Electrophysiology of the peripheral nerve net in the polyclad flatworm Freemania litoricola

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Abstract
A diffuse-conducting system close to the dorsal epithelium of the polyclad flatworm Freemania litoricola is described. Tactile stimuli elicit small action potentials which can be conducted around lesions through the body wall. The potentials can occur in bursts or barrages. This conducting system appears to be insensitive to Mg2+ ions. Conduction velocities (0·26–71 m/sec) vary over the animal. Conduction spread in the anterior half of the animal appears to be greater than that in the posterior portion. Response decrement to repeated stimulation can be recorded in the peripheral system but it is not clear if this is due to habituation or fatigue. Conduction from the peripheral net to the brain occurs. Some central units appear to pick up information only, or mainly, through the anterior nerves, while other units can respond to information conducted through the network to nerves of the contralateral side. Different possibilities to account for this system are discussed, and it is suggested that the animals either possess a unique Mg2+ insensitive synaptic nerve-net or else the network is electrically coupled.