The membrane that surrounds the ovum of animals, from which it has been secreted (e.g. in birds this is the membrane surrounding the yolk of the egg). In Drosophila the term is used rather specifically for the membrane that immediately surrounds the plasma membrane of the ovum. In this case it is formed by the fusion of deposits in the intercellular space between the oocyte and columnar follicle cells that surround it.
Subjects: Zoology and Animal Sciences.