TYPES OF METACHRONAL PATTERN 175 



chronal waves to the waves made by the wind blowing over a 

 field of corn usually refers to this pattern (although Sharpey 

 (1835) used it to describe the diaplectic metachronism of rotifers). 

 This is perhaps unfortunate, since the symplectic pattern seems 

 to be relatively rare. Symplectic waves are easily seen if Opalina 

 is examined under dark-ground illumination. Okajima (1953) 

 and Sleigh (1960) have described the pattern of waves, and the 

 structure and arrangement of the cilia in longitudinal rows is 

 well-known from the work of Pitelka (1956) and Noirot-Timothee 

 (1959). The waves normally travel from the anterior end 

 backwards, so that any cilium is in phase with all cilia in the 

 same transverse line, but at a different stage of beat from 

 neighbouring cilia in the longitudinal direction. Cilia beat at 



Fig. 46. Diagrams illustrating the four main patterns of 

 metachronal co-ordination. In all the diagrams the effective 

 stroke of the beat is towards the right, as indicated by the 

 complete arrows. The direction of movement of the meta- 

 chronal waves is indicated by the single-barbed arrows. The 

 patterns shown are : A, symplectic; B, antiplectic; C, dexi- 

 oplectic; and D, laeoplectic (from Knight- Jones, 1954). 



right angles to the wave front, and, since the effective stroke is 

 in the same direction as the transmission of the metachronal 

 waves, the wave crests are composed of many cilia moving 

 together in their effective stroke (Fig. 47). Because of this, cilia 

 are unlikely to exert much effect on the water individually, but 

 the movement of the whole wave over the body surface as a fairly 

 solid ridge will move the water quite effectively. Since cilia 



