<prompt> During first, 3-4 month of gestation erythrocytes are formed byYolk sacLiverSpleenBone marrow  <response>: Stages of erythropoiesis according to development areIn the first 2 months of gestation - occurs in yolk sac Mesoblastic phasefrom 3rd month of gestation - In liver and spleen Hepatic phaseFrom 20th week of gestation - In red bone marrow myeloid phaseRef: Medical Physiology Indu Khurana 2015 edition, Page No:104 