THE DIPTERA. 



369 



As in Hemiptera, also, the labrum is a more or less elongated 

 pointed plate, and tlie mandibles and maxillae are usually ter- 

 minated by cliitinous cutting setne (Fig. 109). But the bases 

 of these parts are constantly united together ; there is a pair 

 of maxillary palpi, and often a median, more or less styliform 

 structure, usually considered to be the hypopharynx. It 

 seems doubtful, however, whether this may not be formed by 

 the coalesced terminations of the maxillie. In the common 

 House-fly, the labrum, mandibles, and maxillas coalesce at 



Fig. 110.— Upper fl<?ure. Section of the head of Bombvfi. b. ocelhiP ; c, antenna ; rf, 

 clypeus ; e, labrum; /, mandible; (/. epipharynx ; h, maxilla; i, cardo ; j, kj., 

 submentum and nientum ; m, m', labial palpup ; n. parairlossa ; o, linjiua or 

 median process of the ligula; it, occipital foramen ; 1, 2, sclerites of the hypo- 

 pharynx. 



Left lower fisrnre. Terminal portion of a maxilla. 



Middle lower fic^nre. Epipharynx and hvpopharnyx maorified : 1, 2. sclerites of 

 the hypopharynx; .3, cut end of tlie cesophaj^ns : 4. 5. sclerites in the wall of the 

 oesophacrns and sides of the mouth; 6, lip-like projection of the hypopharynx; 

 (/. epipharynx. 



Right lower figure, a, quadrate sclerite connected by a triangular piece with c. one 

 of the lances of the sting; 6, duct of the poison-irland ; /; trrooved median piece 

 in which the lances play; h, one of the lateral setose palpiform sheath-pieces; g, 

 genital aperture. 



their origins to constitute the base of the proboscis, which is 

 mainly formed by the confluent second maxillce. Its longitu- 



