Fig. 15. The principal pathways involved in locomotion, the control of tentacle contractions and food manipulation. Three of the eight longitudinal muscle bands lying in the wall of the peduncle and manubrium are shown. The diagram is based on Mackie and Meech, (2000), but includes two new pathways, the flexion system (F) that mediates the pointing responses seen during feeding, and the endodermal, epithelial system (E_N) that mediates lip flaring and swimming inhibition (via the swimming pacemakers system, P). The exumbrellar epithelial conduction system (E_X) also inhibits swimming, but impulses do not pass between it and E_N, so the two are shown as functionally separate systems. The cells in these epithelial pathways are coupled by gap junctions, shown as incomplete membrane partitions, and conduction in them is unpolarized. Impulses spread in all directions in E_X while in E_N they spread laterally along the ring canal and up or down all eight radial canals (not shown). E_X is not the subject of this paper and in the text `E' simply refers to E_N. MG, motor giant axon; RG, ring giant axon; TF, tentacle nerves that feed into the F system. The experimental basis for other components of the nervous system, the carrier system (C), the nitric oxide pathway (NO), the relay system (R), the rootlet interneurone system (RI) and the tentacle systems (TG, TS), are given in Mackie and Meech (1995a,b, 2000).