The Embryology of Chlamydoselachus 533 



It is impossible to determine with certainty how many eggs are represented in this 

 figure. There seem to be about a dozen and in addition there are various objects not 

 clearly recognizable. There is no date given for the capture of this fish, but from a female 

 taken May 26, 1896, Nishikawa obtained six embryos ranging from 32-60 mm. in length. 

 "Each embryo was attached to its large yolk-sac by means of an umbilical cord, which 

 allowed considerable movement to the embryo". 



Thus Nishikawa in 1898 was the first to demonstrate by dissection and publication 

 that Chlamydoselachus is viviparous. He had dissected seven specimens in 1896. Since 

 Dean kept closely in touch with the literature on the archaic fishes, it is likely that he 

 knew of Nishikawa's article (1898) as is evidenced by his statement (Dean, 1901.1): 

 "I found . . . that if one could secure [at Misaki] many adult [female] specimens [of 

 Chlamydoselachus] there was a fair chance of obtaining embryos, since this shark was 

 known to be viviparous". 



Dean's extensive experience in collecting eggs and embryos at Misaki abundantly 

 confirmed the conclusion that Chlamydoselachus is viviparous. His stages ranged from 

 blastulae to embryos varying in length from 11.5 mm. to 390 mm. (15.35 in.) — all attached 

 to yolk sacs. 



The spawning habits of the frilled shark are unknown to this day. It seems to me 

 that this fish must properly be called not viviparous but ovoviviparous, because it carries 

 in its uterus not eggs in very thin'walled capsules as do some viviparous sharks and rays, 

 but eggs with rather heavy keratinoid shells fit to be expelled into the water (Figures 2 

 to 10, plate I). 



I have found that the tropical littoral nurse shark, Ginglymostoma cirratum, carries 

 in its uteri very large eggs enclosed in very heavy keratinoid shells. Evidence (to be 

 adduced later) leads to the belief that, when the embryo has attained some size the shell is 

 burst and is expelled through the cloaca into the sea, while the egg and embryo are re' 

 tained in the uterus for a considerable time For these reasons, it seems to me that such 

 a shark ought to be designated as ovoviviparous rather than viviparous. I have studied 

 the nurse shark extensively and since its reproductive organs and breeding habits are very 

 similar to those of the frilled shark, comparisons will frequently be made in order to clear 

 up many puzzling questions about the reproduction of Chlamydoselachus. 



The young frilled shark certainly breaks its egg shell long before it is old enough to 

 be extruded from the uterus into the water (Figure 11, plate I). But we do not know at 

 what stage in the development of the embryo the insoluble keratinoid egg capsule is cast 

 off into the uterus nor when it is extruded into the sea. Nor is it known whether the 

 embryo is expelled into the water before all the yolk is absorbed as occurs in the dogfish, 

 but is seems improbable. If the young Chlamydoselachus or Ginglymostoma were extrud' 

 ed early, it would swim poorly because of its great yolk mass (Figure 49, plate V) and 

 would be an easy prey for any marauding fish. One must conjecture that the young of 

 both sharks are retained in the uterus until, when passed out into the sea, they are able 



