Chorion
Chorion is the outermost membrane and it functions to allow gas exchange between oxygen and carbon dioxide.
Amnion
Amnion is the fluid-filled sac that surrounds the embryo. It protects and prevents dehydration of the embryo.
Allantois
Allantois is a fluid-filled sac that is attached to the embryo's gut. It collects waste as the embryo develops. (This waste is like urine waste.)
Yolk
Yolk is a sac that is attached to the embryo that supplies food.