The Frog Tongue: I. General Development and Histogenesis of Filiform Papillae and Mucous Glands in Rana catesbeiana

The development of the tongue and the histogenesis of its filiform papillae and mucous glands have been studied in twelve premetamorphic, ten metamorphic and one adult stage of Rana catesbeiana . The differentiation of the tongue anlage is described macroscopically and histologically. Its dorsal epithelium increases progressively in thickness. A maximum thickness of from then to twelve cell layers is reached just before the onset of metamorphosis. The general epithelium then undergoes degeneration between the developing papillae and mucous glands. Four premetamorphic papillae are known to develop during the larval period. They form a transverse row across the approximate anterior‐posterior center of the tongue anlage. The growth and subsequent regression of these structures is described. A gustatory function is tentatively assigned to these structures. Filiform papillae and mucous glands arise from either conical or rectangular cell groups in the dorsal epithelium of the tongue. The anlagen of these structures are first seen during larval involution at a stage usually just prior to the emergence of the forelimbs. The distal portion of two adjacent halves of an anlage migrate or grow towards each other and fuse to constitute a single papillary rudiment. The papillary core develops between these half anlagen. The epithelium of the papillae consists of but one layer of unciliated cells. Mucous glands differentiate from the basal portion of each cell group. A general similarity in the development and histology of filiform papillae and mucous glands is noted when comparing R. catesbeiana with R. sylvatica . Certain developmental and histological differences do exist, however, between these two species.