178 THE AMERICAN NATURALIST [Vol. LVI 



III. In calculating these constants, the absolute dx fre- 

 quencies, and not the per mille frequencies, were of course 

 used. 



From these data it is at once apparent that these 

 progeny groups shoiv distinct, and in some cases decidedly 

 large, differences both in mean duration of life and in the 

 form of the mortality distributions. Lines 101 (Old Fal- 

 mouth stock) and 201 (New Falmouth stock) show the 

 longest mean duration of life, and they are sensibly iden- 

 tical in the form of the life curve, having regard to the 

 errors of random sampling. The difference in the means 

 for these two lines is 2.62 ± 1.31 days, an obviously insig- 

 nificant difference, only 2 times its probable error. Simi- 

 larly these two lines do not significantly differ in absolute 

 or relative variability, the difference betw^een the stand- 

 ard deviation being .48 ± .92. 



Line 100 (Old Falmouth stock) has a distinctly and sig- 

 nificantly lower mean duration of life than 101 or 201. 

 Comparing it with line 101 the difference in the means is 

 9.57 ± 1.20 days or approximately 8 times its probable 

 error. The Ir curve lies throughout its course below the 

 lines for 101 and 201. Line 100 is also relatively more 

 variable in duration of life than 101 and 201, but largely 

 because of the difference in the means. 



The individuals in line 202 (New Falmouth stock) are 

 the shortest lived of any here dealt with, and the shortest- 

 lived Tvald-type strain we have as yet isolated. Its mean 

 duration of life is less than half that shown by lines 101 

 and 201 and only a little more than half that of line 100. 

 Line 202 shows the highest relative variability in duration 

 of life of any of the lines here discussed. It also has 

 the highest absolute variability with one exception (line 

 303). 



Lines 300, 301 and 303 (Sepia stock) are all relatively 

 short-lived lines. 300 and 303 are substantially identi- 

 cal, while 301 has a lower mean approaching that of line 

 202. These sepia lines are also characterized by high 

 relative variability. 



