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 latitudes, 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 Altai 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 passed 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 latitude, 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
corsicanus_. 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
eustephanus_, _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
cashmirianus_, _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 associated 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 Koeppen, 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 assert
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 pass the
winter in southern latitudes, it may be assumed 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 assume 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 _Phasianus_, 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 passes the confines of
Asia into Greece, Turkey, and Southern Russia. This is _Phasianus
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 shore, 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 assume, 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 participated 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 Japan, 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-shell 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 Japan. 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 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 _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 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 _Papilionidae_ 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.
Some of the Clouded-Yellows--butterflies 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 butterfly 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 principally 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 associating and living in close connection with
others with which they are not tied by any family relations or kinship.
Such a state of close and permanent friendship is called "commensalism."
Now it appears as if the members of this family of beetles
(_Clavigeridae_) had of their own free will formed such a close
connection with colonies of ants--sometimes with one species, sometimes
another. They are the permanent guests of the ants, and in return they
secrete a fluid which is apparently highly prized by them. All of the
_Clavigers_ are provided with peculiar club-shaped antennae, with which
they ungraciously beat their hosts, when they are in want of food.
According to some authorities, they even occasionally gnaw at the pupae
and larvae of the ant with which they live.
Such beetles naturally can only have extremely limited means of
distribution, and they are comparable in that respect with the woodlice
of the genus _Platyarthrus_, to which I have already had occasion to
refer. All the species of _Claviger_ are confined to Europe, chiefly to
the south, but one species, _Cl. testaceus_, has wandered farther north
and occurs in the nest of the ant _Lasius flavus_ in the south of
England, Ireland, and Scotland. Though none of the _Clavigers_ can be
claimed as Oriental migrants, the centre of distribution of the genera
belonging to the _Clavigeridae_ is in Southern Asia, and it is probable
that the ancestors of the European _Clavigers_ have spread westward from
that region to Europe, eastward to Australia and Japan, and southward to
Madagascar and South Africa. The genus _Hopatroides_, belonging to the
same family as the so-called Spanish-fly (_Tenebrionidae_), has twelve
species in Western Asia and Greece. One only, _H. thoracicus_--an
instance of discontinuous distribution--occurs in Andalusia. _Amphicoma_
is represented in Western Asia and the Balkan peninsula by fifteen
species, while three others are met with in North-west Africa and
Southern Spain.
A genus of Dragon-fly, _Onychogomphus_, has in Europe a somewhat similar
distribution to _Claviger_, but it has besides a very extensive foreign
range. There are altogether thirty-five species; of these ten are
Holarctic, twelve Oriental, five Mascarene, and eight Ethiopian. The
centre of distribution is therefore in the Oriental region, and we may
assume that in all probability the genus has originated there, the
European species having travelled west with the Oriental migration at an
early date of the Tertiary Era.
_Ryothemis_, another genus of Dragon-flies, has originated perhaps
somewhat farther east than the last, for no less than thirteen species
are found in Australia, a like number in India, five in Madagascar and
Africa, and five in the Holarctic region. Both of these genera are
entirely absent from America, and they have possibly travelled to Europe
together.
Among the European _Orthoptera_--the group to which our Earwigs and
Grasshoppers belong--there are also a good many instances of Oriental
migrants. One of the most striking of these is the curious "praying
insect" (_Mantis religiosa_). It occurs all over Southern Europe, and
ranges as far north as the north of France. It is also found in Southern
Germany and in Austria, and has a vast extra-European range. There are
even records of its occurrence from all parts of Southern Asia and Java
and a great part of Africa. That it belongs to an extremely ancient
genus is testified by the fact of its presence in Mauritius, Japan,
Australia, New Zealand, South America, and Madagascar. The genus
_Bacillus_--to which the typical Stick-insects belong--has a somewhat
similar geographical distribution. But no less than four species of
_Bacillus_ are known from Europe, according to our great authority Mr.
Brunner von Wattenwyl--all from the south; and some of these also range
into North Africa. There are thirty-two other species distributed over
Southern Asia, Africa, Australia, New Zealand, and the Sandwich Islands.
Volumes, indeed, might be filled with lists of species and genera of
terrestrial invertebrates of Oriental origin, but I will not weary the
reader with further enumeration of such instances. Just two more,
however, before concluding, as I have not alluded to the large group of
the _Arachnida_.
Two peculiar spider-like genera, viz., _Galeodes_ and _Rhax_, are found
in Southern Europe. Both occur also in North Africa, and in Western and
a portion of Southern Asia. As the whole family altogether has an
Asiatic character, I cannot agree with Mr. Pocock, who considers them of
European origin and believes that they are migrating eastward.
But not only terrestrial forms migrated to Europe from Western and
Southern Asia. Freshwater species also took part in this great Oriental
migration. I need only refer to the freshwater Crab (_Thelphusa
fluviatilis_), with which Southern Europeans are familiar. It is the
sole representative of a large genus which ranges east as far as
Australia and southward to Madagascar and the Cape of Good Hope. The
European species is found in Turkey, Cyprus, Greece, Southern Italy,
Sicily, North Africa, Southern Spain, Syria, and Persia.
There is a corresponding flora with a range exactly similar to that of
some of the animals quoted. Thus the Balkan Rhododendron (_Rhododendron
ponticum_) is again met with in the western Mediterranean region in
Southern Spain. The Cedar occurs in local varieties in the Himalayan
Mountains, in the Lebanon, and the Atlas Mountains. Both of these are
instances of discontinuous distribution, a proof of their antiquity; but
a large number of plants have a continuous range between Asia Minor and
Spain.
On looking through these few instances of what have been called Oriental
migrants, one cannot help being struck by the fact that the species
after their entry into Europe evidently did not all follow the same path
during their westward advance. We have seen that a good many seem to
have travelled either due west or north-west on entering our continent
from Asia Minor. They may now perhaps be found in Greece, Southern
Italy, Algiers, and Spain, also probably on some of the intervening
islands in the Greek Archipelago, in Sicily, Sardinia, and Corsica, or
they may have travelled north-east and occur in the Alps. This
distribution indicates undoubtedly, as I have already set forth in
another memoir (_c_, p. 459), that land extended from Asia Minor across
Greece to Southern Italy, that the latter again was disconnected with
Central Italy, but united with Sicily, Sardinia, and Tunis, and that the
Straits of Gibraltar did not exist at the time when these species
migrated westward. Some species are only to be found as far west as
Southern Italy, while others occur in Central and Northern Europe,
scarcely in the South, and not at all in the larger Mediterranean
islands or in North Africa. This appears to me to indicate that the late
comers from the east found that geographical changes had taken place in
Southern Europe which prevented them from following the same track as
the older immigrants. They were now obliged to turn directly northward
and then westward. It may be asked, why should not the earlier migrants
have taken the same route? This question will be answered immediately.
Meanwhile it should be clearly understood that there probably was an
older and a newer migration from the east. The Oriental genera--from
whose general range we know that they must be very ancient indeed, such
as _Mantis_ and _Bacillus_--are almost invariably confined to Southern
Europe. There they are frequently found on some of the Mediterranean
islands. The earlier migrants therefore went westward and the later ones
northward.
Let us now inquire a little into the reasons why such different courses
were pursued by the migrants--why the Oriental migration divided into
two streams, an older and a newer.
During early Tertiary times, and probably throughout the Miocene and
Pliocene Epochs, the AEgean Sea did not exist. From the island of Crete
to the Peloponnesus, and from Asia Minor to Thessaly and Macedonia,
stretched a vast and fertile plain dotted over with numerous freshwater
lakes. Gradually the sea encroached upon this land from the south, owing
chiefly to extensive subsidences having taken place. Only very recently,
says Professor Suess, did the whole of the AEgean continent subside (i.,
p. 437). Huge cliffs of levantine freshwater deposits now mark the new
coast-line, and the Mediterranean advances steadily towards the Black
Sea and the Sea of Asov. A new order of things is now established,
continues the famous author of _Das Antlitz der Erde_; where there were
high mountains we now behold a deep sea, in some places many thousand
feet deep. All this took place quite recently,--geologically
speaking,--certainly in post-glacial times; and man may even have
witnessed these imposing events. Most geologists admit the correctness
of these views. They are, moreover, built upon such solid geological
evidence, that even if the science of zoogeography had not yet taught us
anything, naturalists would not hesitate in accepting them.
Animals and plants were free to migrate from Central and Southern Asia
to Greece by land for untold ages. The vast accumulation of mammalian
bones which have been discovered at Pikermi, and so ably described by
Gaudry, are probably to a large extent the remains of Asiatic immigrants
to Europe. Many of these resemble forms still living in South Africa,
which implies that a highway existed also at that time between Asia and
Africa. Among these is a giraffe and antelopes closely allied to
African species, and other most interesting mammals.
In still earlier European deposits--the Miocene--we find the ancestors
of modern Elephants, which are probably of Asiatic origin. The remains
of several kinds of monkeys occur, whose nearest relations are now
confined to Southern Asia. Altogether the fauna bears a strong Asiatic
facies. Many of our European terrestrial invertebrates probably arrived
about this time from Asia. The struggle for existence being keener and
the facility for migration much greater in the higher vertebrates,
they--or at any rate the mammalian faunas--were subjected to more rapid
changes than the invertebrates. I have repeatedly expressed my belief
that a great number of our familiar insects and mollusca inhabited
Europe long before our present mammals came into existence.[2]
Let us now follow one of the miocene Oriental migrants starting from
Central Asia on its way to Europe. Very soon after leaving its home, it
must have encountered a sea which extended at that time from the Eastern
Mediterranean to the borders of Afghanistan. In following a westward
course, the emigrant was compelled to keep along the northern shore of
it. We do not know the state of the physical geography of the region
between the Black Sea and the Tianshan Mountains, but it seems certain
that a considerable extent of dry land enabled a wanderer from Central
or Southern Asia to reach the Balkan peninsula by skirting the northern
shore of that large miocene sea. No miocene deposits occur north of
Teheran or of the Upper Euphrates, nor are they known from the islands
of the AEgean Sea or the lands surrounding it. From the Balkan peninsula
it was possible for our migrant to reach the European Alps, which were
then slowly rising as a peninsula out of the western portion of the
great miocene sea. What are now the Alps was then hilly ground, which
was being raised from the bottom of the sea. It was no doubt connected
with the Balkan peninsula, so that an intercourse of species could take
place between this newly-formed peninsula and Central Asia. I say
peninsula, because the miocene sea almost completely surrounded it. From
the Western Mediterranean a wide gulf extended up the Rhone valley into
that of the Rhine as far north as Maintz. Then skirting along the
northern outliers of the Tyrol, the gulf can be followed as far east as
Transylvania. It is quite probable that it extended much farther east
still, but there is as yet no geological evidence forthcoming. At any
rate, our Asiatic migrant turning northward from the Balkan peninsula
found its farther progress barred once more by an arm of the same sea
which in its earlier peregrinations had stopped it from going south (cf.
Suess, i., p. 406).
In later miocene times the sea does not seem to have surrounded the
Alps to the same extent as it did before, but it certainly extended from
the Eastern Alps to the shores of the Sea of Asov, so that the direct
northward passage was still more or less barred to the Oriental
immigrants. At the same time Alpine species were now able to emigrate to
the North European provinces. During the last stages of this epoch, the
same sea increased its area very considerably in an eastward direction.
One continuous expanse of water now stretched from the Alps as far as
the Sea of Aral in Central Asia, perhaps even farther.
During pliocene times especially, the northern parts of the Balkan
peninsula were occupied by a series of freshwater lakes, while Greece
was joined to Southern Italy, Sicily, and Tunis. Central and Northern
Italy were represented by a long narrow peninsula connected in the north
with the Alps. Corsica and Sardinia were joined to Sicily, and the
Straits of Gibraltar did not exist. When I first published my views
regarding these geographical conditions of the Mediterranean area,
Professor Deperet was good enough to send me his criticisms from a
purely geological standpoint. He is of opinion that though Sicily and
Sardinia might at this time have still been connected with Tunis, the
Straits of Messina must already have been formed--in other words,
Southern Italy and Sicily could no longer have been connected with one
another. This opinion is based upon the fact that in the upper strata
of the enormously thick Sicilian pliocene deposits are found a number of
arctic or subarctic species of mollusca which are entirely foreign to
the Mediterranean fauna. It is generally supposed that these reached the
Mediterranean area by the newly opened Straits of Gibraltar in later
pliocene times, and that the lower Sicilian deposits must therefore have
been laid down earlier. So far the deductions are perfectly correct, if
we assume the northern mollusca to have arrived in the Atlantic at the
time stated. However, they must have reached the Atlantic much
later--not till pleistocene times--if we adopt the above-stated
suggestions as to the age of the Forest-Bed (cf. p. 125). Moreover, the
great similarity between the faunas of Southern Spain and North-western
Africa indicate that the formation of the Straits of Gibraltar is of
very recent date. The northern mollusca, of course, could not have
reached Sicily till later. To suppose that the Sicilian deposits have
been uplifted 7000 feet since then is no doubt contrary to all our
geological teaching, but we must remember that this is altogether an
exceptional case. The area in question has probably ever since been in
the immediate neighbourhood of an active volcano, and the rate of the
uplift has therefore been immeasurably greater than at other localities
with which this one might be compared. The disconnection between Tunis,
Sicily, and Southern Italy was evidently produced by a subsidence of the
tract of land uniting these countries. If we suppose that this happened
in early pliocene times, we have either to take for granted that the
terrestrial fauna and flora of these countries are of miocene origin, or
that they were joined again during the Pleistocene Epoch. The range of a
very large number of animals and plants is such as can only be explained
by assuming that Tunis, Sicily, Sardinia, Corsica, and Southern Italy
were connected with one another. Of such extensive land-connections
subsequent to the arrival of the northern marine mollusca we possess,
however, no geological evidence whatsoever; and it is extremely
improbable that the land-areas which had sunk were once more raised
before again subsiding. The many animals whose presence in the
Mediterranean Region bears witness to these ancient land-connections
could not have arrived there in miocene times--in fact, they could
hardly have lived there before the end of the Pliocene Epoch. On the
other hand, it seems difficult to believe, once the Straits of Gibraltar
were open and the waters of the Atlantic able to enter the
Mediterranean, that the sunken parts between Sicily, Italy, and Tunis
could have been raised without affecting the entire area of that sea.
Nor is it likely that the junction between these countries could have
then been brought about by a general lowering of the Mediterranean
waters. As it may be asked what evidences we possess at all for the
supposition of such land-connections as I have indicated, also that
Southern Italy and Greece were connected, a few of the more salient
instances of distribution bearing on this problem may be of interest.
I have already referred to the occurrence of the remains of a small race
of Red Deer in the caves of Malta, similar to those still living in
North-west Africa, Corsica, and Sardinia. The Black-mouthed Weasel
(_Mustela boccamela_) inhabits Persia, Asia Minor, Greece, South Italy,
Sicily, and Sardinia, while _Mustela africana_ is found in Malta and
Algiers. The European Porcupine inhabits Asia Minor, the island of
Rhodos, Greece, Southern Italy, Sicily, North Africa, and Spain. Then we
have the Wild Sheep of Asia Minor, Cyprus, Sardinia, and Corsica, all of
which are closely allied. The small shrew-like _Crocidura etrusca_
occurs in South France, Italy, Sicily, and North Africa. Many other
mammalia might be quoted, but these are sufficient for our purpose.
There are a good many reptiles and amphibians with a similar
distribution. The European Chamaeleon (_Chamaeleon vulgaris_) has been
found in South Spain, North Africa, and Sicily. The Snake _Periops
hippocrepis_ is confined to Spain, Sardinia, and Greece. The worm-like
Lizard _Blanus cinereus_ inhabits some of the Greek islands, North
Africa, and Spain. Another Lizard belonging to the _Scincidae_ has also
been found in some of the Greek islands, Sicily, Sardinia, Southern
Spain, and the Canary Islands. _Discoglossus pictus_--a toad--occurs in
Spain, North-west Africa, Malta, Sicily, Sardinia, and Corsica. A
variety of the Tree Frog (_Hyla arborea Savignyi_) is found in Europe
only in Corsica, Sardinia, and the Greek Archipelago.
Eight species of Reptiles and Amphibia--some of which I have just
referred to--are enumerated by Dr. Forsyth Major as occurring eastward
and westward of the Italian peninsula (and almost all also in North
Africa) without being known on the mainland of Italy. And in order to
show that Sardinia and Corsica are more closely related to North Africa
than to Italy, he indicates the general range of the Reptiles and
Amphibians found in these islands. Of the twenty-one species, only
twelve inhabit Italy, but at least sixteen North Africa and seventeen
Spain. Indeed, he shows that Corsica, Sardinia, Sicily, and North-west
Africa form a zoogeographical province, from which Italy, with the
exception of a few localities on its west coast, is excluded. It is a
remarkable fact that there are a few localities on the west coast of
Italy which in their fauna and flora exhibit closer relationship with
Corsica and Sardinia than with the mainland. Thus Dr. Major pointed out
that the _Catena Mettalifera_, the _Monte Argentario_, and _Monte
Circeo_ all belong to what we may call the former Tyrrhenian continent.
They are to be regarded as its eastern limits, which remained standing,
while the central portion--now occupied by the Tyrrhenian Sea--subsided,
and is at present covered by deep sea. Subsequently these remnants of
the old continent became joined with the newly-formed Italian
peninsula, but the plants and animals belonging to the older flora and
fauna were mostly destroyed by newer and more vigorous immigrants. A few
of the more hardy ones survived, and are a standing testimony of the
geographical revolutions of that part of Southern Europe.
That the Mediterranean area has undergone such profound geographical
changes as I have endeavoured to indicate is no new theory. Many
zoologists who have investigated the fauna of that region, and have
attempted to explain the faunistic relations, had to acknowledge that
the migrations must have taken place under geographical conditions
entirely different from those obtaining at present. Ruetimeyer long ago
remarked that it seemed to him much more probable that Morocco, Algeria,
and Tunis were peopled by way of Gibraltar, and perhaps also by Sicily
and Malta from Europe, than Southern Europe from Africa. After careful
conchological researches in the Western Mediterranean region, Dr. Kobelt
came to the conclusion that formerly Southern Spain and Morocco must
have been united by a broad land-connection. Sicily and Algeria do not
apparently show any very intimate relationship conchologically, but
farther west--in the mountains of Tetuan--Dr. Kobelt discovered a colony
of Sicilian forms.[3]
"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 Tunesie, on se croirait sur
le meme 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 AEgean
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 versa_. 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.
The Mammoth, Wild Boar, Badger, the Dippers and Pheasants, are all
Oriental species which have come to us from the south-east; but there
are also Reptiles and Amphibians, and a host of Invertebrates. Not all
the animals, for instance, which have reached us in England from the
south-east are of Asiatic origin. There is an active centre of
distribution in South-eastern Europe itself, from which species radiate
out in all directions. This fact is well illustrated by the genus
_Clausilia_. Species from this centre, and also from the Alps, joined
the Oriental stream in their northward course.
In reviewing a number of instances of Oriental species in Europe, one is
struck by the peculiarity of their having apparently followed two
distinct routes. All entered from Asia Minor, which is proved to have
been connected with Greece until recent geological times. From here some
seem to have proceeded straight west, others northward. Further study
reveals the fact that the first route was followed by a much older set
of migrants at a time when the Mediterranean area was greatly different
from what it is at the present day. Greece was then joined to Southern
Italy, Sicily, and Tunis. The latter was also connected with Sardinia
and Corsica, and the Straits of Gibraltar did not exist. Under such
geographical conditions a direct migration on land from Southern Greece
to Spain was not only possible, but was actually undertaken by a very
large number of Oriental species.
FOOTNOTES:
[1] Since writing the above account, Mr. Boulenger, in his new work on
the Batrachia of Europe, has accepted the specific distinctions between
the two fire-toads.
[2] In some cases the accuracy of this view is proved by fossil
evidence, _Helix rotundata_, a common and widely spread British species,
having been found in miocene strata near Bordeaux.
[3] There are a great many instances of discontinuous distribution among
Oriental Invertebrates. Thus the Freshwater Crab (_Thelphusa
fluviatilis_) occurs in Southern Italy, Greece, Turkey, Cyprus, and Asia
Minor. Another crustacean--a Freshwater Crayfish--(_Hemicaridina
Desmaresti_) inhabits Spain, Corsica, Sardinia, Sicily, and Asia Minor.