818 



U N AU. 



racters of this species, or rather the sub-genus, for the 

 animal differs sufficiently from the Ai to entitle it to 

 that distinction. The unau has only two claws on 

 the fore feet, though it has three on the hind ones. 

 The tail is very short, consisting of only three verte- 

 brae, and wholly concealed in the hair. The fore legs 

 are not so long as in the ai, and they bear a propor- 

 tion to the hind legs of six to five. The bones of the 

 extremities are not so completely soldered together 

 as in the ai, the first phalanges of the toes are free, 

 though always soldered to the sesamoides. The 

 claws are one-half shorter in proportion than those 

 of the other. It is larger than the ai, its head is 

 more elongated, its forehead less round and promi- 

 nent, and its facial line more oblique. Its covering 

 consists of rough hairs, thicker and coarser than those 

 of the ai, but not quite so long and shaggy. They 

 are partly brown and partly white, the former pre- 

 dominating on the back, and the latter on the under 

 part. This mixture, which is not in spots but in 

 single hairs, gives it a peculiar tint of grey, which 

 appears deeper where the brown hairs predominate, 

 which they especially do on the upper part of the 

 neck, on the former of which the hairs are long, and 

 produce a sort of mane. There are also very strong 

 hairs on the thighs, and the hair on the fore arms is 

 reversed. The canines are much larger and more 

 conspicuous than in the ai, and they are separated 

 from the cheek-teeth by a ridge of the jawbone. The 

 proportions may be judged of from the statement that, 

 in a specimen whose body is two feet, the head is 

 about five inches long, the inner claw on the fore foot 

 two inches, and that on the hind foot an inch and 

 three quarters. The claws on the hind feet are 

 longer than those on the fore ones, and the inter- 

 mediate is the longest of three. The claws are in 

 reality hoofs, embracing the whole extremities of the 

 toes, as in the hoofed animals, and therefore are regu- 

 lar parts of the extremities as organs of locomotion. 



Though this animal is not so utterly helpless upon 

 the ground as the ai, it is yet but a very slow walker, 

 and does not get on at a more rapid rate than a tor- 

 toise. It is much more at home in climbing, and can 

 contrive to reach the top of a tall tree in a moderate 

 length of time. Its favourable position, like that of 

 iho otter, is suspending itself by the feet with the 

 back undermost ; and it can thus suspend itself by 

 three feet, and use the remaining one in feeding. It 

 sleeps suspended. 



All its senses, and indeed the whole of its vital 

 energies, are of a very low and imperfect character. 

 Of its hearing we know little, but it is not much 

 startled by sounds. Its sense of smell is obtuse, and 

 it sees badly in a strong light. Altogether it is much 

 more a passive than an active animal. It can endure 

 hunger for a long time, and is not much affected by 

 blows, or even by wounds. All its qualities are in 

 fact more of a passive than of an active nature, and it 

 lives much more by its power of enduring whatever 

 may be going on around it, than by its own activity, 

 exertion, or resource of any kind. 



It is by no. means rare in the thick and close 

 forests of South America ; indeed it appears to be 

 much more abundant, at least in some places, than 

 the three-toed sloth ; and, though it is not perhaps 

 equal to that animal in power of perambulating the 

 upper parts of the trees in the thick forest with the 

 back undermost, it can more readily descend and 

 again remount when it comes to an opening. 



Of the duration of life, either in it or in its conge- 

 ner, we know nothing ; but the numbers are con- 

 siderable as compared with the productive powers, 

 which consist of but one at a birth, which one attaches 

 itself to the mother by means of its claws, and clings 

 to her in all her climbings among the trees. This 

 carrying the young attached to the body bears some 

 resemblance to the marsupialia with a perfect pouch, 

 only the mode of carrying is varied to suit the habit. 

 The young, attached in any way to the belly, woulfl 

 be very inconvenient for the mother, and very unsafe 

 for the young, in an animal which has the back under- 

 most, and the belly in contact with those branches 

 which form its pathway in the forest. The back, on 

 the other hand, is equally safe for both. We must 

 not wonder at this ; for the unau still supports the 

 young in that which is her own position of stability, 

 namely, with the back undermost ; and as the struc- 

 ture of the young one is the same, the back under- 

 most is the position of stability for it also. The 

 sloths of whatever species are reversed animals in 

 their position of action as compared with ordinary 

 animals ; and therefore we must look upon all their 

 performances the other way. In an upright animal, 

 the young are most safe riding upon the upward back 

 of the mother ; but in those reversed animals, they 

 are most safe in clinging to the downward back. 



What may have been the state of South America 

 at the time when the mighty animals of the sloth 

 family were alive, or what may have been the precise 

 scene and mode of their action, it is impossible for us 

 to know ; but we may with the greatest certainty 

 and safety conclude that it must have then been a 

 rough state of things. That there has been no great 

 geological revolution in that part of the world, since 

 the megatherium fed in some way upon some vege- 

 table, we may be assured ; for the remains of the 

 animal have been found in the soft deposite of La 

 Plata, without a single bone displaced or disjointed ; 

 and thus there must have been a common progress of 

 nature in changing the country, from the time of the 

 megatherium to that of the ai and the unau. Along 

 with them, or with either of them, there could dwell 

 no sprightly quadruped of large size feeding upon 

 vegetables ; for the remains of the forests are of such 

 a character that they afford neither food nor footing 

 for any such. This leads us to conclude that there must 

 have been rather a rough state of things at that time, 

 and that, on the part of the mammalia, the power of 

 suffering must have far exceeded that of acting. The 

 great bones of the megatherium are obviously formed 

 for endurance, not for activity ; and the probability 

 is, that it may have been a still slower animal than 

 the present sloths. 



There is one curious point in the progressive zo- 

 ology of South America ; and that is the wonderful 

 productiveness and prosperity of the horse and ox in 

 that country. That there is not a vestige of either of 

 them as having existed there before their introduc- 

 tion subsequent to the discovery of the country by 

 Columbus and his followers, every body knows ; and 

 yet they have bred and multiplied there in wild 

 nature, faster than they have done in the eastern con- 

 tinent, or in North America, by all the arts of the 

 breeder. This is undeniable, and yet it seems some- 

 what strange. Experience has shown that the plains 

 of South America, every where to the southward of 

 the great tropical parts, where the sloths now inhabit, 

 are the places of the earth's surface which are the 



