The cells of this surrounding sheet have become different in some way and they develop into the placenta and the extra embryonic tissues.

环抱在周围的这一层细胞,已经开始逐渐分化,最终成为胎盘,及额外的胚胎组织

耶鲁公开课 - 生物医学工程探索课程节选

As division happens and the developing organism acquires more and more cells, individual cells become differentiated, they become more and more like their final mature form.

分裂过程不断发生,以及发育中的有机体对更多细胞的需求,细胞个体便逐渐分化,它们越来越接近成熟细胞的样子

耶鲁公开课 - 生物医学工程探索课程节选