[THE UNAU, OR FOUR-TOED, AND THE AÏ, OR THREE-TOED, SLOTHS.]
These two animals have had the name of Sloths given to them on account of their slowness, and the difficulty with which they walk. Though they resemble each other in many respects, nevertheless they differ externally and internally by such strong characters that it is impossible to mistake the one for the other, or doubt of their being very distinct species. The unau ([fig. 166.]) has no tail, and only two claws on the fore feet. The aï has a short tail, and three claws on each foot. The nose of the unau is likewise longer, the forehead higher, and the ears larger than the aï. They differ also in the hair. Some parts of their viscera are formed and situated different; but the most distinct and singular character is, the unau has forty-six ribs; and the aï but twenty-eight; this alone proves them to be two species quite distinct from each other. These forty-six ribs in an animal whose body is so short is a kind of excess, or error, in nature; for even in the largest animals, and those whose bodies are relatively longer than they are thick, not one of them is found to have so many; the elephant has only forty, the horse thirty-six, the badger thirty, the dog twenty-six, the human species twenty-four, &c. This difference in the construction of the sloths supposes a greater dissimilitude between these two species than there is between the cat and dog, both of which have the same number of ribs. External differences are nothing in comparison with internal ones. The internal frame of living animals is the groundwork of Nature’s design, it is the constituent form, and the cause of all figure; and the external parts are only the surface or drapery. In our comparative examination of animals, how many have we seen who often differed very much in their outward appearance and yet were perfectly alike internally; and, on the contrary, the least internal distinction has produced great external differences, and even changed the natural habits, faculties, and attributes of the animal? How many also are there armed, cloathed, and even ornamented with superfluous parts, which, nevertheless, in their internal organization entirely resemble others who are deficient in these excrescences? but we shall not here dwell on this subject, which supposes, not only a reflected comparison, but also an exposition of all the parts of organization; we shall only observe, that in proportion as Nature is lively, active, and exalted in the ape species, she is slow, constrained, and cramped in the sloths. These animals have neither incisive nor canine teeth; their eyes are dull, and almost concealed with hair; their mouths are wide, and their lips thick and heavy; their fur is coarse, and looks like dried grass; their thighs seem almost disjointed from the haunches; their legs very short and badly shaped; they have no soles to their feet, nor toes separately moveable, but only two or three claws excessively long and crooked downwards, which move together, and are only useful to the animal in climbing. Slowness, stupidity, and even habitual pain, result from its uncouth conformation. They have no arms either to attack or defend themselves; nor are they furnished with any means of security, as they can neither scratch up the earth nor seek for safety by flight, but confined to a small spot of ground, or to the tree under which they are brought forth, they remain prisoners in the midst of an extended space, unable to move more than three feet in an hour; they climb with difficulty and pain; and their plaintive and interrupted cry they dare only utter by night. All these circumstances announce their wretchedness, and call to our mind those imperfect sketches of Nature, which, having scarcely the power to exist, only remained a short time in the world, and then were effaced from the list of beings. In fact, if it were not a desart country where the sloths exist, but had been long inhabited by man and powerful animals, they would not have descended to our time; the whole species would have been destroyed, as at some future period will certainly be the case. We have already observed, that it seems as if all that could be, does exist; and of this the sloths appear to be a striking proof. They constitute the last term of existence in the order of animals endowed with flesh and blood. One more defect and they could not have existed. To look on these unfinished creatures as equally perfect beings with others; to admit final causes for such disparities, and from thence to determine Nature to be as brilliant in these as in her most beautiful animals, is only looking at her through a straight tube, and making its confines the final limit of our judgment.
Why should not some animals be created for wretchedness, since in the human species the greatest number are devoted to pain and misery from their birth? Certainly, evil is more our own production than that of Nature. For one man who is unhappy from being born weak and deformed, thousands are rendered so by the oppression and cruelty of their fellow-creatures. Animals are, in general, more happy, because each species has nothing to dread from their individuals; to them there is but one source of evil, but to the human species there are two. Moral evil, which he has produced himself, is a torrent which is increased into a sea, whose inundation covers and afflicts the whole face of the earth. Physical evil, on the contrary, is confined to very narrow limits; it seldom appears alone or unaccompanied with an equal if not a superior good. Can animals be denied happiness when they enjoy freedom, and have the faculty of easily procuring subsistence, when they are less subject to ill health, and possess the necessary or relative organs of pleasure in a more eminent degree than the human species? In these respects animals in general are very richly endowed; and the degraded species of the sloths are, perhaps, the only creatures to whom Nature has been unkind, and the only ones which present us the image of innate misery and wretchedness.
Let us now inspect their condition more closely; being unfurnished with teeth they cannot seize upon prey, nor feed upon flesh or vegetables; reduced to live on leaves and wild fruits, they consume much time in crawling to a tree, and still more in climbing up to the branches; and during this slow and painful labour, which sometimes lasts many days, they are obliged to support the most pressing hunger. When they have accomplished their end they cling to the tree, crawl from branch to branch, and, by degrees, strip every twig of its leaves. In this situation they remain several weeks without any liquid; and when they have consumed the store, and the tree is entirely naked, they still continue, unable to descend until the pressure of hunger becomes more powerful than the fear of danger or death, and they suffer themselves to fall to the ground like an inanimate mass, without being capable of exerting any effort to break the violence of the fall.
When on the ground they are exposed to all their enemies, and as their flesh is not absolutely bad they are sought after both by men and beasts of prey. They seem to multiply but little, or if they produce often it is only a small number at a time, as they are furnished with but two teats: every thing, therefore, concurs to their destruction, and the species supports itself with great difficulty. Although they are slow, heavy, and almost incapable of motion, yet they are hardy, strong, and tenacious of life; they can exist a long time deprived of all food; they are covered with a thick, coarse fur, and being unable to take much exercise they waste little by perspiration, and therefore they fatten by rest, however poor their food. Though they have neither horns nor hoofs, nor incisive teeth in the lower jaw, they belong, notwithstanding, to the number of ruminating animals, and have four stomachs, so that they may compensate for the quality of their food by the quantity they take at a time; and what is still more singular, instead of having, like other ruminating animals, very long intestines, they are very short, like those of the carnivorous kind. The ambiguity of Nature seems somewhat discovered by this contrast. The sloths are certainly ruminating animals, as they have four stomachs; but they are deficient in all the other external and internal characters which belong to all animals in that class. There is also another singularity in these animals, instead of distinct apertures for the discharge of the urine, excrements, and the purposes of generation, these animals have but one, which terminates in a common canal, as in birds.
Finally, if the misery which results from a defect of sensation be not the greatest of all, the miserable state of these animals, although very apparent, seems not to be real, for they appear to have little or no sensation, and their dull and heavy look, their indifference to blows, which they receive without being in the least affected, prove their insensibility. But what still further demonstrates this fact is, their not instantly dying upon their hearts and bowels being taken out. Piso, who made this cruel experiment, says, that the heart, after being separated from the body, beat forcibly for more than half an hour, and that the animal continued to contract its limbs in the same manner as when asleep.[AM] From these circumstances this quadruped approaches not only the tortoise but also other reptiles who have no distinct centre of sensation: thus all these animals are miserable without being unhappy; and Nature, even in her most unfinished productions, appears always to act more as a real parent, than a step-mother.
[AM] Sonnini says, that wishing to kill a sloth for the purpose of preparing the skin, he exhausted every possible means to deprive it of life; but such was its principle of vitality that he could not remain any longer a witness of his own barbarous endeavours; and he quitted the room seized with horror at the idea of the evils which this miserable animal must endure, and with astonishment at that impenetrability which prolonged its existence.
Both these animals belong to the southern parts of the New Continent, and are never to be met with in the Old. We have already observed, that the editor of Seba’s cabinet was deceived in calling the unau by the name of the Ceylon sloth. This error, which has been adopted by Klein, Linnæus, and Brisson, is now more evident than formerly. The Marquis de Montmirail has a living unau, which was brought him from Surinam: those in the royal cabinet came from the same place, and from Guiana; and I am persuaded, that both species exist in the desarts of America, from Brasil to Mexico; but as it never inhabited the northern countries, it could not have passed from one continent to the other; and if these animals have been seen either in the East Indies, or on the coast of Africa, it is certain, that they must have been transported thither. They can endure neither cold nor rain; the change from wet to dry spoils their fur, which then resembles bad dressed hemp, rather than wool or hair.