when we know both the efficient cause, also called by Aristotle ἡ αιτια εξ αναγκης, and the final cause, ἡ χαριν του βελτιονος, at once and yet separately, as their concurrence, their wonderful working together, then surprises us, and on account of it the best appears as the absolutely necessary, and the necessary again as if it were merely the best and not necessary; for then arises in us the dim perception that both causes, however different may be their origin, are yet connected in the root, in the nature of the thing in itself. But such a twofold knowledge is seldom attainable; in organised nature, because the efficient cause is seldom known to us; in unorganised nature, because the final cause remains problematical. However, I will illustrate this by a couple of examples as good as I find within the range of my physiological knowledge, for which physiologists may be able to substitute clearer and more striking ones. The louse of the negro is black. Final cause: its own safety. Efficient cause: because its nourishment is the black rete Malpighi of the negro. The multifarious, brilliant, and gay colouring of the plumage of tropical birds is explained, although only very generally, from the strong effect of the light in the tropics, as its efficient cause. As the final cause I would assign that those brilliant feathers are the gorgeous uniform in which the individuals of the innumerable species there, often belonging to the same genus, may recognise each other; so that each male may find his female. The same holds good of butterflies of different zones and latitudes. It has been observed that consumptive women, in the last stage of their illness, readily become pregnant, that the disease stops during pregnancy, but after delivery appears again worse than before, and now generally results in death: similarly that consumptive men generally beget another child in the last days of their life. The final cause here is that nature, always so anxiously concerned for the maintenance of the species, seeks to replace by a new individual the approaching loss of one in the prime of life; the efficient cause, on the other hand, is the unusually excited state of the nervous system which occurs in the last period of consumption. From the same final cause is to be explained the analogous phenomenon that (according to Oken, Die Zeugung, p. 65) flies poisoned with arsenic still couple, and die in the act of copulation. The final cause of the pubes in both sexes, and of the Mons Veneris in the female, is that even in the case of very thin subjects the Ossa pubis shall not be felt, which might excite antipathy; the efficient cause, on the other hand, is to be sought in the fact that wherever the mucous membrane passes over to the outer skin, hair grows in the vicinity; and, secondly, also that the head and the genitals are to a certain extent opposite poles of each other, and therefore have various relations and analogies between them, among which is that of being covered with hair. The same efficient cause holds good also of the beard of the man; the final cause of it, I suppose, lies in the fact that the pathogonomic signs, thus the rapid alterations of the countenance betraying every movement of the mind, are principally visible in the mouth and its vicinity; therefore, in order to conceal these from the prying eye of the adversary, as something dangerous in bargaining, or in sudden emergencies, nature gave man the beard (which shows that homo homini lupus). The woman, on the other hand, could dispense with this; for with her dissimulation and command of countenance are inborn. As I have said, there must be far more apt examples to be found to show how the completely blind working of nature unites in the result with the apparently intentional, or, as Kant calls it, the mechanism of nature with its technic; which points to the fact that both have their common origin beyond their difference in the will as the thing in itself. Much would be achieved for the elucidation of this point of view, if, for example, we could find the efficient cause which carries the driftwood to the treeless polar lands, or that which has concentrated the dry land of our planet principally in the northern half of it; while it is to be regarded as the final cause of this that the winter of that half, because it occurs in the perihelion which accelerates the course of the earth, is eight days shorter, and hereby is also milder. Yet in considering unorganised nature the final cause is always ambiguous, and, especially when the efficient cause is found, leaves us in doubt whether it is not a merely subjective view, an aspect conditioned by our point of view. In this respect, however, it may be compared to many works of art; for example, to coarse mosaics, theatre decorations, and to the god Apennine at Pratolino, near Florence, composed of large masses of rock, all of which only produce their effect at a distance, and vanish when we come near, because instead of them the efficient cause of their appearance now becomes visible: but the forms are yet actually existent, and are no mere imagination. Analogous to this, then, are the final causes in unorganised nature, if the efficient causes appear. Indeed, those who take a wide view of things would perhaps allow it to pass if I added that something similar is the case with omens.
For the rest, if any one desires to misuse the external design, which, as has been said, always remains ambiguous for physico-theological demonstrations, which is done even at the present day, though it is to be hoped only by Englishmen, there are in this class enough examples in contrarium, thus ateleological instances, to derange his conception. One of the strongest is presented by the unsuitableness of sea-water for drinking, in consequence of which man is never more exposed to the danger of dying of thirst than in the midst of the greatest mass of water on his planet. “Why, then, does the sea need to be salt?” let us ask our Englishman.
That in unorganised nature the final causes entirely withdraw into the background, so that an explanation from them alone is here no longer valid, but the efficient causes are rather indispensably required, depends upon the fact that the will which objectifies itself here also no longer appears in individuals which constitute a whole for themselves, but in forces of nature and their action, whereby end and means are too far separated for their relation to be clear and for us to recognise a manifestation of will in it. This already occurs in organised nature, in a certain degree, when the design is an external one, i. e., the end lies in one individual and the means in another. Yet even here it remains unquestionable so long as the two belong to the same species, indeed it then becomes the more striking. Here we have first to count the reciprocally adapted organisation of the genitals of the two sexes, and then also many circumstances that assist the propagation of the species, for example, in the case of the Lampyris noctiluca (the glowworm) the circumstance that only the male, which does not shine, has wings to enable it to seek out the female; the wingless female, on the other hand, since it only comes out in the evening, possesses the phosphorescent light, so that the male may be able to find it. Yet in the case of the Lampyris Italica both sexes shine, which is an instance of the natural luxury of the South. But a striking, because quite special, example of the kind of design we are speaking of is afforded by the discovery made by Geoffroy St. Hilaire, in his last years, of the more exact nature of the sucking apparatus of the cetacea. Since all sucking requires the action of respiration, it can only take place in the respirable medium itself, and not under water, where, however, the sucking young of the whale hangs on to the teats of the mother; now to meet this the whole mammary apparatus of the cetacea is so modified that it has become an injecting organ, and placed in the mouth of the young injects the milk into it without it requiring to suck. When, on the contrary, the individual that affords essential help to another belongs to an entirely different species, and even to another kingdom of nature, we will doubt this external design just as in unorganised nature; unless it is evident that the maintenance of the species depends upon it. But this is the case with many plants whose fructification only takes place by means of insects, which either bear the pollen to the stigma or bend the stamina to the pistil. The common barberry, many kinds of iris, and Aristolochia Clematitis cannot fructify themselves at all without the help of insects (Chr. Cour. Sprengel, Entdecktes Geheimniss, &c., 1793; Wildenow, Grundriss der Kräuterkunde, 353). Very many diœcia, monœcia, and polygamia are in the same position. The reciprocal support which the plant and the insect worlds receive from each other will be found admirably described in Burdach's large Physiology, vol. i. § 263. He very beautifully adds: “This is no mechanical assistance, no make-shift, as if nature had made the plants yesterday, and had committed an error which she tries to correct to-day through the insect; it is rather a deep-lying sympathy between the plant and the animal worlds. It ought to reveal the identity of the two. Both, children of one mother, ought to subsist with each other and through each other.” And further on: “But the organised world stands in such a sympathy with the unorganised world also,” &c. A proof of this consensus naturæ is also afforded by the observation communicated