COMPLETE SEX-REVERSAL IN VIVIPAROUS TELEOST. IOI 



significant and must, to a certain extent, be reviewed here. 

 For further details of description and figures on sex-differentiation 

 the reader is referred to Essenberg (1923). 



As far as the writer knows, the causative factor or factors in 

 sex-reversal have not been successfully demonstrated. That 

 these factors reside in the gonad and possibly in the germ cells 

 themselves has been substantiated beyond a doubt by experi- 

 mental data. Whenever those factors become functional the 

 entire ovary is subject to hopeless degeneration. At first the 

 large ovocytes disintegrate, then the medium-sized ones, and 

 finally the young ovocytes which are found close to the epithelium 

 of the ovarian cavity follow their two predecessors. Also the 

 epithelium covering the ovary, which originates from the peri- 

 toneum of the body cavity, disintegrates completely. The 

 epithelium of the ovarian cavity, however, is not subject to 

 disintegration. It shrinks and assumes more or less a tubular 

 form, its cells, judging from their appearance, undoubtedly 

 undergo retrogressive changes but no disintegration is noticeable. 

 After a period of rest this epithelium becomes active and pro- 

 liferates cells which go to form the gonad of the opposite sex 

 the testis. The process of testicular formation which belongs 

 to the present stage of sex-reversal includes the proliferation of 

 germ cells from the remains of the epithelium of the ovarian 

 cavity and the formation of sex-cords. It includes two stages 

 of sex-differentiation called by the writer "Early and Middle 

 Stages of Tubule Formation" (Essenberg, 1923, pp. 57-58). 



It is interesting to note that the epithelium of the ovarian 

 cavity which gives rise to the definitive male cells originates, 

 as does the epithelium covering the ovary, from the peritoneum 

 of the body cavity. 



While the process of disintegration is taking place, the vitality 

 of the transforming animal is reduced to the minimum. Volun- 

 tary motion which is so characteristic of Xiphophorns helleri is 

 seldom noticed; the fish rests most of the time and moves only 

 to escape danger or because of hunger. As to the latter it may 

 be said that the animal takes very little food of any kind during 

 the process of ovarian disintegration. This is a critical stage to 

 the animal. The least change in the animal's environment, 



