340 ISLAND LIFE part ii 



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 {Lagopits 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 inter- 

 esting 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, beitannicus Closely allied to P. ater of the 



continent ; a local race or 

 sub-species. 



2. Acredula caudata, 52^5. 5J9. ROSEA Allied to A. caudata of the 



continent. 



3. Lagopus scoTicus Allied to L. albus of Scandin- 



avia, a distinct species. 



4. Troglodytes par vulus -yar. HORTENSis.St. Kilda, Hebrides. 



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 of them 

 being extremely limited in distribution. Some are confined 

 to particular river valleys or even to single rivers, others 

 inhabit the lakes of a limited district only, while some are 



