Weakly electric fish occupy a special place in the field of neuroethology as a model system for the study of the neurobiological basis of natural behavior. Comprising two orders of freshwater teleosts, the Gymnotiformes and the Mormyriformes, weakly electric fish have evolved diverse electric organ discharges (EODs) that are used for electrolocation of objects and for sex- and species recognition, courtship, aggression, and appeasement, among other behaviors (Bullock 1982; Heiligenberb & Bastian 1984). Aside from the variety of EODs, the elements of electric communication that make it a model system include the presence of a highly specialized electrosensory system with a subpopulation of receptors and neurons dedicated to communication signal sensing, as well as the structure of the electrical signals themselves, which is relatively simple and amenable to study by experimental manipulation (Hopkins 1988). This paper presents the results of two studies on mormyrid fish and the electric organs (EOs) responsible for weak electrogenesis. In mormyrids, the electric organ is composed of four columns of serially stacked, dish-shaped electrocytes, two on each side of the spinal cord (Bennett 1970; Bass 1986). The central theme of this thesis is the relationship between electric organ morphology and EOD waveform. The first chapter presents a study of Paramormyrops kingsleyae that shows geographic variation in signals correlated with variation in electric organ anatomy. The second chapter is a descriptive study of larval and juvenile Brienomyrus brachyistius that identifies morphological correlates of EOD change in the course of development.