Fig. 4. Distribution of GFP-labelled descendants in the visceral endoderm of post-implantation egg cylinder at E6.5. Blastocyst was labelled with GFP mRNA in an A/PB cell, then examined at early gastrula stage by confocal microscopy (flattened z series). Clones in the extra-embryonic region are coherent, while in the embryonic region they tend to become dispersed. Distribution of visceral endoderm cells reflects characteristic cell displacements (reminiscent of polonaise movements), which are hypothesised to ‘draw’ anterior extra-embryonic cells towards the posterior midline, and spread them along both left and right sides of the embryo. Although similar movements are postulated to occur on both sides of the embryonic part of the egg cylinder, the distribution of labelled cells is not entirely symmetrical, as indicated by differences in clone shapes and the locations of labelled cells on left versus right sides of the egg cylinder. Anterior on the left in the left hand panel