The role of the zona pellucida in the development of mouse eggs in vivo

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Abstract
Up to the present time the function and significance of the zona pellucida in the development of mammalian eggs has not been fully explained. Zona-free mouse eggs will develop in vitro from the 2-cell stage, or later, up to the blastocyst stage (Tarkowski, 1961; Mintz, 1962; Gwatkin, 1963). Single blastomeres isolated at the 2-cell (Mulnard, 1965), 4- and 8-cell stage (Tarkowski & Wrób-lewska, 1967) will also develop in vitro up to the blastocyst stage. Similar experiments on development in vitro of 1- and 2-cell rabbit eggs (Edwards, 1964) showed that in this species also cleavage can occur when the zona pellucida is absent, although the blastomeres exhibit a tendency to fall away from each other.