I'UMACE FLIE8 235 



testing of the manner of inheritance have been energetically carried on 

 during the past few years and have yielded many interesting results. 

 Other factors of evolution, such as the effect of environment, the laws of 

 fluctuating variation, and selection, have also been studied quantita- 

 tively and experimentally, although to a less extent. 



In these experiments it is important to know the characters of both 

 the ancestors of the individuals used and of their progeny. Pedigreed 

 cultures must be made. Therefore, it is desirable to use some rapidly 

 breeding form which can l)e easily reared. Domestic animals and in- 

 sects have been favorite zoological material, and among the latter the 

 common red-eyed Pomace Fly (DrosophUa ampelophila), also known 

 as the Vinegar Fly, Sour Fly and Fruit Fly, has been found to be an 

 excellent laboratory creature. It feeds upon fermenting vegetable mat- 

 ter. At ordinary room temperature a generation can be obtained every 

 two weeks. The eggs are laid directly upon the food (e. g. ripe banana) 



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Fig. 1. 



FIG. I. FORE LEG OF A MALE POMACE FLY. DROSOPHILA AMPELOPHILA. 



and hatch in two or three days into legless larvte, or maggots, which 

 pupate after about a week of feeding. The pupal period is four or 

 five days long, and in a trifle over twenty-four hours after emergence 

 from the pupal case the adults mate and a new generation is started. 

 The adults live, on the average, three weeks or a month and the female 

 may lay as many as three hundred eggs. 



The males differ from the females very strikingly in the adult stage. 

 They are somewhat smaller and the under side of the abdomen is more 

 completely pigmented. The most interesting difference, however, is 

 the possession by the males of a relatively large coml)-like structure, 

 upon the anterior legs (see Fig. 1). This is a secondary .sexual character 

 that is as pronounced as the antlers of deer. It would be explained by 

 many, since no other function is apparent, as a male adornment which 

 is pleasing to the female. However, I have found that the males from 

 which the ".sex combs" have been removed are just as succes.sful in 



