The true stomach, or chylific ventricle (_Magen_ or _Mitteldarm_ of the Germans), is present in all the post-embryonic stages of the Insect's life, existing even in the imagines of those who live only for a few hours, and do not use the stomach for any alimentary purpose. It is so variable in shape and capacity that no general description of it can be given. Sometimes it is very elongate, so that it is coiled and like an intestine in shape; it very frequently bears diverticula or pouches, which are placed on the anterior part, and vary greatly in size, sometimes they are only two in number, while in other cases they are so numerous that a portion of the outside of the stomach looks as if it were covered with villi. A division of the stomach into two parts is in some cases very marked, and the posterior portion may, in certain cases, be mistaken for the intestine; but the position of the Malpighian tubes serves as a mark for the distinction of the two structures, the tubes being inserted just at the junction of the stomach with the intestine. The intestine is very variable in length: the anterior part is the smaller, and is frequently spoken of as the colon; at the extremity of the body the gut becomes much larger, so as to form a rectum. There is occasionally a diverticulum or "caecum" connected with the rectum, and in some Insects stink-glands. In some Hemiptera there is no small intestine, the Malpighian tubes being inserted at the junction of the stomach with the {126}rectum. The total length of the alimentary canal is extremely variable; it is necessarily at least as long as the distance between the mouth and anal orifice, but sometimes it is five or six times as long as this, and some of its parts then form coils in the abdominal cavity. The alimentary canal has two coats of muscles: a longitudinal and a transverse or annular. Both coexist in most of its parts. Internal to these coats there exists in the anterior and posterior parts of the canal a chitinous layer, which in the stomach is replaced by a remarkable epithelium, the cells of which are renewed, new ones growing while the old are still in activity. We figure a portion of this structure after Miall and Denny, and may remark that Oudemans[42] has verified the correctness of their representation. The layers below represent the longitudinal and transverse muscles. [Illustration: FIG. 70.—Epithelium of stomach of Cockroach (after Miall and Denny): the lower parts indicate the transverse and longitudinal muscular layers.] In addition to the various diverticula we have mentioned, there are two important sets of organs connected with the alimentary canal, viz. the salivary glands and the Malpighian tubes.