The corpuscles of Stannius are special endocrine organs in the kidney in fish and are responsible for maintaining calcium balance. They are found only in bony fishes. They were discovered and described by a German anatomist Hermann Friedrich Stannius in 1839. Stannius considered them as functionally similar to adrenal glands in mammals. But they have later been found to be anatomically different as they are derived from different tissues of the embryo. Structurally the corpuscles are a large number of spherical bodies separated from each other by loose connective tissues. Each body or lobule is in turn composed of several columnar cells, which contain secretory granules and are, thus, secretory in function. Each Secretory granule is spherical in shape and measures 0.5 to 1 μm in diameter.