and the macromeres divide meridionally to produce a tier of eight half-macromeres The micromeres divide asymmetrically to produce a of small micromeres at the extreme vegetal pole of tier im the embryo, and a tier of larger micromere derivatives mediately above them(3.8, 3.9). At the sixth cleavage, all cells divide equatorially to produce a 64-cell embryo with five tiers: the daughters of the an, and an, cells lie at the animal pole, the vegu and veg, tiers, derived from the macromeres, lie in the vegetal hemisphere, and the micromere descendants lie at the vegetal pole. At the seventh cleavage, all cells divide meridionally to