STEREOTROPIC ORIENTATION OF THE TUBE FEET OF 

 STARFISH (ASTERIAS) AND ITS INHIBITION BY LIGHT.* 



By a. R. MOORE. 



(From the Physiological Laboratory of Rutgers College, New Brunswick, N. J.) 



(Received for publication, Sept. 19, 1921.) 



Recently Maxwell has shown that the reactions of sharks to con- 

 tact stimuli are due to changes in the relative tension of the antagonist 

 muscles similar to those taking place in the galvanotropic, helio- 

 tropic, and geotropic reactions of animals.^ The writer has recently 

 made observations on the starfish which show that contact stimuli 

 applied to the sides of a ray bring about changes in the orientation of 

 the tube feet which are comparable to heliotropic reactions. These 

 stereotropic reactions of the starfish gain especial significance since 

 they can be inhibited by the reaction to hght. 



In order to demonstrate the stereotropic orientation of the tube 

 feet, the starfish is laid on its back in a dish of sea water. If the ani- 

 mal is prevented from righting itself for 1 or 2 minutes it becomes 

 comparatively quiet; if now a contact stimulus is applied to one of 

 the rays by pressing a foreign body such as a piece of cork, a glass 

 rod, or a linger tip against the side of the ray, a retraction of the 

 tube feet and closure of the ambulacral groove occurs. Next, the 

 groove opens and the tube feet move toward the stimulated area. 

 The reaction is especially marked in the immediate vicinity of exci- 

 tation but in the more sensitive individuals it involves the entire ray. 

 The average length of time which elapses between the moment of 

 contact excitation and the protrusion of the tiibe feet is 2.8 seconds. 

 The contact stimulus may be applied momentarily and removed 

 before the reaction begins, but the series of reactions proceeds as 



* The experiments described in this paper were done in the Botany Labora- 

 tory at Woods Hole, and the writer wishes to express his thanks to Professor 

 Osterhout for many courtesies extended to him during the progress of the work. 



' Maxwell, S. S., /. Gen. Physiol., 1920-1921, iv, 19. von Ue.xkiill, J., Z. Biol., 

 1900, xxxix, 73. 



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