140 



MOVEMENT OF CILIA AND FLAGELLA 



in a single plane, and that a bending wave is propagated up the 

 cilium from base to tip. In some very interesting work using 

 a rapid fixation technique, Parducz (1954) found that the ciliary 

 beat of the body cilia of Paramecium does not take place in a 

 single plane, for in the recovery stroke the cilium swings out to 

 the side, so that the tip of the cilium follows an almost circular 

 path instead of moving to and fro in the same plane. Although 

 it is unwise to lay too much stress on the analysis of the shapes 

 and positions of cilia of fixed animals, especially those in which 

 the direction of beat is known to change practically instantaneously 



Fig. 37. Movements of a membranelle of Stentor in relation 

 to the current of water that they cause. The dotted arrow 

 indicates the movement of the cilium and the full arrow indicates 

 the movement of the water, (a) The eflfective stroke, and 

 (b) the recovery stroke. (See text.) 



in response to a variety of stimuli, the cilia of Paramecium have 

 been shown by Parducz to be worthy of an intensive study in 

 the living state. Some observations on the beating of vestibular 

 cilia of Paramecium by the author did not reveal any obvious 

 movement of the cilia out of a single plane. 



Because of the mode of use of a cilium, its effective activity 

 is unidirectional, so that the beating cycle of a cilium can be 

 separated into an effective phase in which most of the useful 

 work of the cycle is performed, and a recovery phase in which the 



