Extra-embryonic membranes in amniotes
Animal embryonic development · Biology
Study notes
A hen's egg is all membranes: shell (protection), albumen (water/protein), yolk (food) — the amniotic egg that freed vertebrates from water. Human twins sharing one amnion risk tangled cords — obstetricians watch monochorionic twins closely. The placenta (chorion + maternal tissue) does the work of lungs, gut, and kidneys for the foetus until birth.