No. 645] 



THE DURATION OF LIFE 



321 



optimum region has been reached, increasing density is 

 associated with diminished duration of life, which pres- 

 ently falls below the lowest figure found with densities 

 below the optimum. These conclusions must for the 

 present be held as tentative. 



In this paper data as to total duration of imaginal life 

 of 13,117 individuals of Drosophila are presented in re- 

 lation to the density of population. It is definitely shown 

 in the case of Wild, Sepia and Quintuple stocks that there 

 is a significant correlation between these variables. The 

 regression of duration of life upon density appears to be 

 significantly skew in the case of Wild and Sepia stocks. 

 The precise form of the regression and theoretical ques- 

 tions connected therewith are left for discussion in a 

 later paper upon the basis of more extensive material. 



LITERATUEE CITED 



Reports and Writings of William Farr, M.D., D.C.L., C.B., F.E.S. 

 Edit, by Noel A. Humphreys. London, 1885, xxiv + 563 pp. 

 36. Brownlee, J. Notes on the Biology of a Life-Table. Jour. Boy. Stat. 

 Sac, Vol. 82, pp. 34-65, 1919. Discussion, pp. 66-77. 

 Id. Density and Death-Rate: Farr's Law. Ibid., Vol. 83, pp. 280- 

 283, 1920. 



. Semper, K. The Natural Conditions of Existence as they Affect Crimi- 

 nal Life. Fourth Edit., London, 1890. 

 iki, F. iiber den Einfluss des Lebensraumes auf das Wachstum 

 r Kaulquappen. Pfliiger's Arch., Bd. 188, pp. 254-272, 1921. 



