Modification by Experience 247 



and kinaesthetic sensations is its accompaniment in the 

 human mind. 



When the same stimulus is repeated, in many cases the 

 effect of this heightened excitability is shown by the or- 

 ganism's performing in succession different forms of the 

 negative reaction until one of them is successful in getting 

 rid of the stimulus. The ciHate Stentor furnishes us with 

 an example. When attached by its stem, if it is strongly 

 stimulated, say, with a glass rod, several times in succession, 

 it first tries its commonest negative reaction, bending over 

 to one side. If the stimulus continues, it reverses momen- 

 tarily the direction in which the cilia are whirling. If this, 

 several times repeated, does not succeed in getting rid of 

 the stimulus, the animal contracts strongly upon its stem. 

 This also is continued for some time, but if the stimulus 

 too is kept up, the Stentor finally breaks from its moorings 

 and swims off (370). 



There are many examples of similar behavior in other 

 animals. Hydra in certain cases tries first the ordinary 

 negative response of contraction, and later moves away 

 from the region it has been occupying (751 a). Frandsen 

 found that if the slug Limax maximus has a tentacle touched 

 several times in succession, it at first withdraws the ten- 

 tacle and turns away from the stimulus. Later, it may 

 move toward and push against the stimulus, and do the 

 same if the touch is on the side of its body, resisting and 

 curving aroimd the obstacle — another way, of course, of 

 getting rid of it (236). Preyer, again, observed a very 

 pretty instance of this sort of behavior in the starfish. He 

 slipped a piece of rubber tubing over the middle part of 

 one of the arms of a starfish belonging to a species in which 

 those members are very slender, and found that the animal 

 tried successively various devices to get rid of the foreign 



