The Embryology of Chlamydoselachus 537 



The evidence from the ovaries is fairly strong, that from the uteri cumulative and 

 overwhelming, that Chlamydoselachus ripens eggs in batches in its ovaries, and broods 

 and hatches embryos in its uteri throughout the whole calendar year and probably in 

 every month of the year. 



When one thinks the matter out, this does not seem so extraordinary as at first blush. 

 Chlamydoselachus lives at the bottom of the Sagami Sea under uniform conditions of 

 darkness, great pressure, low temperature, with a restricted oxygen supply, and on food 

 with presumably little change in kind and quality. The maximum depth of the habitat of 

 the frilled shark is about 3600 feet, the average 1500 to 1800. At 1800 feet the pressure is 

 814 lbs. to the square inch, the temperature about 43° F. and the human eye would find 

 total darkness. Under the prevailing and unvarying conditions at these depths, the 

 frilled shark would presumably have no special breeding season such as is found in surface^ 

 dwelling sharks in the Sagami Sea. In these, in contrast, breeding might be expected 

 to take place in late spring or early summer due to the lengthening daylight period, the 

 rising temperature, and the more abundant food consequent upon the return of the sun. 

 In Chlamydoselachus, on the contrary, it is to be expected that eggs would ripen in the 

 ovaries at any time during the year as indicated above and that breeding would take place 

 during any month. Thus the findings of eggs with blastulae in October and of embryos 

 10-20 mm. long in January, and others measuring 317-390 mm. in May — as recorded by 

 Dean — are understandable. 



Before leaving this subject, it is pertinent to call attention to the notes above, which 

 show that not all the eggs in a single uterus are in precisely the same stage of development. 

 Even as the eggs break out of the ovary one at time as they ripen, so they make their way 

 into the oviduct one at a time. Hence there must be a continuous process of fertili2;ation, 

 shell formation, and early development going on within a single female during a limited 

 period of time. This I have found to take place in the shallow-water nurse shark of Florida- 

 Likewise, there will be much later, in the uterus of each individual female Chlamydo- 

 selachus, a serial process of breaking and throwing off of egg capsules by the growing 

 embryos, and finally a succession of young sharks being extruded into the sea. 



It should be noted that ovarian eggs are matured in batches or clutches (a small 

 number of approximately the same large siz,e) and that, when nearly mature eggs are 

 present in the ovary, there are no other eggs in the ovaries of the same individual at all 

 comparable in si?e. Also, there are limits to the range of variation in sizes of embryos 

 obtained from a single female at the same time. One does not find very early and very 

 late embryos developing in a single individual at the same time. These observations indi- 

 cate that in each individual Chlamydoselachus there is a definite cycle of reproductive 

 activity, but one quite independent of seasonal influences, hence any single phase of re- 

 production and development may occur in different individuals at different seasons of the 

 year. In this, Chlamydoselachus is unlike most vertebrates, but a comparable condition 

 is found in civilized man. 



