The schematic inset(E) shows the experimental setup to label GCs, which may have formed two collaterals, one to the tectum (Fluorogold) and the other to the contralateral retina (4Di-10ASP).A, B, Same retinal region at E16 with Fluorogold-loaded GCs (A) from the tectum and one single ganglion cell (B) loaded with 4Di-10ASP from the contralateral retina. Arrows point to the position of this cell. Part of the cell is visible within the Fluorogold filter because of the selection of the emission window, but the cell is not double-labeled. C, D, Similar setup, with the single cell in D containing only 4Di-10ASP, thus indicating no collateral formation to the tectum, because it remained unlabeled with Fluorogold (arrows). Scale bar, 25 μm.