THE ANIMAL AXIS

Simple physical principles of engineering design of axial support in flexible cylindrical bodies will be used to frame a notion of possible sequences of evolutionary events leading from polyps and worms to arthropods, echinoderms, and vertebrates. Similarities in design of axes of bodies and appendages will be indicated. How pliant and rigid materials interact harmoniously in axial locomotion is a matter of structural design principles that differ at different size levels. Backbone-like structures in invertebrates will be interpreted in terms of their accompanying muscle structures. How these structures are made from fibrous materials will be a central issue.