202 DOCTRINE OF EVOLUTION 



the word mind to the series of nervous processes going 

 on in the human organ of thought, in so far as these 

 processes are carried on by the pecuhar tissues of the 

 nervous system they cannot be finally distinguished 

 from the functional products or accompaniments of the 

 same kind of active tissues and organs in lower crea- 

 tures. Thus the subject of mental evolution becomes 

 much clarified at the outset by understanding that 

 nervous processes and nervous systems evolve together. 

 In the direct treatment of the facts and principles 

 of mental evolution we can use exactly the same classi- 

 fication and subdivisions of the materials of study as 

 heretofore, because psychological data are the corre- 

 lates of material organic systems, and also because the 

 former, being natural phenomena, are subject to the 

 methods of analysis which can be employed for any 

 series of objects that have undergone evolution. Sepa- 

 rating the matter of fact from the question as to the 

 method, and recalling the main bodies of evidence as 

 to the reality of evolution, we may establish four sec- 

 tions of the subject before us : these are (1) the anatomy, 

 (2) the embryology, and (3) '' palaeontology " of mind, 

 and (4) an inquiry into the way nature deals with the 

 psychical characteristics of organisms in accomplishing 

 their evolution. To specify more particularly, it is 

 possible in the first place to compare the activities 

 belonging to the category of mental and nervous opera- 

 tions, displayed by man and other organisms, and the 

 results form the subject of comparative descriptive 

 psychology; the second division, namely, develop- 

 mental or genetic psychology, deals with the sequence 

 of events in the life of a single individual by which the 



