EFFECTS OF CHEMICAL REAGENTS ON THE CYCLIC CHANGES OF CORTEX AND CYTOPLASM IN THE ACTIVATED ENUCLEATED EGG-FRAGMENTS OF THE SEA URCHIN*

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Abstract
Unfertilized eggs of sea urchins, Anthocidaris crassispina and Hemicentrotus pulcherrimus, were separated by centrifugation into 2 fractions (nucleated light and enucleated heavy fragments). The enucleated egg-fragments were activated by treatment with 1 M urea and then put into sea water solutions of the following 3 reagents; colcemid, cytochalasin B and Monogen at a concentration by which cleavage was suppressed. Whether the egg fragments can exhibit cyclic changes of cytoplasm and cortex in correlation with the cleavage cycle in normally fertilized eggs with no influence of nuclear activity was examined. Colcemid can suppress the cyclic appearance of cytoplasmic changes, but not that of cortical changes. In cytochalasin B and Monogen-treated fragments, the periodicity in cortical activities is suppressed, while the periodic changes in the cytoplasm appear according to a time schedule of the cleavage cycle. Cyclic changes can occur in the cytoplasm and cortex independently, without the direct influence of nuclear activity either of them is arrested, the cleavage does not occur. The normal cleavage requires the simultaneous occurrence of periodic activities both in the cortex and in the cytoplasm after fertilization.