INHIBITION OF LOCOMOTION IN PARAMECIUM. I I 



at times accelerate at some part ; this acceleration is local and lim- 

 ited and soon traverses the entire course, ceasing first where it 

 began. The acceleration seems independent of the functioning of 

 the contractile vacnoles, since it occurs at intervals much greater 

 than those of vacuole closure. The contractile vacuoles, fixed to 

 the ectosarc, can be seen to operate, as in normal animals, at inter- 

 vals of from ten to twenty seconds. 



The gullet of Parameciuni is usually represented in the literature 

 as a short and narrow tube tapering posteriorly to the region of 

 the aggregation of food particles, at which position it expands into 

 a sac of somewhat greater diameter than the gullet proper. This 

 description is doubtless referable to the fact that in the dead animal 

 the oesophagus presents an appearance quite different from that in 

 the living. In specimens carefully killed, fixed and stained the 

 gullet was found to be scarcely recognizable, although the other 

 structural details seemed unimpaired. In animals freshly killed, 

 but not otherwise treated, the gullet presents the appearance indi- 

 cated in the literature. The writer has often observed that in 

 paramecia being killed by dilute poisons a convulsive rearrange- 

 ment in the protoplasm in the posterior half of the body chokes 

 up the oesophagus and tends to elevate the oral depression. The 

 gullet, therefore, shortens and constricts, and if a new food vacuole 

 is aggregating at this time the distal end of the gullet naturally 

 remains relatively larger than the shrunken duct itself. 



In a narcotized living paramecium the gullet can be observed as 

 a smoothly curved and posteriorly tapering tube, approximately one 

 fourth the length of the body. It extends from the peristome 

 posteriorly toward the aboral side, but not through the middle of 

 the body, so that the distal end lies near the ectosarc ; and as seen 

 from the oral surface and the posterior end, it twists obliquely to 

 the left of the longitudinal axis of the animal (Fig. i, a, b, c). 



The undulating membrane, or ciliated lining of the oesophagus, 

 was superficially studied in a few animals which had stopped swim- 

 ming, but still rotated feebly, revealing the gullet in all its aspects. 

 In these animals the undulating membrane was still functioning 

 rapidly, though apparently somewhat slower than in a normal para- 

 mecium. The undulatorv motion can be likened to that of at- 



