44^ 'Journal of Comparative ISfeurology and Psychology. 



stimuli, it ceases to contract and begins to bend in different direc- 

 tions, or, when after increase in the stimulus it breaks loose and 



TABLE III. 



Periodic Occurrence of Prolonged Retraction in No. 41. 



swims away. This prolonged contraction in Hydroides may be 

 simply a difference in the response to stimulation as the result of 

 past experience. This instance seems, in fact, an illustration of 

 one of the conclusions stated by Jennings (p. 445)' in a recent 

 paper on the modifiability in behavior of the earth-worm, to the 

 effect that "the reaction to a given stimulus depends partly on 

 previous stimuli received." 



A second fact which may perhaps be explained by the same 

 hypothesis is brought out in some of the longer series. In the 

 record given above in Table II, for instance, after some thirty- 

 three trials the animal did not respond to the shadow nor to the 

 first touch from the glass rod. Two, three, or five strokes were 

 required to bring about a reaction. The number of strokes needed 

 each time is recorded in parenthesis. This tendency increased 

 throughout the series until in the fifty-fifth trial the filaments 

 were stroked 152 times in rapid succession before they were with- 

 drawn. The touch at first was quick and slight, but producing 

 no reaction it was made heavier until the filaments were stroked 



'Jennings, H. S. Modifiability in behavior. II. Factors determining direction and character 

 of movement in the earth-worm. Jour, of Exper. Zool., Vol. 3, pp. 435-55. 1906. 



