Activation of avian embryo formation by unfertilized quail germ discs: comparison with early amphibian development.

In the present study we placed germ discs (or fragments containing the deep central part of it) from unfertilized laid or extracted quail eggs on the deep side of the upper layer of isolated anti-sickle regions from unincubated chicken blastoderms. After culture in vitro of associations where the central deep part of the germ discs was in contact with the deep side of the upper layer (UL), we observed in about 30% of the cases the onset of embryonic development. Both associated parts play a role in the final formation of an embryo. Our experimental results, suggest that the delta ooplasm of the nucleus of Pander influences the cranial upper layer to segregate an endophyll layer. The definitive embryonic structures i.e. mesoderm, epiblast and neural plate are derived from the chicken upper layer by respectively normal gastrulation and (pre)neurulation phenomena. Our experiments seem to have some homology with the association experiments of isolated cortices from various regions of unfertilized Xenopus eggs implanted into the ventroequatorial core of a recipient 8-cell Xenopus embryo.