35 



between the white breast-spot and the black belly-colour, a 

 character on which naturalists have laid stress, has proved to 

 vary to a wide extent within each single locality. 



Several species here have apparently become the subjects of 

 climatic variation. Let us take examples of the Northern Marsh- 

 Tit, of the Magpie, or of the Lesser Spotted Woodpecker, 

 already mentioned, and it will be seen that they have all altered 

 in a certain direction ; they have become whiter than the 

 individuals from more southern localities. The Magpie occurs 

 thus in a fine race, where the white colour of the wing feathers 

 extends very nearly to their tips, so as to approach the White- 

 winged Magpie (Pica leucoptera), from East Siberia; in Pavus borealis 

 the back is light gray, and the abdomen snow-white, whilst the 

 same species down by Christiania has a darker back, and a dirty- 

 coloured abdomen ; the little Lesser Spotted Woodpecker (Dendro- 

 copus minor) has a white back without the transverse bars, and 

 nearly unspotted outer tail-feathers, answering perfectly to the east 

 arctic D.pipra, whilst coexistent with them, certain individuals are 

 dark coloured, like the normal southern stock. And the Three-toed 

 Woodpecker has here become of a robust form, with a winter 

 plumage of fluffy and particularly purely-coloured feathers, which 

 are decidedly lighter than in individuals further south. 



These phenomena are by no means devoid of physiological in- 

 terest. It would appear that a living being is to a certain degree 

 like a photographer's plate, which receives the impression from 

 its surroundings. The month-long daylight in the summer and 

 the long winter, here strive, generation after generation, to 

 fashion individuals whiter, and have, over the whole of Norway, 

 already given the two Ryper, the Hare, the " Snow-mouse," * the 

 Stoat, and the Arctic Fox, their white winter pelt, exactly as the 

 intense sun of the tropics and the variegated splendour of colour 

 in the vegetation there, produce the parti-coloured and metallic- 

 glistening birds and insects, or the yellow sand of the desert is 

 reflected in the hairy coat of the Fennec Foxf and the Jerboa, 

 or in the feathers of the Sand Grouse (Pteroclidce), and the 

 Desert Lark.! 



* The so-called Mustela nivalis = M. vulgaris. Trans/. 

 t Cam's cerdo. Gin. J Ammonanes deserti. 



