COMPARATIVE HISTOLOGICAL OBSERVATIONS ON THE PEARL-SAC TISSUES FORMING NACREOUS, PRISMATIC AND PERIOSTRACAL PEARLS

1) The present author observed histologically the respective pearl-sac tissues forming nacreous, prismatic and periostracal pearls. 2) The epithelial cells of the pearl-sac tissues forming nacreous and prismatic pearls seem to be essentially similar to each other, except that the latter vary greatly in cell height and are slightly taller in average height in comparison with the former. 3) The epithelial cells of the pearl-sac tissue forming periostracal pearl are structurally quite different from those producing nacreous or prismatic pearl. These epithelial cells are extremely tall and cylindrical, and contain numerous acidophilic small granules in the cytoplasm. On the free end of these epithelial cells, cilia are visible under optical microscope. 4) Some of the pearl-sac epithelia forming periostracal pearls have a great number of ridges caused by the crowding of numerous wandering cells in some subepithelial regions. On the surface of the epithelium, periostracum and many necrosed cells are generally observed. These features seem to indicate that the epithelium is slightly inflamed. In the case where the inflammation worsened not only the epithelium but also its surrounding tissue may have partially fallen off due to necrosis.