Monoamine‐containing neurons in the nerve cord and body wall of Lumbricus terrestris

This study represents an attempt to reconcile recent quantitative findings of large amounts of monoamines in the earthworm with early histological findings of only small numbers of chromaffin cells in that animal. Using the highly sensitive and specific fluorescence method for the histochemical localization of monoamines, it has been demonstrated that the earthworm nervous system contains large numbers of monoaminergic neurons. At least one‐tenth of the motor and interneuronal population in a typical ganglion of the ventral nerve cord contain either serotonin or primary catecholamines. In addition a large number of neurons containing a primary catecholamine form an extensive sensory system with their cell bodies in the epidermis and their axons terminating in the ventral nerve cord.