polar lobe
In some molluscs a polar lobe appears as a clear protrusion close to the vegetal pole of the cell prior to the first cleavage, and becomes associated with only one of the daughter cells. Removal of the first polar lobe, or of any polar lobe that forms at a subsequent mitosis, leads to defects in the embryo; it seems that the polar lobe contains special morphogenetic factors.

Dictionary of molecular biology. 2004.

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