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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 a rate 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. Larvae 

 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 faeces 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 larvae 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 larvae which were subject to dry condi- 

 tions than for those subject to moist conditions. In an 

 experiment at an average temperature of 22 C. larvae 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- 



