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CENTRAL HALL. 
region called Palsearctic, 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 con- 
tinental tracks. Their numbers can only increase under very 
exceptional circumstances, but, on the contrary, 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 all disappeared from Britain 
within the historic period, and 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 rather a vague and uncertain 
one. The constitution of the marine fauna in the same way is 
continually liable to undergo fluctuations. 
Slight but permanent variations from the continental type can 
be recognised in a few of our indigenous species, but the only 
vertebrated animals undoubtedly peculiar to the British Isles are 
the common Bed Grouse {Lagopus scoticus), and several species 
of fresh-water fishes (fifteen are enumerated by Dr. Glinther), 
mostly belonging to the genus Sahno. Some of these have an 
extremely local distribution, being only found in some small 
