VIII PROTECTIVE COLOUR OF SLOTH el 
as hooks to keep them suspended from the lower side of a 
branch. The three-toed sloth, Bradypus (or “ Ai”), has the 
exceptional number of nine cervical vertebrae ; the two-toed sloth, 
Choloepus hoffmanni (or “ Unau”), has the equally exceptional 
number of six. The hair is long and shaggy, and gets an 
adventitious green colour from the presence of minute algae." This 
gives to the animal the appearance of a lichen-covered bough, a 
resemblance which is increased in one species by an oval mark 
upon the back, which suggests forcibly a broken end of such a 
branch. The likeness of a Sloth to its «surroundings is pointed 
fT 
Cer 
Fic. 97.—Skull of Three-toed Sloth. Bradypus tridactylus. Wateral view. j7, Frontal ; 
ju, jugal ; ler, lachrymal ; maz, maxilla ; nas, nasal; par, parietal ; s.oc, swpra- 
occipital ; ty, tympanic. (From Parker and Haswell’s Zoology.) 
out by Dr. Siemann,” who observed that a species occurring in 
Nicaragua “has almost exactly the same ereyish-green colour as 
Tillandsia usneoides, the so-called ‘ Vegetable Horsehair’ common 
in the district. . . . If it could be shown that it frequented trees 
covered with that plant . .. there would be a curious case of 
uumicry between the sloth’s hair and the 7%llandsia, and a good 
reason why so few of these Sloths are seen.” The stomach in the 
Sloths is complicated in structure, with several chambers; one of 
these gives off a long crescent-shaped caecum. The skull of the 
Sloths agrees in a number of particulars with that of the Anteaters. 
" The colour fades in captivity owing to the disappearance of the algae. 
* In a letter addressed to Dr. Gray, quoted by the latter in a revision of the 
Sloths, Proc. Zool. Soc. 1871, p. 428. 
