viii INTRODUCTION 



have certain characteristics in common by means 

 of which they are distinguished from all others. 



FAMILY : A group of animals consisting of one or more 

 genera. A family is, of course, a wider classification 

 than a genus, and the characteristics which its 

 members have in common are fewer in number. 

 Thus a dog and a fox belong to the same family, 

 though of different genera. 



ORDER : An order is a still more comprehensive group, 

 and consists of animals which are alike in only a very 

 few special features. Thus all flesh-eating animals, 

 to whatever family they belong, are placed in the 

 order Carnivora, and all herb-eating animals in the 

 order Herbivora. 



CLASS : This is the largest group of all, and consists 

 of animals which have the broadest and most 

 general characteristics in common. 



The principal of the eight classes into which the Verte- 

 brates, or those animals which are possessed of a back- 

 bone, are divided are : 



(1) MAMMALS : Warm-blooded animals which suckle 



their young. 



(2) BIRDS, which are warm-blooded animals, covered 



with feathers, and usually, though not always, 

 possessed of the power of flight. 



(3) REPTILES, which are cold-blooded primitive animals, 



with a skin formed of horny plates or scales, but 

 which breathe in the same manner as the fore- 

 going. 



(4) AMPHIBIANS : Cold-blooded primitive animals, whose 



young are aquatic and breathe through gills like 

 fishes. Frogs, toads, newts, and salamanders are 

 amphibians. 



