(121) 



362, 0. GORDON HEWITT. 



manner. The larvae of some species breed in human and other 

 excrement, others breed in decaying vegetable substances, 

 while certain species breed in water, especially when polluted 

 with sewage, and these aquatic species have the spiracular 

 apparatus modified accordingly. Although a form, Phlebo- 

 tamus, which occurs in Southern Europe, has blood-sucking 

 habits, the British species have no such annoying habits, and 

 are of little importance in their relation to man. 



IV. PHYSIOLOGY. 



1. The Influence of Food, Temperature, and Light. 



Food. Mention has already been made in the second part 

 of this work of the influence of food on the development of the 

 larvae; the experiments which were carried out showed that 

 the larvae develop more rapidly in certain kinds of food, such 

 as horse-manure, than in others. It has yet to be discovered 

 what are the chemical constituents which favour the more 

 rapid development. It was found that insufficient food in the 

 larval state retarded development and produced flies which 

 were subnormal in size. Bogdanow (1908), in an interesting 

 experiment, fed M. domestica through ten generations on 

 unaccustomed food such as meat and tanacetum in different 

 proportions, and he found that the resulting flies did not show 

 any change. 



Temperature. The influence of temperature on the 

 development of the larvae has been shown also. A high 

 temperature accelerates the development of the egg, larva 

 and pupa. Temperature also affects the adult insect; they 

 are most active at a high summer temperature, and cold 

 produces an inactive and torpid condition. They are able, 

 however, to withstand a comparatively low temperature. 

 Bachmetjew (1906) was able to submit M. domestica to as 

 low a temperature as 10 C., and vitality was retained, as 

 they recovered when brought into ordinary room temperature. 

 Donhoff (1872) performed a number of experiments previous 



