n c e s , I turned to the sharks themselves. Simple v i s u a l comparison of sharks from a l l of the various l o c a t i o n s described revealed no c o n s i s t e n t d i f -ferences inthe c o l o r p a t t e r n v a r i a t i o n s , or apparent d i f f e r -ences i n gross morphology. But, s t a t i s t i c a l comparisons showed that both the f i r s t d o r s a l f i n and the caudal f i n were r e l a t i v e l y l a r g e r i n one population than i n the other. The r a t i o s obtained by d i v i d i n g the t o t a l l e n g t h by, r e s p e c t i v e l y , the height of the f i r s t d o r s a l (T,L./H.D.I.), and the width of the caudal (T.L./c.W.), f o r the samples of -48-Pigure 13. Source l o c a t i o n s of egg-cases. The t r i a n g l e s mark the l o c a t i o n s . Underlined numbers are the approximate numbers of egg-cases l a i d i n the l a b o r a t o r y by sharks from that l o c a t i o n . P l a i n numbers are numbers of egg-cases seen which were found i n nature at that l o c a t i o n . - The + and - signs i n d i c a t e the pres-ence or absence of t e n d r i l s on that sample of egg-cases. L.A. = Los Angeles; S.D. = San Diego; S.C. I s . = Santa Cata-l i n a I s l a n d . IH Jsla Guadaloupe - 49 -Table 1. Comparisons by t w o - t a i l e d t - t e s t of measurements of egg samples from sharks captured at Isthmus Cove, Santa C a t a l i n a I s l a n d , and the mainland near Los Angeles.* Source n x var. p_ Length: M 2Q 114.700 78.01? , <0.01 C 28 1 21.186 2 5.769 Width: M 20 41.850 19.819 C 28 44.714 4.138 05 Weight: M 20 2 6 . 5 9 3 . 3 4 . 5 0 3 C 28 3 2 . 5 4 6 11 . 8 6 5 <0. 01 Weight**: M 14 29.593 11.874 C 26 32.996 9.581 4-01 C .= Santa C a t a l i n a I s . ; M =? mainland; p = p r o b a b i l i t y that the samples are from the same population. The c a l c u l a t i o n s were done by computer. The r e s u l t s were rounded to three decimal places f o r t h i s t a b l e . This comparisonbetween weights was done between only those eggs containing an ovum, because of the d i f f e r e n c e i n weight of eggs without an ovum, and the d i f f e r e n c e i n the propor-t i o n of such eggs i n : t h e two samples. (See appendix 3.) - 50 -the populations of the mainland and Santa C a t a l i n a I s . were compared by t w o - t a i l e d t - t e s t . The r e s u l t s of comparisons between various groupings are given i n Table 2. Note that both samples had sex r a t i o s which were s t r o n g l y biased, but i n opposite d i r e c t i o n s . (See appendix 1). Because of t h i s b i a s , the d i f f e r e n c e i n f i n proportions.between both e n t i r e samples could be a t t r i b u t e d e i t h e r to a population d i f -ference, or to sexual dimorphism, which i s found f o r some para-meters i n some s c y l i o r h i n i d s (Brough, 1937). However, as shown i n Table 2, the d i f f e r e n c e s i n those parameters tested are s i g n i f i c a n t between populations, and not between sexes w i t h i n the same population. My contention that the sharks of Santa C a t a l i n a Island are a separate population from those of the mainland i s based p r i m a r i l y on the d i f f e r e n c e in egg-case t e n d r i l s . The s t a t i s -t i c a l data given on the other d i f f e r e n c e s found - egg-case s i z e and f i n proportions - are too few to stand alone, but are supportive. When the l o c a l submarine topography and the shark's h a b i t s are also considered, the most l o g i c a l conclusion i s that the sharks form separate populations. - 51 -Table 2. Comparisons by t w o - t a i l e d t - t e s t of morphometric r a t i o s of d i f f e r e n t samples of sharks from Isthmus Cove, * Santa C a t a l i n a I s l a n d , and Point Dume, C a l i f o r n i a . Source Sex n ac T.L./H.D.I. x T.L./C.W. var. D both 11 15.509 0.613 / 6).01 C . both 12 13.767 0.781 X D both 16 11.638 0.061 / <0.01 C both 13 11.031 0.116 D P 10 15.600 0.580 / <0.05 C P 2 13.950 0.605 N D ' M 5 11.760 0.027 / <p. 01 C M 11 11.000 0.114 D M 5 11.760 0.027 1.00 C P 11 11.580 0.070 C M 11 11.000 0.114 1 .00 c P 2 11.200 0.180 c M 10 13.730 0.878 , 1 .00 C ' P 2 13.950 0.605 * C = Santa C a t a l i n a I s . ; D = P t . Dume; T.L. = t o t a l length; CW. = width of the caudal f i n ; H.D.I. • height of the f i r s t d o r s a l f i n ; p = p r o b a b i l i t y that samples are from the same population. The c a l c u l a t i o n s were done by computer. The r e s u l t s were rounded to three decimal places f o r t h i s t a b l e . - 52 -DISCUSSION This d i s c u s s i o n w i l l g e n e r a l l y f o l l o w the same sequence of t o p i c s as the foregoing t e x t , with c e r t a i n exceptions. Some of the d e s c r i p t i v e p o r t i o n s are j u s t t h a t , and require no fu r t h e r a t t e n t i o n . Other t o p i c s which were d e a l t w i t h sep-a r a t e l y i n the tex t are s t r u c t u r a l l y or f u n c t i o n a l l y r e l a t e d , and are discussed together. Simultaneous formation of egg-cases i n both oviducts i s the general p a t t e r n seen i n the s w e l l shark, as i t i s i n those other elasmobranchs f o r which the process has been described. I t has been amply demonstrated that the synchronisation of the secretory processes i n the two s h e l l glands i s quite c l o s e . But, i n C_. ventriosum, and other species such as S. caniculus which have but a s i n g l e ostium, the means by which t h i s syn-c h r o n i z a t i o n i s e f f e c t e d presents a problem. The ostium i s of a s i z e which allows the passage of but a s i n g l e ovum at a time. The ova must pass s e r i a l l y through the s i n g l e ostium i n t o the two oviducts, and the encapsulation of ova i n each oviduct i s simultaneous. Considering these two f a c t s , i t becomes apparent that synchronization of the two ova - one "waiting" f o r the other to "catch up" - must occur i n the c r a n i a l oviducts, before the ova reach the s h e l l glands. I have found no clue as to how t h i s might occur i n the s w e l l - 53 -shark. I n i t i a t i o n and c o n t r o l of s h e l l gland s e c r e t i o n i s another unsolved problem. While I have suggested that a l -bumen s e c r e t i o n might exert some in f l u e n c e on k e r a t i n secre-t i o n , the formation of "wind eggs", by the s w e l l shark and other elasmobranchs, shows that the presence of ova i n the oviducts or at the s h e l l .gland i s not the stimulus i n i t i a t i n g s e c r e t -ory a c t i v i t y . Te Winkel (1950) has suggested that ovarian hormones may c o n t r o l s h e l l gland secretory a c t i v i t y . I have described the t o r s i o n shown by the a n t e r i o r ends of the s w e l l shark's egg-cases ( f i g . 8 ) , and the displacement of the r e s p i r a t o r y s l i t s ; those on one edge of the egg-case are one side of the case, those on the other edge are on the op-p o s i t e side ( f i g . 7 ) . The i n t e r e s t i n g t h i n g about these two features of egg-case morphology i s t h a t , despite the f a c t that these eggs come from r i g h t and l e f t p a ired s h e l l glands, a l l eggs have the same "handedness"; the a n t e r i o r end t o r s i o n and the s l i t displacement are the same, i r r e s p e c t i v e of the side of the shark from which the egg came. Here i s , then, another example of departure from b i l a -t e r a l symmetry i n the elasmobranch reproductive system. Others mentioned e a r l i e r are the development of a s i n g l e ovary i n many species, and the asymmetry of the oviduct ostium i n S. caniculus. Another which I have noted i s the d i r e c t i o n of s p i r a l of the flanges on the egg-cases of heterodontid sharks; - 54 -i t i e homologous to the much smaller t h i c k e n i n g of the egg-case edges of s w e l l sharks. The phenomenon may w e l l be general i n oviparous sharks. Despite B a l f o u r ' s statements to the contrary, i t seems most probable that the membrane surrounding the embryo and yolk, described i n s e c t i o n f o u r , i s the v i t e l l i n e membrane. I t i s u n l i k e l y that such a s t r u c t u r e i s unique to t h i s species, considering the conservative nature of ontogeny. I t i s under-standable how i t might be missed i n s t u d i e s of other species; i t i s extremely t h i n and transparent, and can only be seen by i t s r e f r a c t i o n of a f a i r l y strong l i g h t s h i n i n g through the more transparent of the cases of the s w e l l shark, which are g e n e r a l l y more transparent than those of other elasmobranchs I have seen. Upon d i s s e c t i o n to o b t a i n the embryo and y o l k , i t i s e a s i l y l o s t i n the viscous albumen. From t h i s , i t f o l l o w s that the c h a l a z a - l i k e s t r u c t u r e I have described, which cannot i t s e l f be seen, but only i n f e r r e d from i t s a c t i o n on the membrane, could not have been p r e v i o u s l y described. D i s s e c t i o n s of a l l s o r t s are normally c a r r i e d out under strong i n c i d e n t i l l u m i n a t i o n . I f the eggs of the s w e l l shark nnd other species were c a r e f u l l y d i s s e c t e d using strong t r a n s -mitted i l l u m i n a t i o n , the membrane i n question could p o s s i b l y be detected and separated from the albumen. - 55 -The main p o i n t s of the p a t t e r n of reproduction i n the s w e l l shark are: i n t e r n a l f e r t i l i s a t i o n , an extended breeding season, and the production of a r e l a t i v e small number of l a r g e eggs, which have an extended development period r e s u l t i n g i n f a i r l y l a r g e young. This p a t t e r n i s broadly t y p i c a l of a wide v a r i e t y of elasmobranchs, and suggests c e r t a i n conclusions. The extended breeding season has at l e a s t two p o s s i b l e advantages. The production of l a r g e eggs, even though few i n number - the known maximum i n a year f o r any elasmobranch i s 114 (Springer, 1967) - s t i l l e n t a i l s a considerable energy ex-penditure, which i s thus spread out over a long p e r i o d . A l s o , the l o s s of any "year c l a s s " , due to an unfavorable seasonal change i n the environment, i s reduced. Sperm storage i n the female renders t h i s extended egg production independent of repeated courtship and cop u l a t i o n . Sperm storage has now been d i r e c t l y demonstrated i n the s w e l l shark and two other species, and i n f e r e n t i a l l y ehowm.in a few species of rays, but may w e l l prove to be of more general oc-currence. Another p o s s i b l e advantage of sperm storage i s implied by the f a c t that many elasmobranchs segregate by sex during part of the year (Springer, 1967). The data i n appendix 1 suggest that t h i s may occur i n the s w e l l shark. Also, copu-l a t i o n o f t e n r e s u l t s i n / p h y s i c a l damage to the female i n some species (Springer, 1967). - 56 -The extended development period and the l a r g e y o l k supply allow the production of r e l a t i v e l y l a r g e , mature young. The major p o r t i o n of t h i s development period i s a f t e r the r e s -p i r a t o r y s l i t s i n the egg-case have opened, a f t e r which the egg-case serves only as a p r o t e c t i v e b a r r i e r l e s s e n i n g the chances of p h y s i c a l damage to the embryo or the f r a g i l e y o l k sac. P r i c e and Daiber (1967) have suggested that the advantage of more e f f i c i e n t osmoregulation f o r the embryo has been the s e l e c t i o n pressure f a v o r i n g the e v o l u t i o n of i n t r a - u t e r i n e development, from the oviparous mode, i n elasmobranchs. Read (iy68) discounts t h i s j and suggests that p r o t e c t i o n against predation and mechanical i n j u r y are more l i k e l y s e l e c t i o n pressures, but he describes no s p e c i f i c instances of such damage to egg-cases. I have described two types of predation upon shark egg-cases; one a c t u a l l y o c c u r r i n g i n nature at present, and the other conceivably so. I f such damage as t h i s to elasmobranch egg-cases has occurred on any s i z e a b l e scale during t h e i r evolutionary h i s t o r y , i t could w e l l have provided the s e l e c -t i o n pressure that Read has postulated. While d e s c r i b i n g my i n v e s t i g a t i o n s of t e n d r i l - b e a r i n g vs. t e n d r i l - l e s s eggs, I mentioned that many authors have stated or assumed that these t e n d r i l s are f o r attachment. This may - 57 -w e l l be - or have been,in the course of e v o l u t i o n a r y h i s t o r y -true. I have no data on s u r v i v a l r a t e s of the t e n d r i l - l e s s egg-cases on the calm and the surf-swept sides of Santa C a t a l i n a I s l a n d . Another f u n c t i o n ascribed to these t e n d r i l s by N a l i n i and others i s a s s i s t i n g i n o v i p o s i t i o n , by becoming entangled i n seaweeds, e t c . , as they protrude from the cloaca, and a l -lowing a shark to l a y an egg by swimming away from i t , so to speak. But, those elasmobranchs bearing t e n d r i l - l e s s eggs seem to do so s u c c e s s f u l l y - f o r example, I've never seen an "egg-bound" s w e l l shark - and those bearing t e n d r i l e d eggs can void them i n a tank having a completely smooth bottom and w a l l s . U n t i l such time as some d i r e c t proof of one or more of these supposed functions f o r t e n d r i l s on egg-cases i s set f o r t h , I b e l i e v e that the f o l l o w i n g quote must stand as an ac-curate d e s c r i p t i o n of the s t a t e of knowledge of egg-case t e n d r i l s . Kyle (1926), i n a d i s c u s s i o n of various elasmobranch egg forms, says, "In dogfishes ^includes s c y l i o r h i n i d s i n England^ ...the long t e n d r i l s at the corners c u r l round the seaweed... "These are sometimes c a l l e d adaptations, i n t h e i r various ways, and i t i s s i g n i f i c a n t that the egg-capsules of the Chimaeridae l a i d i n deep water, and of most of the r a y s , do not have the a t t a c h i n g t e n d r i l s . But the purpose u s u a l l y as-cribed to the s p e c i a l adaptations become mutually c o n t r a d i c t -- 58 -ory when we take a l l cases i n t o c o n s i d e r a t i o n , so that the sup-posed advantages are purely h y p o t h e t i c a l . " While I have i n d i c a t e d that the l a r g e , primary d e n t i c l e s on the young shark's back appear to serve a f u n c t i o n i n the shark's emergence from the egg-case, I do not wish to suggest that the shark's success i n t h i s maneuver i s e n t i r e l y depend-ant upon these primary d e n t i c l e s . The other d e n t i c l e s cover-t i n g the young shark are smaller, but also have p o s t e r i o r -d i r e c t e d p o i n t s , and could w e l l f u n c t i o n i n the same manner as that postulated f o r the l a r g e r primary d e n t i c l e s , i f some-what l e s s e f f i c i e n t l y because of t h e i r smaller s i z e . However, the opening i n the egg-case i s a t i g h t f i t , and these young sharks have l i t t l e stamina. I f i r r i t a t e d i n an aquarium, they w i l l ; swim a c t i v e l y f o r a very short time, then sink to the bottom, apparently exhausted. I t seems to me' that any adap-t a t i o n that reduced the energy requirements of escaping from the egg-case would have d e f i n i t e s u r v i v a l value. In that section of t h i s d i s c u s s i o n ending with the quote from Kyle, i t should have been apparent that I have had no success i n developing a f a c t u a l l y - s u p p o r t e d explanation of the d i f f e r e n c e i n t e n d r i l morphology between mainland and i s l a n d sharks. But, the d i f f e r e n c e e x i s t s , nevertheless. In a d d i t i o n , I have described the d i f f e r e n c e I found i n egg s i z e s , and i n the body proportions of the sharks themselves. Some doubt w i l l perhaps be cast on the l a t e r two; the egg s i z e d i f f e r e n c e may have been the r e s u l t of some treatment - 59 -d i f f e r e n c e , and the r e l i a b i l i t y of the morphometries would be greater i f they were based upon l a r g e r sample s i z e s , i n which there were no sex biases, despite the s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s between the samples obtained. Thus, the main burden of proof that there are separate populations at Santa C a t a l i n a I s l a n d and the mainland f a l l s upon the d i f f e r e n c e detected f i r s t , that between the t e n d r i l forms. This d i f f e r e n c e , the presence or absence of a s t r u c -t u r e , has proved consistent through time, and i n both l a b o r a t -ory and f i e l d s i t u a t i o n s . I t cannot, I b e l i e v e , be consider-ed an a r t i f a c t . This d i f f e r e n c e i n egg-case morphology i s as v a l i d as any other consistent morphological d i f f e r e n c e between the i n -d i v i d u a l s of two populations. I t has been suggested that I should separate the Santa C a t a l i n a Island and mainland popu-l a t i o n s i n t o species, on the basis of t h i s d i f f e r e n c e alone (pers. comm., C. Hubbs). I have not, however, because of the l a c k of knowledge of the d i s t r i b u t i o n of the . d i f f e r e n c e (no data at a l l from the other c o a s t a l i s l a n d s ) , and the un-c e r t a i n s t a t e of the r e l a t i o n s h i p s w i t h i n the genus as a whole along i t s eastern P a c i f i c d i s t r i b u t i o n (pers. comm., S. Springer). In r e f l e c t i n g back over t h i s t h e s i s , and the checkered progress of the research l e a d i n g to i t , i t eeemsto me that I have r a i s e d more questions.than I have answered, and I see - 60 -a good marry t h i n g s l e f t undone, as w e l l as t h i n g s which could have been more p r o f i t a b l y done d i f f e r e n t l y . But these are, a f t e r a l l , some of the reasons which j u s t i f y the e f f o r t . - 6 1 -SUMMARY The s w e l l shark, Cephaloscvllium ventriosum Garman, i s a small, r e e f - d w e l l i n g , nocturnal s c y l i o r h i n i d . Aspects of i t s oviparous reproduction, r e l a t e d s t r u c t u r e s of the sharks and eggs, and population d i f f e r e n c e s i n these, are the subjects of t h i s t h e s i s . 1 . D e s c r i p t i v e anatomy of the female reproductive system. a. Ovary, ova, and p e r i t o n e a l c i l i a t i o n f u n c t i o n i n g i n ovum transport. These are g e n e r a l l y as described f o r r e l a t -ed species, with a d i f f e r e n c e i n the p a t t e r n of c i l i a t i o n . b. Ostium and oviducts. The s i n g l e ostium admits ova to the two oviducts, and i s d i s s i m i l a r i n s t r u c t u r e to r e l a t -ed species p r e v i o u s l y described. c. C i r c u l a t o r y system. The s t r u c t u r e and volume of the v e s s e l s d r a i n i n g the oviducts and s h e l l glands i s unique, and i s not described i n d e t a i l elsewhere. Each oviduct, i n c l u d i n g the s h e l l gland, i s surrounded by a l a r g e s i n u s . These d r a i n to the p o s t c a r d i n a l s , which are confluent i n t h i s area. d. S h e l l gland s t r u c t u r e , s e c r e t i o n s , and sperm storage. The k e r a t i n - s e c r e t o r y tubules of the s h e l l gland f u n c t i o n as a sperm storage s i t e . While sperm storage has been assumed or i n d i r e c t l y demonstrated f o r s e v e r a l species of elasmobranchs, the s i t e has been h i s t o l o g i c a l l y demonstrated f o r only two other species. Photomicrographs are included which show sperm - 62 -i n the k e r a t i n secretory tubules. 2. Egg-case s t r u c t u r e . No d e t a i l e d d e s c r i p t i o n of the egg-case and the v a r i a t i o n s which occur has been p r e v i o u s l y published. This forms a necessary background to f o l l o w i n g s e c t i o n s . 3. Mechanics and sequence of egg-case formation. P r i o r ob-servations and speculations are discussed i n d e t a i l , and r e -in t e r p r e t e d i n the l i g h t of my own observations, 4. Development of the embryo and egg-case changes. The sequence of development of the embryo i t s e l f i s g e n e r a l l y i n accord with p r i o r d e s c r i p t i o n s published f o r other species, and i t was not an o b j e c t i v e of t h i s study to record them i n d e t a i l . However, I have observed two s t r u c t u r e s which, to my knowledge, have not been p r e v i o u s l y described; a membrane surrounding the embryo and yol k during the e a r l i e r stages of development, and a c h a l a z a - l i k e s t r u c t u r e attached to t h i s membrane. 5. Emergence of the shark from the egg-case. The young of sev e r a l species of sharks and chimaerids have two l o n g i t u d i n a l , d o r s o l a t e r a l rows of large d e n t i c l e s , which disappear some time a f t e r the young emerge from t h e i r egg-cases. No f u n c t i o n has p r e v i o u s l y been a t t r i b u t e d to these d e n t i c l e s . Prom d i r e c t observation and a n a l y s i s of motion p i c t u r e s , i t appears that these s p e c i a l i z e d d e n t i c l e s f u n c t i o n i n the emergence of the young from t h e i r egg-cases. a 63 -6. Predation on egg-cases. I have found no mention i n the l i t e r a t u r e of predation upon elasmobranch egg-cases. Evidence i s presented showing predation, probably by a s t e n o g l o s s i d gastropod, on a high proportion of a number of egg-cases found at one l o c a t i o n . 7. Population d i f f e r e n c e s . The egg-case from sharks from two l o c a t i o n s show consistent d i f f e r e n c e s i n morphology. This and other evidence from the ecology of the species, the l o c a l submarine topography, and morphometries of the eggs and of the sharks themselves, i s presented i n support of the hypothesis that there e x i s t at l e a s t two r e p r o d u c t i v e l y i s o l a t e d popula-30 t i o n s , separated by as l i t t l e as 33f km. - 64 -REFERENCES Aiyar,R. G. , and K. P . N a l i n i , 1938. Observations on the repro-ductive system, egg-cases, and breeding h a b i t s of C h i l i o - sc.yllium griseum M u l l , and Henle. Proc. Ind. Acad. S c i . B7:252-269. Balf o u r , F.M. 1878. A monograph on the development of elasmo-branch f i s h e s . Macmillan , London. , 1880. Comparative embryology. V o l . I . Macmillan, London. , 1881. Comparative embryology. V o l . I I . Macmillan, London. Brough, J . 1937. On c e r t a i n secondary sexual c h a r a c t e r i s t i c s of the common dogf i s h , S c y l i o r h i n u s c a n i c u l u s . Proc. Zool. Soc. London. 107B:217-223. C h i e f f i , G. 1962. Endocrine aspects of reproduction i n e l a s -mobranch f i s h e s . Gen. Comp. Endocr. Suppl. 1;275-285. Clark, E. 1947. Note on the i n f l a t i n g power of the s w e l l shark, Cephaloscyllium uter. Copeia 1947:279-280. Clark, R.S.1922. Rays and skates (Raiae) No. I; Egg capsules and young. J . Mar. B i o l . Assoc. U.K. 12:577-643. Coll e n o t , G. 1966. Observations r e l a t i v e s au developpement au l a b o r a t o i r e d' embrypns et d' i n d i v i d u s juve'niles de Sc y l i o r h i n u s c a n i c u l a L. Cahier de B i o l o g i e Marine 7:319-330. - 65 -Cox, K. W. 1963. Egg-cases of some elasmobranchs and a c y c l o -stome from C a l i f o r n i a n waters. C a l i f . P i s h and Game 49:271-289. Danie l , J.P. 1934. The elasmobranch f i s h e s . Berkeley, C a l i f . Edwards, H.M. 1920. The growth of the s w e l l shark w i t h i n the case. C a l i f . P i s h and Game. 6:153-157. Pord, E.1921. A c o n t r i b u t i o n to our knowledge of the l i f e h i s t o r i e s of the dogfishes landed at Plymouth. J . Mar. B i o l . Assoc. U.K. 12:469-505. H a r r i s , J . E. 1952. A note on the breeding season, sex r a t i o , and embryonic development of the dog f i s h Sc.vliorhinus c a n i c u l a . J . Mar. B i o l . Assoc. U.K. 31:269-275. , 1962. E a r l y embryonic movements. J . Obstet. Gynaec. B r i t . Cwlth. 69:818-821. Herald, E. 1962. L i v i n g f i s h e s of the world. Doubleday, N.Y. Hobson, A. D. 1930. A note on the formation of the egg case of the skate. J . Mar. B i o l . Assoc. U.K. 16:577-581. Kato, 3., S. Springer, and M. H. Wagner, 1957. F i e l d guide to eastern P a c i f i c and. Hawaiian sharks. U.S. Bureau Comm. F i s h e r i e s C i r c u l a r 271. Kyle, H. M. 1926. The biology of f i s h e s . Sidgwick and Jackson, London. Libby, E. L. 1959. M i r a c l e of the mermaid's purse. Nat. Geog. Mag. 116:413-420. L i g h t , S.P., et a l . 1957. I n t e r t i d a l i n v e r t e b r a t e s of the c e n t r a l C a l i f o r n i a coast. Univ. of C a l i f . Press, Berkeley. - 66 -M e l l i n g e r , J . 1965. Stades de l a spermatogenese chez So.vlio-rhinus caniculus ( L . ) : d e s c r i p t i o n , donates histochemi-ques, v a r i a t i o n s normales et experimentales. Z. Z e l l f o r s c h . 67:653-673. Metten, H. 1939. Studies on the reproduction of the do g f i s h . P h i l . Trans. Roy. Soc. London 230:217-238. , 1944. The f a t e of spermatozoa i n the female d o g f i s h . ( S c y l i o r h i n u s c a n i c u l a ) . Quart. J . Micr. S c i . 84:283-294. N a l i n i , K.P. 1940. Structure and f u n c t i o n of the nidamental gland of Chilosc.vllium griseum ( M u l l , and Henle). Proc. Indian Acad. S c i . Sect. B 12:189-214. Norman, J . R.,and P. H. Greenwood. 1963. A h i s t o r y of f i s h e s . H i l l and Wang, N.Y. Prasad, R.R. 1945. Further observations on the s t r u c t u r e and fu n c t i o n of the nidamental glands of a few elasmobranchs of the Madras coast. Proc. Indieja Acad. S c i . Sect. B 22:368-373. , 1951. Observations on the egg-cases of some oviparous and vivaparous elasmobranchs, with a note on the f o r -mation of the elasmobranchs egg-case, J . Bombay Nat. H i s t . Soc. 49:755-762. P r i c e , K.S., and F. C. Daiber. 1967. Osmotic environments during f e t a l development of do g f i s h , Mustelus canis ( M i t c h e l l ) and Squalus acanthius Linnaeus, and some 67 -comparisons with skates and rays. P h y s i o l . Zool. 40: 248-260. Read, L.J. 1968. Urea and trimethylamine oxide l e v e l s i n elasmobranch embryos. B i o l . B u l l . 135:537-547. Setna, S.B., and P.N. Sarangadhar. 1948. Observations on the development of C h i l o s c y l l i u m griseum M. & H., P r i s t i s  cuspidatus Lath, and Rhynchobatus d.iiddensis (Porsk.). Rec. Indian Mus. 46:1-24. Smith, B.G. 1940. The breeding h a b i t s , reproductive organs, and e x t e r n a l embryonic d evelopment of Chlamydoselachus. based on notes and drawings by Bashford Dean. Am. Mus. Nat. H i s t . The Bashford Dean Memorial Volume. Archaic Pishes. A r t i c l e 7:525-633. (E.W. Gudger, ed.) , 1942. The heterodontid sharks: t h e i r n a t u r a l h i s t o r y , and the e x t e r n a l development of Heterodontis .iaponicus based on notes and drawings by Bashford Dean. Am. Mus. Nat. H i s t . The Bashford Dean Memorial Volume. Archaic Pishes. A r t i c l e 8. 651-770. (E.W. Gudger, ed.). Smith, S. 1957. E a r l y development and hatching i n P h y s i o l -ogy of f i s h e s . V o l . 1:323-359. (M. Brown, ed.) Academic Press, N.Y. Springer, S . I 9 6 7 . S o c i a l o r g a n i z a t i o n of shark populations, i n Sharks, skates, and rays. (P. G i l b e r t , R.P. Mathew-son, and D.P. R a i l , eds.) Johns Hopkins Press, Baltimore. - 68 -Te Winkel, L. 1950. Notes on o v u l a t i o n , ova, and e a r l y development i n the smooth do g f i s h , Mustelus c a n i s . B i o l . B u l l . 99:474-486. Threadgold, L.T. 1957. A h i s t o c h e m i c a l study of the s h e l l gland of S c y l i o r h i n u s c a n i c u l u s . J . Histochem. Cytochem. 5:159-166. Appendix 1. Body measurements ( i n cm. used f o r morphometric comparisons. T,L. = t o t a l l e n g t h ; H.D. I . = height of the f i r s t d o r s a l f i n ; CW. = width of the caudal f i n ; F = f i n f r a y e d , not meas-urabl e . Part A. Sharks captured i n or near Isthmus Cove, Santa C a t a l i n a I s l a n d . Sex T.L. H.D.I. CW. Female 796 55 69 805 60 74 Male 906 68 82 . 875 67 80 7 7 1 55 7 0 837 — 78 7 0 0 59 61 869 64 81 895 65 79 « 662 49 62 750 52 65 « 794 55 71 787 51 74 Appendix 2. Pre-caudal v e r t e b r a l counts of sharks from various l o c a t i o n s . Santa C a t a l i n a I s l a n d . 69, 72, 70, 70. C a l i f o r n i a mainland - Los Angeles area. 70, 72, 70, 70, 68, 72, 70, 71 . I s l a G-uadaloupe, Mexico. 67, 67, 68, 68. Appendix 3. Measurements of shark eggs l a i d i n the l a b o r a t o r y . (Dimensions i n mm., weight i n grams.) An a s t e r i s k by the weight i n d i c a t e s those eggs not containing an ovum. Part A. Eggs l a i d i n 1963 by sharks captured near Los Angeles. Date Length Width Weight 22 J u l y 115 48 29.0 n 114 49 29.2 28 J u l y 134 47 34.5 it .111 46 32.0 it . 1 3 4 47. 35.0 ii : 115 45 32.0 1 1 1 46 31.5 II 115 45 *23 .2 26 August 105 37 *18.1 II 111 37 24.3 3 September 128 44 33.1 II 118 42 *23 .7 18 September 115 39 28 .3 II 117 39 26.8 25 October 103 36 *16 . 4 it 103 37 *16 . 4 19 November . 105 37 *17 . 9 II 110 38 25 .4 26 December 118 39 26 .5 II 112 39 26.7 Appendix 1. Part B. Sharks captured near Point Dume, Sex T.L. H.D . I . CW. Female 824 5 0 71 II 831 52 71 ti 820 52 70 n 802 53 69 II 738 P 62 it 809 51 71 II 764 53 67 it 812 53 72 it 731 48 63 II 759 51 68 II 845 50 70 Male 803 55 68 II 718 P 62 it 659 P 57 it 792 P 66 ti 734 62 P = F i n frayed Appendix 3. Part B. Eggs l a i d i n the l a b o r a t o r y i n 1964 by sharks captured i n or near Isthmus Cove, Santa C a t a l i n a I s l a n d . Date Length Width Weight 26 June 119 47 30.5 it 119 46 30.6 II 117 45 29 .7 ti 116 46 30.0 27 June 127 45 34.9 ii 125 41 * 24.8 II 124 46 35.6 II 124 47 34.6 17 J u l y 134 47 38.1 II 134 47 38.3 II 126 45 36.1 II 125 45 37 .0 20 J u l y 125 47 36.9 ti 125 47 36.0 II 122 4'6 35.6 ti 121 47 35.2 31 J u l y 120 44 30 .7 it 120 44 30.1 II 118 45 29 .6 II 118 44 29 .6 21 August 115 43 28 .3 ti 117 43 30.4 ii 118 43 30 .5 ii 118 44 30 .7 8 October 117 4:2 32.4 II 115 43 * 28 .6 14 December ** 116 39 34.1 II • * 121 44 32.4 ** These two eggs were taken while d i v i n g at Isthmus Cove. 

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