Regions of the brain influencing the projection of developing optic tracts in the salamander.

Eye primordia from the Mexican axolotl or the California newt were transplanted into hosts of either species. These "third" eyes often developed an optic nerve that penetrated the host brain and made one of three central projections: bilateral to the dorsal thalami, tecta, and basal optic nuclei; ipsilateral to the same areas; or ipsilateral into the cord. The type of projection made by a transplanted eye seemed to depend on where its nerve first entered the brain. The optic fibers that reached the visual centers of the midbrain were organized retinotopically in the optic tectum and mediated visually-guided behavior.