Rauber's sickle generates only extraembryonic tissues junctonal- and sickle endoblast), and, by positional information, organizes and dominates the whole avian blastoderm (gastrulation, neurulation and blood island formation)

When the Rauber's sickle is (sub)totally mechanically removed from unincubated chicken blastoderms, their further evolution in culture is mostly disturbed. When,after removal of the chicken Rauber's sickle, a quail Rauber's sickle is placed isotopically, the normal development is totally restored. In such quail-chicken chimeras quail cells were found only in extraembryonic tissues, i.e. in junctional- and sickle endoblast and not among cells of the embryo proper (not in upper layer, nor in mesodermal, nor in endodermal cells). Further, we compared the inducing potencies of quail sickle endoblast placed on different regions of unincubated chicken blastoderms, either in the presence or absence of Rauber's sickle material. If a fragment of quail sickle endoblast was placed on the anti-sickle region of an unincubated chicken blastoderm from which the Rauber's sickle was (sub)totally removed, then often starting from this anti-sickle region an embryo presenting gastrulation and/or neurulation phenomena was induced but no blood islands were formed. So our study demonstrates that Rauber's sickle quantitatively and qualitatively dominates or inhibits ectopically-placed sickle endoblast. Earlier studies and the present study indicate the existence of a temporo-spatially bound cascade of gastrulation and neurulation phenomena and blood island formation in the avian blastoderm, starting from Rauber's sickle, the primary major organizer with inducing, inhibiting and dominating potencies.