CONTENTS 



CHAPTER I. 



PAGE 



INTRODUCTORY ..... . . . * . ' 



CHAPTER II. 

 CLASSIFICATION ......... >3 



CHAPTER III. 

 MORPHOLOGY . ... ...... 5 



CHAPTER IV. 

 EMBRYOLOGY ......... .98 



CHAPTER V. 

 PALEONTOLOGY f . . . . .... .156 



CHAPTER VI. 

 GEOGRAPHICAL DISTRIBUTION ....... 204 



CHAPTER VII. 

 THE THEORY OF NATURAL SELECTION ..... 251 



CHAPTER VIII. 

 EVIDENCES OF THE THEORY OF NATURAL SELECTION . . 985 



