192 ROSCOE R. HYDE 



the experiments that only relatively few eggs were giving rise to 

 mature flies. I wished to test the conclusion further and also 

 determine whether or not some factor for egg production was 

 operating, as well as to make the cross between the truncate male 

 and the Woods Hole female which combination was not made in 

 the previous experiment. 



Experiment V. This experiment was carried out in the same manner 

 as the former one. The flies were mated as soon as they emerged and 

 the output of eggs recorded from each female each day during her hfe. 

 The facts in detail are recorded in table 15. 



The results of this experiment are expressed in diagram D. 



Truncate 

 ^1 ? 



t • Tio. egqs isolated 

 h-Tlo. ecjqs hatched- 



Diagram D Effect on fertility of crossing truncate and Woods Hole stocks; 

 from table 16. 



This evidence taken with all the other evidence presented shows 

 conclusively that there is incompatibility between the egg and 

 sperm of the truncates since only one egg in every four or five 

 gives rise to adult flies. It is surprising to find that the truncate 

 male should have actually fertilized more eggs of the female of 

 the Woods Hole stock than a male from its own stock could ferti- 

 lize, and yet a male from the Woods Hole stock can fertilize 

 almost as many eggs of the truncate female as he can fertilize 

 with a female of his own race. If the results given in diagram 

 D are compared with those obtained in Experiment I as expressed 

 in diagram A; it will be found that the results are in general agree- 

 ment. 



Experiment VI. Reference to table 2, where the history of the inbred 

 stock is given, vnW show that the fertility has steadily declined on 

 inbreeding, despite the fact that sterile females had increased to 50 

 per cent and again eliminated. It occurred to me that something like 

 incompatibility between egg and sperm might be operating in this stock 



