So, by its very nature, it is barren to investigation, as there is no means by which investigation may be put to the proof. Driesch reported agreeing with Roux and intending to confirm Roux's results. And cell differentiations that make up complex organisms are predetermined. From that point on, the process is internal and driven by internal causes.
This was the problem for materialists. The early egg was not formed. Each determinant consisted of a number of material particles called biophores, inherited from both parents. Both suggested that development is a good deal more flexible, plastic, and interactive than preformationist interpretations allow.
Both relied on assumptions, and only more evidence could help move the discussion forward. Translated in Willier and Oppenheimer, pp.
Traditional Catholicism agreed. After repeated attempts in which I more than once imagined myself successful, but all of which broke down when further tested by facts. Roux proposed an experiment, a simple and elegant experiment on the face of it. And this is epigenetic.
And histologists and embryologists, especially in Germany and the United States, used rapidly improving microscopic techniques to observe far more than had been possible before.