 Morphological-descriptive natural history is, as Johannsen (1911) desired, downplayed in the pursuit of experimentally generated and repeatable outcomes, yet his writing did not acknowledge that the same pursuit characterized a well-established field of zoological research, “developmental mechanics” (Entwicklungsmechanik). This experimental field had a morphological focus on how cells become arranged into tissues, organs, and the organism’s overall form, and how such organization is regenerated after disturbance or through the formation of germ cells (see entry on  developmental biology).  Important contemporaries of Johannsen grappled with the tensions between Mendelism and development (Deichmann 2014), but he merely evoked development in broad strokes—as the genotypes reacting or “interfering with the totality of all incident factors” (1911: 133)—and left the mechanics or dynamics as a secondary concern. For the new genotype-conception of heredity, stability of the genotype across generations was the primary fact. In putting mechanics to the side, the descriptive side of studies of heredity that Johannsen decried can be seen persisting, to some degree, in his original definitions of phenotype and genotype as classes of organisms. 