Ultrastructural changes in the liver of the sand lamprey,Lampetra reissneri,during sexual maturation

Ultrastructural changes of hepatocytes were examined in the sand lamprey,Lampetra reissneri, during various phases of the life cycle. In hepatocytes of ammocoetes, the rough endoplasmic reticulum was composed of short cisternae and the Golgi apparatus were scarcely developed, showing no sexual differences at this stage of life cycle. In hepatocytes of female lampreys at the metamorphic stages 4 to 5, the rough endoplasmic reticulum was developed to form long parallel cisternae and the Golgi apparatus were well-developed. The rough endoplasmic reticulum developed further to form stacks of long parallel cisternae extending over the cytoplasm in hepatocytes of females at the young adult stage, and became composed of both long parallel and vesicular cisternae in the cells of females at the adult stage. The Golgi apparatus were invariably welldeveloped in hepatocytes of young adult and adult females. No consipcuous development was observed in profiles of the rough endoplasmic reticulum and the Golgi apparatus in hepatocytes of males during and after metamorphosis. The ultrastructural changes of the rough endoplasmic reticulum and the Golgi apparatus observed in hepatocytes of female sand lampreys are considered to have an intimate relation to the activity of vitellogenin synthesis in the liver, and it is suggested that the hepatocytes begin to rapidly synthesize vitellogenin in the sand lamprey at the metamorphic stages 4 to 5.