Like many other animals, the beetle Chlorophanus viridis responds to relative motions of its optical surroundings with optokinetic reactions. These follow not only from the movement of figures distinguishable against their backgrounds, but also from the movement of randomly constructed patterns of shades from white through black. In the latter case the evaluation by the beetle’s central nervous system is made in accordance with the principle of autocorrelation of a time function. The relation between stimuli of the movement and the strength of the reaction, as calculated from this principle, is plotted in Fig. 9.