Zoology · Ch 1 — Reproduction in Organisms
Oviparous, Viviparous and Ovoviviparous Animals
Oviparous, Viviparous and Ovoviviparous Animals
Based on where the embryo develops, and on whether an animal lays eggs (fertilized or unfertilized) or gives birth directly to young ones, animals fall into three broad groups: oviparous, viviparous and ovoviviparous.
Oviparous animals are egg-laying animals, whose young hatch from eggs laid outside the mother's body. Reptiles and birds lay eggs enclosed in hard, calcareous shells, while invertebrates, fishes and amphibians lay eggs that lack a hard shell and are instead covered only by a membrane.
Viviparous animals give rise to young ones directly: the young develops fully inside the mother's uterus, receiving continuous nourishment through a placental connection, and is finally born alive rather than emerging from an externally laid egg. This is the reproductive strategy of the great majority of mammals, including human beings. …
What this figure shows. A photographic-style illustration of a domestic hen standing beside a clutch of hard-shelled eggs it has laid, representing the oviparous mode of reproduction in which the young develop and hatch from an egg laid outside the mother's body - in birds and reptiles this egg is enclosed by a hard calcareous shell, unlike the membrane-covered eggs of inver …
What this figure shows. A photographic-style illustration of a cow standing beside its newly born calf, representing the viviparous mode of reproduction in which the young develops fully inside the mother's uterus, nourished throughout gestation via a placental connection, and is finally born alive rather than hatching from an externally laid egg - the reproductive mode seen in the great majo …
What this figure shows. A photographic-style illustration of a shark shown alongside a three-month-old embryo still developing inside an egg retained within the mother's body, representing the ovoviviparous mode of reproduction in which the embryo develops inside an egg that stays within the mother until ready to hatch - superficially similar to viviparity in that the young emerge alive, but distinct because the embryo has no placental connection and is nourished entirely by the egg's own yolk r …