Changes of the lingual epithelium in Ambystoma mexicanum

Changes in the lingual epithelium during ontogenesis and after induced meta morphosis in Ambystoma mexicanum are described as observed by light microsc opy and scanning electron microscopy. The epithelium of the tongue is alway s multilayered in the larva as well as in the adult. It consists of a strat um germinativum with little differentiated basal cells and a stratum superf iciale (superficial layer) with specialized superficial cells and goblet ce lls. Usually, there are more than two layers because of a stratum intermedi um consisting of replacement cells. The apical cell membrane of the superfi cial cells is perforated by fine pores. Its most typical feature are micror idges. Maturing superficial cells possess microvilli. Goblet cells occur in early larvae primarily in the centre of the tongue. They spread throughout the dorsal face of the tongue as their numbers increase during ontogenesis . The small apices of the goblet cells are intercalated in the wedges betwe en the superficial cells. Leydig cells are not found on the larval tongue b ut on that of adults. Due to metamorphosis, the epithelium of the tongue ch anges. It is furrowed in its anterior part. The furrows house the openings of the lingual glands. The surface is further modulated by ridges which are densely coated by microvilli and which bear the taste buds. The villi of t he tongue which lack extrusion pores show cilia and microvilli but lack mic roridges. The Leydig cells disappear during metamorphosis. In addition to t he two types of goblet cells found in different regions of the glandular tu bules, goblet cells occur in the caudal part. They secrete directly into th e cavity of the mouth. The posterior parr is characterised by a dense coat of cilia.