A few other of the more obvious differences between the native zoology of the Old and New Worlds may be adverted to with advantage. Among carnivorous quadrupeds, the lion, tiger, leopard, panther, and hyena are confined to the eastern half of the globe. In the New World, the puma and the jaguar take respectively the places of the lion and tiger of the Asiatic continent. Of the ruminants, the camel, the giraffe, and the numerous antelopes are only found within the Old World. Of the pachydermata, the elephant, the rhinoceros, the hippopotamus, the horse, the zebra, and the ass are unknown to the native zoology of the lands lying west of the Atlantic. The elephant, and also the rhinoceros, belong to Asia and Africa (the species being different in the case of either continent), the hippopotamus is African only: the zebra (with its kindred species, the quagga) is also peculiar to Africa. Both the horse and the ass probably came originally from Asia. Of the Quadrumana, which are numerously represented in the zoology of either hemisphere, the species (and, in most cases, the genera) are distinct. Again, the opossums of the New World belong to an order (the marsupial) which is altogether unrepresented in the three continents of the Old World, but which exhibits its fullest development in the Australian division of the globe. Numerous other instances might be adduced, but these will suffice. They serve to show that, in the case of animals as of plants, particular regions constitute centres of particular forms of life, which thence spread, within certain limits, around, still leaving to each such region its strongly marked and typical characteristics in such regards. Europe exhibits, in its indigenous zoology, a character less marked and distinctive than belongs to other divisions of the globe. This is in some degree the result of its dense population, and the consequent diminution in the number of wild species, but in a more special manner results from its conditions of geographical form and position. Europe is less a continent in itself than an outlying portion of the vast and unbroken mass of the Asiatic continent. No strongly marked feature intervenes between the plains of eastern Europe and those of northern Asia, and within the continuous range of land that extends, under the same parallels, from the Baltic Sea eastward to the waters of the Pacific Ocean, the animal life exhibits for the most part identity of species and genera. The differences between them, in a vast number of instances, are merely varieties. Many of the fur-bearing animals are common to all the lands that lie within the Arctic circle, as many as twenty-seven species being native to Europe, Asia, and North America alike.