CONTENTS 



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CHAPTER I. 



PAGE 



Introductory i 



CHAPTER II. 

 Classification 23 



CHAPTER ni. 

 Morphology 5c 



CHAPTER IV. 

 Embryology gi 



CHAPTER V. 



PAL.EONTOLOGY 1 56 



CHAPTER VI. 

 Geographical Distribution . 204 



CHAPTER VII. 

 The Theory of Natural Selection 251 



CHAPTER Vill. 

 Evidences of the Theory of Natural Selection . . 285 



