126 Biology of Pediculus humanus 
floor. Three females laid 4 eggs on the sides and top of the strip and 
18 on the floor. 
Expt. 5. Two felt discs were placed in a tube, the one served as 
a floor, the other as a slanting roof to the space in which the lice were 
confined. The upper disc touched the floor on one side and was only 
slightly slanted. The lice confined in the space laid 9 eggs under 
the roof and 14 on the floor. Most of the eggs were laid where the 
discs approached each other to a distance of about 2 mm. 
These experiments show («) that lice prefer to lay on horizontal 
as against vertical surfaces; ( b ) that they greatly prefer to lay on the 
underside of fabrics resting on or near glass; (c) that when confined 
between two surfaces (roof and floor) of felt, the interspace allowing 
of free movement, they lay about equally well on both. 
The Influence of Temperature on Oviposition, 
The temperature at which females are kept markedly influences 
oviposition. For instance in one of my experiments (13—14, v. 16) 
65 corporis were placed at 22° C. and only laid 3 eggs during 46 hours. 
When 35 of these females were placed in a thermostat at 30° C. they 
laid 188 eggs in 24 hours. In a second experiment 10 $$ laid no eggs 
at 21° C. during 24 hours but when placed at 22—23° C. for a similar 
period they laid 8 eggs. They lay rapidly at 37° C. although this tem¬ 
perature shortens their lives under experimental conditions. 
Sikora’s statement (vm. 1915) that lice cease to lay at 25° C. is 
inaccurate; the author has, however, corrected it, having since found 
(xi. 1915, p. 164) that eggs may occasionally be laid at 20° C. Accord¬ 
ing to Hase (1915, p. 75, cited by Muller, 1915) lice do not oviposit 
at 12° C. 
We may conclude therefore that corporis cease to lay at tempera¬ 
tures beneath 20° C. Infested persons who remove their clothing at 
night will consequently become less heavily infested than those who 
wear their clothing continuously—this being in accord with practical 
experience. The periodic cooling of the clothing and of the therein 
contained lice necessarily leads to their progeny being materially 
reduced. 
