Order DIPTEEA. 



Apart from the males of the Coccid^,. or scale-insects, the 

 Diptera stand alone amongst the orders of Insects in the pecu- 

 liarity of possessing only two wings, the hinder wings being 

 represented by a small organ on each side of the thorax behind 

 and below the wing-root, known as the halter. These halteres 

 are invariably present in all the winged forms of the Order, and 

 generally present also in the very few wingless ones. In rare 

 cases the female only is wingless. 



The mouth-parts exhibit a wide diversity in structure, but they 

 are nearly always in the shape of a proboscis, formed for sucking, 

 or, in some groups, for piercing the skin of animals or man for 

 the purpose of imbibing the blood. 



The antennae also show extreme range in form, but are valuable 

 as one of the primary means of classification. The palpi have 

 from one to five joints, the usual number in the Nematoceea 

 being four ; in the Brachyceba and the MusciDiE, two, of which 

 the first is small and often more or less rudimentary. 



The wings exhibit a multiplicity of schemes of venation, all 

 referable ultimately to a common general plan, and this latter 

 character, the venation, perhaps affords the soundest basis for 

 classifying the families, at any rate, so far as the perfect insects 

 only are concerned. 



The larva in the Diptera is apodal, moving by means of small 

 external transverse ridges or stiff bristly hairs, and progressing 

 by a wriggling motion from side to side. In the vast majority 

 of the species, the habitat of the larvae (popularly' known as 

 " grubs" or "maggots ") is decomposing vegetable or animal matter, 

 principally the former (the bulk of the higher Muscid-E and a 

 large proportion of tlie Acalyptrate Muscidje) ; a considerable 

 number of species are root- or leaf -miners (Antromyin^, 

 Trypexix.e) * ; a further considerable number are aquatic 

 (CuLiciD.E, CuiRONOMiD.^, many Tipulid^, Stratiomyid.i; and 

 ACALYPTRATA, somc Tabanid^, and various genera in many other 

 famihes) ; and a few are parasitic on mammals or birds (CEstrid^, 

 HiPPOBOSCiD.E),t insects (Conopid.!;, etc.), spiders (Cyrtid.e), and 

 other creatures. Some live in the earth (Tabanid^, Asilidje, 

 EMPiDiE), a few are carnivorous (certain Syrphid^) ; and one 

 family forms galls (Cecidomyid.e) : in short, the larvae of Diptera 

 as a whole exhibit the most varied methods of existence. 



* Some Indian Tuypetin^ live in rotten wood or in fruit. 

 t Although in Hippoboscid^ the larvae develop in the body of the parent, 

 the life of the imago is passed upon the body of its host. 



