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Ultrastructure of the transzona protrusion (TZP) from cumulus cells through the zona pellucida (ZP) to the oolemma membrane. (A) Ultrastructural details of cumulus–oocyte complexes showing the ZP is traversed by the cumulus cell projection (CCP) or TZP into the perivitelline space (PVS). (B) Zona pellucida of an immature oocyte presenting some CCPs that either end in the PVS (arrow) or form a tight junction (rectangle box) with the plasma membrane (Mb) of oocytes.
