\De*lam`i*na"tion\, n. (Biol.)
Formation and separation of lamin[ae] or layers; one of the
methods by which the various blastodermic layers of the ovum
are differentiated.
Note: This process consists of a concentric splitting of the
      cells of the blastosphere into an outer layer
      (epiblast) and an inner layer (hypoblast). By the
      perforation of the resultant two-walled vesicle, a
      gastrula results similar to that formed by the process
      of invagination.