The Phototropic Excitation of Limax

The photic orientation of Limax creeping geotropically upon a vertical plate is such that the phototropic vector determining the angular deflection beta from the vertical path is proportional to log I. This is proved by the fact that with horizontal illumination tan beta is directly proportional to log I; with non-horizontal light rays from a small source the ratio See PDF for Equation is directly proportional to log I (where A = the angle between light rays and the path of orientation), the vector diagram of the field of excitation being in this case not a right-angled triangle.