368 



THE BIOLOGY OF MARINE ANIMALS 



Ciliary motivity is independent of the cell as a whole; the distal end of the 

 cell, however, appears to be essential to the mechanism, and some ob- 

 servations suggest that the basal granules are involved. 



Examination of a ciliated surface shows that the cilia beat, not in phase 

 but in sequence. Any selected cilium is beating slightly in advance of the 

 one behind it, and is slightly retarded with respect to the one preceding it. 

 This sequence of phasing is termed metachronism. Since all the cilia 

 lying in a line across the epithelium beat in phase with one another, 

 regular waves appear to pass over the surface of the epithelium. 



The direction of the metachronal waves is usually constant for each 

 tissue. In the case of the frontal cilia on the gills of My tilus the metachronal 



Fig. 9.1. Flagellar Activity in the Flagellate Monas 



a, fast forward movement: a, recovery stroke; b, effective stroke, b, slow forward 

 movement: a, recovery stroke; b, effective stroke, c, backward movement, d, lateral 

 (a), and rotational (b) movement. (From Krijgsman, 1925.) 



wave moves in the direction of the effective stroke of the cilia. In the lateral 

 gill epithelium of the same animal the waves move at right angles to the 

 effective stroke. Among ctenophores the metachronal wave of the ciliary 

 plates usually moves in an opposite direction to the effective stroke. 

 Metachronal waves in the direction of effective ciliary beat are probably 

 associated with transport of large particles or mucous masses ; waves at 

 right angles or opposite to the beat are better suited for creating water 

 currents. The relations between metachronism and direction of ciliary 

 beat are explored in detail by Knight- Jones (68). 



Because of the difficult experimental conditions which ciliated cells 

 present, the mechanism of metachronism has not been satisfactorily 

 explained. Regular metachronal waves pass smoothly over long tracts of 



