Amphibious, (from and life). Animals are thus called that are capable of living as well by land, or in the air, as by water.
Though it is not our design to treat of subjects which belong to natural history, yet, respecting this class, there are various facts applicable to the human body in a sound or a diseased state. The term is confined to animals with a single heart, whose respiration is in a great degree voluntary. There is probably no amphibious animal, in the strictest sense of the word; for no animal has, at the same time, lungs and gills. The siren, which induced Linnaeus to form a new order from this circumstance, is probably an imperfect animal in its progressive state. That lately described by Schreber, in the Philosophical Transactions, seems, from the arguments adduced in the Critical Review, to be equally so. Frogs, which in their early state breathe by gills, lose them when more perfect; and, if carefully watched, they may be found, at some period, in possession of both organs. The molluscae, and shell fish, breathe by gills; but it is pretended that some species can breathe air as well as water by those organs. If so, these are truly amphibious. The crustaceous animals, particularly the crab, can apparently breathe both air and water; but this power is limited in its duration. In short, animals are destined to live wholly on land or wholly in water. The real amphibia are very few, and among those whose habits arc little known. Other animals differ in the duration of the period when they can leave the element most congenial to them, but in either it is short.
The lungs of the amphibia differ in their structure from those of more perfect animals; but we have yet to learn how they are better adapted to a longer residence in water than those of the mammalia and aves. The heart, we have said, is single: it is certainly so in every physiological view, and the blood is not necessarily conveyed through the lungs, as in the other classes. It either attracts oxygen more rapidly, while it is exposed to air, or combines more difficultly with carbone. As the cartilaginous fish are now removed to the pisces, we find only two orders of amphibia - those with feet, and those without; the reptiles and the serpents.
The bones of the amphibia are less firm than those of other animals, and they approach, in their mode of reproducing lost parts, the vegetable kingdom. The principle of life is not confined to one organ, but exists in a less degree in different parts, as in the buds of vegetables. Thus they are more tenacious of life, and can endure longer abstinence than other animals. As their eggs are not so much exposed to shocks or the action of hard bodies, they have not, in general, such solid coverings as the eggs of the aves. All the amphibia are perhaps oviparous: those which appear viviparous, arc apparently hatched within the body, and excluded from the egg and the mother about the same time.
Dr. Parsons divides the amphibia into such as chiefly live on land, and dive only occasionally, or those who rise to the air only at times to breathe. The former have, in many instances, the foramen ovale closed. It is so in the otter. Men used from the earliest period to diving, can exist a long time under water, and it has been supposed that the foramen ovale is open. It has, however, never been found so; and of those where the blood does not pass through the lungs, the complexion is of a blue colour. The stories of the Calabrian, and the young Sicilian named fish Colas, have been apparently much exaggerated.