HISTOGENESIS OF NEUROSECRETORY SYSTEM IN THE NERVE RING OF Eudrilus eugeniae DURING ANTERIOR REGENERATION
Epigeic earthworms possess great power of regeneration. The present paper deals with gradual appearance of neurosecretory cells, their axons with stainable inclusions (neurosecretory materials) and blood capillaries in regenerating nerve ring (brain and sub-esophageal ganglia) following anterior amputation in South African epigeic earthworm, Eudrilus eugeniae. Amputation of anterior five segments in earthworm, Eudrilus eugeniae is followed by proliferation of new segments in course of regeneration. After 5 post-operative days, regeneration of 3-4 incipient segments with delicate rudimentary brain and sub-esophageal ganglia intimately associated with pharyngeal epithelium appeared. Histologically the rudimentary ganglia exhibited large masses of undifferentiated cells (neuroblasts). Transformation of these cells to neuronal elements with axon like processes was remarkable in the regenerating nerve ring within 10 - 20 days of cephalic amputation. Full grown 5 regenerated anterior segments were formed during the following 20 days. After 30 days the nerve ring was anatomically separated from the pharyngeal epithelium. A few deep stained AF positive A-type and moderately stained B-type neurosecretory cells in the cortex of regenerated brain and sub-esophageal ganglia were found 40 days after anterior amputation. Small islets of deeply stained AF positive ‘U’ cells appeared at the base of circum- esophageal connectives of the sub-esophageal ganglia. Visual examination under microscope revealed dramatic increase in the number of AF positive A cells in the brain and U cells in the sub-esophageal ganglia along with accomplishment of normal secretory dynamics of the neurosecretory cells following 50 days of anterior regeneration.
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