Viviparous animals are animals that reproduce by giving birth to live young. These young ones develop and are nourished within their mother’s body. Most mammals, including humans, are viviparous. The opposite of viviparous is oviparous, which are organisms that lay eggs.
The egg-laying mammals, on the other hand, are called monotremes. The platypus is an example of monotreme. Most other animals, including all birds and reptiles are oviparous. They lay eggs that hatch. However, most vertebrates retain their eggs and hatch them internally. These animals are called ovoviviparous and include some snakes like the boas. Certain insects give birth to live young, and other insects, such as aphids, do not require a male to reproduce.