INFLUENCE OF PARTIAL DECEREBRATION AND HYPOPHYSEAL ALLOGRAFT ON DIFFERENTIATION OF THYMIC EPITHELIAL-CELLS IN CHICK-EMBRYOS - AN ULTRASTRUCTURAL-STUDY

The thymus of 18-day-old normal-chick embryos, partially decerebrated chick embryos, and partially decerebrated embryos bearing hypophyseal allografts were analysed by light and transmission electron microscopy . The hypophyseal influence on the cytological differentiation of epit helial components has been studied. The thymus of partially decerebrat ed embryos showed a delayed differentiation of some types of epithelia l cells and a marked decrease in number of lymphoid cells. Partially d ecerebrated embryos with hypophyseal implants showed a consistent reco very in the degree of differentiation of epithelial components. These findings indicate the influence of the hypophysis in establishing a co rrect environment for stromal cell differentiation.