The histology and fine structure of the ureter of the European starling (Sturnus vulgaris).

Light and electron microscopic techniques were employed to study the structure of the ureter of the starling (Sturnus vulgaris). Particular attention was paid to the characterisation of the epithelial cell types. Differences were found in the chemical composition of the mucins found in the ureteric epithelial cells and the medullary collecting ducts, which suggested that they might perform different functions. The epithelial cells were of two main types. The basally situated cells were electron-lucent, apparently relatively undifferentiated, and contained little rough endoplasmic reticulum or mucigen. The cells which were directly adjacent to the lumen were highly specialised for mucus secretion and contained extensive rough endoplasmic reticulum and large numbers of mucigen-containing vacuoles. Cells of intermediate character were also observed and the relationships between the epithelial cell types were discussed. The possibility of a holocrine mode of mucus secretion in the avian ureteric epithelium was discussed.