AbstractThe gestation period ofTadaridais approximately four months long extending from late February to June. During the first half of gestation the yolk sac undergoes a complete collapse bringing two layers of endodermal cells into contact with one another and obliterating the cavity of the yolk sac. Both the endodermal and the mesodermal cells hypertrophy and develop into a glandular‐looking organ during the latter half of gestation. Approximately a month before parturition the endodermal cells become progressively laden with lipid and glycogen. Immediately before birth, however, both of these storage materials are depleted. This depletion is preceded by the formation of an extensive array of hexagonal membranous channels within the cytoplasm. Some of the membranes of this organelle are closely applied to lipid droplets and glycogen granules can be observed in linear patterns within the hexagonal channels. Tissues taken at term showed the membranes of the hexagonal channels continuous with a paracrystalline membranous structure. The close morphological association of the membranous organelle to both the lipid and glycogen storage materials indicates that it is involved in their metabolism in the yolk sac of the ba