Spemann's heritage in Finnish developmental biology.

The Finnish school of developmental biology can be considered a direct descendant of Spemann's school as both the original technology and the fundamental problems were introduced into Finland by Gunnar Ekman (1883-1937) who had worked for extended periods in Germany. After his early death, the work was continued by Sulo Toivonen (1909-1995), and until 1968 the group explored the mechanisms of primary induction and the subsequent segregation of the central nervous system. The extensive investigations led to the formulation of the "double-gradient" hypothesis and ultimately to its experimental vindication.