-16 



ex tend themselves out toward the temporary anterior and 

 then lash back vigorously in the opposite direction, exactly 

 parallel with e-ich other* 



The true significance of this is aean if the tube feet 

 of a part of such a starfish be submerged. Then only those 

 tube feet that touoh the surface film of the water, or those 

 entirely exposed to the air execute the step reflem. The 

 submerged tube feet remain pointed in the direction of the 

 temporary anterior until .some- contact stimulation, from the 

 surface film or from some solid object initiates the 

 step refles. 



^hat factors govern tiie orientation oJT the, step reflex? 



The first phase of the reaction, the extension of the 

 tube foot is a function of the physiological orientation of 

 the starfish* This will be analy ed further elsewhere* Now 

 if the lashing bac> is to be effective in locomotion, it must 

 take place (as it does) in the opposite direction from the 

 extension. This, however, merely shows that the response is 

 adaptive and is not a physiological explanation* A physiological 

 explanation may be looted for in the location of the oontaot 

 stimulation on the disc of the tube foot or in the condition 

 of tension in the musculature of the column* The tube foot 

 as it extends may be seen often* tho^not always * to touch 

 the substrate first with the poi^fMMtflfe* ** mi y be 



X. 





expected that exitation to oonw^w. _ ontaot 



stimulus might spread to the side of the column 1*3 and cause 

 its contraction more quickly than to the side 2-4* Furthermore 

 a contact stimulus at the place 2 does not elicit the step 



