[Light and electron microscopic studies on the development of the spiral prominence of the cochlear duct of the fetal guinea pig].

The anlage of the spiral prominence can be seen on the 37th day of development as a small protrusion of the epithelium towards the lumen of the cochlear duct. During the further progress, the spiral prominence more distinctly protrudes by augmentation of the vascularized connective tissue. In the epithelial cells pinocytotic vesicles near the plasmalemma are seen earliest lateral and basal on the 37th day, apical on the 39th day. The epithelial cells send basal cytoplasmic extensions towards the connective tissue. Starting on the 44th day, small invaginations of connective tissue extend into the epithelium, remaining separated from the epithelial cells by the basal lamina. Until the 48th day, the monostratified epithelium remains columnar, thereafter it changes to cuboidal or flat. Towards the end of the development, the invaginations of the connective tissue nearly reach the surface of the epithelium, being separated from the endolymph by a small epithelial area.