193 COLIN CLOUT'S CALENDAR. 



changing its coat in winter before the divergence took 

 place ; and if so, then it is the Scotch grouse which has 

 altered most ; but this is less probable, because the use- 

 fulness of the change would certainly be felt even in a 

 Scotch winter, and the white suit is not, therefore, likely 

 ever to have been lost when once acquired. Though the 

 winter is not severe enough in Scotland to make such a 

 change of coat inevitable where it does not already exist, 

 it is yet quite severe enough to preserve the habit in ani- 

 mals which have once acquired it, as we see in the case 

 of the varying hare, a creature which in colder ages 

 spread over the whole of northern Europe, and which 

 still holds its own among the chillier portions of the 

 Scotch Highlands. Hence we may reasonably infer that 

 if our grouse had ever possessed a winter coat it would 

 have always retained it for an alternative dress, as the 

 ptarmigan still does in the self-same latitudes. Accord- 

 ingly, analogy seems to point to the conclusion that the 

 Scotch grouse is a truly native breed, slightly altered by 

 the conditions of its insular habitat from a closely allied 

 Continental species, whose representatives elsewhere 

 have now all assumed the guise of Scandinavian willow- 

 grouse. In other words, the two isolated groups into 

 which the species has split up have altered each in its 

 own way, but the Continental variety has moved faster 

 away from the primitive type than its British congeners. 



