The spiral prominence of the rabbit is made up of an epithelial cup and of corpuscles (villi), formed by two or more organules containing osmioreducing substance. The prominence of the human foetus is composed of a unique and voluminous organule also contained in an epithelial cup. These epithelial cells derive from those of the outer spiral sulcus that also give rise to an epithelial system of the spiral ligament which in the rabbit is expanded while in man is compact, contained, therefore, in the area of the spiral prominence.