The surface location of a sandwich
Look at the cross-sectional
location of a
Look at the sandwich though its thickness
Because amphibian embryos are opaque and because the movements of gastrulation are inherently complicated, it would be desirable to take out those regions that perform convergence and extension to study them in more detail. Detailed study of the marginal zone of the amphibian gastrula can be performed in this way using Keller sandwiches, named in honor of Ray Keller, who first worked out the procedures for their microsurgical isolation, and in collaboration with his colleagues, worked out the culture conditions for their subsequent development.
Keller sandwiches make it possible to do several things that were previously impossible, or could only be inferred: