CHAPTER XL 



INSECTS TWO-WINGED FLIES. 



THE last Order* of winged insects to which we shall 

 devote a few lines is that in which we find the gnat, 

 the crane fly, the house fly, and their allies. The oral 

 organs in these are of the analogically representative 

 character, of which we have seen so many examples in 

 other orders, and they are more or less developed in 

 the different genera according to the functions they 

 are required to perform. A fleshy tubular suctorial 

 apparatus, adapted to the passage of fluid food, is the 

 common feature of the two-winged flies, but the gnats 

 and Breese flies possess an additional set of fine sharp 

 instruments, specially fitted for puncturing the skin of 

 the animals on which they prey. This typical organi- 

 zation gradually becomes less and less perfect in other 

 groups until in those individuals that take little or no 

 food in the perfect state, both lancets and proboscis 

 totally disappear. The two wings, in many species, are 

 expanded at the base behind into small membranous 

 processes called Alula, or winglets, and in the majority 

 of them two tiny bulbs on slender footstalks, called 

 H alter es or poisers, project horizontally from the tho- 

 rax, one on each side close behind the wings they 

 are even present in those species that are wingless, 

 and are therefore regarded as very important organs 

 in the economy of these insects, but entomologists are 

 not agreed as to their uses. Some are of opinion that 

 they are simply the representatives of a second pair of 

 wings, while others infer that they are subservient to 

 the function of respiration, more particularly as a 



Order DIPTERA from the Greek dis, twice, and pteron, a 

 wing. Wings two, with winglets at the base. 



