Schematic diagram of horizontal vestibulo-ocular reflex circuitry in teleosts and elasmobranchs. "Goldfish" shows the principal three-neuronal vestibulo-ocular reflex linking the horizontal semicircular canal with contralateral abducens (ABD) and ipsilateral MR motoneurons. "Flatfish" shows that after 90º displacement of the vestibular relative to visual axis (metamorphosis) compensatory eye movements are produced by redirecting horizontal canal signals to vertical and oblique (SR-IO and IR-SO) motoneurons. In "Shark" horizontal canal/second order neurons project to contralateral ABD and MR motoneurons including ipsilateral AI neurons. 1∘, first order vestibular neuron; ATD, Ascending Tract of Deiter’s. Schematic diagrams based on results from Graf et al. (1997; goldfish), Graf and Baker (1985a,b; flatfish), and Graf et al. (2001; shark).