Foundations of animal hydraulics: geodesic fibres control the shape of soft bodied animals.

In 1958 R. B. Clark and J. B. Cowey published a paper in which they presented a simple geometric model, based on the idea of a fibre-reinforced cylinder, to explain the mechanism underlying shape changes in ribbon worms and flatworms (Clark and Cowey, 1958). While their results may have been of interest to only a few biologists at that time, the essential idea of this paper, that a structure composed of inextensible fibres could accommodate large extensibility, has endured and its application has become widespread, first in numerous biomechanical case studies and, more recently, in modern biomimetics and mechanical engineering. The basic model that was developed is now entrenched as a design principle in biomechanics. The paper continues to be cited, and its summary concept (as seen in Fig. 1) has been reproduced in numerous texts or reviews over the past several decades (e.g. Alexander, 1968; Alexander, 1979; Alexander, 1988; Chapman, 1975; Clark, 1964; Gray, 1968; Vogel, 1988; Vogel, 2003; Wainwright et al., 1976; Wainwright, 1988).