126 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 



means, do luminous vibrations give it the sensations of 

 light and darkness, of colour and form and distance, which 

 they give to us ? and do sonorous vibrations produce the 

 feelings of noise and tone, of melody and of harmony, as 

 in us ? — it is by no means to be answered hastily, perhaps 

 cannot be answered at all, except in a tentative, probable 

 way. 



The phenomena to which we give the names of sound 

 and colour are not physical things, but are states of con- 

 sciousness, dependent, there is ever}^ reason to believe, 

 on the functional activity of certain parts of our brains. 

 Melody and harmony are names for states of conscious- 

 ness which arise when at least two sensations of sound 

 have been produced. All these are manufactured arti- 

 cles, products of the human brain ; and it would be 

 exceedingly hazardous to affirm that organs capable of 

 giving rise to the same products exist in the vastly 

 simpler nervous sj^stem of the crustacean. It would be 

 the height of absurdity to expect from a meat-jack the 

 sort of work which is performed by a Jacquardloom ; and 

 it appears to me to be little less preposterous to look for 

 the production of anything analogous to the more subtle 

 phenomena of the human mind in something so minute 

 and rude in comparison to the human brain, as the 

 insignificant cerebral ganglia of the crayfish. 



At the most, one may be justified in supposing the 

 existence of something approaching dull feeling in our- 

 selves; and, to return to the problem stated in the begin- 



