An Electron Microscopic Study of the Endocrine Dorsal Bodies in Reproductively Active and Inactive Siphonaria Pectinata (Pulmonata: Mollusca)

The fine structure of the dorsal bodies of the pulmonate limpet Siphonaria pectinata is described in the context of female reproduction involving egg production. In reproductively-active (egg-laying) animals, the ciliated dorsal body cells are filled with lipid droplets and mitochondria. Gap junctions are commonly seen between the cells. The Golgi complexes and the smooth endoplasmic reticulum constitute the other prominent cell organelles. In reproductively-inactive (non-egg-laying) animals, there is a significant reduction in the number of lipid droplets and evidence of reduced synthetic activity in the dorsal bodies. About 12 dorsal body cells are present immediately underneath the perineurium of each cerebral ganglion of the central nervous system. These internal cells are structurally similar to those outside the central nervous system. Cell processes of some of these cells exit the central nervous system at a minimum of three locations on each side and they come in close proximity to the dorsal body cells outside the cerebral ganglia. Like the external cells, the internal cells also communicate via gap junctions and exhibit structural differences according to whether or not the animals are reproductively active. The dorsal body cells, inside and outside the central nervous system, appear to be innervated by neurosecretory axons suggesting neuronal control of dorsal body activity.