Difficulties and Methods 3 



functions of our own to conjecture with any certainty what 

 difference this must make in the conscious life of such animals ; 

 but when we find sense organs, such as the compound eyes 

 of insects or crustaceans, constructed on a plan wholly diverse 

 from that of ours ; when we find organs apparently sensory in 

 function, but so unlike our own that we cannot tell what pur- 

 pose they serve, we are baffled in our attempt to construct 

 the mental life of the animals possessing them, for lack of 

 power to supply the sensation elements of that life. "It is 

 not," said Locke, "in the power of the most exalted wit or 

 enlarged understanding, by any quickness or variety of 

 thought, to invent or frame one new simple idea in the mind" 

 (232, Bk. II, ch. 2); we cannot imagine a color or a sound 

 or a smell that we have never experienced; how much less 

 the sensations of a sense radically different from any that we 

 possess ! Again, a bodily structure entirely unlike our own 

 must create a background of organic sensation which renders 

 the whole mental life of an animal foreign and unfamiliar to 

 us. We speak, for example, of an "angry" wasp. Anger, 

 in our own experience, is largely composed of sensations of 

 quickened heart beat, of altered breathing, of muscular ten- 

 sion, of increased blood pressure in the head and face. The 

 circulation of a wasp is fundamentally different from that of 

 any vertebrate. The wasp does not breathe through lungs, 

 it wears its skeleton on the outside, and it has the muscles 

 attached to the inside of the skeleton*. What is anger like 

 in the wasp's consciousness? W c$n ffrm n* atfeQuate 

 idea of it. 



To this fundamental difficulty of the dissimilarity between 

 animal minds and ours is added, of course, the obstacle that 

 animals have no language in which to describe their expe- 

 rience to us. Where this unlikeness is greatest, as in the 

 case of invertebrate animals, language would be of little use, 



