Wilhelm Roux

1850-1924

German Biologist and Embryologist

Wilhelm Roux, the founder of experimental embryology, was primarily interested in the factors that governed the development of the embryo. Convinced that descriptive and comparative studies of embryonic development were inadequate, Roux demanded a new approach and saw himself as the founder of a new discipline, which he called developmental mechanics. To promote the advancement of this nascent field, he established a new journal called Archive for Developmental Mechanics of Organisms in 1894.

Roux, the son of a fencing master, was born in Jena. His life's work was profoundly influenced by two eminent teaches—Ernst Haeckel (1834-1919) at the University of Jena and Alexander Wilhelm Goette at Strassburg. Roux became a professor at Innsbruck, but soon moved to the University of Halle where he remained from 1895 to 1921. Throughout his life he remained interested in the great problems he took up as a student of Haeckel and Goette—phylogeny and the struggle for existence.

Roux believed that zoologists had focused too much attention on purely descriptive studies of the egg and embryo. He urged his contemporaries to begin experimental studies of the factors that allowed the egg to develop into an embryo. According to Roux, experimental embryology would proceed by breaking down complex developmental processes into simpler and simpler functional processes. Ultimately, these processes could be analyzed in physicochemical terms. The influence of Charles Darwin (1809-1882) and Haeckel is obvious in Roux's 1881 paper "The Struggle of the Parts in the Organism: A Contribution to the Completion of a Mechanical Theory of Teleology."

Roux argued that embryologists must adopt experimental methods that would allow them to analyze the immediate causes of development and abandon useless philosophical debates about preformation and epigenesis. Roux attempted to address the key question of embryology by asking whether development occurred by means of "selfdifferentiation" or "correlative dependent differentiation." In part, Roux did this to avoid the old debates about preformation and epigenesis. Self-differentiation was defined as the capacity of the egg or parts of the embryo to undergo further differentiation independent of outside factors or of other parts of the embryo. Correlative dependent differentiation was defined as differentiation that was dependent on external stimuli or on other parts of the embryo. According to Roux, his definitions were valuable because they laid the framework for experimental testing. If each part of the embryo developed independently, like a mosaic, then the experiment demonstrated that the mechanism of development was self-differentiation. If interactions between groups of cells were necessary to development, then the mechanism was correlative dependent differentiation.

For theoretical reasons, Roux assumed that self-differentiation served as the mechanism of development. It seemed most likely that the fertilized egg was similar to a very complex machine. During development, parts of the machinery would be divided up and distributed the appropriate daughter cells. The mosaic model, therefore, predicted that external conditions should not affect the development of the embryo. Various experiments demonstrated to Roux's satisfaction that the development of embryos could be harmed by extreme changes in their environmental conditions, but that minor changes had little effect. Further experiments addressed the question of whether forces within the egg or embryo could change the pattern of development. First, Roux attempted to determine whether separate parts of the embryo could develop independently. As an experimental test, Roux destroyed one of the cells of a frog embryo at the two-cell stage. He pricked one of the cells with a hot needle and found that the other cell developed into a half-embryo. Roux concluded that his original prediction had been correct. According to his experimental demonstration, each cell develops independent of its neighbors. Under normal conditions, development was the result of the separate differentiation of each part. When other researchers performed similar experiments using embryos of different species, the results were quite different. Hans Adolf Eduard Driesch (1867-1941), another pioneer of experimental embryology, provided compelling evidence against Roux's model of mosaic development.

LOIS N. MAGNER