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Webster's New World College Dictionary » yolk sac
yolk sac
yolk sac definition
yolk sac
- a saclike vascular membrane containing yolk, an outgrowth from the ventral surface of very yolky vertebrate embryos, as those of fishes, birds, or reptiles, that supplies nourishment to the embryo
- a homologous organ in most mammalian embryos that contains no yolk and that becomes a vestige at an early embryonic stage
Webster's New World College Dictionary Copyright © 2005 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.
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