STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 501 
English observations for India. In England, during a period 
of extremely hot weather, flies might develop in about nine 
days, but such arate of development would not usually occur, 
nevertheless, as I shall show in the concluding part of this 
memoir, such a contingency must be guarded against. Larvee 
reared in the open air in horse-manure which had an average, 
but not a constant, daily temperature of 22°5° C., occupied 
fourteen to twenty days in their development according to the 
air temperature. 
The effect of the character of the food on which the rate of 
development also depends is well shown by a comparison of 
the times of the developmental periods in two of the experi- 
ments where the average daily temperature was practically 
the same, namely, 19°3° C. and 20°5°C. In the former experi- 
ment, in which human feeces were used, the development was 
completed in twenty days, and in the latter, in which bananas 
were used, the development occupied twenty-seven days; the 
time was rather lengthened in both cases by the fact that the 
larval food was rather dry, but equally dry in both experi- 
ments as they were kept together ; had more moisture been 
present the times would probably have been correspondingly 
shortened. ; 
It was experimentally proved that when larve were reared, 
in batches on the same.kind of food material with conditions, 
as regards temperature the same, the developmental period 
was longer for those larvee which were subject to dry condi- 
tions than for those subject to moist conditions. In an 
experiment at an average temperature of 22° C. larve reared 
on horse-manure which was kept in a rather dry condi- 
tion took thirty days to complete the development, and 
another batch at the same temperature, but on horse manure 
which was kept moist, the development was completed in 
thirteen days. Under similar conditions, with regard to tem- 
perature, the rate of development is directly proportional to 
the condition of the food as regards moisture. Dry conditions 
not only retarded development in some of my experiments to 
five and six weeks, but also tended to produce flies of sub- 
