ABSTRACT
The literature dealing with the peripheral components of the nervous system of the earthworm has been reviewed recently by Stephenson (1930) and Prosser (19346). Hence it is necessary only to mention the principal elements. The sensory endorgans are said to consist of (1) a variety of epidermal cells (“sensory cells”) which have peripheral terminations, are of different shapes, and may be grouped as “sense organs” or may be isolated, (2) free nerve endings, some of which are closely associated with the glandular cells, and (3) intermuscular cells. Certain of the epidermal sensory cells have been shown to be photosensitive; the function of the others is uncertain. Most of them are connected to a subepidermal plexus which appears to be a true network of anastomosing fibres and to contain nerve cells. In each segment three pairs of nerves lead from the central ganglion to nerve rings from which fibres are distributed either by nerve branches or by the peripheral network to the muscles and sensory cells. There is some evidence for and some against conduction of locomotor impulses by the peripheral plexus across segments lacking the nerve cord. Prosser (19346) concluded that the contrary evidence is slightly stronger.
I am greatly indebted to Mr John Z. Young, Department of Zoology, Oxford, for the loan of the slides from which these measurements were made.
