Cortical Expressions of Polarity in the Starfish Oocyte*

Abstract

The animal‐vegetal (A‐V) axis in oocytes of the starfish Pisaster ochraceus and Asterina pectinifera is described in terms of new cytological observations. Ordinarily, this axis of polarity is revealed by the eccentric germinal vesicle that is displaced toward the animal pole where polar bodies eventually form. In addition, however, the cortex at the animal pole is characterized by a pre‐meiotic aster (centrosomes and bundles of microtubules lying within folds of the nuclear envelope), an absence of large, so‐called “acidic vacuoles” that occur abundantly everywhere else, a diminished ability to form actin‐filled spikes, and local mechanical weakness. These expressions of the A‐V axis within the cortex are documented by micrographs. The problem of distinguishing if any feature is an “expression” or a “determinant” of axial differentiation is briefly discussed.