On the Regional Difference in the Nature of the Cortex of the Sea Urchin Egg During Cleavage

When the susceptibility of the cleaving sea urchin egg to various agents was studied in a previous paper (1954 a), a conclusion was reached that the nature of the egg surface differed between the furrow and the polar region. This conclusion, in turn, may suggest that the egg surface or the cortex might play an important role in cleavage. The former half of the present paper concerns an extension of the previous study. Recently, MOTOMURA (1954) reported a method to isolate the cortex from unfertilized eggs of the sea urchin (Hemicentrotus pulcherrimus). Employing MOTOMURA'S method with a slight modification, the present author found regional differences in the nature of the cortex of cleaving eggs. Similar differences were also found in the cortex isolated from the parthenogenetic merogones.