582 Causes and Course of Organic Evolution 



the interior, the organ that rolls its melodies to each furthest 

 recess, are all so blended in one great harmony of effect that 

 the onlooker often fails to realize that thousands of pairs of 

 hands and arms performed their allotted task and by corre- 

 lated resultant effort — practised patiently and hereditarily 

 through long millenia of effort and action — combined the whole 

 into a noble and enduring edifice. 



As already indicated (p. 207) the architect of it, by highly 

 complex compounded resultant proenvironal response to many 

 and varied previous environal stimuli, evolved by hand action 

 and brain stimulation, the plan of the whole in every detail. 

 Each constructive manager working under him proenvironed 

 his own section of work so that he could guide intelligently 

 the scores of hands working under and for him. 



The enormously strong and interrelated nerves of the 

 brachial plexus that innervate the arm, specially the 6th, 7th, 

 and 8th cervical branches, are proof of the complicated com- 

 munications that exist between the brain and the arm. So 

 the hand-arms of each individual, by mechanotactic and to a 

 much less degree thermotactic relation, gradually convey to 

 the brain stimuli that influence its molecular substance, and 

 which there are combined into resultant responses that, in the 

 early nest- or hut-building activities of man, sufficed as efferent 

 impulses to enable him to construct the whole. But, from that 

 stage of house-building civilization to the one in which the 

 cathedral is reared, added stimuli and groups of stimuli were 

 combined more and more intricately by the Nissl or nerve-cell 

 or neuratin substance, which started complex or compounded 

 resultant responses of an increasingly high order. 



We have, in the foregoing text, repeatedly referred to the 

 contributory action of the eye and naturally the o])tic center, 

 as a conducting sense-pathway from the brain. But, given 

 the arm with its tactile fingers, the eye can at tunes be largely 

 dispensed with. Thus the skill in reading, sewing, weaving, 

 playing, and even writing, shown by the educated blind, is 

 familiar to all, while a visit to an "Institution for the Blind" 

 reveals many surprises in manual effort and brain stimulation. 



