The Mind of 
	a Worm


CEP is a set of four neurons with ciliated endings in the cephalic sensilla (figure 1). The dorsal pair of cell bodies is situated in the pseudocoelomic cavity posterior to the nerve ring (along with those of URX). The ventral cell bodies are situated anterior to the ring and closely apposed to the ring neuropile (b) .Anteriorly directed processes run in four of the six labial process bundles to the receptor endings in the head. Posteriorly directed processes emanate from the ventral CEP pair and loop round the posterior face of the ring neuropile; they then enter it on the inside surface adjacent to the muscle arms (j, c). The processes branch at this point and run both ways round the nerve ring on the inside surface near the posterior face of the ring neuropile. The dorsal branch ends; the ventral branch loops round and runs dorsally in the middle of the anterior regions of the ring neuropile. The dorsal pair of CEP neurons send out anteriorly directed processes, which enter the ring near the dorsal mid-line (i) and then run ventrally on the inside of the ring neuropile adjacent to the muscle arms. These then loop back and run in the middle of the anterior regions of neuropile, eventually moving back to the inner surface, where they end. The main synaptic output is to RIC (a, g), AVE (d, f, h), OLL (f), OLQ (e), ILl (e), RMH (g), RMD (h), RMG, URAand URB. CEP synapses have been shown to contain the neurotransmitter dopamine (Sulston et al. 1975). There is some synaptic input from OLL, ALM (*c), RIH, RIS, and also from URB(*b) and ADE to the dorsal pair only. There are gap junctions to OLQ (*e) and RIH. Magnifications: (a, e, g) x 25500, (b) x 6375, (c, d, f, h) x 12750.

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