188 



BIOLOGY OF DEATH 



then we have about 8 to 10 days as the minimum time 

 duration of a generation. The whole cycle from egg to 

 egg, at ordinary room temperature, falls within this 10- 

 day period with striking accuracy and precision. 



The duration of life of the adult varies in an orderly 

 manner from less than 1 day to over 90 days. The span 



CO 



I 



1,000 



900 



'600 



700 



* 



too 



A6L IN DAYS 



FIG. 47. Life lines for Drosophila melanog aster; showing the survivors at different ages out 



of 1000 born at the same time. 



of life of Drosophila quantitatively parallels in an extra- 

 ordinary way that of man, with only the difference that 

 life's duration is measured with different yardsticks in 

 the two cases. Man's yardstick is one year long, while 

 Drosophila' s is one day long. A fly 90 days old is just 

 as decrepit and senile, for a fly, as a man 90 years old 

 is in human society. 



This parallelism in the duration of life of Drosophila 

 and man is well shown in Figure 47, which represents a 

 life table for adult flies of both sexes. The survivor- 

 ship, or l x figures, are the ones plotted. The curves deal 



