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ACTINOZOA

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Originally appearing in Volume V01, Page 158 of the 1911 Encyclopedia Britannica.
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ACTINOZOA , a See also:

term in systematic See also:zoology, first used by H. M. D. de See also:Blainville about 1834, to designate animals the See also:organs of which were disposed radially about a centre. De Blainville included in his See also:group many unicellular forms such as Noctiluca (see See also:PROTOZOA), See also:sea-anemones, See also:corals, jelly-See also:fish and hydroid polyps, echinoderms, See also:polyzoa and See also:rotifera. T. H. See also:Huxley afterwards restricted the term. He showed that in de Blainville's group there were associated with a number of heterogeneous forms a group of animals characterized"by being composed of two layers of cells comparable with the first two layers in the development of vertebrate animals. Such forms he distinguished as See also:Coelentera, and showed that they had no See also:special See also:affinity with echinoderms, polyzoa, &c. He divided the Coelentera into a group See also:Hydrozoa, in which the sexually produced embryos were usually set See also:free from the See also:surface of the See also:body, and a group Actinozoa, in which the embryos are detached from the interior of the body and See also:escape generally by the oral See also:aperture. Huxley's Actinozoa comprised the sea-anemones, corals and sea-pens, on the one See also:hand, and the See also:Ctenophora on the other. Later investigations, whilst confirming the See also:general validity of Huxley's conclusions, have slightly altered the limits and See also:definitions of his See also:groups.

(See See also:

ANTHOZOA, COELENTERA, CTENOPHORA and HYDROZOA.) (P. C.

End of Article: ACTINOZOA

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