File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14578083089).jpg

Identifier: animalvegetable01roge (find matches)
Title: Animal and vegetable physiology, considered with reference to natural theology
Year: 1836 (1830s)
Authors: Roget, Peter Mark, 1779-1869
Subjects: Biology Physiology Plant physiology Natural theology
Publisher: Philadelphia, Carey, Lea & Blanchard
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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is very amusing to watch the rapidexpansions and retractions of their many coloured tentacula,while they are moving in search of food: to observe thequickness with which they seize on whatever prey comeswithin their reach, and to notice the suddenness with whichthey collapse into a round contracted mass, on receiving theslightest injury. Yet these animals are not of necessity confined to the par-ticular spots where we see them fixed; for they are capable,when disturbed, of seeking, by a slow progressive motion,a more secure abode. Reaumur has minutely examined the ECHINODERMATA. 147 arrangements of their muscular fibres, and has described theaction by which they either attach themselves to the sur-faces of rocks, or effect their sluggish movements.* § G. Ecldnodermata. Ascending in the scale of organization \vc come to theEchinoderinata, a class which comprehends the families ofthe Jislerida^ the Echinida, the Holothitrida, and the Cri-noidea, together with other tribes of less note.
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These animals, both in their general form, and in the ar-rangement of their internal organs, retain, in a very markedmanner, the radiated disposition so characteristic of Zoo-phytes: for we find all their parts symmetrically arrangedeither in lines, or in compartments, which proceed from acommon centre, or axis, and which are repeated, in regularsuccession, all round the circumference (See Fig. SS to 94.)Besides an external horny, or semi-calcareous covering,there is also provided, for the support of the softer parts, akind of internal skeleton, or jointed frame-work. The or-gans in the interior of the body are farther supported by * M^molres de TAcacIemie des Sciences, 1710, p. 490. 148 THE MECHANICAL FUNCTIONS. membranous walls, which impart mechanical firmness to thefabric. The Jisterias, or star-fish (Fig. SS,) is so named from itsstar-like form; and the number of rays composing the staris generally five. Besides the tough coriaceous integument,which protects the mass of the body,

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