504 C. GORDON HEWITT. 
would be reared and ready to assume their customary activity 
under the benign influence of the sunny days of June. 
I have made many experiments with a view to finding out 
the rapidity with which house-flies breed. Anyone who has 
endeavoured to keep flies alive in an enclosed space will 
appreciate the difficulty of the task, those who have not done 
so would hardly realise it. Fewer insects seem less tenacious 
of life when enclosed even in a comparatively large enclosure 
of six or nine cubic feet. It is a remarkable fact, as one 
would imagine a priori that these insects, flying about 
everywhere as they do, could be easily kept in a roomy cage 
if given the necessary food and water. This, however, has 
not been the case in my experience ; the longest period which 
I have been able to keep them in captivity in summer is 
seven weeks. I am pleased to find that Griffith has succeeded 
in keeping a male fly sixteen weeks, and has obtained four 
batches of eggs from females in captivity. In one of my 
experiments I was successful in obtaining flies of the second 
generation bred in captivity. I found that the flies became 
sexually mature in ten to fourteen days after their emergence 
from the pupal state and, four days after copulation, they 
began to deposit their eggs, that is, from the fourteenth day 
onwards from the time of their emergence. 
From these results it may be seen that in very hot weather 
the progeny of a fly may be laying eggs in about three weeks 
after the eggs from which they were hatched had been de- 
posited. As a single fly lays from 120—150 eggs at one time 
and may deposit five or six batches of eggs during its life, it 
is not dificult to account for the enormous swarms of flies 
that occur in certain localities during the hot summer months, 
and algebraical calculations are not required to more vividly 
impress the fact. 
ITV. Dr&vELOPMENT. 
As I have already stated, M. domestica may become 
sexually mature in about ten to fourteen days after emer- 
