Extra-embryonic mesoderm is derived from:
Epiblast
Primary yolk sac
Secondary yolk sac
Hypoblast
Ans: B. Primary yolk sac(Ref Gray's. 41/e p169, 40/e p167, 173, 186-189; Langmuir S 13/e p45,'Pe p54-55)Extra-embryonic mesoderm is derived from primary yolk sac.Formed by delamination of yolk sae cells - later by migration of cells through primitive streak during gastrulation.