A CQ UIRED CHA RA CTERS 



The objection against the influence of external conditions, 

 that these are of variable nature, tending now in this now in 

 that direction, is discussed in the preceding pages. The 

 view, however, that the variations in nutrition to which the 

 body, and as Weismanu acknowledges the germ -cells also, 

 are subjected, must be regarded as transitory and minute, 

 I cannot admit. 



The fundamental difference between "Weismann's view 

 and mine seems to me to lie just in this point. I grant 

 entirely that the permanent action of external conditions on 

 the body of the organism in most cases is not immediately 

 perceptible. From physiological principles this is not in 

 general possible. The question essentially depends on what 

 ideas we possess of the time occupied by organic evolution. 

 It is my opinion that we must accustom ourselves to a much 

 less limited conception than even that introduced by Darwin. 



My theory of the progressive growth of the living world 

 and of the origin of species demands for the modification of 

 a form, according to physiological principles, to the extent 

 shown in any given case, enormous periods of time periods 

 compared with which the few thousand years of the history 

 of Egyptian civilisation may be but as a moment in com- 

 parison with the individual growth of a plant or an animal. 



My evidence of the importance of external conditions for 

 the origin of species requires that this demand shall be borne 

 in mind. None the less, I am able, as shown already in 

 preceding pages, to bring forward cases in which influences 

 show themselves in their effects in a short time. I proceed 

 now to produce further evidence. 



Every character which must have been formed through 

 the activity of the organism, is an acquired character. All 

 characters, therefore, which have been developed by exertion 

 are acquired, and these characters are inherited from genera- 



