14 The Field Naturalist's Quarterly Feb. 



" Certum est eos . . . vesci corticibus arborum pinei, quer- 

 cini, tremulei, ac populei generis," remarks the archbishop 

 with unnecessary detail. But notwithstanding this flash of 

 reason the same authority pledges himself so far as to assert 

 that he saw (" vidi ") Mice which fed upon white sugar become 

 white, and alter the colour when they ceased to feed upon 

 that substance ! This is a curious anticipation of later 

 cayenne-pepper-coloured Canaries and white fowls, and none 

 the less so on account of its obvious falsity. We may fairly 

 dismiss the colour theory in its grosser aspect. But the 

 question of food and whiteness has another side which does 

 demand some careful thinking over. 



White is the hue of senility ; and it has been pointed out 

 that white is not infrequent as a colour among species which 

 are believed on other grounds to be on the wane. The oppo- 

 site, black, is, as an opposite would naturally be, a sign of 

 the precise converse of senility. The Raven, and the Crow 

 tribe generally, have been held (for example, by Prof. New- 

 ton) to be the culmination of bird structure, and black is at 

 the same time one of the rarest of colours, and found as the 

 extreme term in a series commencing with paler hues. If 

 white is evidence of decay and degeneration of species, it is 

 even more probable that the absence of colour is to be at 

 least occasionally looked upon as the expression of imperfect 

 nutrition, as, for instance, in old age. The animals of the 

 boreal regions must have in many cases an extremely severe 

 struggle for existence, not so much in relation to each other 

 as to external nature, who is in these regions hard and cold. 

 Insufficient diet would be most marked in winter, and a cor- 

 responding diminished output of pigmentary substances, the 

 waste products of the body, increasing with the increase of 

 metabolism, would be expected. The view, however, that at 

 present seems to command most adherents is that the change 

 to white in winter — being of direct utility — has been brought 

 about by natural selection. It does seem at first sight as if 

 there were at any rate much to be said for this view. Even 

 the exceptions seem to be in its favour. As has been pointed 

 out, the Musk Ox does not change to white at all ; but there 

 would not appear to be great advantage in its doing so. The 

 chief object of a gregarious species is that the members of 



