VI CONTENTS. 



CHAPTER III. 



Struggle foe Existence. 



Bears on natural selection — The term used in a wide sense — Geo- 

 metrical powers of increase — Eapid increase of naturalised 

 animals and plants — Nature of the checks to increase — Compe- 

 tition 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 be- 

 tween species of the same genus — The relation of organism to 

 organism the most important of all relations . . Page 60-79 



CHAPTER IV. 



Natural Selection. 



Natural Selection — its power compared with man's selection — its 

 power on characters of trifling importance — its power at all ages 

 and on both sexes — Sexual Selection — On the generality of inter- 

 crosses between individuals of the same species — Circumstances 

 favourable and unfavourable to Natural Selection, namely, 

 intercrossing, isolation, number of individuals — Slow action — 

 Extinction caused by Natural Selection — Divergence of Cha- 

 racter, related to the diversity of inhabitants of any small area, 

 and to naturalisation — Action of Natural Selection, through 

 Divergence of Character and Extinction, on the descendants 

 from a common parent — Explains the Grouping of all organic 

 beings .. 80-130 



CHAPTER V. 



Laws of Variation. 



Effects of external conditions — Use and disuse, combined with 

 natural selection ; organs of flight and of vision — Acclimatisa- 

 tion — Correlation of growth — Compensation and economy of 

 growth — False correlations — Multiple, rudimentary, and lowly 

 organised structures variable — Parts developed in an unusual 

 manner are highly variable : specific characters more variable 

 than generic : secondary sexual characters variable — Species of 

 the same genus vary in an analogous manner — Reversions to 

 long-lost characters — Summary 131-170 



