A mature angiosperm embryo sac (megagametophyte) contains 8 nuclei organised into 7 cells: 3 antipodal cells (3 nuclei), 2 synergid cells (2 nuclei), 1 egg cell (1 nucleus), and 1 central cell with 2 polar nuclei (2 nuclei). Total = 3+2+1+2 = 8 nuclei in 7 cells. This is the standard Polygonum-type embryo sac.