Invagination

Invagination means to fold inward or to sheath. In biology, this can refer to a number of processes.

(1) 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, to form coelom, etc.

(2) Invagination is the formation of a cleavage furrow during cytokinesis in animal cells.

(3) 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 ATP.

(4) Invagination occurs during endocytosis and exocytosis when a vesicle forms within the cell and the membrane closes around it.

In development biology, dosal part of cells can inergrate adjacent cells into invagination. No matter what cell it is.

In the humanities.

(1) Used to explain a special kind of meta narrative. Used by for example Rosalyn Krauss and Jacques Derrida (The Law of Genre,” Glyph 7 (1980).