The symbolic representation of the physical structure of living organisms needs an ontologically well-founded and logically sound approach so that formal reasoning can adequately be supported. We describe a set of canonical relations and attributes necessary for the description of biological structures. Based on these epistemological primitives, we sketch how a broad range of organisms can be represented by cascading theories which are ordered by various dimensions, such as granularity, development, species and canonicity. We thus aim at a rational reconstruction and nonredundant representation of biological structure notions.