106 THE COLOUES OF ANIMALS 



spreads the upper margin, gradually eclipsing the 

 rufous-brown shade, which remains the evidence of 

 the previous plumage (fig. 20). Hence are shown 

 two successive stages of the development of the dark 

 brown shade which at last removes all traces of the 

 reddish tint (figs. 21 and 22).' 



If the winter change does not occur in the 

 autumnal feathers, it by no means follows that 

 the power of Variable Eesemblance is absent. The 

 growth of new white feathers may be indirectly due 



to the cold, acting through the medium of the nervous 

 system. This is, however, very far from being proved ; 

 for it does not appear to be certain that there is a 

 single species becoming white in winter which retains 

 its dark colour at this time of the year in the southern- 

 most part of its range. 



Mr. A. C. Billups, of Niagara, Ontario, tells me 

 that during an exceptionally mild winter, about 

 seven or eight years ago, neither the ' snow bird ' 

 nor the American Hare acquired the winter dress. 

 Hence the power of Variable Resemblance appears to 

 be possessed by certain birda. 



