Modifiahihtv m Behavior. 465 



forms. It continues to extend in this manner even when removed 

 from its irregular crevice, and the body is found to have become 

 structurally modified, so that a collection of Aiptasias shows many 

 crooked and zigzag shapes, each being an adaptation to the crevice 

 in which the animal lived. The formation of such habitual 

 methods of extension can be imitated and modified in the labora- 

 tory. 



All together, the activities and their modifications are clearly 

 such as to directly adjust the organism to its environment, enabling 

 the physiological processes to continue under all sorts of conditions. 

 It has become the fashion to neglect such facts, but they fairly 

 force themselves on the attention of the careful student of the 

 behavior, and their existence can hardly be held to be accidental. 

 To remove such an organism to the artificial conditions of the 

 laboratory and then endeavor to understand its behavior is like 

 dissecting an internal organ out of the body and trying to under- 

 stand its functions when thus separated from the other structures 

 with which it interacts. Almost everything the animal does has a 

 direct relation to something in its usual environment, and when 

 cut off from this environment, its activities are likely to become 

 unintelligible. One can hardly resist the belief that the fact that 

 these activities do assist the physiological processes of the organ- 

 isms has determined their selection and retention from among 

 other possible activities. "^ 



This adaptation and adaptive modifiability of behavior in sea 

 anemones and their relatives has not been explicitly set forth in 

 most works dealing with their reactions. Yet when other careful 

 accounts of behavior in such organisms are analyzed we can dis- 

 cover such relations as clearly as in Aiptasia. Let us look for 

 example at the cases of Hydra, studied by Wagner ('05), and of 

 Cerianthus, as described in the classical papers of Loeb ('91). 

 It will be found instructive to consider the conditions on which 

 the retention of a certain position depends. Hydra and the sea 

 anemones tend as a rule to retain a position at rest, with the foot 

 attached and head free. This usual position is often said to be 

 due to a reaction to gravity, or to contact, or to some other simple 

 stimulus. But when we examine into the matter closely, we find 

 that it IS not an entirely simple one. Let us take first the case of 

 Hydra. Suppose the animal is placed on a horizontal surface 

 with head downward and foot upward. It does" not retain this 



