142 MOVEMENT OF CILIA AND FLAGELLA 



The movements of the ciHa of Opalina, on the other hand, are 

 more Uke those of flagella in many respects (Figs. 39 and 47, and 

 PI. XVIIIb); in fact, it might be more satisfactory to regard 

 them as flagella in agreement w^ith the findings of Grasse (1952) 

 and Corliss (1955), who maintain that Opalina shows more 

 affinity with flagellated than with ciliated protozoa. These cilia 

 appear to be rather flexible organelles, and the long ones at the 

 posterior end of the body trail in the w ater in a manner reminiscent 

 of the flagella of Trichony^npha. It seems best to regard the 

 " resting position " of these cilia as that in which they lie close 

 to the body surface (Fig. 39, stage 1). A wave of bending passes 



^^y^^^^Ty/ ^ ^?//> ^// ^ ^ ^/ ^^ yy / ^^^ 



Fig. 39. The sequence of movements of a cilium of Opalina. 



Compare this with Fig. 47 and Plate XVIIIb, where these cilia 



form part of metachronal waves. 



up the cilium, straightening it out in a preparatory phase equivalent 

 to the recovery phase of the Stentor ciliary beat. Before this 

 wave of flexure has reached the tip of the cilium, a second bending 

 wave on the other side of the cilium pulls the shaft back towards 

 the body surface in the effective phase. The cycle of beat is 

 completed when the second bending wave has been propagated 

 to the end of the cilium. In the preparatory phase the cilia are 

 lifted from the body surface in a smooth curve (see Fig. 47, 

 p. 176) and in the effective phase (i.e. that in the direction of the 

 effective movement of water) they are brought back to the body 

 surface. It seems likely that movements of the complete waves 

 are responsible for the movement of the organism through the 

 water, rather than movements of individual cilia ; in this also the 

 motion of Opalina resembles that of Trichonympha (see also 



