ROOT SYSTEMS AND CO-ORDINATION 199 



repeated and extended, although it is difficult to analyse the 

 movements of such a mobile animal. 



The fibrous connections between the membranelles of Stentor 

 were described on p. 64. If this row is cut across, the metachronal 

 co-ordination of the membranelles is interrupted at the cut, but 

 the waves flow smoothly across the position of the cut as soon 

 as it heals, even if the two edges of the cut are not level. It 

 seems unlikely that a cut fibre could heal up this quickly. Also, 

 it has been noticed that the co-ordination may break down 

 without any cutting of the fibre. These fibrous connexions can 

 hardly be regarded as conductors on the basis of this evidence. 



The presence of such organized fibrous connexions between the 

 cilia of metazoans has not been recorded, although Fawcett and 

 Porter (1954) reported knobs on the roots of cilia that project 

 towards the adjacent cilium in the epithelium, and Gibbons 

 (1961b) has found fine roots attached to these knobs. There is 

 no evidence that any such fibre systems are concerned in meta- 

 chronal co-ordination, although the crossed rootlets between cilia 

 of the two rows of cilia that compose the laterofrontal cilia of 

 Mytiliis gill filaments may help to ensure a synchronous beat. 

 It is interesting that prominent rootlets of some sensory ciUa may 

 be responsible for the conduction of the received impulse away 

 from the cilium (e.g. in the locust scolopale cilium), and it may 

 be equally possible for rootlets of this type to conduct impulses 

 to the cilium. The relationship between the nerve endings and 

 the roots and bases of the velar cilia of the nudibranch larvae 

 described by Carter (1926) deserve further examination in the 

 light of this idea, for these cilia are known from Carter's work to 

 be subject to inhibition. 



9. Summary 



When single flagellar organelles are present on motile bodies, 

 the flagellar shaft is usually modified in some way to increase its 

 efficiency. Similarly, where cilia are required to exert larger 

 forces, they tend to be compounded together, with the result that 

 either the rate of beat or the volume of water swept through (or 

 both) may be increased. The beat of many separate flagella or 

 cilia present on the surface of a cell may be used most eflfectively 

 if there is some form of co-ordination. Thus, the beating of 



