Final answer:
The developing embryo floats in the envelope or bag known as the amniotic sac, which is formed by the amnion membrane and filled with amniotic fluid providing protection and an environment for growth.
Step-by-step explanation:
The developing embryo floats in the envelope or bag known as the amniotic sac. This sac is important for providing a protective environment in which the embryo can grow and develop. The amnion, a membrane that forms around the embryo, fills with amniotic fluid. This fluid allows the embryo and later the fetus to move freely, protecting it from trauma and sudden temperature changes. Moreover, the amnion and the amniotic fluid enable the embryo to prepare for life outside the uterus, practicing swallowing and breathing.
Different stages of early embryonic development involve the formation of the amniotic sac. The cells of the inner cell mass form the amnion during the second week of development. The amniotic cavity opens up and eventually, this cavity surrounds the embryo, filling with amniotic fluid.
Early in development, the amniotic fluid consists mostly of a filtrate of maternal plasma, but later on, as the kidneys of the fetus begin to work, they contribute to the amniotic fluid's volume with fetal urine. The development and functions of the amnion are crucial for the proper development and protection of the embryo and fetus during pregnancy.