No. 646] 



THE DURATION OF LIFE 



405 



tained if one compares human and Drosophila life curves 

 for females. Since nothing new in principle is brought 

 out, it is not thought necessary to present the female 

 curves here. 



IV 



In this paper it is shown that if we take as equivalent 

 life spans in Drosophila and man the period between (a) 

 the point in the life history of each organism where the 

 specific death-rate {qx) is a minimum, and (h) the point 

 where there is one survivor out of 1,000 starting at the 

 beginning as defined in (a), and then divide these equiva- 

 lent life spans into 100 portions (thus measuring age not 

 in absolute units but in centiles of the life span), the laws 

 of mortality are fundamentally the same in kind in the 

 two organisms. There is a quantitative difference ex- 

 pressible in the statement that at each centile age 

 throughout the life span the number of survivors, out of 

 the same original number starting together, is higher 

 in man than in Drosophila. 



In a subsequent paper, I hope to take up in detail 

 the functional relations (in a mathematical sense) be- 

 tween the human and Drosophila equivalent h curves 

 here presented. 



LITEEATUEE CITED 

 (The plan of numbering citations is explained in the second of these 

 Studies, Ameb. Nat., Vol. 56, p. 174.) 



49. Pearl, E. and Parker, S. L. Experimental Studies on the Duration of 



tion of Life in Drosophila. Amkr. Nat., Vol. 56, pp. 312-322, 1922. 



50. Id. Experimental Studies on the Duration of Life. V. On the Influence 



of Certain Environmental Factors on Duration of Life in Drosophila. 

 Ibid., Vol. 56, pp. 1922. 



51. Glover, J. W. United States Life Tables 1890, 1901, 1910, and 1901- 



1910. Washington (Bureau of the Census), 1921. Pp. 496, 4to. 



