Egg laying mammals lay eggs. Mostly two eggs are laid in a year. Fertilization of eggs is internal and i.e. Inside the body of mother. Eggs are laid in burrows of animals. Young ones are hatched from the eggs. Their egg laying character shows their relationship with reptiles. Examples are Duck bill platypus and spiny ant eater. These mammals have a pouch outside the belly called marsupium, so they are called marsupial mammals. Fertilization of eggs and development of embryo in pouched mammals is internal. In these mammals, the embryo is at first encapsulated by shell membrane and floats free for several days in the urine fluid. After hatching from the shell membranes, the embryo does not implant or takes root in the uterus and absorbs nutrient secretions from the vascularized yolk sac. The gestation period is brief and marsupials give birth to tiny young that is effectively still an embryo. These young crawl into the marsupium where it gets milk from mother. It lives in marsupium until it can take care of itself. Examples are kangaroo, koala, Tasmanian wolf, and wombat etc. These are found in Australia and Tasmania. Opossum is found in America and it lives on trees.