Figure 6

Contralateral retinotectal projections in E. coqui ( A - C ) and D. pictus ( D-F ) as revealed by biocytin tracing. At two days before hatching, the optic projections of E. coqui (A, B) resemble early larvae of D. pictus (E, F). After crossing in the optic chiasm (OC) the majority of retinofugal fibers forms the marginal optic tract, which courses dorsally in the thalamus and forms a first terminal field in the rostral visual nucleus (RVN; this probably corresponds to the nucleus lateralis of [32]) (A, E). Retinofugal fibers extend further until the optic tectum and cover approximately its rostral half (B, F). In E. coqui, the density of optic fibers on the tectal surface (see arrows in magnified inset of B) is much sparser than in D. pictus. At 12 days after hatching, optic fibers have reached the caudal end of the tectum in E. coqui, but do not yet extend towards its midline (C: section through midtectum; arrowheads indicate medial limit of coverage). In contrast, optic fibers cover the entire tectum in D. pictus at the end of metamorphic climax (G: section through midtectum). Bar: 100 μm in all panels.