TYPES OF METACHRONAL PATTER^f 179 



Stentor, caused by the action of the body ciUa, the membranelles 

 are either quiescent or may waggle feebly without a co-ordinated 

 beat. 



The functional value of these different patterns of metachronism 

 is rather different, as Knight -Jones (1954) has pointed out. 

 Symplectic metachronism is probably the most primitive type; 

 it does not make the best use of the movement of the cilia, for 

 they are bunched together during the effective stroke. Diaplectic 

 metachronism is especially suited for the creation of water currents 

 in locomotion, feeding and respiration, and is probably not very 

 easily adapted for the movement of larger particles or strings of 

 mucous. Perhaps the fact that diaplectic metachronism is normally 

 shown by cilia arranged in short orthoplectic rows reflects this. 

 Antiplectic metachronism may also be used for creating water 

 currents, but it is most commonly found in cilia whose function 

 is the movement of particles or strings of mucus. 



In both diaplectic and antiplectic metachronism the cilia have 

 a greater freedom of movement than in the symplectic type, and 

 are able to sweep through a large body of water quickly; they 

 can be long and compound without interfering with the effective 

 stroke of their neighbours, so that very large water currents can 

 easily be created. The lack of interference in diaplectic types 

 is fairly obvious, but in antiplectic metachronal waves the cilia 

 must be spaced fairly widely to make full use of the beating 

 activity, and the waves must travel sufficiently fast relative to the 

 rate of beat that cilia in their recovery stroke do not get in the 

 way of cilia which are in their effective stroke ; this is particularly 

 necessary with very large cilia like those of ctenophores. While 

 a very large force can be exerted by these comb -plates of cteno- 

 phores, they must either be widely spaced, or lose efficiency by 

 interference and reduced amplitude. The cilia of the rows along 

 which diaplectic waves pass may be packed very tightly together 

 and still retain a large amplitude of beat, and although it seems 

 inconvenient or unnecessary for them to be too large, this may 

 be because of their function in the cases so far examined. 



Ciliated epithelia showing diaplectic metachronism are normally 

 either in the form of narrow diaplectic bands with only a few 

 cilia in each orthoplectic row, e.g. lateral cilia of My tikis gill, or 

 in the form of single diaplectic rows of (usually compound) liaic, 



N 



