192 



BIOLOGY OF DEATH 



using this term "born.' to denote emergence from the 

 pupal stage as imagines. Each following day these small 

 bottles are inspected. Whenever a dead fly is found, it 

 is removed and a record made in proper form of the 

 fact that its death occurred, and its age and sex are noted. 

 Finally, when all the flies in a given small bottle have 

 died, that bottle is discarded, as the record of the duration 



1.000 



900 



600 



700 



<p 



1 



600 



500 



4OO 



300 



ZOO 



too 



45 



54- 60 66 71 



IB 84 9O 



AGL IN 



FIG. 48. Life lines for different inbred lines of descent in Drosophila. 



of life of each individual is then complete. All the 

 bottles are kept in electric incubators at a constant 

 temperature of 25 C., the small bottles being packed for 

 convenience in wire baskets. All have the same food 

 material, both in quality and quantity, so that the envi- 

 ronmental conditions surrounding these flies during their 

 life may be regarded as substantially constant and uni- 

 form for all. 



Figure 48 shows the survival frequency, or l x line 

 of a life table, for six different lines of DrosopMa, which 

 have been bred in my laboratory. Each line represents 



