Animal Life-II (Reproduction in Animals)
The ostrich is the largest living bird, and lays the biggest egg, weighing almost 1400 gm.
- The process by which new living beings resembling their parents are produced is called reproduction.
- Animals reproduce by giving birth to young ones or by laying eggs.
- The animals which reproduce by giving birth to young ones are called mammals. Human oeings, cows, lions, etc., are some examples or mammals.
- Mammals take care of their young ones by giving milk, cleaning them and protecting them from enemies.
- Birds lay eggs and keep them warm. After some days, eggs hatch and young ones come out.
- Eggs are either oval shaped or round shaped with a thick outer protective shell which protects the growing chick inside. Inside the egg, there is a white thick liquid called egg-white (albumen) and a yellow liquid (yolk) at the centre the chick forms and grows inside the yolk. The growing chick is called embryo.
- Fish lay eggs in water and reptiles like crocodiles, snakes and turtles lay their eggs on land.
- Frogs lay eggs in water which hatch into tadpoles. Tadpoles look like fish. They undergo metamorphosis and grow into frogs.
- Some insects like grasshopper and cockroach pass through three stages in their life cycle. Eggs laid by cockroach develop into small 'baby' insects called nymphs. These look mostly like fully grown insect. Caterpillars are the larvae of butterflies and moths. They go through several changes from the egg stage to the adult stage. This kind of changes in growing is called metamorphosis. The youn gone of cockroach shed their skin several times to become an adult cockroach. This process is called moulting.
- Other insects like housefly and butterfly pass through four stages. The youngones hatched from the eggs are called caterpillars.
- After growing for sometime the larva covers itself in a cocoon. This stage is called pupa. Finally pupa bursts and the fully grown insect comes out. Unlike mammals, the 'babies' of the insects are not looked after by their parents.