Fig. 79.—A, hypopharynx of Pulex canis: x, basal portion situated within the head; s. d, common duct of the four bladder-shaped salivary glands; s. d′, opening of the tubular salivary glands into the throat. B, end of the hypopharynx, showing the gutter-like structure and teeth at the end.—After Landois.
Fig. 80.—Beak of Vermipsylla: hyp, hypopharynx.—After Wagner.
In the fleas the hypopharynx is a large, slender, unpaired, long, chitinous trough, as long as the mandibles, and toothed at the end. Figures 79 and 80 show its relations to the other parts of the mouth; in Fig. 79, x, is seen where the salivary duct opens into the pharynx. Although this organ is not unanimously referred to the hypopharynx, yet from the description of Landois and others, it is evident that this structure does not correspond to the labrum or epipharynx, but belongs to or arises from the floor of the mouth, and, being in close relation to the labium, and also receiving the salivary duct, must be a true hypopharynx.
In the Diptera the hypopharynx reaches its highest development as a large, stout, awl-like structure.
Meinert, in his detailed and elaborately illustrated work, Trophi Dipterorum (1881), has made an advance on our knowledge of the hypopharynx and its homologies, both by his evidently faithful descriptions and dissections, and by his admirably clear figures.
Fig. 81.—Culex pipiens, section of head: oe œsophagus; sm, upper muscle, lm, lower muscle of the œsophagus; ph, pharynx; rm, retractor muscle of the receptacle (r) of the salivary duct (s.d); lbr, labrum; ep, left style of the epipharynx; f, part of front of head.—After Meinert.
Fig. 82.—Pharynx and hypopharynx of Simulium fuscipes: lph, lower lamina of the pharynx; p, the salivary duct (s.d) perforating the pharynx; o, orifice of the duct; shp, styles of the hypopharynx; mph, membranous edge of the hypopharynx; m, protractor muscle of the pharynx; gp, gustatory papillæ.—After Meinert.