The microscopic anatomy and ulrastructure of the nervous system in the earthworm (Lumbricus sp.) with emphasis on the relationship between glial cells and neurons

Subesophageal ganglia and the first four ventral chain ganglia from earthworms of the genus Lumbricus were examined by light and electron microscopy. Trypan blue injections indicated that this substance does not pass beyond the cord sheath. Tritiated isoleucine displayed a general non‐neuronal distribution after one‐half hour exposure but the amino acid was progressively concentrated in neurons at 1 and 2 hours. Ultrastructural studies indicated that a form of cytoplasmic inclusion was common to glial cells and neurons, and that a similar type material was present extracellularly in the cord sheath. Three distinct variations of glial cytoplasm were recognized at the ultrastructural level, and these appeared to be conditioned by the location of the glial cell in the nervous system. A sequence of morphology was observed which suggests that glial cells in the earthworm transport material from the cord sheath to the neurons. The glia directly associated with neurons sent a number of invaginating processes into the neuron which may from the anatomical basis for exchange of materials.