228 



JENNINGS AND JAMIESON. 



a 



of the uninjured animal, but somewhat more rapid than usual. 

 The piece runs forward on the bottom, turning to the right when 

 stimulated. It differs from the entire animal in that it much more 

 rarely jerks backward when stimulated, though it does this when 



the stimulus is powerful. When swim- 

 ming through the water, it revolves to 

 the right and swerves to the left, as in 

 the entire animal. Since the anterior 

 half possesses the peristome, the simi- 

 larity of its movements to those of the 

 uninjured animal was to be anticipated. 



2. Posterior half, without peristome 

 (Fig. 2, />). Immediately after the oper- 

 ation the piece jerks rapidly backward, 

 turning at the same time toward the 

 right side. After a time it becomes 

 quieter, and now it reacts essentially like 

 the entire specimen, though it is some- 

 what less active. If stimulated with the 

 glass hair at the posterior end its runs 

 forward ; stimulated at the anterior (cut) 

 surface, it jerks backward and turns to 

 the right. Chemical stimuli cause the 

 same reactions. A little 111/20 NaCl, 

 or a weak solution of methylene blue 

 was introduced with a capillary tube close 

 to the piece ; on coming in contact with 

 the chemical the piece backs and turns 

 to the right, just as is done by the en- 

 tire animal. 



Thus the presence of the peristomal cilia is not the determining 

 factor for the invariable turning to the right as a response to 

 stimuli. 



3. Posterior one fifth. - -The movements are somewhat less 

 well coordinated than in the larger pieces. But after the shock 

 effects have ceased, the piece creeps forward, turning to tJic right. 

 It swims slowly through the water, swerving to the right and 

 revolving to the left, as in the uninjured specimen. 



FIG. 2. Anterior (a) and 

 posterior (l>) halves of Sty- 

 lo tire hia. 



