118 



4. LENtiTii OF Like and Pkoductivity. 



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

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

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

 meet prematiu'e death, there would be a correlation between the length of 

 life and the number of offspring 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 incomi)atibility exists between egg and sperm. 



In the following curves, F, G, II, I. evidence is )»rougbt to'^etbcr that 

 shows the productivity of the F. Truncates. (J. The Inbred. II. The 

 Hybrid that results t'nnw crossing V anil (J: and 1. Tlie F^ generation that 

 results Troll 1 crossing F and (J. 



In these curves vertical distances express the number of ]>airs, while 

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

 Curve II, which givi's tbc iiroductivily ol the hylniils wlicii tbc indixiduals 

 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 tliiiMy d;iys. ("urve I express'.; the outpnt of the F. gen- 

 eration. It is evident that the low i^roduction of the Truncates reap- 

 pears among the grandchildren. 



This evidence goes to show that the coniiilex upon which i»roductivity 

 depends is inherited in the sense that low productivity ski))s a generation 

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

 hybrid fly is greater than the prodnctivity of liotli jiarents comliincd. I 

 have demonstrated in previous studies that the increased pi'oductivity on 

 the part of the hy))rid is not due in this case to the; increased fertilizing 

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

 due to a greatly iau-i-eased output of eggs. 



As a matter of fact tli(> fertilizing power of tlii' gametes of the hylirid 

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

 producing parent. It is evident that the low productivity of the Trun- 

 cate reappears in the I\ generation and that this holds true in both 

 the cross and its reciprocal. 



