No. 578] DROSOPHILA AMPELOPHILA 111 



B. Hed $ (Productivity 22 Per Day) X Pink <? (Prod. 20 Per 



If the proportion of red to pink, realized in the F 2 , 

 depends npon the relative fertility of the two parents 

 which form the cross, we should get in this case, where 

 the parents were supposedly equally fertile, the ideal 3 : 1 

 ratio. The records, however, show considerable fluctua- 

 tions. Nevertheless, these results are perfectly in accord 

 with our hypothesis. Looking back to Table XII, which 

 furnished the parents of this cross, the explanation is 

 obvious. The averages per day for Al-AW were 20, 16, 

 4, 15, 18 and 3, respectively. Similarly, al-aVl gave 22, 

 0.7, 5, 10, 16, 11 and 17, respectively. It is therefore 

 reasonable to assume that among the offspring of AI 

 (productivity 20) and al (productivity 22) individuals 

 should be found which would repeat the series. Fluctua- 

 tion is, therefore, to be expected. The average of many 

 such pairs, however, should be 3:1. The proportion ob- 

 tained was 2.91: 1 in one case; 3.24: 1 in the other, or a 

 general average of 3.08 : 1. 



It should also be noted here that in this as well as in 

 the subsequent experiments, wherever eight pairs are 

 recorded, they are not the offspring of one, but of two 

 distinct crossings of one pair each which were made at 

 the same time ; that pairs 1-4, 5-8 ; I-IV, V-VIII, respec- 

 tively, were brothers and sisters. More than one line is 

 thus represented in each case. With these facts in mind, 

 we may pass on to the remaining experiments. 



