MAMMALS 



CHAPTER I 

 GENERAL CHARACTERISTICS CLASS Mammalia 



IN describing any group of objects, whether they be artificial or whether they 

 be natural, some method of classifying is absolutely essential to a right understand- 

 ing 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 Quadrupeds, 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 many cases, it is by no means always trustworthy, 

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

 dolphins are generally associated in the uninstructed mind with fishes, whereas, as a 

 study of their internal structure at once reveals, they are really Mammals, which 

 have been specially adapted for a purely aquatic life. 



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