68 J. M. ESSENBERG. 



IX. INVERSION OF FEMALES. 



It will be seen in Table II. that all females between 16.7 and 

 26 mm. are retrogressive. Normal females do not occur before 

 they reach approximately 27 mm. in total length. The phenomenon 

 of retrogression in Xiphophorus helleri is not a seasonal fluctuation, 

 as this species produces young practically every month. Nor is it 

 temporary and reversible, once the ova are affected they can not be 

 rejuvenated. Lane (1909) has described retrogressive ovules in 

 Lucifuga and Stygicola. In these teleosts the larger and more 

 favorably situated ova cause the disintegration of smaller ovules 

 which are absorbed as food. It is very clear that this is not the 

 case in Xiphophorus, for it is the larger ova that are affected first. 

 These may be in a hopeless state of degeneration before the smaller 

 ones show signs of disintegration. My material- strongly favors 

 the conclusion that all of the linear descendants of the primordial 

 germ cells disintegrate. 



If the retrogressive females transform into males, it is apparent 

 from the above tables on sex-ratios that approximately half of the 

 females become males. It is doubtful whether any of the females 

 of class i transform, because the ovarian epithelium is actively 

 proliferating definitive germ cells. The activity of the epithelium 

 is relatively slight in females of class 2 and stops entirely in 

 females of class 3, and therefore one would expect that the pros- 

 pective males are recruited from the two latter classes. If so, the 

 sum of the females of classes 2 and 3 must approximately equal 

 the sum of females of class i. This is actually the case, as is 

 evidenced by the following table, in which all of the retrogressive 

 females studied are tabulated. 



TABLE IV. 



Class i. Class 2. Class 3. 



40 25 10 



The question may be raised whether the retrogressive females 

 result in sexual forms. In the first place, no sexless form has 

 been encountered in the 300 fishes used for cytological work unless 

 the females of class 3 be so considered. Careful study shows con- 

 clusively that they are not stationary but transitional forms, and 



