File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14592261220).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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and flexible processes, exceedingly irri-table, and contractile in every part, and providedwith numerous muscles, which are capable ofmoving and twisting them in all directions withextraordinary quickness and precision. Theyare thus capable of being employed as instru-ments; not only of progressive motion, but alsoof prehension. For this latter purpose they arein many species peculiarly well adapted, because,being perfectly flexible as well as highly muscu-lar, they twine with ease round an object of anyshape, and grasp it ^vith prodigious force. Inaddition to these properties they derive a re-markable power of adhesion to the surfaces ofbodies from their being furnished with nume- 2G0 THE MECHANICAL FUNCTIONS. roiis suckers all along their inner sides. Eachof these suckers, as shown separately in Fig.122, is usually supported on a narrow neck, orpedicle, and strengthened at its circumferenceby a ring of cartilage. Their internal mechan-ism is more artificial than the simple construc-
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tion already described (p. 137): for when thesurface of the disk is fully expanded, as shownin Fig. 123* b, we find that it is formed of agreat number of long slender pieces, resembling-teeth closely set together, and extending fromthe inijer margin of the cartilaginous ring, inthe form of converging radii, to within a shortdistance of the centre, where they leave a circularaperture. In the flattened state of the suckei\this aperture is filled by the projecting part of asofter substance, which forms an interior portion,capable of being detached from the fiat circle ofteeth, when the sucker is in action, and ofleaving an intervening cavity. The form of thiscavity is exhibited in Fig. c, which represents aperpendicular section of the whole organ, andwhere the central portion, or principal mass ofthe sucker is drawn away from the circular disk, MOLLUSCA CEPHALOPODA. 261 the inner margin of which appears like a row ofteeth. It is evident that by this mechanism,which combines the propertie

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