The lingual epithelium of Salamandra salamandra: metamorphotic changes during its ontogenesis.

The development of the epithelia of the secondary tongue of Salamandra salamandra is described on the basis of light microscopic and scanning electron microscopic studies of defined developmental stages. A glandular area with radial ridges and furrows is formed anterior to the primary tongue during the larval phase. Epithelial cones--each a compact anlage of a gland lying in the furrows--displace the lamina propria. The glandular area grows upward and latero-caudad during metamorphosis and forms the secondary tongue by fusing with the primary tongue. Lumina within the gland anlage appear at the beginning of metamorphosis. They open as glandular tubules towards the oral cavity at the climax of metamorphosis. The epithelial lining becomes single layered and differentiates into gland cells. The glands are increasingly surrounded by fibers of the musculus genioglossus. At the orifice of the gland, the gland cells mingle with the multilayered epithelium of the surface of the tongue. This contains two types of goblet cells in addition to the villus-shaped covering cells which leave gaps for the taste buds. The goblet cells are formed before (type I) and during (type II) metamorphosis and replace the typical larval goblet cells. The new mushroom-shaped part of the secondary tongue is characterized by aborally running septae of connective tissue, visible after digestion with pankreatin. The tip of the primary tongue which originally covers the glandular part becomes completely integrated. It is characterized by crypts which become shallower caudally.