10 JOURNAL OF THE [May, 



supplied with grease, or whatever the oily material may be with 

 which the outside surfaces are furnished, namely, by the exuda- 

 tion of pigment granules from under the scales to the exterior of 

 the fibre. 



You see, also, why fur is such an excellent non-conductor. It 

 contains an enormous quantity of air cells, in which the air is 

 closely imprisoned, and these, when once warmed by the heat 

 of the animal's body, will keep him warm for a long time. The 

 walls of these cells are of such a character that glycerine will 

 not penetrate them until they have been soaked in it for about 

 two weeks. 



Certain animals, as we all know, grow white in winter and 

 dark again in summer, while others, particularly those that live 

 in the South, such as the marsh-hare, grow black in the winter 

 but become lighter again in the summer This seeming contra- 

 diction I think can be explained. So far as I have been able to 

 discover by experiments on a few rabbits, the pigment cells on 

 the approach of cold weather are discharged, to a great extent, 

 or new fur fibres devoid of pigment are developed ; at any rate, 

 the air cells are enlarged. This change enables the animal to 

 resist dry cold. In the summer, when the animal is called upon 

 to resist moisture, the amount of pigment is increased, while the 

 air cells decrease, since at that season more water-repellent 

 material is needed on the surface. And you will notice, also, 

 that in most animals the back is darker than the stomach. This 

 is because the cold of the ground has to be resisted when the 

 animal lies down, while the back has to resist moisture. On the 

 other hand, the swamp-hare of the South turns darker in winter, 

 I suppose, because, under the conditions of its existence, it re- 

 quires more water-repellent material. 



The Arctic Fox turns almost pure white in winter because 

 it has to resist dry cold, and hi summer, when it has to resist 

 less cold than moisture, it is not so white. This explanation^ 

 however, is simply a theory which opens an interesting field of 

 inquiry, but which would take a long time to prove, and I should 

 be glad if anybody would take the matter up. 



I have observed under the pigment cells a series of colorless 

 cells, but what function they perform in the fibre, I have not as- 

 certained. They are present in almost all of the fibres. 



In a fibre freshly taken from the animal, pigment cells that 



