Fig. 6. Emergence of cell polarity in anterior half embryos. (A) Average cell orientation relative to the mediolateral axis of the notochord rudiment. Note the clear anterior-posterior progression in the emergence of a mediolateral orientation in rows 1-3, while cells in the posteriormost row do not become mediolaterally oriented. (B) The average length/width ratio of individual cells increases with a time course comparable to whole embryos. The initial decrease in L/W ratios for rows 2 and 3 reflect the fact that these cells are initially elongated along the AP axis of the embryoid and subsequently change their orientation by decreasing their cross-sectional extent along the AP axis and increasing it perpendicular to the AP axis in the same way that cells within intact embryos do (data not shown). Cells in the posterior-most row remain extended along the AP axis.