But all this reflects light on the instincts and mechanical tendencies of the brutes. They also are, without doubt, involved in a kind of illusion, which deceives them with the prospect of their own pleasure, while they work so laboriously and with so much self‐denial for the species, the bird builds its nest, the insect seeks the only suitable place for its eggs, or even hunts for prey which, unsuited for its own enjoyment, must be laid beside the eggs as food for the future larvæ, the bees, the wasps, the ants apply themselves to their skilful dwellings and highly complicated economy. They are all guided with certainty by an illusion, which conceals the service of the species under the mask of an egotistical end. This is probably the only way to comprehend the inner or subjective process that lies at the foundation of the manifestations of instinct. Outwardly, however, or objectively, we find in those creatures which are to a large extent governed by instinct, especially in insects, a preponderance of the ganglion system, _i.e._, the _subjective_ nervous system, over the objective or cerebral system; from which we must conclude that they are moved, not so much by objective, proper apprehension as by subjective ideas exciting desire, which arise from the influence of the ganglion system upon the brain, and accordingly by a kind of illusion; and this will be the _physiological_ process in the case of all instinct. For the sake of illustration I will mention as another example of instinct in the human species, although a weak one, the capricious appetite of women who are pregnant. It seems to arise from the fact that the nourishment of the embryo sometimes requires a special or definite modification of the blood which flows to it, upon which the food which produces such a modification at once presents itself to the pregnant woman as an object of ardent longing, thus here also an illusion arises. Accordingly woman has one instinct more than man; and the ganglion system is also much more developed in the woman. That man has fewer instincts than the brutes and that even these few can be easily led astray, may be explained from the great preponderance of the brain in his case. The sense of beauty which instinctively guides the selection for the satisfaction of sexual passion is led astray when it degenerates into the tendency to pederasty; analogous to the fact that the blue‐bottle (_Musca vomitoria_), instead of depositing its eggs, according to instinct, in putrefying flesh, lays them in the blossom of the _Arum dracunculus_, deceived by the cadaverous smell of this plant.