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		Results The embryos were observed for twenty-four hours. Embryos developed normally until reaching the hatched blastula stage (Figure 1 & 2 ). Following this stage development in Treatment A slowed and loss of cadherin adhesion was apparent. Compared to the control after 20 hours (Figure 3), cells, which would have been part of the blastocoel, appeared to separate from the embryo (Figure 4). In Treatment B, cell division appeared normal until gastrulation. Many of the embryos died, and others seemed to be arrested in development. When the embryos were transferred at the vegetal plate stage, they appeared to have lost all adhesion properties, resulting in an unorganized cell mass (Figure 5).       Discussion In this experiment, the effect of calcium during sea urchin fertilization was investigated to find the role and importance of cadherins in the regulation of cell adhesion. Even after 20 hours, the embryos grown in calcium-free seawater show no signs of PMC ingression, vegetal plate thickening, or archenteron formation (Figure 4). From the observations made during this experiment, it can be concluded that the loss of calcium, and therefore cadherins, affects three developmental events. First, the acquisition of cell polarity in cleavage-stage blastomeres, second, the epithelial-mesenchymal conversion of epithelial cells to mesodermal derivatives, and third, the convergent extension movements involved in constructing the archenteron (Miller and McClay, 1997). Without calcium present in the seawater during early development, sea urchin embryos will fail to complete gastrulation.