[Function of the acetabulum of digenetic trematodes, as exemplified by Dicrocoelium dendriticum]

The suckers of animals adhere to the substratum either in air or in aqueous fluids. The varying compressibility of these media causes differences in function, the principles of which are described. The ventral arch of the acetabulum of Dicrocoelium dendriticum, like the remaining body, is limited by the integument, basal lamina and skin muscles. The dorsal arch covers a basal lamina, which is close to a plexus of diagonal, longitudinal and circular muscles. The radical muscles, attached at the ventral basal lamina by thin connective tissue, continue in relatively thick contractile fibers, which split up into several fibrils, which also attached by thin connective tissue at the dorsal basal lamina. In this way the tension of the muscles is likewise distributed over the dorsal and ventral arches of the acetabulum. After contact with the substratum the sucker creates a partial vacuum and attachment by means of the pressure of the radial muscles against the wall of the hole. Because of the fluid content of the hole, the volume does not change much. The dorsal arch of the sucker withstands the pressure of the radical muscles, because its surface area is six times greater than that of the ventral arch and consequently the load is six times less. The sucker, covered with basal lamina, has a constant volume; its layer of muscles resists deformation and supports the stability of the arch.