Todd Wood has an excellent introduction to the form-vs-function debate, focusing on the ideas of Richard Owen. From his post:
Owen's eclectic embracing of functionalism and structuralism were answers to different questions: 1. Why are organisms so well-adapted? and 2. Why are there homologies?....Organismal similarity was to Owen based a [sic] natural law of the archetype. The differences Owen attributed to functional requirements. (Thus he saw two answers for two different questions.)