"Vol. 3] Bovard. — Coitdijlostoma patens. 361 



is the most effective means for directing the anterior part away 

 from the source of stimulus in the backward movement, the 

 degree of efficiency depending on the arc of the circle completed. 

 The body now returns to the normal form and the animal ad- 

 vances in a new direction. At this point there is often noticed 

 a bending of the anterior end towards the right (fig. 12), due to 

 a contraction of the myonemes on the right side. 



The cilia at the moment of stimulation all reverse ; this causes 

 the quick dart backwards. The subsequent action depends on 

 the strength of the stimulus. Under weak stimulus, the reversal 

 of the cilia is but momentary; those of the left side may slow 

 down, not beat at all, or beat slowly forwards. Those of the 

 right side continue a vigorous beating forwards, as also do those 

 of the dorsal surface. In cases of strong stimulus, all the cilia 

 reverse and continue their forward stroke for some time. The 

 cilia of the left side now begin to beat backwards, those of the 

 right side continue beating forwards, the combined action turns 

 the body towards the right, then those of the right side strike 

 backwards, and the animal proceeds in the new direction. A 

 careful search was made for the transverse beat of the cilia at the 

 anterior end, which is such a prominent feature in Paraniaecium, 

 but no evidence was found to indicate that this is the case in 

 CoitdyJostonia. The gelatine method was used, which slowed 

 down the movements and carmine was added to show the action 

 of the cilia better. All observations, with a single exception, 

 seem to point to the fact that the motions of the cilia were con- 

 fined to a forward and backward movement. Certain movements 

 which occur during gliding seem to indicate the transverse action 

 of the cilia. Occasionally animals moving along the bottom of 

 an aquarium stopped and elevated the anterior end. This action, 

 at times, was continued till only the posterior tip was left in 

 contact with the substratum (fig. 13). A further continuation 

 caused the animal to turn completely over, the anterior end now 

 pointing in an opposite direction to that held at the beginning of 

 the movement. Sometimes after the anterior end had been ele- 

 vated it began to swing to the right so that it described an are 

 of a circle (fig. 14). In this position the posterior end remained 

 fixed. The new direction the animal took on settling down w^as 



