REPTILES. 333 



division has been preserved both by this author, by Dumeril in 

 his Elemens des Sciences Naturelles, and by Daudin in his 

 Natural History of Reptiles, written for Sonnini's edition of 

 Buffon. 



Besides the systematic writers, there are many others from 

 whose works much information may be derived in the details of 

 the structure, history, and habits of this class of animals. A 

 list of the chief of these will be given at the end of this volume. 

 The third volume of Shaw's General Zoology may be men- 

 tioned, as containing good figures of the principal species de- 

 scribed, and as easily accessible. 



This department of Natural History is frequently treated of 

 under the general title of Herpetology, the term being derived 

 from egmlos, a reptile, and Xoyog, a discourse. 



In Reptiles the heart is so disposed, that at each contraction 

 only a portion of the blood which it receives is conveyed to the 

 lungs ; and from this it results that the action of oxygen on the 

 blood is much less than in the mammiferous animals and birds, 

 where all the blood is exposed to the action of the air. As re- 

 spiration gives the blood its heat, and muscular fibre its sus- 

 ceptibility for nervous irritation, the temperature of reptiles 

 is comparatively lower, and their muscular strength weaker 

 than that of quadrupeds, and much less than that of birds. 

 Their motions are chiefly confined to crawling and swim- 

 ming ; and though many at times leap and run very quick- 

 ly, yet their general habits are sluggish, their sensations obtuse, 

 their digestion slow, and in cold or temperate countries they 

 pass almost the whole winter in a state of torpidity. 



The heart is composed in Frogs of an auricle and a ven- 

 tricle ; in Serpents of two auricles, and a ventricle of two com- 

 partments ; and in the Tortoises and Lizards of two auricles 

 and a ventricle of communicating cavities. 



The general resemblance in point of form which characterizes 

 the two preceding classes, is not applicable to the present class; 

 for while some, as the Serpents, have no members at all, others 

 have two short legs ; and the Lizards, Tortoises, and Frogs 

 have four, adapted in the two last to progression in the water 

 and on the land. Neither is there a common external cover- 



