is developed at a single point, the pineal gland, which is distinguished by its central, protected position, above all, by the fact that it is the only cerebral organ that is not double. This gland, together with the animal spirits passing to and from it, mediates between mind and body; and as the point of union for the twofold impressions from the (right and left) eyes and ears, without which objects would be perceived double instead of single, is the seat of the soul. Here the soul exercises a direct influence on the body and is directly affected by it; here it dwells, and at will produces a slight, peculiar movement of the gland, through this a change in the course of the animal spirits (for it is not capable of generating motion, but only of changing its direction), and, finally, movements of the members; just as, on the other hand, it remarks the slightest change in the course of the _spiritus_ through a corresponding movement of the gland, whose motions vary according to the sensuous properties of the object to be perceived, and responds by sensations. Although Descartes thus limits the direct interaction of soul and body to a small part of the organism, he makes an exception in the case of _memoria_, which appears to him to be more of a physical than a psychical function, and which he conjectures to be diffused through the whole brain. In spite of the comprehensive meaning which Descartes gives to the notion _cogitatio_, it is yet too narrow to leave room for an _anima vegetativa_ and an _anima sensitiva_. Whoever makes mind and soul equivalent, holds that their essence consists in conscious activity alone, and interprets sensation as a mode of thought, cannot escape the paradox of denying to animals the possession of a soul. Descartes does not shrink from such a conclusion. Animals are mere machines; they are bodies animated, but soulless; they lack conscious perception and appetition, though not the appearance of them. When a clock strikes seven it knows nothing of the fact; it does not regret that it is so late nor long soon to be able to strike eight; it wills nothing, feels nothing, perceives nothing. The lot of the brute is the same. It sees and hears nothing, it does not hunger or thirst, it does not rejoice or fear, if by these anything more than mere corporeal phenomena is to be meant; of all these it possesses merely the unconscious material basis; it moves and motion goes on in it--that is all. The psychology of Descartes, which has had important results,[1] divides _cogitationes_ into two classes: _actiones_ and _passiones_. Action denotes everything which takes its origin in, and is in the power of, the soul; passion, everything which the soul receives from without, in which it can make no change, which is impressed upon it. The further development of this distinction is marred by the crossing of the most diverse lines of thought, resulting in obscurities and contradictions. Descartes's simple, naïve