264 W. J. Chozier, 



the dark region ; this latter result was obtained when the beam of light 

 was so narrow that the forward extension of the anterior end carried the 

 tentacles out of its path. The usual result of these tests was that^ 

 after some preliminary extension of the anterior end , it was swung 

 sharply away from the lighted side; following this, contraction of the 

 longitudinal muscles in some cases brought the whole animal out of the 

 path of the light, while in others locomotion in the direction of the 

 anterior end led to crawling along the path of the light beam. In this 

 latter form of response, any tendency to enter the shadow was checked 

 by the prompt retraction of the tentacles and the customary "avoidance 

 reaction" when the tentacles were shaded, even by the animal's own body. 

 Tests in which the light was limited to the brim region, the tentacles 

 being in the shade, gave identical results. 



b) When unilateral light was allowed to fall on the mid-body region, 

 holothurians moved straight ahead into the dark. There was no perceptible 

 orientation until the light struck the most posterior centimeter and a half 

 of the body, which was then turned away from the light, but the direction 

 of locomotion was not affected. "When so illuminated that several centi- 

 meters of the tentacle end were shaded , the same result was obtained 

 — forward motion without orientation. 



c) Unilateral illumination of the posterior tip caused it to be thrown 

 sharply away from the light, but in a manner indicating, both by the 

 reaction time and the amplitude of the reaction, that the posterior end 

 was less sensitive than the anterior one. 



In all these experiments the illuminated region appeared to be 

 locally constricted — a result to be expected from the previous 

 tests with a spot light. 



Exp. 61,2—62,1. 



Horizontal light parallel to the long axis of the body was thrown on 

 the anterior end. Result: a contraction of the longitudinal muscles, greater 

 on one side than on the other, such that subsequent forward locomotion, 

 carried the animals outside the field of stimulation. 



Exp. 62,4. 



Five holothurians deprived of the tentacles and ring structures did 

 not move about to any extent until a regeneration cone had made its 

 appearance. Such animals were just as strongly negatively phototropic as 

 normal ones. 



Placed in a field of light coming from one side only, the reaction 

 uniformly obtained from Holofhuria was a turning of the anterior end. 

 away from the side illuminated, and continued locomotion away from 

 the source of light in the direction of its rays. 



Holothiiria surinamensis is therefore without question negativeljr 

 phototropic. 



