After the zygote begins to divide, a fluid-filled ball of cells, called blastocyst attaches to the uterine wall. <span>It is the stage of implantation during the prenatal development. The blastocyst consists of an inner cell mass and the outer layer -the trophoblast. Trophoblast surrounds the inner cell mass and a fluid-filled cavity - blastocoele. Inner cell mass will form embryo and trophoblast gives rise to the placenta.</span>
