File:Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget (1834) (14779063855).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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. The order of Batrachia, or Amphibious Rep-tiles, constitutes the first step in the transitionfrom aquatic to terrestrial vertebrata. It is moreparticularly the function of respiration that re-quires to be modified in consequence of thechange of element in which the animal is to reside;and as if it had been necessary, conformably tothe laws of animal creation, that this changeshould not be abruptly made, we find that Ba-trachian reptiles, with which this series com-mences, are constructed at first on the model offishes; breathing the atmospheric air containedin the water by means of gills, and movingthrough the fluid by the same instruments ofprogression as fishes, which indeed they exactly BATRACHIA. 437 resemble in every part of their mechanical con-formation. The tadpole, which is the young ofthe frog, is at first not distinguishable in anycircumstance of its internal skeleton, or in thedisposition of its vital organs from the classof fishes. The head, indeed, is enlarged, but the
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body immediately tapers to form a lengthenedtail, by the prolongation of the spinal column,which presents a numerous series of coccygealvertebrae, furnished with a vertical expansion ofmembrane to serve as a caudal fin, and withappropriate muscles for executing all the motionsrequired in swimming. The appearance of thetadpole in its early stage of developement is seenin Fig. 197 and 198, the former being a side,and the latter an upper view of that animal. Yet with all this apparent conformity to thestructure of a strictly aquatic animal, the tad-pole contains within its organization the germs ofa higher developement. Preparations are si-lently making for a change of habitation, for theanimals emerging from the waters, for the re- 438 THE MECHANICAL FUNCTIONS. ception of atmospheric air into new cavities, forthe acquisition of limbs suited to new modes ofprogression ; in a word, for a terrestrial life, andfor all the attributes and powers which belong toquadrupeds. The succession of fo

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