416 GENERAL ZOOLOGY 



plant of low organization, which gives the hair a green tinge 

 like that of the masses of vegetation of the tropical forest. 

 Sloths rarely descend from the branches of trees. On the 

 ground they are almost helpless. 



Whales, Dolphins, Porpoises, and Allies. The whales, 

 dolphins, and porpoises are true mammals, though so 

 adapted to their aquatic life that they seem, on superficial 



Fig. 218. Photograph of an armadillo 



examination, to be fishes. The name of the order, Ceta'cea, 

 is derived from the Latin cetus, "whale." 



Flower and Lydekker, in their book on Mammals, thus 

 review the principal peculiarities of the group : 



The external fish-like form is perfectly suited for swimming 

 through the water ; the tail, however, is not placed vertically as 

 in fishes, but horizontally, a position which accords better with 

 the constant necessity for rising to the surface for the purpose of 

 breathing. The hairy covering characteristic of all mammals, 

 which, if present, might interfere with rapidity of movement 

 through the water, is reduced to the merest rudiments, — a few 

 short bristles about the chin or upper lip, — which are often 

 present only in very young animals ; and the function of keeping 

 the body warm is performed by the "blubber." The fore limbs, 



