File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14596030619).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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sions of the animalkingdom. This peculiar aspect no doubt arises from the nu-merous small cavities extending between the muscles, and thesecretion of mucus which takes place in them. § 222: In the articulated animals (fig. 34), the solid parts areexternal, in the form of rings, generally of a horny structure, butsometimes calcareous, and successively fitting into each otherat their edges. The tail of a lobster gives a good idea of this THE SKELETON OF AETICULATA. 105 structure. The rings differ in the several classes of this divi-sion, merely as to volume, form, solidity, number of pieces,and the degree of motion which one has upon another. Insome groups they are consolidated, so as to form a shield orcarapace, such as is seen in the crabs. In others, they aremembranous, and the body is capable of assuming variousforms, as in the leeches and worms generally. Fig. 75 is abeautiful fossil Astacus, from the lower greensand, which exhi-bits the character of the skeleton of the Crustacea.
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\Leti. Jtc Fig. 75.—Astacus fectensis, from the lower greensand, Isle of Wight. § 223. A variety of appendages are attached to these rings,such as jointed legs (fig. 34), or, in place of them, stiff bristles,oars fringed with silken threads, wings either firm or mem-branous (fig. 369), antennae, moveable pieces which performthe office of jaws (fig. 195), &c. But, however diversified thissolid apparatus may be, it is universally the case that therings, to which every segment of the body may be referred,as to a type, combine to form but a single internal cavity, inwhich all the organs are enclosed, the nervous system, as wellas the organs of vegetative life (§ 76). § 224. The muscles which move all these parts have thispeculiarity, that they are enclosed within the more solid frame-work, and are not external to it, as in the vertebrata; andalso that the muscular bundles, which are very considerablein number, have the form of ribbons, or fleshy strips, with pa-rallel fibres of r

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