COLD-BLOODED VERTEBRATES 



105 



and the sea snakes Aipysurus, Enhydrina, 

 Hydro-phis, Lapeinis, Laticcuida, and Tha- 

 lassophis (^mith, 1930; Smedk-y. 1930, 1931 ; 

 Bergman, 1943). 



XIX. Viviparity 



Fish 



^'i^'il)al■ity in some fish and in mammals 

 has, it will he seen, mueh in common. Hor- 

 mones from the glands of internal secretion 

 initiate and regulate many aspects of rei)ro- 

 duction in the higher vertebrates, and there 

 is reason to believe that similar controls are 

 important in fish. Although actual evidence 

 for such endocrine regulation is scanty, some 

 phenomena of gestation in this class should 

 hv briefly reviewed. For details, see Turner 

 (1933, lb40c, 1947), Mendoza (1937), and 

 Needham (1942). 



The finding of an eml^ryo within an egg 

 case in a specimen of Rhineodon typus, the 

 whale shark (this adult exceeded 65 feet in 

 length), was taken as strong presumjitive 

 evidence that this species is oviparous 

 ( Baughman, 1955 ) . However, specializations 

 of the uterus of the basking shark, Ceto- 

 rhinus maximus, suggest that it is viviparous 

 (Harrison Matthews, 1950), as is Spinax 

 (Wallace, 1903) and the dogfish, Mustelus 

 (Te Winkel, 1950). It is thought that ovar- 

 ian tissue and immature eggs in another 

 shark, Lamna, disintegrate into the oviduct, 

 are passed into the uterus, and are swallowed 

 as food by the embryo. The gut of the em- 

 bryo becomes greatly distended with this 

 yolk-like material; the actual yolk sac is 

 separate and very small (Shann, 1923). In 

 three genera of ray, Myliobatis, Ftero- 

 plataea and Trygon, the uterine mucous 

 membrane gives off long paj^illae, or tro- 

 phonemata, which secrete a fluid rich in al- 

 bumen. The secretion escapes into the uter- 

 ine cavity and is swallowed by the fetus, as 

 proven by finding the same material in the 

 fetal intestine. In Pteroplataea the uterine 

 pai)illae extend into the fetal spiracle, ac- 

 tually a kind of suckling. The fetuses are 

 not otherwise attached to the mother (Wood- 

 Mason and Alcock, 1891; Alcock, 1892). 



Viviparity in teleosts was known to Aris- 

 totle (Thompson, 1910) and has interested 

 biologists ever since. Embryos develop 

 within the ovarian follicles in representa- 



tives of the Poeciliidae, Anablepidae, and 

 (roodeidae.-^ In the Ernbiotocidae, Zoarci- 

 d(ie, (ioodeidae, and Jenynsiidae the ferti- 

 lized ovum is released promptly into the 

 ovarian cavity and develops there. -^"^ 



The ovary may contribute to the food sup- 

 ply of the embryo by the seci'etion of nu- 

 tritive fluid into the follicular or ovarian 

 ca\-ity ; the embryo is bathed in and swallows 

 or absorbs this fluid through the skin.-*' The 

 food in addition may consist of dead si)erm, 

 dead embryos, and disintegrated ova. Ab- 

 sori)tion is facilitated in Annblepidae, 

 Goodeidae, and Poeciliidae by villi (tro- 

 photaeniae) extending from the yolk sac or 

 gut opening, by specialization of the tips of 

 the embryonic fins, by ovarian wall proc- 

 esses which extend into the branchial cham- 

 ber of the embryo, or by development of the 

 pericardial membrane as an absorptive sur- 

 face.-" In certain Anablepidae and Poecilii- 

 dae there is actually a pseudoplacenta 

 (Fraser and Renton, 1940; Turner, 1940a, 

 1) ) . Respiratory exchange and the removal 

 of waste are effectefl by the same mecha- 

 nisms as is nutrition. 



Mendoza (1940) noted that epithelium of 

 the ovary of the Goodeidae secretes not only 

 when embryos recjuiring nutrition are pres- 

 ent but also in virgin females; he concluded 

 that these changes are cyclic and independ- 

 ent of the presence of embryos. The analogy 

 with the uterine epithelium of mammals is 

 evident. Turner (1937a, 1940c, 1947), com- 

 menting on the regulation of successive 

 broods in those poeciliid fish in which super- 

 fetation occurs, hyi)othesizes that follicle- 

 stinndating hormone from the intuitary may 

 be responsible. In Lebistes an increase in 

 thyroid activity is correlated with the pe- 

 riod of rapid growth and differentiation of 

 theem})ryo (Stolk, 1951a). 



Amphibians 



Vivii:)arity has been described for the Af- 

 rican frog Xectophrynoides. Internal ferti- 



"Kiintz, 1913; Tiiiner, 1933, 1937a, 1940a, c; 

 I^irspr, 1938. 



"■'■Stuhlman, 1887; Eigenmann, 1892b; Scott, 

 1928; Mendoza, 1936, 1937, 1940; Turner, 1937b. 



'"Eigenmann, 1892a, b; Hubbs, 1921; Scott, 

 1928; Turner, 1933, 1938c, 1940a, c, 1947; Mendoza. 

 1936, 1937, 1910; Fra8er and Renton, 1910. 



-■Turner, 1933, 1937b, 1938c; Mendoza, 1937. 

 1910. 1936; Tavolga and Rugh, 1947. 



