Explanation

Blastocyst Formation At the next stage of development (morula), which produces an embryo with about 64 cells, a cavity is formed with in the cell mass. This cavity is called blastocyst cavity (blastocoel) and the embryo is termed as blastocyst. Blastocyst composed of an outer envelops of cells the trophoblast or trophoectoderm and inner mass cell (embryoblast). The side of the blastocyst to which inner mass cell is attached is called embryonic pole (animal pole), while opposite side is the abembryonic pole The trophoblast encircles the blastocoel and inner mass cell. The inner mass cell is the precursor of the embryo. It means that inner mass give rise to embryo. The cells of the trophoblast helps to provide the nutrition to the embryo. The cells of the trophoblast form extra embryonic membranes namely chorion and amnion. The cells of the trophoblast which are in contact with inner mass are called cells of raubers [image:3_image85.png] Blastomeres are of two types (i) Trophoblast It give nourishment to embryo by attaching it to endometrium wall (ii) Inner Mass of Cells They give rise to three germ layers and form embryo