The development of transport ability by embryonic follicle-associated epithelium.

The development of transport ability by follicle-associated epithelium was studied in embryonic chick bursae. Developing lymphoid follicles were divided into three morphological types to determine the relationship of epithelial function to lymphoid development. Transport ability was first observed on day 13, two days earlier than obvious morphological evidence of follicle-associated epithelial development. Functional differentiation of the epithelium was, however, closely associated with lymphoid development rather than a day-specific developmental event. It is probable that the lymphoid cells have an inductive influence on the development of the overlying epithelium. Evidence of early embryonic transport by relatively undifferentiated epithelium also suggests that lymphoid development in the bursa may be influenced by epithelial transport.