Endoderm is the innermost of the three primary germ layers in the very early embryo.

[1] Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.

[3] Liver and pancreas cells are believed to derive from a common precursor.

[5] In humans, the endoderm can differentiate into distinguishable organs after 5 weeks of embryonic development.

This article incorporates text in the public domain from page 49 of the 20th edition of Gray's Anatomy (1918)