Because, then, matter is the visibility of the will, and every force in itself is will, no force can appear without a material substratum, and conversely no body can be without forces dwelling in it which constitute its quality. Therefore a body is the union of matter and form which is called substance (Stoff). Force and substance are inseparable because at bottom they are one; for, as Kant has shown, matter itself is given us only as the union of two forces, the force of expansion and that of attraction. Thus there is no opposition between force and substance, rather they are precisely one. Led by the course of our consideration to this standpoint, and having attained to this metaphysical view of matter, we will confess without reluctance that the temporal _origin_ of forms, shapes, or species cannot reasonably be sought elsewhere than in matter. Some time or other they must have come forth from it, just because it is the mere _visibility of the will_ which constitutes the inner nature of all phenomena. In that the will manifests itself, _i.e._, presents itself _objectively_ to the intellect, matter, as its visibility, assumes _form_ by means of the functions of the intellect. Hence the Schoolmen said: “_Materia appetit formam_.” That such was the origin of all forms of life cannot be doubted: we cannot even conceive it otherwise. Whether, however, now, since the paths to the perpetuation of the forms stand open, and are secured and sustained by nature with boundless care and jealousy, _generatio œquivoca_ still takes place, can only be decided by experience; especially since the saying, _Natura nihil facit frustra_, might, with reference to the paths of regular propagation, be used as a valid argument against it. Yet in spite of the most recent objections to it, I hold that at very low grades _generatio œquivoca_ is very probable, and primarily indeed in the case of entozoa and epizoa, particularly such as appear in consequence of special cachexia of the animal organism. For the conditions of their life only appear exceptionally; consequently their species cannot propagate itself in the regular manner, and therefore has always to arise anew whenever opportunity offers. Therefore as soon as the conditions of life of epizoa have appeared in consequence of certain chronic diseases, or cachexia, and in accordance with them, _pediculus capitis_ or _pubis_ or _corporis_ appears entirely of itself, and without any egg; and this notwithstanding the complex structure of these insects, for the putrefaction of a living animal body affords material for higher productions than that of hay in water, which only produces infusoria. Or is it thought more likely that the eggs of the epizoa are constantly floating about in the air in expectation? (Fearful to think of!) Let us rather remember the disease of phthiriasis, which occurs even now. An analogous case takes place when through special circumstances the conditions of life appear of a species