50 ILLINOIS BIOLOGICAL MONOGRAPHS [220 



genera, but they are present and project toward the cephalo-lateral 

 corners of the labrum. The caudal end of the epipharynx in many in- 

 sects gives rise to long chitinized arms which have been called cornua 

 (cu). The hypopharynx may be subdivided into a distal, unpaired, me- 

 dian piece, which is usually called the hypopharynx, and a proximal 

 paired area. 



The chitinized portion of the anterior end of the alimentary canal 

 of Diptera can be homologized with the epipharynx and the hypophar- 

 ynx of generalized insects. The following hypothetical epipharynx 

 and hypopharynx (Fig. 493) and their closely associated parts have 

 been constructed for Diptera. In the figures of the lateral views of the 

 hypothetical type an enlarged, three-sided, chitinized tube extends cau- 

 dad from the dorsal end of the hypopharynx and epipharynx. It has 

 been called the oesophageal pump (oe. p). This is not a part of the 

 epipharynx or of the hypopharynx, but is a modification of the pharynx, 

 a portion of the alimentary canal. All of the chitinized parts ventrad 

 of the membranous area at the cephalic end of the oesophageal pump 

 belong to the epipharynx and the hypopharynx. The dorsal ends of 

 the epipharynx and the hypopharynx are united and form a single chi- 

 tinized tube, and this has been called the basipharynx (bph). Except 

 for this union, the epipharynx and the hypopharynx are continuous 

 chitinized pieces with lance-like distal ends. The distal portion of the 

 epipharynx is joined to the labrum by a membrane along its lateral 

 margin. The tormae in the hypothetical type project from the lateral 

 margins of the epipharynx and unite with the latero-ventral portions 

 of the fronto-clypeus (fr. c). Two projections occur at the dorsal end 

 of the basipharynx, and these are considered homologous with the cor- 

 nua (cu) of the epipharynx of generalized insects. The distal end of 

 the hypopharynx is a free lance-like organ, and a salivary duct (s. d) 

 enters its proximal end just dorsad of the place where it joins the 

 labium (li). The salivary duct extends thru the hypopharynx to its 

 distal end. 



The oesophageal pump of the alimentary canal is closely associated 

 with the epipharynx and hypopharynx in all the Nematocera and in 

 Promachus (Fig. 517), Tabanus (Fig. 494), Leptis (Fig. 520), and 

 Psilocephala (Fig. 533) of the Brachycera. In a majority of the above 

 forms, the oesophageal pump is an elastic, semi-chitinized, three-sided 

 tube with muscles connecting with each of its surfaces. A contraction 

 of these muscles expands the tube, which upon their relaxation assumes 

 its normal shape. In some forms, as Tabanus and Promachus, there 

 is only one chitinized elastic surface. In a number of genera, as Chi- 

 ronomus (Fig. 531), Psychoda (Fig. 529), and Leptis (Fig. 520), the 



