DIPTERA. 361 



ORDER XII. DIPTERA.* 



THE great character of this Order is easily recog- 

 nised ; it is, that they have but a single pair of 

 wings, but in the place of the second pair there is, 

 on each side, a little slender stalk, bearing a club- 

 shaped head; these are called Jialteres^ or poisers, 

 though their real use seems yet uncertain ; they are 

 certainly essential to flight. The mouth takes the 

 form of a sucker, terminating in fleshy lips, or en- 

 closing a sharp piercing lancet. These insects vary 

 greatly in their transformations. The larvce are 

 always without feet ; some inhabit water, others the 

 wood of trees, others the flesh or the intestines of 

 Mammalia. Those which have a scaly head, change 

 either to an active pupa, as in the Gnats, or to one 

 covered, but in which the limbs are visible, as the 

 Crane-flies ; but such as have the head soft and 

 varying, become pupa without throwing off the 

 larva skin, which, drying, becomes an oval cocoon, 

 from which the papa within separates, and in due 

 time comes forth, bursting off the top of the case. 

 Such is the transformation of the Flies. 



Few Insects are more annoying than the common 

 Gnat, (Culex^ and few are more interesting in 

 their habits. The female Gnat, alighting on the 



* Ava, rfwo, two, and yrri^ov, pteron, a wing, 

 t Halter, a plummet. $ Its Latin name. 



VOL. II. R 



