FERTILITY AND STERILITY IN DROSOPHILA 363 



In table 5 I have added as a matter of record the number of 

 long-wings and short-wings that appeared in a number of bottles 

 from which complete counts were made. No definite ratios can 

 be given for comparison with the study of wing ratios made in 

 Part II, where it was shown that the truncates threw 1 long to 

 7 ± truncates, the longs in turn threw 1 truncate to 7 ± longs. 

 The ratio of the longs to the truncates in the crosses made here is 

 near equality. 



The foregoing experiments bear on the effects on fertility when 

 the extracted truncates are back-crossed with their low-producing 

 grandparents. I wish next to consider the effects on fertility 

 when the extracted truncates are back-crossed with their high- 

 producing grandparents — the Woods Hole stock. The experiment 

 was carried out in the usual way. The results are given in table 6. 



The relations brought out in this experiment are expressed in 

 diagrams C, D, and E. 



Diagrams A and B show the result on fertility of back-crossing 

 the extracted truncates with the low-producing grandparental 

 truncates. It is to be noted first of all that the controls show the 

 fertility of the extracted truncates to be practically twice that of 

 the original truncates. Moreover, the fertility of the extracted 

 truncates is the same whether the truncate male or female is used 

 as the grandparent. On crossin'g, there is no great rise in fertility 

 beyond that shown by the parents, as has been demonstrated in the 

 case of the truncates crossed to wild races. The extracted trun- 

 cate female is able to bring the fertility of the truncate male up to 

 its level but not beyond. The extracted truncate male, on the 

 other hand, does not bring the fertility of the truncate female up 

 to its level by about 15 per cent. It is to be noted that the fertility 

 shown in diagram A is practically the same as in diagram B, indi- 

 cating that here the effect is the same on the truncate grandchil- 

 dren, whether descended from the truncate male or truncate- 

 female. 



In contrast with the conditions found in these crosses, we find, 

 that when the extracted truncates are back-crossed to the high- 

 producing parents there is a sudden and distinct rise in fertility; 

 beyond that of either parent stock (diagrams C and D). The 



