Both the area pellucida epiblast and the area opaca epiblast play roles during chick gastrulation. Which of the following best describes their involvement in this process?
a)
The area pellucida epiblast contributes cells that move through the primitive streak to form the mesoderm and endoderm, while the area opaca epiblast remains static and does not participate in gastrulation.
b)
The area pellucida epiblast forms the hypoblast, while the area opaca epiblast generates the primitive streak and drives gastrulation.
c)
The area pellucida epiblast gives rise to most of the embryonic tissues through cell movements at the primitive streak, while the area opaca epiblast contributes some endoderm and (through the hypoblast) extraembryonic structures such as the yolk sac.
d)
The area pellucida epiblast and the area opaca epiblast both contribute cells to the primitive streak, which completely forms before cell movements result in separation of the mesoderm and endoderm layers from the epiblast.