6- 



Direotipn oj[ extension 



The extension is conditioned in direction by the looomotor 

 activity of the animal as a whole. If the starfish is/ uigra ting 

 in the direction f a certain arm, for instance, the tube feet 

 will, in the absence of contact stimulation extend themselves 

 in this direction, and remain so extended until stimulated 

 either to retract or execute the step reflex. 



In the stationary, non-rigid starfish the tube feet of 

 the outer part of the ray are, in the absence of contact simulation, 

 extended more or less toward the tip of the ray and ant moving 

 (feeling") about in that direction* This of course is not 

 constant and is laost noticeable in the most active specimens. 



Starfish that are inactive or in the rigid state do not 

 extend the tube feet as much as do individuals of the active 

 non-loooaotor type. Vhe most noticeable difference between the 

 behavior of the tafcaartocxxocfxtloi tube feet of such a starfish 



and those of a normally active one is that the former are not 



avyy 

 directed <n*t from the tips of the rays* They may be waving 



about approximately at right angles to the ray or even direc- 

 ted somewhat toward the center. 



The mechanism of extension, first described by Heamur 

 (1910) in a very interesting paper is well known. It involves 

 a contraction of the aabulacral ampulla and a relaxation of the 

 longitudinal musculature of the tube foot* To ascertain the 

 dependence of this relaxation of the longitudinal musculature 

 on the radial nervous system, tube fe ;t were cut off and tied 

 on to the end of a capillary glass tube* This was connected with 

 a column of sea -water arranged so that the pressure could be 



