134 
Variation and Inheritance in Aphis 
the frequency of the newly born broods be exhibited in a graphical form (Fig. 2) 
we see that the polygon conforms to the usual type of a fertility curve — there is 
marked skewness, the mean being considerably larger than the modal value. 
4 5 fi 7 8 !) 10 11 12 13 14 15 1(! 
Fio. 2. Fertility rolygoii. 60 Mothers, 522 Offspring. 
In order to discover whether fertility was in any way related to the dimensions 
measured, correlation tables were prepared for the dimensions of the mother and 
the number in the brood (Table II A. Nos. 1, 2, 3). The coefficients of correlation 
are seen to be small, about '12 + "09, but since the probable errors are so great 
we can only assert that the larger individuals appeared to be slightly more 
fertile than the smaller ones. 
(5) Death-Rate. 
The total number of offspring registered was 522. Out of this number 455 
individuals grew up and were collected. In the population of 455 there were nine 
winged individuals and 78 large corpses. The winged females appeared in only 
four families. The large corpses were the bodies of individuals which had doubt- 
less died of old age, for I purposely allowed the broods to live as long as possible 
so as to insure that the individuals collected were as mature as they would 
become. The remaining 368 animals were measured. 
Those that died before growing up, 67 in all, probably succumbed from weak- 
ness in constitution, etc. This gives a death-rate of 12'8 per cent, for the second 
generation. 
To ascertain whether there was any relation between the death-rate of the 
brood and the deviation of the mother the percentage death-rate for every family 
was calculated and correlation tables for this percentage and the dimensions 
of the parents were prepared (Table II A. Nos. 4, 5, 6). The coefficients of corre- 
lation for the absolute dimensions are about — "20 + "084, that is the larger 
mothers tended to have healthier offspring. 
It was also desirable to know whether deviation in adult families was associated 
with increased death-rate during their growth. The mean ratio of each family 
