Cleavage begins while the egg is still in the hen s oviduct.
At the end of cleavage, a disc of cells called the blastodisc or blastoderm , sits on top of the yolk. Figure 2.12 - Cleavage in chick Early cleavages, extend down from the surface of the cytoplasm. Unlike Xenopus , the cleavage furrows in the chick egg do not extend into the yolk. So cells are not completely separated and the ventral sides of the cells are open to cytoplasm. As cleavage continues, a disc of cells or the blastoderm forms.