part_of part of part of zona pellucida striated membrane zona striata oolemma A glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but not extraneous to it. The zona pellucida first appears in multilaminar primary oocytes. zona pellucida - vitelline membrane zona radiata vitelline membrane pellucid zone vitelline envelope acellular anatomical structure ovary