Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 ALISILXTAIIY CAXAL. 55 vascular canals). In the larger Polyps (Anthozoa) a tiil)e derived from an invagination of the oral disc projects into the central pai't of the digestive cavity. This is known as the stomach of the polyp, although it serves entirely for the introduction of food, and should be called rather the buccal or oesophageal tube (fig. 43). Organs for the prehension of food are found even with this simple digestive system.
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 ALISILXTAIIY CAXAL. 55 vascular canals). In the larger Polyps (Anthozoa) a tiil)e derived from an invagination of the oral disc projects into the central pai't of the digestive cavity. This is known as the stomach of the polyp, although it serves entirely for the introduction of food, and should be called rather the buccal or oesophageal tube (fig. 43). Organs for the prehension of food are found even with this simple digestive system. For near the mouth are placed radially or bilate- rally arranged appendages or processes of the body, which set up Fig. 44.—Aurelia aurita seen from the oral surface. JUA, the four oral tentacles -with the mouth in the centre ; Gl; genital folds; GH, opening of the genital pouches ; RIc, mar- ginal bodies ; KG, radial canals; T, tentacles at the margin of the disc. currents to convey small particles of food, or as tentacles seize foreign bodies and convey them to the movith (Polyps, Medusae) (fig. 44). Such appendages serving for the capture of prey may also be placed further from the mouth (tentacles of Medusjw, Siphonophora, Ctenophora). When the digestive cavity acquires a wall distinct from the body wall, and usually separated from the latter by the body cavity (ex- cepting the parenchymatous worms), it appears in the simplest cases as a blind tube, which may be either simple, bifurcated, or branched
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