216 The Animal Mind 



it into practice? Decided evidence in favor of such a sup- 

 position might be furnished if the " trial and error" needed 

 to be gone through with only once. A human being brought 

 into such conditions and guiding his conduct by ideas would, 

 if placed in a similar emergency soon afterwards, immediately 

 recall the idea of the successful action and waste no time over 

 the unsuccessful ones. But we have no reason to think that 

 such is the fact with our primitive animals. Preyer's star- 

 fish, when confined by large flat-headed pins driven into the 

 board on which it lay, close up in the angles between its 

 arms, managed to escape by trying a large variety of move- 

 ments, and gradually diminished, Preyer says, the number of 

 useless movements made in successive experiments (350). 

 O. C. Glaser, on the other hand, has recently found that the 

 echinoderm Ophiura brevispina does not improve at all with 

 practice in removing obstructions from its arms. The very 

 versatility of the starfish, this writer thinks, tells against 

 its perfecting any one movement through experience (145). 

 Stentor and Hydra go through the same series of reactions 

 each time, without apparently being influenced by their 

 previous behavior. And again we must remind ourselves 

 that there is no reason why their conduct, adaptively regarded, 

 should be otherwise. An animal with so little power of dis- 

 tinguishing qualitative differences among stimuli cannot be 

 in any way aware that the stimulus which affects it a second 

 time is going, as in the previous case, to be so persistent that 

 the ordinary negative reaction will not get rid of it. Further, 

 each reaction of the series performed by the animal is more 

 disturbing to its ordinary course of life than the preceding one. 

 The Stentor can bend to one side and still continue the food- 

 taking process ; if it reverses its ciliary action, feeding must be 

 momentarily interrupted ; while contraction on the stem and 

 breaking loose from its moorings are still more serious in- 



