Fig. 5. Marginal zone internalization without blastopore closure in Xdd1-expressing embryos. Optical flow analysis of control (A; see Movie 2 in supplementary material) and Xdd1-injected (B; see Movie 3 in supplementary material) embryos. As indicated in the key in panel C, color denotes the direction of flow in a' and b' (e.g. yellow lines indicate dorsal movement; blue lines indicate ventral movement). Opposed flow (e.g. yellow meeting blue) represents internalization and is highlighted with white boxes. Cell tracings of Xdd1-injected embryos (D,d') also reveal the internalization of cells in both the marginal zone and yolk plug.