Plainly
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homunculus
noun/hoʊˈmʌŋkjələs/
meaning in plain English
A tiny fake person that some old-time scientists once thought was inside a sperm, like a baby waiting to grow.
Picture a tiny fake person, a homunculus, hidden in a sperm like a secret baby waiting to grow.
for example
In the 17th century, some people believed a homunculus was curled up inside every sperm, ready to become a baby when it met an egg.
Imagine cracking open an egg to find a tiny, fully-formed homunculus curled inside—like a dollhouse version of a person, just waiting to spring to life. That’s what old scientists once believed they’d see under a microscope, as if every sperm carried a secret miniature heir.