Gr. H.'F. Nuttall 
127 
On the Number of Eggs laid by P. human us under Different 
Conditions. 
Observations by Previous Authors. 
I. Corporis. 
The literature on lice contains statements of very unequal value 
in respect to the number of eggs which a female may lay. The text¬ 
books repeat the same misstatements from edition to edition and 
greatly underestimate the fecundity of the insect. For instance 
Railliet (1895, p. 827) states that they lay 70-80 eggs, and Eysell 
(1913, p. 48) gives the figure as 80. Recent writers, Heymann (8, vm. 
1915, p. 253; 18, vm. 1915, p. 306), Fiebiger (vn. 1915, p. 645) like 
many others, merely cite from text-books without acknowledging the 
source of their information. 
Relatively few authors contribute original observations on the 
subject and the data they supply are frequently imperfect, either 
because the conditions under which the observations were made are 
not stated or because the lice were only kept under observation for 
a few days. 
The total number of eggs laid by a single female. 
(a) Under natural conditions. Leeuwenhoek (ed. 1807, pp. 163- 
169) placed 2 in a stocking on his leg, and after 6 days he killed 
and examined the ovaries of one of the insects. From the condition 
of the ovaries and the egg-counts he had made, he estimated that the 
female would have been capable of laying at least 100 eggs. 
( b) Under artificial conditions. Warburton (1910, pp. 23-27), 
who fed an isolated female twice daily and carried her on cloth in a 
tube on his person in the intervals, records that she lived 25 days and 
laid a total of 124 eggs. Sikora (vm. 1915, p. 528), in an experiment 
conducted under similar conditions to Warburton’s, found that 6 
lived 21-45 days and laid 88, 81,175,194, 198 and 197 eggs respectively. 
Swellengrebel (1916, p. 12), without recording the conditions, saw 
a female lay 107 eggs. Bacot (n. 1917, pp. 236-239) records the total 
number of eggs laid by 6 which lived 23, 29, 30, 32, 32 and 34 days 
respectively and laid 118, 102, 180, 123, 172 and 150 eggs apiece. In 
his whole series the number laid ranged from 55 to 295 (maximum); 
the numbers I cite are the highest figures in his protocols. The average 
per female was 177. Bacot kept the females confined in cloth-lined 
