This movie shows ex vivo live imaging of genetically-labeled On SACs from control retinas in mice. The images were taken every 20 minutes for eight hours. At this stage, control On SACs have already established their characteristic, radially symmetric dendritic morphology, which permits normal retina function. This video relates to a paper that appeared in the 1 Nov., 2013, issue of Science, published by AAAS. The paper, by Lu O. Sun at he Johns Hopkins University School of Medicine in Baltimore, MD, and colleagues was titled, " On and Off Retinal Circuit Assembly by Divergent Molecular Mechanisms."