In the ovule, the surviving megaspore undergoes three mitotic divisions to produce a seven-celled eight nuclei as a female gametophyte called an embryo sac.
One of these cells is an egg cell.
The largest cell contains two polar nuclei.
The embryo sac is the mature female gametophyte.
In the majority of flowering plants, one of the megaspores is functional while the other three degenerate.
The functional megaspore only develops into a female gametophyte (embryo sac).
The embryo sac represents a female gametophyte or megagametophyte.