118 



4. Length of Life and Prodi ctivity. 



I shall here analyze the data with respect to the productivity of these 

 stocks as determined by breeding in pairs. It is oljvious that if a female 

 that would give rise to a large number of offspring should for some reason 

 meet premature death, there would be a correlation between the length of 

 life and the number of offspi'ing produced. The problem, however, is more 

 complicated. In the case of the Truncates it is not evident just how much 

 such a factor as the shortened length of life enters into the results, for I 

 have been able to show that this stock is deficient not only in egg produc- 

 tion, but also that marked ineonipatil)ility exists between egg and sperm. 



Li the following curves. F. (i. II, 1. evidence is brought together that 

 shows the productivity of the F. Truncates. G. The Inbred. H. The 

 Hybrid that results from crossing F and (i ; and I. The F^ generation that 

 results from crossing F and (i. 



In these curves vertical distances express the number of pairs, while 

 horizontal distances express the number of offspring produced. A glance at 

 Curve H, which gives tlio productivity of the liyl)rids \\l;cn the individuals 

 expressed by curves F and (J are crossed, moves decidedly to the right. 

 This is evident despite the fact that the experiment was discontinued at 

 the end of thirty days. Curve I exjiresss tlie output of the F^; gen- 

 eration. It is evident that tlie low production of the Truncates reap- 

 pears among the grandchildren. 



This evidence goes to show that the complex upon which i)roductivity 

 depends is inherited in the sense that low productivity skips a generation 

 when cros.sed into a high producing strain. In fact the productivity of the 

 hybrid fly is greater than the productivity of both parents combined. I 

 have demonstriited in previous studies that the increased productivity on 

 the part of the hybrid is not due in this case to the increased fertilizing 

 power of the gametes beyond that of the highest iiroducing stock, but is 

 due to a greatly uicreased output of eggs. 



As a matter of fact the f(>rtilizing power of the gametes of the hybrid 

 {inter sc) is lower than the fertilizing power of the gametes of the high- 

 producing parent. It is e\ ident tlial the low productivity of the Trini- 

 cate reajipears in the 1"\. general ion and that this holds true in both 

 the cross and its reciprocal. 



