DIS TRIE U TWN OF MEM OR Y 229 



arbitrary. Graber also maintained that animals that 

 go to the light do so because they love it, and another 

 author thought that animals fly into the flame out of 

 curiosity. It is not worth while to follow up such an- 

 thropomorphisms in the biological literature. Biol- 

 ogy is as much justified in ignoring them as modern 

 physics is in ignoring the fact that savages explain 

 the locomotive by supposing a horse to be concealed 

 within it. On the contrary, biology should concern 

 itself with a systematic investigation of the differ- 

 ent animals in regard to the existence of associative 

 memory. The total results of such an investigation 

 will furnish the material for a future comparative 

 psychology. 



7. Our conception meets with an apparent difficulty 

 in the fact that stimuli which call forth sensations of 

 pain in us produce also reactions in lower animals 

 which have no memory. These reactions are natur- 

 ally regarded as the expression of sensations of pain. 

 The injured worm writhes and wriggles, and it is diffi- 

 cult to rid ourselves of the impression that these 

 movements are the expression of severe pain. Yet 

 W. W. Norman proved that this conclusion is by no 

 means justified (5, 10). He found that if an earth- 

 worm is divided transversely, only the posterior piece 

 makes these writhing movements, while the anterior 

 piece crawls off as if nothing had happened. It 

 would, of course, be absurd to assume that the pos- 

 terior piece alone is capable of a sensation of pain, 

 while the anterior piece, which contains the brain, 



