AMPHIBIOUS, in Natural History, a term applied to those animals which possess, in a considerable de gree, the power of living with equal facility both on the land and in the water; but, in technical language, it is confined to those animals which constitute the amphibia of naturalists. Strictly speaking, however, amphibious animals ought to respire equally well in water as in air, which we shall find to be the case with only one, or at most two species of perfect animals.
We shall first mention those animals which possess, in a greater or lesser degree, the power of living both in water and on land; and next inquire, what are the truly amphibious species of animals.
The term amphibious has been applied to men who have the faculty of remaining a long time under the water. Divers employed in the pearl fishery possess this faculty in a remarkable degree. We are told by Father Kircher, that a Sicilian, named Fish-Colas, by a long habitude from his youth, had so accustomed him self to live in water, that his nature seemed to be quite altered, so that he lived rather after the manner of a fish, than a man. Other animals of the class mammalia .ore amphibious; these are generally web-footed, as the heaver, seal, otter ; some, however, are not so, as the hippopotamus, tapii, II:ro, brr, t,i sonic degree, amphibious. Water birds, as LIJ• litc nitieli in the water, can a considerable time under its surface, and also nye on toe iai.o.
The greater number of the of ti.e class am phibia, as already mentioned, are aniphib,:.us; but of these the most amphibious are the and turtle.
In the class of fishes, the species •.,.t cider apodes, as the eel, are amphibious.
Sonic kinds of insects, in different stages of their life, may be said to be amphibious. The dy t•scus, notonecta, and nepa, undergo ail their transformations, from the egg, larva, and pupa state in the water, and though fur nished in the perket state with wings, and consequently destined to live on land, seldom quit the water, except in the evenings, and constantly return to it when their flight is over; these are called water-beetles. Others remain in the water only in the first stages of their transformations, and would perish in their native ele ment from the moment they become winged insects; as is frequently observed of the libellula, ephemera, and phryangea, and some of the muscx and culices; amongst the latter, the transformation of the species pipiens, common gnat, is a striking instance of this remark. In
fact, many of those creatures, which are mistaken for aquatic worms, arc no other than the larva, or pupas, of amphibious insects; which their parents deposit in the egg state, on the leaves and stalks of plants, &c. that grow in the water; and those, hatching instinctively, remain in the water till they become winged insects. It is said, that certain species of limax can respire equally well in air as in water, and hence are, in the strictest sense, amphibious; this observation, however, does not appear to be correct. Crustaceous animals are aquatic, and are provided with branchix, yet certain species leave the water and live on the land.
Many of the amphibious animals which have been mentioned, have peculiar provisions in their structure to fit them for such a variety of living; particularly in the heart, lungs, foramen ovale, &c. In some of these animals, as the frog, tortoise, &c. the heart has but one cavity, with an artery to receive the blood coming out of it, and a vein to convey it thither. In others, the fora men ovale appears to be still open for the passage of the blood from the vena cares to the arteria venosa, without the help of breathing.
All animals, to which Linnxus applied the name am phibia, respire only in the air, whether they live in that fluid perpetually, as certain species of lizards, or dive under the water for a longer or shorter time, as frogs and salamanders. On the contrary, the cartilaginous fishes, which the same naturalist united with the am phibia, do not respire but through the medium of water, as is the case with all other fishes; they have only branchke, no lungs. The forked swimming bladder, observed in certain species, was, by Dr Garden, consi dered as lungs ; an error which misled Linnzeus, and induced him to form his order of amphibia nantes. The larva of the common frog, toad, &c. contain both bran chix and lungs, and respire, during part of their lives, both in the elastic air of the atmosphere, and in that contained in water ; thus participating in an equal de gree of the nature of land and aquatic animals, and being thus, in the strictest sense, amphibious. But this is only a temporary state in some species, and a mo mentary one in others. In proportion as the lungs be come more perfect, the branchix are gradually oblite rated and at length entirely disappear, even before the species has arrived at its full growth, or at least before it can procreate its kind.