But what the amnion also does is it prevents the embryo from drying out and it enables the embryo some freedom of movement. So it allows the embryo to actually move as it grows. And that's important in the process of embryological development. Now, let's move on to another extra embryonic membrane known as the umbilical vesicle. So in humans, the yolk sac is actually called umbilical vesicle because it doesn't actually contain any yolk. So what the umbilical vesicle of functions is, in early embryological development, it actually helps produce some of the red blood cells.