Invagination is the infolding of one part within another part of a structure, a folding that creates a pocket. The term, originally used in embryology, has been adopted in other disciplines as well. It has many meanings in each term or subject.
- Invagination is the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism, with differentiated germ layers: endoderm, mesoderm, and ectoderm. More localized invaginations also occur later in embryonic development,
- The inner membrane of a mitochondrion invaginates to form cristae, thus providing a much greater surface area to accommodate the protein complexes and other participants that produce adenosine triphosphate (ATP).
- Invagination occurs during endocytosis and exocytosis when a vesicle forms within the cell and the membrane closes around it.
- Invagination of a part of the intestine into another part is called intussusception.
The term is used to explain a special kind of metanarrative. It was first used by Maurice Merleau-Ponty (French: invagination) to describe the dynamic self-differentiation of the 'flesh'. It was later used by Rosalind E. Krauss and Jacques Derrida ("The Law of Genre", Glyph 7, 1980); for Derrida, an invaginated text is a narrative that folds upon itself, "endlessly swapping outside for inside and thereby producing a structure en abyme". He applies the term to such texts as Immanuel Kant's Critique of Judgment and Maurice Blanchot's La Folie du Jour. Invagination is an aspect of différance, since according to Derrida it opens the "inside" to the "other" and denies both inside and outside a stable identity.
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