Texture of the zona pellucida of the mature pig oocyte. The mammalian egg envelope revisited Jacques E. Fléchon, Vaclav Kopecny, Juraj Pivko, Antonin Pavlok and Jan Motlik Reprod. Nutr. Dev., 44 3 (2004) 207-218 DOI: 10.1051/rnd:2004026