File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14775747761).jpg

Identifier: animalandvegetab01roge (find matches)
Title: Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget ..
Year: 1834 (1830s)
Authors: Roget, Peter Mark, 1779-1869
Subjects: Biology Physiology Plant physiology Natural theology
Publisher: London : W. Pickering
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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polype. Thesecells are generally placed at the extremity ofthe branches, presenting the greatest similitudeto flowers. The Flustra (Fig. 63) is composedof minute and almost microscopic cells, spreadover a flat membraneous substance, resembling,in the flexibility of its texture, and its mode ofsubdivision, the leaves of plants. These cells arearranged in rows, with great regularity, like those 166 THE MECHANICAL FUNCTIONS. of a honey-comb, as is seen in the magnifiedview of them, Fig. 64. In other tribes the inorganic base of supportis internal, constituting a kind of skeleton oraxis; the polypous mouths being spread at in-tervals over the surface of the fleshy layer whichcovers this skeleton. This is the case with theGoiooiiia, Atitipathes, and the Coral, which ex-hibit still closer resemblances to the branchedforms of vegetable stems. The flesh containsgranules of calcareous matter, which, in thedried specimens, adhere to the surface of thestems. Fig. 65 is a branch of the Corallium
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rnbnim, of which Fig. 66 is a magnified portion,showing the appearance of the polypes in theirexpanded and contracted states. The way inwhich the polypes are embedded in the flesh isseen in Fig. 67, which represents a section of theGorgonia Brtaretis. In many cases the polypes are lodged in cup-like depressions in the surface of the calca-reous axis, which aflbrds them some degree ofprotection. In Madrepores these depressions POLYPI. 167 are crossed by radiating plates, adapted to theform and number of the tentacula. In 31ille-pores the cells are closer and more minute, andexhibit none of these star-like radiations. Insome species the plates have more of a parallelarrangement; and in others they form a net-work. The material of which this axis, to which thepolypes are attached, is composed, is of variouskinds. Sometimes it is horny, flexible, andelastic, corresponding in its nature to animalmembrane: at other times it is hard and calca-reous, being composed principally of carbonateof

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