48 INTRODUCTION. 



The Snail, Oyster, Nautilus, &c., are specimens of this 

 Class. 



The Vertebrata form the next and highest step in the 

 animal kingdom. 



This Class, deriving its name from all its members having 

 vertebras or a spine, is principally characterized by the 

 body being symmetrical, the nervous system being composed 

 of a brain and spinal marrow, as well as nervous ganglia, 

 by the blood being red and warm, and there being a heart 

 and five senses. 



These four divisions, constituting the four great varieties 

 of animal organization, have each many subdivisions into 

 the different orders, genera and species. 



Each of these varieties, with its various subdivisions, 

 as already stated in reference to organization in general, 

 owes its existence and preservation entirely to the fixed 

 relation established between its peculiar structure and one 

 or more of the fundamental elements of preservation. 



We shall take the division of the vertebrata by way of 

 illustration. 



The vertebrated Class has four principal branches 

 Fishes, Keptiles, Birds, and Mammalia. 



Now the organization of Fishes is constructed with special 

 reference to the element, water the whole exterior and 

 interior form, as the fins, gills, air-bladder, &c., all clearly 

 show that water is their natural element and that not- 

 withstanding they require air and food, and have more or 

 less relation with these principles, yet the great and prom- 

 inent relation is with water, without which the whole 

 variety would soon cease to live, though there might be 

 free supply of both air and food. 



Eeptiles have a modification of structure which adapts 

 them to both water and air, in each of which some of them 

 alternately live, as in the cases of the turtle, crocodile, 

 frog, &c. 



Birds being made for flight, have their special relations 

 with the atmosphere. This is their essential and peculiar 



