62 



E. CARLETON MACDOWELL 



All matings described below were made in pairs. The vir- 

 ginity of the females mated was determined by the pale pig- 

 mentation which deepens when the cuticula hardens a few hours 

 after hatching. Accurate pedigrees and daily records of the 

 sex and bristle number of each fly observed are on file. The 

 results presented in this paper are based on 350 pedigreed 

 matings and bristle counts of over 54,000 flies. 



Grateful acknowledgment must be made of the assistance 

 rendered by Prof. T. H. Morgan in suggesting that the extra 

 bristles found at times among his flies might form suitable 

 material for the problem the author had in mind, and also in 

 supplying numerous stocks of flies for observing the frequency 

 of the occurrence of the extra bristles. 



4 



^ M — 



5 



Fig. ] Random bristle patterns showing some of the arrangements possible 

 for the most common numbers of extra bristles. The numbers indicate the 

 numbers of extra bristles in the patterns following. 



THE ESTABLISHMENT OF THE RACE WITH EXTRA BRISTLES 



The flies which gave rise to a race of Drosophila ampelophila 

 having extra bristles on the thorax were found in a stock of wild 

 flies that had been caught at Woods Hole in 1912 and bred in 

 mass cultures for a year in Professor Morgan's laboratory. 

 This stock had never been mixed by crossing, and in working 



