Behavior and Form 167 



activities impressed upon the regenerating part are 

 regarded as the directive agents in the process of dif- 

 ferentiation, and if the animal were to act in a very 

 different manner quite different formative processes 

 would result. 



Child found that in pieces of Leptoplana which 

 were caused to creep in a circular course owing to 

 unilateral injury of the anterior end the new tail 

 that was formed, instead of growing out posteriorly, 

 developed in an oblique position in accordance with 

 the altered activity. "The regenerating part grows 

 in the direction of the principal tension, even though 

 this forms an angle of 90° with the principal direc- 

 tion of growth." In speaking of the ordinary activi- 

 ties of Leptoplana, Child says: "It can scarcely be 

 doubted that these movements play a part in shap- 

 ing the regions in which they occur. A comparison 

 between frequency, amplitude, and force of the un- 

 dulating movements and the degree of lateral de- 

 velopment in the regions in which they occur is most 

 striking. According to the usual point of view, this 

 correlation between structure and function is merely 

 one of the many remarkable cases of adaptation, 

 but in my opinion it is, at least in part, the direct 

 result of function in the individual. . . . 



"As regards the manner in which the movement 

 may affect the tissues it is not difficult to see that 

 the movement of these parts to and fro through 

 the water must subject them to tension in the lat- 

 eral direction. This must affect in greater or less 



