INTRODUCTION. XV 



group ; but it is rare that any one species embodies all our 

 ideas of the class, family, or genus to which it belongs. 

 Thus, we have a general idea of a bird ; but this idea does 

 not correspond to any particular bird, or any particular 

 character of a bird. It is not precisely an ostrich, an owl, 

 a hen, or a sparrow ; it is not because it has wings, or 

 feathers, or two legs ; or because it has the power of flight, 

 or builds nests. Any, or all of these characters would not 

 fully represent our idea of a bird ; and yet every one has a 

 distinct ideal notion of a bird, a fish, a quadruped, &c. It 

 is common however, to speak of the animal which embodies 

 most fully the characters of a group, as the type of that 

 group. Thus, we might perhaps regard an eagle as the 

 type of a bird, the duck as the type of a swimming-bird, and 

 the mallard as the type of a duck. 



As we must necessarily make frequent allusions to ani- 

 mals, with reference to their systematic arrangement, it 

 seems requisite to give a sketch of their classification in as 

 popular terms as may be, before entering fully upon that 

 subject, and with particular reference to the diagram front- 

 ing the title-page. 



The Animal Kingdom consists of four great divisions 

 which we call DEPARTMENTS, namely, 



I. The department of Vertebrates. 



II. The department of Articulates. 



III. The department of Mollusks. 



IV. The department of Radiates. 



I. The department of VERTEBRATES includes all animals 

 which have an internal skeleton, with a back-bone for its 

 axis. It is divided into four classes. 



1. Mammals (animals which nurse their young). 



2. Birds. 



3. Reptiles. 



4. Fishes. 



