Time 



Temp 



12:21,5 



30" 



12:25,5 



310 



12 : 30,5 



32« 



12: 37 



320 



12:43 



340 



Sensory reactions of Holothuria surinamensis. 271 



Exp. 38. July 5. 

 Heated in bright sunlight; 10 animals used. 



Observations 

 Shadow reaction normal. 



Tentacles not completely withdrawn when shaded. 

 Tentacles merely waved about gently when shaded. 

 Same. 

 No shadow reaction at 34" or above. 



With the rate of heatings employed in this experiment, then, 

 the shadow reaction disappears at about 33,5o C. In ascertaining 

 the lower temperature limit, holothurians were placed in beakers 

 surrounded by vessels containing cracked ice and salt. The shadow 

 reaction was in no case obtained below 5,0 ^ C, but the actual limiting 

 temperature in any one test was exceedingly difficult to place 

 accurately. 



It was found possible te abolish the shadow reflex by treating 

 the anterior end with a weak solution of cocaine, and, incidentally, 

 to separate in this way tho reactions to photic and to tactile and 

 chemical stimuli. 



Exp. 3. July 2. 



4,8 P.M. Three holothurians placed in 0,5^/^ cocaine hydrochloride 

 for 2 minutes. Tube feet and tentacles slowly retracted, then reexpanded. 

 Papillae retracted. Tentacles after 1 min. gave an exceedingly faint 

 response to shading from bright sunlight. 



4,10 P.M. Returned to seawater. 



4,12 P.M. Tentacles expanded. No shadow reaction perceptible. 

 Tentacles react normally to KCl (M/10), and also to tactile stimuli, but 

 slowly. 



Therefore it is reasonable to conclude that the function of 

 photoreception is exercised by a set of sensory elements distinct 

 from those for mechanical and chemical reception. 



The phenomena of the shadow reflex in Holothuria immediately 

 invite comparison with similar reactions exhibited by sea urchins 

 (von ÜEXKtJLL 1900) serpulids, leeches, barnacles, some lamellibranchs, 

 etc. (cf. Mast, 1911, p. 247, for review of literature). The curves 

 of reactiveness of Hydroids, Glossiphonia (Gee, 1913), Bdlanus 

 and Holothuria to repeated shadows all exhibit the characteristics 

 of rhythmicity and rapid exhaustion. Reactions of the common 

 Bermuda shore barnacle {Balanus sp.) to successive shadows are 

 shown, for comparison, in Table IX; the reactions here consist 



