VIII BIOGENESIS AND ABIOGENESIS 263 



thrown off in all directions by a minute fungus 

 called Empusa muscce, the spore-forming filaments 

 of which stand out like a pile of velvet from the 

 body of the fly. These spore-forming filaments 

 are connected with others which fill the interior 

 of the fly's body like so much fine wool, having 

 eaten away and destroyed the creature's viscera. 

 This is the full-grown condition of the Empusa. 

 If traced back to its earliest stages, in flies which 

 are still active, and to all appearance healthy, it 

 is found to exist in the form of minute corpuscles 

 which float in the blood of the fly. These multiply 

 and lengthen into filaments, at the expense of 

 the fly's substance ; and when they have at last 

 killed the patient, they grow out of its body and 

 give off spores. Healthy flies shut up with 

 diseased ones catch this mortal disease, and 

 perish like the others. A most competent 

 observer, M. Cohn, who studied the development 

 of the Empusa very carefully, was utterly unable 

 to discover in what manner the smallest germs 

 of the Empusa got into the fly. The spores 

 could not be made to give rise to such germs by 

 cultivation ; nor were such germs discoverable in 

 the air, or in the food of the fly. It looked 

 exceedingly like a case of Abiogenesis, or, at any 

 rate, of Xenogenesis ; and it is only quite recently 

 that the real course of events has been made out. 

 It has been ascertained, that when one of the 

 spores falls upon the body of a fly, it begins to 



