The Mind of the Simplest Animals 45 



as we shall learn, it is possible, in all probability, for an ani- 

 mal's conduct to be influenced by its past experience even 

 though the animal be incapable of reviving that experience in 

 the form of a memory image. Therefore, if we find no evi- 

 dence that the Amoeba learns, or modifies its behavior as the 

 result of past stimulation, we may conclude a fortiori that it 

 does not have memory images. 



Now it would be stating the case too strongly to say that 

 past stimulation does not affect the behavior of Amoeba at all. 

 In the first place, this animal shows, in common with all other 

 animals, the power of " getting used" to certain forms of 

 stimulation, so that on long' continuance they cease to provoke 

 reaction. "Thus," Jennings says, "Amoebae react negatively 

 to tap water or to water from a foreign culture, but after trans- 

 ference to such water they behave normally" (211, p. 20). 

 Such cessation of reaction occurs when the continued stimulus 

 is not harmful. In a sense, it may be called an effect of ex- 

 perience; but there is clearly no reason for supposing that 

 it involves the revival of experience in the form of an idea or 

 image. We have parallel phenomena in our own mental 

 life. A continued stimulus ceases to be "noticed," but the 

 process involves rather the disappearance of consciousness 

 than the appearance of a memory image. Jennings, how- 

 ever, is inclined to think that preceding stimulation may 

 modify the Amoeba's behavior in a way more nearly suggest- 

 ing memory in a higher type of mind. He describes an 

 interesting observation to illustrate this. A large Amoeba, 

 c, had swallowed a smaller one, b, but had left a small canal 

 open, through which the swallowed one made efforts to escape, 

 which were several times foiled by movements on the part of 

 the large Amoeba toward surrounding it again. Finally it 

 succeeded in getting completely out, whereupon the large 

 Amoeba "reversed its course, overtook b, engulfed it com- 



