AMPHIBIA, in natured history, a class of animals that live either on land or in water. 'file title Amphibia, applied to this class of animals by Liiiiimus, may perhaps be considered as 110t. absolutely unexceptionable, the power of living with equal facility- both in land and water be ing not granted to all the animals which compose it ; yet, since it is certain that the major part are found to possess that faculty in a considerable degree, the title 1713V be allowed to continue. The Am pliibia, 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 has been a general doctrine among anatomists, that the hearts of the Amphibia 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 Boerhaave, Haller, &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. Linnmus, in his Sys tema Nahum, acquiesces in the general doctrine, and accordingly makes it a cha racter of this class of animals. Among later physiologists, however, there arc 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 Manimalia, 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 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, extremelydeform cd, and of tuipleasing colours. Their bo dies are sometimes defended by a bard, homey shield, or covering; sometimes rather by a coriaceous integument; some times 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 grates*, 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 covering, as it the spawn of the common frog. Some few are viviparous; the eggs first hatch jng internally, andthe young being after wards excluded in their perfect form, as in the viper, &c. &c. In cold and tempe rate climates,most of the Amphibia pass the winter in a torpid state ; and that sometimes in a deg-ree of cold which would seem but ill calculated for the pre servation of animal life. The common large water-newt, in particular, is said to have been occasionally found completely embedded inlarge mssses of ice, in which it must have remained inclosedfor a very considerable period; and yet, on the dis solution of the ice, has been restored to life. The Amphibia may be divided into four distributions, viz. Testudines, Ranz, Lacertx, and Serpentes ; or Tortoises, Frogs, Lizards, and Serpents. The ani mals belonging to the three former of these dirisions constitute the order enti tled Reptilia, containing the Amphibia Pedata, or Footed Amphibia. The last division, or that of Serpents, constitutes the order Serpentes ; containingthe Am phibia Apoda, or Footless Amphibia.