Hans Spemann (1869-1941), Nobel laureate of 1935, is one of the most remarkable biologists of the 20th century and the founder of modern experimental embryology (developmental biology). His embryonic separation experiments contributed greatly to the long-lasting debate between the advocates of the theories of preformation vs. epigenesis, and his subsequent transplantation experiments laid the basis of the concept of embryonic induction. The first of these classic experiments can be precisely dated to May 8, 1921, when one of Spemannn's students, Hilde Pröscholdt, performed a transplantation experiment with a fragment of a new gastrula blastopore lip. The dates, operation strategies and findings have recently been confirmed when the original experimental protocols and slides were found. The findings and the idea of induction were published in 1924, and this fundamental paper is still widely quoted. As shown by a citation analysis, the article is today collecting an increasing number of quotations reflecting a Renaissance of the field. For the Finnish school of development biology, Spemann and his basic ideas have been of pivotal importance.