Photosensory elements in the pineal gland of the Japanese quail, with special reference to the paraboloid.

In 1-day-old Japanese quails, Coturnix coturnix japonica, photosensory elements of the pineal gland were examined by means of histochemical demonstration of glycogen and transmission electron microscopy. The parenchymal cells of the quail show immature structure, especially, small apical protrusion with a few mitochondria in the pinealocyte and rare appearance of the dense body in the supporting cell. The paraboloid is found in cytoplasmic processes projecting into the follicular lumen and in perikarya of the follicular cells. It is composed of a well-developed network of tubular smooth-surfaced endoplasmic reticulum and abundant glycogen granules, but there is not a higher concentration of glycogen in its central region. The paraboloid-containing cell is considered as a type of the pinealocyte, because of occasional appearance of the synaptic ribbon in its perikaryon. In addition to lamellar whorls, regular stacks of lamellar disks are observed in the pineal lumen, being adjoining to the paraboloid-containing cytoplasmic process. The present results may provide further evidence for the direct photoreception by the avian pineal.