Abstract
The aim of this article is to examine the scientific and public functions of two- andthree-dimensional models in the context of three episodes from nineteenth-century biology. Iargue that these models incorporate both data and theory by presenting theoretical assumptions inthe light of concrete data or organizing data through theoretical assumptions. Despite their diverseroles in scientific practice, they all can be characterized as mediators between data and theory.Furthermore, I argue that these different mediating functions often reflect their different audiencesthat included specialized scientists, students, and the general public. In this sense, models innineteenth-century biology can be understood as mediators between theory, data, and their diverseaudiences