Size of Perivitelline Space and Incidence of Polyspermy in Mouse Oocytes Matured In Vivo and In Vitro Ueno, Sayaka and Niimura, Sueo, Journal of Mammalian Ova Research, 25, 44-49 (2008), DOI:http://dx.doi.org/10.1274/jmor.25.44