Fig. 304.—Longitudinal section through the head of Danais, showing the interior of the left half: mx, left maxilla, whose canal leads into the pharynx; hph, floor of the latter, showing some of the taste-papillæ; oe, œsophagus; ep, epipharyngeal valve; sd, salivary duct; d.m, f.m, and cl, as in Fig. 302.—After Burgess.
Meinert (“Trophi Dipterorum”) has made elaborate dissections of the mouth and its armature, including the pharynx of several types of Diptera, with its musculature. He describes the pharynx as the principal, and in most Diptera, as the only part of the pump (antlia), and says: “By the muscles of the pump (musculis antliæ) the superior lamina of the pharynx is varied that the space between the two laminæ may be increased, and the liquid is thus led through the siphon formed by the mouth-parts into the mouth” (Fig. 81).
The œsophagus.—This is a simple tube, largest in those insects feeding on solid, usually vegetable, food, and smallest in those living on liquid food. It usually curves upwards and backwards, passing directly under the brain, and merges into the crop or proventriculus either at the back part of the head or in the thorax, its length being very variable. Its inner walls longitudinally are folded and lined with chitin.
According to Newport, in the œsophagus of the Gryllidæ, of the two layers of the mucous lining the second is distinctly glandular and secretory, and in it there are many thousands of very minute granular glandular bodies, which probably secrete the “molasses” or repellent fluid often ejected by these and other insects when captured.
The crop or ingluvies.—This, when present, is an enlargement of the end of the œsophagus, and lined internally with a muscular coat. It is very large in locusts (Fig. 298), Anabrus (Fig. 299), and other Orthoptera (the Phasmidæ excepted), in the Dermaptera, and most adult Coleoptera. A crop-like dilatation in front of a spherical gizzard is also present in the Synaptera (Poduridæ and Lepismidæ), as well as in the Mallophaga (Nirmidæ).
Fig. 305.—Digestive canal of Calandra: H, pear-shaped œsophagus; I, crop; K, gastric cœca L, ilium; MN, colon; P, urinary tubes.—After Newport.
Fig. 306.—Section of the crop (H), gizzard (I), and stomach (K) of Athalia.-After Newport.
