Sensory reactions of Holothnria surinamensis. 283 



bent toward the stream of solution coming from a pipette. Tannic 

 acid, potassium lij^droxide, and digatilin, in fairly concentrated solu- 

 tions, produced negative reactions of a type not found in connection 

 with any other stimulus. In one curious reflex the anterior and 

 posterior ends were bent slightly toward each other, and the animal 

 rolled over completely, away from the side stimulated. Tannic acid 

 (M/10) stimulated the posterior end so strongly as to cause it to be 

 turned from side to side for three or four times. Hydrogen per- 

 oxide in 37o solution (approximately M/1), and in dilutions down to 

 0,757o> stimulated all parts of Holotlmria's surface so long as bubbles 

 of oxygen appeared on the part bathed by the solution. This test 

 indicates the presence of catalase in the surface integument of 

 HolotJmria, which I believe may be concerned in the production, or 

 destruction, of pigment materials. The solution of AgOg used con- 

 tained a small amount of acetanilid (as a preservative), but when 

 the H2O2 had been destroyed by boiling, and the solution reaerated, 

 no reactions were given to it ; therefore the acetanilid (not destroyed 

 by boiling) was not concerned in the stimulation. 



The effects of sufficiently intense stimuli were rapidly carried 

 anteriorly and posteriorly from points in the mid-region; a good 

 instance of this was seen in the effect of tannic acid solutions, 

 where the anterior and posterior ends of the animals would close 

 up and turn away from the side stimulated before the appearance 

 of an insinking of the body-wall at the {Joint of stimulation. 



No new facts were brought to light by experiments with muti- 

 lated animals. As with tactile and photic stimuli, reactiveness was 

 lower in holothurians with the nerve ring and its associated struc- 

 tures amputated, the region nearest the cut being especially in- 

 sensitive. 



The very slightly soluble materials used were: ethyl ether, 

 chloroform, xylol, clove oil, oil of Bergamot and oil of origanum. 

 Tentacles, brim, and cloacal termination reacted to drops of these 

 substances held at the tip of a pipette at a distance of two centi- 

 meters from them. The pedicels, papillae, and body surface reacted 

 only when actually touched by a drop, sharp reactions then being 

 given. Sea water which has stood in contact with these substances 

 also produced a negative reaction. In all cases the order of re- 

 activeness of the several parts of the animal was the same as that 

 which has already been found for tactile and photic stimuli, namely: 

 tentacles > anterior end ) posterior end > podia ) mid-body surface. 



