BRITISH ZOOLOGY. 
35 
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, the 
most marked among vertebrated animals being the common 
Eed Grouse {Lagopus scoticus), and several species of fresh- 
water fishes, mostly belonging to the genus Salmo. 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 the 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. 43). Of the Seals, but two species are really indigenous, the 
Common Seal (PJioca vitulinct) and the Great Grey Seal (Hcdi- 
cJicerus gryjpus) ; but other species, as the Einged and the Harp 
Seal of the ISTorthern 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 Tox, the Badger, Otter, 
Marten, Polecat, Weasel, and Stoat or Ermine, which only 
occasionally (as in a beautiful example shown) assumes the 
white colour in England, though this change is the rule in 
countries with severer winter climates. The Eodents are 
represented by the Common and the Variable or Mountain 
Hare, which turns white in winter in the Highlands of Scotland, 
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