MOVEMENTS OF TENTACLES IN ACTINIANS 97 



strictions are the first step in a process of tentacular autotomy 

 that seems to be characteristic of Condylactis. 



In an experimental study of the tentacles, it is necessry among 

 other things to cut off the tentacles from the body of the polyp 

 and to study them thus isolated. When a tentacle is treated in 

 this manner, it contracts, as already stated, to about one-third its 

 former length and it will remain in this condition alive in sea- 

 water many days. At the moment the connection of the tenta- 

 cle with the actinian's body is severed its fluid content in part 

 escapes and water flows out of the polyp from the hole left on the 

 stump, thus showing that the tentacle as well as the animal 

 is distended under slight pressure. It might, therefore be as- 

 sumed that the full expansion of the tentacle was due to this 

 slight pressure and that, when the tentacle was cut off, the par- 

 tial contraction that followed was due to the release of the ten- 

 tacle from internal pressure. 



To test this hypothesis a tentacle, after having been cut off 

 from the polyp and allowed to come to as full distension as it 

 would, was tied to the end of a glass tube preparatory to distending 

 it further with sea water. On binding it to the tube it contracted 

 vigorously to only a small fraction of its former length and re- 

 mained thus for hours. Sea- water was finally run into it through 

 the attached tube and when this water stood at a height of 8 to 

 10 cm. in the tube, the tentacle without expanding began to 

 allow the contained fluid to escape through its terminal pore. 

 This was then tied off and the pressure in the tentacle was in- 

 creased by running more water into the tube. At about 14 to 

 15 cm. of pressure the tentacle without having expanded rup- 

 tured on the side and with the escape of the water it contracted 

 completely. During all of this experiment the tentacle was rigid 

 and tight and very unlike the normal tentacle, which when 

 touched gently or moved by water currents is evidently under 

 internal pressure but pressure of only a very slight amount, prob- 

 ably not more than that of a few millimeters of water. It is 

 clear from these observations that the pressure of sea-water as 

 applied in this experiment is not a means of restoring a severed 

 tentacle to a normal state and that the further contraction that 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 22, NO. 1 



