来自《耶鲁大学开放课程：生物医学工程探索 第6集 第6集》

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  here it shows it at the 16 cell stage and then here,
  这里显示的是十六细胞期 然后在这里
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  and this transformation as it goes
  在这里胚胎进一步的产生了变化
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  from 16 cells to more like 64 cells.
  由十六个细胞分裂为约六十四个
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  There's a change in sort of the
  与此同时 胚胎的外形
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  shape of the overall embryo as well.
  也有一定程度的变化
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  It's no longer just a round spherical mass of cells,
  不再只是一个球状的细胞团
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  but it has some structure.
  它有了一定的结构
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  There's a cluster of cells here,
  有一簇细胞
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  there's a sheet of cells that forms an outer lining,
  一层细胞构成了外形轮廓
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  and what is most noticeable is this cavity,
  最明显的结构就是这个空腔
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  this fluid filled cavity which begins to develop.
  这一充满液体的空腔开始发育形成
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  Well, this stage of development is called the blastocyst
  我们称此发育阶段为囊胚期