The number of ganglion cells in the intact and regenerated nervous system in the earthworm (Lumbricus terrestris).

1. The nerve cell number is higher in the cerebral ganglion than in the subesophageal or segmental ganglia of Lumbricus terrestris. 2. The nerve cell number of the subesophageal ganglion is similar to that of the segmental ganglia in spite that the latter developed from a fusion of several ganglia. 3. Segmental ganglia in front and behind the clitellum can be considered as "typical" ganglia. 4. The most caudal segmental ganglia are less differentiated and resembles to the embryological state. 5. Nerve cells of the regenerating ganglia, at least in part, originate from undifferentiated nerve cells of the intact ganglia.