CH. XV.] SPECIES OF DIPTEROUS INSECTS. 215 



the flies which crawl up our windows, there are not 

 only several distinct species, but also that the in- 

 sect at whose tormenting attacks upon our legs in 

 the showery days of summer we are so often en- 

 raged, does not even belong, notwithstanding its 

 apparent identity, to the same genus. If one of 

 these annoying tormentors (which is the Stomoxys 

 calcitrans) be caught and examined, it will be found 

 that the mouth is formed into a horny, sharp-pointed 

 weapon, capable of piercing the flesh, while thesoft 

 blunt apparatus of the mouth of the musca is quite 

 incompetent to such an operation, being fitted only 

 for the sipping of fluids, or the extraction of honeyed 

 sweets; forming, in fact, a long tubular sucker, 



Head of the fly, with the mouth extended ; A. seen side wise, 

 B. seen from above. 



jointed in the middle, so as to fold back close to the 

 head (Fig. A and B), and armed at the base with a 

 pair of exarticulate feelers, and at the extremity 

 TOth two fleshy lobes, which are employed as in- 

 struments of suction. This organ possesses very 

 great muscular power, and we have seen the insect, 

 by its assistance alone, carry off pieces of sugar 

 much larger than its head. The under surface of 



