PROTECTIVE COLOUR OF SLOTH 



171 



as hooks to keep them suspended from the lower side of a 

 branch. The three -toed sloth, Brady pus (or " Ai "), has the 

 exceptional uuniher of nine cervical vertebrae ; the two-toed sloth, 

 ChoJoeims lioffmanni (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.^ Tliis 

 gives to the animal the appearance of a lichen-covered Ijough, a 

 resemblance whicli is increased in one species by an oval mark 

 upon the back, which suggests forcil)ly a broken end of such a 

 branch. The likeness of a Sloth to its surroundings is pointed 



Fir;. 97. — Skull of Tliree-toed Sloth. Bradypus tridactyhis. Lateral view, fr. Frontal ; 

 ,/", jugal : Icr, laehryMial ; max, maxilla ; nas, nasal ; par, parietal ; a.oc, snpra- 

 occipital ; fij, tympanic. (From Parker and Haswell's Zoohvpj.) 



out by Dr. Siemann," who observ^ed that a species occurring in 

 Nicaragua " has almost exactly the same greyish-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 

 mimicry between the sloth's hair and the Till mid sia, 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 numl)er of particulars with that of the Anteaters. 



' The uolour lades 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. " 



