Histochemistry and ultrastructure of amphibian lingual glands and phylogenetic relations

The lingual glands of amphibians are confined to the dorsal face of the tongue and are formed by invaginations of the lingual epithelium. The secretory products have a heterogeneous composition. Mucosubstances are usually associated with proteins. The secretory product of the outer glandular cells is rich in mucosubstances of an acidity varying with species. In Anourans and Urodeles, the secretory product of the tubes contains abundant proteins and, where present, mucosubstances are less abundant and less acid than those produced at the surface of the tongue. Proteins and mucosubstances coexist in the same secretory granules, which exhibit a more or less homogeneous appearance in Gymnophiona and in Anourans while having a complex structure in Urodeles. In spite of their primitive anatomical features, the amphibian lingual glands present histochemical signs of a complete cellular evolution.