39G 
Biology of Phthirus pubis 
Hatching. 
The period required for the hatching of the eggs is given as 6-7 days 
by Blanchard and Railliet {loc. cit.), as 6 days by Brumpt (1910, p. 550). 
Of nine eggs laid on my Assistant’s leg, beginning 25. v. 1917, and 
of which accurate records were kept, six hatched in 7 days and three in 
8 days. Of ten eggs of undetermined age removed from a patient and 
carried in a tube against the skin of the groin, five emerged in 7-8 days, 
none subsequently. 
Influence of lemperalure on hatching. 
Very poor results attended my efforts to hatch out eggs in the 
thermostat at 30-32° C., owing to there being a large percentage of 
deaths, even when the air was kept damp. Marzocchi (1913, p. 314), 
who observed hatching under these conditions, adds that he obtained 
negative results at 18-20° C. The influence of temperature of Phthirus 
is therefore in accord with what has been stated for Pedicuhis (see p. 143). 
Developmental changes in the egg and mode of emergence. 
These are essentially the same as in Pedicnlus (q.v.); the much less 
transparent egg-shell in Phthirus, however, considerably impedes direct 
observation. 
Development from Larva to Adult. 
Fifteen days is stated to be the period required according to authors 
(Blanchard, Railliet, Brumpt, loc. cit.) but none mention the number 
of moults that occur. 
Timed from the hatching of the first stage larva (Day 1) my observa¬ 
tions gave the following results: 
Moult occurred over¬ 
night between days 
c? 
$ 
9 
1st moult 
5-6 
5-6 
5-6 
2nd stage larva emerged 
2nd „ 
9-10 
11-12 
11-12 
3rd ,, ,, ,, 
3rd „ 
13-14 
16-17 
15-16 
Adult emerged. 
It is noticeable that the last two moults took place earlier in the 
male than in the females. The males in Phthirus are usually smaller 
than the females. 
The process of moulting is similar to that in Pediculus, the old skin 
showing corresponding lines of cleavage. The cast skin remains clinging 
to the hair in the same manner as the living insect. 
