202 BEHAVIOR OF THE LOWER ORGANISMS 



including even a region directly opposite that stimulated. The manu- 

 brium, having reacted once, does not cease, but in some way recognizes 

 its failure and tries again. In other words, failure changes its physio- 

 logical state, so that now it bends in a new direction. The whole 

 account given by Romanes is as vivid a description of the method of 

 reaction by the production of varied movements subjecting the organism 

 successively to different conditions, as it would be possible to imagine 

 under these circumstances. 



It would be most interesting to determine whether the animal may 

 thus by trial finally discover the irritated spot, and later through repeti- 

 tion come to bend toward it directly, as it did before the cut was made. 



5. THE REJECTING REACTION OF SEA ANEMONES 



In some sea anemones the presence of masses of waste matter on 

 the disk leads to the performance of activities which result in the re- 

 moval of the waste matter ; this behavior we may call the rejecting reac- 

 tion. Such behavior is well seen in the large sea anemone Stoichactis 

 helianthus, found in the West Indies. This animal has a flat or concave 

 disk 10 to 15 cm. in diameter, covered closely with tentacles about 

 8 mm. in length. If a quantity of dead plankton, or a mass of sand, 

 or other waste matter, is placed on the disk, the animal sets in opera- 

 tion measures which remove it. Food placed on the disk of a speci- 

 men that is not hungry produces the same result. The behavior under 

 such circumstances is complex, and the removal of the waste matter 

 may be accomplished in more than one way. 



The tentacles of that region of the disk bearing the waste body col- 

 lapse, becoming thin and slender and lying flat against the disk. The 

 disk surface in this region begins to stretch, separating the collapsed 

 tentacles widely. As a result the waste mass is left on a smooth, exposed 

 surface, the tentacles here having practically disappeared, while else- 

 where they form a close investment. Thus the waste is left fully ex- 

 posed to the action of the waves or currents, and the slightest disturbance 

 in the water washes it off. Under natural conditions this must result 

 in an immediate removal of the mass of debris. If this does not occur 

 at once, often the region on which the debris is resting begins to swell, 

 becoming a strongly convex, smooth elevation, thus rendering the wash- 

 ing away of the mass still easier. 



But if the debris is not removed by the reaction just described, then 

 new activities set in. If the waste body is near one edge of the disk, 

 this edge usually begins to sink, while at the same time the tentacles be- 

 tween the edge and the waste mass collapse and practically efface them- 



