404 
Biology of Phthiriis pubis 
hind leg-pairs of the adult insect is about 2 mm., these legs being the 
ones that are used for grasping the hair. 
Whilst infestation usually takes place through coitus, there are many 
exceptions to the rule as proved by the occurrence of crab-lice on infants. 
The latter may become infested by their parents or other adults. The 
insect may pass from one infant to another through their sharing a 
cradle, or it may pass from soldier to soldier when crowding occurs in 
barracks or billets. Scratching of their persons by infested individuals 
no doubt aids in the spread of the parasite upon them and the dissemina¬ 
tion of the insect further afield. Both the act of coitus and scratching 
promote the shedding of hairs, and these, when bearing nits or young 
larvae, may be of considerable importance in disseminating the parasite. 
Such hairs, and no doubt occasionally active stages of the louse, are 
shed on clothing, bedding, the seat of the privy, etc., and readily become 
entangled with the pubic or other hair of clean persons who may come 
in contact therewith. A detached louse promptly clings to any hair 
with which it comes in contact. Therefore, whilst Phthinis is commonly 
conveyed directly, it may also be acquired indirectly. It is a helpless 
creature when removed from the hair to which it clings continuously 
upon the body, where it moves about by shifting from hair to hair; it 
is therefore much more likely to be conveyed passively from host to 
host than is Pediculus. 
Unless disturbed, the parasite remains confined throughout its life 
to a limited area upon the host’s skin as I have demonstrated experi¬ 
mentally. 
The females appear to preponderate over the males in number when 
upon the host, their relative proportion being about 3 : 2. In copulation, 
the male does not seize the female as in Pediculus; he seizes the hairs to 
which the female clings, using these as a support. Oviposition occurs 
as in Pediculus. A female that was raised experimentally, laid up to 
three eggs per day, laying a total of 26 eggs. The hatching period (on 
the leg) lasted 7-8 days. Like Pedicidus, the crab-louse passes through 
three moults (there being as many larval stages) before it attains sexual 
maturity. When the adults are about 10 days old they exhibit to a 
well-marked degree the greenish coloration of the fat-body which is seen 
by transparency at the sides of the abdomen in the living insect. The 
life-cycle, from egg to egg, is completed in 22-27 days (on the leg). 
Young unfed larvae usually die within ten hours of emergence. 
When removed from man, they survive longer at 16-20° C. than at 
30° C. and die much more rapidly in a dry than in a moist atmosphere; 
