Two consecutive exocitotic events occur before and after gamete fusion being accomplished. Sea urchin sperm must undergo the acrosomal exocytosis that is triggered by fucose sulfate polymer in jelly coat in order to bind to the vitelline layer of the egg. Species-unique patterns of repetitive sulfates in fucose sulfate polymer confer the species-specificity of their biological activities. The specificity of fertilization is further reinforced by the interaction between sperm’s molecular glue, bindin and its receptor(s), thereby discouraging the generation of lethal hybrids. Sperm-egg fusion leads to crucial exocytosis of the cortical granules underlying the egg plasma membrane, resulting in the formation of the fertilization envelope. This cortical granule exocytosis has been found to occur in mature eggs but not in immature oocytes. In an in vitro experiment, starfish prophase-arrested oocytes, when inseminated, allow extra sperm to enter, whereas monospermy is achieved in mature eggs under the same condition. A maturation-inducing hormone called 1-methyladenine induces the cortical maturation, a condition where cortical granule exocytosis being ready to trigger in response to fusion of a single sperm. It was found, however, that the cortical maturation does not always correlate with reinitiation of meiosis progression. The activation of maturation promoting factor (MPF) that is mandatory for release of MI-arrest may not be required for the cortical maturation. The data suggested that factor(s) that is involved in the cortical maturation do not readily diffuse in the cytoplasm, rather it remains associated with the cortex.