We have the green cells that make up the hypoblast, and we have these blue cells that make up the epiblast. Now, the hypoblast cells eventually give rise to the endoderm, while the epiblast eventually gives rise to the ectoderm. And as we'll see in just a moment, the mesoderm develops in between as a result of a process called invagination, when we form that primitive treat, as we'll see in just a moment. Now, when we go from diagram two to diagram three, what happens is the upper portion of the hypoblast and the upper portion of the epiplast eventually migrates upward towards this pole, and we basically form the following diagram. So notice this entire green portion eventually develops into the umbilical vessel. Now, in nonhumans, it's called the yolksac.