File:Animal and vegetable physiology, considered with reference to natural theology (1836) (14578117029).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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order of Balrachia, or Amphibious Reptiles, con-stitutes the first step in the transition from aquatic to terres-trial vertebrata. It is more particularly the function of res-piration that requires to be modified, in consequence of thechange of element in which the animal is to reside; and asif it had been necessary, conformably to the laws of animalcreation, that this change should not be abruptly made, wefind that Batrachian reptiles, with which this series com-mences, are constructed, at first, on the model of fishes;breathing the atmospheric air contained in the water bymeans of gills, and moving through the fluid by the sameinstruments of progression as fishes, which, indeed, they ex-actly resemble in every part of their mechanical conforma-tion. The tadpole, which is the young of the frog, is, atfirst, not distinguishable in any circumstance of its internalskeleton, or in the disposition of its vital organs from theclass of fishes. The head, indeed, is enlarged, but the body 19;
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immediately tapers to form a lengthened tail, by the pro-longation of the spinal column, which presents a numerousseries of coccygeal vertebrae, furnished with a vertical ex-pansion of membrane to serve as a caudal fin, and with ap-propriate muscles for executing all the motions required in #swimming. The appearance of the tadpole, in its earlystage of development, is seen in Fig. 197 and 198, the 304 THE MECHANICAL FUNCTIONS. former being a side, and the latter an upper view of thatanimal. Yet, with all this apparent conformity to the structure ofa strictly aquatic animal, the tadpole contains within itsorganization the germs of a higher development. Prepara-tions are silently making for a change of habitation, for theanimals emerging from the waters, for the reception of at-mospheric air into new cavities, for the acquisition of limbssuited to new modes of progression; in a word^ for a terres-trial life, and for all the attributes and powers which belongto quadrupeds. The succession

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