The Mind of 
	a Worm

APPENDIX 2. REMAINING AMBIGUITIES

The reconstructions that we have described were done piecemeal, using data obtained from several animals. This was because of the difficulty of serial sectioning a complete individual. Inevitably there were some consequential problems in the identification of equivalent processes in different animals. These problems could, for the most part, be resolved, because of the reproducibility of relative process positions within bundles and the consistent synaptic behaviour of a given process. There are, however, a few remaining ambiguities, notably concerning process identification in the posterior ventral cord. This region was covered by the N2Y series, which was derived from an adult male. The male has significantly more processes running in its ventral cord than the hermaphrodite. These extra processes arise from male-specific neurons in the tail ganglia (Sulston et al. 1980). Their presence made it difficult to identify some of the processes from neurons common to both sexes, particularly those that were rather featureless, with few characteristic synapses. We have listed the cases for which these problems exist.

DVB AND DVC

The processes from these two neurons are always closely associated. They sometimes twist round each other and so cannot be distinguished by their relative positions. We cannot, therefore, be sure whether the cell bodies labelled DVB and DVC connect to the processes labelled DVB and DVC in the nerve ring or whether they have been crossed over. We have chosen the interpretation that is shown on the basis of synaptic criteria, but these are not particularly compelling.

ALA, CAN AND PVD

These neuron classes have processes that run together alongside the two lateral arms of the excretory canal. They have not been followed along the length of the animal, although they have been sampled at intervals along their length. The three processes make virtually no synaptic connections along the canal and look rather similar. Two of the processes end at about the level of the anus; the third enters the lumbar ganglion on each side, where it makes a few synapses onto PVC. This process has been tentatively assigned to ALA, but it could equally well belong to either of the other classes.

PVW, PQR AND PVT

These classes have cell bodies in the lumbar ganglia and the pre-anal ganglion; they send out processes, which project anteriorly up the ventral cord. Processes from these neurons have not been positively identified in the N2Y series and are not present in the anterior ventral cord (i.e. they could not be accounted for in the N2U series). It therefore seems likely that they terminate somewhere in the posterior ventral cord. The process of PQR appeared to be petering out at the end of the JSE series and was almost certainly about to end. The same cannot be said of PVT, however. The single neuron of this class had a large cell body in the pre-anal ganglion with a single, substantial, anteriorly directed process. This process had few synaptic contacts and was still going at the anterior extent of the JSE series. It seems rather surprising that such a process should end, presumably without making any significant synaptic contacts. An alternative interpretation is that this process divides somewhere in the posterior cord and becomes the two processes currently assigned to PVNL/R in the anterior cord. The location of the process of PVT in the cord is consistent with this interpretation. It would mean, however, that in this case PVNL/R would have to terminate in the posterior cord.

RID, PDA AND PDB

These three classes have processes in the dorsal cord, which have not been completely followed. RID sends a process into the anterior end of the cord; a process that looks similar has been identified in the posterior dorsal cord. It therefore seems likely that the dorsal process of RID spans the length of the cord. The process of PDA and PDB enter the dorsal cord near its posterior extremity. They project anteriorly but have not been identified in the anterior cord.


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