CHAPTER 3 

 CLASSIFICATION 



The first impression at the beginning of any study of zoology is 

 that of the diversity of animal form. This diversity is evident in such 

 things as color, size, shape, manner of life, and even in the functioning 

 of the organism itself. While at first this diversity seems important, 

 more careful study shows that relationships do exist and that they exist 

 in varying degrees. 



Among the more familiar animals, it is evident that the dog and 

 cat are closely related. Both possess many similar structures, such 

 as their distinctive canine teeth for tearing meat. More distant rela- 

 tives of these animals are the fish, birds, and reptiles. All these forms, 

 though quite different in appearance, have a number of characteristics 

 in common, one of which is the possession of a backbone. 



If such relationships did not exist, the task of classifying animals 

 would be insurmountable, for more than a million different kinds are 

 known to exist at present. The science of the classification of animals 

 and plants is known as taxonomy or systematics, and those individuals 

 who work in this science are known as taxonomists or systematists. 



History.— These structural likenesses among different animals were 

 probably apparent to even earliest man. Inasmuch as people almost 

 invariably attempt to classify things, it may well be imagined that vari- 

 ous groups were readily recognized. The earliest records of any real 

 attempts to classify animals are those found among the Greeks. Aris- 

 totle, the most important of these, lived from 385 until 322 B.C. He 

 was intensely interested in the animals about him and divided the vari- 

 ous groups into two main categories : the enainia or animals with back- 

 bones, and the anaima or those without backbones. He even realized 

 that certain animals within these two major groups could be classed into 

 smaller groupings. 



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