The royal natural history

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Identifier: royalnaturalhist612lyde (find matches)
Title: The royal natural history
Year: 1893 (1890s)
Authors: Lydekker, Richard, 1849-1915 Sclater, Philip Lutley, 1829-1913 Frostick, W. B., former owner. DSI Brooks, W. T., former owner. DSI
Subjects: Zoology Natural history
Publisher: London and New York : Frederick Warne & Co.
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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ly a system of cavities, allin open communication with one another, occupying almost every corner of thebody. Again, the Coelenterates are radiate in structure, that is, when seen from above,they are typically star-shaped; and if a Ccelenterate be cut across, every horizontalsection shows a symmetrical arrangement of the parts around a centre. There areother radiate animals, such as the Echinoderms, but while in these five is thefundamental number of rays, in the Coelenterates the rays are often far morenumerous, being some multiple of four or six. Again, while the skin of the formeris almost always modified into a skeleton, or is thick like leather, leathery skins arethe exception in the latter. When the Coelenterates do form calcareous skeletalstructures, these are quite different from the tests of the sea-urchins; and, in allss, the anterior end of the body, crowned with one or more circles of tentacles,remains soft and flower-like. The most highly developed of the free forms, how-
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CTENOPHORES. CTENOPHORES. 4 7 5 ever, such as the sea-anemones and the jelly-fish, have no hard skeleton at all, butare amongst the most delicate and beautiful objects in the realm of living nature. In spite of the variety of forms to be found, the Coelenterata are almost asincapable of higher development as the Echinoderms. Like the latter, they havefailed to make any way in fresh water, not to speak of the land. A few free-swimming jelly-fish, a minute attached polyp, and some degenerate sponges are,indeed, found in fresh water, but these can hardly be looked upon as successes.While, at present, it is not easy to connect the Coelenterata with any other group,inasmuch as they appear to stand without any near relatives among the higheranimals, they have a special interest, since they are considered to represent a stagein the development of animal life through which all the higher forms have passed.Some simple form of Coelenterate may have given rise to all the higher animalforms, the

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