Abstract
Present knowledge of the properties of the myoneural systems of the Platyhelminthes and Echinodermata is reviewed. There is, as yet, no compelling evidence for the presence of a non-polarized nerve network in the members of either phylum. Attention is drawn to similarities between the spontaneous activity patterns shown by preparations representative of these two phyla and of sea anemones. The possibility is considered that in all these cases the controlling physiological machinery may be the same.

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