284 MANUAL OF ZOOLOGY. 



common Flea (Pulex irritans}, another well-known and con- 

 siderably more troublesome member of this order is the Chigoe 

 (Pulex penetrans) of the West Indies and South America. 



ORDER VIII. DIPTERA. The anterior pair of wings alone 

 developed ; the posterior pair of wings rudimentary, repre- 

 sented by a pair of clubbed filaments, called " halteres," or 

 "balancers" (fig. 113). In a few the wings are altogether 

 wanting. Mouth suctorial The metamorphosis is complete, 

 the larvas being generally destitute of feet ; but in some cases 

 (e.g., the gnats) the pupse are aquatic and are actively loco- 

 motive. In most cases, however, the pupae are quiescent. 



The proboscis in the Diptera consists of a tubular labium 

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



Fig. 113. Diptera. Crane-fly (TiJ>ula cleracea). 



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 

 part longitudinally disposed. The antennae are generally 

 small and three-jointed, sometimes many-jointed (Tipulidcf), 

 or feathery ( Culiddce). 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, or even spin cocoons. In 

 some the eggs are hatched within the body of the mother, so 



