which he is much superior to nature. Natural forces act in virtue of blind and necessary laws, the result of which is constant. Now man has acquired the knowledge of these laws, he has made use of them to constrain and master the natural forces one after another, he now knows how to exaggerate some and to weaken others. In this manner he changes their resultants, and obtains products which nature herself could not realise. Give to the latter all the time and space that you will, she would never be able either to produce or preserve potassium or sodium in a metallic form; in spite of the physico-chemical forces, or rather by directing them, man has obtained and preserved these two metals, as he has obtained and preserved the Ægilops triticoïdes, which is destroyed by the inflexibility of natural forces as soon as it is exposed to their action.

VIII. The infertility, or, if you will, the restricted and rapidly limited fertility between species, and the impossibility of natural forces, when left to themselves, producing series of intermediary beings between two given specific types, is one of those general facts which we call a law. This fact has an importance in the organic world equal to that rightly attributed to attraction in the sidereal world. It is by virtue of the latter that the celestial bodies preserve their respective distances, and complete their orbits in the admirable order revealed by astronomy. The law of the sterility of species produces the same result, and maintains between species and between different groups in animals and plants all those relations, which, in the palæontological ages, as well as in our own, form the marvellous whole of the Organic Empire.

Imagine the suppression of the laws which govern attraction in the heavens, and what chaos would immediately be the result. Suppress upon earth the law of crossing, and the confusion would be immense. It is scarcely possible to say where it would stop. After a few generations the groups which we call genera, families, orders, and classes would most certainly have disappeared, and the branches also would rapidly have become affected. It is clear that only a few

centuries would elapse before the animal and vegetable kingdoms fell into the most complete disorder. Now order has existed in both kingdoms since the epoch when organised beings first peopled the solitudes of our globe, and it could only have been established and preserved by virtue of the impossibility of a fusion of species with each other through indifferently and indefinitely fertile crossings.

IX. There are some writers, very often entirely unacquainted with the natural sciences, who, labouring under the most varied prejudices, especially that of exaggerating the transmutation doctrines which I shall presently discuss, have denied the reality of species; they affirm that there are no serious barriers between the groups designated by this term, and have compared it in a more or less formal manner to the groups always somewhat arbitrarily called genera, tribes, families, orders, etc. Though only a brief recapitulation, the preceding facts would be sufficient to answer them. It is, however, necessary to mention the principal objections which are brought forward against such ideas, and to shew how they may be refuted.

1st. It is useless to take any notice of the good humoured or malicious banter, of the raillery and sarcasm too often made use of by some writers against those who admit the reality of species. It is evident that those who employ such weapons do not address themselves to men of science, but appeal directly to the passions. We cannot sufficiently express our regret at seeing men of undoubted merit resorting to such means.

2nd. At the present time, perhaps more than ever, those who believe in species are reproached with being orthodox: I could never myself understand why there should be this mixture of scientific discussions and dogmatic and antidegmatic polemics.

3rd. I shall, moreover, refuse to dispute with those who, rejecting on their own authority a whole century of work accomplished by the greatest naturalists, and by a number of men distinguished in botany and zoology, declare that it

is useless to try and discover what species and race are, and laugh at those who take the trouble to do so. I say the same to those who regard species and race as more or less arbitrary groups which may be compared to the genus, family and order. It will be enough to remark that they themselves incessantly employ the word species and race, and we must not be surprised if they take one thing for the other.

4th. After what we have said, discussion is useless with those naturalists who only base the distinction of species upon external characters. They forget all the experiments made from Buffon to the two Geoffroys, from Koelreuter to M. Naudin; they forget the innumerable observations made in our orchards, gardens and stables. To refuse to abandon morphological considerations, and to neglect the data of physiology and the lessons of filiation, is clearly going further back than Ray and Tournefort, and all discussion becomes impossible.

5th. Some of our opponents allow that things are now what we think them to be. "But," say they, "it is possible that at some other time it was different." What answer can be given to those who base their arguments upon possibilities? Is modern science composed of possibilities ?

6th. Naturalists have often been reproached with multiplying the definitions of species. From the variety of terms employed by them in expressing ideas, it has been inferred that they were not agreed as to the ideas themselves. We may easily convince ourselves of their mistake, if we give these definitions a careful reconsideration. We shall see that their several authors have only endeavoured to express with greater clearness and precision, the double idea resulting from the facts of resemblance and filiation. In reality, divergencies only begin where experiment and observation cease. It is this which caused Isidore Geoffroy, however interested he might be in discussions of this nature, to remark—“Such are Species and Races, not only for one of the schools into which naturalists are divided, but for all."

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7th. It has been asserted that the distinction of species and race rests upon a syllogistic circle; that naturalists decided d priori upon calling all those groups incapable of intercrossing, species, and all those amongst which crossing was possible, races. To appeal to the difference of the phenomena presented by the hybrids and mongrels is therefore only solving the question by the question. This is an historical error. Naturalists came into contact with species, races and varieties, before they gave names to them. It was by experiment and observation that they learnt to distinguish them. Knowledge of facts preceded terminology.

8th. Again, it has been said, that the discussions which are always arising between naturalists as to whether a species should be preserved or regarded as a race, as to the genus, family, order, and sometimes the class in which it should be placed, betray a want of precision in general ideas.-Those who talk in this manner forget the immense number of species and races accepted and classified without discussion. They shut their eyes to all cases except those in which divergences of opinion occur. If, however, facts of this nature prove anything against a science and its fundamental data, then even mathematical theorems must be considered as wanting in precision, for there are disputes among mathematicians.

9th. I have already replied to the arguments drawn from the fertility of certain hybrids by showing to what it is reduced. Writers who insist upon this point invariably forget the lesson taught us by disordered variation and reversion without atavism. I regret being obliged to place among them Darwin, who, in his later writings, has shewn much less reserve than in his earlier publications. In the last edition of his book, he quotes what I have said of the cross between the Bombyx cynthia and the Bombyx arrindia; he speaks of the number of generations obtained, but he forgets to mention that disordered variation appeared in the second generation, and that reversion to one of the parental

types was almost complete at the termination of the experiment.

X. Species is then a reality.

Let us take a group of individuals more or less similar, but always capable of contracting fertile unions, and let us, with M. Chevreul, trace it in imagination to its origin. We shall see it divided into families, each of which will have risen either mediately or immediately from one pair of parents. We shall see that the number of these families decrease at each generation, and rising still higher we shall at length find the initial term of a single primitive pair.

Has this really been the case? Has each species indeed arisen from one single pair, or have several pairs, resembling each other perfectly both morphologically and physiologically, appeared simultaneously or successively? These are questions of fact which science neither can nor ought to approach, for neither experiment nor observation is able to furnish us with the smallest data requisite for the solution.

But what science may affirm is that from all appearances each species has had, as point of departure, a single primitive pair.