Transmission electron micrograph (TEM) of the ultrastructure of two macrophages. These cells are common in connective tissues and extracellular spaces. Motile and phagocytic, they engulf and digest dead or dying cells, or extracellular debris. They are important in immune responses where they may destroy pathogens, or act as antigen-presenting cells. Magnification: x3,000 when printed at 10 cm wide.