Tipula oleracea. 



CHAPTER XIII. 



DIPTERA, OR TWO-WINGED FLIES. 



The insects to which I have alluded at the close of the 

 last chapter, are the almost innumerable hosts of the 

 two- winged Flies, forming the Order Diptera. Their 

 most prominent characteristic is that referred to in 

 their name : they possess only a single pair of mem- 

 branous wings, traversed by branching veins, the 

 posterior pair of wings being represented by two small 

 knobbed filaments called halteres or balancers^ placed 

 one on each side of the hinder part of the thorax. The 

 presence of the latter organs, indeed, seems to be the 

 most essential character of the Diptera, as they exist 

 even in a few species which are totally destitute of 

 true wings; they sometimes project so much as to be 



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