Fragments of brain from embryonic fowl of from three to twenty-one days' incubation were cultivated in vitro for from one to twenty-one days. These cultures showed cells closely resembling microglia. These cells showed characteristic staining with silver impregnation methods. Cultures from embryonic periosteum and limb bud showed exactly similar cells. Cultures from embryonic retina showed no such cells. These cells reacted to vital dyes in vitro in the same way as do wandering cells. Microglial cells showed phagocytic properties to trypan-blue in vivo.