392 
Biology of Plithirus pubis 
lens or binocular microscope being used for observing the insects. We 
thus raised Phthirus through its life-cycle’^. By employing a small 
number of insects of different ages, and observing them closely, there 
was no difficulty in identifying the individuals. 
When the females began to oviposit, the eggs that were laid succes¬ 
sively were marked by coloured inks and entered on the day chart, it 
being thereby possible in each case to determine accurately the length 
of time required for hatching. Occasionally the nit-bearing hairs were 
shed, or the larvae fell away from the skin and died upon the stocking, 
but, on the whole, the failures were few. As the charts (Figs. 7 and 8) 
show, Phthirus usually wanders little from the point where it first fixes 
itself on emerging from the egg. It stays on the same small area through¬ 
out its life. Doubtless the scratching of the skin by the host, as it occurs 
in nature, will tend to make the insect wander further afield, and the 
increasing population will thereby become somewhat scattered. There 
was no tendency to wander upward on the leg. The male that was 
raised to maturity became detached twice and gravitated downward on 
the leg, whence it was transferred to a spot near the females. 
III. SPECIAL BIOLOGY OF PHTHIRUS. 
Proportion of the Sexes on the Host. 
In this connection I have but one observation to record. A total of 
232 adults collected by me from a soldier, comprised 88 males and 144 
females, i.e. the sexes were represented roundly in the proportions 
38 per cent, male and 62 per cent, female. This is in remarkably close 
accord with Hindle’s figures (40 per cent, male and 60 per cent, female) 
for P. humanus of which he raised 944 specimens to maturity (see p. 114). 
The three Phthirus raised by me were one male and two females. Further 
observations are required to establish the sex ratio, but so far the indi¬ 
cations are that the females predominate. 
Copulation. 
The process of copulation is somewhat similar to that in Pedictdus. 
On several occasions, when the hairs in the vicinity of a female were 
touched, I observed that, whilst continuing to feed, she raised her 
abdomen in a manner recalling the movement of Pediculus females 
^ Major Hewlett has since informed me that he has also raised Phthirus on his leg 
and that of his assistant in India, likewise employing a stocking. 
