Dr. Lehmann in abandoning the Cartesian theory, says: "The bodily and psychical states are as a matter of experience given as two series intimately connected the one with the other. Their connection can be explained in two different ways: Either the phenomena of the one are effects of the other, or both series are effects of one and the same unknown cause." Dr. Lehmann considers either solution as a priori equally acceptable, yet he favors the latter, which might briefly be called (although the author does not use the expression) "the agnostic solution." Dr. Lehmann characterises it as "_die Spinozistische Annahme_" and calls it Psycho-physical Materialism. One of his colleagues, Professor Kroman has proposed in his "Logik and Psychologie" a theory that is called by the same name. Yet Kroman's psycho-physical materialism, Dr. Lehmann declares, is widely different from his own; the former being "a mutual causal relation between the Physical and Psychical within the limits of the Atom," which, says Dr. Lehmann, "would make the explanation of complex psychical phenomena impossible." The psycho-physical materialism of Dr. Lehmann, our author maintains, agrees in all essential points with the views of Professor Münsterberg (Freiburg in Baden).[65] [65] The observations of Professor Münsterberg were reviewed in _The Open Court_ No. 134. The laboratory work done by Professor Münsterberg was published after Dr. Lehmann had finished his lectures. A certain similarity between Dr. Lehmann's views and those of the Freiburg Professor cannot be denied, yet it is more than doubtful whether Professor Münsterberg would recognise this similarity in the same measure as Dr. Lehmann does. The fact is that Dr. Lehmann has progressed in the direction which the German school of Wundt has taken; yet he has not as yet reached the same clearness; he is still entangled in Cartesian ideas, as is shown by his way of proposing problems: for instance in his treatment of the problem of will, which he justly calls "_der eigentliche Probirstein der Hypothese_," and of Attention, "the most enigmatic of all states of the soul" (_der räthselhafteste aller Seelenzustände_). In these and in other considerations Dr. Lehmann shows that he is still far from the positive standpoint by which Münsterberg's investigations are distinguished. It is very strange that in speaking of Attention M. Ribot's name has not even been alluded to. If the author had shown a familiarity with some of the monographs of this great French psychologist, he might have saved himself much work. κρς. DER HELIOTROPISMUS DER THIERE UND SEINE UEBEREINSTIMMUNG MIT DEM HELIOTROPISMUS DER PFLANZEN. By _Dr. J. Loeb_. Würzburg: Verlag von George Hertz.