Multiple choice Which of the following is the earliest site of hematopoiesis in the developing embryo? Bone marrow Liver Yolk sac Thymus Spleen Reveal answer Fill a bubble to check yourself C Correct answer Explanation Hematopoiesis originates in the early yolk sac, but as embryogenesis proceeds, this function is taken over by the fetal liver and spleen, and then later by the bone marrow, where it continues throughout life.