But the placenta -- the organ that provides material to the embryo from the mother -- is actually formed from the chorion and allantois membranes of the egg.

但是胎盘——为胚胎提供物质器官——实际是由卵子绒毛和尿囊。

Because, the main membranes of an amniotic egg -- known as the sac, the chorion, and the allantois -- are all present in animals that give birth to live young.

因为，羊卵主要——被称为囊、绒毛和尿囊——都存在于生下活幼仔动物身。