OOISTTEIS'TS 



nisTORiCAL Sketch ........ paoe 9 



I.VTBOnUCTION ......... 17 



CHAPTER I. 



VARIATION CNDE.I DOMESTICATION. 



Causes of Variability— EfTocts of Habit— Correlated Variation— Inheritance— Char- 

 acter of Domestic Varieties — Diflftculty 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 followed, 

 their Effects — Methodical and Unconscious Selection— Unknown Origin of our 

 Domestic Productions— Circumstances favorable to Man's Power of Selection 23 



CHAPTER II. 



VARIATION UNDER NATCRE. 



Vailability- Individual Differences— Doubtful Species— Wide-ranging, much dif- 

 fused, 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 . 52 



CHAPTER III. 



STRUGGLE FOR EXISTENCE. 



its bearing on Natural Selection— The Term used in a wide Sense— Geometrical rjutio 

 of Increase — Rai)id Increase of Naturalized Animals and Plants — Nature of tlio 

 Checks to Increase— Competition universal— Effects of Climate— Protection fri)ni 

 the Number of Individuals— Complex Relations of all Animals and Plants through 



