Schematic representation of parts of the germinal disc during early embryonic development The cells in the central zone divide frequently and migrate in laterally between the epiblast and hypoblast (see lateral arrows in C). As this groove looks as a streak, it is also called the primitive streak. The gastrulation process starts with the formation of a groove (see arrow in fig C, transversal section) and forms first the primitive groove at the caudal (tail?) side. The area pellucida is composed by 2 layers, the epiblast (1 in B) at the surface and the hypoblast (3 in B) in the deeper part. This region is transparent and is therefore called the area pellucida (ap in A). The central region of the germ layer is localized at the upper part of a hole (the blastocoel). (opaca means untransparant see for example in fig.A). In a early stage, the area opaca appears as a dark zone at the external border of the germ layer and is in contact with the yolk mass. The cells in the central zone divide frequently and migrate in laterally between the epiblast and hypoblast. The gastrulation process starts with the formation of a groove and forms first the primitive groove at the caudal side. The area pellucida is composed by two layers, the epiblast at the surface and the hypoblast in the deeper part. This region is transparent and is therefore called the area pellucida. In the early stages, the germinal layer confines on the yolk with the area opaca (opaca = untransparent) that appears as a dark zone at the external border of the germ layer.

The embryonic development in birds occurs in the germinal layer separated from the upper side of the yolk by the subgerminal cavity.

Whole mount preparation 20 hours ( More.)Įarliest development phases of the germ layer.

Whole mount preparation 18 hours ( More.).

Earliest developments in the germinal disc ( More.).

Also photographs and schemes of cross sections are available.Įarly embryonic developmental features that are shown on this page:

The images of the in toto (whole mount) preparation show processes in the geminal disc (also called blasto disc) viewed from above, as if one would observe the embryon at the yolk surface through a window in the hatching egg. Using drawings and micrographs of stained samples the early embryonic development in the chicken is depicted.

Pellucid area definition