4 DISTRIBUTION OF ANIMALS, [PART I, 
the soil, the aspect, or the vegetation, was adapted to them or 
the reverse. The marshes, the heaths, the woods and forests, 
the chalky downs. the rocky mountains, had each their peculiar 
inhabitants, which reappeared again and again as we came to 
tracts of country suitable for them. But as we got further away 
we began to find that localities very similar to those we had 
left behind were inhabited by a somewhat different set of species; 
and this diflerence increased with distance, notwithstanding 
that almost identical external conditions might be often met 
with. The first class of changes is that of stations; the second 
that of habitats. The one is a local, the other a geographical 
phenomenon. The whole area over which a particular animal 
is found may consist of any number of stations, but rarely of 
more than one haditat. Stations, however, are often so extensive 
as to include the entire range of many species. Such are the 
great seas and oceans, the Siberian or the Amazonian forests, 
the North African deserts, the Andean or the Himalayan 
highlands. 
There is yet another difference in the nature of the change 
we have been considering. The new animals which we meet 
with as we travel in any direction from our starting point, are 
some of them very much like those we have left behind us, 
and can be at once referred to familiar types; while others 
are altogether unlike anything we have seen at home. When 
we reach the Alps we find another kind: of squirrel, in South- 
ern Italy a distinct mole, in Southern Europe fresh warblers 
and unfamiliar buntings. We meet also with totally new 
forms ; as the glutton and the snowy owl in Northern, the genet 
and the hoopoe in Southern, and the saiga antelope and 
collared pratincole in Eastern Europe. The first series are 
examples of what are termed representative species, the second 
of distinct groups or types of animals. The one represents a 
comparatively recent modification, and an origin in or near the 
locality where it occurs; the other is a result of very ancient 
changes both organic and inorganic, and is connected with some 
of the most curious and difficult of the problems we shall have 
to discuss. 
