Nevertheless, between species so distinct as these, a new hybrid race has been reared by M. Rouy, of Angoulême, who each year sends to market upwards of a thousand of his _Leporides_, as he calls them. His object was primarily commercial, not scientific. His experiments, extending from 1847 to the present time, have not only been of great commercial value—introducing a new and valuable breed—but have excited the attention of scientific men, who are now availing themselves of his skill and experience to help them in the solution of minor problems. It is enough to note here, that these hybrids of the hare and the rabbit are fertile, not only with either hares or rabbits, but _with each other_. Thirteen generations have already been enumerated, and the last remains so vigorous that no cessation whatever is to be anticipated. In presence of this case (and others, though less striking, might be named) there is but one alternative; either we must declare that rabbits and hares form one and the same species—which is absurd—or we must admit _that new types may be formed by the union of two existing types_; and consequently that species _are_ variable. If the doctrine of Fixity of Species acknowledges the touchstone of hybridity, the fate of the doctrine is settled for ever. Although I conceive the doctrine of Fixity of Species to be altogether wrong, I cannot say that the arguments adduced in favour of the development hypothesis rise higher than a high degree of probability, still very far from demonstration; they will leave even the most willing disciple beset with difficulties and doubts. When stated in general terms, that hypothesis has a fascinating symmetry and simplicity, but no sooner do we apply it to particular cases, than a thick veil of mystery descends, and our pathway becomes a mere blind groping towards the light. There is nothing but what is perfectly conceivable, and in harmony with all analogies, in the idea of all animal forms having arisen from successive modifications of one original form; but there are many things perfectly conceivable, which have nevertheless no existence; there are many explanations perfectly probable, which are not true; and when we come to seek for the evidence of the development hypothesis, that evidence fails us. It _may_ be true, but we cannot say that it _is_ true. Ten years ago, I espoused the hypothesis, and believed that it must be the truth; but ten years of study, instead of deepening, have loosened that conviction: they have strengthened my opposition to the hypothesis of fixity of species, but they have given greater force to the difficulties which beset the development hypothesis, and have made me feel that at present the requisite evidence is wanting. I conclude with reminding the reader that the question of the origin of species is at present incapable of a positive answer; of the two hypotheses, that of development seems the more harmonious with our knowledge; but it