No. 641] 



THE DURATION OF LIFE 



503 



It compares, for males, two human L lines nearly 2,000 

 years apart in point of time, with the long-winged Droso- 

 phila L line of Table II. The two human lines are (a) 

 Glover's, 1910 U. S. table (as in Fig. 3), and (h) Mac- 

 donell's (26) observed L line from the population of 

 Eoman provinces in Africa at about the beginning of the 

 Christian era, his data having been taken from grave- 

 stone inscriptions. We calculated the h line here plotted 

 from Macdonell's tabled dx data, determining an L 

 point at each quinquennium. This smooths the Eoman- 

 African figures somewhat, and makes the L line so de- 

 termined lie very slightly higher all along its course than 

 would be the case if we used a more elaborate and exact 

 mathematical procedure. The error, however, is so small 

 that it would scarcely be discernible in the scale at which 

 Fig. 5 is reproduced. 



It is at once apparent from Fig. 5 that the Drosophila 

 survival curve runs, in general throughout its course, 

 between the curve for human beings 18 or 19 centuries 



