QUANTITY, BUNDLE TYPES, AND DISTRIBUTION OF HAIR-CELLS IN THE SACCULUS OF XENOPUS-LAEVIS DURING DEVELOPMENT

Proliferation of saccular hair cells of the amphibian, Xenopus laevis, was examined at various stages of development. Numbers of total hair cells and of hair cell bundle types were determined in larval (stages 47, 52 and 56), recently metamorphosed juvenile (1 g), and adult (60 g ) animals with scanning electron microscopy (SEM). Hair cells were ide ntified by ultrastructural analysis of the stereociliary bundle. Two g eneral bundle types were present on the sensory epithelium: long stere ociliary (LS) and short stereociliary (SS) bundles. Based on the kinoc ilium length, the SS bundle type was further divided into SS1 (kinocil ium greater than or equal to 8 mu m) and SS2 (kinocilium < 8 mu m). Th e sensory epithelium was composed of a central zone containing all LS and some SS bundles, and a peripheral zone containing only SS bundles. Our results show that in X. laevis, the number of LS and SS bundles, as well as the ratio of LS/SS bundles increased continuously during la rval and post-metamorphic development, with an associated enlargement in the sensory epithelium area. These increases were more pronounced d uring larval life. The percentage of hair cells with SS1 bundles was g reater in larval stages, while that of hair cells with SS2 bundles was comparatively higher in juvenile and adult specimens.