V- 



VIII INDIVIDUAL GROWTH 381 



characters from ancestors ; to a small extent it is due to 

 acquirement, i.e. modification, during individual life, or is the 

 consequence of the mingling of the characters of the parents. 

 This latter small element in the constitution of the body is 

 the cause of individual variation; but it is of the greatest 

 importance, because on it depends essentially the continuous 

 modification of forms. 



If the individual growth of the organism is, as according to 

 the preceding we may briefly express it, in the last result 

 nothing but the effect of external stimuli (including food) upon 

 the tissues, and if we assume that there was a primitive 

 organism from which all succeeding living beings have been 

 derived, then the variety of growth which took place in the 

 latter must of necessity have been originally due to the 

 variety of the external influences (stimuli) under various con- 

 ditions. Sexual mixture was not at the be^jinningj in 

 operation. But the peculiarities thus acquired were inherited 

 by the organism in its whole and in its parts, and selection 

 increased them. The greater the number of modifications 

 thus by continued inheritance acquired by a succession of 

 organisms, the greater will be the peculiarity of constitution 

 produced. 



Thus the individual growth of every plant and every 

 animal is a brief and rapid repetition, under the continued 

 influence of similar stimulation, of the series of effects pro- 

 duced by external stimuli in the course of vast periods of time 

 on the tissues of its ancestors. 



The character of the individual growth of every living 

 being therefore depends essentially on phyletic growth, the 

 individual growth includes phyletic growth in itself For 

 even the peculiarities of constitution of different individuals 

 which are due to inheritance are really a consequence of 

 phyletic growth. 



Since the individual growth of every living being is thus a 



