CLASS INSECTS. 



409 



balm cricket (Fig. 398), the pucerons, the cochineal, &c. 

 We may also bring near to this group the flea (Fig. 399), 

 for example, which is always apterous, like the bug, and 

 which has been considered by most naturalists entitled to 

 form a particular order, called suckers. 



Fig. 399. The Flea. Fig. 400. The Nepa. Fig. 401 .The Bug. 



545. The order of diptera is characterized by the ex- 

 istence of a single pair of membranous wings, not unlike 

 those of the hymenoptera, and by the structure of the mouth, 

 arranged for suction only ; we observe in it in general a pro- 

 boscis, sometimes horny and elongated, sometimes soft and 

 retractile, and inclosing stiff and sharp bristles. 



Fig. 402. (Estrua. 



Fig. 403. The Ox-fly, or Gad-fly. 



A sufficiently correct idea of the general form of dipterous 

 insects may be derived from one of them known to all the 

 world the common fly ; and we shall only add, that all un- 

 dergo a complete metamorphosis. The larvae (Fig. 402, a) 

 have no limbs ; their head is soft, and the mouth is generally 



