By day 20 none was left. But that was enough time for a process called gastrulation to take place.

到第20天已一无所剩。但这段时间已经足以发生一个名为“原肠胚形成”的过程。

Using these partial models, they can study things like cell signalling, or even the formation of the primitive streak - the crucial thread of cells which guides the process called gastrulation.

使用这些部分模型，他们可以研究细胞信号传导，甚至原始条纹的形成 - 细胞的关键线程，它指导称为原肠胚形成的过程。