Only those changes which have no other ground than a motive, _i.e._, an idea, have hitherto been regarded as manifestations of will. Therefore in nature a will has only been attributed to man, or at the most to animals; for knowledge, the idea, is of course, as I have said elsewhere, the true and exclusive characteristic of animal life. But that the will is also active where no knowledge guides it, we see at once in the instinct and the mechanical skill of animals.(31) That they have ideas and knowledge is here not to the point, for the end towards which they strive as definitely as if it were a known motive, is yet entirely unknown to them. Therefore in such cases their action takes place without motive, is not guided by the idea, and shows us first and most distinctly how the will may be active entirely without knowledge. The bird of a year old has no idea of the eggs for which it builds a nest; the young spider has no idea of the prey for which it spins a web; nor has the ant-lion any idea of the ants for which he digs a trench for the first time. The larva of the stag-beetle makes the hole in the wood, in which it is to await its metamorphosis, twice as big if it is going to be a male beetle as if it is going to be a female, so that if it is a male there may be room for the horns, of which, however, it has no idea. In such actions of these creatures the will is clearly operative as in their other actions, but it is in blind activity, which is indeed accompanied by knowledge but not guided by it. If now we have once gained insight into the fact, that idea as motive is not a necessary and essential condition of the activity of the will, we shall more easily recognise the activity of will where it is less apparent. For example, we shall see that the house of the snail is no more made by a will which is foreign to the snail itself, than the house which we build is produced through another will than our own; but we shall recognise in both houses the work of a will which objectifies itself in both the phenomena—a will which works in us according to motives, but in the snail still blindly as formative impulse directed outwards. In us also the same will is in many ways only blindly active: in all the functions of our body which are not guided by knowledge, in all its vital and vegetative processes, digestion, circulation, secretion, growth, reproduction. Not only the actions of the body, but the whole body itself is, as we have shown above, phenomenon of the will, objectified will, concrete will. All that goes on in it must therefore proceed through will, although here this will is not guided by knowledge, but acts blindly according to causes, which in this case are called _stimuli_.