362 A. H. STURTEVANT 



SEXUAL SELECTION— ARTIFICIAL ABNORMALITIES 



The male of Drosophila ampelophila bears a small comb on 

 his front metatarsi, a secondary sexual character not found in 

 most species of the genus. 7 Lutz ('11) has shown that the 

 removal ' of this comb has no effect upon the availability of 

 males for copulation. That is, the females were not influenced 

 by the sex-comb in their choice of mates. 



It sometimes seems to be difficult for the male to get the 

 wings of the female out of his way so that he can mount her. 

 For this reason I carried out an experiment the converse of 

 one recorded above; using two virgin females of the same age, 

 one with normal wings, the other with wings removed. These 

 were put with a normal male. In 52 successful trials the normal 

 female was paired with 25 times, the clipped one 27. Again it 

 would seem as though clipping the wings has very little if 

 any effect. 



SEXUAL SELECTION— MUTANTS 



Lutz ('11) found that certain slight abnormalities in wing 

 venation were selected against both 'by normal and abnormal 

 flies of both sexes. The abnormal flies were not noticeably 

 different from the normals in behavior, so that it seems quite 

 unlikely that the results were due to a difference in the activity 

 of the two types. Moreover, if, let us say, the normal male 

 was more active than the abnormal, so that he would be more 

 likely to pair first, it would seem that the normal female would 

 not be so easily paired with as the abnormal; or vice versa, if 

 we suppose the abnormal female to be less active and therefore 

 more likely to be paired with, it is hard to see why the abnormal 

 male should be at a disadvantage. Further evidence bearing 

 out this view of the effect of differences in activity will be given 

 below. Lutz suggested that it seems unlikely that sight could 

 have any influence, and that perhaps there is some unpleasant 

 smell correlated with the abnormality, this being the basis of 

 selection. 



I have conducted a series of experiments upon some of Mor- 

 gan's Drosophila mutants, in an effort to find if there was any 

 selective mating in connection with them. The following 

 mutants were used: 



7 So far as my observation goes it is present only in D. ampelophila, D. confusa^ 

 D. obscura, and three or four undescribed species. 



