CHAPTER VI.

THE ORIENTAL MIGRATION.

The Oriental migration is closely related to the Siberian. Both have originated within the Asiatic continent, and in many respects a strict line cannot be drawn between them. There can be no doubt that some of the species which we regard as Siberian migrants had their original home in more southern lat.i.tudes, and thus may have formed part of the older Oriental migration. The home of that migration I take to be Central and Southern Asia, that is to say, everything south of the Alta Mountains and the Caucasus. Its members have reached Europe across an old land-connection which united Turkey, Greece, and Syria, while the Siberian animals invaded our continent to the north of the Caspian and Caucasus.

The Siberian immigrants into Europe on the whole are not very numerous, but it is different with those from the more southern parts of the Asiatic continent. The members of the Oriental migration form a very large percentage of the European fauna. No other migration has affected our continent so powerfully, because it continued uninterruptedly for a very long time. Hence its results can be traced from one corner of Europe to the other. We have seen that the Siberian migration only commenced after the first portion of the Glacial period had pa.s.sed away.

The Oriental, however, persisted throughout, or at any rate for the greater part of that period. It commenced ages before it, in miocene times, or even earlier. And as the aegean Sea, which broke up the highway of the Oriental migrants, is only of recent formation, there was a steady westward march for a very considerable time. No doubt the migration was also favoured by the fact that scarcely any formidable barriers had to be crossed.

Many instances might be quoted of the same species forming part of the Oriental and also of the Siberian migration, but as a rule the Siberian migrant belongs to a distinct variety, or has such well-marked racial characters as to be at once detected from its more southern relative.

Among the examples of Oriental migrants which I have occasion to bring forward, such instances will be specially dealt with.

In its wild state the Red Deer (_Cervus elaphus_) is almost extinct in the British Islands, though it still occurs in the moorlands of Devonshire and Somersetshire in England, in the south-west of Ireland, and in some localities in Scotland. Fifty years ago it was also found wild in several other of the Irish western counties; and in the seventeenth century it was common in most of the mountainous districts of Ireland. Its remains have been found fossil in the marls and caves of Ireland, and in the Forest-Bed, as well as in a large number of caves in England. The history of the Red Deer in other countries is very similar. In Scandinavia it flourished as far north as the sixty-eighth degree of lat.i.tude, whereas it is now quite extinct on the mainland, though still lingering on in some of the western islands. Denmark and Switzerland know it no more, and it is almost extinct in Belgium. Nearly throughout Europe where it occurs, its numbers are diminishing, greatly owing, perhaps, to the relentless persecution by man, but its gradual disappearance must likewise be partly due to other causes. Formerly it inhabited every country of Europe and all the larger islands. It still exists in Corsica and Sardinia, and at an earlier period it was also met with on the island of Malta. The Red Deer found in Corsica and Sardinia is smaller than that inhabiting Central Europe, and is by some authorities regarded as a distinct species, which has been named _Cervus corsica.n.u.s_. But Sir Victor Brooke has pointed out that the antlers of some of the Scotch Deer agree in every point with those of the Sardinian species. Indeed, the West European Red Deer altogether is a small-antlered form, compared with the Eastern one. This character, however, is only a racial one, and not of specific value. In the pleistocene deposits of Eastern and Central Europe, a very large-antlered race has been discovered, and identified by Professor Nehring with _Cervus canadensis_--the Canadian Red Deer. Tcherski, the Siberian traveller, believed that _Cervus canadensis_ was identical with, or a variety of, the Asiatic species of Deer, _Cervus eustepha.n.u.s_, _Cervus xanthopygus_, and _Cervus maral_. Some authorities--and to these belong Mr. Lydekker--think that we ought perhaps to regard the whole number of Red Deer-like forms as local varieties of one widely-spread species. Besides the deer already referred to, the following belong to this same group:--_Cervus cashmiria.n.u.s_, _Cervus affinis_, _Cervus Roosvelti_, from North America, and the North African _Cervus barbarus_.

The question now is, where have these varieties originated? Or, if we go to the root of the matter, where is the original home of their ancestors? Considering that so many _Cervidae_ have been found in French and English pliocene deposits, and that remains of the Red Deer occur not only in the English Forest-Bed, but have been found a.s.sociated with those of the Pigmy Hippopotamus in Malta, it would only be reasonable to suppose that the genus _Cervus_ had originated in Europe. It might also be argued with equal force that the Red Deer had its birthplace in our continent. But when we carefully study its present range this verdict cannot be accepted. The view of the Asiatic origin of the Red Deer, so ably maintained by Koppen, corresponds far better with its present distribution, especially if we look upon the Asiatic, North American, and North African forms as varieties of the same species.

If the Red Deer were of European origin, it must have come into existence at a time when Malta was part of the mainland, when North Africa and the British Islands were connected with the continent of Europe, and of course before the deposition of the Forest-Bed. Such land-connections existed probably during the Pliocene Epoch. Migrants would have wandered from Europe into Asia. These would have developed into larger races, which again furnished emigrants for North America.

The latter crossed by the old land-connection which once joined America and Asia at Behring's Straits. During pleistocene times the large Siberian race would now have re-migrated to the home of its ancestors in Europe, for we find the remains only in Central and Eastern Europe, indicating that an invasion of the Red Deer from Asia must then have taken place.

Against this view of the European origin of the Red Deer, it may be urged that deer are known from Indian as well as from European pliocene deposits, and that a migration could have taken place from the Oriental Region to Europe just as easily as from the latter to Asia. The majority of the species of the genus _Cervus_ (in a wide sense), moreover, are Asiatic, ranging to Borneo, Sumatra, and the Philippine Islands, all of which islands have been separated from the mainland for a considerable time. Finally, the original home of a species, as we have learned, generally corresponds with the centre of its geographical range, and this lies in the case of the Red Deer in Central Asia.

One of the highest authorities on the deer family, Sir Victor Brooke, also was of opinion that the _Cervidae_ originated in Asia, and from there spread east and west. Of the two divisions into which true deer are divided, viz., the _Plesiometacarpalia_ and the _Telemetacarpalia_, the former is almost confined to the Old and the latter to the New World. The only North American species belonging to the first division is the Canadian Red Deer, which fact clearly indicates its recent immigration to that continent.

There were probably two distinct migrations of the Red Deer into Europe.

An older one coming from Asia Minor into Greece, which stocked Sardinia, Corsica, Malta, and North Africa in the first place, when these were still connected with one another. This same migration likewise affected western continental Europe, the Irish Red Deer being probably the descendant of this very ancient stock. The latter entered the island when it was still part of the Continent. The later migration of a larger form came from Siberia and spread mainly over Eastern and Central Europe, but it appears that it also reached England, although there is no evidence of any of these Siberian deer having ever inhabited Ireland.

The range of this deer, therefore, to some extent corresponds to that of another described on p. 153. We found then that two races of Reindeer had migrated to the British Islands--one from the Arctic Regions, and the other from Siberia, but that only the former had reached Ireland.

The so-called Irish Elk (_Cervus giganteus_) has been referred to the Oriental migration, but, as stated below, it has some claims to be regarded as a European. Unfortunately it is now extinct; it seems not unlikely, however, that it inhabited Ireland when man had already made his appearance on the island. Although its remains are found in such extraordinary abundance in Ireland, it certainly did not originate there. It lived also in England and Scotland, and in the Isle of Man, in France, Denmark, Germany, Austria, North Italy, and Russia. Its remains have been discovered even in Siberia. It must either have originated in Europe and then migrated to Asia, or have had its birthplace in Asia and wandered to Europe. There is nothing to lead any one to a.s.sert positively that either of these two continents was the one in which the original home of the Irish Elk was situated, and we can only be guided in this case by the history of its nearest relatives. These are the Fallow Deer (_Cervus dama_). There are two very closely allied species, the Persian and the European, but several others have been discovered in the Forest-Bed and the pliocene deposits of the Auvergne. As no remains of the Fallow Deer are known from Asia, it seems probable that it and also the Irish Elk originated in Southern Europe, and only invaded Asia in early pleistocene times.

The Mammoth (_Elephas primigenius_) is a familiar example among a large number of mammals which have come to us about the same time from Asia by the Asia Minor route. It had a much wider range than the Irish Elk, since its remains have been discovered in a large number of European localities as far west as Ireland, also in Siberia, and even North America. Though we have had _Proboscidea_ in Europe from the Middle Miocene onwards, Mr. Lydekker (_d_, p. viii.) holds that "our comparatively full knowledge of Lower Miocene and Upper Eocene mammalian faunas of the greater part of Europe and North America, renders it almost certain that neither of those regions was the home of the direct ancestors of the _Elephantidae_; and we must therefore look forward to the discovery of mammaliferous Lower Miocene or Upper Eocene strata in some other region of the (probably old) world which may yield these missing forms."

The genus _Elephas_ makes its first appearance in the Upper Miocene of India. Our European _E. antiquus_ is, according to Professor Zittel, probably identical with _E. armeniacus_ of Asia Minor, while _E.

meridionalis_ agrees in all essential characters with the Indian _E.

hysudricus_. The Indian and European species of fossil elephants altogether are very closely related, and the supposition that they all have had their original home in the Oriental Region offers, I think, no serious obstacle. The view of the European origin of the mammoth especially is open to very serious objections. It does not occur in any European pliocene deposits, and could not therefore have originated in our Continent until pleistocene times. That it should then have commenced its travels through Europe and Siberia to the New Siberian Islands and North America seems almost an impossibility. But if we suppose the mammoth to have had its home in India in pliocene times, it could then easily have migrated to all the parts of the world where its remains have been discovered.

Of the Asiatic mammals still living, some have only just crossed the borders of Europe and then died out again. Similar cases have been referred to in discussing the Siberian migration. Thus remains of the camel have been found in Roumania and in Southern Russia in pleistocene deposits. Others have lingered on to the present day. _Crocidura etrusca_, for instance, still lives in Southern France, Italy, Sicily, and North-western Africa. All its nearest relations are typically Oriental species. In spite of the fact that a _Crocidura_ is known from French and German miocene deposits, the general range of the genus suggests an Oriental origin. In early Tertiary times a section spread into African territory and another eastward as far as the island of Timor. This may possibly have happened in miocene times, when a few species likewise found their way into Europe. Many other mammals have wandered still farther west, and now form an important percentage of the European fauna.

Of Birds, too, a large number might be mentioned which had their home in Asia and have found their way to Europe with the Oriental migrants. A few instances have already been alluded to, and some additional ones may be specified at random, without attempting to give a complete list.

Some of the Wagtails (_Motacilla_), as I mentioned in the last chapter, have certainly come to us with the Siberian migration; but others seem to be Oriental, such as _Motacilla melanope_, which is resident in Southern Europe and migratory in the North. _M. campestris_--the Yellow Wagtail--has a most peculiar discontinuous range. One colony breeds in the British Isles and Western Europe generally, where it is known as a summer visitor, retiring to West Africa during winter; another is found from South-east Russia to Turkestan in summer, and winters in Southern Africa. This fact may possibly be due to two distinct migrations from Asia having taken place: an earlier one from the South-east--that is to say, an Oriental one--and a Siberian one more recently. In this case the members of the two migrations have not become sufficiently differentiated to be regarded as distinct varieties. Though most of the Wagtails have a somewhat northern range, none (except perhaps _M.

borealis_) are truly Arctic; and indeed, as almost all of them pa.s.s the winter in southern lat.i.tudes, it may be a.s.sumed that they are of southern and not of northern origin.

The Dippers (_Cinclus_) are practically unknown in the Central European plain, but they occur in Western Europe as far north as Scandinavia, also in the Alps, Carpathians, and Southern Europe, including Sicily and Sardinia. Some authorities distinguish three species, others only one.

As a matter of fact, the difference between the three forms is very slight, and their nests and eggs are undistinguishable. Eight other species have been recognised, and all these are either Asiatic or American. As one of the American forms is peculiar to Peru and another to Ecuador and Columbia, and since the genus as a whole is a mountain-genus, it probably is an ancient one. Its European range alone, however, implies that it has inhabited our continent for a considerable time and is no new-comer. We may look upon it as of Asiatic origin. The ancestors have spread east and west, the European species having arrived with the earlier Oriental migrants, and wandered along the Mediterranean at a time when the geographical conditions of that sea were vastly different from what they are to-day.

Not quite so ancient as the Dippers, but likewise Asiatic in their origin, are the Bullfinches (_Pyrrhula_). The closely allied Pine-Grosbeak (_Pinicola enucleator_) has already been referred to (p.

191) as a member of the Siberian migration. The distribution of the European Bullfinch (_P. europaea_) is very interesting, as it occurs in two distinct forms, by some authorities regarded as races, by others as species. In all probability these two races owe their origin to two different migrations from the same ancestral stock. We may suppose that _P. europaea_ came to Europe along with the Oriental migration, spreading chiefly over the south and west, while another branch developed in Siberia into the larger and more brilliant race (_P. major_), which subsequently entered the neighbouring continent with the Siberian fauna.

The latter race inhabits, according to Mr. Saunders, Northern and Eastern Europe, and also Siberia. All the other species--there are eight more--except one, are found in Asia. This one species, which inhabits the Azores, appears to be more closely related to one of the Siberian bullfinches than to the European. It stands isolated, and is an extraordinary instance of discontinuous distribution, as no Bullfinch inhabits either Madeira or the Canary Islands. We must a.s.sume that the form connecting it with the Asiatic probably lived in Southern Europe, and has become extinct.

One of the most typically Oriental genera of birds is _Phasia.n.u.s_, to which our Common Pheasant belongs. Out of twenty species, nineteen are found exclusively in Asia, most of them being confined to the central plateaux of that continent. Only one species pa.s.ses the confines of Asia into Greece, Turkey, and Southern Russia. This is _Phasia.n.u.s colchicus_. Formerly, however, the Pheasant appears to have had a wider range in Europe, for three species are known fossil from France.

Altogether, it is not quite certain whether the Pheasant is not really an indigenous bird in the British Islands, having survived from pre-glacial times. It is believed that the Romans brought it to England, but there is no record of an introduction at that time.

Among the older Oriental bird migrants might be mentioned the Fire-crested Wren (_Regulus ignicapillus_), which has even occasionally visited England. It becomes commoner as we go south-eastward. In Asia Minor it is more abundant than the Gold-crest; and throughout the year it is resident in Southern Europe, where it occurs in Turkey, Greece, Italy, Spain, Sardinia, and Malta. On the opposite sh.o.r.e, in North-west Africa, it again makes its appearance, and its range extends westward to the Canaries (_R. teneriffae_) and Madeira (_R. maderensis_).

The genus to which our common Goldfinch belongs, viz., _Carduelis_, is also probably of Oriental origin, and may be looked upon as one of the earlier migrants. That species (_C. elegans_) breeds throughout Europe, except in the extreme north, but it is especially abundant in Southern Europe and North-west Africa. It is also resident in Madeira and the Canaries. Eastward its range extends to Persia. A larger race (_C.

major_) inhabits Western Siberia and crosses the European border into Russia. It interbreeds in Siberia with _C. caniceps_, an East Siberian form.

A few instances of Reptiles and Amphibia with a similar range will show that the Oriental migration was not confined to the higher vertebrates.

Two species of the genus _Eremias_ (_Podarcis_) occur in South-eastern Europe. This is a genus of Lizards with rather a wide distribution, ranging from Central Asia to South Africa southward and China eastward.

Altogether there are twenty-four species, two of which just enter Europe; and of the rest half are Asiatic and half African. Even if the genus were of African origin, it is extremely unlikely that the Asiatic species came by way of Europe. We may a.s.sume, therefore, with a fair degree of probability that the two European species wandered westward along with the Oriental migrants.

The genus _Ablepharus_ belongs to a family of Lizards in which the legs are either very fully developed, or quite absent as in the Slow-worm (_Anguis fragilis_). It is an ancient genus, having a wide range from Central Asia to Australia on the one hand, and to South Africa on the other. One species of this Scink-like Lizard, viz., _Ablepharus pannonicus_, enters Europe in the south-east, inhabiting Greece as far north as Southern Hungary. In Asia it is found in Syria and North Arabia. This clearly signifies that the Lizard is an Oriental migrant.

Among the Snakes which partic.i.p.ated in the Oriental migration might be mentioned _Eryx jaculus_, whose home is probably in Western Asia. It is known in Europe from the Greek islands of Tinos and Naxos, from Turkey and Southern Russia. Another, a peculiar worm-like form, lives underground in damp earth and under stones--_Typhlops lumbricalis_. This species inhabits the mainland of Greece as well as the Greek islands, and Asia Minor as far as the Caucasus.

A most interesting case of distribution is that of the pretty little Toad so well known on the Continent under the name of "fire-toad"

(_Bombinator igneus_). Though some authorities, such as Boulenger, recognise only one form of _Bombinator_,[1] others are of opinion that two well-marked varieties exist in Europe. These are looked upon by Dr.

von Bedriaga as good species, but he acknowledges that they are rather critical and difficult to identify. No other species of _Bombinator_ occur in Europe. _Bombinator pachypus_, the western race,--or if we choose to call it species,--occurs in France, Germany, Switzerland, Austria, Sicily, and Greece. _B. igneus_--the eastern race--is found in Southern Sweden, Denmark, Germany, Austria, and Russia. The latter has therefore a more northerly and easterly range. The species is not known from Siberia, but makes its appearance again in China in a form which, according to Dr. von Bedriaga, does not quite agree with either of the two European races.

Now if we supposed _Bombinator_ to have originated in Europe, its absence from the British Islands, most of the Mediterranean islands, and the greater part of Scandinavia would not be easy of explanation, while as an Asiatic migrant the European range is more readily understood. Its apparent absence from Western Asia might quite likely be due to the fact that the zoology of that part of the Continent is only now being investigated. The latter has, moreover, undergone great physical changes in recent geological times. The supposition that one migration of _Bombinator_ from the south-east has taken place, and then another from the east, seems to explain this case of distribution, as other similar ones, in a most satisfactory manner.

The Tree-Frog (_Hyla arborea_) must be an ancient species, but it is not of European origin. Few genera of Amphibia have a wider distribution than _Hyla_. There are only three species in Asia, Europe, and Africa, the remaining 129 being confined to America and Australia. Two of the three Old World Tree-frogs are so closely allied that until recently they were regarded as mere varieties of one another. These are _Hyla arborea_ and _H. chinensis_. The former is found in Asia Minor, Persia, China and j.a.pan, and in most of the Mediterranean islands and Southern Europe generally. It does not occur in the British Islands, Norway, or North Russia, but in South Sweden, Germany, France, and Spain. It is also known from North Africa and from Madeira, the Canaries, and the Salvages. The occurrence of the Tree-Frog on so many of the Mediterranean islands is of particular interest, especially as four well-marked varieties have been distinguished by our leading herpetologists, so that the more minute features of the various forms can be traced from island to island, adding one more proof--if proof were needed--of their former continuity. Of course, that _Hyla arborea_ must be considered an Oriental migrant seems so evident that it scarcely needs further comment.

A number of mollusca might be mentioned whose range indicates that they have migrated to Europe from Asia Minor. _Buliminus pupa_ is one of these. It is known from Asia Minor, Greece, South Italy, Sicily, and Algeria. _Buliminus detritus_ is perhaps better known, being common in some parts of Germany. From there its range spreads east as far as Asia Minor. Many closely allied species inhabit Western Asia, to which they are confined, while others enter on European territory in some of the Greek islands. _B. fasciolatus_ occurs on the islands of Crete, Rhodes, Cyprus, and in Greece and Syria. Most of the species of _Buliminus_ have a very restricted range, but _Buliminus obscurus_ is found almost all over Europe, from Ireland in the west to the Crimea and Transcaucasia in the east.

Whether the sub-genus _Pomatia_ of the genus _Helix_--to which the so-called Roman Snail belongs--is of Asiatic origin, or whether some of the species have migrated from Europe to Asia, I am not prepared to say; but there can be no doubt that _Helix pomatia_ has reached Western Europe from the east.

On the whole, the number of mollusca which we might point to as having migrated to Europe is not large, the great majority being indigenous to our continent. However, some of the other groups of invertebrates differ very materially in that respect from the mollusca. I cannot leave the consideration of the mollusca without referring to the fact that there appears to be a very important centre of distribution in South-eastern Europe. It is from this centre that many species have spread north and south, east and west. Take, for example, the genus _Clausilia_, a small land-sh.e.l.l shaped like a pointed round tower, and abundant on old walls and tree trunks. In England we have four species of _Clausilia_, in Ireland only two. In the greater part of Spain only our common _Cl.

bidentata_ occurs. As we go east the number of species rapidly increases. A maximum is reached in South-eastern Europe, where hundreds of different kinds are found. Towards Northern Europe a similar decrease of species takes place. So far the history of the _Clausiliae_ seems perfectly simple. An active centre of origin appears to exist in South-eastern Europe, from which the species radiate out in all directions. But when we come to look more closely into the extra-European distribution of the genus, and especially when we examine its past history, we find that its origin is extremely complex, and dates back to a much more remote period than would have been imagined, had we merely taken into account its present range in our own continent. Professor Boettger, who is the highest authority on _Clausilia_, tells us that the genus is known from the earliest deposits of the Tertiary Era. About 700 species are now known, and these have been sub-divided by Professor Boettger and others into a number of sub-genera. Some of these are extinct, but the great majority are still living. The sub-genus _Phaedusa_ occurs in the eocene and oligocene of Southern Europe, but it is extinct as far as our continent is concerned.

Close upon a hundred species, however, still inhabit India, the Malayan Islands, China, Ceylon, and j.a.pan. Then again, the sub-genus _Laminifera_ occurs in the oligocene and miocene of Central Europe, and survives in a single species, _Cl. Pauli_, in South-western France. The groups _Garnieria_ of China, _Macroptychia_ of East Africa, _Boettgeria_ of Madeira, and _Nenia_ of South America, have no fossil representatives. We have here some very remarkable cases of discontinuous distribution which testify to the antiquity of the genus, and this is certainly confirmed by the fossil evidence. However, it is hardly likely that the headquarters, as it were, of _Clausilia_ have always been in South-eastern Europe. Most of that part of the Continent has been submerged since eocene times more than once. The peculiar distribution of the genus might be explained, I think, if we supposed the original home of _Clausilia_ to have been in Southern Asia, that 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 a.s.sumed 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 b.u.t.terflies 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 _Papilionidae_, 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 b.u.t.terflies. Only four different kinds of Swallow-tail b.u.t.terflies 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 _Papilionidae_ with which most lepidopterists are well acquainted is _Parna.s.sius_. What b.u.t.terfly-hunter has been in Switzerland without hearing of, or seeing, the famous _Parna.s.sius Apollo_? We have four European species of _Parna.s.sius_, 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. _Parna.s.sius_ 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.

Some of the Clouded-Yellows--b.u.t.terflies appertaining to the genus _Colias_--formed part of the Oriental migration. The genus is undoubtedly of Asiatic origin, and while many of the species have turned northward, ranging across Siberia and North America, others have taken a southern and westward turn and thus reached Europe. We have two Clouded-Yellows in Western Europe, and both of them must have come with this migration.

A very good example of an Oriental migrant is _Danais chrysippus_, a magnificent b.u.t.terfly found in Greece and Southern Italy. In Asia it is known from Syria, Persia, and from the whole of the southern portion of the Continent. The genus _Danais_ (in its wide sense) is a large one, and princ.i.p.ally occurs in the warmer regions of Asia. Three species are found in North America and only one in Europe.

Among the beetles belonging to this migration, there is one of very considerable interest from a distributional point of view, for all the species of the genus--even the whole family to which the genus belongs--are what is known by zoologists as "Commensalists." These are animals habitually a.s.sociating and living in close connection with others with which they are not tied by any family relations or kinship.