Some evidence for the ampullary organs in the European cave salamander Proteus anguinus (Urodela, Amphibia).

The multicellular epithelial organs in Proteus anguinus, which Bugnion (1873) assumed to be developing neuromasts, have been analyzed by light- and electron-microscopy. Their fundamental structure consists of single ampullae with sensory and accessory cells with apical parts that extend into the pit of the ampulla, and of a short jelly-filled canal connecting the ampulla pit with the surface of the skin. The organs are located intra-epithelially and are supported by a tiny dermal papilla. The cell elements of sensory epithelium are apically linked together by tight junctions. The free apical surface of the sensory cell bears several hundred densely packed stereocilia-like microvilli whereas the basal surface displays afferent neurosensory junctions with a pronounced round synaptic body. The compact uniform organization of the apical microvillous part shows a hexagonal pattern. A basal body was found in some sensory cells whereas a kinocilium was observed only in a single cell. The accessory cells have their free surface differentiated in a sparsely distributed and frequently-forked microvilli. The canal wall is built of two or three layers of tightly coalescent flat cells bordering on the lumen with branching microvilli. The ultrastructure of the content of the ampulla pit is presented. In the discussion stress is laid on the peculiarities of the natural history of Proteus anguinus that support the view that the morphologically-identified ampullary organs are electroreceptive. The structural characteristics of ampullary receptor cells are dealt with from the viewpoint of functional morphology and in the light of evolutionary hypotheses of ampullary organs.