细胞的这种向里推进标志着原肠胚形成的开始.This pushing - in of cells marks the start of gastrulation.外胚层囊胚的外层,在原肠胚形成之后生后外胚层组织.The outer layer of a blastula that gives rise to the ectoderm after gastrulation....

“肠胚”的英语可以翻译为：gastrula ...