When slices of rat palatal shelves removed by dissection from 16 days 8 hours old fetuses, just before fusion, are treated by the periodic acid Schiff reaction (PAS), colored substances may be detected especially in the epithelium of the potential fusion zone; these substances are normally observed at the free surface of the epithelium. Our histochemical research, realized with the aid of the photonic microscope and of the transmission electron microscope, shows that most of the PAS positive material consists in glycogen; at the surface, this polysaccharide remains in the cytoplasm of flat degenerating cells and cannot be confused with the "cell coat" which presents no particularity, at this level, after demonstration by ruthenium red and by lanthanum nitrate.