The hematon was first defined in 1988 as the primary fundamental unit of haematopoiesis, the formation of blood cells.
The hematon is believed to be a low density multicellular spheroid approximately 100-500 micrometres in diameter. These cells are arranged into a complex 3-D network and surround a system of highly vascularised and arbourised fibrous cords which run throughout the structure. The spheroid is composed of a central core of adipocytes/preadipocytes cells, mesenchymal cells, recticular cells and macrophages. This core is surrounded by a peripheral layer of myeloid, erythroid and megakaryocyte progenitor cells and their progeny.