162 
Biology of Pediculus 1mmaims 
egg 8 days, 1st larval stage 2 days; 2nd larval stage 2 days; 3rd larval 
stage 3 days; adults’ pre-oviposition period 1 day. 
(b) Capitis. 
The following experiment was carried out by the wristlet method 
(see p. 107), the insects remaining continuously on the arm and having 
unlimited opportunities of feeding through a screen of chiffon. 
On 2. vi. 17, 4 <J(7 and 6 $?, received that morning from Mr A. Bacot 
in London, were planed in the wristlet and strapped to the arm; the 
females laid their eggs on the hair-grid. The daily record follows: 
3. vx. 17 
Day 
1 31 eggs were laid before 10 a.m. 
7 24 eggs hatched, and as many 1st stage larvae counted. 
11 19 2nd stage larvae counted 
14 — 3rd stage larvae appeared 
16 16 adults (8 8 $) counted; copulation occurred. 
17 first egg laid before 10 a.m. 
The development from egg to egg therefore lasted 17 days, made up 
as follows: Developmental period in the egg 7 days; 1st larval stage 
4 days; 2nd larval stage 3 days.; 3rd larval stage 2 days; adults’ 
pre-oviposition period 1 day. The remaining insects (also the case in 
corporis ) developed more slowly. 
These two experiments, as far as I am aware, are the only ones 
hitherto published which afford a true conception of the rate of develop¬ 
ment of body-lice and head-lice upon the human subject. Feeding 
the insects once or twice a day, and maintaining them in the thermostat 
between feeds under different conditions of temperature and moisture to 
those to which they are accustomed upon man, necessarily must lead to 
fallacious conclusions. Undet natural conditions, lice feed at frequent 
intervals, and head-lice especially cannot be raised successfully unless 
fed frequently; this explains the repeated failures that attended my 
earlier efforts to raise capitis. 
The Hypothetical Number of Descendants of One Female 
within a Limited Period. 
Commencing with Leeuwenhoek (ed. 1807, pp. 163-169), who reckoned 
that a female corporis might have 5000 descendants in 8 weeks, a 
number of authors have referred to the possible number of the offspring 
within a limited period. Railliet (1895, p. 825) reckoned that a female 
capitis would have 125,000 descendants in 12 weeks, assuming that 
