CHAPTER V 



THE HISTORY OF MENTAL DEVELOPMENT AND ITS SEQUENCE 



OF FUNCTIONS 



WE have sketched hastily the development of the 

 human body. This portion of our history is marked 

 by the successive dominance of higher and higher 

 functions. It is a history treating of successive eras. 

 There is first the period of the dominance of reproduc- 

 tion and digestion, purely vegetative functions, charac- 

 teristics of the plant just as truly as of the animal. 

 This period extends from the beginning of life up to 

 the time when the annelid was the highest living form 

 yet developed. But in insects and lower vertebrates 

 another system has risen to dominance. This is 

 muscle. The vertebrate no longer devotes all, or the 

 larger part, of its income to digestion and reproduction. 

 If it did, it would degenerate or disappear. The 

 stomach and intestine are improved, but only that 

 they may furnish more abundant nutriment for build- 

 ing and supporting more powerful muscles better ar- 

 ranged. The history of vertebrates is a record of the 

 struggle for supremacy between successive groups of 

 continually greater and better applied muscular power. 

 Here strength and activity seem to be the goal of 

 animal development, and the prize falls to the strong- 

 est or most agile. The earth is peopled by huge 

 reptiles, or mammals of enormous strength, and by 

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