Problem 18

Background and context

Mammals are the most successful and the most dominant animals today. They are hairy animals, the females of which have milk producing mammary glands to suckle their young ones. There are about 4,000 species of mammals, inhabiting most environments of the world - polar ice caps, desserts, oceans, mountains, forests, grasslands and dark caves. They are also vary in size from the tiny shrews to large blue whales. Human beings is also a mammal. There are divided into three classes - Prototheria, Metatheria, Eutheria.