ASI is a set of two ciliated neurons that are part of the amphid sensilla. The endings are in the amphid channel, which is open to the outside (figure 1). Cell bodies are situated in the lateral ganglia and send processes into the ventral cord via the amphid commissures, which project anteriorly into the nerve ring. They run round the nerve ring near the outside surface and meet and terminate at the dorsal mid-line with a gap junction between them (d). The processes are smaller than those of the other amphid neurons and fewer synapses are seen. The main synaptic output is to AIA (a) to which they also make gap junctions (b). There are also some smaller synapses onto AIB, AWC (c) and ASE. Some of the vesicles in the synaptic terminals have dark cores (a). Magnifications: (a) x 25500, (b-d) x 12750.
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