182 ROSCOE R. HYDE 



24J 



Diagram B Effect on productivity of crossing truncate and Woods Hole 

 stocks; summary from tables 6, 7 and 8. 



production of the truncates. To judge from the history of these 

 strains and from Experiments I and II it would seem as though 

 only one egg in four or five of the truncates gave rise to a mature 

 fly when fertilized by its own sperm. I shall not analyze the data 

 further here as I shall later bring forward better evidence that 

 bears on this relation. 



FERTILITY OF THE Fi AND F2 GENERATIONS FROM THE CROSSES 

 BETWEEN THE LOW-PRODUCING TRUNCATES AND THE HIGH- 

 PRODUCING WILD STOCKS AS DETERMINED BY BREED- 

 ING THE ANIMALS TOGETHER IN PAIRS 



We may next consider the evidence that bears on the behavior 

 of the hybrids in the Fi and F2 generations. In order to deter- 

 mine the productivity of the hybrids from the cross between the 

 truncate female and the inbred male, 65 pairs of the Fi brothers 

 and sisters were made up from the crosses as given in table 3a. 

 From the reciprocal cross 47 pairs of the Fi brothers and sisters 

 were paired. The different families were about equally repre- 

 sented. Both Fi hybrids proved to be most virile animals and 

 excellent producers. In the thirty days from December 22, 



1911, when they were first paired as virgin flies, to January 22, 



1912, when the experiment was discontinued due to an accident 

 the sixty-five pairs produced a total of 16096, an average of 248 

 offspring to the pair, and the 47 pairs of reciprocals produced a 

 total of 11800, an average of 251 offspring to the pair. The differ- 

 ent classes that appeared are given in table 9. 



The experiment shows that the hybrids are excellent producers 

 and that it makes no difference whether the father or the mother 

 was of the low-producing truncate stock. Moreover, it seems as 



