We must here make an important remark. We have inferred by all which precedes this, that the vertebrata of the present day and the fossil vertebrata all descend from the same individual-element prototype, whose existence we have admitted. In one word, we think that all the vertebrata, both present and past, have the same genealogy, and are all relations. That may doubtless be the case; but nothing will make us admit that there once existed on our planet conditions fit for the birth of this individual-element prototype, and that these circumstances have never since been represented; so that the most simple vertebrata of our time may very well descend from a less ancient spontaneous genesis than the mammalia and man himself. Nothing hinders such a supposition. It does not cost us any more to admit that one day or other a simple organic element is formed, endowed with a life of its own, and, even more, with a latent life, which it can, by means of time and circumstances, diffuse around it; it does not cost us more to admit this than to admit that similar elements have arisen at different periods of time. This last supposition may even be regarded as so much more probable, that we must renounce entirely, in order to explain specific transformations, the influence of the geological revolutions of which Étienne Geoffroy took so much account. We have seen higher up that these were far from being proved; we can add, in support of our assertion, a fact which we think has not been sufficiently remarked. If these revolutions ever existed, we have a strong proof that they have only very slightly altered the conditions of life on the surface of the globe, at least since the ancient periods during which the first alluvium was deposited; if we dredge some yards deep in the ocean, the drag brings up terebratulæ and encrini; that is to say, animals identical with those which we find in the most ancient alluvia. Is it not remarkable that the lowest placed fossil in the stratigraphic ladder of the beds of the terrestrial surface, the most ancient fossil which we know, is precisely this same terebratula, which still lives in our seas? What must we hence conclude? That there once existed on the globe, at least to a certain extent, conditions of aquatic life sensibly identical with those which exist at the present day. Whether all the species of vertebrata descend from one original spontaneous beginning, or from many successive ones, signifies very little, since, in the second case, the primordial individual-elements which have thus appeared at various times, would always show a great analogy to one another.