invaginate

1. To enclose or become enclosed in or as if in a sheath.
2. To turn or become turned inward.
3. 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.

[Medieval Latin invāgīnāre, invāgīnāt- : Latin in-, in; see in-² + Latin vāgīna, sheath.]

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 infold one portion of a structure within another portion.

The verb has 2 meanings:

Meaning #1: sheathe, as in botany

Meaning #2: fold inwards, of certain organs
  Synonym: introvert