the Diprotodon, the Zygomaturus, and Nototherium, in the marshy savannahs of Australia, but as these became drained in the course of the gradual elevation of the land and converted into arid plains, swept by sirocco-like winds, the succulent vegetation upon which they lived failed, we may presume, and remaining represented by related animals of comparatively pigmy size, they disappeared utterly as the Megatherium, the Megalonyx, and Mylodon of South America, which likewise leaving small analogues behind, passed from the face of the earth under the influence of some such cause, or destroyed by the irresistible attacks of internal parasites, (as we see hosts of domestic animals now throughout extensive districts of Australia, unable to resist the enemies which had proved less dangerous to the indigenous marsupials, from whom they were derived), or of swarms of pestiferous insects, such as the tsetse fly of Africa, or the calf- and foal-murdering one of Patagonia.[1]
It will not be proposed that any change of temperature destroyed the aboriginal horse of North and South America. Herds of these animals roamed in comparatively recent times from the cold north to the Patagonian plains, and their contemporaries flourish there still. Whatever was the cause of their extinction, it had ceased to act when the Spaniards conquered Mexico, for the new equine race introduced by them has multiplied rapidly, and continues to flourish equally well in a feral as in a domestic state. When the plague or the cholera take their tens of thousands of men, the lower animals remain generally unscathed, and vice-versâ.
The parasitical worms which are so fatal to the flocks of the Australian sheep-farmer abound in the kangaroo and wallabi, and the former, if left to themselves, would ere long become extinct, destroyed in some districts by the parasites, in others starved out by the increasing hordes of hardy marsupials. The increase of this inferior order of animals as it stands in the derivative pedigree has been immense since the balance was destroyed by the extinction of the dingo, and since the aboriginal men have so much decreased in numbers. Thirty thousand kangaroos of large and smaller tribes have lately been killed on a single settler's run without making any observable diminution in their strength, and until some epidemic arises amongst them, their singularly rapid increase will tax the efforts of the white man to check in these thinly peopled regions. If these marsupials are so inferior a grade of animals, they are at all events admirably adapted for the situation they now occupy; so peculiarly well adapted to it that after
- ↑ An interesting circumstance of this kind is now being observed over large districts in the interior of New South Wales, which, if it continued, would lead in time to the disappearance of white cattle and white-legged or piebald horses in the herds, such being attacked by a disease caused by a black Aphis covering the pastures, producing fatal effects upon all young animals, and even many grown ones, whilst those whose coats are of dark colours do not suffer at all.
