The zona pellucida is a transparent, striated (striped) membrane surrounding the ovum and containting the |cytoplasm|, which gives the cell its body. The zona pellucida contains numerous pores through which nutrition is passed to the cell. Once the zona pellucida has been penetrated by a sperm the egg (ovum) becomes resistant to any other sperm. The surface layer of the zona pellucida then moves out to engulf the sperm. The cell membranes of the sperm and egg fuse so that they constitute a single cell called a ~zygote~.
