460 H. S. Jennings. 



disk has been withdrawn some distance below the surface, though 

 no decided reaction has occurred to any one stimulus. These 

 facts are precisely parallel to those which I have described in a 

 previous paper (1902, p. 50) for the infusorian Stentor. 



More marked changes result when the animal is stimulated by 

 light strokes of a rod. At the first stroke on the disk Aiptasia 

 contracts strongly. It then extends in the same direction as 

 before. When it is fully extended the stimulus is repeated. The 

 animal responds in the same way as at first. This is usually con- 

 tinued for about ten or fifteen stimulations, the animal each time 

 extending in the same direction as at first. But at length, when 

 stimulated anew, the animal contracts, bends over to one side, 

 and extends in a new direction. Under natural conditions, where 

 stimulation at every extension would usually be due to some fixed 

 object, this would of course put an end to the series of stimuli. If, 

 however, the stimuli are still continued after each extension, the 

 animal repeats for a number of times the extension in the new 

 direction, then finally turns again and tries a new position. 



This may be repeated many times. But in the course of time 

 the reaction becomes changed in a still different manner. The 

 anemone releases its foothold and moves to a new region. This 

 result I have not succeeded in attaining by striking the animal 

 with a rod each time it extends; the time required is evidently 

 to be measured in hours. But obstructions may be so placed 

 that every time the animal extends, the disk strikes against a solid 

 body. In such a case it is usually found after a few hours that 

 the animal has moved to a new region. 



Thus to the same stimulus when repeated many times the 

 anemone reacts first by contraction, then by turning repeatedly 

 into new positions, then by moving away. The phenomena are 

 parallel to those described by the present author ('02) for the 

 infusorian Stentor, and by Wagner ('05) for Hydra. Beyond 

 doubt other stimuli would here, as in Hydra and Stentor, produce 

 the same series of reactions. 



In the behavior just described there are at times certain phe- 

 nomena which bear a striking resemblance to the formation of new 

 habits. Aiptasia annulata frequently extends its body in most 

 awkward turns, the column retaining an irregular and crooked 

 form. This is evidently due to its method of life. The animal 

 lives in irregular crevices and crannies beneath stones or in the 



