DIPTERA. 337 



are the upper lip, mandible, maxillae, and palpi or some 

 of these completely changed from their form as that 

 is seen in Biting insects. These lancets, always delicate, 

 are nevertheless comparatively strong in the Blood- 

 Suckers ; while in those Flies which live on fluids not 

 enclosed in thick-skinned vessels, they are feeble and 

 flaccid. 



The antennae vary greatly. Under one form there are 

 two or three short joints, of which the terminal is large 

 and sometimes nearly globose, with a bristle springing 

 from its upper side or from its apex. Under another, 

 the several joints form a more or less spindle-shaped 

 antenna, with or without a terminal bristle, while in the 

 Gnats, Daddy Longlegs, &c., the antennae are long, 

 slender, many-jointed, and beautifully decorated with 

 whorls of hair. There are also many intermediate 

 forms. 



The tarsi are five-jointed. The commonest form of 

 foot consists of a pair of curved claws above a pair of 

 flat, sucker-like, hairy pads. The claws vary in form, 

 and the pads both in form and number there being two, 

 three, or, rarely, none. 



The larvae of Flies are generally legless maggots of 

 simple form the " Gentle" used by anglers being a well- 

 known example ; but some of the aquatic species are 

 more complicated externally, and are furnished with 

 ornamental appendages belonging to the breathing ap- 

 paratus. 



The pupae are inactive, a curious exception being 

 found in the Gnat family, of which the pupa (aquatic) 

 is very active, although unable to feed. The pupae are 

 sometimes naked, and sometimes remain enclosed in the 

 larva skin, which either retains much of its original form 



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