J. M. ESSENBERG. 



of degenerating follicles may be found in the body cavity. Occa- 

 sionally such remains may assume activity and form cords of vari- 

 ous sizes, which may persist for a considerable time. 



The fatty tissue which commonly surrounds the gonads in fishes 

 increases immensely during the retrogression. In fact, in the later 

 phases of disintegration of the ovary special care must be taken to 

 discover the remains of the ovary within the fatty mass. The fact 

 that it contains an abundance of large blood vessels leads one to 

 suspect that it might play some role in the disintegration process. 

 Although stroma cells have been noticed among the fatty cells, at 

 no time do the latter engulf, surround, or even come in contact 

 with the disintegrating ova. Whatever physiological role they play 

 as regards the fate of the germ cells can not be discovered by 

 observation. Experimentally it has been noticed that the fatty 

 tissue increases immensely within two days after injury to the 

 reproductive system. 



TABLE I. 



Y. EARLY SEX-DIFFERENTIATION OF THE MALE. 



The testis of Xiphophorus hcllcri belongs to the acinus type in 

 which seminiferous tubule formation is greatly modified. Sex- 

 cords and tubules are formed from peritoneal cells exclusively. 

 Such tubules give rise to the acini by transformation of epithelial 

 cells into germ cells. The early sex-differentiation of the male is 

 principally a process of tubule formation, and thus it may be di- 

 vided into early, middle, and late stages of tubule formation. 



