Mr. Heerkens, after reciting many instances, and producing in his notes many authorities, of swallows having been found in a torpid state, proceeds, in his poem, to describe, very minutely, their ascent out of the water. The drowsy birds appear on the shore, as if unconscious still of life. Some inhale the soft breeze, like one of the finny tribe exiled from its stream. Some begin to adjust their dishevelled wings. -Others, almost revived, essay, with busy bill, to assist their aged companions. All, at length, restored to the unrestrained use of their wings, range, in numerous flights, the aerial way.

Two reasons have been adduced to prove this supposed submersion of swallows impossible. "In the first place, (says

Mr. Smellie,) no land animal can exist so long without some degree of respiration. The otter, the seal, and water fowls of all kinds, when confined under the ice, or entangled in nets, soon perish; yet it is well known, that animals of this kind can remain much longer under water than those who are destitute of that peculiar structure of the heart, which is necessary for any considerable residence beneath that penetrating element."

Mr. John Hunter, in a letter to Mr. Pennant, informs us, "that he had dissected many swallows, but found nothing in them different from other birds, as to the organs of respira. tion; that all those animals which he had dissected, of the class that sleep during the winter, such as lizards, frogs, etc. had a very different conformation as to those organs ; that all those animals, he believes, do breathe in their torpid state, and, as far as his experience reaches, he knows they do; and that, therefore, he esteems it a very wild opinion, that terrestrial animals can remain any long time under water without drowning."Another argument against their submersion arises from the specific gravity of the animals themselves. Of all birds, the swallow tribes are perhaps the lightest. Their plumage, and the comparative smallness of their weight, indicates that Nature destined them to be almost perpetually on the wing, in quest of food. From this specific lightness, the submersion of swallows, and their continuing for months under water, amount to a physical impossibility. Even water fowls, when they wish to dive, are obliged to rise and plunge with considerable exertion, in order to overcome the resistance of the water. Klein's idea of swallows employing reeds and straws as means of submersion, is rather ludicrous; for these light substances, instead of being proper instruments for assisting them to reach the bottom, would infallibly contribute to support them on the surface, and prevent the very object of their intention. Besides, admitting the possibility of their reaching the bottom of lakes and seas, and supposing they could exist for several months without respiration, what would be the consequence? The whole would soon be devoured by otters, seals, and fishes, of various kinds. Nature is always anxious for the preservation of its species. But if the swallow tribes were destined to remain torpid during the winter months, at the bottom of lakes and seas, she would act in opposition to her own intentions; for, in a season or two, the whole genus would be annihilated.

This reasoning is very ingenious, but, on the other hand, the facts related above are very stubborn; and the celebrated Buffon does not hesitate to yield to the force of such strong and concurrent evidence. He had procured some chimney-swallows, and kept them some time in an icehouse, in order to ascertain whether they were of the torpid kind, and he thus relates the result of his experiments. "None of them fell into the torpid state; the greater part died, and not one of them revived by being moved into the warmth of the sun. Those that had not long suffered the cold of the icehouse, had all their movements, and went out briskly. From these experiments I thought I might conclude, that this species of the swallow was not liable to that state of torpor and insensibility, which supposes, notwithstanding, and very necessarily, the fact of their remaining at the bottom of the water during the winter. Having had recourse, moreover, to the most credit-able travellers, I found them agreed as to the passage of swallows over the Mediterranean. And Mr. Adamson has positively assured me, that during the long stay he made in Senegal, he observed the long-tai!ed swallow, the same with the chimney-swallow we are now speaking of, arrive constantly in Senegal about the time it leaves France, and as constantly leave Senegal in the spring. It cannot, therefore, be doubted, that this species of the swallow passes from Europe into Africa in the autumn, and from Africa to Europe in the spring; of consequence, it neither sleeps nor hides itself in holes, nor plunges into the water on the approach of winter. There is, besides, another well authenticated fact, which comes in proof here, and shows that this swallow is not reduced to a torpid state by cold, which it can bear to a certain degree, (and if that degree is exceeded, it dies,) for if we observe these birds towards the end of the warm season, we shall see them, a little before their departure, flying together in families, the father, the mother, and the young brood. Afterwards several families unite, and form themselves into flocks, more or less numerous in proportion as the time of their departure draws near. At last they go all together, three or four days before the end of September, or about the beginning of October. Still, however, some remain, and do not set on till a week, a fortnight, or three weeks after the rest: and some too there are which do not go at all, but stay and perish under the first rigours of the cold. These swallows that delay their flight, or never undertake it, are such as find their young too weak to follow them; such as have had the misfortune to have their nests destroyed after laying, and have been obliged to rebuild them a second or a third time. They stay for the love of their little ones, and choose rather to endure the rigour of the season, than to abandon their offspring. Thus they remain some time after the rest for the purpose of taking their young with them ; and if they are unable to carry them off in the end, they perish with them.

' These facts then plainly demonstrate (concludes Mr. Buffon) that the chimney-swallows pass successively and alter-nately from our climate to another that is warmer; that they spend their summer here, and their winter there; and of consequence never fall into a state of insensibility. But, on the other hand, what have we to oppose to the precise testimony of those, who, on the approach of winter, have seen these swallows in troops throw themselves into the water; nay, not only this, but have seen them taken out in nests from beneath the ice? What answer shall we make to those who have beheld them in the torpid state, and seen them gradually recover motion and life, when they were brought into the warmth, and moved cautiously towards a fire? I know but of one means of reconciling these facts: we must suppose that the sleeping and travelling swallow are of different species, though the difference, for want of attention, has not been observed."

Thus this great philosopher concurs with Mr. Pennant, in his solution, already mentioned, of the difficulty, by supposing two species - the migrating, and the sleeping swallow. With respect to the principal objects of this wonderful instinct, that teaches such various kinds of the feathered race to migrate to different countries, it is obvious, from what has already been said, that they are governed by their food, temperature of air, and convenient situations for breeding.