Cytomorphological changes in the cerebral and ventral ganglionic neurosecretory cells during copulation in epigeic earthworms

In spite of hermaphroditism, most earthworm species reproduce by cross fertilization i.e. by the process of copulation of two mature partners. Mechanism of copulation in few earthworm species (Lumbricus terrestris) is known. However literature on neurosecretory control of copulation in earthworm is lacking. In the present study 30 pairs of conjugating earthworms of Eisenia fetida were collected from laboratory culture beds during 2016 of monsoon season. Cerebral and ventral ganglia of 10 pairs of conjugating earthworms and 20 pairs of post conjugation (2 hrs after separation, 4 hrs after separation) earthworms were fixed in Bouin’s fluid for cytomorphological studies on their cerebral neurosecretory cells. Earthworms (10 numbers) debrained through anterior transection of first five segments (brain present in 3rd segment) by sterilized paragon knife were studied to observe conjugation if any. Cerebral and ventral ganglia of 5 pairs of pre-conjugating earthworms were considered as control. Cerebral and ventral ganglia of earthworms displayed chiefly two types of neurosecretory cells such as A cells and B cells. The A cells are deeply stained AF-positive cells arranged in upper cortical tier beneath the perineurium and generally exhibiting process of axonal transport. The B cells, generally larger in size than A cells, are lightly or moderately stained with or without axonal transport and lie in between cortical A cells and central fibrous neuropile. In the cerebral ganglia the A cells outnumbered the B cells, while in the ventral ganglia the opposite is true. Debrained E. fetida survived but did not conjugate. Secretory dynamics in the cerebral and ventral ganglionic neurosecretory cells A and B were recorded in pre-conjugating, conjugating and post-conjugating earthworms. Absence of conjugation in debrained worms and exhibition of the same in earthworms with brain and its changes in neurosecretory profile clearly indicate involvement of cerebral neurosecretion in the phenomenon of conjugation in earthworm. Our result indicates probable involvement of cerebral neurohormone in the process of conjugation in E. fetida