CONTENTS. 



CHAPTER I. INTRODUCTION. 



Facts Calling for Explanation. . .' ' 1-3 



Small Areas of Distribution for Species of Hawaiian Snails i 



The Intergrading of Species 2 



vSelection not Always the Cause of Divergence 3-6 



In Many Cases Sexual Selection not the Cause 3 



In Many of the Same Cases Natural Selection not the Cause 4 



May not the Prevention of Free Crossing be an Explanation 6 



Investigation of Causes and Effects of Segregation 7 



Segregation the Unifying Principle in Evolution 7 



CHAPTER II. BIONOMIC LAWS. 



Method of Investigation 9-13 



Scope of Bionomics 9 



Why we Commence with the Method of Evolution 9 



Need of Investigation of all Factors 10 



Natural and Sexual Selection not the Only Factors 1 1 



Comparison of Conditions in Natural Species and in Domestic Varie- 

 ties 12 



Production of Domestic Races 13-22 



Continuance of Races 13 



Transformation of Races 14 



Divergence of Races 17 



Stability of Races 19 



Amalgamation of Races 20 



Influence of Acquired Characters on Racial Characters 20 



CHAPTER III. THE EVOLUTION OF NATURAL SPECIES. 



Unity and Diversity 23-29 



Darwin's Explanation of Unity 23 



Divergence Through Variation under Isolation and Unity Through 



Community of Descent 24 



Facts in Distribution of Hawaiian Snails 26 



Diversity of Natural vSelection not a Sufficient Explanation 27 



Divergence through Independent Transformation 28 



Natural vSelection as Explanation of Evolution 29-34 



What Natural Selection does not Explain 29 



Selection, how Far Determined by External Nature 3!~34 



Discontinuity of Species 34~36 



CHAPTER IV. DIVERGENCE UNDER THE SAME ENVIRONMENT. 



Explanation of Plate I 37 



Explanation of Plate II 39 



vii 



