| Abstract: | The infracerebral gland of Nereis consists of an epithelium covering the ventral surface of the posterior region of the brain. The thickness of the epithelium varies greatly in different species, and it appears especially well developed in Nereis limnicola. Cells of the most numerous type are in direct contact with the base of the brain. Their apical surfaces bound a coelomic sinus, below which is a blood plexus. Other cells are fuchsinophilic and contain many inclusions resembling elementary neurosecretory granules. A third type is rare and resembles glial elements. A number of nerve tracts run from the neuropil to the base of the brain in the region of the gland. Where they impinge upon the capsule they form swellings containing elementary granules and small vesicles. Some axons do not end on the capsule but pass through the capsule and then ramify among the cells of the gland. The swollen endings of other fibers, probably nervous in character, are packed with mitochondria and are scattered over the inner surface of the capsule in the region of the gland. The features described are suggestive of a neuroendocrine complex, and the relation between the brain and the infracerebral gland is in need of experimental analysis in view of the important endocrine functions presently ascribed to the brain in nereids. |
