Gr. H. F. Nutt all 
155 
(loc. tit. p. 249), however, records periods of 7-12 days; one isolated 
female laid 70 fertile eggs. 
In judging of these variable results, certain factors must be taken 
into account which do not appear to have been considered by some of 
the authors cited, although they are fairly obvious. These factors are: 
the age and potency of the copulating pair, the fact that hatching under 
experimental conditions is frequently an imperfect test of fertility since 
a variable number of fertile eggs may die under unfavourable conditions 
and be falsely reckoned as sterile. I have seen a male, after prolonged 
copulation with a, female, separate from her and immediately seek a 
second mate, it being evident that he could scarcely fertilize the second 
female with full effect after such a short interval between the acts. The 
brief periods of fertility may therefore be explained either by the 
advanced age or exhausted state of the pairs, the longer periods by the 
pairs being younger or more potent. Finally, unless optimum conditions 
prevail for the .development of the eggs, hatching affords a poor guide as 
to their fertility. 
Fertilizing Power oe the Male. 
The only data relating to the fertility of the male are those recorded 
by Bacot (n. 1917, pp. 236, 239), who states that a S corporis fertilized 
18 ?£, and a <S capitis fertilized 10 
Development from the Larva to the Adult -the Moults. 
There are three larval stages in the developmental cycle of Pediculus, 
and consequently three successive moults occur before the insect 
reaches the adult stage. The time required for development from 
1 st stage larva to adult depends greatly upon the temperature and food 
supply, factors whose importance few have recognized. 
Swammerdam (1682 ed., p. 172) concluded that lice undergo 3H: 
moults, and Warburton (1911) stated that there are “apparently” 
three, their number therefore remained in doubt until Patton and 
Cragg (1913, p. 552) in India, definitely established that there are three. 
This has been amply confirmed by different observers (Hindle, in 
England; Sikora, 1915, p. 523, in Germany; Muller, 1915, p. 47, in 
Austria; Swellengrebel, 1916, p. 4, in Holland, etc.). 
The time required for lice to attain maturity, starting with the 
newly hatched larva, is variously given by different authors; two 
hitherto unpublished observations of my own are included: 
