Primary anlage formation in diphyllobothriid tapeworms

Summary

The primary or genital anlagen in cestodes arise segmentally. They first appear as clusters of a few cells. At the site of anlage formation in the inner parenchyma the dominating cells are germinative cells and dorsoventral muscle cells. In forming anlagen there is no detectable increase of mitotic activity as compared with the surrounding parenchyma. In the initial stage the anlage is composed of loosely packed germinative cells. Even in larger, growing anlagen the mitotic index is not significantly higher than in the parenchyma. However, the mitotically active cells are located in the periphery, mitosis being inhibited in the cells in the core. A comparison of cell density and number in the inner parenchyma in different regions of the neck indicates that the number of cells does not increase posteriorly, in spite of high cell division activity. It is concluded that anlagen are formed by aggregation of germinative cells.