60 MENTAL EVOLUTION IN ANIMALS. 



Choice, and the evidence of Choice we found to consist in the 

 performance of adaptive action suited to meet circumstances 

 which have not been of such frequent or invariable occur- 

 rence in the life-history of the race, as to have been specially 

 and antecedently provided for in the individual by the in- 

 herited structure of its nervous system. The power of learn- 

 ing by individual experience is therefore the criterion of 

 Mind. But it is not an absolute or infallible criterion ; all 

 that can be said for it is that it is the best criterion available, 

 and that it serves to fix the upper limit of non-mental action 

 more precisely than it does the lower limit of mental ; for it 

 is probable that the power of feeling is prior to that of con- 

 sciously learning. 



Having thus arrived at the best available criterion of 

 Mind considered as an eject, we next proceeded to consider 

 the objective conditions under which known Mind is invari- 

 ably found to occur. This led us briefly to inspect the 

 structure and functions of the nervous system, and, while 

 treating of the physiology of reflex action, we found that 

 everywhere the nervous machinery is so arranged that there 

 is no alternative of action presented to the nerve-centres 

 other than that of co-ordinating the group of muscles over 

 the combined contractions of which they severally preside. 

 The question therefore arose — How are we to explain the fact 

 that the anatomical plan of a nerve-centre with its attached 

 nerves comes to be that which is needed thus to direct the 

 nervous stimuli into the channels required ? The answer to 

 this question we found to consist in the property which is 

 shown by nervous tissue to grow by use into the directions 

 which are required for further use. This subject is as yet 

 an obscure one — especially where the earliest stages of such 

 adaptive growth are concerned — but in a general way we can 

 understand that hereditary usage, combined with natural selec- 

 tion, may have been alone sufficient to construct the number- 

 less reflex mechanisms which occur in the animal kingdom. 



Passing from reflex action to cerebral action, we first 

 noticed that as the cerebral hemispheres pretty closely re- 

 semble in their intimate structure ganglia in general, there 

 can be no reasonable doubt that the mode of their operation 

 is substantially the same. Moreover we noted that, as such 

 operation is here unquestionably attended with mental action, 

 a strong presumption arises that the one ought to constitute 



