900 C. GORDON HEWITT. 
which were mixed, when in a rotting condition, with earth to 
make amore solid mass. Although they can be reared in 
such food-stuffs as bread soaked in milk and boiled egg, when 
these are kept at a temperature of about 25° C., I was unable 
to rear them to maturity in cheese, although they fed on the 
substances for a few days and then gradually died, my failure 
may have been due to the nature of. the cheese which was 
used, only one kind being tried. In addition to rearing the 
larvze on isolated human feeces, such as are frequently found 
in insanitary court-yards and similar places, they were found 
in privy middens, and also on a public tip among the warm 
ashes and clinker where the contents of some privy middens 
had also evidently been emptied; I bred the flies out from 
this material. 
III. Factors or DEVELOPMENT, 
The rate of development depends primarily on the tempera- 
ture of the substance on which the larve are feeding. This 
was shown in my experiments in which the larve were reared 
in horse-manure kept in a moist condition in an incubator at 
a constant temperature of 35° C. At this temperature the 
development is completed in eight to nine days. I found that 
a higher temperature of 40° C. was too great for the larvee as 
they were simply cooked and perished at such a temperature. 
This has been confirmed by Griffith (l.c.), who found that 
the life-history was completed in the same time on incubating 
at a temperature of about 22°—23° C. I do not think that a 
shorter time than this for the development—that is, from the 
deposition of the egg to the emergence of the perfect insect 
from the pupee—will ever occur in this country, as we rarely 
enjoy prolonged spells of hot weather which would bring 
about such conditions as regards temperature. It is interest- 
ing to note that Smith (1907) gives the time of development 
in horse-manure in India under natural conditions as eight . 
days; he also bred M. domestica from an artificial latrine 
containing human excreta mixed with earth, which confirms 
