In a nutshell...
The cluster of cell is the Blastocyst and it consist of cells that will grow to form the chorion and the allantois (which will all merge for the most part to form allantachorion) , the yolk as well as the amnion and a set of special cells known as the inner mass of cells. The Blastocyst once it attaches to the Linning of the Endometrium in the Uterus will see where placental material start to generate and it is the placenta which contain the maternal and fetal blood as well as the facilitator for the umbilical chord which all work in tandem to provide the fetus with oxygen and nutrients.
