Here is a critical account of the experimental work of German biologist and Nobel laureate Hans Spemann, one of the founders of experimental embryology. The author, a distinguished developmental biologist, spent almost a decade in Spemann's laboratory. He examines Spemann's work and traces the different lines of investigation which emerged from his mentor's seminal research, and laid the foundation for modern cellular and developmental biology.

Conrad Hal Waddington's Organisers and Genes, published in 1940, is a summary of available research and theoretical framework for many concepts related to tissue differentiation in the developing embryo. The book is composed of two main conceptual sections. The first section explores the action and nature of the organizer, while the second section delves into genes and their influence on development. In this book Waddington explored organizers in terms of their capacity and method of induction. First he examined the nature of induction, discussing crucial experiments concerning the organizer, including Hans Spemann's discovery of the organizer, and his own research into organizers in higher birds and mammals. Waddington separated the action of the organizer into two distinct categories, evocation and individuation, discussed below. The main experimental approach discussed in this book involved grafting organizing tissue from one embryo or region of an embryo to another. Waddington described evocation as non-assimilative induction, or a one-way inducing signal. He presented this as a chemical signal and illustrated evocation with the dead organizer experiment. The dead organizer was shown to be capable of inducing differentiation of neural tissue in the ectoderm. He also included chemical induction by estrogens and steroids as other evocative signals. An important aspect of any signal of evocation, as presented by Waddington, is that the signal is specific to the differentiation of a certain tissue type.

Developmental biology took shape between 1880 and the 1920s Basic concepts like the developmental role of chromosomes and the germ plasm (today's genome), self differentiation, embryonic regulation and induction, gradients and organizers hail from that period; indeed, the discipline was defined as a whole by the programmatic writings of Wilhelm Roux as early as 1889. The present essays cover the period up to the Nobel prize-winning work of Hans Spemann and Hilde Mangold. They were originally published in Roux's Archives of Developmental Biology, from Vol. 200 onward to the journal's centennial issues in 1995/96. The essays aim at introducing current adepts of developmental biology to observations and experiments that have lead their predecessors towards basic concepts still influential today.