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 o£ 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 anti-dogmatic 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.