Viviparity


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Related to Viviparity: territoriality, ovoviviparity

Viviparity

 

a means of reproducing offspring in which the embryo develops in the mother’s body, is nourished directly by the mother through a placenta, and is born more or less developed and free of any egg covering.

Viviparity is counterposed to oviparity, in which the development of the embryo and its release from the egg covering occur outside the mother’s body (after the eggs are laid). The historical connection between viviparity and oviparity is indicated by rare cases of ovoviviparity, in which the embryo develops from an egg in the mother’s body and is nourished chiefly on substances stored in the egg itself, but also is secreted by the mother’s body and is freed of the egg covering, usually after the egg is laid.

Among invertebrates, viviparity is characteristic of some coelenterates, arthropods, mollusks, worms, and echinoderms. Among chordates, it is characteristic of salpas, many sharks and rays, some cyprinodonts, frogs, Caeciliidae, salamanders, tortoises, lizards, and snakes, and of the majority of mammals (except Echidna, Proechidna, and the platypus), including man. Development of the embryo in viviparity may occur in the ovary, the oviducts or dilations of them converted into a uterus, or in the vagina. In many viviparous animals embryonic membranes are formed around the embryo.

References in periodicals archive ?
When reptiles initially moved to colder areas they needed to evolve emergency measures to succeed in these harsh places, and we believe viviparity is one of these key measures.
Reproduction in the lizard Mabuya heathi (Scincidae), a comemntary on viviparity in new world Mabuya.
New record of viviparity for the dominant benthic invertebrate Exogone hebes (Polychaeta: Syllidae) from the Grand Banks of Newfoundland.
252 Viviparity is common in mangrove species, although it is especially clear in the red mangrove (Rhizophora mangle).
To illustrate the breadth of his curiosity-driven insight, consider the following titles of papers he published with co-authors: i) The spiral in the tusk of the narwhal (1988, Arctic 41:236-238); ii) Constraints on brain growth (1989, Nature 340:194); iii) The evolution of viviparity in amniotes: egg retention vs.
If Hozukius is found to be viviparous like Sebastes and Sebastiscus, then viviparity would be another derived character to support this subfamily.
Reconstructing ancestral reaction norms: an example using the evolution of reptilian viviparity.
The latter process allows salps to achieve high densities in short periods of time, while mortality is likely minimal as a result of viviparity (Heron, 1972), and causes the overgrazing of food resources during these short burst increases.
Thermal and reproductive biology of high and low elevation populations of the lizard Sceloporus scalaris: implications for the evolution of viviparity.
Washington, December 11 ( ANI ): Viviparity, the form of birth that produces living young, and not external eggs, could date back to 280 million years ago or even earlier, a new study has suggested.