Fig. 11. Local cellular movement correlates of (A) convergence and extension in the wild-type embryo, and (B) of extension without convergence in the ntl mutant. The sets of panels show time sequences, at 4 minute intervals, for the notochord (WT)/axial (mutant) domains. For every cell in the field in turn (`reference cell', the point at the center of each plot), we calculate the displacements of all other notochord-domain cells relative to this reference cell, i.e. the cell movement toward or away from the reference cell. This is repeated for every cell in the notochord domain, each cell in turn taking the role of a reference cell. The data are then averaged for each time point, and the resulting averaged plots are shown. The arrows represent the average directions and speeds (length of arrow) of these relative movements; their placements on the grid are according to the positions of the cells relative to the reference cell. Inward cellular movements (i.e. horizontal arrows point towards the reference cell) correlate with convergence of the field, and outward movements (vertical arrows point away from the cell) correlate with extension. Inward movements are not sustained in the ntl mutant. Positions along the x-axis reflect positions along the AP axis relative to the reference cell while positions along the y-axis reflect positions along the ML axis relative to the reference cell. See Movies 17 and 18 at http://dev.biologists.org/supplemental/.

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