The extra-embryonic membrane that fills with fluid and surrounds the embryo, protecting it from trauma and rapid temperature changes, is the:

1. Four extra-embryonic membranes support and protect the growing embryo: the amnion, yolk sac, allantois, and chorion. 2. One of these membranes forms a fluid-filled sac that surrounds the embryo directly. 3. This membrane is called the amnion, which fills with amniotic fluid. 4. Floating within this fluid, the embryo is protected from trauma and rapid temperature changes, unlike the chorion, which is the outermost membrane. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 28 "Development and Inheritance", p.1329-1330 §Embryonic Membranes_