By formulating in 1875 his major theoretical achievement, the “principle of succession of functions”, Dohrn was consciously entering the controversy between Darwin and Mivart. Dohrn’s principle enjoyed the approval of Darwin, but not his enthusiasm. The paper examines the evolution of Darwin’s original idea of ‘conversion of functions’ in the 6th edition of his Origin, following Mivart’s criticism, and contrasts the overtly functionalist interpretation entailed in Dohrn’s formulation with Darwin’s increasing structuralist hesitations as to the origin of evolutionary novelty. A (...) more accurate analysis of Dohrn’s principle, however, appears to corroborate the thesis that Dohrn was equally receptive to Darwin’s argument as to Mivart’s criticism. (shrink)