THE DIGESTIVE CANAL AND ITS APPENDAGES 297 



THE DIGESTIVE CANAL AND ITS APPENDAGES 



The alimentary or digestive canal of insects is a more or less 

 straight tube, which connects the mouth and anus, the latter in- 

 variably situated in the last segment of the body, under the last 

 tergite or suranal plate. It lies directly over the ventral nervous 

 cord and under the dorsal vessel, passing through the middle of the 

 body (Fig. 297). It is loosely held in place by delicate retractor 



cut-. 



FIG. 297. Transverse section through an abdominal segment of larva of Megalopyge 

 crixpata, showing the relations of the digestive canal to the other organs : int, hind-intestine, with 

 its mucous or epithelial layer (fp), and ml its outer or muscular layer; ng, ventral ganglion ; M, 

 heart ; mp, urinary tubes ; /', fat-body ; fto, thickened portion of the hypodermis (hy) containing 

 the setigenous cells; m, muscles; ?.', a pair of retractor muscles inserted near the base of the 

 lateral glandular process (Igp) ; eut, cuticula ; I, legs. Also compare Figs. 142-144 and 234. 



muscles (retractores ventriculi, found by Lyonet in the larvae of 

 Lepidoptera, and occurring in those of Diptera), but is principally 

 supported by exceedingly numerous branches of the main tracheae. 



It is in the higher adult insects differentiated into the mouth and 

 pharynx, the oesophagus or gullet, supplementary to which is the 

 crop (ingluvies) or "sucking stomach" of Lepidoptera, Diptera, and 

 Hymenoptera ; the proventriculus or gizzard ; the ventriculus, " chyle- 

 stomach," or, more properly, mid-intestine, and the hind-intestine, 

 which is divided into the ileum, or short intestine, the long intes- 

 tine, often slender and coiled, with the colon and the rectum. 

 Morphologically, however, the digestive or enteric canal is divided 

 into three primary divisions, which are indicated in the embryo 



