THE liOYAL NATURAL HISTORY. 



?>AJ^ 



MAMMALS. 



CHAPTER I. 



Gexeral Chakacteristics, — Class Mammalia. 



Ix describing any group of objects, whetlier they be artificial or whether they be 

 natural, some method of classifying is absolutely essential to a right understanding 

 of their relations to one another; and nowhere is this more important than in 

 Natural History. To a certain extent such a classification is already made in our 

 ordinary language, since we are accustomed to divide the higher animals into several 

 distinct primary groups, under the names of Mammals or Quadi-upeds, Birds, 

 Reptiles, and Fishes ; and these primary groups coincide in the main with those 

 employed by zoologists. Such a popular classification depends almost entirely 

 upon similarity or dissimilarity of outward appearance and form ; and although 

 this is a good and dependable guide in manj^ cases, it is by no means always 

 trastworthy, and may, indeed, frequently lead us into serious error. For instance, 

 whales and dolphins are generally associated in the uninstructed mind with fishes, 

 Avhereas, as a studj'' of their internal structure at once reveals, they are reallj^ 

 Mammals, which have been specially adapted for a purely aquatic life. 



VOL. I. — I 



