A hypopharynx is also present in the highest Lepidoptera, Burgess having detected it in _Danais archippus_. He states that the hypopharynx forms the floor of the pharyngeal cavity; “it is convex on each side of a median furrow (Fig. 78, _hph_) and somewhat resembles in shape the human breast. The convex areas are dotted over with little papillæ, which possibly may be taste-organs.” As a piercing organ the hypopharynx reaches its greatest development in the Siphonaptera and Diptera, where the chitinous parts are greatly hypertrophied, the fleshy tongue-like portion so developed in the mandibulate orders being greatly reduced. The chitinous parts are alike on each side of the median organ, being bilaterally symmetrical. [Illustration: 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. ] [Illustration: 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. [Illustration: 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. ] [Illustration: 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. ]