Cell lineage analysis of the timeline of the first divisions and the spatial positions of the nuclei. A Cell lineage analysis of B. longimanus from the 2-nuclei stage to the 16-cell stage. The four colors represent the quadrants of the 4-nuclei stage, with A - yellow, B - red, C - green, D - blue. The black points mark the time of division. The broken lines show the ‘fixed points’ time line levels of which four are shown as 3D models (B-E). B-E Screen shots of the 3D model in SIMI°BioCell at the 4 fixed points (fxp 1 -4) in A. The vegetal pole faces down in B-D. In B to D the nucleus associated with the ncr is symbolized as gray sphere. In E the embryo has slightly rotated so that the view is from the animal pole. The sister cell relationships are indicated by the black connecting lines. en: endoderm cell, gc: germ cell.