.ri. XM.] THS gVOLUTION OF MIND. 151 



transit-lines to devaT.op by the mere process of nutrition. 

 And wliere the psychical life is very simple, and but little 

 varied from generation to generation, a nervous system em- 

 bodying certain organized aptitudes will be transmitted as 

 surely as the muscular or vascular system is transmitted 

 Nervous discharges will run along pre-established transit- 

 lines as inevitably as in human beings the nervous discharges 

 wliich regulate the respiratory and alimentary 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 conscious- 

 ness, a single inner relation is adjusted to a single outer 

 relation. For the simpler kinds of reflex action nothing is 

 needed but what is called a nervous arc, — that is, an afferent 

 nerve, a ganglion, and an efferent nerve. When a person 

 sound asleep draws away a limb that is touched, the impres- 

 sion 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 assistance of the 

 brain is not needed. In many animals 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 degree removed from purely physical life, is all that is 

 manifested by those lowly-organized animals whose nervoas 

 systems consist of simple arcs. So thoroughly physical is this 

 group of phenomena that it may seem almost inappropriate 

 to call it psychical : nevertheless it forms the transition from 

 the one kind of life to the other. It is the lowly beginning 

 from which higher forms of psychical activity arise. 



Now in reflex action, as it is exemplified alike in the 

 rhythmical niovemsiits of our heart, lungs, stomach, and 

 other viscera, and in the contraction of a polyp's tentacle 

 when food comes against it, we see a series of nervous dis- 

 tharges which are automatically directed along certain definite 

 transit-liues. The lines of least resistance have become per- 



