The Mind of the Simplest Animals 47 



A consequence of this lack of qualitative variety in the 

 sense experiences of an Amoeba is a lack of what we may 

 call complexity of structure in that experience. The 

 number of stimulus differences which are in the human 

 mind represented by differences in the quality of sensations 

 is so great that at any given moment our consciousness of 

 the external world is analyzable into a large number of 

 qualitatively different sensations. At the present instant 

 the reader's consciousness "contains," apart from the re- 

 vived effects of previous stimulation, many distinguish- 

 able sensation elements, visual, auditory, tactile, organic, 

 and so on. The Amoeba's consciousness, if it possesses 

 one, must have a structure inconceivably simpler than that 

 of any moment of our own experience. 



A second point in which the mind of an Amoeba must, if 

 it exists, differ from that of a human being, consists in its 

 entire lack of mental imagery of any sort. Not only has the 

 Amoeba but three or four qualitatively different elements 

 in its experience, but none of these qualities can be re- 

 membered or revived in the absence of external stimulation. 

 How may we be sure of this ? If our primitive animal could 

 revive its experiences in the form of memory images, it would 

 give some evidence of the influence of memory in its be- 

 havior. Indeed, as we shall learn, it is possible, in all 

 probability, for an animal'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 evidence 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 



