Embryonic induction refers to the process by which cells and tissues in embryos direct the development of adjacent cells. One example is the development of the lens from nearby skin tissue as the eye cup grows outward. When a eye grows toward the outer layer of skin, the embryo grows a lens that allows eyes to focus properly.
When the process of induction does not occur properly, specialized tissue malforms. Absence of induction results in stunted organs or tissue. Too much induction means specialized tissue may form in places where it is not needed. The process of induction is not fully understood, but scientists believe RNA somehow communicates between cells to begin induction at certain times.
In an experiment done on embryonic frogs, Dr. Edward De Robertis showed how induction can happen from far away with a part of the frog's body known as dorsal organizer region. An embryo was cut in half, leaving induction cells in both halves. The result was that twin frogs developed in the cut embryo.
Hans Spemann was awarded the Nobel Prize for Medicine in 1935 for his experiments in 1924 during which he discovered regions of cells that induce others. Spemann transplanted these cells among frog embryos by grafting certain cells to parts of frogs that do not normally harbor various tissues. For instance, Spemann's experiments made frog heads or tails grow in the opposite part of the frog embryos.