THESE two animals have been denominated sloths, on account of the slowness of their movements, and the difficulty with which they walk. Though they resemble each other in many respects, they differ, both externally and internally, by characters so marked, that it is  impossible not to recognise them as very distinct species. The unau, or two-toed sloth, has no tail, and only two claws on all the feet. The aï, or three-toed sloth, has a tail, and three claws on all the feet. The muzzle of the former is longer, the front more elevated, and the ears more apparent than those of the latter. Their hair is also very different. The structure  and situation of some parts of their viscera are likewise different. But the most remarkable distinction is derived from this singular circumstance, that the unau has forty-six ribs, and the aï only twenty-eight, which shows them to be species very remote from each other. This number of ribs, in the body of an animal so short, is an excess or error of Nature; for no animal however large, has such a number of ribs: The elephant has only forty, the horse thirty-six, the badger thirty, the dog twenty-six, man twenty-four, &c. This difference in the structure of the sloths indicates a greater distance between these two species than between the dog and cat, who have both the same number of ribs; for external differences are nothing when compared to those which are internal: The former may be regarded as causes, and the latter as effect only. The interior frame of animated beings is the foundation of Natures plan; it is the constituent form, and the origin of a figure: But the external parts are only the surface or drapery. How often have we not found, in the course of our comparative examination of animals, that a very different external appearance covered internal parts perfectly similar; and that, on the contrary, the slightest internal distinction produced great external differences, and changed the natural dispositions, powers, and qualities of the animal? How many animals are armed, covered, and adorned with ex-  crescent parts, whose external structure corresponds exactly with others which are totally deprived of such appendages? But this is not a proper place for such nice disquisitions. We shall only remark, that, in proportion as Nature is vivacious, active, and exalted in the monkey kind, she is slow, restrained, and fettered in the sloths. From a defect in their conformation, the misery of these animals is not more conspicuous than their slowness. They have no cutting teeth; the eyes are obscured with hair; the chops are heavy and thick; the hair is flat, and resembled withered herbs; the thighs are ill jointed to the haunches; the legs are too short, ill turned, and terminated still worse: Their feet have no soles, and no toes which move separately, but only two or three claws disproportionally [sic] long, and bended downward, which move together, and are more hurtful to their walking, than advantageous in assisting them to climb. Slowness, habitual pain, and stupidity, are the results of this strange and bungled conformation. The sloths have no weapons either offensive or defensive. They are furnished with no means of safety; for they can neither fly nor dig the earth. Confined to a small space, or to the tree under which they are brought forth, they are prisoners in the midst of space, and cannot move the length of one fathom in an hour.* They drag themselves up a tree with  much labour and pain. Their cry and interrupted accents they dare only utter during the  night. All these circumstances announce the misery of the sloths, and recall to our minds those defective monsters, those imperfect sketches of Nature, which, being hardly endowed with the faculty of existence, could not subsist for any length of time, and have accordingly been struck out of the list of beings. If the regions inhabited by the sloths were not desert, but had been long occupied by men and the larger animals, these species would never have descended to our times: They would have been annihilated, as in some future period will be the case. We formerly remarked, that every thing that possibly could be, really did exist; of which the sloths are a striking example. They constitute the last term of existence in the order of animals endowed with flesh and blood. One other defect added to the number would have totally prevented their existence. To regard those bungled sketches as beings equally perfect with others, to call in the aid of final causes to account for such disproportioned productions, and to make Nature as brilliant in these as in her most beautiful animals, is to view her through a narrow tube, and to substitute our own fancies for her intentions.
Why should not some animals be created for misery, since, in the human species, the greatest number of individuals are devoted to pain from the moment of their existence? Evil, it is true, proceeds more from ourselves than from Nature.  For a single person who is unhappy, because he was born feeble or deformed, there are millions rendered miserable by the oppression of their superiors. The animals, in general, are more happy, because the species have nothing to fear from individuals: To them there is but one source of evil; to man there are two. Moral evil, of which he himself is the fountain, has accumulated into an immense ocean, which covers and afflicts the whole surface of the earth. Physical evil, on the contrary, is restrained within very narrow bounds: It seldom appears alone; for it is always accompanied with an equal, if not a superior good. Can happiness be denied to animals, when they enjoy freedom, have the faculty of procuring subsistence with ease, and posses more health, and organs capable of affording greater pleasure than those of the human species? Now, the generality of animals are most liberally endowed with all these sources of enjoyment. The degraded species of sloths are perhaps the only creatures to whom Nature has been unkind, and who exhibit to us the picture of innate misery.
Let us take a closer view of the condition of these creatures. By the want of teeth, they can neither seize prey, nor feed upon flesh or herbage. Reduced to the necessity of living upon leaves and wild fruits, they consume much time in trailing their bodies to the foot of a tree, and  still more in climbing to the branches;* and, during this slow and melancholy exercise, which sometimes lasts several days, they are obliged to suffer the most pressing hunger. When arrived  upon a tree, they never descend. They cling to the branches, and devour successively the leaves of every twig. They pass several weeks in this situation, without receiving any drink. When they have rendered the tree entirely naked, they still remain; because they cannot descend. In fine, when the pressure of hunger becomes superior to the dread of danger or death, being unable to descend, they allow themselves to tumble down like an inanimated mass; for their stiff and inactive limbs have not time to extend themselves in order to break the fall.
When on the ground, they are at the mercy of all their enemies. As their flesh is not absolutely bad, both men and rapacious animals go in quest of these animals. It appears that they do not multiply fast, or, at least, if they produce frequently, it must be in small numbers at a time; for they have only two paps. Every circumstance, therefore, concurs to destroy them; and it is extremely difficult for the species to support itself. But, though slow, awkward, and almost incapable of motion, they are obstinate, strong, and tenacious of life. They can live very long without victuals of any kind.* They are covered with thick, dry hair; and, being incapable of exercise, they lose little by perspiration; and, though their food be meager, they fatten by re-  pose. Though they have no horns nor hoofs, nor cutting teeth in the under jaw, yet they belong to the ruminating tribes, and have several stomachs. Hence the quality of their food may be compensated by the quantity they take at a time. What is still more singular, instead of very long intestines, like other ruminating animals, their guts are very short and small, like those of the carnivorous kind. This contrast exhibits the ambiguity of Nature. The sloths are unquestionably ruminating animals: They have four stomachs; and yet they want every other character, both internal and external, which generally belongs to animals of this class. There is still another singularity in the conformation of the sloths: Instead of three distinct apertures for the discharge of urine and excrements, and for the purposes of generation, these animals have but one, which terminates in a common canal, as in birds.
Moreover, if the misery resulting from a defect of sentiment be not the worst of all, the pain endured by the sloths, though very apparent, seems not to be real; for their sensations appear to be blunt. Their calamitous air, their dull aspect, and their reception of blows without emotion, announce their extreme insensibility. This bluntness of sensation is farther demonstrated, by their not dying instantly when their hearts and bowels are entirely cut out. Piso, who made this  cruel experiment,* tells us, that the heart, after being separated from the body, beat in a lively manner for half an hour; and that the animal continued to contract its legs slowly, as commonly happens during sleep. From these facts, this quadruped seems to approach not only the turtle, but other reptiles which have no distinct centre of sensation. All these beings may be said to be miserable, but not unhappy: Nature, even in her most neglected productions, always appears more in the character of a parent than of a stepmother.
These two animals are peculiar to the southern regions of the New Continent, and are no where to be found in the Old. We formerly remarked, that the editor of Sebas cabinet was deceived when he calls the tow-toed [sic] sloth, or unau, the sloth of Ceylon. This error, which has been  adopted by Klein, Linnaeus, and Brisson, is now more evident than it was formerly. The Marquis de Montmirail has a live unau, which was transmitted to him from Surinam: Those we have in the Royal Cabinet were brought from the same place and from Guiana; and I am persuaded that both species exist through the whole deserts of America, from Brasil* to Mexico. But, as they have never frequented the northern regions, they could not pass from the one Continent to the other. If these animals have sometimes been seen in the East Indies, or on the coast of Africa, it is certain that they must have been transported thither. They cannot endure cold; and they likewise dread rain. The alternation of moisture and dryness changes their fur, which has more the appearance of ill dressed hemp than of wool or hair.
I shall finish this article with some observations communicated to me by the Marquis de Montmirail, concerning an unau, or two-toed sloth, which he fed three years in his menagerie: The hair of the unau is much softer than that of the aï ..All that has been said by travellers concerning the excessive slowness of the sloths should, probably, be applied only the aï, or three-toed species. The unau, though very heavy, and of an extremely awkward gait,  mounted and descended the highest tree several times in a day. It is in the evening and during the night that he was most active, which made me suspect that he saw very ill in the day, and that his eyes were of no use to him but in the dark. I purchased this animal at Amsterdam. It was fed with sea biscuit; and I was told, that, during the verdure of the trees, it would require nothing but leaves. We have him leaves, which he eat [sic] freely, when they were tender; but, as soon as they began to dry, or were pierced by caterpillars, he refused them. During the three years that I kept him alive in my menagerie, his ordinary food was bread, apples, and roots; and his drink was milk. He always laid hold, though with difficulty, of what he wanted to eat, with his fore paws; and the difficulty increased in proportion to the largeness of the morsel. He seldom cried; his cry is short, and he never repeats it twice, without a considerable interval. This cry, though plaintive, has no resemblance to that of the aï, if it be true that the aï is the sound of that animals voice. The most natural situation of the unau, and which he prefers to all others, is hanging on a branch, with his body turned downward. He sometimes sleeps in this position, his fore paws being fixed to the same point, and his body forming an arch. The strength of his muscles is incredible; but it becomes useless to him when he walks; for his  motion is constrained and wavering. This structure alone seems to be the cause of the animals slowness, which, besides, has no violent appetites, and does not recognise those who take care of him.
M. de la Borde remarks, that there are two species of these animals in Cayenne, the one called the bashful sloth, and the other the sheep-sloth. The latter is twice as long as the former, and of the same thickness. He has long, bushy, whitish hair, and weighs about twenty-five pounds. He throws himself down upon men from the tops of trees, but in a manner so sluggish, that it is easy to avoid him. He feeds during the day as well as the night.
The bashful sloth, M. de la Borde remarks, has black spots on his body, weighs twelve pounds, keeps always on trees, and eats the leaves of the Surinam fig-tree, which are said to be poisonous. The bowels of this sloth poison dogs, and yet the flesh is good eating; but its use is confined to the common people.
Both species produce only a single young, which they always carry on their back. It is  probable, though I am not certain, that the females bring forth on trees. They feed on the leaves of the Brasilian plumb-tree,* and of the Surinam fig. The two species are equally common; but they are not frequent in the environs of Cayenne. They sometimes suspend themselves by their claws on branches of trees which hang over the rivers; and, when in this situation, it is easy to cut the branch and make them fall into the water; for they never quit their hold.
When ascending a tree, this animal carelessly stretches out one of its fore pats, and fixes its long claw as high as it can reach. It then heavily raises its body, gradually fixes the other pat; and, in this manner, continues to climb. All these movements are incredibly slow and languid. When kept in houses, they always climb upon some post or door, and never choose to rest on the ground. If a stick is held out to them when on the ground, they lay hold of it, and mount to its top, where they firmly adhere with their fore paws, and embrace the stick with their whole body. They have a weak plaintive cry, which is heard at no great distance.
From this passage, it is obvious, that the sheep-sloth is the same with what we have called unau, or the three-toed sloth; and that the bashful-sloth is the aï, or two-toed species.  [Plate CCXII here] [Plate CCXIII here] [Plate CCXIV here]
M. Vosmaër, an able naturalist, and superintendent of the Prince of Oranges cabinet, has criticized two assertions in my history of these animals. He remarks, that we ought to reject the relation of M. de Buffon, when he tells us, that the sloths are unable to descend from a tree, but allow themselves to fall down like blocks.*
I advanced this fact on the authority of eye-witnesses, who assured me, that they had sometimes seen the animal fall down at their feet. The fact is farther supported by the testimony of M. de la Borde. What I have said on this subject, therefore, ought by no means to be rejected.
The second assertion is not equally well founded. I willingly acknowledge my mistake, when I said that the sloths had no teeth, and I thank M. Vosmaër for correcting this error.
* The sloths have no cutting teeth in either jaw; but they have canine teeth and grinders. The fore legs are much longer than the hind, and the claws are long. --- The two-toed sloth has a round head, short projecting nose, ears like the human, lying flat on the head, two long claws on the fore feet, and three on the hind. The hair on the body is long and rough; in some parts curled and woolly, in some, of a pale red above, cinereous below; and in others, of a yellowish white below, and a cinereous brown above. The length of that in the British museum, is eleven inches; I believe it is a young one: It has no tail; Pennants Synops. of quad. p. 321.
Unau, the name of
this animal in Maragnon. P. dAbbeville says, that there
are two kinds, the one about the size of a hare, and the other about
twice as large; Misson au Maragnon, p. 252.
Tardigradus Ceilonicus catulus; Seba, tom. I. p. 54. tab. 33. fig. 4.-----Tardigradus Ceilonicus foemina; Id. ib. tab. 34.
Tardigradus pedibus anticis didactylis; posticis tridactylis; Le Paresseux de Ceilan; Brisson. quad. p. 22.
Bradypus didactylis, minibus didactylis, cauda nulla; Linn. syst. nat. p. 51 .
** The three-toed sloth has a burnt black nose, a little lengthened, very small external ears, and eyes small, black, and heavy. From the corner of each eye, there is a dusky line. The colour of the face and throat is a dirty white. The hair on the limbs and body is long, very uneven, and of a cinereous brown colour. The tail is short, being a mere stump. The legs are thick, long, and awkwardly placed. The face is naked. There are three toes, and three very long claws on each foot. The length of that in the British museum is twelve inches; but it grows to the size of a middle sized fox; Pennants synops. of quad. p. 319.
Aï, the Brazilian name of this animal, taken from its plaintive cry a, i, which it often repeats, Hay, according to Lery; and Hau or Hauthi, according to Thevot. The Perillo ligero of Oviedo, and the Haut of Nieremberg.
Arctopithecus; Gesner. quad. p. 869. Icon. quad. p. 96.
Ignavus; Clus. Exot. p. 110. 372.
Sloth; Raii synops, quad. p. 245. Edwards Gleanings, pl. 310.
Ignavus Americanus, risum fletu miscens; Klein. quad. p. 43.
Tardigradus pedibus anticis et posticis tridactylis; Brisson. quad. p. 21.
Aï, seu tardigradus gracilis Americanus; Seba, tom. I. p. 53. tab. 33. fig. 2.
Ouaikare, Paresseux; Barrère hist. Fr. Equinox. p. 154.
Bradypus tridactylus, pedibus tridactylis, cauda brevi; Linn. syst. nat. p. 50.
Brigritia sive Haut; Nieremb. p. 163.
Aï, sive ignavus; Marcgr. hist. nat. Brasil. p. 221 [back to page 150].
* Perillo ligero, sive canicula agilis, animal est omnium  quae ignavissimum; nam adeo lente movetur, ut ad conficiendum iter longum dumtaxat quinquaginta passus, integro die illi opus sit.----In aedes translatum naturali sua tarditate noventur, nec a clamatikone ulla aut impulsione gradum accelerat; Oviedo in summario Ind. Occid. cap. 23. traduit de lEspagnol en Latin par Clusius, Exotic. lib. 5. cap. 16. Tanta est ejus tarditas ut unius diei spatio vix quiquaginta passus pertransire posit; Hernand. Hist. Mex.---The Portuguese have given the name of sloth to a very extraordinary animal, which is of the size of an opossum.---The hind part of its head is covered with a course mane, and its belly is so gross that it sweeps the ground. It never rises on its legs, and trails so slowly along, that in fifteen days it can hardly accomplish the length of a stone-cast; Hist. des Indes, par. Massé, p. 71. Descript. des Indes Occident. par Herrera, p. 252.--- Tam lentus est illius gressus et membrorum motus, ut quindecim ipsis diebus ad lapidis ictum continuo tractu vix prodeat; Pison. hist. Bras. p. 322. Nota. This assertion of Piso, which he has borrowed from Massé and Herrera, is much exaggerated.----This is the most sluggish of all animals: It is needless to employ greyhounds to overtake him; a tortoise is sufficient; Desmarchias, tom. 3. p. 301, Nota. This is another exaggeration.----They require eight or nine minutes to advance one foot to the distance of three inches, and they move one after another with equal slowness. Blows do not accelerate their pace. I have whipt [sic] some of them, in order to discover whether pain would give them any animation: But they seemed insensible, and I was unable to make them move faster; Dampiers voyage.---The sloths do not move fifty paces in a day. When the hunter wishes to take one of them, he may proceed with his sport, and, on his return, he will find the animal very little removed from its former place; Voyage à Cayenne, par Binet, p. 341.-----This animal receives the epithet of courser, because he requires a whole day to accomplish a quarter of a league; Hist. de lOrenoque, par Gumilla, tom. 2. p. 13. Nota. This author seems to be the only one who approaches the truth, with regard to the slowness of these animals  [back to page 153].
* It is alledged by the natives, that this animal lives solely on the leaves of a certain tree, called in their language Amahut. This tree is higher than any other in that country. Its leaves are very small and delicate; and, because the sloth is commonly found in these trees, they have given it the name of Haut; Singul. de la France Antarc, par Thevet. p. 100.--- The sloth lives solely on the leaves of trees, and the highest branches serve him for a retreat; but it costs him two days journey to arrive at them .. Neither caresses, threatenings, nor even blows, can make him move quicker; Hist. des Indes, par Massè, p. 71. Herrera, p. 252. The sloth is not so large, nor so rough as the tamanoir, or great ant-eater ..He feeds upon leaves ..These animals do much mischief to trees; after eating all the leaves of one tree, they employ five or six days in descending it and climbing another, however nearly situated; and, though plump and fat when they begin their journey, the are reduced to skin and bone before they finish it. They never abandon a tree till they have made it as bare as it can be in the middle of winter; Dampiers Voyage.They climb trees, but so slowly, that they are easily taken. When seized, they make no resistance, and never attempt to fly. If a long pole is presented to the sloth, he begins to mount it; but the slowness of his motion is tiresome: When he arrives at the top, he remains there, without taking the trouble of descending; Voyage de Cayenne, par Binet, p. 341. --- The sloths have four legs, which they employ only in climbing: When perched upon a tree, they never quit it till they have eat the whole leaves. They then descend, and mount another, the leaves of which they devour in the same manner.We placed this animal on the lowest sail of the fore-mast. It spent two hours climbing to the scuttle, which a monkey would have accomplished in half a minute. One would imagine that it moves by a spring, like the pendulum of a clock; Travels by Woods Rogers [back to page 157].
*I had a present of a living haut, which I kept twenty-six days, during which he neither eat nor drank; Singular. de la France Ant. par Thevet, p. 99 [back to page 158].
Secui semellam vivam ..habentem in se foetum omnibus modis perfectum cum pilis, unguibus, et dentribus, amnioni more caeterorum animalium inclusum. Cor motum suum validissime retinebat postquam exemptum erat e corpore per semihoram; placenta uterine constabat multis particulis carneis instar substantiae renum, rubicundis magnitudinis variae, instar fabarum; in illas autem particulas carneas (tenuibus membranulis connexas) per multos ramulos vasa umbilicalia instar funis contorta, inserta errant. Cor foemellae dueas habebat insignes auriculas cavas. Exempto corde caeterisque visceribus, multo post se movebat, et pedes lente contrahebat sicut dormituriens solet. Mammillas duas cum totidem papillis in pectore foemella et foetus gerebant; Pison. hist. Brasil. p. 322 [back to page 160].
* The aï, or three-toed sloth, described and engraven by Edwards, came from the Bay of Honduras; and Ulloa says, that it is found in the environs of Porto-bello [back to page 161].
* Spondias lutea of Linneaus [back to page 164].
* Descript. dun parresseux pentedactile de Bengale, p. 5 [back to page 165].