Page 2 - 2. Lesson notes-Development of embryo

Oviparous animals

The egg laying animals are called oviparous animals. In some group of animals such as
reptiles and birds, the eggs have hard covering. In such animals, the fertilisation is
internal and zygote is present insidethe eggs .The eggs develop into young ones after
incubation. During incubation eggs require proper temperature for growth .The
incubation period of hen’s egg is three weeks.

In fishes and amphibians, the eggs are without having hard outer covering and
fertilization is external.

In oviparous animals development of zygote takes place outside female’s body .

Viviparous animals

Animals those give birth to young ones are called viviparous animals.

All mammals are viviparous except Platypus and Echidna.

In viviparous animals development of zygote takes place inside female’s body.

Oviparous animals Viviparous animals
These animals lay eggs. These animals give birth to young ones.
Development of zygote takes place Development of zygote takes place
outside female’s body. outside female’s body.
Fertilisation may be internal or external. Fertilisation is internal.