Electrical Correlates of Ciliary Reversal in Oikopleura

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Abstract
1. Reversal of the water current through the pharynx of Oikopleura is brought about by a change in the action of the cilia of the two stigmatal ciliated rings. These ‘ciliary reversals’ occur synchronously in the two ciliated rings and can be evoked by the addition of particulate material to the incoming water or by tactile or electrical stimulation of the lips. 2. Nerves run from the lips via the brain to individual ciliated cells, and it is therefore likely that the ciliated cells are under nervous control. 3. At each ciliary reversal an electrical potential can be picked up on the body surface. The same events are recorded by microelectrodes inserted into the ciliated rings. The microelectrode recordings resemble intracellular recordings, and the reversal potentials are considered to represent depolarizations of the membranes of the ciliated cells. 4. Ciliary reversals continue after removal of the brain, suggesting the existence of a peripheral pacemaker.