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 every 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 system 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 Jacquard loom; 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, tu return to the problem stated in the begin- 
