ingression

Etymology

ingress + -ion

noun

1. The act or process of entering or intruding.
   ingression of the sea onto land
2. (metaphysics) The process by which a potentiality enters into actuality.
   […] it is by virtue of the individual essence that an eternal object remains precisely the same eternal object through all its ingressions […] 1967, Whitehead's Metaphysics, Edward Pols, page 164
3. (biology) The inward migration of cells from the blastula during gastrulation.
   Ingression of ectodermal cells from the area between the velar lobes establishes the cerebral ganglia and similar ingressions produce the other ganglia. 1940, Libbie Henrietta Hyman, The Invertebrates, page 496