CHAPTEE XII 



MENTAL PROCESSES 



IF the lowest plants and animals possess mind, and 

 if psychogenesis is a fact, then psychological and 

 biological evolution must have commenced together. 

 And unquestionably they are closely connected. 

 Nevertheless there is a distinction. Biological evo- 

 lution is the action of mind on protoplasm, psycho- 

 logical evolution is the action of mind on itself. 

 And although the latter has its roots in animal life, 

 still it plays so much more important a part in 

 human affairs than in biology that it has always 

 been kept distinct. 



Psychology, like every other branch of science, 

 may be divided into two parts : principles and his- 

 tory. The latter is an enormous subject which no one 

 man could undertake, even if he gave his whole life 

 to it. But the principles are more compact, and, as 

 the facts on which they rest are familiar to all, they 

 can be put into a small compass. These principles, 

 so far as they relate to the evolution of mind, are 

 very similar to those which relate to the evolution 

 of protoplasm, and it is necessary to have a clear 

 conception of the latter before proceeding to the 

 more difficult subject of mind. 



The mental development of animals has been ably 

 treated by various authors, both biologists and 



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