1975. Skin impulses and locomotion in Oz&op/ewra (Tunicata: Larvacea). Biological Bulletin. Marine Biological Laboratory, Woods Hole, Mass., 149, The skin covering the tail and hinder trunk region of Oikopleura propagates impulses at 15-21 cm/s. Spread is non-decremental and unpolarized. The impulses are of short duration (8-12 ms) and in general resemble skin impulses in hydromedusae more than those of amphibian and tunicate tadpole larvae. The skin was examined by optical and electron

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... py. The cells are connected by gap junctions. Impulses are assumed to spread by direct current flow from cell to cell. Electromyograms of tail activity during three behaviour patterns (pumping, swimming, and house rudiment expansion) are analysed in relation to neuromuscular histology. There appear to be at least two classes of pacemakers, both located in the caudal ganglion. There is no evidence that proprioceptive feedback is required for maintenance of rhythmic activity; and isolation of the tail from the trunk, which contains the cerebral ganglion, does not affect rhythmicity. The system differs fundamentally from the locomotory systems of Amphioxus and fishes. Skin pulses evoke swimming bursts in intact animals or briefly accelerate pre-existing rhythms. The conduction pathway from skin to caudal ganglion is shown to be a pair of nerves running from the latter to a receptor located in the skin at the back of the trunk. No other nerves end in the skin. Cutting these nerves blocks the response. As in other cases, the conducting epithelium here functions as an extension of the afferent pathway, mediating an escape response following tactile stimulation.