256 



Morris Rockstein 



population's existence the survival curves for both sexes 

 show a logarithmic-like character (in the extremely retarded 

 rate of dying off of this small proportion of long-lived members 

 of the population). In actual fact, for the males about 90 per 

 cent die off during the period of ten to thirty days after 



100 



90 



. 80 



70 



I 60 



a. 



^ 50 



I- 



a 40 



a. 



UJ 



^ 30 

 20 



r\. 



• MALES 

 o FEMALES 



AGE IN DAYS 

 Fig. 2. Survival curves of male and female 

 houseflies. 



Reprinted from Rockstein and Lieberman (1958), by courtesy of the Editor, Nature, 



"senescence" 



emergence as adults; for females this period of 



occurs during the longer period of ten to fifty days of adult 



Ufe. 



One striking feature of the particular colony studied is 

 the remarkable homogeneity of the population, as regards 

 longevity at least. Thus, both for the total 600 flies per sex, 



