174 CO-ORDINATION OF BEAT 



which the bending wave is propagated up the cihum in the 

 recovery stroke h to/. In the diagram each of the 6 stages shown 

 is \ cycle out of phase with each of its neighbours. Note that 

 while it is possible to folio twhrough the stages of beat by moving 

 along the row from right to left, the metachronal waves move 

 along the row from left to right, since / is the next cilium to be 

 excited and a has already started to beat. Here the cilia at the 

 end of the recovery stroke form the wave crests, and those at 

 the end of the effective stroke form the troughs of the waves. 

 The appearance of waves on other ciliated surfaces will vary 

 according to the pattern of metachronism and the form and 

 amplitude of beat. 



Synchronous beating of cilia may occur in either the orthoplectic 

 or diaplectic rows, and consequently, metachronal whves may 

 travel along either diaplectic or orthoplectic rows, since the plane 

 of beat and the direction of propagation of the metachronal waves 

 may coincide or be at right angles to each other. There are 

 four alternative patterns of relationship between the beat direction 

 and the direction of wave transmission, all of which occur widely 

 in nature, although their distribution is little studied yet. 

 Knight-Jones (1954) named these four patterns as follows : 

 symplectic metachronism^ where the direction of beat and the 

 direction of wave transmission coincide ; antiplectic metachronism^ 

 where these two directions are opposite ; dexioplectic metachronism^ 

 where the effective beat moves to the right with respect to the 

 direction of wave transmission; and laeoplectic metachronismy 

 where the effective stroke moves to the left with respect to the 

 direction of wave transmission. These four patterns are illustrated 

 in Fig. 46; some examples are listed in Table 13 (p. 181), and a 

 few of them are described in detail below. Where the 

 metachronism travels along the diaplectic rows (i.e. in dexioplectic 

 or laeoplectic metachronism) the beat takes plcae at an angle of 

 about 90° to the diaplectic row, though it may vary from this 

 by a few degrees either way. In any particular ciliated tissue, 

 the pattern of metachronism is constant, and, where reversal of 

 beat has been reported, the metachronal wave propagation seems 

 to reverse also. 



The most familiar pattern of metachronal waves is probably 

 the symplectic one, since the analogy of the appearance of meta- 



