Vivipary

Viviparity literally means "giving live birth", from the Latin vivus ("living") and parere ("to beget"). The term is in use both in zoology and in botany as a term for certain classes of modes of reproduction, though it has different meanings in the two contexts.
The adjective viviparous is derived from "viviparity" and describes both the various modes of reproduction and the organisms that reproduce in any such mode.

In zoology viviparity refers to development of the embryo inside the body of the parent, eventually leading to live birth, as opposed to reproduction by laying eggs that complete their incubation outside the parental body. There are several forms of reproductive processes that answer to that description however, and they differ so radically, both in their nature and evolutionary origin, that no definitive and exclusive terminology is universally accepted, and the usage of the term is largely a matter of convenience and preference.

In botany vivipary is a common alternative form of the term, and botanical definitions also vary. One usage refers to reproduction via embryos, such as shoots or bulbils, as opposed to germinating externally from a dropped, dormant seed, as is usual in plants; however, vivipary also may refer to plants arising from buds or seedlings that have formed or germinated while still on the parent plant, and are dropped when ready to establish themselves in the substrate. In botany too, the usage of the term is largely a matter of convenience and preference.

Five modes of reproduction have been differentiated in animals based on relations between zygote and parents. The five include two nonviviparous modes: ovuliparity, with external fertilisation, and oviparity, with internal fertilisation. In the latter, the female lays zygotes as eggs with a large yolk; this occurs in all birds, most reptiles, and some fishes. These modes are distinguished from viviparity, which covers all the modes that result in live birth:

At least some transport of nutrients from mother to embryo appears to be common to all viviparous species, but those with fully developed placentas such as found in the Theria, some skinks, and some fish can rely on the placenta for transfer of all necessary nutrients to the offspring and for removal of all the metabolic wastes as well once it has been fully established during the early phases of a pregnancy. In such species, there is direct, intimate contact between maternal and embryonic tissue, though there also is a placental barrier to control or prevent uncontrolled exchange and the transfer of pathogens.

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