SLOTHS. 



205 



which the length far surpasses that of the hinder-pair. Both pairs of limbs are 

 furnished with long and slender feet, in which there are never more than three 

 toes ; while the toes themselves are invested for nearly their whole length in a 

 common skin, and terminate in long curved claws of great strength. The thick 

 coat of long, coarse, and somewhat brittle hair with which the whole of the body 

 and limbs is invested, is generally of a brownish or dull ashy-grey colour, mingled 

 with a greenish tint ; each individual hair having a fluted or roughened external 

 surface. The most remarkable feature connected with the pelage is, however, the 

 growth of a vegetable a kind of alga on the hairs themselves ; the alga attach- 

 ing itself to the aforesaid flutings, and growing luxuriantly in the moist atmosphere 

 of the South American forests, although quickly withering when the animals are 

 brought to Europe. It is this extraneous vegetable growth which communicates 

 the greenish tinge to the hair during life ; and its object is doubtless to render the 

 coloration of these creatures in still closer harmony with their inanimate surround- 

 ings than would have been otherwise possible. It may be mentioned here that it 

 is almost impossible to conceive that any sort of so-called natural selection could 

 have given rise to this peculiar and unique kind of protective resemblance. In 

 the region of the back between the shoulders many sloths exhibit a patch of fine 

 woolly under-fur marked by longitudinal stripes of rich brown and orange ; the ex- 

 posure of such patches being due, according to Brehm, to the animals having abraded 

 the long hair by rubbing or resting their backs against trees. The coloration of 

 this patch of under-fur approximates to that obtaining in the coat of the ant-eaters, 

 from which it may be inferred that both these groups of animals originally had 

 bright-coloured fur, and that the long external dull-hued coat of the sloths has 

 been a special development suited to the needs of their environment. 



The sloths have five pairs of teeth in the upper, and four in the lower jaw : 

 the individual teeth, with the exception of the first pair in one of the two genera, 

 being nearly cylindrical in form, and in all cases consisting of a core of ivory 

 invested with a thick coating of cement. The skeleton is characterised by the 

 presence of complete collar-bones ; while in the fore-arm the two bones are completely 

 separate, and allow the hand to be supinated like that of man. The claws are, 

 however, permanently fixed parallel to one another, so that the hand, like the foot, 

 can be used merely as a claw. In the hind-limb the foot is articulated obliquely 

 to the bones of the leg ; so that when on the ground the animal can walk only on 

 the outer sides of its feet. Of the soft parts, it will suffice to mention that the 

 tongue is short and soft ; while the large stomach, as in so many leaf-eaters and 

 grass-feeders, is divided into several compartments. The windpipe is peculiar 

 in being folded before reaching the lungs, a feature found elsewhere only in 

 certain birds. Finally, the female sloth has but a single pair of teats on the breast. 

 Three-Toed The typical members of the family are commonly known as 



Sloths. three-toed sloths, or, from their native title, ai's, and constitute the 

 genus Bradypus, readily characterised by the presence of three toes on both the 

 fore and the hind-feet. The teeth are all of nearly the same height, with their 

 grinding surfaces deeply cupped ; the first tooth in the upper jaw being considerably 

 smaller than either of the others, while the corresponding lower tooth is broad and 

 compressed. The most remarkable peculiarity connected with the genus is, how- 



