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RADIATA

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Originally appearing in Volume V22, Page 785 of the 1911 Encyclopedia Britannica.
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RADIATA , a See also:

term introduced by See also:Cuvier in 1812 to denote the lowest of his four See also:great See also:animal See also:groups or " embranchements." He defined them as possessing radial instead of bilateral symmetry, and as apparently destitute of See also:nervous See also:system and sense See also:organs, as having the circulatory system rudimentary or absent, and the See also:respiratory organs on or co-extensive with the See also:surface of the See also:body; he included under this See also:title and See also:definition five classes,—Echinodermata, Acalepha, Entozoa, Polypi and See also:Infusoria. See also:Lamarck (Hilt. nat. d. Anim. s. Vertebres) also used the term, as when he spoke of the Medusae as radiata medusaria et anomala; but he preferred the term Radiaria, under which he included Echinodermata and Medusae. Cuvier's term in its wide See also:extension, however, passed into See also:general use; but, as the See also:anatomy of the different forms became more fully known, the difficulty of including them under the See also:common designation made itself increasingly obvious. Milne-See also:Edwards removed the See also:Polyzoa; the See also:group was soon further thinned by the exclusion of the See also:Protozoa on the one See also:hand and the Entozoa on the other; while in 1848 Leuckart and See also:Frey clearly distinguished the Coelenterata from the Echinodermata as a See also:separate sub-See also:kingdom, thus condemning the usage by which the term still continued to be applied to these two groups at least. In 1855, however, See also:Owen included under Lamarck's term Radiaria the Echinodermata, See also:Anthozoa, Acalepha and See also:Hydrozoa, while See also:Agassiz also clung to the term Radiata as including Echinodermata, Acalepha and Polypi, regarding their separation into Coelenterata and Echinodermata as " an exaggeration of their anatomical See also:differences" (See also:Essay on See also:Classification, See also:London, 1859). These attempts, however, to perpetuate the usage were finally discredited by See also:Huxley's important Lectures on See also:Comparative Anatomy (1864), in which the term was finally abolished, and the " radiate See also:mob " finally distributed among the Echinodermata, Polyzoa, Vermes (Platyhelminthes), Coelenterata and Protozoa.

End of Article: RADIATA

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