<prompt> Teiary stem villi consists of:-Central core of cytotrophoblast covered with synctiotrophoblastCentral core of extra-embryonic mesoderm covered by central cyto- and peripheral synctio- trophoblastCentral maternal blood vessels surrounded by mesoderm and trophoblastCentral fetal blood vessels surrounded by mesoderm and trophoblast  <response>: Secondary villi:- contains a central core of primary extra embryonic mesoderm and is covered by cyto- and syncytio- trophoblast cells. Teiary villicontains fetal blood vessels invading the extra embryonic mesoderm and is covered by trophoblastic cells. 