372 ROSCOE R. HYDE 



pointed out, the incompatibility is removed and we have a 

 distinct rise in fertihty. 



This evidence would seem to indicate that a marked difference 

 in respect to fertility may exist between brothers and sisters 

 of the same stock. In this case we find a great degree of incom- 

 patibility between the flies with a definite wing form — long- wings; 

 the greatest degree of incompatibility between flies with truncate 

 wings. We also find a marked degree of incompatibility when the 

 truncate male is crossed to his long-winged sister but no incom- 

 patibility in the reciprocal cross. 



