214 



HEREDITY AND SEX 



taken in connection with another (or others) gives high 

 productivity. 



The other point to which I wish to call attention 

 relates to a different matter. We have met with some 

 cases where lowered fertility was due to eggs failing 



Fig. 103. — Normal mule of Drosophila (on Left) and male with "rudi- 

 mentary" wings (on right). Note sex comb (lower left). 



to a greater or less degree to be fertilized by sperm of 

 the same strain. 



A striking case of this kind is found in a mutant of 

 the fruit fly that appeared in my cultures. The mu- 

 tant has rudimentary wings (Fig. 103). The females 

 are absolutely infertile with males of the same kind. 



