The link says it is nearly straight at the beginning of the week, not the end, and in any event, it seems the biomechanical analysis, on a more detailed look, involves the rate of growth for particulars in that area, not just the whole embryo. So presumably the folds can occur when the embryo is straight.
Given that the rate of growth is governed by gene exression this appears to be conceding Bernd's position rather than arguing against it.
In support of your contention, that the embryo is not neccessarily curved when the first pharyngeal/visceral arches appear, the same section says...
Cervical and caudal flexures have the effect that the embryo takes on its characteristic C shape.
So the embryo has begun to curve by day 28.
There is a higher detail image of day 29 on the side of the web page where it says 'picture' on the second page covering the
fifth week. This highlights the developing arches and the begining of the head/neck flexion is clearer. The day 30 embryo picture gives a very clear view of the developing arches and I really think it would be hard to make a case for such protuberant structures being the result of the flexion of the head and neck. These folds are almost as wide again as the neck itself.
However, I am not an embryologist, but the professor dismissing gill pouches does so for a reason, it seems to me, and so I am still wondering exactly why you dismiss the concept of tension here.
Because other than Blechshmidt's word for it there is no data to base a conclusion that tension is the source.
This all seems rather academic if you are prepared to concede, as you stated earlier, that it is simply a question of nomenclature for you and that similar patterns of gene expression and gene function in no way affect your preference for 'biomechanical flexion folds' as the correct term and that the terminology does not have any relevance to the question of homology.
If you are prepared to accept that these genes can control the development leading to the formation of the 'biomechanical flexion fold' then you fundamentally diagree with Blechshmidt's approach to embryology, even if you prefer his terminology in this instance.
TTFN,
WK
This message has been edited by Wounded King, 19-Dec-2005 11:15 PM
This message has been edited by Wounded King, 20-Dec-2005 12:05 PM