This being granted, let us see how we can represent the history of organic development upon the earth in a few words, without hiding from ourselves the immense obscurity which covers all origins. We are here expressing merely a hypothesis. It will suffice us to see if this hypothesis will agree in a satisfactory manner with the facts noticed at the present day, on the surface and in the interior of the globe. At the origin of the vertebrate world, since we are only examining this, it seems rational to admit a primordial commencement, which nothing prevents us from considering as a new and special combination of organic matter, derived from the invertebrate world, which we may believe to have formerly existed. In the heart of this _embryo_ will have appeared, by spontaneous generation, the first organism connected with the vertebrate type. This was, doubtless, a simple anatomical element, like that which histologists see every day formed in certain granular liquids. We do not imagine that the origin of life can be otherwise represented; for to admit, as Isidore Geoffroy has done in certain passages of his works, that the will of a God peopled the earth suddenly with perfect beings, fit for producing other beings like themselves, would be to admit a miracle, and science teaches us at the present day what to think of all divine interventions, either past or present.[313] We defy anyone to get out of this alternative,--either that there was an instantaneous and miraculous creation of a certain number of perfect animals;[314] or that there was a successive evolution, which is Lamarck’s idea, modified by the sense of the new knowledge which we have at the present day, arising, on the one hand, from geology, and on the other, from philosophical anatomy. Let us return to this primordial anatomical element which we may call _individual-element_. It virtually represents a vertebrate animal just as the ovum detached from the ovary of the female represents a man, who is only waiting for favourable circumstances in order to develope himself. This individual-element, according to our hypothesis, is at first simply reproduced; then, after some considerable time, its descendants, will, little by little, in their own sphere of activity, give birth to other elements in juxtaposition to themselves, in this manner perfecting it and identifying it more and more with the vertebrate type which it offers for our consideration. After some considerable time vertebrates of as simple an organism as mixinæ and lampreys will have thus appeared. Then, again, after another considerable lapse of time--millions of centuries, rather than thousands--these animals with elementary vertebra will have successively produced, by transformation, all the vertebrata which stock the globe at the present day.