This may also happen by the fusion of the first two blastomeres. With further compaction the individual outer blastomeres, the trophoblasts, become indistinguishable. The action of the determinants on the blastomeres is one of the most important ones. Recently a method was developed allowing to fix metaphase plates from single blastomeres. These mitotic divisions continue and result in a grouping of cells called blastomeres. This first division produces two distinctly different blastomeres, termed AB and P1. The other blastomeres that differentiate, then, will become apolar. And the fate of the blastomeres is not yet determined. Each of the blastomeres that form are also spherical. Finally, the third set of blastomeres are the deep cells. This signaling between particular blastomeres induces differentiation of cell fates and establishes the dorsal-ventral axis. Initial polarization of blastomeres occurs at the 8-16 cell stage. The blastomeres in the blastocyst are arranged into an outer layer called the trophoblast. Blastomere biopsy is a technique in which blastomeres are removed from the zona pellucida. In the "Xenopus" egg, the germ cell determinants are found in the most vegetal blastomeres.