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In order to divide asymmetrically, the vegetal blastomeres at the 8-cell stage must position their mitoticspindles near their vegetal ends, so that the division results in a macromere and a micromere. The image shows the microtubules of the mitotic spindle at the 4th cleavage, shows how asymmetric this division is.
Credit: George von Dassow, Center for Cell Dynamics, University of Washington.
Source: The Hardin Lab, University of Wisconsin