 Roux proposed an experiment, a simple and elegant experiment on the face of it. He proposed to take a developing frog egg, after the first cell division, and to separate the two cells. Finding it impossible to separate the two cells, however, he simply killed one by inserting a hot needle. That cell just hung there like a blob of material and no longer differentiated. The other half organism, or single cell proceeded to develop, in Roux’s interpretation, as it normally would have developed (Roux 1888). The half became a half, just as it should if it were already preformed or predetermined as to its fate in the organism. Roux had, it seemed, confirmed the mosaic hypothesis.