amniotic sac

https://doi.org/10.1351/goldbook.10371

Membranous structure in amniotes, within which the embryo and fetus develop.

Note: It consists of a thin but tough, transparent pair of membranes, the amnion and chorion, that hold the developing embryo (and later fetus) until shortly before birth.
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 721 [Terms] [Paper]