CONTENTS. 



PAGE 



PREFACE vii 



PART i. INTRODUCTION. 



WHAT IS EVOLUTION ? 3 



PART ii. THE EVOLUTION OF LIVING BEINGS. 



CHAPTER I. DEFINITIONS OF TERMS USED 13 



II. DO DIPLOID SPECIES VARY? 29 



III. SPECIES, LINNEONS, GENERA AND OTHER 



,,HIGHER GROUPS" AND EVOLUTION . . 42 



IV. THE ORIGIN OF DIPLOID SPECIES 52 



V. THE PERPETUATION OF THE NEW SPECIES 56 

 VI. HOW TO GET AT THE CONSTITUTION OF 



THE GAMETES 65 



VII. HOW CAN GROUPS OF DIFFERENTLY CON- 

 STITUTED TYPES FORM A LINNEON, SI- 

 MULATING A SPECIES? 67 



VIII. THE LIMITS OF LINNEONS 96 



IX. THE CAUSE OF THE INCREASE OF ,,VARIA- 



BILITY" UNDER DOMESTICATION.... 100 



X. PROGRESSION IN EVOLUTION 115 



XI. THE EVIDENCE FOR THE OCCURENCE OF 

 CROSSES BETWEEN INDIVIDUALS BE- 

 LONGING TO DIFFERENT LINNEONS IN 



NATURE 120 



XII. THE EFFECT OF CROSSING LINNEONS.. 127 



XIII. THE ORIGIN OF THE GREAT CLASSES. . . 132 



XIV. THE QUESTION OF RELATIONSHIP 137 



XV. THE QUESTION OF PHYLOGENY 139 



XVI. HOMOLOGOUS PARTS AND RUDIMENTARY 



ORGANS 142 



