invaginate

To enclose or become enclosed in a sheath or similar covering.

To turn or become turned inward.

To infold or become infolded so as to form a hollow space within a previously solid structure, as in the formation of a gastrula from a blastula.

To sheathe; insert or receive as into a sheath; introvert: opposed to evaginate.

To insert as in a sheath; to produce intussusception in.