FERTILITY AND STERILITY IN DROSOPHILA 179 



crosses averaged even better than the high producing strain. 

 Both were mutually benefitted by the cross, but it may seem that 

 the production of the truncate female was limited because she 

 lives on the average about half as long as the inbred female. The 

 truncate male lives on the average about ten days longer, — long 

 enough apparentlj^ to fertilize all the eggs of the inbred female. 

 It should be stated that I have verified Castle 's observation many 

 times that more than one copulation is necessary to fertilize all of 

 the output of eggs from a female. It seems that the male lives 

 on the average long enough to fertilize this second output of eggs. 



It is evident that the short life of the truncate female does not 

 explain entirely her low production, for if the results of this experi- 

 ment may be relied upon, there was evidently incompatibility of 

 some sort between the egg and sperm in this strain. 



The results of this experiment were very surprising in the light 

 of Castle's work. Castle had made crosses between a low-pro- 

 ducing strain and a high-producing strain with the result: ^'that 

 low productiveness (or sterility) of the female may be transmitted 

 directly through the egg from mother to daughter, but only indi- 

 rectly through the sperm, the character skipping a generation." 

 Castle's conclusion in regard to this case lends support to the 

 assumption which I made in Part I, viz., that he did not dis- 

 tinguish between complete sterility of the female and the low fer- 

 tility that is here shown. 



The problem of the increased fertility of the truncate stock 

 when crossed into a high producing strain was now. put to another 

 test. The experiment was carried out in the same way as the 

 previous one except that the Woods Hole stock was used for the 

 high-producing strain, as it had been observed in other experi- 

 ments to give rise to a rather large number of offspiing. Tables 

 6, 7 and 8 give the result of this experiment. 



At first sight this experiment is not as striking an experiment as 

 Experiment I. Neither cross did as well as would be expected 

 from the controls. Nevertheless, the same relation is evident, for 

 while the truncate female produced an average of 56 offspring by 

 her own male, she produced on an average of 118 by the Woods 

 Hole male. It is to be noted, moreover, that her length of life on 



