25(i 
Bionomics of Pediculus 
the marked disparity in the sexes of the F. 1 generation of some of the 
crosses between P. capitis ^ and P. humanus $ suggests that the payents 
are specifically distinct. 
No such obvious disparity occurred between the sexes of the F. 2 and 
F. 3 hybrid generation, or of either of the pure stocks^. 
Habits. The body louse exhibits some of the habits of a gregarious 
animal especially during the moulting phases, also a preference for 
returning to the same spot for oviposition, which leads to the clustering 
of its eggs. These habits are shown, though in a less marked degree, 
by P. capitis, and it is possible therefore that they are to some extent 
the outcome of confinement. Pairing within both species took place 
at any time during day or night, and was very frequently observed 
after feeding. with but little food in their ahmentary tract were, 
however, often seen in coitus. The period during which the insects 
remained paired was frequently observed to be over an hour, but no 
upper limit was defined. 
A c? of P. humanus fertilized 18 out of 21 placed ■with him in 
succession. Four attempts with P. capitis were less successful; one ^ 
fertilized ten and very possibly might have equalled the P. humanus 
record but for a scarcity of ■virgin while the experiment was in progress. 
The longest period during which a $ of P. humanus retained the power 
to lay fertile eggs in the absence of a d was 20 days, usually it would 
seem to be from 16 to 18 days. In the case of P. capitis the period was 
shorter; 12 days being the longest ascertained period, while it was 
more usually from seven to eleven days. 
The greatest number of eggs laid by any one ? of P. humanus was 
295, an average of 6-4 per day—the daily average of a number of $$ 
being 5-1. P. capitis showed a lower fecundity, the highest record 
being 141 with a daily average of 4-—the general average being 3-7. 
These figures are probably exceeded under natural conditions. An 
experiment in differential feeding with P. humanus (Table VIII) shows 
clearly that fecundity is dependent on feeding. When extra feeding 
time over and above seven hours per day was given the average for 
four $$ was eight per day. It is reasonable to suppose that the average 
for P. capitis would also be increased by unrestricted feeding. 
^ Since the above went to press I have reared two broods of P. humanus from crosses 
between pale and dark forms of this species with a view to discovering if the melanic 
race shows M-ndelian inheritance. In the case of a pairing between a pale ^ and 
a dark 9 there resulted 15 (JJ and 54 9$, while from the reverse cross 102 (J<J and only 
1599 were bred. This result qualifies the above suggestion and necessitates further 
breeding experiments which are now in progress. (See p. 259, paper by Hindle.) 
