PROBLEM OF SEXUAL SELECTION IN DROSOPHILA 361 



and by the following observations. In some of the experiments 

 recorded in table II the number of minutes before courtship 

 began was observed. Table III indicates that the clipped males 

 began courting as quickly as did the normals. 



TABLE III 



Minutes before 

 Courtship Normal Clipped 



1-2 12 9 



3-4 2 3 



5-6 1 2 



7-8 1 2 



9-10 1 



11-12 1 



• 13 and over 7 7 



From these experiments it seems certain that the wings are 

 of value in courtship; but the effect probably is to produce 

 sexual excitement in the female, rather than to cause her to 

 select a male that uses his wings. No " choice " is involved; 

 but, as pointed out by Watson ('14, p. 173), the effect, in nature, 

 would be strongly in favor of the normal male. 



It seems probable that touch is of considerable importance 

 in the sexual process, and all my observations are consistent 

 with that view, but I have no direct experimental evidence to 

 that effect. It is not possible to get evidence from Drosophila 

 such as Kellogg obtained from Bombyx, because the flies are 

 more active, and less easily sexually excited, than is the silk- 

 worm moth. 



Two kinds of experiments have been carried out in an effort 

 to find out what part of the body is responsible for causing 

 sexual excitement. A female without an abdomen, but alive 

 and active, was placed with males that had been isolated from 

 other females for four days. She was vigorously courted. 



Three gynandromorphs have been tested to determine their 

 sexual behavior. None showed any certain indications of male 

 behavior, but all were vigorously courted by males. Of these 

 three gynandromorphs the external characters were as follows: 



(A) All female, except one side of the head, which was male; 



(B) female on one side of the whole body, male on the other 

 side; (C) female, except the genitalia, which were male. It is 

 doubtful what conclusion, if any, is to be drawn from these 

 few observations. 



