Organization of the sensory system of the earthworm Lumbricus terrestris (Annelida, Clitellata) visualized by DiI

The anatomical organization of the peripheral and central sensory structures of the earthworm Lumbricus terrestris was investigated applying a fluorescent carbocyanine dye (DiI) as a neuronal tracer. Using whole-mount preparations and confocal laser scanning microscopy, the pattern of primary sensory cells and pathways of their processes were traced and reconstructed in three-dimensions. Our study shows that a ventral nerve cord ganglion receives sensory fibers from at least two adjacent segments suggesting that the peripheral nervous system is not segmental in its arrangement and the receptive-fields of the body wall overlap in earthworms. Furthermore, our result suggests an integrative function of the basiepidermal plexus consists of sensory and motor fibers.