Neurosecretory cells and their axon pathways in Culiseta inornata (Williston) (Diptera: Culicidae)

Abstract

Paired medial, intermediate, and anterior groups of neurosecretory cells are present in the protocerebrum of Culiseta inornata (Williston). The medial and intermediate cells seem to persist through larval, pupal, and adult stages; the anterior cells become inconspicuous about the time of adult emergence. Axons of the intermediate neurosecretory cells could not be traced for an appreciable distance, but axons of the medial cells could be traced to a neurohaemal organ on the aorta, and they appear to constitute the NCC I. Branches of the anterior-cell axons seem to constitute the NCC II, and other branches of these axons in fourth-instar larvae and young pupae can be traced into the ventral nerve chain. From the neurohaemal organ some neurosecretory axons pass into the oesophageal nerves, and the expanded posterior portion of each oesophageal nerve in adults may be a storage and release organ of neurosecretory material. A neurosecretory pathway can be traced from the neurohaemal organ to the corpora allata in adults; it is probably present also in larvae. Conspicuous neurosecretory axons of uncertain origin, which are distinct from the anterior-cell axons, can be traced from the protocerebrum through the circumoesophageal connectives and along the whole length of the ventral nerve chain in fourth-instar larvae; these axons are present, probably in a similar form, also in younger larvae, in pupae, and in newly emerged adults.