194 



CO-ORDINATION OF BEAT 



swimming of Opalina, and it appears that the wave pattern changes 

 virtually instantaneously over the whole body. Increasing 

 excitation causes a progressive change in the wave pattern, as 

 shown in stages I to VI in Fig. 53, until the waves travel forwards 

 from the posterior end. The change in direction of beat and the 

 increase of excitation were found by Kinosita (1954) to be 

 accompanied by an increased depolarization of the surface 

 membrane of the animal. 



In a recent review of this subject, Kitching (1961) has suggested 

 that the progressive depolarization of the surface membrane 

 changes the site of pacemaker activity from the anterior end along 



c 



Stage// Stage I Stage II Sta^e III Stage IV Stage V Stage yi Stage 1/1/ 



Fig. 53. Metachronal wave patterns at various stages in the 

 reversal of ciliary beat in Opalina. The arrows on the figures 

 indicate the direction of metachronal wave movement. The 

 wave patterns on the ventral surface were observed through the 

 transparent protoplasm (from Okajima. 1953). 



the " right " side of the body in transverse beating to the posterior 

 end in reversed beating. Indeed, Okajima (1953) implies that 

 the frequency of beat increases with increased excitation, and this 

 would allow different pacemakers to control the beating activity 

 of the cilia by their higher rate of stimulation. However, the 

 direction of beat of cilia on a small area of the body surface is 

 changed by a localized depolarization under conditions where the 

 main pacemakers of the body (if these exist) are not affected at 

 all. This leads to the alternative suggestion that the depolariza- 

 tion of the surface membrane affects every cilium, not just the 

 pacemaker, so that the direction of beat of every cilium is changed 

 by a greater or lesser extent according to the amount of 



