CONTENTS. 



PiSB. 



Intbodtjction 1 



CHAPTER I. 



TAEIATION UNDER DOMESTICATION. 



Causes of Variability — EfEects of Habit and tlie use or disuse 

 of Parts — Correlated Variation — Inberitance — Character of 

 Domestic Varieties — Difficulty of distinguisMng between 

 Varieties and Species — Origin of Domestic Varieties from 

 one or more Species — Domestic Pigeons, their Differences 

 and Origin — Principles of Selection, anciently followed, 

 their Effects — Methodical and Unconscious Selection — 

 Unknown Origin of our Domestic Productions — Circum- 

 stances favorable to Man's power of Selection 6 



CHAPTER II. 



TABIATION UNDBS 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 39 



CHAPTER III. 



STRUGGLE FOE EXISTENCE. 



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

 sense — Geometrical ratio of increase — Rapid increase of 

 naturalized animals and plants — Nature of the checks to 

 increase — Competition universal — Effects of climate — Pro- 

 tection from the number of individuals — Complex relations 

 of all animals and plants throughout nature — Struggle for 



