264 



THE THEORY OF THE GENE 



genes that ordinarily suffices in frogs to give males or 

 females may be "overridden" by environmental factors 

 and testes may develop in an individual whose internal 

 chromosomal balance would produce a female. Stated in 

 another way, this may mean that each frog is capable of 

 developing both testes and ovary ; that under normal cir- 

 cumstances the XX individual develops only the ovary 



a b c 



Fig. 146. 

 Three hermaphroditic frogs. (After Crew and Witschi.) 



and the XY individual a testis, but under exceptional con- 

 ditions a female of the XX type may develop a testis. 

 The possibility of the reciprocal change has not been 

 demonstrated. 



There are many records of "hermaphrodite" adult 

 frogs (Fig. 146). Crew has listed 40 recent cases. Whether 

 these hermaphrodites are related in any way to the in- 

 versions just described is unknown. It is significant per- 

 haps that a few individual hermaphrodites have also been 

 reported from those experiments. On the other hand, it is 

 possible that some of the hermaphrodites have a different 

 origin. There is not much evidence that they can be ex- 

 plained as gynandromorphs or mosaics due to elimination 



