Again, if we consider the difference of the temperament, disposition, and manners; in a word, the organization of these two animals, and, above all, the impossibility of mixing the breed, so as to make one common species, or even an intermediate species, which may be renewed; it appears a better founded opinion to think that these animals are of a species equally ancient, and originally as essentially different as they are at present. The ass differs materially from the horse in the smallness of the size, largeness of the head, length of the ears, hardness of the skin, nakedness of the tail, the form of the rump, and the dimensions of the neighbouring parts, the voice, the appetite, manner of drinking, &c. Can we then suppose that the horse and the ass came originally from the same stock? are they of the same family, or not? and have they not always been different animals? This question of which philosophers will find the generality, difficulty, and consequences, and which we treat of in this article, because it here offers itself for the first time, appertains to the production of beings nearest to each other, and renders it necessary that we should consider nature under a new point of view. If from the immense variety of animated beings which people the universe, we chuse an animal, or even the body of man, to serve as a foundation to our knowledge, and to find out, by way of comparison, the other organized beings, we shall find that each possesses an independent existence, and that all vary, by different gradations, almost to infinity; there exists also, at the same time, a primitive and general design, which we may trace very far, and of which the gradations are much slower than those of the form, and other apparent relations, for, without mentioning the organs of digestion, circulation and generation, which appertain to all animals, and without which they could neither subsist nor reproduce, there is even in the parts which contribute most to the variety of the exterior form a prodigious resemblance, which necessarily calls to our minds an original design, upon which all seem to have been projected and executed. The body of a horse, for example, which, by a single glance of the eye, appears so different from the body of a man, when it is compared part by part, instead of surprising by the difference, only astonishes by the singular and almost perfect resemblance, in fact, take the skeleton of a man, bend downwards the bones of the pelvis, shorten those of the thighs, legs, and arms, lengthen those of the feet and hands, join the phalanges, lengthen the jaws, by shortening the frontal bone, and extend the spine of the back, this skeleton would cease to represent the remains of a human figure, and would be the skeleton of a horse; for it is easy to suppose, that in lengthening the spine of the back and jaws we augment, at the same time, the number of the vertebræ, ribs, and teeth; and it is only by