IMMORTALITY 359 



mammalia from the Eocene period to man that as their 

 evolution proceeded so did the development of the brain 

 as far as size is concerned ; but intelligence is correlated 

 not only with size but also with structure, such as an 

 increase in convolutions and grey matter, etc. 



As Evolution proceeds in accordance with use, and 

 the structure of their limbs, peculiar to each kind of 

 animal, are formed in direct response to the animals' 

 physical activities, according to the " principle of Least 

 Action," so brains develop in response to mental use; 

 and the brains of animals were presumably evolved in 

 accordance with an increasing intelligence simultane- 

 ously ; and not much exceeding their requirements for 

 efficiency. 



With man, not only has all this been equally true ; 

 but having acquired the power of realising abstract, 

 mental ideals, he can bring about an alteration in the 

 brain by volitional thought alone ; and secondly, in the 

 shape of his skull in adaptation to the increasing size of 

 the brain within it. 



I know a man who as a boy had a remarkably re- 

 treating forehead. His former schoolmaster met him 

 when he was fifty-five. He said in my presence, " Let 

 me look at your profile, for it was a remarkable one when 

 you were at school ". He found, however, that there 

 was nothing to remark about it. The boy had grown 

 into a great reader and student. His brain had de- 

 veloped in response to use, and something like a hemi- 

 sphere had grown where a retreating forehead had been. 



Darwin somewhere alludes to the same phenomenon. 



Here, then, the Soul acted as a power over the 

 material structure of the brain and skull ; just as 

 muscular exercise develops the muscles and bones of 

 the limbs ; but while actual movements of these bring 



