It is generally assumed that biology an historical science, species morphology being the result of random variation and natural selection of functionally adapted forms. These forms are therefore not intelligible in terms of generative principles. Structuralism assumes that there is a logical order to the biological realm and that organisms are generated according to rational dynamic principles. The life cycle of a particular species is used to illustrate what these principles might be in terms of a mathematical model of morphogenesis. The analysis, involving computer simulation, suggests that characteristic morphological sequences during development may be understood as the expression of dynamic attractors in the space of morphogenetic field solutions of moving boundary problems. The broader implications of this view in relation to a theory of organisms as dynamic forms and an altered perspective on the theory of evolution are considered.