MOVEMENTS OF TENTACLES IN ACTINIANS 101 



When an attached tentacle is gently touched on one side mid- 

 way its length, the tentacle as a whole contracts but without much 

 bending. If it is touched on the tip, the response is mostly a 

 terminal waving back and forth. If it is stimulated on one side 

 near the base, the contraction is chiefly basal and on the stimu- 

 lated side. These responses are reproduced quite clearly by 

 isolated tentacles. Thus the responses of the two classes of 

 tentacles to localized stimuli are strikingly similar. 



If a small amount of one per cent acetic acid is discharged on an 

 expanded severed tentacle, the tentacle contracts quickly with 

 a curious appearance as though it were withering. After it has 

 been washed with seawater, it will expand again in about three 

 to four minutes. A second and a third response have been 

 elicited from such tentacles and these responses reproduce most 

 strikingly the movements of attached tentacles. To a tenth 

 per cent acetic acid both classes of tentacles showed a slight 

 local shortening. To a hundredth per cent they responded by a 

 slight curving. To a thousandth per cent neither kind of ten- 

 tacle showed any response whatever as was also the case when 

 pure seawater was discharged on them from a pipette. 



In none of my experiments on Condylactis did I get evidence 

 of a specific contraction of the circular muscle fibers to stimula- 

 tion by very weak acetic acid as von Uexkiill ('09) found for 

 Anemonia. 



To rain water discharged on the tentacles from a small pipette, 

 no noticeable response was made by either class, but to seawater 

 containing the juice from a crushed mussel the attached tentacle 

 exhibited active writhings often accompanied by elongation." It 

 was remarkable how strikingly similar to these were the re- 

 sponses of the isolated tentacles to the same juice. 



To a one per cent solution of quinine hydrochloride in rain 

 water both classes of tentacles responded by quick contractions 

 and often local constrictions. The solution was applied by a 

 pipette to limited areas on the outside of the tentacles. 



In all the tentacular reactions studied the responses of the 

 isolated tentacles agreed most strikingly with those of the nor- 

 mally attached tentacles. Of course the reactions of the iso- 



