ABSTRACT
It is now many years since Kiaer (1924) demonstrated the existence of the hypocercal tail in the Anaspida, and subsequently it has been found to be universally present in the Heterostraci (Stetson, 1931; Kiaer, 1932; White, 1935). No experimental attempt seems to have been made, however, to investigate its functional significance (see Harris, 1936), although it has been realized for a considerable time that the hypocercal tail would tend to depress the hinder end of the body during swimming (Ahlborn, 1896; Grove & Newell, 1936). An attempt is made in this paper to determine, by experimental methods, this functional significance.
It is to be noted that the centre of gravity of the model is really the centre of buoyancy of the actual Pteraspis, since, while the model was uniform in density, Pteraspis was not necessarily so. The pitching moments in the graph (Fig. 4) are therefore calculated about a horizontal axis through the centre of buoyancy of the animal itself.
