Bio

• The ability to move in animals is made possible by the combination of a semi rigid skeletal system with joints that act as hinges and a muscular system attached that can produce a change in body shape, which places control over different parts of the outside environment.
• When a horse runs, its feet exert a force that moves its body forward rapidly.
• When a bird takes off into flight, the force on the air produces a change in body shape that moves the bird forward.
• A swimming fish moves by pushing against the water.
• The semi rigid skeletal system in animals is combined with joints that act as hinges and a muscular system attached that can produce a change in body shape, which places control over different parts of the outside environment.
• In earthworms, a fluid-filled central body cavity or coelom is encompassed by two sets of muscles in the body wall: circular muscles that are repeated in segments and run the length of the body and longitudinal muscles that oppose the action of the circular muscles.
• Short and bristle-like structures called setae are on the underside of a worm's body.
• Muscles act on the fluid in the body's central space which represents the hydrostatic skeleton.
• The locomotion process in earthworms proceeds as waves of circular-muscle contraction that are followed by waves of longitudinal muscle contraction which pass backward.
• In the anterior end of an earthworm, circular muscles contract and longitudinal muscles relax.
• Setae lose contact with the ground.
• The front end of the body extends forward.
• Next, the circular muscles contract; the longitudinal muscles relax.
• The anterior of the body swells and setae anchor the ground.
• The body region behind the anterior end is pulled forward.
• Setae prevent slipping backward of the front end.