The production of the cells of the blood is carried out by the foetal liver during later stages of embryonic development. F4/80-positive cells are the first recognisable haematopoietic elements in the liver. They are followed by erythroid cells, which associate with the F4/80-positive macrophages in structures that resemble haematopoietic islands of the bone marrow (except that the central macrophages appear smaller). This view at day 16 is around the peak of haematopoiesis in the liver, where most of the tissue is blood elements. The central F4/80-positive macrophages are surrounded by proliferating blood cell precursors.