The layer of cells formed by the cleavage of a fertilized mammalian egg.It later divides into the three germ layers from which the embryo develops.是什么意思_The layer of cells formed by the cleavage of a fertilized mammalian egg.It later divides into the three germ layers from which the embryo develops.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句