138 Journal New York Entomological Society. tVoi. xxii. 



accompanied by degeneration of external parts even when accom- 

 panied by disuse.^ 



The normal length of adult life, like all similar characters, is 

 largely dependent upon environment. !Moenkhaus states that they 

 kept females alive for 153 days but does not say what the conditions 

 were. Among 267 females which I kept well supplied with food at 

 room temperatures but isolated from males, only one lived to be 80 

 days old. The average age at death was 26.4 days. The longest 

 lived, unmated male under the same conditions died in 90 days, the 

 average being 32.8 days. 



Another series of unmated flies (116 males and 124 females) 

 were kept at a relatively constant temparature of 20° C. and furnished 

 water but no food. Three females and one male lived 96 hours. The 

 average age at death was 68.6 hours for the females and 66.4 for the 

 males. In another series in which the conditions were the same 

 except that the temperature was five degrees higher, the females with- 

 stood starvation for only 60.7 hours, on the average, and the males 

 55.6 hours. In still another series the temperature was 20° C. but. 

 in addition to withholding food, no water was supplied except that 

 evaporating from their own bodies. The average females lived 56 

 hours and the average males 53.5 hours. It is difficult to say why 

 the females can withstand starvation better than the males but have 

 a shorter natural life, at least when unmated. 



The materials which kept these starved individuals alive were all 

 laid up by the feeding larv?e for no food was supplied after the 

 fly emerged and, of course, the pupse did not feed. I was surprised, 

 therefore, to find that those which were better able to withstand 

 starvation in the adult stage had had a shorter larval period, and fed 

 for a shorter time, than the others. The data for this are still being 

 worked up and will be published later but the explanation probably 

 is that the physiologically strong larvae were able to complete their 

 larval history quickly and gave rise to physiologically strong adults. 



1 Lutz, F. E., 191 1, "Experiments with Drosopliila ampelopliila Concerning 

 Evolution," Carnegie Institution of Washington, Publication No. 143. 



