During movement a cilium oscillates like a pendulum. Each oscillation comprises of a fast effective stroke and a slow recovery stroke. During the effective stroke, the cilium becomes slightly curved and rigid and strikes the water like an oar, so that body is propelled forward in opposite direction of stroke.
The recovery stroke which follows immediately brings the cilium again into position for the next effective stroke. All cilia of the body don’t move simultaneously and independently, but progressively in a characterstic wave-like manner called metachronal rhythm. During forward movement of Paramecium, the metachronal waves pass from the posterior end forward. (ii) Mode of swimming: The animal does not follow a straight tract but rotate spirally along a left-handed helix. The reason for this is two fold Rotation and Gyration.
Rotation occurs because body cilia do not beat directly backwards but somewhat obliquely towards right, so that the animal rotates over to the left on its long axis. Gyration occurs because the cilia of oral groove strike obliquely and more vigorously so as to turn the anterior end continuously away from the oral side and moves in circles. In backward movement a Paramecium follows a straight course. In this case the metachronal wave passes from anterior end to backward.
This is due to the fact that effective stroke is carried out anteriorly. Mechanism of ciliary movement in Paramecium is little studied. It is now known that cilia move in a coordinated system. They move by the contraction of peripheral fibres located within them. The energy needed for fibrillar contraction is supplied by ATP.