The vertebrate retina has a form that is closely and clearly linked to its func tion. Though its fundamental cellular architecture is conserved across verte brates, the retinas of individual species show variations that are also of clear and direct functional utility. Its accessibility, readily identifiable neuronal types, and specialized neuronal connectivity and morphology have made it a model system for researchers interested in the general questions of the genet ic, molecular, and developmental control of cell type and shape. Thus, the questions asked of the retina span virtually every...