38 



Direct orientation of the leading ray or rays to one side 

 is dependent upon a unilateral stimulation of either the dermis, 

 the eye spot or the tube feet of these rays and a consequent 

 orientation of these rays toward (or away from?) the stimulus. 

 If the stimulus acts also on the rays that are situated on the 



side of the starfish from which the stimulus comes, the anterior 



^ X 

 is apt to be shifted (Pless*er 1913) to these arms b^t if it 



acts only on the side of the anterior arms it is more likely to causa 

 a rotation of the animal as a whole. This is dependent upon 

 the angle of the stimulus to the direction of the starfish and 

 various other factors that have been analyzed by Bohn (1903). 

 The relative acceleration and retardation of the lateral 

 arms is of course a necessary result of the above described 

 lateral movements of the anterior rays. As a result of 

 stimulation the same factors which we have discussed above act- 

 ing in a positive direction on the tube feet, dermis or eye 

 pot would cause acceleration and in a negative direction would 

 cause retardation, provided the stimulus did not reach the 

 more sensitive (to a direct stimulation) tips of the anterior 

 or posterior rays. A mechanical obstacle to the progress of the 

 rays on one side of the animal will result in a change in 

 orientation that may or may not involve a change in the physio- 

 logical anterior. This, however, will be taken up in connection 

 with the"dviation reaction" and the breaking up of the 

 functional unity of the coordinated impulse. 



GJiNflRAk CONSIDERATION COORDINATION 



t 



The categories into which we have analyzed the reactions 

 of the locomotor starfish are not the separate and distinct 

 unities that they appear above. All of the factors that we 

 have recognized are usually at work at one and the same time* 



