cells formed in the process of cleavage of the ovum in multicellular animals. Absence of growth is characteristic of blastomeres, in consequence of which they are diminished by half with each succeeding division (until the formation of the blastula). In the cleavage of holoblastic ova, large blastomeres (macromeres) and small blastomeres (micromeres) are formed with unequal distribution of nutritive substances.