From the middle of this sickle a process next grows forward into the area pellucida.
They are almost entirely confined to the posterior part of the area pellucida, and give rise to the opacity of that part.
Section through anterior part of area pellucida in front of embryonic shield.
In the course of further growth the area pellucida soon becomes pyriform, the narrower extremity being the posterior.
The primitive streak is however the most interesting structure in the area pellucida at this stage.
The epiblast spreads rapidly over the white yolk, and the area pellucida also increases in size.
Junction between the white-yolk spheres and the hypoblast cells at the passage from the area pellucida to the area opaca.
In the region of the area pellucida there is placed below the epiblast a more or less irregular layer of cells.
Outside the area pellucida, an area vasculosa has become very well defined.
In surface views the primitive streak often appears to stop short of the hinder border of the area pellucida.