The caudal neurosecretory system of the teleostean Clupea melanostoma

Summary The caudal neurosecretory system of Clupea melanostoma is described. The urophyseal area in this species is merely a spinal cord enlargement divided into two distinct zones: a ventral and ventrolateral vascular zone where neurosecretory material is concentrated, and a dorsal cell-rich area where the perikarya of the neurosecretory cells are found.The hypothesis is advanced that the first-named vascular area has developed into the more differentiated urophysis of the less primitive teleosts while the dorsal cell-rich area has become part of the filum terminale. Two main types of neurosecretory cells are described.This work was supported by grant L 96 Z from the Consejo Nacional de Investigaciones Cientificas y Técnicas.