The yolk sac is derived from -
High-Yield Explanation
Ans. is 'a' i.e., Hypoblasts o The yolk sac initially appears as a transient primary yolk sac, develops from hypoblast cells. By the end of 2nd week, the lower half of primary yolk sac pinches off to form definitive yolk sac, while the second wave of hypoblast cells from the inner lining of the definitive yolk sac.