256 



THE THEORY OF THE GENE 



144). The ovary in the male disappears when the insect 

 becomes adult, and the testes produce normal sperma- 

 tozoa. In this instance, then, we must infer that, in the 

 young stages of the male, the absence of one X does not 



Pe-pla marginata 



ovary 



Fig. 143. 



Perla marginata to the left. The ovotestis of a young male to the 



right. (After Junker.) 



suffice to suppress the development of an ovary, but when 

 the individual becomes adult its chromosome composition 

 asserts itself. 



Sex and Sex Reversal in Frogs. 

 It has been known ever since the work of Pfliiger in 

 1881-1882 that sex ratios in young frogs are peculiar, and 

 that, at the time of metamorphosis of the tadpole into 



