The interdependence of retinotectal and intertectal connections in the ontogeny of the visual system of the frog (Rana pipiens) was studied. To remove the direct afferent input from retina to one side of the tectum one eye was taken out at different embryonic and larval stages of development. Animals were allowed to pass through metamorphosis, at which time intertectal connections linking the visual input to the two sides of the tectum normally develop. Responses to visual stimulation were then recorded with extracellular microelectrodes from both sides of the tectum. In all animals eye removal resulted in size reduction of the tectum on the side of the remaining eye. Eye removal prior to the onset of metamorphosis (stage XIX) resulted in gross abnormalities of visually evoked responses in the tectum ipsilateral to the remaining eye; receptive fields were much larger than normal, localization was poor, and responses fatigued rapidly upon repeated stimulation. Eye removal after the onset of metamorphosis, on the other hand, did not result in any detectable abnormalities of the ipsilateral visual responses; receptive fields were small and well localized. This normal ipsilateral visuotectal projection persisted indefinitely (up to 273 days) in the absence of one eye. We conclude that there is a Necessary interaction between the developing intertectal pathways and the afferent fibers linking retina and tectum. This interaction appears to be completed during metamorphosis. The data presented in this and the preceding paper12argue against any subsequent interactions between the retinotectal and intertectal connections. Furthermore, the two papers together suggest that the interactions taking place during metamorphosis are the result of intrinsic developmental mechanisms and are not altered by sensory stimulation. © 1973.
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