This is probably the only way in which to make the inner or subjective process, from which spring all manifestations of instinct, intelligible to us. The outer or objective process, however, shows in animals strongly controlled by instinct, as insects for instance, a preponderance of the ganglion--_i.e., subjective_ nervous system over the _objective_ or cerebral system. From which it may be concluded that they are controlled not so much by objective and proper apprehension as by subjective ideas, which excite desire and arise through the influence of the ganglionic system upon the brain; accordingly they are moved by a certain illusion.... The great preponderance of brain in man accounts for his having fewer instincts than the lower order of animals, and for even these few easily being led astray. For instance, the sense of beauty which instinctively guides a man in his selection of a mate is misguided when it degenerates into the proneness to pederasty. Similarly, the blue-bottle (_Musca vomitoria_), which instinctively ought to place its eggs in putrified flesh, lays them in the blossom of the _Arum dracunculus_, because it is misled by the decaying odour of this plant. That an absolutely generic instinct is the foundation of all love of sex may be confirmed by a closer analysis of the subject--an analysis which can hardly be avoided. In the first place, a man in love is by nature inclined to be inconstant, while a woman constant. A man's love perceptibly decreases after a certain period; almost every other woman charms him more than the one he already possesses; he longs for change: while a woman's love increases from the very moment it is returned. This is because nature aims at the preservation of the species, and consequently at as great an increase in it as possible.... This is why a man is always desiring other women, while a woman always clings to one man; for nature compels her intuitively and unconsciously to take care of the supporter and protector of the future offspring. For this reason conjugal fidelity is artificial with the man but natural to a woman. Hence a woman's infidelity, looked at objectively on account of the consequences, and subjectively on account of its unnaturalness, is much more unpardonable than a man's. In order to be quite clear and perfectly convinced that the delight we take in the other sex, however objective it may seem to be, is nevertheless merely instinct disguised, in other words, the sense of the species striving to preserve its type, it will be necessary to investigate more closely the considerations which influence us in this, and go into details, strange as it may seem for these details to figure in a philosophical work. These considerations may be classed in the following way:--