Cleavage is the division of cells in early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth. The different cells derived from cleavage called blastomeres and form a compact mass called morula. cleavage ends with the formation of blastula. 

Cleavage can be holoblastic, entire cleavage or meroblastic, partial cleavage.

At the end of eight cell stage, embryo goes through some changes. Most of the blastomeres become polarised and develop tight junctions with other blastomeres causing development of two types of cells. Polar cells are outer called trophoblast , apolar are inside .

The trophoblasts give rise to embryonic contribution to placenta called chorion and inner cells pushed to one side of cavity ro form the inner cell mass. It will give rise to embryo and embryonic membranes.