260 The Animal Mind 



same reaction, but after this experience had been repeated 

 a certain number of times they ceased to respond to the 

 cotton, although they still took meat eagerly. The point 

 which especially concerns us is this : "I rarely," says Her- 

 rick, "after the first trials, got a prompt gustatory reflex 

 with the cotton." The learning persisted for a day or 

 two. The axolotl learned in a similar way to discriminate 

 between pieces of meat and pieces of wood (276). Hermit 

 crabs, which when young try to take up their abode in all 

 sorts of unsuitable objects, glass balls, for instance, later 

 in life make no such efforts (194). 



Whether or not a movement which brings no favorable 

 results will be dropped off and a state of no movement will 

 take its place depends on how strongly prepotent the move- 

 ment is ; upon the strength, that is, of the innate tendency to 

 make it. In the experiments by Professor Bentley and the 

 writer on color discrimination in the creek chub, our first 

 method failed because it required the dropping off, as use- 

 less, of a strongly prepotent reaction, and the substitution 

 of no response at all. Red forceps and green forceps, each 

 containing food, were plunged one at a time into the water ; 

 the fish was allowed to get the food from the red forceps, 

 but the green ones were withdrawn before it had a chance 

 to bite. The time which the fish took to rise and snap 

 at the forceps was measured by a stop-watch, and in the 

 course of 131 experiments the fish had not learned to rise 

 to the green any less promptly than to the red. In other 

 words, no tendency to drop off the useless movement of 

 rising to the green was detected, although later experiments 

 showed that the fish could distinguish between the two 

 forceps. The movement of rising to and biting any small 

 object in the water was so vitally important to the fish 

 that it could not be dropped off (757). On the other 



