AMERICAN MUSEUM GUIDE LEAFLETS 

hibernate in any stage. Atthe termination of the pupal stage the fly 
comes out of the pupal case and crawls up to the surface of the ma- 
terial in which it pupated. Here its wings quickly harden and it is 
ready to fly away. 
The rate at which generations of flies follow each other is deter- 
mined by the temperature. Studies made in the Laboratory of 
Public Health of the American Museum gave a total period from 
egs laying to the emergence of the adult of 9.3 days at 35° C., 10.3 
days at 30° C., and 22.3 days at 20° C. , 
The adult fly lives upon liquid food, since its mouth parts are in 
the form of a sucking proboscis, but by discharging a free flow of 
saliva it is able to turn foods like sugar into the fluid form it can 
absorb. 

Fig. 3 

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