St04-1.9hpf

8-cell embryo (1.9 hours). The third cleavage plane separates animal from vegetal territories. At this stage, the 4 founder lineages are defined: a animal anterior; b animal posterior, A vegetal anterior; B vegetal posterior. It is possible to identify each blastomere in living embryos, according to their size (B-line is biggest) and spatial arrangement. The embryos compact towards the end of the stage.

Two-headed arrows indicate the pair of daughter cells. The number of cell-lineages are drawn on each blastomere. Scale bar = 50 micro m.