256 Charles Darwin. 



involved in the simple act of walking are such that it 

 would be impossible ever to perform it were it 

 necessary to think what had to be done, and weigh 

 in the judgmept the precise amount of force neces- 

 sary to distribute to each muscle at each moment of 

 the act. It is now known that the cerebral centres 

 which control the separate muscles put in action are 

 closely contiguous in the brain, and that they prob- 

 ably intercommunicate and excite each other in a 

 definite manner, predetermined by habit and hered- 

 ity. The conscious mind has only to set in motion 

 the subordinate apparatus, when it goes on, and 

 works out the problem with matchless skill, like the 

 system of cogs and eccentrics that produce the intri- 

 cate pattern in an engraver's lathe. All have noticed 

 the uncouth manner in which children and untrained 

 persons follow with lips and tongue the motions of 

 their hands when using a tool of any kind. Darwin 

 ascribes this to unconscious imitation, but it can be 

 explained more strictly in accordance with his own 

 principles. The facial muscles are actuated from a 

 cerebral centre in close proximity to those which 

 move the arms and hands. In the lower animals this 

 is necessary, for the mouth is an organ of prehension, 

 used in strict association with the fore-limbs in seiz- 

 ing prey, and in other acts. As this associated move- 

 ment became strongly fixed by long habit, it survives 

 with greai; obstinacy, and though it has not been 

 useful to the race since the historical period, we have 

 yet to caution our children not to put their tongues 

 out when they write. 



My limit of time forces me to conclude this hasty 

 and imperfect summary. The practical bearing of 



