Early Formation of the Coelomo-Cardiovascular Complex in the Chick Blastoderm

Although it is known that small areas in the unincubated avian blastoderm undergo regulation under influence of the surrounding large Rauber's (Koller's) sickle-dependent anlage fields, this seems not to be true for these anlage fields themselves. Indeed, after removal of whole anlage fields or regions in the unincubated avian blastoderms, no restoration of a complete embryo occurs, suggesting predisposition (mosaicism). In the unincubated chicken blastoderm, in the absence of Rauber's (Koller's) sickle horn regions, the isolated median region (with included middle part of Rauber Koller's sickle) is not able, after culture, to give rise to primary heart tubes. Our present study indicates that the earliest anlage field of the coelomo-cardiovascular system in the unincubated chicken blastoderm (giving rise to both the area vasculosae laterales and the area vasculosa caudalis) is localized in the upper layer between the definitive endoderm anlage field (in the concavity of Rauber Koller's sickle) and the more rostral and lateral neighbouring sickle-shaped lateral plate anlage.