62 MENTAL EVOLUTION IN ANIMALS. 



of Mind. Here the object was to trace the ultimate principles 

 of physiology that might be taken as constituting the objec- 

 tive side of those phenomena which on their subjective and 

 ejective sides we regard as mental. These principles we 

 found to be the power of discriminating between different 

 kinds of stimuli irrespective of their relative degrees of 

 mechanical intensity, coupled with the power of performing 

 adaptive movements suited to the results of such discrimina- 

 tion. These two powers, or faculties, we saw to occur in 

 germ even among the protoplasmic and unicellular organisms, 

 and we saw that from them upwards all organization may be 

 said to consist in supplying the structures necessary to an 

 ever-increasing development of both these faculties, which 

 always advance, and must necessarily advance, together. 

 When their elaboration has proceeded to a certain extent, 

 they begin gradually to become associated with Feeling, and 

 when they are fully so associated, the terms Choice and Pur- 

 pose become to them respectively appropriate. Continuing 

 in their upward course of evolution, they next become con- 

 sciously deliberative, and eventually rational. But although 

 when viewed from the subjective or ejective side they thus 

 appear, during the upward course of their development, to 

 become transformed from one entity to another, such is not 

 the case when they are viewed from their objective side. 

 Tor, when viewed from their objective side, the most elaborate 

 process of reasoning, or the most comprehensive of judg- 

 ments, is seen to be nothing more than a case of exceedingly 

 refined discrimination, by highly -wrought nervous structures, 

 between stimuli of an enormously complex character ; while 

 the most far-sighted of actions, adapted to meet the most 

 remote contingencies of stimulation, is nothing more than a 

 neuro-muscular adjustment to the circumstances presented by 

 the environment. 



Thus, if we again take mental operations as indices 

 whereby to study the more refined working of nervous centres, 

 as we take muscular movements to be so many indices, 

 " writ large," of the less refined working of such centres, 

 we again find forced upon us the truth that the method of 

 nervous evolution has everywhere been uniform ; it has 

 everywhere consisted in a progressive development of the 

 power of discriminating between stimuli, combined with the 

 complementary power of adaptive response. 



