CONTENTS 



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

 varjdug 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 DOIVIESTICATED 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 



CHAPTER 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 



CHAPTER 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 



