74 MENTAL EVOLUTION IN ANIMALS. 



response (however complex this may be), it has to give rise 

 in the nerve-centre to a play of stimuli before the appropriate 

 response is yielded. In the higher planes of conscious life 

 this play of stimuli in the presence of "difficult circum- 

 stances " is known as indecision ; but even in a simple act of 

 consciousness — such as that of signalling a perception—more 

 time is required by the cerebral hemispheres in supplying an 

 appropriate response to a non-habitual experience, than is 

 required by the lower nerve-centres for performing the most 

 complicated of reflex actions by way of response to their 

 habitual experience. In the latter case the routes of nervous 

 discharge have been well worn by use ; in the former case 

 these routes have to be determined by a complex play of 

 forces amid the cells and fibres of the cerebral hemispheres. 

 And this complex play of forces, which finds its physiological 

 expression in a lengthening of the time of latency, finds also 

 a psychological expression in the rise of consciousness. 



The function, then, of the cerebral hemispheres is that of 

 dealing with stimuli which, although possibly and in a com- 

 parative sense simple, are yet so varied in character that 

 special reflex mechanisms have not been set aside to deal 

 with them in one particular way ; and it is the consequent 

 perturbation of these highest nerve-centres in dealing with 

 such stimuli that is accompanied by the phenomena of con- 

 sciousness. Or, in the words of Mr. Spencer, " there cannot 

 be co-ordination of many stimuli without some ganglion 

 through which they are all brought into relation. _ In the pro- 

 cess of bringing them into relation, this ganglion must be 

 subject to the influence of each — must undergo many changes. 

 And the quick succession of changes in a ganglion, implying 

 as it does perpetual experiences of differences and likenesses, 

 constitutes the raw material of consciousness."* 



Thus we see, so far as we can ever perhaps hope to see, 

 how conscious action gradually arises out of reflex. As the 

 stimuli to be dealt with become more complex and varied 

 (owing to the advancing evolution of organisms bringing 



* Principles of Psychology, vol. i, p. 435. I think, however, that Mr. 

 Spencer is not sufficiently explicit, either in the ahove quoted passage or else- 

 where, in showing that " the raw material of consciousness " is not necessarily- 

 constituted hy the mere complexity of ganglionic action. Indeed, as I have 

 said, such complexity in itself does not appear to nave anything to do with the 

 rise of consciousness, except in so far as it may be conducive to what we may 

 term the ganglionic friction, which is expressed by delay of response. 



