Instinct everywhere works as with the conception of an end, and yet it is entirely without one.  Nature implants instinct where the acting individual is not capable of understanding the end, or would be unwilling to pursue it.  Consequently, as a rule, it is only given prominently to animals, and in particular to those of the lowest order, which have the least intelligence.  But it is only in such a case as the one we are at present considering that it is also given to man, who naturally is capable of understanding the end, but would not pursue it with the necessary zeal—­that is to say, he would not pursue it at the cost of his individual welfare.  So that here, as in all cases of instinct, truth takes the form of illusion in order to influence the will....

All this, however, on its part throws light upon the instinct of animals.  They, too, are undoubtedly carried away by a kind of illusion, which represents that they are working for their own pleasure, while it is for the species that they are working with such industry and self-denial.  The bird builds its nest; the insect seeks a suitable place wherein to lay its eggs, or even hunts for prey, which it dislikes itself, but which must be placed beside the eggs as food for the future larvae; the bee, the wasp, and the ant apply themselves to their skilful building and extremely complex economy.  All of them are undoubtedly controlled by an illusion which conceals the service of the species under the mask of an egotistical purpose.

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.