MOVEMENTS, ETC., OF FUl'^Sn-WATER PLANARIANS. Oil 



becomes immediately very much lowered. In view of these 

 facts it is impossible to get any very trustworthy results 

 from the stimulation of such a piece. 



There is another operation, however, which, while it does 

 not isolate completely two longitudinal halves of the body, 

 yet does separate into longitudinal halves the essential 

 reacting parts, namely, the head regions. This is the 

 splitting- ot' the worm in the middle line for a short distance 

 back from the anterior end, as shown in Fig, 12. After this 

 operation the two anterior pieces move about violently and 

 independently for a time, taking all the various positions 

 shown in Fig-, ]{). The animal soon recovers from the immc- 



FiG. 19. — Diagram sliowing tlie different positions taken by the two 

 components resulting from longitudinal splitting of the liead. 



diate effects of the opei-ation, glides about in a normal way, 

 only at a rather slow rate, and responds well to stimuli. The 

 anterior piece keeps comparatively straight, there being much 

 less tendency to contraction on the cut side than when the 

 split extends the whole length of the body. The reactions of 

 such a specimen to mechanical stimuli are as follows. To 

 stimuli applied at the posterior end along the sides of the 

 body the reactions are precisely the same as those already 

 described for the normal individual. Stimulation in the 

 regions a a (Fig. 20) of moderate or strong intensity produces 

 the negative reaction. The organism turns away from the 



