Oviparous animal s lay eggs outside their body .As a result the egg of these animals are under continuous threat from various environmental factors .Other the  other hand, in viviparous animals, the development of the egg takes place inside the body of the female .Hence, the off-spring of an egg laying or oviparous animal is at greater risk as compared to the off-spring of a viviparous animal, which gives birth to its young ones.