Modifiahihty in Behavior. 461 



hollows of the coral reefs. In order that its disk may protrude into 

 the free water, it is often compelled to extend in the irregular way 

 mentioned, and to retain the crooked forms thus reached. When 

 removed from the natural habitat it still retains these irregularities 

 of form and action. The lower part of the column may stand at 

 right angles to the upper part, or there may be permanent S-shaped 

 bends, or still more irregular forms. It would appear that these 

 must have arisen as a result of the way in which it extends in its 

 natural habitat. The peculiar methods of extension found in 

 given individuals could then hardly be characterized otherwise 

 than as habits, the peculiarities of form being the structural cor- 

 relates of the habits. 



In searching for experiments that w^ould test the possibility of 

 the formation of new habits in sea anemones, the following sug- 

 gested itself. It should be possible to produce new habits in 

 Aiptasia by so arranging the surroundings as to compel the animal 

 to extend in a new way whenever it extends, and to retain the new 

 form thus induced. If the animal when thus compelled by 

 obstacles to extend in a new direction, still extends in the same 

 direction after the obstacles are removed, one w^ould be inclined 

 to hold that a new habit had been formed. 



I supposed that this result would require a long period of time. 

 But some preliminary experiments showed it to be attained, in 

 some cases, with such absolute ease as to raise the doubt whether 

 we have here anything that can be called habit formation. Thus 

 an individual attached to a plane horizontal glass surface was bent 

 in extension far over to the left. Stimulating it repeatedly, it con- 

 tracted at each stimulation, then bent, in extending, again to the 

 left. This continued for fifteen stimulations, one succeeding 

 another as soon as the animal had become fully extended. At the 

 next contraction the animal turned and bent over to the right. 

 Now when stimulated it contracted as before, then bent regularly, 

 in extending, over to the right. It seemed to have acquired a new 

 habit — bending to the right instead of to the left. 



Attentive examination showed that when the animal contracted 

 in response to stimulation, the concave side of the column con- 

 tracted a little more than the rest, so that that side remained a 

 little shorter. In other words, the animal did not take on an 

 entirely symmetrical structure, but the region which was most con- 

 tracted in extension remained most contracted also in the con- 



