Glycogen and development of outer segment in monkey fetuses.

Glycogen particles in developing photoreceptors were investigated in monkey fetuses of various ages under the electron microscope. Glycogen particles were first observed at 100 gestational days in primitive outer segment sacs and inner segments, prior to the appearance of tubulous disc membranes in the peripheral region of outer segment sacs. The particles gradually increased in number as the outer segments differentiated, decreased in number by 143 gestational days, and finally disappeared in the photoreceptors by 160 gestational days, when the photoreceptors were almost formed as in adult monkeys. It is therefore postulated that glycogen particles seen in the photoreceptors are closely concerned with the rapid differentiation of outer segments for a short duration in the developing stages.