The acrosome is the cap-like structure that found over the anterior portion of the sperm head. Acrosome reaction is the term used to refer to the reactions that take place in the acrosome of a sperm as it penetrates an egg. A number of changes take place in the acrosome that enables it to penetrate its otherwise non-welcoming environment. In 1952, J.C Dan was the first person to study acrosome reaction in the sea urchin.