BEHAVIOR. 5 



Mixtures of some of these substances in certain proportions are more 

 effective in producing the reaction than are the pure substances. The 

 reaction consists in a definite orientation toward the source of the 

 odor, followed by movement toward it in a fairly direct path. Re- 

 moval of the third antennal joints causes the disappearance of this 

 reaction, so that flies so operated on find their food only by accident, 

 if at all. 



COURTSHIP AND MATING. 



I have described elsewhere (Sturtevant, 1915) the courtship and 

 mating of Drosophila melanogaster and certain experiments on sex 

 recognition and sexual selection. It is my purpose here to compare 

 the mating habits of the different species and then to present an 

 abstract of the experimental evidence. The process occurring in 

 D. melanogaster may be outlined first, in order to describe certain terms 

 to be used in discussing other species. 



Drosophila melanogaster: The first sign of sexual excitement in the 

 male is given "when he extends one wing at a right angle to his body 

 and vibrates it very rapidly for a few seconds. This ''vibration^' is 

 repeated at intervals until copulation occurs, and is done now with 

 one wing, now with the other. Between vibrations there is a partial 

 spreading and closing of the wings, done slowly, which I have called 

 "scissors movement." During both these movements the male faces 

 the female, but he may face any part of her body. He usually swings 

 around her in a semicircle several times, facing her as he moves. This 

 I have called "circling J' He now licks the ovipositor of the female. 

 He bends his abdomen in such a way as to bring his genitalia under- 

 neath his thorax, and jerks them toward the female genital organs. 

 If he is successful in copulating he then mounts on the back of the 

 female, between her wings, and holds on to her thorax, wings, or 

 abdomen with his legs. The pair remains in copula for about 21 

 minutes. The following times have been observed: 1, 5, 16, 17, 17, 

 18, 18, 19, 20, 20, 21, 21, 21, 21, 22, 22, 23, 24, 24, 25, 26, 27, 29, 33, 

 35 minutes. 



Drosophila affinis: Vibration (both wings at once), scissors move- 

 ment, circling^ male genitalia brought up underneath, as in D. melano- 

 gaster. As a rule, however, there is not much preliminary to copula- 

 tion. The same pair was observed to mate twice in 10 minutes. 

 In copula 2, 3 minutes. 



Drosophila busckii: Vibration, scissors movement, circling, licking, 

 male genitalia go up underneath. The male has difficulty in getting 

 his head between the wings of the female, and sometimes fails to do so. 

 His front legs rest on her abdomen. His position is always farther 

 back than that of D. 7nela7iog aster. In copula 2, 2, 2, 3, 3 minutes. 



Drosophila cardini: Scissors movement, circling, licking; no vibra- 

 tion seen. In copula 11 minutes. Two pairs seen mated for 23 and 



