Structure of gill epithelium in Triturus vittatus larvae.

The gill epithelium ultrastructure of the larval stage of the newt, Triturus vittatus, has been studied. Two layers can be distinguished: an outer layer and an inner layer. The outer layer is composed of four cell types: pavement cells, ciliary cells, mitochondria-rich cells (MRC) and round, granule-containing cells. Large numbers of vesicles containing PAS (+) material can be seen in the apical part of the pavement cells. Their outer face is covered with short microvilli. The ciliary cells contain many mitochondria and their surface is adorned with cilia. The mitochondria-rich cells are fully packed with mitochondria. They are unique in having elaborate tubular membranous infoldings, which open on to the surface in a net-like arrangement of long, slender microvilli. Finally, the outer layer contains very few (29 cells in a 35 mm length tissue, or 0.8/1 mm) rounded, granule-containing cells. These granules, of various sizes and shapes, are PAS (-) and contain elaborate Golgi figures. The inner layer is characterized by the presence of numerous, large Leydig cells; 19.56 cells/mm tissue. Finally, large, germinative cells rich in tonofilaments are situated on the basement membrane.