2o6 BEHAVIOR OF THE LOWER ORGANISMS 



Sea Anemones. — In some sea anemones, as in Hydra, repeated 

 strong stimulation causes the animal first to contract, then to bend into 

 new positions, and finally to move away. Each of these reactions may 

 be repeated several times before the succeeding one occurs. There are 

 certain features of this behavior that are of much interest, since they lead 

 to results analogous to habit formation in higher animals. The facts 

 have been most carefully studied in Aiptasia annulata. 



Aiptasia is a rather slender, somewhat elongated actinian living in 

 crevices beneath and between stones. If stimulated by touching the 

 disk or tentacles with a rod, it contracts strongly. It then extends in 

 the same direction as before. When it is fully extended we repeat the 

 stimulus. The animal responds in the same way as at first. This con- 

 tinues usually for about ten or fifteen stimulations, the animal extending 

 each time in the same direction as at first. But at length, when stimu- 

 lated anew, the polyp contracts, bends over to one side, and extends in 

 a new direction. As the stimuH are continued, the animal repeats for a 

 number of times the contraction and extension in the new direction, 

 then finally turns and tries a still different position. 



This change of position 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 

 same reaction is produced in Cerianthus, as we have seen, by hunger. 



Aiptasia frequently extends in most awkward turns, the body taking 

 and retaining an irregular and even crooked form. This is evidently 

 due to its hfe in irregular crevices and crannies. In order that its disk 

 may protrude into the open water, it is compelled to extend in the irreg- 

 ular ways mentioned, and to retain the crooked shapes thus produced. 

 When removed from its natural habitat, it still retains these irregulari- 

 ties of form and action, so that a collection of Aiptasias shows all sorts 

 of right-angled and zigzag shapes. It would appear that these irregu- 

 larities must have arisen as a result of the way in which the animal 

 extends in its natural surroundings. From this it would appear that a 

 method of extension frequently repeated must in the course of time 

 become stereotyped, forming what we are accustomed to call in higher 

 animals a habit. 



If this is the case, then it should be possible to produce new stereo- 

 typed reaction forms, by so arranging the conditions that the animal 

 shall be compelled to extend always in a certain way (differing from 

 its former way), and to retain the form thus induced. In some speci- 

 mens this result is obtained with the greatest ease, and in a very simple 

 manner. Thus, in a certain case, an individual attached to a plane 

 horizontal glass surface was bent in extension far over to the left. Stimu- 



