CHAPTER IX. 



ILLUSTRATION OF THE METHOD OF GROWTH AND DE- 

 VELOPMENT, AND OF THE ORIGIN OF VARIATIONS. 



In the previous chapter it was said that, while the 

 forces of the environment remained the same, yet 

 the constant change in the relations of the organism 

 to the environment, might produce new changes in 

 the organism to an apparently infinite extent. (I 

 refer to the organism here as a species, something 

 which passes through a succession of rounds of life, 

 i.e. generations.) Should any one be inclined to 

 doubt this statement, let him consider for a moment 

 that the very fact of life implies a constant change, 

 — metabolism and katabolism of the body substance. 

 In order that this may go on, food must be supplied. 

 There are alternate periods of hunger and satiety, 

 for, in the animal kingdom, food is obtained period- 

 ically. This brings periods of activity and rest, and 

 thus already we have the elements of nervous change 

 and development. After a number of such periods, 

 the animal may return to its previous condition in 



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