Most animals , like plants, reproduce by fertilization: the female reproductive cell ( egg ) is fertilized by the male reproductive cell ( sperm ). Their union gives rise to the embryo, which as it develops gives life to a new organism of the same species. The development of the embryo varies from one animal to another.
3 Types of Reproduction In Animals
In animals, three types of reproduction can be distinguished: oviparous , viviparous and ovoviparous .
- Oviparousare the animals that lay eggs. The egg contains the nutrients that the embryo needs to develop. When the new being is fully formed, it breaks the shell and comes out. Almost all fish, amphibians, reptiles, birds and many invertebrates, including insects, are oviparous. The eggs of reptiles and birds have a hard and robust shell, which protects them and prevents them from drying out in the air, while those of animals are soft and fragile.
In most fish , the female lays a large number of eggs, which are fertilized by the male and then abandoned.Almost all reptiles allow their eggs to hatch on their own in warm and protected places; some dig a nest.The birds prepare cozy nests for their eggs, hatch them for a long time and take care of the newborn babies, providing them with the food they need and supporting them in the first flights.
Organisms very different from adult individuals emerge from insect eggs . They are called larvae or nymphs and go through different stages and changes (metamorphosis) during growth.
- In viviparous animals the embryo develops in the mother’s body and a special organ, the placenta, nourishes the embryo, then the young are born, that is, they grow outside, already formed. The new born are called inept because they are unable to look after themselves, in particular the mother feeds them with her own milk for a certain period. Parents protect their children and often teach them many things, such as hunting, respecting leaders. All mammals, including aquatic ones, are viviparous.
The female of the kangaroo, the koala, the opossum and a few other mammals has a pocket on the belly, called a pouch , in which the new being, as soon as it is born, takes refuge and completes its development, feeding on its mother’s milk.
- Very few animals are ovoviparous: some fish such as sharks, some reptiles such as vipers and some insects. These animals reproduce with eggs, which however remain inside the mother’s body until the new organism is perfectly formed. At this point the shell is broken and the baby is delivered.