CONTENTS. 



Additions and Corrections, to the Sixth Edition .. Page si-sii 



Historical Sketch .. .. xhi-sxi 



Introduction 1-4 



CHAPTER I. 



Variation under Domestication. 



Causes of Variability — Effects of Habit and the use or disuse of Parts — 

 Correlated Variation — Inheritance — Character of Domestic Varieties 

 — Difficulty of distinguishing between Varieties and Species — Origin 

 of Domestic Varieties from one or more Species — Domestic Pigeons, 

 their Differences and Origin — Principles of Selection, anciently fol- 

 lowed, their Effects — Methodical and Unconscious Selection — Un- 

 known Origin of our Domestic Productions — Circumstances favour- 

 able to Man's power of Selection 5-32 



CHAPTER II. 



Variation under Nature. 



Variability — Individual differences — Doubtful species — Wide ranging, 

 much diffused, and common species, vary most — Species of the larger 

 genera in each country vary more frequently than the species of the 

 smaller genera — Many of the species of the larger genera resemble 

 varieties in being very closely, but unequally, related to each other, 

 and in having restricted ranges 33-47 



CHAPTER III. 



Struggle for Existence. 



Its bearing on natural selection — The term used in a wide sense — Geome- 

 trical ratio of increase — Rapid increase of naturalised animals and 

 plants — Nature of the checks to increase — Competition universal — 

 Effects of climate — Protection from the number of individuals — 

 Complex relations of all animals and plants throughout nature — 

 Struggle for life most severe between individuals and varieties of the 

 same species : often severe between species of the same genus — The 

 relation of organism to trganisTi the most important of all rela- 

 tions .. .. .. .. '.. „ .. 48-61 



