Tracked cells were sorted into four different groups depending on their Otx status and position: Otx(+) boundary cells are color-coded red, Otx(−) boundary cells blue and cells further away from the interface yellow and green, respectively. The position of cells and their descendants is shown at sequential time periods and in dorsal (all images except lower right) and lateral (lower right) views. Otx(+) and Otx(−) cells remain separated during the developmental time analyzed, while mixing of cells in general is not restricted. See Langenberg et al., Developmental Dynamics 235:928-933. © 2006 Wiley-Liss, Inc.