The structure of the kidney from the freshwater teleost Carassius auratus.

The structure of the kidney of the crucian carp (Carassius auratus; a freshwater teleost, Cypriniformes) was studied by means of reconstruction from serial paraffin and semithin sections. In C. auratus, the Wolffian duct traverses the entire kidney. At various levels collecting ducts of different length and thickness join the Wolffian duct at right angles. Each collecting duct accepts a large number of connecting tubules, which are established by the joining of many nephrons. A regular pattern concerning the distribution of nephrons and the fusion of renal tubules is not apparent. Four segments have been distinguished in renal tubules; 1) proximal tubule, 2) distal tubule, 3) connecting tubule and 4) collecting duct. A neck and an intermediate segment are absent. The proximal tubule is established by proximal tubule cells which bear a brush border and have a conspicuous apical cytoplasmic rim containing few cell organelles, ciliated cells, mucous cells and dark cells. In the first part of the proximal tubule the brush border and the apical cytoplasmic rim of proximal tubule cells are well developed. Ciliated cells are interposed between proximal tubule cells, decreasing in number toward the end of this part. In the second part ciliated cells are absent and dark cells are numerous. In the third part the brush border and the apical cytoplasmic rim of proximal tubule cells are scarcely developed. Ciliated cells reappear and increase in number toward the distal tubule. The distal and connecting tubule are similar in epithelial structure. Connecting tubules are joined distal tubules and thus they belong to two or more nephrons.(ABSTRACT TRUNCATED AT 250 WORDS)