 In the late 19th and early 20th century the topic of development returned with a vengeance in the controversy over vitalism (sometimes termed “organicism”). A general movement towards more mechanistic or materialistic interpretations of living systems was emerging at this time (e.g., Loeb 1912; cf. Allen 1975) and disagreements about explaining development loomed large (Maienschein 1991). However, the famous example of vitalism in Hans Driesch’s interpretation of development and the autonomy of the organism should be seen as an issue of epistemology as much as metaphysics (Maienschein 2000). Instead of materialism versus vitalism (i.e., ontological reduction questions), the explanatory conflict involved the nature of differentiation in early ontogeny and to what degree it is prespecified. The theme of order and organization in living systems pervades many writings about methodological, epistemological, and ontological types of reductionism at this time (emphasizing both relations between physics and biology and between parts and wholes). Examples include Joseph Needham’s Order and Life (1936), Kurt Goldstein’s The Organism (1934/1963), E.S. Russell’s The Interpretation of Development and Heredity (1930), D’Arcy Thompson’s On Growth and Form (1917), Ludwig von Bertalanffy’s Modern Theories of Development (1933), and J.H. Woodger’s Biological Principles (1929). Philosophers of science who have had less influence on contemporary Anglo-American philosophy were keenly aware of these discussions. For example,  Ernst Cassirer  (1950, Part II) explored reductionist themes related to causal explanations of development, including the debates about mechanism and vitalism surrounding Driesch, as well as the relations between physical science and biology. These topics also appeared in the pages of Philosophy of Science (e.g., Lillie 1934, 1942, 1948, Singer 1934, 1946), although not necessarily utilizing the specific terminology of reduction (Byron 2007).