THE AMERICAN NATURALIST [Vol. XLIX 



bottle. All the offspring were examined with a hand lens but no 

 unusual forms appeared until the fourth or fifth generation when 

 jaunty C was discovered. Subsequently three or four similar 

 mutants were found in the cultures, which would seem to indi- 

 cate that they arose from heterozygous stock. Pure stock was 

 obtained by crossing to the wild flies and "extracting." 



When jaunty C is crossed to the wild type all of the flies of the 

 F x generation have long wings. No exact record was kept but 

 this statement is true of several hundred that were observed. 

 The sex ratio was practically one of equality. In the F 2 genera- 

 tion jaunty C reappeared, as shown in the following tables. 



-Tat 



' C <? 



c 2 



Among the grandchildren from the jaunty C male the ratio is 

 one jaunty C to 4.18 long, while among the grandchildren of the 

 reciprocal cross the ratio is one jaunty C to 4.54 long. The 

 sex ratios were near equality. 



These ratios do not conform very closely to Mendelian ex- 

 pectations, but I have found this species very hard to breed, and 

 since the flies were bred in mass cultures it may be that jaunty C 

 was unfavorably affected by crowding of the larvae. 



I had hoped to carry out more elaborate experiments during 

 the summer of 1914 and had about twenty bottles of the new 

 stock in pure culture and also some wild stocks, when the flies 

 commenced to die during the hot days in the latter part of May 

 and June. Finally the last individual disappeared despite all 

 the care that I could exercise, and no larvae were left in the 

 bottles to take their place. As the June temperature increased 

 other stocks failed to reproduce and died out. That the warm 

 weather was in all probability responsible is shown by the results 

 which were obtained by placing the stocks in a refrigerator. All 

 those stocks placed in the refrigerator remained very active and 

 continued to reproduce while all the stocks left on the outside 

 died out with the exception of the wild stocks of D. ampelophila. 



