54 The Animal Mind 



is identical with any sensation quality entering into our 

 own experience, we cannot say. The light rays which 



' Ito us are red and blue may for an animal's consciousness 

 also differ from each other, and yet if our experience could 



Ibe exchanged for the animal's, we might find in the latter 

 nothing like red and blue as we know them. 



Thus much being premised, what sort of evidence can 

 be obtained that an animal does discriminate between two 

 stimuli? Again, as in considering the evidence for the 

 existence of consciousness in general, there is an argiunent 

 from structure and an argument from behavior. 



"^ § II. Structure as Evidence of Discrimination 



The argument from structure consists primarily in the 

 fact that an animal possesses sense organs recognizably 

 like our own. If a creature has an organ suggesting 

 strongly the construction of the human cochlea, or an 

 organ with a lens and a membrane composed of rods and 

 cones, it is highly probable that auditory stimuli in the one 

 case and light in the other produce specific sensations. This 

 argument from the morphology of sense organs is, however, 

 limited in two ways. First, it is only a small part of the 

 animal world whose sense organs resemble ours closely 

 enough to make the analogy safe. And second ly, we do 

 not after all know very much about the relation of our own 

 sense-organ structure to function. We know, for example, 

 that our own organ with a lens and retina gives us visual 

 sensations, but we cannot say with certainty which struc- 

 tures in the retina furnish brightness sensations and which 

 color sensations, nor do we know anything about the 

 retinal structures that underlie different qualities of color 

 sensations. We can say that sensations of hearing come 



