Cleavage (embryo)
（重定向自Bilateral cleavage）
![D quadrant specification through equal and unequal cleavage mechanisms. At the 4-cell stage of equal cleavage, the D macromere has not been specified yet. It will be specified after the formation of the third quartet of micromeres. Unequal cleavage occurs in two ways: asymmetric positioning of the mitotic spindle, or through the formation of a polar lobe (PL).](/Images/godic/202412/24/Equal_vs_unequal_cleavage3001.jpg")
![Spiral cleavage in marine snail of the genus Trochus.](/Images/godic/202412/24/Spiral_cleavage_in_Trochus3001.png")
![The initial stages of human embryogenesis.](/Images/godic/202412/24/HumanEmbryogenesis.svg3001.png")
In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula. Cleavage ends with the formation of the blastula.