8. The time courses of the recovery of the membrane capacitance and of the early inward current were similar, suggesting that the number of voltage-sensitive Ca channels is proportional to the ciliary membrane area.9. We conclude that the voltage-sensitive Ca channels reside in the ciliary membrane (in confirmation of Dunlap, 1976; Ogura & Takahashi, 1976), while mechanoreceptor channels, rectifier channels and resting conductances are localized in the somatic membrane.

1. In forward-swimming Paramecium the direction of metachronal wave propagation is turned progressively clockwise from forward-right to backward-left if the viscosity of the medium is increased to more than 100 cP. 2. With increasing viscosity the direction of the power stroke is turned clockwise at a lower rate than the direction of waves. This leads to a gradual transformation of the dexioplectic metachrony toward a symplectic pattern. 3. As viscosity is raised the polarization of the ciliary cycle in time and space is Progressively reduced, so that the beat becomes increasingly helicoidal. 4. Metachronal coordination gradually breaks down at viscosities of more than about 100 cP, but is retained better at the anterior end of the cell than in more posterior regions. 5. At viscosities above 12 cP the left-handed swimming helix of Paramecium is changed into a right-handed helix. This is produced primarily by the viscositydependent clockwise shift in the direction of the power stroke from backward-right to backward-left. 6. The frequency of peristomal cilia (32/s. at 20°C) decreases with rising viscosity. Under constant conditions, a posteriorly directed gradient of decreasing frequency can be observed with the stroboscope. 7. Raising the viscosity leads to an increase of the average wavelength from 10.7 µm at 1 cP to 14.3 µm at 40 cP. In the same range of viscosity the wave velocity, which is the product of frequency and wavelength, is reduced from 340 to 200 µm/s, since the drop in frequency exceeds the increase in wavelength. 8. The wave velocity tends to be stabilized by reciprocal relations between frequency and wavelength, if all other factors are kept constant. However, the wavelength is found to be different in forward-swimming and backward-swimming animals at 40 cP without a change in frequency (14.1 bps; 14.3 compared to 12.7 µm). This is explained if the metachronal wavelength is increased by decreasing polarization of the ciliary cycle. 9. A working hypothesis is put forward which explains the origin of a metachronal system by the distribution of forces parallel to the cell surface produced by polarized or unpolarized cycles of ciliary movement.

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. This essay considers the responses of Paramecium and other ciliates to the inorganic ion environment from an elec‐trophysiological point of view. In reviewing data from published and unpublished sources it is shown that ions affect the cellular behaviour in multiple ways because the transmembrane potential can change due to the alteration of equilibrium potentials, ion conductances and surface charges of the membrane. Sensory input including effects from the ionic environment converge upon the membrane potential which has a temporal and spatial summing function. Hyperpolarizing and depolarizing potential shifts from the set point are near‐simultaneously and omnidirectionally transmitted along the membrane including the ciliary boundaries. The membrane potential regulates ciliary motility via an intraciliary messenger, Ca2+, which can enter, and presumably leave, the cytosol directly adjacent to the ciliary motor. Integration of the responses of thousands of cilia occurs in accordance with the electrical and structural provisions of the cell. Potential‐regulated motor and behavioural responses attenuate with time. This phenomenon, which has been loosely termed adaptation, has an electrophysiological basis in analogy to membrane accommodation following sustained stimulus input. The mechanisms of adaptation serve to restore, in principle, the membrane resting state and, thereby, the sensitivity to depolarizing and hyperpolarizing shifts of the membrane potential and the cell's responsiveness to environmental stimuli, respectively. For the inorganic ions involved in chemosensation the terms attractant and repellent are not applicable. They should be reserved to signalling substances which per se can define the behaviour of the cell.

We investigated the contributions of lateral intracortical connections to the orientation tuning of area 17 cells using micro-iontophoresis of the inhibitory transmitter gamma-aminobutyric acid (GABA) to inactivate small cortical sites in the vicinity of a recorded cell. GABA was ejected from an array of micropipettes each with an average horizontal distance of 500 microns from the recording site. Of 54 cells tested, 33 showed a reduction and 3 a loss of orientation selectivity due to an increase in responses to non-optimal orientations during GABA inactivation. The response to the optimal orientation remained constant in more than half of the cells and increased or decreased in others. Given that a complete cycle of orientations occupies a tangential distance of 1000 microns, the observed broadening of orientation tuning is presumably due to GABA-mediated inactivation of inhibitory interneurones with different preferred orientations from those of their target cell.

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