Patterns of cell division during visual streak formation in the frog Limnodynastes dorsalis

The site and extent of cell division were determined in midlarval tadpoles, animals at metamorphic climax and 2-month juvenile Limnodynastes dorsalis using untreated animals and those injected with colchicine or [3H]thymidine shortly before sacrifice. Mitosis was restricted to the ciliary margin at all stages and there were significantly more dividing cells nasally and temporally than dorsally and ventrally. In animals injected with [3H]thymidine and killed at a subsequent stage, labelled cells were grouped at a distance from the ciliary margin and were more frequent in nasal and temporal than in dorsal and ventral retina. These results suggest that differing extents of mitosis around the ciliary margin, reflected in the number of cells entering the ganglion cell layer, may largely underlie the postmetamorphic formation of a visual streak observed using wholemounts.