就胚胎学的历史而言，在20世纪之前，人们对人类胚胎的发育阶段和分类都知知甚少。

As far as it is known from the history of embryology, little was known about the staging and classification of human embryos until the twentieth century.

youdao

就胚胎学的历史而言，在20世纪之前，人们对人类胚胎的发育阶段和分类都知知甚少。

As far as it is known from the history of embryology, little was known about the staging and classification of human embryos until the twentieth century.

youdao