194 



BEHAVIOR OF THE LOWER ORGANISMS 



It is clear that the reaction is directed toward getting the organism 

 into its usual position, which might perhaps be called the "normal" one; 

 this normal position has various factors, — attachment of foot, freedom 

 of head, comparative straightness of the body, and tentacles outspread. 



This is, of course, exactly the 

 position which is most favorable 

 for obtaining food. 



Suppose now that our Hydra 

 has reached this position, and 

 all the conditions remain con- 

 stant ; is this sufficient ? We 

 find that it is not. If the con- 

 ditions remain so constant that 

 no food is obtained, the Hvdra 

 becomes restless and changes the 

 position of its body repeatedly, 

 though still retaining its attach- 

 ment by the foot. But later 

 even this is given up, and the 

 animal, of its own internal im- 

 pulse, quite reverses the position 

 attained through the "righting 

 reaction." It now bends its 

 body, attaches its head, and re- 

 leases its foot, thus bringing it 

 back into the inverted position. 

 Is this because the irritability 



Fig. 121.— Process by which Cerianthus rights of nead ail 1 foot have become 

 itself when inverted in a tube. The figures are taken reversed, SO that the head now 

 at intervals during the course of one hour. After , . , , , 



Loeb (1891). tends to remain attached, the 



foot free? Apparently not, for 

 no sooner has the organism taken the inverted position than it draws 

 its foot forward and now performs the "righting reaction" again, so that 

 it stands once more on its foot. These alternations of behavior are 

 repeated, and we find that by this means the animal is moving from 

 place to place, as in Fig. 117. 



It seems clearly impossible to refer each of these acts or the whole 

 behavior to any particular present external stimulus. Through hunger 

 the Hydra is driven to move to another region, and these different oppo- 

 site acts are the means by which another region is reached. Each step 

 in the behavior is partly determined by the preceding step, partly by 

 the general condition of hunger. The same behavior is often seen^ as 



