June, 1914] LuTz: Drosophila Ampelophila. 137 



However, acetic acid or fruit odors will overcome this reaction and 

 they will go into dark places to get at their food. Payne^ has found 

 that even after these flies had been reared in darkness for sixty-nine 

 generations they still reacted to light with nearly normal vigor. The 

 reaction is slow among newly emerged flies but soon becomes more 

 rapid, reaching a maximum in about eighteen hours, and then very 

 gradually sinks as the flies age. My experience also indicates that 

 the females react about twice as quickly and definitely as the males. 

 Moenkhaus, on the other hand, found the males to be slightly more 

 responsive than the females. Possibly the fact that the tube in his 

 apparatus was inclined at an angle of twenty-five degrees explains the 

 difference since it introduces the reaction against gravity. 



Both males and females become sexually active the second day 

 after emerging. There is usually a sort of courtship dance before 

 mating in which the male or males go frdm side to side and around 

 the female, flitting their wings and attempting to crawl on her back. 

 Unless the female be an old one which has not recently mated this 

 courting is usually kept up for from several minutes to an hour or 

 more, the female preventing mating by curling the tip of her abdomen 

 downwards and keeping her wings together. The duration of actual 

 copulation is also variable. It averages about half an hour but may 

 continue for an hour and a half. A vigorous male will mate re- 

 peatedly during a single day and occasionally the same is true of the 

 females. It seems to be necessary for the female to mate several 

 times during a normal life or the late developed eggs will not be 

 fertile. 



Apparently inbreeding is not detrimental. Castle and his co- 

 workers- have found that, if it does reduce productiveness, fertility 

 may be maintained nevertheless by selection. Sterility is not rare in 

 wild material. Thus among twenty-five random matings of wild 

 flies I found two to be sterile. Neither does inbreeding seem to be 



1 Payne, F., 191 1, "Drosophila ampelophila Loew Bred in the Dark for 

 Sixty-nine Generations," Biological Bulletin, XXI, pp. 297—301. 



2 Castle, W. E., Carpenter, F. W., Clark, A. H., Mast, S. O., and Barrows, 

 W. M., 1906, "The Effects of Inbreeding, Cross-breeding and Selection upon 

 the fertility and variability of Drosophila," Proc. Amer. Acad, of Arts and 

 Sciences, XLI, pp. 731-786. 



