Then we have this sleeve structure. We have the hook, and finally, this entire portion, which basically extends this way, our Flagellum. Now, the Flagellum, this portion is the rigid hollow cylinder that is composed of the protein Flagellum. So this section is the hook that is attached to our sleeve, to the rod, and these proton rings. Now, the proton rings basically serve as proton pumps. They essentially pump our protons, the hydrogen ions, across our cell membrane.