Cytology and Histology of the Cerebral Neurosecretory Systems in some Tropical Earthworm Species

Abstract

The cerebral ganglia of tropical earthworms, Metaphire houlleti, Metaphire posthuma (Megascolecidae), Eutyphoeus gammiei (Octochaetidae) and Eudrilus eugeniae (Eudrilidae) revealed mainly two categories of neurosecretory cells (NSCs) – A cells and B cells. Thick cortical tier of A cells stained intensely with AF and were differentiated into A1, A2 and A3 types on the basis of their shape, size and location. The sub-cortical B cells, lying close to the neuropile stained lightly with AF. While the axons of A1 cells discharged neurosecretory material (NSM) beneath the perineurium, those of A2, A3 and B cells generally transported NSM at the margin of the neuropile forming “accumulation zone”. Our present study revealed that in earthworms, in absence of any well-defined neurohaemal organ, there was a phenomenal deposition of NSM in the “accumulation zone” or tissue spaces beneath the highly vascular perineurium from where the secretion readily entered the capillaries by diffusion to meet the physiological demand of the animal.