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phibia, from the peculiar structure of 

 their organs, and the power which they 

 possess of suspending- respiration at 

 pleasure, can not only support a change 

 of element uninjured, but can also occa- 

 sionally endure an abstinence, which 

 would infallibly prove fatal to the higher 

 order of animals. It bus been a general 

 doctrine among anatomists, that the hearts 

 of the Amphibia were, in the technical 

 phrase, unilocular, or furnished with only 

 one ventricle or cavity ; a doctrine main- 

 tained by many eminent anatomists, and, 

 in general, assented to by the greatest 

 physiologists, as Boerhauve, I-Ialler, &c. 

 &c. and only occasionally called in ques- 

 tion, on viewing in some animals of this 

 tribe a seemingly different structure. 

 Thus the French academicians of the 

 seventeenth century pronounce the heart 

 of an Indian land tortoise, which they 

 examined, to have in reality three ventri- 

 cles instead, of one. Linnaeus, in his Sys- 

 tema Naturae, acquiesces hi the general 

 doctrine, and accordingly makes it a cha- 

 racter of this class of animals. Among 

 later physiologists, however, there are not 

 wanting some who think it more correct 

 to say, that the hearts of the Amphibia 

 are in reality double, or furnished with 

 two ventricles, with a free or immediate 

 communication between them. The lungs 

 of the Amphibia differ widely in their ap- 

 pearance from those of other animals; 

 consisting, in general, of a pair of large 

 bladders or membranaceous receptacles, 

 parted, in the different species, into more 

 or fewer cancelli, or subdivisions, among 

 which are beautifully distributed the pul- 

 monary blood-vessels, which bear but a 

 small proportion to the vesicular part 

 through which they ramify ; whereas, in 

 the lungs of the Mammalia, so great is 

 the proportion of the blood-vessels, and 

 so very small are the vesicles, or air-cells, 

 that the lungs have a fleshy rather than 

 a membranaceous appearance. In the 

 Amphibia, therefore, the vesicular sys- 

 tem may be said greatly to prevail over 

 the vascular ; and in the Mammalia, or 

 warm-blooded animals, the vascular 

 system to prevail over the vesicular. 

 Many of the Amphibia are possessed 

 of a high degree of reproductive power, 

 and will be furnished with new feet, 

 tails, &c. when those parts have by 

 any accident been destroyed. Many are 

 highly beautiful in their colours, as well 

 as elegant in their forms ; while others, 

 on the contrary, are, in the common ac- 

 ceptation of the words, extremely deform- 

 ed, and of unpleasing colours. Their bo- 



dies are sometimes defended by a hard, 

 horny shield, or covering ; sometimes 

 rather by a coriaceous integument ; some- 

 time by scales ; and sometimes have no 

 particular defence or coating, the skin be- 

 ing merely marked by soft, pustular warts, 

 or protuberances, more or less visible in 

 the different species. The bones of the 

 Amphibia, except in a very few instances, 

 are of a more cartilaginous nature than in 

 either the Mammalia or Birds : many spe- 

 cies are destitute of ribs, while others have 

 those parts very numerous : some are 

 furnished with formidable teeth ; others 

 are toothless : some are fierce and pre- 

 dacious ; others inoffensive. Few, ex- 

 cept among the serpent tribe, are of a 

 poisonous nature, the general prejudice 

 against them having arisen rather on ac- 

 count of their form, than from any real 

 poisonous quality; but among the ser- 

 pents, we meet with some species pos- 

 sessed of the most dreadful poison, as 

 well as with the power of applying it with 

 fatal force to the animals which they at- 

 tack. The number of poisonous serpents 

 is, however, not so great as was formerly 

 imagined ; perhaps not more than a sixth 

 part of the whole number of known spe- 

 cies being of that character. Among no 

 animals do we meet with beings of a more 

 singular form than the Amphibia; some 

 of which present appearances so unusual, 

 so grotesque, and so formidable, that even 

 the imagination of the poet or painter can 

 hardly be supposed to exceed the reali- 

 ties of nature. The amphibia in general 

 are extremely tenacious of life, and will 

 continue to move, and exert many of their 

 animal functions, even when deprived of 

 the head itself. The experiments which 

 have been occasionally made on these 

 subjects can hardly be recited without 

 horror. The natural life of some of the 

 Amphibia, more particularly of the tor- 

 toise tribe, is extremely long; and even 

 to the smaller tribes of frogs and lizards 

 a considerable space seems allotted. The 

 same is also highly probable with respect 

 to the serpent tribe. By far the major 

 part of the Amphibia are oviparous, some 

 excluding eggs covered with a hard or 

 calcareous shell, like those of birds ; 

 others, such as are covered only with a 

 tough skin, resembling parchment ; and 

 in many, they are perfectly gelatinous, 

 without any kind of external cpvering, as 

 is the spawn of the common frog. Some 

 few are viviparous ; ihe eggs first hatch- 

 ing internally, and the young being after- 

 wards excluded in their perfect form, as 

 in the viper, &c. &c. In cold and tempe- 



