-40 



Orientation of re t rao ted tube feet and the independence 

 mechanisms of orientation and that o withdrawal ojr stepping* 



It has been shown (dole 1913} that the coordinated im- 

 pulse may retain its orientation even after the starfish is removed 

 from water and held inverted for two minutes* This procedure causes 

 the retraction of the tube feet (in Pisaster) and the droping of 

 the arms aborally* vhen put back in the dish of sea water, the 

 animal usually walks in nearly the same direction as before, Thii 

 persistence of direction and the fact that the tube feot are quite 

 retracted after each step, indicates that the mechanism of retrac- 

 tion and extension, of which as we h*ve seen, the step reflex is ft 

 modification, is, perhaps, in no way dependent upon or implicated 

 in the mechanism of orientation* The only point of contact of these 

 two mechanisms is the fact that they both act upon the tube foot* 

 In the locomotor state then oveiy tube foot is oriented, whether it 



*t 



be retracted or not, but retracting and extending in such tube feet 

 are accomplished usually as parts of the step reflex* 



B3HAKING UP TMS SoORPlffATidD BiPUL^ INTft 

 AR^AS IN WHICH ms TUM RCST A!f 

 IN 



Perhaps the most puzzling thing about the unified impulse 

 is the fact that under certain conditions it may be broken up so 

 that it may exist in only a part of the starfish, or tube feet of 

 different parts of the animal became orientsd in different direc- 

 tions* 



Adap j tj.T; j ene j a. j s 



In case of some types (Jennings 1907) of the righting 

 reaction, and in going around an obstacle this orienting of 



