For centuries, amphibians have been used as animal models for embryogenesis, based on their well-organized pattern of embryonic development. As early as the 1920s, scientists attempted to transplant mesodermal tissue from the dorsal side of one embryo to the ventral side of another embryo, which resulted in the establishment of an additional body axis. This classic experiment has stimulated the next generations of biologists to investigate various processes associated with development. Subsequent studies involving the African toad Xenopus laevis showed that the differentiation of embryonic tissues could be manipulated using various conditions, such as mixing these with cells from other regions of a blastula. For example, when cells from the blastocoel roof were mixed with cells from the vegetal pole, these would differentiate into dorsal, ...