THE MECHANISM OF METACHRONISM 189 



may be increased by as much as 100 per cent, but the wavelength 

 remains practically unchanged. Similarly, Gray and Lucas found 

 that the wavelength remained unchanged when the frequency was 

 changed by altering the temperature, although Aiello found a 

 small increase in wavelength when the temperature was raised. 

 An important observation was made by Gosselin (1958), who 

 found that an increase in viscosity did not change the frequency 

 of beat, but reduced the amplitude of beat and increased the 

 metachronal wave velocity. All of these observations could be 

 adequately explained on the basis that these cilia are co-ordinated 

 mechanically through the medium and do not depend on an 

 internal conduction mechanism. 



The metachronism of the lateral gill cilia is laeoplectic (Knight- 

 Jones, 1954; Aiello, 1960). The metachronal wave-front is at 

 right angles to the line of transmission of the waves, yet the rows 

 of ciliary basal bodies are at an angle of about 120° to the gill 

 filament axis. Aiello found that the cilia beat roughly along 

 these rows, i.e. obliquely, while Lucas found that the cilia beat 

 directly across the axis of the gill filament. If the cilia are very 

 close together and beat slightly obliquely, then mechanical 

 co-ordination could take place through a combination of viscous 

 drag and the cilia striking the cilia obliquely ahead along the 

 axis of wave transmission. If the beat is exactly transverse, only 

 the viscous drag can be effective. The metachronism of these 

 cilia is certainly more irregular than that of Stentor, and varies 

 from place to place along the row as one might expect if the 

 metachronal co-ordination is mechanical rather than neuroid. 

 Lucas thought that an internal transmission mechanism, was likely 

 because waves of the normal frequency and size appeared on the 

 distal side of quiescent regions, but this could equally be the 

 result of the action of a pacemaker distal to the quiescent cilia 

 which communicated its rhythm mechanically to the distal cilia. 

 Further work on these cilia, with a view to establishing the 

 possibility of mechanical co-ordination, is eagerly awaited. 



It is evident that many groups of metachronally co-ordinated 

 cilia will have to be studied in considerable detail before we can 

 see whether any general pattern exists, and that any further 

 suggestions at this time would be pure guesswork. However, 

 it is probably reasonable to speculate that where cilia show 



