Each egg has a hard protective outer shell. Inside the shell there is a clear sticky Iiquid called albumen [ also called egg white ). Inside it there is a yellow liquid called yolk that provides food to the body growing inside. This body is called the embryo. The embryo develops into a chicken  only when an egg is kept  warm . The parent bird keeps the egg warm by sitting on it. After 21 days the fully grown chick breaks the egg and comes out. This is called hatching.                                Animals that give birth to young ones produ e milk to feed them are called mammals. These Animals carry their yound ones inside their bodies till they are born. Cow horse tat elephants cat squirrel mongoose etc. belong to this group of Animals Human beings are also mammals.