I should have mentioned that the species wandering westward and northward from this South-European centre of distribution, would naturally have joined the migrants which came from beyond the borders of our continent. They might thus appear to be true Oriental migrants, and on a previous occasion I grouped all these together under the term of "Southern Fauna," as I assumed the observer to be stationed in the British Islands. All new-comers from the south-east, south, or south-west of Europe would be to him southerners quite irrespective of their original home, which might be in Southern Europe, Asia, or Africa.
The Swallow-tail is well known to all collectors of Butterflies in England, though it has of late years become very rare and is now confined to a few localities in the east of England. The members of the family _Papilionidæ_, to which it belongs, are mostly large and striking species, and their distribution is therefore more accurately known than that of the smaller and less conspicuous butterflies. Only four different kinds of Swallow-tail Butterflies inhabit Europe, but in Southern Asia and the Malay peninsula they attain their maximum as regards numbers; and there we find a great many species of this genus _Papilio_. Of the four European species only one, viz., _Papilio hospiton_, is peculiar to Europe; all the others range into Asia. It would seem, therefore, as if this genus was an Asiatic one and had migrated to Europe, and that the route taken was the one from Asia Minor across to Greece. We have a similar case in the closely allied genus _Thais_ two of the three European species living also in Asia Minor. _Thais cerisyi_ inhabits some of the Greek islands, as well as the mainland of Turkey and Greece.
Another genus of the great family _Papilionidæ_ with which most lepidopterists are well acquainted is _Parnassius_. What butterfly-hunter has been in Switzerland without hearing of, or seeing, the famous _Parnassius Apollo_? We have four European species of _Parnassius_, only one of which is peculiar to our continent, but the locality where it occurs, the Caucasus, is on the borders of Asia. Almost all the other species are Asiatic, none however range to the south. Its headquarters, and I think its original home, are the mountains of Central Asia. From there it has spread--some species to the Himalayas, and a few to Europe and North America. But these migrations are not of very recent date. _Parnassius_ no doubt arrived accompanied by a large number of other Central Asiatic mountain insects and plants. I shall refer to the latter again when dealing with the origin of the Alpine fauna, but meanwhile it might be mentioned that the famous Swiss "Edelweiss" (_Leontopodium alpinum_), which we are accustomed to regard as a typical Alpine plant, is certainly of Asiatic origin. In some parts of Southern Siberia it is one of the common meadow-flowers, and ranges from there south into Kashmere, but not northward. Like the _Apollo_, it does not occur in Scandinavia or Northern Siberia. Both plant and insect evidently migrated from Central Asia, directly westward along the southern border of the sea, which extended from that region as far as the European Alps in early Tertiary times. At that time the Caucasus was possibly still connected with the Balkan Mountains, across what is now the Black Sea, and that may have been the highway on which they travelled west.