THE DIPTERA. 



369 



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

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

 minated by chitinous cutting setae (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 maxilla?. In the common 

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



Fig. 110.— Upper figure. Section of the head of Bombus. b, ocellus : c, antenna ; d, 

 clypeus ; e, labrum ; /, mandible ; g. epipharynx ; A, maxilla ; i, cardo ; ,;, k, I, 

 submentum and men turn : m, m'. labial palpus ; n, paraglossa ; o. lingua or 

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

 pharynx. 



Left lower figure. Terminal portion of a maxilla. 



Middle lower figure. Epipharynx and hypopharnyx magnified ; 1, 2, sclerites of 

 the hypopharynx; 3, cut end of the oesophagus; 4, 5, sclerites in the wall of the 

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

 _ g. epipharynx. 



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

 of the lances of the sting; b, duct of the poison-gland ; f, grooved 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 maxillae. Its longitu- 



