GENERAL LIFE HISTORY 57 



rapidity; and the corpse becomes suffused with an 

 appearance of white mouldy excrescences, filiform 

 conidiophores, of which the club-like tips make a 

 copious aerial discharge of white spores ; when these 

 adhere to a glass or window-pane they imprint thereon 

 a remarkable halo. Attempts to artificially infect other 

 flies with these spores are common failures or have led 

 to contrary conclusions. 



The period from the first symptoms of distress to 

 the death of the fly, and from that time to the spore 

 discharge is wonderfully short. The infectious germs 

 may have been long dormant in the fly, and very likely 

 may have been acquired in the maggot stage. In the 

 absence of exact knowledge, we can only make con- 

 jectures from observations of some kindred fungic 

 parasites, which are not very uncommon amongst the 

 chrysalids of certain moths, beetles, and the pupae of 

 some annual wild bees. In these cases it seems very 

 unlikely that the infection was incurred otherwise than 

 in the caterpillar or larval feeding stage. Dampness 

 and insanitary conditions seem to favour the spreading 

 of such disease, especially amongst artificially reared 

 larvae when crowded together and closely confined. 



Other kinds of flies do not, so often as the house- 

 fly, perish from Empusa musca, but I have seen a 

 common yellow cowdung-fly, as early as June, thus 

 affected. 



In spite of all antagonists the brood of the house- 

 fly flourishes and multiplies, but this is because great 

 opportunity and encouragement is provided by the 

 neglect of good sanitation by mankind. 



