Egg water from the amphibian Bufo arenarum modulates the ability of homologous sperm to undergo the acrosome reaction in the presence of the vitelline envelope.
Krapf D, O'Brien ED, Cabada MO, Visconti PE, Arranz SE. Egg water from the amphibian Bufo arenarum modulates the ability of homologous sperm to undergo the acrosome reaction in the presence of the vitelline envelope. Biol Reprod. 2009 Feb; 80(2):311-9.