[Illustration: FIG. 69.—Digestive system of _Xyphidria camelus_ (after Dufour): _a_, head capsule; _b_, salivary glands; _c_, oesophagus; _d_, crop; _e_, proventriculus; _f_, chyle, or true stomach; _g_, small intestine; _h_, large intestine; _i_, Malpighian tubes; _k_, termination of body.] The alimentary canal is more complex anatomically than it is morphologically, and various parts are distinguished, viz. the canal and its appendicula; the former consisting of oesophagus, crop, gizzard, true stomach, and an intestine divided into two or more parts. It should be remarked that though it is probable that the morphological distinctions correspond to a great extent with the anatomical lines of demarcation, yet this has not been sufficiently ascertained: the origin of the proctodaeum in _Musca_ is indeed a point of special difficulty, and one on which there is considerable diversity of opinion. In some Hemiptera the division of the canal into three parts is very obscure, so that it would be more correct, as Dufour says, to define it as consisting in these Insects of two main divisions—one anterior to, the other posterior to, the insertion of the Malpighian tubes. It should be borne in mind that the alimentary canal is very different in different Insects, so that the brief general description we must confine ourselves to will not be found to apply satisfactorily to any one Insect. The oesophagus is the part behind the mouth, and is usually narrow, as it has to pass through the most important nervous centres; extremely variable in length, it dilates behind to form the crop. It may, too, have a dilatation immediately behind the mouth, and in such case a pharynx is considered to exist. The crop is broader than the oesophagus, and must be looked on as a mere dilatation of the latter, as no line of {125}demarcation can be pointed out between the two, and the crop may be totally absent. In some of the sucking Insects there is a lateral diverticulum, having a stalk of greater or less length, called the sucking-stomach; it is by no means certain that the function this name implies is correctly assigned to the organ. The gizzard or proventriculus (French, _gésier_; German, _Kaumagen_) is a small body interposed in some Insects between the true stomach and the crop or oesophagus. It is frequently remarkable for the development of its chitinous lining into strong toothed or ridged processes that look as if they were well adapted for the comminution of food. The function of the proventriculus in some Insects is obscure; its structure is used by systematists in the classification of ants. The extremity of the proventriculus not infrequently projects into the cavity of the stomach.