The Mind of 
	a Worm

Members: VD1 to VD13.

VDn is a set of thirteen motoneurons, with cell bodies in the ventral cord, which innervate ventral muscles. Each cell has an anteriorly directed process emanating from its cell body. This process has a branch, which leaves the ventral cord on the right as a commissure (c) and runs round to the dorsal cord. (VD2 is exceptional; it has a left-hand commissure.) The commissure splits, as it enters the dorsal cord, into an anteriorly and a posteriorly directed process, which span approximately the same region of the body as their ventral counterparts (e). (VD1 is exceptional in that its dorsal process is anterior to its ventral counterpart.) Both the dorsal and the ventral processes run adjacent to the basal lamina bounding the cord, in close association with the processes of DDn neurons. The ventral process lies between the processes of VCn dorsally and the other motoneuron classes ventrally (figure 18). The dorsal process runs ven trally to the other motoneuron axons (figure 19). The VDn processes in the dorsal cord are exclusively postsynaptic, receiving synaptic input from DAn (*a), DBn (*a) and ASn (*a) motoneurons at points where they have NMJs. The processes in the ventral cord are predominantly presynaptic and have many NMJs (a, b), most of which have only muscle as the postsynaptic partner. The processes of VDn and DDn do not have extended, apparently undifferentiated distal regions, as do the other motoneuron classes; instead, they end abruptly in close proximity to the end of a neighbouring process of the same class, often with a gap junction between them (d). VDn also has gap junctions to DDn and a few with PVP. VD1 has several additional Œoddı gap junctions. Magnifications: (a, d) x 25500, (b) x 12750, (c) x 17000.

Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002