 Divergent approaches to measuring time. Instead of time “in the mechanism,” time is measured with external standardized stages (see below,  Section 5.2).  Stages facilitate the study of different kinds of developmental mechanisms, with different characteristic rates and durations for their stages, within a common framework for a model organism (e.g., Drosophila), while also permitting conserved molecular mechanisms to be studied in different species because the corresponding mechanism description is not anchored to the temporal sequence of the model organism.