URY is a set of four neurons with cell bodies situated anterior to the nerve ring. Processes project anteriorly from the cell bodies into the two sub-dorsal and the two sub-ventrallabial process bundles. These processes enlarge and flatten at their endings (which are not ciliated), at which point they are closely apposed to the inner labial and the outer labial sheath cells (figure 1). A posteriorly directed branch from the sub-dorsal cell bodies forms a complete loop round the underside of the ring and then across to a point where it meets up with itself; it then runs dorsally round the ring near the outside surface. The sub-ventral cells are similar except that they do not loop round the ring but briefly enter the middle of the ring neuropile before returning to the outside regions of the neuropile and running ventrally. When the processes of the URY neurons run round the ring, they are in close association with the processes of RIB (b). The main synaptic output is to SMD via large monadic synapses (a), RMD, usually in association with AVE at dyadic synapses (b, c) and possibly also RIB. There are gap junctions to RIG (d) and AVA. Magnifications: (a) x 25500, (b-d) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002