These two endoderm-rudiments embryonic membrane formed by delamination from the blastoderm, ultimately grow together and give rise to the epithelium of the midwhile in a few insects, including the wingless spring-tails, the emgut.
In the Coelentera the ectoderm and endoderm are set apart from one another at a very early period in the life-history; generally either by delamination or invagination, processes described in the article Embryology.
A quadratic average stress failure criterion is suggested to predict delamination and the interlayer at which it occurs.
Allies and Morrison had been concerned initially about possible delamination.
The germ-layer formation is always by immigration or delamination, never by invagination.