lii INTRODUCTION 



extent ; and even the continued operation of those factors 

 through a long succession of generations will cause the 

 germ-cell to swerve quite inappreciably from its inherited 

 career. 



I do not adduce this analogy for the purpose of defending 

 the inheritance of acquired characters : far from it. I 

 adduce it for the following purpose. We find that the 

 bodies of animals and plants are adapted to their environ- 

 ment, and we may affirm that they have been moulded into 

 their present shape by exposure to the forces of the environ- 

 ment throughout vast periods of time. We may affirm this 

 without raising any question of the process by which the 

 moulding occurs : — whether it is exclusively of an indirect 

 character (like natural selection), or whether more direct 

 factors are in operation. In any case the structure of the 

 organism is an expression of the sum-total of the forces 

 which have acted upon the germ-cell, ever since that early 

 time when it first became differentiated from inorganic 

 matter. Now an acquired modification, impressed upon the 

 soma, can affect the germ, if at all, only as one new force, 

 whose individual effects will surely be totally obscured 

 amidst the multitude of the older forces. Yet those effects 

 may be registered in the hereditary qualities of the germ : 

 and a gradual repetition of them in the course of innumerable 

 generations may give rise to a specific and visible variation. 



That a functionally-produced modification should so deeply 

 impress the germ-cell as to leave visible effects on the soma 

 of the next generation is at present a discredited h5rpothesis. 

 Indeed, the direct environmental influence has to be con- 

 tinued for some little time before it can produce any functional 

 reaction or modification of the soma at all. A physiological 

 somatic modification can only be caused by a factor which 

 operates for an appreciable proportion of the life of the 

 soma. Now the organism consists of two parts : — of the 

 newly-developed and ephemeral soma, and of the germ-cell 

 which has existed from the most extreme antiquity. If 

 such germ-cell can be affected by direct specific influence, 



