Horseradish peroxidase (HRP) tracings showed a bidirectional connection between the optic tectum (OT) and the ipsilateral nucleus isthmi (NI) pars magnocellularis (Imc) in nocturnal Gekko gekko and diurnal Shinisaurus crocodilurus. We found that, in addition to a direct neuronal pathway, there is an indirect pathway from OT to Imc via the nucleus profundus mesencephali (NPM). The morphology of cells in OT, NPM and NI was studied. Visual units extracellularly recorded from NI were located within Imc based on cobalt sulphide markings. They responded to moving contrast targets, without reacting to tactile and auditory stimulation. HRP and Golgi-Cox studies showed that Imc is a nucleus independent of its parvocellular partner, Ipc.