Embryonal migration and spacing starts on day ___ and is completed by day ___. On day ___, the blastocyst begins to elongate bilaterally and can reach a length of 1,5 m by day ___; at this stage it is only 2-5 mm wide. The elongated lateral extensions of the blastocyst later become folded in a concertina-like fashion, with the embryonal disc situated in its middle.