118 HEREDITY AND SEX 



wing, then the other, and shows other signs of excite- 

 ment. The male has sex combs on his fore legs, the 

 female lacks them. Lutz cut them off and gave the 

 female a choice between such a male and a normal 

 male. One was chosen as often as the other. The 

 wings of the male and female are wonderfully irides- 

 cent. Sturtevant cut off the wings of a male and 

 matched him against a normal male. The female 

 showed no marked preference. The converse experi- 

 ment, when a clipped female competed with a normal 

 female, showed no selection on the part of the males. 



If instead of allowing two males (a normal and a 

 clipped) to compete for one female, a female is given to 

 each male separately, and the interval before mating is 

 noted, it is found that on an average this interval is 18 

 minutes for the normal and 40 minutes for the clipped. If 

 any such difference existed in the first case, when the two 

 males were competing, we should expect a much greater 

 selection in favor of the normal male than was actually 

 found. This would seem to mean that the female is 

 more quickly aroused by the normal male, and hence 

 when both males are present she will accept the clipped 

 male more quickly than when he alone is present. This 

 suggests that normal courtship precipitates copulation. 



In the following experiments the female was offered 

 a choice between a new type (mutant) with white eyes 

 and a normal male. Conversely, the white-eyed fe- 

 male had a like alternative. The evidence shows that 

 the more vigorous male the red-eyed male is 

 more successful. 



Since vision itself is here involved, for the white- 

 eyed flies are probably partly blind, the observations 



