3) 
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 ustake 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 Parus 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 (Dendvo- 
copus minov) 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 Fox} and the Jerboa, 
or in the feathers of the Sand Grouse (Pteroclide), and the 
Desert Lark.t 
* The so-called AZustela nivalis = M. vulearis.— Transl. 
+ Canis cerdo. Gm, t Ammonanes deserti. 
