How to create siamese twins?

In 1924 some of the most interesting and important experiments in developmental biology were preformed by the German embryologist Hans Spemann and his PhD student Hilde Mangold . For these experiments they isolated some tissue from different parts of early embryos of salamanders and transplanted it to different locations in similar embryos . When they transplanted this special part of tissue, the dorsal lip of the blastopore to the ventral side of an other embryo, the most extraordinary thing happened… As the embryo developed they saw that not only at the original dorsal lip of the blastopore, but also at the transplanted one, gastrulation occurred and a complete embryo was formed . Closer research pointed out that this dorsal lip of the blastopore plays a very important role in the inductive processes that occur during embryonic development . Therefor this interesting region is nowadays called the Spemann organizer .