In oviparous animals such as reptiles and birds, fertilised eggs are covered by hard calcareous shell and are laid in a safe place. After incubation period, young ones hatch out. In viviparous animals such as majority of mammals including human beings, the zygote develops into a young one inside the body of the female individual. After a certain growth, theyoung ones are delivered by the female individual. Due to
proper care and protection, the chances of survival of young
ones are more in viviparous individuals.