[Histological study of the teleost liver. III. The system of biliary pathways].

In the liver of Haplochromis burtoni four divisions of the intrahepatic biliary pathways can be distinguished: canaliculus, canaliculus ductulus transition, ductulus biliferus, ductus biliferus. There are no transitional stages between the hepatocytes and biliary epithelial cells. The results of the investigation suggest that the ductules open into the ducts in two ways, directly and by graded transition of structure. The first part of the ductulus has a very narrow lumen and therefore is similar to the "Schaltstück" of salivary glands. Terminal ductulus cells can protrude into the canaliculus (= lumen of the liver tubulus), giving the appearance of centrotubular cells in cross-section. In the liver of most of the teleosts investigated here the canaliculi are intercellular. Tangentially cut diverticuli of the canaliculi appear to be unicellular ("intracellular") canaliculi, but are, however, merely unicellular ("intracellular") protrusions of the intercellular canaliculi. On the other hand the three cyprinid species (Barbus tetrazona, Idus idus, Carassius auratus) possess true unicellular ("intracellular") canaliculi. These can definitely be distinguished from the diverticuli of intercellular canaliculi by several criteria. Phylogenetically the unicellular ("intracellular") canaliculus must be regarded as derivative, and the intercellular canaliculus as the original form. The morphology of the wall of the gall-bladder of Haplochromis burtoni indicates that transfer of substances is increased together with transportation and drainage of fluids and variations in volume. The ultrastructure of the epithelial cells reveals a zonal arrangement.