CONTENTS. 



PAGS 



INTRODUCTION I 



I. 



THE ARGUMENT FROM CLASSIFICATION 17 



II. 



THE ARGUMENT FROM MORPHOLOGY OR STRUCTURE . . 26 



III. 



THE ARGUMENT FROM GEOLOGY 46 



IV. 



THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION . . 48 



V. 

 THE ARGUMENT FROM EMBRYOLOGY 63 



VI. 



ARGUMENTS DRAWN FROM CERTAIN GENERAL CON- 

 SIDERATIONS 70 



