MOVKMENTS, ETC., OF FRESH-WATRR TLANArjAN?. 571 



If a planai-ian is cut scjiiai-ely across the body in tlie 

 I'egion a short distance behind the head, as indicated in 

 Fig. 9, the anterior piece will continue to move after tlie 

 operation at approximately the same rate as the whole 

 animal did before. After the immediate effect of the opera- 

 tion is past the glide is its ordinary movement, and it will go 

 al)out the dish and behave in general like a whole individual. 

 At the outstart its pei-iods of activity and rest are distributed 

 about as in a normal individual, or, in other words, its power 

 of spontaneous movement is not inipnired, at least for a time. 

 On the other hand, the posterior piece comparatively soon 

 comes to rest after the operation. Its gliding movement is 

 slower, and the periods of rest become longer and longer in 

 compai'ison with the periods of activity. Its power of spon- 

 taneous movement becomes very greatly diminished within a 

 comparatively short time after the operation, and it remains 



Fig. 10. — Diagrammatic side view of a decapitated specimen performing 

 the gliding movement. 



in the relaxed resting condition during the greater pnrt of 

 the time spent in the process of regeneration. When this 

 posterior piece does glide about soon after the operation its 

 anterior end is usually raised off the bottom considerabl}- 

 higher than is the head of a normal flat- worm under similar 

 circumstances. This is shown in Fig. 10. There are no 

 ''feeling" movements of the anterior end of such a piece, 

 but instead this end is held very stiffly in the raised position. 



If, instead of making the cut so close behind the head, it is 

 made back in the middle region of the body, the anterior 

 piece behaves as before, i. e. like the normal animal. The 

 posterior piece, however, moves slower thau did the corre- 

 sponding piece in the previous experiment, and it comes to 

 rest sooner after the operation, and remains quiet longer. 



In the same way cuts may be made nearer and nearer the 

 posterior end ; the posterior piece will move more and more 



