I PROLOGUE 47 



structural evolution, consciousness makes its ap- 

 pearance. I have frequently expressed my in- 

 capacity to understand the nature of the relation 

 between consciousness and a certain anatomical 

 tissue, which is thus established by observation. 

 But the fact remains that, so far as observation and 

 experiment go, they teach us that the psychical 

 phenomena are dependent on the physical. 



In like manner, if fishes, insects, scorpions, and 

 such animals as the pearly nautilus, possess 

 feeling, then undoubtedly consciousness was pres- 

 ent in the world as far back as the Silurian 

 epoch. But, if the earliest animals were similar 

 to our rhizopods and monads, there must have 

 been some time, between the much earlier epoch 

 in which they constituted the whole animal 

 population and the Silurian, in which feeling 

 dawned, in consequence of the organism having 

 reached the stage of evolution on which it 

 depends. 



5. Consciousness has various forms, which may 

 be manifested independently of one another. 

 The feelings of light and colour, of sound, of 

 touch, though so often associated with those of 

 pleasure and pain, are, by nature, as entirely 

 independent of them as is thinking. An animal 

 devoid of the feelings of pleasure and of pain, 

 may nevertheless exhibit all the effects of sensa- 

 tion and purposive action. Therefore, it would be 

 a justifiable hypothesis that, long after organic 



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