The ?iatural History of the Frilled Shar}{ 301 



is the one reading "Habits in Spawning." However, since this fish is taken at great 

 depths, it is doubtful if we will ever know either the mating behavior or the manner of 

 parturition. The heading quoted above may possibly indicate that Dean saw young 

 extruded from the body of the mother after these were brought on board the fishing boats, 

 or possibly after they were brought to the laboratory at Misaki. This is a thing not un' 

 known in other viviparous sharks. 



A final word may be said as to the methods by which viviparity is known to be 

 effected in various Elasmobranchs. In some the embryos, enclosed in a thin diaphanous 

 shell or membrane, lie free in the uterine enlargement of the oviduct. After the yolk is 

 almost all absorbed, they are nourished by a milky fluid secreted by the uterine mucosa 

 which at the time of gestation is developed into villi or thread-like prolongations. In 

 others, having a similar egg-membrane, when the yolk is absorbed the emptied yolk-sac 

 becomes applied to the lining mucosa of the uterus, the two develop interdigitations and 

 there is thus formed a functional placenta — a so-called "yolk-sac placenta." By what 

 process the young of Chlaynydoselachus are nourished during their last stages cannot be 

 said, since, so far as we know, full-term embryos or fetuses have never been taken. Pos- 

 sibly neither of the above methods is found in Chlamydoselachus, since in the earHer 

 stages the egg is surrounded by a fairly thick horny egg-case, of which there are several in 

 our material. Gudger has found that the large egg of the nurse shark, Ginglymostoma 

 cirratum, likewise contained in a huge thick shell, is carried in the uterus for a long period 

 of time. The embryos of both sharks have short yolk-cords, which seem to preclude the 

 formation of a yolk-sac placenta. On the other hand, all the Elasmobranchs that nourish 

 the young on a uterine "milk" or by means of a yolk-sac placenta have the eggs enclosed in 

 the exceedingly thin diaphanous shells referred to above, which offer no resistance to the 

 passage ot fluids. Probably it will be eventually found that all the food required for the 

 prenatal growth of the embryonic frilled shark is contained in the huge egg, the most 

 enormous in any shark known to us. In this matter, as in many others touching the struc- 

 ture and habits of Chlamydoselachus, there is room for further investigation. 



Since in this section of our article we are dealing largely with the views of earUer 

 investigators, we have used their term "viviparity." In our opinion the method of 

 reproduction in this shark should be called "ovoviviparity." Presumably, the egg is re- 

 tained in the uterus until the young embryo is able to burst the shell. Doubtless, this 

 useless shell is then cast out through the cloaca, while the embryo with the huge yolk- 

 sac remains in the uterus until the yolk is all absorbed, and the young shark is fully 

 developed and ready for birth. The question of viviparity versus ovoviviparity in 

 Chlamydoselachus will be considered further in the introduction to the article on the outer 

 development of the embryo of this shark. 



