Gr. H. F. Nuttall 
145 
Some authors, without mentioning the conditions, state that eggs hatch as follows: 
In 3-8 days (Railliet, 1895, 827); 5-6 days (Fantham, 1912, p. 514); 6 days rarely in 4 
(Jeanneret-Minkine, 1915, p. 126); rarely in 5.days usually in 6 (Hase, 1916, abstract); 
8 days (Fiebiger, 1915, p. 657; vn. 1915, p. 645); Eysell (1913, p. 48) asserts that corporis 
eggs hatch in 3^ days, and appears to be the not-cited authority for the similar statements 
of Prowazek (i. 1915, p. 67), Fasal (n. 1915, p. 225), Heymann (m. 1915, p. 253), Nocht 
and Halberkann (v. 1915, p. 626); Eysell is perhaps quoting from Railliet, but there is no 
evidence that either author made original investigations. I have only once seen an egg 
hatch in 4 days, at 37° C., and no recent observer has seen hatching in 3 days. 
The following are the only detailed experiments that have been 
carried out to my knowledge on corporis eggs ox accurately determined 
age: 
■No. of 
eggs that 
Temp, of 
thermostat 
Hatching occurred after days 
# 
hatched 
in °C. 
4 
5 
6 7 8 
9 10 
11 12 
13 14 
1283 
30° damp 
— 
— 
— 3 56 
33 8 
0-2% - 
- - 
Bacot, ii. 
1917, p. 248 
160 
30°, dry 
9 46 
92 11 
2 _ 
Hindle ms. 
105 
30°, dry, 
constant 
— 
— 
— 1 3 
2 6 
35 41 
10 7 
Nuttall 
Expt. n. 16 
93 
37°, dry, 
constant 
1 
36 
54 2 — 
Nuttall 
Expt. v. 16 
The observations recorded in the foregoing table show that eggs 
laid on the same day may take a variable time to undergo development. 
This is also shown by my experiments on capitis. Incidentally they 
disprove the statement by Sikora (vm. 1915, p. 529) that there is great 
uniformity in the hatching period of eggs of the same age. 
( b) Capitis. 
These lice were raised by the wristlet method, as described on p. 107. 
No. of 
eggs that 
Hatching occurred after days 
hatched 
Temp. ° C. 
5 6 7 
8 9 10 
103 
32-35° on wrist. 
4 23 60 
14 2 — 
Nuttall, 
Expt. vi. 17 
244 
30-33°, in bag on 
— 23 166 
51 3 1 
9 9 
Expt. b. vn. 17 
neck, warmer 
weather 
9-4% 68% 
20-9% 1-2% 0'4% 
500 
Ditto, cooler 
— 7 307 
167 19 — 
99 
Expt. a. vn. 17 
weather 1-4% 61'4% 33'4% 3’8% 
Without giving any particulars, Railliet (1895, p. 825) states that capitis eggs hatch 
in 5-6 days; Eysell (1913, p. 47), who perhaps intends to quote Railliet, gives 6 days 
as the hatching period. There is no evidence that either author made personal 
observations. 
Parasitology x 
10 
