HOUSE FLIES AND BLUEBOTTLES 203 



disappearance as soon as the weather becomes cold 

 again, when they return to their hiding-places. In cold 

 weather they appear to be partly paralysed, and have 

 scarcely any power over their wings, and but little over 

 their legs. They are truly creatures of the sunshine. 



Like many other insects, the two house flies are 

 subject to the attacks of a parasitic fungus which 

 destroys great numbers of them, especially towards the 

 end of autumn. We sometimes see the corpses of such 

 as have met this fate glued to the window-panes in the 

 attitude of life, with legs widely spread and wings 

 raised, as if in preparation for flight, but with a white 

 halo on the glass all round them, and with bodies pale, 

 unhealthy-looking, and distended. The spores of the 

 fungus, which are excessively minute and are present 

 in the air, are carried against the fly's body ; and such 

 as strike its under surface may become adherent, when 

 each spore sends out a long tubular projection which 

 penetrates the skin and enters the body. Once here, its 

 host's doom is certain, for it meets with suitable nourish- 

 ment in the shape of the fluids of the fly's body, by aid 

 of which it will speedily propagate itself until its victim, 

 drained of its life support, finally succumbs. The thread- 

 like tube first produces a series of detached rounded 

 bodies, something like the cells of the yeast plant. 

 These cells, which have an indefinite power of self- 

 multiplication, are carried by the blood to all parts of 

 the body, and thus the disease spreads. They, in their 

 turn, give rise to a number of branching tubular threads, 

 similar to those of the earlier stage, which in process of 

 time penetrate the skin. Each thread which thus makes 

 its appearance outside gives rise to a sort of head, which 

 contains spores like those with which the series started. 

 These are cast off with considerable force, and multitudes 



