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Recently Maxwell has shown that the reactions of sharks to contact stimuli are due to changes in the relative tension of the antagonist muscles similar to those taking place in the galvanotropic, heliotropic, and geotropic reactions of animals. 1 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 reaction~ of the starfish gain especial significance since they can be inhibited by the reaction to light. In order to demonstrate the stereotropic olffentation of the tube feet, the starfish is laid on its back in a dish of sea water. I f the animal 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 finger tip against the side of the ray, a retraction of the tube fe~t 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 excitation 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 tube 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

STEREOTROPIC ORIENTATION OF THE TUBE FEET OF STARFISH (ASTERIAS) AND ITS INHIBITION BY LIGHT