SECTION II. 



THE CLASS OF MAMMALIA OR MAMMALS. 



SUB-SECTION I. 



THE MAMMALIA CONSLDEKED AS A CLASS. 



ALL vertebrate animals which bring forth living young 

 and nourish them with milk, belong to the Class of Mam- 

 malia. The members of this class are more or less covered 

 with hair in some one of its forms, as ordinary hair, fur, or 

 wool ; although some kinds of mammals, as the Cetaceans 

 or Whales, have this covering only before they are born ! 



The various forms of the hair of the Mammalia are mere horny 

 modifications of the epidermis or outside skin. 



Man, Monkeys, Beasts of Prey, all of our herds and flocks 

 and their wild allies, are familiar examples of this class. 



The form and size of the Mammals vary exceedingly. 

 They are of all sizes, from the little shrews hardly two 

 inches in length, up to the whales, some of which attain 

 an enormous bulk and the length of a hundred feet ! All 

 except the Cetaceans have two pairs of limbs, and have 

 the terminal phalanges protected by a nail, claw, or hoof ; 

 and the forward pair of limbs is present in all. 



Of all animals, the Mammals most fully and perfectly 

 exhibit the true animal structure and functions. 



Their digestive system is extensive and complicated. 



Their circulatory system consists of a heart with four 

 cavities, arteries which carry the blood to all parts of the 

 body, veins which conduct the blood back to the heart, and 



