Modifiability m Behavior. 467 



evidently partly determined by the fact that a certain other phase 

 has just been performed, partly by the general state of hunger. 

 The same behavior is shown by Hydra under continued injurious 

 stimuli of different sorts. 



In speaking of righting reactions, it is often said that the 

 organism is forced by the different irritabilities of diverse parts of 

 the body to take a certain orientation with reference to gravity or 

 to the surface of contact (see for example Loeb, 1900, p. 184). 

 The facts just brought out (taken from Wagner) show that we 

 cannot in Hydra consider this orientation forced, save in the general 

 sense that all things which occur may be considered forced — 

 including of course the behavior of man. Man takes sometimes a 

 sitting position, sometimes a standing one, sometimes a reclining 

 one, depending upon his "physiological state" and past history, 

 and the facts are quite parallel for Hydra. So far as objective 

 evidence shows, the behavior is not forced in Hydra in any other 

 sense than it is in man. Both organisms take that position which 

 seems best adapted to the requirements of their physiological 

 processes; these requirements vary from time to time. 



In the sea anemone Cerianthus the conditions for staying in a 

 certain position are somewhat more complex than in Hydra, accord- 

 ing to the account given by Loeb (1891). Cerianthus is usually 

 found in an upright position, inhabiting a tube made of mucus and 

 imbedded in the sand. If placed head downward in a test tube, 

 it rights itself in the same way as Hydra and Aiptasia, freeing the 

 head, bringing the foot into contact, and straightening the body. 

 But in Cerianthus Loeb showed clearly that gravity plays a part 

 in the behavior. If the animal is placed on its side on a wire 

 screen of large mesh, it bends its foot down through the meshes, 

 lifts up its head, and takes its usual position with reference 

 to gravity. If now the screen is turned over, the animal again 

 directs its head upward, its foot downward — as a human being 

 under similar circumstances would do if possible. It may thus 

 weave itself in and out through the meshes. 



But to be in line w^ith gravity, with head above and free, is not 

 the only requirement for Cerianthus. Loeb found that it wpuld 

 not remain indefinitely in this position on the wire screen, as it 

 does in the sand. After a day or so it pulls its foot out of the wire 

 and seeks a new abode. Only when it can get the surface of the 

 body in contact with something, as is the case when it is imbedded 



