Fetal macrophages are indented cells that contain an abundance of polyribosomes, and extended microvili or filopodia, and are negative for peroxidase activity. They are found in the sinusoidal lumen or attached to the surface of endothelial cells. At E12, the number of macrophages that phagocytose other blood cells increases and most of the macrophages are attached to the endothelial cells in the hepatic sinusoid.