Hematopoiesis in liver. Liver at 1 (Top), 2 (Middle) and 6 (Bottom) weeks. Liver appears normal at week 1. Islands of extramedullary hematopoiesis are seen at week 2 and extensive hematopoiesis throughout the liver is apparent at week 6. Note increased proportion of nucleated cells in blood vessels at weeks 2 and 6. Specimens were obtained from the experiment described in Figure 3.