U. H. F. Nuttall 
115 
between capitis and corporis, we find that he raised 882 d and 624 <j>. 
Assuming that it is permissible to combine the figures of both authors 
we obtain a grand total of 1274 d and 1176 $, indicating that perhaps 
in nature the sexes balance out in equal proportions. On the other 
hand, of 100 insects, the progeny of 4 d and 6 $ capitis (Lot 210) 
raised by me on man, 43 were d and 57 $, these figures harmonizing 
with those of Hindle for corporis. My figures, however, appear to 
afford better evidence of the true sex ratio (in a mixture of six broods) 
than those of Hindle or Bacot, because the mortality among the indi¬ 
viduals raised by me was practically nil 1 ; Hindle’s figures especially 
indicate a great mortality, which might have affected the males more 
than the females 2 . As previously stated, however, further enumera¬ 
tions of a large number of lice from a number of persons, coupled with 
more raising experiments, are required before final conclusions can be 
reached as to the relative numbers of both sexes. 
The Disparity in the Proportion of the Sexes in Different Broods. 
As previously stated, the results of raising experiments, especially 
on a small scale, may be very contradictory. Sikora (vm. 1915, p. 528) 
raised two broods which yielded respectively (a) 10 d, 14 $, and 
(6) 5 dj 6 $. The only authors who have raised lice on a large scale 
are Hindle (n. 1917, p. 258) and Bacot (n. 1917, p. 253). 
Although Hindle raised descendants of many pairs of corporis, the 
number of adults of each brood was usually small. Nevertheless a 
striking disparity in the proportion of the sexes was observable in some 
of these partial broods, in that a number yielded only dd, others only 
$?, and still others dd and $$ in varying proportions. He raised one 
stock of lice through several generations, the insects being fed twice 
daily on man and maintained during the intervals at 30° C. in the 
thermostat. Excluding details that are irrelevant to the problem 
under discussion, I append some of his results in condensed form. 
1 Of 106 eggs, four were sterile and 102 hatched, only two larvae failing afterwards to 
reach maturity. 
2 Vide Doncaster, L. (1914), The Determination of Sex, Cambridge Univ. Press, 
pp. 73-89 (Sex-ratio). 
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