for example in Australia, new sloths and armadilloes in South America, new heaths at the Cape, new roses in the northern, and new camelias in the southern hemisphere. But to this line of argument Mr. Darwin and Dr. Hooker reply, that when animals or plants migrate into new countries, whether assisted by man, or without his aid, the most successful colonisers appertain by no means to those types which are most allied to the old indigenous species. On the contrary, it more frequently happens that members of genera, orders, or even classes, distinct and foreign to the invaded country, make their way most rapidly, and become dominant at the expense of the endemic species. Such is the case with the placental quadrupeds in Australia, and with horses and many foreign plants in the pampas of South America, and numberless instances in the United States and elsewhere, which might easily be enumerated. Hence, the transmutationists infer that, the reason why these foreign types, so peculiarly fitted for these regions have never before been developed there, is simply that they were excluded by natural barriers. But these barriers of sea, or desert, or mountain, could never have been of the least avail, had the creative force acted independently of material laws, or had it not pleased the Author of Nature that the origin of new species should be governed by some secondary causes analogous to those which we see preside over the appearance of new varieties, which never appear except as the offspring of a parent stock very closely resembling them.
