Gr. H. F. Nuttall 
163 
they escaped the accidents which destroy many of them in nature. 
Dore (1916, abstr. p. 630) calculates that a female may have 8000 
descendants during her lifetime, and Alessandrini (1916, p. 96) also 
gives an estimate. Bacot (n. 1917, p. 258), writing of corporis, 
estimates the egg period at 12 days and the larva-to-adult period at 
12 days; allowing an average of 8 eggs laid per day during 40 days, 
he computes that a female may have 4160 descendants during her 
lifetime. 
The data obtained by me in raising corporis upon the body, differ 
from those of Bacot and other authors. The egg-to-egg period was 
found to be 16 days; the average number of eggs laid per day per female 
being 10, laid in 28 days. Taking the life of the adult female as lasting 
30 days upon man; assuming that but 70 % of the eggs hatch and that 
only 60 % of the larvae attain sexual maturity, we allow a consideraole 
margin for loss during development 1 ; we must assume that the sexes 
are equally represented among the descendants. Given these data, 
Miss H. P. Hudson has kindly calculated for me that a female would 
have 1918 descendants during her lifetime, and that the offspring of 
her daughters, during their lifetime, would number 112,778. This 
offspring would include all stages of development from egg to adult. 
I may add that this large figure would be reached in 48 days from the 
date when the original female began ovipositing. 
Judging from the enumerations that have been made of the numbers 
of lice that may be present on an individual (see p. 86), it is evident 
there must be a very great loss of life among the lice that infest 
a man, even when the clothing is worn continuously and no special 
measures are taken to destroy the vermin. A very large number are 
undoubtedly destroyed merely by the constant scratching of the person. 
When this combative action of the host becomes less active through 
debility or disease, it will be readily understood why enormous numbers 
of lice may occur on the individual as recorded in older reports on 
pedicular disease. We have parallel instances in animals which on 
becoming old or decrepit are super-parasitized by fleas, lice or ticks; 
the animal in health would have prevented this or, as the saying goes, 
would have “kept itself clean.” 
1 No such heavy losses have occurred in my best raising results either with corporis or 
capitis. 
11—2 
