 It might seem that Roux would have had to acknowledge the superiority of Driesch’s approach, since Driesch had actually separated the cells. But no. Instead Roux countered with an additional hypothesis. The nucleus retains the capacity to adapt, especially in simpler organisms. They need the capacity to regenerate when injured, and therefore the mosaic determination simply has not occurred yet. Each cell retains a “reserve idioplasm”, he argued, and this provides the necessary backup determination needed to form a whole organism (see Churchill 1966, 1973).