BRITISH ZOOLOGY, 
31 
land of Europe, probably before the formation of tlie 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 emij^ration 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 Eed Grouse (Lagoj^iis scoticus), and several species 
of fresh-water fishes, mostly belonging to the genus Sahno. 
Some of these have an extremely local distribution, being 
only found in some small groups of mountain lakes. Many 
species, or at all [events, well-marked varieties of insects, and 
a few land and fresh- water molluscs, have at present been only 
found within the limits of our islands. 
The upright cases on the south side of the room, between the 
two entrances, contain^fche larger mammals which still inhabit 
the British Islands, except the Cetacea (Whales and Dolphins), 
which on account of their size are placed in the gallery appro- 
priated to the general collection of animals of that order (see 
p. 41). Of the]Seals, but two species are really indigenous, the 
Common Seal {Phoca vitulina) and the Great Grey Seal {Hali- 
chcerus grypus) ; but other species, as the Panged and the Harp 
Seal of the Northern Seas, are exhibited in their capacity of 
occasional but rare visitors to our shores. Of the land Carnivora, 
specimens 'are'seen of the Wild Cat, the Fox, the Badger, Otter, 
