NTo. 643] STUDIES ON THE DURATION OF LIFE 



187 



These facts, based upon the determination experi- 

 mentally of the duration of life of 3,039 individual flies in 

 18 experiments, under constant environmental conditions, 

 place this character " duration of life " in the category 

 of genetically definite and workable characters, and indi- 

 cate that it will just as well repay careful analytical study 

 as the characters more usually dealt with. Furthermore, 

 duration of life is a character of great general biological 

 significance. 



LITERATURE CITED 



27. Pearl, R. and Parker, S. L. Experimental Studies on the Duration of 



Life. I. Introduetory Discussion of the Duration of Life in Droso- 

 Vhila. American Naturalist, Vol. 55, pp. 481-509, 1921, 



28. Johaimsen, W. Ueber Erblichkeit in Populationen und in reinen Lioien. 



Jena (Fisher), 1903. 



29. Johannsen, W. Elemente der exakten Erblichkeit slehre, 3d Edit., 1913. 



30. Pearl, R. On the Results of Inbreeding Mendelian Population ; a Oorrec- 



VoL 48, pp. 57, 62, 1914. 



31. Jennings, H. S. Formula for the Results of Inbreeding. American 



Natukalist, Vol. 48, pp. 693-696, 1914. 



