Structure and coiling of the stalk in the peritrich ciliates Vorticella and Carchesium.

The stalk of Carcliesium and Vorticella coils by the action of a contractile organelle. The organelle lies within a thread of cytoplasm which is encased in a complex extracellular tube. Study with the light microscope and the electron microscope suggests that the structure of the tube and the course of the organelle determine the form of the coiling. The contractile organelle contains a system of interconnected membranous tubules and the cytoplasm around it also contains membranous saccules. Both tubules and saccules extend along the length of the stalk.