BODY MOVEMENT -II | GAITS OF ANIMALS

Are muscles and bones always required for movement? How do other animals move? Do all animals have bones? What about an earthworm or a snail?

Earthworm

Movement Of Earthworm

The body of an earthworm is made up of many rings joined end to end. An earthworm does not have bones. It has muscles which help to extend and shorten the body. 

During movement, the earthworm first extends the front part of the body, keeping the rear portion fixed to the ground. Then it fixes the front end and releases the rear end. It then shortens the body and pulls the rear end forward. This makes it move forward by a small distance. Repeating such muscle expansions and contractions, the earthworm can move through soil. The body secretes a slimy substance to help the movement.

How does it fix parts of its body to the ground?

Under its body, it has a large number of tiny bristles (hair like structures) projecting out. The bristles

are connected with muscles. The bristles help to get a good grip on the ground.

The earthworm, actually, eats its way through the soil! Its body then throws away the undigested part of the material that it eats. This activity of an earthworm makes the soil more useful for plants.

Snail

A Snail

Notice the rounded structure in above image, which snail carries on its back This is called the shell and it is the outer skeleton of the snail, but is not made of bones. The shell is a single unit and does not help in moving from place to place. It has to be dragged along.

Place a snail on a glass plate and watch it. When it starts moving, carefully lift the glass plate along with the snail over your head.

You will observe that a thick structure and the head of the snail may come out of an opening in the shell. The thick structure is its foot, made of strong muscles. Now, carefully tilt the glass plate. The wavy motion of the foot can be seen.

Cockroach

Cockroaches walk and climb as well as fly in the air. They have three pairs of legs. These help in walking. The body is covered with a hard outer skeleton. This outer skeleton is made of different units joined together and that permits movement.

There are two pairs of wings attached to the breast. The cockroaches have distinct muscles — those near the legs move the legs for walking. The breast muscles move the wings when the cockroach flies.

Birds

Birds fly in the air and walk on the ground. Some birds like ducks and swans also swim in water. The birds can fly because their bodies are well suited for flying. Their bones are hallow and light. The bones of the hind limbs are typical for walking and perching.

The bony parts of the forelimbs are modified as wings. The shoulder bones are strong. The breastbones are modified to hold muscles of flight which are used to move the wings up and down.

Fish

The head and tail of the fish are smaller than the middle portion of the body – the body tapers at both ends. This body shape is called streamlined. The shape is such that water can flow around it easily and allow the fish to move in water.

Movement in Fish

The skeleton of the fish is covered with strong muscles. During swimming, muscles make the front part of the body curve to one side and the tail part swings towards the opposite side. The fish forms a curve. Then, quickly, the body and tail curve to the other side. This makes a jerk and pushes the body forward. A series of such jerks make the fish swim ahead. This is helped by the fins of the tail.

Fish also have other fins on their body which mainly help to keep the balance of the body and to keep

direction, while swimming. Did you ever notice that under water divers wear fin like flippers on their feet, to help them move easily in water?

How do snakes move?

Snakes have a long backbone. They have many thin muscles. They are connected to each other even though they are far from one another. They also interconnect the backbone, ribs and skin. The snake’s body curves into many loops. 

Each loop of the snake gives it a forward push by pressing against the ground. Since its long body makes many loops and each loop gives it this push, the snake moves forward very fast and not in a straight line.

Summary : What we learnt?

• Bones and cartilage form the skeleton of the human body. It gives the frame and shape to the body and helps in movement. It protects the inner organs.
• The skeleton comprises the skull, the back bone, ribs and the breast bone, shoulder and hipbones, and the bones of hands and legs.
• The bones are moved by alternate contractions and relaxations of two sets of muscles.
• The bone joints are of various kinds depending on the nature of joints and direction of movement they allow.
• Strong muscles and light bones work together to help the birds fly. They fly by flapping their wings. 
• Fish swim by forming loops alternately on two sides of the body.
• Snakes slither on the ground by looping sideways. A large number of bones and associated muscles push the body forward.
• The body and legs of cockroaches have hard coverings forming an outer skeleton. The muscles of the breast connected with three pairs of legs and two pairs of wings help the cockroach to walk and fly.
• Earthworms move by alternate extension and contraction of the body using muscles. Tiny bristles on the underside of the body help in gripping the ground.
• Snails move with the help of a muscular foot.

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