II. Ultrastructure of the type B sense organ of the specific lateral line system of Gymnarchus niloticus

Summary The type B cutaneous receptor represents one of the three kinds of specific organs of the lateral line system of Gymnarchus niloticus (Szabo and Barets, 1963). Electron microscopic observations reveal that the elementary unit (Fig. 18) of the type B organ consists of a well organized assembly of different epithelial elements grouped around each sensory cell. Several such units compose a type B organ innervated by a single myelinated nerve fiber.The cytoplasm of the sensory cell is characterised by a deep invagination lined by long and densely packed microvilli covered by a jelly-like substance. This jelly substance of allongated stylet form is situated in an intraepidermal cavity, overlaid by vacuolised epithelial cells oriented perpendicularly toward the external epidermal surface.Certain morphological characteristics of the organ B allows the conclusion that this organ is one of the possible electroreceptors of the Gymnarchus niloticus.This work was supported by grant No. 659535 of the Direction de Recherches et Moyens d'Essais (D.R.M.E.) to Dr. Szabo.This work was carried out on the electronmicroscope of the Service de Microscopie Electronique du Laboratoire de Médecine Experimentale (RCA) et du Laboratoire d'Histologie Normale et Pathologique du Système Nerveux (Siemens).With the technical assistance of Miss L. Seguin and Mr. C. Pennarun.