Migration of haemopoietic cells from the yolk sac to the thymus and the bursa of Fabricius in the chick embryo.

Abstract

The haemopoietic cells of the yolk sac wall of 16‐day‐old chick embryos were locally labelled with 3H‐thymidine in situ. Appropriate controls for the isotope leaking to other parts of the embryo during the local labelling procedure were performed. With autoradiographic technique heavily labelled haemopoietic cells derived from the yolk sac were demonstrated in the thymus and in the bursa of Fabricius 24 hours later. These results directly support the view that the haemopoitic areas of the yolk sac is at least one origin of the lymphoid precursor cells entering the embryonic chick thymus and bursa of Fabricius.