Electron Microscopic Studies of the Ultimobranchial Body of the Elasmobranchs

Abstract

The ultimobranchial bodies of two species of elasmobranchs-smooth dog fish, Mustelus manazo BLEEKER and sting ray, Dasyatis akajei MULLER and HENLE-were observed with the electron microscope.1. In the ultimobranchial bodies of smooth dog fish many vesicles are scattered in abundant connective tissue, while in those of sting rays vesicles and cell cords are closely packed.2. Two types of cells, barrel cells and finger cells, are found in the vesicles in both species. The barrel cells are more endocrine in nature, and the finger cells are more exocrine or supporting. In sting rays the barrel cells are more prevalent in number than the finger cells and the cell cords are exclusively composed of the barrel cells.3. The barrel cells are round to oval and do not directly limit the vesicle cavity. Many secretory granules are stored in the cytoplasm, and are often in direct contact with the lateral or basal plasma membranes without changing their size and density. The secretory granules appear to be formed in the Golgi zone. Occasionally, filament bundles appear around the nucleus where mitochondria, secretory granules and rough-surfaced endoplasmic reticulums are entangled. The secretory granules are larger and denser in sting rays than in smooth dog fish.4. The finger cells have elongated cell bodies, well developed interdigitations and desmosomes and surround the barrel cells. They limit the vesicle cavity with free apical surfaces from which short microvilli project to the lumen.