1. The structure and physiological properties of the somatic neuromuscular system of the nematode Ascaris lumbricoides var. suum are discussed taking into account early work from this laboratory, the results of other workers, and experiments in progress. 2. Anatomically, the central feature of the somatic musculature is the presence of a specialized muscular, but not contractile, structure: the syncytium or sarcopile, formed by the terminal processes of the muscle cell arms that contact the nerve cord. In this region, they are electrically coupled to one another and form chemical synapses with the nerve fibres. 3. The syncytium serves, primarily, as a nerve-muscle manifold, or device which allows the neural control of the muscle fields with great economy in the amount of nervous tissue, numbers of chemical junctions and quantities of synaptic transmitters. 4. The structure of the syncytium is being studied with the scanning electron microscope. The results reveal the convergence of the arms on discrete sites as they approach the cords, as well as a longitudinal arrangement of the terminal processes as they course over the cords, at least in the posterior region of the animal. 5. The characteristics of the electrical coupling between the muscle cells are being investigated. A pattern has been observed that is dependent on the position of the cell pairs with respect to the longitudinal axis of the animal. 6. A study of signal propagation in the arms has revealed that the morphology of the muscle cells contributes to the extent and preferential direction of propagation.