Experimental embryology, which was founded in the 1880's and came of age in the first decades of this century, became the foundation for modern cellular and developmental biology. One of the embryology's uncontested leaders was the German biologist Hans Spemann. Professor Hamburger presents a critical account of Spemann's Nobel Prize in 1935. The author traces the different lines of research which emerged from Spemann's seminal discovery and carries the history up to the 1950's when classical embryology was superseded by molecular-developmental biology. Hamburger is uniquely qualified to write this volume: he spent almost a decade in Spemann's laboratory, first as a graduate student, and later as research colleague. As a mature and distinguished scientist working in the United States, Hamburger played a crucial role in establishing the field of developmental neurobiology.