lay before this learned fociety, were occafioned by a conversation, that paffed between me and a gentleman well acquainted with natural hiftory, however mistaken in the fubject before us. His opinion was, that amphibious animals liv. ed more in the water than on the land: but I believe the contrary will appear by the fequel of this treatife.

If we confider the words up and Bios, from which the term amphibious is derived; we should understand that animals, having this title, fhould be capable of living as well by land or in the air, as by water, or of dwelling in either conftantly at will; but it will be difficult to find any animal that can fulfil this definition, as being equally qualified for either; and in claffing creatures of this kind, authors are much divided, and sometimes mistaken.

Now if any natural hiftorian fhould deduce his diftinction of this clafs, from the ftructure or characteristic of any part of the animal, I think he would be a little out of the way; becaufe the

term comprehends nothing but what regards its living in both air and water at difcretion; however, fince the word amphibious is a. dopted by the writers of the hif. tory of animals, let us retain it

clafs, and, by confidering their natural œconomy respectively, endeavour to range them, according to that ftandard, in the following manner. They are fuch as,

1. Enjoy their chief functions by land, but occafionally go into the water.

2. Such as chiefly inhabit the water, but occafionally go afhore. Of the latter there are but very few fpecies. And although none of the winged tribe are to be ranged under this clafs, yet as many of them remain long upon the water in fearch of their proper food, we fhall enumerate fome peculiar advantages, which have been allowed to feveral of them by the bountiful wifdom of the creator, in order to render them the more able to obtain it; and this will make one curious part of my prefent purpofe, not gene. rally known.

The difpute mentioned between my friend and me, turned upon the clafs of the phocæ, which confifts of a very numerous tribe of different fpecies: I fhall therefore endeavour to fhew that none of

them

them can live chiefly in the waters, but that their chief enjoy. ment of the functions of life is on

fhore.

Thefe animals are really quadrupeds; but, as their chief food is fith, they are under a neceffity of going out to fea to hunt their prey, and to great diftances from fhore; taking care that, however great the diftances, rocks or small lands are at hand, as refting places when they are tired, or their bodies become too much macerated in the water; and they return to the places of their ufual refort to fleep, copulate, and bring forth their young, for the following reafons; viz. It is well known that the only effential dif. ference (as to the general ftruc. ture of the heart) between amphibious and mere land animals, or fuch as never go into the water, is, that in the former the oval hole remains always open. Now, in fuch as are without this hole, if they were to be immerfed in water for but a little time, refpiration would ceafe, and the animal muft die; becaufe a great part of the mafs of blood paffes 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 mafs to the head and extremities, &c,

Now the blood paffes through the lungs in a continual uninter. rupted ftream, while refpiration is gentle and moderate; but when it is violent, then the circulation is interrupted, for infpiration and expiration are now carried to their extent; and in this ftate the blood cannot pafs through the langs either during the total infpiration

or total expiration of the air in breathing; for in the former cafe the inflation compreffes the returning veins, and in the latter, by the collapfion of the lungs, thefe veins are interrupted alfo, fo that it is only between thefe two vio lent actions that the blood can pafs; and hence it is that the lives of animals are fhortened, and their health impaired, when they are fubjected to frequent violent refpiration; and thus it is that in animals who have once breathed, they must continue to refpire ever after; for life is at an end wher that ceafes,

There are three neceffary and principal ufes of refpiration in all land animals, and in these kinds that are counted amphibious; the firft is that of promoting the cir culation of the blood through the whole body and extremities: in real fishes, the force of the heart is alone capable of fending the blood to every part, as they are not furnished with limbs or extremities; but in the others mentioned, being all furnished with extremities, refpiration is an affiftant force to the arteries in fending blood to the extremities, which, being fo remote from the heart, have need of fuch affiftance; otherwife the circulation would be very languid in thefe parts; thus we fee, that in perfons fubject to afthmatic complaints, the cir çulation grows languid, the legs grow cold and cedematous, and other parts fuffer by the defect in refpiration.

A fecond ufe of breathing is, that, in infpiration, the variety of particles, of different qualities, which float always in the air, might be drawn into the lungs,

to

to be infinuated into the mafs of blood, being highly neceffary to contemperate and cool the agitated mafs, and to contribute refined pabulum to the finer parts of it, which, meeting with the daily fupply of chyle, ferves to affimiTate and more intimately mix the mafs, and render its conftitution the fitter for fupporting the life of the animal. Therefore it is, that valetudinarians, by changing foul or unwhole fome air for a free, good, open air, often recover from ling'ering difeafes.

And a third principal ufe of refpiration is, to promote the exhibition of a voice in animals; which all thofe that live on the land do according to their specific

natures.

From thefe confiderations ir appears, beyond contradiction, that the phoco of every kind are under an abfolute neceffity of mak ing the land their principal refidence; but there is another very convincing argument why they refide on fhore the greateft part of their time, and that is, that the flefh of thefe creatures is analogous to that of other land animals; and therefore, by overlong macerátion, added to the fatigue of their chacing their prey, they would fuffer fuch a relaxation as would deftroy them. It is well known that animals, which have lain long under water, are reduced to a very lax and even putrid ftate; and the phoca muft bask in the air on fhore; for while the folids are at reft, they acquire their former degree of tenfion, and the vigour of the animal is restored; and while he has an uninterrupted placid refpiration, his blood is refreshed by the new fupply of air,

as I have explained it above, and he is rendered fit for his next cruize: for action waftes the most exalted fluids of the body, more or lefs, according to its duration and violence; and the restorative reft must continue a longer or fhorter time, according to the quantity of the previous fatigue.

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

All thefe have the oval hole open between the right and left auricles of the heart, and, in many, the canalis arteriofus alfo: and while the phoca remains under water, which he may continue an hour or two, more or lefs, his refpiration is ftopped, and the blood, not finding the paffage through the pulmonary artery free, rufhes. through the hole from the right to the left auricle, and partly through the arterial canal, being a fhort paffage to the aorta, and thence to every part of the body, maintaining the circulation: but, upon rifing to come afhore, the blood finds its paffage again through the lungs the moment he refpires.

Thus the foetus in utero, during his confinement, having the lungs compreffed, and confequently the pulmonary arteries and veins impervious, has the circulation of the blood carried on through the oval hole and the arterial canal; now fo far the phoca in the water and the fœtus in utero are, analogous; but they differ in other material circumftances; one is, that the foetus, having never refpired, remains fufficiently nourifhed by the maternal blood circulating through him, and conti

nucs

nues to grow till the time of his birth, without any want of refpiration during nine months confinement; the phoca, having refpired the moment of his birth, cannot live very long without it, for the reafons given before; and this hole and canal would be clofed in them, as it is in land animals, if the dam did not, very foon after the birth of the cub, carry him into the water to teach him, fo very frequently; by which practice thefe paffages are kept open during life; otherwife they would not be capable of attaining the food defigned for them by providence.

Another difference is, that the phoca, as I faid before, would be relaxed by maceration in remain ing too long in the water; whereas the foetus in utero fuffers no injury from continuing its full number of months in the fluid he fwims in the reafon is, that water is a powerful folvent, and penetrates the pores of the fkins of land animals, and in time can diffolve them: whereas the liquor amnii is an infipid foft fluid, impregnated with particles more or lefs mucilaginous, and utterly incapable of making the leaft alteration in the cutis of the foetus.

Otters, beavers, and fome kinds of rats, go occafionally into the waters for their prey, but cannot remain very long under water; I have often gone to fhoot ofters, and watched all their motions; I have feen one of them go foftly from a bank into the river, and dive down, and in about two minutes rife, at ten or fifteen yards from the place he went in, with a middling falmon in his mouth, which he brought on

fhore; I fhot him, and faved the fish whole. Now, as all foetufes have thefe paffages open, if a whelp of a true water-fpaniel, was, immedi ately after its birth, ferved as the phoca does her cubs, immerfed in water, toftop refpiration for a little time every day, I make no doubt but 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 foever of remaining in the water, yet can. not avoid living on land, for they refpire; and if, as I have often done, a frog be thrown into a river, he makes to the fhore as faft as he can.

The lizard kind, fuch as may be called water lizards, or lacerte aquaticæ, all are obliged to come to land and depofit their eggs, reft, and fleep; even the crocodiles, who dwell much in rivers, fleep and lay their eggs on fhore; and, while in the water, are compelled to rife to the furface to breathe; yet, from the texture of his fcaly covering, he is capable of remaining in the water longer by far than any fpecies of the phoca, whofe fkin is analogous to that of a horfe or cow.

The hippopotamus, who wades into the lakes or rivers, is a quadruped, and remains under the water a confiderable time; yet his chief refidence is upon land, and he must come on thore for refpiration.

The teftudo, or fea-tortoife, tho' he goes out to fea, and is often found far from land; yet, being a refpiring animal, cannot remain long under water. He has indeed a power of rendering him, felf fpecifically heavier or lighter

than

than the water, and therefore can , let himself down to avoid an enemy or a ftorm; yet he is under a ne. ceffity of rifing frequently to breathe, for reafons given before, and his molt ufual fituation, while at fea, is upon the furface of the water, feeding upon the various fubftances that float in great abundance every where about him; thefe animals fleep fecurely upon the furface, but not under water, and can remain longer at fea than any others of this clafs, except the crocodile, becaufe, as it is with the latter, his covering is not in danger of being too much macerated; yet they must go on fhore to copulate, and lay their eggs.

The confideration of thefe is fufficient to inform us of the nature of the firft order of the clafs of amphibious animals; let us now, fee what is to be faid of the fecond in our divifion of them, which are fuch as chiefly inhabit the waters, but occafionally go on fhore.

These are but of two kinds; the eel, and water ferpents, or fnakes of every kind. It is their form that qualifies them for locomotion on land, and they know their way back to the water at will; for by their ftructure they have a ftrong 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 fhore; and therefore, as foon as fuch fish are brought out of the water, after having flounced a while, they lie motionlefs, and foon die.

Let us now examine into the reason why these vermicular fish,

the eel and ferpent kinds, can live: a confiderable time on land, and the vertical and horizontal kinds die almoft immediately when taken out of the water: and, in this refearch, we fhall come to know what analogy there is between land ani mals and thofe of the waters. All land animals have lungs, and can. live no longer than while these are inflated by the ambient air, and al ternately compreffed for its expulfion; that is, while refpiration is duly carried on, by a regular infpiration and expiration of air.

In like manner, the fish in general have, instead of lungs, gills, or branchia; and, as in land ani. mals, the lungs have a large por. tion of the mafs of blood circulating through them, which muft. be stopped if the air has not a free ingrefs and egrefs into and from them; fo, in fish, there is a great fhare of blood-veffels that pafs through the branchia, and a great portion of their blood circulates through them, which muft in like manner be totally stopped, if the branchia are not kept perpetually. wet with water; fo that, as the air is to the lungs, in land animals, a conftant affiftant to the circulation, fo is the water to the branchia of thofe of the rivers and feas; for when thefe are out of the water, the branchiæ very foon grow crifp and dry, the blood veffels are fhrunk, and the blood is obftructed in its paffage; fo, when the former are immerfed in water, or otherwife prevented having refpiration, the circulation ceafes, and the animal dies.

Again, as land animals would be deftroyed by too much maceration in water, fo fishes would, on the other hand, be ruined by

I