134 University of California Publications in Zoology. [Vol. 4 



The observer at the appearance of this unified impulse is 

 tempted to express the facts in an anthopomorphic way by saying 

 that at that moment the starfish has decided which way to turn. 

 The impression given is exactly that of the making of a decision, 

 and there are few organisms, even among the highest, in which 

 there are such clear outward signs of the moment when the de- 

 cision is made'. 



After this impulse appears, all the activities of the starfish 

 are directed toward turning in a certain definite way. Difl:erent 

 rays and different tube feet play difl:erent roles; some attach, 

 some release, some pull ; certain rays walk under other rays ; cer- 

 tain ones walk over the backs of others, — in fact, all the varia- 

 tions mentioned in our introductory classification are possible, 

 though all are directed toward the same end. The impulse is 

 toward the performance of a certain complex act, — namely, the 

 righting reaction^. In view of the variations in method of per- 

 formance, it seems impo&sible to express the nature of the im- 

 pulse in any simpler way. The starfish reacts as a unit, not as 

 a bundle of independent organs. 



This unified impulse is perhaps the central fact in the right- 

 ing reaction. In view of its existence, the remainder of our 

 analysis centers about three questions : 



1. What determines the varied actions of each part of the star- 

 fish before the impulse appears? Why does one ray twist and 

 go down, another rise, etc., etc. ? 



2. How is the direction of the impulse determined? That 

 is, how is it determined whether the starfish shall turn to the left. 

 — toward the rays a and b, or toward d and e, or the like ? How 

 is it decided which rays shall play the role of attaching and pull- 

 ing, which that of swinging over, etc. ? 



3. After the impulse has appeared, what determines the 

 varied activities of the different parts ? Why do certain tube feet 

 now become released, others attached? Why do certain rays 

 twist, others swing over without twisting; some walk in one 



^ I have given above an account of the typical cases. Sometimes the 

 impulse is not so fully unified, and at times there is indecision; these im- 

 portant facts will be taken up later. 



* As we have before seen, there is a similar coordinated impulse toward 

 locomotion in a certain direction. 



