loo C. M. Child. 



the part which it represents new conditions of pressure and ten- 

 sion arise as well as powerful nervous stimuli which probably 

 affect growth and differentiation directly or indirectly. 



When for instance the posterior part of the body of one of 

 these worms is removed the animal continues to move about and 

 " attempts " to carry out the same movements as when the pos- 

 terior end was present, but in the absence of the parts the move- 

 ments fail more or less completely of success. In fact observation 

 of these cases leads me to believe that in the absence of the part 

 the attempts to attain the usual result are often more powerful 

 than when it is present. For example, a specimen of Leptoplana 

 with the tail removed makes violent attempts to hold to the 

 substratum by the cut posterior end of the body as well as by 

 other parts; a specimen with the lateral lobes of the head removed 

 makes violent but unsuccessful attempts to swim; and finally, to 

 take another case somewhat removed from the present considera- 

 tions, a fish with the tail or part of it removed uses the remaining 

 stump much more vigorously than would be the case if the whole 

 were present. 



It may appear at first glance that these statements involve 

 unwarranted assumptions regarding the psychological activities of 

 forms as low in the scale as the Turbellaria, but I believe such a 

 conclusion is not justified. Conscious recognition of the successful 

 or unsuccessful character of the movement is by no means neces- 

 sary, but on the other hand it is diflicult to understand how these 

 creeping worms could advance in a regular, definite manner if 

 the movement over the substratum or the movement of the parts 

 of the body upon each other did not afford certain characteristic 

 stimuli. The movements of these forms as well as those of higher 

 animals are coordinated, and for coordination some stimulus re- 

 resulting from the movement seems to be necessary. Removal of 

 a part, e. g., the posterior end by which the animal has been ac- 

 customed to attach itself, must bring about a change in the rela- 

 tion of the various stimuli. The animals behave in such cases 

 as if they were moving over surfaces to which their bodies do 

 not adhere readily. They appear to make violent efforts to use 

 the parts which are'missing. These changes in behavior are dis- 



