The centrifugal innervation of the retina has been extensively described in birds (Cowan, 1970), but only recently has the existence of efferents been demonstrated in a variety of other species, including several species of fish (Witkovsky, 1971; Ebbesson and Meyer, 1981; Munz and Claas, 1981; Munz et al, 1982; Gerwerzhagen et al, 1982; Crapon de Caprona and Fritzsch, 1983; Meyer et al, 1983; Springer, 1983). Retrograde tracing methods have shown that there may be as many as five central sources of fish retinal efferents (Ebbesson and Meyer, 1981). Reports on the number and location of these efferent sources are inconsistent, but there is agreement that one source of retinal efferents is the terminal nerve (TN) (Springer, 1983).
