No. 575] 



AN APTEROUS DROSOPHILA 



681 



It will be noted that the apterous classes fall a little 

 below the expected numbers in most cases. This is char- 

 acteristic of all weak races of Drosophila, and is doubtless 

 due to the inability of some flies to mature. Of the winged 

 classes the first two and the fifth exceed the Mendelian 

 ratios, while the other two fall short, due to linkage be- 

 tween white, vermilion and miniature. 5 The distribution 

 of apterous, however, is entirely independent of the 

 others, showing that the factor responsible for it is not a 

 member of the group containing those responsible for 

 vermilion eyes, white eyes, or miniature win--. 



The ratio of winged to apterous in this particular cul- 

 ture is 4.2:1. Table III includes a summary of this and 

 nineteen similar cultures in which the parents were all 

 descendants of the long-winged, vermilion-eyed female by 

 the apterous male mentioned above. The first nine are 

 mass cultures, the next two are pairs, from F t flies. Below 

 these are offspring from nine pairs of F 2 flies. 



It is noticeable that the ratio of apterous to winged is 

 greater in cultures where pairs are used than in mass cul- 

 tures, though all parents in the latter are heterozygous. 

 This, I believe, is unquestionably due to the low viability 

 of the apterous flies, which prevents some of them from 

 maturing in cultures where the competition is severe. For 

 this reason the averages are given separately for pairs 

 and for mass cultures. The average from pairs is 4.06: 1, 

 while that from mass cultures is 5.5 : 1. This low viability 

 is. also shown by pairs, if the food conditions are not good, 

 or if the culture becomes very dry. 



Experiment I II. — To determine the relation between 

 apterous and characters in Group III. 



It is obvious from Experiments I and II that apterous 

 is not a sex-linked character (Group I). The present ex- 

 periment is for the purpose of determining its relation to 

 characters of Group III. As a representative of the latter 

 group pink eye color was chosen. The results of the cross 

 between this and apterous may be passed over briefly 



