Organization of Ampullary Electric Receptors in Gymnotidae (Pisces)

Investigation of 14 species of gymnotid has established that large numbers of ampullary lateralis sense organs are present in each case. These organs have been examined with the light and electron microscopes. Two distinct types occur, and these are referred to as type I and type II; the latter is more common. The fine structure of the receptors in one species (Eigenmannia virescens) is described in detail, and is discussed from two points of view: (i) the function and mode of operation of the organs, and (ii) the evolutionary relationships to different receptors of the vertebrate acoustic-lateralis system.