esent well-marked differences of colour as compared with
continental specimens; and in Mr. Dresser's work on the _Birds of Europe_
they are considered to be distinct species, while Professor Newton, in his
new edition of Yarrell's _British Birds_, does not consider the difference
to be sufficiently great or sufficiently constant to warrant this, and
therefore classes {340} them as insular races of the continental species.
We have, however, one undoubted case of a bird peculiar to the British
Isles, in the red grouse (_Lagopus scoticus_), which abounds in Scotland,
Ireland, the north of England, and Wales, and is very distinct from any
continental species, although closely allied to the willow grouse of
Scandinavia. This latter species resembles it considerably in its summer
plumage, but becomes pure white in winter; whereas our species retains its
dark plumage throughout the year, becoming even darker in winter than in
summer. We have here therefore a most interesting example of an insular
form in our own country; but it is difficult to determine how it
originated. On the one hand, it may be an old continental species which
during the glacial epoch found a refuge here when driven from its native
haunts by the advancing ice; or, on the other hand, it may be a descendant
of the Northern willow grouse, which has lost its power of turning white in
winter owing to its long residence in the lowlands of an island where there
is little permanent snow, and where assimilation in colour to the heather
among which it lurks is at all times its best protection. In either case it
is equally interesting, as the one large and handsome bird which is
peculiar to our islands notwithstanding their recent separation from the
continent.

The following is a list of the birds now held to be peculiar to the British
Isles:--

1. Parus ater, _sub. sp._ BRITANNICUS Closely allied to _P. ater_ of
the continent; a local race or
sub-species.

2. Acredula caudata, _sub. sp._ ROSEA Allied to _A. caudata_ of the
continent.

3. LAGOPUS SCOTICUS Allied to _L. albus_ of
Scandinavia, a distinct species.

_Freshwater Fishes._--Although the productions of fresh waters have
generally, as Mr. Darwin has shown, a wide range, fishes appear to form an
exception, many