contrac'tile vac"uole

Cell Biol.
a membrane-enveloped cellular organelle, found in many microorganisms, that periodically expands, filling with water, and then contracts, expelling its contents to the cell exterior: thought to be important in maintaining hydrostatic equilibrium. See diags. under ameba, paramecium.

Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.


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