MORPHOLOGICAL FEATURES OF DIFFERENT REGIONS IN FROG CRISTA-AMPULLARIS(RANA-ESCULENTA)

The cellular organization of different regions of the crista epitheliu m from the frog posterior semicircular canal was studied by light, tra nsmission and scanning microscopy, The sensory epithelium consists of hair cells surrounded by supporting cells and basal cells located clos e to the basement membrane, Three types of hair cells, namely club-lik e, cylindrical and pear-like cells differentially distributed along th e crista could be recognized on the basis of their shape, Club-like ce lls are located only in the peripheral regions, cylindrical cells both in the central and in the peripheral regions, and pear-like cells app ear segregated into the intermediate regions, Sensory cells of the cen tral region are characterized by a ciliary apparatus consisting of ste reocilia usually shorter-and in some cases less numerous-than those of cells of the other regions, The presence of large evaginations of the apical membrane of hair cells and of several vesicles of microexocyto sis demonstrates that receptor cells have a considerable secretory act ivity, This secretory activity is also proven by the presence in the s upranuclear region of hair cells of numerous Golgi complexes, Moreover , the presence of two kinds of Golgi complexes, one constituted by dil ated cisternae containing a moderately electron-dense material and the other made up of flattened electron-transparent cisternae, suggests a diversified secretion of material by the hair cells, This heterogeneo us material may provide substances important for cupula formation and the composition of the endolymph.