NOTES ON SOME PROBLEMS OF ADAPTATION. IK) 



such rhythm exists. The behavior of different specimens is 

 anything but synchronous in the subsequent periods of opening 

 and closing, and there is no tidal periodicity evident, except 

 perhaps in the matter of remaining expanded for about three 

 hours after being immersed in water. But this interval is much 

 the same regardless of the period of antecedent exposure; for 

 specimens taken from the rock just after being left bare by the 

 receding water are in this respect indistinguishable from those 

 removed at the natural termination of the interval of exposure. 

 After a sea-anemone has contracted, in still water, it may remain 

 so for days, or it may after a time open "spontaneously." At 

 any time it may be caused to expand by a faint local agitation 

 of the water in its vicinity. In this behavior A. bermudensis 

 was very similar to Metridium as described by Parker ('17). 

 Sea-anemones attached to the rocks could always be caused to 

 open by splashing over them a small amount of water; in this 

 kind of response is to be seen the explanation of a sort of "antici- 

 patory" expansion sometimes seen on the shore, w r ave-dashed 

 droplets of spray being sufficient to induce some relaxation of the 

 column-sphincter before the animals are actually covered by the 

 sea. 



Young A. bermudensis "born" in the laboratory aquaria 

 exhibit precisely the same phenomena. In a group of six, one 

 or two individuals may be found at any time tightly contracted, 

 the others being in various degrees of expansion. But this 

 behavior is not synchronous. One such group was rather care- 

 fully watched at intervals during 3 weeks. No rhythm of 

 contraction was detectable in the individual behavior of these 

 animals. Nevertheless, if they be taken from the water for a 

 short time and then replaced, such young individuals promptly 

 open and remain extended for about as long as do the adults 

 under similar treatment, but after this they contract for variable 

 periods. 



Hence the rather fixed interval of expansion consequent upon 

 immersion in sea water, although it agrees fairly well with the 

 period of natural submergence, can hardly be ascribed to the 

 establishment of a tidal habit; for the young actinians inexperi- 

 enced in the matter of tides go through the same performance 



