"The close relationship," remarks Dr. Major (a, p. 106), "shown in the fauna of Corsica and Sardinia to Africa, permits the supposition that the connection with these islands had persisted to a much more recent date than that with Europe."
Many other authors have pointed out the close similarity existing between the faunas of Southern Europe and North Africa. We need only refer to the writings of Professor Suess, Milne-Edwards, and Boyd Dawkins. Mr. Blanchard went even so far as to say, "a comparer les plantes et les animaux de la Sicile et de la Tunésie, on se croirait sur le même terrain" (p. 1047).
No less than 113 species of phanerogamic plants are enumerated by Professor Engler (p. 53) as occurring in the Mediterranean coast region east and west of Italy without being found in that peninsula, or at least only in the extreme south of it. But he tells us that these species represent only a portion of such plants, which are extremely numerous.
In taking a general survey of these plants, Professor Engler is of opinion that their range implies that a large number of the Mediterranean species have migrated along a line which can be drawn between North Africa, Sicily, Greece, Crete, and Asia Minor, and that from this line the distribution started northward again.
Many of these plants then, and also some of the animals I have referred to, formed part of the older stream of migration which entered Europe from Asia Minor (vide [Fig. 5], p. [117]). There were only two courses open to them as they arrived on our continent during earlier Tertiary times. They could either go straight west towards Greece, or in a more northward direction to the newly-formed Alps. As the latter were raised, some of the immigrants were modified so as to adapt themselves to the new surroundings. Others became extinct; but a great many have persisted in the Alps to the present day and exhibit discontinuous distribution, having meanwhile disappeared in the intermediate tract between the latter and their original home in Asia. The lowlands of Eastern and Central Europe were either occupied by the sea or by large freshwater lakes, so as effectually to prevent a direct migration northward.
When the newer migrants arrived from Asia not only had the Alps risen to a lofty mountain chain acting as an effectual barrier, but Southern Italy and Greece had become disconnected. Some time after, Sicily and Southern Italy also became separated. Meanwhile the stream of migrants which consisted less and less of typically southern forms, emigrants from Central Asia and even Southern Siberia, mingled with the southern forms on their way to Europe, and these now poured across the newly opened plain of Central and Northern Europe. But it was not until some time after this that the Mediterranean Sea broke across the Ægean region, and that the Northern Sea retired from the plains of Eastern Russia to admit the typical Siberian fauna and flora into our continent (vide pp. [189]-[241]).
I cannot close this chapter without referring to the active distributional centre—or I might say, centre of origin—of species situated in South-eastern Europe. No group of animals is more instructive in elucidating the paths of migration from this centre than the terrestrial mollusca. Wherever the original home of the genus Clausilia may have been in early Tertiary times, it is certain that the most active centre of origin is now, and has been for a considerable time past, in South-eastern Europe. One of the earliest migrants from that modern centre of this interesting genus is Clausilia bidentata, which is the only species found in Southern Spain, and one of the two met with in Ireland, and which has been observed in high altitudes in the Alps and in Scandinavia. As we go eastward from Western Europe the number of species of Clausilia, as we have seen, increases until we reach a maximum in the Balkan peninsula and the region of the Caucasus. Limax, Agriolimax, and Amalia, three genera of slugs, likewise appear to have originated in the same region and spread over Europe from there. Some species like Limax maximus and L. marginatus are very ancient, and probably commenced their wanderings in early Tertiary times. In this manner many animals of European origin have joined the Oriental migrants in their westward and also in their later northward travels. In a similar way species of plants and animals of Alpine origin might have joined these migrants in their northward course, and it is only when we come to carefully analyse the constituent parts of all these members which have come to us in England from the south, that we realise the complexity of their origin. Finally, even the Siberian migrants mingled with the later Oriental ones, and in some cases the decision as to whether a certain species belongs to the former or to the latter migration becomes a matter of great difficulty.
SUMMARY OF CHAPTER VI.
Like the last chapter, this deals with the Asiatic migrants. But while the former described the history of the northern invasion, those animals which entered Europe from the south-east are here more particularly referred to. They originated in Central, Southern, and Western Asia. It is not easy to discriminate in all cases between this Oriental migration and the Siberian. To a certain extent, even an entry of Northern Asiatic species has taken place by the southern route, and vice versâ. On the other hand, southern species might have come to Europe by the southern route—that is to say, to the south of the Caspian—and also by the northern, which lay to the north of that great inland sea. The Red Deer is a good example. It arrived on our continent by both routes. However, there is a racial difference in the members of the two migrations. The small race now found in Corsica, Sardinia, North-west Africa, and Western Europe, is probably the older of the two, while the larger one—resembling the American Wapiti Deer—arrived very much later from Siberia.