CHAPTER 



7 



THE CLASSIFICATION 



The preceding chapters have presented an introduction to zoology through 

 the study of structure and function in vertebrate animals. This introduction 

 has illustrated the organization of vertebrates and their capacities of metab- 

 olism, responsiveness, and reproduction, as well as the nature of development 

 and heredity. From the standpoint of function such an introduction would 

 suffice for animals in general; the characteristics and activities of the cells 

 are essentially alike in the bodies of all animals. It may be said that all 

 living things are faced with common problems of survival, and the functional 

 .solutions of these problems are similar in many diverse types of animals. 

 From the standpoint of structure, however, study of the vertebrates alone is 

 inadequate. There are many kinds of animals very different from vertebrates 

 in their organization, although their general functions may be very similar. 

 In the chapters to follow some of these different types of animals will be ex- 

 amined, particularly as they illustrate principles of morphology, ecology, and 

 evolution. As an introduction to this survey, we may consider briefly the 

 diversity of animal life and some of the evidence indicating that all the diverse 

 types will fit into an orderly system, based on structural similarities and be- 

 lieved to indicate evolutionary relationships. Let us begin by examining the 

 principles, methods, and implications of the classification of animals. 



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