THE YEETEBEATA. 259 



THE VEETEBEATA. 



The Vertebrate animals are those which have a brain and 

 spinal cord inclosed within a bony case, an internal skeleton, 

 to which are affixed the muscles, and which is moved by 

 them ; they all possess four extremities, more or less modified 

 in form, with the exception of the Serpents. They are divided 

 into four classes, Fishes, Eeptiles, Birds, and Mammals. 



FISHES. 



The Fishes live in water, and are unable to live in the air ; 

 they receive oxygen from the water, but this is received 

 much more slowly than by air-breathing animals, and as the 

 combination of oxygen with the carbon of the system gives the 

 elevated temperature of animals, so in Fishes, the oxygen 

 being received slowly, their temperature rises but little 

 above the temperature of the water they inhabit ; they have 

 thence received the name of " cold-blooded." Fishes live 

 upon the marine animals which they capture, the various 

 sea- weeds which grow in the water, and insects which fall 

 into, or breed there. They have fins instead of legs, but 

 the two pairs of fins known as " Pectoral " and " Ventral " 

 are analogues of them, and in a pectoral fin may be 

 found bones analogous to all the bones of the arm and 

 hand of Man, or the fore-feet of the other Vertebrata. 

 Fishes urge themselves through the water chiefly by the 

 action of the tail from side to side, and in those members 

 which have more extended forms (as Eels), by a wavey 

 motion of the body itself; and the rapidity with which they 

 swim is such, that Sharks have been known to go round the 

 ship they are following many times in a very short space, 

 although it may be sailing at a great speed before the wind. 

 Fishes are covered with scales, and the head is united to the 

 body without any constriction which can be considered as 

 a neck ; they are mostly of a form such as can easily pass 

 through the water, without offering much resistance, and 

 their specific gravity is so nearly that of water, that, by the 

 compression of a small vessel filled with air, called the 



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