What part of the chicken egg acts as placenta in mammals?

There is no part of the chicken egg that acts as a placenta in mammals. The placenta is a specialised structure that is formed in mammals during pregnancy. It allows the exchange of oxygen and carbon dioxide between the mother's blood and the fetus's blood. The chicken egg, on the other hand, does not have a placenta. Instead, the developing embryo receives oxygen and nutrients from the yolk and the albumen of the egg.