Sensory reactions of Holothuria surinamensis. 263 



îind they were much more readily exhausted, two or three reactions 

 being all that could be obtained from the tentacles. This exhaustion 

 might be due either to a condition of prompter muscular fatigue, 

 •caused by the removal or damage of tonus centers, or to the more 

 rapid using up of photoreceptive materials in the mutilated animals. 

 The latter possibility is important, because the interference with 

 the circulatory apparatus tends to make reconstructive processes 

 slow; hence to produce equivalent reactions a higher intensity 

 •of light ^) had to be used with these decapitated individuals than 

 with normal holothurians. The greater length of time consumed in 

 the responses of mutilated individuals may have been quite as much 

 due to the damaged state of the ambulacral system as to the loss 

 of muscular tone. Stimulation of the body surface near the new 

 -anterior termination, or at the posterior end, produced a contraction 

 tending, as with normal holothurians, to bend the stimulated part 

 away from the light. 



A strictly dorsal stimulus produced one of two eifects, — 

 (1) a general shortening of the region affected, or (2) a turning 

 of that part to the right or left, the frequency of the turns in 

 either direction depending on the direction and extent of the 

 •curvature of the, animals body as it rested on the bottom of the 

 aquarium. Usually — in 20 out of 25 trials — the response was 

 .such as to increase the established curvature. 



Orientation under the influence of light from a single source 

 was examined in a dark chamber consisting of a large wooden box, 

 light-tight, painted dead black, inside, and provided at one end with 

 adjustable diaphragms through which sunlight reflected from a mirror, 

 •or light from an artificial source, was allowed to enter. Glass 

 ■aquaria containing the holothurians were placed within this dark 

 box. A narrow slit at the top of the box, at the end opposite from 

 the diaphragm, served as the observation window; when used in a 

 ■dark room, the whole top of the box could be removed without 

 interfering with the conditions of the experiment. 



Exp. 61,1. July 12. 



a) A narrow beam of horizontal light thrcfwn on the tentacles and 

 brim from one side. Result: first, a slight forward movement, then a 

 sharp turning back. When the tentacles first came into the light, they 

 contracted, hut not completely. Other animals moved straight ahead into 



1) That is, the source of light had to be brought nearer. 

 Zool. Jahrb. XXXV. Abt. f. allg. Zool. u. Physiol. 18 



