LIFE HISTORY 
39 
with such possibilities of multiplication; but it must be 
remembered that in the supposed instance upon which 
we have figured, all of the eggs hatched and all of the 
progeny have survived, whereas in nature a fly has 
many chances of death, not only between the egg and 
the adult, but as an adult before the period of sexual 
maturity has been reached. And it is upon this period 
which must elapse between the issuing of a fly and the 
time when it shall lay eggs that one of the several ex¬ 
cellent plans for the warfare against this species has 
been based. It must be remembered, on the other hand, 
that in the table we have assumed that each female 
has laid only 120 eggs, that is one batch, while in 
reality she may lay four such batches. The task of 
estimating the possibilities on the larger basis is left 
to some reader who likes to multiply. Does not a con¬ 
templation of these possibilities, even with all the pos¬ 
sible accidents of nature to limit them, indicate in the 
strongest possible way, even if the carriage of disease 
by these pernicious creatures were not considered, the 
necessity of an effort on the part of people to assist 
nature in limiting a nuisance to humanity? 
Number by Actual Count in Relation to 
Quantity of Food 
On August 9th in Washington a quarter of a pound 
of rather well-infested horse manure was taken from a 
manure pile, and in it were counted 160 larvae and 146 
puparia. This would make about 1,200 house flies to 
the pound of manure. This, however, cannot be taken 
