Explanation:

The formation of the female gametophyte from a single functional megaspore is called as monosporic development.

The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles. This forms a two-nucleate EMBRYO SAC.

Two more sequential MITOTIC nuclear divisions result in the formation of four-nucleate and eight-nucleate stages of embryo sac.

These mitotic divisions are free nuclear type in which karyokinesis is not followed immediately by cytokinesis.

After the eight-nucleate stage, the walls are laid down leading to the ORGANIZATION of the typical female gametophyte. SIX of eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.

A typical angiosperm embryo sac at maturity is eight nucleate and seven cells. Three cells lie at micropylar end forming egg apparatus. Three ends at chalazal end called as antipodal cells. A single large central cell which has two polar nuclei.