A I. 



53 



the fervour of the tropical sun, into an arid waste, 

 upon which no living thing could exist. If the forests 

 were, in thus manner, to be destroyed, or indeed in any 

 way but one in which their place should be occupied 

 by a close surface vegetation (and in those climates 

 there is none such known, save culture by man), 

 the rain would be gone also, and the land would be 

 put beyond the power of human skill and labour to 

 bring it back to usefulness, cither for man himself or 

 for any other living creature. On the deserts with 

 -.which we are acquainted, in the tropical parts of the 

 world, there are sometimes pestilent dews, from the 

 difference of temperature between the night and the 

 day, the cold of the former being increased by the 

 partial melting of the salt with which the surface of 

 such places is generally strewn ; and the heat of the 

 latter augmented both by reflection and radiation 

 from the burning surface ; but there fall no kindly 

 showers ; and, " once a desert, always a desert," till 

 sonic of those mightier movements of nature, of 

 which the records are written in the strata of the 

 deepest mines, and the loftiest mountains, shake the 

 ruin to picccs,a7id mould and temper its elements anew. 

 Wherever the earth is green, there are browsing 

 animals. But" in those tropical forests, the green is 

 not upon the surface, but on the tops of the trees; 

 and the browsing animals must be fitted for making 

 these their pasture. A pasture suspended in the 

 air must have those which feed upon it suspended in 

 the same element ; and the question may here be put, 

 "should they be suspended nfmvc their food or below 

 it?" Green loaves cannot form a footing for any 

 animal of sufficient, size to feed upon them wholesale 

 as a browser; and it is not easy to see how an 

 animal could browse on the wing; so that, according 

 to all that we know of the laws of animal action and 

 of those of matter, it does not seem consistent, or 

 even possible, that the leaves of a tropical forest could 

 be browsed by an animal above them. But an 

 animal suspended from the twigs or branches upon 

 which the leaves grow, and " holding on" by the 

 action of its weight on the points of suspension, could 

 have command of itself and feed; and this is exactly 

 the habit of the sloths, and their organisation agrees 

 with that habit. Their position is reversed as com- 

 pared with that of animals which walk the earth ; 

 and it is in keeping that their organs of motion 

 should be reversed also. 



Much as has been said and written about the 

 clumsy and helpless structure of the sloth (for even 

 Baron Cuvier, while forming a system of animals 

 according to their structure, says, they are formed as 

 if Nature had " wished to amuse herself in the pro- 

 duction of something imperfect and grotesque"), 

 there are cases in which we take him as our model. 

 When a sailor " warps" along a rope, he is obliged 

 to do it as the sloth does ; and the chief difference 

 is, that he does it more clumsily. The arms in man 

 close toward the centre of the body with their most 

 powerful hold ; and though the hands can grasp at 

 different angles, the firmest grasp, and that which 

 can be maintained the longest, is when the grasp is 

 in a plane parallel to the mesial plane of the body, 

 as nearly coincident with it as possible, and the fin- 

 gers turned inwards. The quadrumana grasp in the 

 same manner ; but their grasp, as well as our own, is 

 by iiMisciihir effort, and as such it is labour, whereas 

 the holding on of the sloth is repose, in the same 

 e as is the suspension of bats by their hooks. 



Their suspension is wholly by the claws, so that no 

 part in wnich there is any circulation is pressed by 

 their weight ; and thus, whether in their progressive 

 motion or in their repose, they really appear to suffer 

 less than any other animals. In tneir repose, they 

 hang by all the four feet, which are as nearly straight 

 as possible, till the last phalanges of the toes are ar- 

 rived at, and these are " stopped" by processes of the 

 bones, just like a stop hinge, so that they cannot 

 make other than a hook, with its point directed to 

 the mesial plane of the body. When they exert 

 themselves, the claws can be brought close to the 

 upper part of the wrist, and thus they can hold 

 firmly by the most tender twig ; and the hind feet, 

 which hold on while the fore ones arc bringing the 

 leaves within reach of the mouth, have a projecting 

 heel bone, for greater security. Each foot can act 

 separately, and thus they can feed on the trees as 

 near the extremities of the branches, as four twigs, 

 or as many times four of the smaller ones as they 

 can grasp between the foot and the long claws, 

 will bear their weight. In ascending the stems of 

 trees, their claws act much in the same manner as 

 " climbing irons ;" but even then they are always 

 most secure, and move fastest, when the stem leans 

 over them, and they can bring their weight to the aid 

 of their grasp. 



Mr. Waterton, in whose " Wanderings" in the 

 forests of Surinam, there is the most correct, and cer- 

 tainly the most lively account of these singular ani- 

 mals, mentions that they avail themselves of those 

 winds which agitate the trees, and bring their 

 branches into contact, in order to make their migra- 

 tions from part to part of the forest, which they do 

 with considerable velocity ; and that "they should 

 choose for their most active motions those times 

 when the qnadrumana and the climbing birds are 

 forced to descend for shelter, is another proof of how 

 admirably their structure is adapted to their haunts. 



That they should be awkward on the ground is 

 not to be wondered at ; for as they are seldom then; 

 except in cases of accident, to hare given them the 

 power of walking well would not only have been 

 giving a superfluous power, but one which could 

 have been obtained only by the injury of that which 

 is most essential to the animals ; for it is a principle 

 of the animal structure that the perfection of two 

 systems for the same kind of action, whether that 

 action be locomotion or not, are incompatible with 

 each other, in any one species. On the ground, the 

 sloth is out of its element ; but it is not so helpless 

 there as a herring upon dry land, or a peacock in the 

 sea. The turning inward of the wrist and ankle 

 joints, so as to make the claws shut on the mesial 

 plane, necessarily brings the side of the foot to the 

 ground, and not the Bole, which prevents any of the 

 joints of the foot from coming into play there ; and 

 the most ready and powerful action of the knee and 

 elbow joints being in the same direction, renders 

 them of little use ; so that the M'hole of the motion 

 there is at the articulations of the humeral and femo- 

 ral bones, and not very perfect or powerful even 

 there. We have only to imagine how a man would 

 walk if he had the power of progressive motion only 

 at the hip joints, and that the knees and ankles had 

 a continual tendency to have the parts articulated at 

 them inwards, and then we can form some idea of 

 the sloth's motion along the ground. 



The generic characters of the Ai are : no cutting 



