464 H . S. 'Jennings. 



animals. If the food reaction were an invariable reflex, occurring 

 whenever food is present, without regard to internal conditions, 

 the results would be disastrous. The fact that the very hungry 

 animal will take indiff^erent bodies that would otherwise be 

 rejected is of course likewise adaptive; as Torrey ('04) remarks 

 "substances with a very small food value must be of some impor- 

 tance to a starving polyp although they would not be desirable as 

 food to a well nourished animal." 



The tendency of Aiptasia to remain in the dark and to contract 

 when strongly lighted keeps it in the crevices where it finds pro- 

 tection for its soft body. The fact that it faces and bends toward 

 the lighted side keeps its tentacles and disk directed toward the 

 entrance to the crevice, where food may be captured; if they were 

 directed toward the darkest part of the crevice little or no food 

 would be obtained. While the contraction under light is protec- 

 tive, it would result, if continued indefinitely by a lighted polyp, 

 in starvation; we find that after a considerable period of light the 

 animal extends. In correlation with its life in irregular crevices 

 or under stones we find that Aiptasia does not take any definite 

 position with reference to gravity, as some other anemones do. 

 Such a reaction would render its usual habitat impossible. The 

 tendency to react by a quick contraction when there is a slight dis- 

 turbance in the water is undoubtedly protective. Yet such a dis- 

 turbance when not' followed by an attack from its author is not 

 harmful and the animal under such circumstances quickly resumes 

 its usual behavior, even though the disturbance continues. But 

 such a disturbance maintained indefinitely would result in loss of 

 opportunity for obtaining food, and the animal after a time 

 shrinks gradually away from such a disturbed region. Injurious 

 stimuli, interfering with the natural physiological processes of the 

 polyp, cause contraction — the animal withdrawing from the field 

 of action for a time. But this continued indefinitely would result 

 in a loss of food and doubtless other injurious eff^ects. We find 

 that the animal has recourse then to extension in another direction, 

 and finally to creeping away and establishing itself elsewhere. 

 Located in an irregular crevice, we find that the polyp extends in 

 various directions, until it finds a direction in which its disk and 

 tentacles are unimpeded in their spreading to form a trap for prey. 

 It then continues to extend in this manner, even though this may 

 require the body to bend at right angles or to take other irregular 



