354 MANUAL OF ZOOLOGY. 



ORDER IX. DIPTERA. The anterior pair of wings alone 

 developed ; the posterior pair of wings rudimentary, represented 

 by a pair of clubbed filaments, called " halter es" or "balancers" 

 (fig. 1 88). In a few the wings are altogether wanting. Mouth 

 suctorial The metamorphosis is complete, the larvcz being gener- 

 ally destitute of feet ; but in some cases (e.g., the gnats] the pupce 

 are aquatic and are actively locomotive. In most cases, however, 

 the pupce are quiescent. 



The proboscis in the Diptera consists of a tubular labium 

 enclosing the other parts of the mouth, and is placed on the 

 under surface of the head. Ocelli are present in addition to 

 the compound eyes. The wings are generally horizontal and 

 transparent, the nervures not very numerous, and for the most 



Crane-fly ( Tipula oleracea). 



part longitudinally disposed. The anterior wings usually have 

 appended to their hinder margin, at their base, a pair of little 

 membranous flaps (the " alulae "), which are to be regarded as 

 separate and detached elements of the front wings. The an- 

 tennae are generally small and three-jointed (Brachycera), some- 

 times many- jointed (Tipulidce], or feathery (Cutiddce). The 

 larva is soft and fleshy, with a soft indistinct head, usually 

 apodal, never with thoracic legs, and rarely with pro-legs. 

 The larval skin mostly forms a hardened case for the pupa, 

 but the larvae sometimes cast their skin when becoming pupae, 



