752 



THE AMEBIC AN NATURALIST [Vol. XLVIII 



So soon that I did not realize it, nor think to connt the 

 generations, I had one stock that gave offspring much 

 more extremely Beaded than the ordinary stock, and this 

 stock is the one on which most of this report is based. 

 About December, 1912, 1 started one stock bottle to form 

 the basis for a "No selection" test. The parents of this 

 brood were "pure stock Beaded" males and females. 

 The first generation, no normal-winged flies appeared. 

 The generations following were made up by shaking at 

 random from the bottle of the generation before a dozen 

 or two 'flies into a new bottle. 



The second, third and fourth generations gave three 

 normal-winged flies to 325 Beaded. The sixth, 3 normal 

 to 100 Beaded. In later generations I occasionally found 

 normal flies. The stock is in its 27th generation now, 

 the 25th generation having given rise to a large brood 

 of which I counted 541 flies (284 ? and 257 all of 

 which had Beaded wings of a type averaging like those of 

 Figs. 4-6. It is very apparent that the stock is not under- 

 going any marked change, though I can not guarantee 

 that it would give exactly the same results in other 

 respects as the extreme (selected) Beaded stock that I 

 have used in the linkage tests. 



On the other hand, I have not been able thus far to 

 increase the Bea^edness of the selected stock beyond a 

 point which it apparently reached many generations ago. 

 The Figs. 1-12 (excepting 2 and 4), which are here re- 

 produced, were made under Dr. Morgan's direction long 

 before I took up the work, and the forms he had drawn 

 then are as extreme as any that I now have. 



If this extreme stock be allowed to go without selection 

 for two or three generations, it "reverts" to a less ex- 

 treme form, from which it can apparently be recovered 

 by one mass selection. I feel confident that in selecting 

 the extreme forms one merely selects a large percentage 

 of individuals that are heterozygous for 1, and of course 

 when the stock is not selected for a while, LL forms be- 

 come relatively more numerous. This would account for 

 all the facts here recorded. 



