हु इज विविपारस एनिमल्स
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Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the mother.
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Viva
An animal that is viviparous gives birth to developed live young. The embryos are raised with special organs in the parents as they develop, that supply nutrients to the growing embryos. This condition is known as matrotrophy, when the embryo receives nutrients directly from the mother and not from the yolk. The difference between ovoviviparity and viviparity is that viviparous animals feed their embryos with nutrients from the mother. Without a large egg, there is no large yolk sac for the embryo to survive on. Different groups of viviparous animals have evolved throughout time, weighing in on the various pros and cons of being viviparous.
Viviparous animals exist in almost every vertebrate taxa, while there are few, if any, in the invertebrate taxa (though many invertebrates are ovoviviparous). Of the recognizable groups of animals, only the birds do not show some form of viviparity. Fish, amphibians, reptiles, and mammals all have viviparous members, while none of the group are exclusively viviparous. Developing the young viviparously appears to be a derived trait from oviparous animals. The theory is that some oviparous animals tend to develop eggs longer than others internally. In some species, this leads to the young being hatched within the mother, or ovoviviparity. In ovoviviparous animals, it is often the case that the young feed on each other for nourishment after hatching but while in the womb. Some of larvae inside the mother, and feed on special secretions from her reproductive tract. Mammals have taken this concept one step further, birthing young earlier and feeding them on a nutritive substance from the mammary glands. This combines benefits of viviparous animals with the ability to shorten the gestation time and demand on the mother.
Viviparous animals must reproduce sexually through internal fertilization, for that is where their fertilized eggs develop. Males must have some structure to fertilize the female. This can be a penis in mammals, claspers in sharks, or even the strange gel-like structure that male salamanders leave behind for their mates to find, which the females deposit internally. It is interesting that birds are the only group of animals which does not contain any viviparous species. This is thought to be because of how birds evolved. Early in the evolution of birds, they became endothermic. This means they could simply brood their eggs and receive similar results as viviparous animals. Some snakes and reptiles, on the other hand, developed viviparity and ovoviviparity in order to move their eggs to the sun to warm them up in colder climates. While the groups of animals that are viviparous vary widely, it has common pros and cons.
Examples of Viviparous
Humans
Humans, like most mammals, are viviparous animals. Humans reproduce via internal fertilization. As in all higher mammals, the egg implants in the uterine wall while it develops. The uterine wall develops a structure known as the placenta, containing many blood vessels. This tissue surrounds the embryo, supplies it with nutrients, and removes waste products. The embryo develops into a small fetus, and the fetus into a baby. Unlike some viviparous animals, humans are born well before they are fully developed. This is seen in many mammals, as milk provides a rich and nutritive substance for babies. Further, it lessens the burden of the mother as she doesn’t have to carry the baby for the many years it would take for it to become fully developed. This frees her up to gather food for the baby and become impregnated again. While most mammals show high levels of parental care, it is not a requirement of viviparous animals.