SCANNING ELECTRON-MICROSCOPY OF ENDODERMAL SENSORY CELLS OF HYDRA-MAGNIPAPILLATA

The free surface of the endoderm of Hydra magnipapillata was observed by scanning electron microscopy in order to analyze the fine structure of the apical receptive sites of the sensory cells. Endodermal sensor y cells had a small round exposed surface provided with a single ciliu m. Two types of sensory cells, tufted and papillary, could be distingu ished from each other by their apical features. The former projected 5 0 or more microvilli on their apical surface, which was at level with the surface of neighboring epithelial cells. The latter displayed a ro unded swelling on their apex, on which 10-30 microvilli of various len gths were found pointing random directions. Both types of receptor reg ions were compared with those of previously reported sensory cells in Hydra ectoderm and in the gut epithelium of other animal species.