TYPES OF METACHRONAL PATTERN 



173 



sense that the excitation and contraction times of a single ciUum 

 would not permit a single contraction to occupy such a long time. 

 The cilia of many epithelia are not compounded, but it is 

 probably important that the synchronous beat of a number of 

 cilia in the direction at right angles to the metachronal waves 

 must be advantageous in that the viscous drag on each cilium is 

 reduced (provided that the cilia are near enough to each other), 

 and the fluid can be moved over the surface faster than it could 

 if the beat were asynchronous. 



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ry ' "-• • ./I 



Fig, 45. Diagram showing two metachronal waves of Stentor 



membranelles. The compound cilia are beating in a direction 



directly towards the observer, and the metachronal waves are 



moving from left to right (see text). 



3. Types of Metachronal Pattern 



The metachronal waves that are seen to pass across any ciliated 

 epithelium result because each cilium of the wave is at a slightly 

 different stage in its beat from its neighbours that lie along the 

 line of wave transmission. For example, a cilium may be at the 

 beginning of its effective stroke, while the cilium before it in the 

 wave has started its effective stroke and the cilium behind it has 

 not completed its recovery stroke. Two metachronal waves of 

 the type shown by the membranelles of Stentor are represented 

 diagrammatically in Fig. 45. At/ the cilium is at the end of the 

 recovery stroke, it then bends at right angles to the plane of the 

 page in the effective stroke to pass through stage a to h, after 



