Reproduction in Animals - Viviparous and Oviparous Animals

Viviparous animals are those that give birth to young ones. In these animals, the development of the zygote into a young one takes place inside the body of the female organism. Examples include humans, dogs, cows, and lions.

Oviparous animals are those that lay eggs. The development of the embryo occurs outside the mother's body, usually protected by a hard shell. Examples include hens, frogs, lizards, and butterflies.

The process of development from a single cell can be represented as: $Zygote \rightarrow Embryo \rightarrow Foetus \rightarrow Young \text{ } Individual$.

In oviparous animals like hens, after internal fertilization, the zygote divides repeatedly and moves down the oviduct. As it moves, many protective layers are formed around it, the outermost being the hard shell composed largely of calcium carbonate ($CaCO_3$).

Metamorphosis is the biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. This is common in oviparous animals like frogs ($Egg \rightarrow Tadpole \rightarrow Adult$) and silkworms ($Egg \rightarrow Larva \rightarrow Pupa \rightarrow Adult$).