146 MODIFICATIONS OF 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 débris or the rejected food body collapse, becoming thin 
and slender, and lying flat against thedisk. Atthesame 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 débris. 
If this does not occur at once, often the region on which 
the débris 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 débris is 
not removed in the way just described, new reactions set in, 
