No. 576] VARIATION IN DROSOPIIILA 753 



On the other hand, selection for less extreme Beading 

 is also rapidly effective and normal-winged forms appear 

 soon, but this effect soon reaches its limit apparently, 

 and a normal strain or even a strain throwing a high 

 percentage of normals has not yet been obtained. I am 

 not yet certain that it can not be done. I selected in each 

 direction for eleven generations without marked success 

 beyond that here recorded. 



V. MUTATION IN BEADED STOCK 



A. General Statement 



As will be gathered from statements made in the last 

 section, the Beaded stock has been prolific in giving muta- 

 tions. There has been no especial attempt made to see 

 how many different mutants could be obtained from the 

 stock, and yet a goodly number have appeared. Most of 

 these have been marked types showing little variation and 

 coming out regularly and distinctly in Mendelian propor- 

 tions in crosses with other types. They have in general 

 bred true from the start without further selection. 



A few of these have been of a sort to confuse for a time 

 the study that I have been making, because of their re- 

 semblance to certain types of Beaded flies. The criterion 

 in every case as to whether or not a fly was an ordinary 

 Beaded fly or a new "mutant" was its genetic behavior, 

 and the cases to be here described have, with the excep- 

 tion of Stumpy, shown themselves to be due to a single 

 gene conforming in general to those of other well-known 

 mutants of Drosophila. 



B. Perfect Notched Wings 

 In the beginning of my work on Beaded wings I thought 

 it might be possible to isolate definite types from the 

 Beaded stock by crossing out to Wild and extracting the 

 F 2 types that appeared ; or by back-crossing the F, forms 

 to Wild again and extracting new types, etc. Several 

 thousand flies were raised in the hope of accomplishing 

 this, but the "types" found did not breed true, but con- 

 tinued to behave like ordinary Beaded flies, from whose 



