Fig. 1. Regular mosaics of cholinergic and horizontal cells appear when and where a continuous net of dendrites connects neighbouring array cells. (A) The ChAT-positive cells of the GCL are regularly spaced at P0, and a continuous net of dendrites links neighbouring elements. (B) An incomplete net of ChAT immunoreactive processes is observed at E21, and irregular cell spacing is observed close to the gaps in the net of processes (e.g. cell clusters indicated by arrows). (C) At P4, the horizontal cells are regularly spaced in the central retina, and linked by a continuous net of processes. (D) At the same age, irregular cell spacing and gaps in the net of horizontal cell processes are observed in the peripheral retina. Confocal images. Scale bars: in B, 10 µm for A,B; in D 10 µm for C,D.