as indicating Affinities of Species. 395 



throughout the mammiferous subclass of vertebrate animals ; 

 thus, the squirrels and the shrews renew their covering twice 

 in the year, and the rats and rabbits but once. The common 

 squirrel's seasonal changes have never, that I am aware of, 

 been remarked by any naturalist, though it is so common an 

 inhabitant of our island : its summer coat is very different 

 from that of winter, the fur being much coarser, more shin- 

 ing, and of a bright rufous colour ; while the ornamental 

 tufts to the ears are wholly wanting : these grow in autumn, 

 while the animal is renovating its coat, and continue usually 

 till about the beginning of July, the time varying somewhat 

 in different individuals. Their winter fur, besides being of a 

 much finer quality and texture, is considerably longer, thicker 

 and more glossy, and quite of a different hue from that of 

 summer, inclining to greyish brown. The first young ones, 

 too, which are produced very early in the season, push forth 

 the winter garb, which, I believe, they then retain throughout 

 the summer; whereas the second race of young ones, which, 

 for the most part, make their appearance about midsummer, 

 are first clad in the summer dress, which is exchanged, before 

 they have become half grown, for that of winter. It is not 

 improbable, also, that diversities of a like kind may obtain 

 in the renewal of the scales of fishes. 



What the definite purpose effected by very many of these 

 peculiar and dissimilar changes may be, I confess myself 

 utterly unable to say ; nor can I suggest even a plausible hy- 

 pothesis upon the subject. Why, for example, should the 

 pipits (^4'nthus) shed their plumage twice in the year, and 

 the larks (^lauda) but once ? And why, also, should the 

 latter change all their nestling primaries at the first moult, 

 while the former retain theirs until the third (including the 

 vernal) general renovation of plumage? It is easy enough 

 to say, with Mr. Mudie, that, in the wagtails, and certain 

 other species, the colours of the summer and winter dresses 

 are each, in so far as they differ, more peculiarly adapted to 

 the particular season of the year ; but this is merely a con- 

 comitancy : in other words, this adaptation is not the purpose 

 of the change ; for we find that, in certain species which regu- 

 larly moult twice in the year (as the tree pipit), the summer 

 and winter plumage hardly differ ; whilst, on the other hand, 

 as complete an adaptation of colour to season is effected in 

 others (as the stone chat, and most of the JFringillidae), which 

 moult in autumn only, by the wearing off of the extreme 

 tips of the feathers ; these in winter having covered and con- 

 cealed another, and, in many instances, a very diverse, colour 

 beneath. By what reason can we ever hope to account for 



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