Ultrastructural study of embryonic and post-hatching development in the pineal organ of the chicken (brown leghorn, gallus demosticus).

The pineal organ of the chicken was investigated electron microscopically during embryonic and post-hatiching development with special regard to photosensory and secretory features. Throughout the developmental period both pinealocytes and supporting cells, of which the pineal parenchyma is composed, were rich in ribosomes, granular endoplasmic reticulum and mitochondria, but lacked agranular endoplasmic reticulum. The outer segments of pinealocytes barely showed formation of lamellar structures (disks) at the 17th and 21st day of incubation. Before and after hatching the follicular lumen was ofter filled with amorphous material presumed to be derived from outer or inner segments. By 15 days after hatching thw whorl-like structures were occasionally connected to bulbous outer segments, and their relation appeared similar to that of the adult. Mitochondria disappeared from the inner segments after 21 days of incubation. Dense core vesicles (about 80-120 nm in diameter), regarded as secretory granules, appeared first at the 10th day of incubation in the supranuclear region of the pinealocyte. With the extending of basal processes the dense core vesicles gradually migrated into these processes, attained maximum number one month after hatching and increased further in the adult; they are located both around the Golgi apparatus and in the basal process. These results provide evidence that secretory activity is maintained from embryonic stages to adulthood.