VI 



ANTENNATA~THE ENTERIC CANAL 



461 



a narrow 



straight enteric canals present no complications. The canal is most specialised in 

 carnivorous Insecta, while in those Iiiseda that feed on plants it is generally uniform, 

 but much coiled. 



The fore-gut often has 3 divisions ; (1) a pharynx or oral cavity, (2) 

 oesophagus passing through the oesophageal ring, 

 and (3) a variously shaped fore-stomach widened 

 out like a sac. The latter may be wanting as a 

 separate division. If the fore-stomach is provided 

 with a strong muscular wall it is called a crop 

 (ingluvies). In the honey bee it is called the honey 

 stomach. In Insects with sucking mouth parts, 

 and especially in the Lcpidoptera (Fig. 348, p. 488) 

 and Diptera, it is constricted off in the form of a 

 stalked sac, which opens into the posterior part 

 of the fore -gut and is unsuitably called sucking 

 stomach ; it is more correctly a receptacle for food. 

 Between the crop and the mid-gut in many carni- 

 vorous Iiisecta (many Coleoptera, N'europtera, and 

 Orthoptera) a muscular masticatory stomach is 

 interposed ; the chitinous intima of this stomach is 

 much thickened, and in the form of spikes, spines, 

 ridges, teeth, etc. projects into the lumen ; these 

 processes in transverse section form most beautiful 

 and ornamental patterns, A peculiar pumping 

 apparatus is in a few Shynchota connected with 

 the pharynx. The fore-gut is internally provided 

 with a chitinous intima, the continuation of the 

 chitinous exoskeleton. 



The mid-gut, which lies in the abdomen, is the 

 most important division of the enteric canal for 

 the assimilation of food ; its epithelium consists of 



glandular cells and often projects into the lumen in 



°-, „ r I- Tj -IT Tj. ■ 1 i -J P'G- 319.— Digestive apparatus 



the form of folds or villi. It is a somewhat wide „f oaraSus auratus (after Dufour). 



tube fi-equently forming loops, and in it we can ;,-, Head with moutli parts ; oe, osso- 



often distinguish an anterior wider portion, the phagus ; in, crop (ingluvies) ; pv, 



chyle stomach, and a longer thinner posterior masticatory stomacli ; cd, chyle stom- 



,. , 11 - i J.. > m, 1, 1 , 1 ■ ach covered with villi ; iiMijMalpighian 



portion (small intestine). The chyle stomach in ^^^^^j^. ^^_ y,i^a-gat with rectum 



the carnivorous Coleoptera is beset with short diver- (r) ; ad, aual glands with muscular 

 tieula, as if with vilU ; in the Orthoptera longer vesicular appendages ab. 

 diverticula enter its anterior portion. 



The hind-gut is lined with a delicate chitinous intima and has a muscular wall 

 which, at the terminal 'portion ending in the anus, is of considerable thickness. Its 

 length varies, it is often very long and coiled. 



The limit between the mid- and hind-guts is often difficult to define, since the 

 mid-gut also may have an intima, and its ontogenetic development is not sufficiently 

 worked out. It is assumed, somewhat arbitrarily, that the hind-gut begins at the 

 point where the Malpighian vessels enter. Although these are undoubtedly forma- 

 tions of the hind-gut, they do not necessarily always appear at its anterior end. 

 The hind-gut is often further subdivided. Its last division sometimes carries an 

 unpaired ciecum. Paired anal glands (stink glands) may also enter it. The anal 

 papillffi, etc. classed as glands have already been mentioned. The intestine of certain 

 Hhynchota, Psyllidce, and Cicadce is peculiarly constituted. The mid-gut and part 



