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VORTICELLA , the See also:Bell-Animalcule, a genus of Peritiichous See also:Infusoria (q.v.) characterized by the bell-shaped See also:body, with See also:short oral disk and See also:collar, attached by a hollow stalk, inside and around which passes, attached spirally, a contractile bundle of See also:myonemes . By their contraction the stalk is brought into the See also:form of a corkscrew, the See also:thread being now on the shorter, i.e. the inner, See also:side of the turns; and the See also:animal is jerked back near to the See also:base of the stalk . As soon as the contraction of the thread ceases, the See also:elasticity of the stalk ex-tends the animal to its previous position . On fission, one of the two animals swims off by the development of the temporary posterior See also:girdle of membranelles, the disk being retracted and closed over by the collar, so that the See also:cell is ovoid: on its See also:attachment the posterior girdle of See also:cilia disappears and a stalk forms . The other cell remains attached to the old stalk . In the allied genera Carchesium and Zoothamnium the two produced by fission remain See also:united, so that a branching See also:colony is ultimately produced . The genus is a large one, and many See also:species are epizoic on various See also:water animals . |
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