398 S. J. HOLMES 



burrowing in the sand, and there are specialized structures 

 adapted to respiration in the peculiar habitat of these animals. 



The earthworms tested by Yerkes (40) were induced to crawl 

 through a passage which led to a second one running at right 

 angles to it, so that the animals had a choice of crawling either 

 to the right or to the left. One of these passages was furnished 

 with sand paper and electric wires, so that the worms which 

 crawled into this passage would encounter stimuli which would 

 cause them to turn back. Most of the experiments were carried 

 on with a single specimen which was given a certain number 

 of trials a day for some months. The worm after from .twenty 

 to one hundred trials came to avoid the branch of the tube 

 where it received a shock, but its subsequent behavior was far 

 from constant. The habits of turning that were formed were 

 found to persist after the removal of the first five segments of 

 the body and hence the brain. As the brain regenerates the 

 worm shows more initiative and variability in its behavior. 



Whether the modified behavior of the worm studied rests 

 upon the formation of associations or upon some other physio- 

 logical factor or factors is a question difficult to determine in 

 a creature like the earthworm, but if associative memory should 

 be proven in this case it would afford the first instance of this 

 faculty among animals so low in the scale of life. 



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