574 RAYMOND PEARL. 



the performance of any single set of activities in excess must 

 cause a corresponding diminution in other activities. This 

 is exactly what we find to be the case with the regenerating 

 planarian. While the processes concerned in regeneration 

 are at their masimiuu activity^ we get a decided reduction in 

 the amount of movement. It would seem, then, that a large 

 part of the energy which is ordinarily expended in movement 

 is used after operatiou or injury in the processes of regene- 

 ration. As the regeneration nears completion more and 

 more energy is available for, and used in movement. This 

 would seem to be a sort of "energy regulation." The 

 behaviour is evidently further beueficial in the case of the 

 posterior pieces, because their anterior ends are very insensi- 

 tive as compared with the head of the normal animal, and 

 if they moved about they would certainly be more apt 

 in the long run to get into difficulties than if they remained 

 quiet. 



It may be well in closing the section to point out the 

 relation of the nervous system to the movements. Loeb 

 (:00) has maintained that "if we divide a fresh-water 

 planarian, for instance Planaria torva, transversely, the 

 posterior half, that has no brain, crawls just as well as the 

 oral half. Spontaneity in Planaria torva is, therefore, by 

 no means a function of the brain." If by "crawl" in the 

 first sentence we understand "glide" to be meant, the state- 

 ment is not strictly accurate. The posterior pieces do not 

 "move just as well as the oral" (anterior), but, as has 

 already been brought out, more slowly. For a very short 

 time after the operation the statement would in some cases 

 be correct, but it certainly would not be twenty-four hours 

 later, according to all the observations I have been able to 

 make on the subject. As for the spontaneity of the move- 

 ment, that also becomes very much lowered with the loss of 

 the brain, as I have attempted to show above. The very 

 much lessened activity of posterior pieces of planarians has 

 been mentioned by Lillie (: 01, pp. 182, loo). 



From my own observations it seems clear that the principal 



