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 
afemale as mates. By astudy 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 seemsas thougha 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 isa clear case of the 
undoing of artificial selection by sexual selection. 
