File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14578093518).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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re artificially framed than that of the Asterias. Ithas a spheroidal form, like that of an orange; the calcareousmaterial employed in its construction, instead of formingisolated grains, is accumulated and extended into polygonal plates (Fig. 98,) the edgesof which are dove-tailedinto each other. Theform of each piece is thatof a lengthened hexagon;and the whole are regular-ly arranged in rows, likea mosaic or tesselated pavement. Ambulacra are also seenon the surface of the shell, passing vertically down the sidesof the sphere, similar to the meridians of a globe; and con-taining, like those of the Asterias, a double row of perfora-tions.t On the outer spherical surface of the external crust, thereare formed a great number of calcareous tubercles, arrangedwith beautiful regularity and symmetry in double lines,passing, like meridian circles, fromi the upper to the lowerpole of the sphere. Each appears, when magnified, to be asmooth and solid ball, projecting from the surface of one of
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* In adclltioa to these larger tubes, there exists also a smaller set, whichpierce the skin in different places, and are channels for the absorption of thewater used in respiration. These I shall have occasion to notice more parti-cularly hereafter. ■\ An architecture of a still more curious description is exhibited in thecalcareous frame-work that has been provided for the support of the teeth,and other organs of mastication, with which this animal is furnished. Theetructure of these organs will be noticed when treating of that function. ECHINUS. 151 the polygonal plates of the crust. These balls serve for thesupport of the spines,* which have grooves or sockets attheir base, allowing of their accurate application to the sphe-rical surface of the tubercles. They thus constitute ball-andsocket joints, allowing of free motion in all directions. Eachjoint is connected with the plate on which it turns, by meansof the integument, which acts the part of a capsular ligament;and sets of ra

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