invaginate
verb
Definitions
To fold up or enclose into a sheath-like or pouch-like structure, either naturally or as part of a surgical procedure.
To turn or fold inwardly.
To fold inward to create a hollow space where none had existed, as with a gastrula forming from a blastula.
adjective
Definitions
Sheathed
Having one portion of a hollow organ drawn back within another portion.