CONTENTS. ix 



PART III. 

 VARIATION IN ITS RELATION TO EVOLUTION. 



CHAPTER XI. 



THE ACTION OF NATURAL SELECTION ON 



VARIATIONS. 



PAGE 



Proof of Natural Selection in the crab, and in the sparrow 

 Selection in man Evolution of the mouse Inheritance of 

 acquired characters seems to be shown by cumulative effects 

 of conditions of life, as European climate acting on Ameri- 

 can maize; domestication acting on wild turkeys and ducks; 

 changed climate acting on sheep and dogs Environment 

 may act on germ-plasm through specific excretions and 

 secretions Cases of inherited effects of use and disuse, and 

 of epilepsy, accounted for Somatic variations may increase 

 variability, and so afford Natural Selection a better handle 

 to work upon, 335 



CHAPTER XII. 

 ADAPTIVE VARIATIONS. 



Adaptability a fundamental property of protoplasm In- 

 stances of adaptive variations in plants Acclimatisation 

 of Protozoa to high temperature, to poisons, to mechanical 

 stimuli, to saline solutions Acclimatisation of fresh-water 

 Mollusca to salt water, and of various marine animals to 

 fresh water Acclimatisation of Mammals to vegetable 

 poisons, and to toxins Sum total of somatic variations 

 always in direction of adaptation Somatic variations of 

 importance in evolution, but they can effect little without 

 Natural Selection Germinal Selection, .... 371 



