v CONATION 65 



methods, which belong to its structure and may be re- 

 garded as hereditary, but it appears to vary and adjust 

 them from moment to moment in relation to the be- 

 haviour of an external object. If this is the case the 

 action is sensori-motor. 1 With regard to higher animals 

 that follow the turnings and twistings of a prey, or, 

 if themselves dogged, the rapidly changing movements of 

 an enemy, the case admits of no doubt. Mechanism may 

 be wholly hereditary or may be improved by experience 

 as the case may be, but the combination and adjustment 

 from moment to moment require the combination of 

 many co-present elements, and the only question which 

 we shall have to raise later on will be whether we must 

 not carry some of these actions a grade higher and 

 frankly regard them as purposive. 



1 To go a little higher in the animal scale we may usefully compare 

 the behaviour of a starfish that has been placed on its back. First of all 

 it moves its tube feet about and twists the tubes so that some are directed 

 downwards. In this way one or more find the bottom. u They begin to 

 pull on the arm to which they belong, turning it further over, and bring 

 other tube feet into contact with the bottom. These now assist in the 

 process. If two or three adjacent rays become thus attached, the other 

 rays cease their searching, twisting movements and allow themselves to 

 be turned over" . . . If two or more opposite rays become attached, "one 

 releases its hold." The righting reaction is by no means performed 

 always in the same manner but is various and flexible (Jennings, p. 239). 

 I do not know whether the righting reaction should be classed as 

 sensori-motor directed to the ground as an object, or as a selective 

 adaptation. It is certainly an interesting instance of. the determination 

 of a series of acts by reference to the immediate requirements of the 

 animal. 



