A CONTRIBUTION TO THE STUDY OF THE HISTOGENESIS OF THE BURSAL LYMPHOID FOLLICLES IN GALLUS-DOMESTICUS

Numerous investigators have shown that the development of the bursal lymphoid follicle in chicken begins with the formation of epithelial gemmations called epithelial buds. The mesenchymal stem cells migrate into these epithelial buds and give rise to the lymphoid cells of the follicle medulla. However, research carried out in our laboratory, using the semi-thin serial section technique and the electron microscope, leads us to think that the early stages of the development of the bursal lymphoid follicle might take place in the following way: the stem cells migrate towards the proximal surface of the lining epithelium where they collect in an invagination. These cells gradually increase in number and a cellular mass is formed which, therefore, does not grow in the epithelial framework but under it. The epithelial invagination near the mesenchymal mass becomes more and more pronounced, making the epithelium progressively thinner until it is finally necrotized. At this point, the cells of the mesenchymal anlage protrude into the bursal lumen