Summary(i) The general disposition of the sensory, association (internuncial) and motor elements of the starfish arm as revealed by intra‐vitam staining is described and figured (Fig. i), and (2) the nature of the nervous arcs responsible for reflex activities is discussed. (3) It is pointed out that the nature of the activities of an organ and the degree of integration of groups of organs are conditioned by the form and properties of the neurones and tracts through which they are innervated. (4) The pedicellariae, papulae and spines which are situated on, or are part of the dorsal body wall of a starfish are innervated through a plexus which has peripheral qualities. (5) There is little evidence of anatomical differentiation within the peripheral plexus except for the presence of groups of transversely running tracts which may correspond to the through‐conduction tracts (vide infra(8)). (6) The properties of the peripheral plexus are those of a nerve net as defined by Pantin (1935a, c) and the movements of the pedicellariae are analysed in relation to these properties. (7) The net shows evidence of differential capacity for facilitation in its various parts, in particular (8), there are transverse through‐conduction tracts in the plexus which, when coupled with the lateral motor systems of neurones (Eof Fig. i) are the means of innervating the papulae and muscles of the body wall. (9) The movements and postures of the tube feet are described. (10) Together with the capacity of the feet to be co‐ordinated throughout the entire animal they demonstrate the central nervous properties of the circumoral ring and radial cords through which they are innervated. (11) These central nervous properties derive from the presence of special centres of co‐ordination, from a marked polarity of conduction, and from a certain configuration of the motor neurones within the central nervous system and the tube feet. (12) An account is given of the probable location and functions of the nerve centres and of the disposition of the nerve tracts within the central nervous system. (13) A brief reference is made to the effects of peripheral excitation on the pattern of coordinated movement of