MOVEMENTS, KTO., OF FKESH-WATEK PLANAKIANS. 573 



nioveineut upon stimulation of the posterior end of either 

 piece, but in a peculiar way, whicli will be described later. 



Putting all these results together, we see that there is a 

 general tendency for animals on which operations have been 

 performed to glide at a slower rate than normal. In some 

 of the pieces this tendency is very slight, and frequently 

 hardly noticeable. In others the movement is very much 

 slower than normal. In all cases the periods of rest are 

 longer during the time of regeneration than normally. Tiiis 

 tendenc}^ for the animals to remain quiet during regenera- 

 tion increases up to a certain point as regeneration proceeds. 

 A piece of a planarian njay be quite active for three or four 

 hours after the operation, while during the following three 

 or four days it will scarcely move at all. After the regenera- 

 tion is practically complete the worm will begin to move about 

 again approximately as it normally does. During the re- 



JflG. 13. — Operation diagram. The heavy line indicates the cut made. 

 For results see text. 



generating process the anterior pieces, bearing an uninjured 

 head, are much more inclined to move about than are the 

 posterior parts. These latter usually remain entirely quiet 

 during regeneration. 



This behaviour of the posterior parts during regeneration 

 appears to be distinctly purposive, and to belong to the class 

 of phenomena called regulatory. The general tonus of these 

 pieces is immediately lowered by the operation, and conse- 

 quently they keep quiet. Yet at the same time the processes 

 of morphallaxis and, in many cases, growth begin at once, 

 and proceed very vigorously till the missing parts are 

 restored. If we consider that the worm or part of a worm 

 has at the beginning a certain sum-total of energy available 

 for all activities, including movement, growth, morphallaxis, 

 and all its other vital processes, then it would appear that 



VOL. 46, PART 4. NEW SKRIES. P P 



