The first few specialized divisions of an activated animal egg; Stage consisting of 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. [ http://en.wikipedia.org/wiki/Cleavage_(embryo) http://amigo.geneontology.org/amigo/term/GO:0040016 ]