Plural of amnion; the innermost membrane surrounding a developing fetus.
Direct plural of amnion, from Greek amnion, possibly derived from amnos (lamb) or from a root meaning 'to wrap around.' The scientific term became standard in embryology during the 18th century.
The amnion is why human babies are born so wet—that 'wrapper' keeps the fetus floating in protective fluid, which is why premature babies born with intact amnia survive much better.
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