in Zoology, the name of Linnaeus's third class of animals; including all those which live partly in water and partly on land. This class he subdivides into four orders, viz. the amphibia reptiles; the amphibia serpentes; the amphibia nantes; and the amphibia meanses.

It has been a question whether the animals commonly called amphibious, live most in the water or on land. If we consider the words ευγενικός (utrinque, both ways) and βιος (vita, life), from which the term amphibious is derived; we should understand, that animals, having this title, should be capable of living as well by land, or in the air, as by water; or of dwelling in either constantly at will: but it will be difficult to find any animal that can fulfil this definition, as being equally qualified for either. An ingenious naturalist *, therefore, * Dr Par from considering their economy respectively, divides them, in a into two orders, viz. 1. Such as enjoy their chief paper read functions by land, but occasionally go into the water, before the Royal So. 2. Such as chiefly inhabit the water, but occasionally ciety; go ashore. What he advances on this subject is curious, and well illustrates the nature of this class.

1. Of the first order, he particularly considers the phoece; and endeavours to show, that none of them can live chiefly in the water, but that their chief enjoyment of the functions of life is on shore.

These animals (he observes) are really quadrupeds; but, as their chief food is fish, they are under a necessity of going out to sea to hunt their prey, and to great distances from shore; taking care that, however great the distance, rocks or small islands are at hand, as resting places when they are tired, or when their bodies become too much macerated in the water; and they return to the places of their usual resort to sleep, copulate, and bring forth their young, for the following reasons, viz. It is well known, that the only essential difference (as to the general structure of the heart) between amphibious and mere land animals, or such as never go into the water, is, that in the former the oval hole remains always open. Now, in such as are without this hole, if they were to be immersed in water for but a little time, respiration would cease, and the animal must die; because a great part of the mass of blood passes from the heart by the pulmonary artery through the lungs, and by the pulmonary veins returns to the heart, while the aorta is carrying the greater part of the mass to the head and extremities, &c.

Now, the blood passes through the lungs in a continual uninterrupted stream, while respiration is gentle and moderate; but when it is violent, then the circulation is interrupted, for inspiration and expiration are now carried to their extent; and in this state the blood cannot pass through the lungs either during the total inspiration. Amphibia, inspiration or total expiration of the air in breathing; for, in the former case, the inflation compresses the returning veins; and in the latter, by the collapse of the lungs, these veins are interrupted also; so that it is only between these two violent actions that the blood can pass; and hence it is, that the lives of animals are shortened, and their health impaired, when they are subjected to frequent violent inspiration; and thus it is, that when animals have thus breathed, they must continue to respire ever after, for life is at an end when that ceases.

There are three necessary and principal uses of respiration in all land animals, and in those kinds that are counted amphibious. The first is that of promoting the circulation of the blood through the whole body and extremities. In real fishes, the force of the heart is alone capable of sending the blood to every part, as they are not furnished with limbs or extremities; but in the others mentioned, being all furnished with extremities, respiration is an afflant force to the arteries in sending blood to the extremities; which, being so remote from the heart, have need of such assistance, otherwise the circulation would be very languid in these parts: thus we see, that in persons subject to asthmatic complaints, the circulation grows languid, the legs grow cold and oedematous, and other parts suffer by the defect in respiration.—A second use of breathing is, that in respiration, the variety of particles, of different qualities, which float always in the air, might be drawn into the lungs, to be infumated into the mass of blood, being highly necessary to temperate and cool the agitated mass, and to contribute refined panaculum to the finer parts of it, which, meeting with the daily supply of chyle, serves to assimilate and more intimately mix the mass, and render its constitution the fitter for supporting the life of the animal. Therefore it is, that valetudinarians, by changing foul or unwholesome air for a free, good, open air, often recover from lingering diseases.—A third principal use of respiration is, to promote the exhibition of voice in animals: which all those that live on the land do according to their specific natures.

From these considerations it appears, that the phoca of every kind are under an absolute necessity of making the land their principal residence. But there is another very convincing argument why they reside on shore the greatest part of their time; namely, that the flesh of these creatures is analogous to that of other land animals; and therefore, by over long maceration, added to the fatigue of their chasing their prey, they would suffer such a relaxation as would destroy them. It is well known, that animals which have lain long under water are reduced to a very lax and even putrid state; and the phoca must bask in the air on shore: for while the solids are at rest, they acquire their former degree of tension, and the vigour of the animal is restored; and while he has an uninterrupted placid respiration, his blood is refreshed by the new supply of air, as explained above, and he is rendered fit for his next cruise: for action wastes the most exalted fluids of the body, more or less, according to its duration and violence; and the restorative rest must continue a longer or shorter time, according to the quantity of the previous fatigue.

Let us now examine by what power these animals are capable of remaining longer under water than land Amphibia animals.

All these have the oval hole open between the right and left auricles of the heart; and, in many, the canalis arteriosus also: and while the phoca remains under water, which he may continue an hour or two more or less, his respiration is stopped; and the blood, not finding the passage through the pulmonary artery free, rushes through the hole from the right to the left auricle, and partly through the arterial canal, being a short passage to the aorta, and thence to every part of the body, maintaining the circulation: but, upon rising to come ashore, the blood finds its passage again through the lungs the moment he respites.

Thus the fetus in utero, during its confinement, having the lungs compressed, and consequently the pulmonary arteries and veins impervious, has the circulation of the blood carried on through the oval hole and the arterial canal. Now, so far the phoca in the water, and the fetus in utero, are analogous; but they differ in other material circumstances. One is, that the fetus having never respired, remains sufficiently nourished by the maternal blood circulating through him, and continues to grow till the time of his birth, without any want of respiration during nine months confinement: the phoca, having respired the moment of his birth, cannot live very long without it, for the reasons given before; and this hole and canal would be closed in them, as it is in land animals, if the dam did not, soon after the birth of the cub, carry him so very frequently into the water to teach him; by which practice these passages are kept open during life, otherwise they would not be capable of attaining the food designed for them by Providence.

Another difference is, that the phoca, as we said before, would be relaxed by maceration in remaining too long in the water; whereas the fetus in utero suffers no injury from continuing its full number of months in the fluid it swims in: the reason is, that water is a powerful solvent, and penetrates the pores of the skins of land animals, and in time can dissolve them; whereas the liquor amnii is an insipid soft fluid, impregnated with particles more or less mucilaginous, and utterly incapable of making the least alteration in the cutis of the fetus.

Otters, beavers, and some kind of rats, go occasionally into the water for their prey, but cannot remain very long under water. "I have often gone to shoot otters (says our author), and watched all their motions; I have seen one of them go softly from a bank into the river, and dive down: and in about two minutes rise at 10 or 15 yards from the place he went in, with a middling salmon in his mouth, which he brought on shore: I shot him, and saved the fish whole." Now, as all foetuses have these passages open, if a whelp of a true water spaniel was, immediately after its birth, served as the phoca does her cubs, and immersed in water, to stop respiration for a little time every day, it is probable that the hole and canal would be kept open, and the dog be made capable of remaining as long under water as the phoca.

Frogs, how capable soever of remaining in the water, yet cannot avoid living on land, for they respire; and if a frog be thrown into a river, he makes to the shore as fast as he can. The lizard kind, such as may be called water lizards (see Lacerta), are all obliged to come to land, in order to deposit their eggs, to rest, and to sleep. Even the crocodiles, who dwell much in rivers, sleep and lay their eggs on shore; and, while in the water are compelled to rise to the surface to breathe; yet, from the texture of their scaly covering, they are capable of remaining in the water longer by far than any species of the phoca, whose skin is analogous to that of a horse or cow.

The hippopotamus, who wades into the lakes or rivers, is a quadruped, and remains under the water a considerable time; yet his chief residence is upon land, and he must come on shore for respiration.

The teftudo, or sea-tortoise, though he goes out to sea, and is often found far from land; yet being a respiring animal, cannot remain long under water. He has indeed a power of rendering himself specifically heavier or lighter than the water, and therefore can let himself down to avoid an enemy or a storm; yet he is under a necessity of rising frequently to breathe, for reasons given before; and his most usual situation, while at sea, is upon the surface of the water, feeding upon the various substances that float in great abundance everywhere about him: these animals sleep securely upon the surface, but not under water; and can remain longer at sea than any other of this class, except the crocodile, because, as it is with the latter, his covering is not in danger of being too much macerated; yet they must go on shore to copulate and lay their eggs.

2. The consideration of these is sufficient to inform us of the nature of the first order of the class of amphibious animals; let us now see what is to be said of the second in our division of them, which are such as chiefly inhabit the waters, but occasionally go on shore:

These are but of two kinds: the eels, and water serpents or snakes of every kind. It is their form that qualifies them for loco-motion on land, and they know their way back to the water at will; for by their structure they have a strong peristaltic motion, by which they can go forward at a pretty good rate; whereas all other kinds of fish, whether vertical or horizontal, are incapable of a voluntary loco-motion on shore; and therefore, as soon as such fish are brought out of the water, after having flounced a while, they lie motionless and soon die.

Let us now examine into the reason why these vermicular fish, the eel and serpent kinds, can live a considerable time on land, and the vertical and horizontal kinds die almost immediately when taken out of the water: and, in this research, we shall come to know what analogy there is between land animals and those of the waters. All land animals have lungs, and can live no longer than while these are inflated by the ambient air, and alternately compressed for its expulsion; that is, while respiration is duly carried on, by a regular inspiration and expiration of air.

In like manner, the fish in general have, instead of lungs, gills or branchiae: and as in land animals the lungs have a large portion of the mass of blood circulating through them, which must be stopped if the air has not a free ingress and egress into and from them; so, in fish, there is a great number of blood vessels that pass through the branchiae, and a great portion of their blood circulates through them, which must in like manner be totally stopped, if the branchiae are not perpetually wet with water. So that, as the air is to the lungs in land animals a constant assistant to the circulation; so is the water to the branchiae of those of the rivers and seas: for when these are out of the water, the branchiae very soon grow crisp and dry, the blood vessels are shrunk, and the blood is obstructed in its passage; so, when the former are immersed in water, or otherwise prevented from having respiration, the circulation ceases, and the animal dies.

Again, as land animals would be destroyed by too much maceration in water; so fishes would, on the other hand, be ruined by too much efflorescence: the latter being, from their general structure and constitution, made fit to bear, and live in, the water; the former, by their constitution and form, to breathe and dwell in the air.

But it may be asked, Why eels and water snakes are capable of being longer in the air than the other kinds of fish? This is answered, by considering the providential care of the great Creator for these and every one of his creatures: for since they were capable of locomotion by their form, which they need not be if they were never to go on shore, it seemed necessary that they should be rendered capable of living a considerable time on shore, otherwise their loco-motion would be in vain. How is this provided for? Why, in a most convenient manner; for this order of fishes have their branchiae well covered from the external drying air; they are also furnished with a slimy mucus, which hinders their becoming crisp and dry for many hours; and their very skins always emit a mucous liquor which keeps them supple and moist for a long time: whereas the branchiae of other kinds of fish are much exposed to the air, and want the slimy matter to keep them moist. Now, if any of these, when brought out of the water, were laid in a vessel without water, they might be preserved alive a considerable time, by only keeping the gills and surface of the skin constantly wet, even without any water to swim in.

It has been advanced, that man may, by art, be rendered amphibious, and able to live under water as well as frogs. As the fetus lives in utero without air, and the circulation is there continued by means of the foramen ovale; by preserving the passage open, and the other parts in statu quo, after the birth, the same faculty would still continue. Now, the foramen, it is alleged, would be preserved in its open state, were people accustomed, from their infancy, to hold their breath a considerable time once a day, that the blood might be forced to resume its pristine passage, and prevent its drying up as it usually does. This conjecture seems, in some measure, supported by the practice of divers, who are taught from their childhood to hold their breath, and keep long under water, by which means the ancient channel is kept open.—A Calabrian monk at Madrid laid claim to this amphibious capacity, making an offer to the king of Spain, to continue twice twenty-four hours under water, without ever coming up to take breath. Kircher gives an account of a Sicilian, named the fish Colas, who by a long habituïte from his youth, had so accustomed himself 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.