154 MODIFICATIONS OF BEHAVIOR 



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." Observation showed 

 that the bend of the body persisted in the contracted as well 

 as the extended state, and that all parts extended propor- 

 tionately and thus led to a repetition of the previous action. 

 The habit of action in this case had a persistent structural 

 basis in the bend of the body. If now the anemone was 

 caused to contract very strongly in all parts so that it was 

 no longer bent to one side in the contracted state it would 

 lose its habit of bending when it subsequently expanded. 

 The role of the nervous system in this case is a very doubtful 

 one and it is not improbable that the so-called habit is 

 merely a result of purely mechanical factors. The same 

 may also be true of the habit of irregular bendings acquired 

 as a result of living in crevices between the rocks, which 

 might be compared to the difficulty experienced by a person 

 whose body and limbs have been confined for a long time 

 in any one position in making new movements. 



Jennings has performed numerous experiments on the 

 formation of righting habits in the starfish Asterias forrei. 

 Starfish when placed on their backs have several methods 

 of turning over. Different individuals have their personal 

 peculiarities in this as in other respects, and in most speci- 

 mens there is a tendency to use one particular ray or set of 

 rays upon which to turn. These differences as Moore 

 has pointed out may be due to inequalities in the size of 

 the arms, injuries to certain arms, or any initial twist an 

 arm may have had due to its previous position. Before 

 any attempt to train a starfish was made the animal was 

 put through a set of tests to determine the rays most com- 

 monly employed in the righting reaction. After this the 



