ABSTRACT
The origin of the hemopoietic stem cell that arises from an intraembryonic locus in the avian embryo and serves as the progenitor of the permanent, definitive population of erythrocytes has been a subject of long-standing interest. Contemporary studies of amniotes have linked the origination of the stem cell to an intraembryonic region termed the aorta-gonad-mesonephros area. H. E. Jordan addressed the intriguing question of why aortic hemogenic activity was localized or focused in the ventral area of the embryonic abdominal aorta. Contemporary investigations have verified and extended the initial observations that hemopoietic cells arise in the mesenchyme of the early avian embryo. In regard to the quail embryo, while its presentation of hemopoietic cell development in mesenchyme was the same as the chick up to five days of incubation, it was decidedly different thereafter. With the recognition of the allantois as another locus for de novo production of hemopoietic progenitor cells, it remains to be conclusively established to what degree.
