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　　在性交过程中，大约有3亿精子可能会进入阴道，但是只有一个精子可能穿过重重障碍，使卵子受精，最终制造出一个胚胎。



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　　受精后8天。胚芽完成“着陆”，微微嵌入子宫内膜。此时它分裂发育为几百个细胞。



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　　卵子的外层被一层透明的薄膜保护着，这使它看起来像一个悬浮在天体中的漂亮的星球。此时经过种种障碍的精子终于与卵子相遇。



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一个精子试图进入卵子的瞬间。



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　　此时精子的头已经钻进去了，我们还可以看到它的中部和尾部，它就像一个不断旋转的钻头，在尾部拍打的驱动下，努力进入卵子。



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　　第1周，在受精之后几小时之内，受精卵开始分裂。1周以后，这个小圆球将自己附着在子宫壁上。



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　　受精后8天。胚芽完成“着陆”，微微嵌入子宫内膜。此时它分裂发育为几百个细胞。



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