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Figure 4. — Records of activity from red (R) and white ( W) regions of a carp myotome at different swimming speeds. A: 0.75 body length 

 per second; B: 0.9 body length per second; C: 1 .26 body lengths per second; and D: 2.0 body lengths per second. Note that the white fibres 

 are active even at low swimming speed and that there is spikelike activity at each tail beat in C. The lowest record (D) taken at higher 

 chart speed shows the appearance of irregular bursts containing spikelike potentials. Note pick-up of these events by the overlying red 

 fibre electrode. Vertical bar; 500 /nV; time marker; seconds. 



zone of the myotome: 1-200 /xV potentials of the 

 usual kind were obtained from the lateral red 

 musculature (Figure 5A). When startled, a few 

 rapid tail beats drove the fish forward and, under 

 these conditions, larger spikelike potentials 

 around 0.5 mV peak to peak were recorded from 

 the white zone of the myotome corresponding to 



the rapid tail beats. As can be seen from Figure 5B, 

 these events were picked up at lower amplitude by 

 the electrodes whose tips lay in the lateral red 

 muscle layer. After a few rapid tail beats, the fish 

 coasted forward before dropping back and resum- 

 ing regular swimming: the normal rhythm of the 

 red fibre system was inhibited for a few cycles. 



695 



