TEMPERATURE-INDEPENDENT PERIOD IMMEDIATELY AFTER FERTILIZATION IN SEA-URCHIN EGGS

The experiments described here explore the regulation of the duration of cleavage cycles in sea urchin eggs. We measured the timing of early cleavages in individual fertilized eggs under various temperature con ditions and applied methods of statistical analysis to the data obtain ed. At least for the first three cleavages, the temperature dependence of the cleavage intervals was nearly equal. In addition, we identifie d a temperature-independent period at the beginning of the first cleav age cycle. This period occurs immediately after fertilization and last s for several minutes. Our results suggest that this interval of tempe rature independence is related to the process of egg activation.