Schematic representation of the cells and terms within the emerging hematopoietic hierarchy. Non–pre-HSCs are those cells that have potential for the hematopoietic lineage as well as other lineages. Predefinitive HSCs are those cells that have only a hematopoietic fate. Definitive HSCs are defined as those cells possessing their own ability to differentiate and expand on definitive, adult, hematopoietic territories. As noted by the dotted arrow, the lineage relationship between day-9 predefinitive HSCs and definitive HSCs has not been proven experimentally. The question mark between the AGM and fetal liver denotes the following. Although AGM-derived HSCs can directly repopulate adult bone marrow in transplantation experiments, experimental evidence showing embryonic migration of these cells through fetal liver before colonization of the bone marrow is 1acking.