Biology: Different kinds of Mammals

Source: Mammal's Locomotion

Monotremes 

Source: World Atlas

Monotremes are mammals that lay eggs.

Marsupials

Source: San Diego Zoo

Marsupials are mammals whose young are born alive, but at an early stage of development, and they usually continue to develop in a pouch on their mother's body.

Placental Mammals 

Source: World Wild Life

A placental mammal develops inside its mother's body until its body systems can function independently.