Describe a well-controlled experiment to determine if the rise in internal free calcium observed in the cytoplasm of unfertilized sea urchin eggs in the presence of A23187 is due to in flux of calcium from seawater. Include experimental treatments, controls, and briefly describe experimental methods.

Note: As mentioned in the lab manual, the calcium concentration in seawater is 10mM while the concentration in unfertilized egg cytoplam is greater that 10-6 M. Immediately after fertilization or in unfertilized eggs treated with A23187 the internal calcium concentration increases.