This leads to the formation of a cellular blastoderm with central yolk and no blastocoele. Small region of more fluid cytoplasm containing nucleus is found on top of the yolk. Cytokinesis is limited to the original fluid cytoplasmic region. There is no fixed cleavage plan. This organization leads to a discoidal meroblastic cleavage.
Subgerminal space is formed between cell mass and yolk.
Cells at one end of the disc start moving and migrating underneath the disc within the subgerminal space. The blastocoele forms between the two layers. Epiblast will give rise to the embryo whereas the hypoblast will form all extraembryonic membranes. Cytokinesis is slowed down by the large yolk amount but still occurs, this leads to an holoblastic cleavage. The cleavage plan is fixed, following a radial pattern.