Noun
The reception of one part within another.
The abnormal reception or slipping of a part of a tube, by inversion and descent, within a contiguous part of it; specifically, the reception or slipping of the upper part of the small intestine into the lower; introsusception; invagination.
The interposition of new particles of formative material among those already existing, as in a cell wall, or in a starch grain.
The act of taking foreign matter, as food, into a living body; the process of nutrition, by which dead matter is absorbed by the living organism, and ultimately converted into the organized substance of its various tissues and organs.
Source: Webster's dictionarythe invagination of the blastula Source: Internet