KELATING TO SECONDARY SEXUAL CHARACTERS. 61 



wings jerkily, and walks around rapidly, but seems unable to follow the female 

 accurately or to locate her quickly. The penis is directed forward by bending 

 up the abdomen underneath, towards the thorax, and is jerked toward the 

 female (the male always standing facing her at this stage), but not always 

 toward her genitalia, as I have seen it strike her in the eye. (The male in 

 this case, however, had white eyes, and so was perhaps blind. Normally the 

 aim is accurate.) If it does strike the mark the male mounts on the female's 

 back, between her wings. Mounting never takes place until after the actual 

 copulation has occurred, in which respect Drosophila differs from some related 

 flies (e. g., Muscidse, Anthomyidse, Sepsidse, Borboridae, and Ephydridse, so far 

 as my observations go) . In these forms the male flies and lights on the female, 

 after which copulation may or may not take place, probably depending upon 

 the way the female responds." l 



To test whether the wings have any significance in courtship, the 

 wings of a male were clipped off and he was put into competition with 

 a normal male of the same stock, age, and size. A virgin female 

 sexually mature was given to these two males. The normal male 

 mated 72 times before the other, the clipped male 53 times. It might 

 appear that the female selected the normal male in preference to the 

 clipped one, or possibly that the male with normal wings drove the 

 other male away. That the operation on the wings may have an 

 influence on the male himself is shown in McEwen's results. He found 

 that clipped males lost their heliotropism. It was also possible that 

 the courtship of the normal male might make the female ready to 

 copulate and then she would mate with either male. Sturtevant 

 tested the last supposition by placing single pairs in vials, testing each 

 day an equal number of normal and clipped males. The length of 

 time before copulation was noted. The clipped male began to court 

 as soon as the normal, but a larger number of normal males mated in 

 the first 12 minutes than clipped males (59 to 25). Had the females 

 discriminated against the clipped males to an equal extent we would 

 have expected a much greater excess than 72 to 53 when they were in 

 competition. It appears, then, that the wings are useful in shortening 

 the time between the meeting of the individuals and copulation. The 

 display acts, however, almost as favorably for the other male as for 

 the exhibitor himself. The results show, therefore, that here an esthetic 

 sense of the female need not be postulated, for she actually shows little 

 preference when she has been brought to the point of mating between 

 the male that aroused her and the other male that did not. This 

 critical test puts the problem in a different relation from that which 

 Darwin's theory of female choice was meant to throw light upon. 



The reverse experiment a clipped and a normal female of the same 

 age, size, etc. showed that the male did not discriminate between 

 them, for in 52 first trials the normal female was paired with 25 times, 

 the clipped 27 times. 



1 A. H. Sturtevant. Experiments on Sex Recognition and the Problem of Sexual Selection in 

 Drosophila. Journ. Animal Behavior, Sept.-Oct. 1915, vol. 5, No. 5, pp. 352, 353. 



