Her RICK, Cerebrum of the Opossum. 23 



it is in the remaining portion of the work relating to mental processes in ani- 

 mals and man that the author's mastery of thought and style are most obvious. 



Impressions are the bricks in the house of knowledge. A certain amount 

 of mortar (cognition and recognition) is supplied by the builder. A sensation is 

 an impression that has been discriminated from others. 



Objecting to the familiar simile "eye-gate," " ear-gate," he says : A much 

 closer analogy is this: Something stands without and knocks at the doorway of 

 sense, and from the nature of the knocks we learn somewhat concerning that 

 which knocks." 



At first one is inclined to quarrel with the coinage of new terms for familiar 

 ideas, but becomes reconciled to '-construct," "predominants" etc. on the ground 

 of unambiguity. The felicities of the dicti6n even in intricate discussions are 

 illustrated by the following. "In ordinary speech, when we pass and repass 

 from motives to actions and from actions to feelings they may give rise to, we 

 are apt to be forgetful of the depth of the chasm we so lightly leap. And this 

 is no doubt because the chasm, though so infinitely deep, is so infinitely narrow " 

 The whole discussion of habit and instinct is admirable. 



In the origin of instinctive activities he recognizes three factors, i. Elim- 

 ination through natural selection. 2. Selection through preferential mating. 

 3. The inheritance of individually acquired modifications. In all three, intelli- 

 gence may or may not have been a factor. 



The author concludes this topic with the statement that without inhibition, 

 volition properly so-called has no existence and, by distinguishing the perceptual 

 volition of animals from the conceptual volition of man, prepares the way for the 

 interesting chapter on mental evolution. This subject would carjy us too far, 

 but the position taken is concisely expressed in the following sentence. " Paral- 

 lel to the evolution of organic and neural kinesis there has been an evolution of 

 metakinetic manifestations culminating in conscious thought.' " Phenomenal 

 reality has two aspects — an inner aspect as metakinesis, and an outer aspect as 

 kinesis." " What are for me states of consciousness are for you neural processes 

 in my brain." 



At one point — the discutsion of the ego does the discussion, as it seems to 

 us, leap the track and one holds his breath for the crash that must ensue. It is 

 possible that some readers may refuse to follow the argument beyond this point, 

 but they will be well paid by the suggestive if not entirely convincing discussion 

 of the selective influence of metakinetic activities inter se and the law of con. 

 gruities. 



