Journal of Entomological Research

The cephalic neuroendocrine system in the water beetle, Cybister tripunctatus, consists of four paired groups of neurosecretory cells in the brain, corpora cardiaca and corpora allata. In each hemisphere of the brain, the medial and lateral groups of neurosecretory cells are located in the mid-dorsal and lateral regions of the protocerebrum while the ventral and optic groups of neurosecretory cells are confined to the tritocerebral and optic lobes respectively. The axons of both the groups of the medial neurosecretory cells co-inhere into the distinct medial neurosecretory pathways which run dorso-ventrally, cross each other at the mid region and after emerging out from the ventral region of the brain, constitute the nervi corporis interni (NCCI). Similarly, the axons of both the groups of lateral and ventral neurosecretory cells form the lateral and ventral neurosecretory pathways and after emerging out from the ventral region of the brain, both pathways collectively constitute the nervi corporis externi (NCCII). The optic neurosecretory pathways, however, terminate in the optic lobes. Both the NCCI and NCCII run for a short distance and enter the corpora cardiaca (CC). The CC are bluish-white, paired, fusiform bodies lying ventral to the brain on the mid-dorsal region of the anterior part of oesophagus. The wall of the CC consists of an outer thin, transparent peritoneal membrane and internal layer of connective tissue intermingled with some axonal fibers and trachea. It is internally filled with the extrinsic cerebral neurosecretory axons loaded with NSM, the intrinsic neurosecretory cells and few glial cells. The intrinsic neurosecretory cells (INC) are of two types, the chromophilic and chromophobic cells.