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 among 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 relatively low power view at day 13 of gestation shows the formation of haematopoietic islands centred on F4/80-positive macrophages. By this time the liver is making adult enucleated erythrocytes, and the macrophages are actively involved in elimination of red cell nuclei.