CONTENTS 



Variation among birds— Diagrams of bird- variation— Number of 



varying individuals— Variation in the mammalia— Variation in 

 internal organs— Variations in the skull— Variations in the habits of 

 animals— The variability of plants—Species which vary little— Con- 

 cluding remarks ..... Pages 41-82 



CHAPTER IV 



VARIATION OF DOMESTICATED ANIMALS AND CULTIVATED 

 PLANTS 



The- facts of variation and artificial selection— Proofs of the generality of 

 variation— Variations of apples and melons— Variations of flowers- 

 Variations of domestic animals — Domestic pigeons— Acclimatisation 

 — Circumstances favourable to selection by man— Conditions favour- 

 able to variation— Concluding remarks . . . 83-101 



CHAPTEE V 



NATURAL SELECTION BY VARIATION AND SURVIVAL OF THE 

 FITTEST 



Effect of struggle for existence under unchanged conditions — The effect 

 under change of conditions — Divergence of character — In insects — In 

 birds — In mammalia — Divergence leads to a maximum of life in each 

 area — Closely allied species inhabit distinct areas — Adaptation to 

 conditions at various periods of life — The continued existence of low 

 forms of life — Extinction of low types among the higher animals — 

 Circumstances favourable to the origin of new species — Probable 

 origin of the dippers — The importance of isolation — On the advance 

 of organisation by natural selection — Summary of the first five 

 chapters ....... 102-125 



CHAPTEE VI 



DIFFICULTIES AND OBJECTIONS 



Difficulty as to smallness of variations — As to the right variations occur- 

 ring when required — The beginnings of important organs — The mam- 

 mary glands — The eyes of flatfish — Origin of the eye — Useless or 

 non-adaptive characters — Recent extension of the region of utility in 



