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CHAPTER XXI 

 SUMMARY 



PREFACE. — The more we learn of the world in 

 which we live the more clearly do we see 

 that an orderly and definite plan underlies 

 and dominates all the phenomena of nature. The 

 living world of animals and plants is no exception. 

 It is not chaotic. To picture it as chaotic is simply 

 to confess our ignorance. What, then, is the plan 

 upon which the living world is based? What is 

 the relationship between the various types of liv- 

 ing things? 



Four different problems are involved in the answer 

 to this question. F^rsf, how and in what form did 

 animals first appear? Second, what has been the his- 

 tory of animal life from its first appearance to the 

 present day? Third, how do animal forms giYC rise 

 to other and different forms? Fourth, what is the rela- 

 tionship of man to the living world? 



Before taking up these problems let us review the 

 evidence which leads us to believe that these questions 

 can be answered. We know that some definite rela- 

 tionship exists between the different types of animals 

 because of two important facts. 



In the first place, all living things arise only as the 

 children of other living things. This rule has no 

 exceptions, and it is inconceivable that there should 

 be exceptions. Since all living things arise only from 



[2.08] 



