VERTEBRATA. .267 



6. CLASS V. MAMMALIA, or Mammals. These are warm- 

 blooded Vertebrates possessed of mammary glands. They 

 suckle their young. The thorax and abdomen are sepa- 

 rated by a diaphragm, the red corpuscles of the blood 

 are doubly concave and round, (except in the Camel and 

 the Llama,) and either a part or all of the body is hairy. 



All Mammals use their lips for prehension, which are 

 assisted in some orders by their fore-limbs. The Car- 

 nivora tear their prey with their claws, but do not use 

 them as prehensile organs. The proboscis of the Ele- 

 phant, the snout of the Tapir, the long viscid tongue of 

 the Ant-eater, and the long tongue of the Giraffe, are 

 special prehensile organs. 



The teeth of Mammalia differ in the different orders, 

 as to number, size, and shape. The true Ant-eater has 

 no teeth, the Narwhal has but two, one of which is rudi- 

 mentary, but the Dolphin has one hundred and ninety. 

 The Whalebone-whale (Balcena mysticetus) has, instead 

 of true teeth, a series of plates of whalebone ranged in 

 rows along the upper jaw. From these plates a long 

 fringe of whalebone threads hangs down, which acts as a 

 sieve in straining the water from the myriads of little 

 mollusca which constitute the chief food of the whale. 



There are three distinct types of stomach among 

 Mammals : the simple, the compound, and the complex 

 stomach. The simple stomach is a single cavity lined 

 by epithelium, which secretes gastric juice. The com- 

 pound stomach has the cavity divided by folds into two 

 or more spaces. The tissue-elements, however, are the 

 same throughout. The complex stomach is peculiar to 

 the Ruminants. It consists of four cavities: the paunch 



