Abstract: By scanning electron microscopy,the epithelial buds bulging from the surface of the plicae were observed on the 13th day of incubation.At the same time the surface epithelium began to differentiate into follicle-associated epithelium (FAE) and interfollicular surface epithelium (ISE).Microvilli scattered evnly on the surface of the cells in these two kinds of epithelium,and those on the cells of ISE were more slender than those of FAE.The lymphoid follicles of the buras of Fabricius developed well in the newly hatched chicks,and there was a marked furrow between FAE and ISE.When the chicken was at the age of one month,the lymphoid follicles were fully developed and their cortex and medulla were clearly differentiated.The lymphoid follcles of the bursa of Fabricius of the two months chick began to involute and some of the follicles embedded in the mesenchymatous tissue.