Page:Jardine Naturalist's library Entomology.djvu/134

128, as among vertebral animals, of three tunics or coats, the mucous, cellular, and muscular, the first being internal, and the others superimposed in the order in which they have just been named. The first is delicate and soft, without any decided texture, frequently transparent, and of such tenuity that its presence is not always easily detected. The second layer, (which Strauss names membrane propre, or proper skin,) is likewise for the most part smooth and thin, although it sometimes becomes thicker and spongy. It is generally almost without fibres, but, when highly magnified, a few globules or granulations appear, arranged transversely in its tissue. These have been called by Strauss, gastric glands. According to Leon Dufour, the membrane in question is entirely wanting in hemipterous insects. The muscular membrane is firm, fibrous, and contractile, surrounding and protecting the exterior, and distinct longitudinal and transverse vessels pervade its texture. It is it which causes the peristaltic movement of the digestive tube, and it forms the contractions and sphincters observable in different parts of it. These contractions, as already intimated, form various divisions in the intestinal tube which have names assigned to them in accordance with their functions. The following divisions are recognised, the pharynx, the esophagus, the crop, the gizzard, the chylific ventricle, the slender intestine, the cœcum, and the rectum. Besides these integral parts of the canal, there are various vessels appended to it, which discharge juices