DIPTERA. 333 



" bringing " disease. In some years the large swarms 

 of so-called " Cholera Flies " have been flights of 

 Aphides. In this case it is less easy to trace either the 

 final cause of the presence of these insects or their 

 connexion with the appearance of cholera (if such con- 

 nexion exists), than in that of the true Flies, numbers 

 of which, bred in and feeding on the substances which 

 induce disease, are both dependent on the presence of 

 those substances, and corrective of their noxious in- 

 fluences. We may, however, believe that certain con- 

 ditions of the air favourable to the development of 

 disease, may be equally favourable to the development 

 of vegetable life, and consequently to that of vegetable- 

 feeding insects. 



Enough has already been said of the usefulness of 

 Scavenger insects, and of their almost universal presence 

 where their labours are required, to suggest the thought 

 that where pestilence is rife, whether from careless un- 

 cleanliuess or from such noxious atmospheric influences 

 as produce the same effects, there will be found the 

 myriads of Flies, whose office it is, in their earlier stages, 

 to consume the deadly substances which fill the air with 

 poison. It is easy to conceive that the heathen feasts 

 and sacrifices, unguarded by the regulations which sur- 

 rounded those of the Jews, might well call for the 

 presence of these little guests; while in their bestowing 

 the names of Mwcu, muscte, on the uninvited and un- 

 welcome human parasites, who thrust themselves upon 

 their feasts, we may read the feelings which they, ignorant 

 and ungrateful, entertained towards their little bene- 

 factors. 



But it may be said of the carrion -eating, dung-eating, 

 Scavenger Flies, that their purpose is apparent, and for 



