COMPLETE SEX-REVERSAL IN VIVIPAROUS TELEOST. IO5 



become segregated and thus never take part in definitive germ 

 cell production (males). The epithelium of the ovarian cavity 

 which gives rise to definitive ovocytes proliferates cells which go 

 to form the testes of the transforming fish. The epithelium of 

 the ovarian cavity originates in the following fashion. As the 

 primordial germ cells of this teleost project into the body cavity, 

 they are covered by the peritoneal epithelium. During the 

 indifferent stage the gonads are paired. If the young fish 

 develop in the male direction, the paired or bilateral relation is 

 retained permanently. In case the animal develops into a female, 

 the undifferentiated bilateral gonads fuse medially in such a 

 manner that the medial parts of the covering of the gonads 

 form the epithelium of the ovarian cavity. In the course of 

 sex-reversal the entire ovary disintegrates except the epithelium 

 of the ovarian cavity. From it cells proliferate which form sex 

 cords and later seminiferous tubules. 



Proof to the effect that the same is true in birds was furnished 

 by the excellent work of Fell (1923). This author had the 

 unique opportunity to study the gonads of eight arrhenoid birds 

 which represented the various stages in sex-reversal from female 

 to male. It was found that the germ cells of the opposite sex 

 proliferate from the peritoneal epithelium of the degenerating 

 ovary as well as from the peritoneal epithelium of the vestigial 

 right ovary. These cells form sex cords which in due time give 

 rise to seminiferous tubules. The sperm cells from such tubules 

 are known to be functional. The author concludes that "we 

 have here a case of direct transition of ordinary somatic peritoneal 

 cells into germ cells." 



Similar observations have been made by Gatenby (1916), 

 Firket (1920), and by Swingle (1921). In the light of our present 

 knowledge, it may indeed be questioned if definitive germ cells 

 ever are lineal descendants of primordial germ cells in higher 

 animals. 



It has been claimed that the peritoneal epithelium covering 

 the ovary is "packed" with primordial germ cells which have 

 reached the epithelium by migration and that those are the 

 primordia of sex cord formation. Whatever might be the 

 validity of this claim in case of birds the writer is not in position 



