34 
BRITISH VERTEBRATES. 
The British land and freshwater representatives of each 
group of Invertebrates will eventually be exhibited in separate 
cases placed in the galleries severally devoted to such groups. 
Here it may be mentioned that the animal inhabitants of 
any country or district are collectively termed its ''fauna!' 
Our country in this respect belongs to the great zoogeographical 
region called Palsearctic, or Eastern Holarctic, embracing all 
Europe, the north of Africa, and the western and northern 
portions of Asia. As in the case of all islands, the species 
belonging to groups whose powers of locomotion are limited to 
the land or fresh water, are not numerous compared with those 
inhabiting large continental tracts. Their numbers can only 
increase under exceptional circumstances, and have a tendency 
to diminish, as the growth of human population and increase 
of the area of cultivated land gradually circumscribe their 
native haunts. In this way, the Brown Bear, the Wolf, the 
Beaver, and the Wild Boar have disappeared from Britain 
within the historic period, while others, as the Badger, Marten, 
and Wild-Cat, with difficulty maintain a somewhat precarious 
existence. These have all been originally derived from the main- 
land of Europe, probably before the formation of the channel 
which now makes our country an island. The wider and older 
channel which separates Ireland from Great Britain has proved 
a greater barrier to the emigration of animal life than that 
between the latter and the Continent, many species (as the 
Polecat, Wild-cat, Mole, Squirrel, Dormouse, Harvest-mouse, 
Water and Land Vole, Common Hare, Eoedeer, as well as 
Snakes and Toads) never having crossed it, unless by aid of 
human agency. 
On the other hand, those species that have the power of 
travelling through the air or traversing the ocean are far less 
fixed in their habitat, and thus the list of so-called "British 
birds" receives accessions from time to time from stragglers 
which find their way from the European continent or even across 
the Atlantic, and doubts as to the authenticity of some of 
the recorded occurrences make the list somewhat vague and 
uncertain. 
Slight but permanent variations from the continental type 
may be recognised in a few of our indigenous species, some of 
