Organization of motoneurones in the prothoracic ganglion of the cockroach Periplaneta americana (L.).

The location within the prothoracic ganglion of neurone somata with axons in identified peripheral nerves is examined by the cobalt iontophoresis technique. Axons are filled with cobalt by diffusion through their cut ends and the cobalt is then precipitated as the black sulphide inside the neurone. It is assumed that neurones with axons in peripheral nerves and somata in central ganglia are either motor or neuro-secretory. Fifteen nerves are examined and maps of the location of somata with axons in each nerve are presented. The axon distribution in peripheral nerves of three common inhibitory neurones is described. Dendritic morphology of one common inhibitory neurone and two coxal depressor motoneurones is illustrated. It is proposed that some individual neurones can be reliably identified from their soma dimensions and location within the ganglion. The number of motoneurones with somata in the prothoracic ganglion and their homology with cells in the other thoracic ganglia are discussed.