1376 THE EDENTATES 



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 in- 

 vested, is generally of a brownish or dull ashy-gray color, 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 attaching 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 green- 

 ish 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 surroundings than 

 would have been otherwise possible. It may be mentioned here that it is almost im- 

 possible 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 wooly under- fur 

 marked by longitudinal stripes of rich brown and orange; the exposure 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-colored fur, 

 and that the long external dull-hued coat of the sloths has been a special develop- 

 ment 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 characterized 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, per- 

 manently 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 reach- 

 ing the lungs, a feature found elsewhere only in certain birds. Finally, the female 

 sloth has but a single pair of teats on the breast. 



The typical members of the family are commonly known as three- 

 Si th toe ^ s l tns > or > fro m their native title, ai's, and constitute the genus 

 Bradypus, readily characterized 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, 



