File:Lectures on the comparative anatomy and physiology of the invertebrate animals - delivered at the Royal College of Surgeons (1855) (14803746403).jpg

Identifier: lecturesoncompar02owen (find matches)
Title: Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons
Year: 1855 (1850s)
Authors: Owen, Richard, 1804-1892
Subjects: Invertebrates Anatomy, Comparative
Publisher: London : Longman, Brown, Green & Longmans
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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of excrement. These anenterous Echinoderms (^Ophiuridce,Luidea^ Asterias proper, Astropecten,) belong to the order Asteroidea\yin which the radiated form is most complete and general, whence thespecies have received the common appellation of *^ star-fishes, and sea-stars. The almost extinct order Crmoidea, in which the radiated body issupported on a jointed and rooted stem, is connected with the orderAsteroidea by the genus Comatida, wliich in its last stage becomesfree. In certain starfishes (Asteroidea) we trace a shortening, flattening,and expansion of the rays, until the body assumes a pentangulardiscoid form. In the next order (Echinoidca), the angles disappear, and the discexpands until a spheroid or globular form is obtained, which charac- * ex^os a hedge-hog, Icpjia skin. f See the Sumraaiy at the conchision of the Lecture, for the characters of thisand other orders of the class. ECUINODERMATA. 191 terises the Echinoderms commonly called Sea-urchins, and Eckinoiby the Greeks.
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The Echinoderms of the order Holothurioidea may be described asbeing constituted by a softening of the calcareous skin of the spheroidalspecies, and by the reduction of the earthy matter to a greater orless number of reticulate calcareous corpuscles, the globe being thendrawn out by the two opposite poles into an elongated cylindricalform. These vermiform Echinoderms seem to lead, by the concludingorder Sipunculoidea^ to the true worms, which stand on the loweststep of the Articulate division of the Animal Kingdom. The name Echinodermata has been applied to these diversifiedforms of the higher organised Zoophytes of Cuvier, because in manyof the species the integument is defended by spines : they, however,possess, and are associated together by, another and more generaltegumentary character ; the skin is perforated in most of the speciesby minute foramina, through which a multitude of small tubes orhollow suctorial tentacles (^ tube-feet) can be protruded and retracted,and these const

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