The lorenzinian ampullae of Polyodon spathula

Summary Light and electron microscopic observations on the ampullary organs of Polyodon spathula (Chondrostei, Osteichthyes) reveal a sensory epithelium similar to that found in the Lorenzinian ampulla, an electroreceptor found in marine Elasmobranchs.The sensory cells have a very small luminal part provided with a cilium. They are innervated by many nerve endings. Each nerve fibre apparently makes synaptic contact with several sensory cells. The synaptic structure in the sensory cell is composed of a flat sheet, the outermost part of which is surrounded by 3 or 4 annuli of densely staining material. The sheet extends into a protrusion of the sensory cell, and there is a corresponding invagination in the nerve terminal.The conclusion that these organs are electroreceptors, is supported by the finding that the fish responds to the introduction of an iron tube in the aquarium, whereas a wooden rod introduced in the same way causes no response.