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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
[Eusebius] Such is their zoogony. Following that the same writer adds:
Eusebius distinguishes the cosmogony from the zoogony, but they are clearly integral parts of a single account, and I shall use 'the cosmogony' to cover the two together.
next let us see how he (Philo) describes their zoogony', makes it as clear as we could wish that he has not just told us about the generation of living things.