Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 ALIMENTARY CANAL OF ARTHROPODA. 269 They become organs wliicli will be considered wlien we come to speak of tlie appendages of tlie mid- gut. The hind-gut forms the shortest, and generally a narrower portion of the enteric tract. It is seldom widened mesially, and in a few only is it provided with cEecal appendages. The function of the enteric canal is not, in all Crustacea, limited to digestion. In some (Astacus, Limnadia, Daphnia) an almost rhythmical taking-in and driving- out of water
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 ALIMENTARY CANAL OF ARTHROPODA. 269 They become organs wliicli will be considered wlien we come to speak of tlie appendages of tlie mid- gut. The hind-gut forms the shortest, and generally a narrower portion of the enteric tract. It is seldom widened mesially, and in a few only is it provided with cEecal appendages. The function of the enteric canal is not, in all Crustacea, limited to digestion. In some (Astacus, Limnadia, Daphnia) an almost rhythmical taking-in and driving- out of water may be observed in the hind- gut, so that this portion appears to have a respiratory function also. In many lower Crustacea the enteric canal undergoes degeneration. It disap- pears in the degenerate males of the para- sitic Copepoda, and in some Cirripedia and most Rhizocephala, where nutrition is efiected by other means (cf. supra, p. 236). § 209. Fig. 137. Digestive organs of a Spider, oe Qilsopliagus. c Snpraoesophageal ganglion (Cerebrum). v Stomach. v' Its lateral processes. v' Appendages directed up- wards, i Mid-gut. r Cloacal widened end of the enteron. lih Openings from the liver into the enteron. e Urinary canals (after Dages). The three divisions of the enteric tube are distinctly marked off in the Protra- cheata; the mid-gut, which is distinguished by its width, forms the largest part of it. The enteric tube of the Arachuida is divided into a larger number of segments, except in the degenerate forms. The narrow fore-gut (Fig. 137, oe) leads into a mid-gut, which is generally elongated, and has its more anterior portion (v) frayed out into lateral ctecal sacs. These are absent in the Phrynida and Scorpionea. In the Aranea there are five pairs of them {v'), which extend to the base of the legs and palps. In the Galeodea four pairs, the last two of which are bifurcated, extend into the appendages (feet, claws, and palps); in the Pycnogo- nida these cseca extend al
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