221] HEAD OF DIPTERA— PETERSON 51 



tube is more or less membranous and not distinctly three-sided. The 

 oesophageal pump is wanting in all the Diptera except those named, 

 and the membranous oesophagus connects directly with the basipharynx. 

 The oesophageal pump shows considerable variation in its shape, posi- 

 tion, and size, as can be seen in the figures of Bibio (Fig. 523), Rhyphus 

 (Fig. 508) and others. 



The basipharynx (bph) is interpreted as including all of the united 

 portions of the epipharynx and the hypopharynx, but the extent of 

 this union varies somewhat in the different genera. In a majority of 

 the Nematocera no sutures or constrictions occur between the basiphar- 

 ynx and the lance-like portions of the epipharynx and the hypophar- 

 ynx. Such constrictions and secondary sutures do occur in a majority 

 of the Brachycera, as in Leptis (Fig. 520) and Promachus (Fig. 517), 

 and in all of the Cyclorrhapha. The basipharynx (bph) varies in size 

 and shape, as can be seen in the figures. Muscles connect with the 

 cephalic and caudal aspects of the basipharynx, those on the cephalic 

 aspect expanding the basipharynx and thus producing suction. This 

 sucking apparatus is well developed in all forms which have no oesophag- 

 eal pump. The chitinized projections at the dorsal end of the basiphar- 

 ynx, called the cornua (cu), vary in shape and size. Some are blunt, 

 others long and narrow, as in Leptis and the Calyptratae, and still 

 others are disk-shaped, as in Promachus (Fig. 517). 



Distinct tormae (to) are present in Diptera except in a few species 

 of the Nematocera. In all the Nematocera and in Leptis (Fig. 520), 

 Psilocephala (Fig. 533), Platypeza (Fig. 543), Aphiochaeta (Fig. 544), 

 Lonchoptera (Fig. 539), and Scenopinus (Fig. 538), they resemble the 

 hypothetical type in that they join with the fronto-clypeus. In other 

 genera the tormae have an exposed portion located ventrad of the 

 fronto-clypeus and all connection between the fronto-clypeus and the 

 tormae is lost, except in Simulium (Fig. 497) and Tabanus. The 

 variations in the shape and the extent of the tormae is well illustrated 

 by the numerous figures. The so-called fulcrum described by numerous 

 morphologists for the Calyptratae is composed of the tormae and the 

 basipharynx. A more or less distinct secondary suture (s. s) is shown 

 in the drawings as separating the tormae from the basipharynx, and 

 the broken line on the tormae indicates the place of connection of the 

 membrane of the basiproboscis with the tormae. In figures of the 

 Nematocera and of forms in which the tormae connect with the fronto- 

 clypeus the broken line indicates the place of union between these parts. 



The epipharynx (ep) is present and closely associated with the 

 labrum in all Diptera having functional mouth-parts. The interrela- 

 tionship between the epipharynx and the labrum has been discussed 



