Embryo sac is the female gametophyte. It is an eight nucleated structure consisting of egg apparatus, polar nuclei and antipodal cells.
Egg Apparatus: After fertilization, gives rise to diploid zygote which later on develops into an embryo.
Polar nuclei: The two polar nuclei fuse to form single diploid secondary nucleus. The secondary nucleus forms the triploid endosperm nucleus, which produces endosperm in which food for the embryo is stored.
Antipodal cells: These are nutritive cell. They degenerate during seed formation.