After the formation of the zygote, it undergoes
cleavage that leads to the formation of daughter cells called
blastomeres. The embryo with 8 to 16 blastomeres is called
a morula. Morula continues to divide and transforms into
blastocyst. Blastocyst consists of 64 cells and has a cavity
present within the cell mass. This cavity is called blastocyst
cavity or blastocoel. Implantation takes place at blastocyst
stage. Gastrulation is the transformation of implanted
blastocyst into gastrula which forms three germ layers by
rearrangement of the cells.