RADIATA, the lowest of Cuvier's four great divisions of the animal kingdom, derive their name from the organs of sense and motion being disposed as rays round a center; the other three, in ascending order, being the articulate, the mollusca, and the vertebrate. Before Cuvier's time all invertebrate animals were divided into worms and insects. In 1795 he presented a memoir to the natural history society of Paris, in which, to use his own words, he "marked the characters and limits of the mollusks, crustaceans, insects, worms, echinoderms, and zoophytes;" and in a memoir read before the institute in July, 1812, he "distributed these various classes under three grand divisions, each of which is comparable to that of the vertebrate animals." The necessity for the' dismemberment and rearrangement of, this heterogeneous assemblage which Cuvier grouped together in his RADIATA has long been felt; and at the present day "the radiate mob" (as prof. Huxley terms it) may be regarded as effectually demolished. To show how these ani mals have been rearranged, it is necessary first to mention that Cuvier himself divided them into five elaases—namely (1) the echinodermata, (2) the entozoa-(or intestinal worms), (3) the acaleplee (or sea-nettles), (4) the polypi, and (5) the infusoria. The echinodermata
are now included by Huxley (Elements of Comparative Anatomy, 1864) in the annuloida (one of the eight primary groups into which he divides t-he whole animal kingdom); while J. Victor Carus (Handbuch der Zoologie, 1863), makes them an independent group. The entozoa are placed by Huxley under the annuloida, and by Carus under the vermes. The acalephm are by unanimous consent placed in the coelenterate, a primary group estab fished by Frey and Of the polypi, those with ciliated arms (the bryozoa or polyzoa, of which the sea-mat or finstra is a well-known example) are now placed among the lower mollusks, which, under the term moll-uscoida, are considered by Huxley as one of the eight primary groups; the remainder are placed amongst the calenterate. The infnsoria are now regarded by most zoologists as a class of the protozoa (q.v.), a primary group established by Siebold. See SUBICLNGDOMS, ANIMAL.