BRAIN PHYSIOLOGY OF WORMS 365 



in this paper on stereotropism in brainless Planarians, and 

 the reaction of brainless animals toward light. 



3. Even though the brain, or more accurately that part of 

 the body containing the brain, determines in the main the bio- 

 logical or psychic reactions of worms which are typical for 

 each species in the same way as in higher animals, there never- 

 theless exists a specific difference between the brain of worms 

 and that of many of the higher animals. The worms lack asso- 

 ciative memory and consequently also consciousness, which is 

 only a function of the former. By associative memory we 

 understand that arrangement of the brain by virtue of which 

 a stimulus brings about not only the effects corresponding 

 with its nature and the specific structure of the irritable 

 tissue, but also the stimulating effects of other causes which 

 at a previous time once affected the organism at the same or 

 almost the same time with the stimulus. No trace of such an 

 associative effect of stimuli can be proved to exist in worms, 

 and consequently also no trace of consciousness. 



One might go farther and speak of memory, when the 

 effect of a stimulus depends upon previoSis^ffscte-of stimula- 

 tion at all. Under these circumstances, for example, we 

 would have to designate it as memory when a plant which 

 was originally cultivated in the tropics does not withstand 

 low temperatures as well as a plant of the same species culti- 

 vated in the North. We would also have to call it memory 

 when a Medusa of the temperate zone is moved to the regions 

 of the midnight sun and here continues its depth migrations 

 in a period corresponding with the changes of day and night 

 in its home. No objection could be made to this, only I do 

 not believe that this kind of memory can be looked upon as 

 a lower form of associative memory. And I am convinced 

 that it is something entirely different from associative mem- 

 ory. When the plant which has been cultivated in the South 

 does not do as well in the North as the same species of plant 



