370 



t>4't 



^1.9 



73.8 



ROSCOE R. HYDE 



10.7 



Diagrams I, J and K Showing the effects on fertility of crossing within and 

 without the inconstant truncate stock. T= truncate. L = long-wing thrown 

 by truncates. \VH = Woods Hole. 



Diagram I Crosses between truncates and their long-winged brothers and 

 sisters. 



Diagram J 



Diagram K 



Crosses between truncates and the Woods Hole stock. 



Crosses between the long-winged flies thrown by the truncates and 



the Woods Hole stock. 



good sperm and yet only 31.3 of the eggs from the truncate females 

 hatched when mated to the truncate males (diagram J). 



It remains to be pointed out that a certain degree of incompati- 

 bility exists in the cross made between the truncate male and his 

 long-winged sister. For their fertility when tested together is 

 47.1 and yet he is producing 88.5 fertile sperm and she is producing 

 73.8 fertile eggs as shown by outbreeding into the Woods Hole 

 stock. In the cross between the truncate female and the long- 

 winged male the incompatibility seems to be removed. For while 

 the long-winged male is producing 90.7 fertile sperm the female is 

 producing only 54 per cent of fertile eggs. Here, as I have 



