No. 57G] VARIATION IN DROSOPHILA 



731 



genes are in the second chromosome are still perplexing; 

 for while the second chromosome exerts an influence on 

 the statistical results, as will be evident from the figures 

 to be presented, the nature of this influence is not fully 

 determined. 



The second chromosome characters with which tests 

 have been made are the wing characters, Arc, Curved, 

 Vestigial, Antlered, and Strap, 1 the body color, Black; 

 and the eye color, Purple. 



Vestigial, Antlered, and Strap stand for wing char- 

 acters of such a nature that it is not possible to distin- 

 guish Beaded- winged individuals if any of these other 

 characters are also present. They are therefore of no 

 use for determining whether or not there is a second 

 chromosome gene for Beaded wings. The crosses be- 

 tween Beaded flies and flies with these characters do not 

 especially interest us here. It may be said in passing, 

 however, that in every case in the F, generation between 

 these flies and Beaded flies, from 60 to 90 per cent, of the 

 offspring had non-normal wings, and the author was put 

 to serious straits to classify the new wing types that 

 appeared. These were similar in all the crosses, however, 

 and on the whole resembled Beaded wings. 



In the F 2 generation, and in back crosses to Beaded 

 Stock and to Vestigial Stock further complications arose 



tion" which bred true from the start, and which will be 

 discussed briefly and described under the name ' 1 Spread" 

 in the section that concerns mutation. 



We may now return to the crosses between Beaded flies 

 and Black, or Purple, or Arc, or Curved. These crosses 

 give results that can be used for the study of linkage, 

 and they present in common a number of distinguishing 



