HIGHWAY OF ANIMAL EVOLUTION 233 



sistent improvement in the two great systems of convey- 

 ance, vascular and nervous, which is very impressive; 

 but the material, or anatomical, evidences of these im- 

 provements are very different. In one case, it is very 

 largely a visible increase in the relative volume of the 

 nervous system and the number of nerve units; in the 

 other, the rise of a multitude of striking architectural, 

 mechanical and chemical devices. 



That is to say, the evolution of nervous conveyance, 

 of reflexes, instincts, and intelligence, is not evidenced 

 so much by striking architectural changes in the brain 

 itself, as by the steady increase in the number of those 

 particular coordinating cells which unite all the other 

 systems into one, and which facilitate and supplement 

 their cooperative actions. This in itself is a very sig- 

 nificant fact, and stands out in sharp contrast with the 

 evolutionary history of all other functions. For every 

 other system has its own formal, or material register of 

 progress, chiefly in its anatomical structure. The nerv- 

 ous system alone is a material register of the coopera- 

 tive actions of all the other systems. 



Hence the increase in volume of the cerebral hemi- 

 spheres, where these coordinating cells are chiefly lo- 

 cated, gives us a single tangible measurement of the 

 evolution of organic cooperation and constructive 

 Tightness. For the hemispheres represent, like any other 

 representative body, the functioning of the whole or- 

 ganism. Their more special function is to discrimi- 

 evil, and to direct and regulate the services of each 

 nate between what is good for the whole, and what is 

 part in the best interests of all. 



The cerebral hemispheres are the chief intermedi- 

 aries between the administration of the inner and of 



