Chrysalis

... the rest of the way to a butterfly, one would think that the evolution process would end when the creature dissolves into liquid mush inside its chrysalis (or cocoon for other such creatures). Then it would have to undergo millions of years worth of evolution in just a few days or weeks before ...

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eclosure is when the chrysalis (pup in a cocoon) breaks open and the, for example, butterfly comes out. In the case of your Drosophila melanogaster, it is when the fly comes out of its cocoon.

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