viviparity/Ovoviviparity

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viviparity/Ovoviviparity

Post  Admin on Sat Apr 21, 2012 6:02 pm

Ovoviviparity is a mode of reproduction in certain animals in which embryos develop inside eggs that are then retained within the mother's body until they are ready to hatch. Ovoviviparity is a topic of some interest, since most of us assume that egg-layers do not give birth to live young.We are all familiar with vivipary, in which an animal gives birth to live young after it has developed in the uterus,The primary difference between ovoviviparity and vivipary other than the obvious presence of eggs is that ovoviviparous animals do not provide nutrition to their young through a placenta. Instead, they developing young inside the egg feed on the egg yolk, just as their ovoparous cousins do.Embryos of oviparous squamate reptiles depend on calcium-rich yolk as the primary source of calcium for development, but calcium extracted from the eggshell contributes an important secondary source Viviparity has evolved independently in multiple lineages of squamates and the eggs of viviparous species lack a calcareous eggshell Loss of a thick, calcified eggshell is a predicted requisite to the evolution of viviparity because such a structure would impede respiratory exchange between the uterus and the embryo.viviparity among squamate reptiles has been attributed to their pattern of embryonic calcium provision based on the premise that oviparous embryos are not dependent on calcium from the eggshell.
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