It appears that the outer ditch was dug with wooden and bone implements. 有跡象表明外層的壕溝是由木製和骨制的工具挖成的。
The rearrangement of the blastula into a three-dimensional organism with inner, middle, and outer layers occurs during gastrulation. 在原腸胚形成過程中，囊胚重新排列，形成包括內層，中層，外層的三圍組織。
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