File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14578052380).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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to support tlic body whilethe insect is walking, and to prevent its hinder part fromtrailing on the ground. They are frequently terminated bysingle or double hooks; and also by a marginal coronet ofrecurved spines. These hooks, or spines, enable the insectto cling firmly to smooth surfaces; and also to grasp the mostslender twig, which could not have been laid hold of bv Icirsof the usual construction. The speed with which these larvae can advance is regu-lated by many circumstances, independently of the mere 224 THE MECHANICAL FUNCTIONS. possession of legs: for some caterpillars move slowly, whileothers can run very nimbly. The following is the order inwhich the legs are usually moved: namely, the anterior andthe posterior leg on the same side are advanced at the samemoment, tosether with the intermediate one on the otherside; and this takes place alternately on both sides. There is one tribe of caterpillars called Surveyors, orGeometers, (Fig. 148,* a) which walk by first fixing the
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fore feet, and then doubling the body into a vertical arch;this action brings up the hind part of the caterpillar, whichis furnished with prolegs, close to the head. The hind ex-tremity being then fixed by means of the prolegs situated atthat part, the body is again extended into a straight line;and this process being repeated, the caterpillar advancesby a succession of paces, as if it were measuring the distance,by converting its body into a pair of compasses. At thesame time that they employ this process, they farther pro-vide for their security by spinning a thread, v/hich theyfasten to different points of the ground as they go along. Many other species of caterpillar practise the same art ofspinning fine silken threads, which especially assist them intheir progression over smooth surfaces, and also in descend-ing from a height through the air. The caterpillar of thecabbage butterfly is thus enabled to climb up and down apane of glass, for which purpose it fixes the threads that it

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