[mass noun](Zoology & Embryology)the outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis, nerve tissue, and nephridia (动,胚)外胚层;由外胚层形成的组织;外层。 比较 endoderm 和 mesoderm
派生 ectodermal adjective 语源
mid 19th cent.: from ecto- 'outside' + Greek derma 'skin'