from this centre Southern Europe was colonised, where a new centre developed in oligocene and miocene times, sending colonies off to Madeira and across the old land-connection which united Northern Africa and South America about that time. The most active centre of development then gradually shifted eastward again, while the older centres were perhaps submerged during the physical changes in the distribution of land and water. 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.