94 THE COLOURS OF ANIMALS 



Sudden change of colour determined by sudden 

 exposure to extreme cold 



A classical experiment made by Sir J. Eoss, con- 

 siderably over fifty years- ago, seems decisive on the 

 above-mentioned point, as far as the species ex- 

 perimented upon is concerned. A Hudson's Bay 

 Lemming kept in the cabin, and thus shielded from 

 the low temperature, retained its summer coat through 

 the winter : ' It was accordingly placed on deck in a 

 cage on February 1, and next morning, after having 

 been exposed to a temperature of 30° below zero, the 

 fur on the cheeks and a patch on each shoulder had 

 become perfectly white. On the following day the 

 patches on each shoulder had extended considerably, 

 and the posterior part of the body and flanks had 

 turned to a dirty white ; during the next four days the 

 change continued but slowly, and at the end of a week 

 it was entirely white, with the exception of a da]"k 

 band across the shoulders, prolonged posteriorly down 

 the middle of the back. . . .' No further change took 

 place, and the lemming died of the cold on February 

 18, the thermometer having been between 30° and 

 40° below zero every night. ' On examining the 

 skin it appeared that all the white parts of the fur 

 were longer than the unchanged portions, and that 

 the ends of the fur only were white so far as they 

 exceeded in length the dark-coloured fur; and by 



