St05a-2.35hpf

16-cell embryo (2.35 hours). All animal and vegetal cells have undergone a fourth cleavage. First sign of a clear antero-posterior polarity in the shape of embryo, resulting from the action of the CAB: the B5.2 blastomere is significantly smaller than the others. This stage is split into early, uncompacted,16-cell stage (Stage 5a) and late, compacted, 16-cell stage (Stage 5b).

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