This is Volume V of twenty-one in the Cognitive Psychology series. First published in 1930, this study looks at the most important aspect of Eidetics-the theory of eidetic or perceptual images (Anschauungsbilder)-as being its development that represents the first systematic application of typological methods of investigation. The author suggests that if these methods are consistently applied, they will, it seems, throw new light on many departments of psychology.