140 EMIL WITSCHI. 



There are indeed a considerable number of cases like No. 44, 

 in which one animal possesses normal testes, while the other has 

 ovaries, which do not show any apparent deviation from the 



FIG. 2. Parabiotic twins 8844. (Both are Rana sylvatica.) Left larva, 34 mm. 

 total length. 68 days after the operation. Male. Transverse section through 

 one of the testes. The germ cells (primary spermatogonia) are in the sex cords. 

 X444- 



typical female conditions (compare Figs. 2 and 3). Later 

 investigations, however, showed, that some of the females 

 twinned with males underwent sex-reversal. In three such 

 cases large parts of the gonads show a nearly typical testicular 

 structure (Fig. 4), while other parts are ovarial or show pro- 

 gressive stages in the transformation process. In seven more 

 cases the gonads are in the first stages of that transformation 

 (Fig- 5)- Such ovaries are, without exception, very slender. 

 The same thing is observed in some cases, in which the re- 

 organization has not yet begun. Obviously an inhibition in 

 ovarial growth is the first visible effect exerted by the male 

 co-twin. 



