152 NATURE STUDIES. 



Here tlie bird- characters have disappeared, although 

 the included animals are of low structure as compared 

 with such forms as the dogs, horses, seals, &c., of 

 higher orders. The " Marsupials," as the name 

 implies, usually possess a " pouch," supported on the 

 " marsupial bones " that rise from the front of the 

 haunch (see a a, Fig. 7, p. 136). Even if the " pouch 

 itself be wanting (as in some opossums), the bones 

 supporting it are developed. 



The Higher Mammals introduce us to order the 

 third, that of the Cetacea, or Whales. A fish-like 

 body, one fully-developed pair of limbs (the fore 

 limbs) assisting in the shape of swimming-paddles, a 

 horizontal tail- fin, and nostrils forming " blow-holes/' 

 are the characters of which the whales, dolphins,, 

 porpoises, and the like are characterised. The fourth 

 order is that of the Sirenia, represented by two 

 genera of animals the Manatees, or Sea Cows, and 

 Dugongs long classified with the whales. Here tho 

 body is again fish-like, and the fore limbs, which are 

 alone developed, form swimming-paddles; but the 

 nostrils do not form " blow-holes," and the skin is 

 sparsely covered with bristles. The Edentata, or 

 Ant-eaters, Armadillos, Sloths, and Pangolins, con- 

 stitute the fifth order, whose head- quarters exist in 

 South America. There is only a single set of teeth 

 in these animals, and the teeth are further destitute 

 of distinct roots, whilst they want enamel. Scales or 

 bony plates, as in the Armadillos, often cover the 

 body. 



