Mammals are those living beings whose females produce milk to suckle their young. They are warm-blooded and have welldeveloped brains. They give birth to young ones and feed them with their own milk. Mammals breathe through lungs and their bodies are covered with hair. Do you know how the female mammals produce milk? Milk in the female mammals is produced by ‘mammary glands’ that are located in the breasts. They are bag-shaped and big in size. Shortly before the birth of her young, hormonal changes in the mothers result in increased development of the mammary glands. They produce large drops of fats which when mixed with fluids present in the breasts become milk. Corpus luteum of the ovary also produces a hormone that helps in the process of milk production. Most of female mammals have teats or nipples from which the young can suck milk. At present, there are about 4400 living species of mammals grouped into 19 orders and about 120 families. They, of course, differ from one another in their bodies, shapes, sizes and habits. Most of them live on land but some live in water and air also. For example, whales and the dolphins are mammals, which live in water. And, the bat is a mammal that flies in the air. They exist in different climatic conditions — hot, cold, dry or humid. Most mammals give birth to less than 10 young ones a year. Humans usually give birth to only one baby at a time. Apart from human beings, cow, buffalo, sheep, goat, etc. also come under the category of mammals.