The part of an egg most similar to the cell membrane is the vitelline membrane.

Here's why:

* Cell Membrane Function: The cell membrane acts as a barrier, controlling what enters and exits the cell. It also helps maintain the cell's shape and structure.

* Vitelline Membrane Function: The vitelline membrane surrounds the yolk of an egg and acts as a protective barrier. It also plays a role in fertilization, allowing sperm to penetrate and reach the egg.

While the eggshell provides an outer protection, it's analogous to the cell wall in plant cells, not the cell membrane.