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Attention, chocolate lovers: You may not be able to help yourselves. Swiss and British scientists have linked the widespread love of chocolate to a chemical "signature" that may be programmed into our metabolic systems.
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Yolk sac
Yolk sac: Not all yolk has to do with birds’ eggs. Human embyros have a yolk sac, a membane outside the embryo but connected by a tube (the yolk stalk) though the umbilical opening to the embryo’s midgut. The yolk sac serves as an early site for the formation of blood and in time is incorporated into the primitive gut of the embryo.