A pattern of optic axons in the normal goldfish tectum consistent with the caudal migration of optic terminals during...

Optic axons were cut in the goldfish optic nerve or tectum, filled with horseradish peroxidase and traced in tectal wholemounts. Many of them ran in conspicuous fascicles which curved across the tectum. Axons from central nasal retina, which ran in the most rostral fascicles, turned abruptly as they left these fascicles; ran caudally in a diffuse, parallel array for up to half the tectal length; and passed beneath more caudal fascicles to innervate the caudal half-tectum. Axons from peripheral nasal retina ran in the most caudal fascicles and terminated near their turning-points. Axons from temporal retina entered the tectum at its rostral margin and ran caudally from their points of entry to innervate the rostral half-tectum. The resultant pattern was entirely consistent with the proposal that a slow caudal migration of optic terminals compensates during normal development for disparate modes of retinal and tectal growth.