The majority of recent investigations have concluded that the thickening of the rim of the blastoderm, and the new layer which is derived from it, is brought about by a true invagination of the segmented blastoderm. On the other hand, Klein and Kupffer hold that the newly formed layer is not derived from the segmented blastoderm (archiblast), but is mainly produced from an unsegmented portion of the blastoderm (parablast), which is intermediate in position between the archiblast and the yolk.