HOW ARCTIC ANIMALS TURN WHITE 67 
viduals. The species in question is the Arctic fox, of 
which the beautiful fur, in both the white and the blue 
phase, is, as mentioned in a later article, now much 
affected by ladies. That both the white and the blue 
individuals of this species are in the winter dress will 
be evident to every one who examines such furs carefully, 
the length and thickness of the hair being quite decisive 
on this point. 
With the single exception of Iceland, where they are 
always blue, it appears that the white and the blue phase 
are met with throughout the habitat of the species. In 
other words, the animal is “dimorphic,” if it be permis- 
sible to apply this term to a case where the difference 
between the two phases of a species is restricted to 
coloration. 
What makes the matter so puzzling is this: if blue foxes 
are able to thrive during winter in a snow-clad country, 
what necessity is there for their fellows—and, indeed, for 
any species—to turn white at that season of the year? 
An explanation of the case of the blue foxes has been 
attempted in the article already referred to. 
Since the present article was written important additional 
information with regard to the manner in which hair 
bleaches has been afforded by a communication from 
Mr. E. Metchnikoff, published in the Proceedings of the 
Royal Society for 1902. It is there stated that the all- 
devouring cells known as phagocytes are the cause of 
the mischief. These cells, which frequently have amoeba- 
like processes, are developed in the central or medullary 
part of the hair, whence they make their way into the 
outer or cortical layer, where they absorb, and thus destroy, 
the pigment-granules. Numbers of these phagocytes may 
be seen in hair which is commencing to turn white. 
