No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 



8. A culture that was giving F, normal females (that 

 were heterozygous for abnormal) was made extremely 

 wet ; into a sort of swamp. The flies that emerged dur- 

 ing the next six days were normal, on the seventh day 

 the flies were slightly to fairly abnormal, on the eighth 

 and ninth clays the flies that emerged were slightly to 

 quite abnormal. It is evident that the influence of the 

 wet conditions does not appear unless the flies are sub- 

 jected to it throughout most of the larval life, or else that 

 tlie first few days of larval life is the critical period. 



9. Larva 1 that were about ready to pupate were trans- 

 ferred to very wet new food, where they pupated, in 

 from 12 to 24 hours. The pupse remained in the same 

 bottles until the flies emerged. These flies were entirely 

 normal in appearance; the stock from which the larvae 

 came were also giving rise to normal flies. The sojourn 

 of one or two or even three days in a wet environment 

 at the end of the larval life does not suffice to alter the 

 effects that have already been induced in an earlier stage. 



Conclusions.— The preceding evidence makes clear 

 that the amount of water in the food, determines the 

 realization of the "abnormal" type. The water may 

 produce its effect either by being taken in with the food, 

 or by being directly absorbed; or it may determine the 

 nature of the bacterial or yeast flora that in turn deter- 

 mines the nature of the fermentative changes that take 

 place within or without the larva?. It would be a very 

 difficult matter to find out in which one of these ways the 

 effects are brought about. However this may be, it is 

 possible for the experimenter to determine at will the 

 nature of the flies that will be produced in his cultures 

 by controlling the food supply. 



Owing to the overlapping of the abnormal and normal 

 types, the study of the linkage has presented unusual 

 difficulties. The following experiments were made for 

 the most part during the second year when the influence 



