Cleavage Becoming Multicellular Zygote is activated and begins to divide. Cleavage gives rise over a number of hours to hundreds of cells.
Daughter cells are blastomeres.
Patterns of cleavage influenced by distribution of egg yolk. Formation of the Blastula Blastula is a hollowed out morula. The blastomeres are pushed to the periphery. Fluid filled cavity is blastocoel. If there is little or no yolk, the hollow blastula is punched in on one side, giving rise through invagination to a second layer of cells.