大卫爱登堡：蛋的奇迹 Natural World: Attenborough's Wonder of Eggs

David Attenborough has a passion for birds' eggs. These remarkable structures nurture new life, protecting it from the outside world at the same time as allowing it to breathe. They are strong enough to withstand the full weight of an incubating parent and weak enough to allow a chick to break free. 　　But how is an egg made? Why are they the shape they are? And perhaps most impor...