2 3 2 



JENNINGS AND JAMIESON. 



revolving to the left, and turning toward the aboral side when 

 stimulated mechanically or chemically. 



2. Posterior half, without oral groove or 

 mouth (Fig. 4, b}. Much pains was taken to 

 remove the entire oral groove and mouth, so 

 that the posterior piece was usually a little 

 less than one half the body. It was possible 

 to distinguish the aboral side by the presence 

 there of the contractile vacuole. The pos- 

 terior half swims in a spiral, revolving, like the 

 uninjured animal, to the left, and keeping the 

 aboral side to the outside of the spiral. Its 

 movements are slower than those of the an- 

 terior half, and it is much less sensitive, not 

 reacting so readily to stimuli. The reaction 

 to mechanical and chemical stimuli is by jerk- 

 ing backward and turning toward the aboral 

 side, as in the uninjured individual. Thus the 

 presence of the oral groove and oral cilia is 

 not necessary in order that the usual move- 

 ments and reactions may occur. 



3. Middle third of Parainccinin (anterior 

 with mouth and oral and posterior ends removed). This behaves 



cilia. , posterior half, . .. ... , . . 



essentially like the anterior and posterior halves, 

 or the entire animal. 



FIG. 4. Parame- 

 cium cut transverse- 

 ly, a, anterior half, 



without mouth or oral 

 cilia. 



SUMMARY AND CONCLUSIONS. 



In all the Ciliata studied, including several of the Hypotricha 

 (Stylony cilia, Oxytricha, etc.), two of the Heterotricha (Stentor 

 and Spirostomuni], and one of the Holotricha (Paramecium)> the' 

 movements and reactions of pieces of the organisms, if these are 

 not too minute or too irregular in form, are essentially similar to 

 those of the entire animal. The pieces swim in a spiral, swerv- 

 ing continually toward a certain side, just as do the entire organ- 

 isms. They react to chemical and mechanical stimuli by back- 

 ing and turning toward the same structurally defined side, as do 

 the entire animals. This is true of pieces forming one fourth to 



