File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14761539071).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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d it is doubtful how far they are to be considered asappertaining to the living portion of the body, or as mereextraneous appendages. Yet, however they may difier intheir forms, uses, and external appearance, they all are pro-duced by the same kind of vascular structure, variously ar-ranged to suit the particular circumstances in each case: andthe mode of their development and growth is essentially thesame in all. An extremely delicate and finely organized pulp, com-posed partly of a congeries of minute vessels, and partly ofa gelatinous substance, in which these vessels are embedded,constitutes the apparatus by which the nutrient particles areselected, combined and elaborated into the materials of theintended structure. The original form, situation, and dis-position of this vascular pulp, determines the future figureand extent of growth of the production which is to arisefrom it. The materials w^iich compose it are depositedsometimes in masses, as in the scales of the crocodile; more
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generally in layers, as in hoofs and nails, and also in thescales of fishes;* and occasionally in filaments, as in hair; • The laminated structure of the scales of fishes is easily distinguished by-applying to them a high magnifying power. As the breadth of each newlayer is greater than the last, its edges project farther, the whole surface ANIMAL ORGANIZATION. 93 which latter, again, are often agglutinated together by astrong cement, uniting them into a hard and solid structure,of which the horn of the rhinoceros is a remarkable exam-ple. In all cases, the portions thus successively produced,are no longer susceptible of being nourished, and from themoment of their deposition, undergo no farther change, ex-cept from the action of external agents. By the continualadditions that are made to them at their base, or root, wherethe vessels deposite fresh materials, they gradually increasein size, protrude through the skin, and continue to grow bythe same process as long as these vessels c

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