THE EFFECT OF SEXUAL SELECTION. 37 



I cut them off of a plain-winged male and left them on a male of the 

 extra- veined race and vice versa. These two males were then given to 

 a female as mates. By a study of her offspring I could tell, in a rough 

 way, which mate she preferred. To my surprise she chose almost exclu- 

 sively the normal male, whether he had tibial adornments or not. 



Then, without removing the tibial combs, I gave plain-winged and 

 extra-veined individuals the choice between mates which, as far as I 

 could determine, were alike in all particulars such as age, nutrition, 

 activity, and time since last copulation, but differed in that one had 

 extra veins while the other had not. I watched each experiment until 

 copulation had taken place. When the extra venation in one mate was 

 great, the chooser, whether male or female, normal or extra-veined, 

 chose the normal mate. I then tried weaker degrees of the character and 

 in 85 experiments, mostly with flies having the extra veins only very 

 slightly developed, 61 of the choices were in favor of the wild type. 



The basis upon which these flies discriminate against extra-veined 

 individuals when choosing a mate is a matter for further study. There 

 is an elaborate "courtship," in which the flirting of the wings in front 

 of the prospective mate plays a large part. It seems as though a choice 

 were made on the basis of sight, but I doubt whether that is the case. 

 However, there is no doubt of the choice. It is a clear case of the 

 undoing of artificial selection by sexual selection. 



