Fig. 5. Serotonin affects both the frequency and the waveform of the ciliary beat as seen at higher temporal resolution. (A) Control trace of cilia in seawater without serotonin. Both the phases 1 and 2 are evident. The subsequent phase 3 is not shown. Perfusion with 10^-7 mol l^-1 (B) and 10^-6 mol l^-1 (C) serotonin increases the speed of ciliary beating. Phase 2 is less regular and phase 3 is no longer apparent. Scale bar, 50 ms for all traces.