154 
Biology of Pediculus humanns 
during 21 days (24. vi.—14. vii. 17); the females died one after the other. 
Of these eggs, 28 were sterile (ca. 10 %) and three larvae (ca. 1-2 %) 
failed to complete their development. Therefore ca. 90 % of the eggs 
were fertile and 244, or ca. 88%, hatched. The lower percentage of 
fertile eggs in this case was due to the death of the two accompanying 
males on the 9th and 15th days of oviposition, only four sterile eggs 
out of the 28 having been laid during the lives of the males. 
The Length of Time a Female remains Fertile after 
Fecundation. 
As copulation commonly takes place at frequent intervals, once a 
day, or oftener, and the female possesses no receptaculum seminis, 
it might be supposed that females would soon cease to lay fertile eggs 
after being isolated apart from the males. Whilst some observations 
show that certain females lay fertile eggs for but a brief period, others 
clearly demonstrate the contrary; fortunately there are a number of 
observations recorded by independent authors which elucidate the 
matter, and I have classified the data as follows: 
(a) Corporis. 
(a) Brief periods of fertility were observed by Harrison (ms.) in 
three batches of females, that only laid fertile eggs during two days 
after they had been isolated from males. 
(b) Longer periods of fertility. Sikora (vm. 1915, pp. 523-537) 
relates of two females: (1) that laid 64 fertile eggs during 12 days, 
after which she laid infertile eggs; (2) that laid 20 fertile eggs during 
nine days. Hindle (ms.) records that 20 females continued to oviposit 
for 20 days after isolation from as many males; for the first eight days 
after isolation 75 % of the eggs hatched, whereas after 9, 10, 11 and 12 
days’ isolation there hatched respectively 6/29, 4/32, 2/28, 1/27, in short 
only one out of 27 eggs laid on the 12th day hatched; the females were 
maintained at 30° C. and fed twice daily. Swellengrebel (1916, p. 12) 
saw an isolated female lay fertile eggs for a period of 15 days. The 
longest periods have, however, been observed by Bacot (n. 1917, pp. 240, 
243, 251), who records isolated females as having laid fertile eggs for 
12, 17, 18, 19 and 21 days respectively. 
( b) Capitis. 
Similar results have been obtained with head-lice. The longest 
period of continued fertility observed by me was five days. Bacot 
