Mesenchymal origin of bursal lymphoid cells in Japanese quails.

The origin of bursal lymphoid cells in Japanese quails was studied by means of a quantitative morphological method during a 6 to 12 day incubation period. The findings obtained in this study are summarized as follows. At 6 to 7 days' incubation, no lymphoid cells were observed in the bursal primordium. In 8 day embryonic bursa, the first appearance of lymphoid cells was found in the tunica mucosa. In the epithelium, the first appearance of lymphoid cells was observed at 9.5 days' incubation. At 9.5 to 11 days' incubation, lymphoid cells were frequently observed to pass through the epithelial basement membrane. It may be concluded that the lymphoid cells found in the epithelial region had migrated from the bursal mesenchymal region. The formation of epithelial buds began at about 11 days' incubation, but were never found prior to penetration of lymphoid cells into the epithelium. It may be concluded from the present results that bursal lymphoid cells derive from mesenchymal cells in Japanese quails.