Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 ALIMENTARY CANAL. 531 the simple narrower portion which follows it. Larger caeca, too, after the manner of hepatic glands, may be inserted at the com- mencement of the chylific ventricle (Orthoptera). The commencement of the hind gut or posterior portion of the alimentary canal is indicated by the opening of filiform csecal tubes, the MabpigJdan vessels. It is divided into two or more rarely three regions, which are di
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 ALIMENTARY CANAL. 531 the simple narrower portion which follows it. Larger caeca, too, after the manner of hepatic glands, may be inserted at the com- mencement of the chylific ventricle (Orthoptera). The commencement of the hind gut or posterior portion of the alimentary canal is indicated by the opening of filiform csecal tubes, the MabpigJdan vessels. It is divided into two or more rarely three regions, which are distinguished as the small intestine, the larya intestine and the rectum. The last region is provided with a strong layer of muscles, and contains in its walls four, six or more longitudinal ridges, the so-called rectal glands (fig. 439, .ft). Sometimes two glands, the so-called anal glands (, Ad], open into the rectum immediately in front of the anus. Their secretion, on account of its irritating qualities and dis- agreeable smell, seems to serve as a pro- tection to the animal. In exceptional cases the larva alone takes up nutriment, the sexually mature apterous form being without a mouth (Ephemera). Finally the stomach of the larva in a few cases ends blindly, and does not communicate with the hind gut (larva? of Hymenoptera, Pupipara, Ant-lion). The Malpighian vessels already men- tioned, which were formerly erroneously held to be bile organs, undoubtedly func- tion as urinary organs. Their contents, secreted by the large nucleated cells of their walls, are usually of a brownish yellow or white colour, and consist of an aggregation of small granules and con- cretions, which, for the most part, consist of uric acid. Crystals of oxalate of lime and taurin have also been found. The numbers and grouping of these filiform tubes, which are usually very long and wound round about the chy- lific ventricle, varies very much. As a rule there ai-e four or six, or more rarely eight o
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