146 MODIFICATIONS OP BEHAVIOR 



Aiptasia when a drop of water falls on its disk suddenly 

 contracts. To several subsequent drops there is no further 

 response. Then if the drops continue to fall the animal 

 contracts still further and draws in its disk. If stimulated 

 lightly by a rod the anemone contracts strongly. If, when 

 it subsequently extends, it is again stimulated it responds in 

 the same way, and continues to do so during a number of 

 trials. Finally the anemone as it extends bends over in a 

 new direction, and if the stimulus persists this reaction is 

 repeated several times; then another direction of extension 

 is tried and finally if the stimulus is not avoided the animal 

 releases its foothold and crawls into a new locality. 



Anemones have various methods of getting rid of foreign 

 bodies on the disk, or even morsels of food, if much food has 

 already been taken. The procedure in Stoichactis as 

 described by Jennings is as follows: "The tentacles bearing 

 the debris or the rejected food body collapse, becoming thin 

 and slender, and lying flat against the disk. At the same time 

 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 though under usual conditions they 

 form a close investment almost completely hiding the surface 

 of the disk. Thus the waste mass is fully exposed to the 

 action of waves or currents, and the slightest disturbance 

 in the water washes it off. Under natural conditions this 

 must usually result in an immediate removal of the debris. 

 If this does not occur at once, often the region on which 

 the debris is resting begins to swell, and becomes a strongly 

 convex, smooth elevation, thus rendering the washing away 

 of the mass still easier. 



" But the process may go much farther. If the debris is 

 not removed in the way just described, new reactions set in. 



