As this is maybe a first point of agreement between Fleury and myself I promised to make of it a post.
In a recent comment he wrote:
This one is quite short but certainly the most important points. Fleury presents:
We assume that the blastodisc is a composite structure, namely a “sandwich”: Extra-Cellular Matrix/ cellular layers/Extra-Cellular Matrix. (p8, c1)
I suppose that here what is described is not the blastodisk but the epiblast. But this is not clear as there are several cellular layers. But later on it seems that the epiblast is considered to be the “sandwich”, the cell movements described being those of cells in epiblast, at least until ingression through the PS starts. What is bothering is that the “sandwich” is described as ECM/cellular layers/ECM.