Fig. 2. Three orientations of cell division occur in early Xenopus development. (A-D) Stained mitotic spindles (red) of whole-mount embryos showed three orientations of division. The division plane was extrapolated based on the observation that the spindle orientates at 90° to future division plane (Strome, 1993). Chromosomes are shown in yellow. (A) top view of parallel and perpendicular divisions; (B) side view showing parallel, oblique and perpendicular divisions. (C) side view showing parallel and perpendicular divisions in anaphase. (D) Side view showing oblique division in anaphase. Blue arrows, parallel spindles. Red arrows, perpendicular spindles. Green arrows, oblique spindles. (E) Schematic showing the three orientations of division. Parallel divisions generate two superficial daughter cells. Oblique divisions generate one superficial cell with a large and one superficial cell with a small external surface. Perpendicular divisions generate a superficial and a deep cell. (F) The three orientations of division can be seen in isolated blastomeres judged by the distribution of the pigmented, originally external, surface.