DEVELOPMENT OF THE OLFACTORY EPITHELIUM AND VOMERONASAL ORGAN IN THE JAPANESE REDDISH FROG, RANA-JAPONICA

Histological and ultrastructural development of the olfactory epitheli um (OE) and vomeronasal organ (VNO) was investigated in the Japanese r eddish frog, Rana japonica. Tadpoles, from hatching to the end of meta morphosis, and adult frogs were examined. In the adult, olfactory cell s of the OE were equipped with olfactory vesicles with long cilia, but supporting cells with microvilli. The supporting cells of the OE cont ained secretory granules, PAS-positive by light microscopy, in their a pical cytoplasm. On the contrary, sensory cells of the VNO were equipp ed with microvilli, and supporting cells of the VNO were equipped with cilia, but without secretory granules. Embryologically, the olfactory cells were indistinguishable from the supporting cells in the olfacto ry placode (primitive OE) lining the nasal pit, at hatch. The VNO appe ared as a concave of the ventral part of the OE at 4 days after hatch. At this time, the olfactory and supporting cells of the OE became dis tinguishable from each other. Secretory granules were formed in the su pporting cells of the OE at 36 days after hatch, and the OE was simila r in fine structure to that in the adult. While, the VNO remained imma ture at 24-36 days after hatch, and did not complete its ultrastructur al development at 60 days after hatch, the end of metamorphosis. These findings suggest that the OE may take part in the olfaction earlier t han the VNO in ontogeny.