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Riesenzellen, goblet cells, Leydig cells and the large clear cells of Xenopus, in the amphibian larval epidermis: fine structure and a consideration of their homology.

The origin, fate and fine structure of the epidermal Riesenzellen of larvae of Bufo bufo, have been described by electronmicroscopy throughout their ontogeny. Riesenzellen are uncommon in the epidermis relative to the epithelial cells. In young larvae they differentiate from basal epithelial cells, which enlarge and become rounded, lucent and glandular, some at least to open at the epidermal surface. They have disappeared by the end of metamorphosis. Among amphibian larval specialized cells of the skin, the Riesenzellen so far are known to occur only in bufonid larvae. They differ in fine structure from goblet cells but show greater similarity with them than with other specialized epidermal cells. Riesenzellen are not homologous with Leydig cells of larval urodeles and Ichthyophis among the Gymnophiona. True Leydig cells are not represented by the Riesenzellen or Kugelzellen or other large cells, for example the so-called unicellular gland of Xenopus, in the larval anuran epidermis. Leydig cells do not occur in this group, a fact that could well be of significance in any assessment of amphibian phylogeny.