246 THE HOUSE FLY— DISEASE CARRIER 



summarizes his conclusions in the following words : 

 **It may be regarded as proved that Stomoxys calcitnnis 

 L., as also S. nigra, Macq., and probably other species 

 of the genus, can convey trypanosomes directly from 

 an infected to a healthy animal, when the bites follow 

 one another immediately. On the other hand, the evi- 

 dence tends to show that when the interval between 

 the bites is longer (the maximum period within which 

 a bite is infectious has not yet been determined), al- 

 though active trypanosomes may be present in the in- 

 testine of the fly, its life is innocuous. There is no 

 indication that trypanosomes ingested by S. calcitrans 

 pass through a developmental cycle, and they appar- 

 ently disappear within twenty-four hours. With re- 

 gard to diseases other than trypanosomiases, there are 

 some grounds for thinking that 5'. calcitrans, like other 

 biting flies, may occasionally disseminate the bacillus 

 of anthrax, and, in Europe, it would appear that the 

 fly is the intermediate host of a species of Filaria para- 

 sitic in cattle. 



The Little House Fly 

 (Fannia [Homalomyia] canicularis L.) 



In discussing the size of the adult house fly in Chap- 

 ter I, we mentioned this little fly which is found rather 

 commonly upon window-panes in houses, and stated 

 that it was the source of the prevalent error to the 

 effect that house flies grow after they become winged 

 and that these little flies are the young of the larger 

 flies. They belong, however, not only to an entirely 



