THE EVOLUTION OF MIND 



embodying certain organized aptitudes will be 

 transmitted as surely as the muscular or vascu- 

 lar system is transmitted. Nervous discharges 

 will run along preestablished transit lines as 

 inevitably as in human beings the nervous dis- 

 charges which regulate the respiratory and ali- 

 mentary movements run in permanent channels. 

 The character of the process is best exemplified 

 in reflex action^ the simplest form of psychical 

 life. In reflex action, which is unaccompanied 

 by consciousness, a single inner relation is ad- 

 justed to a single outer relation. For the sim- 

 pler kinds of reflex action nothing is needed but 

 what is called a nervous arc ; that is, an afferent 

 nerve, a ganglion, and an eflferent nerve. , When 

 a person sound asleep draws away a limb that is 

 touched, the impression is simply carried along 

 an afferent nerve" to one of the spinal ganglia, 

 and thence reflected along an efferent nerve to 

 the muscle which moves the limb. The assist- 

 ance of the brain is not needed. In many ani- 

 mals the limbs thus respond to stimuli after the 

 head has been cut off or the brain sliced away. 

 This kind of psychical life, which is but one de- 

 gree removed from purely physical life, is all 

 that is manifested by those lowly organized ani- 

 mals whose nervous systems consist of simple 

 arcs. So thoroughly physical is this group of 

 phenomena that it may seem almost inappro- 

 priate to call it psychical : nevertheless it forms 



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