Modifiability in Behavior. 469 



removed for a long time from the influence of the tides, this alter- 

 nation of reactions to gravity ceases, showing it to be a true habit, 

 resulting from individual experience. Many other instances oi 

 reactions to gravity, of the most diverse sorts and variable charac- 

 ter, could be given. Gravity affects organisms in many diverse 

 ways — determining the distribution of internal substances of dif- 

 fering specific gravity, causing differences in the ease of move- 

 ments in diverse directions, inducing strains or pressure in unac- 

 customed parts of the body when an unusual position is taken — 

 indeed, influencing the life processes in almost every detail. Any 

 of the points at which it comes in contact with the life processes 

 may serve as the basis for a reaction, so that we find behavior 

 induced by relations to gravity in different organisms to be of the 

 most diverse character. We have been assured by various writers 

 that the reaction to gravity must be explained in the same way in 

 all cases, but this is evidently said rather in the capacity of a seer 

 or prophet, than in the capacity of a man of science whose con- 

 clusions are inductions from observation and experiment. 



Returning to Cerianthus, we find, according to Loeb, that even 

 the usual position in line with gravity and with sides in contact, 

 does not satisfy the animal indefinitely, if left quite undisturbed. 

 If it secures no food it again leaves its place and seeks another region. 



Thus in order that Cerianthus may remain quiet in a given 

 position, a considerable number of conditions should be fulfilled, 

 constituting the usual, and perhaps what we may call the "normal" 

 state of affairs for this animal. These conditions are the following: 

 (i) The foot should be in contact; (2) the head should be free; 

 (3) the body should be straight; (4) the axis of the body should 

 be in line with gravity, with the head above; (5) the general body 

 surface should be in contact; (6) food should be received at inter- 

 vals. If these conditions are largely unfulfilled, the animal 

 becomes restless, moves about, and finds a new position. But no 

 one of these conditions is an absolute requirement at all times, 

 unless it be that of having the head free. In the wire screen the 

 animal remains for a day or two in the required position with 

 reference to gravity, even though foot and body surface are not in 

 contact. In the horizontal tube it remains with foot and surface 

 in contact, though the body is not straight nor in line with gravity. 

 If all conditions are fulfilled save that of food, the animal remains 

 for a time, then moves away. 



