A fine structural analysis of the ventral nerve cord and associated sheath of Lumbricus terrestris L.

This study is a fine structural analysis of the earthworm nervous system and its sheath. The bulk of the findings consists of the addition of fine structural detail to the extant descriptions of the general organization of this system. These findings were of particular interest, (1) that the nervous system possesses one basic type of supportive glial cell, (2) that the zonula occludens was not found anywhere in the structures studied here, and (3) that the sheath of the ventral giant axon is not myelin but consists of a thick covering of many tiny axons and synaptic terminals.