yolk sac

https://doi.org/10.1351/goldbook.11389

Fluid-filled, membrane-bound pouch on the ventral side of the early embryo that provides nourishment until the circulatory system develops.

Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 822 [Terms] [Paper]