AMPHIBIA, in zoology, the third class of animals in the Linnaan system. These animals are characterised by having vertebra, and cold blood, respiring by means of lungs ; and being destitute of hair, feathers, and mamma.
The amphibia, 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 occasionally endure an abstinence, which would prove fatal to the higher or ders of animals. Their lungs differ from those of ani mals in the classes mammalia and ayes, consisting, in general, of a pair of large bladders, or membranaceous receptacles, variously subdivided in different species; and the heart is furnished with one ventricle only. Some physiologists, however, think it more correct to say, that the hearts of the amphibia are, in reality, dou ble, or furnished with two ventricles, with a free or im mediate communication between them.
Being provided with lungs, many of the species emit particular sounds, which are harsh and unmusical ; others, however, as the true salamander, (lacerta sala mandra,) common lizard, (lacerta agilis,) are entirely dumb. The genera differ from each other considerably in their general conformation; some genera, as the tor wise, frog, and lizard, have four feet; while others, as the coluber, boa, &c. have a lengthened cylindrical body destitute of external organs of motion.
The external teguments of the bodies of the amphi bia are much more varkd than in warm-b1(“aled animals ; thus their bodies are sometimes defended by a hard, horny shield, or covering; sometimes by a coriaceous integument, sometimes by scales, and sometimes have no particular defence or covering; the skin being mere ly marked by soft, pustular warts or protuberances, more or less visible in the different species.
Many are highly beautilul in their colours, as well as elegant in their forms; whilst others are deformed, and of unpleasing colours. Certain animals of this class, as the different species of tortoise, and certain genera of serpents, live on a great variety of food; whilst others, as the chamelion, and tree-trog, are very delicate in their choice of food, living only on particular species of live insects.
Many species, when confined, cat extremely little for a surprisingly long period; thus the tortoise will live nearly a year and half without nourishment.
Most of the amphibia are possessed of an astonishing reproductive power; when feet, tail, &c. are by any ac cident destroyed, others will grow in their place.
Some of•the amphibia, for example certain species of serpents, are provided with poison, as a mean of defence ; the salamander, and other genera, exude a frothy fluid when they arc in danger; many species, particularly among the serpent tribe, when in danger, exhale a spe cific and most loathsome odour.
In cold and temperate climates, nearly all the amphi bia pass the winter in a torpid state. During this sea son, they arc often found perfectly stiff in holes in the ice, or in the water. Thus the common water-newt, in particular, is said to have been occasionally found com pletely imbedded in large masses of ice, in which it must have remained inclosed for a very considerable period ; and yet on the melting of the ire, has been re stored to life. They continue ill this state, until revived by the returning heat of spring. They hybcrnate either singly, or collect together in numbers, as is the case with frogs and salamanders. But if they arc kept in a warm chamber, they continue lively during the whole winter.* Most of the amphibia are oviparous, or deposit their eggs, and afterwards hatch them. The eggs, or ova, of some species are covered with a hard calcareous shell; whilst those of others have a soft tough skin or cover ing, somewhat resembling parchment ; the eggs of se veral are gelatinous. Some few are viviparous, the eggs first hatching internally, and the young being afterwards excluded in their perfect form.