Studies in situ on the neurosecretory system of the earthworm, Pheretima posthuma



The neurosecretory system of the earthworm, Pheretima posthuma, has been studied by PF, PATh and PAVB bulk-stained preparations and sections. There are three types (a, b and c) of neurosecretory cells in the cerebral ganglion, suboesophageal ganglion and the nerve cord ganglia. Axons of a- and b-cells are observed in toto in the cerebral and the suboesophageal ganglions. The axons are short and their axonal ends are bulb-like. While the axons of the neurosecretory cells of the cerebral ganglion remain directed ventrally, those of the suboesophageal ganglion converge in a small area. This area has been considered as the neurohaemal organ, but of an elementary type.

In the cerebral ganglion b-cells exhibit a vacuolated cytoplasm. Vacuoles of varying size and number have been observed in those cells whose perikarya are loaded heavily with NSM. The vacuoles and the associated neurosecretory material extrude from the cell after rupturing the cell wall and the released material, associated with the vacuoles, is observed in the form of discrete bodies between the neurosecretory cells. After traversing the intercellular spaces the NSM accumulates on the ventral surface of the cerebral ganglion and some material is found to extend towards the suboesophageal ganglion, via the circumoesophageal connectives. It is suggested that a part of the NSM is absorbed into the blood vessels in the region of the cerebral ganglion and the remainder in the region of the suboesophageal ganglion; but the mechanism by which the liberated material is absorbed in the blood has not been determined. Thus in Pheretima there are two neurosecretory pathways—intracellular and intercellular—for the transportation of NSM elaborated by the perikaryon.