CHAPTER XVII. 



ORDER VII. DIPTERA ( Aristotle). 



AXTLIATA ( Fabiucius). HALTERIPTERA (Clairville). 



The obvious characteristic of this order is the possession of two wings only, and a pair of 

 small knobbed appendages just behind them, which are called halieres or poisers, as in the 

 common fly. The wings are membranous and placed upon the mesothorax, and, when at 

 rest, remain expanded as in the Hymesoptera ; that is, they are never folded upon them- 

 selves. The tarsi are five-jointed. The mouth has a fleshy proboscis, which is merely a 

 modified labium. This proboscis encloses several lancet-like organs, capable of penetrating 

 flesh or the softer parts of vegetables : the mouth is therefore suctorial. In a few genera, 

 as the (Estris, the mouth is closed. The thorax is compact, and the prothorax is reduced 

 to a collar. The wings, which represent the fore pair in other four- winged insects, are 

 membranous, naked, or rather clothed with scales. The disc is divided into a moderate 

 number of areolets, by the inosculation or junction of the nervures or veins. 



This order of insects is clearly separated from each of the other orders : where some 

 species belonging to the Order Xeiroptera are deprived of a pair of wings, they may still 

 be distinguished by the absence of halter es or balancers. The jaws of the diptera are never 

 formed for biting or nipping : so the neuration of the wings of the diptera are quite dif- 

 ferent from that in the other orders. 



The size of the individuals composing this order may be called small ; but what is 

 lacking in this respect is more than made up in numbers, and this whether we take into 

 consideration the number of species, or the vast number of individuals that sometimes 

 swarm together. 



Some of the diptera have domesticated themselves in our dwellings, to the great an- 

 noyance of all good housekeepers ; and notwithstanding the brush and the broom is freely 

 used to drive them away, they seem to entertain no fears of the consequences of returning 

 to their old quarters. Arsenic fly-powder, and all the various traps that the ingenuity of 

 man has yet devised, have not thinned the ranks of the housefly. Wherever man goes, the 

 fly follows in his steps, and makes a free use of his dwelling whenever the weather with- 

 out becomes uncomfortable. 



