Ultrastructural study of the developing blood capillaries in the pineal gland of the domestic fowl.

The ultrastructure of the pineal gland capillaries in chick embryos of 7, 14 and 19 days of incubation and in three month chicks has been analyzed. The results show that vascular primordia are detectable among the pineal developing vesicles on the 7th incubation day. Significant maturative changes in the capillary wall (flattening of the endothelial cells, appearance of pores, narrowing of the perivascular spaces and formation of the endothelial basement lamina) take place during the last days of the embryonic life and are concluded only after the hatching. Relationships between the vasculogenetic and the morpho-histogenetic processes in the pineal body, and some differences in the maturative changes of the vascular wall of the pineal and other chick embryo endocrine glands, have been briefly discussed.